Poliomyelitis: Ankle and Foot Deformities

ANKLE AND FOOT DEFORMITIES

An equinus deformity of the foot in children with polio is the commonest deformity seen and nearly always requires operation. A tight tendo Achillis is the major cause when there is no associated varus, and this is easily corrected by subcutaneous elongation of the tendon.

Contraindications to operation in children

The only contraindications to operation in children are:-

(1) A child who will never walk because of weak arms.

(2) Where there is a minimal degree of deformity and the child is managing well with a shoe or boot with or without a caliper.

(3) Infection of toes or feet, or lack of permission for operation. These are indications for delay only.

Contraindications to operation in adults

In an adult the same criteria apply, but in addition in the following cases operation is not usually required:-

(1) Where a slightly equinus foot is stabilising an unstable knee.

(2) Where an equinus foot is compensating for shortening in a patient who does not wear shoes.

OPERATION

Type of knife

The knife is preferably a small tenotomy knife. If this is not available an old cataract knife can be used. Care must be taken not to break the blade. A gentle sawing motion should be used.

Sterility

All subcutaneous operations should be carried out under full sterile precautions, with the use of adquate sterile towels.

OPERATIVE TECHNIQUE (Fig. 24(a))

The rotation present in most tendons must be taken into account and this may be up to 90°.

subcutaneous elongation of tendo achillis

First incision

This should be in the upper third of the tendo Achillis (tendo calcaneus) about 3(7.5 cm) from its insertion. The posterior two thirds of the upper part of the tendon should be divided. The tenotomy knife should be inserted transversely from the side at the junction of the anterior third and posterior two thirds of the tendon. It should then be twisted through 90° and a cut made backwards until the blade can be felt under the skin.

Second Incision

This should be about 1-2 above the insertion of the tendo Achillis. The medial two-thirds of the tendon should be divided at this site, and also the plantaris tendon which is inserted slightly anterior and medial to the tendo Achillis. Care must be taken not to injure the posterior tibial vessels and nerves. The knife is inserted in a posterior-anterior direction at the junction of the lateral third and the medial two-thirds of the tendon with the blade pointing downwards. It is then twisted through 90°, and a cut made medially until the blade can be felt under the skin. The blade should try to cut the plantaris tendon, and it must be deep enough to do this without injuring the vessels and nerves. The tendon should be under moderate tension while the cuts are being made.

Manipulation

If the equinus cannot be corrected after these two incisions it usually means that not enough of the upper third of the tendon has been divided and a deeper incision should be made. The foot should then be forcibly dorsi-flexed, and in young children with polio more than 30° of dorsi-flexion can be easily obtained.

It is important that more tendon is divided if a good correction is not obtained, otherwise a recurrence of contracture is likely.

In adults, and older children with long-standing polio, a lesser degree of correction may be obtained, and in these patients a second manipulation after two weeks may be necessary. There is usually only slight bleeding, but it is important that all subcutaneous blood clot is squeezed out. No sutures are necessary and a plastic spray and a small dressing are all that are required.

Post-operative care

In children with a stable knee, a well padded below-knee walking plaster should be applied with the foot in at least 30° dorsi-flexion.

Post-operatively the leg is well elevated, and the child can usually be sent home after a day or two.

Young children return to the clinic after three weeks, and older children and adults after six weeks. The plaster is then removed as an outpatient, and a below-knee caliper with backstop fitted. In the case of an unstable knee with no contracture, an above-knee plaster should be applied instead of a below-knee one. The subsequent treatment is identical with that in a patient with a stable knee, except that an above-knee caliper is fitted instead of a below-knee one.

Complete division of tendo Achillis

Occasionally the whole tendo Achillis may be divided accidentally. The vast majority of these patients achieve a good repair within the sheath of the tendon. With rare exceptions, there is no indication for operative repair.

Recurrence of Deformity

It is essential that a child wears a caliper with a backstop after elongation of the tendo Achillis, otherwise some deformity will nearly always recur.

ASSOCIATED FLEXION CONTRACTURES OF HIP AND KNEE

There is often a flexion contracture of the hip and knee associated with an equinus of the ankle. These contractures should be dealt with at the same time as the ankle, and the post-operative treatment is that of the hip and knee contractures.

It is always important to assess the equinus deformity of the ankle with the knee as straight as possible. If this is not done, the equinus of the ankle will appear to be less than it really is, as the gastrocnemei will be relaxed when the knee is flexed. It is important also to foresee the effects on the ankle of straightening a flexed knee. For instance, an ankle with only 10° equinus with a 60° flexion contracture of knee may theoretically go into 70° equinus if the knee is fully straightened. This will occur if the gastrocnemius is entirely responsible for the equinus.

OTHER DEFORMITIES OF THE FOOT AND ANKLE

Although an equinus deformity is by far the commonest and most important of the ankle and foot contractures, other contractures do frequently occur. These are:-

Calcaneus deformity

In this deformity the calf muscles are weak and the dorsiflexors of the foot strong. The only treatment for mild cases is a lace-up boot on the affected side. In more severe cases a below-knee caliper may be required as well with a reversed backstop to prevent dorsiflexion of the foot.

Varus deformity (Fig. 24(b) & (c))

In this deformity the foot is inverted, and there is often associated adduction of the forefoot. This deformity is caused by overaction of the inverters of the foot with weakness of the evertors. Mild degrees of varus are best treated by a below-knee caliper with double irons. A single inside iron and outside T-strap, as classically advocated is not usually kept adjusted well enough to be of use in developing countries.

Severe degrees of varus may warrant manipulation, a soft tissue correction, or a subtaloid triple arthrodesis. It is essential that the deforming tendons be transferred as well. If this is not done, deformities will tend to recur.

Valgus deformity (Fig. 24(d))

This is a very common deformity in polio and is often associated with a tight tendo Achillis. Elongation of the tendo Achillis, followed by a below-knee caliper with backstop, will usually correct most deformities. A more permanent correction may necessitate a transfer of one or both peroneal tendons medially, and also a small bone graft into the subtaloid joint. (Grice operation).

Cavus Deformity (Fig 24(e))

This will sometimes require tenotomy or tendon transfer or even arthrodesis of the toes as illustrated.

Indications for Tendon Transfers and Major Operations

In countries where beds and operating time are in short supply the indications must be very good before major operations on feet and ankle are embarked upon. It is usually not worth doing a major operation on an ankle if a caliper will still be needed to support an unstable knee, unless a boot or clog cannot be worn due to deformity.

Tendon transfers require prolonged physiotherapy post-operatively, and are seldom indicated as isolated procedures. The best operation on the foot is a triple arthrodesis (not done before the age of twelve) when and only when this will enable a caliper to be completely discarded, or where it will enable the patient to wear a boot or clog.

It can be done for either a varus or valgus foot, and is particularly indicated in the weak equinus foot when the knee is stable. Conversely, it is also indicated where it will enable a weak knee to be stabilised and braced back by the resulting stable foot. Transfer of the tibialis anterior tendon laterally may also be indicated if of sufficient power (i.e. over power 4).