Flexor tendon and synovial gliding during simultaneous and single digit flexion in idiopathic carpal tunnel syndrome

Abstract

The characteristic pathological finding in carpal tunnel syndrome (CTS) is non-inflammatory fibrosis of the subsynovial connective tissue (SSCT), which lies between the flexor tendons and the visceral synovium (VS). How this fibrosis might affect tendon function is unknown. To better understand the normal function of the SSCT, the relative motion of the middle finger flexor digitorum superficialis (FDS III) tendon and VS was observed during finger flexion in patients with CTS and cadavers with a history of CTS and compared to normal cadavers. A digital camcorder was used to monitor the gliding motion of the FDS III tendon and SSCT in eight patients with idiopathic CTS undergoing carpal tunnel release surgery (CTR), in eight cadavers with an antemortem history of CTS and compared these with eight cadaver controls. There were no significant differences noted in the total movement of the SSCT relative to the FDS III. However, the pattern of SSCT movement relative to the FDS III in the CTS patients and cadavers with an antemortem history of CTS differed from the controls in one of two patterns, reflecting either increased SSCT adherence to FDS III or increased SSCT dissociation from FDS III. In CTS, the gliding characteristics of the SSCT are qualitatively altered. These changes may be the result of increased fibrosis within the SSCT, which in some cases has ruptured, resulting in SSCT-tendon dissociation. Similar changes are also identified postmortem in the CTS patient.

Figure 1

The structure of the sliding unit in the carpal tunnel region (Ettema et al., 2004). Copyright JBJS; used with permission.

Figure 2

Markers on the middle superficial flexor tendon (FDS III), visceral synovium and parietal synovium in a patient hand during CTR surgery.

Figure 3A

Setup to test full fist motion.

Figure 3B

Setup to test isolated middle finger FDS motion.

Figure 4

Movement of the tendon (blue) and SSCT of the eight patients (red) versus the eight cadaver controls (black) as a percentage of each maximum tendon movement. Six out of the eight patients show a decreased displacement as compared to the controls. In two patients the SSCT moves en bloc with the tendon.

Figure 5

Movement of the tendon (blue) and SSCT of the eight cadaver CTS hands (red) versus the eight cadaver control hands (black) as a percentage of each maximum tendon movement. Four out of the eight cadaver CTS hands show a decreased displacement as compared to the controls. Three cadaver patients moved similar to the controls. Number 1−8 represent individual specimens.

Figure 6

Movement of the tendon (blue) and SSCT of eight patients and eight controls during single digit (differential) motion as a percentage of each maximum tendon movement.