eMedicine Specialties > Orthopedic Surgery > Spine

Spinal Muscle Atrophy

Jose A Herrera-Soto, MD, Assistant Program Director of Pediatric Orthopedic Fellowship, Orlando Regional Healthcare
Alvin H Crawford, MD, FACS, Professor of Pediatrics and Orthopedic Surgery, University of Cincinnati College of Medicine; Director, Division of Pediatric Orthopedic Surgery, Department of Orthopedic Surgery, Cincinnati Children's Hospital Medical Center; Charles T Mehlman, DO, MPH, Director, Musculoskeletal Outcomes Research, Associate Professor, Division of Pediatric Orthopedic Surgery, Cincinnati Children's Hospital Medical Center

Updated: Aug 21, 2008

Introduction

Background

Spinal muscle atrophy (spinal muscular atrophy, SMA) is an autosomal recessive hereditary disease characterized by progressive hypotonia and muscular weakness. The characteristic muscle weakness occurs because of a progressive degeneration of the alpha motor neuron from anterior horn cells in the spinal cord. The weakness is more severe in the proximal musculature than in the distal segments. In certain patients, the motor neurons of cranial nerves (especially the CNV-CNXII) can also be involved. Sensation, which originates from the posterior horn cells of the spinal cord, is spared, as is intelligence. Several muscles are spared, including the diaphragm, the involuntary muscles of the gastrointestinal system, the heart, and the sphincters.^1,2,3,4

In 1890, G. Werdnig described for the first time the classic infantile form of SMA.⁵ Many years later, in 1956, Kugelberg and Welander described the less severe form of SMA.⁶ Werdnig, in 1890,⁵ and J. Hoffman, in 1891,⁷ reported cases of muscular dystrophy occurring in infants that were otherwise similar to cases of muscular dystrophy found in older children and adults (eg, Duchenne muscular dystrophy).

SMA is the most common diagnosis in girls with progressive weakness. It is one of the most common genetic causes of death in children.

Related eMedicine topics:
Spinal Muscular Atrophy (Neurology)
Kugelberg Welander Spinal Muscular Atrophy (Physical Medicine and Rehabilitation)

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Pathophysiology

Spinal muscle atrophy (spinal muscular atrophy, SMA) is caused by a mutation in the survival motor neuron gene. This gene is normally inactive during the fetal period and allows normal apoptosis in the developing fetus. This gene becomes active in the healthy mature fetus to stabilize the neuronal population. In its absence, programmed cell death persists.⁸ The mechanism and timing of abnormal motor neuron death remain unknown.^9,10

Frequency

United States

Incidence of spinal muscle atrophy (spinal muscular atrophy, SMA) is about 1 case in 15,000-20,000 (5-7 per 100,000) live births. The prevalence of persons with the carrier state is 1 in 80.

In North Dakota, the incidence is about 1 case in 6,720 (15 per 100,000) live births, prevalence is 1.5 cases in 10,000, and prevalence of persons with the Werdnig-Hoffman disease carrier state is 1 in 41. SMA appears to be 3-10 times more common in North Dakota than in other areas.¹¹

SMA is the most common degenerative disease of the nervous system in children. It is the second most common disease inherited in an autosomal recessive pattern, after cystic fibrosis, to affect children. It is the leading heritable cause of infant mortality.¹²

International

The incidence of spinal muscle atrophy (spinal muscular atrophy, SMA) in Slovakia is 1 case in 5631 (18 per 100,000) live births (all types).
In Germany, the incidence of Werdnig-Hoffmann disease is 1 case in 10,202 (9 per 100,000) live births.¹³
In Italy, the incidence is 7.8 cases in 100,000 live births (all types).
In Poland, the incidence of Werdnig-Hoffmann disease is 1 case in 19,474 (5 per 100,000) live births.
In England, the incidence is 1 case in 24,100 (4 per 100,000) live births. Prevalence is 1.2 cases per 100,000 population.
The incidence is higher in Central and Eastern Europe than in Western Europe.

Mortality/Morbidity

In spinal muscle atrophy (spinal muscular atrophy, SMA), death occurs because of respiratory compromise. The younger the patient is at onset, the worse the prognosis is. The overall median age at death exceeds 10 years. Intelligence is unaffected by SMA.

Race

The incidence of spinal muscle atrophy (spinal muscular atrophy, SMA) in black Africans is very low.

Sex

Males are more commonly affected with spinal muscle atrophy (spinal muscular atrophy, SMA) than females. The male-to-female ratio is 2:1. The clinical course in males is more severe. Life expectancy has not been demonstrated to be influenced by sex.¹⁴
As the age at onset increases, incidence of SMA in females decreases. With age at onset older then 8 years, females are affected much less frequently. In cases in which the patient is older than 13 years at onset, incidence in females is the exception.

Age

The 3 different types of spinal muscle atrophy (spinal muscular atrophy, SMA) are genetically similar but differ in patient age at presentation and in their clinical courses.

Type I (Werdnig-Hoffmann disease): This acute infantile SMA is usually identified in patients from birth to age 6 months.
Type II: This chronic infantile SMA is diagnosed in infants aged 6-12 months.
Type III (Kugelberg-Welander disease): This type of SMA is diagnosed in children aged 2-15 years.

Clinical

History

Type I: Most mothers report abnormal inactivity of the fetus in the latter stages of pregnancy. The patient with type I spinal muscle atrophy (spinal muscular atrophy, SMA) is unable to roll over or sit. Progressive clinical deterioration occurs. Death usually occurs from respiratory failure and its complications in patients by age 2 years.
Type II: Patients with type II SMA have normal development for the first 4-6 months of life. They may be able to sit independently, but they are never able to walk. They require a wheelchair for locomotion. They have a longer life span than patients with type I SMA. Some patients with type II SMA live into the fifth decade of life.
Type III: In patients with type III SMA, the presenting complaint is difficulty climbing stairs or getting up from the floor (due to hip extensor weakness). The life span is nearly normal.¹⁵

Physical

Physical findings specific for each type of spinal muscle atrophy (spinal muscular atrophy, SMA) are as follows:
- Type I: Newborns with type I SMA are floppy and inactive. They move the extremities little, if at all. The hips are flexed, abducted, and externally rotated. The knees are flexed. Because the distal musculature is usually spared, the fingers and toes move. Infants cannot control or lift the head. Areflexia is universal.
- Type II: Patients with type II SMA have head control, and 75% of these patients can sit independently. Muscular weakness is greater in the lower extremities than the upper extremities. Patellar reflex is absent. The young may demonstrate bicipital and triceps tendon reflexes. Tongue fasciculations are present, as are upper extremity tremors. Scoliosis is universal, and most patients develop hip dislocation, either unilateral or bilateral, when younger than 10 years.
- Type III: These patients walk early in life and maintain their ambulatory capacity into adolescence. Weakness may cause foot drop, and patients have limited endurance. A third of the patients become wheelchair bound as adults (mean age 40 years).
Other physical findings associated with SMA are as follows:
- A long C-shaped thoracolumbar scoliotic curve is present in patients with type II SMA and in half of patients with type III SMA. The curve progresses to a severe and incapacitating deformity if not treated. Thirty percent of patients have kyphotic deformities as well.
- Pseudohypertrophy of the calf is present, which may confound the diagnosis (ie, with Duchenne muscular dystrophy and Becker muscular dystrophy). Bouwsma reported that this finding was associated with elevated serum creatine kinase (CK).¹⁶ This combination was only observed in males; no females in his series had hypertrophy of the calves.¹⁶
- Tongue fasciculations are pathognomonic of SMA (all types), as opposed to all other neuromuscular diseases of infancy. Presence of tongue fasciculations can aid in the diagnosis, as 56% of patients exhibit this symptom.

Causes

Patients with spinal muscle atrophy (spinal muscular atrophy, SMA) have a homozygous deletion of the telomeric SMN1 (survival motor neuron) gene found in arm 5q (bands q11.2-13.3).⁹ This deletion has been demonstrated in up to 98% of patients with SMA. SMN is part of a multiprotein complex required for the biogenesis of small nuclear ribonucleoproteins.^17,18 SMN1 has been linked to pre-mRNA splicing, spliceosome biogenesis, and the nucleolar protein fibrillarin. The absence or dysfunction of SMN is reflected by an enhanced neuronal death. A heterozygous deletion leads to an asymptomatic carrier state.¹⁹

A significant increase in nuclear DNA vulnerability was detected in fetuses with SMA at 12-15 weeks' gestational age. It reflected a decrease in the number of anterior horn neurons. This vulnerability is no longer seen in the rest of the prenatal or postnatal period. Abnormal cell morphology was seen only in the postnatal period.²⁰

Differential Diagnoses

Muscular Dystrophy

Workup

Laboratory Studies

Aldolase and serum CK findings are within reference ranges in patients with spinal muscle atrophy (spinal muscular atrophy, SMA), as opposed to findings in patients with Duchenne muscular dystrophy and Becker muscular dystrophy. In later-onset SMA, these muscle enzymes may be slightly elevated.

Imaging Studies

Pelvis anteroposterior (AP) and lateral views: Most patients with type II spinal muscle atrophy (spinal muscular atrophy, SMA) develop hip dislocations. The dislocations are only temporarily symptomatic and do not influence function in these patients because they are nonambulatory.
Complete spine and scoliosis series: All patients with type II SMA and most patients with type III SMA develop a long C-shaped scoliotic curve (see Image 5, Image 6, Image 7, Image 8, Image 9, Image 10, Image 11, Image 12, Image 13).

Other Tests

Electromyograms and nerve conduction studies: Electromyogram findings in patients with spinal muscle atrophy (spinal muscular atrophy, SMA) are characteristic of a neuropathic disorder; they reveal fibrillation potentials, denervation, and increased amplitude. However, nerve conduction velocity test results are normal.
Prenatal DNA testing: Prenatal DNA analysis is available to diagnose the deletion of arm 5q.

Procedures

Incisional biopsy: Muscle biopsies reveal a uniform smaller diameter of all fibers in patients with spinal muscle atrophy (spinal muscular atrophy, SMA). This contrasts with biopsy findings for other muscular dystrophies, which consist of degenerating muscle with variable muscle fiber sizes. Biopsies in patients with hypotonic cerebral palsy reveal normal muscle fibers.

Histologic Findings

Two subtypes of spinal muscle atrophy (spinal muscular atrophy, SMA) deserve special mention regarding their typical histologic appearance. Werdnig-Hoffmann disease is typically diagnosed in patients from birth to age 6 months. Its histologic pattern is usually one of extremely small and reasonably uniform small muscle fibers (see Image 1, Image 2). In the Kugelberg-Welander type of SMA (usually diagnosed in patients aged 2-15 y), the same tendency toward small muscle fiber diameter is seen but with much less uniformity (see Image 3, Image 4). Substantial variation, with intermixing of larger and smaller muscle fibers, may be observed.

In both forms of the disease, substantial increases in muscular connective tissue lead to both characteristic histologic findings (see Image 2, Image 3) and clinical findings such as increased muscle firmness. Centrally migrated or otherwise internalized nuclei are considered pathologic if they are present in more than about 3% of muscle fibers. Such nuclear findings are common in a variety of muscle diseases, including SMA.

(Also see Procedures, above).

Treatment

Medical Care

Patients with type I spinal muscle atrophy (spinal muscular atrophy, SMA) require little, if any, involvement of an orthopedist due to their short life span. Splinting is used for fractures. For patients with type II and type III SMA, physical therapy may be employed for contractures. See Surgical Care below for an in-depth discussion of treatment of contractures.²²

Surgical Care

Posterior spinal fusion and segmental instrumentation: The most common orthopedic problem is scoliosis, which is often severe. It is universal in nonambulatory patients. Their curve progression is about 8° per year, despite brace treatment. Half of ambulatory patients develop scoliosis as well, but at a slower rate of progression.
- Posterior spinal fusion with segmental instrumentation is indicated in young patients whose curve cannot be controlled with a brace and in patients older than 10 years with curves greater than 40° with forced vital capacities 40% above normal levels. The entire thoracic and lumbar spine down to the pelvis should be fused in order to obtain a balanced trunk and a leveled pelvis. Concomitant anterior spinal fusion to prevent crankshaft phenomenon is usually avoided, as the risk of potential problems of anterior spinal surgery in a patient with SMA outweighs the benefits.
- In ambulatory patients, spinal surgery that excludes the pelvis is preferred. A compensatory lumbar lordosis and pelvic motion has been observed to compensate for the proximal motor weakness in these patients. The ambulatory capacity of some of these patients may be lost following surgery. Surgery should be delayed as long as medically possible; remember that curve progression is slower in patients with type III spinal muscle atrophy (spinal muscular atrophy, SMA), and these patients present later in life. However, when necessary, surgery should be performed while the patient is still ambulatory. This is in contrast to the preferred timing for surgery in patients with Duchenne muscular dystrophy.
Physical therapy or surgery for contractures: Joint flexion contractures of the hips and knees are associated with nonambulatory status. Surgical releases are performed, as the rate of recurrence is extremely high, especially in sitting patients. Equinus is occasionally present. Ambulatory patients rarely have equinus or cavovarus deformities. Surgical releases are rarely needed for patients with type II or III SMA, as the loss of function is due to weakness and not contractures. Some form of tendon transfer may be needed in patients with type III SMA to correct foot or ankle functional defects.
Pelvic stabilization procedures: Hip subluxations or dislocations are due to proximal musculature weakness that leads to coxa valga and loss of femoral head coverage. Half of ambulatory patients have hip pathology. Unilateral dislocation in nonambulatory patients invariably leads to pelvic obliquity (which may be manifested in uneven sitting pressure sores). Hip reconstruction may be successful, but recurrence of the problem even after surgical stabilization is a concern. Therefore, surgical correction is not indicated in most patients, and treatment remains controversial.

Consultations

Pneumologist: A preoperative pneumology consultation for pulmonary function tests (PFTs) is necessary. Consensus is clear that curve progression correlates with deterioration of pulmonary function. However, no clear-cut consensus exists that surgery improves or halts the pulmonary deterioration in spinal muscle atrophy (spinal muscular atrophy, SMA). It is clear, though, that in order to avoid pulmonary infections or prolonged postsurgical intubations, aggressive preoperative pulmonary care must be offered.
Physical and occupational therapists: Physical therapy may be employed for joint contracture prevention or stretching. Occupational therapy may be employed for adaptive equipment for activities of daily living (ADLs).
Geneticist: A geneticist may be consulted for DNA evaluation of the patient and parents for counseling purposes.
Orthotics specialist: An orthotics consultation may be necessary for splinting and spine bracing (soft, custom-molded thoracolumbosacral orthosis [TLSO]) for young children with flexible curves of 20-40°.^23,24

Diet

History of nutritional intake, nutritional needs, and associated medical conditions with a thorough physical examination, anthropometric measures, body composition, and biochemical markers are important elements of the assessment in spinal muscle atrophy (spinal muscular atrophy, SMA).²⁵ Intervention may include increase or decrease of energy intake. For example, dysphagia may be treated with position changes, volume changes, or thickening of liquids. A percutaneous endoscopic gastrostomy was found to be safe with minimal risks in almost all situations.

Activity

Physical therapy should be instituted for gentle motion exercises to prevent joint contractures. Physical and occupational therapy may be beneficial for maintenance of strength and endurance, independence in self-care, and educational, social, psychological, and vocational activities.²⁶

Medication

No drug treatment is available for spinal muscle atrophy (spinal muscular atrophy, SMA). Some interest has arisen in the use of inhibitors of g -aminobutyric acid synthesis, with promising results.

Follow-up

Further Inpatient Care

To avoid pulmonary infections or prolonged postsurgical intubations, aggressive preoperative pulmonary care must be provided in patients with spinal muscle atrophy (spinal muscular atrophy, SMA).

Further Outpatient Care

Pediatric orthopedic surgeon evaluation: Patients with spinal muscle atrophy (spinal muscular atrophy, SMA) must be monitored periodically to evaluate their nutritional status and their spine and hips, as well as to evaluate for contracture development.
Physical therapy: Physical therapy is useful for joint contracture prevention and stretching.
Occupational therapy: Occupational therapy is useful for adaptive equipment for activities of daily living (ADLs).

Transfer

In cases of pulmonary compromise in patients with spinal muscle atrophy (spinal muscular atrophy, SMA), transfer to the pediatric pneumology service for stabilization and treatment of complications should be considered.

Deterrence/Prevention

See Patient Education.

Complications

The most common medical complications associated with spinal muscle atrophy (spinal muscular atrophy, SMA) are recurrent respiratory system infections.
One of the drawbacks to posterior spinal fusion in patients with SMA is that these patients have decreased ability to perform ADLs. The now rigid and straight spine creates several difficulties. Independent feeding and hygiene are impaired, as the patient can no longer bring the hands to the face secondary to the proximal upper extremity weakness. This possibility must be discussed with the family and patient prior to surgery.

Prognosis

As a general rule, the younger the patient at disease onset, the worse the prognosis is. Patients with type I spinal muscle atrophy (spinal muscular atrophy, SMA) usually die by age 2 years. Patients with type II SMA have a greater expected life span than patients with type I SMA. Some patients with type II SMA live into the fifth decade of life. Patients with type III SMA have nearly normal life expectancy.
Death occurs as a result of respiratory compromise. The life span of affected individuals has significantly increased with the use of intermittent positive pressure ventilation with or without a tracheostomy.

Patient Education

Prenatal diagnosis in the first trimester and proper genetic counseling are possible with DNA analysis. This enables more accurate carrier detection. Not all parents of children with spinal muscle atrophy (spinal muscular atrophy, SMA) are obligate carriers.²⁷
Carrier testing is important for reproductive decision-making. Three percent of cases are sporadic.

Miscellaneous

Medicolegal Pitfalls

Failure to provide genetic counseling
Failure to correctly diagnose spinal muscle atrophy (spinal muscular atrophy, SMA)
Delayed diagnosis
Poor counseling of parents and patients regarding possible complications prior to surgical treatment (These patients lose function following spinal stabilization. Their ability to ambulate may be hindered. The possibility of recurrence or worsening of the hip dislocation must be emphasized. Risk of recurrent deformity is present even with foot and ankle procedures.)

Special Concerns

No curative treatment is currently known for spinal muscle atrophy (spinal muscular atrophy, SMA).
The survival rate is poor among young patients.

Multimedia

Media file 1: Spinal muscle atrophy, Werdnig-Hoffman disease. Small muscle fibers within separate muscle fascicles.

Media file 2: Spinal muscle atrophy, Werdnig-Hoffman disease. Marked variation in muscle fiber size as well as a relative increase in associated connective tissue.

Media file 3: Spinal muscle atrophy, Kugelberg-Welander disease. Marked variation in muscle fiber size along with increased perimysial connective tissue.

Media file 4: Spinal muscle atrophy, Kugelberg-Welander disease. Muscle fiber variation with some demonstrating internal nuclei.

Media file 5: Spinal muscle atrophy. At age 4 years, this boy's chest radiograph already reveals the presence of significant 32° left thoracic scoliosis. His diagnosis is type I spinal muscle atrophy (Werdnig-Hoffmann disease). This radiograph captures the lumbar curvature incompletely.

Media file 6: Spinal muscle atrophy. By age 6 years, the child's curve is starting to decompensate. Note the development of a right-sided truncal shift. He now has a 40° thoracic curve and a 60° lumbar curvature.

Media file 7: Spinal muscle atrophy. Spine anteroposterior view. The spinal curvature is progressing. The lumbar curve now is 70° and the thoracic curve is 35°. Note that one can now clearly see that the right hip is dislocated. Also note the marked pelvic obliquity in this patient.

Media file 8: Spinal muscle atrophy. By age 9 years, this patient with type I spinal muscle atrophy now has a thoracic curve of 60° and a lumbar curve of 110°. Note that the patient has a tracheostomy tube and a nasogastric tube as well.

Media file 9: Spinal muscle atrophy. Immediate postoperative anteroposterior radiograph of the patient at age 9 years. The thoracic curve is now at 18° and the lumbar curve is 35°, which represents more than 67% curvature correction.

Media file 10: Spinal muscle atrophy. Immediate postoperative lateral view with good sagittal balance.

Media file 11: Spinal muscle atrophy. Follow-up radiographs in the patient at age 13 years reveal some spinal decompensation. Note the so-called coat hanger appearance of the ribs in the patient's dysplastic right hemithorax.

Media file 12: Spinal muscle atrophy. Anteroposterior radiograph of the pelvis demonstrating right hip dislocation.

Media file 13: Spinal muscle atrophy. Lauenstein lateral view of the hips on the patient with spinal muscle atrophy type I. Note the near universal pelvic dysmorphology (eg, widened obturator foramina) in addition to the dislocated right hip.

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Keywords

spinal muscle atrophy, spinal muscular atrophy, SMA, muscle atrophy, muscular atrophy, Werdnig-Hoffmann disease, Werdnig-Hoffmann, Werdnig Hoffmann, Kugelberg-Welander disease, Kugelberg-Welander, Kugelberg Welander, hypotonia, muscle weakness, spinal fusion, spinal muscular atrophies of childhood, spinal muscular atrophy of childhood, spinal cord disease, spinal infantile muscular atrophy, spinal infantile muscle atrophy

Contributor Information and Disclosures

Author

Jose A Herrera-Soto, MD, Assistant Program Director of Pediatric Orthopedic Fellowship, Orlando Regional Healthcare
Jose A Herrera-Soto, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, North American Spine Society, Pediatric Orthopaedic Society of North America, and Scoliosis Research Society
Disclosure: Nothing to disclose.

Coauthor(s)

Alvin H Crawford, MD, FACS, Professor of Pediatrics and Orthopedic Surgery, University of Cincinnati College of Medicine; Director, Division of Pediatric Orthopedic Surgery, Department of Orthopedic Surgery, Cincinnati Children's Hospital Medical Center
Alvin H Crawford, MD, FACS is a member of the following medical societies: Ohio State Medical Association and Scoliosis Research Society
Disclosure: Nothing to disclose.

Charles T Mehlman, DO, MPH, Director, Musculoskeletal Outcomes Research, Associate Professor, Division of Pediatric Orthopedic Surgery, Cincinnati Children's Hospital Medical Center
Charles T Mehlman, DO, MPH is a member of the following medical societies: American Academy of Pediatrics, American Fracture Association, American Medical Association, American Orthopaedic Foot and Ankle Society, American Osteopathic Association, Arthroscopy Association of North America, North American Spine Society, Ohio State Medical Association, Pediatric Orthopaedic Society of North America, and Scoliosis Research Society
Disclosure: Nothing to disclose.

Medical Editor

James F Kellam, MD, Vice-Chair, Department of Orthopedic Surgery, Director of Orthopedic Trauma and Education, Carolinas Medical Center
James F Kellam, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, Orthopaedic Trauma Association, and Royal College of Physicians and Surgeons of Canada
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

William O Shaffer, BS, MD, Professor, Vice-Chairman and Residency Program Director, Department of Orthopedic Surgery, University of Kentucky at Lexington
William O Shaffer, BS, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Orthopaedic Association, International Society for the Study of the Lumbar Spine, Kentucky Medical Association, Kentucky Orthopaedic Society, North American Spine Society, Southern Medical Association, and Southern Orthopaedic Association
Disclosure: DePuySpine 1997-2007 (not presently) Royalty Consulting; DePuySpine 2002-2007 (closed) Grant/research funds SacroPelvic Instrumentation Biomechanical Study; DePuyBiologics 2005-2008 (closed) Grant/research funds Healos study just closed

CME Editor

Dinesh Patel, MD, FACS, Associate Clinical Professor of Orthopedic Surgery, Harvard Medical School; Chief of Arthroscopic Surgery, Department of Orthopedic Surgery, Massachusetts General Hospital
Dinesh Patel, MD, FACS is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Association of Physicians of Indian Origin, American College of International Physicians, and American College of Surgeons
Disclosure: Nothing to disclose.

Chief Editor

Mary Ann E Keenan, MD, Professor, Vice Chair for Graduate Medical Education, Department of Orthopedic Surgery, University of Pennsylvania School of Medicine; Chief of Neuro-Orthopedics Program, Department of Orthopedic Surgery, Hospital of the University of Pennsylvania
Mary Ann E Keenan, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Orthopaedic Surgeons, American Orthopaedic Association, American Orthopaedic Foot and Ankle Society, American Society for Surgery of the Hand, and Orthopaedic Rehabilitation Association
Disclosure: Nothing to disclose.

Further Reading