9.18\ Temporomandibular Joint

Hemiarthroplasty

9.18.1\ Discussion

Hemiarthroplasty consists of resurfacing one side of the temporomandibular joint with either prosthesis for the fossa-eminence (Fig. 9.40) or

ramus-condyle (Figs. 9.41 and 9.42), which directly contacts the opposing articular surface. Sometimes a fat graft is also applied adjacent to the prosthesis. Revision surgery is ultimately required in over 20% of cases without fat graft and about 6% of cases with fat graft.

Fig. 9.40  Temporomandibular joint hemiarthroplasty glenoid implant. Sagittal CT image shows a metallic implant seated in the glenoid fossa (arrow) (Courtesy of Joel Curé, MD)

Fig. 9.42  Lorenz prosthesis. Lateral radiographs shows right mandibular ramus osteotomy and a prosthesis that includes a metallic condylar component and a radiolucent glenoid fossa component (encircled), both of which are secured via titanium screws

9.19\ Temporomandibular Total

Joint Arthroplasty

9.19.1\ Discussion

Total temporomandibular joint resurfacing is performed in order to restore normal jaw motion and provide pain relief for a variety of conditions, such as neoplasms, arthritis, and ankylosis. The main types of temporomandibular prostheses include fossa-eminence, condylar, and total temporomandibular replacement. Although success rates of at least 90% have been achieved with some designs and materials, proper fitting of the prosthetic components to the skull is challenging. As a result, presurgical CT is often used to customize TMJ prostheses, thereby optimizing stability and function. The implants usually consist of radiopaque metallic condylar component and either radiolucent polymer components (plastic-­on-­metal) (Fig. 9.43) or metallic glenoid fossa components (metal-on-metal) (Fig. 9.44). In addition, three component prostheses have been introduced, such as the Concepts total temporomandibular joint prosthesis, which includes a plastic spacer positioned between the glenoid and condylar implants (Fig. 9.45).

Fig.9.43  Synthes total joint prosthesis. 3D CT image shows both metallic mandibular and glenoid fossa components

9.20\ Temporomandibular Joint

Disc Implant and Prosthesis

Failure

9.20.1\ Discussion

Proplast-Teflon laminate implants were first used in temporomandibular joint meniscectomy (interpositional arthroplasty) for treatment of internal derangement in 1974 and became available as precut discs in 1983. However, Proplast-Teflon implants were prone to perforation, fragmentation, migration, and foreign body reaction, which can lead to severe condylar, glenoid fossa, and articular eminence erosion, as well as penetration into the middle cranial fossa (Figs. 9.45 and 9.46). Patients may present even after many years with temporomandibular joint pain, decreased joint range of motion, crepitus, preauricular swelling, regional lymphadenopathy, malocclusion, and facial deformity, often requiring implant removal and debridement of the joint. The degree of facial pain correlates with perforation and breakdown of the implants. Due to their high failure rate, Proplast-Teflon temporomandibular joint implants were removed from the market in 1993. Failed Proplast-Teflon temporomandibular joint implants often result in bony erosions, which could be poorly or well defined, with or without sclerotic margins. CT can reveal soft tissue mass corresponding to foreign body granuloma and

accurately delineates migration and fragmentation of the hyperattenuating Proplast-­Teflon implant, soft tissue calcifications, and destructive changes of the adjacent osseous structures. MRI is well suited for depicting the soft tissue changes, including the intermediate T1 and T2 signal-enhancing foreign body granuloma and the presence of associated avascular necrosis in the surrounding bone, which can appear as decreased marrow signal on T1. Ultimately, erosive change of the glenoid fossa and the mandibular condyle can result. The integrity of the glenoid fossa is critical since erosions can extend into the middle cranial fossa (Fig. 9.47). Osteolysis with loosening of temporomandibular joint prostheses is another complication that can be associated with pain and is recognized by the presence of lucency between the bone and the prosthesis that measures greater than 2 mm (Fig. 9.48). Loosening can be accompanied by dislocation of the prosthesis. Alternatively, new bone formation can result in ankylosis and limitation of mouth opening. Pseudoarthroses can sometimes form in the bony mass and can appear as linear lucencies on CT (Fig. 9.49). Evaluation of temporomandibular joint prosthetic complications often requires both MRI and CT. MRI readily shows the extent of infection, fragmentation of the implant material, and distension of the joint capsule, while CT is useful for evaluating the integrity of the implants and associated osseous structures.

Fig. 9.45  Teflon granuloma. Axial CT image (a) shows the linear hyperattenuating implant in the temporomandibular joint space. The glenoid fossa is markedly expanded secondary to a soft tissue mass. Sagittal proton

Fig. 9.46  Implant perforation. Sagittal CT image shows a fragmented silicone implant (arrow)

density MR image in a different patient (b) shows an expanded joint capsule and intermediate-signal-intensity material surrounding the low-signal-intensity implant (arrow)

Fig. 9.47  Implant intracranial migration. Coronal sagittal CT image shows erosion of the Teflon portion of the implant into the middle cranial fossa (arrow)