Supinator to Posterior Interosseous Nerve Transfer for Recovery of Hand Opening in the Tetraplegic Patient: A Case Series

Abstract

Background and objectives: Cervical spinal cord injury results in devastating loss of function. Nerve transfers can restore functional use of the hand, the highest priority function in this population to gain independence. Transfer of radial nerve branches innervating the supinator to the posterior interosseous nerve (SUP-PIN) has become a primary intervention for the recovery of hand opening, but few outcome reports exist to date. We report single-surgeon outcomes for this procedure.

Methods: The SUP-PIN transfer was performed on adults with traumatic spinal cord injury resulting in hand paralysis. Outcome measures include Medical Research Council strength grade for extension of each digit, and angles representing critical apertures: the first web space opening of the thumb, and metacarpophalangeal angle of the remaining fingers. Factors affecting these measurements, including preserved tone and spasticity of related muscles, were also assessed.

Results: Twenty-three adult patients with a C5-7 motor level underwent SUP-PIN transfers on 36 limbs (median age 31 years, interquartile range [21.5, 41]). The median interval from injury to surgery was 10.5 (8.2, 6.5) months, with 9 (7.5, 11) months for the acute injuries and 50 (32, 66) months for the chronic (>18 months) injuries. Outcomes were observed at a mean follow-up of 22 (14, 32.5) months. 30 (83.3%) hands recovered at least antigravity extension of the thumb and 34 (94.4%) demonstrated successful antigravity strength for the finger extensors, providing adequate opening for a functional grasp. Chronic patients (>18 months after injury) showed similar outcomes to those who had earlier surgery. Supination remained strong (at least M4) in all but a single patient and no complications were observed.

Conclusion: SUP-PIN is a reliable procedure for recovery of finger extension. Chronic patients remain good candidates, provided innervation of target muscles is preserved. Higher C5 injuries were more likely to have poor outcomes.

FIGURE 1.

Flow diagram for inclusion of patients who had the SUP-PIN transfer performed after spinal cord injury. SUP-PIN, supinator to the posterior interosseous nerve.

FIGURE 2.

Surgical view. Preoperative. A, The nonfunctional muscles innervated by the PIN are depicted in gray. The surgical site is shown at the proximal, posterior aspect of the forearm between the brachioradialis and the extensor carpi radialis longus muscles. B, Graphical and C, surgical views of the deep radial nerve giving off branches to the SUP and continuing as the PIN diving under the SUP. Postoperative. D, The PIN distribution is reinnervated (red) by the former SUP axons and now capable of finger extension. E, Graphical and F, surgical views of the coaptation of the SUP branches to the PIN. PIN, posterior interosseous nerve; SUP, supinator.

FIGURE 3.

Preoperative motor level and ICSHT. ICSHT, International Classification for Surgery of the Hand in Tetraplegia Score.

FIGURE 4.

Hand angles. A, The MCP angle is the angle of the first metacarpal in reference to the proximal phalanx. A neutral (straight) MCP was represented as 0° with finger hyperextension recorded as a positive angle and flexion as negative. Any substantial variation between D2–5 was noted. B, The FWS was measured from the interphalangeal joint of the thumb to the first carpometacarpal joint to the MCP of D2. The angles shown approximate the median value. FWS, first web space; MCP, metacarpophalangeal.

FIGURE 5.

Hand variations. A, Preserved innervation and spasticity of the intrinsics will provide extension of the proximal IP with an associated decrease in the metacarpophalangeal angle, providing an overall improvement in hand opening, compared with B, a hand with loss of intrinsic innervation. Intrinsic correction may be performed with a volar plate advancement. C, Hand opening may be restricted with a spastic FDS resulting in strong flexion of the proximal IP joint, which may be alleviated by denervation or tendon lengthening of the FDS. D to E, There were few instances where a discrepancy of digit extension was observed. D, Extension lag is shown in D2, which may benefit from a side-to-side tenodesis with D3. E, A progressive lag is seen from D2–5 from a severely spastic flexor digiti minimi brevis. FDS, flexor digitorum superficialis; IP, interphalangeal.