1. Subjects
Of all 26 patients in the intertrochanteric fracture group, 6 (23.1%) were males and 20 (76.9%) were females. Of all 22 patients in the femoral neck fracture group, 9 (40.9%) were males and 13 (59.1%) were females. In chi-square analyses, there was no significant difference between the two groups. The mean age was 79.8 (64–91) years in the intertrochanteric fracture group and 79.5 (68–93) years in the femoral neck fracture group. The average height was 156.6 (146–168) cm and 157.1 (148–170) cm in the intertrochanteric and femoral neck fracture groups, respectively. The average weight was 54.2 (38–77) kg and 52.8 (35–67) kg at the time of surgery, and 55.4 (34–80) kg and 54.2 (38–69) kg at the final follow-up in the intertrochanteric and femoral neck fracture groups, respectively. The mean BMI was 22.31 (15.98–32.34) and 21.32 (15.56–32.76) at the time of surgery, and 22.85 (14.15–38.05) and 21.98 (16.53–31.79) at the last follow-up in the intertrochanteric and femoral neck fracture groups, respectively. The mean BMD was − 2.94 (-1.9~-4.9) and − 2.91 (-1.3~-4.3) in the intertrochanteric and femoral neck fracture groups, respectively. The mean HHS was 82.65 (54.15–97.65) and 85.36 (51.3-93.65), and the mean HHS related with function was 48.69 (32–61) and 50.18 (32–65) at the final follow-up in the intertrochanteric and femoral neck fracture groups, respectively. The postoperative duration until the last follow-up was 20.23 (12–91) months in the intertrochanteric fracture group and 21.51(13–88) in the femoral neck fracture group. An independent t-test was performed to compare the means for two groups, but no statistically significant difference was exhibited (p > 0.05). (Table 1)
2. Cross-sectional area of muscles
The cross-sectional area of the gluteus medius and gluteus minimus was 1713.64 (1147.12-3167.34) mm2 and 566.59 (337.67-1072.92) mm2 in the intertrochanteric fracture group and 1815.56 (1157.47-2755.86) mm2 and 619.97(379.23-1125.71) mm2 in the femoral neck fracture group preoperatively; and 1815.56 (1249.01-3138.09) mm2 and 619.17 (361.07-1095.83) mm2 in the intertrochanteric fracture group and 2144.98 (1331.21-2946.68) mm2 and 764.39 (328.97-1384.49) mm2 in the femoral neck fracture group postoperatively. Both pre- and postoperative CSAs were significantly higher in the femoral neck fracture group (G.med preoperative p = 0.033, postoperative p = 0.028; G.min preoperative p = 0.002, postoperative p = 0.038). The CSA of the iliopsoas and rectus femoris was 810.86 (370.41-1543.30) mm2 and 503.66 (304.52-802.49) mm2 in the intertrochanteric fracture group and 661.88 (341.65-1175.15) mm2 and 386.72 (246.23-515.72) mm2 in the femoral neck fracture group preoperatively; and 681.98 (369.42-1313.32) mm2 and 426.24 (181.27-666.21) mm2 in the intertrochanteric fracture group and 571.32 (238.49-870.55) mm2 and 349.31 (161.79-575.83) mm2 in the femoral neck fracture group postoperatively. Both pre- and postoperative CSAs were significantly higher in the intertrochanteric fracture group (IP preoperative p = 0.036, postoperative p = 0.039; RF preoperative p = 0.041, postoperative p = 0.017). (Table 2)
The cross-sectional area/weight of the gluteus medius and gluteus minimus was 32.74 (19.24–58.62) mm2/kg and 10.96 (5.19–25.85) mm2/kg in the intertrochanteric fracture group and 38.87 (24.63–56.66) mm2/kg and 14.32 (5.66–22.74) mm2/kg in the femoral neck fracture group preoperatively; and 32.78 (24.27–53.22) mm2/kg and11.25 (6.56–24.35) mm2/kg in the intertrochanteric fracture group and 37.48 (27.78–49.94) mm2/kg and 14.78 (7.79–23.07) mm2/kg in the femoral neck fracture group postoperatively. Both pre- and postoperative measures were significantly higher in the femoral neck fracture group (G.med preoperative p = 0.011, postoperative p = 0.016; G.min preoperative p = 0.007, postoperative p = 0.001). The CSA/weight of the iliopsoas and rectus femoris was 17.73 (5.88–34.01) mm2/kg and 9.42 (4.83–12.35) mm2/kg in the intertrochanteric fracture group and 13.50 (6.82 ~ 24.55) mm2/kg and 7.23 (5.00-11.46) mm2/kg in the femoral neck fracture group preoperatively; and 12.68 (6.60-19.91) mm2/kg and 7.17(4.53–10.58) mm2/kg in the intertrochanteric fracture group and 9.88 (5.69–19.75) mm2/kg and 5.23 (3.24–9.33) mm2/kg in the femoral neck fracture group postoperatively. Both pre- and postoperative measures were significantly higher in the intertrochanteric fracture group (IP preoperative p = 0.016, postoperative p = 0.001; RF preoperative p = 0.014, postoperative p < 0.001). (Table 3) In the correlation analysis between postoperative CSA and HHS related with function, Pearson’s correlation coefficient was 0.19, 0.20, 0.01, and 0.05 in the gluteus medius, gluteus minimus, iliopsoas, and rectus femoris, respectively. All p-values were greater than 0.05, indicating no significant correlation. In the correlation analysis between postoperative cross-sectional area per weight (CSA/Wt, mm2/kg) and HHS related with function, Pearson’s correlation coefficient was 0.18, -0.33, -0.21, and 0.27 in the gluteus medius, gluteus minimus, iliopsoas, and rectus femoris, respectively. All p-values were larger than 0.05, showing no significant correlation. (Table 4)
3. Attenuation of muscles
The attenuation (Hounsfield unit, HU) of the gluteus medius and gluteus minimus was 32.19 (6–56) and 23.65 (4–38) in the intertrochanteric fracture group and 30.59 (11–61) and 17.36 (8–33) in the femoral neck fracture group preoperatively; and 23.54 (5–45) and 10.92 (3–23) in the intertrochanteric fracture group and 21.18 (4–36) and 11.09 (3–29) in the femoral neck fracture group postoperatively. No significant difference was found in pre- and postoperative attenuation between the two groups (G.med preoperative p = 0.693, postoperative p = 0.689; G.min preoperative p = 0.182, postoperative p = 0.972) A significant decrease in attenuation was shown after surgery in both groups (G. med intertrochanteric fracture group p = 0.005, femoral neck fracture group p = 0.011; G. min intertrochanteric fracture group p = 0.001, femoral neck fracture group p = 0.041). The attenuation of the iliopsoas and rectus femoris was 48.65 (12–71) and 45.38 (15–64) in the intertrochanteric fracture group and 44.55 (13–68) and 44.73 (17–62) in the femoral neck fracture group preoperatively; and 38.54 (11–52) and 36.00 (14–58) in the intertrochanteric fracture group and 35.09 (12–52) and 35.68 (13–55) in the femoral neck fracture group postoperatively. No significant difference was shown in pre- and postoperative attenuation between the two groups (IP preoperative p = 0.319, postoperative p = 0.417; RF preoperative p = 0.760, postoperative p = 0.936). A significant decrease in attenuation was demonstrated after surgery in both groups (IP intertrochanteric fracture group p = 0.006, femoral neck fracture group p = 0.034; RF intertrochanteric fracture group p = 0.005, femoral neck fracture group p = 0.002). (Table 5)
The pre- and postoperative attenuation of all 48 patients enrolled to the study was 31.46 (6–61) and 22.46 (4–45) in the gluteus medius; 20.77 (4–38) and 11.00 (3–29) in the gluteus minimus; 46.77 (12–71) and 36.96 (11–58) in the iliopsoas; and 45.08 (15–68) and 35.85 (13–58) in the rectus femoris, respectively. A significant reduction was shown in all muscles (p < 0.001). (Table 6)