Treatment of Bilateral Medial Femoral Condyle Articular Cartilage Fissures in a Horse Using Bone Marrow-Derived Multipotent Mesenchymal Stromal Cells

Abstract

The objective of this study was to describe the use, and outcome, of multipotent mesenchymal stromal cells (MSCs) in the treatment of equine articular cartilage defects of the medial femoral condyle. A 4-year-old Thoroughbred gelding (n = 1) with bilateral stifle athroscopy was found to have bilateral articular cartilage fissure defects of the medial femoral condyles with concurrent cranial cruciate ligament injury. Bone marrow derived MSCs were isolated, expanded, and suspended in a partially autologous fibrin glue. The initial cell/fibrin glue mixture was delivered arthroscopically into the articular cartilage defects 90 days after the initial arthroscopic examination. Follow-up treatments included two additional injections of MSCs suspended in lactated Ringers solution, 5 and 13 months after the initial examination, directly into the joint. Post-treatment outcome was assessed by arthroscopic examination and by comparison of preinjury and post-treatment performance records. Arthroscopic evaluation 4 months after the initial MSC treatment revealed marked smoothing, reduction in the depth of cartilage defects and observation of moderate improvement in the cranial cruciate ligament. Approximately 15 months after the initial MSC treatment the horse returned to racing. Analysis of race records demonstrated that the post-treatment (including all three MSC treatments) average race earnings (earnings per start) were comparable with those predating the initial injury. The favorable clinical response in the face of an unknown, but likely, guarded prognosis suggest that MSC therapy is not deleterious and may augment healing of articular cartilage fissures of the medial femoral condyle. MSCs represent a viable and promising alternative therapy in the treatment of articular cartilage injuries in performance horses.

Introduction

Joint pathology has been reported to be a major cause of lameness in horses and is estimated to account for 42%-60% [1], [2] of lameness cases. The relatively avascular and hypoxic nature of cartilage as a tissue, in addition to the nonproliferative characteristics of mature chondrocytes, often results in a poor prognosis for complete recovery. In addition, these cartilage injuries present with highly variable clinical signs and recovery outcomes. Factors that determine the extent of healing include the depth, location, size, and weight-bearing environment of the lesion(s), in addition to patient age and conformation [3], [4]. Current treatments for injuries related to articular cartilage in horses are ever evolving. A diagnosis is generally confirmed through arthroscopic examination and treatments include partial meniscectomy, curettage or drilling into the subchondral bone, cartilage flap/fragment fixation, and surgical debridement and microfracture [5], [6], [7], [8], [9], [10], [11], [12]. In horses with lameness localized to the medial femorotibial joint having subtle radiographic changes of the medial femoral condyles, it was found that only two of six horses with generalized cartilage lesions were reported as being sound and without any evidence of joint effusion after arthroscopic-guided abrasion arthroplasty and microfracture [12]. Prognosis depends on the severity and location of the lesion(s), among other factors, and it is generally accepted that the percentage of patients making a complete recovery decreases with increasing severity of injury [13]. In another series, 86% of horses with focal lesions of the medial femoral condyle treated with arthroscopic curettage and debridement returned to normal function, whereas none of the horses that presented with extensive and diffuse damage, in which arthroscopic treatment was not performed, recovered completely [6]. Both studies highlight a guarded prognosis for horses with moderate to extensive damage to the cartilage of the medial femoral condyle.

With limited options available for articular cartilage repair and the efficacy of such options being variable, especially for extensive injuries, clinicians and researchers in both human and veterinary medicine have, over the past decade, looked into the potential of progenitor or stem cells to aid in tissue regeneration and repair. Currently, only one cell-based therapy has been approved by the Food and Drug Administration for use in human beings (Carticel, Genzyme). This uses autologous chondrocytes harvested from a non- or low load-bearing location that are then expanded in vitro, implanted into articular defects, and covered by a periosteal flap. The efficacy of such therapy, as measured by a combination of function and pain [14], has been reported to be >80% in human beings [15], with comparable results in horses using a similar technique for the repair of manufactured full-thickness defects in minor load-bearing areas of the tibiotarsal joint [16]. However, induction of defects to harvest chondrocytes is a concern with this type of cell therapy and comparable clinical results have been obtained with microfracture [17]. Thus, other tissue sources for cellular therapy as well as implantation methods are being considered.

Mesenchymal stromal cells (MSCs) are a multipotent adult stem cell population capable of differentiating into tissues of the mesenchymal lineages including bone, cartilage, and fat, and may also serve as trophic mediators aiding in attenuating the inflammatory response [18], [19], [20]. These cells have been referred to in the published data and by industry by a variety of names including mesenchymal stem cells and bone marrow stromal cells; we have chosen to use the name multipotent MSCs, as recommended by the International Society for Cellular Therapy [21]. With the relative abundance and accessibility of MSCs for clinical harvest, many clinicians and researchers have begun looking at the use of MSCs for cartilage [22], tendon [23], [24], ligament [23], [24], and bone repair [25]. Recently, there was a report of the use of autologous MSCs in a fibrin glue enhancing the early repair of manufactured full-thickness articular cartilage/subchondral bone defect in the equine femoropatellar joint [26]. Although the report noted that long-term healing at 8 months was not significantly different between individuals receiving MSC-laden fibrin glue or control (MSC-free fibrin glue), the study did not compare an untreated control, thus it is difficult to determine whether the fibrin glue alone may have played a role in healing. There is evidence in the published data that fibrin may serve as a scaffold for tissue repair, including that of cartilage, thereby contributing to the healing process [27], [28]. The apparent benefits of MSCs on early healing should not be disregarded and may provide a foundation for additional intra-articular cellular therapy to improve overall joint health. Although experimental studies are limited, there is less evidence for the efficacy of such treatment in naturally occurring superficial lesions in which the subchondral bone is intact. In this case report, we describe the use of arthroscopically delivered autologous MSCs in a partially autologous fibrin glue to treat bilateral diffuse fissure fractures of the medial femoral condyles of a horse.