Restoration of active key pinch: Brachioradialis and pronator teres to flexor pollicis longus transfer

Indications

• Restoration of a strong, stable pinch between the pad of the thumb and the radiolateral aspect of the index finger is critical for spinal cord injury (SCI) patients. This facilitates manipulation of small objects, including pens and utensils for writing and feeding, respectively.

• Active key pinch can be restored in International Tetraplegia Classification (ITC) group 2 and higher patients who have intact wrist extension and expendable brachioradialis (BR) or pronator teres (PT) available for transfer to the flexor pollicis longus (FPL).

• FPL activation with tendon transfer may result in exuberant IP flexion (Froment sign) and unpredictable position of the thumb pulp with lateral portion of the index finger. In this situation, a split FPL to extensor pollicis longus (EPL) may be performed to minimize excessive thumb interphalangeal (IP) flexion. In addition to the BR to FPL transfer, thumb carpometacarpal (CMC) arthrodesis or metacarpophalangeal (MCP) capsulodesis may also be performed if laxity is noted at the respective joints.

Clinical examination

• An organized examination of the entire upper extremity is performed, with focus on the BR and PT as donor muscles. Muscles must be at least Medical Research Council (MRC) grade 4 for transfer because often one grade of muscle strength is lost in transfer. See Chapter 69 for details.

• Assess the patient’s ability to perform lateral pinch with wrist in flexion, neutral, and extension to assess motion with tenodesis. The thumb must lie in a position so that it can oppose to the radial surface of the index finger to establish key pinch. If it does not, other procedures may be necessary to place the thumb or index finger in a more favorable position.

• Assess the patient’s two-point discrimination (2PD) at the thumb and index fingertips; 2PD must be less than 10 mm to avoid a “visual pinch.”

Imaging

If a joint is immobile, obtain plain radiographs to evaluate for arthrosis.

Surgical anatomy

• The BR originates from the lateral supracondylar ridge of the humerus and inserts onto the radial styloid. It is innervated on its deep surface directly by the radial nerve above the elbow.

• The PT originates from the medial epicondyle and coronoid process of the ulna and inserts on the volar radial aspect of the midradial shaft.

• The FPL is found deep in the volar forearm compartment and originates from the radius; it inserts on the base of the distal phalanx of the thumb.

• The radial artery is interposed between the BR and flexor carpi radialis (FCR).

• The superficial radial nerve lies deep to the BR muscle proximally; at 7 cm proximal to the wrist crease, it pierces the fascia to lie in a more superficial plane.

Positioning

The patient is placed supine with the arm supinated and extended on a hand table.