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

Abstract

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.

Keywords: Epiphyseal plate; Epiphyseal tubercle; Epiphysiolysis; Hip; Load; Perichondrial fibrocartilaginous complex; Porcine.

Figure 1

Set-up for lateral loading of the specimens. The major trochanter was removed to facilitate access for the loading rod.

Figure 2

Set-up for vertical loading of the specimens.

Figure 3

Set-up for anterior loading of the specimens.

Figure 4

Photomicrograph showing damaged epiphyseal plate. In the anterior and lateral loaded specimens, the damage wandered between the resting and ossifying zones. Sample stained with hematoxylin-eosin solution. Magnification X25. Scale bar equals 1 mm.

Figure 5

Epiphysiolysis with a damaged PFC (arrow). Sample stained with hematoxylin-eosin solution. Scanned slide, no magnification.

Figure 6

A small cleavage (arrow) over the epiphyseal line can be seen after failure.

Figure 7

The epiphyseal tubercle (arrow) pressing against the medial wall of the metaphyseal socket. The PFC is damaged. Sample stained with hematoxylin-eosin solution. Scanned slide, no magnification.

Figure 8

Anterior loaded specimen sample load/deformation curve.

Figure 9

Photomicrograph showing microscopic epiphyseolysis (arrowhead) with the PFC (arrow) intact. Sample stained with hematoxylin-eosin solution. Magnification X20. Scale bar equals 1 mm.

Figure 10

Porcine proximal femur split coronally. The major trochanter is relatively larger than in a human and the femoral neck shorter. The growth plate and the epiphyseal tubercle are clearly visible in this specimen (arrow).

Figure 11

The different zones of the porcine epiphyseal plate. Sample stained with hematoxylin-eosin solution. Magnification X40. Scale bar equals 1 mm.