Evaluation of adductor pollicis muscle elasticity in patients with trapeziometacarpal osteoarthritis

Trapeziometacarpal osteoarthritis (TMC OA) is the second most common type of arthritis in the hand. It is among the most important causes of upper extremity-related disability. It is observed in 57% of women and 42% of men over the age of 75. Its incidence increases up to 33% especially in women in the postmenopausal period due to estrogen deficiency. The most common symptom of TMC OA is pain at the base of the thumb. Patients complain of severely pain especially during grasping activities. As osteoarthritis progresses, almost every activity causes pain and eventually a persistent pain may occur. Grip strength decreases over time due to disuse of the hand. This leads to difficulty or inability to perform daily life activities such as opening door handles, using knives, opening jar lids and turning keys. In the presence of TMC OA, the adductor pollicis (AP) muscle may become fibrotic and changes in muscle tone and muscle length may be observed. In the later stages, AP spasm and contracture may develop, causing narrowing of the web space. When the thumb is abducted to initiate grasping, hyperextension develops in the MCP joint due to spasm or contracture, and the volar plate is overstretched and flexed. The development of MCP joint hyperextension deformity as a functional compensatory mechanism during fine grasping causes the forces transmitted proximally by the MCP joint to be concentrated in the palmar compartment of the TMJ joint and the disease process to accelerate. Recent studies have emphasised the importance of Oponens Pollisis and First Dorsal Interosseal (FDI) muscles which contribute to joint stabilisation in TMC OA treatment. It has been shown that especially FDI muscle activity plays a role in thumb TMC joint stabilisation and its maximum contraction against resistance provides reduction in the TMC joint. This effect is thought to be achieved by creating an antagonist force to the activity of the AP muscle which causes shear force and radial subluxation at the TMC joint. In this respect, approaches to protect the viscoelastic properties of the AP muscle, which has a larger cross-sectional area and torque generation potential compared to other thenar muscles, have an important place in rehabilitation in terms of reducing the stresses on the TMC joint, restoration of the web space and prevention of deformities that may occur. Therefore, stretching exercises for the thumb, transverse friction massage for the AP muscle and abduction orthoses are recommended to be added to the treatment programmes. Changes in quantitative (muscle thickness, cross-sectional area, volume, etc.) and qualitative (echogenicity, elasticity, fat infiltration, etc.) parameters that occur in the thenar muscles during the degeneration process of the TMJ joint are still not clearly known. These parameters play an important role in both static and dynamic function of the joint as they affect the force generating potential of the muscles. In this respect, evaluation of thickness and cross-sectional area, which are indicators of the degree of hypertrophy or atrophy; pennation angle and muscle fibre length, which are related to the contractile capacity and the number of muscle fibres per unit area; stiffness, which is one of the viscoelastic properties; and echogenicity, which gives information about the content of contractile tissue, is necessary to determine the changes that occur in the presence of TMC OA, to understand the pathomechanics of the disease, to generate hypotheses, and to develop preventive and therapeutic strategies. In a study by Nwawka et al., the stiffness of the thenar muscles (OP, Abductor Pollisis Brevis (APB), Flexor Pollisis Brevis and Flexor Pollisis Longus) in TMC OA patients and healthy subjects were compared using elastography method and it was shown that muscle stiffness was less in the TMC OA group compared to the control group (10). In another study investigating the morphometry of the thenar muscles in TMC OA patients, it was reported that 4-week conservative treatment with short oponens splint did not affect the cross-sectional area and muscle thickness parameters of the OP and APB muscles. In the literature, there is not yet a study in which changes in morphometric and morphological parameters of all thenar muscles are determined in the presence of TMC OA, which can help to understand the pathomechanics of the disease and guide rehabilitation strategies. TMC OA is an important problem in terms of causing secondary complications, significantly affecting functionality and decreasing quality of life. This study will determine the changes in qualitative and quantitative parameters in the thenar muscles of TMC OA patients and contribute to the creation of the most appropriate rehabilitation programme. The hypotheses of the study are as follows: H0: There is no difference between adductor pollicis muscle elasticity of trapeziometacarpal osteoarthritis patients and healthy individuals.