Bundle pattern of the flexor digitorum profundus tendon in zone II of the hand: A quantitative assessment of the size of a laceration

Assessing the cross-sectional area of a partial laceration of a flexor digitorum profundus tendon based on its width, using magnificantion and calipers, is often inaccurate. As the threshold for repairing a partial laceration for most surgeons is the involvement of 50% of the tendon area, an accurate method of naked-eye evaluation to detect a 50% (or larger, or smaller) laceration was developed. This assessment is based on the sizes of the radial and ulnar bundles in the tendon. The relative area of the two bundles at four levels in zone II in the index, middle, ring, and small fingers was measured. In the index and small fingers the ulnar bundle had a mean area consistently greater than and the radial bundle consistently less than 50% of the total tendon area. In the middle finger, the mean areas of both bundles were close to 50% of the tendon area, but the radial bundle was reduced at the level of the proximal interphalangeal joint and distally. In the ring finger, both bundles remained close to 50% of the total tendon area at all levels. The bundles involved in a laceration can be easily identified with the naked eye; the data provided by this study may improve the accuracy of partial laceration size assessment.