Background For patients with glenohumeral osteoarthritis, the surgical plans of total shoulder arthroplasty are very challenging, such as the selection of prosthesis, the accuracy of prosthesis placement and the correction effect of deformity, which are the problems orthopedics surgeons facing. Currently, most of the shoulder prostheses are from foreign countries. The size, design model and anatomical and functional requirements of the Chinese people are not fully adapted. The special anatomy and specificity of patients add difficulties to repair and reconstruction, which requires customized implants. 3D printing technology has the features of precise processing, rapid production, without applying any mold. It can "customize" high precision surgical procedures for patients with joint surgery and choose more suitable implant, thus improving the success rate of complicated and difficult surgery. In this study, the patients' bilateral shoulder joint model was prepared by 3D printing technique, and the anatomical parameters of the healthy side were measured to determine the type of prosthesis and the placement of the prosthesis, to make the best operation plan, and to guide the operation of individual shoulder joint replacement. Evaluating the condition and operative drill on the affected side can also make the operation more precise, so as to shorten operative time and reduce intraoperative bleeding.
Methods (1) General information: From May 2014 to May 2016, 12 patients with primary and secondary glenohumeral osteoarthritis were treated in the department of orthopedics, Sichuan Provincial People's Hospital. There were 4 males and 8 females, with an average age of 58.5 years (13.2 years, 48-81 years old) . There were 5 cases in the left and 7 in the right. There were 5 cases of primary glenohumeral osteoarthritis, 4 cases of humeral head ischemic necrosis and 3 cases of traumatic osteoarthritis. (2) Inclusion and exclusion criteria: (a) Inclusion criteria: Diagnosis of primary or secondary glenohumeral osteoarthritis and rheumatoid arthritis through medical history and related imaging examinations. Lesions with severe shoulder pain and limitation of function, involving both glenoid and humerus. The rotator cuff was intact or repairable and without severe glenoid bone loss. the operation indication was clear, no absolute contra-indication. All patients signed the informed consent. Patients were able to cooperate with rehabilitation exercise after operation. More than 12 months’ follow-up with complete documentation. (b) Exclusion criteria: Traumatic fracture of the proximal humerus or pathological fracture. Chronic osteomyelitis of the proximal humerus or scapula. Bone tumor of proximal humerus. Massive or irreparable rotator cuff tear. the proximal humerus deformity could not support and fix the prosthesis, or no enough bone of glenoid to fix the base plate. Nerve disease with deltoid dysfunction. unable to tolerate the operation because of age, body condition and so on. unable to cooperate with rehabilitation exercise after operation. Irregular follow-up with incomplete documentations. (3) Preparation: (a) pre-operative routine examination: Before surgery, we assessed the level of erythrocyte sedimentation rate, C-reactive protein, blood routine and IL-6 to determine whether there was infection. If infection was suspected, the culture period of joint fluid was at least 8 days. Imaging examinations included standard anteroposterior and axillary lateral X-ray films, thin-section CT of bilateral shoulder joint and shoulder MRI for rotator cuff assessment. The electromyography and nerve conduction function examination should be performed as well. The elderly patients were also assessed for a variety of basic diseases. (b) 3D printing model: The patients' bilateral shoulder thin CT scanning data (scanning voltage 120 kV, current 205.59 mA) were collected, and DICOM format was introduced to Mimics 14 software for three-dimensional reconstruction, and the three-dimensional model of bilateral shoulder joints was obtained. The DICOM format scan data was converted to STL format file. We transformed the 3D printing software MarkerBot to STL format, adjusted the printing orientation and printed out 1:1 physical model (completed in Sichuan University Manufacturing Institute) . (c) Determination of anatomical parameters on 3D printing model: Measuring tool: a vernier caliper with a precision of 0.1 mm; a unit with an accuracy of 0.1 degrees; a compass, a set of triangles and rulers; 1.5 mm K-wire. Data measurement: the 3D shoulder joint model of the healthy side is used as a template (Figure 1) . The center of the humeral head is determined by the compass and the vernier caliper and marked as the A point. Under the guidance of the vertical guide, the 1.5 mm K-wire is vertically penetrated, the lateral bone cortex of the humerus is penetrated, and the intersection of the guide needle and the lateral humerus plane is marked as the G point. This point is the positioning point. The F point is the highest point of the humeral head; the E point is the highest point of the greater tuberosity of the humerus; the most lateral margin of the coracoid tip is C; the most lateral edge of the greater tuberosity of the humerus is D; the AG line intersects the curve of the humerus anatomic neck at B point; the AG connection and the bottom of the inter-tuberosity groove intersects H point (Figure 2) . the distance between A and B is the thickness of the humeral head and the radius of the humeral head, which is of reference value for the selection of the size of the head of prosthesis. the vertical distance between the F point and the E point is the distance between the head and greater tuberosity. The height control of the prosthesis is of reference significance. the distance from C to D is the lateral eccentricity of the lateral humerus. This parameter is of reference to the evaluation of the soft tissue and the prognosis. the determination of retroversion angle: the adjustment of the Mimics three-dimensional image, the observation of the healthy side of the humeral head, the overlap of the distal humeral head and the medial condyle when the distal humeral joint is overlapped. The line between point A and point B of the lateral condyle is the distal definition line, which is a central line of on the line of C D of the joint surface of the humeral head, that is, the near end line, and the E F is the central axis of the humeral head. B A and E F extended line intersects at G, D B G E is the retroversion angle. Determination of the healthy side angle for the affected side to place personalized prosthesis has a certain reference value. (4) Surgical methods: All 12 operations were performed by the same group of doctors. Shoulder prosthesis is provided by Shanghai Jie Mai company. 0.5 h preoperatively prophylactic antibiotics were used. After the successful general anesthesia, we use the beach chair position and take the deltoid-pectoralis approach and pull the cephalic vein laterally. The proximal humerus was released under the deltoid, coracoid process and the acromion. The long head of biceps is cut off and marked with the suture, the shoulder joint is opened from the rotator interval and the humeral head is exposed. Then the humeral head is extremely external rotated to dislocate, and the lower of glenoid is revealed. Attention should be paid to protect the medial neurovascular and the upper rotator cuff. The osteotomy plane of the humeral head is marked on the affected side, and its surrounding osteophyte is removed. Scraping the remaining articular cartilage of the glenoid and locating the center of the glenoid. According to the preoperative 3D printing model, the appropriate size of the glenoid prosthesis was selected and fixed with bone cement. After the bone cement was fully bonded, the humerus prosthesis was implanted. The position of the humeral head osteotomy was restored, and the model of the prosthesis was put in step by step. The height and retroversion of the prosthesis were adjusted according to the data measured on the healthy side. The prosthesis of humerus side was fixed by press fit technique. During operation, we should pay attention to the integrity of rotator cuff tendon, if there is rotator cuff tear, it should be repaired at the same time. In this group, there were 3 cases associated with a rotator cuff tear, of which 1 case with partial tear of supraspinatus and 2 cases with complete supraspinatus tear. All the rotator cuff tears were repaired anatomically with Ethibond sutures. (5) Postoperative treatment: After the operation, 48 h of antibiotics were used, and the plasma drainage tube was removed at 24-48 h after operation. All cases were immobilization with neck wrist strap for 6 weeks after operation. Passive functional exercises of wrist and elbow should be carried out as soon as possible after L days. After discharge, all 12 patients were transferred to rehabilitation department for further treatment, and functional exercises were conducted under the guidance of professional rehabilitation instructor. Third weeks after the operation, the passive exercise of the shoulder joint was started and the neck wrist strap began to exercise sixth weeks after the operation; the muscle strength exercises began at twelfth weeks after the operation, and the daily activities were gradually restored according to the patient's specific rehabilitation. (6) Follow-up and evaluation methods: At 3, 6, 12 weeks and 6, 12 months, and the last follow-up, the patients were given the position of the external rotation of the neutral shoulder joint and the lateral X ray to determine the position of the prosthesis. At the last follow-up, the visual analogue scale (VAS) and Constant Score were used to evaluate the functional recovery of shoulder joint. (7) Statistical analysis: Data analysis was carried out by SPSS 17 (SPSS, USA) statistical package, and the data were described with ±s. The independent sample t test was used to compare the continuous variables of shoulder joint activity and function score before and after operation. All the analyses were both bilateral test, and P <0.05, the difference was statistically significant.
Results (1) The effect of operation: All of the 12 cases were successfully completed. The operative plan is completely consistent with preoperative design. The prosthesis, the osteotomy plane, the prosthesis height and retroversion are consistent with the simulated operation. The operation time was 90-150 min, with an average of 110 min. The average C-arm X-ray machine was used for 2 times during the operation. The amount of bleeding during the operation was 130-210 ml, with an average of 180 ml. The average drainage was 80 ml after operation. No infection was found in the 12 patients. The average time of inpatient care was 10.5 days. (2) Evaluation of effect: All 12 patients were followed up for 13-25 months, with an average of 16 months (3.8 months) . At the last follow-up: VAS score was (1.5±1.2) points, compared with (6.6±3) points before surgery (P = 0.003) . the ROM of shoulder was (138.50±24.40) ° compared with (57.10±27.30) ° before surgery, P = 0.012; external rotation was (35.80±16) ° VS (10.30±8.7) °, P = 0.025. The internal rotation level was L1, compared with L5 before surgery, P = 0.003. Constant score was (86.3±13) , compared with (33.3±11.4) before surgery, P = 0.001. Regular follow-up by X-ray. No complications such as prosthesis loosening and humeral head shift occurred during the last follow-up.
Conclusions 3D printed personalized joint model, can accurately assess the condition and operation difficulty, communicate with patients in an intuitive and image condition. For a number of more complicated patients, such as the patients with severe joint deformity and loss of anatomical markers, the prosthesis model was selected by the determination of the anatomical parameters of the healthy side and the individual joint replacement surgery was conducted to ensure the stability and excellent matching degree of the prosthesis in the body. Simulated operation was performed on the model of 3D printing before operation, making the surgery simple and precise. It can improve the success rate of complex and difficult operation in joint surgery.