TELEMETERIZED LOAD MEASUREMENT USING INSTRUMENTED SPINAL INTERNAL FIXATORS IN A PATIENT WITH DEGENERATIVE INSTABILITY

Study Design. in the present study, the loads in an internal spinal fi xation device were measured in vivo. Objective. To determine the impla nt loads for different activities before and after additional anterior stabilization of the spine. Summary of Background Data. Mathematical models exist for predicting spinal loads. The intradiscal pressure has been measured for many body positions and activities. The loads on in ternal spinal fixation devices have not been measured before in vivo. Methods. Telemeterized AO spinal internal fixators were implanted in a patient with degenerative instability. The implants allow the in vivo measurement of three force components and three moments, acting in th e implant. Results. When the patient was lying in relaxed positions, t he implant loads were small. Before additional anterior stabilization, the loads were also small for sitting, standing, and walking. The ben ding moment in the sagittal plane was less than 3 Nm for these activit ies. The highest loads within the first 4 weeks after implantation wer e measured while the patient turned from a supine to a lateral positio n against the advice of the physiotherapist. After anterior stabilizat ion,the maximum loads for the relaxed lying positions were altered onl y slightly. Much higher axial forces and bending moments were measured for sitting, standing, and walking. The maximum bending moment increa sed to 5-8 Nm for these activities. the implant loads for sitting were not higher than for standing. Conclusion. Flexion and lateral bending of the upper body and weight-carrying during sitting, standing, or wa lking should be avoided in the first few months after anterior stabili zation.