THE PREVALENCE OF FLEXOR MUSCLES IN THE CARPAL TUNNEL USING SONOGRAPHY IN CARPAL TUNNEL SYNDROME (CTS) PATIENTS AND NORMALS

Problemstellung: The objective of this study is to investigate whether there is an association between the presence of muscle bellies beyond the proximal limit of the carpal tunnel and carpal tunnel syndrome (CTS) using sonography. Furthermore, the prevalence of flexor muscles around the carpal tunnel is correlated to the hand and wrist configuration in order to define predisposing factors for CTS.

Methoden: Fivty patients with the diagnosis of CTS (based on history, clinical findings, nerve conduction studies and cross sectional area of the median nerve at the entrance of the CT) are included in this study and compared to 50 healthy volonteers without signs and history for median nerve compression. The external hand, wrist and forearm dimensions are measured in all patients using the same criterias. Using ultrasonography (En Visor Philips Medical Systems, Bothwell,WA; 5–12MHz linear array transducer), the cross-sectional area of the median nerve is measured at the entrance of the carpal tunnel (between the pisiform bone and the scaphoid tubercule), as well as 2cm proximal in a transverse plane. The presence of flexor muscle bellies (deep and superficial) at the entrance of the carpal tunnel is analysed during flexion and extension of the fingers in correlation to the location of the median nerve in a transverse and longitudinal plane.

Ergebnisse: Patients with CTS have a shorter hand length than the control (hand length 18.2cm, SD 1.1cm, control: 19.0cm, SD 1cm, palm width in both groups 8.6cm) and a squarer wrist (carpal tunnel patients: wrist depth, 4.6cm, SD 0.5, wrist width, 6.3cm, SD 0.1; control: wrist depth 4.4cm, SD 0.5, wrist width 6.13cm, SD 0.1) During flexion, there is musculature at the entrance of the carpal tunnel in 88% of patients with CTS and in 80% of controls. During extension, there are flexor muscles in 47% of patients with CTS compared to 43% of controls. The median nerve experiences a considerable motion between muscles proximal of and in the carpal tunnel during flexion and extension of the digits.

Schlussfolgerungen: Patients with CTS seem to have a shorter hand and a squarer wrist compared to controls. Statistically, there is no higher prevalence of muscles reaching the carpal inlet during flexion and extension in patients with CTS compared to controls. However, the specific hand and wrist configuration combined with the presence of flexor muscles in the carpal inlet might favour median nerve compression. In addition, the increased volume of the carpal tunnel with the presence of muscles and the motion of the median nerve during flexion and extension might promote CTS.