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Injury to muscles is very common. We have previously observed that basic fibroblast growth factor (b-FGF), insulin growth factor type 1 (IGF-1) and nerve growth factor (NGF) are potent stimulators of the proliferation and fusion of myoblasts in vitro. We therefore injected these growth factors into mice with lacerations of the gastrocnemius muscle. The muscle regeneration was evaluated at one week by histological staining and quantitative histology. Muscle healing was assessed histologically and the contractile properties were measured one month after injury. Our findings showed that b-FGF, IGF and to a less extent NGF enhanced muscle regeneration in vivo compared with control muscle. At one month, muscles treated with IGF-1 and b-FGF showed improved healing and significantly increased fast-twitch and tetanus strengths. Our results suggest that b-FGF and IGF-1 stimulated muscle healing and may have a considerable effect on the treatment of muscle injuries.

Muscle injuries represent a large number of professional and recreational sports injuries. Muscle strains habitually occur after an eccentric contraction, which often leads to an injury located in the myotendinous junction. Treatment varies widely, depending on the severity of the trauma, but has remained limited mostly to rest, ice, compression, elevation, antiinflammatory drugs, and mobilization. The authors' research group aims to develop new biologic approaches to improve muscle healing after injuries, including muscle strains. To achieve this goal, the authors investigated several parameters that will lead to the development of new strategies to enhance muscle healing. The authors first evaluated natural muscle healing after strain injuries and showed that muscle regeneration occurs in the early phase of healing but becomes impaired with time by the development of tissue fibrosis. Several growth factors capable of improving muscle regeneration were investigated; basic fibroblast growth factor, insulin-like growth factor, and nerve growth factors were identified as substances capable of enhancing muscle regeneration and improving muscle force in the strained injured muscle. The current study should aid in the development of strategies to promote efficient muscle healing and complete recovery after strain injury.

The anterior cruciate ligament (ACL) has poor capabilities of healing. Maturation or "ligamentization" of the ACL following autograft or allograft reconstruction has been found slow and remains under investigation. In vitro and in vivo studies have shown that platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-beta), and epidermal growth factor (EGF) have the potential to improve ligament healing. Gene therapy approaches may represent a new alternative in delivering these specific growth factors to the ACL. The aim of this study was to investigate the feasibility of three different gene therapy approaches (direct-, fibroblast-, and myoblast-mediated gene transfer) to the ACL. Rabbit myoblasts and ACL-fibroblasts were transduced with 5 x 10(7) recombinant adenoviral particles carrying the LacZ reporter gene (MOI = 50). Myoblasts and fibroblasts (1 x 10(6)) were each injected into the right ACL of 10 adult rabbits; direct injection of 5 x 10(7) adenoviral particles was performed in 10 other rabbits. The left side was used as sham. The beta-galactosidase production was revealed using the LacZ histochemical technique. The transduced fibroblasts and myoblasts were found in the ligament tissue and in the synovial tissue surrounding the ACL at 4, 7, 14, and 21 days postinjection. The myoblasts fused and formed myotubes in the ligament. The direct approach also allowed the transfer of the marker gene in the ligament at 4, 7, 21, and 42 days postinjection. X-gal staining revealed no expression of beta-galactosidase in the sham ligament. The presence of cells expressing the marker gene in the ACL opens up the possibility of delivering proteins (i.e., PDGF, TGF-beta, and EGF) capable of improving ACL healing and graft maturation. Furthermore, engineered myoblasts may mediate and accelerate the intraligament neovascularization. This new technology based on gene therapy and tissue engineering may allow a persistent expression of selected growth factors to enhance ACL healing following injury.

Segmental bone defects and nonunions are relatively common problems facing all orthopaedic surgeons. Osteogenic proteins, i.e., BMP-2, can promote bone healing in segmental bone defects. However, a large quantity of the human recombinant protein is needed to enhance the bone healing potential. Cell mediated gene therapy in the bone defect can allow a sustained expression of the osteogenic proteins and further enhance bone healing. Muscle cells can be easily isolated and cultivated, and they are known to be an efficient gene delivery vehicle to muscle and nonmuscle tissues. Furthermore, they are capable of transforming into osteoblasts when stimulated by BMP-2. Thus, the utilization of muscle cells as the gene delivery vehicle to a bone defect would be an important step in establishing a less invasive treatment for non-unions and segmental bone defects. Muscle cells were transduced when the adenoviral-lacZ vector and injected into the bone defect and the muscles surrounding the defect. Expression of the marker gene was visualized 7 days after the injection, both macroscopically and microscopically, using lacZ histochemistry. The lacZ expressing cells in the defect tissue were also stained for desmin, a muscle specific marker, indicating the presence of muscle cells that have fused into myofibers in this nonmuscle bone defect area. With successful myoblast mediated gene delivery into the segmental bone defect, future experiments would focus on delivering viral vectors expressing osteogenic proteins to eventually improve bone healing postinjury.

Muscle laceration remains a difficult problem for orthopaedic surgeons. Despite many studies related to the muscle's ability to regenerate after muscle degeneration, very few reports are available regarding structural and functional recovery after skeletal muscle laceration. We developed an animal model of muscle laceration in mice, where the gastrocnemius muscles were reproducibly transected. We compared the effect of a surgical repair versus a short period of immobilization (5 days) on the muscle healing. The natural course of muscle recovery was monitored at several points after injury using histologic, immunohistochemical, and functional testing. In the injured muscle, we observed a high number of regenerating myofibers and development of fibrotic scar tissue. Suturing the lacerated muscle immediately after injury promoted better healing of the injured muscle and prevented the development of deep scar tissue in the lacerated muscle; conversely, immobilization resulted in slower muscle regeneration and the development of a large area of scar tissue. Tetanus strength 1 month after injury was 81% of control muscles for the sutured muscles, 35% for the lacerated muscles with no treatment, and 18% for the immobilized muscles. Based on this study, suturing a muscle laceration with a modified Kessler stitch results in the best morphologic and functional healing.

Muscle injuries are a challenging problem in traumatology, and the most frequent occurrence in sports medicine. Muscle contusions are among the most common muscle injuries. Although this injury is capable of healing, an incomplete functional recovery often occurs, depending on the severity of the blunt trauma. We have developed an animal model of muscle contusion in mice (high energy blunt trauma) and characterized the muscle's ability to heal following this injury using histology and immunohistochemistry to determine the level of muscle regeneration and the development of scar tissue. We have observed a massive muscle regeneration occurring in the first 2 wk postinjury that is subsequently followed by the development of muscle fibrosis. Based on these observations, we propose that the enhancement of muscle growth and regeneration, as well as the prevention of fibrotic development, could be used as approach(es) to improve the healing of muscle injuries. In fact, we have identified three growth factors (bFGF, IGF-1, and NGF) capable of enhancing myoblast proliferation and differentiation in vitro and improving the healing of the injured muscle in vivo. Furthermore, the ability of adenovirus to mediate direct and ex vivo gene transfer of beta-galactosidase into the injured site opens possibilities of delivering an efficient and persistent expression of these growth factors in the injured muscle. These studies should help in the development of strategies to promote efficient muscle healing with complete functional recovery following muscle contusion.

Several genetic and acquired pathologic conditions of the musculoskeletal system, such as arthritis and damage to ligament, cartilage, and meniscus, may be amenable to gene therapy. Even though ex vivo gene transfer with synovial cells has been shown to deliver genes encoding for anti-arthritic proteins into the rabbit knee joint, its success has been limited by a transient transgene expression. In this study, data were investigated regarding the use of muscle cells as an alternative gene-delivery vehicle to the joint in newborn rabbit and adult severe combined immunodeficiency mice. We demonstrated that myoblasts were transduced more efficiently than synovial cells with use of the same adenoviral preparation in vitro. After intra-articular injection, the engineered muscle cells adhered to several structures in the joint, including the ligament, capsule, and synovium. In addition, myoblasts fused to form many post-mitotic myotubes and myofibers at different locations of the joint of the newborn rabbit 5 days after the injection. In the knee of the adult mouse, myoblasts fused and expressed the reporter gene for at least 35 days after the injection. The presence of post-mitotic myofibers in the knee joint raises the possibility of long-term expression of the secreted protein. Currently, numerous tissues in the joint (ligament, meniscus, and cartilage) have poor intrinsic healing capacity and frequently need surgical corrections. A stable gene-delivery vehicle to the joint producing proteins that ameliorate these different musculoskeletal conditions may change the clinical implications of these pathologies.