Chang-Hung Huang1,2,3, Lin-I Hsu1, Ting-Kuo Chang1,4, Tai-Yuan Chuang5, Shih-Liang Shih2,6, Yung-Chang Lu7,8,9, Chen-Sheng Chen10, Chun-Hsiung Huang1,3,4. 1. Biomechanics Research Laboratory, Mackay Memorial Hospital, No. 45, Mingsheng Rd, Tamshui District, New Taipei City, 25160, Taiwan. 2. Department of Physical Therapy and Assistive Technology, National Yang-Ming University, No. 155, Sec. 2, Li-Nung St., Taipei, 112, Taiwan. 3. Institute of Biomedical Engineering, National Yang-Ming University, Taipei, Taiwan. 4. Department of Orthopaedic Surgery, Mackay Memorial Hospital, Taipei, Taiwan. 5. Department of Orthopedic Surgery, Taipei Medical University-Wan Fang Hospital, Taipei, Taiwan. 6. Department of Orthopaedic Surgery, Zhong-Xing Branch of Taipei-City Hospital, Taipei, Taiwan. 7. Biomechanics Research Laboratory, Mackay Memorial Hospital, No. 45, Mingsheng Rd, Tamshui District, New Taipei City, 25160, Taiwan. yungchanglu@hotmail.com. 8. Department of Orthopaedic Surgery, Mackay Memorial Hospital, Taipei, Taiwan. yungchanglu@hotmail.com. 9. Mackay Junior College of Medicine, Nursing, and Management, Taipei, Taiwan. yungchanglu@hotmail.com. 10. Department of Physical Therapy and Assistive Technology, National Yang-Ming University, No. 155, Sec. 2, Li-Nung St., Taipei, 112, Taiwan. cschen@ym.edu.tw.
Abstract
PURPOSE: Whether to resurface the patella in knee replacement remains a controversial issue. The geometrical design of the trochlear groove in the femoral component could play an important role in determining the stress distribution on the patellofemoral joint, but this has not been sufficiently reported on. This study attempted to determine the effect of implant design on contact mechanics by means of a finite element method. METHODS: Two designs, an anatomical V-shape design (VSD) and a dome-shape design (DSD), for the anterior trochlear surface in a contemporary femoral component were chosen for examining the contact characteristics. The use and absence of patella resurfacing was simulated. The stress and strain distribution on the patellar bone and the polyethylene component were calculated for comparison. RESULTS: Without patellar resurfacing, the maximal compressive strain in the patellar bone in the VSD model was about 20 % lower than the DSD model. On the other hand, with resurfacing, the maximal strain for the VSD model was 13.3 % greater than for DSD. Uneven stress distribution at the bone-implant interface was also noted for the two designs. CONCLUSION: The femoral component with a V-shape trochlear groove reduced the compressive strain on the unresurfaced patella. If resurfacing the patella, the femoral component with a curved domed-shape design might reduce the strain in the remaining patellar bone. Uneven stress could occur at the bone-implant interface, so design modifications for improving fixation strength and medialization of the patellar button would be helpful in reducing the risk of peg fracture or loosening. LEVEL OF EVIDENCE: III.
PURPOSE: Whether to resurface the patella in knee replacement remains a controversial issue. The geometrical design of the trochlear groove in the femoral component could play an important role in determining the stress distribution on the patellofemoral joint, but this has not been sufficiently reported on. This study attempted to determine the effect of implant design on contact mechanics by means of a finite element method. METHODS: Two designs, an anatomical V-shape design (VSD) and a dome-shape design (DSD), for the anterior trochlear surface in a contemporary femoral component were chosen for examining the contact characteristics. The use and absence of patella resurfacing was simulated. The stress and strain distribution on the patellar bone and the polyethylene component were calculated for comparison. RESULTS: Without patellar resurfacing, the maximal compressive strain in the patellar bone in the VSD model was about 20 % lower than the DSD model. On the other hand, with resurfacing, the maximal strain for the VSD model was 13.3 % greater than for DSD. Uneven stress distribution at the bone-implant interface was also noted for the two designs. CONCLUSION: The femoral component with a V-shape trochlear groove reduced the compressive strain on the unresurfaced patella. If resurfacing the patella, the femoral component with a curved domed-shape design might reduce the strain in the remaining patellar bone. Uneven stress could occur at the bone-implant interface, so design modifications for improving fixation strength and medialization of the patellar button would be helpful in reducing the risk of peg fracture or loosening. LEVEL OF EVIDENCE: III.
Authors: Julie A Thompson; Michael W Hast; Jeffrey F Granger; Stephen J Piazza; Robert A Siston Journal: J Orthop Res Date: 2011-02-24 Impact factor: 3.494