Proximal Femoral Physis Shear in Slipped Capital Femoral Epiphysis-A Finite Element Study

Abstract

The following finite element study was conducted to determine whether increased body weight, femoral retroversion, and varus hip loading could sufficiently raise physeal shear strains and stresses above the yield point and predispose an adolescent hip to a slip. A computer tomography scan of a 13-year-old child with slipped capital femoral epiphysis was used to generate a solid model of the proximal femur and physis. The model was parameterized using 3-dimensional software to generate three difference angles of femoral neck version-neutral, 15 degrees retroversion, and 15 degrees anteversion. Loads of 2.7 times body weight in a 46- and 86-kg child were applied to the proximal femur to model stance on one leg. In addition, the loading vector was reoriented at various degrees of varus to study the effect of varus loading on physis shear. The results demonstrated that physis stress, strain, and displacement increased with greater body weight, retroversion, and varus displacement of the loading vector. Physis shear strain in hips with a combination of varus loading and femoral neck retroversion exceeded the reported ultimate strain values for cartilaginous soft tissues. The finite element models suggest that in an overweight child, the combination of retroversion and varus hip load may be sufficient to increase physeal strains above the yield point and result in a slip.

Is the Acetabulum Retroverted in Slipped Capital Femoral Epiphysis?

“…An LCEA of greater than 39°was found in 16.7% (four of 24) of the affected hips, 22.7% (five of 22) of the unaffected hips, and 6.5% (10 of 152) of the controls. Additionally, biomechanical etiology theories of SCFE have demonstrated increase in femoral retroversion, coxa vara, and varus displacement of the load vector will increase physeal shear forces [8,27,38]. The medialization of the femoral head of patients with SCFE (as demonstrated in our study by the increased LCEA) may cause varusization of the force vector, increasing the shear forces across the physis and therefore potentially increasing the risk for SCFE [8,13,25].…”

“…While its origin remains an enigma [5,8,27,37,38], treatment methods have continued to evolve [21]. Gelberman et al [10] reported an association of SCFE and femoral retroversion.…”

Significance of clinical and radiographic findings in young adults after slipped capital femoral epiphysis

“…Other biochemical or biomechanical factors such as shear stress to the affected and to the opposite hip that contribute to the development of OA may be at work and need further investigation [25,26].…”

Slipped Capital Femoral Epiphysis: Prevalence, Pathogenesis, and Natural History

“…Ultrastructural analysis shows slippage of the physis occurs secondary to weakness of the supporting fibrous network caused by collagen disturbance [2,19,57]. Mechanical [4,20,45,68], endocrine [52,85,86], and metabolic disorders of puberty [60] have been postulated to cause the pathological disturbance in the growth plate that ultimately fail mechanically and slip. Despite previous reports on the association of human leukocyte antigen in identical twins with SCFE [3], a genetic basis has not been established.…”

“…resistance to shear or that increase the stresses across the proximal femoral physis [20,45,68]; for example, endocrine disorders [52,83], obesity [9,14,34,61,63,67,71,82], femoral [28] or acetabular retroversion [17], and coxa profunda [72]. The natural history is largely dependent on both the degree of deformity [11] and the occurrence of complications of treatment, mainly avascular necrosis of the femoral head (AVN) and chondrolysis [37,39,50,53].…”