Mechanical alignment technique for TKA: Are there intrinsic technical limitations?

Not all knees are the same

The aim of mechanical alignment in total knee arthroplasty is to align all knees into a fixed neutral position, even though not all knees are the same. As a result, mechanical alignment often alters a patient's constitutional alignment and joint line obliquity, resulting in soft-tissue imbalance. This annotation provides an overview of how the Coronal Plane Alignment of the Knee (CPAK) classification can be used to predict imbalance with mechanical alignment, and then offers practical guidance for bone balancing, minimizing the need for soft-tissue releases.

Higher satisfaction and function scores in restricted kinematic alignment versus mechanical alignment with medial pivot design total knee arthroplasty: A prospective randomised controlled trial

PURPOSE

Restricted kinematic alignment (rKA) in total knee arthroplasty (TKA) and medial pivot (MP) knee designs already showed superior outcomes in independent comparative studies. The objective of this study was to assess whether rKA with MP TKA provides better clinical and functional outcomes compared to mechanical alignment (MA) with MP TKA.

METHODS

This is a randomised, parallel two group study involving a total of 98 patients with end-stage knee osteoarthritis. Patients were randomly allocated to either rKA or MA TKA procedures conducted with a MP prothesis using patient-specific instruments between 2017 and 2020. Final follow-up was at 2 years postoperatively. Demographic data and clinical and functional scores (Oxford knee score, knee society score [KSS], Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC], forgotten joint score [FJS]) were collected and compared preoperative, 1 year postoperative and 2 years postoperative. Coronal plane alignment of the knee and functional knee phenotype classification were recorded.

RESULTS

A total of 47 patients (rKA) and 51 patients (MA) were included in final analysis. Superior joint awareness scores (FJS) were found at 1 year postoperative for rKA (62.2 vs. 52.4, p = 0.04). KSS subscores (expectation score, satisfaction score) improved with rKA with significant differences at both 1 and 2 years postoperatively. Major differences between rKA and MA were found in subgroup analysis of varus and neutral CPAK phenotypes. Both 1 year and 2 years postoperatively, FJS was significantly better in KA compared with MA in varus CPAK phenotypes (63.1 vs. 44.9, p = 0.03; 71.1 vs. 46.0, p = 0.005). Further clinical and functional scores showed improvement in the varus CPAK phenotypes with predominantly significant improvement in the expectation and satisfaction KSS subscores. No significant differences were found in the comparison of rKA and MA in neutral CPAK phenotypes.

CONCLUSION

The rKA of MP TKA design shows superior patient satisfaction and self-reported function when compared to MA MP TKA. Furthermore, rKA MP TKA shows superior joint awareness at early postoperative stage. The most important clinical relevance of this study is the clear superiority of rKA in varus phenotypes.

LEVEL OF EVIDENCE

Level II.

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.

Ten Flaws of Systematic Mechanical Alignment Total Knee Arthroplasty

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

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

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

The coronal plane alignment of the knee classification does not correlate with the functional knee phenotype classification

PURPOSE

It is now well established that the coronal anatomy of the lower limb is highly variable both in non-arthritic subjects and subjects undergoing total knee arthroplasty (TKA). Two new classifications were recently described independently, but never compared: functional knee phenotypes classification and coronal plane alignment of the knee (CPAK) classification. The hypothesis of this study was that there was a significant difference between the values of the hip-knee-ankle angle (HKA) and the arithmetic hip-knee-ankle angle (aHKA) measures in the same patient at the time of TKA.

METHODS

Five hundred and twenty cases were randomly selected among patients operated on for a TKA with navigation assistance. Anatomical parameters were collected during surgery by a navigation system, and the corresponding data of the CPAK classification were calculated. The numerical values of measured HKA and aHKA in the same patient were compared.

RESULTS

The measured HKA had a mean of 3.0° varus (standard deviation of 6.0°). The calculated aHKA had a mean of 1.8° varus (standard deviation 4.8°). There was a significant difference between the values of the two measurements in the same subject (p = 0.005) and a weak negative correlation between the values of the two measurements in the same subject. In addition, there was no relationship between HKA values and joint line obliquity values or CPAK class.

CONCLUSION

A significant difference and a weak correlation between the values of the HKA and aHKA measures in the same subject were observed. The two analysis techniques used provide different information, and their correlation is only partial. These two techniques therefore appear to be complementary rather than exclusive. The clinical relevance of using these techniques during TKA remains unknown.

LEVEL OF EVIDENCE

III.

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.

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.

Are modern knee outcomes scores appropriate for evaluating anterior knee pain and symptoms after total knee arthroplasty?

BACKGROUND

Up to 45% of patients who undergo primary total knee arthroplasty (TKA) with contemporary implants have residual anterior knee pain. While a specific evaluation of anterior knee symptoms is mandatory, little is known about the capability of patellofemoral scores to be used individually. This study aimed to assess the distribution of patellofemoral scores after TKA from a uniform cohort and to investigate their external validity and ability to detect anterior knee symptoms using floor and ceiling effects.

HYPOTHESIS

Patellofemoral scores have high construct validity and fewer floor/ceiling effects than general knee scores.

METHODS

We prospectively included 113 consecutive patients who underwent primary TKA for primary osteoarthritis at a single University Hospital. Clinical outcomes included patellofemoral scores (HSS Patella, Kujala and Lille scores) and general knee scores (KOOS and new KSS) at 1-year follow-up. The floor and ceiling effects were considered as significant when greater than 15%. These were determined for each score individually and for composite scores (combination of patellofemoral scores and new KSS). The construct validity of each score and their ability to detect anterior knee pain was evaluated.

RESULTS

Patellofemoral scores showed no floor effect but a significant ceiling effect (from 25% to 65%). This ceiling effect decreased when composite scores were used. The convergent validity test showed strong correlation between patellofemoral scores (from 0.741 to 0.819, p<0.00001) and a better ability to discriminate anterior knee pain than the general knee scores.

CONCLUSIONS

Patellofemoral scores showed no floor effect and a very good construct validity for anterior knee pain after TKA. However, studies aiming to monitor anterior knee symptoms after TKA should combine scoring systems to included patellofemoral-related items rather than use patellofemoral scores alone due their ceiling effects.

LEVEL OF EVIDENCE

III; prospective study.

Tibiofemoral lift-off and resulting laxity following total knee arthroplasty: Frequency in a series of 906 continuous cases and functional consequences at 4 years' follow-up in a case-control study

BACKGROUND

Tibiofemoral instability is one reason for early revision of total knee arthroplasty. It can be the consequence of tibiofemoral laxity, especially in the coronal plane with tibiofemoral lift-off. But does femoral condyle lift-off on conventional postoperative radiographs suggest the presence of laxity or potential instability? To our knowledge, this question has not yet been answered. This led us to conduct a retrospective study to evaluate (1) the frequency of lift-off on postoperative radiographs, (2) the relationship between lift-off and laxity in the short term and (3) the functional consequences of lift-off.

HYPOTHESIS

Postoperative lift-off is a rare event that is predictive of laxity.

METHODS

We carried out a single-center retrospective study using postoperative radiographs from patients who underwent primary total knee arthroplasty between 2014 and 2016. The sample consisted of 906 patients. Lift-off was defined as a tibiofemoral angle of 3° or more on immediate postoperative radiographs (day 0) that were non-weightbearing and had no stress applied. The functional outcomes were determined in the 17 patients identified as having lift-off who had been operated in the first year (2014) to ensure the follow-up was long enough. These patients were compared to 34 matched control patients who were operated the same year and chosen randomly among patients not having lift-off. The matching ratio was 2 controls to 1 case. Preoperative and surgical data were compiled from each patient's electronic medical record. Patients were evaluated at 4 years postoperatively using the subjective Oxford-48, objective HSS score, IKS score, overall patient satisfaction and stress radiographs of the knee. The cases of lift-off observed in 2014 (n=17) were paired with a control group of patients selected randomly during 2014.

RESULTS

The frequency of the lift-off event was 63/906 or 7%. The frequency was consistent over the three years studied: 7.1% in 2014 (19/269), 6.2% in 2015 (22/354) and 7.8% in 2016 (22/283). There was no significant difference between the two groups (17 with lift-off and 34 without) in the sex, age, body mass index and coronal plane deformity (preoperative HKA angle). At a mean follow-up of 4 years (range 12-49 months), the knees with postoperative lift-off had more laxity (p=0.002), particularly laxity when varus stress was applied (p=0.009). There were no other significant differences in the outcomes.

DISCUSSION

Immediate postoperative lift-off after total knee arthroplasty is not a rare event, with a 7% frequency in our study. While it reveals that laxity is present in the particular compartment, there is no evidence of functional consequences at 4 years' follow-up; however, a long-term assessment is required to verify this finding.

LEVEL OF EVIDENCE

III - case-control study.

Wide variation in tibial slopes and trochlear angles in the arthritic knee: a CT evaluation of 4116 pre-operative knees

PURPOSE

As surgeons continue to grapple with persistent issues of patient dissatisfaction post-TKA, the literature has focused on the coronal plane when considering alignment strategies but has largely ignored the sagittal and axial planes. The purpose of this retrospective observational cohort study is to evaluate variability in knee anatomy and alignment beyond the coronal plane and rationalise how this relates to existing arthroplasty alignment philosophies.

METHODS

4116 knee CTs from 360 Knee Systems© database of arthritic pre-operative TKA patients were evaluated. Standardised bony landmarks were used in each CT to determine the hip-knee angle, medial proximal tibial angle, lateral distal femoral angle, medial plateau posterior tibial slope, lateral plateau posterior tibial slope, trochlea angle (TA) to distal femoral angle (TA-DFA) and TA to posterior condylar angle (TA-PCA). Analysis was performed to determine the distributions of each measure across the cohort population.

RESULTS

Both the medial and lateral PTS ranged from 5° anterior to 25° posterior. 22.6% of patients had differential PTS greater than 5°. 14.5% have greater lateral PTS (mean difference to medial PTS of 4.8° ± 5.0°), whilst 31.0% have greater medial PTS (mean difference to lateral PTS of 5.7° ± 3.2°). 14% of TA-DFAs and 5.2% of TA-PCAs vary greater than 10°.

CONCLUSION

This study demonstrates a wide variation in tibial slope, differential slope between the medial and lateral tibial plateau as well as variation in the trochlear geometry. There has been an overemphasis in the literature on coronal alignment, ignoring the considerable variability present in tibial and patellofemoral morphology. Existing arthroplasty techniques are based on assumptions that may not adequately address the anatomy of morphologic outliers and could lead to dissatisfaction.

LEVEL OF EVIDENCE

III-retrospective cohort study.

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.

Using a patella reduced technique while balancing a TKA results in restored physiological strain in the collateral ligaments: an ex vivo kinematic analysis

INTRODUCTION

Poor soft tissue balance in total knee arthroplasty (TKA) often results in patient dissatisfaction and reduced joint longevity. Patella-in-place balancing (PIPB) is a novel technique which aims to restore native collateral ligament behavior without collateral ligament release, while restoring post-operative patellar position. This study aimed to assess the effectiveness of this novel technique through a detailed ex vivo biomechanical analysis by comparing post-TKA tibiofemoral kinematics and collateral ligament behavior to the native condition.

MATERIALS AND METHODS

Eight fresh-frozen cadaveric legs (89.2 ± 6 years) were tested on a validated dynamic knee simulator, following computed tomography imaging. Specimens were subjected to passive flexion (10-120°), squatting (35-100°), and varus/valgus laxity testing (10 Nm at 0°, 30°, 60°, 90° flexion). An optical motion capture system recorded markers affixed rigidly to the femur, tibia, and patella, while digital extensometers longitudinally affixed to the superficial medial collateral ligament (MCL) and lateral collateral ligament (LCL) collected synchronized strain data. Following native testing, a Stryker Triathlon CR TKA (Stryker, MI, USA) was performed on each specimen and the identical testing protocol was repeated. Statistical analyses were performed using a linear mixed model for functional motor tasks, while Wilcoxon signed-rank test was used for laxity tests (p < 0.05).

RESULTS

Postoperative laxity was lower than the native condition at all flexion angles while post-operative ligament strain was lowered only for MCL at 30° (p = 0.017) and 60° (p = 0.011). Postoperative femoral rollback patterns were comparable to the native condition in passive flexion but demonstrated a more pronounced medial pivot during squatting.

CONCLUSIONS

Balancing a TKA with the PIPB technique resulted in reduced joint laxity, while restoring collateral ligament strains. The technique also seemed to restore kinematics and strains, especially in passive flexion.

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.

Primary osteoarthritic knees have more varus coronal alignment of the femur compared to young non-arthritic knees in a large cohort study

PURPOSE

Many surgeons are performing total knee arthroplasty (TKA) with an aim to reproducing native anatomical coronal alignment. Yet, it remains unclear if primary osteoarthritic and non-osteoarthritic populations have similar knee coronal alignment. This study aims to describe and compare the distribution of femoral and tibial coronal alignment in a large primary osteoarthritic cohort and a young non-osteoarthritic cohort.

METHODS

This is a retrospective analysis of a monocentric prospectively gathered data, from 1990 to 2019, of 2859 consecutive primary osteoarthritic knees in 2279 patients. Patients underwent standardized long-leg radiographs. Femoral mechanical angle (FMA) and tibial mechanical angle (TMA) were digitally measured using software. Femoral, tibial and knee phenotypes were analyzed, and descriptive data were reported. Data were compared to a young non-osteoarthritic population previously described.

RESULTS

In osteoarthritic knees, the mean FMA was 91° ± 2.9° (range 86°-100°) and the mean TMA was 87° ± 3.1° (range 80°-94°). No significant difference was observed for FMA and TMA between genders. The most common femoral and tibial phenotypes were varus (38.7%) and neutral (37.1%). The most frequent knee phenotype was a varus femoral phenotype with a neutral tibial phenotype (15.5%), which is different to the non-osteoarthritic population.

CONCLUSION

This study showed the wide distribution of knee phenotypes in a large osteoarthritic cohort. There was more varus distribution of the femoral coronal alignment compared to a non-osteoarthritic population, suggesting consideration and potential adaptation of the realignment strategy of the femoral component during TKA.

LEVEL OF EVIDENCE

III.

Correctability of the knee joint observed under a stressed state

BACKGROUND

Well-balanced postoperative knee joints are often based on subjective 'feel' of experienced surgeons rather than quantifiable references. Most alignment strategies continue to reference the bone despite the complexity in anatomical variations and presence of deformity. Categorical prescription of a singular alignment philosophy for all patients may not be appropriate. This study aims to characterize coronal alignment correctability in relation to anatomical measures to develop a mechanism for distinguishing patients for whom repeatable strategies are optimal in the form of alternative alignment techniques or advanced soft tissue balancing.

METHODS

A consecutive series of 103 pre-operative knees who underwent primary total knee arthroplasty (TKA) were analysed. Pre-operative supine computer tomography (CT) scans were segmented, with output STL bone models placed against several stressed positions determined by the TELOS SD-900 (METAX, Germany) device. Anatomical analysis using two-dimensional (2D) -3D image registration was performed. Statistical analysis was conducted for variations in anatomical morphology and regression modelling was used to determine the relationship between these measurements and correctability of a patient.

RESULTS

The mean preoperative supine hip-knee-ankle (HKA) angle was 5.1° and 2.3°, lateral distal femoral angle (LDFA) was 2.0° and 3.1°, medial proximal tibial angle (MPTA) was 3.7° and 3.0° varus for male and female, respectively. The mean laxity range was 4.3°. We found 36% of valgus patients and 55% of mild varus patients to be correctable. Supine HKA was a statistically significant predictor for correctability (P < 0.001). A statistically significant correlation between laxity and the HKA (P = 0.01) as well as LDFA angles (P = 0.01) exist for the mild varus cohort.

CONCLUSION

Relationship between HKA angle and the correctability of the knee joint to neutral in patients presenting with mild to moderate varus cannot be consistently predicted using bony anatomy. If there is a desire to avoid ligament release during TKA, careful consideration of both a patient's bony anatomy and soft tissue laxity envelope must be made prior to surgery.

A ligament tensor-guided extramedullary alignment technique for distal femoral cut in total knee replacement: results at a minimum 3 years follow-up

BACKGROUND

Femoral intramedullary canal referencing is used by most knee arthroplasty systems for distal femoral cut; to avoid the opening of the femoral canal different solutions have been presented such as navigation, patient-specific instruments (PSI) or the use of an extramedullary device. The FuZion^® system is a tensor device, created to merge the two main techniques for performing a total knee arthroplasty: the ligament balancing and measured resection techniques. Our idea was to use the tensor as an extramedullary cutting guide for the distal femoral cut, based on a 90° tibial resection.

METHODS

A total of 110 patients were operated on with this technique. Patients were evaluated with weight-bearing long-standing X-rays, knee a-p and lateral views, validated PROMs (Oxford Knee Score, EQ-5D and EQ-VAS), the Knee Society Scoring System (KSS) and the Forgotten Joint Score (FJS). Minimum follow up was 3 years (range 38-50 months).

RESULTS

Complete results were available for 104 patients (5 were lost in follow up and 1 died). Significant improvements were registered for all the evaluated scores from pre-op to the final follow up. Pre-op long-standing X-rays showed 21 valgus knees (20%) with a mean HKA of 187.6° (± 3.2°), 70 varus knees (62%) with a mean 172.2° (± 3.7°) HKA and 19 neutrally aligned knees, with a mean HKA of 179.5° (0 ± 2°). The radiographic evaluation at 3 months post-op showed 20 valgus knees (mean HKA 183.7° ± 1.5°), 67 varus knees (mean HKA 176.1° ± 1.8°) and 23 neutrally aligned knees with a mean HKA of 179.3° (0 ± 2°). At final follow up the survival rate was 100% for revision of the implant as the endpoint. With any reoperation as the endpoint Kaplan-Meier survival estimate showed a survival rate of 95.1% at 3 years.

CONCLUSIONS

This technique for performing a ligament driven alignment in total knee arthroplasty showed encouraging clinical outcomes at mid-term follow up leaving a residual deformity on the coronal plane.

Clinical and Radiological Changes of Ankle in Knee Osteoarthritis With Varus After Total Knee Arthroplasty: A Systematic Review

Background: Arthritis with severe varus deformity remains a challenge in total knee arthroplasty (TKA). Until recently, surgeons aimed at a neutral lower limb alignment when performing a TKA. However, the impact of TKA on the ankle joint has been ignored. Therefore, we conducted a systematic review to assess the clinical and radiological changes in the ankle joint after TKA on knees with severe varus deformity. Methods: A systematic search was conducted in four English (PubMed, Embase, Cochrane Library, and Web of Science) and four Chinese (CBM, VIP, CNKI, and Wan Fang Database) databases. Screening of literature and extraction of data were independently performed by two researchers. The modified methodological index for non-randomized studies (MINORS) was used to assess the quality. Results: A total of eight studies were eligible, namely, four prospective and four retrospective studies. TKA resulted in a negative clinical effect in the ankle joint in patients with ankle osteoarthritis. Seven studies reported changes in the mechanical tibiofemoral angle, and four studies reported radiological changes in the hindfoot. The mean score of the MINORS was 9.8 out of eight (9-11). Conclusion: As a result of the correction of the knee osteoarthritis with severe varus deformity following mechanically aligned TKA, the radiological malalignment of the ankle joint was improved. However, some patients experience increased ankle pain after undergoing TKA, especially, if there was a residual knee varus deformity, a stiff hindfoot with varus deformity, or ankle arthritis.

Multi-color and Multi-Material 3D Printing of Knee Joint models

Objective

This study reports on a new method for the development of multi-color and multi-material realistic Knee Joint anatomical models with unique features. In particular, the design of a fibers matrix structure that mimics the soft tissue anatomy.

Methods

Various Computer-Aided Design (CAD) systems and the PolyJet 3D printing were used in the fabrication of three anatomical models wherein fibers matrix structure is mimicked: (i) Anterior cruciate ligament reconstruction (ACL-R) model used in the previous study. (ii) ACL-R model, incorporating orientations, directions, locations, and dimensions of the tunnels, as well as a custom-made surgical guide (SG) for avoiding graft tunnel length mismatch. (iii) Total knee arthroplasty (TKA) model, including custom-made implants. Before models 3D printing, uni-axial tensile tests were conducted to obtain the mechanical behaviors for individual No. 1 (A60-A50), No. 2 (A50-A50), No. 3 (A50-A40), and No. 4 (A70-A60) soft tissue-mimicking polymers. Each material combination represents different shore-hardness values between fiber and matrix respectively.

Results

We correlated the pattern of stress-strain curves in the elastic region, stiffness, and elastic modulus of proposed combinations with published literature. Accordingly, material combinations No. 1 and No. 4 with elastic modules of 0.76-1.82 MPa were chosen for the soft tissues 3D printing. Finally, 3D printing Knee Joint models were tested manually simulating 50 flexo-extension cycles without presenting ruptures.

Conclusion

The proposed anatomical models offer a diverse range of applications. These may be considered as an alternative to replacing cadaver specimens for medical training, pre-operative planning, research and education purposes, and predictive models validation. The soft tissue anatomy-mimicking materials are strong enough to withstand the stretching during the flexo-extension. The methodology reported for the design of the fiber-matrix structure might be considered as a start to develop new patterns and typologies that may mimic soft tissues.

Personalized alignment in total knee arthroplasty: current concepts

Traditionally in total knee arthroplasty (TKA), a post-operative neutral alignment was the gold standard. This principle has been contested as functional outcomes were found to be inconsistent. Analysis of limb alignment in the non-osteoarthritic population reveals variations from neutral alignment and consideration of a personalized or patient-specific alignment in TKA is challenging previous concepts. The aim of this review was to clarify the variations of current personalized alignments and to report their results. Current personalized approaches of alignment reported are: kinematic, inverse kinematic, restricted kinematic, and functional. The principle of “kinematic alignment” is knee resurfacing with restitution of pre-arthritic anatomy. The aim is to resurface the femur maintaining the native femoral joint line obliquity. The flexion and extension gaps are balanced with the tibial resection. The principle of the “inverse kinematic alignment” is to resurface the tibia with similar medial and lateral bone resections in order to keep the native tibial joint line obliquity. Gap balancing is performed by adjusting the femoral resections. To avoid reproducing extreme anatomical alignments there is “restricted kinematic alignment” which is a compromise between mechanical alignment and true kinematic alignment with a defined safe zone of alignment. Finally, there is the concept of “functional alignment” which is an evolution of kinematic alignment as enabling technology has progressed. This is obtained by manipulating alignment, bone resections, soft tissue releases, and/or implant positioning with a robotic-assisted system to optimize TKA function for a patient’s specific alignment, bone morphology, and soft tissue envelope. The aim of personalizing alignment is to restore native knee kinematics and improve functional outcomes after TKA. A long-term follow-up remains crucial to assess both outcomes and implant survivorship of these current concepts.

Medio-Lateral and Flexion-Extension Gap Imbalances in Mechanically Aligned Total Knee Arthroplasty Using Measured Resection Technique in Korean Patients: 3D Simulation

Background: It is well known that the measured resection (MR) technique in mechanically aligned (MA) total knee arthroplasty (TKA) generates significant gap imbalances, but little is known about whether this applies to the knees of Asian patients. The aim of this study was to evaluate the medio-lateral and flexion-extension gap imbalances and to find the most optimal posterior femoral condyle resection method for operating on the knees of Asian patients. Methods: In total, 738 magnetic resonance imaging (MRI) scans of consecutive patients who underwent TKA were obtained. Four posterior femoral condylar resection methods were used: alignment by the surgical transepicondylar axis (TEA), Whiteside’s line (WSL), 3° external rotation to the posterior condylar axis (PCA), and flexion-extension axis (FEA). Results: For the medial compartments, there were significant differences between the flexion and extension gaps in the varus knee group in all four methods, but there were no differences between the flexion and extension gaps in the valgus knee group. For the lateral compartment, all the methods showed significant differences except for WSL of the valgus knee group and FEA of the varus knee group. Conclusions: In Asian patients, the use of the MA MR technique inevitably leads to medio-lateral or flexion-extension imbalances. Therefore, surgeons should consider which methods can minimize imbalances and choose the best method within the technically possible range.

Undercoverage of lateral trochlear resection is correlated with the tibiofemoral alignment parameters in kinematically aligned TKA: a retrospective clinical study

BACKGROUND

A mismatch between the femoral component and trochlear resection surface is observed in kinematically aligned total knee arthroplasty (KA-TKA) when conventional prostheses are employed. This mismatch is mainly manifested in the undercoverage of the lateral trochlear resection surface. The aim of the present study was to assess the relationship between the mismatch and the alignment parameters of the tibiofemoral joint.

METHODS

Forty-five patients (52 knees) who underwent KA-TKA in our hospital were included. Patient-specific instrumentation was used in 16 patients (16 knees), and conventional instruments with calipers and other special tools were employed in the other 29 patients (36 knees). The widths of the exposed resection bone surface at the middle (MIDexposure) and distal (DISexposure) levels on the lateral trochlea were measured as dependent variables, whereas the hip-knee-ankle angle (HKAA), mechanical lateral distal femoral angle (mLDFA), joint line convergence angle (JLCA), medial proximal tibial angle (MPTA) and transepicondylar axis angle (TEAA) were measured as independent variables. Correlation analysis and subsequent linear regression were conducted among the dependent variables and various alignment parameters of the tibiofemoral joint.

RESULTS

The incidence of undercoverage of the lateral trochlear resection surface was 86.5 % with MIDexposure and DISexposure values of 2.3 (0-6 mm) and 2.0 (0-5 mm), respectively. The widths of the two levels of exposed bone resection were significantly correlated with mLDFA and HKAA but were not related to TEAA.

CONCLUSIONS

The undercoverage of the trochlear resection surface in KA-TKA is mainly correlated with the degree of valgus of the distal femoral joint line. The current study suggests that this correlation should be considered in the development of KA-specific prostheses.

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.

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.

Kinematic alignment in total knee arthroplasty

Kinematic alignment (KA) is an alternative philosophy for aligning a total knee replacement (TKR) which aims to restore all three kinematic axes of the native knee.

Many of the studies on KA have actually described non-KA techniques, which has led to much confusion about what actually fits the definition of KA.

Alignment should only be measured using three-dimensional cross-sectional imaging. Many of the studies looking at the influence of implants/limb alignment on total knee arthroplasty outcomes are of limited value because of the use of two-dimensional imaging to measure alignment, potentially leading to inaccuracy.

No studies have shown KA to be associated with higher complication rates or with worse implant survival; and the clinical outcomes following KA tend to be at least as good as mechanical alignment.

Further high-quality multi-centre randomized controlled trials are needed to establish whether KA provides better function and without adversely impacting implant survival.

Cite this article: EFORT Open Rev 2020;5:380-390. DOI: 10.1302/2058-5241.5.200010

[Alignment techniques for implantation of a total knee endoprosthesis with particular focus on kinematic alignment]

BACKGROUND

This review introduces various techniques for implantation of a total knee endoprosthesis and scrutinizes the "mechanical alignment" of a total knee endoprosthesis, whereby the various alignment concepts are examined. In particular, kinematic alignment, in terms of its significance, the individual steps of the implantation technique and the data collected, will be examined in more detail.

METHODS

Improvement in the clinical results after implantation of a total knee endoprosthesis can be achieved by a personalized, individualized, physiological implantation that respects the unique anatomical characteristics of each patient. In recent years, many alternative alignment techniques have been developed, some of them showing promising approaches.

RESULTS

The kinematic implantation technique can be performed reliably and inexpensively, and shows good biomechanical results. Although the first clinical results are encouraging, further studies should be carried out to determine the limits of optimal alignment.

[Balancing technique using bone cuts]

BACKGROUND

Kinematic alignment means a surgical technique that focuses on intraarticular balance and laxity and takes into consideration the prearthritic state of the knee joint.

AIM

The aim of kinematic alignment is a constitutionally aligned joint space line and balanced tension of the soft tissue covering. By avoiding the proximalization of the joint line and the release of the ligaments, the risk of destabilization of the original physiology of the joint is reduced.

METHODS

After resections and recuts of the distal femur, a natural distal femoral joint line in full extension and the posterior line in 90° should be maintained or restored. Therefore, the flexion-extension axis of the femur, around which the knee joint moves, does not change. The principle of KA unequivocally requires the distal femoral cut to be performed before resection of the posterior femoral condyles.

RESULTS

The result is a natural knee joint alignment that approximately replicates the anatomy of the femoral and tibial axes. Release of the ligaments is rarely required and all necessary adjustments are usually made using bone recuts.

Bone resection for mechanically aligned total knee arthroplasty creates frequent gap modifications and imbalances

PURPOSE

The objective of this study was to calculate bone resection thicknesses and resulting gap sizes, simulating a measured resection mechanical alignment (MA) technique for total knee arthroplasty (TKA).

METHODS

MA bone resections were simulated on 1000 consecutive lower limb CT scans from patients undergoing TKA. Femoral rotation was aligned with either the surgical trans-epicondylar axis (TEA) or with 3° of external rotation to the posterior condyles (PC). Imbalances in the extension space, flexion space, medial compartment and lateral compartment were calculated.

RESULTS

Extension space imbalances (≥ 3 mm) occurred in 25% of varus and 54% of valgus knees and severe imbalances (≥ 5 mm) were present in up to 8% of varus and 19% of valgus knees. Higher flexion space imbalance rates were created with TEA versus PC (p < 0.001). Using TEA, only 49% of varus and 18% of valgus knees had < 3 mm of imbalance throughout the extension and flexion spaces, and medial and lateral compartments.

CONCLUSION

A systematic use of the simulated measured resection MA technique for TKA leads to many cases with imbalance. Some imbalances may not be correctable surgically and may result in TKA instability. Modified versions of the MA technique or other alignment methods that better reproduce knee anatomies should be explored.

LEVEL OF EVIDENCE

2.

The stiff total knee arthroplasty: causes, treatment modalities and results

It is clear that the stiff total knee arthroplasty (TKA) is a multifactorial entity associated with preoperative, intraoperative and postoperative factors.

Management of the stiff TKA is best achieved by preventing its occurrence using strategies to control preoperative factors, avoid intraoperative technical errors and perform aggressive, painless postoperative physical medicine and rehabilitation; adequate pain control is paramount in non-invasive management.

Careful attention to surgical exposure, restoring gap balance, minimizing surgical trauma to the patellar ligament/extensor mechanism, appropriate implant selection, pain control and adequate physical medicine and rehabilitation (physiotherapy, Astym therapy) all serve to reduce its incidence.

For established stiff TKA, there are multiple treatment options available including mobilization under anaesthesia (MUA), arthroscopic arthrolysis, revision TKA, and combined procedures.

Cite this article: EFORT Open Rev 2019;4:602-610. DOI: 10.1302/2058-5241.4.180105

Kinematically aligned total knee arthroplasty reproduces more native rollback and laxity than mechanically aligned total knee arthroplasty: A matched pair cadaveric study

BACKGROUND

A growing body of evidence supports that kinematically aligned (KA) total knee arthroplasty (TKA) provides superior clinical outcomes and satisfaction than mechanically aligned (MA) TKA. In theory, KA TKA would restore knee kinematics closer to the native condition than MA TKA, but the current biomechanical evidence is lacking.

HYPOTHESIS

KA TKA would restore knee biomechanics to the native condition better than MA TKA.

METHODS

Seven pairs of cadavers were tested. For each pair, one knee was randomly assigned to KA TKA and the other to MA TKA. During KA TKA, the sizes of femur and tibia resections were equivalent to implant thickness to align with the patient-specific joint line. MA TKA was performed using conventional measured resection techniques. All specimens were mounted on a customized knee-testing system and digitized. Knee motions measured during flexion included rollback, axial tibiofemoral rotation, and laxities, specifically varus-valgus laxity, anterior-posterior translation, and internal-external rotation.

RESULTS

The pattern of knee motion following KA TKA was similar to the native knee. However, following MA TKA, both medial and lateral rollback and tibiofemoral axial rotation were decreased relative to those of the native knee. Valgus laxity was restored only after KA TKA, whereas varus laxity was restored only after MA TKA. Anterior translation was increased regardless of the alignment strategy. In addition, rotational laxities were restored after KA TKA, but external rotation laxity increased after MA TKA.

CONCLUSION

KA TKA restores femoral rollback and laxity to the native condition better than MA TKA. KA TKA may enhance functional performance and provide a more normal knee sensation.

LEVEL OF EVIDENCE

II, Controlled laboratory study.

Poor relationship between frontal tibiofemoral and trochlear anatomic parameters: Implications for designing a trochlea for kinematic alignment

BACKGROUND

The kinematic alignment (KA) technique for total knee arthroplasty (TKA) is an emerging implant positioning philosophy that aims to restore constitutional knee anatomy to improve knee kinematics. At present, the KA technique aims to reconstruct native femorotibial (FT) joint alignment, however there is still insufficient consideration towards the inter-individual trochlear anatomy variability. Poor trochlear restoration may compromise clinical outcomes. Our study aimed at assessing the anatomical relationship between the native trochlea and other FT anatomical parameters.

METHODS

Fifty-eight preoperative CT scans of low-grade knee arthritic patients were segmented to create 3D bone models. The FT and the PF anatomical parameters were measured using in-house software. Values were compared between different groups of lower limb and FT joint line (JL) orientation, and correlations between FT and PF anatomical parameters were assessed.

RESULTS

We were unable to detect any significant correlation between groove orientation (frontal and axial) or groove radius and either the hip-knee-ankle (HKA), or the lateral distal femoral (LDFA), or the medial proximal tibial (MPTA), or the FTJL-mechanical axis (FTJLMAA) Angles. When considering the correlation within sub-groups of limb or JL orientation, we only found a positive correlation (r = 0.464, p = 0.022) in the varus lower limb (HKA ≤ 180°) sub-group between groove frontal orientation and LDFA.

CONCLUSION

Our study shows that the determination of several limb, knee, and JL parameters is of poor value to predict individual trochlea anatomy. This raises the issue of how to improve femoral component design to achieve individualised FT and PF anatomical restoration with KATKA.

LEVEL OF EVIDENCE

Level 1 - computational study.

Kinematic alignment of current TKA implants does not restore the native trochlear anatomy

INTRODUCTION

Preserving constitutional patellofemoral anatomy, and thus producing physiological patellofemoral kinematics, could prevent patellofemoral complications and improve clinical outcomes after kinematically aligned TKA (KA TKA). Our study aims 1) to compare the native and prosthetic trochleae (planned or implanted), and 2) to estimate the safety of implanting a larger Persona^® femoral component size matching the proximal lateral trochlea facet height (flange area) in order to reduce the native articular surfaces understuffing generated by the prosthetic KA trochlea.

METHODS

Persona^® femoral component 3D model was virtually kinematically aligned on 3D bone-cartilage models of healthy knees by using a conventional KA technique (group 1, 36models, planned KA TKA) or an alternative KA technique (AT KA TKA) aiming to match the proximal (flange area) lateral facet height (10 models, planned AT KA TKA). Also, 13postoperative bone-implant (KA Persona^®) models were co-registered to the same coordinate geometry as their preoperative bone-cartilage models (group 2implanted KA TKA). In-house analysis software was used to compare native and prosthetic trochlea articular surfaces and medio-lateral implant overhangs for every group.

RESULTS

The planned and performed prosthetic trochleae were similar and valgus oriented (6.1 and 8.5, respectively), substantially proximally understuffed compared to the native trochlea. The AT KA TKAs shows a high rate of native trochlea surface overstuffing (70%, 90%, and 100% for lateral facet, groove, medial facet) and mediolateral implant overhang (60%). There was no overstuffing with conventional KA TKAs having their anterior femoral cut flush.

CONCLUSION

We found that with both the planned and implanted femoral components, the KA Persona^® trochlea was more valgus oriented and understuffed compared to the native trochlear anatomy. In addition, restoring the lateral trochlea facet height by increasing the femoral component size generated a high rate of trochlea overstuffing and mediolateral implant overhang. While restoring a native trochlea with KA TKA is not possible, the clinical impact of this is low, especially on PF complications. In current practice it is better to undersize the implants even if it does not restore the native anatomy. Longer follow-up is needed for KA TKAs performed with current implant, and the debate of developing new, more anatomic, implants specifically designed for KA technique is now opened.

LEVEL OF EVIDENCE

II, Laboratory controlled study.