[Clinico-functional results of constrained knee endoprostheses]

To assess the clinical and functional outcome after implantation of a constrained knee arthroplasty.

14 patients with a revision of the primary prostheses with constrained knee arthroplasties ("Genesis constrained" and "Blauth") were evaluated in the operated and non operated leg at an average follow-up of 8.5 months (range 6.5 to 61.4 months). The study included clinical examinations as well as gait analysis and surface electromyography. The results were compared with a group of healthy volunteers. The clinical examinations were scored with the HSS, the Knee Society Score, the Tegner Activity Score, the Patella Score and the Visual Analogue Scale. Gait analysis was performed with a three dimensional motion analysis system. Surface electromyography was evaluated bilaterally from the rectus femoris, vastus medialis and lateralis, semitendinosus, biceps femoris (long head), tibialis anterior and gastrocnemius (medial head).

The comparison between the healthy volunteers and the patients showed significant functional deficits in the patient group. The electromyography demonstrated significantly lower peak amplitudes in 5 of 7 muscles. In all parameters--except for knee extension--gait analysis resulted in significant differences between the patient and control group. The comparison between the operated and non operated leg showed a significant difference only for knee extension. The patients revealed a bilateral functional deficit so that gait symmetry was preserved.

The presented results indicate that the functional deficits may be caused by preoperative deficits and are not only due to the operation. It can be supposed that the gastrocnemius is more important because of the high correlation with the clinical results. The value of pre- and postoperative rehabilitation programs to prevent postoperative functional deficits can be concluded.