Combined Nerve and Tendon Transfer for the Restoration of Hand Function in Individuals With Tetraplegia

Tetraplegia after a cervical spinal cord injury (C-SCI) radically alters an individual's ability to perform normal activities of daily life due to paralysis in all extremities, resulting in lifelong dependence.\[1\] Traditional tendon transfer surgery has proven successful in restoring grip functions which greatly improves autonomy, but with a restricted passive opening of the hand. The number of transferrable muscles in the arm is however limited, why nerve transfer surgery is a new attractive option to further improve hand function by enabling active opening of the hand. Significant advantages of distal nerve transfers include less extensive surgical dissection, greatly reduced hospital stay, rehabilitation and restrictions, and thereby less health care use and costs. In an effort to further improve hand function and independence in patients with tetraplegia, hand surgeons at Centre for Advanced Reconstruction of Extremities (C.A.R.E.), Sahlgrenska University Hospital (SUH)/Mölndal have developed a strategy in which a nerve transfer procedure aiming to restore active opening of the hand is done prior to reconstruction of grip functions. To date, no study has compared the efficacy of this combined nerve and tendon transfer (CNaTT) procedure to traditional grip reconstruction by means of tendon transfer alone, thus constituting a major gap in the literature. The purpose of this study is therefore to fill that knowledge gap by comparing the clinical outcomes of a cohort of patients who undergo the CNaTT procedure to restore hand function, to those treated by means of tendon transfer alone.

Despite its incurability, surgical reconstruction of arm and hand function is a powerful tool to restore upper limb functions, as well as independence and control in individuals with tetraplegia. Patients with tetraplegia rank better use of the upper limb as their top functional priority, and surgical rehabilitation of the upper limb is proven highly rewarding. Starting in the 70s, pioneering work by dr. Moberg, and continued work by professor Fridén at SUH has guided the development of reconstructive surgical procedures in tetraplegia. As one of the leading units in the field C.A.R.E., SUH/Mölndal is responsible to continue the refinement of surgical treatment strategies. The center works in a value-based patient-oriented environment, with high demands on quality.

The traditional approach to surgical reconstruction of hand function in SCI uses tendon transfer, in which a functionally intact muscle is detached, rerouted and re-attached to a nonworking muscle to replace its original function. By this procedure, finger- and thumb flexion can be successfully and predictably restored, enabling strong active grip functions, but with passive and limited hand opening. Successful nerve transfer surgery in brachial plexus injuries has inspired interest in nerve transfers for patients with C-SCIs. Nerve transfers are conceptually quite similar to tendon transfers but are rarely applied in tetraplegia. To maximize outcome, nerve transfers must be done no later than 1 year after injury. In this procedure, a healthy nerve serving one function is cut and reconnected to a nonfunctional nerve (below the injury level), serving a more important function. Within 6-12 months, the recipient muscle has begun to receive nerve impulses. The preliminary results are very promising and show re-innervation of paralyzed muscles, enabling active opening of the hand. It is an attractive surgical procedure since it allows direct reanimation of the muscle, which is anatomically and mechanically designed to perform that function.

Further advantages of nerve transfers include less extensive surgical dissection, minimal hospital stay, rehabilitation and restrictions, and thereby less health care use and costs. Although the utility of nerve transfers in tetraplegia has yet to be fully determined, early results show promise.

The application of nerve transfer surgery to incomplete tetraplegia offers novel and exciting reconstructive possibilities when combined with tendon transfer techniques, especially in groups with very limited resources. Due to nerve regeneration factors, nerve transfers are not as reliable as tendon transfers, why restoring finger flexion in terms of strength is preferably performed with tendon transfers. It has been suggested that research should be directed at evaluating combined tendon and specific nerve transfer techniques, such as the Bertelli S-PIN (supinator to posterior interosseous nerve transfer) procedure. The S-PIN nerve transfer procedure can reanimate not only the finger extensors, but also allows independent thumb extension and abduction, and thereby enables active opening of the hand. Opening of the hand does not require much strength, and partial outcomes may work satisfactory. The S-PIN procedure combined with the tendon transfer technique has the unique potential to restore hand function to a level as near normal as possible in patients with tetraplegia. This strategy referred to as Combined Nerve and Tendon Transfer (CNaTT) procedure thus allows both opening and strong active closing of the hand, and most likely also result in fewer compensatory movements, which reduces the risk for shoulder pain that interfere with daily activities. At C.A.R.E. there is empirical evidence that support the potential of the combined procedure, such as patients' satisfaction and reporting of being able to better engage in activities in daily life that requires active opening of the hand.

The study has an observational controlled design to which the investigators plan to include 40 cases of CNaTT. As control, patients who undergo tendon transfer alone will be included (due to lack of the prerequisite for nerve transfer; \>12 months since injury), in parallel with the cohort of patients who have undergone the traditional procedure in the past (20 prospective cases and 100 historical cases). The results at one year after the tendon transfer procedure will constitute the main outcome.

SURGICAL PROCEDURES

Nerve transfer to achieve opening of the hand by means of Bertelli S-PIN

In this procedure performed bilaterally, the supinator motor nerve gets transferred to the posterior interosseous nerve (S-PIN) according to the technique described by Bertelli. Preoperatively, both donor and recipients nerves and muscles are assessed with electromyography to make sure they are stimulatable on both sides. After a short immobilization period of 2 weeks in a hinged orthosis restricting full extension of the elbow, patients are free to move and train without restrictions. When the first evidence of re-innervation is noticed, patients are instructed to enhancing strength in extensor muscles. Initially, patients activate the donor nerve movement (supination) while the forearm is locked in pronation to facilitate thumb- and finger extension.

The traditional approach to surgical reconstruction of grip by means of tendon transfer

The so-called grip reconstruction is a combination of surgical procedures, customized according to the patient´s needs that can be done many years after a C-SCI. The procedure is developed at SUH by professor Fridén, and has been entitled the alphabet or ABCDEFG procedure, an abbreviation for Advanced Balanced Combined Digital Extensor Flexor Grip reconstruction. The procedure is a one-stage grip and release procedure, a result from several previous studies to improve strength of tendon attachments, early active mobilization etc. The active tendon transfers will typically include brachioradialis to flexor pollicis longus (BR-FPL) transfer and extensor carpi radialis longus to flexor digitorium profundus (ECRL-FDP) transfer. The balancing procedures differ depending on the muscle strength (MRC) after the nerve transfer procedure. A typical OCu 4 patient with some finger extension will undergo: split flexor pollicis longus (FPL)- extensor pollicis longus (EPL) tenodesis, passive reconstruction of the interossei, carpometacarpal (CMC) joint capsulodesis, EPL tenodesis and extensor digiti minimi (EDM)- abductor pollicis brevis (APB) transfer/tenodesis. Our specific and active rehabilitation protocol start within 24 hours after surgery and has previously been described in detail.

Eligibility Criteria:
Inclusion criteria:

* Subjects must be between 15-55 years of age
* Subjects must be diagnosed with a spinal cord injury AIS level C5 to C7
* Time after injury ≤ 12 months
* The strength of the muscle supplied by the donor nerve (supinator) must be graded ≥ 4 according to Medical Research Council (MRC)
* The strength of musculus brachioradialis and wrist extensors must be graded ≥ 4 according to MRC (to be used in grip reconstruction)

Exclusion criteria:

* Finger extensor strength ≤ MRC 1
* Evidence of lower motor neuron injury in muscles supplied by the donor nerve
* Subjects must not have any current serious or unstable illness that could interfere with the study
* Medically unstable to undergo surgery as determined by physician
* Spasticity in the forearm or hand graded \> 1 according to Modified Ashworth Scale