Chondrosarcoma usually occurrs in adults over the age of 50. It is more common in men than women . It commonly presents on the cartilage cells of the thigh bone (femur), shoulder, or pelvis. In contrast, it rarely starts in the knee, ribs, skull. The most common clinical symptoms of chondrosarcoma may include the following: Dull pain that increases gradually over time, pain is usually worse at night, and a large lump (mass) presents on a bone.. Chondrosarcomas are divided into three grades :
□ Chondrosarcoma grade 1: Low malignancy, lesions/atypical cartilaginous tumors rarely metastasize, rarely recur, and have a 10-year survival rate of >80%.
□ Chondrosarcoma grade 2, 3: A malignant tumor is associated with a poor prognosis, high local recurrence rates, a lung metastasis rate of >50%, and a 10-year survival rate of <30%.
The prognosis of a patient with low-grade malignancy is very good, the 5-year survival rate is over 90%.There are 1-9% of Enchondroma that transform into malignancy. . Treatment of endochondral tumors can be wide resection combined with bone grafting.. However, it is necessary to carefully evaluate the size of the tumour and determine the extension of invasion, and remove all of a cancerous tumour. Our patient was a typical case of secondary bone cancer which appeared in middle-aged people. Her tumor was the malignant transformation from the benign endochondral tumour.Fortunately, she went to our centre to conduct a medical examination and was treated promptly when the tumour just transformed into malignant. She underwent the radical resection of the tumor with a safe margin which means that no malignant cells tumor cells are seen at the resection surface with a microscope. There was no sign of metastasis.
Although the patient underwent 3 times of tumour resections in the past, the tumour still relapsed and converted to chondrosarcoma. The reason was that because the patient was treated at a non-specialist facility, the resection surgeries were not effective in completely removing the tumour cells. In addition, it was challenging to differentiate between enchondroma and low-grade chondrosarcomas. Therfore, periodic examination plays an important role in the early detection of disease progression for patients with tumor bone.
After recognition of malignant transformation to chondrosarcoma, it was necessary to have a plan of wide surgical resection. Because our patient presented large lesions that caused significant bone destruction, the total scapular replacement was compulsory. Total scapular resection is the treatment for tumors of the scapula and has succeeded in preserving elbow and hand function. Limited range of motion and shoulder instability are the major complications of this method. Despite several reconstruction methods have been tested such as bone suspension, prosthetic replacement, bone grafting or soft tissue reconstruction, functional outcomes were poor.
Before the 1970s, surgical tumor resections at the shoulder were almost always treated with amputation However, when the Tickhoff-Linberg procedure was introduced, the indication for amputation was gradually reduced 
Scapular prostheses were presented with an acceptable range of motion and function in recent reports  . However, long term positive outcomes were still not confirmed. Furthermore, a scapular prosthesis was not popularly available, and its design is not well manufactured yet.
The development of artificial materials offers many options for the reconstruction of the shoulder joint. The reconstruction materials were originally made simple from allograft, PEEK or industrial plastic. .
In the past, most scapular prostheses do not match the patient's anatomy and may affect shoulder function. Nowadays, 3D printing technology represents a big opportunity to allow for customized and printed patient-specific scapular prostheses. These prostheses may increase the patient's chances of functional improvement.In recent years, using 3D printing techniques for reconstruction of the scapula with similar patient's anatomy has been applied more and more frequently and has very positive initial results. A study by Beltran et al.  showed that the MSTS score for a personalized scapula prosthesis replacement after tumour resection was 87%. Liu et al.  described the treatment of scapula tumours that applied the 3D-printed PEEK scapular prosthesis and achieved satisfactory shoulder joint function. 3D printing allows for accurate reconstruction, improving mobility, and facilitating the early recovery of patients' functions.
The shoulder prothesis was designed to match the patient's anatomy and combined with the contraint structure to help stabilize the shoulder joint. Although the use of 3D printing technology for scapular reconstruction had not yet been reported clinically and needs more time to evaluate, it would be a new trend that will be popularized in the future . The material was a titanium alloy, which was widely used in the artificial joints and other implant materials. Titanium alloy had very good resistance to bending and compression forces. Furthermore, an advantage of this material is excellent compatibility .
In addition, the scapula closely connected to the shoulder joint and surround complex system of muscles. Reconstruction in an effort to optimally restore the shoulder function requires understanding the biomechanics and anatomy of each muscle group. The artificial shoulder joints are designed with suture holes corresponding to the original attachment points of muscles to restore the anatomy and function for each muscle group. In our intraopterative, after identifying and cutting the muscles, they were immediately sutured to mark their attached point for reattaching to the the prosthesis later. Because the tumor invades some muscle groups, there may be a lack of length for tendon reconstruction, which can cause pain and imbalance in the soft tissues around the scapula. To overcome this challenge, it is extremely important to move the attachment point of muscles as little as possible, and at the same time the muscle groups were carefully released from the surrounding soft tissues. However, functional impairment caused by tendon insufficient is inevitable. Accompanied by a lot of damage to the rotator cuff tendons. This affects the arc of motion of the shoulder joint. When raising the arm, the rotator cuff no longer responds well to keep the rotator cuff at the center of the socket, instead, the deltoid muscle tends to pull the rotator upward, causing the arm to not be raised further.
At the same time, we evaluated preoperatively the patient's tumor and recognized that it invaded extensive the joint capsule and the surrounding soft tissue. The large lesion may lead to soft tissue deficiency after wide tumor resection and instablize the artificial shoulder joint. Therefore, total scapular replacement with constrained reverse shoulder prosthesis was our surgery plan and implemented for this patient.
Both constrained reverse shoulder prosthesis and non-constrained reverse shoulder prosthesis are design with medialisation of the centre of rotation of the glenohumeral joint to enhance range of shoulder motion. However, constrained reverse shoulder prosthesis has glenosphere retained in humeral head without affecting shoulder rotation.
In cases of non-constrained reverse shoulder replacement, it is necessary to reconstruct the joint capsule firmly to prevent glenohumeral dissociation and stabilize the entire construct for shoulder active function. However, shoulder instability often occurs in cases of large soft tissue lesion in extensive tumor resection .
The constrained total scapular prosthesis had a locking mechanism between the scapular part and humeral part. The constrained prothesis stabilized the shoulder by restoring the active function of the rotator cuff, compensating for the lack of the joint capsule as well as the point of contact support to convert the deltoid straight upward pull into abductor motion. 
Compared with the non-constrained structure, the constrained reverse shoulder prosthesis has several advantages: a) create a similar structure as a joint capsule, b) Stabilize the humerus head and the scapula and prevent upward movement of the humerus, and c) simulate the normal joint force vector of the muscles at the artificial shoulder joint.
Up to now, there have not been many reports of scapula replacement with a constrained total scapula prosthesis. Most authors agreed that this treatment was a safe and reliable method for scapula reconstruction after resection of high-grade sarcomas. This treatment also provided acceptable functional outcomes and a low complication rate  .
The first report on constrained total scapula replacement in patients with scapular tumours was done by James C Wittig et al. in 2002. They described three patients who identified as a high-grade sarcoma. At latest the follow-up, the MSTS score was from 80-90%, the shoulder joints were stable, and there was no shoulder pain .
William J.Cundy et al. retrospectively compared outcomes of 41 patients of reverse shoulder replacement, of which 21 were unconstrained prosthesis and 19 were constrained shoulder replacements. At a mean follow-up of 4.2 years, there were 5 patients in the constrained group (26%) who had to undergo surgery again due to dislocation, none of which were in the unconstrained group. The authors believed that the impact of repeated movement lead to the polyethene being deformed causing dislocation.
However, the constrained implants used in the author's report were semi-constrained prosthesis, which had a high dislocation rate. Our patient was reconstructed by a fully-constrained implant which provided greater stability. Most of the authors reporting on the constrained reverse shoulder prosthesis used the fully-constrained type and had good results.
Mavrogenis et al. (2009) reported a case study treated with total constrained shoulder prosthesis and reverse-linked proximal humerus arthroplasty in a patient with Ewing's sarcoma of the scapula. Twelve-month follow-up after surgery, the shoulder joint was stable and painless. Forward flexion and abduction ranged about 30 degree .
Ten patients who underwent the total scapular replacement with constrained reverse shoulder prosthesis for bone malignant tumor were retrospectively reviewed by Tang et al. (2011). The implant was manufactured at ChunLi Co (Beijing, China). At latest follow-up, there was one case of dislocation, one case of infection and the average MSTS score was 76.7% .
Wang B et al. (2018) reported a series of 8 cases treated with total scapular replacement with a constrained reverse shoulder prosthesis after malignant tumor resection. At the final mean follow-up of 61.8 months, the mean MSTS score was 23.5. There were no cases of dislocation or loose joints .
Abdulla I et al. (2018) implemented a test on six cadaveric shoulders. He used an instrument of measuring forces across the joint with varying constraints to record the joint kinematics, loads and muscle forces. Finally, he concluded when the constraint joint was implanted to improve the joint stability, joint load and deltoid forces during active abduction were not affected significantly. Simultaneously, the range of motion was also not significantly different from that of a conventional reverse shoulder .
William J.Cundy et al. conducted a systematic review on functional shoulder assessment of inverse shoulder joints. He showed that there was no functional difference between the two types of joints. MSTS scores of the unconstrained inversion shoulder joint and constrained inversion shoulder joint fluctuated 63 - 90% and 60 -77.7%, respectively .
Our patient had a post-operative follow-up for 6 months. The MSTS score reached 26/30, and the functional elbow and hand were completely preserved. The range of active movement in the abduction and forward reaches 60 degrees, back 45 degrees. The range of passive motion was normal. The patient did not have shoulder pain and could use her operated hands for daily activity. The function of the shoulder joint was restored well because of our effort to optimally preserve the tendon and muscle system around the scapula during surgery. The design of constrained shoulder combined with 3D printing technology in accordance with the patient's parameters helped to stabilize the shoulder joint, thereby preserving almost completely the function of the elbow and hand.