The Chitranjan S. Ranawat Award : No Difference in 2-year Functional Outcomes Using Kinematic versus Mechanical Alignment in TKA: A Randomized Controlled Clinical Trial

Mechanically aligned total knee arthroplasty carries a risk of bony gap changes and flexion-extension axis displacement

PURPOSE

The flexion-extension axis (FEA) of the femur is substantially changed after mechanically aligned total knee arthroplasty (TKA) due to a discrepancy in bone cut thickness between the posterior and distal femoral regions. This study assessed the bony gap changes and FEA displacement caused by this problem in osteoarthritis patients.

METHODS

The study enrolled 60 knees from 60 patients for whom primary TKA was planned due to medial knee osteoarthritis. All patients underwent computed tomography, and 3-dimensional (3D) bone models were reconstructed on 3D-planning software. Bone cuts of the distal femur and proximal tibia were simulated to be perpendicular to each mechanical axis. Bony gap change was computed as the difference in bone cut thickness between medial and lateral compartments. Each femoral condyle was assessed for potential FEA displacement, as the difference in bone cut thickness between posterior and distal femoral regions.

RESULTS

The mean magnitude of bony gap discrepancy necessary for mediolateral balancing was 1.6 ± 3.3 mm (range -7 to 8.2 mm) at 0° extension and -0.2 ± 2.6 mm (range -6.4 to 4.3 mm) at 90° flexion. At least 2 mm of bony gap discrepancy at 0° extension and 90° flexion was found in 40 patients (67%) and 26 patients (43%), respectively. In terms of femoral bone cut, posterior bone cut thickness was significantly larger than distal bone cut thickness in the medial compartment (p < 0.001). Bony gap discrepancy between distal and posterior regions of the femoral condyle was ≥2 mm in 28 patients (47%).

CONCLUSIONS

This study focused on two flaws of mechanically aligned TKA in OA patients. Substantial numbers of patients inevitably required >2 mm of medial collateral ligament release at 0° extension and showed a bone cut discrepancy between distal and posterior regions, carrying a risk of FEA displacement and subsequent unnatural knee motions during knee extension and flexion. Level of evidence IV.

The kinematic alignment technique for TKA reliably aligns the femoral component with the cylindrical axis

INTRODUCTION

Kinematic alignment (KA) technique is an alternative technique for positioning a TKA, which aims a patient-specific implant positioning in order to reproduce the pre-arthritic knee anatomy. Because reliability in implant positioning is of interest to obtain reproducible good functional results, our study tests the hypothesis that the medial and lateral distal and posterior positions of the planned and surgically implanted kinematically aligned femoral component are similar.

METHODS

Preoperative knee magnetic resonance imaging (MRI) and postoperative knee computed tomography (CT) of 13 patients implanted with a KA Persona^® TKA (Zimmer, Warsaw, USA) using manual instrumentation (kinematically-aligned TKA procedure pack^®, Zimmer Biomet, Warsaw, USA) were segmented to create 3D femoral models. The kinematic alignment position of the femoral component was planned on the 3D model created from the preoperative MRI. Differences in the positions of the planned and surgically implanted kinematically-aligned femoral component were determined with in-house analysis software.

RESULTS

The average differences between the medial and lateral distal and posterior positions of the planned and surgically implanted kinematically-aligned femoral component were inferior to 1mm and no statistically significant. In terms of variability, 62% (8/13) of performed implants matched all four positions within 1.5mm, and the maximum difference was 3mm.

CONCLUSION

In this small series, intraoperative kinematic positioning of the femoral component with the specific manual instrumentation closely matched the planned position, which suggests that this technique reliably aligned the flexion-extension axis of the femoral component to the cylindrical axis.

LEVEL OF EVIDENCE

Level 3.

Kinematic alignment is a possible alternative to mechanical alignment in total knee arthroplasty

PURPOSE

A systematic review was conducted to answer the following questions: (1) Does kinematically aligned (KA) total knee arthroplasty (TKA) achieve clinical outcomes comparable to those of mechanically aligned (MA) TKA? (2) How do the limb, knee, and component alignments differ between KA and MA TKA? (3) How is joint line orientation angle (JLOA) changed from the native knee in KA TKA compared to that in MA TKA?

METHODS

Nine full-text articles in English that reported the clinical and radiological outcomes of KA TKA were included. Five studies had a control group of patients who underwent MA TKA. Data on patient demographics, clinical scores, and radiological results were extracted. There were two level I, one level II, three level III, and three level IV studies. Six of the nine studies used patient-specific instrumentation, one study used computer navigation, and two studies used manual instrumentation.

RESULTS

The clinical outcomes of KA TKA were comparable or superior to those of MA TKA with a minimum 2-year follow-up. Limb and knee alignment in KA TKA was similar to those in MA TKA, and component alignment showed slightly more varus in the tibial component and slightly more valgus in the femoral component. The JLOA in KA TKA was relatively parallel to the floor compared to that in the native knee and not oblique (medial side up and lateral side down) compared to that in MA TKA. The implant survivorship and complication rate of the KA TKA were similar to those of the MA TKA.

CONCLUSION

Similar or better clinical outcomes were produced by using a KA TKA at early-term follow-up and the component alignment differed from that of MA TKA. KA TKA seemed to restore function without catastrophic failure regardless of the alignment category up to midterm follow-up. The JLOA in KA TKA was relatively parallel to the floor similar to the native knee compared to that in MA TKA. The present review of nine published studies suggests that relatively new kinematic alignment is an acceptable and alternative alignment to mechanical alignment, which is better understood. Further validation of these findings requires more randomized clinical trials with longer follow-up.

LEVEL OF EVIDENCE

Level II.

Do varus or valgus outliers have higher forces in the medial or lateral compartments than those which are in-range after a kinematically aligned total knee arthroplasty? limb and joint line alignment after kinematically aligned total knee arthroplasty

AIMS

The aims of this study were to determine the proportion of patients with outlier varus or valgus alignment in kinematically aligned total knee arthroplasty (TKA), whether those with outlier varus or valgus alignment have higher forces in the medial or lateral compartments of the knee than those with in-range alignment and whether measurements of the alignment of the limb, knee and components predict compartment forces.

PATIENTS AND METHODS

The intra-operative forces in the medial and lateral compartments were measured with an instrumented tibial insert in 67 patients who underwent a kinematically aligned TKA during passive movement. The mean of the forces at full extension, 45° and 90° of flexion determined the force in the medial and lateral compartments. Measurements of the alignment of the limb and the components included the hip-knee-ankle (HKA) angle, proximal medial tibial angle (PMTA), and distal lateral femoral angle (DLFA). Measurements of the alignment of the knee and the components included the tibiofemoral angle (TFA), tibial component angle (TCA) and femoral component angle (FCA). Alignment was measured on post-operative, non-weight-bearing anteroposterior (AP) scanograms and categorised as varus or valgus outlier or in-range in relation to mechanically aligned criteria.

RESULTS

The proportion of patients with outlier varus or valgus alignment was 16%/24% for the HKA angle, 55%/0% for the PMTA, 0%/57% for the DLFA, 25%/12% for the TFA, 100%/0% for the TCA, and 0%/64% for the FCA. In general, the forces in the medial and lateral compartments of those with outlier alignment were not different from those with in-range alignment except for the TFA, in which patients with outlier varus alignment had a mean paradoxical force which was 6 lb higher in the lateral compartment than those with in-range alignment. None of the measurements of alignment of the limb, knee and components predicted the force in the medial or lateral compartment.

CONCLUSION

Although kinematically aligned TKA has a high proportion of varus or valgus outliers using mechanically aligned criteria, the intra-operative forces in the medial and lateral compartments of patients with outlier alignment were comparable with those with in-range alignment, with no evidence of overload of the medial or lateral compartment of the knee. Cite this article: Bone Joint J 2017;99-B:1319-28.

Can kinematic tibial templates assist the surgeon locating the flexion and extension plane of the knee?

PURPOSE

We performed virtual feasibility and in-vivo validation studies to test whether the use of a kinematic tibial template (KTT) assists the surgeon in accurately locating the orientation of the F-E of the knee with low bias and high precision.

METHODS

With use of 166 3-dimensional bone models of normal knees, we designed seven KTTs that located the orientation of the F-E plane of the knee when best-fit within the cortical edge of the tibial resection. The virtual feasibility study asked 11 evaluators with different levels of surgical experience to use software and select, orient, and best-fit the KTT within the tibial resection of each bone model. The in-vivo validation study analyzed tibial component rotation on postoperative CT scans of 118 consecutive patients after one surgeon set the I-E rotation of the tibial component with a KTT when performing kinematically-aligned TKA. Bias and precision were computed as the mean and standard deviation of the differences between the A-P axis of the KTT and the F-E plane of the knee.

RESULTS

For the virtual feasibility study, the bias was 0.7° external and the precision was ±4.6° for 1826 KTT fittings, which were not affected by the level of surgical experience. For the in-vivo validation study, the bias was 0.1° external and the precision was ±3.9°.

CONCLUSIONS

The virtual feasibility and in-vivo validation studies suggest a KTT can assist the surgeon in accurately setting the I-E rotation of the tibial component parallel to the F-E plane of the knee when performing kinematically-aligned TKA.

Leaving Residual Varus Alignment After Total Knee Arthroplasty Does Not Improve Patient Outcomes

BACKGROUND

Recent popularity of kinematic alignment and constitutional varus has caused some surgeons to leave varus limbs in residual varus after total knee arthroplasty (TKA). This study assessed whether if patients left in residual varus have improved outcomes compared with those fully corrected to neutral alignment.

METHODS

A retrospective review of 361 consecutive primary TKAs was performed. Anatomic tibiofemoral alignment was measured and knees were categorized as neutral, varus, or valgus. Modern Knee Society scores and University of California Los Angeles Activity Level scores were collected at minimum 1-year follow-up.

RESULTS

After exclusions for confounds and loss to follow-up, 262 knees were available for analysis, 67% (176) of which were preoperatively varus. Sixty-six percent of varus knees were corrected to neutral, 25.6% were left in residual varus, and 8.5% were corrected to valgus. Median Knee Society objective scores at latest follow-up were greater in knees corrected to neutral (97), followed by knees corrected to varus (95), and valgus (93; P = .025), but post hoc comparisons between pairs of medians were not significant. There was no difference between groups in any other outcome measure (P ≥ .245) or the amount of improvement from baseline (P ≥ .423). Sixty percent of native varus patients corrected to neutral, 64% of those corrected to varus, and 40% of those corrected to valgus reported that their knee felt normal (P = .193).

CONCLUSION

Findings fail to support the notion that leaving varus knees in residual varus will improve outcomes and pain. Caution is advised when leaving limbs in residual varus after TKA.

Comparison of kinematic and mechanical alignment techniques in primary total knee arthroplasty: A meta-analysis

BACKGROUND

This meta-analysis compared clinical and radiographic outcomes and complications of kinematic alignment (KA) and mechanical alignment (MA) techniques in primary total knee arthroplasty (TKA).

METHODS

All studies comparing the operation time, change in hemoglobin, length of hospital stay, postoperative complications, and clinical and radiographic outcomes as assessed with various measurement tools, from direct interview to imaging methods, in patients who underwent primary TKA through the KA or MA technique were included.

RESULTS

Six studies were included in the meta-analysis. The proportion of patients who developed postoperative complications (OR: 1.10, 95% CI: 0.49-2.46; P = .69) did not differ significantly between the KA and MA techniques. The 2 groups were also similar in terms of change in hemoglobin (95% CI: -0.38 to 0.34; P = .91), length of hospital stay (95% CI: -0.04 to 0.55; P = .10), hip-knee-ankle angle (95% CI: -1.76 to 0.75; P = .43), joint line orientation angle (95% CI: -4.27 to 4.23; P = .99), tibial component slope (95% CI: -0.53 to 3.56; P = .15), and femoral component flexion (95% CI: -2.61 to 7.57; P = .34). In contrast, operation time (95% CI: -27.16 to -3.71; P = .01), overall functional outcome (95% CI: 6.59-11.51; P < .0001), knee anatomical axis (95% CI: -1.38 to -0.01; P = .05), femoral component relative to the mechanical axis (95% CI: -2.47 to -1.40; P < .0001), and tibial component relative to the mechanical axis (95% CI: 1.56-2.95; P < .0001) were significantly different between the 2 groups.

CONCLUSIONS

There were no significant differences in postoperative complications, change in hemoglobin, length of hospital stay, hip-knee-ankle angle, joint line orientation angle, tibial component slope, or femoral component flexion between the KA and MA techniques for primary TKA. However, the KA technique resulted in a significantly shorter operation time and better overall functional outcome than the MA technique, even though the femoral component was placed in a slightly more valgus position relative to the mechanical axis and the tibial component in a slightly more varus position with the KA technique.

Variability in static alignment and kinematics for kinematically aligned TKA

BACKGROUND

Total knee arthroplasty (TKA) significantly improves pain and restores a considerable degree of function. However, improvements are needed to increase patient satisfaction and restore kinematics to allow more physically demanding activities that active patients consider important. The aim of our study was to compare the alignment and motion of kinematically and mechanically aligned TKAs.

METHODS

A patient specific musculoskeletal computer simulation was used to compare the tibio-femoral and patello-femoral kinematics between mechanically aligned and kinematically aligned TKA in 20 patients.

RESULTS

When kinematically aligned, femoral components on average resulted in more valgus alignment to the mechanical axis and internally rotated to surgical transepicondylar axis whereas tibia component on average resulted in more varus alignment to the mechanical axis and internally rotated to tibial AP rotational axis. With kinematic alignment, tibio-femoral motion displayed greater tibial external rotation and lateral femoral flexion facet centre (FFC) translation with knee flexion than mechanical aligned TKA. At the patellofemoral joint, patella lateral shift of kinematically aligned TKA plateaued after 20 to 30° flexion while in mechanically aligned TKA it decreased continuously through the whole range of motion.

CONCLUSIONS

Kinematic alignment resulted in greater variation than mechanical alignment for all tibio-femoral and patello-femoral motion. Kinematic alignment places TKA components patient specific alignment which depends on the preoperative state of the knee resulting in greater variation in kinematics. The use of computational models has the potential to predict which alignment based on native alignment, kinematic or mechanical, could improve knee function for patient's undergoing TKA.

Early Outcomes of Kinematic Alignment in Primary Total Knee Arthroplasty: A Meta-Analysis of the Literature

BACKGROUND

Kinematic alignment in total knee arthroplasty (TKA) seeks to more anatomically align the knee prosthesis to promote more physiological kinematics. However, there are questions about the durability, function, and complication rate of a non-mechanically aligned TKA. Therefore, the purpose of this study is to perform a systematic review and meta-analysis to evaluate early outcomes after kinematic alignment.

METHODS

Two independent reviewers performed a systematic review of the English literature using both the MEDLINE and Embase databases searching for studies on kinematic TKA. Of the initial 839 published reports, 9 studies were included in the review. Four randomized, controlled trials comparing outcomes of kinematic and conventional alignment TKA were identified. Data were extracted and aggregated using inverse variance and Mantel-Haenszel fixed effects meta-analysis.

RESULTS

Of an aggregated 877 kinematic TKAs, the cumulative survivorship was 97.4% at a weighted mean follow-up of 37.9 months. The most common reasons for revision were patellofemoral problems in 8 patients (1.2%). We found no difference in the complication rate between the 229 kinematic and 229 conventional TKA patients (3.9% vs 4.4%; P = .83). The kinematic TKA group had a higher combined postoperative Knee Society Score than the conventional TKA group (mean difference, 9.1 points; 95% confidence interval, 5.2-13.0 points; P < .001).

CONCLUSION

Small deviations from the traditional mechanical axis alignment in TKA do not appear to impact overall survivorship or complication rates at short-term follow-up. Functional outcome as measured by the Knee Society Score favored kinematic alignment. These preliminary results illustrate the concept that there may be more than a single alignment target for all patients undergoing primary TKA.

What mechanisms are associated with tibial component failure after kinematically-aligned total knee arthroplasty?

PURPOSE

Eight patients treated with kinematically-aligned (KA) total knee arthroplasty (TKA) presented with tibial component failure. We determined whether radiographic measurements and clinical characteristics are different between patients with and without tibial component failure to identify mechanisms of failure and strategies to reduce the risk.

METHODS

Out of 3,212 primary TKAs (2,725 TKAs with a two-year minimum follow up), of which all were performed with KA, eight patients presented with tibial component failure. Radiographic measurements, clinical characteristics (e.g. age, gender, BMI, etc.), revision surgical records, and Oxford knee scores were compared to control cohort patients matched 1:3.

RESULTS

Tibial component failure presented at an average of 28 ± 15 months after primary TKA. Patients with tibial component failure had a 6 kg/m² greater body mass index (p = 0.034) and 5° greater posterior slope of the tibia component (p = 0.002) than controls. Final follow-up averaged 56 ± 19 months after the primary TKA and 28 ± 24 months after the revision TKA. The final Oxford knee score was 39 ± 4.6 for patients with tibial component failure and 44 ± 6.5 for the controls (p = 0.005).

CONCLUSIONS

The incidence of tibial component failure after KA TKA was 0.3% and was caused by posterior subsidence or posterior edge wear and not varus subsidence. The strategy for lowering the risk of tibial component failure when performing KA is to set the tibial component parallel to the flexion-extension plane (slope) and varus-valgus plane of the native joint line.