Clinical and functional outcome of the Thrust Plate Prosthesis: short- and medium-term results

Objectives. The purpose of this study was to objectively assess the functional outcome after implantation of a Thrust Plate Prosthesis. Design. This retrospective study compared the gait patterns of 33 patients to a control group. Background. Few studies have been published about this type of prosthesis describing clinical and radiographic outcome. Even though the evaluation of the functional outcome is a commonly accepted way to measure the success of an implant it has not been reported in previous studies. Methods. Beside clinical (SF-36, and Harris Hip Score) and radiographic evaluation subjects were examined by three dimensional gait analysis and surface electromyography from seven leg and trunk muscles bilaterally. Results. The average Harris Hip Score was 85.7 points, and the SF-36 only differed significantly from controls regarding physical functioning. The radiography showed considerable radiolucencies under the Thrust Plate. Kinematic parameters indicated a slight impairment of the operated limb. The analysis revealed a decreased hip (28.2%) and knee (51.2%) range of motion during gait. The joint moments on the operated side were reduced in hip (72%) and knee abduction (59%) in comparison to controls. The average electromyographic parameters indicated a significantly higher mean and peak amplitude of the tensor fasciae latae (mean 56%, peak 54%), and gluteus medius (mean 33%, peak 21%) and a lower peak activity of the gluteus maximus (19%). Conclusions. The results indicate a generally good functional outcome even though a slightly asymmetrical loading was observed. No major limitations in physical functioning and health-related quality of life was seen. The radiographic signs of loosening might indicate difficulties in achieving the proximal load transfer of this implant.