Tip-apex distance of intramedullary devices as a predictor of cut-out failure in the treatment of peritrochanteric elderly hip fractures

Abstract

A tip-apex distance (TAD) of greater than 25 mm has been shown to be an accurate predictor of lag screw cut-out when sliding hip screws (SHS) are used to treat peritrochanteric (PT) hip fractures. The purpose of this study was to determine which factors, including TAD, correlated with successful clinical outcomes of PT hip fractures surgically treated with intramedullary (IM) devices. A total of 192 patients were included in this retrospective study. The TAD values of this cohort were radiographically analysed at a mean follow-up of 13 months. This was correlated with limited functional status and the rate of revision for implant failure or inability to achieve fracture union. Only 82 patients had adequate follow-up to fracture union or definitive failure. There were 46 intertrochanteric (IT) hip fractures and 36 subtrochanteric (ST) fractures. Overall, seven patients (8.5%) went on to experience lag screw cut-out. The average TAD of the patients who did not cut-out was 18 mm, compared to 38 mm for those who did (p = 0.012). All patients who cut-out had IT fractures (p = 0.017). The percentage of cut-outs correlated directly to both the severity of IT fractures and the TAD. Using a cutoff of 25 mm there was a statistically significant difference in the incidence of lag screw cut-out (p < 0.001). As in sliding hip screws, surgeons should strive for a TAD less than 25 mm when using IM devices in the treatment of PT hip fractures to help avoid lag screw cut-out.

Figures

Fig. 1

Illustration of tip-apex distance (TAD) with its corresponding equation for correcting radiographic magnification. Xap and Xlat refer to the measured distance as illustrated on the anteroposterior and lateral X-rays, respectively. Dtrue refers to the actual diameter of the lag screw; whereas, Dap and Dlat refer to the measured diameter of the lag screw as illustrated on the anteroposterior and lateral X-rays. (Used with permission from Baumgaertner et al. [7])

Fig. 2

Percentage of cut-outs and non-cut-outs for all subtrochanteric (ST) and intertrochanteric (IT) fracture pattern subtypes. The IT fracture patterns were classified according to the system of Muller and Evans as modified by Kyle et al. [13], with types III and IV considered unstable

Fig. 3

Percentage of cut-outs and non-cut-outs withing each respective tip-apex distance (TAD) (mm) range