Biomechanical Study On Stress Distribution In Knee Joints By The Method Of Three-Dimensional Finite Element After Different Types Of Meniscectomy

Objective: To provide biomechanical basis for the comparison of different types of meniscectomy and offer theoretical instructions for the treatment of meniscus injuries, stress distribution and shift rules after different types of meniscectomy in knee joints (femorotibial surface) were studied using three-dimensional finite element method. Methods: A set of consecutive transectional computerized tomography images of normal male knee joint in upright weight-bearing position (scan range, 10cm superior and inferior to the joint) was selected and each image was divided into 2120 nodes and 1382 units as per the principle of three-dimensional finite element. The three-dimensional finite element model of the normal knee joint was then established through the Super-Sap finite element calculation procedure. On the basis of the normal model, fifteen three-dimensional finite element models of the different types of meniscectomy were sequentially formed by deleting corresponding units and nodes of the meniscus model according to different parts and degrees of meniscal excisions. Appropriate pressure mimicking the virtual magnitude and orientation of load on articular surfaces of upright weight-borne knees was applied to 16 models respectively, to calculate out the stress values of all nodes and units of each model. Therefore, the stress distribution in the knee joint after different types of meniscectomy may be expected to be comprehensively understood, and be able to be analyzed and compared. Results: 1 The stress on the lateral side of normal knee joint is more even-distributed than that on the medial side. No obvious stress centralization was seen on both lateral and medial side but front parts of articular surfaces were found to bear the most stress. The maximal and mean stresses on the medial side of articular surfaces were 1.59 and 1.03 times more than those on the lateral side, respectively. More stress was distributed on the medial side of articular surface compared with the opposite. 2 After the partial meniscectomy of different parts of either meniscus, slightly raises in both the maximal and the mean stresses on both side of articular surface was observed, whereas no conspicuous stress centralization was shown. However, peak values of stress distribution on articular surfaces increased by a range of 3% to 22%, whilst the mean stress rose from 4% to 27%. The maximal stress increase onarticular surfaces was induced after the partial excision of anterior angles of both lateral and medial menisci, and second maximal increase was measured following the partial excision of body and posterior angles of both menisci. 3 The maximal and mean stresses on both medial and lateral articular surfaces increased moderately corresponding to different parts of unilateral subtotal meniscectomy. A trend, indicating minor stress centralization towards the intermediate part of articular surface (close to intercondylar eminence of tibia) was observed on the meniscectomy side, whereas the distribution of stress on the opposite side remained even. Peak and mean values of stress distribution on articular surfaces were increased more apparently than partial excision by ranges of 4% to 37% and 4% to 41%, respectively. The maximal stress increase on articular surfaces was induced after the anterior angle subtotal excision of both lateral and medial menisci, and second maximal increase was measured following the subtotal excision of intermediate body and posterior angle of both menisci. 4. Dramatic increases in the maximal and mean stresses on both medial and lateral side of articular surfaces were seen after total meniscectomies of different menisci. With a unilateral total meniscectomy, stress was centralized on the intermediate part of the articular surface (close to intercondylar eminence of tibia) on the operated side, whereas the stress on the opposite side remained relatively even-distributed. However, a bilateral excision of menisci resulted in the stress centralization to the intermediate part (close to intercondylar eminence of t...