Spontaneous subcapital femoral neck fracture complicating osteonecrosis of femoral head.

Spontaneous subcapital fracture (SSF) of femoral neck in pre-existent osteonecrosis of femoral head (ONFH) is a rare presentation. Only a few cases have been reported so far and majority of them have been reported to have unilateral hip involvement. We retrospectively reviewed clinical-radiological data of 10 patients (12 hips) with SSF complicating ONFH. All of them underwent uncemented total hip arthroplasty. All the available publications in the English language based medical literature were critically reviewed and results were summarized. The median age of presentation was 32 years (range : 24 years to 61 years). They were followed up for a mean duration of 25 months (range : 12 months to 59 months). The most common risk factor was corticosteroid consumption (7 out of 10 patients). All except one (modified Ficat and Arlet stage II) belonged to advanced stage of ONFH {stage III 3 patients (3 hips), stage IV 6 patients (8 hips)}. The mean time lag of ONFH to presentation was 22.3 months (range : 5 months to 60 months), and SSF to presentation was 13.8 days (range : 1 day to 28 days). Mean pre- operative Harris Hip Score was 10.8 (range : 8 to 14), which improved to 93 (range : 91 to 96) after total hip arthroplasty when last followed up (p<0.05). Corticosteroids induced ONFH has a propensity to develop SSF. This entity should find a place in existing classification system.