We developed a three-dimensional finite element model of the shoulder glenohumeral joint after shoulder arthroplasty including humerus shaft, scapular, scapular cartilage and eight muscles, while each of the muscles was simulated with 50 spring elements. To reduce the element number and improve the analytical precision, we used mixed tetrahedral and hexahedral elements in the model. We then used the model to calculate the biomechanics of the shoulder glenohumeral joint after hemiarthroplasty during humeral external rotation. Results showed that the maximum joint reaction force was 374.72 N and the maximum contact stress was 6.573 MPa together with the contact areas at 40° external rotation. These might be one of the reasons for prosthetic disarticulation, and would provide theoretical bases to prosthetic design.
Objective To evaluate the effectiveness of distal femoral osteotomy aided by three-dimensional (3D) printing cutting block for correction of vaglus knee with osteoarthritis. Methods Between January 2014 and January 2016, 12 patients (15 knees) with vaglus deformity and lateral osteoarhritis underwent medial closing wedge distal femoral osteotomy. There were 5 males and 7 females, aged 30-60 years (mean, 43.8 years). The mean disease duration was 6.6 years (range, 1–12 years). The unilateral knee was involved in 9 cases and bilateral knees in 3 cases. According to Koshino’s staging system, 1 knee was classified as stage I, 9 knees as stage II, and 5 knees as stage III. The X-ray films of bilateral lower extremities showed that the femorotibial angle (FTA) and anatomical lateral distal femoral angle (aLDFA) were (160.40±2.69)° and (64.20±2.11)° respectively. Mimics software was used to design and print the cutting block by 3D printing technique. During operation, the best location of distal femoral osteotomy was determined according to the cutting block. After osteotomy, internal fixation was performed using a steel plate and screws. Results All incisions healed primarily; no complication of infection or deep vein thrombosis was observed. All patients were followed up 6-18 month (mean, 12.2 months). At 6 months after operation, the hospital for special surgery (HSS) score for knee was significantly improved to 89.07±2.49 when compared with preoperative score (65.27±1.49,t=–28.31,P=0.00); the results were excellent in 10 knees, good in 4 knees, and fair in 1 knee with an excellent and good rate of 93.3%. The bony union time was 2.9-4.8 months (mean, 3.3 months). Bone delayed union occurred in 1 case (1 knee). The postoperative FTA and aLDFA were (174.00±1.41)° and (81.87±1.06)° respectively, showing significant differences when compared with preoperative ones (t=–18.26，P=0.00;t=–25.19,P=0.00). The percentage of medial tibial plateau in whole tibial plateau was 49.78%±0.59%, showing no significant difference when compared with intraoperative measurement (49.82%±0.77%,t=0.14,P=0.89). Conclusion 3D printing cutting block can greatly improve the accuracy of distal femoral osteotomy, and ensure better effectiveness for correction of vaglus knee with osteoarthritis.