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Tibialis tendon transfer is performed for drop foot, when the foot and ankle dorsiflexor muscles are not working. This may be due to disc disease (or surgery) when the L5 nerve root is damaged, after trauma or compartment syndrome when the muscles are damaged, or as part of neurological disease.
Historically the commonest cause for loss of dorsiflexion from nerve disease was polio. Although the disease is probably eradicated now, there are still many patients with old polio and drop foot in the underdeveloped world, but in the UK commoner causes are CMT and mononeuritis .
Loss of dorsiflexing power can usually be ameliorated by drop foot devices, but for a variety of reasons, including cosmesis, this may not always be accepted.
To perform successful tendon transfer, it is necessary to have a motor unit that works, and examination and testing of the tibilalis posterior tendon is important prior to transfer .
Meticulous surgery, prolonged splinting and prolonged rehabilitation are also necessary to obtain well-functioning results.
INDICATIONS:
Tibialis posterior tendon transfer is performed when dorsiflexion power has been permanently lost. Common indications worldwide include post-polio and trauma. In developed countries the underlying cause may often be disc disease or surgery, or Hereditary Sensory Motor Neuropathies (HMSNs) such as Charcot Marie Tooth disease. Trauma – either directly to nerves, or with compartment syndrome may also cause drop foot.
The surgery can only be performed when the passive ankle movement has been preserved (at least to neutral dorsiflexion) by splintage and physiotherapy, which must always be started when the lesion manifests itself. In cases of closed nerve injury, time must be allowed for recovery before considering surgery, and a splint should be worn – both to increase function and to prevent contracture – throughout this waiting time.
Tibias posterior tendon transfer should only be performed when the dorsiflexing muscles are irreversibly denervated (for example 18 months after closed nerve injury), and when the tibialis posterior is both functioning and is likely to continue to function. When performing this procedure for progressive neurological disease, a neurologist should advise on future progression of the disease if doubt exists.
SYMPTOMS & ASSESSMENT: the patient will complain of tripping over the dropped foot, and having to use a high stepping gait to avoid tripping. When the long toe extensors are affected, it is difficult to put on socks and hosiery.
Assessment is mainly clinical – to assess the range of movement of the ankle and to check it still comes up to neutral with no uncorrectable deformity of the ankle, hind, mid or forefoot. The skin must also be checked to ensure that the quality of skin allows wound closure.
The activity of the tibialis posterior tendon is tested by getting the patient to invert their plantar flexed foot against the examiners resistance.It must be active and strong if the transfer is to work.
INVESTIGATION: For most cases no special tests are needed.
Electrical conduction tests may , on occasions, be helpful to make a diagnosis of nerve disease or to check that spontaneous re-innervation is not occurring to the dorsiflexion muscles after closed nerve injury.
Occasionally plain films are needed to exclude degeneration within the foot or ankle.
OPERATIVE ALTERNATIVES: Historically, posterior bone block operations have been performed to prevent plantar flexion at the ankle, but these are rarely performed now. For patients without a functioning tibial posterior tendon, alternatives include ankle or double ankle and subtalar fusion, or tenodesis of the dorsiflexing tendons.
NON-OPERATIVE ALTERNATIVES: Drop foot devices should always be tried before undertaking surgery. According to the clinical status of the patient, they may range from rigid AFOs, through dorsiflex-assist flexible braces, or smaller splints which tie around the lower leg, and have elastic ties which fix to the laces of a shoe.
CONTRAINDICATIONS: The surgery is contra-indicated by the following:
1.General contra-indications such as concurrent illness etc
2. Local indications such as local infection or poor quality skin (in cases where there has been previous flaps or skingrafts performed a plastic surgeon should advise, and if necessary assist in the operation.
3. Non-permanent lesion – when time should be allowed for recovery to occur.
4. Where the tibialis posterior tendon does not function, or is expected to lose power in the near future (as in some nerve diseases).
The following special equipment is needed.
A drill
A robust long slightly curved clamp
An anchor to attach the tendon to bone (Anthrax 5.0mm Corkscrew used in this case).
A 2-3cm curved surgical needle to use in conjunction with the fibrethread sutures on the anchor.
The operation can be performed under general or regional/spinal anaesthesia.
The patient is positioned supine, a thigh tourniquet is applied and inflated after preparing all the skin to the level of the knee. Drapes should be applied at about the level of the knee, leaving the lower leg and foot exposed.
The leg is allowed to roll out, exposing the inner (medial) side of the foot to allow harvest of the graft. Later the leg and foot will need to be held unrotated, with the toes pointing straight up, and this can be achieved during surgery either by placing a large sterile bowl under the calf, with the knee slightly flexed to prevent rotation, or by getting an unscrubbed assistant to position a sandbag under the drapes at the level of the thigh.
A below knee cast is applied in neutral position with the metatarsal heads well padded.
Sutures may be removed at 2 weeks, but enough staff must be present at any plaster change to ensure the foot is not allowed to fall into plantar flexion whilst the plaster is off.
The patient may weight bear – with crutches if needed – subject to the requirements of other operations performed at the same time.
At eight weeks the patient can be mobilised into an ankle foot orthosis – or a walking boot – which must be worn all the time.
Assisted physiotherapy may start then , but the patient must again be supported from periods in plantarflexion.
At sixteen weeks physiotherapy can be increased, but active plantarflexion or standing exercises should be avoided for the first six months, and the boot or AFO should be retained all the time until the end of this period – as early stretching of the graft will lead to detachment or lengthening -either of which may lead to failure.
Formal re-educative physiotherapy, gait re-education and proprioceptive re-education may start at 6 months.
Most patients get a good result. Even if the graft does not function as an active extensor, it may function as a tenodesis.
Yeap et al (Int Orthop 2001; 25(2):114-118) reviewed 12 patients with drop foot secondary to sciatic or common peroneal palsy.
10 had an excellent or good result, although the measured power (torque) was only 30% of the normal side. They reported better results in men under 30 years of age.
Hove and Nilsen (Acta Orthopaedica Scand 1998; 69:6,: 608-610) reviewed 20 transfers in 17 patients with mixed neuromuscular disease(11) and injury(6) as cause.
At follow up between 2 and 15 years all had active dorsiflexion, with median dorsiflexion 5 deg. Gait was good or normal in 15 and improved in 2.
Reference
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