Outcomes of distally un-threaded screw fixation of slipped capital femoral epiphysis at skeletal maturity: a matched cohort study.

ABSTRACT

The most common treatment for slipped capital femoral epiphysis worldwide is in situ fixation with a threaded screw. Un-threaded screws are designed to prevent slip progression without hindering residual growth of the proximal femur. This study aimed to compare growth, remodelling and long-term outcomes after fixation with un-threaded screws and a matched cohort of patients treated with a standard screw. Six patients (nine hips) treated with un-threaded screws and 16 patients (21 hips) treated with standard screws matched for age, skeletal maturity, sex and Southwick angle were recruited. Clinical records were reviewed for patient demographics, medical history and complications. Radiographs were reviewed for residual growth and time to physeal closure. Growth velocity was calculated. Absence of cam deformity signified complete remodelling. Clinical assessment was graded from excellent to poor and patient-reported outcomes were recorded. There was significantly more growth recorded in the un-threaded screw group in femoral neck length (7.6 mm, P = 0.003), articulo-lesser trochanter distance (5.3 mm, P = 0.028), pin-joint ratio (7.439%, P = 0.006) and pin-physis ratio (8.244%, P = 0.001). The probability of revision operations due to ongoing growth was higher in this group (risk ratio 6.57, P = 0.0008). Time to physeal closure was not significantly different, but growth velocity was significantly higher in the un-threaded group. The lower probability of cam deformity was not significant. Functional and clinical results were not significantly different at average 11.2 years' follow-up. Un-threaded screws allow for significantly more growth than standard threaded screws. The un-threaded screw could not be recommended due to the higher re-operation rates, without any proven benefit.