Evaluation of triceps surae muscle length and resistance to passive lengthening in patients with acquired brain injury.
OBJECTIVE
To examine changes in muscle length and resistance to passive lengthening in the triceps surae muscles in patients with recently acquired brain injury.


BACKGROUND
Increased passive resistance in the triceps surae muscles is common following acquired brain injury. Adaptive shortening secondary to relative immobility, and increased stiffness due to rheologic changes within the musculo-tendinous unit, may be exacerbated by plantarflexor muscle overactivity related to the brain injury itself.


METHODS
Three variables representing resistance to passive lengthening and soleus muscle length were compared between subjects with recent brain injury and age matched normal controls. Comparison between limbs was made for subjects with unilateral neurological impairment.


METHODS
Slow passive dorsiflexion stretches were performed using a computer controlled dynamometer. Muscle stiffness in the initial and latter portion of the range, and the angles achieved at torques of 5 and 10 N m were determined from torque-angle curves. Maximal ankle dorsiflexion with the knee flexed was considered to reflect soleus muscle length.


RESULTS
Significant differences were demonstrated for all variables, except passive stiffness near the end of available range. The limb ipsilateral to unilateral brain injury differed from control limbs in that significantly less passive range of dorsiflexion was available and initial resistance to passive stretch was significantly less.


CONCLUSIONS
The reduction in soleus muscle length evident in subjects with recent acquired brain injury, even in neurologically unaffected limbs, may reflect the influence of relative immobility. Although plantarflexor muscle overactivity was found to be associated with increased resistance to slow passive stretch, the mechanism was unable to be elucidated from these data. The limb ipsilateral to unilateral neurological impairment cannot be considered to be a 'normal' control for comparative purposes.


CONCLUSIONS
Adaptive shortening and increased resistance to passive lengthening limit active ankle dorsiflexion, and alter ankle biomechanics. Tonic muscle overactivity has the potential to exacerbate these changes. Prophylactic management of inappropriate muscle activity and maintenance of muscle length may facilitate the achievement of rehabilitation goals and reduce subsequent disability following acquired brain injury.
Singer
B
B
The Centre for Musculoskeletal Studies, Department of Surgery, University of Western Australia, Level 2, MRF Building, Rear 50, Murray Street, 6000, Perth, Australia.
Dunne
J
J
Singer
K P
KP
Allison
G
G
D000293:Adolescent; D000328:Adult; D000843:Ankle Joint / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D001930:Brain Injuries / Q000503:physiopathology*; D004576:Electromyography; D005260:Female; D006801:Humans; D020300:Intracranial Hemorrhages / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology*; D026741:Physical Therapy Modalities; D011446:Prospective Studies; D016059:Range of Motion, Articular