Guided growth of the proximal femur: a pilot study in the lamb model.

BACKGROUND

The concept of guided growth has been used for decades in the lower extremities of children, but has not been applied to correct varus or valgus deformity in the hip, such as those that occur in children with cerebral palsy or developmental dysplasia of the hip. The purpose of this study is to determine whether guided growth techniques are effective at altering the morphology of the proximal femur in a lamb model.

METHODS

Ten, 2-month-old mixed-breed male lambs underwent hemiepiphyseal drilling and screw placement. Drilling occurred eccentrically (inferiorly) in an attempt to close only a portion of the growth plate. In 5 lambs, a sham surgery was performed in which the screw did not cross the proximal femoral physis. Growth was compared between groups and with the opposite hip in which no procedure was performed in both groups. Standardized radiographs were obtained preoperatively and monthly. A 3-dimensional computed tomography scan and standard histology were obtained postnecropsy. Version and neck shaft angle (NSA) was determined and recorded at the time of the index procedure with the aid of fluoroscopy. Radiographs were assessed by measurement of the NSA and the articular trochanteric distance (ATD). Results were compared by using the t test: paired 2 sample for means.

RESULTS

The NSA and ATD were compared preoperatively and at a mean of 3.3 months after surgery. They were no significant differences preoperatively between the screw or sham group. Postoperatively, the NSA was 132 versus 143 (P=0.006) and the ATD -0.6 mm versus 10 mm (P=0.033) for the screw and sham hips, respectively. The sham group showed no statistical differences between the operative and nonoperative sides postoperatively, although the ATD trended toward a larger number on the "sham" side, possibly because of a growth stimulation effect.

CONCLUSIONS

Screw hemiepiphysiodesis seems to alter the growth of the proximal femur in the lamb model.

SIGNIFICANCE

Further studies are ongoing and with more research this technique could be used to correct or prevent proximal femoral deformity in the growing child.

LEVEL OF EVIDENCE

Level II.