Muscle strength has been previously reported to correlate with muscle CSA. Sarcopenia is defined as excessive muscle mass loss with aging that impairs activities of daily living (ADL) in older adults [5]. Sarcopenia affects ADL, such as walking and standing, and may lead to the need for nursing care and increased susceptibility to falls. Sarcopenia has also been reported to affect the severity and mortality of other diseases and is currently being focused on by a variety of medical specialties [12-14].
In general, femoral neck fractures reduce the ambulatory status. Various factors, such as end-stage renal disease, cirrhosis, cerebrovascular disease, and pre-fracture ambulatory status, have been reported as predictors of postoperative ambulatory status.
Regarding the relationship between femoral neck fractures and sarcopenia, the American Society of Anesthesiologists Physical Status classification system was reported as an independent prognostic factor [15,16].
However, few studies have previously reported on the relationship between sarcopenia and the postoperative ambulatory status of femoral neck fractures. Jung et al. reported that muscle mass in the hip flexors decreased after surgery for hip fractures [17]. Recently, the serum creatinine to cystatin C ratio was reported to reflect preoperative and early postoperative walking ability in older patients with hip fracture [18].
Muscle CSA and fatty degeneration were assessed using preoperative CT slices. A CT scan is usually performed as a preoperative evaluation allowing us to assess the muscle without additional examination.
Our results show that the CSA of the paraspinal and gluteus medius muscles correlated with pre-injury ambulatory status. According to these results, the CSA of the paraspinal and gluteus medius muscles can be used to identify sarcopenia.
Second, the CSA of the paraspinal, gluteus maximus, and gluteus medius muscles correlated with ambulatory status at discharge, and the CSA of the paraspinal and gluteus medius muscles correlated with final ambulatory status. This result suggests that the assessment of muscle CSA using preoperative CT could be useful in predicting postoperative ambulatory status.
Third, the improvement in ambulatory status from one week after surgery to discharge was significantly correlated with the CSA of the paraspinal muscle. Onuma et al. reported the activities of the gluteus medius muscle on the stepping side and paraspinal muscle on the stance side prior to the onset of movement in older adults. However, no activity was observed in the paraspinal muscles of young adults at the onset of movement [12]. The action of the paraspinal muscles for trunk stabilization during walking in older adults might support and explain our results.
Kuno et al. reported that even in older adults, muscle strength training increases muscle mass. However, they also mentioned that aerobic exercise alone, such as walking, does not increase muscle mass [13]. Thus, postoperative ambulatory status can be improved by increasing the muscle CSA, muscle mass, and muscle strength through effective rehabilitation.
In future studies, muscle strength measurements should be performed before and after surgery. Moving forward, a more aggressive rehabilitation regimen should be considered as a therapeutic intervention to increase muscle strength. Comparing the muscle strength and CSA between aggressive and normal rehabilitation will be the next step in solving our hypothesis.
Adequate therapeutic intervention after adjusting the workout intensity for individuals could potentially improve the postoperative ambulatory status after injuries such as femoral neck fractures. We believe that the results and insights from this study will help manage patients.
This study had a few limitations. First, we used the muscle CSA to evaluate muscle volume without correcting for the patient’s habitus. Previous studies have included corrected values by dividing CSAs by BMI. We did not examine height and body weight in this study. Second, the patient’s position on the CT scan and pelvic alignment might have impacted the variance of the CSA in axial slices. Other methods to directly measure muscle volume should be considered to improve the accuracy of evaluation. Third, the Goutallier classification is a qualitative grading system for evaluating fatty infiltration, degeneration, and atrophy of muscles. Quantitative evaluation of the muscles should be considered to obtain a more accurate analysis.