26: Reconstruction of Key Pinch in Tetraplegia Patients

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Procedure 26 Reconstruction of Key Pinch in Tetraplegia Patients

Pao-Yuan Lin, Sandeep J. Sebastin, Kevin C. Chung

imageSee Video 21: Tendon Transfer for Lateral Pinch in Tetraplegic Patients (BR to FPL, FPL to EPL, ECRL to FDP)

Indications

image Procedure is used in patients with cervical spine injury with partial upper limb paralysis (spinal cord injury at or below C5 cervical segment) with at least grade 4 strength of the brachioradialis (BR).

image General considerations

• More than 12 months have passed after the injury with stabilized motor recovery.
• Patient is medically stable and motivated.
• Patients with poor sensation of the hand may not be candidates for tendon reconstruction because the lack of sensory feedback may present difficulties in use of the reconstructed hand.

image Specific considerations for key pinch

• Patients with intact wrist extensors (extensor carpi radialis longus [ECRL]) (group 2) are the best candidates for key pinch reconstruction because the BR can be transferred to the flexor pollicis longus (FPL) to get an active key pinch.
• Only a passive key pinch can be achieved in group 1 patients because they lack wrist extension, and the priority is to get wrist extension. The BR is transferred to the extensor carpi radialis brevis (ECRB) to restore wrist extension, and a passive key pinch is obtained by tenodesis of the FPL, extensor pollicis longus (EPL), and abductor pollicis longus (APL) to the distal radius.

Examination/Imaging

Clinical Examination

image Tetraplegia patients are classified based on the number of functional muscles with grade 4/5 Medical Research Council (MRC) strength below the elbow (Table 26-1). Based on what the patient has, the patient’s needs are matched by using a combination of tendon transfers, tenodesis, and arthrodesis to optimize surgical reconstruction.

image The purpose of the key pinch reconstruction is to allow the patient to produce a tenodesis effect to firmly pinch an object between the tip of the thumb and the radial border of the index finger. The differential excursion between the extrinsic flexor and extensor tendon system results in the tenodesis effect. When the wrist is extended, the flexor tendon becomes tight, resulting in finger flexion. With the wrist flexed, the fingers extend secondary to tightening of the extrinsic extensor tendons. Patients with tetraplegia use the tenodesis effect to help develop patterns of pinch function to assist in activities of daily living.

image It is important to assess the strength of the BR. Muscles chosen for transfer should be at least MRC grade 4 because they lose one grade after transfer. This is done by holding the patient’s elbow in midprone position and asking the patient to flex the elbow against resistance (Fig. 26-1). This will contract the BR. The examiner tries to move the contracted BR. If the BR cannot be moved easily with BR contraction, it is suitable for transfer. On the other hand, if the BR is flaccid and can move easily during contraction, the muscle may not be strong enough for transfer.

image The index finger should also be assessed. If the index finger is flaccid, it may not provide a strong post for the thumb. The flexor digitorum superficialis (FDS) of the index finger can be sutured to the A1 pulley or the volar plate in a lasso procedure so that the index finger can be flexed to act as a post for the reconstructed thumb.

image The procedures required to achieve key pinch in group 1 and group 2 tetraplegia patients are as follows:

• Group 1 (only BR)
♦ Split FPL-to-EPL transfer (to stabilize thumb interphalangeal [IP] joint)
♦ FPL tenodesis to volar radius (to provide passive key pinch during wrist extension)
♦ EPL and APL tenodesis to dorsal radius and lateral radius, respectively (to allow thumb to abduct and extend during wrist flexion for the release phase of key pinch)
♦ BR to ECRB (to provide active wrist extension and passive key pinch by tenodesis)
♦ FDS lasso procedure (if index finger metacarpophalangeal [MCP] joint flexion is deemed inadequate for key pinch)
• Group 2 (BR and ECRL)
♦ Split FPL-to-EPL transfer (to stabilize thumb IP joint)
♦ BR to FPL (to provide active thumb pinch)
♦ EPL and APL tenodesis to dorsal radius and lateral radius, respectively (to allow thumb to abduct and extend during wrist flexion for the release phase of key pinch)
♦ FDS lasso procedure (if index finger flexion is deemed inadequate for key pinch)

Table 26-1 International Classification for Surgery of the Hand in Tetraplegia

Motor Group Functioning Muscles (Grade 4 or Greater)
0 No available muscles
1 BR
2 BR and ECRL
3 BR, ECRL, and ECRB
4 BR, ECRL, ECRB, and PT
5 BR, ECRL, ECRB, PT, and FCR
6 BR, ECRL, ECRB, PT, FCR, and finger extensors
7 BR, ECRL, ECRB, PT, FCR, finger and thumb extensors
8 Lacks only intrinsics

BR, brachioradialis; ECRL, extensor carpi radialis longus; ECRB, extensor carpi radialis brevis; FCR, flexor carpi radialis; PT, pronator teres.

image

FIGURE 26-1

Surgical Anatomy

image Figure 26-2 presents the segmental innervation (C5 to T1) of muscles of the elbow, forearm, and hand, and Figure 26-3 shows the relevant anatomy of the procedure.

image

FIGURE 26-2

image

FIGURE 26-3

Positioning

image The procedure is performed under general or regional anesthesia and tourniquet control. The patient is positioned supine with the affected extremity on a hand table.

Exposures

image A 3-cm longitudinal incision is centered over the IP joint on the radial side of the thumb (Fig. 26-4). This incision is used for the split FPL-to-EPL transfer. The A2 pulley is identified and released to expose the FPL tendon. The FPL tendon must be dissected quite proximally to obtain a sufficiently long tendon that can reach the EPL over the dorsum of the thumb IP joint.

image A 6-cm longitudinal incision is made on the dorsoradial aspect of the wrist extending proximally from the radial styloid. This incision is used to expose the APL tendon and the BR insertion.

image A 6-cm longitudinal incision is made on the dorsum of distal forearm extending 2 cm beyond the Lister tubercle and 4 cm proximal to it. This incision is used to expose the ECRB and EPL tendons.

image A 6-cm longitudinal incision is made on the volar aspect of the distal forearm over the flexor carpi radialis (FCR) tendon. This incision is used to expose the FPL tendon.

image A 3-cm longitudinal chevron-shaped incision is made over the palmar aspect of the index finger MCP joint. This incision will be required only if a lasso procedure of the index finger FDS is planned.

image

FIGURE 26-4

Pitfalls

Care should be taken to avoid injury to the radial digital nerve of the thumb, superficial sensory branches of the radial nerve, and palmar cutaneous branch of the median nerve during these exposures.

Procedure

Step 1: Split FPL-to-EPL Transfer

image One half of the FPL tendon is transected distally, and this half is then sutured to the EPL tendon to achieve extension of the IP joint to neutral position. The tendons are sutured using 3-0 horizontal mattress sutures (Fig. 26-5).

image

FIGURE 26-5

Step 1 Pearls

The FPL-to-EPL tenodesis procedure is performed first. This is particularly important because the reconstructed FPL tendon for the key pinch procedure will result in maximum flexion at the MCP joint level and not at the IP level. Extensive flexion of the thumb IP joint will cause a mallet deformity that is not the optimal posture to pinch between the thumb and the index finger (Fig. 26-6).

image

FIGURE 26-6

Step 2: APL Tenodesis

image The APL tendon is identified in the first dorsal compartment and divided proximal to the first dorsal compartment.

image The distally based APL tendon is brought out of the first dorsal compartment distally and secured to the radius using a Mitek Mini bone anchor. It should be secured to the dorsal surface of the radius so that the direction of pull during wrist flexion will result in maximal thumb abduction (Fig. 26-7).

image

FIGURE 26-7

Step 3: EPL Tenodesis

image The EPL tendon is then isolated from the dorsal incision and divided proximal to the extensor retinaculum. It can be secured to either the radius or the extensor retinaculum (Fig. 26-8).

image

FIGURE 26-8

Step 3 Pearls

When the tendons are secured to the bone, the result is more predictable, and loosening should not be a problem. Loosening with attachment to the extensor retinaculum may be an issue. The tendon inset in Figure 26-8C shows a method of EPL tenodesis to the extensor retinaculum by making a loop around Lister tubercle. By this method, one can also suture the EPL to Lister tubercle to strengthen the attachment.

Step 4: Tenodesis of FPL

image This is done in patients who do not have a strong wrist extensor, and the BR is used for wrist extension rather than transferred to the FPL. The FPL is identified below the FCR in the same plane as the flexor digitorum profundus, but radial to it.

image The FPL is divided 1 cm proximal to the proximal edge of the pronator quadratus (PQ) and anchored to the volar surface of the distal radius proximal to the PQ using a Mitek Mini bone anchor (Fig. 26-9).

image

FIGURE 26-9

Step 4 Pearls

A tenodesis of the extensor pollicis brevis (EPB) to the dorsum of the thumb metacarpal has been described to avoid excessive flexion at the MCP joint.

Step 5: BR-to-ECRB Transfer

image The BR tendon is dissected off its insertion and mobilized proximally.

image A short subcutaneous tunnel is made so that the BR tendon can reach the ECRB.

image The ECRB is identified ulnar to the ECRL, and an end-to-side Pulvertaft weave repair is performed between the BR and ECRB using 2-0 Ethibond (Fig. 26-10). The end-to-side repair is more secure, and the direction of pull will still be straight.

image The tension is set such that the repair is able to hold the wrist in neutral position with the elbow in 45 degrees of flexion. With the elbow flexed, the wrist should passively flex, and with the elbow extended, the transfer should tighten.

image

FIGURE 26-10

Step 5 Pearls

Care must be taken to protect the superficial radial nerve as it passes below the BR and becomes superficial by passing between the BR and ECRL about 5 to 9 cm proximal to the radial styloid.

The BR is invested in fascia along its course in the forearm and must be mobilized from the distal radius and forearm fascia to provide adequate excursion.

Step 6: BR-to-FPL Transfer

image This is done in patients who have strong wrist extension. Here the BR is used to provide active pinch by transferring it to the FPL.

image The FPL and BR are divided as described previously. A short subcutaneous tunnel allows the BR to reach the FPL.

image A repair of the FPL and BR is done using a Pulvertaft weave with 2-0 Ethibond sutures (Fig. 26-11).

image Tension is set so that with wrist flexion, the patient’s thumb will abduct and extend in this release phase of the operation (Fig. 26-12A). With the wrist extended, sufficient tension on the FPL tendon must achieve a strong enough flexion of the thumb metacarpophalangeal joint so that the pulp of the thumb will press firmly against the radial side of the middle phalanx of the index finger (Fig. 26-12B).

image

FIGURE 26-11

image

FIGURE 26-12

Step 6 Pearls

The BR is passed deep (dorsal) to the radial artery.

Step 7: Index Finger MCP Joint Flexion Using an FDS Lasso

image If the index finger MCP joint is flaccid and not sufficiently flexed to meet the thumb, the Zancolli lasso procedure will flex and stabilize the index MCP joint so that the thumb pulp will meet the radial border of middle phalanx of the index finger during key pinch.

image The A1 and A2 pulleys are defined clearly, and a space is developed between them by dissection.

image Both slips of the FDS are divided distal to the A1 pulley (Fig. 26-13A and B).

image The distal ends of the tendon slips are folded over the A1 pulley and sutured to the proximal tendon and the A1 pulley using horizontal 2-0 Ethibond mattress sutures (Fig. 26-13C and D).

image Tension is adjusted to maintain the index finger MCP joint in 50 to 60 degrees of flexion.

image

FIGURE 26-13

Step 7 Pearls

Check the tenodesis effect to ensure that with flexion of the wrist, the thumb abducts and extends in the release phase of the operation, and with the wrist extended, the pulp of the thumb pinches strongly against the radial border of the index finger.

Postoperative Care and Expected Outcomes

image A long-arm cast that immobilizes the elbow in midprone position and 90 degrees of flexion, the wrist in extension, and the thumb in abduction is given to patients who undergo a BR-to-ECRB transfer (group 1).

image A long-arm cast that immobilizes the elbow in midprone position and 90 degrees of flexion, the wrist in 10 to 20 degrees of flexion, and the thumb in abduction is given to patients who undergo a BR-to-FPL transfer (group 2).

image Patients wear a splint for 4 weeks to allow healing of the tendon junctures. This is followed by mobilization, when the patient learns to adapt to the tenodesis effect and achieve sufficiently strong key pinch to perform activities of daily living.

image In selected patients with sufficient muscle function and sensibility, effective lateral pinch can be predictably restored by use of appropriate tendon transfer and tenodesis to provide flexion and extension of the digits and maintain intrinsic balance.

image If a postoperative key pinch strength can reach 2 kg, the patient is able to perform a large range of activities of daily living, such as pushing a button on a remote control, manipulating a key in and out of an entrance lock, opening and closing a vertical or horizontal zipper, inserting a standard card into an automated teller machine and retrieving it, and even manipulating a three-prong plug out of a wall socket. The mean postoperative strength was 1 kg higher for procedures using an active motor than for procedures applying a tenodesis.

Evidence

Hamou C, Shah NR, Curtin CM, et al. Pinch and elbow extension restoration in people with tetraplegia: a systematic review of the literature. J Hand Surg [Am]. 2011;34:692-699.

A systematic review between 1966 and 2007 about pinch and elbow extension was addressed. Results from 377 pinch reconstructions in 23 studies were summarized. The overall mean postoperative strength measured after surgery for pinch reconstruction was 2 kg. The most common complications were flexion contracture of the elbow or of the thumb (25% of the complications), stretching or rupture of repair (22% of the complications), and loosening of pins across the thumb interphalangeal joint (21% of the complications). (Level III evidence)

Paul SD, Gellman H, Waters R, et al. Single-stage reconstruction of key pinch and extension of the elbow in tetraplegic patients. J Bone Joint Surg [Am]. 1994;76:1451-1456.

A retrospective review of BR-to-FPL transfer to restore key pinch and deltoid-to-triceps transfer to restore elbow extension in nine patients was conducted. The average time from the injury to the operation was 5 years, and the average duration of follow-up was 31 months. Key pinch improved from essentially none preoperatively to an average of 0.9 kg postoperatively: an average of 1.4 kg for the patients who had tetraplegia at the C6 level and an average of 0.4 kg for those who had tetraplegia at the C5 level. (Level IV evidence)

Vastamäki M. Short-term versus long-term comparative results after reconstructive upper-limb surgery in tetraplegic patients. J Hand Surg [Am]. 2006;31:1490-1494.

A retrospective review of short-term and long-term comparative studies was conducted. The surgical procedures of key pinch reconstruction included FPL tenodesis to radius, release A1 pulley of the thumb, and fixation of the IP joint of the thumb with a K-wire. Twenty-nine key pinch procedures in 27 patients were evaluated at 4-year follow-up (short-term), and 10 key pinch procedures were evaluated at 21-year follow-up (long-term). In the 21 years between surgery and evaluation, the strength of key pinch had diminished by 21%, from a mean of 1.4 kg (range, 0.6 to 3.0 kg) to 1.1 kg (range, 0.3 to 3.0 kg), a 1% strength loss each year. (Level IV evidence)

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