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Principles of Tendon Transfers

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2 Principles of Tendon Transfers

3 What is a tendon transfer?
The tendon of a functioning muscle is detached from its insertion and reattached to another tendon or bone to replace the function of a paralysed muscle or injured tendon. The transferred tendon remains attached to its parent muscle with an intact neurovascular pedicle. Or “Using the power of a functioning muscle unit to activate a non functioning nerve/muscle/tendon unit”. Tendon transfers work to correct instability, imbalance, lack of co-ordination and restore function by redistributing remaining muscular forces

4 Indications Paralysed muscle
Nerve injury – peripheral or brachial plexus High cervical quadriplegia (needs some input to brachial plexus/hand) Neurological disease Nerve repair with early transfer as internal splint Injured (ruptured or avulsed) tendon or muscle Considerations Graft vs. transfer (adhesions more likely in graft – 2 anastomoses) Quality of available donors Length of time since injury Nature of tendon bed Balancing deformed hand e.g. cerebral palsy or rheumatoid arthritis Some congenital abnormalities

5 General principles 1. Only justified in restoring functional motion of the hand, not just motion Not all patients require the same functions/motions 2. Patient factors Age Functional disabilities with poor non operative prognosis Ability to understand nature and limitations of surgery, including aesthetic goals Motivated to co-operate with post operative physiotherapy 3. Recipient site “Tissue Equilibrium” concept as per Steindler/Boyes Tissue bed into which transfer is placed should be soft and supple Good soft tissue coverage Stable underlying skeleton Full passive range of motion of joints to be powered Area to be powered must be sensate

6 4. Donor muscle factors (APOSLE)
Amplitude of the donor muscle Should be matched to the unit being replaced Finger flexors  mm, finger extensors and EPL  mm, wrist flexors / extensors  mm, brachioradialis  mm Amplitude of motion of any tendon can be increased by :- Increasing the number of joints its crosses eg the amplitude of a tendon crossing the wrist joint is increased by 20 – 30mm by full ROM of wrist Tenodesis effect during active movement Freeing fascial attachments to donor tendons Inserting the tendon closer to the joint being moved, but this requires a motor unit of increased power (due to leverage); and vice versa Power of the donor muscle Any transferred muscle loses at least one grade of strength, so only Grade 5 muscles are satisfactory (Grade 4, or 85% normal strength, can be sufficient for some transfers). Donor muscle strength should be maximised pre-operatively. Strongest are brachioradialis and FCU. Donor power correlated roughly with cross sectional area of muscle and fibre length Overly powerful muscles will unbalance and, over time, deform a joint. So muscle power should be matched if possible. Effective power of a transfer can be increased by placing the tendon insertion farther from the joint axis and as close to 90° as possible Brachioradialis does not adapt well to transferred functions One tendon, One function Effectiveness reduced in transfer designed to produce multiple functions Synergistic muscle groups are generally easier to retrain Fist group – wrist extensors, finger flexors, digital adductors, thumb flexors, forearm pronators, intrinsics Open hand group – wrist flexors, finger extensors, digital abductors, forearm supinators Use of synergistic muscles tends to help retain joint balance Line of transfer Should approximate pull of original tendon if possible Acute angles should be avoided Expendability Transfer must not cause loss of an essential function

7 5. Other muscle factors of secondary importance
Innervation - Donor muscle should be independently innervated and not act in concert with other motors (eg lumbricals) Availability or necessity of antagonists eg brachioradialis is an effective wrist extensor only if triceps is functioning to resist its normal elbow flexor action 6. Tension of the transfer “All transfers should be sutured at the maximum tension in the position that reverses their proposed activity” (Lister’s 4th Edn) 7. Location and nature of pulley if required 8. Selected arthrodeses Simplify polyarticular system Stabilise joints Radiocarpal arthrodesis in combined nerve lesions Thumb CMC in adducted thumb unable to be stabilised by transfers eg cerebral palsy, quadriplegia, combined nerve injury Glenohumeral arthrodesis in upper truck brachial plexus palsy Arthrodeses useful in providing stable pinch grip Thumb MPJ and IPJ Index PIPJ and DIPJ

8 10. Comparison to alternatives
9. Timing “The timing of tendon transfers depends upon the aetiology and prognosis of motor imbalance, the neurophysiologic problems for the patient, and the constitution of the involved extremity” (Omer GE: Timing of tendon transfers to the hand. Hand Clin 4(2):317, 1988) Usually last stage in reconstruction, after skeletal stability, soft tissue coverage, sensation and joint mobility Early transfers are appropriate in problems that are expected to deteriorate with time eg opponensplasty to prevent predictable supination/adduction deformity in poor prognosis median nerve injury 10. Comparison to alternatives Nerve repair or transfer Tendon repair or graft Tenodesis (joint stabilisation by anchoring tendons that move the joint) Arthrodesis Amputation Muscle lengthening, release or denervation (in spasticity) 11. Contraindications Age – due to joint stiffness, decreased need for power movements and difficult rehabilitation Motivation – patients must be concerned about disability and highly motivated to perform hand rehabilitation Task analysis – transfers must be designed to accomplish tasks rather than just specific motions. Eg opening doors requires grasp and twist Nature of disability – systemic and local disease factors must be controlled before reconstruction attempted 12. Disadvantages No increase in strength Normal function of transferred muscle is lost Transferred tendon may perform a different force, amplitude of movement and functional pattern Transferred tendon must learn a new movement/function

9 Selecting donor tendons
Based on Smith & Hastings (Principles of tendon transfers to the hand. Instr Course Lect 29:129, 1980) 1. List functioning muscles 2. List which of those muscles are expendable 3. List hand functions requiring restoration 4. Match #2 and #3 5. Staging

10 Example of planning tendon transfers in complex upper extremity palsies
Working Available Needed BR Thumb flexion PT Finger extension Thumb extension ECRL Finger flexion ECRB ECU ECU and graft MP flexion / IP extension (intrinsics) FCU (fair) Thumb opposition FCR PQ PP Thumb adduction Stage 1: BR to FPL, ECRL to FDP, FCU to EPB for thumb opposition Stage 2: PT to EPL & EDC, thumb IP arthrodesis Stage 3: ECU + plantaris graft to lateral bands of index to little fingers (routed volar to deep transverse metacarpal ligament)

11 Maximising Success / Surgical Technique
Incisions should not cross the path of the transferred tendon Avoid interference with normal structures Tendon should insert into the joint of motion at 90 to maximise power and excursion. Insertion can be moved away from the joint to improve power, but this is at the expense of decreased excursion The transferred tendon should insert into another tendon or bone. Strong insertions allow earlier mobilisation. A single insertion is best. Dual insertions tend to provide motion to the tighter insertion. Can be an advantage in complex movements, where one insertion is tighter during one phase of motion, and the other takes over during another phase. Tension should be set to produce the necessary joint movement with maximal muscle contraction. Some initial over correction should be planned, as some tendon stretch is usual. Joint should be initially immobilised in a position that relieves tension at the insertion of the transfer Reverse order – harvest grafts, prepare recipient site and tunnel before raising muscle

12 General Post Operative Management
Rehabilitation is equally important in tendon transfer success as surgical execution Rehabilitation / physiotherapy is essential in Regaining joint mobility lost during splinting Training tendon to glide in new course Teaching patients to activate a new muscle to achieve a certain function, which requires development of new neural pathways The more that a patient notices a disability, the greater the motivation, so the easier the retraining Children are usually managed with static protocols or longer protective phase

13 Basic Principles of Post Operative Rehabilitation
Described by Toth 1986 1. Protective phase Begins at surgery and lasts 3 – 5 weeks Objectives:- Protective splinting Oedema control Mobilise uninvolved joints 2. Mobilisation phase Begins when tendon healing is adequate for activation (usually 3 – 5 weeks post op) Objectives Mobilise tendon transfer Immobilise soft tissue Continue immobilisation of uninvolved joints to prevent joint stiffness from disuse Reinforce preoperative teaching and patient education Continue oedema control and protective splinting Begin home rehabilitation program Usually day time dynamic splinting with nightly static splinting 3. Intermediate phase Begins 5 – 8 weeks post operatively Gradually increases hand activity and passive range of motion exercises Limited functional movements permitted 4. Resistive phase Beginning at 8 – 12 weeks Tendon junctions are strong enough to withstand increasing resistance Therapeutic objective is to increase endurance and strength of transferred muscles Work related simulated tasks are begun to patient tolerance

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