Prognostic factors associated with a subchondral insufficiency fracture of the femoral head

Objective

The aim of this study was to identify the risk factors associated with the prognosis of a subchondral insufficiency fracture of the femoral head (SIF).

Methods

Between June 2002 and July 2009, 25 patients diagnosed with SIF were included in this study. Sequential radiographs were evaluated for the progression of collapse. Clinical profiles, including age, body mass index, follow-up period and Singh’s index, were documented. The morphological characteristics of the low-intensity band on T₁ weighted MRI were also examined with regards to four factors: band length, band thickness, the length of the weight-bearing portion and the band length ratio (defined as the proportion of the band length to the weight-bearing portion of the femoral head in the slice through the femoral head centre).

Results

Radiographically, a progression of collapse was observed in 15 of 25 (60.0%) patients. The band length in patients with progression of collapse 22.5 mm; 95% confidence interval (CI) 17.7, 27.3] was significantly larger than in patients without a progression of collapse (13.4 mm; 95% CI 7.6, 19.3; p<0.05). The band length ratio in patients with progression of collapse (59.8%; 95% CI 50.8, 68.9) was also significantly higher than in patients without a progression of collapse (40.9%; 95% CI 29.8, 52.0; p<0.05). No significant differences were present in the other values.

Conclusion

These results indicate that the band length and the band length ratio might be predictive for the progression of collapse in SIF.Subchondral insufficiency fractures of the femoral head (SIF) often occur in osteoporotic elderly patients 1-9]. Patients usually suffer from acute hip pain without any obvious antecedent trauma. Radiologically, a subchondral fracture is seen primarily in the superolateral portion of the femoral head 4,5,10]. T₁ weighted MRI reveal a very low-intensity band in the subchondral area of the femoral head, which tends to be irregular, disconnected and convex to the articular surface 2,4,5,7,9,11]. This low-intensity band in SIF was histologically proven to correspond with the fracture line and associated repair tissue 5,9]. Some cases of SIF resolve after conservative treatment 5,11-14]; other cases progress until collapse, thereby requiring surgical treatment 4-10,15]. The prognosis of SIF patients remains unclear.The current study investigated the risk factors that influence the prognosis of SIF based on the progression to collapse.