Cyclical loading causes injury in and around the porcine proximal femoral physeal plate: proposed cause of the development of cam deformity in young athletes.

BACKGROUND: The repetitive load to which the adolescent athlete's body is exposed during training and competition affects bone growth. In previous studies, abnormalities of the spine and extremities of adolescent athletes have been described on radiographs and this also applies to the hip. The cam deformity of the hip is an extension of the physeal plate and develops during the adolescent athlete's growth. Studies of the porcine spine have shown that the vertebral endplates, apophyseal rings and intervertebral discs are susceptible to both static and repetitive loads. The proximal physeal plate of the porcine femur is susceptible to static loads, but no studies have been performed on its susceptibility to repetitive loads. The purpose of this study was to investigate the susceptibility of the proximal porcine femur to repetitive loads. METHODS: Descriptive laboratory study. Seven proximal femurs from four young (5 months) pigs were loaded repetitively (50,000 cycles) using a previously developed model. Three were loaded vertically, three antero-superiorly and one was used as a control. All femurs were examined macroscopically, histologically and with MRI after loading. RESULTS: No macroscopic injuries were detected on any of the femurs after loading. Fluid redistribution was seen in all femurs on MRI compared with the unloaded control. Injuries were seen in all loaded femurs on microscopic examination of histological samples. Injuries, perpendicularly to the physeal plate and fractures adjacent to the plate, were seen in the vertically loaded specimens. In the antero-superiorly loaded specimen, the injury in the growth plate was parallel to the plate. CONCLUSION: Repeated loading of the young porcine hip leads to histological injuries in and adjacent to the physeal plate. These injuries are likely to cause growth disturbances in the proximal femur. We propose that such injuries may be induced in adolescent athletes and offer a plausible explanation for the development of the cam deformity.

Strength of the porcine proximal femoral epiphyseal plate: the effect of different loading directions and the role of the perichondrial fibrocartilaginous complex and epiphyseal tubercle - an experimental biomechanical study.

BACKGROUND: The high loads on adolescent athletes' musculoskeletal system are known to cause morphological and degenerative changes in bone, intervertebral discs and joints. It has been suggested that the cam deformity of the proximal femoral head originates from a subclinical slipped capital femoral epiphysis (SCFE) as a result of non-physiological loading. The perichondrial fibrocartilaginous complex (PFC) and the epiphyseal tubercle are believed to stabilise the proximal femoral epiphysis, but their role is still unclear. The aim of the present study was to develop an experimental, biomechanical model to evaluate the strength of the porcine proximal femoral epiphysis in different loading directions and, furthermore, to investigate the stabilising role of the PFC and the epiphyseal tubercle. METHODS: A descriptive laboratory study. An in-vitro model was developed and nine young (5 months) porcine proximal femoral epiphyses were loaded to failure; three in the anterior-posterior direction, three in the lateral-medial direction and three in the vertical direction. The injured proximal femoral epiphyses were then examined both macroscopically and histologically. RESULTS: Anterior and lateral loading of the proximal femoral epiphysis resulted in failure of the epiphyseal plate, while vertical loading resulted in a fracture epiphyseolysis. The epiphysis was weakest when exposed to a lateral load and strongest when exposed to a vertical load. Despite histological epiphyseolysis, the PFC was intact in 15 of 27 (56%) slices. In histological examinations, the epiphyseal tubercle appears to halt the slide of the epiphysis. CONCLUSIONS: We have developed an experimental, biomechanical model to measure the strength of the proximal femoral epiphyseal plate in different loading directions. The strength of the proximal femur was weakest through the epiphyseal plate. The epiphysis was weakest when exposed to a lateral load and strongest when exposed to a vertical load. The epiphyseal tubercle and the PFC stabilise the epiphysis when the epiphyseal plate is damaged. The findings in the present study indicate that overloading the hips in growing individuals can disrupt the epiphyseal plate. These findings may have implications when it comes to understanding the pathogenesis of cam deformity of the hip.