Evaluation Of Contact Pressure On Total Surface Bearing And Patellar Tendon Bearing Sockets During Stair Ascent And

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1 Evaluation Of Contact Pressure On Total Surface Bearing And Patellar Tendon Bearing Sockets During Stair Ascent And Descent Koji Totoribe, Etsuo Chosa, MD, PhD, Xin Zhao, MD, PhD, Go Yamako, PhD, Shinji Watanabe, MD, Hiroaki Hamada, MD, PhD, Gang Deng, PhD. University of Miyazaki, Miyazaki, Japan. Disclosures: K. Totoribe: None. E. Chosa: None. X. Zhao: None. G. Yamako: None. S. Watanabe: None. H. Hamada: None. G. Deng: None. Introduction: Stair ascent and descent is a functional skill needed for independent daily living, but it is particularly difficult for individuals with leg amputation. Prosthetic sockets play a key role in joining a residual limb to a prosthesis, and to ensure a perfect fit, the socket needs to match the shape of the residual limb and meet the needs for activities of daily living. Some studies have investigated pressure distribution between the prosthetic socket and residual limb in level-ground walking, the pressure distribution associated with stair ascent and descent has not been elucidated. In addition, no detailed comparison has been made to reveal the differences in pressure distribution between the currently popular total surface bearing (TSB) and patellar tendon bearing (PTB) sockets during stair ascent and descent. In this study, we used the finite element (FE) method to develop an elaborated prosthetic model and performed a biomechanical study to assess the impact of stair ascent and descent and socket configurations on the residual limb by taking into account the load measured in motion analysis. Methods: To develop an FE model, geometric data were obtained by computed tomography from a 34-year-old woman with left trans-tibial amputation, who gave informed consent to participate in this study (Fig. 1). A three-step stair (rise height, 17.5 cm; tread depth, 30 cm) was built for motion analysis, and six force plates were placed on the floor and on the first and second steps from the bottom (Fig. 2). Kinematic data were collected using a three-dimensional motion analysis system and calibration errors were kept below 0.3 mm. In a previous study, McFadyen et al. divided the stance phase in stair ascent into the subphases of weight acceptance (WA), pull-up, and forward continuance and the stance phase in stair descent into the subphases of WA, forward continuance, and controlled lowering (CL). Using their terminology and also based on the analysis of kinematic and kinetic data in the present study, we divided the stance phase in stair ascent and in stair descent into three subphases each and used the peak value of the moment and force on the knee joint in each subphase as the loading condition in the FE method. Four nodes of linear solid tetrahedral elements were used to form meshes of the cortical bone, trabecular bone, soft tissue, and linear elements for the FE models. Young's modulus of these elements was assigned to MPa, 400 MPa, 1.0 MPa, and 0.38 MPa, respectively, and the corresponding Poisson's ratio was 0.3, 0.3, 0.45, and 0.3. The interface between the residual limb and prosthetic socket was treated as a nonlinear contact problem, with friction set at 0.5 according to the literature. Fixed restraints were applied to the external surface of the socket and load was applied at the center of the knee. Results: In the TSB socket model, contact pressure at the boundary between the socket liner and residual limb was relatively equally distributed during stair ascent, and pressure appeared to be greater at the stump and front of the residual limb in the early (WA) subphase (Fig. 3A). Similar pressure distribution was observed during stair descent, and pressure was also higher at the stump and front of the residual limb in the early (WA) subphase and at the front of the residual limb in the final (CL) subphase (Fig. 3B). In the PTB socket model, pressure concentration was observed in the patellar ligament and popliteal region during stair ascent (Fig. 4A). During stair descent, pressure was concentrated in the patellar ligament, on the anterior, medial, and lateral sides of the tibia, and in the popliteal region in the early (WA) subphase and at the front of the residual limb in the final (CL) subphase (Fig. 4B). Furthermore, the PTB socket model generated higher pressure loads than the TSB socket model in all subphases, but particularly in the final CL subphase during stair descent. Discussion: The TSB socket has a cylindrical shape and the entire surface of the stump can disperse the load. Although the TSB socket in this study exerted pressure on the stump at the junction between the socket liner and residual limb, load bearing was clearly low overall and the fitting was satisfactory compared with the PTB socket. In contrast to the TSB pocket, the PTB socket is almost triangular with anterior convexity and has specific load-bearing areas. With the PTB socket, loads were higher and concentrated in the patellar ligament, on the anterior, medial, and lateral sides of the tibia, and in the popliteal region, particularly during stair descent. This suggests that to improve the fitting of a prosthesis, it is important to focus on pressure distribution at these sites in particular subphases. The FE analysis combined with actual motion analysis was useful for evaluating the effects of the different socket shapes during stair ascent and descent and will help to optimize prosthetic sockets for individual patients. Significance: With TSB sockets, contact pressure at the junction of the liner and residual limb is relatively equally distributed during stair ascent and descent. However, to obtain proper fitting of a prosthesis, it is important to remember that load bearing peaks in the WA subphase during stair descent. Acknowledgments: Supported by Grant-in-Aids from Establishment of the sport medical support system, a partnership

2 program with MEXT, and from MEXT/JSPS (# ). References:

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5 ORS 2014 Annual Meeting Poster No: 0778

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