The outcome of a temporomandibular joint compression test for the diagnosis of arthralgia is confounded by concurrent myalgia

Temporomandibular disorders (TMD) are considered musculoskeletal disorders that embrace pain or dysfunction of the temporomandibular joint (TMJ) and masticatory muscles [1, 2]. TMD is the most common reason for chronic pain in the orofacial region [3] and is commonly associated with interference in daily life [4, 5].

The Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) is a valid process to diagnose the most common TMD conditions. In the DC/TMD, both TMJ pain (arthralgia) and myalgia diagnoses are based on self-reported pain modified by function, in combination with familiar pain elicited during jaw movements or palpation [6]. Both these diagnoses have a high diagnostic sensitivity and specificity. In the clinical setting, it is important to discriminate between a TMJ pain disorder and jaw muscle pain since both the etiology and the management of these conditions may differ. A discriminating diagnostic test is therefore warranted in order to recognize arthralgia and myalgia independently. This can be of special clinical relevance when the arthralgia is related to arthritis. In such case, anti-inflammatory pharmacological management may be considered as a primary treatment regimen in order to reduce inflammatory activity, to reduce pain, and to prevent further degeneration of the cartilage and bone tissue in the TMJ [7].

We previously reported a substantial overlap between TMJ arthralgia and masticatory myalgia in a validation study of three screening questions (3QTMD) in relation to DC/TMD diagnoses [7]. These findings are in line with those reported by Schiffman and co-workers [8]. In the clinical examination to reach the diagnosis arthralgia, palpation of the lateral pole affects also tissues outside the TMJ proper that includes muscle tissue, skin, and connective tissue. Moreover, mandibular movements probably do not cause solely TMJ pain but also muscle pain, given that the muscles are activated. The location of pain, especially in patients with chronic pain, is an uncertain indicator for its origin due to pain spreading, referred pain, and sensitization mechanisms [9]. Even though pain location may still be relevant for an arthralgia diagnosis, the close location of the lateral pterygoid and masseter muscles in relation to the TMJ complicates the diagnostics. In addition, local or generalized hyperalgesia may lead to positive signs from palpation of jaw muscles and/or the TMJ and thereby affect the outcome of the diagnostic procedure. There is thus a need for evaluating diagnostic tests that are hypothesized to more precisely determine if the origin of pain is located to the muscles, to the TMJ, or to both.

One such diagnostic test may be a TMJ compression test [10]. In this test, the patient bites hard on a wooden spatula placed between the teeth in the molar region on one side in order to physically compress intraarticular structures, especially on the contralateral side. A previous experimental study showed that biting on a rigid interference placed unilaterally in the molar region caused a frontal, upward rotation of the mandibular condyle contralateral to the interference in all subjects [11]. A recent study reported that patients with unilateral TMJ disc displacement had a higher prevalence of elicited contralateral TMJ pain when biting on a bite force transducer in the molar region [12]. Unilateral clenching in the molar region has been shown to induce a significant reduction of the TMJ joint space contralateral to the biting side [13]. These studies indicate that unilateral clenching in the molar region induces a compression of the contralateral TMJ, and may thus elicit a nociceptive response if the intraarticular tissues are sensitized.

In addition to contralateral TMJ pain, it was also suggested that unilateral clenching can provoke ipsilateral fatigue and pain in the masticatory muscles [14]. In clinical practice, ipsilateral pain during unilateral clenching may, therefore, be indicative for myalgia of the masticatory muscles. However, the association between myalgia and ipsilateral pain during a TMJ compression test has not been evaluated. An evaluation of the TMJ compression test can thus add relevant diagnostic information.

The first aim of this study was to determine if the TMJ compression test could predict a DC/TMD arthralgia or myalgia diagnosis. The second aim was to determine possible confounders of such associations. Our hypothesis was that contralateral elicited familiar pain would be predictive for a TMJ pain condition (arthralgia), and that an ipsilaterally elicited familiar pain would be predictive for a masticatory muscle pain condition (myalgia).

In total, 60 participants (20% of the study population) had a positive compression test outcome on the contralateral side of the clenching (36 on the right side, and 45 on the left TMJ side) (Table 1). In addition, the test provoked an ipsilateral familiar pain outcome in 68 participants (51 times on the right side and 49 times on the left side).

A DC/TMD arthralgia diagnosis was established in 66 individuals (Table 1), representing 22% of the study population (13 men and 53 women, mean age 38.1 years; SD 15.0). Three individuals (1%) qualified for an arthralgia diagnosis without concurrent myalgia.

The sensitivity and specificity for a positive outcome of the TMJ compression test on the contralateral side in relation to an arthralgia diagnosis on the contralateral side were 0.40 (95% CI 0.31–0.50) and 0.91 (95% CI 0.88–0.94), respectively (Table 2). The sensitivity and specificity for an ipsilateral familiar pain in relation to a myalgia diagnosis were 0.35 (95% CI 0.29–0.42) and 0.93 (95% CI 0.90–0.95), respectively (Table 3).

The positive contralateral outcome of the TMJ compression test was associated with a contralateral arthralgia diagnosis (B = 1.737; OR 5.7, 95% CI 3.3–9.9) (Table 4). This association was confounded by concurrent myalgia (B = 1.737 → B = 0.996, 42.7%), but not by widespread pain or limitation of vertical jaw movements. Ipsilateral positive test outcomes were associated with a myalgia diagnosis (B = 1.962; OR 7.1 95% CI 3.9–13.0) (Table 5). This association was confounded by a concurrent ipsilateral arthralgia diagnosis (B = 1.962 → B = 1.270, 35.2%) and widespread pain (B = 1.280 → B = 1.003, 21.6%), but not by the limitation of vertical jaw movements.

The main finding from this study is that the TMJ compression test has a high specificity and it generates a high negative predictive value for contralateral DC/TMD diagnosis of arthralgia. This indicates that a negative TMJ compression test is strongly associated with the absence of a contralateral TMJ arthralgia diagnosis according to DC/TMD. On the other hand, a positive outcome of the TMJ compression test is only modestly associated with contralateral TMJ arthralgia diagnosis. In addition, the association between the TMJ compression test and a contralateral TMJ arthralgia diagnosis is confounded by the presence of myalgia. This indicates that the predictive value of the TMJ compression test for a diagnosis of contralateral TMJ arthralgia is even lower in the case of concurrent myalgia.

In clinical practice, the outcome of a diagnostic test should preferably provide reliable and valid guidance for the selection of specific treatment strategies. For any pain condition, early identification and intervention are important to prevent chronicity [24]. Chronic pain conditions also tend to embrace more complex and widespread symptoms. Therefore, in these conditions, specific diagnostic strategies are required in order to distinguish a local symptom from a widespread condition. Since TMJ pain and masticatory muscle pain may, at least in part, have different etiologies, there is a clinical need for a diagnostic test that accurately distinguishes these conditions. However, the findings from the present study indicate a low sensitivity, when only a minority of the individuals with TMJ arthralgia report a positive TMJ compression test outcome. With regard to the potential confounding factors, myalgia was found to influence the association between the test outcomes and the diagnosis of arthralgia. There may be multiple possible explanations. Firstly, the results may indicate that the DC/TMD criteria do not sufficiently discriminate myalgia from arthralgia, which may be supported by the fact that 95% of those with arthralgia also fulfilled the criteria for myalgia. Secondly, it may indicate that myalgia and arthralgia are in fact concurrent conditions and mirror a local, regional, or generalized sensitization. The complexity of the temporomandibular region means that any diagnostic test may be hampered by the presence of comorbidity [25].

The ipsilateral positive test outcome also showed a moderate diagnostic precision for the detection of myalgia with low sensitivity and high specificity. In clinical practice, the absence of an ipsilateral positive test outcome may thus be indicative for the absence of myalgia. Since the association with myalgia was not only confounded by a concurrent arthralgia but also by widespread pain, this may indicate that myalgia could be related to general hyperalgesia rather than to local factors [26]. This finding indicates that general pain conditions may be incorrectly interpreted as a local TMD pain condition.

Taken together, the results suggest that the TMJ compression test is associated with the absence of TMJ arthralgia if there is a negative outcome of the test, even after the correction of possible confounders. Future studies should explore whether the addition of the compression test to the test battery of the DC/TMD would improve the sensitivity and specificity of the current DC/TMD algorithms.