IntroductionDynamic knee recurvatum during gait, defined as hyperextension of the knee during the stance period of the gait cycle, is common in patients with a variety of neurologic based impairments. It has been reported in 46% of patients with strokes or traumatic brain injury (Hogue, et al., 1982), in cerebral palsy (Simon, et al, 1978), and poliomyelitis (Irwin, et al, 1942) and is commonly the direct result of quadriceps weakness, ankle plantar flexor spasticity, and / or a heel cord contracture (Perry, 1992). A primary concern for patients presenting with this problem is the potential risk for injury to the capsular and ligamentous structures of the posterior aspect of the knee. Such injury could lead to pain, ligamentous laxity or bony deformity. Gait laboratory analysis may provide more information about the forces involved at the knee to better assess the risk for injury. Presented here are the knee joint kinematics and kinetics associated with 52 limbs in 41 patients presenting with knee recurvatum during the stance period of gait.MethodologyThe kinematic and kinetic data from 41 patients with knee recurvatum (52 limbs), secondary to neurologic injury, presenting to the Spaulding Rehabilitation Hospital Gait Laboratory were retrospectively analyzed. Patients had neurologic injury secondary to stroke, traumatic brain injury, cerebral palsy, multiple sclerosis, poliomyelitis, or lower motor neuron spinal cord injury. The criteria for inclusion in the study were that knee hyperextension was noted from observational analysis and was confirmed by motion analysis. A 4-camera, ELITE passive marker motion analysis system (Bioengineering Technology Systems, Milan Italy) and force plates (Advanced Mechanical Technology Inc., AMTI, Newton, MA, USA) were used. A protocol (Pedotti, et al) which was commercialized by Bioengineering Technology Systems as SAFLo (Servizio di Analisi della Funzionalita' Locomotoria, Milan, Italy), was used to measure the kinematics and kinetics. Kinetics were calculated using the force plate data and inverse dynamic techniques. Torques were reported as external. Analysis of the sagittal plane kinematics and kinetics was performed for barefoot walking and, in 23 limbs, with ankle-foot-orthoses (AFO's). Kinematic and kinetic data obtained from 40 normal subjects, obtained in the same manner, were used for comparisons.ResultsPeak knee hyperextension ranged from -1 to -18 degrees with a mean of -5.9 (4.7) degrees. This peak knee hyperextension was statistically significantly different (p < 0.000001) from normal peak extension of 4.9 (3.9) degrees. The peak average external extensor torque (external) was 0.27 (0.18) Newton-meters which was also statistically significantly different (p = 0.00001) from normal peak average extensor torque of 0.13 (.06) Newton-meters. A poor correlation (r = 0.37, p = 0.003) was found between the peak hyperextension angle and peak extensor torque.For those patients in whom stroke or traumatic brain injury was the underlying neurologic injury, (n = 21) there was no relationship found between peak extensor torque and time since the neurologic event. In those limbs for which the patient wore an AFO (n = 23), the knee extensor torque was, in each case, less with the AFO than without the AFO. The average difference was also statistically significant (p = 0.003).DiscussionPerhaps the most important finding is the poor correlation between peak knee hyperextension and peak extensor torque. This implies that for a given amount of knee hyperextension, it is difficult to predict the extensive torque across the knee. Many patients had exceptionally high knee extensor torques which could not be predicted on the basis of the kinematics. Studying knee extensor torque is probably useful to study individual patient' risk for biomechanical injury and to assess the effect of treatments such as an AFO aimed to reduce the risk.