Comparison of passive stiffness variables and range of motion in uninvolved and involved ankle joints of patients following ankle fractures.

BACKGROUND AND PURPOSE: The purpose of this study was to quantify several variables of ankle stiffness and dorsiflexion (DF) range of motion (ROM) in the casted (fractured) and noncasted ankles of humans after cast removal.

SUBJECTS: Thirty subjects (mean age = 32.4 years, SD = 15.8) with malleolar ankle fractures were tested within 4 days of cast removal but before they began physical therapy.

METHODS: A torque motor system generated torque-versus-displacement graphs by recording angular displacement and resistive torque during a 6 0/s passive cycling of the ankle from 10 degrees of plantar flexion to the limit of DF ROM: Maximum passive DF ROM, passive torque, and passive elastic stiffness at the neutral position and energy loss were measured. Testing was performed in the absence of triceps surae muscle electromyographic activity. For analysis, subjects were separated into two groups based on fracture severity.

RESULTS: There was no difference in passive torque between the fractured ankles and the matched noncasted ankles. There was a small difference in passive elastic stiffness between the more severely fractured ankles and the matched noncasted ankles. The fractured ankles were different in terms of energy loss from the matched noncasted ankles. For maximum passive DF ROM, there was a large difference between the fractured ankles (more severe: mean = 4.4 degrees; less severe: mean = 6.8 degrees) and the matched noncasted ankles (more severe: mean = 15.1 degrees; less severe: mean = 19.1 degrees).

CONCLUSION AND DISCUSSION: Altered length-tension relationships and neuromuscular mechanisms have been suggested to produce postimmobilization joint contractures. The results of this study on humans are consistent with both possibilities and support the theory that changes that occur during immobilization result in protection from overstretching of the fragile calf musculature after a period of ankle fixation. The time course of normalization of stretch reflexes warrants investigation.