Avoiding the posterior interosseous nerve during 2-incision distal biceps tendon repair: an anatomic study

The posterior interosseous nerve (PIN) is the most commonly injured motor nerve during distal biceps tendon repair resulting in severe functional deficits. Anatomic studies of distal biceps tendon repairs have evaluated the proximity of the PIN to the anterior radial shaft in supination, but limited studies have evaluated the location of the PIN in relation to the radial tuberosity (RT), and none have examined its relation to the subcutaneous border of the ulna (SBU) with varying forearm rotation. This study evaluates the location of the PIN in relation to the RT and SBU to help guide surgeons in safe placement of the dorsal incision and the safest zones of dissection.

The PIN was dissected from arcade of Frohse to 2 cm distal to the RT in 18 cadaver specimens. Four lines were drawn perpendicular to the radial shaft at the proximal, middle, and distal aspect of and 1 cm distal to the RT in the lateral view. Measurements were recorded with a digital caliper along these lines to quantify the distance between the SBU and RT to the PIN with the forearm in neutral, supination, and pronation with the elbow at 90° flexion. Measurements were also made along the length of the radius at the volar, middle, and dorsal surfaces at the distal aspect of the RT to assess its proximity to the PIN.

Mean distances to the PIN were greater in pronation than supination and neutral. The PIN crossed the volar surface of the distal aspect of the RT -6.9 ± 4.3 mm (-13, -3.0) in supination, -0.4 ± 5.8 mm (-9.9, 2.5) in neutral, and 8.5 ± 9.9 mm (-2.7, 13) in pronation. One centimeter distal to the RT, mean distance to the PIN was 0.54 ± 4.3 mm (-4.5, 8.8) in supination, 8.5 ± 3.1 mm (3.2, 14) in neutral, and 10 ± 2.7 mm (4.9, 16) in pronation. In pronation, mean distances from the SBU to the PIN at points A, B, C, and D were 41.3 ± 4.2, 38.1 ± 4.4, 34.9 ± 4.2, and 30.8 ± 3.9 mm, respectively.

PIN location is quite variable, and to avoid iatrogenic injury during 2-incision distal biceps tendon repair, we recommend placement of the dorsal incision no more than 25 mm anterior to the SBU and carrying out deep dissection proximally first to identify the RT before continuing the dissection distally to expose the tendon footprint. The PIN was at risk of injury along the volar surface at the distal aspect of the RT in 50% with neutral rotation and 17% with full pronation.