Intrinsic tendon reconstruction

Indications

• The goal of these procedures is to correct the absence of intrinsic function in the tetraplegic hand and to improve the functional result of extrinsic reconstruction.

• Intrinsic reconstruction can enhance grip in patients who have an extensor carpi radialis longus (ECRL) to flexor digitorum profundus (FDP) transfer.

  • Although the ECRL to FDP transfer restores finger flexion, it brings the fingertips to the base of the fingers rather than the palm, making it difficult for the patient to grasp large objects.

• Intrinsic reconstruction can enhance index finger metacarpophalangeal (MCP) joint flexion for effective pinching.

  • The index finger MCP flexion and additional support from the other MCP flexed fingers are necessary because the thumb must meet the radial aspect of the digit for effective key pinch.

• The following procedures are useful for tetraplegic patients in certain situations: intrinsic tenodesis using tendon graft and flexor digitorum superficialis (FDS) lasso procedure.

Clinical examination

• For patients with spinal cord injury, an organized examination is necessary to document the muscle strength of the patient’s upper limb joint flexion/extension and intrinsic hand function. The specific pattern of dysfunction depends on the level of injury.

• The available functional muscles are categorized using the ICSHT ( Table 69.2 ).

• The passive range of motion (ROM) of each joint, including the shoulder, elbow, wrist, and fingers, is assessed for joint and muscle contracture.

• The general appearance is examined because lack of intrinsic muscles can lead to MCP joint hyperextension and IP joint flexion deformities (clawing; Fig. 75.1 ), resulting in inadequate prehensile grasp and insufficient grip/pinch strength.

  

Imaging

Imaging is unnecessary unless a joint lacks passive ROM. In this case, radiographs are necessary to evaluate arthrosis at the MCP and IP joints.

Surgical anatomy

• The seven interosseous muscles ( Fig. 75.2 ) are innervated by the deep branch of the ulnar nerve.

  • Four dorsal interosseous muscles (bipennate muscles) originate between the metacarpals and abduct the fingers from the axial line. They act with the lumbricals to flex the MCP joints and extend the IP joints.

  • Three palmar interosseous muscles (unipennate muscles) are located on the palmar portion of the second, fourth, and fifth metacarpals. They adduct the fingers toward the axial line and act with the lumbricals to flex the MCP joints and extend the IP joints.

  • The lumbricals run between the metacarpals and originate from the FDP. The median nerve innervates the first and second lumbricals. The third and fourth lumbricals are innervated by the deep branch of the ulnar nerve. They flex the fingers at the MCP joints and extend the IP joints (see Fig. 75.2 ).

  • The interosseous tendons and lumbricals pass palmar to the axis of the MCP joint to form the common intrinsic tendon, which then divides into a medial band that inserts along with the central slip into the dorsal base of the middle phalanx and a lateral band that continues to the dorsal base of the distal phalanx. They couple MCP joint flexion with IP joint extension ( Fig. 75.3A–B ).