Thermography in lateral epicondylitis or tennis elbow
On the occasion of the recent publication of a systematic review with meta-analysis by Dr. José Jamacy Almeida Ferreira‘s group on the detection of tendinopathy with infrared thermography, we have carried out an objective critique of the state of the art in this matter. In addition, it gives us the opportunity to teach real clinical cases, focusing on the tendinopathy of the lateral muscles of the forearm, known as epicondylitis or tennis elbow.
This publication, which can be found here, comes from the research group of the University of Paraíba, in João Pessoa (Brazil), who have done an excellent job that we would love to comment on.
The tendon when injured
The tendon is the tissue that transfers the kinetic energy generated by the muscles to the bones, thus producing movement. It is an elastic fabric, which characterizes it for having very good load absorption capacities.
However, this also makes it susceptible to injury, by destruction, inflammation or degeneration, especially in the limbs. This is probably the reason why the most common tendinopathies are those of the rotator cuff, gluteus, Achilles, patellar and epicondylar region (Millar et al., 2021), as in the example in Figure 1:
The temperature of tendinopathies
The appearance of pain in a tendinopathy is related to the anatomical and mechanical changes of the tendon. However, despite what it might seem, these changes cause the tenocytes and peripheral nerves to react and activate the higher centers through nociceptive pathways. In this way, the role of the Central Nervous System (CNS) is key, since the innervation of the affected region tends to be greater than that of the healthy area (Andersson et al. 2007; Jewson et al. 2015; Dean et al. 2017).
In fact, the intervention of the CNS is key in the activation of adrenergic receptors, which stimulate vasoconstriction or vasodilation, thus altering local blood flow and temperature (Liu et al. 2020). Despite this, there is some evidence that calls this claim into question (Oskarsson et al. 2007).
For several decades, localized hyperthermic asymmetry has been detected in 98% (Binder et al. 1983) and 94% of epicondylitis cases (Thomas et al. 1992), as can be seen in Figure 2. However, no significant asymmetries have been found in intra-articular tendon pathologies (Vecchio et al. 1992).
In Figure 2, we can see three examples from the literature where patients with epicondylitis are thermally analyzed. In (Binder et al. 1983), that we observed a thermogram of an elbow with epicondylitis, with the hottest point located at the insertion of the epicondylar musculature. The image extracted from (Thomas et al. 1992) shows us the entire side of the elbow always warmer in cases of epicondylitis. Lastly, the study by Meknas et al. (2008), analyze patients with epicondylitis and in the image, an example where an arrow points to the hyperthermic area at the insertion of the epicondylar musculature.
More recently, the latest systematic review in this regard already confirmed that the skin covering an inflamed tendon has a higher temperature (Chaudhry et al. 2016). On the other hand, the tendons of healthy people are thermally symmetrical (Tumilty et al. 2019), a fact that we have already explained in detail in this publication.
Our experience in lateral epicondylitis
From our clinical experience, we have treated patients with epicondylitis and the results seem to indicate that the region with pain consistently tends to be hyperthermic, as we can see in figure 3:
These results are in line with those shown by authors such as Binder et al. (1983), Thomas et al. (1992) or Meknas et al. (2008). They affirm that epicondylitis offers a localized hyperthermic pattern, due to the increased blood supply in the area. Some authors even affirm that thermography is a valid tool to support the diagnosis in epicondylitis (Haake et al. 2002).
Results of the systematic review with meta-analysis
Similarly, the research group at the University of Paraíba, in João Pessoa (Brazil), led by Dr. José Jamacy Almeida Ferreira, includes 7 studies in its review (Dias de Lacerda et al. 2022).
Of which, Vecchio et al. (1992) and Park et al. (2007) investigated shoulder tendinopathies; Mangine et al. (1987) on patellar tendinopathy; and Sillero-Quintana et al. (2015) on tendinopathies in general. Binder et al. (1983), Thomas et al. (1992) and Meknas et al. (2008). , who were already commented in the previous section, investigated tendinopathy in the epicondylar region or epicondylitis.
In figure 4, we can see the sensitivity and specificity graphs of these studies, which give us an average result of sensitivity of 0.72 and specificity of 0.95.
Conclusions on thermography and epicondylitis
The results of the systematic review with meta-analysis by Dr. José Jamacy Almeida Ferreira demonstrated that infrared thermography shows appropriate specificity without heterogeneity between studies for the evaluation of lateral epicondylitis and shoulder tendinopathy. However, the sensitivity results have significant heterogeneity, which significantly reduces their precision.
In general, the tendon tends to have hyperthermic behavior when there is tissue damage, especially if it is in an acute phase of the process. Thermography helps us to assess the severity of the injury and guide treatment based on the thermal response of said tendon.
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