Giant synovial chondromatosis of hip

Abstract

Synovial chondromatosis is a rare, benign condition occurring due to metaplasia of synovium. A 65-year-old woman presented with pain in her right hip for 6 years. On examination, a swelling was palpable at the base of scarpa’s triangle and her right hip movements were restricted. Imaging modalities showed ossified nodules in the antero-inferior aspect of the hip joint, joint effusion and arthritic changes. We diagnosed the patient to have synovial chondromatosis with secondary arthritis of the hip joint. We performed a total hip arthroplasty with simultaneous synovectomy and extraction of the osteochondral loose bodies, 5 of which were about 2×2 cm in size. We found that excessive acetabular reaming was required due to craters, the osteochondral masses formed on the acetabular surface. Histopathological analysis confirmed the diagnosis. The patient had an excellent functional outcome and no recurrence 5 years following the surgery.

Background

Synovial chondromatosis is a rare, benign condition occurring due to metaplasia of synovium leading to cartilaginous nodules, which may mineralise, break free to form loose bodies or even ossify.¹ The aetiology still remains unknown. It usually involves the knee joint, and very rarely involves the hip. It usually occurs in the third to fifth decades of life and is more common in males. The clinical presentation is usually of pain, swelling and restriction of movements of the joint involved.² Radiographs, CT and MRI can diagnose the condition in most cases. We present a case of giant synovial chondromatosis of the hip presenting with secondary osteoarthritis of the hip joint.

Case presentation

A 65-year-old woman presented with pain in her right hip for 6 years. She was a known hypertensive on treatment. On examination, an ill-defined swelling was palpable in the scarpa’s triangle, which was firm in consistency and was immobile. Anterior joint line tenderness was also present. She was found to have an external rotation deformity of the right hip. Movements of the right hip were found to be restricted in all planes and were associated with pain and crepitus. Axis deviation was noted. She was measured to have 2 cm of supratrochanteric shortening on the right side. Muscle wasting of the right lower limb and gluteal muscles was also noticed. Examination of the left hip was normal with full range of movements.

Investigations

Radiographs of the hip (figure 1A and B) revealed multiple calcifications around the hip joint, which were mainly located inferior to the femoro-acetabular joint surface. Symmetric reduction of joint space and subchondral sclerosis of head of the femur were also noted. The opposite hip appeared normal on radiographs. MRI of the right hip (figure 2) showed joint effusion and multiple large osseous loose bodies in the antero-inferior aspect of the effusion. Articular cartilage was completely eroded. CT (figure 3) clearly showed ossified nodules in the antero-inferior aspect of the hip joint, with multiple irregularities in the head of the femur.

Figure 1.

(A) Antero-posterior and (B) lateral radiographs of hip showing concentric reduction of joint space of right hip joint. Multiple ill-defined calcifications are visible inferior to the joint surface.

Figure 2.

MRI showing fluid collection (red arrows) in the right hip joint. Highly hypointense lesions (blue arrows) noted antero-inferior to the joint suggestive of calcifications, with five large calcifications discernible.

Figure 3.

Three-dimensional CT reconstruction showing the exact location of the calcifications (white arrows) lying antero-inferior to the head of the femur. Large craters (red arrow) noted over the head of the femur and acetabular rim.

Differential diagnosis

The clinical finding of painful restriction of movements in all planes indicated the presence of arthritis of the hip joint. The presence of a firm, immobile swelling at the base of the scarpa’s triangle suggested the presence of an underlying tumour. No findings suggestive of malignancy were present. Primary (degenerative) arthritis was ruled out as it is usually bilateral, and the opposite in this case was asymptomatic and appeared normal on radiographs as well. Furthermore, it would be extremely unusual for one hip to have such an advanced degenerative arthritis, while the other hip is normal. The differentials we thus considered were of a synovial tumour, either synovial chondromatosis or pigmented villonodular synovitis (PVNS) causing secondary arthritis of the joint. The radiograph, MRI and CT showed osseous lesions, which was the most significant finding in differentiating it from PVNS. Another pathology that needed to be considered was chondrosarcoma, which was ruled out based on the absence of lytic lesions involving the femur, the absence of cortical breach on CT and lack of hyperintense lesion on T2 MRI, and no involvement of muscles surrounding the femur.

Treatment

Intraoperatively, we approached the hip joint using the posterior approach. After opening the hip joint capsule and extracting the head of femur, we were able to extract multiple large loose bodies from the antero-inferior aspect of the joint, the average dimension of these loose bodies was 2×2 cm (figure 4). We sent the excised loose bodies and synovium for histopathological examination. The acetabular surface was found to be grossly irregular, with several deep troughs and humps. We then performed a total hip arthroplasty (THA) using uncemented prosthesis (figure 5). The histopathological evaluation of the excised tissue (figure 6) showed lobulated masses of hyaline cartilage surrounded by fragments of synovial tissue. The hyaline cartilage was hyper cellular. The presence of extensive bony trabeculae indicated the presence of calcification. The articular cartilage showed degenerative changes corresponding with occurrence of secondary arthritis. The marrow of the excised head of the femur appeared unremarkable. No evidence of granuloma/malignancy was found. These findings confirmed our diagnosis of synovial chondromatosis.

Figure 4.

Intraoperative image of the excised osteochondral bodies. Five large masses measuring 2×2 cm or larger noted.

Figure 5.

Postoperative radiograph following total hip arthroplasty. Bone grafts (red arrow) were used to help fill craters and provide a smooth base for the acetabular cup. No calcifications visible in the location where they were previously found (blue arrow).

Figure 6.

Histopathological examination of the excised mass showing cartilaginous tissue (black arrow) surrounded by bony trabeculae (yellow arrow).

Outcome and follow-up

The patient was followed up for a period of 5 years and not found to have recurrence. The patient had an excellent functional outcome with a Harris Hip Score of 86.

Discussion

Giant synovial chondromatosis is an extremely rare type of synovial chondromatosis, which was first described in 1994.³ They described it as a mass larger than 1 cm in size. The mass is formed by clumping of multiple small chondroid nodules, or by growth of a single chondroid nodules. The size of the masses would make arthroscopic excision difficult. Only few such reported cases are available in the literature. Hence, the rate of recurrence after surgical treatment and the rate of malignant transformation are uncertain.⁴ In our case, we found 5 masses, which were larger than 2×2 cm in size. No features of malignancy were found histologically.

Long standing synovial chondromatosis is known to occasionally cause secondary arthritis of the joint.⁵ While arthroscopic and open techniques of removal of the osteochondral fragments have been described,⁶ the presence of severe secondary osteoarthritis of the joint warrants the addressal of the joint pathology in addition to the chondromatosis. THA done simultaneously with synovectomy and excision of loose osteochondral fragments would address both the conditions. The functional outcome following THA in the setting of synovial chondromatosis has been found to be excellent; however, the rate of aseptic loosening and need for revision have been found to be higher.⁷ There is no available literature or reports of THA performed for a case of giant synovial chondromatosis of the hip. In our case, we found large craters on the surface of the head of the femur and acetabular surface as well. These craters would provide an uneven surface for the placement of the acetabular cup. Hence, excess reaming was required in order to obtain a smoother acetabular surface. Small bits of the excised femur head were used as bone grafts to fill up the remaining troughs in the acetabular surface. We, therefore, believe giant synovial chondromatosis may necessitate acetabular reaming of larger sizes compared with initial estimates on radiographs, and requires appropriate planning and implants to be kept available at the time of surgery. Whether such cases would warrant a staged procedure involving a provisional excision biopsy followed by THA after histological confirmation, or a more convenient single procedure, would require a risk–benefit analysis that can be performed only after many more such cases are published and researched.

Patient’s perspective.

Following the surgery, I have had complete relief from the pain. I have been able to get back to my normal routine and am able to do almost all my activities as I did before the problem started.

Learning points.

• Giant synovial chondromatosis is an extremely rare variant of synovial chondromatosis characterised by masses which are larger than 1 cm in size.

• It is more likely to cause mechanical block to movement and advanced secondary arthritis of the joint.

• It may warrant excessive acetabular reaming during arthroplasty due to craters the osteochondral masses may form on the acetabular surface.

Ethics statements

Patient consent for publication

Consent obtained directly from patient(s).