Facioscapulohumeral Muscular Dystrophy (FSHD)

FSHD is one of the most common muscular dystrophies, with an estimated prevalence of about 1 in 15,000 (UK FSHD registry). The registry described 518 patients between 2013 and 2015, and 91.7% of them had FSHD1.

For the orthopaedic surgeon the principal problem is scapular winging, and the operation that addresses it is scapulothoracic arthrodesis.

FSHD1. In about 95% of patients the disease follows a contraction of the D4Z4 macrosatellite repeat array on chromosome 4q35. The contraction relaxes the chromatin over the array and allows aberrant expression of the normally silenced DUX4 gene. Inheritance is autosomal dominant, with variable penetrance.

The permissive haplotype. A contraction is pathogenic only on a "permissive" chromosomal background. The permissive (4qA) haplotype carries specific SNPs distal to the last repeat that create a canonical polyadenylation signal for DUX4 transcripts. Polyadenylation stabilises the DUX4 mRNA (Lemmers 2010), and the resulting DUX4 protein is toxic to skeletal muscle: a toxic gain of function.

FSHD2. The rarer form has D4Z4 hypomethylation without contraction and is usually digenic, with an SMCHD1 mutation. It reaches the same endpoint, DUX4 de-repression, and produces the same phenotype.

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The pattern. Weakness descends in a facioscapulohumeral order and is characteristically asymmetric. In the UK registry the face was the commonest site of weakness at onset (59.2%), followed by the shoulder girdle (53.3%), then the distal (22.4%) or proximal (14.8%) lower limb. The sequence runs:

• Face: difficulty whistling, drinking through a straw, or burying the eyelashes on eye closure
• Shoulder girdle and periscapular muscles: scapular winging
• Humeral muscles: biceps and triceps wasting with relative sparing of the forearm, the 'Popeye arm'
• Trunk and abdomen: a positive Beevor's sign, the umbilicus moving upward on neck flexion
• Lower limb: foot drop

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Genetic confirmation. Diagnosis is the clinical pattern confirmed by genetic testing, not by biopsy. For FSHD1 the test must show a contracted D4Z4 array on 4q35 and that it sits on a permissive 4qA haplotype; a contraction on a non-permissive haplotype does not cause disease. FSHD2, which has no contraction to find, needs methylation and SMCHD1 analysis.

Supporting tests place FSHD among the dystrophies but do not make the diagnosis:

• Creatine kinase is normal or only mildly raised, unlike the very high CK of the dystrophinopathies, so a normal CK does not exclude FSHD
• EMG is myopathic
• Muscle biopsy shows a non-specific myopathic picture and is usually unnecessary now that genetic testing is available; it no longer makes the diagnosis, but it excludes the treatable mimics
• Muscle MRI shows the characteristic selective, asymmetric pattern of fatty muscle replacement, and can guide a biopsy if one is ever needed

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The biopsy trap. FSHD muscle frequently contains an inflammatory infiltrate, so a biopsy taken without the clinical pattern in mind is readily reported as an inflammatory myopathy. The patient is then committed to immunosuppression that cannot work and carries real harm. The face is the safeguard: an inflammatory myopathy does not produce the facial weakness, the asymmetry or the family history, so look for lagophthalmos and a transverse smile before accepting a diagnosis of polymyositis in someone whose real problem is a scapular dystrophy.

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The eye. Peripheral retinal telangiectasia occasionally progresses to an exudative Coats-like retinopathy that can threaten vision. Ophthalmology screening matters especially in early-onset, short-array or severe disease.

The ear. Sensorineural hearing loss occurs notably in infantile-onset disease. Audiology screens children so that it does not impair speech and development.

The lungs. Restrictive respiratory involvement occurs in advanced disease, and 7.9% of the UK registry reported respiratory insufficiency: uncommon, but real. Respiratory function is stable in most patients, but a subgroup deteriorates (Teeselink 2022). In 92 genetically confirmed patients re-tested after 5 years, mean FVC fell only modestly (79.0 to 76.7% predicted), driven by 15 patients who lost more than 10% predicted. They were more severely affected at baseline (Ricci score 6 or more) and had more spinal and thorax deformity and faster axial decline.

Spirometry surveillance is warranted, especially in severe or infantile-onset disease, and restrictive involvement is the reason to assess respiratory reserve before scapulothoracic arthrodesis.

The heart. Cardiac involvement and atrial arrhythmia are uncommon, far less so than in the dystrophinopathies or myotonic dystrophy. Assess for arrhythmia at baseline and when symptoms arise, but routine intensive cardiac surveillance is not generally required.

Repeat size and severity. A shorter residual D4Z4 array (fewer repeats) generally means earlier onset and more severe disease. That includes the severe infantile-onset form, which carries the greatest extra-muscular burden and in which the extra-muscular features (Coats retinopathy, hearing loss) and rapid progression are most common. In early-onset, short-array FSHD the extra-muscular disease dominates morbidity and warrants surveillance. Repeat size therefore guides surveillance and counselling, tempered by variable penetrance and somatic mosaicism.

Supportive, multidisciplinary care. There is no cure and no disease-modifying drug in routine use: albuterol showed no functional benefit, and ACE-083 did not reduce winging in a phase II trial. Care is supportive and shared between neurology, genetics, orthopaedics, physiotherapy, respiratory medicine, ophthalmology and audiology.

Exercise is safe and beneficial, and this corrects older advice. Moderate aerobic activity and submaximal strength training improve function without accelerating muscle damage. What genuinely harms these patients is deconditioning and prolonged immobilisation, so post-operative and post-injury plans should minimise time immobilised.

Bracing. Scapular stabiliser braces may help some patients functionally, but they do not change the disease.

Why the shoulder fails. Weakness of the scapular stabilisers, serratus anterior, trapezius and rhomboids, leaves the scapula unanchored to the chest wall. When the deltoid contracts, the scapula rotates and wings instead of acting as a stable base for glenohumeral elevation. Active abduction and flexion are severely limited despite a frequently well-preserved deltoid.

What the operation does. Scapulothoracic arthrodesis (STA) fuses the scapula to the ribs and turns the unstable scapula into a fixed platform, from which the preserved deltoid can elevate the arm. Fixation is by multifilament cables alone, or cables or cerclage wires combined with plates, ideally with autograft. Regardless of the technique, STA reliably improves active elevation and quality of life.

Who should have it. Painful, severe, symptomatic winging with functional loss from failed periscapular stabilisation, a preserved deltoid, and good bone stock at the scapulothoracic interface. It is not for generalised weakness: the operation is intended to stabilise a scapula when the distal limb is still worth stabilising for. Patient selection (preserved deltoid, realistic goals, acceptable respiratory reserve) is the key determinant of a good result, and the operation is evidence-limited, its literature small retrospective series rather than trials.

Testing the deltoid. "Assess the deltoid" is only useful if you know how. The manoeuvre below does at the bedside exactly what the operation does surgically, so the arc achieved with the scapula held is a direct rehearsal of the arc the patient can expect afterwards, which makes it worth more than any imaging in the selection decision.

This is what "preserved deltoid" means in practice, and it is the single most useful part of the assessment. If the deltoid itself is weak the operation will not restore useful elevation, so a patient who fails the test should be counselled away from surgery regardless of how dramatic the winging looks.

What it does not do. It makes no muscle stronger. It converts existing deltoid power into useful motion by removing the wasted scapular excursion, and it does not restore the dystrophic muscle or arrest the disease. It trades motion for stability, at the cost of thoracic mobility and a meaningful perioperative burden.

It caps the arc. Scapulohumeral rhythm normally contributes roughly a third of elevation, and fusion deliberately abolishes the scapulothoracic component. The realistic endpoint is useful function around or a little above shoulder height rather than full overhead elevation: in the best-documented bilateral series (Boileau), active forward elevation improved from 62 to 102 degrees and abduction from 58 to 89.

The gain can erode. FSHD continues to progress, and a deltoid that weakens later will wear away the improvement. That is an argument for operating while deltoid power is good rather than waiting until function is desperate.

What it does well is abolish the painful, prominent, cosmetically distressing winging and restore hand-to-face and hand-to-table function. In the Boileau series the Subjective Shoulder Value rose from 25% to 72%, and every patient said they would recommend the operation.

The respiratory question. The concern that fusing the scapula to the ribs splints the chest wall is theoretical but reasonable, particularly in a disease that itself causes restrictive impairment and when both sides are done. With bilateral, sequentially performed fusions there was no significant change in vital capacity, and in the Eren series pulmonary function in the 19 patients tested was unchanged. Two caveats belong with that reassurance: the bilateral series comprised five patients, far too small to exclude a clinically meaningful effect, and within it the forced vital capacity fell numerically from 86% to 77% of predicted.

In practice, obtain baseline pulmonary function tests, treat poor reserve as a genuine selection issue, stage the two sides rather than doing them together, and plan analgesia and chest physiotherapy that let the patient breathe deeply afterwards.

The shoulder dominates the exam, but it is not the whole of what an orthopaedic surgeon contributes.

Foot drop from tibialis anterior weakness is managed with an ankle-foot orthosis. Tendon transfer is generally inappropriate: the donor is itself dystrophic and will weaken, so a transfer that works initially fails as the disease advances. The same logic rules out tendon transfers around the scapula and sends those patients to fusion instead.

Contractures, particularly of the Achilles tendon, are managed with stretching and orthoses, with surgical release reserved for a contracture that is genuinely blocking function.

The spine. Lumbar hyperlordosis is characteristic and follows abdominal and paraspinal weakness. Scoliosis occurs but is far less prominent than in the dystrophinopathies, and bracing is poorly tolerated where respiratory function is already reduced.

Anaesthesia. FSHD carries no established association with malignant hyperthermia, unlike some other myopathies, so it is not a reason to avoid volatile agents on that basis. Respiratory reserve, positioning and post-operative pulmonary care do require planning.

Complications of arthrodesis. In the largest series (Eren 2020, JBJS Am; 64 shoulders, mean follow-up 71 months) the overall complication rate was 26.6%, and 7 revision procedures were needed:

• Pulmonary (7): 4 pneumothoraces, 2 pleural effusions and 1 major atelectasis, with 5 chest tubes
• Fixation-related (10): 3 rib fractures, 1 brachial plexus palsy, 2 cases of implant irritation, 2 nonunions, 1 delayed union and 1 scapular fracture

In the same series fusion was achieved in all but one shoulder, elevation improved from 60.6 to 123.7 degrees, and qDASH fell from 34.7 to 13.3.

Because the operation involves thoracic dissection and rib fixation, pulmonary complications (pleural effusion, pneumothorax, atelectasis) are common, but they usually resolve spontaneously. Scapular fixation complications relate to the surgeon's learning curve. Meticulous technique, careful positioning of the fusion (around 20-30 degrees of scapular abduction), and good postoperative analgesia reduce these, and because FSHD is a systemic neuromuscular disorder, surgery should always sit within multidisciplinary care with realistic, shared goals.

Prognosis. The dystrophy is usually slowly progressive, and age at onset and residual D4Z4 repeat-array length are the strongest prognostic signals. Most patients remain ambulant (85.6% of the UK registry were ambulant or ambulant with assistance), but a meaningful minority progress to wheelchair use, especially with early onset.