The Effect of Combined Exercise Training With Neuromuscular Electrical Stimulation on Muscle Strength, Proprioceptive Sense, Reaction Time, and Functionality in Patients Diagnosed With Scapholunate Instability

Among upper extremity injuries, hand/wrist injuries are frequently observed. The hand is an important organ that enables individuals to perform daily life activities. Hand and wrist problems can cause limitations in the person's activities and prevent the person from fulfilling daily life roles. This can lead to a decrease in quality of life.

n terms of biomechanical properties, extrinsic ligaments of wrist show greater elasticity but are less resistant to traction, resulting in lower durability compared to most intrinsic ligaments. As a result, extrinsic ligaments are prone to rupture in the medial portions, whereas intrinsic ligaments are more prone to rupture injuries rather than a complete tear (1).

The scapholunate (SL) joint relationship is provided by several carpal ligaments. The most important of these is the scapholunate interosseous ligament (SLIL; scapholunate interosseous ligament) (2). SLIL injury results in scapholunate joint instability (3). Scapholunate instability is the most common carpal instability (4). When this instability is left untreated, the mechanical relationship between the carpal bones is permanently disrupted, resulting in progressive degenerative changes in the radiocarpal and midcarpal joints (5). These degenerative changes are called scapholunate advanced collapse (SLAC) and are the most common cause of wrist osteoarthritis (6). In SL instability, extension and falling on the hand in ulnar deviation typically constitute the mechanism of injury. The combined pattern of carpal instability and degenerative arthritis is called scapholunate advanced collapse (SLAC) (7).

The fact that the scaphoid and lunate have different articular structures allows them to rotate at different rates during wrist flexion and extension movements. In addition, the dorsal fibers of the SLIL are short and thick and the palmar fibers are loose and elastic, allowing different rotations of the scaphoid and lunate during flexion and extension movements. With loading, the scaphoid tends to go into flexion and the lunate tends to go into extension. These different movement patterns of the scaphoid and lunate result in a high potential energy stored in the SLIL ligament. When ligament rupture occurs, the carpal bones are expected to move to the opposite side due to this energy. Therefore, after SLIL rupture, the scaphoid flexes and the lunate goes into extension due to the pulling effect of the triquetrum through the lunatriquetral interosseal ligament (LTIL). This instability pattern is called dorsal intercalary segment instability (DISI) (7).

Until recently, most biomechanical theories suggested that wrist stability was mainly determined by the shape of the joint and the interaction between ligaments and capsules. The dynamic stabilization mechanisms of other joints such as the knee or shoulder have been extensively investigated. Less emphasis has been placed on understanding how muscles and tendons contribute to wrist stability. However, over the last 15 years, increasing interest and research has started to shed light on this topic. In fact, more than 350 articles on wrist proprioception have been published since 2011. One of the triggers for this fact was the description of mechanoreceptors in the wrist ligaments by Hagert et al. Proprioception is related to joint stability. The term "wrist stability" refers to the ability of the wrist to maintain balance under load (kinetic) and/or during movement (kinematic), and can persist strongly without twisting and becoming symptomatic. A stable wrist does not twist under physiological load and can adjust its internal alignment to become a solid block from which forces can be distributed. Kinetic stability of the wrist requires many contributing factors, including bone morphology, robust static (ligaments) and strong dynamic stabilizers (forearm muscles and tendons crossing the wrist), preserved articulating surfaces, and a competent sensory and motor system that includes nerves connecting the static and dynamic stabilizers. Failure of any of these five factors can lead to wrist instability (13).