Principles of tendon transfer surgeries in rehabilitation

Tendon transfers, a fundamental aspect of reconstructive surgery, represent a sophisticated intervention in the domain of orthopedics and plastic surgery. This intricate procedure involves the repositioning or redirection of tendons to restore lost function, correct deformities, or alleviate debilitating conditions resulting from tendon injuries, neurological disorders, or musculoskeletal anomalies. By harnessing the body's inherent capacity for adaptation and regeneration, tendon transfers offer a transformative solution to patients grappling with impairments affecting mobility, dexterity, and overall quality of life.

Within the realm of medical science, tendon transfers stand as a testament to the innovative intersection of anatomy, biomechanics, and surgical expertise. Guided by meticulous anatomical knowledge and informed by patient-specific considerations, surgeons meticulously navigate the intricate network of tendinous structures to achieve optimal outcomes. This precise manipulation of tendons demands not only technical proficiency but also a profound understanding of functional anatomy, pathological processes, and the dynamic interplay between muscles and joints.

The rationale underlying tendon transfers rests upon the principle of functional restoration through strategic tendon re-routing. Whether addressing paralysis resulting from nerve injury or rectifying muscular imbalances precipitated by congenital anomalies, the overarching goal remains consistent: to enhance musculoskeletal function and foster meaningful improvements in patient well-being. By redistributing the forces exerted by muscles across joints, tendon transfers serve as a cornerstone in the rehabilitation arsenal, offering a pathway towards enhanced motor control, stability, and range of motion.

In this discourse, we embark on a comprehensive exploration of tendon transfers, delving into the intricacies of surgical technique, patient selection criteria, rehabilitative protocols, and outcomes assessment. Through a synthesis of clinical insights, scientific inquiry, and empirical evidence, we endeavor to illuminate the multifaceted dimensions of this therapeutic modality. By elucidating the underlying principles and practical applications of tendon transfers, we aspire to equip healthcare practitioners with the requisite knowledge and insights to navigate this dynamic landscape and empower patients with newfound avenues for functional restoration and renewed vitality.

1. Principles of tendon transferS Dr Joe Antony MBBS, MD(PMR), FCPC, CCEPC, ASTEP(AMERICAN SPINAL INJURY ASSOCIATION), INSTEP, WEESTEP

2. Contents Introduction Principles of tendon transfers Biomechanical considerations of Tendon transfer surgeries Pic- Greens operative hand surgery, 8 th edition 2

3. Introduction A tendon transfer is the re-routing of a functioning muscle-tendon unit (MTU) to a new insertion , in order to restore a function that has been lost. History Tendon transfers were first developed in the 19th century to restore ambulation in patients with poliomyelitis. During the subsequent World Wars, thousands of soldiers returned home with upper extremity nerve injuries. This influx of patients caused development of established tendon transfer procedures Grabb And Smith's Plastic Surgery 8th Edition 3

4. Indicated in loss of a function due to loss of muscle power that has no potential for recovery, which can be due to Grabb And Smith's Plastic Surgery 8th Edition 4 Peripheral nervous system Central nervous system Musculotendinous unit Nerve root avulsion Traumatic brain injury Loss of muscle or tendon due to trauma Failed nerve repair/reconstructions Stroke Tendon rupture ( in rheumatological conditions like RA) Delayed presentation of nerve injuries Cerebral palsy Hansen's disease Spinal cord injuries Other non progressive peripheral neuropathies and residual nerve palsies Other non progressive myelopathies and focal neurological deficits

5. Principles of tendon transfers Supple joints Soft tissue equilibrium Adequate excursion Appropriate strength of donor Expendable donor Straight line of pull Synergy Single Transfer, single function Established by Mayer and Bunnell Greens operative hand surgery, 8 th edition, Grabb And Smith's Plastic Surgery 8th Edition 5

6. Supple Joints A passive , fluid , adequate range of movement of joint to improve function should be present before tendon transfer A transferred tendon can not mobilize a stiff or deformed joint Stiff joints should be released before tendon transfers either operatively or non-operatively. Joint release and tendon transfers should not be done in same sitting Joint release warrants rehab protocol with immediate and aggressive mobilization Tendon transfer needs at least 4 weeks for healing Grabb And Smith's Plastic Surgery 8th Edition 6

7. Soft tissue equilibrium Means, Tissue induration and inflammation have resolved , Scars have matured and are as soft as they are likely to become Tendon should pass through plane between the subcutaneous tissue and deep fascia Gentle tunneling using a blunt-tipped instrument and probing natural tissue planes to find the path of least resistance. If scars are obstructing the pathway even after scar maturation, it should be resurfaced with a fasciocutaenous flap Surgeons should avoid creating scars on tunneling pathways by planning incisions away. Non-conventional pathways can be selected to avoid scars Grabb And Smith's Plastic Surgery 8th Edition 7

8. Adequate excursion/ Amplitude of motion D onor MTU should have enough excursion, or linear movement, to achieve the desired motion at the target joint. Excursion of the donor MTU should be equal to or greater than that of the MTU it is replacing For Example, Wrist flexors have an excursion 35mm Finger extensors have an excursion of 50mm Finger flexors have an excursion of 70mm Greens operative hand surgery, 8th edition 8

9. Appropriate strength of donor The strength of the donor MTU should be matched to that of the MTU whose function is being restored. Relative power should be considered rather than absolute power Greens operative hand surgery, 8th edition 9 Donor MTU is weaker Donor MTU is stronger Result Transferred tendon not able to move the joint through functional ROM Muscle imbalance and abnormal posture Particularly in Joint stiffness, Strong antagonist group present Weak antagonist group Example Palmaris longus in replacing wrist extensor Brachioradialis replacing EPL will end up in extention contracture

10. If the donor has been injured or denrevated , transfer must be delayed till complete recovery In general, a donor MTU will lose up to one grade of motor strength simply by being transferred This must also be kept in mind while selecting the donor Grabb And Smith's Plastic Surgery 8th Edition 10

11. Expendable Donor Donor MTU function should not be lost by trasfering it . There must be another MTU performing same function For example, Wrist has two flexors, Hence either FCU or FCR can be trasfered without losing wrist flexion Fingers has two flexors, FDS can be used as a donor MTU , while FDP will preserve the finger flexion Grabb And Smith's Plastic Surgery 8th Edition 11

12. Straight line of pull A tendon transfer that has a direct path to its insertion is most effective . increased force needs to be expended to overcome f riction with the surrounding soft tissues the transfer will try to migrate so that it does run in a straight line. However, there are instances in which a direct line of pull is not ideal. In that case , single robust pulley must be used Change of direction should be as small as possible For example, EIP Opponensplasty Greens operative hand surgery, 8th edition 12

13. Synergy Synergy refers to certain movements that are typically combined during routine use . For example- Wrist extension and finger flexion The original function of the donor MTU should be synergistic with the function that is being restored. A tendon transfer that is synergistic, as opposed to antagonistic, is easier for the patient to learn to use. So, patients find it easier to learn when finger extension is restored with wrist flexors Rehabilitation is much more difficult if finger extension restored with wrist extension . This principle doesn’t hold true always, Its not always possible to find a synergistic group. Certain donor MTUs, such as the FDS, are able to adapt to a new function readily, whether that function is synergistic or not Grabb And Smith's Plastic Surgery 8th Edition 13

14. Single transfer, Single function A single tendon transfer should only perform a single function . Attempting to restore multiple functions with a single donor MTU will result in loss of strength and motion . Exception, a single donor MTU may be used to restore the same movement in multiple digits . For example, it is acceptable to use the FDS or FCR to restore MCP extension for all four fingers. But, FDS or FCR would be inadequate to restore both wrist and finger extensions 14

15. https://media.cheggcdn.com/study/dd0/dd0e3d3b-76f9-4aee-bf67-aaf4c3fb38d1/2009691218116338014669186162509356.png 15 Biomechanical Considerations of tendon transfers Selecting the insertion point Tension in donor MTU

16. Selection of insertion point Generally, The insertion point of a tendon transfer is determined by the normal insertion of the recipient tendon. However. there are instances in which the surgeon can choose the insertion point of the tendon transfer. A tendon transfer with a large moment arm will generate greater torque, but at the expense of the arc of motion (greater muscle excursion will be required for a given degree of rotation) A smaller moment arm will have an increased arc of motion (less muscle excursion is required for a given degree of rotation), but the transfer will not generate as much torque. 16

17. Setting tension in donor MTU Setting the tension o£ the tendon trans£er is the most aitical and difficult part of the operation. Ideally, a tendon transfer should be tensioned in such a way as to maximize actin myosin overlap. Unfortunately, it is impossible to determine this intraoperatively. Solution is that the tendon transfer should be set at a tension as close as possible to the donor MlUs preoperative resting tension. The donor muscle belly is marked at regular intervals before dividing its insertion, and the tendon transfer is tensioned in such a way as to restore the distance between the intervals. 17

18. A tendon transfer tends to loosen or stretch out during rehabilitation . However, a tendon transfer that is set too loosely will not tighten postoperatively. 18