Carpometacarpal synovial osteochondromatosis

INTRODUCTION

Primary synovial osteochondromatos, also known as synovial chondromatosis, is a benign condition of idiopathic etiology characterized by metaplasia of the synovial membrane resulting in the accumulation of intra-articular cartilaginous loose bodies. Clinical symptoms are mostly non-specific, which may include swelling, pain, and a restricted range of motion. The common age of presentation is from 3^rd to 4^th decade, with male predominance.^[1] This entity is most commonly seen in larger joints such as knee, hip, elbow, and shoulder and is rare in the hand and wrist.^[2,3] To our knowledge, in English literature, only two cases of carpometacarpal synovial osteochondromatosis, both involving the thumb, have been described to date.^[2,4] In this case report, we present a rare case of synovial osteochondromatosis of the wrist suspected as 2^nd carpometacarpal arthritis.

CASE REPORT

A 59-year-old male presented with complaints of pain in the left thenar region at the base of the second and third metacarpals. There was a history of a trivial injury to the left hand. No movement restriction of the second and third digits was noted. On palpation, tenderness was elicited on the dorsal and volar aspects of the base of the second and third metacarpals. Flexion and extension of the 2^nd or the 3^rd digits were normal and pain-free without any focal neurological deficit. A digital radiograph of the hand was acquired in anteroposterior and oblique views [Figure 1]. The radiograph revealed small radiopaque densities overlying the trapezio-trapezoid and the trapezoid-metacarpal joints and narrowing of the joint space. All baseline investigations were within normal limits.

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Figure 1: (a) Frontal (b) oblique view radiographs of the left hand showing an ill-defined area of osteopenia in the trapezium with narrowing of the trapezio-metacarpal joint space. Few tiny foci of calcifications (black arrow) are seen over the trapezio-trapezoid and trapezio-metacarpal joints.

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Unenhanced computed tomography (CT) of the left wrist was performed for better delineation of the lesion. CT scan showed an ill-defined soft-tissue-density lesion in the volar compartment closely abutting the trapezium and trapezoid with multiple punctate ring and arc type of calcifications within. There was smooth cortical scalloping of the volar aspect of the trapezium and trapezoid without erosion. The base of the 2^nd metacarpal was intact. The trapezio-metacarpal joint space was narrowed. Articular surfaces were smooth; there was no erosion or joint effusion. The lesion was located between the dorsal aspect of the flexor tendons sheath and volar aspect of the trapezoid and trapezium. On the volar aspect, the lesion was abutting the flexor tendon sheath [Figures 2 and 3]. The rest of the bones did not show any abnormality. In our case, there was only joint space reduction and no other signs of arthritis. Hence, we concluded that this was a case of primary synovial osteochondromatosis and not secondary. Further, the joint space reduction may be sequelae to primary synovial osteochondromatosis, which is a commonly recognized complication. Based on the above findings, a diagnosis of synovial osteochondromatosis was made.

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Figure 2: Axial computed tomography scan. (a-d). Ill-defined soft tissue density lesion in the volar compartment abutting the trapezium and trapezoid dorsally and flexor digitorum tendon sheath ventrally (yellow arrows). There are multiple punctate hyperdense (calcific) foci within the lesion. There is also smooth cortical-scalloping of trapezium and trapezoid without erosion (red arrows). Tm: Trapezium, Tz: Trapezius, FT: Flexor digitorum tendon.

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Figure 3: Computed tomography scan of hand. (a-c). Multiple punctate hyperdense (calcific) foci are seen adjacent to the flexor tendons (circle & yellow arrow). Base of the 2nd metacarpal (MC) is intact. Trapezio-metacarpal joint space is narrowed (red arrow). No erosion or irregularity of articular surface seen.

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Excision of the lesion was planned, and intra-articular loose bodies were removed with synovectomy, and the tissue was sent for histopathology (HPE). HPE revealed multiple fragments of cartilaginous tissue consisting of lobules of hyaline cartilage showing chondrocytes lying within the lacunae surrounded by abundant chondroid matrix with tiny specks of enchondral ossification. A few fragments of bony trabeculae, fibroadipose tissue with skeletal muscle bundles were also seen [Figure 4]. There was no evidence of malignancy. The lesion was diagnosed as primary synovial osteochondromatosis in correlation with radiological findings.

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Figure 4: Histopathology (Hematoxylin & eosin stain), (a) low power view of mature looking cartilage fragments (arrow) (100x), (b) cartilage fragments with enchondral ossification (arrow) (100x), (c) lobules of mature chondrocytes with no significant atypia (arrow) (400x).

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DISCUSSION

Primary synovial osteochondromatosis is a rare benign condition characterized by subsynovial connective tissue metaplasia resulting in multiple cartilaginous nodules in the synovial membrane of joints, bursae, or tendon sheaths.^[5] It was originally described by Laennec in 1813 and is common in larger joints. This condition is rarely described in the hand and wrist. It can also arise from the tendon sheath or bursae.^[1] A retrospective case report by Maurice et al. reported an incidence of only 7.5% in the wrist as compared to the knee (74%).^[5] Wong et al. reported three cases of synovial osteochondromatosis involving the proximal interphalangeal and metacarpophalangeal joints.^[6] In English literature, the first case of carpometacarpal synovial osteochondromatosis of the thumb was reported by Nakashima et al. in 2007,^[2] followed by Yonekura et al. in 2017.^[4] Our case is unique as it involves the second carpometacarpal joint, which has not been described in any of the previous literature.

Although the etiology of synovial chondromatosis is unclear, it preferentially affects the dominant hand. The majority of the patients do not have a significant traumatic history.^[7] Our patient presented with a history of minor trauma in the past. However, previous traumatic history does not increase the probability of synovial chondromatosis.^[8]

Milgram et al. classified the disease into three phases: (1) early phase – active intrasynovial disease without loose bodies, (2) transitional phase – intrasynovial disease with loose bodies, and (3) dormant phase – multiple osteochondral bodies without intrasynovial disease.^[8] As the mass matures, bone erosions and calcified loose bodies are apparent. Our case was in the dormant phase as HPE demonstrated cartilaginous loose bodies and enchondral ossification without synovial disease.

Plain radiograph findings are usually non-specific and may reveal scattered foci of calcifications in the form of loose bodies. These loose bodies may result in mechanical damage to the adjacent joint, resulting in secondary arthritis as seen in our case. CT or magnetic resonance imaging (MRI) can reliably detect the exact location of the osteochondral loose bodies in addition to synovial thickening.^[9] In our case, the CT scan clearly identified the precise anatomical location of the lesion. There was also cortical scalloping of the adjacent trapezium and trapezoid, and hence, we were able to arrive at this diagnosis.

The common differential diagnoses for synovial osteochondromatosis include osteoarthritis, rheumatoid arthritis, osteochondritis dissecans, tuberculous arthritis, psoriatic arthropathy, crystal arthropathy, and pigmented villonodular synovitis [Table 1].^[1] Tissue biopsy with histopathological examination remains the gold standard for diagnosis.^[8] Reported complications of synovial chondromatosis include secondary degenerative osteoarthritis, mechanical locking, limitation of movements due to loose bodies, and nerve compression.^[9]

Synovial osteochondromatosis is locally aggressive without metastatic potential. Malignant transformation of synovial chondromatosis to synovial chondrosarcoma is rare and estimated to be between 1 and 7%.^[9] The current treatment for synovial chondromatosis involves excision of chondromatous loose bodies with synovectomy. Roulot and Le Viet, in their case series of synovial osteochondromatosis of the hand and wrist, reported a recurrence rate of 24% even after synovectomy.^[10]

CONCLUSION

Synovial osteochondromatosis is a rare condition affecting the wrist, and it may be confused with other common pathologies affecting the wrist. A definite diagnosis of synovial osteochondromatosis aids the clinician in going for excision of the loose bodies and synovectomy. In our case, although a CT scan aided in the diagnosis of synovial osteochondromatosis, the role of MRI cannot be underestimated. Hence, whenever feasible, MRI should be performed to assess the synovial involvement.

TEACHING POINTS

• Primary synovial osteochondromatosis is a benign condition affecting the synovial membrane of joints, bursae, or tendon sheaths and is characterized by subsynovial connective tissue metaplasia resulting in cartilaginous nodules.

• Chondroid loose bodies may result in mechanical damage to the adjacent joint, resulting in secondary arthritis.

• A definite diagnosis of synovial osteochondromatosis aids the clinician in going for excision of the loose bodies and synovectomy. Plain radiographs and CT scans aid in the diagnosis of this condition.

MCQs

1. Most common joint involved in primary synovial chondromatosis?

   1. Shoulder

   2. Knee

   3. Hand and Wrist

   4. Elbow

   Answer key: b

2. Dormant phase of synovial chondromatosis is characterized by?

   1. Active intrasynovial disease without loose bodies

   2. Intrasynovial disease with loose bodies

   3. Multiple osteochondral bodies without intrasynovial disease

   4. None

   Answer key: c

3. Which of the following statements are correct regarding synovial chondromatosis?

   1. Locally aggressive without metastatic potential

   2. Malignant transformation is rare

   3. Current treatment involves excision of loose bodies with synovectomy

   4. All of the above

   Answer key: d