Femoral morphology due to impingement influences the range of motion in slipped capital femoral epiphysis

Abstract

Femoroacetabular impingement due to metaphyseal prominence is associated with the slippage in patients with slipped capital femoral epiphysis (SCFE), but it is unclear whether the changes in femoral metaphysis morphology are associated with range of motion (ROM) changes or type of impingement. We asked whether the femoral head-neck junction morphology influences ROM analysis and type of impingement in addition to the slip angle and the acetabular version. We analyzed in 31 patients with SCFE the relationship between the proximal femoral morphology and limitation in ROM due to impingement based on simulated ROM of preoperative CT data. The ROM was analyzed in relation to degree of slippage, femoral metaphysis morphology, acetabular version, and pathomechanical terms of "impaction" and "inclusion." The ROM in the affected hips was comparable to that in the unaffected hips for mild slippage and decreased for slippage of more than 30 degrees. The limitation correlated with changes in the metaphysic morphology and changed acetabular version. Decreased head-neck offset in hips with slip angles between 30 degrees and 50 degrees had restricted ROM to nearly the same degree as in severe SCFE. Therefore, in addition to the slip angle, the femoral metaphysis morphology should be used as criteria for reconstructive surgery.

Fig. 1

Diagrams illustrate Type 1 to 3 proximal femoral remodeling classified according to the criteria of Jones et al. [9]. Type 3: The proximal femoral epiphysis is positioned dorsal in relation to the metaphysis. A ventral located bony prominence in the region of the proximal femoral metaphysis can be observed. Type 2: The femoral epiphysis and metaphysis are on the same level in ventral direction. Type 1: The normal anatomic morphology of the ventral transition between the femoral epiphysis and metaphysis is shown.

Fig. 2A–B

Diagrams illustrate the assessment of the acetabular version based on a three- dimensional model of the acetabulum: (A) dorsolateral view of the acetabulum and (B) position of the acetabular version (α).

Fig. 3A–E

Using a three-dimensional model of the proximal femur, ROM is assessed in relation to neutral position: (A) neutral position in lateral view, (B) neutral position in frontal view, (C) rotation, (D) flexion, and (E) abduction.

Fig. 4A–C

Diagrams illustrate the model for validation of the ROM measurement program: (A) simulation of flexion, (B) simulation of abduction, and (C) simulation of rotation. EXT = extension; FLEX = flexion; ADD = adduction; ABD = abduction; IRO = internal rotation; ARO = external rotation.

Fig. 5

The influence of femoral metaphysis morphology (Jones type) in addition to the amount of slippage for restriction in ROM is shown in the histogram. For mild slippage, a decrease for flexion is shown between Types 1 and 2 but no changes for internal rotation and abduction. For moderate slippage, ROM decreased as femoral metaphysis deformity increased (emphasized by the red line). For severe slippage, there was near-complete loss of normal ROM regardless of the proximal femoral anatomy. The correlation coefficients (Spearman) are −0.837 for flexion, −0.852 for abduction, and −0.825 for internal rotation.