Magnetic Resonance Imaging (MRI) Anatomy of the Ovine Stifle

Ex vivo study correlating the stiffness of the ovine patellar tendon to age and weight

Tendons play a crucial role in the musculoskeletal system. In humans, tendon injuries, especially chronic tendinopathy, are very common and the patellar tendon is a frequent location for tendinopathy or injuries. The biomechanical characteristics of the patellar tendon, such as elasticity and stiffness, are of paramount importance and constitute major outcome measures in research studies. We aimed to assess whether the stiffness of the healthy ovine patellar tendon changes with age and weight in a population of normal animals. Sixty-eight 'patella-patellar tendon-tibial tuberosity' units from thirty-four Ile-de-France ewes of body mass 65 to 95 kg, euthanized for reasons other than musculoskeletal diseases, underwent a tensile test providing a measure of the tendon stiffness. Animals were sorted into three categories of age (1-2 yo, 3-5 yo, 6-10 yo). We found a positive but not significant correlation between age category and stiffness (r = 0.22, p = 0.27). There was a significantly positive correlation between weight and stiffness (r = 0.39, p = 0.04). In conclusion, the study characterized biomechanical properties of healthy tendons, provided useful reference values, and established the basis for future biomechanical tests on healing tendons in sheep. The most appropriate sheep population for those future studies would be non-overweight young adults presenting with no lameness.

Comparative anatomy and morphology of the knee in translational models for articular cartilage disorders. Part I: Large animals

BACKGROUND

The human knee is a complex joint, and affected by a variety of articular cartilage disorders. Large animal models are critical to model the complex disease mechanisms affecting a functional joint. Species-dependent differences highly affect the results of a pre-clinical study and need to be considered, necessitating specific knowledge not only of macroscopic and microscopic anatomical and pathological aspects, but also characteristics of their individual gait and joint movements.

METHODS

Literature search in Pubmed.

RESULTS AND DISCUSSION

This narrative review summarizes the most relevant anatomical structural and functional characteristics of the knee (stifle) joints of the major translational large animal species, comprising dogs, (mini)pigs, sheep, goats, and horses in comparison with humans. Specific characteristics of each species, including kinematical gait parameters are provided. Considering these multifactorial dimensions will allow to select the appropriate model for answering the research questions in a clinically relevant fashion.

Ultrasound anatomy of the normal stifle in the sheep

Though the ovine stifle is commonly used as a model in research, there is no description of its anatomy at ultrasonography (US). The objective of this study was to provide reference US images of the ovine stifle that are relevant in musculoskeletal research. Four pairs of hindlimbs were scanned, whilst four other pairs were frozen and cut in different planes to compare gross anatomy to US scans. In another pair, the synovial compartments of the stifle were injected and scanned. This study demonstrated that US could be used to assess the ovine stifle. Several structures of clinical interest could be identified with cranial, lateral and medial approaches, such as (a) the tendons of m. quadriceps femoris, m. gluteobiceps, m. popliteus, (b) the common tendon of m. peroneus tertius-extensor longus digitorum-extensor digiti III proprius, (c) the patellar ligament, (d) the medial and lateral collateral ligaments, (e) the cranial horn and middle segment of medial and lateral meniscus, and (f) the synovial recesses. However, the caudal approach was not successful to identify caudal anatomical structures of the joint, due to the muscular mass, that is the caudal aspects of the articular surfaces of the femoral and tibial condyles, the caudal horns of the menisci and the supracondylar synovial recesses. In addition, US remained challenging to assess the internal structures such as cruciate ligaments and articular surfaces. The feasibility of US needs to be tested in vivo.

* The Ovine Model for Meniscus Tissue Engineering: Considerations of Anatomy, Function, Implantation, and Evaluation

Meniscus injuries represent one of the most-common intra-articular knee injuries. The current treatment options include meniscectomy and allograft transplantation, both with poor long-term outcomes. Therefore, there is a need for regenerative techniques to restore meniscal function. To preclinically test scaffolds for meniscus replacement, large animal models need to be established and standardized. This review establishes the anatomical and compositional similarities between human and sheep menisci and provides guidance for implantation and evaluation of such devices. The ovine meniscus represents a scaled-down version of the human meniscus, with only slight structural differences that can be addressed during device fabrication. Implantation protocols in sheep remain a challenge, as the meniscus cannot be visualized with the arthroscopic-assisted procedures commonly performed in human patients. Thus, we recommend the appropriate implantation protocols for meniscus visualization, ligamentous restoration, and surgical fixation of both total and partial meniscus replacement devices. Last, due to the lack of standardization in evaluation techniques, we recommend a comprehensive battery of tests to evaluate the efficacy of meniscus replacement implants. We recommend other investigators utilize these surgical and testing techniques to establish the ovine model as the gold standard for preclinical evaluation of meniscus replacement devices.

Longitudinal Evaluation of Effects of Intra-Articular Mesenchymal Stromal Cell Administration for the Treatment of Osteoarthritis in an Ovine Model

In this study, the therapeutic effect of intra-articularly injected autologous mesenchymal stromal cells (MSCs) was evaluated in an ovine osteoarthritis (OA) model using consecutive magnetic resonance imaging (MRI), radiography, and macroscopic and histologic postmortem examination. In 12 sheep, OA was induced by bilateral, lateral meniscectomy. After 6 weeks, 20 × 106 bone marrow-derived MSCs (50% MSCs were superparamagnetic iron oxide particle labeled) were injected intra-articularly into one knee joint. The contralateral knee served as negative control. MR images were acquired before OA induction, immediately before and after MSC injection, and 1, 4, 8, and 12 weeks thereafter using a 0.5T unit and a T2* gradient echo sequence. Radiographs were obtained before OA induction, at MSC injection, and 12 weeks thereafter. The MRI scoring system included articular cartilage, bone, joint capsule, and synovial fluid evaluation. The radiographic scoring system included the joint space and bone. Postmortem evaluation entailed macroscopic and histologic assessment. Longitudinal MRI revealed a significant deceleration of OA progression in MSC-treated joints. However, at the conclusion of the study, there was no significant difference in the degree of OA detected by MRI, radiography, and postmortem evaluation between the treatment and control group. The degree of OA on MRI varied among the 12 animals at the time of injection, but there was no difference between the left and right limb. In conclusion, intra-articular MSCs decreased OA progression. However, no significant treatment effects were seen at the conclusion of the study at 12 weeks. This somewhat contradicts previously published results. Nevertheless, the choice of OA model, outcome measures, or lack of additional medication might explain the differences. Our results indicate that OA might benefit from intra-articular MSC injection, but further studies are needed to refine patient selection and injection parameters for a more substantially improved outcome.

Evaluation of the marsh deer stifle joint by imaging studies and gross anatomy

This study aimed to evaluate the stifle joint of marsh deer using imaging studies and in comparison with gross anatomy. Ten hindlimbs from 5 marsh deer (Blastocerus dichotomus) were used. Radiography, computed tomography (CT) and magnetic resonance imaging (MRI) were performed in each stifle joint. Two hindlimbs were dissected to describe stifle gross anatomy. The other limbs were sectioned in sagittal, dorsal or transverse planes. In the craniocaudal radiographic view, the lateral femoral condyle was broader than the medial femoral condyle. The femoral trochlea was asymmetrical. Subsequent multiplanar reconstruction revealed in the cranial view that the external surface of the patella was roughened, the medial trochlea ridge was larger than the lateral one, and the extensor fossa at the lateral condyle was next to the lateral ridge. The popliteal fossa was better visualized via the lateral view. Sagittal MRI images identified lateral and medial menisci, caudolateral and craniomedial bundles of cranial cruciate ligament, caudal cruciate ligament, patellar ligament and common extensor tendon. In conclusion, the marsh deer stifle presents some anatomical characteristics of the ovine stifle joint.