Ultrasound changes to intramuscular architecture of the quadriceps following intramedullary nailing

Disuse atrophy is the basis for profound physiological changes of the muscles of immobilised limbs. The aim of this study was to use high resolution real-time ultrasonography (HRRTU) to assess the quadriceps musculature and to try and measure atrophy.

We monitored the effects of enforced reduction of mobility due to trauma on the intramuscular architecture of the quadriceps using HRRTU in 13 skeletally mature male patients (43.2 years, range 16 to 82 years), with an isolated unilateral diaphyseal fracture of the femur or of the tibia. All patients had undergone interlocked intramedullary nailing (IIN). Using HRRTU, the pennation angles and muscle fibre lengths of vastus lateralis, the cross sectional area (CSA) of the rectus femoris, and the quadriceps muscle layer thickness (MLT) were measured in the injured and the normal contralateral limb.

Repeated measurements showed the technique of measurement of the variables used in this study to be highly reproducible. There was a significant difference in the angle of pennation of the vastus lateralis in the nailed (15.4 degree) and the unnailed limb (21.2 degree), documenting that muscle atrophy causes a change to muscle architecture that results in a significant decrease in pennation angle (p=0.0002). The muscle fibre length was significantly different (p=0.002) and there was a significant correlation between pennation angle and muscle fibre length (r=-0.51, p=0.001). There was also a significant difference in the quadriceps MLT (p=0.001) and CSA of the rectus femoris (p=0.0004) implying that the whole of the quadriceps muscle is affected.

These simple, reproducible, non-invasive ultrasound measurements can easily demonstrate differences in the quadriceps morphology in the nailed and unnailed limb, which could allow individual exercise programme prescription.