The Accommodation of Bone Anchors Within the Distal Phalanx for Repair of Flexor Digitorum Profundus Avulsions

Avulsion injury of the flexor digitorum profundus (FDP) tendon has been traditionally repaired with a pull-out suture over the nail plate. Complication rates with this method and improvements in anchor design have led to the increased use of bone anchors to give a rigid all-inside repair. However, the dimensions of the distal phalanx may limit their use. The primary hypothesis was that 2 micro bone anchors could fit in either perpendicular or 45° proximally angled positions within each distal phalanx. A further hypothesis was that 1 mini bone anchor could fit in similar positions in the distal phalanx.

Thirty-two fresh frozen fingers were dissected, and the FDP tendon was removed from the distal phalanx footprint. Two bone anchor types were used, mini and micro sizes, and inserted at 2 angles, perpendicular and 45° proximally angled. Observations of dorsal cortex and joint space penetration were recorded. Distal phalanx dimensions were measured for each finger.

The micro anchors penetrated the dorsal cortex in perpendicular tests in little fingers only. The micro anchor did not penetrate the joint in any angled tests. The mini bone anchor penetrated the dorsal cortex in 100% of perpendicular tests and the joint in 63% of angled tests, although none of these included the middle finger.

Two micro bone anchors fit within the distal phalanx in all fingers tested, except the little finger, when placed in the perpendicular position. At a 45° angle, the distal phalanx of the little finger can also accommodate micro bone anchors without any evidence of complication when placed 4 mm from the joint. The mini anchors were too large to fit in a perpendicular position within the distal phalanx. In the 45° angled position, the joint was not penetrated by the mini anchor in only middle fingers.

The study provides anatomical evidence of the accommodation of micro bone anchors within the distal phalanx in perpendicular or 45° angled positions for the repair of FDP tendon avulsion injury.