Thickness of the Tendons of the First and Second Extensor Compartment at the Intersection: Measurements with Ultrasound in Asymptomatic Volunteers

Purpose: A sign of intersection syndrome is thickening of the tendons at the area where the first extensor compartment tendons cross over te second compartment. The normal values for the thickness of the tendons has not been reported. Our purpose was to measure the thickness of the tendons at the level of the intersection in normal volunteers with ultrasound, and compare differences between men and women, between dominant and non dominant side, and between proximal and distal tendon segments.

Materials and Methods: Forty-one asymptomatic volunteers (25 women, 16 men) were examined by two radiologists experienced in musculoskeletal ultrasound. The thickness of the tendons of the first and second compartment was measured at the intersection at well defined proximal and distal levels. Descriptive statistics were obtained. Differences between men and women, between dominant and non-dominant side, and between proximal and distal segments were evaluated with a Student's t-test.

Results: The mean age of the volunteers was 40 years (range, 20, 56 years). The 95 % confidence interval (pooled men and women) for the extensor carpi radialis longus varied from 18-26 mm (proximal and distal), for the extensor carpi radialis brevis from 18-27 mm (proximal and distal), for the extensor pollicis brevis from 9-18 mm (proximal) and 8-16 mm (distal) and for the abductor pollicis longus 10-16 mm (proximal). For the proximal extensor carpi radialis longus, distal extensor carpi radialis brevis, and proximal extensor pollicis brevis no statistically significant difference was found between men and women. For the distal extensor carpi radialis longus, proximal extensor carpi radialis brevis, distal extensor pollicis brevis, and proximal abductor pollicis longus a significant difference was found between men and women. There was no significant difference between the dominant and non dominant side. Differences between the proximal and distal segments were statistically significant for the extensor carpi radialis brevis and extensor pollicis brevis.

Conclusion: As a clinically applicable guideline we suggest the following cut-off values for thickness: extensor carpi radialis longus and extensor carpi radialis brevis, 27 mm but slightly less in women for the distal extensor carpi radialis longus and proximal extensor carpi radialis brevis. The upper limit for the extensor pollicis brevis and abductor pollicis longus is 18 mm but slightly less for the extensor pollicis brevis in women. The extensor carpi radialis brevis is slightly thinner proximally and the extensor polllicis brevis distally.