Mechanical alignment for primary TKA may change both knee phenotype and joint line obliquity without influencing clinical outcomes: a study comparing restored and unrestored joint line obliquity

Impact of changes in native coronal plane alignment of the knee (CPAK) on patient-reported outcome measures (PROMS). A bilateral single implant study

Background

A contemporary trend favours a restricted kinematic alignment (rKA) strategy, incorporating safe boundaries to restore a variable percentage of a patient's natural alignment.This study aims to compare preoperative and postoperative coronal plane knee alignment (CPAK) in patients undergoing bilateral TKA with SAIPH implants (MatOrtho, UK). The concept was to control the implant (same prosthesis both sides), patient (bilateral model) and assess what effect any surgical alteration in alignment had on patient's outcomes measured by patient-reported outcome measures (PROMS) and patient satisfaction.

Method

A total of 70 patients and 140 knees who underwent bilateral sequential TKA with a SAIPH implant between 2012 and 2022 were included in this study. PROMS, clinical assessment, pre and postoperative CT scans and plain x-rays were obtained. The CPAK phenotype, lateral distal femoral angle, medial proximal tibial angle, joint line obliquity (JLO), and arithmetic Hip-Knee-Ankle (aHKA) angle were measured pre and postoperatively.

Results

Postoperative CPAK phenotype recreation was achieved in 27.9 %, while in 72.1 % it was not. PROMS did not significantly differ when CPAK phenotype was not recreated. Additionally, isolated changes to aHKA or JLO did not significantly impact outcomes, nor was a TKA that recreated the native coronal alignment more likely to be the patient's preferred side.

Conclusion

Tailoring alignment approaches to individual patient characteristics may be crucial for optimal functional outcomes but in this study, we were not able to show a difference between those with CPAK recreated versus those who did not have native CPAK recreated following TKA when using PROMS as the outcome measure.

Restoration of anatomical knee phenotype is associated with improved postoperative clinical outcomes after total knee arthroplasty

BACKGROUND

A comprehensive assessment of knee phenotypes is crucial for optimizing surgical realignment strategies in total knee arthroplasty (TKA). This study aimed to investigate the relationship between the restoration of preoperative phenotypes, such as joint line orientation (JLO) and alignment, and clinical outcomes following TKA.

METHODS

A retrospective review was performed on the records of 1052 primary osteoarthritic knees that underwent mechanically aligned (MA) TKA between March 2016 and October 2021. Patient-reported outcome measures (PROMs) were assessed preoperatively and at 2 years postoperatively. Patients were categorized according to the coronal plane alignment of the knee (CPAK) classification system, which incorporates the arithmetic hip-knee-ankle angle (aHKA) as an indicator of constitutional alignment and JLO. Clinical outcomes were compared between patients whose knee phenotype was maintained and those in whom it was not restored.

RESULTS

Among osteoarthritic knees, the majority (59.4%) were classified as CPAK type I (varus aHKA, apex distal JLO) preoperatively. Using mechanical axis techniques, the native phenotype was restored in 127 (12.1%) of the 1052 cases. These patients demonstrated significantly better postoperative clinical outcomes, as measured by WOMAC function and Forgotten Joint Scores (FJS), compared with the non-restored group (P < 0.05). When alignment was adjusted through detailed analyses of patients with maintained alignment between preoperative and latest follow up assessments, the significant differences in WOMAC function and FJS outcomes between restored JLO and non-restored JLO groups persisted (all P < 0.05). No significant association was observed between the restoration of aHKA and clinical outcomes.

CONCLUSION

The restoration of the anatomical knee phenotype, particularly JLO, is associated with improved postoperative PROMs, notably in functional outcomes, following TKA. These findings underscore the clinical importance of prioritizing preoperative JLO for optimizing surgical outcomes, rather than focusing exclusively on overall limb alignment.

Functional alignment in robotic-assisted total knee arthroplasty for valgus deformity achieves safe coronal alignment and excellent short-term outcomes

PURPOSE

Functional alignment (FA) in total knee arthroplasty (TKA) prioritizes soft tissue balancing and anatomical restoration without systematic correction to neutral alignment. Most studies have focused on varus deformity, with little evidence available about FA in valgus deformity. The hypothesis of the present study was that FA in robotic-assisted TKA for valgus deformity would demonstrate correction of the coronal alignment and yield satisfactory short-term outcomes.

METHODS

This retrospective study included 58 patients with valgus coronal alignment (hip-knee-angle [HKA] ≥ 183°) who underwent robotic-assisted TKA using the FA technique with a minimum of 1-year follow-up. Outcomes were assessed through the Knee Society Score (KSS), Oxford Knee Score (OKS), Forgotten Joint Score (FJS) and radiographic measurements of alignment and phenotypes. Complication and revision rates were also analyzed.

RESULTS

The cohort included 39 females and 19 males with a median age of 70. Post-operatively, 86.2% of cases achieved coronal alignment within the safe zone (HKA 177-183°). Significant improvements were observed in KSS (part 1: 69.5-95, part 2: 65-94, p < 0.001), while OKS and FJS exhibited optimal outcomes. Two complications were recorded: one aseptic loosening (1.7%) and one early infection (1.7%). Kaplan-Meier survival analysis indicated favourable implant survivorship at a median follow-up of 18 months.

CONCLUSION

FA in image-based robotic TKA is a safe and effective approach for patients with valgus deformity. This procedure resulted in a modest correction of the coronal alignment, where no soft tissue releases were needed. The majority of the cases fell within the target coronal alignment boundaries by only accommodating the individual laxities, suggesting the aim of FA to restore each knee's pre-pathological alignment.

LEVEL OF EVIDENCE

Level IV.

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.

Is limb overcorrection following total knee arthroplasty compromising functional outcome?

Purpose

Many patients remain unsatisfied after total knee arthroplasty (TKA). Personalized alignment strategies have gained popularity in the search to improve patient satisfaction and function. This study aimed to examine the impact of limb overcorrection in the coronal plane on patient satisfaction and functional outcome. The secondary aim was to investigate how a change in knee phenotype following TKA affects clinical outcome.

Methods

A retrospective matched case-control study was designed between patients with limb overcorrection (N = 37) and a control group (N = 104). Mean follow-up was 68 months. Satisfaction and function were compared by means of the new 2011 Knee Society Score (KSS) and the Knee Injury and Osteoarthritis Outcome Score (KOOS). Radiological evaluation was performed on weight-bearing full-leg radiographs. Overcorrection was defined as a mechanical HKA (mHKA) angle of 2° or more and opposite to the preoperative alignment. The control group consisted of TKAs that were corrected to neutral or left in slight undercorrection. Finally, component alignment (lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA)) and Coronal Plane Alignment of the knee (CPAK) phenotypes were evaluated.

Results

The overcorrection group performed better than the control group in terms of KSS subscores satisfaction and functional activities, total KSS score, all KOOS subcategories, and total KOOS score. Subdivision of the control group into a neutral and undercorrection group, and the overcorrection group into mild and severe overcorrection, revealed similar findings.A chance in knee phenotype as per aHKA, JLO or CPAK did not result in worse clinical outcomes.

Conclusion

Accidental limb overcorrection after TKA does not result in inferior clinical outcomes or patient satisfaction at midterm follow-up.The present study could not identify an optimal coronal alignment target. This suggests that coronal alignment as a predictor of patient satisfaction and function is likely less important than previously believed.

Level of evidence

Level III, retrospective case-control study.

Change of CPAK class does not affect functional outcomes in robotic arm-assisted total knee arthroplasty performed with functional alignment

PURPOSE

The purpose of this study was to assess the impact of post-operative coronal plane alignment of the knee (CPAK) class change on functional outcomes and determine the rate and type of CPAK class change after image-based robotic arm-assisted (RA)-total knee arthroplasty (TKA) performed with functional alignment (FA) at two different centres.

METHODS

The present retrospective, observational, multicentre study included 201 patients treated with RA-TKA between October 2020 and April 2022 at two different centres. The radiographic CPAK classification was adapted using CT images to achieve pre- and post-operative knee categorization into CPAK classes. At a minimum of 1 year post-operatively, patients were administered the Forgotten Joint Score-12 (FJS-12) and surveyed about their post-operative satisfaction level using a 5-level Likert scale (5-LLS).

RESULTS

The most common preoperative overall CPAK classes were: Types II, I, III, IV and V. Implant positioning after RA-TKA with FA within the alignment boundaries, determined distribution in the CPAK classification, predominantly maintaining classes I, II, IV, and V. No statistically significant FJS-12 differences were detected between subjects who maintained and changed their preoperative CPAK class. The mean 5-LLS for satisfaction in patients where the preoperative CPAK class was maintained intraoperatively was 4.4 ± 1.1 (range = 1-5), while subjects having the CPAK class changed had a mean 5-LLS of 4.4 ± SD 1.0 (range 1-5).

CONCLUSION

In the setting of image-based RA-TKA with FA, CPAK can be changed within a 'functional safe-zone', without compromising functional outcomes. Good functional outcomes are the result of a stable and balanced knee with soft-tissue preservation, regardless of the maintenance of the preoperative CPAK class.

LEVEL OF EVIDENCE

Level III.

Reproducibility of coronal plane alignment of the knee (CPAK) using tibia-first restricted inverse kinematic alignment

INTRODUCTION

The Coronal Plane Alignment of the Knee (CPAK) classification categorizes knee phenotypes based on constitutional limb alignment and joint line obliquity (JLO). Restricted Inverse Kinematic Alignment (RIKA) is a surgical philosophy that incorporates calculated perioperative parameters to achieve patient-specific alignment. This study investigated the reproducibility of restoring preoperative CPAK phenotypes via the tibia-first RIKA concept in total knee arthroplasty (TKA).

METHODS

This prospective study assessed 129 patients who underwent RIKA TKA using an imageless navigation robotic-assisted arm with a single implant design for primary osteoarthritis between January 2022 and December 2023. Preoperative and postoperative angles for the lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) were measured from full-length standing anteroposterior X-ray imaging. Arithmetic HKA (aHKA) was defined as MPTA - LDFA, and JLO was outlined as MPTA + LDFA to classify each knee into one of nine CPAK phenotypes. CPAK boundaries for neutral aHKA and JLO were 0° ± 2° and 180° ± 3°, respectively.

RESULTS

The mean pre- and postoperative aHKA were - 2.73° (SD ± 4.9°) vs. -2.83° (SD ± 3.0°), respectively. The most common preoperative CPAK phenotypes were I (n = 74, 42.5%) and II (n = 40, 23.0%). Among patients with preoperative type I phenotype, 39.2% (29/74) preserved their composition postoperatively, while 48.6% (36/74) converted to type IV. Of 40 Type II knees, 65.0% (26/40) preserved alignment, with 25.0% (10/40) shifting to type V. In preoperative types IV and V, 75% (12/16) and 88.5% (23/26) preserved their phenotypes, respectively. Valgus categories (III, VI, IX) were neutralized into types II and V. CPAK types VII, VIII, and IV were rare throughout.

CONCLUSION

The use of tibia-first RIKA achieved adequate preservation of the native coronal alignment postoperatively. These findings suggest that balancing a knee using tibia-first approach with the use of imageless navigation robotic-assisted systems is a valid tool for surgeons who seek contemplating RIKA 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.

Distribution of phenotypes of coronal plane alignment of the knees and functional phenotypes in the healthy young Iranian population: A cross-sectional study

Purpose

The functional phenotypes and the coronal plane alignment knee (CPAK) classification have recently been introduced. This study aimed to describe the phenotypes of normal knees in the healthy young Iranian population based on these systems.

Methods

This cross-sectional study included 402 knees in 201 healthy young adults. Phenotypes were reported using hip-knee-ankle (HKA) angle, femoral mechanical angle (FMA) and tibial mechanical angle (TMA) for functional phenotypes and joint line obliquity (JLO) and arithmetic HKA (aHKA) for CPAK classification. Also, a distinct combination of knee alignment parameters (HKA, FMA and TMA) that reflects the functional alignment characteristics of the knee, as described by Hirschmann, was used. Statistical analysis was performed using the Student's t test.

Results

The mean HKA, FMA and TMA were 176.03 ± 3.01°, 92.01 ± 2.77° and 86.52 ± 2.73°, respectively. All angles of female participants were significantly more varied compared to men (p < 0.05). The most common phenotypes were VAR(Varus)HKA3°, NEU(Neutral)TMA0° and NEUFMA0°. The distribution of the 10 most common functional phenotypes was not significantly different between men and women (p = 0.201). The most common CPAK types were type I (33.6%), II (26.6%) and III (16.7%), and types VII, VIII and IX were rarely seen (2.0% overall). The distribution of CPAK phenotypes significantly differed between men and women (p = 0.015), and CPAK type III was more frequently seen in women. Clinically, the predominance of varus phenotypes and the sex-specific differences observed underscore the importance of tailoring surgical alignment strategies to individual anatomy.

Conclusion

In conclusion, our study reveals that knee alignment in the healthy Iranian population tends to exhibit neutral or mild varus characteristics, with significant differences between men and women. These findings suggest that ethnicity may play a role in the natural alignment of the knee, which has important implications for surgical planning and outcomes.

Level of Evidence

Level III.

Relationship Between Coronal Plane Alignment of the Knee Phenotypes and Distal Femoral Rotation

Background: The coronal plane alignment of the knee (CPAK) classification categorises nine phenotypes based on constitutional limb alignment and joint line obliquity and can be used in healthy and arthritic knees. In total knee arthroplasty surgery, some morphological variables in planes other than the coronal plane are particularly interesting. One example is the distal femoral rotation. Our study aimed to search for relationships between phenotypes based on CPAK classification and distal femoral rotation. Methods: Data from 622 cases in 535 osteoarthritic patients who underwent primary total knee arthroplasty were retrospectively analysed. Computed tomography imaging was employed to ascertain the mechanical lateral distal femoral angle, the mechanical medial proximal tibial angle, and the distal femoral rotation (quantified using the condylar twist angle). Results: The variables were perfectly uncorrelated according to the regression equations, with a Coefficient of Determination of 0.0608 for the condylar twist angle. Upon visualising the condylar twist angle function using a contour map or surface curves with low interpolation, it became evident that the data did not follow any discernible pattern. Employing ANOVA, we found some statistically significant differences between the distributions of the CPAK groups for the condylar twist angle (F = 5.81; p < 0.001). Conclusions: Our study found no relevant relationships between coronal plane alignment, according to the CPAK classification, and the distal femoral rotation in the sample population studied. Perhaps the stratification of the CPAK groups (i.e., a purely arithmetical aspect) hides possible relationships between the coronal and the axial planes.

Is the coronal plane alignment of the knee (CPAK) classification useful to plan individualized total knee arthroplasty surgery for the Spanish population? A critical analysis of the CPAK classification

INTRODUCTION

The CPAK classification aims to categorize knee phenotypes. The original study was based on Australian and Belgian population, but significant variation in CPAK distribution exists between different geographic areas. The primary objective is to evaluate knee phenotypes of osteoarthritic Spanish population based on the CPAK system. The secondary objective is to compare the Spanish CPAK distribution with that observed in the original study to analyse if proposing modifications is necessary when applying the classification to our population. Finally, we aim to critically analyse the utility of this classification to plan individualized TKA.

METHODS

It is a cross-sectional observational study analysing radiological datasets from 121 patients with knee osteoarthritis treated with a Mako assisted TKA in three Spanish institutions. The preoperative lower limb CT-scan was used to measure the MPTA and LDFA of each patient. Then, the aHKA (MPTA-LDFA) and JLO (MPTA+LDFA) were calculated to categorize patients into the nine CPAK phenotypes.

RESULTS

The commonest knee phenotypes of osteoarthritic Spanish population were the distal apex JLO CPAK types (74%: II (28%), I (23%) and III (23%)). No patient presented a proximal apex type (VII, VIII and IX). The 30% of the patients had a varus alignment and 26% a valgus. No relevant differences were found between the Spanish CPAK distribution and that observed in the original study.

CONCLUSIONS

No modifications to the CPAK classification should be necessary for the Spanish population. The CPAK classification can be useful to describe and categorize osteoarthritic patients. However, relevant limitations have been found to the classification, questioning its utility to plan and guide individualized TKA surgery.

Distribution and gender-specific differences of coronal plane alignment of healthy knee

BACKGROUND

Understanding optimal prosthesis alignment in TKA remains crucial despite ongoing debate. While current research focuses on osteoarthritic knees, a gap exists in characterizing healthy young adult knees in Asians. This study aims to fill this gap by identifying the distribution of CPAK phenotypes in this population, including potential gender variations and individual differences.

METHODS

A total of 390 knees from 195 young adults aged 20 to 35 years without knee pain who underwent hip-knee-ankle radiography were prospectively collected between February 2024 and March 2024. The average MPTA, LDFA, aHKA, and JLO were measured. The overall CPAK distribution was analyzed to assess gender variations and individual differences. On average, participants were 25.7 years old, 165.7 cm tall, and had a BMI of 23.6 kg/m². LDFA, MPTA, aHKA, and JLO averaged at 86.8°, 87.2°, 0.3°, and 174.0°, respectively.

RESULTS

This study demonstrates significant differences in knee alignment between men and women, as measured by the CPAK system. While zone II was the most common overall (43.3%), the distribution of CPAK zones varied by gender, with men exhibiting a higher prevalence of distal apex point alignments (89.9%) and women having a higher prevalence of CPAK zone V (18.3%). Finally, analysis of paired knees revealed a comparable zonal distribution for both genders (approximately 56%).

CONCLUSION

This study examined CPAK distribution in young Asian adults without knee osteoarthritis and identified potential sex-based variations. The findings suggest a predominance of distally pointed CPAK (76.9%) and a possible benefit for slightly varus tibial cuts during TKA in this population for optimal joint alignment. Additionally, gender-specific considerations should be incorporated into knee alignment assessments and treatment planning.

LEVEL OF EVIDENCE

II, A prospective descriptive study.

Alignment Strategies in Total Knee Arthroplasty: The Rise and Role of Enabling Technology

Total knee arthroplasty (TKA) remains the gold standard surgical care for end-stage knee arthritis. Since its inception, TKA has seen many transformative factors with advances in material properties, implant design, and fixation. Improvements in implant longevity has culminated in TKA being recognized as one of modern medicine's most successful surgical procedures. Patient satisfaction, however, remains a significant challenge. Recent studies report that patient satisfaction with current implants and techniques remains at 80 to 90%, suggesting that up to one in five patients remain dissatisfied with their procedure. A balanced knee, defined as equal medial and lateral gaps in knee extension and flexion, is a desired outcome in TKA. This has been shown to be associated with improved clinical outcomes. Given the poor rate of surgeon-defined balance, intraoperative knee balance can be confirmed with objective load data using sensor-embedded smart inserts or by measuring gaps using computer-assisted or robotic platforms. Currently, there is no consensus on the correct alignment or laxity targets for individualized alignment strategies in TKA, and further research in this area is required to answer this. Tremendous advances in our understanding of knee anatomy and kinematics have come to light in the recent past, and these insights have spawned interest in alternative alignment techniques in TKA. More recently, an appreciation of individual knee phenotypes and associated classification systems have provided a platform and the scientific justification behind these contemporary alignment strategies. Paired with enabling technologies, it is becoming an accepted paradigm that surgeons have the ability to select a desired alignment target when undertaking an individualized alignment strategy in TKA and execute the surgery with a high degree of precision. It is hoped that this may reduce the rate of dissatisfaction following TKA and improve clinical outcomes. This review article provides an overview of the concepts of knee phenotypes, current alignment strategies in TKA, and the emerging benefits of enabling technologies.

The distribution of Coronal Plane Alignment of the Knee (CPAK) phenotypes in the Malaysian population and their correlation with demographic variables

BACKGROUND

Only 80% of patients are satisfied with their outcomes post-TKA. Mounting attention has been paid to constitutional limb alignment and individualized alignment strategies in recent years. MacDessi et al. proposed the CPAK classification, which takes into account the patients' arithmetic hip-knee-ankle axis (aHKA) and joint line obliquity (JLO). In this study, we aimed to establish local demographic data, compare them with published data, and assess their correlations with modifiable variables.

METHODS

A total of 500 end-stage osteoarthritic knees subjected to TKA were radiologically analyzed. The lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) were calculated from long limb radiographs before the aHKA and JLO were derived and a CPAK phenotype was assigned. Demographic data were harvested and analyzed for possible correlations.

RESULTS

There were 160 males (32%) and 340 females (68%), with a mean age of 66.42 years (range, 47-88). The mean MPTA was 85.8° (± 3.0)°, and the mean LDFA was 87.6° (± 2.4)°. The average aHKA was a varus of 1.8° (± 4.2)°, and the average JLO was 173.4° (± 3.45)°. The most common CPAK phenotype was Type 1 (43.4%). The Intraclass Correlation Coefficient demonstrated excellent reliability (> 0.9). No correlation existed between CPAK phenotypes and age, height, weight, or body mass index (BMI), but CPAK phenotype was significantly correlated with gender.

CONCLUSION

An urban Malaysian population with osteoarthritic knees was found to be constitutionally varus, with the most common phenotype being varus aHKA with an apex-distal JLO. Constitutional alignment is not influenced by factors such as age, height, weight, or BMI.

LEVEL OF EVIDENCE

Retrospective Observational Study-III.

Joint-line obliquity angle is significantly affected by hip abduction and adduction: A simulated analysis

PURPOSE

Different methods for quantifying joint-line obliquity (JLO) have been described, including joint-line obliquity angle (JLOA), Mikulicz joint-line angle (MJLA) and medial proximal tibial angle (MPTA). The goal of the present study was to quantify the variation of JLOA based on the position of the hip. The hypothesis of our study is that JLO is significantly influenced by the abduction/adduction of the limb, unlike MJLA.

METHODS

One hundred long-leg-weightbearing X-rays were used. At time 0 and after 30 days, two observers performed different measurements, including (1) distance between pubic symphysis and center of the femoral head, (2) distance between center of the femoral head and center of the ankle joint, (3) distance between center of the ankle and medial malleolus, (4) hip-knee-ankle angle, (5) MPTA, (6) lateral distal femoral angle, (7) joint-line congruency angle, (8) JLOA, (9) MJL and (10) angle between Mikulicz line and line perpendicular to the ground. The changes of the JLOA based on the position of the hip (abducted, neutral, bipedal stance adduction and monopodal stance adduction) were calculated with trigonometric formulas and with simulation on an orthopaedic planning digital software.

RESULTS

The JLOA change between adducted and abducted positions was on average 12.8° (SD 0.9 mm). The MJL did not vary significantly based on hip position.

CONCLUSIONS

The adduction/abduction of the lower limb has a considerable impact on JLOA. Methods like MJLA which are not affected by hip position should be preferred for JLO evaluation.

LEVEL OF EVIDENCE

Level III, diagnostic study.

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.

Gender, BMI, and Age-Related Variations in Lower Limb Alignment Parameters and CPAK Phenotypes in Chinese Patients with Knee Osteoarthritis

OBJECTIVES

Research on the distribution of and the variation in coronal plane alignment of the knee (CPAK) in the Chinese osteoarthritis population is limited. We aimed to establish the CPAK classification based on the characteristics of lower limb alignment in the Chinese osteoarthritis population. We also investigated variations in lower limb alignment parameters and CPAK phenotypes based on gender, body mass index (BMI), and age.

METHODS

A retrospective study was conducted on a total of 944 knees diagnosed with osteoarthritis in 479 patients from January 2017 to December 2023. A scatterplot was used to describe the distribution of the CPAK classification, and the differences in lower limb alignment parameters and the CPAK classification were compared across genders (male, female), ages (middle-aged/<65 years, elderly/≥65 years), and BMI categories (normal/<25 kg/m2, overweight and obese/≥25 kg/m2) using the chi-squared test or Fisher's exact test.

RESULTS

The average arithmetic hip-knee-ankle angle and joint line obliquity (JLO) were -3.03° ± 5.69° and 174.45° ± 4.29°, respectively. There was a higher prevalence of constitutional varus alignment in males and the overweight or obese group, while constitutional valgus alignment was more common in females and the normal BMI group (p < 0.05). Additionally, females had a greater apex distal JLO than males (p < 0.05). There were no statistically significant differences in lower limb alignment parameters among different age groups (p > 0.05). Although there were variations in alignment parameters across different genders and BMI categories in the knee osteoarthritis population, the predominant CPAK classifications were type I (38.03%), followed by type II (20.02%) and type IV (17.06%).

CONCLUSION

The most common CPAK types were I, II, and IV, and they were not influenced by gender, BMI, or age, indicating that the CPAK classification can reliably reflect constitutional alignment. A better understanding of native alignment variability can aid in providing patient-specific recommendations when considering orthopedic alignment strategies.

The Restoration of the Prearthritic Joint Line Does Not Guarantee the Natural Knee Kinematics: A Gait Analysis Evaluation Following Primary Total Knee Arthroplasty

Background

Unrestricted kinematic alignment (uKA) in total knee arthroplasty (TKA) has the theoretical advantage of reproducing patients' constitutional alignment and restoring the pre-arthritic joint line position and obliquity. However, modifications of the original uKA technique have been proposed due to the potential risk of mechanical failure and instability. Given the significant variability in soft tissue behavior within the same bony morphology group, uKA pure knee resurfacing could be occasionally detrimental. This study aimed to kinematically compare the outcomes of uKA TKA with those of a robotic-assisted KA TKA technique based on specific soft-tissue boundaries.

Methods

In this retrospective gait analysis study, 24 TKA patients and 12 healthy controls were recruited. Inclusion criteria were a 9-month minimum follow-up from successfully, primary medial-pivot or medially-congruent TKA performed for isolated degenerative joint disease. Preoperatively, patients were randomly assigned to two surgical groups: A) uKA (#12) and B) robot-assisted (#12), KA (hybrid-kinematic) with boundaries (±3° from hip-knee-ankle neutral axis) and a slight intercompartmental gap asymmetry (max 2 mm lateral-opening). The gait analysis was performed using instrumented treadmills equipped with 3D cameras.

Results

Sagittal knee kinematic data: during the early-stance phase of gait, the uKA group showed a less consistent weight-acceptance phase and a less efficient transition between the first knee-flexion peak and mid-stance-extension plateau with respect to the hybrid-kinematic alignment group. Spatiotemporal and overall gait quality data: no significant differences were found between the two TKA groups regarding walking speed (P = .51) and step length (P = .8534). Control group patients walked more efficiently compared to TKA groups, showing inferior trunk flexion and inferior variation in step length (P < .0001).

Conclusions

This study showed that restoring the pre-arthritic joint line, as advocated by surgeons following the uKA philosophy, does not guarantee a closer-to-normal knee kinematics.

Effect of joint-line obliquity on long-term survivorship of total knee arthroplasty: A postoperative phenotype analysis

PURPOSE

Whether the longevity of total knee arthroplasty (TKA) differs between postoperative phenotypes has not been investigated. This study aims to examine which phenotype has a worse long-term survival rate than the reference phenotype (neutral alignment-parallel joint line), and whether joint-line obliquity (JLO) affects the survivorship of TKA.

METHODS

A total of 945 knees that underwent primary TKAs for primary osteoarthritis from January 2000 to January 2009 were included. These were classified into nine postoperative phenotypes based on the combined assessment of the hip-knee-ankle (HKA) angle and JLO, measured on standing radiographs. The 5-, 10- and 15-year survival rates were analysed using Kaplan-Meier methods and log-rank tests. The long-term survival rates of each phenotype were compared with the reference phenotype.

RESULTS

There were 55 aseptic mechanical failures within a period of 10.4 ± 5.0 years. The most frequently observed phenotypes were the reference phenotype (n = 527), neutral alignment-lateral joint-line inclination (n = 162), varus alignment-lateral joint-line inclination (n = 104) and varus alignment-parallel joint line (n = 101). The overall failure rate for each phenotype was 3.6%, 3.7%, 18.3% and 7.9%, respectively. Only the 10- and 15-year survival rates of the varus alignment-lateral joint-line inclination phenotype were significantly different from those of the reference phenotype (97%-93% vs. 90%-69%; p = 0.017, <0.001).

CONCLUSION

The lateral joint-line inclination phenotype had an inferior long-term survival rate after varus-aligned TKA. This suggested that alignment and JLO affected the long-term survival rate of patients who underwent TKA.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Medial Deviation of a 6° Prosthetic Trochlear Groove After Kinematically Aligned Total Knee Arthroplasty Occurs in Four Types of Coronal Plane Alignment of the Knee (CPAK) and Decreases the Forgotten Joint Score

Background

The study focused on kinematically aligned total knee arthroplasty (KA TKA). It identified which coronal plane alignment of the knee (CPAK) types are associated with a higher proportion of medial deviation of the 6° prosthetic trochlear groove (PTG) relative to the quadriceps' line of pull and whether medial deviation adversely affected the Forgotten Joint Score (FJS). The research calculated the minimum PTG angle required to prevent medial deviation by at least 2° in all patients.

Methods

The study analyzed 296 KA TKAs with a postoperative long-leg scanogram and a 2-year FJS score. Radiographic measurements were used to determine the CPAK type and to identify the deviation of the 6° PTG relative to the quadriceps' line of pull as medial (-) or lateral (+).

Results

Fifty-one percent of KA TKAs had a medial deviation of the PTG, and the proportion was higher in CPAK I, II, III, and VI than in IV and V types (P < .05). The median FJS of CPAK III was significantly lower than I and IV (P < .0262) and comparable to II, V, and VI (P > .085). The minimum PTG angle required to prevent medial deviation by at least 2° in all patients is 17°.

Conclusions

A medial deviation of the 6° PTG occurred in more than half of the KA TKAs and was observed in 4 of 6 CPAK types. Because medial deviation was associated with a lower FJS, it is suggested that the femoral component should have a minimum PTG of 17° to prevent medial deviation by at least 2° in all patients.

Level of evidence

IV.

The Distribution of Coronal Plane Alignment of the Knee Classification in a Sample of Spanish Southeast Osteoarthritic Population: A Retrospective Cross-Sectional Observational Study

Background and Objectives: The Coronal Plane Alignment of the Knee (CPAK) classification is a pragmatic distribution of nine phenotypes for coronal knee alignment that can be used on healthy and arthritic knees. Our study aimed to describe the CPAK distributions in a Spanish southeast osteoarthritic population and compare them to other populations' published alignment distributions. Method and Materials: Full-leg standing X-rays of the lower limb from 528 cases originating from the so-called Vega Alta del Segura (southeast of the Iberian Peninsula) were retrospectively analysed. We measured the mechanical hip-knee-ankle, lateral distal femoral, and medial proximal tibial angles. We calculated the arithmetic hip-knee-ankle angle and the joint line obliquity to classify each case according to the criteria of the CPAK classification. Results: Based on the aHKA result, 59.1% of the cases were varus (less than -2°), 32.7% were neutral (0° ± 2°), and 8.2% were valgus (greater than +2°). Based on the JLO result, 56.7% of the cases had a distal apex (less than 177°), 39.9% had a neutral apex (180° ± 3°), and 3.4% had a proximal apex (greater than 183°). The most common CPAK distribution in our Spanish southeast osteoarthritic population was type I (30.7%), followed by type IV (25.9%), type II (21%), type V (11.2%), type III (5%), type VI (2.8%), type VII (2.4%), type VIII (0.6%), and type IX (0.4%). Conclusions: We described the distribution according to the CPAK classification in a sample of the osteoarthritic population from southeastern Spain. In our sample, more than 75% of the patients were classified as type I, II, and IV.

Variability of three-dimensional knee morphology cannot be effectively assessed using a coronal plane knee alignment classification in total knee arthroplasty patients

Purpose

Optimal reproduction of the native three-dimensional (3D) alignment in total knee arthroplasty (TKA) influences outcomes; however, much of the modern TKA alignment research, such as the coronal plane alignment of the knee (CPAK), focuses only on coronal alignment. Tibial, femoral and tibiofemoral measurements on the axial and sagittal planes were evaluated for their relationship to the arithmetic hip-knee-ankle angle (aHKA) and joint-line obliquity (JLO). These 3D anatomical measurements are also evaluated across CPAK groups.

Methods

A retrospective analysis of the 360 Med Care computed tomography (CT) database was performed. Patient CT scans were segmented and landmarked. Linear regression analysis compared 12 axial and sagittal plane measurements (representing tibial, femoral and tibiofemoral rotation, tibial slope and femoral flexion) with both aHKA and JLO. Nonparametric tests assessed these anatomical measurements across the different CPAK groups, while Cohen's delta (d) determined the effect size.

Results

With a sample size of 7450 osteoarthritic knees, significant but weak relationships (r < 0.30) were observed between all 12 anatomical measurements and both aHKA and JLO. Tibiofemoral rotations between Insall's axis and both the posterior condylar and the surgical transepicondylar axes demonstrated large effect sizes (d > 0.80). However, trivial to small effect sizes (d < 0.50) were broadly observed across the 12 axial and sagittal measurements, underscoring their limited clinical significance.

Conclusions

While useful for describing coronal knee anatomy, CPAK phenotypes fail to differentiate tibial, femoral and tibiofemoral rotation, tibial slope or femoral flexion-crucial aspects of 3D surgical planning. Therefore, more comprehensive knee phenotyping solutions are required to guide individualised TKA alignment strategies.

Level of Evidence

Level II.

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.

Boundaries in Kinematic Alignment: Why, When, and How

The use of alternative alignments in total knee arthroplasty (TKA) has recently been increasing in popularity: many of these alignments have been included in the broad spectrum of "kinematic alignment." This alternative approach was recommended to increase patients' satisfaction since many studies based on patient-reported outcome measures (PROMs) showed that every fifth patient is not satisfied with the surgical outcome. In fact, the original kinematic alignment technique was designed as a "pure resurfacing" technique, maintaining the preoperative axes (flexion-extension and axial rotation) of the knee. In adjunct, many new classifications of the preoperative limb deformity have been proposed to include a large range of knee anatomies, few of them very atypical. Following those classifications, many surgeons aimed for a reproduction of unusual anatomies putting in jeopardy the survivorship of the implant according to the classical "dogma" of a poor knee kinematics and TKA biomechanics if the final hip-knee-ankle (HKA) axis was not kept within 5 degrees from neutral. This article reviews the literature supporting the choice of setting alignment boundaries in TKA when surgeons are interested in reproducing the constitutional knee anatomy of the patient within a safe range.

Better restoration of joint line obliquity in tibia first restricted kinematic alignment versus mechanical alignment TKA

INTRODUCTION

In total knee arthroplasty (TKA), suboptimal restoration of joint line obliquity (JLO) and joint line height (JLH) may lead to diminished implant longevity, increased risk of complications, and reduced patient reported outcomes. The primary objective of this study is to determine whether restricted kinematic alignment (rKA) leads to improved restoration of JLO and JLH compared to mechanical alignment (MA) in TKA.

MATERIALS AND METHODS

This retrospective study assessed patients who underwent single implant design TKA for primary osteoarthritis, either MA with manual instrumentation or rKA assisted with imageless navigation robotic arm TKA. Pre- and post-operative long standing AP X-ray imaging were used to measure JLO formed between the proximal tibial joint line and the floor. JLH was measured as the distance from the femoral articular surface to the adductor tubercle.

RESULTS

Overall, 200 patients (100 patients in each group) were included. Demographics between the two groups including age, sex, ASA, laterality, and BMI did not significantly differ. Distribution of KL osteoarthritis classification was similar between the groups. For the MA group, pre- to post-operative JLO significantly changed (2.94° vs. 2.31°, p = 0.004). No significant changes were found between pre- and post-operative JLH (40.6 mm vs. 40.6 mm, p = 0.89). For the rKA group, no significant changes were found between pre- and post-operative JLO (2.43° vs. 2.30°, p = 0.57). Additionally, no significant changes were found between pre- and post-operative JLH (41.2 mm vs. 42.4 mm, p = 0.17). Pre- to post-operative JLO alteration was five times higher in the MA group compared to the rKA group, although this comparison between groups did not reach statistical significance (p = 0.09).

CONCLUSION

rKA-TKA results in high restoration accuracy of JLO and JLH, and demonstrates less pre- and post-operative JLO alteration compared to MA-TKA. With risen interest in joint line restoration accuracy with kinematic alignment, these findings suggest potential advantages compared to MA. Future investigation is needed to correlate between joint line restoration accuracy achieved by rKA and enhanced implant longevity, reduced risk of post-operative complications, and heightened patient satisfaction.

Increased prevalence of valgus constitutional alignment subtypes in a South African arthritic population group using the coronal plane alignment of the knee (CPAK) classification

BACKGROUND

Knee alignment philosophies and patient specific models to improve patient reported outcomes are gaining increasing attention. The coronal plane alignment of the knee (CPAK) classification describes nine knee phenotypes and then proposes surgical alignment strategies to achieve constitutional alignment. The CPAK classification has been validated in Australian, European, Asian and North American population groups. To date no African data has been analyzed using CPAK.

METHODS

A total of 344 arthritic patients (608 knees) with appropriate long leg radiographs were classified based on the CPAK type. Measurements included mechanical hip-knee-angle(mHKA), medial proximal tibial angle (mMPTA) and lateral distal femoral angle (mLDFA) and the derived calculations of joint line obliquity (JLO) and arithmetic hip-knee-angle (aHKA).

RESULTS

The sample population was 77.9% (n = 268) female with a mean age of 68.4 ± 9.2 years. The most common CPAK types in order were type 3 (n = 174; 28.6%), type 2 (n = 155; 25.5%), type 1 (n = 94; 15.5%) and type 6 (n = 80; 13.2%). The most common limb alignment types were valgus (CPAK types 3,6,9; 41.8%).

CONCLUSION

This study, which investigated arthritic patients from a single institution in South Africa, shows a divergence of CPAK phenotypic knee patterns relative to other international studies, with much higher proportions of valgus phenotypes (3 and 6). This regional difference should be further investigated in other South African and African population samples and used to adapt the surgical strategies employed by local surgeons.

No Difference in Limb Alignment Between Kinematic and Mechanical Alignment Robotic-Assisted Total Knee Arthroplasty

BACKGROUND

Individualized alignment techniques have gained major interest in an effort to increase satisfaction among total knee arthroplasty patients. This study aimed to compare postoperative alignment between kinematic alignment (KA) and mechanical alignment (MA) and assess whether KA significantly deviates from the principle of aligning the limb as close to neutral alignment as possible.

METHODS

There were 234 patients who underwent robotic-assisted total knee arthroplasty using an unrestricted KA and a strict MA technique (KA: 145, MA: 89). The lateral distal femoral angle, medial proximal tibia angle, and the resultant arithmetic hip-knee-ankle angle (aHKA) were measured. The aHKA < 0 indicated varus alignment, while the aHKA > 0 indicated valgus knee alignment. The primary outcome was the frequency of cases that resulted in an aHKA of ± 4° of neutral (0°), as assessed on full-leg standing radiographs obtained at 6 weeks postoperatively. The secondary outcome was the change in coronal plane alignment of the knee classification type from preoperative to postoperative between the MA and KA groups.

RESULTS

The mean preoperative aHKA was similar between the 2 groups (P = .19). The KA group had a mean postoperative aHKA of -1.4 ± 2.4°, while the MA group had a mean postoperative aHKA of -0.5 ± 2.1°. No significant difference in limb alignment was identified between KA and MA cases that resulted in hip-knee-ankle angle of ± 4° being neutral (91.7 versus 96.6%, P = .14). There were 97.2% of cases in the KA group that fell within the ± 5° range. The MA group was associated with a significantly higher rate of coronal plane alignment of the knee classification type change from preoperatively to postoperatively (P < .001).

CONCLUSIONS

Kinematic alignment achieved similar postoperative aHKA compared to MA, and thus did not significantly deviate from the principle of aligning the limb as close to neutral alignment as possible. Surgeons should feel comfortable starting to introduce individualized alignment techniques. Without being restricted by boundaries, postoperative alignment will be within 5 degrees of neutral 97% of the time.

Knees with isolated lateral compartment osteoarthritis show a substantial variability in functional knee phenotypes with demographic-specific variations: Phenotypic analysis of 305 knees

BACKGROUND

The primary aim of this study was to assess and describe the phenotypic variation in the coronal plane of knees affected by isolated lateral compartment osteoarthritis (OA). The secondary aim was to investigate the potential gender-specific and age-related differences in functional knee phenotypes among knees with isolated lateral compartment OA.

METHODS

A comprehensive classification system was used to categorize 305 knees with isolated lateral compartment OA based on their mechanical hip-knee-ankle angle (HKA), femoral mechanical angle (FMA), and tibial mechanical angle (TMA). The phenotypic variation of functional knee phenotypes was assessed for the entire cohort and stratified by gender and age category.

RESULTS

Among knees with isolated lateral compartment OA, a total of 60 distinct functional knee phenotypes were identified, with phenotype VALHKA6°NEUFMA0°VALTMA3° being the most prevalent (10.8 %). Gender-specific differences were evident, with females exhibiting significantly greater valgus alignment in both mean HKA and TMA values compared with males (HKA: -6.4° vs. -5.4°, respectively; P = 0.02 and TMA 94.4° vs. 89.0°, respectively; P = 0.005). Age-related variations included younger patients predominantly displaying femoral deformities, while older patients primarily exhibited isolated tibial- or combined femoral and tibial deformities.

CONCLUSIONS

There is a broad variation of functional knee phenotypes among knees affected by isolated lateral compartment OA, with gender-specific and age-related differences. Recognizing this inherent phenotypic diversity during preoperative planning may facilitate the implementation of tailored approaches that account for the unique characteristics and bony deformities of the individual knee.

Coronal Plane Alignment Classification of Arthritic Knees in a South Indian Population and Functional Outcome Comparison Post-mechanical Alignment Total Knee Arthroplasty

Study Background

Mechanical alignment has always been considered as the gold standard in total knee arthroplasty (TKA), but various other coronal alignment strategies have been proposed to enhance native knee kinematics and thus elevate patient satisfaction levels. Coronal plane alignment of the knee (CPAK) classification introduced by MacDessi is a simple yet comprehensive system to classify knees based on their coronal plane alignment. It categorizes knees into nine phenotypes based on medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA).

Materials and Methods

This study investigates the distribution of classification of primary arthritic knees (CPAK) types among arthritic knees in the South Indian population and compares the functional outcomes following total knee arthroplasty (TKA) using traditional mechanical alignment among various CPAK types. The research, spanning from September 2021 to August 2023, encompasses a comprehensive analysis of 324 patients with 352 knees in the first part and 48 patients with 72 knees in the second part of the study who underwent TKA, incorporating demographic data and radiological evaluations.

Results

Results indicate a predominant distribution of CPAK type 1, followed by type 2 and type 4 among the South Indian population. In the functional outcomes analysis, regardless of CPAK type, patients exhibited significant improvements in Knee Injury and Osteoarthritis Outcome Score (KOOS), Oxford Knee Score (OKS), and visual analog scale (VAS) scores post-operatively.

Conclusion

CPAK distribution among the South Indian population is comparable to other Indian study and studies with an Asian population, but varies with studies among the White population. Significant improvement of functional outcome among all CPAK types signifies the robust nature of conventional mechanical alignment strategy. Thus, our study serves as an initial exploration into the knee phenotype of the South Indian population and findings contribute to ongoing research on optimal alignment strategies in knee arthroplasty, paving the way for future, more extensive studies in this dynamic field.

Radiologic Assessment of Knee Phenotypes Based on the Coronal Plane Alignment of the Knee Classification in a Korean Population

Background

The Coronal Plane Alignment of the Knee (CPAK) classification system has been developed as a comprehensive system that describes 9 coronal plane phenotypes based on constitutional limb alignment and joint line obliquity (JLO). Due to the characteristics of Asian populations, which show more varus and wider distribution in lower limb alignment than other populations, modification of the boundaries of the arithmetic hip-knee-ankle angle (aHKA) and JLO should be considered. The purpose of this study was to determine the knee phenotype in a Korean population based on the original CPAK and modified CPAK classification systems.

Methods

We reviewed prospectively collected data of 500 healthy and 500 osteoarthritic knees between 2021 and 2023 using radiographic analysis and divided them based on the modified CPAK classification system by widening the neutral boundaries of the aHKA to 0° ± 3° and using the actual JLO as a new variable. Using long-leg standing weight-bearing radiographs, 6 radiographic parameters were measured to evaluate the CPAK type: the mechanical HKA angle, medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA), aHKA, JLO, and actual JLO.

Results

From 2 cohorts of 1,000 knees, the frequency distribution representing all CPAK types was different between the healthy and arthritic groups. The most common categories were type II (38.2%) in the healthy group and type I (53.8%) in the arthritic group based on the original CPAK classification. The left and upward shift in the distribution of knee phenotypes in the original classification was corrected evenly after re-establishing the boundaries of a neutral aHKA and the actual JLO. According to the modified CPAK classification system, the most common categories were type II (35.2%) in the healthy group and type I (38.0%) in the arthritic group.

Conclusions

Although the modified CPAK classification corrected the uneven distribution seen when applying the original classification system in a Korean population, the most common category was type I in Korean patients with osteoarthritic knees in both classification systems. Furthermore, there were different frequencies of knee phenotypes among healthy and arthritic knees.

Functional knee phenotypes appear to be more suitable for the Chinese OA population compared with CPAK classification: A study based on 3D CT reconstruction models

PURPOSE

The aim of this study was to investigate the distribution of coronal plane alignment of the knee (CPAK) classification and functional knee phenotypes in a Chinese osteoarthritis (OA) population and to compare different lower limb alignment targets according to the distribution characteristics to find suitable total knee arthroplasty (TKA) bone cut strategies for the Chinese OA patients.

METHODS

The computed tomography (CT) images were retrospectively collected and the three-dimensional (3D) models were reconstructed from 434 Chinese OA patients, including 93 males and 341 females, with a mean age of 66.4 ± 9.3 years. Femoral mechanical angle (FMA), tibial mechanical angle (TMA) and mechanical hip-knee-ankle angle (mHKA) were measured on the 3D models. Arithmetic hip-knee-ankle angle (aHKA) was calculated using FMA plus TMA, and joint line obliquity was calculated as 180 + TMA-FMA. The CPAK according to MacDessi and the functional knee phenotypes according to Hirschmann were performed. In addition, the suitable TKA bone cut strategies were explored according to the phenotypes and based on the characteristics of different alignment targets, such as mechanical alignment, anatomic alignment (AA), kinematic alignment, restricted KA (rKA) and adjusted MA (aMA). Statistical differences were determined using the independent-samples t-test or the two independent-samples Wilcoxon test, with p < 0.05 considered statistically significant.

RESULTS

The Chinese OA population showed a varus alignment tendency (mHKA = 172.1° ± 7.2°), to which the TMA was a major contributor (TMA = 84.7° ± 4.4° vs. FMA = 91.3° ± 3.2°). The mHKA was on average 3.9° more varus than the aHKA. A total of 140 functional knee phenotypes were found and 45.6% were concentrated in VARFMA3°-NEUFMA0° to VARTMA3°-NEUTMA0°. More than 70% of patients had different FMA and TMA phenotypes. There were 92.9% of CPAK distributed in types I to IV, with type I accounting for 53.9%. The FMA phenotypes were less changed if the aMA and rKA were chosen, and the TMA phenotypes were less changed if the AA and rKA were chosen.

CONCLUSION

Compared with the CPAK, the functional knee phenotypes were more suitable for the Chinese OA population with a wide distribution and a varus tendency, and it seemed more appropriate to choose aMA and rKA as TKA alignment targets for resection.

LEVEL OF EVIDENCE

Level Ⅲ.

Superiority of kinematic alignment over mechanical alignment in total knee arthroplasty during medium- to long-term follow-up: A meta-analysis and trial sequential analysis

PURPOSE

To compare and determine the reliability and conclusiveness of the medium- and long-term efficacy in terms of patient-reported outcome measures and the risk of revisions or reoperations (RRRs) of kinematic alignment (KA) and mechanical alignment (MA) in total knee arthroplasty.

METHODS

A comprehensive search was conducted in Medline, EMBASE, Web of Science and Cochrane Database Library to identify relevant literature. Only randomised clinical trials (RCTs) published before July 2023 were included. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Oxford Knee Score (OKS), Forgotten Joint Score (FJS) and RRR were compared. Additionally, OKS and RRR were subjected to a trial sequential analysis.

RESULTS

Seven RCTs involving 572 knees were identified. The pooled analysis of the included studies demonstrated that KA showed better medium-term WOMAC and OKS (mean difference [MD] = -6.3, 95% confidence interval [CI]: -9.52 to -2.99, p < 0.05 and MD = 1.1, 95% CI: 0.05-2.15, p < 0.05), respectively), but no significant differences were observed in the long-term follow-up (MD = 2.1, 95% CI: -3.21 to 7.31, not significant [n.s.] and MD = 0.01, 95% CI: -2.43 to 2.46, n.s., respectively). FJS (standardised MD = -0.03, 95% CI: -0.25 to 0.19, n.s.) and RRR (risk ratio = 1.0, 95% CI: 0.57 to 1.74, n.s.) showed no significant intergroup differences (n.s.). The evidence quality ranged from moderate to high, and the trial sequential analysis indicated the need for additional high-quality RCTs to draw more conclusive results.

CONCLUSIONS

KA showed better medium-term WOMAC and OKS, while KA and MA had similar FJS without increasing the RRR in medium- and long-term follow-up. Further research is needed for more conclusive results.

LEVEL OF EVIDENCE

Level II (meta-analyses).

Significant difference in femoral torsion between coronal plane alignment of the knee type 1 and 4

PURPOSE

The purpose of this study was to find out whether the torsions of the femur and tibia are dependent on the coronal plane alignment of the knee (CPAK) type.

METHODS

Five hundred patients (1000 legs) were included, who received a whole leg standing three-dimensional (3D) radiograph using EOS imaging (EOS Imaging, Paris, France). SterEOS software was used for digital reconstruction. Femoral and tibial torsions were determined by analysing 3D reconstructions of each leg. Femoral torsion was defined as the angle between the femoral neck axis (FNA) and the posterior condylar axis (PCA). Tibial torsion was defined as the angle between the axis tangent to the posterior part of the tibia plateau and the transmalleolar axis. Arithmetic hip-knee-ankle angle (aHKA) and joint-line obliquity (JLO) were also determined, allowing each leg to be assigned one of nine possible phenotypes according to CPAK.

RESULTS

The mean femoral torsion in CPAK type 1 was significantly higher (+ 2.6° ± 0.8°) than in CPAK type 4 (p = 0.02). All other CPAK types did not differ in the degree of femoral torsions. No differences could be demonstrated for the tibial torsion.

CONCLUSION

There is a correlation between the coronal alignment of the lower limb and femoral torsion. This may provide the basis for extending the CPAK classification beyond the coronal plane.

LEVEL OF EVIDENCE

Level III.

Impact of change in coronal plane alignment of knee (CPAK) classification on outcomes of robotic-assisted TKA

BACKGROUND

Mechanical alignment with total knee arthroplasty (TKA) has been widely used since the implantation of the first prosthetic knee. Multiple studies have reported 80% patient satisfaction with TKA. However, the reported patients' dissatisfaction is believed to be caused by having to convert different knee alignments to neutral alignments. It is postulated that a change in the CPAK classification of knees leads to patient dissatisfaction. Thus, we hypothesized that a change in CPAK classification with robot-assisted TKA with mechanical alignment does not significantly lead to patient dissatisfaction.

METHODS

We retrospectively analyzed 134 patients who underwent robot-assisted mechanical alignment total knee arthroplasty (MA-TKA) using cementless implants and classified them into CPAK system pre- and post-operatively. One year after TKA surgery, we recorded binary responses to patients' satisfaction with the outcome of surgery and analyzed if a change in CPAK classification is associated with the outcome of surgery.

RESULTS

We found that 125 out of 134 patients (93.28%) were happy with the outcome of surgery. CPAK classification was changed in 116 patients (86.57%) and maintained in 18 patients (13.43%). Our results also showed that 111 (95.7%) out of 116 patients who had a change in CPAK and 14 (77.8%) out of 18 patients who maintained their CPAK post-surgery were happy with the outcome of surgery (OR = 6.3, CI 1.741-25.17, P value = 0.019).

CONCLUSION

We concluded that changing the patient's native joint line and CPAK classification does not significantly change the outcome of surgery in terms of satisfaction. The dissatisfaction rate of 20% as published by previous researchers may be confounded by other reasons and not just due to changes in alignment and joint line.

Tibia-first, gap-balanced patient-specific alignment technique achieves well-balanced gaps in 90% of cases by rebuilding bony anatomy within boundaries

PURPOSE

Patient-specific alignment (PSA) technique tries to achieve balanced gaps and simultaneously rebuild the individual bony phenotype. The hypothesis was: PSA technique achieves balanced knees in a high percentage with more anatomical resections than adjusted mechanical alignment (AMA).

METHODS

Three hundred sixty-seven patients underwent navigated total knee arthroplasty (TKA) with a tibia-first gap-balanced PSA technique. Resection boundaries for medial proximal tibia angle (MPTA) of 86-92°, mechanical lateral distal femoral angle (mLDFA) of 86-92°, and hip-knee-ankle angle (HKA) of 175-185° were defined. Preoperative and intraoperative parameters of HKA, MPTA, mLDFA, and gap widths were recorded. Depending on the coronal deformity, the patients were divided into three groups: varus HKA < 178°; straight 178-182° and valgus HKA > 182°. The stability was analysed by assessing the difference between medial and lateral extension and flexion gaps as well as between flexion and extension gaps. All PSA measurements were compared with data from a previously published AMA series.

RESULTS

PSA achieved balanced gaps in extension, flexion and between flexion/extension in over 90% of cases, being similar to AMA. In PSA, MPTA and mLDFA were restored within 1°, except in extreme varus (MPTA difference 2°) and valgus knees (mLDFA difference 3°). This was caused by the defined boundaries of the alignment technique. This individualised reconstruction led to significantly more anatomical resections of all tibia and femur resections.

CONCLUSION

A tibia-first, gap-balanced PSA technique achieves balanced joints in more than 90% of cases. By maintaining preoperative MPTA and mLDFA to a high extent, far more anatomical resections, compared to AMA were performed. Future studies need to be conducted to investigate whether those promising intraoperative results correlate with postoperative patient outcomes and whether patients outside the 5° corridor have higher failure rates.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Multi-Planar Expansion of the Coronal Plane Alignment of the Knee Classification? A Computed Tomographic Study Indicates No Significant Correlation With Alignment Parameters in Other Planes

BACKGROUND

The Coronal Plane Alignment of the Knee (CPAK) classification categorizes knee phenotypes based on constitutional limb alignment (arithmetic hip-knee-ankle angle or aHKA) and joint line obliquity (JLO). This study aimed to determine if sagittal and rotational knee alignments vary among CPAK types in order to establish whether this classification should be expanded beyond coronal plane assessment.

METHODS

Coronal, sagittal, and rotational alignment measurements were made and CPAK types were calculated from computed tomographic data of 437 patients (509 knees) who underwent robotic-assisted total knee arthroplasty (TKA). Differences in femoral, tibial, and tibio-femoral angular measurements were compared across CPAK types, and correlations were made to aHKA and JLO. Nonparametric and linear regression tests were used to analyze between-type differences.

RESULTS

There were no differences in tibial slope or femoral rotational measures across CPAK phenotypes. However, CPAK Type III knees had a greater tibio-femoral rotation mean difference than CPAK Type I, II, IV, and V knees (P < .05). We also found increased femoral flexion in Type I knees when compared to Type VI knees (P = .01). The aHKA had a weak correlation with femoral flexion angle, and JLO had a weak correlation with femoral posterior condylar axis to tibial antero-posterior axis angle.

CONCLUSION

Few clinically important differences in sagittal and rotational alignments were found between CPAK types, indicating that CPAK phenotype has little correlation to 3-dimensional alignment characteristics. Need for an expansion of the CPAK classification beyond coronal plane alignment is not supported from these results.

Preserving coronal knee alignment of the knee (CPAK) in unicompartmental knee arthroplasty correlates with superior patient-reported outcomes

BACKGROUND

The optimal alignment target for unicompartmental knee arthroplasty (UKA) remains controversial, and literature suggests that its impact on patient-reported outcome measures (PROMs) varies. The purpose of this study was to identify the relationship between changes in the coronal plane alignment of the knee (CPAK) and PROMs in patients who underwent UKA.

METHODS

A retrospective analysis of 164 patients who underwent UKA was conducted. The types of CPAK types categorized into unchanged, minor (shift to an adjacent CPAK type, e.g., type I to II or type I to IV), and major changes (transitioning to a nearby diagonal CPAK type or two types across, such as type I to V or type I to III). PROMs were assessed preoperatively and 1 year postoperatively using the Hospital for Special Surgery (HSS) scores, Knee Society (KS) scores, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Forgotten Joint Scores (FJS). Comparison was performed between patients who experienced and who did not experience any changes in the CPAK.

RESULTS

Patients with preserved native CPAK alignment demonstrated significantly superior 1 year postoperative outcomes, with higher HSS, KS knee, and WOMAC pain scores (p = 0.042, p = 0.009, and p = 0.048, respectively). Meanwhile, the degree of change in CPAK did not significantly influence the PROMs, and patients who experienced minor and major changes in the CPAK showed comparable outcomes.

CONCLUSION

Preserving the native CPAK in UKA procedures is important for achieving favorable clinical outcomes at 1 year postoperative. The extent of change in the CPAK type exerted a limited impact on PROMs, thus emphasizing the importance of change in alignment itself.

Restricted kinematic alignment is clinically non-inferior to mechanical alignment in the short and mid-term: A systematic review

BACKGROUND

In recent years, kinematic alignment (KA) is becoming a valid alternative to mechanical alignment (MA) in total knee arthroplasty (TKA). However, to avoid early failures, the restricted kinematic alignment (rKA) approach has been developed to restore native knee kinematics without reproducing extreme knee phenotype. This systematic review aims to evaluate clinical and radiological outcomes between rKA and MA for TKA.

METHODS

A systematic literature search was conducted following PRISMA guidelines on Pubmed, Scopus and Cochrane Library. The following search string was adopted: (((restricted kinematic) AND (mechanical)) AND (alignment)) AND (knee). We included studies that analyzed rKA versus MA in terms of clinical outcomes and complications with a minimum of 6 months of follow up. The following rKA- and MA-related data were evaluated: patient-reported outcome scores (PROMs), radiographic analysis of lower limb alignment, and complications. Criteria from the Methodological Index for Non-Randomized Studies were used to assess the methodological quality of the articles.

RESULTS

This systematic review included seven clinical studies with a total of 892 knees (471 for MA group and 421 for rKA group, respectively). Overall, post-operative PROMs were similar between rKA and MA. Moreover, rKA reached better results regarding Forgotten Joint Score and post-operative patient satisfaction. Finally, no higher complication rate was observed with the rKA approach.

CONCLUSION

The rKA aims to restore native knee kinematics, avoiding extreme deformities. Clinical outcomes are not inferior or even better for rKA compared with MA, without increasing the risk of short-middle-term implant failure. However, there is a high heterogeneity regarding the 'restricted' protocols used.

Knees with anteromedial osteoarthritis show a substantial phenotypic variation prior and following medial unicompartmental knee arthroplasty

PURPOSE

The primary aim of this study was to evaluate the phenotypic variation using the Coronal Plane Alignment of the Knee (CPAK) classification among 1000 knees with anteromedial osteoarthritis (OA) both prior to and following medial unicompartmental knee arthroplasty (UKA). The secondary aim of this study was to investigate whether knees maintained their preoperative CPAK phenotype and to evaluate the phenotypic alterations following medial UKA.

METHODS

The CPAK classification was used to analyze 1000 knees that underwent medial UKA as treatment for anteromedial OA. Knees were categorized into nine distinct CPAK phenotypes based on their arithmetic hip-knee-ankle angle (aHKA), which estimates the pre-arthritic alignment, and joint line obliquity (JLO), both pre- and postoperatively. Phenotypic variation was analyzed by sex and age, and the phenotypic alterations following medial UKA were evaluated by phenotype.

RESULTS

Preoperatively, CPAK phenotype I had the highest prevalence (45.0%). Among males, the preoperative prevalence of CPAK phenotype I was significantly higher compared to females (53.2% vs. 35.0%, respectively; p ≤ .001), whereas females exhibited a significantly higher occurrence of CPAK phenotype V compared to males (9.8% vs. 4.4%, respectively; p ≤ .015). Following medial UKA, CPAK phenotype II had the highest prevalence (53.3%). Overall, 45.1% of knees maintained their preoperative CPAK phenotype following medial UKA, which was most frequently observed among CPAK phenotype II (67.7%) and III (65.8%).

CONCLUSION

There is a substantial variation in CPAK phenotypes among knees with anteromedial OA, as well as following treatment with medial UKA. This variability challenges the assumption of uniform characteristics among knees with an identical wear pattern associated with anteromedial OA and emphasizes the complexity and variability of this specific form of OA.

LEVEL OF EVIDENCE

III, Retrospective cohort study.

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.

Comparable accuracy of femoral joint line reconstruction in different kinematic and functional alignment techniques

PURPOSE

A key part of kinematic alignment (KA) and functional alignment (FA) is to restore the natural femoral joint line, in particular the medial joint line. KA is known to reproduce the femoral joint line accurately; however, direct comparisons with other surgical techniques such as FA are currently lacking. The purpose of this study was to evaluate differences of alignment parameters in KA and FA techniques with a special focus given to the femoral joint line.

METHODS

We performed a retrospective radiological analysis of pre- and postoperative long leg radiographs of 221 consecutive patients with varus or neutral leg alignment, who underwent primary total knee arthroplasty (TKA) procedures from 2018 to 2020. Patients were assigned to one of four groups: (1) FA: image-based robotic-assisted TKA, (2) FA: imageless robotic-assisted TKA, (3): restricted KA: 3D cutting block-assisted (patient-specific instruments, PSI) TKA, (4): unrestricted KA: calipered technique. Patients' radiographs were (re)-analyzed for overall limb alignment, medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA), as well as medial and lateral femoral joint line alteration. Statistical significance was determined using unpaired t testing (FA vs. KA group) and one-way ANOVA (subgroup analyses).

RESULTS

Comparisons of KA vs. FA, as well as individual subgroups of KA and FA did not show any differences in the accuracy of medial joint line reconstruction (< 2 mm, p = 0.384, p = 0.744, respectively) and LDFA alteration (< 2°, p = 0.997, 0.921, respectively). Correction of MPTA (3.4° vs. 2.2°) and lateral femoral joint line (2.1 mm vs. 1.5 mm) was higher for FA and FA subgroups compared to KA and KA subgroups (both p < 0.001).

CONCLUSION

Kinematic and functional alignments showed a comparable accuracy in reconstruction of the medial femoral joint line and femoral joint line orientation. Increased correction of MPTA and lateral femoral joint line was recorded with FA techniques.

LEVEL OF EVIDENCE

III.

Geographic Variation in Knee Phenotypes Based on the Coronal Plane Alignment of the Knee Classification: A Systematic Review

BACKGROUND

The extent of geographic variation in knee phenotypes remains unclear. The Coronal Plane Alignment of the Knee (CPAK) Classification proposes 9 coronal plane phenotypes based on constitutional limb alignment and joint line obliquity. This systematic review aims to examine differences in the distributions of CPAK types across geographic regions.

METHODS

A systematic review of the literature was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Studies reporting distributions of knee phenotypes according to the CPAK classification for healthy and/or arthritic knees were included.

RESULTS

There were 7 studies included, accounting for 5,964 knees in 3,917 subjects. Among healthy knees (n = 1,214), CPAK type II was the most common type in Belgium (39.2%), Taiwan (39.3%), and India (25.6%). Among arthritic knees (n = 2,804), CPAK type I was the most common in France (33.4%), India (58.8%), and Japan (53.8%), whereas CPAK type II was the most common in Australia (32.8%). The proportion of CPAK type I and II knees varied significantly across geographic regions among healthy (P < .01) and arthritic knees (P < .01).

CONCLUSION

Significant variation in CPAK distributions exists between countries. Further work is needed to delineate racial and sexual differences in CPAK types, which were not explored in this article. A better understanding of population-level variability in knee phenotypes may enable orthopaedic surgeons to offer a more personalized approach to knee arthroplasty.

Independent of the preoperative coronal deformity, adjusted mechanical alignment leads in a high percentage to non-anatomical tibial and femoral bone cuts

PURPOSE

The technique of adjusted mechanical alignment (AMA) in total knee arthroplasty (TKA) has been described to achieve alignment and balancing goals in varus knees in a high percentage, albeit at the price of non-anatomical bone cuts. The purpose of this study was to analyze (1) whether AMA achieves similar alignment and balancing results in different types of deformity and (2) whether they can be achieved without altering the native anatomy.

METHODS

A series of 1000 patients with hip-knee-ankle (HKA) angles from 165° to 195° were analyzed. All patients were operated using AMA technique. According to the preoperative HKA angle, three groups of knee phenotypes (varus, straight, valgus) were defined. The bone cuts were analyzed for being anatomic (< 2 mm deviation of individual joint surface) or non-anatomic (> 4 mm deviation of individual joint surface).

RESULTS

AMA reached the goals for postoperative HKA in over 93% in every group (varus: 636 cases, 94%, straight: 191 cases, 98%, valgus: 123 cases, 98%). In 0° extension, the gaps were balanced in varus knees in 654 cases (96%), in straight knees in 189 cases (97%) and in valgus knees in 117 cases (94%). A balanced flexion gap was found in a similar number of cases (varus: 657 cases, 97%, straight: 191 cases, 98%, valgus: 119 cases, 95%). In the varus group, non-anatomical cuts were performed at the medial tibia (89%) and the lateral posterior femur (59%). The straight group showed similar values and distribution for non-anatomical cuts (medial tibia: 73%; lateral posterior femur 58%). Valgus knees showed a different distribution of values, being non-anatomical at the lateral tibia (74%), distal lateral femur (67%) and posterior lateral femur (43%).

CONCLUSION

In all knee phenotypes, the AMA goals were achieved in a high percentage by altering the patients' native anatomy. In varus knees, the alignment was corrected by non-anatomical cuts at the medial tibia, and in valgus knees at the lateral tibia and the lateral distal femur. All phenotypes showed non-anatomical resections on the posterior lateral condyle in approximately 50% of cases.

LEVEL OF EVIDENCE

III.

Arithmetic hip knee angle measurement on long leg radiograph versus computed tomography-inter-observer and intra-observer reliability

BACKGROUND

Pre-operative alignment is important for knee procedures including total knee arthroplasty (TKA), especially when considering alternative alignments. The arithmetic Hip Knee Angle (aHKA) is a measure of coronal alignment calculated using the medial proximal tibial (MPTA) and lateral distal femoral angles (LDFA). Traditionally, aHKA is measured on long leg radiographs (LLR). This study assesses the reproducibility of aHKA measurement on LLR and robotic-assisted TKA planning CT.

METHODS

Sixty-eight TKA patients with pre-operative LLR and planning CTs were included. Three observers measured the LDFA, MPTA and aHKA three times on each modality and intra-observer and inter-observer reliability was calculated. Statistical analysis was undertaken with Pearson's r and the Bland-Altman test.

RESULTS

Mean intra-observer coefficient of repeatability (COR) for LLR vs. CT: MPTA 3.50° vs. 1.73°, LDFA 2.93° vs. 2.00° and aHKA 2.88° vs. 2.57° for CT. Inter-observer COR for LLR vs. CT: MPTA 2.74° vs. 1.28°, LDFA 2.31° vs. 1.92°, aHKA 3.56° vs. 2.00°. Mean intra-observer Pearson's r for MPTA was 0.93 for LLR and 0.94 for CT, LDFA 0.90 for LLR and 0.91 for CT and aHKA 0.92 for LLR and 0.94 for CT. Inter-observer Pearson's r for LLR compared to CT: MPTA 0.93 vs. 0.97, LDFA 0.91 vs. 0.90, aHKA 0.91 and 0.95.

CONCLUSION

When compared to LLR, CT measurements of MPTA, LDFA and aHKA are more reproducible and have a good correlation with LLR measurement. CT overcomes difficulties with positioning, rotation, habitus and contractures when assessing coronal plane alignment and may obviate the need for LLRs.

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.