The Childrens Hospital,

Temple Street,

Dublin 1.

Central Remedial Clinic,

Vernon Avenue,

Clontarf,

Dublin 3.

P. Connolly, J. Noel, P. Fleming, D. Collins, D. Mc Cormack.

Duchenne's muscular dystrophy is the most common form of muscular dystrophy. It is an X-linked recessive disorder, and thus seen only in males (except for rare cases associated with Turner syndrome). The disorder is characterized pathophysiologically by the absence of dystrophin, a cell membrane protein representing approximately 0.01 % of skeletal muscle protein. The distribution of dystrophin within skeletal, smooth and cardiac muscle cells correlates with the features of Duchenne's muscular dystrophy. The disorder has a high mutation rate and a positive family history is present in 65% of cases. The incidence of Duchenne's muscular dystrophy is approximately 1 in 3500 live male births with about 30% of involved children getting the disease from a new mutation.(1)

Patients with this disorder most often present to the primary-care physician or orthopaedic surgeon between the ages of 3 and 5 years, although it may be earlier. The usual parental complaint is that the child cannot run or keep up with his peers, or maybe is frequently tripping or falling. There may be a family history of the disorder. Careful questioning will usually reveal that the affected child was delayed in reaching motor milestones, that he never managed stairs very well and rarely if ever has been able to keep up with his peers in gross motor activity.

On examination one observes a male child with weakness of the proximal muscle groups. This progressive weakness descends symmetrically in both lower extremities. The gluteus maximus, gluteus medius and quadriceps muscles are normally the first muscles noticed to be affected. A valuable clinical sign is the Gower sign. The patient is placed prone or in a sitting position and asked to rise, the patient will use his hands to grasp the lower legs and force the knees into extension. The patient then walks his hands up the lower extremities to compensate for quadriceps and gluteal muscle weakness. Calf pseudohypertrophy caused by fat accumulation may also be present. Contractures of the upper or lower extremities are not typically found on presentation at this age, but they are sure to develop with time.

As the disorder affects all types of muscle fibres, patients may have serious cardiac involvement. Life threatening dysrhythmia or heart failure develops in about 10 %. A static encephalopathy with some degree of mental retardation is not uncommon in this disease(2). Death from pulmonary failure and occasionally from cardiac failure usually occurs in the second or third decades of life.

From an orthopaedic perspective the course of Duchenne's muscular dystrophy may be divided into three phases: early childhood, later childhood or preadolescence, and adolescence. Each phase has itís own orthopaedic problems that need to be addressed.

The most important aspect of this phase is the early recognition of the presence of the disorder. As mentioned previously, the orthopaedic surgeon is often the first specialist to be consulted. The presenting complaint may be delayed walking, the development of toe walking in a child who has previously been walking normally, or most commonly because the patient has difficulty in running or similar gross motor tasks and is unable to keep up with his peers. It is vital that the orthopaedic surgeon is alert to the possible diagnosis of Duchenne's muscular dystrophy and arrange appropriate further investigations and referral to a neurologist or paediatrician.

At early presentation, the affected child will typically have no lower extremity contractures, but careful physical examination may reveal proximal muscle weakness. The role of the orthopaedic surgeon at this stage is limited. The main priority is to be alert to the diagnosis and perform a good muscle biopsy when requested. At the earliest sign of the development of contractures, the patientís carers should be instructed in proper stretching techniques, this will help delay the development of contractures that will interfere with continued ambulation.

Muscle contractures are common in patients with Duchenne's muscular dystrophy. The main reasons for their development are asymmetric muscle weakness and also because of the presenced of areas of fibrosis within affected muscles. Certain patterns of muscle contracture develop quite consistently. Equinus, or more commonly equinovarus deformity develops in the feet and ankles, due to the contracture of the gastroesoleus and posterior tibial muscles, this is exacerbated by weakness of the tibialis anterior muscle and peroneal muscles which are affected earlier by the disease process. Gentle passive stretching of the contracted muscle groups should be carried out on a daily basis once the earliest sign of contracture has manifested itself. Another modality to be considered is the use of night time splinting of the feet in plastic ankle foot orthoses (AFOs) in a neutral position. However, the efficacy of these modalities in preventing or stemming the rate of progression of this deformity is not clearly established.

Contractures also commonly occur at the hip and knee. The most significant contributor to contractures of these joints is fibrosis and contracture of the tensor fascia lata muscle and of the fascia lata itself. Contracture of this structure leads to a quiet typical flexion and external rotation contracture of the hip, combined with a knee flexion contracture. These deformities are accentuated by weakness of the proximal muscle groups particularly the gluteus maximus and quadriceps muscles. Carers should also be instructed on stretching techniques for these. Gentle passive stretching exercises to extend, adduct and internally rotate the hip, and extend the knee should begin at the first sign of a contracture developing. Knee immobilizers may be used at night if early-morning knee flexion stiffness or pain are problems for patients.

A mild equinous contracture at the ankle is often fairly well tolerated by the ambulatory patient with Duchenne's muscular dystrophy. This type of contracture produces an external extension moment at the knee during stance. When the knee is stable in full extension, this moment compensates for quadriceps weakness and in this sense is at least somewhat beneficial (fig 1).

Aggressive therapy or surgery to correct a mild pure ankle equinus contracture in the ambulatory is usually not warranted and can even be detrimental. However, when the equinus contracture is combined with a varus deformity, uneven weight-bearing at the foot occurs, the foot and ankle are unstable, and the beneficial effect of a passive extension moment at the knee in this situation is not realized.

While a mild equinus contracture at the ankle may be well tolerated, any flexion contractures of the hip and knee are not. Neither the hip nor the knee is stable in the partially flexed position during stance or when walking.

This position places the centre of gravity anterior to the hip and posterior to the knee (Fig 2), causing further flexion of these joints unless counterbalanced by gluteus maximus and quadriceps contraction.

Unfortunately, because these muscle groups are among the earliest and most severely affected, the child is unable to compensate for the deformities and will rapidly lose ambulation ability as a consequence of hip and knee flexion contractures. To appreciate the nature of this deformity, try standing up on your toes with your knees bent even slightly. You will feel a burning sensation in your quadriceps muscle within a few minutes, if not seconds! Factor in the fact that Duchenne muscular dystrophy patients have an underlying quadriceps weakness compounding the problem of trying to stand and the detrimental nature of this deformity on standing and walking is readily appreciated.

Upper limb contracture deformities are also seen in Duchenne's, most commonly contractures causing shoulder adduction, elbow flexion and occasionally flexion of the digits may develop. However, these deformities rarely impede the functional status of the upper limb. The primary problem affecting upper extremity function is the loss of muscle strength. Once again, the proximal musculature is first to be affected. One most commonly finds weakness of the deltoid, triceps and biceps producing loss of active shoulder abduction and elbow motion.

The main features occurring during this phase are:

Increasing contractures in the lower extremities.

Decreasing muscle strength in the musculature particularly in the lower extremity.

These factors will ultimately result in the child loosing the ability to walk. The first changes in functional status are usually decreased exercise tolerance and an increased frequency of falling episodes. As mentioned previously, weakness of the quadriceps must be compensated for by passive knee extension which produces an external moment. This is usually accomplished by the presence of a mild equinus contracture at the ankle. However, if the child stubs his toes or otherwise tries to bear weight with the knee flexed, he is unable to compensate by quadriceps contraction and falls owing to collapsing of the knee.

The first modality to be used in addition to stretching exercises is the application of bilateral long-leg moulded plastic orthoses (knee-ankle-foot orthoses, or KAF0s) to provide knee stability to compensate for increasing quadriceps weakness. Several basic principles must be appreciated for successful application of bracing.

1. The lower-limb deformities must not be so severe as to prevent successful fitting of orthoses. In general, 5 or 10 degrees of equinus contracture at the ankle and 15 to 20 degrees of knee flexion contracture can be accommodated by the orthotist fitting these children. Some children have minimal problems with contractures at the time when decreased exercise tolerance and failing episodes have made bracing necessary. These children simply require the fitting of proper braces by an experienced orthotist. More frequently however, the affected child may have more severe flexion contractures of the knee, or equinovarus ankle contractures thereby preventing comfortable and effective fitting of KAFOs. These children should be considered for soft-tissue surgery before brace fitting (see below).

2. As Duchennes also affects the upper limb, upper extremity weakness, specifically of shoulder adductors and elbow extensors preclude the use of upper extremity walking aids such as walkers or crutches. Therefore, the child himself must be well motivated to continue to walk with the aid of KAF0s because they are bulky, hot and result in a very laboured gait.

3. Braces should be sturdy but lightweight and are usually made from lightweight moulded plastic. The knee joint should be lockable in the upright position, but unlockable to allow the child to sit comfortably with the knees flexed. Hinged ankle joints are generally not helpful because the child requires a fixed ankle to maintain the knee in as straight a position as possible. We generally prescribe long leg braces with polypropylene thigh cuffs and fixed ankle-foot components, and drop-lock knee joints. These orthoses allow some ischial weight bearing to occur.

Very often children with Duchenne's muscular dystrophy are not braceable without preliminary surgical soft-tissue releases to relieve contractures (3). Typically, one observes an equinovarus deformity of the foot, a knee flexion contracture, while the hip is flexed and externally rotated. These contractures can be corrected or at least improved with soft tissue procedures such as lengthening of the fascia lata at the hip and knee, with or without hamstring lengthening. Lengthening of the tendo- achilles, and transfer of the posterior tibial tendon to the dorsum of the foot helps to correct the equinovarus deformity and also helps prevent recurrence due to the unopposed pull of the posterior tibial tendon. Postoperatively, the patient is immobilized in long leg casts and begins ambulating in these casts as soon as tolerated. This is usually within 24 to 48 hours postoperatively. The physiotherapist should institute a program of standing for example, in a standing box or prone stander, this should be followed by encouraging the patient to walk walking as much as tolerated. As stated previously, the patient will not be able to use crutches due to upper limb weakness. A walker may be tried, or alternatively the child may be allowed to walk independently without any upper extremity aid. The physiotherapist should provide standby assistance to the child, holding onto a belt around the waist during the early phase of the postoperative rehabilitation. Approximately three to four weeks after surgery the casts are removed and are replaced with long leg braces described previously. The child is encouraged to continue walking.

It is vital to discuss openly with the family and patient the nature of any surgical procedure, and also of the expected outcome. This surgical approach when properly timed and performed in a motivated patient may extend ambulation for 2 to 3 years on average (4). However, it is important to emphasise that this gain is temporary and that the loss of independent ambulation is still inevitable. The post operative course may be difficult due to the combination of postoperative pain, the need for bracing and the inability of the child to support himself with upper extremity aids. It is essential that the patient himself and not just the caretakers are strongly motivated to walk under these conditions. The timing of surgery is important. Any operative procedures and the subsequent need for post operative casting will at least temporarily aggravate weakness, so it is generally wise to defer surgery until the child has little independent ambulation. However, surgery should not be delayed for more than a few weeks after independent ambulation is lost because rehabilitation from this level of deterioration is very difficult, if not impossible. When all these considerations are taken in mind, some families and patients wisely choose not to proceed through this stage of trying to prolong ambulation. During this stage of the disease process, it is reasonable for the child to have both braces for independent ambulation and transfers, and a standard wheelchair for travelling longer distances. Inevitably, the child becomes more and more dependent on the wheelchair for mobility and loses the ability to even assist with transfers, with or without braces.

Standard wheelchairs are adequate initially for most patients because they are easier for the family to manage and allow the patient to continue to use his upper extremities to some extent. Low-profile, Quickie, or similar-type wheelchairs are not usually suitable for patients with Duchenne's muscular dystrophy because they lack trunk support. With increasing weakness and full-time use of a wheelchair, motorised chairs are generally more suitable and practical for the patient, and they allow them relative independence in the operation of the chair. Patients with Duchenne's muscular dystrophy who are in a wheelchair full time will typically slump to one side, with or without the development of scoliosis, and they require some support of the trunk with a moulded back or adjustable supports. Modifying the wheelchair back to force an erect sitting posture will not significantly influence the development or rate of progression of scoliosis, so support should be provided to the extent necessary to enable the child to sit comfortably.

Adolescence (Age 10 to 15 Years)

Once the patient has lost independent ambulation and has become a full time user of a wheelchair, joint contractures tend to progress rapidly despite a program of passive stretching exercises. Fortunately, the hip and knee flexion contractures do not impede sitting and present little problem to the child or his caretakers while he is in a wheelchair. However, care need to be taken in positioning the legs comfortably in bed so as to avoid pressure sores developing. Equinovarus deformity of the feet also tends to be progressive and can prevent the child from wearing normal shoes or placing his feet on the foot plates of a wheelchair. In such cases, lengthening of the Tendo-Achilles with posterior tibial tendon transfer and postoperative bracing in a polypropylene ankle foot orthosis (AFO) can be performed solely to allow the child to wear normal shoes and sit comfortably. The strictly cosmetic nature of this procedure must be understood by all the parties involved, but the motivated child can be very appreciative of this improvement in their appearance and improved ability to sit.

The most significant deformity to develop, almost exclusively in the nonambulatory child, is scoliosis. Scoliosis may be apparent before the cessation of walking but is usually minor and non-progressive at this stage. The incidence of scoliosis after loss of ambulation increases to nearly 100%, (5,6) with only the occasional child escaping this deformity. Once a curvature has progressed beyond 20-30 degrees, continued progression is certain (7). Wheelchair modifications and spinal braces are ineffective in appreciatively altering the natural history of this deformity, so they should be used only to improve the childís sitting comfort (8)

The most common curve patterns are thoracolumbar curves associated with a kyphosis i.e. a kyphoscoliosis. This usually leads to progressive pelvic obliquity. The primary significance of the development of this deformity is increasing difficulty sitting because of the loss of truncal balance over the pelvis. The impact the spinal deformity has on deteriorating pulmonary function is somewhat controversial, Kurz and colleagues (9) observed a 4% decrease in percentage of functional vital capacity (FVC) for each year of age, or each 10 degrees of scoliosis, and that it stabilised at about 25% until death. Whether or not correction of the curvature allows for any improvement in respiratory function is also controversial. Some studies suggest that longevity is not increased by posterior spinal fusion (10), whereas others appear to indicate that the rate of pulmonary function deterioration is ameliorated by this procedure(11). Successful spinal fusion however, definitely improves the quality of remaining life, and prevents progression of the spinal deformity

As already mentioned, progression of the deformity is inevitable after the curve has exceeded 20-30 degrees and there will be an associated deterioration of cardiac and pulmonary function, most spinal surgeons therefore recommend posterior spinal fusion once this threshold has been reached. Generally at this stage, pulmonary and cardiac function are still relatively good, and the child is better able to tolerate the stress of this significant surgery than he will be at a later stage when the deformity has progressed. Careful preoperative evaluation including pulmonary function tests and cardiology consultations are mandatory before surgery. Most patients are about 12 to 14 years old when they are candidates for surgery. While posterior spinal fusion may be successfully carried out in the presence of greater deformity or at later ages, the surgery is technically more difficult, and more residual deformity is expected postoperatively. Pulmonary function deterioration in the older child will make postoperative respiratory management more difficult.

Controversy also exists as to the level to which the spine needs to be fused. Although the standard recommendation has been to perform posterior spinal fusion with instrumentation from the upper thoracic spine (T2) to the pelvis, some recent studies have suggested that fusion to the lower lumbar spine (L5) will produce satisfactory results (12). Fusion to the lower lumbar spine is technically easier to perform with fewer instrumentation failures, but a potential argument against this procedure is that it may allow for progression of the deformity between the lower end of the fusion and the pelvis. Fusing to the L5 level leaves some mobility at the L5/S1 segment which may aid in seating.

Posterior spinal fusion is a major procedure with many significant complications. These complications include superficial and deep wound infection; pseudarthrosis of the fusion mass, which may result in pain, progression of the deformity, and implant failure. Surgery may cause neurological injury potentially resulting in loss of sensation and bowel and bladder control. Furthermore, because of the cardiopulmonary compromise of these patients, they are more susceptible to postoperative pneumonia, prolonged respirator dependence, and death. Significant complication rates of as high as 30% have been reported in some studies.

In addition to these significant complications, posterior spinal fusion presents a number of other practical considerations. The affected child will sit much more erect, resulting in the face being a long way from the tray table. Horizontal arm rests or elevated traytables may be required to allow the child to continue to feed himself independently. Prolonged back and buttocks pain may also be very problematic to the family and child because of the new sitting position and loss of spinal flexibility, this may last up to 6 months postoperatively.

Despite all these daunting considerations, most children will be well served by prompt and effective fusion of the spine to prevent relentless progression of the curvature and its attendant difficulties of back pain and inability to sit.

Finally, while this article has concentrated on the orthopaedic management of the child with Duchenne's muscular dystrophy, it must be remembered that the treatment of a child with this disorder requires a multidisciplinary approach, involving the childís family, primary care physician, occupational and physical therapist, as well as a child psycholoist.

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