Children with spinal muscular atrophy (SMA) suffer from a number of orthopedic conditions. Scoliosis of the spine is quite common and is usually treated with bracing and/or instrumentation. However patients with SMA also experienced chest deformities that can lead to thoracic insufficiency and compromise pulmonary health. Hip instability is common, as are muscle contractures and bone fractures. Orthopedic surgical interventions may be appropriate in some cases, but the data on the topic is unsettled. Thus, healthcare providers may use expert consensus guidelines to drive clinical care.1 2,3
Due to atrophy of the muscles in the spine and thorax made worse by concomitant scoliosis and rib cage distortion, children with SMA often have significant deformities of the chest that lead to thoracic insufficiency.4,5 The rib cage appears to collapse, akin to an umbrella closing, which is led to the moniker of “parasol rib” deformity.5 While it may seem reasonable to use rib-based or spine-based instrumentation to ameliorate this deformity, these interventions appear to have little benefit and experts in the field do not recommend them.5
The management of hip instability in patients with SMA has evolved. Older recommendations suggested that surgical repair of hip instability should be avoided since repeated subluxation or dislocation after surgery was common.4,6 When hip instability does not cause pain, experts would still caution against performing surgical repair of the hip joint.7 On the other hand, when hip instability causes substantial pain, surgery for unilateral and bilateral hip stabilization using modern techniques should be offered to patients and their families.1
Joint contractures are common in patients with SMA and can cause considerable pain and physical dysfunction. Every effort should be made to prevent and reduce contractures through physical medicine and rehabilitation. Night braces, for example, may be able to slow the progression of contractures, if they are tolerated.8 When conservative measures fail to prevent pain or functional impairment, however, orthopedic surgery should be considered, especially for lower extremity contractures. Tenotomy or lengthening of the sartorius, tensor fascia lata, rectus femoris, iliopsoas, adductors, and knee flexor muscles may help relieve symptoms in patients with severe contractures of hip and knee joints.7,9 Tenotomy or transposition of the tibialis posterior and tenotomy of the flexor digitorum longus or flexor hallucis longus and peroneal tendons may be beneficial. Likewise, achillotenotomy and capsulotomy of the ankle joint can be used judiciously to benefit patients with foot/ankle contractures.9 since long periods of immobilization can spark rapid deterioration of motor function in patients with SMA, postoperative recovery and rehabilitation programs are of particular importance in this patient population.10
Fractures are common in patients with SMA. Congenital fractures may be present in patients with type 0 and type 1 SMA.11 In patients with type 2 SMA and early-onset cases of type 3 SMA, bone fractures may occur early and often.12 The most common place for fracture in type 2 and 3 SMA patients is the femur, specifically supracondylar fractures. Lower leg and ankle fractures are also common. For reasons that are unclear (presumably due to greater mobility than patients with more severe forms of the disease), patients with type 3 SMA, commonly have fractures in the upper extremities.12
The small size, fragility, and demineralization of bones in non-ambulatory SMA patients make osteosynthesis unlikely to be successful.7 Surgical treatment almost certainly leads to postsurgical immobilization which exacerbates the muscular problems that these patients face. As such, conservative treatment with casting is generally the best course of action in treating fractures. The situation is quite different for ambulatory patients with SMA. Due to better bone health and overall function, intramedullary rods or bridging fracture plates can restore bone stability, allow early range of motion, and promote fracture healing in ambulatory SMA patients with long bone fractures.1
1. Mercuri E, Finkel RS, Muntoni F, et al. Diagnosis and Management of Spinal Muscular Atrophy: Part 1: Recommendations for Diagnosis, Rehabilitation, Orthopedic and Nutritional Care. Neuromuscul Disord. 2018;28(2):103-115. doi:10.1016/j.nmd.2017.11.005
2. Finkel RS, Sejersen T, Mercuri E, et al. 218th Enmc International Workshop:: Revisiting the Consensus on Standards of Care in Sma Naarden, the Netherlands, 19–21 February 2016. Neuromuscular Disorders. 2017;27(6):596-605.
3. Wang CH, Finkel RS, Bertini ES, et al. Consensus Statement for Standard of Care in Spinal Muscular Atrophy. Journal of Child Neurology. 2007;22(8):1027-1049. doi:10.1177/0883073807305788
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7. Haaker G, Fujak A. Proximal Spinal Muscular Atrophy: Current Orthopedic Perspective. The Application of Clinical Genetics. 2013;6(11):113-120. doi:10.2147/TACG.S53615
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9. Fujak A, Kopschina C, Gras F, Forst R, Forst J. Contractures of the Lower Extremities in Spinal Muscular Atrophy Type Ii. Descriptive Clinical Study with Retrospective Data Collection. Ortop Traumatol Rehabil. 2011;13(1):27-36.
10. Wang HY, Ju YH, Chen SM, Lo SK, Jong YJ. Joint Range of Motion Limitations in Children and Young Adults with Spinal Muscular Atrophy. Arch Phys Med Rehabil. 2004;85(10):1689-1693.
11. Shanmugarajan S, Swoboda KJ, Iannaccone ST, Ries WL, Maria BL, Reddy SV. Congenital Bone Fractures in Spinal Muscular Atrophy: Functional Role for Smn Protein in Bone Remodeling. Journal of child neurology. 2007;22(8):967-973. doi:10.1177/0883073807305664
12. Fujak A, Kopschina C, Forst R, Gras F, Mueller LA, Forst J. Fractures in Proximal Spinal Muscular Atrophy. Arch Orthop Trauma Surg. 2010;130(6):775-780. doi:10.1007/s00402-010-1096-1