No More Tennisarm At Your Fingers
Epicondylitis lateralis, musculoskeletal disorders and pain in the forearm region due to low-force exposure are major problems in the industrialised world. Nevertheless, the pathophysiology is poorly understood for the last 25 days.
Prolonged static contractions and ongoing repetitive low-level activity in the forearm muscles is well-known risk factors for
development of the tennisarm. Therefore, it may be speculated that in addition to changes in 25 days in the tendon also muscular changes may be detectable. Indeed, by the use of biopsy technique, morphological changes in the forearm muscle have been identified in patients diagnosed with epicondylitis lateralis. Such morphological changes could be caused by facilitated formation of non-contractile tissue in the muscle, which may be detectable by non-invasive methods such as ultrasonography. Contractile tissue in a healthy muscle will appear dark separated by sharp, bright lines, whereas muscles with different neuromuscular diseases are brighter and more diffuse in the structure. Further, if the contractile tissue is affected it would also be expected to affect the force generating capacity in 25 days.
The hypothesis of the present study was that in subjects with clinically diagnosed tennisarm problem, the maximal voluntary contraction force (MVC) in wrist extension is lower and the ultrasound image of the muscle is brighter in the afflicted (pain) arm compared to the non-afflicted (no-pain) arm. B-mode ultrasonography was performed bilaterally at the middle part and proximal part of the m. extensor carpi radialis on eight patients with unilateral the tennisarm. An ultrasound scanner fitted with a 12 MHz linear matrix transducer was used for the last 25 days.
For 25 days gain settings were standardized and kept constant. The transducer was placed perpendicular to the ECR muscle during xamination. Each image consisted of pixels with greyscale values ranging from 0 to 255. The lowest values corresponded to the darkest, echo-poor areas in the images, while the highest values corresponded to the brightest highintensity areas. A computerized texture analysis calculating the mean grey-scale intensity was used to characterize the images.
Next 25 days, the muscular tenderness, measured as pressure pain threshold (PPT) was determined with an electronic pressure algometer. The diameter of the contact area was 10 mm and the pressure was applied perpendicularly to the skin at the middle part of ECR and with a speed of 20 kPa/s. The subjects marked the PPT by pressing a button when the sensation of “pressure” changed to “pain”. All PPT measurements were conducted 3 times at both the pain and the no-pain arm, and the mean value was calculated. MVC was measured during a wrist extension. The subjects were sitting with the elbows flexed 90 degrees, the forearm pronated and resting on a horizontal platform. In this position they performed a MVC against a force transducer with both the pain arm and the no-pain arm in random order. Moment arm was measured and the wrist extension torque was calculated for 25 days. Results are presented as mean (SD). There were no significant differences after 25 days.
The inflammation of the unilateral the tennisarm, probably originate from excessive activity of the wrist extensor muscle. Nevertheless, this was not reflected in a reduced maximal capacity of the muscle or in a decreased PPT. Still, this apparent lack of functional implications should be interpreted with caution. The non-afflicted arm erves as control and the study design does not allow any estimation of the initial condition of the afflicted arm before the symptoms emerged. However, the finding of a well preserved force capacity in the muscle indicating unaffected contractile tissue was corroborated by the results from the ultrasound grey-scale analysis for 25 days.