Mark E. Easley and Aaron T. Scott
DEFINITION
Pathology leading to a spectrum of motor function loss that includes loss of ankle dorsiflexion
Common peroneal nerve palsy, L5 radiculopathy, cerebrovascular accident
Loss of ankle dorsiflexion and hindfoot eversion
Retained posterior tibial tendon (PTT) function
Hereditary sensory motor neuropathy
A constellation of motor function deficits and associated deformity
Includes loss of dorsiflexion and hindfoot eversion
Retained PTT function
Flaccid paralysis
Global loss of motor function to the ankle and foot
ANATOMY
Posterior tibialis
Muscle originates on the posterior tibia, interosseous membrane, and fibula.
Muscle and then tendon course in the deep posterior compartment.
Tendon travels directly posterior to the medial malleolus.
Tendon has numerous insertions on bones of plantar midfoot, spring ligament, and medial aspect of navicular.
Interosseous membrane (IOM) and distal tibia–fibula syndesmosis
Thick fibrous bands between tibia and fibula
Distal tibia–fibula syndesmosis is narrow, with little space for tendon transfer even when a generous window is created in the distal IOM.
Inferior extensor retinaculum
On the dorsum of the foot to prevent bowstringing of the extensor tendons as they transition across the anterior ankle to the dorsal foot
Sciatic nerve
Comprises tibial and common peroneal nerves that separate immediately proximal to the popliteal fossa
Common peroneal nerve often affected in these neuropathies
Superficial peroneal nerve
Motor function to anterior and lateral compartment muscles
Dorsiflexion and eversion, respectively
Sensory distribution to dorsum of the foot
Deep peroneal nerve
Courses between tibialis anterior and extensor hallucis longus tendons proximal to the ankle
Located directly on the dorsum of midfoot
Immediately deep to extensor hallucis brevis muscle belly
Motor function to intrinsic muscles of foot
Sensory distribution to first web space
Tibial nerve function typically spared
Tibial nerve must be intact to create a dynamic tendon transfer
If tibial nerve is not intact, then transfer can only be a tenodesis
Anterior ankle and dorsal midfoot neurovascular structures at risk
Superficial peroneal nerve (may be insensate as part of the neuropathy)
Deep neurovascular bundle
Anterior tibial artery
Deep peroneal nerve (may also be insensate as part of the neuropathy)
Peroneal artery branch
Situated directly on anterior distal IOM
PATHOGENESIS
Loss of common peroneal nerve function
Loss of ankle dorsiflexion and hindfoot eversion
Loss of major antagonists
Eventual equinus contracture
Imbalance of hindfoot inverter (PTT) and everters (peroneus brevis) and usually, but not always, peroneus longus)
Eventual hindfoot varus deformity
Imbalance of hindfoot inverters (PTT) and everter (peroneus longus)
Flaccid paralysis
Tibial and common peroneal nerve palsies
No motor function distal to knee
Since both sets of major antagonists lost, typically no contractures
NATURAL HISTORY
Foot drop may eventually recover.
Tendon transfers should not be considered until a chance for recovery has been ruled out.
Common peroneal nerve palsy may lead to progressively worsening equinocavovarus foot deformity due to overpull of plantarflexors and inverters powered by intact tibial nerve and loss of dorsiflexors and everters powered by compromised common peroneal nerve.
Flaccid paralysis remains relatively stable since both sets of antagonists are compromised.
PATIENT HISTORY AND PHYSICAL FINDINGS
Gait abnormality
“Slap foot gait”
Inability to dorsiflex ankle and control tibialis anterior from heel strike to stance phase
Exaggerated hip and knee flexion
Inability to dorsiflex ankle or great toe from push-off through swing phase
Compensation to allow toes to clear during swing phase
Hindfoot inversion
Patient walks on lateral border of foot.
Inability to dorsiflex ankle
May check by asking patient to walk on heels
Manual muscle testing with patient seated on examining table with knee flexed
Lack of eversion
Varus hindfoot
Over time, may become a fixed inversion contracture
In some disease processes (eg, Charcot-Marie-Tooth disease) toe dorsiflexion is spared, creating claw toe deformities.
Patient attempts to compensate for lack of ankle dorsiflexion with toe extensors, worsening claw toe deformities.
Even when toe extensors are involved in the palsy, flexor tendons may become contracted.
Passive dorsiflexion of the ankle will reveal this.
With equinocavovarus foot contracture, calluses may form under metatarsal heads, particularly the fifth.
Sensation may be diminished on the dorsal and lateral aspects of the foot.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Imaging is typically unnecessary for patients with foot drop except in the following situations:
Consideration should be given to MRI:
If there is concern for mass effect creating a compressive neuropathy: lumbar spine, common peroneal nerve at fibular head
To rule out tibialis anterior tendon rupture (should be evident on clinical examination alone)
Consideration should be given to radiographs of foot or ankle:
To rule out stress fracture
To better define bony deformity (fixed deformity, associated ankle or foot arthritis; important because arthrodesis may need to be considered in lieu of or in combination with tendon transfer)
Electrodiagnostic studies
Absence of recovery at 1 year and particularly at 18 months is highly suggestive that recovery of nerve function will not occur.
Nerve conduction studies and electromyography
Baseline and follow-up studies to determine if any recovery evident
Important to determine if tendon transfer is warranted
Tendon transfer should not be performed if nerve function may recover!
Absence of recovery at 1 year and particularly at 18 months is highly suggestive of no recovery.
We recommend consultation with a neurologist to confirm interpretation of electrodiagnostic studies.
Studies may also define function of PTT.
Important when considering dynamic PTT transfer versus PTT tenodesis
A tendon transfer of a healthy tendon immediately reduces its strength on manual muscle testing from 5/5 to 4/5, so if it is already compromised, then the tendon transfer will do little more than create a tenodesis.
Useful in determining if a more proximal compressive neuropathy exists
DIFFERENTIAL DIAGNOSIS
Tibialis anterior tendon rupture
Cerebrovascular accident
Lumbar spine radiculopathy
Hereditary sensorimotor neuropathy
Leprosy
Poliomyelitis
Cerebral palsy (spastic)
NONOPERATIVE MANAGEMENT
Bracing with an ankle–foot orthosis (AFO)
Requires a fixed AFO in flaccid paralysis
May be a flexible AFO with common peroneal palsy
Requires plantarflexion stop
Equinus contracture may need to be corrected to facilitate bracewear.
Achilles stretching
Botulinum toxin injection
Tendo Achilles lengthening (TAL)
Varus deformity
If flexible may be corrected with bracing
If fixed, bracing is difficult.
SURGICAL MANAGEMENT
Preoperative Planning
The surgeon must confirm that motor function will not recover before proceeding with tendon transfer.
Serial clinical examination
Serial electrodiagnostic studies (at least one compared to baseline)
The surgeon must determine what motor function persists:
Tibial nerve
PTT (inversion)
Gastrocnemius–soleus (plantarflexion)
None (flaccid paralysis)
The surgeon must evaluate for equinus contracture.
The surgeon should be prepared to perform TAL if necessary (see Tech Fig 1A–D).
Flexible versus fixed deformities
Flexible deformity typically corrects with tendon transfer alone.
Fixed deformity
May require capsular release or even arthrodesis
Toe contractures
Although claw toe deformity may not be evident with the ankle plantarflexed, once the deformity is corrected, toe contractures may become obvious.
Dorsiflexing the ankle will put the contracted flexor hallucis and digitorum on stretch, thereby revealing the toe contractures.
The surgeon should be prepared to address toe contractures as part of the procedure.
Tendon transfer anchoring
We routinely use interference screws to anchor tendon transfers to bone.
Need to have an anchoring system available
Alternatively, anchoring to existing distal tendon or existing soft tissues in the foot may be possible.
In our experience, anesthesia should maintain complete muscle relaxation and paralysis during the procedure; otherwise, the success of the tendon transfer may be compromised.
At the conclusion of the procedure we often perform botulinum toxin injections into the gastrocnemius–soleus complex to further protect the tendon transfer postoperatively.
Positioning
Supine
If the PTT will be transferred through the IOM or if a peroneal tendon will be used for correction of flaccid paralysis, we routinely place a bolster under the ipsilateral hip to afford optimal lateral exposure. Once the lateral tendon is harvested or the PTT transferred through the IOM, the bolster may be removed.
We routinely use a thigh tourniquet.
Approach
Multiple relatively small incisions are needed; extensile exposures are unnecessary.
PTT harvest
Medial harvest over navicular
Posteromedial tibia at musculotendinous junction of PTT
PTT transfer through the IOM
Incision over distal IOM
Incision over dorsolateral foot
PTT transfer anterior to tibia
Incision over central midfoot
Bridle procedure
Same PTT harvest
PTT transfer through IOM with incision directly anterior over distal tibia; may be extended to dorsal foot. Alternatively, separate small incision over centrodorsal midfoot.
Lateral incisions: incision over musculotendinous junction of peroneus longus and another incision over lateral cuboid where peroneus longus courses around cuboid
TECHNIQUES
ACHILLES LENGTHENING
Indications
Not always necessary, but typically required when foot drop occurs
Without active dorsiflexion the gastrocnemius– soleus' antagonist is lost, often leading to an Achilles contracture.
Occasionally patients maintain an active stretching program, thereby avoiding an Achilles contracture.
Weakening of the gastrocnemius–soleus complex may be beneficial since a transfer of a healthy muscle–tendon unit is subject to an automatic onegrade loss of power (5/5 manual muscle testing drops to 4/5 with transfer).
Occasionally we use botulinum toxin in the gastrocnemius–soleus complex when performing a PTT transfer for foot drop.
Technique
Determined by the Silfverskiold test
Equinus contracture with the knee in extension and flexion (Tech Fig 1A)
Tech Fig 1 • Tendo Achilles lengthening. A. Equinus with knee in flexion and extension suggests tight gastrocnemius and soleus. B. Initial Achilles hemisection. C. Second Achilles hemisection (opposite direction from first), to be followed by third and final hemisection in same direction as first. D. Dorsiflexion re-established after Achilles lengthening.
Triple hemisection (Hoke procedure) because both the gastrocnemius and soleus are contracted (Tech Fig 1B–D)
Equinus contracture only with the knee in extension: gastrocnemius–soleus recession (Strayer procedure) because only the gastrocnemius is contracted
Posterior Tibial Tendon Transfer Through the Interosseous Membrane
Advantages
PTT in direct line from its muscle through the IOM to the lateral cuneiform (our preferred site for tendon anchoring)
Anchor point slightly lateral of midline to promote dorsiflexion and eversion
Disadvantage
PTT may be constricted and stenosed within narrow window created in distal IOM.
Posterior Tibial Tendon Harvest
Make a 4-cm longitudinal incision over the medial navicular and PTT on the medial foot.
Open the PTT sheath to expose the tendon.
Release the PTT insertion on the medial navicular.
Alternatively, use a chisel to elevate some medial navicular bone with the PTT release from the medial navicular (may allow for another centimeter of tendon for transfer) (Tech Fig 2A).
Isolate the PTT attachment on the medial navicular and the tendon fibers that begin to course to the plantar midfoot (Tech Fig 2B).
With the PTT fibers isolated, transect them to release the PTT distally.
Be sure to fully isolate the PTT fibers; the medial plantar nerve and the plantar medial complex of veins is in close proximity.
Accidentally transecting the nerve leads to loss of sensation in the plantar medial forefoot.
Violating the veins may make it difficult to achieve satisfactory hemostasis as these veins may then retract under the foot.
Thin the distal stump of the PTT to be transferred to facilitate its transfer into an osseous tunnel that will be created in the foot (Tech Fig 2C).
Tech Fig 2 • Posterior tibial tendon (PTT) harvest A. Elevating PTT with a sliver of medial navicular may allow longer tendon harvest. B. Isolating PTT. C. Distal PTT needs to be trimmed to allow it to pass into dorsal foot osseous tunnel. D, E. Tag suture in distal PTT. F. Transfer of PTT to proximal medial wound. A 3-cm incision is made over PTT musculotendinous junction. G. Tendon transfer is mobilized. H. PTT is transferred to proximal wound.
Place tag sutures in the distal PTT (Tech Fig 2D,E).
Make a more proximal medial incision at the PTT musculotendinous junction on the posterior tibia.
3-cm incision (Tech Fig 2F)
Flexor digitorum tendon is usually encountered first.
Deep to the FDL, directly on the posteromedial tibia, the PTT is identified.
Place a blunt retractor around the PTT through this more proximal wound to isolate it.
Mobilize the distal PTT.
Alternate tension on the proximal tendon through the proximal wound and the distal tag sutures (Tech Fig 2G), then apply tension proximally only.
This may not work.
The medial incision may need to be extended proximally to allow access to the posterior medial malleolus, a common location where the tendon may bind.
Once mobilized, the distal aspect of the PTT may be transferred to the proximal wound (Tech Fig 2H).
Tendon will desiccate rapidly, so we keep it tucked in the proximal medial wound.
Posterior Tibial Tendon Transfer Through the Interosseous Membrane
Lateral incision on anterior aspect of distal fibula, at distal tibiofibular syndesmosis
Careful exposure of anterior IOM
Elevate the anterior compartment soft tissues.
A branch of the peroneal artery courses on the anterior IOM and is at risk.
Create a generous window in the distal IOM (Tech Fig 3A).
From tibia to fibula
About 3 to 4 cm long
Pass a tonsil clamp through the IOM directly on the posterior aspect of the tibia to exit in the proximal medial wound (Tech Fig 3B).
The posterior neurovascular structures (tibial nerve and posterior tibial artery) are at risk, so be sure the clamp is directly on the posterior tibia.
Tech Fig 3 • PTT transfer through the interrosseous membrane (IOM). A. A window is carefully created in the interosseous membrane (IOM) (perspective with view of lateral distal leg [foot to the left and knee to the right]). B. A blunt clamp is passed through IOM, directly on posterior tibia. C. Posterior tibial tendon (PTT) tag sutures are grasped. D. PTT is transferred to anterolateral wound, with tendon immediately on posterior tibia. E. The surgeon must be sure tendon does not bind in IOM window.
Use the tonsil clamp to grasp the tag sutures of the PTT (Tech Fig 3C).
Pull the tag sutures and PTT from the medial wound to the lateral wound, keeping the tendon directly on the posterior aspect of the tibia (Tech Fig 3D,E).
Be sure that the window in the IOM does not impinge on the transferred tendon.
If there is stenosis, then further enlarge the window so that the tendon easily glides between the tibia and fibula.
Keep the tendon end in the wound to limit desiccation.
Preparation of the Dorsal Foot Anchor Site
Fluoroscopically identify the center of the lateral cuneiform.
Oblique foot views usually best define the lateral cuneiform (Tech Fig 4A).
Center a 3to 4-cm longitudinal skin incision directly over the lateral cuneiform.
Dissect to the lateral cuneiform.
Protect the superficial peroneal nerve and extensor tendons.
Deep neurovascular bundle is usually medial to this approach.
Expose and define the cuneiform.
We routinely use small-gauge hypodermic needles or Kirschner wires to mark the joints surrounding the lateral cuneiform and fluoroscopically confirm that the lateral cuneiform is defined by these markers (Tech Fig 4B).
Periosteum and capsular tissue are left intact.
Create an osseous tunnel in the center of the lateral cuneiform.
We routinely predrill the center with a Kirschner wire and confirm the starting point and trajectory of the wire fluoroscopically.
Remove the wire and introduce sequentially larger drill bits to enlarge the tunnel (Tech Fig 4C).
Tech Fig 4 • Preparing dorsal foot osseous tunnel. A. Lateral cuneiform is identified fluoroscopically. B. Borders of lateral cuneiform are exposed and marked. C. Drill hole is created in lateral cuneiform and proper position is confirmed fluoroscopically. D. Osseous tunnel is gradually enlarged, first with drill bits, then dedicated reamer system for interference screw. E. Prepared osseous tunnel in lateral cuneiform.
We use drill bits to a diameter of 4.5 mm.
With fluoroscopic confirmation, slight adjustments may be made with each successive drill bit to center the tunnel optimally in the cuneiform.
Introduce the reamer system for the interference screw system to enlarge the tunnel to the desired diameter (Tech Fig 4D).
Typically, we enlarge the tunnel to 6.5 to 7.0 mm in the lateral cuneiform (Tech Fig 4E).
Posterior Tibial Tendon Transfer to Dorsum of Foot
Transferring the PTT deep to the extensor retinaculum with the extensor tendons diminishes the power of the transfer (which is by definition already weakened by one grade with transfer).
Create a subcutaneous soft tissue tunnel from the dorsal foot incision to the more proximal and lateral lower leg incision using a curved Kelly or tonsil clamp (Tech Fig 5A).
Use the clamp to grasp the tag sutures and pull the tendon through the subcutaneous tunnel to the dorsal foot incision (Tech Fig 5B).
Before anchoring the tendon in the osseous tunnel, pull the tendon via the tag sutures into the tunnel to be sure that the tunnel diameter is appropriate.
Pass a Beath pin or drill bit (has an eye to place suture) through the tunnel and the plantar skin (Tech Fig 5C).
Because of the midfoot arch and the drill hole centered in the lateral cuneiform foot this pin or the drill bit will exit in the medial arch (Tech Fig 5D).
Dorsiflex the ankle.
With the tag sutures secured, pull the pin or drill bit through the plantar skin, thereby pulling the distal tendon end into the tunnel (Tech Fig 5E).
If the tunnel does not accommodate the tendon, then the tendon and tag sutures must be withdrawn and the tunnel enlarged.
Because of the angle at which the tendon enters the tunnel, we often need to guide the tendon into the tunnel with a forceps.
Anchoring the tendon to bone
Some degree of stretching or accommodation is anticipated, so we routinely anchor the tendon with the ankle maintained in 10 degrees of dorsiflexion and pull firmly on the plantar suture (Tech Fig 5F,G).
Tech Fig 5 • Posterior tibial tendon (PTT) transfer from lateral lower leg wound to dorsum of foot. A. Subcutaneous tunnel created with a blunt clamp. B. Grasping tag sutures. C. Passing Beath drill with tag sutures through osseous tunnel. D. Pulling Beath drill through plantar foot. E. The surgeon must be sure the tendon fits appropriately into the osseous tunnel. F. Tendon tensioning. Tendon advances appropriately into osseous tunnel (note ankle is held in dorsiflexion). G. Tension applied on plantar tag sutures. H. Augmenting anchoring. Suture anchor being placed within osseous tunnel. I. Two anchors secured in tunnel (note separate tag suture of PTT). J.Final fixation of tendon transfer in dorsal foot. Tendon fully tensioned with ankle dorsiflexed. K, L. Securing tendon to anchors and adjacent periosteum. M. Interference screw positioned. N. Screw advanced. O. Screw fully seated.
A properly sized isolated interference screw is probably adequate.
However, we typically augment the anchor point with several nonabsorbable sutures from the periosteum surrounding the tunnel to the tendon directly at the entrance to the tunnel.
To further augment the anchor point: before advancing the tendon and tag suture into the tunnel, place one or two suture anchors within the tunnel (Tech Fig 5H,I). Then advance the tendon into the tunnel and secure the tendon with the anchors (Tech Fig 5J,K). By tightening these sutures, the tendon may be pulled even further into the tunnel (Tech Fig 5L). An interference screw and periosteal sutures may still be used (Tech Fig 5M–O).
Have the assistant maintain full ankle dorsiflexion and tension on the tag sutures on the plantar foot.
We usually cut the tag sutures so they retract beneath the skin.
Rarely, we have used a well-padded button on the plantar foot to further augment the tendon's anchor point. We do not routinely do so because of the risk for plantar skin necrosis from the button despite adequate padding.
In select patients, the dorsiflexed ankle will unmask claw toes due to flexor hallucis longus and flexor digitorum longus contractures. Consider flexor hallucis longus and flexor digitorum longus lengthenings, posterior to the ankle and tibia via the more proximal medial approach, or percutaneous tenotomies at the plantar toes.
POSTERIOR TIBIAL TENDON TRANSFER ANTERIOR TO THE TIBIA
Advantages
PTT has no opportunity to stenose in the IOM.
Glides smoothly around anteromedial tibia
Anchor point slightly lateral of midline to promote dorsiflexion and eversion
Tech Fig 6 • Adequate dorsiflexion (essential for successful tendon transfer to re-establish dorsiflexion).
Disadvantage
PTT is not in direct line from its origin to anchor point in the foot; it must travel around medial tibia.
Anchor point is in the middle (second) cuneiform.
Central location so it cannot provide an eversion moment
However, typically unimportant since with PTT transfer the agonist–antagonist balance between PTT and peroneus brevis is again re-established by being neutralized.
Achilles Lengthening
Same as for PTT transfer through IOM described earlier (Tech Fig 6)
Posterior Tibial Tendon Harvest
Same as for PTT transfer through IOM described earlier (Tech Fig 7)
Preparation of the Dorsal Foot Anchor Site
Similar to preparation of dorsal foot anchor site described earlier for PTT transfer through IOM
Tech Fig 7 • Approach to posterior tibial tendon (PTT) harvest. A. The two planned medial incisions. B. Planned dorsal foot incision. C–E. Harvesting PTT. C. PTT is isolated. D. Distal tendon is trimmed (contoured). E. Tag suture in distal end of tendon. PTT is mobilized. F. PTT is identified at its musculotendinous junction. G. PTT is mobilized to allow transfer to proximal wound. H, I. Transferring PTT to proximal medial wound. H. Tendon is pulled into proximal wound. I. Proposed course for transfer to dorsum of foot.
However, when transferring the PTT through the IOM we typically anchor the tendon to the lateral (third) cuneiform.
In contrast, when we transfer the PTT anterior to the medial tibia, we typically anchor the tendon in the middle (second) cuneiform.
Middle cuneiform is smaller than the lateral cuneiform.
In our experience, greater risk of fracture with drill hole, tendon transfer, and interference screw
Fluoroscopically identify the center of the middle cuneiform.
AP and sometimes oblique foot views best define the middle cuneiform.
Center a 3to 4-cm longitudinal skin incision directly over the middle cuneiform.
Dissect to the middle cuneiform.
Protect the superficial peroneal nerve and extensor tendons (Tech Fig 8A).
Protect the deep neurovascular bundle, usually encountered in this approach; it is directly deep to the muscle of the extensor hallucis brevis.
Expose and define the cuneiform.
We routinely use small-gauge hypodermic needles or Kirschner wires to mark the joints surrounding the medial cuneiform and fluoroscopically confirm that the medial cuneiform is defined by these markers (Tech Fig 8B).
Leave the periosteum and capsular tissue intact.
Create an osseous tunnel in the center of the medial cuneiform.
We routinely predrill the center with a Kirschner wire and confirm the starting point and trajectory of the wire fluoroscopically.
Remove the wire and introduce sequentially larger drill bits to enlarge the tunnel (Tech Fig 8C).
We use drill bits to a diameter of 4.5 mm.
With fluoroscopic confirmation, slight adjustments may be made with each successive drill bit to center the tunnel optimally in the cuneiform.
Tech Fig 8 • Preparation of dorsal foot osseous tunnel. A. Dorsal incision over middle cuneiform. B. Middle cuneiform is identified and marked.C. Increasingly largerdiameter drill bits. D. Increasingly larger reamers (judiciously, since the middle cuneiform is not particularly large).
Use the reamer from the interference screw system to enlarge the tunnel to the desired diameter (Tech Fig 8D).
Typically, we enlarge the tunnel to 5.5 to 6.0 mm in the medial cuneiform.
Posterior Tibial Tendon Transfer to Dorsum of Foot
Transferring the PTT deep to the extensor retinaculum with the extensor tendons diminishes the power of the transfer (which is by definition already weakened by one grade with transfer).
Create a subcutaneous soft tissue tunnel from the dorsal foot incision to the more proximal and medial lower leg incision using a curved Kelly or tonsil clamp (Tech Fig 9A,B).
Use the clamp to grasp the tag sutures and pull the tendon through the subcutaneous tunnel to the dorsal foot incision.
Before anchoring the tendon in the osseous tunnel, pull the tendon via the tag sutures into the tunnel to be sure that the tunnel diameter is appropriate.
Pass a Beath pin or drill bit (has an eye to place suture) through the tunnel and the plantar skin (Tech Fig 9C,D). Because of the midfoot arch, this pin or drill bit will exit in the medial arch (Tech Fig 9E).
Dorsiflex the ankle.
With the tag sutures secured, pull the pin or drill bit through the plantar skin, thereby pulling the distal tendon end into the tunnel (Tech Fig 9F).
If the tunnel does not accommodate the tendon, then the tendon and tag sutures must be withdrawn and the tunnel enlarged.
Tech Fig 9 • Transfer of posterior tibial tendon (PTT) to dorsum of foot. A. Subcutaneous tunnel for blunt clamp to grasp tag suture in PTT. B. PTT is transferred subcutaneously to dorsum of foot. C–F.Ensuring that PTT will pass through osseous tunnel in middle cuneiform. C. Beath drill through tunnel with tag suture from PTT secured. D. Entry point of Beath drill in dorsal tunnel. E. Exit of Beath drill in plantar foot. F. Tendon advancing appropriately with ankle in dorsiflexion and tension on tag sutures passed through plantar foot. G, H. Tendon fixation. G. Augmentation possible with suture anchors placed directly in tunnel before advancing tendon into tunnel. H. Interference screw with ankle dorsiflexed and tension maintained on plantar tag suture. I. Suture button. In this case middle cuneiform fractured with insertion of interference screw and therefore a suture button was used. Note also the use of two Kirschner wires in the medial foot to further stabilize fracture in cuneiform.
Because of the angle at which the tendon enters the tunnel, we often need to guide the tendon into the tunnel with a forceps.
Anchoring the tendon to bone
Some degree of stretching or accommodation is anticipated in the posterior tibial muscle and tendon, so we routinely anchor the tendon with the ankle maintained in 10 degrees of dorsiflexion.
A properly sized isolated interference screw is probably adequate.
However, we typically augment the anchor point with several nonabsorbable sutures from the periosteum surrounding the tunnel to the tendon directly at the entrance to the tunnel.
To further augment the anchor point
Before advancing the tendon and tag suture into the tunnel, place one or two suture anchors within the tunnel (Tech Fig 9G).
Then advance the tendon into the tunnel and secure the tendon with the anchors. By tightening these sutures, the tendon may be pulled even further into the tunnel. An interference screw and periosteal sutures may still be used (Tech Fig 9H).
Have the assistant maintain full ankle dorsiflexion and tension on the tag sutures on the plantar foot.
We usually cut the tag sutures so they retract beneath the skin.
Rarely, we have used a well-padded button on the plantar foot to further augment the tendon's anchor point (Tech Fig 9I). We do not routinely do so because of the risk for plantar skin necrosis from the button despite adequate padding.
BRIDLE PROCEDURE
Advantages
The “bridle” creates a balance to the foot and ankle.
Potentially can make the patient with flaccid paralysis brace-free
Disadvantage
With flaccid paralysis, the tendon transfer is static, not dynamic.
Functions as a tenodesis
If procedure is successful, foot and ankle remain in neutral position at all times.
Tech Fig 10 • Harvest of posterior tibial tendon for bridle procedure.
Achilles Lengthening
Same as for PTT transfer through IOM described earlier
Posterior Tibial Tendon Harvest
Same as for PTT transfer through IOM described earlier (Tech Fig 10)
Harvest of the Peroneus Longus
With an adequate skin bridge from the anterior ankle distal tibial incision, make a 2to 3-cm incision immediately posterior to the fibula, about 8 cm proximal to the tip of the fibula at the level of the peroneus longus' musculotendinous junction (Tech Fig 11A).
Protect the superficial peroneal nerve. However, with common peroneal nerve palsy, an injury to this terminal sensory branch will probably be inconsequential.
Sharply divide the peroneal retinaculum 2 to 3 cm longitudinally over the musculotendinous junction of the peroneus longus.
Divide the peroneus longus tendon at its musculotendinous junction (Tech Fig 11B).
Place a tag suture in the transected distal end of the tendon.
Make another 2to 3-cm incision over the lateral cuboid (Tech Fig 11A).
Protect the sural nerve.
Isolate the peroneus longus tendon and pull its released proximal portion through this lateral foot wound (Tech Fig 11C,D).
Tuck the peroneus longus tendon in the distal lateral foot wound to keep it from desiccating.
The peroneus longus tendon will be passed to the anterior ankle wound (see below).
Tech Fig 11 • A–C. Harvest of peroneus longus for bridle procedure. A, B. Two small incisions, the first at the musculotendinous junction of peroneus longus and the second where the tendon courses around the cuboid. C.Peroneus longus transferred to distal lateral incision. D. Anticipated course for peroneus longus in bridle procedure (note also approximate course of posterior tibial tendon transfer).
Posterior Tibial Tendon Transfer Through the Interosseous Membrane
Make an incision over the lateral aspect of the distal anterior tibia.
Carefully expose the anterior IOM (Tech Fig 12A).
Protect the superficial peroneal nerve.
Divide the extensor retinaculum over the tibialis anterior and extensor hallucis longus tendons.
Protect the deep neurovascular bundle (Tech Fig 12B).
Protect the peroneal artery branch that courses on the anterior IOM.
Create a generous window in the distal IOM (Tech Fig 12C).
From tibia to fibula
About 4 cm long
Pass a curved Kelly or tonsil clamp through the IOM directly on the posterior aspect of the tibia to exit in the proximal medial wound (Tech Fig 12D).
The posterior neurovascular structures (tibial nerve and posterior tibial artery) are at risk, so be sure the clamp is directly on the posterior tibia.
Use the tonsil clamp to grasp the tag sutures of the PTT.
Pull the tag sutures and PTT from the medial wound to the lateral wound, keeping the tendon directly on the posterior aspect of the tibia (Tech Fig 12E).
Be sure that the window in the IOM does not impinge on the transferred tendon. If there is stenosis, then further enlarge the window so that the tendon easily glides between the tibia and fibula.
Keep the tendon end in the wound to limit desiccation.
Transfer of the Peroneus Longus
Using a Kelly clamp, create a subcutaneous tunnel from the anterior distal tibial wound to the lateral foot wound (Tech Fig 13A).
Spread this tissue carefully with the clamp to avoid any soft tissue impingement within the tunnel.
Grasp the tag suture in the peroneus longus and pull the tendon from the lateral foot wound to the anterior distal tibial wound (Tech Fig 13B).
Transfer of Posterior Tibial Tendon Through the Tibialis Anterior Tendon
Make a stab incision in the tibialis anterior tendon with proximal tension placed on the tibialis anterior tendon while the ankle is held in dorsiflexion.
This will tension the distal extent of the tibialis anterior tendon before it is secured to the PTT.
Avoid simply creating an incision in the tibialis anterior tendon in situ; this will render the tension in the medial aspect of the “bridle” ineffective.
Tech Fig 12 • Creating an interosseous membrane (IOM) window to transfer the posterior tibial tendon to the anterior lower leg. A. Approach. B. Protecting deep neurovascular bundle and peroneal artery. C.Creating the window in the IOM. D, E. Transfer of the posterior tibial tendon (PTT) to the anterior lower leg. D. Blunt clamp is passed directly on the posterior tibia from anterior to proximal medial wound to grasp tag suture in PTT. E.Ensuring that the tendon does not bind in the IOM window.
Tech Fig 13 • Transferring peroneus longus tendon from distal lateral foot wound to anterior lower leg wound. A. Subcutaneous tunnel to grasp free end of peroneus longus. B. Tendon transferred.
Pass the PTT through this stab incision in the tibialis anterior (Tech Fig 14).
If a more secure fixation between the tibialis anterior and PTT is desired, then consider a Pulvertaft weave.
While more weaving of the PTT through the tibialis anterior may afford greater fixation, it may in turn diminish the excursion of the PTT, thereby limiting the amount of distal PTT that will rest within the middle cuneiform's osseous tunnel.
Preparation of the Dorsum of the Foot and Anchoring the Posterior Tibial Tendon
Similar to that described for PTT transfer anterior to the tibia (see earlier)
Transfer to the middle cuneiform
A separate incision may be made (two limited incisions anteriorly) or the anterior distal tibial approach may be extended to the dorsum of the foot (single extensile anterior incision).
Tech Fig 14 • Posterior tibial tendon is transferred through the tibialis anterior. Note the pretensioning of the tibialis anterior to optimize tension in the bridle.
Create an osseous tunnel in the middle cuneiform (Tech Fig 15A).
Create a subcutaneous soft tissue tunnel from the dorsal foot incision to the more proximal and anterior lower leg incision using a curved Kelly clamp.
Use the clamp to grasp the tag sutures and pull the tendon through the subcutaneous tunnel to the dorsal foot incision (Tech Fig 15B).
Before anchoring the tendon in the osseous tunnel, pull the tendon via the tag sutures into the tunnel to be sure that the tunnel diameter is appropriate.
Pass a Beath pin or drill bit (has an eye to place suture) through the tunnel and the plantar skin (Tech Fig 15C). Because of the midfoot arch, this pin or drill bit will exit in the medial arch (Tech Fig 15D).
Dorsiflex the ankle.
With the tag sutures secured, pull the pin or drill bit through the plantar skin, thereby pulling the distal tendon end into the tunnel (Tech Fig 15E).
Tech Fig 15 • A. Creating the osseous tunnel in middle cuneiform. B–G. Transferring posterior tibial tendon (PTT) from anterior lower leg wound to dorsum of foot. B. Tendon passed through subcutaneous tunnel to dorsum of foot. C. Beath needle with tag sutures from PTT passed through osseous tunnel. D. Tension on tag sutures on plantar foot. E. Tendon passed into middle cuneiform osseous tunnel. F.Positioning interference screw. G.Interference screw fully seated with appropriate PTT tension achieved.
With the PTT properly tensioned in the second cuneiform's osseous tunnel, the PTT is anchored in a manner similar to that described earlier for the other techniques (interference screw with or without suture anchor in tunnel) (Tech Fig 15F,G).
Securing and Tensioning Tibialis Anterior and Peroneus Longus to the Posterior Tibial Tendon
Maintain the ankle in 10 degrees of dorsiflexion.
Balance the foot with respect to varus or valgus; it should have a neutral to slight valgus heel.
Tibialis anterior
Tension the tibialis anterior proximally and suture the tibialis anterior and PTT to one another at the point where the PTT passes through the tibialis anterior.
Reinforce this connection with several more side-to-side sutures between the two tendons, both proximal and distal to where the PTT passes through the tibialis anterior.
Peroneus longus
Approximate the peroneus longus to the PTT where it passes anterior to the distal tibia and ankle, with maximum tension applied (Tech Fig 16).
Without support, the ankle should maintain dorsiflexed ankle and neutral hindfoot positions.
Tech Fig 16 • With the foot balanced, tibialis anterior and peroneus longus are secured to posterior tibial tendon transfer to create the bridle.
POSTOPERATIVE CARE
We routinely place a well-padded short-leg cast in the operating room to protect the transfer, with the ankle in maximum dorsiflexion.
At first follow-up (2 to 3 weeks), we remove the cast while maintaining ankle dorsiflexion.
To protect the transfer, the ankle should not be allowed to plantarflex.
A new short-leg cast is applied, one that allows touchdown weight bearing.
Follow up at 5 to 6 weeks from surgery.
The short-leg cast is removed, again protecting dorsiflexion.
Wound inspection
Without allowing the ankle to plantarflex, the cast is removed.
Consideration may be given to creating a temporary AFO.
We typically place the patient in a short-leg walking cast at this point, with the ankle in near-maximum dorsiflexion. The patient is encouraged to walk.
At 8 to 10 weeks
The patient can typically discontinue use of the cast.
AFO for ambulation is typically worn until 4 to 5 months after surgery. During the final month of brace wear, the surgeon can consider hinging the AFO and placing a plantarflexion stop at neutral.
A cam boot is used for sleeping; it is typically worn until 4 to 5 months after surgery.
A physical therapy program is initiated to train the PTT to function as an ankle dorsiflexor.
Return to brace-free full function is not recommended before 6 months.
OUTCOMES
Select case series of PTT transfers for foot drop and bridle procedures suggest a satisfactory outcome in a majority of cases.
COMPLICATIONS
Infection
Wound dehiscence. The wound must be healed before initiating active dorsiflexion (usually not a problem because cast is maintained for at least 8 weeks).
Failure of the tendon transfer anchoring point; less common with newer anchoring system
Imbalance of bridle procedure: tibialis anterior and peroneus longus must be properly tensioned intraoperatively
REFERENCES
1. Elsner A, Barg A, Stufkens SA, et al. Lambrinudi arthrodesis with posterior tibialis transfer in adult drop-foot. Foot Ankle Int 2010;31:30–37.
2. Hove LM, Nilsen PT. Posterior tibial tendon transfer for drop-foot: 20 cases followed for 1–5 years. Acta Orthop Scand 1998;69:608–610. 3. Mizel MS, Temple HT, Scranton PE Jr, et al. Role of the peroneal tendons in the production of the deformed foot with posterior tibial tendon deficiency. Foot Ankle Int 1999;20:285–289.
3. Morita S, Muneta T, Yamamoto H, et al. Tendon transfer for equinovarus deformed foot caused by cerebrovascular disease. Clin Orthop Relat Res 1998;350:166–173.
4. Rodriguez RP. The Bridle procedure in the treatment of paralysis of the foot. Foot Ankle 1992;13:63–69.
5. Soares D. Tibialis posterior transfer for the correction of foot drop in leprosy: long-term outcome. J Bone Joint Surg Br 1996 Jan;78(1):61–2.
6. Sundararaj GD. Tibialis posterior transfer (circumtibial route) for foot-drop deformity. Indian J Lepr 1984;56:555–562.