Comparison of Strength, Weight Bearing, Proprioception, Reaction Time and Function in Scapholunate Instability

Overview

Scapholunate (SL) instability is the most common type of instability seen in the wrist, resulting from SLI injury or excessive mobility \[1,2\]. It usually occurs after trauma and can range from mild injury to severe malalignment \[3\]. Symptoms include dorsal pain, clicking sound, limited movement, increased pain with weight-bearing, and weakness \[4,5\]. Pain reduces joint movement and grip strength, limiting daily activities \[6\]. If there is no dislocation, conservative treatment (education, exercise, splinting) is applied \[7\]. The wrist absorbs and transfers load through ligaments. During flexion-extension, the scaphoid and lunate follow the capitate \[10\]. SLIL injuries alter forearm muscle activation. EKRL, EKRB, APL, and FKR are "scapholunate-friendly" muscles; EKU is not recommended due to its pronator effect \[12-15\]. SLIL mechanoreceptors enhance dynamic stability \[11,19\]. There are no studies objectively measuring the strength of these muscles. Isokinetic muscle assessment has not been performed in SL instability. These measurements objectively determine muscle strength and imbalances, personalizing treatment. Weight transfer capacity, reaction time, and proprioception have also not been studied. However, weight transfer is an indicator of stability, proprioception is critical for functionality, and reaction time reflects neuromuscular response speed \[23-27\]. The aim of this study is to compare forearm isokinetic muscle strength, grip strength, weight transfer, proprioception, reaction time, and functionality in individuals with SL instability with those in healthy individuals.

Scapholunate (SL) instability is the most common type of instability in the wrist, resulting from injury or excessive mobility of the scapholunate interosseous ligaments (SLIL) \[1,2\]. This condition, which typically arises following trauma, can range in severity from partial ligament injury to irreparable ligament damage and malalignment \[3\]. Symptoms include dorsal pain, clicking sounds, limited range of motion, a sensation of catching, pain exacerbated by loading, and weakness \[4,5\]. Pain that occurs during weight-bearing can reduce joint range of motion and grip strength, thereby limiting daily living activities \[6\]. In cases without radiological findings of dislocation, conservative treatment (education, exercise, splinting) is preferred \[7\]. The wrist facilitates load absorption and transfer through complex mechanisms and ligaments. During flexion and extension, the scaphoid and lunate follow the movement of the capitate \[10\]. In SLI injuries, impaired ligament-muscular reflexes alter the activation patterns of the forearm muscles. Among these muscles, the extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), abductor pollicis longus (APL), and flexor carpi radialis (FCR) are defined as scapholunate-friendly; the extensor carpi ulnaris (ECU) has been reported as a muscle to be avoided due to its intracarpal pronator effect \[12-15\]. In recent years, it has been emphasized that static stability approaches are insufficient and that neuromuscular control has gained importance \[2\]. It has been shown that the SLIL and wrist ligaments are rich in mechanoreceptors and that these structures increase dynamic stability by activating the forearm muscles \[11,19\]. However, there are no studies that objectively measure the strength of the scapholunate-friendly muscles. There is no information in the literature regarding the evaluation of wrist muscles in SL instability using an isokinetic system. Isokinetic measurements are also extremely limited in other pathologies affecting the wrist \[20-22\]. Isokinetic devices measure muscle strength at a constant speed, objectively determining performance at different speeds and revealing muscle imbalances. This enables treatment plans to be personalized. Similarly, there are no studies examining parameters such as weight transfer capacity, reaction time, and proprioception in SL instability. However, upper extremity load transfer is an important indicator of stability \[23-25\], and proprioception is critical for functionality. Reaction time indicates the neuromuscular system's ability to respond quickly, and it is thought that this mechanism may be affected in instability \[26,27\]. This study aims to investigate forearm isokinetic muscle strength, grip strength, weight transfer capacity, proprioceptive sensation, reaction time, and functionality in individuals with scapholunate instability compared to healthy individuals. Hypotheses H1: Isokinetic forearm muscle strength in patients with SL instability differs from that in healthy individuals. H2: Grip strength differs between patients with SL instability and healthy individuals. H3: Proprioceptive sensation differs between patients with SL instability and healthy individuals. H4: Reaction time differs between patients with SL instability and healthy individuals. H5: Weight transfer onto the hand differs between patients with SL instability and healthy individuals. H6: Upper extremity functionality differs between patients with SL instability and healthy individuals.