Neuromuscular orthopaedics

In neuromuscular conditions such as polio, spina bifida, cerebral palsy and the muscular dystrophies, imbalance of muscles and the effects of gravity can result in deformity. Orthopaedic surgery has a valuable role in properly selected patients. However, it is important to remember that surgery is only an incident in the continuing care of these patients. The support of parents, other medical specialists, therapists, orthotists and teachers is essential for good results. The care of these children should be delivered in a co-ordinated way, usually through a paediatrician or general practitioner.

  Poliomyelitis

This is usually due to infection by one of three types of poliomyelitis virus, although other members of the enterovirus group can cause clinically and pathologically indistinguishable disease. Effective vaccination has been present for almost 40 years but the disease has not been eliminated from certain parts of the world. The virus enters the oropharyngeal route, passing via the alimentary lymph nodes to enter the circulation with an incubation period of 6—20 days. One or 2 per cent of patients develop neurological disease as the virus affects the anterior horn cells, particularly in the cervical and lumbar enlargements (as well as parts of the brain including the medulla). Weakness in a muscle is in proportion to the number of motor units destroyed. Up to 60 per cent of units have to be damaged before weakness is clinically detectable. Muscles innervated by the cervical and lumbar enlargements are most commonly affected and paralysis is twice as common in the lower than in the upper limb. Orthopaedic surgery is not indicated in the acute or convalescent stages although careful physiotherapy in the convalescent stage is helpful to work individual muscles to maximum capacity without letting normally working muscles become hypertrophied. Paretic muscles must not be over-exercised and contractures in paralysed muscles must be stretched out before exercising them.

In the chronic stage which can be as much as 2 years after onset of the disease, orthopaedic surgery may be indicated. Joint deformities will largely be dictated by the muscle groups affected, although certain patterns of deformity, such as flexion contracture of the knee and hip and calcaneus of the hindfoot, are common. Patients with a weak quadriceps and a flexion contracture may develop ‘knee—hand gait’ in which the hand supports the knee which cannot be locked into extension. In severe cases patients have to crawl and the pattern adopted is a guide to the muscle groups affected. When all muscles acting on a joint are paralysed it will become flail and unstable. It is surprising that such joints rarely show degenerative changes. When the paraspinal muscles are affected a scoliosis may develop. A disused lower limb grows shorter than normal and leg-length discrepancy is common.

If surgery is to be undertaken in poliomyelitis, it should be preceded by a full assessment, including muscle charting. If orthoses are being considered, it is important to be certain these will be appropriate in the patient’s home environment.

 The surgical options in polio include:

tendon transfer to augment or replace weak muscles;

release of contractures by soft-tissue release and/or corrective osteotomy. The knee—hand gait can often be abolished by extension osteotomy of the distal femur which allows the knee to lock in extension. However, in some cases a contracture may help the patient and the surgeon must be circumspect about releasing it (Fig. 28.24);

stabilisation of flail joints by arthrodesis;

spinal fusion and instrumentation for scoliosis;

leg equalisation surgery.

Cerebral palsy

This is classically a nonprogressive injury to the developing brain that usually occurs in the neonatal period. There are several potential causes such as anoxia, intracerebral haemorrhage and infection. There is a strong association with prematurity. In such cases it is debatable whether the neurological damage is due to a naturally impaired brain or caused during delivery. Severe neurological impairment may also be part of syndromic or genetic conditions. Finally there may not be any obvious cause for a child’s neurological condition. On rare occasions such a child presenting as ‘cerebral palsy’ may respond to dopamine treatment.

Cerebral palsy is often not apparent at birth and may only be suspected as an infant fails to reach milestones or shows evidence of altered muscle tone. For all of these reasons it is important to try and accurately assess the cause and scale of neurological impairment, be it cerebral palsy or otherwise. The skills and armamentarium of the paediatric neurologist are usually required for this.

In cerebral palsy there are various patterns of disability depending on the type and distribution of the motor disturbance (Table 28.5). It is also helpful to grade the condition according to function which should include intellectual ability and whether there is epilepsy (Table 28.6).

The commonest type of disturbance is spasticity which tends to affect flexors rather than extensors. Orthopaedic surgery can only have limited goals in cerebral palsy as it deals with peripheral effects rather than the central problem. Moreover, the orthopaedic surgeon is usually part of a large team involved in the care of the child.

The aim of surgery should be to improve function and facilitate the care of these patients by correcting or prevent­ing deformity. Regular physiotherapy to stretch contractures (Fig. 28.25a and b) and supervise the use of orthoses is essential (Fig. 28.26). Realistic goals must be set. It has to be explained that results can be unpredictable and disappointing especially in dystonic cases. The immediate postoperative care may be hampered by difficulties with nursing and skin problems due to pressure from casts. Rehabilitation is usually prolonged.

The goals and scope of treatment are usually determined by the anatomical distribution and functional ability as follows.

Hemiplegia

The children walk independently and the hip is not at risk. The common problems in the lower limb are equinus or internal rotation. Equinus usually requires physiotherapy, an ankle/foot orthoses (AFO) and frequently elongation of the tendo achilles (ETA). Severe internal rotation can be due to femoral torsion and an external rotation osteotomy may be justified.

The upper limb in hemiplegia is often badly affected. Surgical options to improve function significantly are sadly few but some help can also be given to improve the cosmetic appearance of the hand.

  Diplegia

  These children can usually walk but in an awkward and difficult fashion (Fig. 28.27). The hips are unlikely to be at risk of displacement. The aim of treatment is to achieve a more energy-efficient gait.

The common deformities are equino valgus, knee flexion and adduction, internal rotation and flexion at the hip. There may also be rotational deformities of the femur and tibia. Surgery must be carefully planned and gait analysis can be helpful. Whereas operations can be undertaken sequentially, combined multilevel surgery is sometimes preferable. A typical combination would be femoral rotation osteotomies followed by release of adductors, hamstrings and tendo achilles. The rehabilitation after such surgery is prolonged and demanding. It is a year before the final benefits are likely to be felt.

Total body involvement

The children are usually very impaired mentally as well as physically. However, in some, whereas the physical disability may be severe the child can be intellectually bright. There are usually difficulties with incontinence, feeding, nutrition and epilepsy.

The orthopaedic goals in such cases can be summarised as follows.

    Spine. Scoliosis is likely and should be anticipated. Early curves can be treated by postural exercises, seating supports and braces. More severe curves require surgical stabilisation to prevent them progressing to unmanageable deformities.

  Hips. These are at risk of dislocation because of adductor and psoas spasm. The joints should be monitored clinically and radiologically. Preventive measures include exercises, abduction splints and seating adaptation. If the hip is displacing early surgical options include adductor release of femoral osteotomy (Fig 28.28 and Fig 28.29). In late dislocations which are painful and pose severe nursing or seating problems, the combination of open reduction, femoral osteotomy and acetabular augmentation may be necessary.

Seating. Proper seating is important and is a major factor in maintaining posture and minimising deformity (Fig. 28.30). If hips, knees or ankles pose problems in achieving good seating and transfers usually because of flexion deformities, then soft tissue releases will have to be considered.

Communication skills. The child should be in the school best suited to his or her particular needs and potential. Computers and electronics can help parents and teachers in this regard.

  Spina bifida

Unfortunately, most children with spina bifida have profound lower limb weakness and sensory loss (Fig. 28.31). They regularly need multidisciplinary help from paediatricians, orthopaedic surgeons, neurosurgeons, therapists and orthotists.

However, not all spina bifida produces severe disability (Fig. 28.32). Occult forms may cause subtle changes in neurology as a child grows. If a lower limb deformity, weakness or urinary symptoms develop it is advisable to seek neurosurgical help as, with growth, there may be tethering of nerve roots or other pathology such as a syrinx which can be amenable to surgery.

In severe cases the extent of disability depends on the level of the lesion. In the majority there is some upper motor neuron involvement as well as the classical lower motor neuron lesion. Spasticity may therefore complicate the motor and sensory loss.

The lack of protective sensation means that minor cuts and abrasions may pass unnoticed and lead to infection. Once this involves bone it is extremely difficult to eradicate. Patients and carets must therefore adopt a daily routine of foot inspection and must always try to protect skin. Surgery to the foot in spina bifida is largely to achieve a plantigrade foot which can be fitted with an orthosis and moulded footwear to avoid areas of pressure.

Hip dislocation is common in spina bifida. Most surgeons do not operate for dislocation because of the relatively poor results and prefer to advise it to be left mobile and painless.

Flexion contractures at hip or knee can be treated by soft-tissue release and/or osteotomy. External rotation of the tibia may cause the medial side of the foot to drag along the ground. This can be helped by internal rotation osteotomy of the tibia. Spina deformity is common in higher level lesions and usually takes the form of a kyphosis. This can be controlled with a brace but spinal fusion and instrumentation may be necessary (see Chapter 20).

Muscular dystrophy

The details of the many types of muscular dystrophy which vary in severity and age at presentation are beyond the scope of this book. However, a short discussion of a severe and classical type, namely Duchenne dystrophy, exemplifies the diagnostic and therapeutic approaches, which may be applicable throughout the spectrum of the muscle dystrophies.

Duchenne dystrophy is inherited as a sex-linked condition and only boys are affected. They are not usually diagnosed until after walking, which is delayed. They may present as toe walkers or show difficulties with mobility. For example, when getting up from the floor they use their hands on their thighs to push themselves up into the erect position. They often have thick calves (pseudohypertrophy) and the Achilles tendons are tight. The clinical features plus a raised creatine phosphokinase (CPK) confirm the diagnosis.

The condition is sadly progressive. The children usually come off their feet in late childhood or early teens and die in late adolescence or early adult life. At present there is no cure but gene therapy holds some hope for the future.

Treatment is multidisciplinary and aims to keep the children as mobile as possible and prevent deformity. Immo­bilisation after any surgery must be for as short a time as possible. Walking can be prolonged by percutaneous lengthening of the Achilles tendons and orthoses.

The spine is particularly liable to deformity. This may be lessened by bracing and seating. However, it regularly pro­gresses beyond these measures whereupon surgical stabilisanon is worthwhile, otherwise the deformity may become very severe and the management difficult and unpleasant for the child during his or her final years. The timing of spinal surgery is important. It should be done before the vital capacity has deteriorated to a dangerous level.

Torticollis (wryneck)

This is frequently related to neurological or muscular conditions. The causes of the abnormal neck posture can be summarised as:

cervical — congenital and acquired conditions of the cervical spine, painful or otherwise;

pharyngeal — usually infection, e.g. tonsillitis;

ocular — squints or visual field defects;

intracranial — posterior fossa tumours;

muscular — contracture of the sternomastoid;

habitual — no obvious organic cause.

The classical type is due to contracture of either or both anatomical heads of the sternomastoid muscle (Fig. 28.33). The cause of contracture is usually unknown. It can follow a sternomastoid tumour, which is probably a traumatic lesion sustained during delivery and usually resolves without long-term effects (Fig. 28.34).

Treatment is usually by surgical release of the contracture followed by physiotherapy and exercises to re-educate the child back to normal posture and movement.