SPINAL MUSCULAR ATROPHY

DAVID J. ABRAHAM, M.D. Resident, Orthopaedic Surgery

J. RICHARD BOWEN, M.D. Chief Department of Orthopaedic Surgery

ALFRED I. DUPONT INSTITUTE

April 16, 1996

CASE HISTORY:

Kg is a 6+6 year old white female evaluated in the orthopaedic clinic for progressive scoliosis, bilateral hip dislocations and diffuse hypotonia with inability to walk.

Past medical history significant for recurrent upper respiratory infections occasionally requiring hospitalization.

Developmental History: 8 pound 6 ounce, full term female with no perinatal events and normal intrauterine movement was developing normally until 6 months of age when parents noticed she stopped moving her legs and lost the ability to roll over.

Pediatric neurologist diagnosed Spinal Muscular Atrophy after reviewing the muscle Biopsy.

Managed with physical therapy and inpatient rehabilitation consisting of intensive physical, occupational and aquatic therapy and the use of long leg braces at age of 2.

Radiographic evaluation at age of 3 showed mild scoliosis and bilateral dislocated hips.

Parents were informed that scoliosis would likely progress and PSF would be needed in the future.

Age 6 scoliosis progressed to 78 degrees and PSF with the unit rod was performed.

DISCUSSION :

A group of disorders characterized by degeneration of the anterior horn cells of the spinal cord and occasionally the neurons of the lower bulbar motor nuclei resulting in muscle weakness and atrophy.

Autosomal recessive disorder that occurs in one in 20,000 live births.

One in 40 to 80 people are carriers of the gene.

Loss of the anterior horn cell is acute event without neurologic progression.

The progression of muscle weakness is a reflection of normal growth that exceeds muscle reserve.

Respiratory function is compromised causing atelectasis and pneumonia and eventually resulting in death .

CLINICAL CLASSIFICATION:

Based on age of onset and functional capacity at time of presentation .

1. Type I: Acute Werdnig Hoffman Disease
• Clinical onset is from birth to 6 months
• Typically have severe involvement with weakness and severe hypotonia
• No head control, will never roll over or sit unassisted
• Usually die secondary to respiratory failure before age 2
2. Type II: Chronic Werdnig Hoffman Disease
• Onset from 6 months to 24 months of age
• Less involved than Type I, will sit, but will never walk
• May live 30 to 40 years
3. Type III: Kugelberg-Welander Disease
• Onset from 2 to 10 years of age
• Usually walk until late childhood or early adolescence, never run
• + Gower sign secondary to proximal muscle weakness with pseudohypertrophy of claves

CLINICAL FEATURES:

• Symmetric limb and trunk weakness with muscle atrophy greater in the lower extremities than the upper extremities; and greater atrophy in the proximal muscle groups than the distal muscle groups.
• Hypotonia and areflexia
• Sensation and intelligence are normal.
• Diffuse muscle involvement involves all muscles except diaphram, sternohyoid, sternothyroid and involuntary muscles of heart, bladder, intestine, and sphincters.

DIAGNOSTIC STUDIES:

• Labs: usually normal
• EMG/NCS: Fibrillation potentials associated with denervation are the best diagnostic signs
• Muscle Biopsy: Loss of fibers and atrophy within normal groups of fiber bundles

No evidence of primary myopathy

TREATMENT:

Orthopaedic concerns involve the treatment of soft tissue contractures of the lower extremities, hip subluxation or dislocation and inevitable spinal deformity.

1. Soft tissue contracture:
• Results from progressive muscle degeneration and replacement with fibrous tissue
• Ambulation preserved by orthoses
• Worsens quickly after pt is confined to wheelchair
2. Hip subluxation/dislocation
• Treatment may preserves sitting balance, pelvic alignment and increase comfort
• Some authors recommend treatment of dislocated hips however the redislocation rate has proven to be significant due to the progressive degeneration of the proximal muscles (8)
• Others recommend symptomatic treatment of dislocated hips ie, adductor tenotomy for contracture
3. Spinal Deformity

• 100% of type II, and most of Type III develop scoliosis with resulting decrease in pulmonary function
• Typically begins in the first decade of life, is progressive and resistant to bracing
• Bracing may slow the progression to delay fusion until adolescence (2)
• Surgery indicated for

1. Curve greater than 40 degrees

2. FVC less than 40 % of normal

• Schwentker (7) reviewed nine patients with SMA treated with PSF and concluded that 8 of 9 lost function but 7 of 9 stated gains in comfort and spinal stability outweighed functional loss
• Aprin and Bowen (1) reviewed 22 patients with SMA who underwent spine fusion and concluded that:

1. Long posterior fusion was the best way to prevent secondary curves above and below the fusion

2. Anterior arthrodesis alone was not sufficient to maintain spinal stability

3. Anterior arthrodesis was associated with significant increase in pulmonary complications

4. Pre and post operative PT were essential to preserve function.

5. Spine arthrodesis reduced the rate of pulmonary deterioration but did not prevent its progression

• Granata (6) reviewed the natural history of spinal deformity in SMA and concluded that scoliosis is inevitable and progressive in nonambulatory patients and rarely becomes significant in ambulatory patients
• Furumasu (5) reviewed 40 pateints after PSF and showed that fusion caused a significant decrease in gross motor funcion and an increase in the use of upper extremity assistance devices
• Brown (3) noted that PSF patients never attain thair preoperative functional levels

Recommendation: Presently we recommend posterior spinal arthrodesis with segmental fixation from T1 to the pelvis and currently use the Unit Rod System.

REFERENCES:

1. Aprin H, Bowen JR, MacEwen GD, Hall JE. Spine arthrodesis in patients with spinal muscular atrophy. J Bone Joint Surg A-64, 1982, 1179.
2. Bowen JR, Forlin E. Spinal muscular atrophy. In: Weinstein SL, ed. The pediatric spine. Principles and practice. New York: Raven Press, 1994:1025.
3. Brown CJ, Zeller JL, Swank SM, it al. Surgical and functional results of spine fusion in spinal muscular atrophy. Spine 1989; 14: 763.
4. Daher YH, Lonstein JE, Winter RB, Bradford DS. Spinal surgery in spinal muscular atrophy. JPO 1985; 5: 391.
5. Furumasu J, Swank SM, Brown JC, et al. Functional activities in spinal muscular atrophy patients after spinal fusion. Spine 1989; 14: 771.
6. Granata C, Merlini L, Magni E, et al. Spinal muscular atrophy. Natural history and orthopaedic treatment of scoliosis. Spine 1989; 14:760.
7. Schwentker EP, Gibson DA. The orthopaedic aspects of spinal muscular atrophy. JBJS 1976; 58, 32.
8. Thompson CE, Larsen LF. Recurrent hip dislocation in immediate spinal atrophy. JPO 1990; 10: 638.