Risk factors for avascular necrosis in Delbet type II paediatric femoral neck fractures: a case-control study

Paediatric femoral neck fractures (PFNFs) are rare but carry a significant risk of avascular necrosis (AVN) of the femoral head. Delbet type II fractures are the most common variant, yet specific predictors of AVN within this subgroup remain unclear. This study aimed to identify risk factors for AVN in Delbet type II PFNFs and evaluate the functional outcomes following management with weight-bearing restriction and bisphosphonate therapy.

A retrospective case-control study conducted from June 2011 to May 2022 included a total of 15 Delbet type II fractures. 5 patients who developed AVN (cases) were matched in a 1:2 ratio with 10 patients who did not develop AVN (controls). Quality of reduction was quantified using the neck-shaft angle (AP view) and Southwick angle (lateral view). Functional outcomes were evaluated at final follow-up (mean 35.2 months) using the Ratliff criteria and modified Harris Hip Score (mHHS).

An increased Southwick angle was significantly associated with AVN (mean 14.8° vs. 5.95°, p = 0.012; OR 1.30, 95% CI, 1.01-1.68). Age >7 years and non-anatomic reduction showed high odds ratios (OR 6.00), but did not achieve statistical significance. Reduction method, type of fixation and injury-surgery interval were not significantly associated with AVN. 4 out of 5 AVN cases achieved good functional outcomes, and 1 achieved a fair outcome following a 12-month regimen of oral bisphosphonates and restricted weight-bearing.

An increased Southwick angle following fracture reduction is a significant predictor of AVN in Delbet type II PFNFs, emphasising the critical importance of achieving anatomical reduction in the sagittal plane. If AVN develops, conservative management with oral bisphosphonates and protected weight-bearing yields favourable functional outcomes.