Phasic vs non phasic tendon transfers as an essay for ortho pg exam
Reading File
Finding Sources
Finding Sources
Finding Sources
Reading File
Finding Sources
Finding Sources
Reading File
Finding Sources
Finding Sources
Finding Sources
Reading File
Finding Sources
Reading File
Finding Sources
I now have sufficient material from the library to compose a comprehensive PG exam essay. Here is the full essay:
Phasic vs Non-Phasic Tendon Transfers
Introduction
Tendon transfer is a reconstructive procedure in which a functioning, expendable muscle-tendon unit is rerouted to restore the lost function of a paralysed or absent muscle. The concept of muscle phasing — the temporal pattern of activity of a muscle during the gait cycle or during a functional movement — is one of the most important determinants of the success or failure of any tendon transfer. Based on this criterion, tendon transfers are classified as phasic (synergistic, in-phase) or non-phasic (antagonistic, out-of-phase).
Definitions
Phasic (Synergistic) Transfer
A phasic transfer is one in which the donor muscle is normally active at the same time (same phase of the functional cycle) as the muscle whose function it is replacing. The donor and recipient muscles are therefore synergists with respect to timing. Because the central nervous system (CNS) already activates the donor in the same temporal window, cortical re-education is straightforward and functional outcomes are superior.
Examples:
- Pronator teres → ECRB (wrist extension in radial nerve palsy): both are active during grip
- Flexor carpi radialis → Extensor digitorum communis: wrist flexors co-contract with finger extensors during hand opening — a classic synergistic pairing
- Palmaris longus → Extensor pollicis longus (radial nerve palsy)
- Tibialis posterior → Tibialis anterior (poliomyelitis drop foot): both are active during swing phase as part of dorsiflexion demand
Non-Phasic (Antagonistic) Transfer
A non-phasic transfer is one in which the donor muscle fires at the opposite phase of the movement cycle compared to the recipient. The donor muscle must be retrained by the CNS to fire at a new, opposite time — a significantly more demanding process.
Examples:
- Tibialis anterior → Peroneus brevis (spastic varus foot in cerebral palsy): the anterior tibialis, normally a swing-phase muscle, is transferred to a stance-phase function
- Rectus femoris → Hamstrings (stiff-knee gait in spastic diplegia): rectus fires in stance/pre-swing but is transferred to a swing-phase flexor role
- Split-anterior tibial tendon transfer (SPLATT): one half transferred to the peroneus brevis for varus correction — represents a partially non-phasic arrangement
Principles of Tendon Transfer (General Framework)
Before addressing phasing in detail, the standard prerequisites for any tendon transfer must be met:
- Full passive range of motion at all joints the transfer will act upon (no fixed contracture)
- Expendable donor: at least one other muscle must remain to perform the original function — if two muscles share a task, one may be sacrificed
- MRC grade 4–5 power in the donor; approximately one grade of power is lost following transfer (— Miller's Review of Orthopaedics, 9th ed.)
- Adequate amplitude and excursion: excursion ≈ one-third of resting fiber length; wrist extensors have ~3.3 cm excursion, finger flexors ~7 cm
- Straight line of pull: redirecting through pulleys or subcutaneous tunnels increases friction loss
- Appropriate tensioning: the transfer should be set at appropriate resting tension at surgery; too lax = weak transfer; too tight = restricts antagonist movement
- Stable soft tissue envelope: the transfer must glide through pliable, well-vascularised tissue
- Single transfer = single function: one transfer should not be expected to simultaneously perform two separate functions
Importance of Phasing in Tendon Transfer
Muscle phasing is assessed by dynamic electromyography (EMG) during gait or functional activity. This is particularly important in:
- Cerebral palsy (spastic muscles may fire out of phase)
- Poliomyelitis (flaccid paralysis with selective muscle loss)
- Charcot-Marie-Tooth disease (selective intrinsic weakness)
- Spinal dysraphism / myelomeningocele (predictable level-based patterns)
Phasic Transfers in Detail
Why Phasic Transfers Work Better
The motor cortex has already established the neural programme for the donor muscle. After transfer, the patient simply learns to redirect force through the new anatomical pathway. The timing of voluntary activation remains essentially unchanged. This results in:
- Faster and more complete motor re-education
- Higher final functional grade
- Greater patient satisfaction and earlier independence
Clinical Examples
| Paralysis | Transfer | Rationale (Phasic) |
|---|---|---|
| Radial nerve palsy | Pronator teres → ECRB | Both active during grip/power activities |
| Radial nerve palsy | FCR → EDC | Wrist flexors synergise with finger extensors |
| Radial nerve palsy | PL → EPL | PL fires with wrist extension, same phase |
| Low median palsy | FDS ring → APB (Bunnell's opponensplasty) | FDS is a flexor phase muscle; APB assists grip |
| Ulnar nerve palsy (claw) | ECRB → lateral bands (Brand) | Extension transferred to intrinsic function |
| Drop foot (polio) | Tibialis posterior → dorsum of foot | Tibialis posterior converted from stance to swing phase — requires active re-education but ultimately a favoured transfer |
Note on the Tibialis Posterior Transfer: Tibialis posterior normally fires in stance phase (a non-swing function), while the dorsiflexors fire in swing phase. This is technically a non-phasic transfer — yet it is one of the most commonly performed and successful transfers for drop foot (Watkins procedure; through interosseous membrane). Its success is attributed to:
- The powerful excursion of tibialis posterior
- Gravity assistance in swing
- Excellent cortical plasticity allowing re-education within 3–6 months of intensive physiotherapy
This illustrates that phasic classification, while important, is not the sole determinant of success.
Non-Phasic Transfers in Detail
Challenges
When the donor fires at the wrong phase, the patient must achieve voluntary suppression of the original reflex arc and establishment of a new cortical programme. This requires:
- Prolonged, intensive physiotherapy
- Higher patient compliance and intelligence
- Longer time to functional use (6–12 months vs 3–6 months for phasic transfers)
- Risk of "cocontracting" — donor fires at both old and new phase, reducing net effectiveness
Clinical Examples
| Condition | Transfer | Issue |
|---|---|---|
| Spastic diplegia (cerebral palsy) | Distal rectus femoris → hamstrings | Rectus fires in stance/early swing — must be retrained to fire in swing phase only |
| Spastic equinovarus (CP) | Split tibialis anterior → peroneus brevis | Half of tibialis anterior (stance active) redirected to eversion function |
| Spastic varus (CP) | Tibialis posterior → peroneus brevis | Tibialis posterior, hyperactive in swing phase (out-of-phase), transferred to lateral stabiliser role |
| Polio drop foot | Tibialis posterior → dorsum | As discussed, technically non-phasic but successfully reprogrammed |
Dynamic EMG-Guided Decision Making
In cerebral palsy, the decision between split transfer and complete transfer depends on dynamic EMG:
- Continuous activity or out-of-phase firing of tibialis anterior → SPLATT (split-anterior tibial tendon transfer) is preferred
- In-phase overactivity → lengthening rather than transfer is appropriate
- Miller's Review notes: "Lengthening of continuously active muscles and transfer of muscles out of phase are often helpful" in cerebral palsy management (— Miller's Review of Orthopaedics, 9th ed., block5/block2)
Comparison Table
| Feature | Phasic Transfer | Non-Phasic Transfer |
|---|---|---|
| Definition | Donor fires in same phase as recipient | Donor fires in opposite phase |
| Synonyms | Synergistic, in-phase | Antagonistic, out-of-phase |
| Re-education | Rapid, straightforward (3–6 months) | Prolonged, intensive (6–12+ months) |
| Functional outcome | Superior — higher grade, faster | Good to excellent if well selected |
| Examples | PT→ECRB; FCR→EDC; PL→EPL | Rectus→hamstrings; SPLATT; TP→dorsum |
| EMG requirement | Less critical | Mandatory for correct selection |
| Neural reprogramming | Minimal | Significant cortical adaptation required |
| Failure mode | Technical (tension, line of pull) | Neural (failure to reprogram phase) |
| Preferred context | Peripheral nerve palsies | Cerebral palsy, spastic conditions |
Motor Re-Education After Transfer
Regardless of phasing, motor re-education follows a predictable sequence:
- Stage 1 — Sensory imagery (pre-operative): patient practises activating the donor in isolation
- Stage 2 — Facilitation: post-operatively, patient activates the donor in its original role to feel the new tendon move
- Stage 3 — Transfer of control: patient gradually learns to fire the donor through the new arc of motion
- Stage 4 — Automatic integration: movement becomes subconscious and fluid
For phasic transfers, stages 2–4 are compressed and rapid. For non-phasic transfers, intensive occupational therapy and biofeedback may be required at every stage.
Special Contexts
Poliomyelitis
Polio involves flaccid paralysis of selected muscles. The muscles are chosen on the basis of:
- Which muscles are spared (MRC grading)
- Whether they are in-phase or out-of-phase with the lost function
- The classic Watkins tibialis posterior transfer for drop foot — despite being technically non-phasic — remains successful due to the brain's preserved plasticity in a non-spastic context
Cerebral Palsy
Spasticity and out-of-phase firing are hallmarks. Dynamic EMG is mandatory. Transfers are performed for muscles with out-of-phase activity (transferred) vs continuously overactive muscles (lengthened, not transferred). Poor candidates: muscles with co-contraction (active in both phases), poor voluntary control, or severe spasticity.
High vs Low Nerve Lesions
- High lesions (e.g., high radial nerve palsy): multiple muscles paralysed; fewer donors available; phasic matching becomes more difficult
- Low lesions (e.g., low median nerve palsy): isolated thenar paralysis; FDS ring → APB is the prototypic phasic opponensplasty
Common Transfers and Their Phasing Classification
Hand and Upper Limb
| Transfer | Indication | Phase Classification |
|---|---|---|
| Pronator teres → ECRB | High radial nerve palsy | Phasic |
| FCR → EDC | High radial nerve palsy | Phasic |
| PL → EPL | High radial nerve palsy | Phasic |
| FCU → EDC (Jones transfer) | High radial nerve palsy | Phasic |
| FDS ring → APB (Bunnell's) | Low median nerve palsy | Phasic |
| EIP → APB (Burkhalter's) | Low median nerve palsy | Phasic |
| ADM → APB (Huber) | Median nerve palsy | Phasic |
| ECRB → lateral bands (Brand) | Ulnar claw hand | Phasic |
| FDS → lateral bands (Stiles-Bunnell) | Intrinsic minus hand | Phasic |
Lower Limb
| Transfer | Indication | Phase Classification |
|---|---|---|
| Tibialis posterior → dorsum (Watkins) | Polio drop foot | Non-phasic (but reprogrammable) |
| SPLATT | Spastic equinovarus (CP) | Non-phasic |
| Rectus femoris → hamstrings | Stiff-knee gait (CP) | Non-phasic |
| Peroneus longus → brevis | Cavovarus foot | Phasic |
| Tibialis anterior → lateral cuneiform | Rigid drop foot | Context-dependent |
Conclusion
The phasic vs non-phasic classification is fundamental to surgical planning and prognosis in tendon transfer surgery. Phasic (synergistic) transfers exploit pre-existing neural programmes, enabling rapid re-education and superior functional outcomes. Non-phasic transfers demand significant cortical adaptation and are associated with longer rehabilitation, but remain valuable — particularly when no phasic donor is available or when the abnormal firing pattern of a spastic muscle itself is the pathological target.
Dynamic EMG is the gold standard for assessing muscle phasing, particularly in upper motor neurone conditions like cerebral palsy, where the temporal pattern of muscle activation is unpredictable from clinical examination alone. The fundamental surgical principles — expendable donor, adequate power (MRC 4–5, accepting one grade loss), appropriate excursion, straight line of pull, passive joint mobility, and single function per transfer — must be met regardless of phasing classification. However, synergistic donor selection remains the single most powerful predictor of post-operative motor re-education success.
Sources: Rockwood and Green's Fractures in Adults, 10th ed. | Miller's Review of Orthopaedics, 9th ed. | Current Surgical Therapy, 14th ed.
This is a shared conversation. Sign in to Orris to start your own chat.