Biomechanical Comparison of Short-, Mid-, and Long-Length Proximal Femoral Nails for Femoral Intertrochanteric Fracture (AO/OTA 31A3.3) Fixation.

Introduction: In surgeries for unstable AO/OTA 31A3.3 fractures, surgeons use various lengths of intramedullary nails (IMNs). However, there is insufficient evidence regarding the appropriate nail length for these fractures. This study compared the biomechanical properties of IMNs of different lengths for AO/OTA 31A3.3 fractures.

Methods: 30 synthetic femora of AO/OTA 31A3.3 fracture model were randomly assigned to the following three groups: short- (170 mm), mid- (235 mm), and long-length (300 mm) nail groups, and were performed fixation surgery. The translation patterns of the constructs were examined by cyclic testing and compared among three groups. Additionally, changes in the neck-shaft and shaft-nail angles after cyclic testing were evaluated using radiological images.

Results: The translation patterns during cyclic loading did not differ among the groups. Conversely, one-way analysis of variance (ANOVA) revealed a significant difference in the neck-shaft angle change (5.8° ± 1.8°, 2.8° ± 1.3°, and 1.9° ± .9° in the short-, mid-, and long-length groups, respectively; P < .001), and post-hoc analysis revealed that the change was greater in the short-length group than in the mid- and long-length groups (P < .001 and P < .001, respectively). Furthermore, one-way ANOVA revealed a significant difference in the shaft-nail angle change (3.1° ± 2.1°, 1.4° ± 1.4°, and .1° ± .6° in the short-, mid-, and long-length groups, respectively; P < .001), and post-hoc analysis revealed that the change was greater in the short-length group than in the mid- and long-length groups (P = .044 and P < .001, respectively).

Conclusions: Short-length nails were associated with relevant changes in the neck-shaft and shaft-nail angles in our AO/OTA 31A3.3 fracture model. Thus, the selection of mid- or long-length nails instead of short-length nails might be better in IMN surgery for these fractures to prevent postoperative varus deformity.