Extensive Type II Muscle Fiber Atrophy in Elderly Female Hip Fracture Patients

• Background: Sarcopenia, or the loss of muscle mass and strength, is known to increase the risk for falls and (hip) fractures in older people. The objective of this study was to assess the skeletal muscle fiber characteristics in elderly female hip fracture patients.Method: Percutaneous needle biopsies were collected from the vastus lateralis muscle in 15 healthy young women (20 +/- 0.4 years), 15 healthy elderly women (79 +/- 1.7 years), and 15 elderly women with a fall-related hip fracture (82 +/- 1.5 years). Immunohistochemical analyses were performed to assess Type I and Type II muscle fiber size, and myonuclear and satellite cell content.Results: Type II muscle fiber size was significantly different between all groups (p <.05), with smaller Type II muscle fibers in the hip fracture patients (2,609 +/- 185 mu m(2)) compared with healthy elderly group (3,723 +/- 322 mu m(2)) and the largest Type II muscle fibers in the healthy young group (4,755 +/- 335 mu m(2)). Furthermore, Type I muscle fiber size was significantly lower in the hip fracture patients (4,684 +/- 211 mu m(2)) compared with the healthy elderly group (5,842 +/- 316 mu m(2), p =.02). The number of myonuclei per Type II muscle fiber was significantly lower in the healthy elderly and hip fracture group compared with the healthy young group (p =.011 and p =.002, respectively). Muscle fiber satellite cell content did not differ between groups.Conclusion: Elderly female hip fracture patients show extensive Type II muscle fiber atrophy when compared with healthy young or agematched healthy elderly controls. Type II muscle fiber atrophy is an important hallmark of sarcopenia and may predispose to falls and (hip) fractures in the older population.

Nyckelord

Falls

Hip fracture

Muscle

Sarcopenia

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