Medical Engineering & Physics 33 (2011) 1175–1182 Contents lists available at ScienceDirect Medical Engineering & Physics jou rnal h omepa g e: www.elsevier.com/locate/medengphy Biomechanical evaluation of proximal tibial behavior following unicondylar knee arthroplasty: Modified resected surface with corresponding surgical technique Tsung-Wei Chang a , Chan-Tsung Yang b , Yu-Liang Liu a , Wen-Chuan Chen a , Kun-Jhih Lin a , Yu-Shu Lai b , Chang-Hung Huang c , Yung-Chang Lu d , Cheng-Kung Cheng a,b,∗ a Institute of Biomedical Engineering, National Yang-Ming University, Taipei, Taiwan b Orthopaedic Device Research Center, National Yang-Ming University, Taipei, Taiwan c Biomechanics Research Laboratory, Department of Biomedical Research, Mackay Memorial Hospital, Tamshui, Taiwan d Orthopedics and Surgery Department, Mackay Memorial Hospital, Tamshui, Taiwan a r t i c l e i n f o Article history: Received 16 February 2011 Received in revised form 11 May 2011 Accepted 11 May 2011 Keywords: Unicondylar knee arthroplasty Tibia plateau fracture Finite element analysis Strain distribution a b s t r a c t Persistent pain and periprosthetic fracture of the proximal tibia are troublesome complications in modern unicondylar knee arthroplasty (UKA). Surgical errors and acute corners on the resected surface can place excessive strains on the bone, leading to bone degeneration. This study attempted to lower strains by altering the orthogonal geometry and avoiding extended vertical saw cuts. Finite element models were utilized to predict biomechanical behavior and were subsequently compared against experimental data. On the resected surface of the extended saw cut model, the greatest strains showed a 50% increase over a standard implant; conversely, the strains decreased by 40% for the radial-corner shaped model. For all UKA models, the peak strains below the resection level increased by 40% relative to an intact tibia. There was no significant difference among the implanted models. This study demonstrated that a large increase in strains arises on the tibial plateau to resist a cantilever-like bending moment following UKA. Surgical errors generally weaken the tibial support and increase the risk of fractures. This study provides guidance on altering the orthogonal geometry into a radial-shape to reduce strains and avoid degenerative remodeling. Furthermore, it could be expected that predrilling a posteriorly sloped tunnel through the tibia prior to cutting could achieve greater accuracy in surgical preparations. © 2011 Published by Elsevier Ltd on behalf of IPEM. 1. Introduction Up to 30% of knees displaying degenerative changes originat- ing in one compartment of the tibiofemoral joint will succumb to degeneration in the opposite compartment [1]. In recent years there has been a resurgence of interest in unicondylar knee arthro- plasty (UKA). Recently UKA has been the treatment of choice for medial osteoarthritis of the knee. The functional advantages of UKA over total knee arthroplasty (TKA) include greater range of motion, better proprioception, more normalized joint kinematics, and excellent long-term survival rates [2–4]. Although early post- operative failures rarely happen, conversion from UKA to TKA is still unavoidable at the onset of persistent pain and serious peripros- thetic fracture of the proximal tibia [5–7]. ∗ Corresponding author at: Institute of Biomedical Engineering, National Yang- Ming University, No. 155, Sec. 2, Li-Nong St., Taipei 112, Taiwan. Tel.: +886 2826 7020; fax: +886 2 2822 8577. E-mail address: ckcheng@ym.edu.tw (C.-K. Cheng). Sourcing from clinical experience and relevant literature, it has been found that knee pain and tibial plateau fracture occur more commonly in the early postoperative period [8,9]. These complica- tions have been attributed to a large increase in strains following UKA [8]. Excessive strains on the cortical bone may impair bone remodeling, leading to bone degeneration [10]. It is believed that this abnormally high bone strain may be related to the geometry of the resection corner on the resected surface. Referring to mod- ern UKA prostheses, the resected tibial surface shows discontinuity at the intersection between the sagittal and transverse planes. The stress/strain concentration and fracture initiation site can both be traced to the orthogonal geometry of the acute corner. In the standard procedure for a modern UKA, the current sur- gical technique is to use an extramedullary cutting jig to make an orthogonal resected surface via vertical and horizontal cuts. It is demanding to resect a neat right angle at a precise location with- out a stopper on the dorsal of the tibia. Extended vertical saw cuts are frequently found, especially when the resection is performed by inexperienced surgeons [11]. Relevant literature suggests that incompetent surgical techniques increase the risk of periprosthetic 1350-4533/$ – see front matter © 2011 Published by Elsevier Ltd on behalf of IPEM. doi:10.1016/j.medengphy.2011.05.007