Abstract
Early temporomandibular joint (TMJ) prostheses articulated on material with poor wear resistance. Wear debris was deposited in the surrounding tissues, causing severe foreign body cell reactions. Recent TMJ prostheses use modern orthopaedic materials, such as ultra high molecular weight polyethylene (UHMWPE) for the fossa component, and cobalt–chromium, or cobalt–chromium–molybdenum for the condylar head. These designs are reliable in long-term follow-up studies. The authors report histological findings in soft tissue samples obtained from around two types of TMJ prostheses after up to 8 years of function. The devices were four Biomet (Biomet Microfixation, Jacksonville, FL, USA), and two TMJ Concepts (TMJ Concepts, Ventura, CA, USA). All joint capsule samples demonstrated dense, fibrous connective tissue with no inflammatory cells or foreign body reactions. The joint disc tissues showed even denser fibrous connective tissue, free from inflammatory reactions. Some samples from the junction between capsule and disk demonstrated synovial-like tissue. The observations reported in this paper indicate that modern TMJ prostheses with Cr–Co–Mb or Cr–Co articular condyles articulating on UHMWPE fossa components appear to function without foreign body reactions in he surrounding tissues.
Alloplastic temporomandibular joint (TMJ) total joint reconstruction (TJR) is not new in reconstructive maxillofacial surgery. D riemel et al. described the historical development of this treatment modality up to 1945 , and V an L oon et al. published a thorough overview of various TMJ TJR devices utilised between 1946 and 1994 . In the 1980s, TMJ TJR was completed in many cases with the Vitek Kent TMJ TJR device . After reporting initial good results, it later became apparent that because the fossa and ramus components were backed with Proplast, and the articulating surface of the fossa was Teflon, the prosthesis had poor wear properties. Large amounts of wear debris were deposited around these artificial joints resulting in severe foreign body reactions . In the wake of the poor clinical results with Proplast–Teflon in the TMJ, the American Association of Oral and Maxillofacial Surgeons published guidelines for the revision of implants containing this material . As a result of this problem, some authors have suggested that all alloplastic TMJ devices may lead to the same problems .
Two improved TMJ TJR prosthesis systems were subsequently developed and approved by the US Food and Drug Administration (FDA): TMJ Concepts (TMJ Concepts, Ventura, CA, USA); and Biomet (previously Lorenz) (Biomet Microfixation, Jacksonville, FL, USA). A third FDA-approved TMJ TJR device, TMJ Implants (also known as Christensen) (TMJ Implants, Golden, CO, USA), is different from the other two because both articulating surfaces are made of cast Cr–Co alloy. This metal-on-metal geometry may function in a hip joint, where perfectly spherical articulating components may result in a joint prosthesis articulating smoothly, but this is not the case with TMJ prostheses where the geometry and kinematics are more like the non-constrained knee than the constrained hip . The metal-on-metal articulation results in point contact that produces large amount of metallic wear debris. The TMJ Implants prosthesis has been reported to produce foreign body and possible immune reactions . TMJ Implants used to produce mandibular components with an acrylic head that produced wear debris and foreign body reactions; they have been removed from the market .
The TMJ Concepts (TMJC) TMJ TJR device is a computer assisted designed, computer assisted manufactured (CAD CAM) patient-fitted prosthesis, designed and manufactured on a stereolithic 3D model developed from the patient’s protocol CT scan data. The fossa component is composed of an ultra high molecular weight polyethylene (UHMWPE) articulating surface attached to a commercially pure titanium mesh base. The mandibular component is made of machined alloyed titanium with a condylar head of chrome–cobalt–molybdenum (Cr–Co–Mb) alloy.
The Biomet TMJ TJR prosthesis is a stock prosthesis made in various sizes. A patient-fitted version is also made for the European market. The Biomet fossa component is completely composed of UHMWPE. The mandibular component is made of cast Cr–Co alloy with a titanium spray on the surface that interfaces with the mandible.
Both devices have similar articulating surfaces in terms of materials: Cr–Co–Mb (TMJC), Cr–Co (Biomet) articulating on UHMWPE. This material combination has been considered the gold standard in orthopaedic prostheses for over 45 years .
These two new TMJ prostheses were subject to rigorous and thorough mechanical laboratory tests to obtain FDA approval. In laboratory settings they were loaded kinetically corresponding to, or exceeding, 20 years of normal wear. A 14-year follow-up of TMJC reveals no sign of material failure . This, and other published results, indicates that these TMJ TJRs have reliable clinical behaviour .
Histological specimens of tissue obtained from reconstructed joints that had been in function for 2 and 3 years have been published and show no inflammatory cells or giant cells. Apart from that paper, and one containing the same samples , there are no other published papers demonstrating adverse histological findings or pathological findings after TMJ TJR using TMJC or Biomet prostheses. To some extent this lack of pathology is the result of the good long-term results with these devices. Few cases have required further revision and/or replacement surgery so few situations have arisen for tissue sampling from around these devices.
Material and methods
The histological findings from 6 patients (4 female; 2 male) who have had TMJ prostheses for 2–8 years are presented. Two cases were TMJC, and four Biomet. Owing to the low number of cases they are presented as individual case reports.
Results (surgeon initials)
Case 1 (AW)
A 44-year-old woman underwent bilateral TMJ TJR with TMJC patient-fitted devices, having suffered from longstanding and progressive condylar resorption following several orthognathic surgery procedures performed more than 10 years earlier. One year after bilateral TMJ TJR surgery, she experienced pain and discomfort from the muscles and both joint areas. She feared that she had developed a latent infection or an allergic reaction and demanded exploration of at least one of the joints. During surgery a dense capsule surrounding the prosthetic joint was found, and a similar tissue in the joint space. There were no clinical signs of any inflammatory process or any other type of pathology ( Fig. 1 ). Soft tissue samples from the lateral capsule and from the tissue in the joint space were obtained for microscopy. Stained with hematoxylin–eosin, the specimens demonstrated a dense, fibrous, connective tissue, not unlike the tissue surrounding a normal TMJ ( Figs. 2 and 3 ). There were no signs of inflammatory cells or foreign body reaction.
Case 2 (AW)
A 43-year-old woman underwent bilateral TMJ TJR with Biomet stock joint prostheses. Ten years earlier she had been involved in a motor vehicle accident resulting in her TMJ problems. She was treated in another hospital for disc ruptures, and underwent bilateral discectomies. Shortly thereafter both TMJs ankylosed. She underwent bilateral gap arthroplasties, but without interposition of soft tissue. She reankylosed, now with a marked retrognathia as a result of the gap arthroplasty. After TMJ TJR she functioned well, with restored occlusion and an interincisal opening of 39 mm. After another motor vehicle accident, 2 years after TMJ TJR, she experienced a discomfort that she described as a malposition of the joint components on the right side. There were no clinical or radiological signs of device failure. At the patient’s request the right joint, implanted 3 years before, was explored. The surgical approach involved tissue that was heavily scarred from previous procedures. The fossa component was covered laterally by a dense fibrous capsule. The capsule was dissected off the prosthetic device. This tissue extended into the joint space, where it appeared to be perforated by the condylar component. The capsule was cut below the condylar equator. Microscopic examination was carried out after hematoxylin–eosin staining, and revealed a dense, collagenous connective tissue without inflammatory cells or foreign body reactions ( Figs. 4 and 5 ). At the junction between capsular tissue and disc, there was an area with an appearance resembling regular synovial tissue ( Fig. 5 ).
Case 3 (AW)
A 20-year-old woman with hemifacial microsomia underwent reconstruction with a unilateral TMJC patient-fitted TMJ TJR prosthesis. Two years earlier an attempt had been made to construct the mandibular ramus and condyle with an autogenous costochondral graft. This graft failed to maintain the mandibular position, and it was decided to replace the failed autogenous rib with an alloplastic total joint prosthesis. During the TJR procedure it was found that there was a total lack of pterygo-masseteric sling so it was difficult to maintain the vertical dimension of the ramus and mandibular angle. An attempt was made to stabilise the vertical dimension with a Teflon band between the mandibular angle and the zygomatic arch. This arrangement maintained the condylar component in the prosthetic fossa for over 2 years. Thereafter the suspension failed. The condyle dropped gradually, and was pulled backwards, finally compressing the external autitory canal. A revision was carried out 4 years after the installation of the joint prosthesis. The fossa component was replaced with one that had a longer posterior flange. On removal of the original fossa component, the soft tissue lining around it was sampled for microscopic examination. Hematoxylin–eosin staining of the specimen demonstrated a dense, fibrous connective tissue with no sign of inflammatory cells or foreign body reaction ( Fig. 6 ).
Case 4 (EA)
A 54-year-old woman was referred with limited mouth opening. She had pain and joint crepitation from her right TMJ. A course of non-surgical management had failed, and a CT scan revealed resorption of the right condyle. Arthroscopic examination demonstrated synovial changes and severe chondromalacia. She underwent unilateral TMJ TJR with a Biomet custom-made total joint prosthesis.
After TMJ TJR the patient demonstrated a right preauricular swelling. Antibiotic treatment did not resolve the problem. The swelling was followed by an itching sensation. A patch test was not consistent with an allergic reaction to the metallic component of the TMJ TJR prosthetic component. The patient feared she was allergic to the slight nickel content (<1%) of the Co–Cr alloy, and demanded the mandibular component be replaced with one composed of pure titanium. During the revision procedure, the original joint prosthesis was found surrounded by a dense, capsule that also extended into the joint space. Clinically, there were no signs of inflammation or pathology. Samples from the capsule and disc were obtained for histological examination. This microscopic examination revealed a dense, fibrous connective tissue in both samples ( Figs. 7 and 8 ). At the junction between capsule and disc, there was an area with a pattern resembling that of synovial tissue. No inflammatory cells or foreign body reactions were observed. Six months after replacement of the mandibular component, the patient’s itching had decreased, and there was no swelling in the right preauricular area.
Case 5 (CL, AW)
A 38-year-old man underwent removal of Biomet stock total joint prostheses implanted 4 years earlier. Before prosthetic TMJ TJR, the patient had undergone a series of maxillofacial operations during a 10-year period. He had undergone three TMJ procedures including one with discectomy, and silastic sheet installation. Thereafter, a bimaxillary orthognathic procedure for skeletal class III malocclusion was carried out. Owing to developing fibrous ankylosis he underwent removal of the silastic sheets and simultaneous condylar shave. He developed a bony ankylosis, and underwent another condylar shave that resulted in ankylosis. As a result of developing this severe bilateral re-ankylosis, he had bilateral TMJ TJR with Biomet stock devices, after which he functioned reasonably well. He had an episode of heterotopic bone formation medially and underwent another procedure after 2 years He developed a muscle problem that made him unable to close his mouth. In order to close his mouth the TMJ TJR prostheses were removed to let the mandibular ramii collapse vertically. At the time of removal of the prostheses, the joint capsules and the tissue in between the TMJ TJR components appeared to be clinically in good condition, with no clinical signs of inflammation ( Fig. 9 ).
