Posterior-stabilized versus mid-level constraint polyethylene components in total knee arthroplasty.

Aims: Mid-level constraint designs for total knee arthroplasty (TKA) are intended to reduce coronal plane laxity. Our aims were to compare kinematics and ligament forces of the Zimmer Biomet Persona posterior-stabilized (PS) and mid-level designs in the coronal, sagittal, and axial planes under loads simulating clinical exams of the knee in a cadaver model. Methods: We performed TKA on eight cadaveric knees and loaded them using a robotic manipulator. We tested both PS and mid-level designs under loads simulating clinical exams via applied varus and valgus moments, internal-external (IE) rotation moments, and anteroposterior forces at 0°, 30°, and 90° of flexion. We measured the resulting tibiofemoral angulations and translations. We also quantified the forces carried by the medial and lateral collateral ligaments (MCL/LCL) via serial sectioning of these structures and use of the principle of superposition. Results: Mid-level inserts reduced varus angulations compared to PS inserts by a median of 0.4°, 0.9°, and 1.5° at 0°, 30°, and 90° of flexion, respectively, and reduced valgus angulations by a median of 0.3°, 1.0°, and 1.2° (p ≤ 0.027 for all comparisons). Mid-level inserts reduced net IE rotations by a median of 5.6°, 14.7°, and 17.5° at 0°, 30°, and 90°, respectively (p = 0.012). Mid-level inserts reduced anterior tibial translation only at 90° of flexion by a median of 3.0 millimetres (p = 0.036). With an applied varus moment, the mid-level insert decreased LCL force compared to the PS insert at all three flexion angles that were tested (p ≤ 0.036). In contrast, with a valgus moment the mid-level insert did not reduce MCL force. With an applied internal rotation moment, the mid-level insert decreased LCL force at 30° and 90° by a median of 25.7 N and 31.7 N, respectively (p = 0.017 and p = 0.012). With an external rotation moment, the mid-level insert decreased MCL force at 30° and 90° by a median of 45.7 N and 20.0 N, respectively (p ≤ 0.017 for all comparisons). With an applied anterior load, MCL and LCL forces showed no differences between the two inserts at 30° and 90° of flexion. Conclusion: The mid-level insert used in this study decreased coronal and axial plane laxities compared to the PS insert, but its stabilizing benefit in the sagittal plane was limited. Both mid-level and PS inserts depended on the MCL to resist anterior loads during a simulated clinical exam of anterior laxity.

Bayesian Calibration of Computational Knee Models to Estimate Subject-Specific Ligament Properties, Tibiofemoral Kinematics, and Anterior Cruciate Ligament Force With Uncertainty Quantification.

High-grade knee laxity is associated with early anterior cruciate ligament (ACL) graft failure, poor function, and compromised clinical outcome. Yet, the specific ligaments and ligament properties driving knee laxity remain poorly understood. We described a Bayesian calibration methodology for predicting unknown ligament properties in a computational knee model. Then, we applied the method to estimate unknown ligament properties with uncertainty bounds using tibiofemoral kinematics and ACL force measurements from two cadaver knees that spanned a range of laxities; these knees were tested using a robotic manipulator. The unknown ligament properties were from the Bayesian set of plausible ligament properties, as specified by their posterior distribution. Finally, we developed a calibrated predictor of tibiofemoral kinematics and ACL force with their own uncertainty bounds. The calibrated predictor was developed by first collecting the posterior draws of the kinematics and ACL force that are induced by the posterior draws of the ligament properties and model parameters. Bayesian calibration identified unique ligament slack lengths for the two knee models and produced ACL force and kinematic predictions that were closer to the corresponding in vitro measurement than those from a standard optimization technique. This Bayesian framework quantifies uncertainty in both ligament properties and model outputs; an important step towards developing subject-specific computational models to improve treatment for ACL injury.

Lateral Extra-articular Tenodesis Alters Lateral Compartment Contact Mechanics under Simulated Pivoting Maneuvers: An In Vitro Study.

BACKGROUND: There is concern that utilization of lateral extra-articular tenodesis (LET) in conjunction with anterior cruciate ligament (ACL) reconstruction (ACLR) may disturb lateral compartment contact mechanics and contribute to joint degeneration. HYPOTHESIS: ACLR augmented with LET will alter lateral compartment contact mechanics in response to simulated pivoting maneuvers. STUDY DESIGN: Controlled laboratory study. METHODS: Loads simulating a pivot shift were applied to 7 cadaveric knees (4 male; mean age, 39 ± 12 years; range, 28-54 years) using a robotic manipulator. Each knee was tested with the ACL intact, sectioned, reconstructed (via patellar tendon autograft), and, finally, after augmenting ACLR with LET (using a modified Lemaire technique) in the presence of a sectioned anterolateral ligament and Kaplan fibers. Lateral compartment contact mechanics were measured using a contact stress transducer. Outcome measures were anteroposterior location of the center of contact stress (CCS), contact force from anterior to posterior, and peak and mean contact stress. RESULTS: On average, augmenting ACLR with LET shifted the lateral compartment CCS anteriorly compared with the intact knee and compared with ACLR in isolation by a maximum of 5.4 ± 2.3 mm (P < .001) and 6.0 ± 2.6 mm (P < .001), respectively. ACLR augmented with LET also increased contact force anteriorly on the lateral tibial plateau compared with the intact knee and compared with isolated ACLR by a maximum of 12 ± 6 N (P = .001) and 17 ± 10 N (P = .002), respectively. Compared with ACLR in isolation, ACLR augmented with LET increased peak and mean lateral compartment contact stress by 0.7 ± 0.5 MPa (P = .005) and by 0.17 ± 0.12 (P = .006), respectively, at 15° of flexion. CONCLUSION: Under simulated pivoting loads, adding LET to ACLR anteriorized the CCS on the lateral tibial plateau, thereby increasing contact force anteriorly. Compared with ACLR in isolation, ACLR augmented with LET increased peak and mean lateral compartment contact stress at 15° of flexion. CLINICAL RELEVANCE: The clinical and biological effect of increased anterior loading of the lateral compartment after LET merits further investigation. The ability of LET to anteriorize contact stress on the lateral compartment may be useful in knees with passive anterior subluxation of the lateral tibia.

Lateral Extra-articular Tenodesis Reduces Anterior Cruciate Ligament Graft Force and Anterior Tibial Translation in Response to Applied Pivoting and Anterior Drawer Loads.

BACKGROUND: The biomechanical effect of lateral extra-articular tenodesis (LET) performed in conjunction with anterior cruciate ligament (ACL) reconstruction (ACLR) on load sharing between the ACL graft and the LET and on knee kinematics is not clear. PURPOSE/HYPOTHESIS: The purpose was to quantify the effect of LET on (1) forces carried by both the ACL graft and the LET and (2) tibiofemoral kinematics in response to simulated pivot shift and anterior laxity tests. We hypothesized that LET would decrease forces carried by the ACL graft and anterior tibial translation (ATT) in response to simulated pivoting maneuvers and during simulated tests of anterior laxity. STUDY DESIGN: Controlled laboratory study. METHODS: Seven cadaveric knees (mean age, 39 ± 12 years [range, 28-54 years]; 4 male) were mounted to a robotic manipulator. The robot simulated clinical pivoting maneuvers and tests of anterior laxity: namely, the Lachman and anterior drawer tests. Each knee was assessed in the following states: ACL intact, ACL sectioned, ACL reconstructed (using a bone-patellar tendon-bone autograft), and after performing LET (the modified Lemaire technique after sectioning of the anterolateral ligament and Kaplan fibers). Resultant forces carried by the ACL graft and LET at the peak applied loads were determined via superposition. ATT was determined in response to the applied loads. RESULTS: With the applied pivoting loads, performing LET decreased ACL graft force up to 80% (44 ± 12 N; P < .001) and decreased ATT of the lateral compartment compared with that of the intact knee up to 7.6 ± 2.9 mm (P < .001). The LET carried up to 91% of the force generated in the ACL graft during isolated ACLR (without LET). For simulated tests of anterior laxity, performing LET decreased ACL graft force by 70% (40 ± 20 N; P = .001) for the anterior drawer test with no significant difference detected for the Lachman test. No differences in ATT were deteced between ACLR with LET and the intact knee on both the Lachman and the anterior drawer tests (P = .409). LET reduced ATT compared with isolated ACLR on the simulated anterior drawer test by 2.4 ± 1.8 mm (P = .032) but not on the simulated Lachman test. CONCLUSION: In a cadaveric model, LET in combination with ACLR transferred loads from the ACL graft to the LET and reduced ATT with applied pivoting loads and during the simulated anterior drawer test. The effect of LET on ACL graft force and ATT was less pronounced on the simulated Lachman test. CLINICAL RELEVANCE: LET in addition to ACLR may be a suitable option to offload the ACL graft and to reduce ATT in the lateral compartment to magnitudes less than that of the intact knee with clinical pivoting maneuvers. In contrast, LET did not offload the ACL graft or add to the anterior restraint provided by the ACL graft during the Lachman test.

Single- Versus Double-Row Repair of Hip Abductor Tears: A Biomechanical Matched Cadaver Study.

PURPOSE: The purposes of this study were (1) to evaluate the percentage of gluteus medius and minimus tendon footprint restoration that can be achieved with fixation using single-row repair versus double-row repair and (2) to evaluate the yield load of a repair of the gluteus medius and minimus tendon using single-row versus double-row repair techniques. METHODS: Twelve human fresh-frozen cadaveric hip specimens (6 matched pairs, 4 female, mean age 47.5 ± 14.5 years) were tested. Specimens were excluded if they had any prior hip surgery or injury, if any abnormality of the tendon was noted on dissection, or if they had a body mass index <20 or >35 or a T-score <2.0 on dual-energy x-ray absorptiometry scanning. Matched pairs were randomized to receive either double-row repair with 2 standard suture anchors and 2 knotless anchor devices or a single-row repair with suture anchors only. The percentage of the footprint area covered after repair was determined using a computer-assisted digitization algorithm. With a mechanical testing system, each repaired specimen was tested for mechanical strength first with cyclic loading and then load to failure testing. RESULTS: Footprint coverage of the lateral facet was significantly greater for double-row repair (mean 76.6%) compared with single-row repair (mean 50.3%) (P = .03). There was no significant difference between single- and double-row repair for posterior-superior or anterior facet coverage. Mechanical testing showed a higher mean yield load for double-row anchor repair (197.6 ± 61.7 N vs 163.5 ± 35.4 N for single-row repair), but this did not reach statistical significance (P = .15). The predominant mode of failure was suture pullout through the musculotendinous unit (9/12 specimens: 5 double-row and 4 single-row). CONCLUSIONS: For hip abductor tears, double-row suture repair yields improved footprint coverage compared with single-row repair. Although it did not reach statistical significance, there was a higher mean yield load in the double-row group. CLINICAL RELEVANCE: Double-row suture fixation technique for hip abductor tears maximizes strength and footprint coverage of the repair.

The lateral collateral ligament complex of the elbow: quantitative anatomic analysis of the lateral ulnar collateral, radial collateral, and annular ligaments.

BACKGROUND: Injury to the lateral ulnar collateral ligament (LUCL) complex of the elbow often results in posterolateral rotatory instability. Although surgical reconstruction of the LUCL is often required, gaps in our understanding of the LUCL complex remain. The purpose of this study was to provide a robust and accurate characterization of the lateral elbow ligamentous complex. METHODS: The LUCLs, radial collateral ligaments, and annular ligaments in 10 cadaveric elbows were 3-dimensionally digitized and reconstructed using computed tomography. Surface areas, origin and insertion footprint areas, distances between perceived footprint centers and geometric footprint centroids, distances to key landmarks, and ligament isometry were measured. RESULTS: The mean surface area of the LUCL was 229.3 mm2. The mean origin and insertion footprint areas were 26.0 mm2 and 22.9 mm2, respectively. The mean distance between the apparent centers and the geometric centroids of the footprints was 1 mm. The center of the LUCL origin was 10.7 mm distal to the lateral epicondyle and 8.2 mm from the capitellar articular margin. The center of the LUCL insertion was 3.3 mm distal to the apex of the supinator crest. The LUCL showed anisometric properties as elbow flexion increased (P < .001). CONCLUSIONS: The LUCL origin center was 10.7 mm from the lateral epicondyle, whereas the insertion center was 3.3 mm from the apex of the supinator crest. The visually estimated footprint centers were generally within 1 mm of the geometric centroid. These geometries and distances to key landmarks will be informative for surgeons seeking to perform anatomic ligament reconstruction procedures.

Quantitative Anatomic Analysis of the Medial Ulnar Collateral Ligament Complex of the Elbow.

BACKGROUND: A more detailed assessment of the anatomy of the entire medial ulnar collateral ligament complex (MUCLC) is desired as the rate of medial elbow reconstruction surgery continues to rise. PURPOSE: To quantify the anatomy of the MUCLC, including the anterior bundle (AB), posterior bundle (PB), and transverse ligament (TL). STUDY DESIGN: Descriptive laboratory study. METHODS: Ten unpaired, fresh-frozen cadaveric elbows underwent 3-dimensional (3D) digitization and computed tomography with 3D reconstruction. Ligament footprint areas and geometries, distances to key bony landmarks, and isometry were determined. A surgeon digitized the visual center of each footprint, and this location was compared with the geometric centroid calculated from the outline of the digitized footprint. RESULTS: The mean surface area of the AB was 324.2 mm2, with an origin footprint of 32.3 mm2 and an elongated insertional footprint of 187.6 mm2 (length, 29.7 mm). The mean area of the PB was 116.6 mm2 (origin, 25.9 mm2; insertion, 15.8 mm2), and the mean surface area of the TL was 134.5 mm2 (origin, 21.2 mm2; insertion, 16.7 mm2). The geometric centroids of all footprints could be predicted within 0.8 to 1.3 mm, with the exception of the AB insertion centroid, which was 7.6 mm distal to the perceived center at the apex of the sublime tubercle. While the PB remained relatively isometric from 0° to 90° of flexion (P = .606), the AB lengthened by 2.2 mm (P < .001). CONCLUSION: Contrary to several historical reports, the insertional footprint of the AB was larger, elongated, and tapered. The TL demonstrated a previously unrecognized expansive soft tissue insertion directly onto the AB, and additional analysis of the biomechanical contribution of this structure is needed. CLINICAL RELEVANCE: These findings may serve as a foundation for future study of the MUCLC and help refine current surgical reconstruction techniques.

Evaluation of Knee Ligament Mechanics Using Computational Models.

The steady maturation of computational biomechanics is providing the musculoskeletal health community with exciting avenues for enhancing orthopedic practice and rehabilitation. Computational knee models deliver tools that may improve the efficiency and outcomes of orthopedic research and methods through analysis of virtual surgeries and devices. They also provide insight into the interaction of knee structures and can predict what cannot be directly measured such as loading on our cartilage and ligaments during movement. This project created subject-specific computational knee models of two young adult females using magnetic resonance imaging-derived knee geometries and passive leg motion measured by a motion capture system. The knee models produced passive ligament lengthening patterns similar to experimental measurements available in the literature. The models also predicted cruciate ligament forces during passive flexion with and without applying anterior-posterior tibia forces that were similar to experimental measurements available in the literature. The biomechanics of the posterior oblique ligament (POL) and the anterior cruciate ligament bundles during combined tibia internal-external rotation torque and anterior-posterior forces through deep flexion were then examined. The study showed that the central arm of the POL: (1) produces a maximum constraining force when the knee is at full extension, (2) constrains internal tibial rotation at extension, and (3) constrains posterior tibial translation at extension. The POL reinforces the constraint of the anterior cruciate ligament to internal rotation at extension and provides constraint for posterior tibial translation at extension, a position where the posterior cruciate ligament provides minimal posterior translation constraint.

Predicted loading on the menisci during gait: The effect of horn laxity.

Radiographic measurements have established a link between meniscus extrusion and meniscus degeneration as well as with knee osteoarthritis. The presented work combines medical imaging with motion capture data from two healthy female subjects to create subject specific knee models that predict tibio-menisco-femoral contact forces and ligament forces during muscle driven simulations of barefoot gait. The developed computational models were used to explore the relationship between the extent of meniscal extrusion and biomechanical function by altering the laxity of the meniscal horn attachments during gait. The extrusion distance increased as laxity increased and the amount of contact force transferred through the menisci during gait decreased rapidly as the meniscal attachments became more lax. Horn attachment lengths that were 20% longer than MRI attachment lengths resulted in an almost complete loss of force transfer through the menisci during the gait cycle. Relatively small changes (2-3mm) in the lengths at which horn bundles first become taut, manifested in large changes in the capacity of the tissue to transmit forces. As meniscal horn attachment laxity increased from 80% to 120% of the MRI measured horn distance, medial meniscus extrusion increased 3.9mm for the first subject and 2.7mm for the second subject. For the same horn laxity changes, the percent of medial tibiofemoral contact force transmitted through the medial meniscus during early stance decreased from 51% to 8% and from 36% to 14% for the two subjects. The results of our study show that increased meniscal extrusion occurs with increased laxity of the meniscal tibia attachments and this increased laxity results in loss of meniscal function.