1. Study design and patient selection
This retrospective study was approved by the relevant institutional review board. We first reviewed patients diagnosed with hip fractures and treated with internal fixation using IMNs at our institution from January 2013 to October 2018. The inclusion criteria were as follows: 1) patients with an intertrochanteric femoral fracture, 2) patients without surgical or interventional histories of the contralateral hip before and after surgery, 3) patients who were followed for a minimum of 3 months after treatment, and 4) patients who were able to walk before surgery. We then divided the patients into two groups based on the nail device used for fixation. We used the proximal femoral nail (PFN, Synthes, Paoli, Switzerland), which has an anti-rotation screw for additional rotational stability, in earlier periods of the study. Later, we used a cephalomedullary nail (CMN, Zimmer, Warsaw, USA), a simpler device with a single lag screw. Both devices have similar design characteristics, except for the proximal lateralization angle (PFN: 6°, CMN: 4°) and the existence of an anti-rotation pin in PFNs versus an anti-rotation set screw in CMNs (Fig. 1). All patients in both groups were treated using a lag screw to fix the proximal segment, and for patients in the PFN group, the surgery was performed using a dual screw system with an anti-rotation screw. A total of 138 out of 273 patients (300 cases) were finally enrolled in the study based on the inclusion criteria, of which 83 patients were in the PFN group (group 1) and 55 patients were in the CMN group (group 2) (Fig. 2).
2. Fracture classification
The fracture pattern was classified by two skilled physicians (JYY and GII) according to the AO Foundation/Orthopaedic Trauma Association classification, which was revised in 2018 [11]. Simple radiographs and 3D computed tomography were used to assess fracture patterns and the presence of a BCF extending to the trochanteric area. We considered a BCF as an ECF only when accompanied by a trochanteric fracture extension [12].
3. Surgical procedures and postoperative rehabilitation
All surgical procedures were performed by a single senior surgeon (GII) at our institution. Patients were placed in the supine position on a fracture table, and a c-arm image intensifier was used to assess fracture reduction quality. Most surgeries were performed using the closed reduction technique, but in rare cases of irreducible or unmaintainable fractures, we performed mini-open reduction using a Hohmann retractor or curved Kelly forceps. When acute severe pain subsided, 2 or 3 days after the operation, we trained the patients to start protected weight-bearing (approximately 1/3 of the individual body weight) using a walker. After discharge, patients were followed up at 6 weeks, 3 months, 6 months, and 12 months postoperatively, and then annually.
4. Radiologic assessment
The Singh index is a radiographic grading system for osteoporosis and is measured from the normal contralateral hip of the patients [13]. The grade ranges from 1 (principal tensile and compressive trabeculae are markedly reduced or absent) to 6 (all normal trabecular groups are visible), and patients with Singh’s grades ≤3 were considered to have significant osteoporosis. The lag screw positioning was analyzed using the Cleveland index (zones 1–9) [14]. Cleveland index zones 5 (center, center) and 8 (center, inferior) were considered as ideal, and zones 4, 6, 7, and 9 (non-central) were considered as non-ideal. The tip-apex distance was calculated from immediate postoperative X-rays, based on the method suggested by Baumgaertner et al [7]. Fracture reduction status was evaluated by several measurement methods. Restoration of the neck-shaft angle and axis deviation angle between the femoral neck and the lag screw was measured using anteroposterior radiographs, which were graded as good (<5 varus or valgus), acceptable (5–10), and poor (>10) [7, 15]. Medial and anterior cortical continuity was evaluated in the anteroposterior and translateral views and fracture reduction quality was classified as extramedullary, anatomical, and intramedullary. Finally, postoperative complications, such as surgical site infection (superficial or deep), fracture nonunion, post-traumatic osteonecrosis, fixation failure, screw cut-out, and reoperation of any cause were also investigated.
5. Statistical Analysis
Normality and equity of variance were used to assess the differences between the two groups. The metric data were presented as mean values ± 95% confidence intervals (CIs), while categorical data were presented as absolute frequency and percentage distributions. The student’s t-test or the Mann–Whitney U test was used for processing continuous data, and the Chi-square test or the Fisher’s exact test for categorical data. Stepwise selection was performed to control multiple collinearities between independent variables, with an entry condition of p<0.05 and a removal condition of p>0.10. Finally, multivariate logistic regression analysis was performed using variables that were found to be statistically significant (p<0.05) in the univariate analysis.