Effects of rolling resistances on handrim kinetics during the performance of wheelies among manual wheelchair users with a spinal cord injury.

STUDY DESIGN: Repeated cross-sectional study. OBJECTIVES: To compare the effects of rolling resistances (RRs) on handrim kinetic intensity at the non-dominant upper limb and on handrim kinetic symmetry during wheelies performed by manual wheelchair users (MWUs) with spinal cord injury (SCI). SETTING: Pathokinesiology Laboratory. METHODS: Sixteen individuals with SCI who were able to perform wheelies participated in this study. During a laboratory assessment, participants randomly performed wheelies on four RRs: natural high-grade composite board, 5-cm thick soft foam, 5-cm thick memory foam, and with the rear wheels blocked by wooden blocks. Four trials were conducted for each of the RRs. Participant's wheelchair was equipped with instrumented wheels to record handrim kinetics, whereas the movements of the wheelchair were recorded with a motion analysis system. RESULTS: The net mean and peak total forces, including its tangential and mediolateral components, were greater during take-off compared with the other phases of the wheelie, independently of RR. During take-off, the greatest net mean and peak total and tangential forces were reached with the wheels blocked. Symmetrical tangential and mediolateral force intensities were applied at the dominant and non-dominant handrims. CONCLUSION: Wheelies performed on low or moderate density foam generate similar forces at the handrim than on a natural surface and significantly less forces than with the wheels blocked. Hence, when teaching individuals with an SCI to perform a stationary wheelie, the use of low or moderate density foam represents a valuable alternative for minimizing upper limb effort and may also optimize quasi-static postural steadiness.

Biomechanical modeling of anterior spine instrumentation in AIS.

This study is part of a larger project regarding the development of a Spine Surgery Simulator (S3), which has shown good results for posterior instrumentation surgeries. The aim was to develop a biomechanical model for the anterior instrumentation of the scoliotic spine. A biomechanical model using flexible mechanism was developed and surgical manoeuvres (instrumentation, rod installation and compression) were reproduced. Validation of the model was done by comparing the results for the instrumented part of the spine to the post-operative data (analytical Cobb angles in the frontal and sagittal planes, plane of maximum deformity, etc.). To date, surgeries of four patients operated by thoracotomy were reproduced. Preliminary results show that anterior instrumentation of the scoliotic spine can be adequately modelled using pre-operative geometric data and using mechanical properties from literature. Once validated with a larger sample of cases, the anterior instrumentation model could be implemented into S3 and used by orthopaedic surgeons to test various instrumentation strategies in virtual reality before performing the actual surgery.

Preoperative planning simulator for spinal deformity surgeries.

STUDY DESIGN: Proof of concept of a spine surgery simulator (S3) for the assessment of scoliosis instrumentation configuration strategies. OBJECTIVE: To develop and assess a surgeon-friendly spine surgery simulator that predicts the correction of a scoliotic spine as a function of the patient characteristics and instrumentation variables. SUMMARY OF BACKGROUND DATA: There is currently no clinical tool sufficiently user-friendly, reliable and refined for the preoperative planning and prediction of correction using different instrumentation configurations. METHODS: A kinetic model using flexible mechanisms has been developed to represent patient-specific spine geometry and flexibility, and to simulate individual substeps of correction with an instrumentation system. The surgeon-friendly simulator interface allows interactive specification of the instrumentation components, surgical correction maneuvers and display of simulation results. RESULTS: The simulations of spinal instrumentation procedures of 10 scoliotic cases agreed well with postoperative results and the expected behavior of the instrumented spine (average Cobb angle differences of 3.5 degrees to 4.6 degrees in the frontal plane and of 3.6 degrees to 4.7 degrees in the sagittal plane). Forces generated at the implant-vertebra link were mostly below reported pull-out values, with more important values at the extremities of the instrumentation. CONCLUSION: The spine surgery simulator S3 has proven its technical feasibility and clinical relevance to assist in the preoperative planning of instrumentation strategies for the correction of scoliotic deformities.