Abstract
Introduction
Patients with hip osteoarthritis have a substantial loss of muscular strength in the affected limb compared to the healthy limb preoperatively, but there is very little quantitative information available on preoperative muscle atrophy and degeneration and their influence on postoperative quality of life (QOL) and the risk of falls. The purpose of the present study were two folds; to assess muscle atrophy and degeneration of pelvis and thigh of patients with unilateral hip osteoarthritis using computed tomography (CT) and to evaluate their impacts on postoperative QOL and the risk of falls.
Methods
We used preoperative CT data of 20 patients who underwent primary total hip arthroplasty. The following 17 muscles were segmented with our developed semi-automated segmentation method: iliacus, gluteus maximus, gluteus medius, gluteus minimus, rectus femoris, tensor facia lata, adductors, pectinus, piriformis, obturator externus, obturator internus, semimenbranosus, semitendinosus, vastus medialis and vastus lateralis/intermedius (Fig. 1). Volume and radiological density of each muscle were measured. The ratio of those of affected limb to healthy limb was calculated. At the latest follow-up, the WOMAC score was collected and a history of falls after surgery was asked. The average follow- up period was 6 years.
Comparison of the volume and radiological density of each muscle between affected and healthy limbs was performed using the Wilcoxon signed rank test. Correlations between the volume and radiological density of each muscle and each score of the WOMAC were evaluated with Spearman's correlation coefficient. The volume and radiological density of each muscle between patients with and without a history of falls were compared using Mann-Whitney U test.
Results
13 of 17 muscles showed significant decrease in muscle volume in affected limb compared to healthy limb. The mean muscle atrophy ratio was 18.6±7.1 (SD) % (0–28.3%). Iliacus, psoas, adductors and piriformis showed a significant volume reduction more than 25 %. All 17 muscles showed reduced radiological density along the affected limb compared to the healthy side. The difference was 8.7±4.2 (SD) Hounsfield units (3.2 to 16.4). Gluteus medius and gluteus minimus showed a significant decrease of radiological density more than 15 HU. The radiological density of gluteus minimus showed higher correlation (R>0.7) with physical function scores of WOMAC for descending stairs, rising from sitting, walking on flat surface, going shopping and rising from bed. Seven of 20 patients had a history of falls, who showed significant reduced radiological density of gluteus minimus and obturator internus compared to the 13 patients without a history of falls
Conclusion
Almost all muscles of pelvis and thigh along the affected limb showed marked atrophy and fatty degeneration compared to the healthy side. Especially, the degree of fatty degeneration of gluteus minimus showed significant impacts on postoperative physical function and the risk of falls of patients.
