Clinical and functional results of constrained knee arthroplasties

Aim of the study. To assess the clinical and functional outcome after impla ntation of a constrained knee arthroplasty. Material and methods. 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 exam inations as well as gait analysis and surface electromyography. The results were compared with a group of healthy volunteers. The clinical examination s were scored with the HSS, the Knee Society Score, the Tegner Activity Sco re, the Patella Score and the Visual Analogue Scale. Gait analysis was perf ormed with a three dimensional motion analysis system. Surface electromyogr aphy was evaluated bilaterally from the rectus femoris, vastus medialis and lateralis, semitendinosus, biceps femoris (long head),tibialis anterior an d gastrocnemius (medial head). Results. The comparison between the healthy volunteers and the patients sho wed significant functional deficits in the patient group. The electromyogra phy demonstrated significantly lower peak amplitudes in 5 of 7 muscles. In all parameters - except for knee extension - gait analysis resulted in sign ificant differences between the patient and control group. The comparison b etween the operated and non operated leg showed a significant difference on ly for knee extension. The patients revealed a bilateral functional deficit so that gait symmetry was preserved. Conclusion. 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 postopera tive rehabilitation programs to prevent postoperative functional deficits c an be concluded.