Proceedings of The Physiological Society

University of Oxford (2011) Proc Physiol Soc 23, PC83

Poster Communications

Effects of immobilization and rehabilitation on human lower leg muscles measured using magnetic resonance imaging

M. Psatha1,2, Z. Wu3,4, F. M. Gammie1, A. Ratkevicius5, H. Wackerhage5, J. H. Lee6, T. W. Redpath3, F. J. Gilbert3, G. P. Ashcroft1, J. R. Meakin1,7, R. M. Aspden1

1. Musculoskeletal Research Programme, University of Aberdeen, Aberdeen, United Kingdom. 2. Neuromuscular Diseases Group, University of London, Royal Veterinary College, London, United Kingdom. 3. Aberdeen Biomedical Imaging Centre, University of Aberdeen, Aberdeen, United Kingdom. 4. Imaging Sciences, Imperial College, London, United Kingdom. 5. Molecular Exercise Physiology, University of Aberdeen, Aberdeen, United Kingdom. 6. Wyeth Research, Collegeville, Pennsylvania, United States. 7. Biomedical Physics, University of Exeter, Exeter, United Kingdom.

Muscle atrophy occurs rapidly during cast immobilization, rehabilitation is a clinical challenge and the time course of changes during these phases is poorly understood. The aim of this study was to use magnetic resonance imaging (MRI) to generate imaging biomarkers of muscle function and we report here the changes occurring during 8 weeks of rehabilitation following 6 weeks of cast immobilization. Eighteen patients (8 M, 10 F), who had one lower leg (13 right, 5 left) immobilized in a cast were reported previously (1). Seventeen completed a rehabilitation phase comprising a strength training regime with strength assessment (KinCom dynamometer) and MRI (Philips Achieva 3.0 T) at two-weekly intervals. The same protocol was followed by 44 volunteers in 3 age groups (20-30yrs, 7 M, 9 F; 50-65yrs, 7 M, 7 F; and >70 yrs, 8 M, 6 F). Cross-sectional area (CSA) was measured for tibialis anterior (TA), gastrocnemius (Gast) and soleus (Sol) from high-resolution T1-weighted spin-echo images. Volume was calculated from the product of CSA and the distance from the tibial plateau to the insertion of Gast into the Achilles tendon. Pennation angle was measured in Gast from a high resolution T1-weighted spin-echo image. Fractional fat/water ratios were calculated using a 3-point Dixon method. T2 relaxation time before and after exercise was determined using a multi spin-echo scan. Measurements other than volume were taken at a point 70% of the distance from the lateral malleolus to the tibial tuberosity. In patients, strength increased by 3.4 N/day in plantarflexion and 1.1 N/day in dorsiflexion. CSA largely recovered to baseline values apart from Sol which was still ~5% smaller than the contra-lateral leg at day 99. T2 peaked at the end of the cast period for TA and Sol but continued to rise until day 57 for Gast before returning to baseline. In the contra-lateral leg T2 was unchanged. Pennation angle decreased during immobilization but recovered rapidly following cast removal. In volunteers, strength increased by 2.8 N/day in plantarflexion and 0.4 N/day in dorsiflexion. No changes were found in any MRI measures. T2 in each muscle increased with age and in Gast showed the largest response to exercise. In healthy volunteers, exercise had no effect on any of the MRI measurements, despite an increase in strength. Strength increases in patients were slightly larger than volunteers and were reflected in changes in T2. The increase in T2 with age in the volunteers is in the same direction as that induced by atrophy, although not so marked. T2 may, therefore, provide an imaging marker for atrophy and sarcopenia.

Where applicable, experiments conform with Society ethical requirements