Purpose To evaluate if there was a correlation between in vivo kinematics of a medial-stabilized (MS) total knee arthroplasty (TKA) and post-operative clinical scores. We hypothesized that (1) a MS-TKA would produce a medial pivot movement and that (2) this speciic pattern would be correlated with higher clinical scores. Methods 18 patients were evaluated through clinical and functional scores evaluation (Knee Society Score clinical and functional, Womac, Oxford), and kinematically through dynamic radiostereometric analysis (RSA) at 9 months after MS-TKA, during the execution of a sit-to-stand and a lunge motor task. The anteroposterior (AP) Low Point translation of medial and lateral femoral compartments was compared through Student's t test (p < 0.05). A correlation analysis between scores and kinematics was performed through the Pearson's correlation coeicient r. Results A signiicantly greater (p < 0.0001) anterior translation of the lateral compartment with respect to the medial one was found in both sit-to-stand (medial 2.9 mm ± 0.7 mm, lateral 7.1 mm ± 0.6 mm) and lunge (medial 5.3 mm ± 0.9 mm, lateral 10.9 mm ± 0.7 mm) motor tasks, thus resulting in a medial pivot pattern in about 70% of patients. Signiicant positive correlation in sit-to-stand was found between the peak of AP translation in the lateral compartment and clinical scores (r = 0.59 for Knee Society Score clinical and r = 0.61 for Oxford). Moreover, we found that the higher peak of AP translation of the medial compartment correlated with lower clinical scores (r = − 0.55 for Knee Society Score clinical, r = − 0.61 for Womac and r = − 0.53 for Oxford) in the lunge. A negative correlation was found between Knee Society Score clinical and VV laxity during sit-to-stand (r = − 0.56) and peak of external rotation in the lunge motor task (r = − 0.66). Conclusions The MS-TKA investigated produced in vivo a medial pivot movement in about 70% of patients in both examined motor tasks. There was a correlation between the presence of medial pivot and higher post-operative scores. Level of evidence IV.

PurposeThe aim of the present study was to compare the in vivo under weight‐bearing kinematic behavior of a posterior‐stabilized (PS) and an ultra‐congruent (UC) total knee arthroplasty (TKA) model during a sit‐to‐stand motor task, a common activity of daily life. MethodsA cohort of 16 randomly selected patients (8 PS Persona Zimmer, 8 UC Persona Zimmer) was evaluated through dynamic radiostereometric analysis (RSA) at a minimum of 9 months after TKA, during the execution of a sit‐to‐stand. The anteroposterior (AP) translation of the femoral component and the AP translation of the low point of medial and lateral femoral compartments were compared through Student’s t test (p < 0.05). ResultsA significantly greater anterior translation of the femoral component was found for the PS group compared to the UC group. The flexion interval where statistical significance was found was between 30° and 0° (p = 0.017). Both groups showed a significantly greater anterior translation of the low point of the lateral compartment with respect to the medial one (PS: p = 0.012, UC: p = 0.018). This was consistent with a medial‐pivot pattern. Furthermore, a significantly greater anterior translation of the medial compartment was found in the PS group compared to the UC group (p = 0.001). The same pattern was observed for the lateral compartment (p = 0.006). ConclusionsThe TKA designs evaluated in the present study showed comparable in‐vivo kinematics with regards to medial pivot pattern but differences in absolute AP translation. Specifically, the UC design showed greater AP stability than the PS design. This finding could be positive in terms of implant stability, but negative in terms of premature polyethylene wear and thus implant failure. This remains to be verified in studies with a larger sample size and longer follow‐up. Level of evidenceIV.

Purpose To investigate if postoperative clinical outcomes correlate with specific kinematic patterns after total knee arthroplasty (TKA) surgery. The hypothesis was that the group of patients with higher clinical outcomes would have shown postoperative medial pivot kinematics, while the group of patients with lower clinical outcomes would have not. Methods 52 patients undergoing TKA surgery were prospectively evaluated at least a year of follow-up (13.5 ± 6.8 months) through clinical and functional Knee Society Score (KSS), and kinematically through dynamic radiostereometric analysis (RSA) during a sit-to-stand motor task. Patients received posterior-stabilized TKA design. Based on the result of the KSS, patients were divided into two groups: “KSS > 70 group”, patients with a good-to-excellent score (93.1 ± 6.8 points, n = 44); “KSS < 70 group”, patients with a fair-to-poor score (53.3 ± 18.3 points, n = 8). The anteroposterior (AP) low point (lowest femorotibial contact points) translation of medial and lateral femoral compartments was compared through Student’s t test (p < 0.05). Results Low point AP translation of the medial compartment was significantly lower (p < 0.05) than the lateral one in both the KSS > 70 (6.1 mm ± 4.4 mm vs 10.7 mm ± 4.6 mm) and the KSS < 70 groups (2.7 mm ± 3.5 mm vs 11.0 mm ± 5.6 mm). Furthermore, the AP translation of the lateral femoral compartment was not significantly different (p > 0.05) between the two groups, while the AP translation of the medial femoral compartment was significantly higher for the KSS > 70 group (p = 0.0442). Conclusion In the group of patients with a postoperative KSS < 70, the medial compartment translation was almost one-fourth of the lateral one. Surgeons should be aware that an over-constrained kinematic of the medial compartment might lead to lower clinical outcomes. Level of evidence II.

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PurposeThe purpose of the present study was to assess the kinematical behavior of a multi-radius posterior-stabilized (PS) mobile-bearing (MB) total knee arthroplasty (TKA) during an activity of daily living (Sit-To-Stand-STS) and a high demanding motor task (Deep-Knee-Lunge-DKL) using model-based dynamic RSA. We hypothesized the achievement of medial pivoting movement in both motor tasks due to the congruent geometry of the inlay with the femoral component, which should allow good stability of the medial compartment, and to the high magnitude of rotations guaranteed by the MB on the tibial side. Methods Twenty-two randomly selected patients were recruited and prospectively evaluated. The PS MB cemented TKA was implanted with the standard technique (medial parapatellar approach, adjusted mechanical alignment). At minimum 9-month follow-up, patients were examined with model based Dynamic RSA developed in our Institute (BI-STAND DRX 2) during the execution of two motor tasks: STS and DKL. The motion parameters were evaluated using the Grood and Suntay decomposition and the low-point kinematics methods. ResultsIn the extension phase of DKL femur performed a greater antero posterior translation of 3.8 mm compared to STS between 0° and 20° of knee lexion (p < 0.05). Low-point analysis showed a medial pivoting movement in both motor tasks: in 62% of patients during STS and 48% during DKL. Varus-valgus rotations were lower than 1° during all the range-of-motion in both motor tasks without diferences. Conclusions Medial pivot was partially produced by this multi-radius PS MB TKA with some diferences during activity of daily living (STS) and high demanding motor task (DKL). Level of evidence IV.