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.

Incorporating population-level variability in orthopedic biomechanical analysis: a review.

Effectively addressing population-level variability within orthopedic analyses requires robust data sets that span the target population and can be greatly facilitated by statistical methods for incorporating such data into functional biomechanical models. Data sets continue to be disseminated that include not just anatomical information but also key mechanical data including tissue or joint stiffness, gait patterns, and other inputs relevant to analysis of joint function across a range of anatomies and physiologies. Statistical modeling can be used to establish correlations between a variety of structural and functional biometrics rooted in these data and to quantify how these correlations change from health to disease and, finally, to joint reconstruction or other clinical intervention. Principal component analysis provides a basis for effectively and efficiently integrating variability in anatomy, tissue properties, joint kinetics, and kinematics into mechanistic models of joint function. With such models, bioengineers are able to study the effects of variability on biomechanical performance, not just on a patient-specific basis but in a way that may be predictive of a larger patient population. The goal of this paper is to demonstrate the broad use of statistical modeling within orthopedics and to discuss ways to continue to leverage these techniques to improve biomechanical understanding of orthopedic systems across populations.

Quantification of the passive behavior of the glenohumeral joint: A biomechanical study.

Shoulder stabilization and arthroplasty procedures aim to restore the complex motion innate to the glenohumeral joint relying on proper tensioning of the surrounding soft-tissues at the time of surgery. Joint instability remains a leading cause for revisions of these procedures necessitating a deeper understanding of the passive constraint of the intact glenohumeral joint. The current literature lacks comprehensive analysis of the passive glenohumeral joint in all degrees-of-freedom (DOF). The objective of the present study is to better understand this complex joint by quantifying the passive laxity of the glenohumeral joint in multiple DOFs over a range of motion. Sixteen fresh-frozen cadaveric shoulders were tested in the intact state using a robotic simulator capable of six-DOF motion. The limits of range of motion was quantified in separate laxity tests applying a ± 2 Nm internal-external (IE) torque, ±20 N anterior-posterior (AP) force, ±20 N superior-inferior (SI) force and a 44 N distraction force at six levels of glenohumeral abduction. Overall, glenohumeral joint laxity was greatest between 15° and 45° of abduction except for SI translation which increased with abduction. IE rotation and AP translation were dominated by external rotation and anterior translation, respectively. Although early abduction and late abduction produced similar laxities, the increase in laxity in the mid abduction range indicates it is important to assess the shoulder joint throughout the range of motion and not just at these two end points. The presented laxity data establishes a baseline for intact shoulder laxity over a range of motion in multiple DOFs under known loading conditions.

Treatment of Medial Collateral Ligament Injury During Total Knee Arthroplasty With Internal Suture Brace Augmentation: A Cadaveric and Biomechanical Study.

Intraoperative medial collateral ligament (MCL) injury during total knee arthroplasty (TKA) is a serious complication. External bracing and/or conversion to a constrained implant has previously been studied. The technique of using an internal high-strength suture brace to augment an MCL repair has been evaluated in the nonarthroplasty patient and could provide an alternate solution. The goal of this study was to determine whether MCL repair with internal suture bracing restores stability of the implanted knee joint. A robotic simulator completed laxity testing on 5 cadaveric knee specimens in 4 sequential phases: (1) intact knee, (2) after implantation with TKA, (3) after sectioning of the MCL, and (4) after MCL repair with suture brace augmentation. Laxity was compared between the different test phases throughout range of motion. Subsequently, the internal brace was tested to failure under valgus load. The MCL repair with internal bracing was effective at restoring laxity in varus-valgus, internal-external, and medial-lateral degrees of freedom through midflexion, with limited support at deeper flexion angles and in anterior-posterior laxity. Rotational laxity was not significantly different than intact knee laxity. Generally, medial-lateral translations were less and anterior-posterior translations were greater and were significantly different at 30° to 45° and 90°, respectively. The mean failure moment was 46.4±9.1 Nm, with the primary mode of failure being MCL repair. Primary MCL repair with internal bracing using a high-strength suture augment showed the potential to provide adequate stability and strength to correct MCL incompetence in TKA without the use of an external knee brace or constrained implants. [Orthopedics. 2022;45(5):e269-e275.].

A Morphometric Fixed-Bearing Unicompartmental Knee Arthroplasty Can Reproduce Normal Knee Kinematics. An In Vitro Robotic Evaluation.

Background: A new morphometric fixed-bearing unicompartmental knee arthroplasty (UKA) system has been introduced to address the anatomical patient-specific challenges. It was our hypothesis that accurate restoration of the patient-specific anatomy would restore normal knee kinematics after UKA. Therefore, we aimed in this cadaveric study to analyze the impact of a medial morphometric UKA on (1) the varus-valgus and anterior-posterior stability of the knee, (2) the knee kinematics during standardized activities of the daily living, and (3) the patellar tracking, measured using a dedicated robotic testing protocol. Methods: Eight human knee specimens underwent full-leg computed tomography CT scanning and comprehensive robotic assessments of tibiofemoral and patellofemoral kinematics. Specimens were tested in the intact state and after implantation of a fixed-bearing medial UKA. Assessments included passive flexion, laxity testing and simulations of level walking, lunge, and stair descent. Results: Medial and lateral joint laxity after UKA closely resembled intact laxity across the full arc of flexion. Anterior-posterior envelope of motion showed a close match between the intact and UKA groups. Net rollback and average laxity were both not statistically different. Simulation of activities of daily living showed a close match in the anterior-posterior motion profile between the medial condyle and lateral condyle. Patellar tilt and medial-lateral shift during knee flexion matched closely between groups. Conclusion: Functional assessment of this UKA system shows nearly identical behavior to the intact knee. Fixed-bearing UKA with morphometric, compartment-specific geometry and precise mechanical instrumentation replicates complex knee balance and kinematics.