Experimental models of bone marrow lesions in ovine femoral condyles.

OBJECTIVE: To develop an in vivo experimental model for bone marrow lesions (BMLs) in ovine femorotibial joints. STUDY DESIGN: Randomized, prospective experimental study. ANIMALS: Eighteen healthy, skeletally-mature Dorper cross ewes. METHODS: One medial femoral condyle was penetrated with a 1.1 mm pin, and the contralateral medial femoral condyle was treated with transcutaneous extracorporeal shockwave (ESW) at 0.39 ± 0.04 mJ/mm2 . Clinical examination, magnetic resonance imaging (MRI), computed tomography (CT), and histopathological analyses were used to detect and characterize the development and progression of BMLs in the medial femoral condyle at 4, 8, and 12 weeks post-surgery. RESULTS: Pin penetration induced a BML detected on MRI within 2 weeks and lasted at least 12 weeks. BMLs were not observed in ESW-treated condyles. Histologically, BMLs were characterized by hemorrhage and inflammatory cellular infiltrate, and progressed to more dense fibrous tissue over time. Pathological changes were not observed in the articular cartilage overlying the region of BMLs. CONCLUSIONS: Direct, focal trauma to all layers of the osteochondral unit was sufficient to create an experimentally-induced BML which persisted for at least 90 days. The protocol used for ESW in this study did not induce BMLs. CLINICAL SIGNIFICANCE: Experimental induction of BMLs is possible and mimicked naturally occurring disease states. Volumetric imaging is a sensitive method for characterization of the dynamic nature of these lesions.

A prospective study comparing tendon-to-bone interface healing using an interposition bioresorbable scaffold with a vented anchor for primary rotator cuff repair in sheep.

BACKGROUND: The purpose of this study was to evaluate the biomechanical and histologic properties of rotator cuff repairs using a vented anchor attached to a bioresorbable interpositional scaffold composed of aligned PLGA (poly(l-lactide-co-glycoside)) microfibers in an animal model compared to standard anchors in an ovine model. METHODS: Fifty-six (n = 56) skeletally mature sheep were randomly assigned to a repair of an acute infraspinatus tendon detachment using a innovative anchor-PLGA scaffold device (Treatment) or a similar anchor without the scaffold (Control). Animals were humanely euthanized at 7 and 12 weeks post repair. Histologic and biomechanical properties of the repairs were evaluated and compared. RESULTS: The Treatment group had a significantly higher fibroblast count at 7 weeks compared to the Control group. The tendon bone repair distance, percentage perpendicular fibers, new bone formation at the tendon-bone interface, and collagen type III deposition was significantly greater for the Treatment group compared with the Control group at 12 weeks (P ≤ .05). A positive correlation was identified in the Treatment group between increased failure loads at 12 weeks and the following parameters: tendon-bone integration, new bone formation, and collagen type III. No statistically significant differences in biomechanical properties were identified between Treatment and Control Groups (P > .05). CONCLUSIONS: Use of a vented anchor attached to a bioresorbable interpositional scaffold composed of aligned PLGA microfibers improves the histologic properties of rotator cuff repairs in a sheep model. Improved histology was correlated with improved final construct strength at the 12-week time point.

Computed Tomography Provides Improved Quantification of Trabecular Lumbar Spine Bone Loss Compared to Dual-Energy X-Ray Absorptiometry in Ovariectomized Sheep.

Early detection of osteoporosis using advanced imaging is imperative to the successful treatment and prevention of high morbidity fractures in aging patients. In this preclinical study, we aimed to compare dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT) to quantify bone mineral density (BMD) changes in the sheep lumbar spine. We also aimed to determine the relationship of BMD to microarchitecture in the same animals as an estimate of imaging modality precision. Osteoporosis was induced in 10 ewes via laparoscopic ovariectomy and administration of high-dose corticosteroids. We performed DXA and QCT imaging to measure areal BMD (aBMD) and trabecular volumetric BMD (Tb.vBMD)/cortical vBMD (Ct.vBMD), respectively, at baseline (before ovariectomy) and at 3, 6, 9, and 12 months after ovariectomy. Iliac crest bone biopsies were collected at each time point for micro-computed tomography (microCT) analysis; bone volume fraction (BV/TV), trabecular number (Tb.N), thickness (Tb.Th), and spacing (Tb.Sp) were reported. aBMD and Tb.vBMD both decreased significantly by 3 and 6 months (p < 0.05) compared with baseline, whereas no changes to Ct.vBMD were observed. Combined (Tb. and Ct.) vBMD was significantly correlated with aBMD at all time points (all p < 0.05). Additionally, greater significant correlations were found between BV/TV and Tb.vBMD at all five time points (R 2 = 0.54, 0.57, 0.66, 0.46, and 0.56, respectively) than with aBMD values (R 2 = 0.23, 0.55, 0.41, 0.20, and 0.19, respectively). The higher correlation of microCT values with QCT than with DXA indicates that QCT provides additional detailed information regarding bone mineral density changes in preclinical settings. Because trabecular bone is susceptible to rapid density loss and structural changes during osteoporosis, QCT can capture these subtle changes more precisely than DXA in a large animal preclinical model. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.