Abstract
The purpose of this 2-year prospective study was to investigate outcomes achieved with a stock temporomandibular joint (TMJ) replacement system in the management of end-stage TMJ disorders. Fifty-two patients requiring reconstruction (36 unilateral/16 bilateral) were operated on during the period 2006–2012; 68 total prostheses were implanted (Biomet Microfixation TMJ Replacement System). The mean age at surgery was 52.6 ± 11.5 years. Changes in the values of inclusion diagnostic criteria at entry were assessed. These included persistent and significant TMJ pain, functional impairment after failure of other surgical therapies, and imaging evidence consistent with advanced TMJ disease of more than 1-year duration. Subjects were excluded if they presented insufficient quantity/quality of bone to support the TMJ replacement, severe hyperfunctional habits, active infectious disease, or an inability to follow postoperative instructions. Over the 2 years of postoperative follow-up, mean pain intensity was reduced from 6.4 ± 1.4 to 1.6 ± 1.2 ( P < 0.001), and jaw opening was improved from 2.7 ± 0.9 cm to 4.2 ± 0.7 cm ( P < 0.001). During the study period, three of 68 implants (4%) were explanted and new TMJ replacements fitted. The results of this study support the view that the surgical placement of stock TMJ prostheses provides significant long-term improvements in pain and function, with few complications.
Temporomandibular joint (TMJ) replacement is a biomechanical solution to end-stage TMJ disease. The physical environment into which the prosthesis is implanted is extremely challenging. Not only do biochemical, biological, and biomechanical characteristics have to be considered, but also the fact that the tissue surrounding the prosthetic components remains living; this means that the joint replacement interface and environment can change continually with time. These changes are related not only to the natural ageing of the patient, but can also occur in response to the function and properties of the prosthetic device itself. This results in a complex interactive biological and biomechanical environment involving the living tissue and prosthetic joint in the host, which can determine the lifespan of the TMJ replacement.
Over the years it has proven very difficult to predict many of these interactions preclinically, and it is only as a result of clinical experience and research that particular clinical success and failure scenarios have emerged. This has resulted in more rigorous and demanding requirements for joint replacement designs and materials, although the ultimate test is the long-term clinical follow-up.
The objectives of this study were to evaluate the procedures and complications associated with total TMJ replacement to re-establish TMJ function, and to assess pain relief in the long-term management of end-stage TMJ disorders.
Materials and methods
All patients who had a TMJ replacement implanted during the study period from January 2006 through December 2012 and who were operated on by the senior author were included in this 2-year prospective study. All procedures were performed using the Biomet Microfixation TMJ Replacement System (stock prosthetic system), and all involved replacing both the skull base component (glenoid fossa) and the mandibular condyle with prostheses. The glenoid fossa and mandibular components were available in three different sizes. The mandibular component was manufactured from cobalt–chromium alloy with a roughened titanium plasma coating on the host bone side of the ramal plate for increased bony integration. The specific cobalt-based alloy used was American Society for Testing and Materials (ASTM) type F799. The fossa prosthesis was made of ultra-high-molecular-weight polyethylene (UHMWPE).
Under general anaesthesia, the total TMJ replacement prostheses were implanted using a combination of a pre-auricular incision and a posterior mandibular incision (retromandibular approach). Templates were used intraoperatively to determine the fit and only then was the final TMJ prosthesis inserted ( Fig. 1 ). Screws used in the procedure were made of 6Al/4V titanium alloy. Active jaw opening motion initiated by the patient’s masticatory musculature was started immediately postoperative using the TheraBite Jaw Motion Rehabilitation System.
The following diagnostic inclusion criteria were assessed: a history of persistent and significant pain in the TMJ area accompanied by functional impairment after failure of other non-surgical and surgical therapies, and imaging evidence consistent with advanced TMJ disease (panoramic radiography, computed tomography (CT), and/or magnetic resonance imaging (MRI)) of more than 1-year duration. Previous surgical therapies included arthrocentesis, arthroscopic surgery, remodelling of the joint surface, removal of the articular disc, and partial replacement of TMJ components. Subjects were excluded if they presented with one or more of the following conditions: insufficient quantity or quality of bone to support the TMJ replacement, severe hyperfunctional habits, active infectious disease, and inability to follow postoperative care instructions. This study was approved by the institutional committee for research and clinical ethics. Before inclusion, all patients signed an informed consent form.
Clinical evaluations were carried out on preoperative day 1, and at months 3, 6, 12, and 24 following the TMJ replacement. Data were collected at each visit by the same observer. Pain intensity changes (preoperative vs. current) were measured using a visual analogue scale (VAS, 10 cm) ranging from 0 to 10, with higher scores indicating more severe pain. Jaw opening was evaluated with a TheraBite scale between the incisal edges of the upper and lower central incisors. Panoramic and cephalometric radiographs were obtained immediately postoperative and at follow-up visits for evaluation and comparison ( Fig. 2 ). Surgical morbidity and implant survival were documented.
The main parameters used to assess the effectiveness of the treatment were (1) pain at rest and upon mastication as measured with the VAS, and (2) range of mandibular movements associated with mouth opening, measured with a TheraBite ruler. Continuous normally distributed data were expressed as the mean ± standard deviation (SD) and compared with the Student t -test; the remaining data were expressed as percentages (%). Signs that were evaluated as indicators of the effectiveness of the TMJ replacement were the following: significant reduction in TMJ pain at rest and with mastication, and recovery of normal ranges of mouth opening movements.
Data were analysed with IBM SPSS Statistics version 19.0 statistical software (IBM Corp., Armonk, NY, USA). The Kolmogorov–Smirnov test for normality was used for quantitative variables, which were expressed as the mean ± SD or as the 25th–75th percentile (P25–P75, interquartile range). Values of P < 0.05 were considered to indicate statistical significance.
Results
Fifty-two patients with severe disease requiring reconstruction were operated on consecutively; 35 were female (67.3%) and 17 were male (32.7%). Sixteen patients (30.8%) had bilateral joint reconstructions and 36 patients (69.2%) had unilateral joint reconstructions (30.8% right TMJ, 38.4% left TMJ), thus 68 total joint prostheses were implanted during the study period (Biomet Microfixation TMJ Replacement System). The mean age of the patients at surgery was 52.6 ± 11.5 years (range 29–74 years).
The mean follow-up period from initial TMJ symptoms to TMJ replacement surgery was 5 years (range 1–8 years). Nine patients (17.3%) had an obvious history of mandibular trauma. The average number of previous TMJ surgeries, including arthrocentesis and arthroscopy, was 2 (range 0–10) for each joint.
Twenty-one patients (40.4%) had a tumoural TMJ pathology (one TMJ in 18 patients, both TMJs in three patients), 15 patients (28.8%) had severe degenerative osteoarthritis (nine bilateral, six unilateral), nine patients (17.3%) had total fibrous/bony TMJ ankylosis (six unilateral, three bilateral), six patients (11.5%) had post-traumatic sequelae (five unilateral, one bilateral), and one patient (1.9%) had unilateral severe rheumatoid arthritis. All diagnoses were confirmed by histopathological examination. All patients were followed up for at least 2 years.
At 2 years following TMJ replacement, results showed a reduction in pain intensity from an average pain score of 6.4 ± 1.4 to 1.6 ± 1.2 ( P < 0.001), and an improvement in jaw opening from the preoperative average of 2.7 ± 0.9 cm to 4.2 ± 0.7 cm ( P < 0.001) ( Table 1 and Fig. 3 ). No patient had worse symptoms postoperatively.
| Pain (10-cm VAS) | Maximum jaw opening (mm) b | |||||
|---|---|---|---|---|---|---|
| Mean (P25–P75) | SD | P -value | Mean (P25–P75) | SD | P -value | |
| Preoperative | 6.44 (5.00–7.87) ( n = 52) |
1.43 | – | 2.70 (2.00–3.47) ( n = 52) |
0.97 | – |
| 3 months | 2.55 (1.20–6.35) ( n = 52) |
1.77 | <0.05 * | 3.50 (2.00–4.00) ( n = 52) |
0.99 | <0.05 * |
| 6 months | 2.03 (1.00–4.90) ( n = 52) |
1.49 | <0.05 * | 3.90 (2.00–4.15) ( n = 52) |
0.77 | <0.05 * |
| 12 months | 1.65 (1.00–2.55) ( n = 52) |
1.29 | <0.001 * | 4.11 (3.62–4.72) ( n = 52) |
0.60 | <0.001 * |
| 24 months | 1.57 (1.00–2.00) ( n = 52) |
1.22 | <0.001 * | 4.17 (3.62–4.72) ( n = 52) |
0.66 | <0.001 * |
a Patients were treated with TMJ replacement; all procedures were done using the Biomet Microfixation TMJ Replacement System (stock prosthetic system).
b The range of mandibular movement was measured using a TheraBite System ruler.
Patients had a pain reduction of 76.5 ± 18.5 percentage points. A summary of the data, showing the number of patients with improved pain scores and the degree of pain reduction in comparison to the preoperative values, is given in Fig. 4 . There was a significant reduction in pain for 25 patients with TMJ replacement (48% of the patients studied); these patients reported a pain reduction of over 80% (in comparison with the preoperative pain values). Twelve of these 25 patients (23% of the cases) were in the ‘100%’ pain reduction category, because the postoperative pain score was 0 (absence of pain).
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