Tissue-specific changes in size and shape of the ligaments and tendons of the porcine knee during post-natal growth

Equine subchondral lucencies: Knowledge from the medial femoral condyle

Equine subchondral lucencies (SCL) have been described since the first availability of suitable radiographic equipment. The initial clinical sign can be lameness, but SCLs are often first found on surveys of juvenile horses and are primarily a radiographic concern for public auctions. When lameness is present, it varies from subtle to obvious and can be intermittent. Some SCLs heal spontaneously, and some remain blemishes, but when the SCL and lameness are persistent, further damage to the joint and limitations to an athletic career are likely. SCLs were initially described in the distal limb followed by the stifle, and the medial femoral condyle (MFC) is now considered the most common location. The aim of this review is to highlight the initial pathology and discuss the clinical and experimental information available on equine SCLs. SCL treatment has evolved from rest alone and has progressed to debridement, grafting, intralesional injection, and most recently, transcondylar screw and absorbable implant placement. Comparison of success rates between techniques is difficult due to variations in follow-up and outcome measures, and no single technique is best for all SCLs. Treatment appears to increase success by 15%-20% over rest alone, but the method chosen depends on many factors. This review emphasizes the need for further work to fully understand SCL formation and all aspects of trabecular bone healing to optimize surgical therapy and improve treatment success.

Preclinical tendon and ligament models: Beyond the 3Rs (replacement, reduction, and refinement) to 5W1H (why, who, what, where, when, how)

Several tendon and ligament animal models were presented at the 2022 Orthopaedic Research Society Tendon Section Conference held at the University of Pennsylvania, May 5 to 7, 2022. A key objective of the breakout sessions at this meeting was to develop guidelines for the field, including for preclinical tendon and ligament animal models. This review summarizes the perspectives of experts for eight surgical small and large animal models of rotator cuff tear, flexor tendon transection, anterior cruciate ligament tear, and Achilles tendon injury using the framework: "Why, Who, What, Where, When, and How" (5W1H). A notable conclusion is that the perfect tendon model does not exist; there is no single gold standard animal model that represents the totality of tendon and ligament disease. Each model has advantages and disadvantages and should be carefully considered in light of the specific research question. There are also circumstances when an animal model is not the best approach. The wide variety of tendon and ligament pathologies necessitates choices between small and large animal models, different anatomic sites, and a range of factors associated with each model during the planning phase. Attendees agreed on some guiding principles including: providing clear justification for the model selected, providing animal model details at publication, encouraging sharing of protocols and expertise, improving training of research personnel, and considering greater collaboration with veterinarians. A clear path for translating from animal models to clinical practice was also considered as a critical next step for accelerating progress in the tendon and ligament field.

Age- and sex-specific differences in ACL and ACL bundle size during adolescent growth

Anterior cruciate ligament (ACL) injuries are increasingly common in adolescents, and injuries in this age-group are associated with many unique challenges. Recent large animal studies suggest that the size and function of the major bundles of the ACL change differently throughout skeletal growth. To better aid clinical treatment of pediatric partial ACL tears and better predict outcomes from age-specific treatments, there is a need to measure changes in ACL bundle size in humans during growth. As such, the objective of this study was to compare changes in the length and cross-sectional area (CSA) of the ACL and its primary bundles in adolescent human subjects. Magnetic resonance imaging (MRI) scans were analyzed to determine the visibility and integrity of the ACL and its anteromedial and posterolateral bundles. MRI scans were considered from a retrospective database of subjects ranging from 10 to 18 years of age. The ACL and its anteromedial and posterolateral bundles were segmented and reconstructed into 3D models, and length and CSA were calculated. Total ACL length and CSA were greater in males compared with females, with a statistically significant interaction between age and sex for CSA. Sex had a significant effect on the CSA of both bundles. These sex-dependent differences emerge with moderate to large effect sizes (range: d = 0.50 to d = 1.23) beginning around 13 years of age. Along with ACL bundle structure-function relationships previously established in preclinical animal models, these findings may point toward biomechanical changes in the adolescent human ACL.