Gamma loop dysfunction of the quadriceps femoris of elderly patients hospitalized after fall injury.

BACKGROUND AND PURPOSE: Gamma loop dysfunction may increase the risk of falls. Therefore, we evaluated gamma loop function in subjects hospitalized after fall injury and examined whether aging affects the gamma loop. METHODS: Maximal voluntary contraction (strength) of knee extension and integrated electromyography (I-EMG) of the quadriceps femoris were examined to evaluate the activities of alpha motoneurons before and after 20-min vibration applied to the quadriceps femoris. Mean percentage changes were calculated as: (previbration value-postvibration value)/previbration valuex100). As strength and I-EMG of both uninjured (UG) and injured limbs (IG) of patients with a history of falls resulting in hospitalization were examined in each group, the mean percentage changes of the 4 groups were compared with those of controls [young control group (YCG) and elderly control group (ECG)]. RESULTS: Mean percentage changes in strength of UG and IG were significantly different from YCG but not the ECG. Mean percentage changes in I-EMG for VL (vastus lateralis) and VM (vastus medialis)in IG were significantly different from YCG. However, I-EMG of RF of IG were not significantly different from YCG. Although mean percentage changes in I-EMG of UG were not significantly different from ECG, those for VL and VM of IG were different from ECG. CONCLUSIONS: As the gamma loop dysfunction exited in the uninjured limbs of subjects with a history of falls resulting in hospitalization, a dysfunctional gamma loop could be a risk factor for falling. Further studies are needed to identify the effects of aging on gamma loop function.

Knee-flexion torque and morphology of the semitendinosus after ACL reconstruction.

PURPOSE: The present study aimed to clarify the relationship between deficits in knee-flexion torque and morphological changes in the semitendinosus muscle-tendon complex after harvesting the semitendinosus tendon for anterior cruciate ligament (ACL) reconstruction. METHODS: Isometric knee-flexion torque at 45 and 90 degrees of knee flexion was measured in limbs of 23 patients (22 +/- 4 yr) who underwent unilateral ACL reconstruction (12-43 months postoperation) using ipsilateral semitendinosus tendon. Magnetic resonance imaging scans were used to calculate the muscle volume and the muscle length of the semitendinosus and to confirm the presence of the regenerated semitendinosus tendon. RESULTS: The percentage of the knee-flexion torque of the ACL-reconstructed limb compared with that of the contralateral limb was lower at 90 degrees than at 45 degrees . The regeneration of the semitendinosus tendon-like structure was confirmed in 21 of the 23 patients. However, muscle volume and muscle length of the semitendinosus in the ACL-reconstructed limb were significantly smaller compared with in the contralateral limb. CONCLUSION: Deficits in knee-flexion torque at deep knee flexion were associated with the atrophy and shortening of the semitendinosus after harvesting the semitendinosus tendon for ACL reconstruction.

Decrease of knee flexion torque in patients with ACL reconstruction: combined analysis of the architecture and function of the knee flexor muscles.

A decrease of deep knee flexion torque after anterior cruciate ligament (ACL) reconstruction, using a semitendinosus (and gracilis) tendon, has been reported. However, the cause of this weakness remains controversial. Architectural and functional differences in the knee flexor muscles influence this weakness. the fiber length of the semitendinosus, gracilis, semimembranosus, and biceps femoris were directly measured in six human cadavers. The flexion torque and EMG of the hamstrings were measured in both limbs of 16 patients (23+/-5 years) after ACL reconstruction (12-43 months post-operation), using ipsilateral semitendinosus tendon. Magnetic resonance imagings were taken, over both the thighs of those patients, to measure muscle volume and to confirm a state of semitendinosus tendon regeneration. The position of the musculotendinous junction of the semitendinosus was also analyzed. The fiber length of the semitendinosus and gracilis were three to four times longer than that of the semimembranosus and biceps femoris. The difference of flexion torque between the normal and ACL reconstructed limbs significantly increased as the knee flexion angle increased. The EMG value for the semimembranosus and biceps femoris of both limbs as well as the semitendinosus of the ACL reconstructed limbs, significantly reduced as the knee flexion angle was increased. The volume of the semitendinosus in the reconstructed limb was significantly smaller than in normal limbs. The regeneration of the semitendinosus tendon was confirmed in all subjects, and the musculotendinous junction position of the reconstructed limb in almost all subjects was found in further image from the knee joint space than that for the normal limb. The decrease of deep knee flexion torque, after ACL reconstruction, could be due to the atrophy and shortening of the semitendinosus after its tendon has been harvested, as well as the lack of compensation from the semimembranosus and biceps femoris, due to the architectural differences between the semitendinosus and the semimembranosus and biceps femoris.