Patients with progressive neuromuscular diseases like Spinal Muscular Atrophy (SMA) have extremity weakness that can predispose to contractures, defined as “a lack of full passive range of motion due to joint, muscle, or soft tissue limitations.”1 The etiology of contractures in SMA is multifactorial and includes muscle fiber loss, fatty infiltration of muscle, imbalances of agonist and antagonist muscles’ relative strengths, and static positioning.1,2
Reduced passive range of motion (ROM) at joints (the clinical evidence of contracture) is a common physical examination finding in patients with SMA types 2 and 3.3 In one study, the authors noted 22% of patients with SMA type 2 had decreased ROM > 20 degrees at the elbows and ankles, 44% in the wrists, 38% in the hips, and 50% at the knees.4 The same publication reported that 15% of patients with SMA type 3 had decreased ROM > 20 degrees at their wrists.4 Decreased ROM in the hip, knee, and ankle joints appears early in SMA type 2 and progress with age.5 Lower limb contractures are less common in ambulatory patients with SMA type 3, but when present in any type of SMA, are seen most often at the knee, hips, and ankles, in order from most to least common sites.1 Significant weight gain during puberty is a risk factor for new or worsening contractures.3
Contractures limit function and can be painful for patients with SMA types 2 and 3.2,6 The consensus of experts in SMA is that prevention of contractures using conservative management is a priority.2 SMA experts advocate that patients with SMA who are unable to sit should use orthoses in the upper limbs, knee orthoses, and hand splints daily.2 Patients with SMA who are unable to sit should have stretching and ROM exercises at least 3-5 times per week.2 Patients with SMA who can sit unassisted should utilize orthoses in the upper and lower limbs to encourage function and maintain ROM.2 Sitting patients should have ROM exercises and stretching 5-7 times per week in the highest risk joints (hip, knee, ankle and wrist) and ensure joint segment alignment during treatments.2 Non-ambulatory patients should have standing exercises 60 minutes daily with a goal of 5-7 times per week.2 Experts in SMA recommend that ambulatory patients pursue exercise to maintain ROM with a goal of 30 minutes of daily aerobic exercise.2
When contractures of the upper or lower extremities are painful or impeding function despite appropriate rehabilitation, experts in SMA recommend surgical consultation.2 Upper limb contractures require surgical intervention less often than lower limb contractures.1
References
1. Skalsky AJ, McDonald CM. Prevention and management of limb contractures in neuromuscular diseases. Phys Med Rehabil Clin N Am. Aug 2012;23(3):675-687.
2. 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. Feb 2018;28(2):103-115.
3. Mercuri E, Finkel R, Montes J, et al. Patterns of disease progression in type 2 and 3 SMA: Implications for clinical trials. Neuromuscul Disord. Feb 2016;26(2):126-131.
4. Carter GT, Abresch RT, Fowler WM, Jr., et al. Profiles of neuromuscular diseases. Spinal muscular atrophy. Am J Phys Med Rehabil. Sep-Oct 1995;74(5 Suppl):S150-159.
5. Fujak A, Kopschina C, Gras F, et al. Contractures of the lower extremities in spinal muscular atrophy type II. Descriptive clinical study with retrospective data collection. Ortop Traumatol Rehabil. Jan-Feb 2011;13(1):27-36.
6. Salazar R, Montes J, Dunaway Young S, et al. Quantitative Evaluation of Lower Extremity Joint Contractures in Spinal Muscular Atrophy: Implications for Motor Function. Pediatr Phys Ther. Jul 2018;30(3):209-215.