Kinematic alignment in total knee arthroplasty better reproduces normal gait than mechanical alignment

Patellar alignment compared between kinematic and mechanical unicompartmental knee arthroplasties

Background

Surgical treatment of unicompartmental knee arthritis is typically treated by unicompartmental knee arthroplasty (UKA). UKA may be performed by more traditional mechanical alignment, or alternatively, kinematic alignment. The purpose of this study is to compare pre- and post-operative patellar tendon alignment between mechanical and kinematic UKA.

Methods

A retrospective study at Medstar Washington Hospital Center from 2015 to 2022 identified 156 cases of partial knee arthroplasties. Of these, 95 had mechanical alignments and 61 had kinematic alignments. Patients were evaluated pre and post-surgically for Insall-Salvati and Blackburne-Peel ratios. Analysis of joint imaging x-ray imaging was performed by a blinded MSK-trained radiologist.

Results

Pre-and-post-operative Insall-Salvati and Blackburne-Peel ratios were calculated for kinematic and mechanical knee replacement patients. The ratio differences for the kinematically aligned cohort demonstrated an average for Blackburne-Peele operative ratio difference of 0.089 ( ± 0.30) and an average Insall-Salvati ratio difference of 0.18 ( ± 0.34), whereas for mechanically aligned patients, the Blackburne-Peele ratio difference was 0.054 ( ± 0.47) and the Insall-Salvati ratio difference was 0.41 ( ± 0.31). There was a statistically significant difference in operative Insall-Salvati ratios between kinematic and mechanical patients. Additionally, a two-sample t-test found a significant difference between the postoperative Blackburne-Peel and Insall-Salvati ratios for the kinematically aligned knees with a p-value of 2.33 × 10-16 below the significance level of 0.05. A two-sample f-test found a significant difference in the standard deviation of the difference between mechanical and kinematically aligned knees with respect to the Blackburne-Peel ratio, with a p-value of 0.00183.

Conclusion

This study demonstrates that sagittal patella-femoral knee alignment when comparing Blackburne-Peel and Insall-Salvati ratios are more accurately reproduced with kinematically aligned knees, and a greater variability among the kinematically aligned knees.

A retrospective comparison of Coronal Plane Alignment of the Knee

Background

Unicompartmental arthritic degeneration is treated by unicompartmental knee arthroplasties (UKA). The two current standards are mechanical alignment, where knee placement is perpendicular to the leg's mechanical axis and kinematic alignment, that consists of aligning the knee with the angles specific to the patient's innate bone structure. The purpose of this study was to compare knee alignment between mechanical and kinematic UKA.

Methods

A retrospective study at Medstar Washington Hospital Center from 2015 to 2022 identified 156 cases of knee arthroplasties. Of these, 95 had mechanical alignments and 61 had kinematic alignments. Patients were evaluated post-surgically for Coronal Plane Alignment of the Knee (CPAK). Analysis of post-operative joint x-ray imaging was performed, and the mechanical medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA) were measured. The arithmetic hip knee ankle angle (aHKA) and joint line obliquity (JLO) were calculated.

Results

The CPAK results for mechanically aligned group demonstrated an average MPTA of 87.12 (±3), LDFA average of 86.04 (±3), aHKA average of 0.62 (±4) and JLO average of 172.57 (±4). The CPAK results for the kinematically aligned group demonstrated an average MPTA of 86.96 (±3), LDFA average of 84.67 (±3), aHKA average of 2.09 (±4), and JLO average of 171.1 (±4). A two-sample t-test on this data demonstrates statistically significant p-values of 0.004 for LDFA, 0.03 for aHKA, and 0.02 for JLO all below the 0.05 significance level. Both cohorts only contained CPAKs alignment types I and III.

Conclusion

This study demonstrated that there is a statistically significant difference in knee alignment when comparing mechanically versus kinematically aligned knees which suggests that there is an advantage for patients that undergo kinematically aligned knee replacements.

Coronal plane alignment of the knee phenotypes distribution varies significantly as a function of geographic, osteoarthritic and sex-related factors: A systematic review and meta-analysis

PURPOSE

The coronal plane alignment of the knee (CPAK) classification is a nine-phenotype matrix based on limb alignment and joint line obliquity. This study aimed to provide a global overview of CPAK distribution, hypothesising significant geographic, osteoarthritic and sex-related variations.

METHODS

A systematic literature search (Embase, Medline/PubMed and Cochrane Library) following PRISMA guidelines was conducted, utilising the search terms "Coronal Plane Alignment of the Knee" OR "CPAK". Studies considering image modalities other than long-leg radiographs were excluded. A random-effects meta-analysis of proportions was performed, and statistical significance was defined as p < 0.05.

RESULTS

A total of 38 studies comprising 46,966 knees were analysed. The most common phenotypes worldwide were CPAK I (33.1%), II (25.9%) and III (14.4%) in the osteoarthritic population and CPAK II (34.9%), I (21.5%) and III (19.3%) in the healthy population. Among osteoarthritic populations, CPAK type I was predominant in Europe (29.2%), Asia (41.9%) and America (33.6%), type II in Australia (32.6%) and type III in Africa (28.6%). In healthy populations, type II was predominant in Europe (42.8%) and Asia (35.3%), whereas type I was most common in South America (44.8%). Significant regional differences were observed among both osteoarthritic and healthy knees, and between osteoarthritic and healthy knees in individual countries. In Europe, significant sex differences were observed in the distribution of types I (39.1% M; 23.5% F) and III (11.4% M; 24.6% F) in the osteoarthritic population, and in the distribution of types I (26.7% M; 9.4% F), II (43.9% M; 34.4% F) and III (11.3% M; 20.6% F) in the healthy population. In Asia, significant sex differences were found for type III in osteoarthritic knees (6.3% M; 11.4% F).

CONCLUSION

CPAK distribution varies significantly as a function of geographic, osteoarthritic, and sex-related factors. A personalised approach to TKA may be desirable to better accommodate these differences.

LEVEL OF EVIDENCE

Level IV.

Increased prevalence and severity of femoral bone wear in Japanese patients with varus knee osteoarthritis

PURPOSE

The calliper technique in kinematic alignment total knee arthroplasty assumes nearly identical medial and lateral femoral condylar radii and negligible subchondral bone wear. However, racial differences were not considered. This study aimed to assess the degree and severity of bone wear in Japanese patients with varus knee osteoarthritis.

METHODS

This cross-sectional study included 155 knees from 130 patients who underwent total or unicompartmental knee arthroplasty for primary varus-type knee osteoarthritis between April 2020 and March 2024. Preoperative computed tomography scans were used to measure the femoral condylar radii via a circle-fitting technique. Bone wear was assessed at 0° and 90° by measuring the distance between the best-fit circle and the subchondral bone periphery, with additional measurements at the peak wear angle, if present.

RESULTS

Among 155 knees, 16 (10.3%) exhibited bone wear. Bone wear >1 mm at 0° was observed in 3.2% of the cases. The peak wear angle was 43.1 ± 5.0°, with a mean depth of 2.0 ± 0.7 mm. The medial and lateral condylar radii were nearly identical (18.3 ± 1.2 mm vs. 18.2 ± 1.2 mm, p = 0.002), with a strong correlation (R2 = 0.94, p < 0.001).

CONCLUSION

Bone wear exceeding 1 mm at 0° was observed in 3.2% of cases, while overall bone wear was present in 10.3% of knees. Although the difference in radii between the medial and lateral femoral condyles was statistically significant, it was clinically negligible. This finding supports the reliability of the cylindrical axis as a reference for surgical techniques. These results highlight the importance of recognizing potential racial differences in bone wear and underscore the need for accurate assessment to achieve anatomic restoration in kinematic alignment total knee arthroplasty.

LEVEL OF EVIDENCE

Level III.

A systematic review of geographic differences in knee phenotypes based on the coronal plane alignment of the knee (CPAK) classification

BACKGROUND

The extent of geographic variation in knee phenotypes remains insufficiently documented. This systematic review intends to elucidate the regional disparities in the distribution of Coronal Plane Alignment of the Knee (CPAK) types across different geographic areas.

METHODS

A systematic review of the literature was conducted in adherence to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Studies reporting the distribution of knee phenotypes, as classified by the CPAK system, in both healthy and arthritic populations, were included in the analysis. Based on the methods in the literature, the Hoy Risk of Bias Tool was used to assess the methodological quality of the included studies. To compare geographical differences in CPAK types among patients with arthritis, as well as healthy people.

RESULTS

A total of 29 studies (28 retrospective and 1 prospective) were included in this review, encompassing 27,660 knees in 22,342 subjects. The methodological quality of the included studies was assessed using the Hoy Risk of Bias Tool, and the quality was good. Among the healthy knees (n = 4,082), CPAK type II was predominant in Europe (41.7%) and Asia (36.7%). In contrast, among arthritic knees (n = 21,632), CPAK type I was most common in Asia (51.3%), North America (32.8%), and Europe (32.8%), while CPAK type II was prevalent in Australia (29.3%) and Africa (25.5%). Notably, the proportions of CPAK type I (P < 0.001) and II (P = 0.002) knees varied significantly across different geographic regions among arthritic knees, while no significant differences were observed among healthy knees (P = 0.48, P = 0.305).

CONCLUSION

Significant variations in CPAK distributions among arthritic knees were observed across countries, while no significant differences were observed among healthy knees. Surgeons in different regions need to make individual surgical plans according to the CPAK types of patients. Video Abstract.

Comparison of Patellar Tracking Following Kinematic Alignment Versus Mechanical Alignment Total Knee Arthroplasty via the Mini-Subvastus Approach

OBJECTIVES

Different alignment strategies (kinematic alignment [KA] versus mechanical alignment [MA]) during total knee arthroplasty (TKA) significantly influence postoperative patellar tracking. This study aimed to compare radiological parameters of patellar tracking and clinical outcomes between KA-TKA and MA-TKA via the mini-subvastus approach.

METHODS

This prospective randomized controlled study included 234 patients who underwent KA-TKA and MA-TKA from January 2022 to October 2023. The preoperative and postoperative patellar tilt, lateral patellar shift, knee society score (KSS), oxford knee score (OKS), and intraoperative patellar lateral retinacular release (LRR) rate were measured. In addition, radiological parameters and clinical outcomes were compared between the LRR and non-LRR groups. Independent samples t test and chi-square test were used to compare the differences between groups.

RESULTS

Two-hundred and thirty-four patients were followed up for 12 months post-TKA. No significant differences were observed between the two groups in terms of the demographics and pre- or post-operative radiological parameters of patellar tracking (p > 0.05). The postoperative KSS and OKS were significantly higher in the KA group than in the MA group (p < 0.05). The LRR rate was 6.7% (8/120) in the KA group and 25.4% (29/114) in the MA group, and the difference was statistically significant (x 2 = 15.476, p < 0.001). The preoperative patella tilt and lateral patellar shift were greater in the LRR group (p < 0.001) and the postoperative OKS was lower (p < 0.05).

CONCLUSIONS

KA-TKA via the mini-subvastus approach can achieve both good patellar tracking and clinical outcomes. Avoiding muscle damage and refraining from excessive soft tissue release are crucial to improving postoperative patient comfort. In our opinion, KA-TKA via the mini-subvastus approach may be a more suitable surgical option.

Revision of Well-Fixed Mechanically-Aligned Total Knee Arthroplasty Using Kinematic Alignment for the Restoration of Joint Line Obliquity: Report of a Surgical Technique

Despite advances in technology and procedures, primary total knee arthroplasty can still result in an unsatisfied patient up to 20% of the time. Many indications for revising total knee arthroplasty have been established, including infection, aseptic loosening, wear, and instability. A newer indication being used in our center is that of a mechanically aligned knee, in which the prosthetic joint line has been substantially altered with respect to the native joint line. In this surgical technique report, we describe a method of revising a painful mechanically aligned total knee arthroplasty using the principles of kinematic alignment, using either the patient's preoperative long-axis radiographs, if available, or those of their contralateral limb, as a guide for the measurement of native joint line obliquity. Although this may be controversial, in our practice, this diagnosis has become an established indication for revision knee arthroplasty, with high success rates and patient satisfaction. In this brief surgical technique report, we present the details of one of our cases.

Comparative outcomes of kinematically aligned TKA with medial stabilized design vs. mechanically aligned TKA with bi-cruciate stabilized design: A propensity score-matched analysis

Purpose

Patient dissatisfaction after total knee arthroplasty (TKA) is often linked to altered knee kinematics and stability. This study compared the short-term clinical outcomes of kinematically aligned TKA (KA-TKA) and mechanically aligned TKA (MA-TKA) using bi-cruciate stabilized (BCS) implants.

Methods

In this propensity score-matched study, 60 patients who underwent either KA-TKA or MA-TKA (30 per group) with BCS implants were analyzed. Baseline characteristics, including age, sex, preoperative range of motion (ROM), and hip-knee-ankle alignment, were matched. ROM and clinical outcomes were evaluated preoperatively and at 1 year postoperatively using the 2011 Knee Society Score (KSS) subscales and Forgotten Joint Score-12 (FJS).

Results

At 1 year, the KA group achieved higher scores in KSS subscales for symptoms (23.2 vs. 20.0, p < 0.001), satisfaction (28.1 vs. 22.5, p < 0.001), functional activities (82.1 vs. 74.2, p = 0.011), and FJS (83.8 vs. 62.5, p < 0.001). No significant differences were observed in maximum extension, flexion, or KSS expectations.

Conclusions

KA-TKA demonstrated superior satisfaction and functional recovery than MA-TKA with BCS implants in the short term. These results suggested that KA-TKA, which reconstructs patient-specific alignment, may provide a more natural knee feel, leading to higher patient satisfaction compared to implant-driven BCS-TKA.

Coronal plane alignment changes do not affect outcome for total knee implant design with 3 degree varus joint line

BACKGROUND

Total knee arthroplasty (TKA) is a widely performed surgical intervention for symptomatic knee osteoarthritis (OA). However, the influence of coronal plane alignment on clinical outcomes remains unclear. This study evaluates whether alterations in the coronal plane alignment of the knee (CPAK) classification, using the same implant system, affect postoperative outcomes in patients undergoing robotic-assisted TKA.

METHODS

We conducted a retrospective review of 202 patients who underwent primary robotic-assisted TKA between 2019 and 2023 using NAVIO or CORI systems and Journey II implants. Patients were classified based on changes in CPAK classification and functional outcomes assessed using the Knee Society Score (KSS) and Knee Society Function Score (KSFS) at multiple postoperative time points. Statistical analyses compared outcomes between groups with changed and unchanged CPAK.

RESULTS

A total of 202 patients were included. Preoperative demographic characteristics were comparable between groups. Functional outcome scores at 6 weeks, 3 months, 6 months, and 12 months postoperatively showed no significant differences between the changed CPAK group and the unchanged CPAK group (p > 0.05 for all comparisons). Subgroup analyses further revealed no statistically significant disparities in functional outcomes based on the type or degree of CPAK changes.

CONCLUSION

Our findings suggest that changes in coronal plane alignment do not adversely affect functional outcomes following robotic-assisted TKA. This implies that alignment strategy may be less critical to patient satisfaction and functional recovery than previously assumed. Implant-induced alignment changes may contribute to comparable clinical outcomes and could be a key factor in patient recovery. Understanding the relationship between CPAK changes and clinical outcomes can inform best practices in knee arthroplasty, ultimately enhancing patient satisfaction and quality of life post-surgery.

The Benefit of Combining Kinematic Alignment and a Medial Pivot Implant in Total Knee Arthroplasty, The KA-MP Knee: Why and How

Kinematic alignment (KA) has emerged as an alternative alignment technique for total knee arthroplasty with the goal of duplicating the pre-arthritic joint surface. Medial pivot (MP) total knee implants duplicate the medial stability of the natural knee and recreate the medial rotational axis of the knee. Each has had favorable results. Combining the two, the KA-MP knee, creates a synergy and achieves better results than KA or MP alone.

Femoral resection accuracy and precision in manual caliper-verified kinematic alignment total knee arthroplasty

Introduction

The accuracy and precision of bone resections in total knee arthroplasty (TKA) are essential to avoid poor implant positioning, which can lead to component wear, pain, and instability, reducing patient satisfaction and implant survivorship. Technology-assisted TKA techniques aim to improve accuracy but come with added costs, increased operative time, and varying success in clinical outcomes. Caliper-verified kinematic alignment (KA) attempts to restore the joint line by precisely measuring resections to equal implant thickness. We evaluated the accuracy and precision of caliper-verified KA-TKA performed with manual instruments. We hypothesised that this technique would achieve high accuracy and precision, with an average absolute difference between actual and target distal and posterior femoral resection measurements of ≤ 0.5 mm.

Methods

385 consecutive patients underwent primary unrestricted caliper-verified KA-TKA with manual instrumentation. The thickness of the distal medial (DM), distal lateral (DL), posterior medial (PM) and posterior lateral (PL) femoral condyle resections were measured with a caliper and compared to a target determined by the degree of cartilage loss, saw blade kerf, and femoral component thickness.

Results

The mean differences between the resected and target thicknesses for DM, DL, PM and PL femoral resections were 0.1 ± 0.2 mm, 0.1 ± 0.3 mm, 0.3 ± 0.5 mm and 0.2 ± 0.4 mm, respectively (mean ± std. dev.). Most femoral resections were within 0.5 mm of the target-97.7%, 94.5%, 85.7% and 89.4% of DM, DL, PM and PL resections, respectively.

Conclusion

Manual caliper-verified KA-TKA achieved highly accurate and precise femoral resections with absolute differences from target that averaged 0.175 mm. This simple, logical, efficient, and reproducible surgical technique may be an option for surgeons contemplating the use of technology-assisted options, such as patient-specific instrumentation or robotic arm-assisted TKA, and surgeons without access to such technologies.

Level of Evidence

Level II.

Functional alignment restores native kinematics more consistently than mechanical axis alignment in total knee arthroplasty

Aims

Functional alignment (FA) and adjusted mechanical alignment (aMA) are recognized techniques for performing total knee arthroplasty (TKA). The native femur rolls back further on the lateral tibial plateau than the medial side during flexion, resulting in a medial pivot pattern of movement. We have assessed whether an individualized alignment technique affects the kinematic pattern observed and the clinical outcomes, when compared to a systematic alignment technique in TKA.

Methods

A total of 60 consecutive patients were randomized to a robotically assisted TKA with either FA (n = 29) or aMA (n = 31), using a cruciate-retaining (CR) implant. After definitive implantation of the prostheses, a trial pressure monitor was inserted recording contact points between the femoral component and monitor in the medial and lateral compartments as the knee was taken through a range of motion. The kinematic pattern was observed, contact pressures measured, and patient-reported outcome measures (PROMs) assessed at 12 months.

Results

The FA-TKA group produced a medial pivot in 58.6% of cases (17/29), symmetrical rollback in 37.9% (11/29), and a lateral pivot in 3.4% (1/29). The aMA-TKA group produced a medial pivot in 19.4% of cases (6/31), symmetrical rollback in 45.2% (14/31), and a lateral pivot in 35.5% (11/31) (p < 0.001). No differences in knee balance were recorded between the two alignment groups at any flexion point. Patients with a medial pivot kinematic pattern had superior one-year PROMs in some measures. Patients producing a lateral pivot had lower Kujala scores.

Conclusion

FA CR-TKA generates an intraoperative medial pivot kinematic pattern through soft-tissue balance more often than those that use aMA. Lateral pivot kinematic patterns are more commonly found with aMA. These intraoperative kinematic patterns are related to clinical outcomes, with knees producing a medial pivot performing better than those with lateral pivot.

Accuracy of matching tibial slope in manual kinematically aligned total knee arthroplasty

Background

Reproduction of the posterior tibial slope (PTS) during total knee arthroplasty (TKA) improves patient outcomes and minimizes complications including subsidence, polyethylene wear, and instability. The use of imaging has been previously studied as a way of measuring PTS angle and its association with surgical outcomes. There is a lack of literature on the accuracy of matching PTS during manual kinematically aligned (KA) TKA.

Methods

This is a retrospective study including 299 primary manual KA TKAs between October 2021 and August 2024 by a single surgeon. The primary outcome was comparison of pre-operative and post-operative PTS angles. Measurements were performed on lateral radiographs as the angle between the tangent line of the tibial plateau and a line perpendicular to the tibial shaft axis.

Results

The average pre-operative tibial slope was 10.3° (std dev, 4.8) compared to an average post-operative measurement of 5.3° (std dev, 3.2) (p < 0.00001). Range of motion improved post-operatively, with average extension increasing from 4.4° to 0.9° and flexion maintained from 118.5° to 117.2°. Complications were infrequent, with one superficial infection, two prosthetic joint infections requiring revision, two additional reoperations for polyethylene exchanges, and five manipulations under anesthesia with subsequent improvement in range of motion.

Conclusion

In this study, we found a significant difference in pre-operative and post-operative tibial slope angle on radiographic measurements following manual KA TKA.

Optimal arithmetic hip-knee-ankle angle for performing prearthritic/kinematic alignment in unicompartmental knee arthroplasty

BACKGROUND

This study aimed to investigate whether arithmetic hip-knee-ankle angle (aHKA) can be a surrogate for valgus stress radiography (VSR). Furthermore, we investigated the optimal cutoff values for preoperative radiographic parameters, thereby validating the appropriate inclusion criteria for prearthritic/kinematic unicompartmental knee arthroplasty (prearthritic-UKA).

METHODS

We retrospectively analyzed 123 patients who underwent medial UKA. We measured the HKA on VSR, termed sHKA. The aHKA was calculated by subtracting the lateral distal femoral angle from the medial proximal tibial angle. Prearthritic-UKA was defined as a postoperative HKA angle within 3° of the aHKA. We divided the patients into the prearthritic-UKA and non-prearthritic-UKA groups. To assess whether the aHKA serves as a surrogate for VSR, Spearman's rank correlations were performed among the radiographic parameters. These radiographic parameters calculated the proper criteria for prearthritic-UKA using receiver operating characteristic (ROC) curve analysis and logistic regression analysis.

RESULTS

Overall, 59 patients were classified into the prearthritic-UKA group. The aHKA was larger than the sHKA and exhibited no significant correlation with the sHKA. ROC analysis revealed that the cutoff values of aHKA for detecting overcorrected UKA (i.e., postoperative HKA - aHKA >3°) was -5.0°. Similarly, the cutoff values for detecting undercorrected UKA (i.e., postoperative HKA - aHKA <-3°) were -3°. Logistic regression analysis revealed that the aHKA was significantly associated with prearthritic-UKA.

CONCLUSION

The aHKA was not identified as a surrogate for the sHKA. Comprehensive preoperative radiographic assessment, including both aHKA and VSR, is crucial for optimizing UKA outcomes and minimizing risks of misalignment.

Two-Year Outcome Comparison of a Matched Set of Total Knee Arthroplasties Performed With Robotic-Arm-Assisted Functional Alignment Balancing or Manual Instrument-Assisted Adjusted Mechanical Alignment

BACKGROUND

Alternative strategies in total knee arthroplasties (TKAs) have been developed to obtain improved outcomes utilizing implant realignment and positioning to balance the soft tissues while accepting a nonneutral mechanical alignment. The purpose of our study was to compare 2-year outcomes of a matched set of TKAs with soft-tissue gaps either "functional" balanced via robotic-arm-assisted changes to implant position and alignment prior to bone cuts (R-TKA) or manual instrument-adjusted mechanical alignment (M-TKA). We hypothesized that the R-TKA cohort would have superior patient outcomes.

METHODS

A consecutive series of 210 TKAs matched 2:1 by selecting patients in each cohort with no statistically significant preoperative differences in sex, age, American Society of Anesthesiologist physical status classification system score, Knee Society knee scores (KS-KS) and Knee Society function scores (KS-FS), range of flexion (ROF), and knee coronal alignment. There were 140 R-TKA and 70 M-TKA with the same implants that were reviewed. Tibial pressure sensors were used in all cases to verify balance. Postoperative KS-KS, KS-FS, and ROF were compared at 3 months and 2 years, and Forgotten Joint Scores (FJS) were obtained at 2 years.

RESULTS

Both groups achieved equivalent quantitative balance with the pressure sensors. The functional alignment-balanced R-TKA cohort had more component realignments (100 versus 35.7%), fewer soft-tissue releases (40 versus 61.4%), and statistically significant higher mean KS-KS, KS-FS, and ROF at 3 months and 2 years than the M-TKA group. The mean FJS was higher in the R-TKA group (66.3 versus 60.4), but this did not represent a statistical significance.

CONCLUSIONS

A functional alignment balancing technique using robotic-arm assistance resulted in fewer soft-tissue releases and higher Knee Society outcome scores and knee flexion than with M-TKA at 3 months and 2 years, despite equivalent soft-tissue balance per the pressure sensors. The mean FJS at 2 years was greater, but not statistically significant.

Excellent results of restricted kinematic alignment total knee arthroplasty at a minimum of 10 years of follow-up

PURPOSE

While restricted kinematic alignment (rKA) total knee arthroplasty (TKA) with cemented implants has been shown to provide a similar survivorship rate to mechanical alignment (MA) in the short term, no studies have reported on the long-term survivorship and function.

METHODS

One hundred four consecutive cemented cruciate retaining TKAs implanted using computer navigation and following the rKA principles proposed by Vendittoli were reviewed at a minimum of 10 years after surgery. Implant revisions, reoperations and clinical outcomes were assessed using knee injury and osteoarthritis outcome score (KOOS), forgotten joint score (FJS), patients' satisfaction and joint perception questionnaires. Radiographs were analyzed to identify signs of osteolysis and implant loosening.

RESULTS

Implant survivorship was 99.0% at a mean follow-up of 11.3 years (range: 10.3-12.9) with one early revision for instability. Patients perceived their TKA as natural or artificial without limitation in 50.0% of cases, and 95.3% were satisfied or very satisfied with their TKA. The mean FJS was 67.6 (range: 0-100). The mean KOOS were as follows: pain 84.7 (range: 38-100), symptoms 85.5 (range: 46-100), function in daily activities 82.6 (range: 40-100), function in sport and recreation 35.2 (range: 0-100) and quality of life 79.1 (range: 0-100). No radiological evidence of implant aseptic loosening or osteolysis was identified.

CONCLUSION

Cemented TKA implanted with the rKA alignment protocol demonstrated excellent long-term implant survivorship and is a safe alternative to MA to improve patient function and satisfaction.

LEVEL OF EVIDENCE

Level IV, continuous case series with no comparison group.

Kinematic Alignment Compared With Mechanical Alignment Techniques Results in Greater Peak Three-Dimensional Knee Joint Moments During Stair Negotiation

BACKGROUND

This study investigated the influence of surgical alignment techniques on knee joint biomechanics during stair negotiation tasks. Our hypothesis was that a more personalized joint alignment would result in reduced medial knee loading biomechanics to negotiate the stairs.

METHODS

There were 28 adults (14 mechanical alignments [MAs] and 14 kinematic alignment [KA]) who underwent total knee arthroplasty at least one year postoperatively and performed five stair ascent and descent trials at their preferred velocities. The three-dimensional knee joint moments were calculated using a six-degree-of-freedom model in Visual 3D. Data were tested for normality using the Shapiro-Wilk test. Cohen's d was used to quantify effect size magnitude.

RESULTS

The KA technique methods were associated with greater knee moments compared with the MA technique. Due to the minimal differences in joint line between the groups, the greater trunk lean observed in the MA technique, and the preservation of soft tissue structures in the KA technique, the KA technique's lower extremity biomechanics enabled patients to move in a more symmetric manner within the frontal plane. This contrasted with the MA technique, which might result in an avoidance strategy during stair negotiation.

CONCLUSIONS

Since our joint line did not significantly change between technique groups, future work is warranted to understand the effects of joint line-driven changes on lower extremity joint biomechanics in total knee arthroplasty populations.

LEVEL OF EVIDENCE

Level 2 prospective cohort study.

Image-based robotic (ROSA® knee system) total knee arthroplasty with inverse kinematic alignment compared to conventional total knee arthroplasty : Study protocol and the inverse kinematic alignment in 8-steps using the ROSA® Knee system for knee balancing technique explained

INTRODUCTION

In 2020, 368 million people globally were affected by knee osteoarthritis, and prevalence is projected to increase with 74% by 2050. Relatively high rates of dissatisfactory results after total knee arthroplasty (TKA), as reported by approximately 20% of patients, may be caused by sub-optimal knee alignment and balancing. While mechanical alignment has traditionally been the goal, patient-specific alignment strategies are gaining interest. Robotic assistance could potentially facilitate implementation of these alignment strategies through data-based surgical planning, accurate execution of the surgical plan and validation. The clinical value of surgical assistance in diverging from mechanical alignment remains to be investigated. In the present study, robotic-assisted TKA will be performed to pursue inverse kinematic alignment (iKA) within predefined boundaries, focusing on restoring native tibia joint line.

METHODS

This randomized controlled trial evaluates clinical effectiveness of robotic-assisted TKA (ROSA® Knee System, Zimmer Biomet, Montreal, Quebec, Canada) aiming for iKA compared to conventional TKA aiming for mechanical alignment. A total of 150 participants will be randomized (1:1) to either treatment to provide an 80% power for a 4.8-point clinically important difference in the primary outcome measure, the Oxford Knee Score (OKS) 12 months after surgery. Allocation was achieved using computer-based randomization. Outcomes will be analyzed using linear mixed models with time and group as main factors and interaction-term. Secondary outcomes include clinical metrics (leg alignment, implant and patient survival), surgical parameters (adverse events, surgery duration, blood loss, hospital stay length, medication use), patient-reported outcomes (symptoms, quality of life, pain), mobility and physical activity measurements, metabolic syndrome, cost-efficacy, and gait and continuous glucose monitoring.

ETHICS AND DISSEMINATION

This study has been approved by the Medical Ethical Committee Zuyd and Zuyderland Medical Centre (NL79161.096.21/METCZ20220006), September 2022.

TRIAL REGISTRATION NUMBER

NCT05685693 (clinicaltrials.gov).

Functional alignment is a feasible alignment strategy in robotic assisted total knee arthroplasty for knee osteoarthritis with extra-articular deformity - A case series

INTRODUCTION

Extraarticular deformity (EAD) with knee arthritis is a complex condition involving tri-planar bone deformity with pathological malalignment and chronic soft tissue contracture or laxity in the knee joint. Intraarticular correction by TKA, which was previously performed with conventional manual jig by mechanical alignment technique, had its limits and difficulties especially extensive soft tissue release and risk of jeopardizing the collateral ligaments. Robotic technology allows for reproducible and precise execution of surgical plan and allows adjustment to various new personalised alignment philosophy including functional alignment (FA). FA technique involves the adjustment of components positioning that least compromise the soft tissue envelope while restoring the limb alignment and joint obliquity to create a balanced knee. The aim is to study the outcome of intra-articular correction by robotic assisted TKA using Functional Alignment (FA) technique.

METHODOLOGY

This is a single surgeon series of 8 patients with extraarticular deformity who underwent robotic assisted total knee arthroplasty (TKA) with FA technique. Soft tissue release was gradually released and followed by adjustments of implant positioning in order to achieve a balanced medio-lateral gap.

RESULTS

Postoperatively, the lower limb alignment of all patients were restored within 6° (mean 4.54°) based on functional alignment boundaries. Knee phenotype and joint line obliquity (JLO) were restored in comparison to contralateral lower limb. There were 6 varus and 2 valgus malalignment. 7 patients were implanted with posterior stabilized implants while 1 was implanted with cruciate retaining implant. Arc of knee flexion and extension improved (P = 0.002). There was a large postoperative improvement in the Knee Society Score (KSS) (P < 0.001).

DISCUSSION

Intraarticular correction by TKA for EAD with knee arthritis is technically reliable with robotic technology. It allows intraoperative adjustment following functional alignment philosophy, thereby, restoring pre-arthritic alignment, knee phenotype and joint line obliquity.

Cartilage thickness can be accurately measured intraoperatively in total knee arthroplasty: A step further in calipered kinematic alignment

Introduction

Kinematic alignment (KA) in total knee arthroplasty (TKA) is by definition a pure femoral resurfacing procedure aiming to restore the individual prearthritic anatomy. However, when a 2 mm compensation is systematically used on the worn side, the variability in cartilage thickness in the unworn compartment might alter the accuracy of the technique. This study aimed to validate two intraoperative femoral cartilage thickness measurement techniques by comparing them to the photographic method, which measures cartilage thickness through pixel analysis of bone-cut images. The study hypothesized that the two intraoperative methods are comparable and similarly accurate within 0.5 mm of the photographic method.

Methods

Seventy cartilage thickness measurements from seventy patients with end-stage knee osteoarthritis were prospectively collected. Two intraoperative techniques were evaluated: the electrocautery tip method (Method A) and the ruler method (Method B), performed before and after distal femoral bone resections, respectively. The postoperative photographic analysis (Method C) served as the reference method. Measurements were rounded to the nearest 0.5 mm for consistency. Data were analyzed using Kruskal-Wallis test, Wilcoxon rank-sum tests, Spearman's rank correlation, percentage of agreement and intraclass correlation coefficients (ICCs).

Results

No significant differences were observed between Method A and Method B in measuring femoral cartilage thickness. Agreement with Method C was 100% for Method B and 85% for Method A. In the 15% of discordant cases, Method A overestimated the measurements by one category of 0.5 mm compared to Method C. Correlation coefficients between the methods were high (ρ = 0.88-1.0). Intra- and interobserver reliability was high for all methods (ICCs 0.91-0.95).

Discussion

Both intraoperative methods are reliable and comparable to the photographic method when rounded to the closest 0.5 mm, with no significant differences among them. The electrocautery method has the added advantage of measuring cartilage thickness before bone cuts are performed.

Level of Evidence

Level IV.

Coronal Plane Alignment of the Knee (CPAK) Type Shifts Toward Constitutional Varus with Increasing Kellgren and Lawrence Grade: A Radiographic Analysis of 17,365 Knees

BACKGROUND

Studies investigating constitutional alignment across various grades of osteoarthritis (OA) are limited. This study explored the distribution of Coronal Plane Alignment of the Knee (CPAK) types and associated radiographic parameters with increasing OA severity.

METHODS

In this retrospective cross-sectional study, 17,365 knees were analyzed using deep learning software for radiographic measurements. Knees were categorized on the basis of the Kellgren and Lawrence (KL) grade and CPAK type. Radiographic measurements were the hip-knee-ankle angle (HKAA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), arithmetic HKAA (aHKA), joint line obliquity (JLO), and joint line convergence angle (JLCA). Age-stratified analysis was performed to differentiate the impact of age on OA severity.

RESULTS

A shift in the most common CPAK type from II to I was found with increasing KL grade (p < 0.05). Furthermore, there was a corresponding increase in LDFA and JLCA with increasing KL grade, while HKAA, MPTA, and aHKA decreased after KL grade 2. Age exhibited limited association with LDFA and MPTA, suggesting that OA severity is the dominant factor related to the CPAK distribution.

CONCLUSIONS

The study found a shift in CPAK type with worsening OA. It is possible that constitutional varus types are more susceptible to OA, or that their increased OA prevalence is related to anatomical changes. This analysis offers new insights into alterations in CPAK type that occur with OA and underscores the importance of understanding pre-arthritic anatomy when performing joint reconstruction.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

A new tibial insert design with ball-in-socket medial conformity and posterior cruciate ligament retention has low tibial baseplate migration after unrestricted kinematically aligned total knee arthroplasty: a cohort study using radiostereometric analysis

BACKGROUND AND PURPOSE

 In total knee arthroplasty (TKA), an insert with ball-in-socket (BS) medial conformity (MC) and posterior cruciate ligament (PCL) retention restores kinematics closer to native than an insert with intermediate (I) MC. However, high medial conformity might compromise baseplate stability as indicated by maximum total point motion (MTPM). Using the BS MC insert with PCL retention, we aimed to determine whether (i) the baseplate is stable as indicated by mean MTPM < 0.5 mm, (ii) baseplate stability is not strongly correlated to varus baseplate alignment, and (iii) baseplate stability, clinical outcome scores, and flexion are comparable with that of an I MC insert cohort which has demonstrated high stability, clinical outcome scores, and flexion.

METHODS

 Unrestricted kinematic alignment (unKA) TKA was performed on a cohort of 35 patients using a cemented baseplate. Biplanar radiographs acquired at timepoints up to 12 months were processed with model-based radiostereometric analysis (RSA) software to determine MTPM.

RESULTS

 At 1 year, mean MTPM of 0.35 mm was significantly below 0.5 mm (P < 0.001). MTPM was not strongly correlated to varus baseplate alignment up to 9° (r = 0.12, 95% confidence interval -0.22 to 0.44). Equivalence analyses revealed that MTPM, Forgotten Joint Score, Oxford Knee Score, and maximum flexion for the sBS MC insert were comparable with the I MC insert.

CONCLUSION

 Using the new BS MC insert with PCL retention, the tibial baseplate was stable at the group level at 1 year. Baseplate stability was not strongly related to varus baseplate and limb alignment. Comparable patient-reported outcome scores and maximum flexion/extension at 1 year were shown between the 2 insert designs.

A case-matched series comparing functional outcomes for robotic-assisted unicompartmental knee arthroplasty versus functionally aligned robotic-assisted total knee arthroplasty

Aims

Unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) have both been shown to be effective treatments for osteoarthritis (OA) of the knee. Many studies have compared the outcomes of the two treatments, but less so with the use of robotics, or individualized TKA alignment techniques. Functional alignment (FA) is a novel technique for performing a TKA and shares many principles with UKA. Our aim was to compare outcomes from a case-matched series of robotic-assisted UKAs and robotic-assisted TKAs performed using FA.

Methods

From a prospectively collected database between April 2015 and December 2019, patients who underwent a robotic-assisted medial UKA (RA-UKA) were case-matched with patients who had undergone a FA robotic-assisted TKA (RA-TKA) during the same time period. Patients were matched for preoperative BMI, sex, age, and Forgotten Joint Score (FJS). A total of 101 matched pairs were eligible for final review. Postoperatively the groups were then compared for differences in patient-reported outcome measures (PROMs), range of motion (ROM), ability to ascend and descend stairs, and ability to kneel.

Results

Both groups had significant improvements in mean FJS (65.1 points in the TKA group and 65.3 points in the UKA group) and mean Oxford Knee Score (OKS) (20 points in the TKA group and 18.2 in the UKA group) two years following surgery. The UKA group had superior outcomes at three months in the OKS and at one year in ROM (5°), ability to kneel (0.5 points on OKS question), and ascend (1.3 points on OKS question) and descend stairs (0.8 points on OKS question), but these were not greater than the minimal clinically important difference. There were no differences seen in FJS or OKS at one year postoperatively. There were no statistically significant differences between the groups at 24 months in all the variables assessed.

Conclusion

FA-RATKA and RA-UKA are both successful treatments for medial compartmental knee arthritis in this study. The UKA group showed a quicker recovery, but this study demonstrated equivalent two-year outcomes in all outcomes measured including stair ascent and descent, and kneeling.

Principles and biomechanical response of normal gait cycle to measure gait parameters for the alignment of prosthetics limb: A technical report

The limb amputations caused due to emergent incidents of trauma injuries and vascular diseases currently represent crucial global problems. The patients/amputees with limb amputation who lost the residual limb (knee-ankle foot system) must depend on the prosthetic limb. Prosthetic clinicians and technicians have attempted to develop optimal limb prosthetics that will enhance the ability and functional elements of the patients/users. However, the amputees still do not gain the same level of comfort and functional stability as compared to normal limbs (without amputation). Thus, to provide that comfort and stability, proper construction with accurate positioning and alignment of constructed prosthetic limb is crucial to reconstitute these amputees/patients to do their activities for daily life. The objective of technical report is to provide the brief summary about basic principle and biomechanics regarding gait analysis, construction, and alignment of prosthetic limb during gait cycle. The study also summarized the kinematics and kinetic biomechanical response of prosthetic limbs to assess the biomechanics of limb prosthetics, socket assembly principle, gait parameters, and static and dynamic alignment during walking. The basic principle of positioning and alignment with different flexion and torque moment at hip, knee, and ankle joint has been analyzed.

Impact of Joint Laxity on 2-Year KOOS Outcomes of Posterior Stabilized Total Knee Arthroplasty

The objective of this study was to determine relationships between intraoperative posterior cruciate ligament (PCL) sacrificing posterior stabilized (PS) total knee arthroplasty (TKA) laxity measurements throughout flexion and patient outcomes at 2 years post-TKA and to define clinically relevant laxity thresholds to optimize patient outcomes.In a single-surgeon study, PCL sacrificing TKA using a robotics-assisted platform with a digital joint tensioning device was performed in 115 knees in 115 patients. Final intraoperative joint laxity was recorded, and 2-year Knee Injury and Osteoarthritis Outcome Scores (KOOSs) were obtained. A Simulated Annealing optimization algorithm was used to identify medial and lateral laxity windows which maximized the 2-year KOOS pain score. Wilcoxon nonparametric tests were used to compare outcomes between groups.Significant associations were found between intraoperative joint laxity and 2-year KOOS pain outcomes throughout flexion. Clinically relevant laxity windows were defined medially and laterally in mid-flexion and flexion for improved outcomes, whereas only a lateral laxity window could be defined in extension. When all laxity windows were satisfied, a 14.5-KOOS point improvement was found (97.2 vs. 77.8, p = 0.0060) compared to knees which did not satisfy any window. Improvements in Activities of Daily Living (Δ8.8, p = 0.0143), Sports (Δ22.5, p = 0.0108), and Quality of Life (Δ18.7, p = 0.0011) KOOS subscores were also found in knees which satisfied all windows versus 0-1 window.Intraoperative joint laxity is associated with postoperative outcomes in a PS knee design, wherein patients balanced within identified laxity targets reported improved outcomes over those that did not. Clinically significant thresholds were defined and were predominately found in mid-flexion and flexion for medial and lateral laxity. When target windows were combined further improved outcomes were identified.

Mechanically aligned total knee arthroplasty does not yield uniform outcomes across all coronal plane alignment of the knee (CPAK) phenotypes

PURPOSE

Patient dissatisfaction rates following total knee arthroplasty (TKA) reported in the literature reach 20%. The optimal coronal alignment is still under debate. The aim of this retrospective study was to compare clinical outcomes in different coronal plane alignment of the knee (CPAK) phenotypes undergoing mechanically aligned (MA) TKA. The hypothesis was that knees with preoperative varus arithmetic hip-knee-ankle angle (aHKA) would achieve inferior clinical outcomes after surgery compared to other aHKA categories. Additionally, another objective was to assess CPAK phenotypes distribution in the study population.

METHODS

A retrospective selection was made of 180 patients who underwent MA TKA from April 2021 to December 2022, with a 1-year follow-up. Coronal knee alignment was classified according to the CPAK classification. Clinical outcome evaluations were measured using the Knee Society Score (KSS), Oxford Knee Score (OKS), Short Form Survey 12 and Forgotten Joint Score (FJS). Differences in clinical outcomes were considered statistically significant with a p value <0 .05.

RESULTS

Patients with varus aHKA achieved significantly inferior outcomes at final follow-up compared to other aHKA categories in KSS pt. 1 (79.7 ± 17.2 vs. 85.6 ± 14.7; p = 0.028), OKS (39.2 ± 9.2 vs. 42.2 ± 7.2; p = 0.019) and FJS (75.4 ± 31.0 vs. 87.4 ± 22.9; p =0 .003). The most common aHKA category was the varus category (39%). The most common CPAK phenotypes were apex distal Types I (23.9%), II (22.8%) and III (13.3%).

CONCLUSION

MA TKA does not yield uniform outcomes across all CPAK phenotypes. Varus aHKA category shows significantly inferior results at final follow-up. The most prevalent CPAK categories are varus aHKA and apex distal JLO, with phenotypes I, II and III being the most common. However, their gender distribution varies significantly.

LEVEL OF EVIDENCE

Level IV.

Inverse kinematic total knee arthroplasty using conventional instrumentation restores constitutional coronal alignment

PURPOSE

Restricted inverse kinematic alignment (iKA) is a contemporary alignment strategy for total knee arthroplasty (TKA), commonly performed with robotic assistance. While superior clinical results are reported for kinematic-type alignment strategies, registry data indicate no survivorship benefit for navigation or robotic assistance. This study aimed to determine the efficacy of an instrumented, restricted iKA technique for achieving patient-specific alignment.

METHODS

Seventy-nine patients undergoing 84 TKAs (five bilateral procedures) using an iKA technique were included for preoperative and postoperative lower limb alignment analysis. The mean age was 66.5 (range: 43-82) with 33 male and 51 female patients. Artificial intelligence was employed for radiographic measurements. Alignment profiles were classified using the Coronal Plane Alignment of the Knee (CPAK) system. Preoperative and postoperative alignment profiles were compared with subanalyses for preoperative valgus, neutral and varus profiles.

RESULTS

The mean joint-line convergence angle (JLCA) reduced from 2.5° to -0.1° postoperatively. The mean lateral distal femoral angle (LDFA) remained unchanged postoperatively, while the mean medial proximal tibial angle (MPTA) increased by 2.5° (p = 0.001). By preservation of the LDFA and restoration of the MPTA, the mean hip knee ankle angle (HKA) moved through 3.5° varus to 1.2° valgus. The CPAK system was used to visually depict changes in alignment profiles for preoperative valgus, neutral and varus knees; with 63% of patients observing an interval change in classification.

CONCLUSION

Encouraged by the latest evidence supporting both conventional instrumentation and kinematic-type TKA strategies, this study describes how a restricted, conventionally instrumented iKA technique may be utilised to restore constitutional lower limb alignment.

LEVEL OF EVIDENCE

Level III.

Modified kinematic alignment better restores plantar pressure distribution than mechanical alignment in total knee arthroplasty: a randomized controlled trial

Kinematic alignment (KA) in the short to medium term clinical outcomes is superior to the mechanical alignment (MA), but whether it will improve patients' postoperative gait is still controversial. Understanding whether and how KA influences postoperative gait mechanics could provide insights into optimizing alignment philosophy to improve functional outcomes. To investigate the impact of KA versus MA in total knee arthroplasty (TKA) on the operated and contralateral native lower limbs by analyzing plantar pressure distribution during walking gait. This study was designed as a secondary analysis from a randomized controlled trial. Thirty-seven patients were included, nineteen underwent KA-TKA and eighteen underwent MA-TKA, each with a native knee in the contralateral limb. Pressure-sensitive insoles were used to collect plantar pressure distribution of both limbs simultaneously during walking defined as medial-lateral load ratio (MLR). Perioperative characteristics including radiographic metrics (Hip-Knee-Ankle angle (HKA), mechanical lateral distal femoral angle (mLDFA), and mechanical medial proximal tibial angle (mMPTA) and clinical outcomes (Oxford Knee Scores (OKS)) were compared between the two groups pre-operatively and 2-year postoperatively. Significant differences were found in postoperative radiographic metrics, with KA showing better OKS 1 year postoperatively (p = 0.021), lower mean HKA (p = 0.009) and mMPTA (p < 0.001). Other perioperative characteristics were similar between groups. In the pedobarographic analysis, the MA group demonstrated greater medial pressure distribution in forefoot compared to both the KA group (p < 0.001) and the contralateral native knee (p = 0.002). Besides, the MA group revealed a more lateral pressure distribution in rearfoot compared to the KA group (p = 0.007) and the contralateral native knee (p = 0.001). While there was no significant difference between KA and native group (p = 0.064 and p = 0.802, respectively). KA offered advantages over MA in restoring a more physiologic plantar pressure distribution at two years postoperatively. These results underscore the potential clinical benefits of adopting KA techniques in TKA procedures.

Gait analysis of a kinematic retaining implant for Total knee replacements during walking and running

Background

The analysis of gait is an important tool for evaluating postoperative outcomes of a Total Knee Replacement (TKR). There are few studies which have evaluated the gait parameters of a Kinematic retaining (Kr) prosthesis. This study therefore aims to investigate the kinetic and kinematic differences of running and walking, in the ankle, knee and hip joints in patients who underwent a Kr TKR.

Methods

This study assessed the gait of 12 patients with physica lima Kr TKRs at 1 year follow up and 8 healthy controls using 3D video analysis. Data was collected on the kinetics and kinematics of walking and running at the ankle, knee and hip. Comparison was made between the operated and non-operated limbs of the patients, and between the operated and control limbs.

Results

Gait analysis showed no statistically significant difference in the hip, ankle and knee angles or moments between the non-operated and operated legs during walking and running. However, there was a statistically significant difference between the knee angles of initial contact, maximum flexion during stance and swing in the TKR knees vs controls in walking and running. Similarly, there was also a statistically significantly higher max knee flexion moment between operated knees and controls in both walking and running.

Conclusion

This study has shown that a quadriceps avoidance gait persists in patients after TKR, and that there was symmetry and reciprocated gait parameters in non-operated limbs. These findings suggest that Kr TKRs could be capable of replicating normal knee kinematics when running and walking.

Pre- and postoperative Coronal Plane Alignment of the Knee classification and its impact on clinical outcomes in total knee arthroplasty

Aims

The Coronal Plane Alignment of the Knee (CPAK) classification has been developed to predict individual variations in inherent knee alignment. The impact of preoperative and postoperative CPAK classification phenotype on the postoperative clinical outcomes of total knee arthroplasty (TKA) remains elusive. This study aimed to examine the effect of postoperative CPAK classification phenotypes (I to IX), and their pre- to postoperative changes on patient-reported outcome measures (PROMs).

Methods

A questionnaire was administered to 340 patients (422 knees) who underwent primary TKA for osteoarthritis (OA) between September 2013 and June 2019. A total of 231 patients (284 knees) responded. The -Knee Society Score 2011 (KSS 2011), Knee injury and Osteoarthritis Outcome Score-12 (KOOS-12), and Forgotten Joint Score-12 (FJS-12) were used to assess clinical outcomes. Using preoperative and postoperative anteroposterior full-leg radiographs, the arithmetic hip-knee-ankle angle (aHKA) and joint line obliquity (JLO) were calculated and classified based on the CPAK classification. To investigate the impact on PROMs, multivariable regression analyses using stepwise selection were conducted, considering factors such as age at surgery, time since surgery, BMI, sex, implant use, postoperative aHKA classification, JLO classification, and changes in aHKA and JLO classifications from preoperative to postoperative.

Results

The preoperative and postoperative CPAK classifications were predominantly phenotype I (155 knees; 55%) and phenotype V (73 knees; 26%), respectively. The change in the preoperative to postoperative aHKA classification was a significant negative predictive factor for KOOS-12 and FJS-12, while postoperative apex proximal JLO was a significant negative predictive factor for KSS 2011 and KOOS-12.

Conclusion

In primary TKA for OA, preoperative and postoperative CPAK phenotypes were associated with PROMs. Alteration in varus/valgus alignment from preoperative to postoperative was recognized as a negative predictive factor for both KOOS-12 and FJS-12. Moreover, the postoperative apex proximal JLO was identified as a negative factor for KSS 2011 and KOOS-12. Determining the target alignment for each preoperative phenotype with reproducibility could improve PROMs.

Kinematic and mechanical alignments in total knee arthroplasty: A meta-analysis with ≥1-year follow-up

BACKGROUND

Kinematic and mechanical alignment outcomes in total knee arthroplasty remain controversial. This study compared the clinical and radiological outcomes of total knee arthroplasty using kinematic and mechanical alignments.

METHODS

We systematically searched PubMed, EMBASE, Web of Science, and Cochrane Library databases for randomized controlled trials and cohort studies published before November 2022. The data of interest were extracted and analyzed using Review Manager V.5.4.

RESULTS

Nineteen randomized controlled trials and cohort studies involving 880 kinematic alignment total knee arthroplasties and 965 mechanical alignment total knee arthroplasties were included. In this meta-analysis, the kinematic alignment group achieved better knee joint function scores, including the Oxford Knee Score, Knee Injury and Osteoarthritis Outcome Score, and Knee Society Score, and better flexion angles. No statistical differences were detected in the Western Ontario and McMaster Universities Osteoarthritis Index, extension angle, Forgotten Joint Score, European Quality of Life five-dimension measure, hip-knee-ankle angle, or complications between the kinematic and mechanical alignment groups.

CONCLUSION

This meta-analysis indicated that kinematic alignment total knee arthroplasty provides clinical benefits in terms of the Oxford Knee Score, Knee Injury and Osteoarthritis Outcome Score, Knee Society Score (knee), Knee Society Score (function), and better flexion angles. In addition, kinematic alignment total knee arthroplasty led to similar clinical outcomes as mechanical alignment total knee arthroplasty without increasing complications.

SYSTEMATIC REVIEW REGISTRATION

http://www.crd.york.ac.uk/PROSPERO/CRD42022373227.

The Viability and Success of Noncemented Kinematic Total Knee Arthroplasty

BACKGROUND

The prevalence of noncemented total knee arthroplasty (TKA) is increasing as personalized knee alignment strategies deviate from implanting components on a strict mechanical axis. This retrospective study evaluated the outcomes of 74 consecutive noncemented unrestricted kinematic TKA procedures.

METHODS

This study included 74 consecutive noncemented kinematic TKAs performed by one surgeon at a tertiary academic medical center from 2021 to 2023. The technique used was unrestricted femur-first caliper kinematic TKA. The outcomes included revision, pain scores, and radiographic measurements.

RESULTS

Of the 74 procedures performed, there were no revisions or readmissions for problems related to TKA. The mean follow-up was 17.6 months, with 74% of patients being followed up for more than 1 year postoperatively. On the day of surgery, postoperative measurements showed that the average tibial mechanical, distal femoral, and anatomic tibiofemoral angles were 3.3°, 7.7°, and 5.8°, respectively. 5 knees were observed initially with signs of radiolucency, which all resolved by the most recent appointment. None of the knees was radiographically loose. Of the patients, 65%, 19%, and 16% reported no pain, minimal pain, and some pain, respectively, at the 6-week follow-up visit. This improved to 78%, 19%, and 3% at the most recent follow-up.

CONCLUSION

Combining kinematic alignment with noncemented fixation showed excellent clinical and radiographic outcomes with short-term survivorship. Although the use of both kinematic alignment and noncemented TKAs has been controversial, these early data suggest that noncemented kinematic TKA is safe and effective.

Total knee replacement with an accelerometer-based, hand-held navigation system improves knee alignment: reliable in all patients

BACKGROUND

Achieving adequate alignment has traditionally been an important goal in total knee arthroplasty to achieve long-term implant survival. While accelerometer-based hand-held navigation systems (ABN) has been introduced as a way to achieve alignment, there is a limited body of evidence on its accuracy, especially in patients under 65 years with differing etiologies for knee arthritis. This study aimed to assess the precision of a specific ABN system in restoring the mechanical axis and report surgical variables and complications, with particular attention to younger patients.

METHODS

We conducted a retrospective review of 310 primary TKA performed with ABN from May 2016 to February 2021. The mean patient age was 67.4 (SD 8.9) years, with 43% under 65 years and mean body mass index of 33.2 (SD 6.8). The average surgical time was 96.8 min (57-171) and the average follow-up was 3.3 years (1.9-6.7). Data regarding length of stay, pain, range of motion (ROM), complications, and reinterventions were collected from the institutional joint arthroplasty registry and the medical records. Preoperative mechanical axis measurements and postoperative radiological data, including mechanical axis, component alignment and mechanical alignment outliers were analyzed.

RESULTS

The mean preoperative mechanical axis was 175.4° (SD 7.6), with 248 knees (80%) in preoperative varus. The mean postoperative mechanical axis was 179.5° (SD 1.96) with 98% of knees falling within ± 3° of the neutral mechanical axis. Only 6 knees (2 varus, 4 valgus) fell outside the ± 3° range. And 3 knees (1 varus, 2 valgus) fell outside the ± 5° range. In the sagittal plane, 296 knees (95.5%) knees were within ± 3° of goal of 3 degrees of femoral flexion and 302 (97.4%) knees were within ± 2° of goal 1° of slope for tibial component. Far outliers (alignment outside ± 5° of targeted position) were found in 3 knees. Factors such as posttraumatic arthrosis, previous surgery, presence of retained hardware, and age below 65 years were not associated with increase in alignment outliers and far outliers. No complications related to the navigation system were observed. There were 22 complications and 20 reoperations, including 2 revisions for periprosthetic joint infection and 1 revision for flexion instability. Patients that required knee manipulation achieved an ultimate flexion of 110° (SD 14.1).

CONCLUSIONS

The ABN system proved to be user-friendly and accurate in reducing alignment outliers in both coronal and sagittal planes in all patient populations. It offers a straightforward navigation solution while preserving surgeon autonomy and the use of traditional surgical tools. These findings advocate for the integration of this navigation system as a valuable tool to enhance the precision of TKA surgery in all patient groups.

Predictive Accuracy Analysis of a Novel Robotic-Assisted System for Total Knee Arthroplasty:A Prospective Observational Study

Background

Robotic-assisted total knee arthroplasty (RATKA) has been reported to enhance operative decision-making. The purpose of this study was intended to assess the predictive accuracy of bone cuts, lower limb alignment, and component size of a novel system for RATKA preoperatively and intraoperatively.

Methods

Preoperatively planned bone cuts, limb alignment, and component size were projected using a reconstructed 3D model. Intraoperative bone cuts and postoperative limb alignment were measured. Errors between planned and real bone cuts, limb alignment, and component size were compared.

Results

The mean absolute errors for bone cuts and alignment were within 1.40mm/1.30° with a standard deviation (SD) of 0.96mm/1.12°. For all errors of bone cuts and alignment compared with the plan, there were no statistically significant differences except for the lateral distal of femoral cuts (P=0.004). The accuracy for predicting the femoral, tibial, and polyethylene component sizes was 100% (48/48), 90% (43/48), and 88% (42/48), respectively. Regarding all mean absolute errors of bone cuts and alignments, no significant differences were observed among surgeons.

Conclusion

The novel robotically-assisted system for RATKA donated reliable operative decision-making based on the predictive accuracy regardless of the surgeon's level of experience.

A Restricted Functional Balancing Technique for Total Knee Arthroplasty With a Varus Deformity: Does a Medial Soft-Tissue Release Result in a Worse Outcome?

BACKGROUND

A functional alignment technique for total knee arthroplasty (TKA) utilizes implant position modifications to balance the soft tissues. There is concern that, in some cases, extreme coronal and tibial component alignment could facilitate early implant failure. To be cautious, a restricted functional alignment may be used. The purpose of our study was to evaluate the results of TKA in patients who have varus deformities using a restricted functional alignment technique. We hypothesized that adding a medial soft-tissue release within restricted boundaries would not result in inferior outcomes.

METHODS

A retrospective review was performed on robotic arm-assisted TKA patients with varus deformities utilizing a functional balancing strategy with a three-degree varus coronal limb and tibial component alignment restriction. Outcome scores of those patients still requiring a medial-soft tissue release were compared to those without for inferior outcomes.

RESULTS

A total of 202 of 259 (78.0%) knees were able to be balanced without any medial soft-tissue release with an average final hip-knee-ankle alignment of 1.9° varus. The remaining 57 knees required a medial soft-tissue release. They had an average final hip-knee-ankle of 2.8° varus and an average medial proximal tibial angle of 2.5° varus. Comparing the cohorts without and with a release, at final follow-up averaging two years, there was not a statistically significant difference in Knee Society-Knee Score (97.7 and 98.4, P = .525), Functional Score (86.7 and 88.7, P = .514), Forgotten Joint Score (59.8 and 66.6, P = .136), and Knee Injury Osteoarthritis Outcome Survey for Joint Replacement Junior Score (79.5 and 84.8, P = .066).

CONCLUSIONS

Utilizing a restrictive functional balancing strategy for TKA minimizes the need for soft-tissue releases and provides for excellent overall outcomes. An additional medial soft-tissue release can still be utilized without an inferior average two-year outcome.

A retrospective comparison of mechanically vs. kinematically aligned unicompartmental knee arthroplasties

Background

Unicompartmental Knee Arthroplasties (UKAs) treat unicompartmental arthritic degeneration. Traditionally, they are placed in a mechanical alignment with bone cuts perpendicular to the leg's mechanical axis. Kinematic alignment, an alternative, considers the patient's pre-arthritic alignment.

Methods

A retrospective study at Medstar Washington Hospital Center from 2015 to 2022 identified 72 UKA patients. Among them, 53 had mechanical alignments, and 20 had kinematic alignments. Using the Forgotten Joint Score (FJS) and Oxford Knee Score (OKS), Patient Reported Outcome Measures for these surgeries were recorded. Individuals were additionally analyzed post-surgically for Coronal Plane Alignment of the Knee (CPAK). Analysis was performed within the post-operative joint imaging, where mechanical medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA) were measured. The arithmetic hip knee ankle angle (aHKA) and joint line obliquity (JLO) were calculated according to the results of MPTA-LDFA and MPTA + LDFA respectively and grouped in accordance with the CPAK classification.

Results

Overall, there was a statistically significant response rate of 51% (>50%). According to the FJS, the mechanical cohort averaged a score of 39.1 (±33.8), while the kinematical cohort averaged 56.5 (±35.2). A two-sample t-test of this data demonstrated a statistically insignificant p-value of 0.1537. According to the OKS, the mechanical cohort averaged a score of 29.1 (±10) and the kinematical cohort averaged 38.4 (±8). A two-sample t-test of this data demonstrated a statistically significant p-value of <0.001. Of note, 7 patients had to undergo revisions in the mechanical alignment cohort compared to 0 in the kinematic alignment cohort due to aseptic loosening.

Conclusion

This study demonstrates the potential benefit in patient outcomes for individuals who undergo a kinematic rather than mechanical alignment of their UKAs. The results of the CPAK data with the significance of LDFA are consistent with the goals of the mechanical and kinematic alignment respectively.

Methods of alignment in total knee arthroplasty, systematic review

Introduction

Although total knee arthroplasty (TKA) is a very frequent surgery, one in five patients is not completely satisfied. Mechanical alignment (MA) is the most popular technique for implanting TKA. However, to improve clinical outcomes, new techniques that aim to rebuild the native alignment of the knee have been developed.

Objective

The aim of this study is to perform a systematic review of the available clinical trials and observational studies comparing clinical and radiological outcomes of different methods of alignment (kinematic, anatomic, functional) to MA.

Methods

A systematic review is performed comparing results of patient reported outcome measures (PROMs) questionnaires (WOMAC, OKS, KSS, KOOS, FJS), radiological angles (HKA, mLDFA, MPTA, JLOA, femoral rotation and tibial slope) and range of motion (ROM).

Results

Kinematic and functional alignment show a slight tendency to obtain better PROMs compared to mechanical alignment. Complication rates were not significantly different between groups. Nevertheless, these results are not consistent in every study. Anatomic alignment showed no significant differences compared to mechanical alignment.

Conclusion

Kinematic alignment is an equal or slightly better alternative than mechanical alignment for patients included in this study. However, the difference between methods does not seem to be enough to explain the high percentage of dissatisfied patients. Studies implementing lax inclusion and exclusion criteria would be needed to resemble conditions of patients assisted in daily surgical practice. It would be interesting to study patient's knee phenotypes, to notice if any method of alignment is significantly better for any constitutional deviation.

Preoperative phenotype has no significant impact on the clinical outcomes and long-term survival of mechanically aligned total knee arthroplasty in Asian patients with osteoarthritis

Aims

The aim of this study was to investigate the distribution of phenotypes in Asian patients with end-stage osteoarthritis (OA) and assess whether the phenotype affected the clinical outcome and survival of mechanically aligned total knee arthroplasty (TKA). We also compared the survival of the group in which the phenotype unintentionally remained unchanged with those in which it was corrected to neutral.

Methods

The study involved 945 TKAs, which were performed in 641 patients with primary OA, between January 2000 and January 2009. These were classified into 12 phenotypes based on the combined assessment of four categories of the arithmetic hip-knee-ankle angle and three categories of actual joint line obliquity. The rates of survival were analyzed using Kaplan-Meier methods and the log-rank test. The Hospital for Special Surgery score and survival of each phenotype were compared with those of the reference phenotype with neutral alignment and a parallel joint line. We also compared long-term survival between the unchanged phenotype group and the corrected to neutral alignment-parallel joint line group in patients with Type IV-b (mild to moderate varus alignment-parallel joint line) phenotype.

Results

The most common phenotype was Type I-b (mild to moderate varus alignment-medial joint line; 27.1% (n = 256)), followed by Type IV-b (23.2%; n = 219). There was no significant difference in the clinical outcomes and long-term survival between the groups. In Type IV-b phenotypes, the neutrally corrected group showed higher 15-year survival compared with the unchanged-phenotype group (94.9% (95% confidence interval (CI) 92.0 to 97.8) vs 74.2% (95% CI 98.0 to 100); p = 0.020).

Conclusion

Constitutional varus was confirmed in more than half of these patients. Mechanically aligned TKA can achieve consistent clinical outcomes and long-term survival, regardless of the patient's phenotype. The neutrally corrected group had better long-term survival compared with the unchanged phenotype group.

Functional alignment maximises advantages of robotic arm-assisted total knee arthroplasty with better patient-reported outcomes compared to mechanical alignment

PURPOSE

Robotic arm-assisted total knee arthroplasty (RTKA) enables adjustment of implant position to achieve the surgeon's preferred alignment. However, the alignment concept that most effectively enhances patient satisfaction remains unclear. This study compares the clinical outcomes of patients who underwent functionally aligned RTKA (FA-RTKA), mechanically aligned conventional TKA (MA-CTKA) and mechanically aligned RTKA (MA-RTKA).

METHODS

A prospectively collected database was retrospectively reviewed for patients who underwent primary TKA for knee osteoarthritis. One hundred and forty-seven knees were performed with MA-CTKA, followed by 72 consecutive knees performed with MA-RTKA, and subsequently, 70 consecutive knees performed with FA-RTKA were enrolled. After 1:1 propensity score matching of patient demographics, 70 knees were finally included in each group. The extent of additional soft tissue release during surgery was identified, and the Coronal Plane Alignment of the Knee classification was utilised to categorise the alignment. At the 1-year follow-up, patient-reported outcomes, including the pain Visual Analogue Scale, Knee Society Score, Western Ontario and McMaster Universities Arthritis Index and Forgotten Joint Score-12, were also compared among the groups.

RESULTS

The FA-RTKA group showed significantly less additional soft tissue release than the MA-CTKA and MA-RTKA groups (15.7%, 38.6% and 35.7%, respectively; p = 0.006). Statistically significant differences in functional scores were observed in the postoperative 1-year clinical outcomes in favour of the FA-RTKA group, which had a significantly larger percentage of knees that maintained constitutional alignment and joint line obliquity than those of the other groups.

CONCLUSIONS

Functionally aligned TKA showed superior 1-year postoperative patient-reported outcomes compared with those of conventional and robotic arm-assisted mechanically aligned TKA. Therefore, the advantage of RTKA is maximised when the implant positioning is based on functional alignment. The application of RTKA with mechanical alignment has been proven ineffective in improving the clinical outcomes of patients.

LEVEL OF EVIDENCE

Level III.

Imageless robotic total knee arthroplasty determines similar coronal plane alignment of the knee (CPAK) parameters to long leg radiographs

BACKGROUND

The coronal plane alignment of the knee (CPAK) classification was first developed using long leg radiographs (LLR) and has since been reported using image-based and imageless robotic total knee arthroplasty (TKA) systems. However, the correspondence between imageless robotics and LLR-derived CPAK parameters has yet to be investigated. This study therefore examined the differences in CPAK parameters determined with LLR and imageless robotic navigation using either generic or optimized cartilage wear assumptions.

METHODS

Medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA) were determined from the intraoperative registration data of 61 imageless robotic TKAs using either a generic 2 mm literature-based wear assumption (Navlit) or an optimized wear assumption (Navopt) found using an error minimization algorithm. MPTA and LDFA were also measured from preoperative LLR by two observers and intraclass correlation coefficients (ICCs) were calculated. MPTA, LDFA, joint line obliquity (JLO), and arithmetic hip-knee-ankle angle (aHKA) were compared between the robotic and the average LLR measurements over the two observers.

RESULTS

ICCs between observers for LLR were over 0.95 for MPTA, LDFA, JLO, and aHKA, indicating excellent agreement. Mean CPAK differences were not significant between LLR and Navlit (all differences within 0.6°, P > 0.1) or Navopt (all within 0.1°, P > 0.83). Mean absolute errors (MAE) between LLR and Navlit were: LDFA = 1.4°, MPTA = 2.0°, JLO = 2.1°, and aHKA = 2.7°. Compared to LLR, the generic wear classified 88% and the optimized wear classified 94% of knees within one CPAK group. Bland-Altman comparisons reported good agreement for LLR vs. Navlit and Navopt, with > 95% and > 91.8% of measurements within the limits of agreement across all CPAK parameters, respectively.

CONCLUSIONS

Imageless robotic navigation data can be used to calculate CPAK parameters for arthritic knees undergoing TKA with good agreement to LLR. Generic wear assumptions determined MPTA and LDFA with MAE within 2° and optimizing wear assumptions showed negligible improvement.

Ten Flaws of Systematic Mechanical Alignment Total Knee Arthroplasty

Mechanical alignment (MA) and its tenets have been considered essential for total knee arthroplasty (TKA) success since they were introduced in 1973. However, over time, there have been colossal advances in our knowledge and understanding of the anatomy and kinematics of the knee, as well as in surgical precision and implants. However, the MA systematic principles of prosthetic arthroplasty and implant position related to the lower-extremity mechanical axis, have only recently been called into question. The high rates of dissatisfaction and residual pain reported after MA TKA prompted this questioning, and that leaves plenty of room for improvement. Despite the general consensus that there is great variability between patients' anatomy, it is still the norm to carry out a systematic operation that does not consider individual variations. Evolving to a more personalized arthroplasty surgery was proposed as a rational and reasonable option to improve patient outcomes. Transitioning to a personalized TKA approach requires questioning and even disregarding certain MA TKA principles. Based on current knowledge, we can state that certain principles are erroneous or unfounded. The aim of this narrative review was to discuss and challenge 10 previously accepted, yet we believe, flawed, principles of MA, and to present an alternative concept, which is rooted in personalized TKA techniques.

Functional Outcome of Mechanical Alignment in Total Knee Arthroplasty Surgery: A Short-Term Cohort Study at an Indian Tertiary Care Hospital

Background

In severe arthritis cases, goal of total knee arthroplasty (TKA) management is to attain pain-free joint and restore the overall limb alignment. There are limited short-term studies published from Indian hospitals that investigated the importance of neutral mechanical component alignment in TKA patients.

Methods

Retrospective and prospective study was conducted at the Department of orthopaedics, Sancheti Institute for Orthopaedics and Rehabilitation, Pune from June 2020 to September 2022. Enrolled patients were assessed preoperatively and postoperatively using clinical examination, radiological assessment and functional outcomes through the Oxford knee score, Knee society score and VAS score.

Results

204 patients enrolled, and 267 knees were evaluated for the study. Osteoarthritis was the commonest diagnosis (254 knees, 95.13%). Pre-operatively, 92.13% knees were varus, 4.87% valgus and 3% neutral while post-operatively, 51.69% were varus, 16.1% were valgus, and 32.32% were with neutral axis. Majority of patients with a pre-operative neutral axis converted to varus axis (62.5%), while most valgus axis cases preoperatively converted to a neutral axis (53.84%). For pre-operative varus subgroup, the majority patients with < 10° pre-operative axis converted to neutral (41.28%). Majority patients with 10°-20° pre-operative axis remained varus (60.53%) and with > 20° pre-operative axis remained varus (78.26%). Functional outcome parameters were significantly improved at follow-up (P < 0.05).

Conclusion

Short-term postoperative functional scores were significantly improved in postoperative cases, with the postoperative alignment of 0° ± 3° relative to the mechanical axis was achieved. Thus, postoperative neutral mechanical alignment of 0° ± 3° can be the standard of care for patients undergoing TKA.

Graphical abstract

Knee kinematics are primarily determined by implant alignment but knee kinetics are mainly influenced by muscle coordination strategy

Implant malalignment has been reported to be a primary reason for revision total knee arthroplasty (TKA). In addition, altered muscle coordination patterns are commonly observed in TKA patients, which is thought to alter knee contact loads. A comprehensive understanding of the influence of surgical implantation and muscle recruitment strategies on joint contact mechanics is crucial to improve surgical techniques, increase implant longevity, and inform rehabilitation protocols. In this study, a detailed musculoskeletal model with a 12 degrees of freedom knee was developed to represent a TKA subject from the CAMS-Knee datasets. Using motion capture and ground reaction force data, a level walking cycle was simulated and the joint movement and loading patterns were estimated using a novel technique for concurrent optimization of muscle activations and joint kinematics. In addition, over 12'000 Monte Carlo simulations were performed to predict knee contact mechanics during walking, considering numerous combinations of implant alignment and muscle activation scenarios. Validation of our baseline simulation showed good agreement between the model kinematics and loading patterns against the in vivo data. Our analyses reveal a considerable impact of implant alignment on the joint kinematics, while variation in muscle activation strategies mainly affects knee contact loading. Moreover, our results indicate that high knee compressive forces do not necessarily originate from extreme kinematics and vice versa. This study provides an improved understanding of the complex inter-relationships between loading and movement patterns resulting from different surgical implantation and muscle coordination strategies and presents a validated framework towards population-based modelling in TKA.

Definitions and consequences of current alignment techniques and phenotypes in total knee arthroplasty (TKA) - there is no winner yet

Dissatisfaction following total knee arthroplasty (TKA) has been extensively documented and it was attributed to numerous factors. In recent years, significant focus has been directed towards implant alignment and stability as potential causes and solutions to this issue. Surgeons are now exploring a more personalized approach to TKA, recognizing the importance of thoroughly understanding each individual patient's anatomy and functional morphology. A more comprehensive preoperative analysis of alignment and knee morphology is essential to address the unresolved questions in knee arthroplasty effectively. The crucial task of determining the most appropriate alignment strategy for each patient arises, given the substantial variability in bone resection resulting from the interplay of phenotype and the alignment strategy chosen. This review aims to comprehensively present the definitions of different alignment techniques in all planes and discuss the consequences dependent on knee phenotypes.Level of evidence V.

Restoration of the native tibial joint line obliquity in total knee arthroplasty with inverse kinematic alignment does not increase knee adduction moments

PURPOSE

Patient-specific alignment in total knee arthroplasty (TKA) has shown promising patient-reported outcome measures; however, the clinical and biomechanical effects of restoring the native knee anatomy remain debated. The purpose of this study was to compare the gait pattern between a mechanically aligned TKA cohort (adjusted mechanical alignment-aMA) and a patient-specific alignment TKA cohort (inverse kinematic alignment-iKA).

METHODS

At two years postoperatively, the aMA and iKA groups, each with 15 patients, were analyzed in a retrospective case-control study. All patients underwent TKA with robotic assistance (Mako, Stryker) through an identical perioperative protocol. The patients' demographics were identical. The control group comprised 15 healthy participants matched for age and gender. Gait analysis was performed with a 3D motion capture system (VICON). Data collection was conducted by a blinded investigator. The primary outcomes were knee flexion during walking, knee adduction moment during walking and spatiotemporal parameters (STPs). The secondary outcomes were the Oxford Knee Score (OKS) and Forgotten Joint Score (FJS).

RESULTS

During walking, the maximum knee flexion did not differ between the iKA group (53.0°) and the control group (55.1°), whereas the aMA group showed lower amplitudes of sagittal motion (47.4°). In addition, the native limb alignment in the iKA group was better restored, and although more in varus, the knee adduction moments in the iKA group were not increased (225 N mm/kg) compared to aMA group (276 N mm/kg). No significant differences in STPs were observed between patients receiving iKA and healthy controls. Six of 7 STPs differed significantly between patients receiving aMA and healthy controls. The OKS was significantly better in patients receiving iKA than aMA: 45.4 vs. 40.9; p = 0.05. The FJS was significantly better in patients receiving iKA than aMA: 84.8 vs. 55.5; p = 0.002.

CONCLUSION

At two years postoperatively, the gait pattern showed greater resemblance to that in healthy controls in patients receiving iKA rather than aMA. The restoration of the native coronal limb alignment does not lead to increased knee adduction moments due to the restoration of the native tibial joint line obliquity.

LEVEL OF EVIDENCE

Level III.

Alignment strategy for different types of varus knee with generic instruments: Mechanical alignment or kinematic alignment?

OBJECTIVE

A thorough examination of the available approaches is crucial to comprehensively understand the variance among the alignment strategies employed in total knee arthroplasty (TKA). In this study, we assessed the functional outcomes during the perioperative and postoperative periods of TKA in patients using generic instruments with varus knee to compare the mechanical alignment (MA) and kinematic alignment (KA) procedures.

METHODS

A total of 127 patients from the First Affiliated Hospital of Wannan Medical College who had undergone unilateral TKA between November 2019 and April 2021 were included. The patients with varus knee deformity were categorized into two groups [type I (n = 64) and type IV (n = 63)] based on the modified coronal plane alignment of the knee (mCPAK) classification. The type I and IV groups were further subdivided into MA (n = 30 and n = 32) and KA subgroups (n = 34 and n = 21), respectively. The clinical information collected included sex, surgical side, age, body mass index, and perioperative data [including operation time, intraoperative blood loss, length of hospital stay, and the American Society of Anesthesiologists (ASA) classification]. All patients were monitored for 12 months post-surgery to evaluate the recovery of knee joint function. During this period, the Knee Disability and Osteoarthritis Outcome Score for Joint Replacement (KOOS JR) and the active range of motion (AROM) and visual analog scale (VAS) pain scores were compared at different time points, i.e., before the operation and 6 weeks, 6 months, and 12 months post-operation. Additionally, the patients' subjective experiences were assessed at 6 and 12 months post-surgery using Forgotten Joint Score Knee (FJS-12 Knee), while complications were recorded throughout the monitoring period.

RESULTS

No significant variances were observed in ASA classification, operation duration, blood loss volume during surgery, and hospital stay length between the patients who underwent KA TKA and those who received MA TKA (P > 0.05). During the initial 6 weeks post-operation, the KA group exhibited a significantly reduced average VAS pain score (P < 0.05), with no such differences at 6 months and 1 year after the surgery (P > 0.05). Furthermore, the KA group had significantly higher scores on the KOOS JR at 6 weeks, 6 months, and 1 year following the surgery (P < 0.05). Moreover, the AROM score of the KA group significantly improved only at 6 weeks after the surgery (P < 0.05); however, no prominent differences were found at 6 months and 1 year after the operation (P > 0.05). The KA cohort also exhibited a significant increase in FJS-12 Knee at 1 year following the operation (P < 0.05), whereas no such difference was detected at 6 months following the surgery (P > 0.05). Thus, compared to the MA method, the KA procedure provided pain relief and improved active motion range within 6 weeks after the surgery in patients undergoing TKA. Further, the KOOS JR exhibited significant increases at 6 weeks, 6 months, and 1 year while the FJS-12 Knee demonstrated a significant increase at 1 year after the KA TKA procedure.

CONCLUSION

Therefore, our study results suggest that the KA approach can be considered in patients using generic instruments with varus alignment of the knee, particularly those with mCPAK type I and IV varus knees, to help improve patient satisfaction.

Current Concepts in Alignment in Total Knee Arthroplasty

BACKGROUND

In an effort to increase satisfaction among total knee arthroplasty (TKA) patients, emphasis has been placed on implant positioning and limb alignment. Traditionally, the aim for TKA has been to achieve a neutral mechanical alignment (MA) to maximize implant longevity. However, with the recent spike in interest in individualized alignment techniques and with the advent of new technologies, surgeons are slowly evolving away from classical MA.

METHODS

This review elucidates the differences in alignment techniques for TKA, describes the concept of knee phenotypes, summarizes comparative studies between MA and individualized alignment, and provides a simple way to incorporate the latter into surgeons' practice.

RESULTS

In order to manage patients by applying these strategies in day-to-day practice, a basic understanding of the aforementioned concepts is essential. Transition to an individualized alignment technique should be done gradually with caution in a stepwise approach.

CONCLUSION

Alignment and implant positioning are now at the heart of the debate and surgeons are investigating a more personalized approach to TKA.

Comparison of accuracy for hip-knee-ankle (HKA) angle by X-ray and knee motion analysis system and the relationships between HKA and gait posture

BACKGROUND

The lower limb mechanical axis was used to assess the severity of knee osteoarthritis (KOA) with varus/valgus deformity and the accuracy of targeted lower limb alignment correction after operation by conventional X-rays. There are lots of parameters to assess the gait in elder patients such as velocity, stride length, step width and swing/stance ratio by knee joint movement analysis system. However, the correlation between the lower limb mechanical axis and gait parameters is not clear. This study is aimed at obtaining the accuracy of the lower limb mechanical axis by the knee joint movement analysis system and the correlation between the lower limb mechanical axis and gait parameters.

METHODS

We analysed 3D knee kinematics during ground gait of 99 patients with KOA and 80 patients 6 months after the operations with the vivo infrared navigation 3D portable knee joint movement analysis system (Opti-Knee®, Innomotion Inc, Shanghai, China). The HKA (Hip-Knee-Ankle) value was calculated and compared to X-ray findings.

RESULTS

HKA absolute variation after the operation was 0.83 ± 3.76°, which is lower than that before the operation (5.41 ± 6.20°, p = 0.001) and also lower than the entire cohort (3.36 ± 5.72). Throughout the cohort, a significant correlation with low coefficients (r = -0.19, p = 0.01) between HKA value and anterior-posterior displacement was found. In comparing the HKA values measured on the full-length alignment radiographs and 3D knee joint movement analysis system (Opti-Knee), there was a significant correlation with moderate to high coefficients (r = 0.784 to 0.976). The linear correlation analysis showed that there was a significant correlation between the values of HKA measured by X-ray and movement analysis system (R² = 0.90, p < 0.01).

CONCLUSIONS

Data with equivalent results as HKA, the 6DOF of the knee and ground gait data could be provided by infrared navigation based 3D portable knee joint movement analysis system comparing with the conventional X-rays. There is no significant effect of HKA on the kinematics of the partial knee joint.