The Biomechanical And Adaptability Analysis Of Individualized Shoulder Prosthesis And The Early Clinical Outcome Of Shoulder Arthroplasty With This Prosthesis

Background and ObjectiveShoulder arthroplasty was widely used to treat serious lesion of shoulder. With the four generations of modern shoulder prosthesis, shoulder arthroplasty had got a good clinical outcome. In the past there were some shortages and limitation for shoulder arthroplasty, such as persistent pain, limitation of motion, prosthesis loosening, subsidence, etc. Most commonly used prosthesis in China were the second and third generations shoulder prosthesis, which adapte to the anatomy of the shoulder not very well and lead to limited clinical outcome. To solve these problems, our group had designed Individualized shoulder prosthesis according to the shoulder anatomical features of Chinese people. We do not know the biomechanics and adaptability of Individualized shoulder prosthesis. The purpose of this study was to evaluate the biomechanics and adaptability of Individualized shoulder prosthesis, and analyse the early clinical outcome.Materials and MethodsThis study was divided into 3 parts.The first was to test the stability of Individualized shoulder prosthesis, and analyse the biomechanical changes after shoulder arthroplasty with Individualized shoulder prosthesis. 7 prostheses were randomly selected, and underwent fatigue test. The displacement, looseness, fault were investigated after fatigue test. A finite element model of shoulder arthroplasty with Individualized shoulder prosthesis had been established. We used the model to calculate the biomechanics of the glenohumeral joint after hemiarthroplasty.The second was to measure the anatomy parameters of 407 shoulders of Chinese people. The measurement parameters included: neck-shaft angle, retroversion angle, humeral head height and diameter, radius of curvature, etc. The parameters of Individualized shoulder prosthesis were compared with anatomy parameters of Chinese people. We compared anatomical shoulder prostheses with the proximal humeral of Chinese people and evaluated the adaptability of these prostheses. The prostheses include: Zimmer anatomical shoulder prosthesis, Tornier Aequalis shoulder prosthesis, Smith & Nephew Cofield2 shoulder prosthesis, Aequalis shoulder prosthesis, Global AP prosthesis.The third was to summary the early clinical outcome of shoulder arthroplasty. There were 10 cases were treated with Individualized shoulder prosthesis and 11 cases were treated with Bigliani/Flatow shoulder prosthesis. The Constant-Murley score, Normalized Constant score, operating time, operating time, blood loss were observed and compared between two groups. The anatomical parameters of patients were compared with the data from normal side.Result:Part 1: The biomechanical of Individualized shoulder prosthesis.1. In the mechanics test of Individualized shoulder prosthesis, 7 prosthesis have passed the fatigue test. The biggest displacement(0.682mm) of there prosthesis were below the failure point(1mm). The displacement, looseness, fault were not investigated in either prostheses.2. A finite element model of shoulder arthroplasty with Individualized shoulder prosthesis had been established. Finite element analysis showed that surface stress distribution in the proximal humerus did not significantly alter after shoulder arthroplasty with Individual shoulder prosthesis. The average stress shielding rate was 32.01% and 32.40%, lower than other titanium-cobalt-chromium-molybdenum implant. The contact force of glenohumeral joint increased in a neutral position and different internal rotation, external rotation, abduction maximum after shoulder arthroplasty with Individual shoulder prosthesis.Part 2: Evaluate adaptability of Individualized shoulder prosthesis to Chinese people.1. The anatomy parameters of 407 Chinese cases had been measured. The normal neck-shaft angle was 136.1±4.5°(range 124-149°), the retroversion angle was 21.2±10.6°(range 0-56°), the humeral head height was 43.6±4.0mm(range 35-58mm), the humeral head diameter was 15.5±1.8mm(range 12-20mm), the radius of curvature was 23.2±2.4mm(range 18-36mm).2. The adaptability of Individualized shoulder prosthesis compared with Chinese people. The neck-shaft angle of Individualized shoulder prosthesis was 120 to 150 degree, covered the parameters(124-149°) of Chinese people. The prosthesis retroversion angle was 0 to 40 degree, satisfied 97.1% Chinese people. The humeral head height of prosthesis was 13 to 22 millimeter, satisfy 95.1% Chinese people. The humeral head diameter of prosthes was 37 to 53 millimeter, satisfy 94.1% Chinese people. The radius of curvature of prosthesis was 19.7 to 28.0 millimeter, satisfy 95.1% Chinese people.3. By comparing adaptability of five prostheses with anatomy parameters of Chinese people, we found that each of prosthesis had its own advantage and disadvantage. The neck-shaft angle of Individualized shoulder prosthesis was 120 to 150 degree, covered the parameters(124-149°) of Chinese people; the retroversion angle was 0 to 40 degree, satisfied 97.1% Chinese people, and the Diameter- Height curve was closed to the curve of Chinese people. The retroversion angle of Anatomical shoulder prosthesis covered the parameters of Chinese people, but the neck-shaft angle was fixed at 130°. The neck-shaft angle of Global AP shoulder prosthesis covered the parameters of Chinese people, but the retroversion angle and head size did not fit Chinese people. The retroversion angle of Aequalis shoulder prosthesis had good adaptability, but the neck-shaft angle was fixed at 125 °,130 °,135 °,140 °. The neck-shaft angle and retroversion angle of Cofield2 shoulder prosthesis was fixed, and the head size was larger than the parameters of Chinese people.Part 3: The early clinical outcome of shoulder arthroplasty with this prosthesis.1. There were 10 cases treated with Individualized shoulder prosthesis and 11 cases treated with Bigliani/Flatow shoulder prosthesis. There was no looseness or shift in the two groups. The Constant score of Individualized group(75.40 ±10.71 score) and B/F groups(64.18±9.23) were higher than that in the preoperative stage. Individualized group were better than B/F groups in Constant score, activity score, activity mobility score and strength score, and the differences were statistically significant. There was no difference in pain score and normalized Constant score between the two groups.2. The anatomical parameters of patients underwent shoulder replacement with Individualized shoulder prosthesis was compared with the data from normal side. The difference of NSA was no more than 3°, RA no more than 3°, HH no more than 3mm, and HD no more than 2mm. Comparing the post-operative anatomy parameters of proximal humeral with the normal side, there was no significant difference(P>0.05).ConclusionsAccording to the research results can be concluded:1. The parameters of Individualized shoulder prosthesis were adjustable because of the special structure of head-neck-stem. The prosthesis was stable enough to meet with physical loading of human glenohumeral joint. Finite element analysis showed that the surface stress distribution in the proximal humerus did not significantly altered after shoulder arthroplasty with Individual shoulder prosthesis, and the average stress shielding rate was low. Individual shoulder prosthesis had very good stable and biomechanics.2. There was significant difference in parameters of most Chinese people. The neck-shaft angle of Individualized shoulder prosthesis covered the parameters of Chinese people; the retroversion angle and head size satisfied most Chinese people. Individualized shoulder prosthesis had very good adaptability to shoulder.3. Shoulder arthroplasty with Individualized shoulder prosthesis got a good early clinical outcome, Constant score, activity score, activity mobility score and strength score were better than patiens with B/F shoulder prosthesis. The imaging measure and analysis showed that Individualized shoulder prosthesis was freely adjustable in the core parameters of shoulder. Compared with the third prosthesis, Individualized shoulder prosthesis got better clinical outcomes.In a word, Individualized shoulder prosthesis was good at biomechanics and adaptability to shoulder, has gotten a good early clinical outcome.