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Wrist Angles That Help Wrist and Thumb Tendons

Stick your thumb out to hitch a ride and you'll see the extensor pollicis longus (EPL) pop up. This tendon runs along the back of the wrist and thumb. Sometimes this tendon ruptures without warning. It could be job-related, or it can occur after the lower arm is broken. But many times it happens with no known cause.

There are two theories about spontaneous EPL tendon rupture. One is based on poor blood supply to the area (a vascular cause). The other is a mechanical theory. After fracture, the tendon rubs against the bone and tears. It's possible that both vascular and mechanical problems occur at the same time.

Researchers at the Mayo Clinic measured the gliding resistance of the normal EPL tendon. Then they compared it to another tendon. They used the extensor digitorum communis tendon (EDC) as the model tendon because it's in the same area of the thumb, has a similar function, and has a much lower risk of rupture.

Frozen human cadavers were used in the study. The hand and lower hand were attached to a device to move the thumb. Researchers put two marks on the tendon and measured how far the marks moved when the thumb was moved. A weight attached to a special ring at the joint and pulled through a pulley system made it possible to measure motion. By changing the position of the pulley, the wrist angle and direction of motion was changed.

The authors found wrists position with the least resistance. One position was with the wrist in neutral. A second was with the wrist angled back and slightly toward the pinky-side of the hand. The authors suggest that gentle, active motion of the thumb in this position will reduce mechanical irritation of the tendon. At the same time, the tendon will get lubricated. Doctors and therapists use this information to know the optimal positions for splinting the wrist when treating the EPL tendon.

References: Keiji Kutsumi, MD, et al. Measurement of Gliding Resistance of the Extensor Pollicis Longus and Extensor Digitorum Communis II Tendons Within the Extensor Retinaculum. In The Journal of Hand Surgery. March 2004. Vol. 29A. No. 2. Pp. 220-224.

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