"A tendon transfer procedure relocates the insertion of a functioning muscle-tendon unit in order to restore lost movement and function at another site.”
The science of tendon transfer is well developed – relocating a functioning muscle’s tendon to a paralysed muscle. This is most commonly done in cases where the peripheral nerve supply has been permanently damaged in injury. When the transferred muscle contracts, it pulls on the tendon it has been transferred to, creating a different movement than it used to.
Through years of development the muscles used in tendon transfer surgeries and their transfer targets are well established. In the case of a current patient with a proximal radial nerve laceration following humerus fracture – pronator teres was used to re-activate wrist extension with the aim of strengthening their tenodesis grip.
Tenodesis grip utilizes the natural biomechanical phenomenon where wrist active extension creates passive tension of the flexor muscles, creating a grip pattern between the thumb and fingers. In conjunction, the patient’s Palmaris Longus was transferred to EPL and nerve transfers nFCR to Posterior Interosseous Nerve (which supplies the thumb, wrist and finger extensor muscles & supinator) & nFDS to ECRB with the aim of regaining finger and thumb extension to allow a release of pinch and grip and to further strengthen wrist extension & grip.
For the surgeon some of the art of tendon transfer lies in achieving a tendon tension that is “just right”- balancing graft length for functional ROM and for developing the tension needed so muscle contraction will extend the wrist well. For the Hand Therapist the art is in helping the patient re-learn how to use the transferred muscle in this new way – how do you “tell” a muscle which was a forearm pronator, to now activate to extend the wrist? This requires close work between the patient and therapist to facilitate and strengthen this new message pathway. Once you see a flicker of the correct action, careful practice is needed so the patient understands how to activate the transfer, then promote and develop good patterns of movement before working to strengthen the muscle and use it to improve functional grip. All this while preventing complications such as tendon transfer site adhesions or graft tearing or stretch-out (stretch-out renders the transfer less effective as a graft that is too long cannot develop the power to extend the wrist sufficiently for effective grip).
Its slow work and takes great patience and perseverance from the patient but is hugely rewarding for them, the therapist and the surgical team when function is regained. Thank you to our patient for letting us discuss the case and use the photos.
Main principles of rehabilitation after tendon grafting: