This study was a crossover clinical trial that investigated the immediate effects of forearm clasp and forearm strap orthoses on pain intensity, pain-free grip strength, proprioception, and hand function, with a focus on enhancing sensorimotor function via sensory stimulation. Both orthoses improved the sensorimotor function of the affected arm in LET patients. Elbow proprioception showed large improvements with both orthoses. Both orthoses showed moderate to large improvements in pain level and hand function. In terms of pain intensity and hand function, both orthoses showed moderate to large improvements. Pain-free grip strength improved only slightly with both orthoses. Since there was no significant difference between the orthoses for any of the outcome measures, these data did not demonstrate the superiority of one orthosis over the other. In addition, since no follow-up was performed, the purpose of this study was to evaluate the immediate effects rather than establishing the effectiveness.
Both orthoses improved pain intensity and pain-free grip strength, which is in line with other research showing how orthoses can help people with LET experience less pain and have stronger grip [17, 27–29]. It is thought that forearm orthoses operate through two interrelated mechanisms: effects on muscle tendons and effects on the nervous system. The forearm orthosis was shown to decrease forces acting on the lateral epicondyle by functioning as a secondary attachment for the tendons of the wrist extensor muscles [30]. In the event that a forearm orthosis prevents the muscle enthesis from receiving excessive stress, the sensory nerve endings for elbow proprioception could be influenced by this force redistribution. It is unclear what exact mechanism in this study improved elbow proprioception with forearm orthoses. However, limited previous research on this subject has suggested that the application of external support over the elbow could stimulate peripheral sensory receptors, inhibit pain, and increase grip strength prior to the onset of pain at the lesion area in people with LET [20, 31, 32]. Increasing the amount of sensory input to the central nervous system has been shown to lower the motor unit threshold and increase the involvement of inactive muscle fibers, improving hand function [33].
According to previous research, LET results in proprioceptive deficits at the elbow [6]. It was expected that forearm orthoses could improve elbow proprioception, as explained above. In this study, elbow proprioception was evaluated using the JPS test. This test could be easily employed in the clinical setting of this study since it is noninvasive and simple and does not require complicated or expensive equipment. Proprioception in large articulations such as the elbow is mostly dependent on mechanoreceptors found in the muscles and tendons (34). Therefore, we chose to conduct the active JPR assessments because, in an active test, muscle spindles contribute more to sensory inputs than they do in a passive test [34]. The JPR task for the participants in this study was to match target angles in the flexion direction that were 20° from the initial joint position. Previous studies supported the sensitivity of this target angle (110° of elbow flexion) in measuring proprioceptive changes at the elbow [6, 17]. We chose 110° of elbow flexion as the target angle since elbow movement is directed toward flexion, where muscle spindles and tendon mechanoreceptors of the wrist extensors become more prominent in feeling proprioception than in extension movement. Three previous studies investigated the effects of forearm orthoses on sensorimotor outcome measures [17, 35, 36]; two of these found significant but opposite results on joint position sensation [17, 35]. When forearm orthoses were applied, the JPR error at the wrist increased by 2.4° [35] but decreased by 1.4° at the elbow [17]. The elbow JPR improved by 1.39° with a forearm strap and 1.67° with a forearm clasp in our study; this improvement is also comparable to the 1.4° improvement that was shown with taping in people with LET [32].
A pain-free grip was chosen for this study to demonstrate the changes caused by therapeutic interventions. The pain-free grip is more sensitive than the forceful grip strength [37]. The decision to choose pain-free assessment over maximal hand grip strength was also made by considering the participants' safety. A maximal grip during testing may increase the local pressure behind the forearm strap, preventing normal blood flow during prolonged testing. The accuracy of the JPR and pain reports could then be impacted by this obstructive condition that occurred during testing.
The use of a forearm strap resulted in a significant reduction in pain; however, a forearm clasping orthosis did not show the same level of efficacy. The structure of the pressure pads in the two orthoses most likely contributed to the disparity in their effectiveness. The forearm band has a double-layer pad made of soft neoprene rubber that allows for a larger area of contact and a more even force distribution. However, the circular spikes on the textured pad of the forearm clasp had a relatively small contact surface, with a limited capacity to transfer the compression force over the lesion region, which could worsen local pressure and discomfort. The VAS has been used to assess pain in most investigations on LE, and it has been suggested that a 1-point shift in the VAS score may have clinical importance [38]. Compared to patients who did not wear an orthosis, those who used a forearm strap in the present study experienced a decrease in the VAS score of 0.29 to 1.63 points. This indicated that the forearm strap could clinically alleviate pain intensity in people with LET.
The neuromuscular features of LET often include impairments in time-dependent activity of the affected upper limb [39]. This study evaluated hand function with the Minnesota test to determine how sensory-induced effects might affect the neuromuscular control of coordinated movements in the upper limb. The Minnesota test was chosen due to its greater emphasis on elbow motions compared to finger dexterity assessments such as the nine-hole peg test, which was employed in a prior study [17]. The elbow, as a connecting joint between the hand and the shoulder, is important for maintaining the stability of the upper limb during daily activities. Therefore, the function of the hand should be influenced by successful interventions intended to improve neuromuscular control and proprioception of the elbow. Orthotic interventions designed for the elbow include a range of mechanisms, including joint stabilization, pain reduction, and enhancement of strength, function, and performance [40]. Orthoses can alter proprioceptive signals to the central nervous system by applying controlled strain to the capsuloligamentous tissue, a structure rich in many kinds of mechanoreceptors [41]. Enhancing proprioception and functional capacities may be possible when the CNS receives increased sensory information because it reduces the motor unit threshold and improves the recruitment of previously inactive muscle fibers [41]. The forearm strap's ability to reduce pain may have a positive impact on the integration or processing of afferent and efferent signals, which could explain why hand function has improved. The precise cause of the improvement in hand function is still unclear according to this methodology and needs further investigation.
This study has several limitations. First, using a crossover design in a single-arm study during one session could increase the risk of potential carryover or learning effects. This study was based on previous research suggesting that the effects of long-lasting and reversible counterforce orthoses are not reversible once they are removed. A 5-minute acclimation time was used for more confidence. Second, participants and examiners could not be blinded, but this was mitigated by using patient-rated scales and automated equipment. Third, the investigator applied the orthoses according to clinical practice recommendations, ensuring that they were snugly fitted but comfortable. The level of tension may have varied between tests because this was not quantified. The study's limitations highlight the need for further research and adjustments to ensure accurate results.
One of our concerns in conducting this trial was that using a forearm clasp to provide additional stimulation could be harmful and cause a distracting effect on upper limb performance because it would require more cognitive effort to perceive and process the additional afferent information. This could interrupt attention from regulating optimal muscle forces and hand function, increasing the risk of orthotic withdrawal, or it could have interfered with the afferent signals from the joints, making movement imperceptible. The findings of this study do not support this hypothesis: greater grip strength suggests that the neuromuscular function of the hand has improved. Additionally, there was an improvement in the awareness of the JPS at the elbow, which, if practiced for a longer time, may enhance neuromuscular control of the upper limb. There were few (small) adverse events noted as a result of discomfort beneath the textured pad of the clasping orthosis during testing. This could be resolved by using a softer material when producing textured pads. Therefore, we aimed to conduct additional studies on the use of sensory-enhanced forearm clasping orthoses during daily activities.