90° Spinning of Polyethylene Inserts in Mobile Bearing Unicompartmental Knee Arthroplasty

<b>Background</b> The objective of this article is to describe for the first time a case of 90^° spin out of a mobile bearing unicompartmental knee arthroplasty (UKA) polyethylene insert. In this report, we present a 57-year-old gentleman with a medial compartment UKA for osteoarthritis in 2017 who developed dislodgement and 90^° rotation subsequent to traumatic injury when he was involved in a bus crash and impacted the anterolateral knee sustaining a valgus type injury 1 week postoperatively. Following the injury, he reported medial knee pain and a sensation of something moving within the joint. He was initially managed conservatively and progressed to full weight bearing; however, he experienced intermittent symptoms of catching and blocking of the joint, as well as medial knee swelling, that inhibited his ability to perform activities involving walking, kneeling, or pivoting. Imaging taken in 2018 show a 90° rotation of the polyethylene insert. These images showed the longitudinal metallic marker on the insert facing in an anteroposterior direction as opposed to the normal medial-lateral orientation. Failing conservative management, he presented to our clinic in 2019 and proceeded for revision of his UKA. Intraoperatively, his insert was reviewed and seen to easily spin on axis. The liner was therefore removed and upsized from a size 5 medium to a size 7 medium insert which provided excellent stability and stopped any further spinning. He has done tremendously well since the operation and reports full range of motion and no concerns. In patients with a history of pain, swelling, or locking following a UKA, it would be prudent to consider insert spinning, as well as the more common dislocation, through confirming the orientation of the metallic insert marker. Revision surgery to correct the spinning defect has proven effective with good resolution of symptoms and return to full range of motion.

Biomechanics of the medial meniscus in the osteoarthritic knee joint

Background Increased mechanical loading and pathological response of joint tissue to the abnormal mechanical stress can cause degradation of cartilage characteristic of knee osteoarthritis (OA). Despite osteoarthritis is risk factor for the development of meniscal lesions the mechanism of degenerative meniscal lesions is still unclear. Therefore, the aim of the study is to investigate the influence of medial compartment knee OA on the stress state and deformation of the medial meniscus. Methods The finite element method was used to simulate the stance phase of the gait cycle. An intact knee model was prepared based on magnetic resonance scans of the left knee joint of a healthy volunteer. Degenerative changes in the medial knee OA model were simulated by nonuniform reduction in articular cartilage thickness in specific areas and by a decrease in the material parameters of cartilage and menisci. Two additional models were created to separately evaluate the effect of alterations in articular cartilage geometry and material parameters of the soft tissues on the results. A nonlinear dynamic analysis was performed for standardized knee loads applied to the tibia bone. Results The maximum von Mises stress of 26.8 MPa was observed in the posterior part of the medial meniscus body in the OA model. The maximal hoop stress for the first peak of total force was 83% greater in the posterior horn and only 11% greater in the anterior horn of the medial meniscus in the OA model than in the intact model. The reduction in cartilage thickness caused an increase of 57% in medial translation of the medial meniscus body. A decrease in the compressive modulus of menisci resulted in a 2.5-fold greater reduction in the meniscal body width compared to the intact model. Conclusions Higher hoop stress levels on the inner edge of the posterior part of the medial meniscus in the OA model than in the intact model are associated with a greater medial translation of the meniscus body and a greater reduction in its width. The considerable increase in hoop stresses shows that medial knee OA may contribute to the initiation of meniscal radial tears.

Midterm Outcomes, Complications, and Return to Sports After Medial Collateral Ligament and Posterior Oblique Ligament Reconstruction for Medial Knee Instability: A Systematic Review

Background: In cases of multiple ligaments or medial collateral ligament (MCL) reconstruction, restoring the native anatomy of the posterior oblique ligament (POL) to address chronic valgus instability has been attracting increased attention. Purpose: To review the current literature on postoperative outcomes, complications, and return to sports after superficial MCL-POL (sMCL-POL) reconstruction to restore medial knee integrity. Study Design: Systematic review; Level of evidence, 4. Methods: A systematic review was conducted based on the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Two independent reviewers searched the PubMed, Scopus, Embase, and Cochrane Library databases using the terms “posterior oblique ligament,” “posteromedial corner of the knee,” and “reconstruction.” Included were studies that reported postoperative clinical and functional outcomes in patients who had undergone a combined sMCL-POL reconstruction for medial knee instability. The authors evaluated surgical technique, rehabilitation protocol, postoperative outcomes (Lysholm, International Knee Documentation Committee [IKDC], and Tegner scores and valgus stress radiograph), and return to sports and complication rates across the included studies. Results: A total of 6 studies were reviewed. The cohort consisted of 199 patients (121 men and 78 women), with a mean age of 32.7 ± 3.9 years (range, 27.4-36.6 years). The Lysholm and IKDC scores improved from pre- to postoperatively (Lysholm, from 67.2 ± 20.4 to 89.4 ± 3; IKDC, from 45.8 ± 2.1 to 84.8 ± 7.5). The Tegner score produced satisfactory results, from a preoperative mean of 3.3 ± 2.4 to 6.3 ± 0.9 postoperatively. The medial joint opening on valgus stress radiographs ranged from 7.5 ± 1.1 mm preoperatively to 3 ± 3.1 mm postoperatively. After passing activity-specific functional and clinical tests, 88% to 91.3% of the patients were reported to have returned to recreational sports within 6 to 12 months postoperatively, whereas 10% of the patients developed postoperative complications. Conclusion: Satisfactory clinical and functional outcomes, a high rate of return to recreational sports, and a low rate of postoperative complications were reported after an sMCL-POL reconstruction to restore medial knee integrity.