| Summary: | 博士 === 國立陽明大學 === 醫學工程研究所 === 100 === Unicompartmental knee arthroplasty（UKA）is a well-established surgical procedure with failure rates averaging 10% at ten years post-surgery. A revision arthroplasty is often performed after an inadequate primary UKA. Tibial baseplate subsidence, persistent pain and periprosthetic fracture of the proximal tibia are the predominant indicators for revision. Optimizing coverage of the resected tibial surface is an important consideration in UKA, and surgical errors and acute corners on the resected surface can place excessive strains on the bone, leading to bone degeneration. The purpose of this study was to analyze the morphology of the medial and lateral tibial plateau of Chinese knees and to compare measurements and features with the plateau dimensions of different commercial unicondylar tibial baseplates. Additionally, we attempted to lower strains by altering the orthogonal geometry of resected surface and avoiding extended vertical saw cuts. Finite element models were utilized to predict biomechanical behavior and were subsequently compared against in vitro experimental data. We anticipate that the results could provide guidelines for surgeons in selecting a tibial baseplate and surgical technique for patients with isolated medial or lateral tibiofemoral osteoarthritis prior to UKA.
The results showed significant differences between the shapes of the medial and lateral tibial plateaus for the patients analyzed. For the lateral tibial plateau, the shape was symmetric about the mediolateral (ML) axis. The medial plateaus presented their widest ML width in an obviously more posterior position than the lateral compartment. Moreover, the results showed that the majority of the commercial baseplates studied tended to display overhang for all measured mediolateral dimensions. Additionally, the plateau aspect ratio decreased with increasing mediolateral dimensions, in contrast to the constant aspect ratio shown by conventional UKA prostheses. On the other hand, 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 amongst the implanted models.
Our study suggests using UKA prostheses that take into account the morphological differences between the medial and lateral tibial compartments. Compartment-specific designs may optimize coverage between the prosthesis and resected tibial surface. The morphometrical measurements presented can allow manufacturers to design UKA baseplates that accommodate the structural variability for different ethnic groups. The finite element models 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.
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