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

Coronal alignment in total knee arthroplasty: a review

Total knee arthroplasty (TKA) alignment has recently become a hot topic in the orthopedics arthroplasty literature. Coronal plane alignment especially has gained increasing attention since it is considered a cornerstone for improved clinical outcomes. Various alignment techniques have been described, but none proved to be optimal and there is a lack of general consensus on which alignment provides best results. The aim of this narrative review is to describe the different types of coronal alignments in TKA, correctly defining the main principles and terms.

Posterior Compartment Debridement and Varus Deformity Correction in Total Knee Arthroplasty

BACKGROUND

Restoration of joint-line position and deformity correction remain important tenets for preserving stability and function after total knee arthroplasty (TKA). We sought to characterize the role of posterior osteophytes in the correction of alignment deformity during TKA.

METHODS

We evaluated 57 patients (57 TKAs) who participated in a trial of robotic-arm assisted TKA outcomes. Weight-bearing and fixed preoperative alignment was measured using long-standing radiographs and tools of the robotic-arm tracking system, respectively. Total volume (cm²) of posterior osteophytes was quantified using preoperative planning computed tomography scans. Joint line position was evaluated using bone resection thicknesses measured using a caliper.

RESULTS

The mean (minimum to maximum) initial fixed deformity was 4 degrees (range, 0 to 11) of varus. All patients showed asymmetric posterior osteophytes. Mean total osteophyte volume was 3 cm³ (range, 1 to 9). Total osteophyte volume was positively correlated with severity of fixed deformity (r=0.48, P=0.0001). Removal of osteophytes allowed for the correction of functional alignment to within three degrees of neutral in all cases (mean 0 deg), with none requiring release of the superficial medial collateral ligament. Tibial joint line position was restored to within 3 millimeters in all but 2 cases (mean increase of height, 0.6 (range, -4 to +5)).

CONCLUSION

In the end-stage diseased knee, posterior osteophytes typically occupy space in the posterior capsule on the concave side of the deformity. Thorough debridement of posterior osteophytes may help facilitate management of modest varus deformity with decreased need for soft-tissue releases or adjustments to planned bone resection.

An orthopaedic intelligence application successfully integrates data from a smartphone-based care management platform and a robotic knee system using a commercial database

PURPOSE

To evaluate the feasibility of using a smartphone-based care management platform (sbCMP) and robotic-assisted total knee arthroplasty (raTKA) to collect data throughout the episode-of-care and assess if intra-operative measures of soft tissue laxity in raTKA were associated with post-operative outcomes.

METHODS

A secondary data analysis of 131 patients in a commercial database who underwent raTKA was performed. Pre-operative through six week post-operative step counts and KOOS JR scores were collected and cross-referenced with intra-operative laxity measures. A Kruskal-Wallis test or a Wilcoxon sign-rank was used to assess outcomes.

RESULTS

There were higher step counts at six weeks post-operatively in knees with increased laxity in both the lateral compartment in extension and medial compartment in flexion (p < 0.05). Knees balanced in flexion within < 0.5 mm had higher KOOS JR scores at six weeks post-operative (p = 0.034) compared to knees balanced within 0.5-1.5 mm.

CONCLUSION

A smartphone-based care management platform can be integrated with raTKA to passively collect data throughout the episode-of-care. Associations between intra-operative decisions regarding laxity and post-operative outcomes were identified. However, more robust analysis is needed to evaluate these associations and ensure clinical relevance to guide machine learning algorithms.

[Kinematic Alignment of Total Knee Arthroplasty]

Nowadays, kinematic alignment is a widely used alignment philosophy in total knee arthroplasty. The concept of kinematic alignment respects the patient's individual prearthrotic anatomy and is based on the reconstruction of the femoral anatomy and thus the axes of motion of the knee joint. Only then the alignment of the tibial component is adapted to the femoral component. By means of this technique soft tissue balancing is reduced to a minimum. Due to the risk of excessive outlier alignment technical assistance or calipered techniques are recommended for precise implementation. This article attempts to provide an understanding of the fundamentals of kinematic alignment, and it focusses on how it differs from alternative alignment strategies and the way the philosophy is implemented in different surgical techniques.

Variation in knee balance as a function of hip-knee-ankle angle and joint line obliquity in robotic assisted total knee arthroplasty

PURPOSE

To describe the mediolateral (ML) gap balance in pre-resection arthritic knees undergoing robot-assisted (RA) total knee arthroplasty (TKA) within the nine phenotypes of the Coronal Plane Alignment of the Knee (CPAK) classification.

METHODS

A total of 1124 RA TKA cases were retrospectively reviewed. ML balance was calculated using a digital ligament tensioning device following tibial resection and prior to any femoral resection throughout flexion (10°, 40°, and 90°). Lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) were landmarked intra-operatively and adjusted for wear based on hip-knee-ankle angle (HKA). Knees were then subdivided into CPAK categories based on the arithmetic HKA (aHKA) and joint line obliquity (JLO). Differences in balance between CPAK phenotypes were compared.

RESULTS

For aHKA, a greater medial gap was observed in varus compared to neutral or valgus knees at 10° (5.2 ± 3.0 mm vs 3.3 ± 3.2 mm vs - 0.4 ± 5.0 mm respectively; p < 0.0001). A similar trend was observed for JLO in distal apex compared to neutral and proximal apex knees at 10° (3.4 ± 3.6 vs 1.1 ± 5.0 vs - 2.4 ± 6.3 respectively; p < 0.0001). The greatest ML balance differences were found when combining JLO and aHKA at 10° (type I vs type VI: ∆6.6 mm; p < 0.0001).

CONCLUSION

There is a high degree of variability in arthritic ML balance within and between each CPAK phenotype. A single alignment philosophy based on bony landmarks alone may not be sufficient to balance all knees. Utilisation of robotics and digital ligament tensioning devices serves as important adjuncts to characterize the patient-specific soft tissue profile.

Computer Navigation Assisted Restricted Kinematic Alignment Improves Short-Term Outcomes in Total Knee Arthroplasty: An Ambispective Cohort Study

OBJECTIVES

Mechanical alignment (MA)-total knee arthroplasty (TKA) has been challenged due to the excessive soft tissue release and the evidence of the clinical outcomes of computer assisted navigation is still limited. The aim of this ambispective cohort study was to: (i) investigate whether computer assisted navigation is capable to achieve restricted kinematic alignment (rKA)-TKA; and (ii) compare the short-term outcomes between rKA-TKA and MA-TKA.

METHODS

We retrospectively included 41 patients diagnosed with osteoarthritis who received MA-TKA between April 2019 and January 2021 and 43 patients diagnosed with osteoarthritis who received rKA-TKA were included in the prospective cohort from January 2021 to September 2021. Demographical, peri-operative, and radiological data were collected and compared. Unpaired two-sample t-test for continuous variables and χ2 test for categorical variables were used to compare various measurements in two groups. The patient-reported outcome measures at baseline, 10 days (T1), and 6 months (T6) after surgery were statistically analyzed by generalized estimating equation (GEE) models.

RESULTS

Fourty-one patients (45 knees) and 43 patients (48 knees) were included in the MA and the rKA group respectively. Three constitutional knee phenotypes (II, I, IV) were the commonest in our population. Navigation improved the surgical accuracy (1.5° vs 3.5°, p < 0.001) and precision (interquartile range 4.0 vs 2.0, p < 0.001) in the rKA group than the MA group. The changes in Knee Injury and Osteoarthritis Outcome Score 12 (KOOS12), EuroQol five-dimension questionnaire (EQ5D) from baseline to T1 and T6 for patients with on-target rKA were larger than on-target MA counterparts (26.053 vs 18.607, P < 0.001(KOOS12, T1) , 0.457 vs 0.367 p < 0.001(EQ5D, T1) ; 51.017 vs 46.896, P = 0.023(KOOS12, T6) , 0.606 vs 0.565, P = 0.01(EQ5D, T6) ). Patients with on-target rKA had better Forgotten Joint Score (FJS) at T1 (54.126 vs 40.965, P = 0.002) compared with on-target MA counterparts.

CONCLUSIONS

Computer assisted navigation achieved the level of accuracy required by rKA-TKA. rKA-TKA offered significantly better short-term outcomes than MA-TKA.

Restricted Inverse Kinematic Alignment Better Restores the Native Joint Line Orientation While Achieving Similar Balance, Laxity, and Arithmetic Hip-Knee-Ankle Angle to Gap Balancing Total Knee Arthroplasty

Background

Both restricted inverse kinematic alignment (iKA) and gap balancing aim for a balanced total knee arthroplasty by adjusting femoral component position based on ligamentous gaps. However, iKA targets a native tibial joint line vs resecting perpendicular to the mechanical axis. This study compares how these 2 techniques impact the balance and laxity throughout flexion and joint line obliquity (JLO), arithmetic hip-knee-ankle angle (aHKA), and the coronal plane alignment of the knee (CPAK).

Methods

Two surgeons performed 75 robot-assisted iKA total knee arthroplasties. A digital joint tensioner collected laxity data throughout flexion before femoral resection. The femoral component position was determined using predictive gap-planning to optimize the balance throughout flexion. Planned gap balancing (pGB) simulations were performed for each case using neutral tibial resections. Mediolateral balance, laxity, and CPAK were compared among pGB, planned iKA (piKA), and final iKA.

Results

Both piKA and pGB had similar mediolateral balance and laxity, with mean differences <0.4 mm. piKA had a lower mean absolute difference from native JLO than pGB (3 ± 2° vs 7 ± 4°, P < .001). aHKA was similar (P > .05) between pGB and piKA. piKA recreated a more native CPAK distribution, with types I-V being the most common ones, while most pGB knees were of type V, VII, and III. Final iKA and piKA had similar mediolateral balance and laxity, with a root-mean-square error <1.4 mm.

Conclusions

Although balance, laxity, and aHKA were similar between piKA and pGB, piKA better restored native JLO and CPAK phenotypes. The neutral tibial resection moved most pGB knees into types V, VII, and III. Surgeons should appreciate how the alignment strategy affects knee phenotypes.

Kinematic alignment results in clinically similar outcomes to mechanical alignment: Systematic review and meta-analysis

PURPOSE

It is unclear whether a difference in functional outcome exists between kinematically aligned (KA) and mechanically aligned (MA) knee replacements. The aim of this study is to perform a comprehensive systematic review and meta-analysis of the available level I-IV evidence.

METHODS

A meta-analysis of randomised controlled trials and observational studies comparing patient reported outcome measures (PROMs), range of motion (ROM), gait analysis and complications in TKA with KA and MA was performed. Quality assessment was performed for each study using the Joanna Briggs Institute (JBI) critical appraisal tools.

RESULTS

Twelve randomised controlled trials and fourteen observational studies published between 2014 and 2022 were included in the final analysis. Meta-analysis revealed KA to have significantly better Oxford Knee Score (OKS) (p = 0.02), Forgotten Joint Score (FJS) (p = 0.006), Knee Society Score (KSS) Objective Knee (p = 0.03) and KSS Functional Activity (p = 0.008) scores. However, these improvements did not exceed the minimum clinically important difference (MCID) values reported in the literature. Subgroup analysis showed robotic assisted KA-TKA to have a clinically superior FJS (p = 0.0002) and trend towards KSS Objective Knee score (p = 0.10), compared to PSI. Gait and plantar pressure distribution of KA cohorts more closely represented healthy cohorts, and KA showed a weak association of a decreased knee adduction moment (KAM) compared to MA. Differences in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Knee Injury and Osteoarthritis Outcome Score (KOOS), range of motion and complications were not significant between groups.

CONCLUSION

Although KA results in several improved functional outcomes, these do not reach clinical significance. Further standardised large-scale randomised studies are required to improve the quality of evidence. As it stands, it is difficult to recommend one philosophy over the other.

Patient-reported impairment following TKA is reduced when a computationally simulated predicted ideal alignment is achieved

PURPOSE

Joint dynamics following Total Knee Arthroplasty (TKA) may influence patient-reported outcome. Simulations allow many knee alignment approaches to a single patient to be considered prior to surgery. The simulated kinematics can be matched to patient-reported outcome to predict kinematic patterns most likely to give the best outcome. This study aims to validate one such previously developed algorithm based on a simulated deep knee bend (the Dynamic Knee Score, DKS).

METHODS

1074 TKA patients with pre- and post-operative Computerised Tomography (CT) scans and 12-month post-operative Knee Injury and Osteoarthritis Outcomes (KOOS) Scores were identified from the 360 Med Care Joint Registry. Landmarking and registration of implant position was performed on all CT scans, and each of the achieved TKAs was computationally simulated and received a predictive outcome score from the DKS. In addition, a set of potential alternative surgical plans which might have been followed were simulated. Comparison of patient-reported issues and DKS score was evaluated in a counter-factual study design.

RESULTS

Patient-reported impairment with the knee catching and squatting was shown to be 30% lower (p = 0.005) and 22% lower (p = 0.026) in patients where the best possible DKS result was the one surgically achieved. Similar findings were found relating attainment of the best tibial slope and posterior femoral resection DKS plans to patient-reported difficulty straightening the knee (40% less likely, p < 0.001) and descending stairs (35% less likely, p = 0.006).

CONCLUSION

The DKS has been shown to correlate with presence of patient-reported impairments post-TKA and the resultant algorithm can be applied in a pre-operative planning setting. Outcome optimization in the future may come from patient-specific selection of an alignment strategy and simulations may be a technological enabler of this trend.

LEVEL OF EVIDENCE

III (Retrospective Cohort Study).

Overview of the different personalized total knee arthroplasty with robotic assistance, how choosing?

Current limitations in total knee arthroplasty (TKA) function and patient satisfaction stimulated us to question our practice. Our understanding of knee anatomy and biomechanics has evolved over recent years as we now consider that a more personalized joint reconstruction may be a better-targeted goal for TKA. Implant design and surgical techniques must be advanced to better reproduce the anatomy and kinematics of native knees and ultimately provide a forgotten joint. The availability of precision tools as robotic assistance surgery can help us recreate patient anatomy and ensure components are not implanted in a position that may compromise long-term outcomes. Robotic-assisted surgery is gaining in popularity and may be the future of orthopedic surgery. However, moving away from the concept of neutrally aligning every TKA dogma opens the door to new techniques emergence based on opinion and experience and leads to a certain amount of uncertainty among knee surgeons. Hence, it is important to clearly describe each technique and analyze their potential impacts and benefits. Personalized TKA techniques may be classified into 2 main families: unrestricted or restricted component orientation. In the restricted group, some will aim to reproduce native ligament laxity versus aiming for ligament isometry. When outside of their boundaries, all restricted techniques will induce anatomical changes. Similarly, most native knee having asymmetric ligaments laxity between compartments and within the same compartment during the arc of flexion; aiming for ligament isometry induces bony anatomy changes. In the current paper, we will summarize and discuss the impacts of the different robotic personalized alignment techniques, including kinematic alignment (KA), restricted kinematic alignment (rKA), inverse kinematic alignment (iKA), and functional alignment (FA). With every surgical technique, there are limitations and shortcomings. As our implants are still far from the native knee, it is primordial to understand the impacts and benefits of each technique. Mid to long data will help us in defining the new standards.

Posterior-stabilized total knee arthroplasty kinematics and joint laxity: A hybrid biomechanical study

BACKGROUND

Posterior-stabilized (PS)-total knee arthroplasty (TKA) arose as an alternative to cruciate-retaining (CR)-TKA in the 1970s. Since then, it has become a popularly utilized TKA design with outcomes comparable to CR-TKA. The post-cam mechanism is unique to PS-TKA as it substitutes the function of the posterior cruciate ligament (PCL). The study aimed to understand the kinematic and laxity changes in PS-TKA with under- and overstuffing of the tibiofemoral joint space with the polyethylene (PE) insert.

METHODS

This study employed a hybrid computational-experimental joint motion simulation on a VIVO 6 degrees of freedom (6-DoF) joint motion simulator (AMTI, Watertown, MA, USA). Physical prototypes of a virtually-performed TKA in mechanical alignment (MA) and kinematic alignment (KA) based on cadaveric CT scans and a virtual ligament model were utilized. The reference, understuffed (down 2 mm) and overstuffed (up 2 mm) joint spaces were simulated, neutral flexion and laxity testing loads and motions were performed for each configuration.

RESULTS

The PE insert thickness influenced post-cam engagement, which occurred after 60º in the overstuffed configurations, after 60º-75º in the reference configurations and after 75º in the understuffed configurations. The understuffed configurations, compared to the reference configurations, resulted in a mean 2.0º (28%) and 2.0º (31%) increase in the coronal laxity in MA and KA respectively. The overstuffed configurations, compared to the reference configuration, resulted in an increase in the mean joint compressive forces (JCFs) by 73 N (61%) and 77 N (62%) in MA and KA models, respectively.

CONCLUSIONS

The under- and overstuffing in PS-TKA alter the kinematics with variable effects. Understuffing decreases the stability, JCFs and inverse with overstuffing. Subtle changes in the PE insert thickness alter the post-cam mechanics.

Kinematic Alignment May Reduce Opioid Consumption and Length of Stay Compared to Mechanically Aligned Total Knee Arthroplasty

OBJECTIVE

Previous studies have sought to determine the effects of total knee arthroplasty (TKA) using kinematic alignment (KA) versus mechanical alignment (MA) to reproduce the native knee alignment and soft tissue envelope for improved patient satisfaction. There are limited studies that compare acute perioperative outcomes between KA and MA patients as it pertains to pain-related opioid consumption and hospital length of stay (LOS). This study aims to compare early KA and MA in restoring function and rehabilitation after surgery to reduce hospitalization and opioid consumption.

METHODS

A retrospective review of 42 KA and 58 MA primary TKA patients performed by a single surgeon between 2020-2021 was conducted. Demographics were controlled between groups and radiographic measurements and functional outcomes were compared. Pain was evaluated with inpatient/outpatient morphine milligram equivalents (MME) and visual analogue scale (VAS) scores. Mobility was assessed using multiple measures by a physical therapist. Mean preoperative and 3-month postoperative flexion range of motion (ROM) were analyzed, and overall complications, LOS, and non-home discharge between groups compared. Continuous variables were compared using the Wilcoxon rank-sum test, and categorical variables were compared using the chi-square or Fisher exact test. Statistical significance was set at P < 0.05.

RESULTS

KA patients had shorter LOS (1.8 vs 3.1 days) and less cumulative opioid requirements compared to MA patients (578 vs 1253 MME). On postoperative day 0, KA patients ambulated on average twice the distance of MA patients (20 vs 6.5 feet). KA patients had residual tibia component in varus (1.4° vs -0.3°), femoral component in valgus (-1.9° vs 0.2°), and valgus joint line obliquity compared with MA (-1.5° vs 0.2°). There were no significant differences between 3-month postoperative flexion arc motion, discharge destination, KOOS or SF-12 outcomes, and surgical complication rates between groups.

CONCLUSIONS

By restoring the native joint line obliquity and minimizing the frequency of ligament releases, KA for TKA may improve pain relief, early mobility, and decreased length of stay compared with traditional methods of establishing neutral limb axis by MA.

Low tibial baseplate migration 1 year after unrestricted kinematically aligned total knee arthroplasty using a medial conforming implant design

PURPOSE

Varus alignment of the tibial baseplate and limb > 3° might adversely affect baseplate fixation after total knee arthroplasty (TKA), especially for unrestricted kinematically aligned (KA) TKA which aligns a majority of baseplates in varus. The purposes of this study were to determine whether baseplate migration at 1 year (1) was significantly less than a stability limit of 0.5 mm, (2) increased over time, and (3) was related to varus alignment of the baseplate and limb after unrestricted KA TKA.

METHODS

Thirty-five patients underwent unrestricted KA TKA using a fixed-bearing, cemented, medial conforming tibial insert with posterior cruciate ligament retention. Using model-based radiostereometric analysis, maximum total point motion (MTPM) (i.e., largest displacement on the baseplate) was computed at 6 weeks, 3 months, 6 months, and 1 year postoperatively relative to the day of surgery. Baseplate and limb alignment were measured postoperatively on long-leg CT scanograms.

RESULTS

At 1 year, mean MTPM of 0.35 mm was significantly less than the 0.5 mm stability limit (p = 0.0002). Mean MTPM did not increase from 6 weeks to 1 year (p = 0.3047). Notably, 89% (31/35) of tibial baseplates and 46% (16/35) of limbs were > 3° varus. Baseplate and limb alignment had no relationship to MTPM at 1 year (|r|≤ 0.173, p ≥ 0.3276).

CONCLUSION

Low and non-progressive tibial baseplate migration 1 year after unrestricted KA TKA with a medial conforming design should allay any concern that unrestricted KA TKA increases risk of baseplate loosening due to varus alignment of the baseplate and limb.

LEVEL OF EVIDENCE

Level II, therapeutic prospective cohort study.

Kinematic alignment matches functional alignment for the extension gap: a consecutive analysis of 749 primary varus osteoarthritic knees with stress radiographs

PURPOSE

The alignment goal in total knee arthroplasty (TKA) remains debated. Two major strategies have emerged based on recreating the native knee: kinematic and functional alignment (KA and FA). Recently a new Coronal Plane Alignment of the Knee (CPAK) classification for KA, based on bony landmarks, was described considering joint line obliquity and the arithmetic HipKneeAnkle angle (aHKA). Valgus corrected HKA medial angle (vcHKA) was measured on distractive valgus preoperative radiographs compensating for cartilage wear and ligament balance in varus osteoarthritis. The purpose of this study was to determine if aHKA accounts for differences in medial laxity for the extension gap by comparing vcHKA to aHKA. The hypothesis was that no significant difference would be observed between the two measurements.

METHODS

This is a retrospective analysis of 749 knees in consecutive patients presenting to a single-centre with primary medial osteoarthritis. Patients underwent standardized weight bearing long-leg and valgus stress radiographs. Tibial mechanical angle (TMA), femoral mechanical angle (FMA) and vcHKA were measured using digital software. aHKA and vcHKA were compared to determine differences due to soft tissue balancing.

RESULTS

The mean FMA was 91.3 ± 2.2° (range 82°-97°), the mean TMA was 85.7 ± 2.5° (range 75°-98°), the mean aHKA was 177.0 ± 3.0° (range 164°-185°) and the mean vcHKA was 176.6 ± 3.1° (range 165°-192°). No significant difference was observed between aHKA and vcHKA (p = 0.06). A significant correlation was found between vcHKA and TMA (ρ = 0.3; p < 0.001) and between vcHKA and FMA (ρ = 0.41; p < 0.001).

CONCLUSION

This study showed that vcHKA was similar to aHKA confirming that aHKA accounts for ligamentous medial laxity. Therefore, kinematic alignment based on the CPAK classification matches the pre-arthritic coronal alignment of the knee for the extension gap.

LEVEL OF EVIDENCE

IV.

The importance of joint line obliquity: a radiological analysis of restricted boundaries in normal knee phenotypes to inform surgical decision making in kinematically aligned total knee arthroplasty

PURPOSE

Restricted kinematic alignment (rKA) in total knee arthroplasty (TKA) aims to restore native soft tissue laxities while limiting alignment extremes that risk prosthetic failure. However, there is no consensus where restricted boundaries (RB) should be set. This study aims to determine the proportion of limbs in which constitutional alignment and joint line obliquity (JLO) would be restored with various RB scenarios, to inform decision making in rKA TKA.

METHODS

The mechanical hip-knee-ankle (mHKA) angle, arithmetic hip-knee-ankle (aHKA) angle, lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) were measured on radiographs of 500 normal knees. Incrementally wider RBs were then applied. The proportion of limbs within each increment was determined when RBs were applied only to HKA, or to HKA, LDFA and MPTA together. In addition, the proportion of limbs within published adjusted mechanical alignment (aMA) and rKA protocols were determined, as well as those within one, two and three standard deviations of the means for HKA, LDFA and MPTA.

RESULTS

When restrictions to mHKA alone were applied, 74.0% and 97.8% of knees were captured with boundaries of ± 3° and ± 6° respectively. However, when the same boundaries to HKA were also applied to MPTA and LDFA, 36.2% and 91.0% of knees were captured respectively, highlighting the limiting effect that JLO has on restoration of normal knee phenotypes. When comparing previously published boundaries, aMA of 0° ± 3° captured 36.2%; rKA of 0° ± 3 for HKA and 85° to 95° for LDFA/MPTA captured 67.8%; rKA of - 5° to 4° HKA and 86°-93° for LDFA/MPTA captured 63%; and rKA of - 6° to + 3° for HKA and 84°-93° for LDFA/MPTA captured 85.4%.

CONCLUSION

The greatest proportions of normal knee phenotypes were captured with boundaries that were centred around population means for HKA and JLO. Further, these findings demonstrate that restricting the JLO has a significant limiting influence on restoration of normal knee phenotypes beyond that of restricting HKA alone.

LEVEL OF EVIDENCE

III.

Similar kinematic patterns between revision total stabilized (TS) and primary posterior stabilized (PS) knee prostheses: a prospective case-controlled study with gait assessment

PURPOSE

There are increased surgical considerations when revising total knee arthroplasty (TKA) in active patients. Few studies have assessed if a semi-constrained [Total Stabilized (TS)] prostheses has similar knee biomechanics to a primary posterior stabilized (PS) prosthesis. The aim was to compare the gait parameters in patients with PS or TS TKA and normal controls.

METHODS

32 patients with TKA were prospectively included with either a primary PS (n = 15) or a revision TS (n = 17) prosthesis. Gait analysis was performed at 6 months postoperatively for each patient, with an optoelectronic knee assessment device (KneeKG®) assessing the displacement of the tibia relative to the femur during the different gait phases (flexion/extension, anterior/posterior translation, adduction/abduction, internal/external rotation). A control group (n = 12) of healthy knees was compared with the TKA groups.

RESULTS

There were no significant kinematic differences between PS and TS groups. The maximum knee flexion during gait was 53° ± 8.1° in the PS group vs 52° ± 8.7° in the TS group. The antero-posterior translation was similar in both group (2.3 ± 0.5 mm vs 2.6 ± 0.9 mm, respectively). Peak varus angle during loading and swing phase was slightly higher in the TS group (2.7° ± 0.7° and 5.2° ± 0.9°) than in the PS group (2.9° ± 0.6° and 5.6° ± 1.2°), without significant difference. The ranges in internal/external rotation were similar between PS and TS TKA (3.7° ± 0.5° vs 3.3° ± 0.6°, respectively). Both designs approached closely the normal gait patterns of the control group except in the frontal plane.

CONCLUSION

Single radius TS TKA has gait parameters similar to single radius PS TKA. Use of a single radius TS TKA in revision TKA is not detrimental to a patient's gait pattern. Both designs approached closely the normal gait patterns of the control group.

LEVEL OF EVIDENCE

Prospective, case-control study; Level III.

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

PURPOSE

In total knee arthroplasty (TKA), knee phenotypes including joint line obliquity are of interest regarding surgical realignment strategies. The hypothesis of this study is that better clinical results, including decreased postoperative knee pain, will be observed for patients with a restored knee phenotype.

METHODS

A retrospective analysis was performed on prospective data, including 1078 primary osteoarthritic knees in 936 patients. The male:female ratio was 780:298, mean age at surgery was 71.3 years ± 8.0. International Knee Society Scores and standardized long-leg radiographs (LLR) were collected preoperatively and at 2 years follow-up after TKA. Patients were categorized using the Coronal Plane Alignment of the Knee (CPAK) classification including the lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) measured on LLR by a single observer, allowing knee phenotypes to be categorized considering the arithmetic hip-knee-ankle (aHKA) angle (MPTA-LDFA) as measure of constitutional alignment, and joint line obliquity (JLO) (MPTA + LDFA). Clinical results were compared between patients with surgically restored preoperative constitutional knee phenotype to patients without restored constitutional knee phenotypes. Descriptive data analysis such as means, standard deviations and ranges were performed. T tests for independent samples were performed to compare group differences. Comparisons of categorical data were performed using the χ² test. Significance was set at p < 0.05.

RESULTS

A third of patients (33.4%) had constitutional knee varus with apex distal JLO. 63.5% of patients had preoperative apex distal JLO. Postoperatively, 57.8% of patients had a neutral HKA (- 2° to 2°) and a neutral JLO (- 3° and 3°), with only 18% of patients with restored constitutional knee phenotype. Of these patients, statistically less postoperative pain was observed in patients where apex distal JLO was restored compared to non-restored apex distal JLO (pain score 46.7 vs. 44.6; p = 0.02) without clinical relevance. Other categories of restored JLO or arithmetic HKA angle were not associated with improved outcomes.

CONCLUSION

This study showed that performing mechanical alignment for primary TKA resulted in most cases in a change of the preoperative knee phenotype. These results emphasize the relevance of considering joint line obliquity to better understand preoperative knee deformity and better restore knee phenotypes with a more personalized realignment strategy to potentially improve TKA postoperative results.

LEVEL OF EVIDENCE

III.

Restricted kinematic alignment may be associated with increased risk of aseptic loosening for posterior-stabilized TKA: a case-control study

PURPOSE

The purpose of the study was to compare clinical and radiological results between kinematic alignment (KA) and mechanical alignment (MA) with a posterior-stabilized (PS) total knee arthroplasty (TKA) with a post-cam mechanism at a minimum follow-up of 3 years. The authors hypothesized a higher risk of aseptic loosening when performing KA using PS TKA.

METHODS

A retrospective monocentric single surgeon case control study was performed comparing 100 matched patients who had TKA performed using a MA philosophy to 50 patients receiving TKA with a KA technique between January 2016 and October 2017. All patients had the same knee prosthesis (GMK primary posterior-stabilized, Medacta^®, Switzerland). Patient specific cutting blocks were used in both groups and a restricted KA (rKA) was aimed in the KA group. A hybrid cementation technique was performed. The new Knee Society Score (KSS) and radiological assessment were collected preoperatively and at the final follow-up. Comparisons between groups were done with the T test or Fisher exact test. Global survival curves were estimated with Kaplan-Meier model. Significance was set at p < 0.05.

RESULTS

Mean follow-up was 42.9 months ± 3.6 (range 37.6-46.7) and 53.3 months ± 4.1 (range 45.5-59.8) for rKA and MA groups. Postoperatively, no significant differences were found for clinical scores between both groups. Radiological assessment found similar postoperative Hip-Knee-Ankle angle for rKA and MA groups (178° versus 179° respectively, NS). At last follow-up, a significant higher survivorship was found for the MA group compared to the rKA group (97 versus 84%; p < 0.001) for aseptic loosening revision as the endpoint.

CONCLUSION

An increased risk of tibial implant loosening was found with rKA compared to MA using a posterior-stabilized TKA with a post-cam system at short-term follow-up. Caution should be taken when choosing the TKA design while performing rKA.

LEVEL OF EVIDENCE

Retrospective case-control study, Level IV.

Surgeon Dominated Design Can Improve the Accuracy of Patient-Specific Instruments in Kinematically Aligned TKA

Precise bone resection is mandatory for kinematically aligned total knee arthroplasty (KA-TKA). This study is to investigate whether surgeon-dominated design can alter the accuracy of patient-specific instrumentation (PSI) in KA-TKA compared with the engineer design. A total of 24 patients (24 knees) who underwent KA-TKA in our institution were assigned to an engineer design group (10 knees) and surgeon design group (14 knees) chronologically. A novel portable medical-engineer interactive application can greatly enhance the surgeon’s participation in PSI design. The bone resection discrepancies were used to evaluate the accuracy of PSI in bone resection. The overall discrepancy of bone resection was reduced by surgeon-designed PSI compared to engineer-designed PSI by 0.33 mm. Surgeon-designed PSI seems to reduce the outliers in terms of relative discrepancies in bone resection as well, but it does not reach statistical significance. Moreover, surgeon-designed PSI could significantly improve the accuracy of PSI in the restoration of the joint line in terms of medial proximal tibial angle and mechanical lateral distal femoral angle. This study indicates that the dominance of surgeons in both PSI design and subsequent surgical operation should be emphasized in efforts to improve the accuracy of PSI.

Minimum 2-Year Radiographic and Clinical Outcomes of Kinematic Alignment Total Knee Arthroplasty in the Valgus Knee

Kinematic alignment (KA) total knee arthroplasty (TKA) has gained popularity in the past decade, but outcomes of KA-TKA in the valgus knee have never been specifically evaluated. In this retrospective single institution study, we analyzed patient reported outcomes and radiographic measurements at minimum 2 years following KA-TKA for valgus knees (n = 51) and compared the results to KA-TKA performed for non-valgus knees (n = 275). The same approach, technique, and implants were used in both groups without the need to release soft tissues or use constrained implants. Surgery duration was similar between groups (p = 0.353). Lateral distal femoral angle was lower in the valgus group postoperatively (p = 0.036). In both groups significant improvement was seen in relieving pain and improving function, while average scores were superior in the non-valgus group for visual analog score (p = 0.005), oxford knee score (p = 0.013), and knee injury and osteoarthritis outcome score (p = 0.009). However, these differences did not translate to statistically significant differences in minimal clinical important difference achievement rates. In conclusion, KA-TKA is efficient in relieving pain and improving function, as reported in subjective questionnaires, and holds advantage in patients with valgus alignment by avoiding soft tissue releases and use of constrained implants. Future studies should examine whether bone loss occurs in the lateral distal femur.

An anatomo-functional implant positioning technique with robotic assistance for primary TKA allows the restoration of the native knee alignment and a natural functional ligament pattern, with a faster recovery at 6 months compared to an adjusted mechanical technique

PURPOSE

An anatomo-functional implant positioning (AFIP) technique in total knee arthroplasty (TKA) could restore physiological ligament balance (symmetric gap in extension, asymmetric gap in flexion). The purposes were to compare (1) ligament balancing in extension and flexion after TKA in the AFIP group, (2) TKA alignment, implant positioning and patellar tracking between AFIP and adjusted mechanical alignment (aMA) techniques, (3) clinical outcomes between both groups at 12 months.

METHODS

All robotic-assisted TKA with an AFIP technique were included (n = 40). Exclusion criteria were genu valgum (HKA angle > 183°), extra-articular deformity more than 10°, and patellar maltracking (high-grade J-sign). One control patient with a TKA implanted by an aMA technique was matched for each case, based on age, body mass index, sex, and knee alignment. Ligament balancing (medial and lateral gaps in millimeters) in full extension and at 90° of flexion after TKA in the AFIP group was assessed with the robotic system. TKA alignment (HKA angle), implants positioning (femoral and tibial coronal axis, tibial slope, joint-line orientation), patellar tracking (patellar tilt and translation) and the Knee Society Score (KSS) at 6 and 12 months were compared between both groups. The ligament balancing was compared using a t test for paired samples in the AFIP group. The radiographic measurements and KSS scores were compared between groups using a t test for independent samples.

RESULTS

In the AFIP group, there was no significant difference between the medial and lateral gap laxity in extension (NS). A significant opening of the lateral gap was observed in flexion compared to extension (mean: + 2.9 mm; p < 0.0001). The mean postoperative HKA angle was comparable between both groups (177.3° ± 2.1 in the AFIP group vs 176.8° ± 3.2; NS). In the AFIP group, the femoral anatomy was restored (90.9° ± 1.6) and the tibial varus was partially corrected (87.4° ± 1.8). The improvement of Knee and Function KSS at 6 months was better in the AFIP group (59.3 ± 11.9 and 51.7 ± 20, respectively, versus 49.3 ± 9.7 and 20.8 ± 13; p < 0.001).

CONCLUSION

The AFIP concept allowed the restoration of the native knee alignment and a natural functional ligament pattern. With a more physiological target for ligament balancing, the AFIP technique had equivalent clinical outcomes at 12 months compared to aMA, with a faster recovery.

LEVEL OF EVIDENCE

III retrospective therapeutic case control series.

Effect of varus alignment on the bone-implant interaction of a cementless tibial baseplate during gait

Component alignment in total knee arthroplasty is a determining factor for implant longevity. Mechanical alignment, which provides balanced load transfer, is the most common alignment strategy. However, a retrospective review found that varus alignment, which could lead to unbalanced loading, can happen in up to 18% of tibial baseplates. This may be particularly burdensome for cementless tibial baseplates, which require low bone-implant micromotion and avoidance of bone overload to obtain bone ingrowth. Our aim was to assess the effect of varus alignment on the bone-implant interaction of cementless baseplates. We virtually implanted 11 patients with knee OA with a modern cementless tibial baseplate in mechanical alignment and in 2° of tibial varus alignment. We performed finite element simulations throughout gait, with loading conditions derived from literature. Throughout the stance phase, varus alignment had greater micromotion and percentage of bone volume at risk of failure than mechanical alignment. At mid-stance, when the most critical conditions occurred, the average increase in peak micromotion and amount of bone at risk of failure due to varus alignment were 79% and 59%, respectively. Varus alignment also resulted in the decrease of the surface area with micromotion compatible with bone ingrowth. However, for both alignments, this surface area was larger than the average area of ingrowth reported for well-fixed implants retrieved post-mortem. Our findings suggest that small varus deviations from mechanical alignment can adversely impact the biomechanics of the bone-implant interaction for cementless tibial baseplates during gait; however, the clinical implications of such changes remain unclear.

Comparison of Biomechanical Gait Parameters and Patient-Reported Outcome in Patients After Total Knee Arthroplasty With the Use of Fixed-Bearing Medial Pivot and Multi-radius Design Implants—Retrospective Matched-Cohort Study

Background

Total knee arthroplasty (TKA) is considered to be highly successful in treatment of end-stage osteoarthritis. There are multiple implant designs available on the market, and it is difficult to point which one is the best. The aim of this study was to compare the clinical and functional outcomes and gait pattern after TKA with the use of fixed-bearing medial pivot (K-Mod) vs multi-radius design (NexGen) implants and to compare them to norms for healthy patients with no osteoarthritis or arthroplasty procedure in anamnesis.

Methods

A group of 30 patients who received the medial pivot (MP) TKA and 33 patients who received the posterior-stabilized (PS) TKA between May and August of 2018 were included. All surgeries were performed in the level III academic hospital by a single surgeon. Every patient was asked to fulfill the The Western Ontario and McMaster Universities Arthritis Index (WOMAC) questionnaire preoperatively and 2 years postoperatively. Standard X-ray, biomechanical gait analysis using a motion capture system, and statistical analysis were performed at 2 years postoperatively.

Results

A total of 28 patients from either MP cohort (93%) or PS (85%) matched-control cohort completed the whole assessment at the final follow-up. There were statistically significant differences in a few gait parameters such as shorter mean step length both in operated and healthy limb, lower mean gait velocity, and lower mean walking cadence than the norm in both MP and PS groups. As to the WOMAC score, there was statistically significant improvement in both groups comparing preoperative and postoperative outcomes. Nevertheless, in the MP group, there was a significantly higher score, indicating worse outcomes, in the stiffness part of the WOMAC score than in the PS group. No significant differences were found between groups during radiological evaluation.

Conclusions

There were satisfying and promising clinical, radiographic, and patient-reported outcomes in both MP and PS groups with very little difference in relation to norm values. However, both implants failed in fully restoring gait patterns similar to the healthy limb of the same patient.

A Portable Wearable Inertial System for Rehabilitation Monitoring and Evaluation of Patients With Total Knee Replacement

Knee osteoarthritis is a degenerative disease, which greatly affects the daily life of patients. Total knee replacement (TKR) is the most common method to treat knee joint disorders and relieve knee pain. Postoperative rehabilitation exercise is the key to restore knee joint function. However, there is a lack of a portable equipment for monitoring knee joint activity and a systematic assessment scheme. We have developed a portable rehabilitation monitoring and evaluation system based on the wearable inertial unit to estimate the knee range of motion (ROM). Ten TKR patients and ten healthy adults are recruited for the experiment, then the system performance is verified by professional rehabilitation equipment Baltimore Therapeutic Equipment (BTE) Primus RS. The average absolute difference between the knee ROM and BTE Primus RS of healthy subjects and patients ranges from 0.16° to 4.94°. In addition, the knee ROM of flexion-extension and gait activity between healthy subjects and patients showed significant differences. The proposed system is reliable and effective in monitoring and evaluating the rehabilitation progress of patients. The system proposed in this work is expected to be used for long-term effective supervision of patients in clinical and dwelling environments.

Approximately 80% of Japanese osteoarthritic patients fall out of the safety range in restricted kinematically-aligned total knee arthroplasty in an analysis of preoperative long-leg radiograms

BACKGROUND

Restricted kinematically-aligned total knee arthroplasty (KA-TKA) is a reasonable modification to avoid the alignment outlier that may cause implant failure. However, despite a noted high incidence of constitutional varus in Japanese individuals, there has been no investigation into how many knees require the restriction in restricted KA-TKA (RKA-TKA) among Japanese patients. Therefore, we conducted a study using preoperative long-leg radiograms.

METHODS

We studied long-leg radiographs of 228 knees in 114 consecutive patients. The numbers of knees within the safety range and their corrective osteotomy angle in the restriction algorithms advocated by Almaawi et al. (2017) and MacDessi et al. (2020) were evaluated.

RESULTS

According to the algorithms used by Almaawi et al. and MacDessi et al., out of 228 knees, 46 (20%) and 39 (17%) fell within the safety range, respectively. The mean correction angles of the hip-knee-ankle angle, lateral distal femoral angle and medial proximal tibial angle were 2.8 ± 3.4°, 0.4 ± 1.4° and 2.4 ± 2.8° in the algorithm used by Almaawi et al., while they were -4.9 ± 4.7°, 1.1 ± 2.5° and -6.0 ± 3.4° in the algorithm used by MacDessi et al. Most of the knees needed to be restricted in order to perform RKA-TKA, regardless of the algorithm used.

CONCLUSIONS

Based on a preoperative analysis of long-leg radiograms in a Japanese population, most knees fall out of the safety range in RKA-TKA. Surgeons must consider whether to allow component outlier or to perform corrective osteotomy that likely requires soft tissue release.

Slight femoral under-correction versus neutral alignment in total knee arthroplasty with preoperative varus knees: a comparative study

Background

This study aimed to compare the short-term clinical results of slight femoral under-correction with neutral alignment in patients with preoperative varus knees who underwent total knee arthroplasty.

Methods

The medical records and imaging data were retrospectively collected from patients who had undergone total knee arthroplasty in our hospital from January 2016 to June 2019. All patients had varus knees preoperatively. Upon 1:1 propensity score matching, 256 patients (256 knees) were chosen and divided into a neutral alignment group (n=128) and an under-correction group (n=128). The patients in the neutral group were treated with the neutral alignment. In the under-correction group, the femoral mechanical axis had a 2° under-correction. The operative time, tourniquet time and the length of hospital stay in the two groups were recorded. The postoperative hip-knee-ankle angle, frontal femoral component angle and frontal tibial component angle were measured. Patient-reported outcome measures were also compared.

Results

The operative time, tourniquet time and the length of hospital stay in the under-correction group were significantly shorter than the neutral alignment group (P<0.05). At the 2-year follow-up, the under-correction group had a larger varus alignment (P<0.05) and a larger frontal femoral component angle (P<0.05), and the frontal tibial component angles of the two groups were comparable. Compared with the neutral alignment group, the slight femoral under-correction group had significantly better patient-reported outcome measures scores (P<0.05).

Conclusion

For varus knees treated with total knee arthroplasty, alignment with a slight femoral under-correction has advantages over the neutral alignment in terms of the shorter operative time and better short-term clinical results.

Level of evidence

III

Under-correction of preoperative varus alignment does not lead to a difference in in-vivo bone loading in 3D-SPECT/CT compared to neutral alignment

BACKGROUND

The aim was to investigate the correlation of bone tracer uptake (BTU) in SPECT/CT and changes in coronal knee alignment after total knee arthroplasty (TKA). We questioned if undercorrection of preoperative varus alignment leads to a difference in BTU compared to neutral alignment.

METHODS

Consecutive 66 patients who received SPECT/CT before and after TKA were retrospectively included. Adjusted mechanical alignment was the alignment target. The alignment of the knee was measured on 3D-CT by selecting standardized landmarks. Maximum (mean ± SD) and relative BTU (ratio to the reference) were recorded using a previously validated localization scheme (p < 0.05).

RESULTS

In the native group, 20 knees were aligned (30.3%) in valgus (HKA > 181.5°), 12 (18.2%) in neutral (178.5°-181.5°) and 34 (51.5%) in varus (HKA < 178°). Overall TKA changed the alignment towards neutral. 48.5% remained in the same groups, whereas 50% of native valgus and 33% of varus knees changed to neutral after TKA. In native varus alignment mean BTU was significantly higher in some medial tibial and femoral regions (fem1ia (p = 0.010), fem1ip (p = 0.002), tib1a.mid (p = 0.005), tib1a.tray (p = 0.000), tib1p.tray (p = 0.000)); in native valgus alignment mean BTU was higher in the corresponding lateral tibial and femoral regions (fem2ip (p = 0.001), tib2a.tray (p = 0.011), tib2p.tray (p = 0.002)). After TKA, a significant decrease in femoral and tibial BTU (femoral preoperative BTU 1.64 +/-0.69; femoral postoperative BTU 0.95 +/-0.42; p = 0.000// tibial preoperative BTU 1.65 +/- 0.93; tibial postoperative BTU 1.16 +/- 0.48; p = 0.000) and an increase in patellar BTU was observed (p = 0.025). Native varus alignment correlated with a higher medial BTU decrease medially. Undercorrection of preoperative varus alignment showed no higher BTU after TKA.

CONCLUSION

Preoperative varus alignment correlated with a higher decrease in BTU in specific femoral and tibial medial regions. Preoperative valgus alignment correlated with a higher decrease in the corresponding lateral regions. Undercorrection of preoperative varus alignment did not lead to higher bone loading reflected by BTU after TKA.

Arithmetic hip-knee-ankle angle and stressed hip-knee-ankle angle: equivalent methods for estimating constitutional lower limb alignment in kinematically aligned total knee arthroplasty

PURPOSE

Kinematically aligned total knee arthroplasty (KA TKA) relies on precise determination of constitutional alignment to set resection targets. The arithmetic hip-knee-ankle angle (aHKA) is a radiographic method to estimate constitutional alignment following onset of arthritis. Intraoperatively, constitutional alignment may also be approximated using navigation-based angular measurements of deformity correction, termed the stressed HKA (sHKA). This study aimed to investigate the relationship between these methods of estimating constitutional alignment to better understand their utility in KA TKA.

METHODS

A radiological and intraoperative computer-assisted navigation study was undertaken comparing measurements of the aHKA using radiographs and computed tomography (CT-aHKA) to the sHKA in 88 TKAs meeting the inclusion criteria. The primary outcome was the difference in the paired means between the three methods to determine constitutional alignment (aHKA, CT-aHKA, sHKA). Secondary outcomes included testing agreement across measurements using Bland-Altman plots and analysis of subgroup differences based on different patterns of compartmental arthritis.

RESULTS

There were no statistically significant differences between any paired comparison or across groups (aHKA vs. sHKA: 0.1°, p = 0.817; aHKA vs. CT-aHKA: 0.3°, p = 0.643; CT-aHKA vs. sHKA: 0.2°, p = 0.722; ANOVA, p = 0.845). Bland-Altman plots were consistent with good agreement for all comparisons, with approximately 95% of values within limits of agreement. There was no difference in the three paired comparisons (aHKA, CT-aHKA, and sHKA) for knees with medial compartment arthritis. However, these findings were not replicated in knees with lateral compartment arthritis.

CONCLUSIONS

There was no significant difference between the arithmetic HKA (whether obtained using CT or radiographs) and the stressed HKA in this analysis. These findings further validate the preoperative arithmetic method and support use of the intraoperative stressed HKA as techniques to restore constitutional lower limb alignment in KA TKA.

LEVEL OF EVIDENCE

III.

[Optimal lower limb alignment and soft tissue balancing strategy for robot-assisted total knee arthroplasty]

Lower limb alignment and soft tissue balance are important factors affecting patient satisfaction, clinical functional outcome, and prosthetic long-term survival rate after total knee arthroplasty (TKA). Robot-assisted TKA (rTKA) has the advantages of achieving precise osteotomy and soft tissue balance. However, rTKA under the guidance of classic mechanical alignment principles does not significantly improve the functional outcome after operation. The new TKA alignment principles, such as kinematic alignment (KA) and functional alignment (FA), can better consider the patient's own knee joint morphology and kinematic characteristics, which may help improve the clinical results of TKA. With the help of more objective and accurate soft tissue balance assessment tool such as pressure sensors, KA and FA have been proven to better achieve soft tissue balance. rTKA can achieve non-neutral alignment goals such as KA or FA more accurately and reproducibly. The use of these lower limb alignment and soft tissue balancing strategies will be expected to further increase the patients' satisfaction rate after rTKA.

Clinical impact of component placement in manually instrumented total knee arthroplasty : a systematic review

AIMS

The goal of the current systematic review was to assess the impact of implant placement accuracy on outcomes following total knee arthroplasty (TKA).

METHODS

A systematic review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines using the Ovid Medline, Embase, Cochrane Central, and Web of Science databases in order to assess the impact of the patient-reported outcomes measures (PROMs) and implant placement accuracy on outcomes following TKA. Studies assessing the impact of implant alignment, rotation, size, overhang, or condylar offset were included. Study quality was assessed, evidence was graded (one-star: no evidence, two-star: limited evidence, three-star: moderate evidence, four-star: strong evidence), and recommendations were made based on the available evidence.

RESULTS

A total of 49 studies were identified for inclusion. With respect to PROMs, there was two-star evidence in support of mechanical axis alignment (MAA), femorotibial angle (FTA), femoral coronal angle (FCA), tibial coronal angle (TCA), femoral sagittal angle (FSA), femoral rotation, tibial and combined rotation/mismatch, and implant size/overhang or offset on PROMs, and one-star evidence in support of tibial sagittal angle (TSA), impacting PROMs. With respect to survival, there was three- to four-star evidence in support FTA, FCA, TCA, and TSA, moderate evidence in support of femoral rotation, tibial and combined rotation/mismatch, and limited evidence in support of MAA, FSA, and implant size/overhang or offset impacting survival.

CONCLUSION

Overall, there is limited evidence to suggest that PROMs are impacted by the accuracy of implant placement, and malalignment does not appear to be a significant driver of the observed high rates of patient dissatisfaction following TKA. However, FTA, FCA, TCA, TSA, and implant rotation demonstrate a moderate-strong relationship with implant survival. Efforts should be made to improve the accuracy of these parameters in order to improve TKA survival. Cite this article: Bone Joint J 2021;103-B(9):1449-1456.

Higher Component Malposition Rates with Patient-Specific Cruciate Retaining TKA than Contemporary Posterior Stabilized TKA

Customized individually manufactured total knee arthroplasty (CIM-TKA) was developed to improve kinematic total knee arthroplasty (TKA) performance. Component placement accuracy may influence the success of CIM-TKA designs. We performed this study to compare radiographic component alignment and revision rates of a cruciate retaining (CR) CIM-TKA and a contemporary posterior stabilized TKA (PS-TKA). After obtaining Institutional Review Board approval, we identified 94 CR CIM-TKAs (76 patients) and 91 PS-TKAs (82 patients) performed between July 1, 2013 and December 31, 2014 with a minimum 2-year follow-up (mean 41.1 months, range 24-59 months). We performed a retrospective electronic medical record review to identify patient demographic characteristics and revision procedures performed. Postoperative plain radiographs were reviewed to assess component alignment including cruciate ligament imbalance, femoral overhang, and femoral notching. Demographic characteristics, component malalignment, and revision surgery rates were assessed using a student's t-test or two-tailed Fisher's exact test, with a p-value < 0.05 designating significance. Technical errors were more commonly identified with CR CIM-TKA (29.8 vs. 9.9%, p < 0.001), including higher rates of tibiofemoral instability (13.8 vs. 1.1%, p < 0.01), femoral notching (12.8 vs. 3.3%, p = 0.03), and patellofemoral malalignment (20.2 vs. 7.7%, p = 0.02). CR CIM-TKA had more frequent coronal plane malposition (26.6 vs. 9.9%, p < 0.01) or sagittal plane reconstruction > 3 degrees outside of an optimized range (20.2 vs. 9.9%, p = 0.06). Aseptic revisions occurred more frequently with the CR CIM-TKA design (9.6 vs. 3.3%, p = 0.13). Demographic characteristics were not significantly different between the treatment groups. CR CIM-TKA may improve kinematic performance for patients undergoing knee replacement surgery. However, our study observations suggest that careful attention to surgical technique is important for optimizing implant survivorship with the CR CIM-TKA design. Additional study is needed to determine whether higher revision rates identified during this study are related to patient selection, surgical technique, or implant design.

Restricted Kinematic Alignment, the Fundamentals, and Clinical Applications

Introduction: After a better understanding of normal knee anatomy and physiology, the Kinematic Alignment (KA) technique was introduced to improve clinical outcomes of total knee arthroplasty (TKA). The goal of the KA technique is to restore the pre-arthritic constitutional lower limb alignment of the patient. There is, however, a large range of normal knee anatomy. Unusual anatomies may be biomechanically inferior and affect TKA biomechanics and wear patterns. In 2011, the leading author proposed the restricted kinematic alignment (rKA) protocol, setting boundaries to KA for patients with an outlier or atypical knee anatomy. Material and Equipment: rKA aims to reproduce the constitutional knee anatomy of the patient within a safe range. Its fundamentals are based on sound comprehension of lower limb anatomy variation. There are five principles describing rKA: (1) Combined lower limb coronal orientation should be ± 3° of neutral; (2) Joint line orientation coronal alignment should be within ± 5° of neutral; (3) Natural knee's soft tissues tension/ laxities should be preserved/restored; (4) Femoral anatomy preservation is prioritized; (5) The unloaded/most intact knee compartment should be resurfaced and used as the pivot point when anatomical adjustment is required. An algorithm was developed to facilitate the decision-making. Methods: Since ~50% of patients will require anatomic modification to fit within rKA boundaries, rKA is ideally performed with patient-specific instrumentation (PSI), intra-operative computer navigation or robotic assistance. rKA surgical technique is presented in a stepwise manner, following the five principles in the algorithm. Results: rKA produced excellent mid-term clinical results in cemented or cementless TKA. Gait analysis showed that rKA TKA patients had gait patterns that were very close to a non-operated control group, and these kinematics differences translated into significantly better postoperative patient-reported scores than mechanical alignment (MA) TKA cases. Discussion: Aiming to improve the results of MA TKA, rKA protocol offers a satisfactory compromise that recreates patients' anatomy in most cases, omitting the need for extensive corrections and soft tissue releases that are often required with MA. Moreover, it precludes the reproduction of extreme anatomies seen with KA.

Robotic-assisted total knee arthroplasty improves accuracy and precision compared to conventional techniques

AIMS

Robotic-assisted total knee arthroplasty (RA-TKA) is theoretically more accurate for component positioning than TKA performed with mechanical instruments (M-TKA). Furthermore, the ability to incorporate soft-tissue laxity data into the plan prior to bone resection should reduce variability between the planned polyethylene thickness and the final implanted polyethylene. The purpose of this study was to compare accuracy to plan for component positioning and precision, as demonstrated by deviation from plan for polyethylene insert thickness in measured-resection RA-TKA versus M-TKA.

METHODS

A total of 220 consecutive primary TKAs between May 2016 and November 2018, performed by a single surgeon, were reviewed. Planned coronal plane component alignment and overall limb alignment were all 0° to the mechanical axis; tibial posterior slope was 2°; and polyethylene thickness was 9 mm. For RA-TKA, individual component position was adjusted to assist gap-balancing but planned coronal plane alignment for the femoral and tibial components and overall limb alignment remained 0 ± 3°; planned tibial posterior slope was 1.5°. Mean deviations from plan for each parameter were compared between groups for positioning and size and outliers were assessed.

RESULTS

In all, 103 M-TKAs and 96 RA-TKAs were included. In RA-TKA versus M-TKA, respectively: mean femoral positioning (0.9° (SD 1.2°) vs 1.7° (SD 1.1°)), mean tibial positioning (0.3° (SD 0.9°) vs 1.3° (SD 1.0°)), mean posterior tibial slope (-0.3° (SD 1.3°) vs 1.7° (SD 1.1°)), and mean mechanical axis limb alignment (1.0° (SD 1.7°) vs 2.7° (SD 1.9°)) all deviated significantly less from the plan (all p < 0.001); significantly fewer knees required a distal femoral recut (10 (10%) vs 22 (22%), p = 0.033); and deviation from planned polyethylene thickness was significantly less (1.4 mm (SD 1.6) vs 2.7 mm (SD 2.2), p < 0.001).

CONCLUSION

RA-TKA is significantly more accurate and precise in planning both component positioning and final polyethylene insert thickness. Future studies should investigate whether this increased accuracy and precision has an impact on clinical outcomes. The greater accuracy and reproducibility of RA-TKA may be important as precise new goals for component positioning are developed and can be further individualized to the patient. Cite this article: Bone Joint J 2021;103-B(6 Supple A):74-80.

Restoration of Joint Inclination in Total Knee Arthroplasty Offers Little Improvement in Joint Kinematics in Neutrally Aligned Extremities

Kinematically aligned total knee replacements have been shown to better restore physiological kinematics than mechanical alignment and also offer good postoperative satisfaction. The purpose of this study is to evaluate the extent to which an inclined joint line in a kinematically aligned knee can alter the postoperative kinematics. A multi-body dynamic simulation was used to identify kinematic changes in the joint. To accurately compare mechanical alignment, kinematic alignment and a natural knee, a “standard” patient with neutral alignment of the lower extremities was selected for modeling from a joint database. The arthroplasty models in this study were implanted with a single conventional cruciate-retaining prosthesis. Each model was subjected to a flexion movement and the anteroposterior translation of the femoral condyles was collected for kinematic analysis. The results showed that the mechanical alignment model underwent typical paradoxical anterior translation of the femoral condyles. Incorporating an inclined joint line in the model did not prevent the paradoxical anterior translation, but a 3° varus joint line in the kinematic alignment model could reduce the peak value of this motion by about 1 mm. Moreover, the inclined joint line did not restore the motion curve back to within the range of the kinematic curve of the natural knee. The results of this study suggest that an inclined joint line, as in the kinematic alignment model, can slightly suppress paradoxical anterior translation of the femoral condyles, but cannot restore kinematic motions similar to the physiological knee. This finding implies that prostheses intended to be used for kinematic alignment should be designed to optimize knee kinematics with the intention of restoring a physiological motion curve.

Impact of Valgus vs Varus Mechanical Axis Correction During Primary Total Knee Arthroplasty on Postoperative Periarticular Bone Mineral Density

BACKGROUND

Knee periarticular bone mineral density (BMD) is influenced by limb malalignment. The purpose of this study is to determine if the nature and magnitude of alignment correction (ΔAlign°) performed during primary total knee arthroplasty (TKA) had an impact on BMD at the metaphysis of the distal femur (DFmr) and proximal tibia (PTb).

METHODS

Seventy-one patients (male = 37 |female = 34; age: 65 ± 2 years) underwent full-length standing X-rays and knee-specific BMD measurements using dual-energy X-ray absorptiometry before and 3 and 6 months following TKA. A t-test was used to compare baseline demographics and knee-specific BMD measures (medial/lateral DFmr/PTb) between patients with preoperative valgus (VAL, N = 18) and varus (VAR, N = 53) malalignment. Pearson correlation analysis was used to determine if ΔAlign° correlated with site-specific knee BMD changes. A 2 (varus/valgus) by 3 (time) analysis of variance was used to compare site-specific BMD (%ΔBMD) changes following TKA. Type I error was set at α = 0.05 for all analyses.

RESULTS

VAR patients had higher preoperative BMD for medial measurement at both the DFmr (VAR: 1.17 ± 0.06 g/cm²; VAL: 1.00 ± 0.09 g/cm²) and PTb (VAR: 1.41 ± 0.07 g/cm²; VAL: 1.29 ± 0.14 g/cm²) (P < .05). ΔAlign° and %ΔBMD were correlated on the medial side of the DFmr (r = 0.393, P < .05) and lateral/medial BMD ratio at the PTb (r = -0.670, P < .01) in VAL patients. Only VAL patients had significant %ΔBMD changes at 6 months postoperative with increases on the medial side only for the DFmr and PTb (+4%-8%, P < .05).

CONCLUSION

Valgus patients exhibited reduced medial BMD at DFmr and PTb and showed sustained improvements 6 months postsurgery. Mechanical axis correction may be clinically impactful to bone remodeling when correcting valgus malalignment.

LEVEL OF EVIDENCE

Level II, prospective cohort study.

The accelerometer-based navigation system demonstrated superior radiological outcomes in restoring mechanical alignment and component sagittal positioning in total knee arthroplasty

Background

This study aimed to determine whether the accelerometer-based navigation (ABN) could improve the accuracy of restoring mechanical axis (MA), component positioning, and clinical outcomes compared to conventional (CON) total knee arthroplasty (TKA).

Methods

A total of 301 consecutive patients (ABN: 27, CON: 274) were included. A 1:4 propensity score matching (PSM) was performed between the two groups according to preoperative demographic and clinical parameters. The postoperative MA, femoral coronal angle (FCA), femoral sagittal angle (FSA), tibial coronal angle (TCA) and tibial sagittal angle (TSA) were compared. Absolute deviations of aforementioned angles were calculated as the absolute value of difference between the exact and ideal value and defined as norms if within 3°, otherwise regarded as outliers. Additional clinical parameters, including the Knee Society knee and function scores (KSKS and KSFS) and range of motion (ROM), were assessed at final follow-up (FU) (mean FU was 21.88 and 21.56 months respectively for ABN and CON group). A secondary subgroup analysis and comparison on clinical outcomes were conducted between norms and outliers in different radiological parameters.

Results

A total of 98 patients/102 knees were analyzed after the PSM (ABN: 21 patients/24 knees, CON: 77 patients/78 knees). In the ABN group, the mean MA, FCA and TSA were significantly improved (p = 0.019, 0.006, < 0.001, respectively). Proportions of TKAs within a ± 3°deviation were significantly improved in all the postoperative radiological variables except for TCA (p = 0.003, 0.021, 0.042, 0.013, respectively for MA, FCA, FSA, and TSA). The absolute deviations of FSA and TSA were also significantly lower in the ABN group (p = 0.020, 0.048, respectively). No significant differences were found in either mean value, absolute deviation or outlier ratio of TCA between two groups. On clinical outcomes, there were no significant differences between two groups, although KSKS, KSFS and ROM (p < 0.01, respectively) dramatically improved compared to baseline. The subgroup analysis also demonstrated no statistical difference on clinical outcomes between the outliers and norms in varied radiological parameters.

Conclusions

The ABN could improve the accuracy and precision of mechanical alignment and component positioning without significant improvement of clinical outcomes. Further high quality studies with long term FU are warranted to comprehensively evaluate the value of the ABN.

Linked kinematic knee balancing in unicompartmental knee arthroplasty

The traditional approach of restoring a neutral mechanical axis to the lower extremity during total knee arthroplasty (TKA) and unicompartmental knee arthroplasty (UKA) has long been favored due its consistency and reproducibility. The kinematic alignment approach, which accounts for the patient's natural knee alignment and is commonly a few degrees varus to the mechanical axis, has gained popularity in recent years as a technique which reestablishes a more anatomic alignment. Linked Anatomic Kinematic Arthroplasty (LAKA), an extension of the kinematic approach that employs computer-assisted surgical (CAS) navigation, can improve the accuracy and precision of kinematic measurements in unicompartmental knee arthroplasties. This article will describe the LAKA technique in UKA and review early clinical outcomes associated with this technique.

Coronal Plane Alignment of the Knee (CPAK) classification

Aims

A comprehensive classification for coronal lower limb alignment with predictive capabilities for knee balance would be beneficial in total knee arthroplasty (TKA). This paper describes the Coronal Plane Alignment of the Knee (CPAK) classification and examines its utility in preoperative soft tissue balance prediction, comparing kinematic alignment (KA) to mechanical alignment (MA).

Methods

A radiological analysis of 500 healthy and 500 osteoarthritic (OA) knees was used to assess the applicability of the CPAK classification. CPAK comprises nine phenotypes based on the arithmetic HKA (aHKA) that estimates constitutional limb alignment and joint line obliquity (JLO). Intraoperative balance was compared within each phenotype in a cohort of 138 computer-assisted TKAs randomized to KA or MA. Primary outcomes included descriptive analyses of healthy and OA groups per CPAK type, and comparison of balance at 10° of flexion within each type. Secondary outcomes assessed balance at 45° and 90° and bone recuts required to achieve final knee balance within each CPAK type.

Results

There was similar frequency distribution between healthy and arthritic groups across all CPAK types. The most common categories were Type II (39.2% healthy vs 32.2% OA), Type I (26.4% healthy vs 19.4% OA) and Type V (15.4% healthy vs 14.6% OA). CPAK Types VII, VIII, and IX were rare in both populations. Across all CPAK types, a greater proportion of KA TKAs achieved optimal balance compared to MA. This effect was largest, and statistically significant, in CPAK Types I (100% KA vs 15% MA; p < 0.001), Type II (78% KA vs 46% MA; p = 0.018). and Type IV (89% KA vs 0% MA; p < 0.001).

Conclusion

CPAK is a pragmatic, comprehensive classification for coronal knee alignment, based on constitutional alignment and JLO, that can be used in healthy and arthritic knees. CPAK identifies which knee phenotypes may benefit most from KA when optimization of soft tissue balance is prioritized. Further, it will allow for consistency of reporting in future studies.

Cite this article: Bone Joint J 2021;103-B(2):329–337.

What you need to know about kinematic alignment for total knee arthroplasty

This lecture outlines the various alignment philosophies for total knee arthroplasty (TKA). It is logical that our desire to improve clinical outcomes for TKA involves a more personalized and physiological implantation process that preserves each patient's anatomical features. We will take a deep dive into the kinematic alignment concept by describing its rationale, surgical steps and results. Kinematic implantation of TKA can be done reliably at a low cost and appears to achieve acceptable implant biomechanics. While its short-term clinical results are encouraging, it must be evaluated further. The thresholds for acceptable alignment (indications for restricted kinematic alignment) still need to be specified. LEVEL OF EVIDENCE: V; Expert opinion.

A patient-specific 3D model of the knee to compare the femoral rollback before and after total knee arthroplasty (TKA)

PURPOSE

Total knee arthroplasty (TKA) is nowadays performed as a standard procedure on a large number of patients suffering from arthrosis. Replacing the knee joint causes changes in the geometry and kinematics of the knee, which are unique to each individual. This research focuses on the method to detect these changes after TKA and on the impact on the knee movement. This approach could reduce complications in patients with post-operative pain and reduce the number of revisions.

METHODS

A 3D model of a patient's knee was made by measuring the movement with a medically certified infrared stereo camera. This measurement was combined with the 3D model of the patient's bones, previously segmented from the CT scan. This model is printed in 3D, one part being the mechanism that follows the movement of the patient, and the other part being the 3D copy of the femur and tibia bones. The knee replacement operation is performed directly on the model and the resulting rollback is being measured before and after TKA.

RESULTS

We observe a difference in the rollback before and after TKA on the 3D printed model. The variation in size and shape of the femoral implant compared to the natural femur condyles is one of the reasons for the changes in the rollback effect. The rollback is half as large after the prosthesis insertion, which confirms the fact that the femoral prosthesis geometry influences the knee kinematics.

CONCLUSIONS

In this study, a first 3D model combining the patient-specific kinematic and the geometry of his bones has been constructed. This model allows the surgeon to validate the plan of the operation, but also to understand the problems and consequences generated by the prosthesis insertion. The rollback is one of the most important motion of the knee joint and this behavior could be quantified, providing comparative analysis of the knee joint before and after the operation. As a future study, the model could be used to analyse more parameters of the TKA such as the impact of different implantation methods.

Effect of Coronal Alignment on 10-Year Survivorship of a Single Contemporary Total Knee Arthroplasty

Debate remains regarding the utility of mechanical axis alignment as a predictor of durability after total knee arthroplasty (TKA). Our study aimed to assess the effects of coronal alignment on implant durability, clinical outcomes, and radiographic results with a single fixed-bearing TKA design. All patients undergoing primary cemented TKA of a single design (Stryker Triathlon) from 2005–2007 with >10 years of follow-up and available pre-operative and post-operative hip–knee–ankle radiographs were included (n = 89). Radiographs were measured to determine coronal alignment and assessed for loosening. Mean preoperative mechanical axis alignment was −6° ± 6.7° (varus, range, −16°–23°), while mean post-operative alignment was −1° ± 2.7° (varus, range, −3°–15°). The aligned group was defined as knees with a post-operative mechanical axis of 0° ± 3° (n = 73) and the outlier group as those outside this range (n = 16). No patients underwent revision. Ten-year survivorship free from any reoperation was 99% and 100% in the aligned and outlier groups, respectively (p = 0.64). Knee Society scores improved significantly in both groups (p < 0.001) and did not differ at final follow-up (p = 0.15). No knees demonstrated radiographic evidence of loosening. Post-operative mechanical axis alignment within 3° of neutral was not associated with improved implant durability, clinical outcomes, or radiographic results at 10 years following primary TKA.

Postoperative alignment in revision total knee arthroplasty, a comparison between intra and extra-medullary tibial alignment

BACKGROUND

Revision total knee arthroplasty commonly involves stemmed components. If the diaphysis is engaged, this technique may be problematic for mechanical alignment (MA) in cases of tibial bowing, which are not infrequent (up to 30%). The aim of this study is to compare an intra-medullary(IM) and extra-medullary(EM) alignment method. We hypothesized that IM technique and canal-filling stems may result more frequently in valgus MA. On the other hand, an EM technique could produce less valgus knees but is at risk of creating MA outliers.

METHOD

A retrospective radiographic analysis of revision TKAs was performed. The patients were divided to either the EM or IM alignment group and compared on the overall post-operative MA. The following parameters were measured on standing, long leg x-rays: Hip-knee-Ankle angle (HKA), mechanical lateral distal femoral angle and mechanical medial proximal tibial angle (mMPTA).

RESULTS

119 cases of revision TKAs were included (EM = 80, IM = 39). There was a difference between the EM and IM group for the mean mMPTA (89.94° vs 90.92°, effect size = 0.45, p = 0.013) and HKA angle (1.64° vs 0.05°, effect size = 0.52, p = 0.0064). A higher proportion of IM patients were in overall valgus alignment (16/39, 41%) vs EM group (16/80, 20%, p = 0.0134). Both techniques showed the same proportion of outliers, defined as HKA angle more than 5 degrees from neutral mechanical alignment (11/80 vs 5/39, p = 0.286).

CONCLUSION

The extra-medullary alignment method with short cemented stems creates less valgus mechanical alignment than the intra-medullary technique with press-fit stems, without creating more MA outliers.

Combining kinematic alignment and medial stabilized design in total knee arthroplasty: Basic rationale and preliminary clinical evidences

Objective: kinematic alignment technique has been recently described as a new surgical procedure able to restore the patient specific physiological knee alignment; furthermore, new prosthesis, as medial stabilized (MS) third generation TKA, were designed to better reproduce the anatomical shape of the knee. In this prospective study, the authors evaluated early clinical improvement and radiological outcomes of patients having pre-operative small coronal limb deformity underwent TKA using a surgical technique combining a "restricted kinematic alignment" with medial stabilized polyethylene insert.

Methods

Fifteen consecutive patients (8 female and 7 male) scheduled for a total knee replacement have been enrolled for this study and treated using a modern third generation knee implant with a medial congruent tibial polyethylene. Clinical improvements have been assessed pre-operatively and at 6 and 12 months Follow up (FU) using the Oxford knee Score (OKS)( Ishikawa et al., Jun. 2015) 12 the Knee Society Score (KSS)( Pinskerova and et al., Aug. 2004) 13 and Forgotten Joint Score (FJS) as patient reported outcomes measurement system (PROMs). A radiological evaluation was made by a single physician at 6 months.

Results

Average improvement in OKS was from 20.2 (SD 5.5) pre-operatively to 41.3 (SD 2.1) at the final FU. KSS pain/motion improved with a mean score from 40.1 (SD 4.0) pre-op to 89.1 (SD 6.3) while KSS function improved with an average score from 51.0 (SD 6.2) pre-op to 81.8 (SD 8.4) showing good to excellent results in all the knee treated. The mean FJS at 6 months follow up was 75.1 (SD 4.2) improving to 79.3 (SD 3.3) at one year FU. Post-operative XR showing an average varus Hip-Knee-Ankle (HKA) angle of 178.8° (range from 176° to 182°, SD 2,3°); We found no statistically significant difference between pre-operative and post-operative HKA (p < 0,05).

Conclusion

The current authors assumed appropriate to combine a modern TKA implant designed replicating the anatomical shape of the native knee with a surgical technique able to better reproduce the physiological, patient specific, knee biomechanics. Our findings suggest that combining MS implant with KA technique may results in better short-term functional results, helping the patient to "forget" their replaced joint and restoring their pre-arthritic quality of life.

Clinical outcomes of kinematic alignment versus mechanical alignment in total knee arthroplasty: a systematic review

Although mechanical alignment (MA) has traditionally been considered the gold standard, the optimal alignment strategy for total knee arthroplasty (TKA) is still debated.

Kinematic alignment (KA) aims to restore native alignment by respecting the three axes of rotation of the knee and thereby producing knee motion more akin to the native knee.

Designer surgeon case series and case control studies have demonstrated excellent subjective and objective clinical outcomes as well as survivorship for KA TKA with up to 10 years follow up, but these results have not been reproduced in high-quality randomized clinical trials.

Gait analyses have demonstrated differences in parameters such as knee adduction, extension and external rotation moments, the relevance of which needs further evaluation.

Objective improvements in soft tissue balance using KA have not been shown to result in improvements in patient-reported outcomes measures.

Technologies that permit accurate reproduction of implant positioning and objective measurement of soft tissue balance, such as robotic-assisted TKA and compartmental pressure sensors, may play an important role in improving our understanding of the optimum alignment strategy and implant position.

Cite this article: EFORT Open Rev 2020;5:486-497. DOI: 10.1302/2058-5241.5.190093

Short-term follow-up of kinematically vs. mechanically aligned total knee arthroplasty with medial pivot components: A case-control study

INTRODUCTION

The kinematic alignment (KA) technique for total knee arthroplasty (TKA) and the medial pivot (MP) component design are two options promoting a physiologic prosthetic knee kinematics when used in combination that could improve TKA outcomes. Case-control study is initiated to compare the 1-year radio-clinical outcomes between kinematic alignment medial pivot total knee arthroplasty (KA MP-TKAs) and mechanical alignment medial pivot total knee arthroplasty (MA MP-TKA). Goal of a study was to answer the following questions: Do KA MP-TKAs patients have improved functional outcomes compared to MA MP-TKAs patients? (Q1); Do prosthetic knee and lower limb alignments differ between KA and MA patients (Q2)? And does kinematic implantation of MP TKA has higher risk of reoperations and revisions (Q3)?

MATERIAL AND METHODS

A case-control study was carried out to compare the 1-year clinical and radiographic outcomes between 24 consecutive KA-TKA patients and 24 matched MA-TKA patients. All patients had implantation with manual instruments and a cemented medial pivot TKA with excision of the PCL. All data were collected prospectively, and outcome scores were patient reported.

RESULTS

KA patients had superior values in Forgotten Joint Score (FJS) at 1-year (KA 77 vs. MA 51) (p=0.05) follow-up. After one year KA patients scored better in objective section of the new Knee Society Score (KSS) (p=0.02), and in sport section of the Knee Osteoarthritis Outcome Score (KOOS) (p=0.01). Eleven out of 24 patients (46%) in KA group and 7/24 patients (29%) in MA group had limb alignment out of 180°±3°, whereas 17/24 (70%) of KA patients, and 14/24 (58%) of MA patients had orientation of tibial component with more than 3° of varus. No reoperation or revision occurred in either group.

DISCUSSION/CONCLUSION

The KA of MP TKA design seems to have a good efficacy at early-term, with some 1-year functional performance higher to the ones from MA MP TKAs. Further research is needed to define if those early results will last over time.

LEVEL OF EVIDENCE

III, case-controlled study.