Performing Department
Clinical Science
Non Technical Summary
Deterioration of the joint cartilage and the bone beneath it (subchondral bone) - collectively termed the osteochondral unit - secondary to injury is a well-recognized cause of osteoarthritis (OA). OA is a debilitating disease that impacts human and animal species alike, affecting over 30 million adults in the United States and causing up to 60% of clinical lameness cases in equine athletes, accounting for the greatest single economic loss to the horse industry. Addressing changes in both the subchondral bone and cartilage has become increasingly important for the treatment of joint disease, as the relationship between the two plays a significant role in the progression of OA. There are limited management options for joint injury in horses, with current techniques often failing to re-establish normal joint structure and function, resulting in these techniques being ineffective long-term. Recent work has identified a treatment focused on the subchondral bone that provides crucial support to the joint and has the potential to enhance the integration of cartilage repair tissue, both of which are critical for long-term joint function. Subchondroplasty®, a technique involving injection of a calcium-based, bioresorbable bone cement into damaged or diseased subchondral bone, was developed to treat bone marrow lesions associated with OA in humans, with significant improvement in joint pain and function.Our objective is to demonstrate the use of a modified Subchondroplasty® technique as a potential treatment for joint disease in horses, with minimal negative effects and improved integration with surrounding tissues. Three normal horses will undergo general anesthesia and two circular defects will be made in the cartilage of the medial trochlear ridge of each femur, down to the level of the subchondral bone. Defects will be filled with a fibrin glue-gelatin treatment matrix meant to stimulate cartilage healing via one of four techniques: 1) subchondral injection, 2) direct injection, 3) direct injection combined with subchondral injection of the calcium-based bone cement, and 4) untreated. Humane euthanasia will be performed two weeks later for evaluation of the integration and retention of the matrix with the surrounding bone and cartilage, as well as damage to tissues. This evaluation will be done via diagnostic imaging (radiographs, MRI, CT), gross examination, and histology. We anticipate the modified Subchondroplasty® technique will be an easy, minimally-invasive technique with improved integration of therapeutics as compared to direct injection. The results of this study will lay the groundwork for future cartilage repair studies comparing modified Subchondroplasty® to more commonly used techniques.This project is the first step toward addressing a problem that currently lacks a successful long-term treatment in horses, combining equine and human medical experts, as well as those in industry, for a comprehensive approach to a debilitating disease process. Although we have demonstrated the potential of this technique in equine cadavers, a limited live animal model is needed to provide pilot data for submission of more definitive projects in the future. We predict that by restoring the structural integrity of the affected subchondral bone and promoting local bone remodeling, this procedure may provide a durable option for joint preservation and alter the progression of disease, resulting in an improved long-term outcome for equine athletes.
Animal Health Component
100%
Research Effort Categories
Basic
0%
Applied
40%
Developmental
60%
Goals / Objectives
The overall objective of the proposed study is to provide in-vivo proof of concept of a modified Subchondroplasty® technique as a potential treatment for osteochondral disease in horses. Our central hypothesis is that the administration of biologic therapeutics (hydrogels, bioscaffolds or implant materials) via a modified Subchondroplasty® technique will enhance the local therapeutic effects targeted at subchondral tissues and integration of repair tissue to the host tissues, providing better support to the entire osteochondral unit and establishing a more positive mechanical environment for joint healing. Future testing of this hypothesis first requires evaluation of the degree of integration of injected materials when using this technique, as well as the response of the tissues to subchondral administration of therapeutics. The specific aims and corresponding hypotheses are as follows:Specific Aim 1: To evaluate the administration of biologic therapeutics to full-thickness articular cartilage defects using a modified Subchondroplasty® technique. This will be tested using an established medial trochlear ridge of the femur defect model in horses, filled with subchondral injection of either a fibrin glue-gelatin composite matrix or subchondral injection of a calcium phosphate bone substitute material combined with direct injection of the composite material.Hypothesis 1: The use of a modified Subchondroplasty® technique will be a simple and reproducible surgical technique for the filling of osteochondral defects in the medial trochlear ridge of the femur in horses.Specific Aim 2: To evaluate biologic therapeutic integration and host tissue response to the modified Subchondroplasty® technique. This will be done using diagnostic imaging (digital radiography, computed tomography, magnetic resonance imaging) of the joints, and histologic evaluation of decalcified bone sections 2 weeks post-operatively.Hypothesis 2: The use of a modified Subchondroplasty® technique will result in perfusion of the injected biologic material through the underlying subchondral and trabecular bone, and extending into the osteochondral defect, creating continuous integration of injected material and host tissues without significant injury to host tissues.
Project Methods
The project in question is a randomized, controlled, pilot study to be performed in 3 skeletally mature research horses using a bilateral hindlimb model. Horses will be free of hind limb lameness without palpable effusion in the femoropatellar joint of either stifle, or radiographic evidence of stifle disease. All 3 horses will undergo general anesthesia for bilateral femoropatellar joint arthrotomy. Routine pre-operative bloodwork will be performed prior to surgery. Horses will receive perioperative antimicrobials and an anti-inflammatory, intravenously, at standard dosages.Using a previously-established defect model, two 15mm-diameter full thickness cartilage defects will be created on the medial trochlear ridge of each femur for a total of 4 defects per horse. These defects are large enough to mimic those treated in humans, and the thickness of the articular cartilage in this location is comparable with that of humans. Studying the effectiveness of the technique in this location offers the opportunity to address a significant problem in both species. The calcified cartilage layer, which connects the subchondral bone to the overlying articular cartilage, will be removed with a bone curette to optimize the volume and attachment of repair tissue. A surgical awl will be used for 3mm-depth microfracture into the subchondral bone. Using a 2.0mm drill bit from an extra-articular approach, a pilot hole will be created through the abaxial surface of the medial trochlea, aimed in a caudal-abaxial to cranial-axial direction. Under radiographic guidance and with the aid of a drill guide, the drill bit will be advanced toward and ending at the center of the defect, several millimeters below the subchondral plate. A short Jamshidi cannula will be inserted into the drill tract and the defects will be filled as listed below. The incisions will be closed routinely, the joints refilled with sterile isotonic fluid, and the incisions covered with stent bandages for recovery from general anesthesia. Defect treatment will be randomly assigned, with each defect within a horse filled via 1 of 4 treatments:Subchondral injection of a fibrin glue-gelatin composite matrix until the defect is appropriately filled.Direct injection of a fibrin glue-gelatin composite matrix into the cartilage defect through the arthrotomy incision, without any subchondral drilling. This is the standard method of injection when using fibrin glue in clinical cases.Subchondral injection of a bone substitute material until it barely extravasates into the defect, at which time the fibrin glue-gelatin matrix will be directly injected into the defect to incorporate the two at the base of the defect.Untreated negative control, including creation of the cartilage defect and subchondral drill tract (each horse is its own control).By filling the defects in this manner, we can evaluate tissue integration, matrix retention, and response of host tissues for each of the different techniques. Randomly assigning the treatments among defects also reduces the variability in responses by individual horses. Horses will be kept on box stall rest and monitored for changes in stifle effusion for 14 days. Lameness evaluations will be performed 14 days post-operatively, with lameness scores in each hind limb recorded and compared to baseline. Radiographs will be taken of each stifle on days 1 and 14, post-operatively. The radiographs will be graded by a board-certified radiologist blinded to defect treatment. Changes in subchondral bone on day 14, for comparison with day 1, will be graded using a previously reported grading system (1 = flat subchondral bone, 2 = defect in subchondral bone, 3 = lytic areas deep to subchondral bone, 4 = large lytic area deep to subchondral bone/cystic lesion).All horses will be humanely euthanized with an overdose of pentobarbital sodium, intravenously, on day 14. Immediately following euthanasia, hind limbs will be harvested from each horse for diagnostic imaging and post-mortem evaluation.Magnetic resonance imaging will be performed on each stifle immediately following euthanasia, using both high (3 Tesla) and low field (0.31 Tesla) magnets, to evaluate the integration of the injectate into the surrounding bone. T2-weighted dual echo steady state and intermediate fat-suppressed sequences will be used to track the injectate and detect changes in the surrounding bone and associated articular cartilage. Images will be assessed by a board-certified radiologist blinded to treatment, and graded on a semi-objective scale based on the amount of injectate or tissue filling the defects (0=no filling; 1=1- to 3-mm defect filled; 2=4- to 6-mm defect filled; 3=7- to 10-mm defect filled; 4 = >10-mm defect filled). Appearance of repair tissue and underlying bone and distribution of injectate will be described. Computed tomography will then be performed on each stifle immediately following MRI, including both pre- and post-cationic CA4+ scans. Hounsfield units will be used to determine incorporation of cationic contrast into cartilage. A similar semi-objective scoring method will be used for CT images, as described above.Following imaging, stifle joints will be disarticulated and the osteochondral defects grossly evaluated. All defects will be photographed and graded semi-objectively for injectate retention and defect filling (graded; 1=0-25%, 2=26-50%, 3=51-75%, 4=76-100% of the defect filled with tissue), as well as secondary lesions in other area of the joint, and overall injectate distribution and integration will be described.Histology: Representative sections from each defect and drill tract will be decalcified over 3 weeks, embedded in paraffin, sectioned, and stained with H&E, as well as safranin O and fast green. Each section will be subjectively assessed for presence of tissue or injected material within the defect, drill tract, or surrounding subchondral bone, including the amount and histologic character, and integration with the subchondral bone and surrounding cartilage. The host response to the injected materials will be determined microscopically via blinded histologic examination by a pathologist trained in examining joint histology. A previously reported modified histological grading system will be used to generate scoring for nonparametric analysis of variances of the defect treatments.Statistical Analysis: The goal of this study is to obtain pilot data for more definitive studies. Due to the exploratory nature, a limited sample size (3 horses = 3 defects/treatment) was determined as the lowest possible number required to achieve variance between treatment groups, and it is assumed that any resulting data will be non-parametric. Detection of statistically significant differences between defect treatments will also be unlikely; therefore, descriptive data including details of the surgical technique, clinical side effects, gross examination and imaging findings, histologic characteristics of the tissues, and subjective comparison of each treatment will be provided, with frequency statistics reported for all categorical data. A mixed model of variance will be used to evaluate the following dependent variables: clinical lameness, subchondral bone changes, % defect filling, and histologic scores of host tissue response. Independent variables for the analysis will include horse and defect treatment. There are no current data published for the measured outcome variables in this study as related to Subchondroplasty®; therefore, data retrieved will help establish the horse numbers required to perform an appropriately-powered, objective evaluation of the technique in future efficacy studies.Efforts for Distribution of Knowledge: In addition to publishing this information in the scientific literature, efforts to provide information gained will include presentation in research-related rounds, seminars, and formal continuing education platforms.