Use of a Torque-Range-of-Motion device for objective differentiation of diabetic from normal feet in adults

Background: The ability of the foot and ankle complex to act as an energy absorber is reflected in its viscoelastic properties. The Torque-Range-of-Motion (TROM) device was designed to provide an effective objective assessment of foot and ankle passive mechanical function. The hypothesis of this study was that mechanical parameters derived from passive TROM curves of otherwise normal feet of adults with diabetes would be significantly different from those of adults without diabetes. Methods: The TROM device is a single-degree-of-freedom hinge transducer system that is manually rotated through plantarflexion and dorsiflexion. The device was rotated manually with the muscles relaxed during a 50-second data acquisition period. A strain gauge provided the torque signal and a precision single-turn potentiometer provided plantarflexion-dorsiflexion angle to a two-channel portable data acquisition system. With the TROM device connected to a computer, input for instantaneous torque and range of motion was acquired and displayed as angle (degrees) versus torque (Newton-meters) on an output screen. The period provided sufficient data to average 16 to 20 cycles of motion. The study included 41 feet in adults without diabetes and 42 age-matched feet in adults with diabetes but no known foot problems. Results: For a probability level of .0001 there were significant differences in hysteresis area (normal: 91.1 ± 46.9 Nm-deg and diabetic: 161.7 ± 65.7 Nm-deg) and both dorsiflexion (normal: 0.4 ± 0.1 Nm/deg and diabetic: 0.9 ± 0.3 Nm/deg) and plantarflexion stiffness (normal: 0.34 ± 0.1 Nm/deg and diabetic: 0.7 ± 0.3 Nm/deg). Conclusions: The feet of adults with diabetes absorb more energy during cyclic motion (thus must dissipate more energy per cycle) and are stiffer in the terminal regions (where muscle-tendon-ligament properties prevail) than are the feet of adults without diabetes. These results suggest that this passive TROM method may be a sensitive, objective measurement of the viscoelastic properties of the foot and ankle, which may be an early indicator of diabetic patients who are at risk for the development of foot problems.