This purpose of this study was to investigate whether prophylactic pinning of the contralateral hip in unilateral slipped upper femoral epiphysis affects subsequent femoral morphology.

To determine the effect of prophylactic pinning on growth we compared contralateral hip radiographs of 24 proximal femora prophylactically pinned with 26 cases observed, in a cohort of patients with unilateral SUFE. Validated measurements were used to determine hip morphology; the articulo-trochanteric distance (ATD) and the ratio of the trochanteric-trochanteric distance (TTD) to articulo-trochanteric distance (TTD:ATD) in addition to direct measurement of the femoral neck length. Post-operative radiographs were compared to radiographs taken at a 12–84 months follow-up.

Comparing pinned and unpinned hips the neck length was shorter (mean 5.1 mm vs 11.1 mm) and the ATD was lower (p=0.048). The difference between initial and final radiograph TTD:ATD ratio for each case was calculated. The average was 0.63 in the prophylactically pinned group and 0.25 in the unpinned group (p=0.07).

When hips of the same patient were compared on final radiographs, there was a smaller difference in TTD:ATD between the two sides when the patient had been prophylactically pinned (0.7) as opposed to observed (1.47). This was not statistically significant (p=0.14).

Universal prophylactic pinning of the contralateral hip in slipped upper femoral epiphysis is controversial and alteration of the proximal femoral morphology is one reason for this.

Our results show that prophylactic pinning does not stop growth but does alter subsequent proximal femoral morphology by causing a degree of coxa vara and breva. Some loss of growth in the prophylactically pinned hip contributes to reduction in leg length inequality at skeletal maturity which is advantageous.

No iatrogenic complications were observed with single cannulated screw fixation. Prophylactic pinning prevents the potential catastrophe of a subsequent slip, is safe and the effect on growth is, if anything, beneficial.

Level of evidence: III

Between July 1994 and June 2004, 60 patients with 76 slipped upper femoral epiphyses were managed within the adult trauma service of three hospitals. Treatment was by a single cannulated screw.

Of these cases, 53 were unilateral, in 17 of which uncomplicated prophylactic fixation of the contralateral hip was performed. Of the other 36 cases, nine presented with a subsequent slip despite ongoing out-patient care. The subsequent slip was unpredictable in timing and unrelated to the age at the initial slip. It was more often unstable and in one case avascular necrosis developed. The overall rate of avascular necrosis, although in accordance with the literature, was 60% in acute unstable slips with a slip angle greater than 40°.

In our experience, prophylactic fixation was safer than continued observation of the contralateral hip.