Poster 78: Comparison of Graft Types for Acetabular Labrum Reconstruction in a Preclinical Canine Model

Abstract

Objectives:

Acetabular labrum pathology is a rapidly growing concern affecting a large population of patients. Trauma, overuse injuries, and femoracetabular impingement (FAI) often result in labral deficiency, and ultimately hip osteoarthritis if left untreated. A fully functioning labrum is critical to maintaining hip joint health by contributing to hip joint stability, maintaining the suction-seal effect, distributing loads, and protecting the articular cartilage. While repairing the native labrum can be successful, many defects are irreparable such that acetabular labrum reconstruction (ALR) is required to restore function. Fresh-frozen tendon allografts have traditionally been used for ALR, however, more recently, fresh (viable) meniscus allografts have been reported to have potential advantages as a graft choice for ALR. Cellular, extracellular matrix, and material property characteristics, as well as biomechanical and clinical advantages for use of fresh meniscus allograft transplantation (MAT) over fresh-frozen tendon allograft transplantation (TAT) have been reported. However, a direct head-to-head comparison of functional outcomes in a valid preclinical animal model has not been performed to the authors’ knowledge. The objective of this study was to test the hypothesis that for ALR, MAT will be associated with superior functional, diagnostic imaging, gross, and histologic outcomes with respect to hip joint health when compared to TAT in a preclinical canine model.

Methods:

With Institutional Animal Care and Use Committee (IACUC) approval, anterior tibialis tendons and menisci were aseptically recovered from skeletally mature purpose-bred hounds humanely euthanized for reasons unrelated to the present study. Tendons were washed, wrapped in saline-soaked gauze, placed in sterile bags, and frozen at -20 ^oC. Menisci were washed and preserved in individual containers filled with Missouri Osteochondral Preservation System media and stored in a clean room at room temperature for 28 days. On the day of ALR surgery, purpose-bred hounds (n=12 age-, breed-, and size-matched to donors) underwent aseptic surgery on one randomly assigned hip with the contralateral hips serving as unoperated controls (Native). Using an anterolateral approach to the hip with arthrotomy but without dislocation, the anterosuperior 2/3 of the acetabular labrum was resected to bleeding bone and then treated in 1 of 3 ways based on random assignment (Figure 1):

• TAT (n=4) - ALR using fresh-frozen tendon allograft trimmed to match the defect size and transplanted using 2 knotless suture anchors in acetabular bed bone with mattress suture repair to remaining caudal (posterior) native labrum

• MAT (n=4) – ALR using fresh meniscus allograft trimmed to match the defect size and transplanted using 2 knotless suture anchors in acetabular bed bone with mattress suture repair to remaining posterior native labrum

• Resected (n=4) – acetabular labrum defect left untreated

Post-operatively, the dogs were monitored for pain, general health, and complications, treated with analgesics, and restricted to their kennels for 4 weeks with enrichment items followed by daily monitored group socialization, leash walking, and enrichment items for the remainder of the study. Before surgery and at 1, 3, and 6 months post-operatively, a board-certified veterinary surgeon blinded to treatment type and time point assessed each dog for comfortable hip range of motion (CROM), visual analog scale (VAS) function, and VAS hip pain. At the same time points, gait kinetics were quantified by having the dogs trot across a pressure-sensing walkway to obtain at least three valid trials. Mean percent body weight distribution and total pressure index (%TPI) were measured for each footfall with operated hindlimb values compared to unoperated native control hindlimb values. Dogs were humanely euthanatized 6 months after surgery. Both hips were evaluated using magnetic resonance imaging (MRI) by a board-certified veterinary radiologist blinded to treatment to subjectively assess joint health as well as labral graft integrity, integration, and healing using a 15-point scoring system. The hips were then disarticulated and processed for gross assessments and histologic scoring. One-way ANOVA tests were used to compare treatment outcomes with significance set at p <0.05.

Results:

At 6 months following ALR, MAT was associated with the most normal functional outcomes (CROM, pain, function, %TPI), all of which were significantly better than the Resected group and not significantly different from Native (Figure 2). In addition, MAT was associated with significantly better MRI scores compared to TAT and Resected groups, however, MAT MRI scores were still inferior to Native MRI scores (Figure 2). Histologic assessments are pending and will be presented.

Conclusions:

The data from this preclinical canine model study support allograft-based ALR over labral resection and indicate better restoration of hip joint architecture, function, and health after ALR using MAT when compared to ALR using TAT. Based on previous work demonstrating the importance of cellular, extracellular matrix, material property and biomechanical characteristics for maintaining the acetabular labrum’s critical roles in hip joint function and health, the differences noted in the present study between MAT and TAT for ALR are thought to be primarily related to the maintenance of viable cells in fresh meniscus allografts as well as the biochemical, architectural, and material property similarities of meniscus to native acetabular labrum.