Case report

A 74-year-old woman presented with a complaint of left TMJ pain during jaw movement, which she had had for about 10 years. There was no history of trauma. Physical examination revealed a slight swelling in the left preauricular region and her maximal mouth opening was 35 mm with pain. Panoramic radiography and computed tomography (CT) revealed multiple calcified bodies in the anterior part of the left condyle ( Fig. 1 A ). Magnetic resonance imaging (MRI) revealed the normal position of the disk, normal contour of the condyle, and some calcification in the expanded superior joint space. MRI showed expansion of the inferior joint space ( Fig. 1 B). Following a clinical diagnosis of SC of the left TMJ, open surgery using a preauricular approach was carried out. When the superior joint space was opened, viscous fluid containing multiple milky-white loose bodies 1–5 mm in diameter was discharged.

Preoperative CT (A) and MRI (B). Axial CT showed multiple calcified bodies in the anterior part of the left condyle (arrowhead). MRI revealed normal position of the disk and some calcifications in the expanded superior joint spaces. MRI also showed expansion of the inferior joint space (arrow).

Using an arthroscope, all the remaining loose bodies were located and removed from the superior joint space. Arthroscopic findings revealed slight inflammation of the synovium without pedunculated lesions. When the inferior joint space was opened, several similar sized particles were found and removed ( Fig. 2 ). About 150 and 30 loose bodies were removed from the superior and inferior joint spaces, respectively. The disk was in a clinically normal position without perforation, so diskectomy and synovectomy were not performed.

Surgical finding of the inferior joint compartment. Multiple particles discharged from the inferior joint space. Small arrowhead, condyle; arrow, loose bodies; large arrowhead, disk.

Histological evaluation confirmed both loose bodies from the superior and inferior compartments comprised mature cartilage. In some a synovium-like lining of connective tissue was found ( Fig. 3 A and B ).

Histological findings of the loose bodies from the superior (A) and inferior (B) compartments. All loose bodies comprised mature cartilage, some of which had a lining of synovium-like connective tissue (hematoxylin-eosin, original magnification ×100).

After surgery, the patient recovered well without temporary facial nerve palsy. Regular postoperative follow-up examinations over 30 months showed complete resolution of the symptoms and radiography revealed no recurrence of the lesion.

Discussion

It has been suggested that SC of the TMJ affects only the synovial lining of the superior compartment. In the authors’ review, 5 of the 87 published cases (6%) of SC of the TMJ involved the superior and the inferior compartments. Holmulund et al. speculated that loose bodies in the inferior joint space originated from the upper compartment following perforation of the articular disk. In the authors’ review of the five cases, two showed perforation of the disk. The remaining three cases did not describe perforation of the disk. In the present case, no perforation was evident under arthroscopic observation. The inferior joint space was expanded in the preoperative MRI and contained about 30 loose bodies. The authors think this is the first report of histologically confirmed loose bodies in the inferior joint space.

The pathogenesis of SC is more of an active metaplastic than a neoplastic process. The pathogenesis of SC is poorly understood, but the chondrocytes in loose bodies are thought to arise from the primitive mesenchymal cells in the synovium. The trigger mechanisms of metaplasia are unknown, but trauma and inflammation are possible causes. As long as synovial membrane exists and receives some pressure, SC can develop, even in the inferior compartment of the TMJ. The authors think it is natural that SC of the TMJ also affects the synovial lining of the inferior compartment. The authors cannot compare the pathology of the synovium in the superior and inferior joint compartments, because synovial biopsies of both compartments were not carried out.

The inferior joint compartment is narrower than the superior compartment, and the area of the synovial membrane in the inferior compartment is smaller, so its ability to produce loose bodies must be less than that of the superior compartment. Some loose bodies in the inferior compartment may also have been overlooked because of inadequate investigation. Although MRI is helpful for diagnosing SC, it only showed loose bodies in the inferior joint space in 3 of the 87 cases (3%). Even in surgical findings, there were records of involvement of the inferior joint compartment in only 26 of 87 cases (30%). In the present case, involvement of the inferior joint space was confirmed by pre-operative MRI and operation findings. In general, it is difficult to predict lesions in the inferior joint compartment from clinical symptoms. Some of the symptoms of the above 5 cases were similar to those of the other 82, such as unilateral swelling over the joint area, pain in the joint area, and limitation of jaw movement. In the present case, the patient also complained of unilateral TMJ pain, swelling in the left preauricular region, and limitation of jaw movement.

SC treatment ranges from nonsurgical treatment, through operative removal of only the particles, to removal of particles with resection of synovium, condyle and disk. A total resection of the synovial membrane has been advocated because the remnants may be a source of recurrence. Various treatments have been used for SC of the TMJ. Synovectomy may not be required if only loose bodies are found without involvement of the synovium. In the present case, the synovium was diagnosed as having only slight inflammation by arthroscopy, and the disk did not show any abnormalities. The authors decided to conserve the disk and synovium to maintain the structure and function of the TMJ.

Inadequate removal of loose bodies may lead to recurrence and malignant transformation of the disease, so consideration should be given to the possible involvement of SC in the inferior joint compartment of the TMJ.