Search Results (3)

Background: Patellofemoral instability arises from the interplay between trochlear morphology and malalignment of the extensor vector. Although each factor is individually well described, their combined mechanical effects have not been quantified within a single finite element framework. Objective: To investigate how lateral trochlear inclination (LTI) and tibial tuberosity position interact to influence patellofemoral contact mechanics and stability across clinically relevant knee flexion angles. Methods: A subject-specific finite element model of the femur–patella–tibia complex was reconstructed from high-resolution CT data. Cortical and cancellous bone, patellar cartilage, the MPFL, and patellar tendon were included. Three trochlear morphologies were simulated (LTI = 15°, 10°, 5°) under native alignment (Case A) and after 10 mm lateral tibial tuberosity translation (Case B). Flexion at 30°, 60°, and 90° was imposed via solver-applied tibial displacement. Primary outcomes were contact pressure, contact area, MPFL stress, and lateral patellar translation. Instability was defined as >5 mm lateral translation or >50% reduction in contact area, consistent with the biomechanical literature. Model convergence (<5% variation) and validation against cadaveric pressure data were performed; a sensitivity analysis tested material property variation (±15%). Results: The native model reproduced peak pressures (3.6 MPa at 60°) within 9% of experimental benchmarks. Decreasing LTI enlarged the contact patch and lowered mean pressures (−18%) but increased MPFL stress (+37%). Tibial tuberosity lateralisation reduced mean pressures further (−25%), yet, when combined with shallow trochlear slopes (≤8°), produced >5 mm lateral patellar translation and near-complete loss of cartilage contact by 60°, simulating lateral dislocation. Sensitivity testing confirmed robustness to material property uncertainty. Conclusions: Shallow trochlear inclination dissipates articular load but destabilises the patella, an effect magnified by tibial tuberosity lateralisation. While these findings highlight thresholds at which stability may be compromised, they derive from a single-subject model and should be interpreted as hypothesis-generating rather than prescriptive. Broader validation across multiple geometries and loading conditions is required before clinical translation. Full article

A non-reducible tibial tuberosity fracture is a rare complication of tibial tuberosity transposition performed during correcting of medial patella luxation (MPL) in dogs. This condition severely disrupts the quadriceps extensor mechanism, leading to significant pelvic limb lameness. An 11-year-old, 1.8 kg spayed female Yorkshire Terrier sustained a comminuted left tibial tuberosity fracture during surgical correction of an MPL. Six months after surgery, the dog was markedly lame and unable to extend the left stifle. Radiographs revealed patella alta and resorption of the fragmented tibial tuberosity. A composite frozen allogeneic calcaneal tendon–bone block was utilized to reconstruct the tibial tuberosity and reattach the patellar ligament. Initial postoperative radiographs confirmed restoration of a normal patellar ligament to patella length ratio (1.42). Both the allogeneic bone used for tibial tuberosity reconstruction and the tendon used to reattach the patellar ligament were successfully integrated. The dog regained satisfactory limb function without recurrence of patella luxation, as reported by the owners 29 months postoperatively. The use of a calcaneal tendon–bone allograft effectively restored the functional integrity of the quadriceps extensor mechanism, providing a viable option for addressing quadriceps insufficiency resulting from the loss of the osseous tibial insertion. Full article

Background: While off-the-shelf cones and sleeves yield good results in AORI type 2 and 3 defects in revision knee surgery, massive longitudinal defects may require a proximal tibia replacement. To achieve the best anatomical as well as biomechanical reconstruction and preserve the tibial tuberosity, we developed custom-made metaphyseal sleeves (CMSs) to reconstruct massive defects with a hinge knee replacement. Methods: Between 2019 and 2022, 10 patients were treated in a single-center study. The indication for revision was aseptic loosening in five cases and periprosthetic joint infection in five cases. The mean number of previous revisions after the index operations was 7 (SD: 2; 4–12). A postoperative analysis was conducted to evaluate the functional outcome as well as the osteointegrative potential. Results: Implantation of the CMS in rTKA was carried out in all cases, with a mean operation time of 155 ± 48 (108–256) min. During the follow-up of 23 ± 7 (7–31) months, no CMS was revised and revisions due to other causes were conducted in five cases. Early radiographic evidence of osseointegration was recorded using a validated method. The postoperative OKS showed a significant increase (p < 0.001), with a mean score of 24 (SD: 4; range: 14–31). Conclusion: Custom-made metaphyseal sleeves show acceptable results in extreme cases. As custom-made components become more and more common, this treatment algorithm presents a viable alternative in complex rTKA. Full article