Analysis of risk factors for femoral head necrosis after internal fixation of femoral neck fractures with dynamic hip screw and anti-rotation screw

Objective To explore the influence factors for femoral head necrosis after treatment of femoral neck fractures with dynamic hip screw (DHS) and anti-rotation screw. Methods A retrospective case series analysis was made on the clinical data of 106 cases of femoral neck fractures who had undergone fixation with DHS and anti-rotation screw between May 2010 and May 2015. There were 59 males and 47 females, with an average age of 57.0 years (range, 27-76 years). By Garden classification, there were 27 cases of type Ⅱ, 51 cases of type Ⅲ and 28 cases of type Ⅳ. All cases were divided into femoral head necrosis group (18 cases) and none-necrosis group (88 cases) according to the radiographs of the fractured hip at the follow-up. Univariate analyses and a multivariate logistic regression analysis were made to test whether the following factors were significantly associated with femoral neck necrosis: sex, age, Garden classification, Pauwels classification, Singh index, injury-to-surgery time interval, reduction methods, reduction quality, complete weight-bearing time, implant removal and the time cost of implant removal surgery. Results All the 106 patients obtained a mean follow-up of 49 months (range, 26-76 months). Femoral head necrosis occurred in 18 cases (17.0%). In univariate analyses, Garden classification, reduction quality, implant removal and long time of the implant removal surgery were significantly associated with femoral head necrosis(P<0.01). In multivariate logistic regression analysis, high level of Garden classification(95%CI 0.008, 0.998, P<0.05), implant removal and long time of the implant removal surgery(95%CI 0.000, 0.143, P<0.01) were found to have a significant effect on femoral head necrosis development. Conclusions Fracture displacement, removal of internal fixation and broadening the screw canal, which cand hinder the blood supply of femoral head, will enhance the rate of femoral head necrosis. As a result, it needs prudent consideration to remove internal fixation after internal fixation with DHS combined with anti-rotation screw for femoral neck fractures. When it is difficult to remove the anti-rotation screw, it is better to give up, rather than to force a removal. Key words: Femoral neck necrosis; Femoral neck fractures; Fracture fixation, internal; Bone nails