Abstract
Slipped upper femoral epiphysis (SUFE) is a condition, which affects the immature hip joint. Many theories have been postulated as to its underlying aetiology however; its exact cause is, as yet unknown. The final common pathway appears to be failure of the of the growth plate to resist shearing forces, giving rise to displacement of the femoral head. We hypothesized that the lubricating ability of the synovial fluid in hip joints of children with SUFE was defective, thereby allowing increasing shear forces on the physis to occur, so that when the joint is loaded it will fail at its weakest point, namely the capital epiphysis.
Aim: The aim of this study was to establish a biomechanical porcine cadaveric model to study SUFE and use this model to determine how defective joint lubrication may increase the probability of SUFE.
Methods: Using immature porcine femurs and a custom-made rig, a torsional load was applied about an axis perpendicular to the growth plate in order to cause the femur to fail along the growth plate. The Hounsefield testing machine applied a tensile load and recorded the associated elongation. From these figures the torque applied to the femoral head and the associated angular rotation could be computed. Using Weibel analysis we were able to determine the probability of SUFE occurring for a range of synovial fluid coefficients of friction, a range of joint reaction forces and neck-shaft angles.
Results: We found that it is possible to induce a SUFE in an immature porcine loaded hip joint and that there was an increased probability of slip with increased coefficient of friction of synovial fluid, increased percentage body weight and increased neck-shaft angle.
Conclusion: Defective lubrication may be a key underlying aetiological factor responsible for SUFE.
The abstracts were prepared by Emer Agnew, Secretary to the IOA. Correspondence should be addressed to him at Irish Orthopaedic Association Secretariat, c/o Cappagh National Orthopaedic Hospital, Finglas, Dublin 11, Ireland.
