A Dual-Pivot Pattern Simulating Native Knee Kinematics Optimizes Functional Outcomes After Total Knee Arthroplasty

Background Kinematics after total knee arthroplasty (TKA) have been studied for decades; however, few studies have correlated kinematic patterns to patient reported outcomes. The purpose of this study was to determine if a pattern of lateral pivot motion in early flexion and medial pivot motion in high flexion, simulating native knee kinematics, produces superior clinical outcomes. A second study objective was to determine if a specific kinematic pattern throughout the various ranges of flexion produces superior function and patient satisfaction. Methods 120 consecutive TKAs were performed using sensor embedded tibial trials to record intraoperative knee kinematics through the full range of motion. Established criteria were used to identify lateral (L) or medial (M) pivot kinematic patterns based on the center of rotation within three flexion zones -- 0 to 45° (early flexion), 45 to 90° (mid flexion) and 90° to terminal flexion (late flexion). Knee Society Scores, pain scores, and patient satisfaction were analysed in relationship to kinematic patterns. Results Knee Society function scores were significantly higher in TKAs with early lateral pivot/late medial pivot intraoperative kinematics compared to all other kinematic patterns (p = 0.018) at minimum one-year follow-up. There was a greater decrease in the proportion of patients with early lateral/late medial pivot kinematics who reported that their knee never feels normal (p = 0.011). Higher mean function scores at minimum one-year follow-up (p < 0.001) and improvement from preoperative baseline (p = 0.008) were observed in patients with the most ideal “LLM” kinematic pattern (lateral pivot 0 to 45o and 45 to 90o; medial pivot beyond 90o) compared to those with the least ideal “MLL” kinematic pattern. All patients with the optimal “LLM” kinematic pattern compared to none of those with the “MLL” kinematic pattern reported that they were very satisfied with their TKA (p = 0.003). Conclusion Patients who exhibited an early flexion lateral pivot kinematic pattern accompanied by medial pivot motion in later flexion, as measured intraoperatively, reported higher functional outcome scores along with higher overall patient satisfaction. Replicating the dual-pivot kinematic pattern observed in native knees may improve function and satisfaction after TKA. Further study is warranted to explore a correlation with in-vivo kinematic patterns

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

Do Medial Pivot Kinematics Correlate With Patient-Reported Outcomes After Total Knee Arthroplasty?

Background Many total knee arthroplasty (TKA) implants are designed to facilitate a medial pivot kinematic pattern. The purpose of this study was to determine whether intraoperative medial pivot kinematic patterns are associated with improved patient outcomes. Methods A retrospective review of consecutive primary TKAs was performed. Sensor-embedded tibial trials determined kinematic patterns intraoperatively. The center of rotation (COR) was identified from 0° to 90° and from 0° to terminal flexion, and designated medial-pivot or non-medial pivot based on accepted criteria. Patient-reported outcomes were measured preoperatively and at minimum one-year follow-up. Results The analysis cohort consisted of 141 TKAs. Mean age and median BMI were 63.7 years and 33.8 kg/m2, respectively. Forty-percent of TKAs demonstrated a medial pivot kinematic pattern intraoperatively. A medial pivot pattern was more common with posterior cruciate-retaining (CR) and posterior cruciate-substituting/anterior lipped (CS) implants when compared to posterior stabilized (PS) TKAs (P ≤.0150). Regardless of bearing type, minimum one-year Knee Society scores and UCLA activity level did not significantly differ based on medial vs non-medial pivot patterns (P ≥.292). For patients with posterior cruciate-sacrificing implants, there were trends for greater median improvement in Knee Society objective (46 vs 31.5 points, P =.057) and satisfaction (23 vs 14 points, P =.067) scores in medial pivot knees. Conclusion A medial pivot pattern may not significantly govern clinical success after TKA based on intraoperative kinematics and modern outcome measures. Further research is warranted to determine if a particular kinematic pattern promotes optimal clinical outcomes

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