An account of NSAA score in relation to age is in Figure 1. The slope is reported with a break in the line at 7 years of age determined by minimum Akaike information criterion. Prior to 7 years of age, the general trend shows improvement as measured by the NSAA slope as 3.09 points per year, SE 0.25, P < .0001. After 7 years of age, the data decline in NSAA slope −1.86 points per year, SE 0.11, P < .0001. Our cohort is consistent with previously publish data on changes in function in boys with DMD as measures by NSAA.12–14
Ankle dorsiflexion declines as ambulatory individuals with DMD get older (Figure 2). Observed average LR ankle dorsiflexion range of motion was between 32.5 and 25 degrees for participants who could walk. Progression of ankle range of motion has a trend line: slope −1.43, standard error (SE) 0.08, and P < .0001.
Figure 3 graphs the relationship between NSAA scores and ankle dorsiflexion range of motion. According to Mazzone et al,12 , 14 participants with an NSAA score of 22 or greater have a reduced risk of losing walking within 2 years. The graph has a low number of observations with NSAA score of greater than or equal to 22 and less than 0 degree of dorsiflexion range of motion.
NSAA scores were dependent on average ankle dorsiflexion range of motion. The progression of ankle range of motion in individuals with DMD is graphed with, slope −0.23, SE 0.023, and P < .0001 (Figure 3). The NSAA score declined with an increase in plantarflexion contracture. Summary of data in relation to performance-based cutoff values of NSAA score 22 and dorsiflexion range of motion 0 or more is shown in Table 2 and Figure 3. Gross motor performance as measured by NSAA and 6-minute walk test has improved for individuals with DMD until 7 years of age, which is further supported by analysis of NSAA performance in this cohort (Figure 1).14 , 15 When NSAA data for participants younger than 7 years are removed, the decline is more severe, slope −0.36, SE 0.02, and P <.0001. This shows a trend of decreased performance of 0.36 points on the NSAA for every degree of ankle dorsiflexion lost.
The effect of ankle range of motion accounting for participant age produced the following regression model:
NSAA score = 27.1 + 0.26 × LR − 0.68 × Age + 0.05 × LR × Age
In this model, Age = age in decimal years and LR = average of left and right ankle dorsiflexion range of motion. Using this model, a 9-year-old with 10 degrees of ankle dorsiflexion would have a predicted NSAA of 28 (28.1) while that same 9-year-old with 0 degrees ankle dorsiflexion range of motion would have a predicted NSAA of 21 (20.9).
Summary statistics for a subgroup of participants in which loss of walking was confirmed are shown in Table 3. The summary statistics are from the visit prior to confirmed loss of walking, although exact date of loss was not available in the records.
The data demonstrated that a decline in the dorsiflexion range of motion for individuals with DMD was correlated with a decline in function as measured by NSAA. The regression model can help PTs understand how plantarflexion contractures progress as well as the correlation with function. The results of the study offer insight and preliminary quantitative parameters for PTs to help anticipate contracture progression and justify implementation of interventions to address this such as orthotics, serial casting, surgical intervention, increased intensity of home stretching program, and initiation of supported standing programs.
Main et al16 review supplemental intervention for contracture management such as serial casting and surgical correction and discuss considerations for choosing appropriate interventions. A reasonable prediction of contracture progression could help ensure individuals receive supplemental interventions at optimal times, allowing them to use these measures before their contracture becomes too great to benefit from these interventions. It also provides additional information to the child's family, as they seek to understand the progression of contractures and the importance of their role in managing contractures as a part of their home program.
Understanding and predicting the effect of contractures on function can provide insight regarding timing of equipment needs. Decline in function and ultimately loss of walking are currently primary drivers for clinical recommendations regarding equipment procurement such as the stander or wheeled mobility device. Understanding the rate of disease progression can improve anticipatory care and timing of equipment and intervention recommendation prior to loss of functional mobility and standing. Literature supports the use of standing devices to positively affect bone mineral density, slow progression of scoliosis, improve lung function, and help maintain lower extremity range of motion.17 , 18 Recommended doses for children with neuromuscular dysfunction is 60 to 90 minutes per day for effects on bone mineral density and 45 to 60 minutes per day for range of motion.17 , 18
A study of tolerability of supported standing in boys with DMD identified ankle plantarflexion contracture as a possible limiting factor in tolerance for duration and position of supported standing.19 Obtaining a stander can take several months, during which time further loss of range of motion, function, and reduced tolerance to supported standing may occur. Understanding the progression of plantarflexion contractures may be useful to inform clinical decision-making regarding timing of device procurement and implementation of supported standing program to improve tolerance and optimize benefits.
Current care guidelines recommend receiving a comprehensive multidisciplinary evaluation and standardized assessment at least every 6 months as well as individualized ongoing physical therapy. Improvements in management of DMD provide an opportunity to prolong mobility and participation, but consistent monitoring of contractures, equipment, and orthotic needs is vital to optimize care and outcomes.
Despite evidence to support the necessity of close monitoring to enhance outcomes, many individuals with DMD are seen at lower-than-recommended frequency both in multidisciplinary clinics and by local PTs. Many factors may influence a child and family's ability to attend recommended care, such as access to services, health literacy, level of acceptance, and financial hardships. The updated care considerations state, “Assessment and anticipatory management must be provided across all domains of the international Classification of Functioning, Disability and Health (ICF), from diagnosis onwards, to minimize contractures, deformity, loss of function, compromised skin integrity, pain, and compromised cardiorespiratory status.”5 , 6 The ability to anticipate needs is critical when considering care for people with a progressive disease especially for those whose health care outcomes may be further complicated by decreased access or adherence to recommendations.
Due to the retrospective nature of the study, the authors could not control for variation in medical or physical therapy intervention. All individuals at this center received standard education at initial evaluation including activity recommendations, risk of loss of range of motion, orthotic use, and importance of home stretching program. Standard recommendations for preservation of range of motion at this center are custom solid ankle foot orthotics set at a comfortable end range worn 8 hours per day (typically overnight), passive ankle stretching once per day for a total of 90 seconds, and positional and self-stretching as the child is able. It is also recommended that the individual see a local PT at least every 3 to 4 months to monitor range of motion and coordinate ongoing needs with primary neuromuscular team. At late walking stage, stander use is recommended; however, initiation is limited depending on equipment availability and participant tolerance. The effect of these recommended interventions has not fully been studied. Prospective analysis controlling for these factors could provide additional information on the efficacy of these interventions on maintaining range of motion and function.
Steroids have become the standard of care for individuals with muscular dystrophy due to the documented effect of glucocorticosteroids on function in people with DMD and potential to prolong ambulation.20–22 Steroid use can vary with regard to the type of steroid, time of initiation, and dosage. Due to the retrospective nature of the study, complete steroid history of each participant was not available. The following steroid regimen guidelines were used at this center to titrate to participants' responses and side effects in line with guideline recommendations: (1) children may be started on intermittent dosing regimen of 10 days on/10 days off to allow for normal height growth while receiving the motor benefits of steroid therapy depending on the severity of motor dysfunction, (2) optimal deflazacort dose is 0.9 mg/kg per day—maximum dose 36 mg per day, (3) optimal prednisone dose is 0.75 mg/kg per day, maximum dose is 30 mg per day.
All measurements were obtained by PTs trained in neuromuscular evaluation; however, with functional testing and range-of-motion measurements, some inter- and intrarater reliability error is expected. With a progressive diagnosis of DMD, a study visit window of 6 to 14 months between appointments provides opportunity for changes in mobility and function during that period. Decline in performance may be accelerated as an individual nears loss of walking. Depending on where the decline falls in the window between visits, some meaningful information may be missed by the care providers. In addition, events such as a fall or fracture can lead to sudden loss of walking prior to when it might otherwise be expected to occur. There is variability in the number of visits per subject due to the nature of the data set. Despite the effect of these limitations, the authors believe that the robust sample size and consistency of measurement provides valuable data from which to discuss the management of ankle contractures in for people with DMD.
The results from this study document plantarflexion contracture progression and functional mobility decline for a cohort of people with DMD. Clinicians can use this information to assist in anticipating the progression of plantarflexion contractures and changes in function in people with DMD and make timely decisions regarding intervention and equipment needs. With continued improvements in disease-modifying therapies, clinicians will benefit from information to assist in the understanding of disease progression, as it relates to contractures and functional mobility, to provide more focused anticipatory and preventative care. A multicenter prospective study, controlling for adherence to care recommendations and closer monitoring of participants, could provide further validation of the result in the current study while improving the ability to predict the rate of contracture progression and functional decline.
1. Bushby K, Finkel R, Birnkrant DJ, et al Diagnosis and management of Duchenne muscular dystrophy
, part 1: diagnosis, and pharmacological and psychosocial management. Lancet Neurol. 2010;9(1):77–93. doi:10.1016/S1474-4422(09)70271-6.
2. Birnkrant DJ, Bushby K, Bann CM, et al Diagnosis and management of Duchenne muscular dystrophy
, part 1: diagnosis, and neuromuscular, rehabilitation, endocrine, and gastrointestinal and nutritional management. Lancet Neurol. 2018;17(3):251–267. doi:10.1016/S1474-4422(18)30024-3.
3. Bushby K, Finkel R, Birnkrant DJ, et al Diagnosis and management of Duchenne muscular dystrophy
, part 2: implementation of multidisciplinary care. Lancet Neurol. 2010;9(2):177–189. doi:10.1016/S1474-4422(09)70272-8.
4. Mercuri E, Muntoni F. Muscular dystrophies. Lancet. 2013;381(9869):845–860. doi:10.1016/S0140-6736(12)61897-2.
5. Birnkrant DJ, Bushby K, Bann CM, et al Diagnosis and management of Duchenne muscular dystrophy
, part 2: respiratory, cardiac, bone health, and orthopaedic management. Lancet Neurol. 2018;17(4):347–361. doi:10.1016/S1474-4422(18)30025-5.
6. World Health Organization. The ICF: An Overview. Geneva, Switzerland: World Health Organization; 2010:1–10.
7. Lue YJ, Chen SS, Lu YM. Quality of life of participants with Duchenne muscular dystrophy
: from adolescence to young men. Disabil Rehabil. 2017;39(14)1408–1413. doi:10.1080/09638288.2016.1196398.
8. Bakker JPJ, De Groot IJM, Beelen A, Lankhorst GJ. Predictive factors of cessation of ambulation in participants with Duchenne muscular dystrophy
. Am J Phys Med Rehabil. 2002;81(12):906–912. doi:10.1097/01.PHM.0000034954.48339.F5.
9. Gaudreault N, Gravel D, Nadeau S. Evaluation of plantar flexion contracture
contribution during the gait of children with Duchenne muscular dystrophy
. J Electromyogr Kinesiol. 2009;19(3):e180–e186. doi:10.1016/j.jelekin.2007.09.004.
11. Mazzone ES, Messina S, Vasco G, et al Reliability of the North Star Ambulatory Assessment
in a multicentric setting. Neuromuscul Disord. 2009;19(7):458–461. doi:10.1016/j.nmd.2009.06.368.
12. Mazzone ES, Pane M, Sormani MP, et al 24 month longitudinal data in ambulant boys with Duchenne muscular dystrophy
. PLoS One. 2013;8(1):e52512. doi:10.1371/journal.pone.0052512.
13. Ricotti V, Ridout DA, Pane M, et al The NorthStar Ambulatory Assessment
in Duchenne muscular dystrophy
: considerations for the design of clinical trials. J Neurol Neurosurg Psychiatry. 2016;87(2):149–155. doi:10.1136/jnnp-2014-309405.
14. Mazzone E, Vasco G, Sormani MP, et al Functional changes in Duche-nne muscular dystrophy
: a 12-month longitudinal cohort study. Neurol-ogy. 2011;77(3):250–256. doi:10.1212/WNL.0b013e318225ab2e.
15. Mazzone E, Martinelli D, Berardinelli A, et al North Star Ambulatory Assessment
, 6-minute walk test and timed items in ambulant boys with Duchenne muscular dystrophy
. Neuromuscul Disord. 2010;20(11):712–716. doi:10.1016/j.nmd.2010.06.014.
16. Main M, Mercuri E, Haliloglu G, Baker R, Kinali M, Muntoni F. Serial casting of the ankles in Duchenne muscular dystrophy
: can it be an alternative to surgery? Neuromuscul Disord. 2007;17(3):227–230. doi:10.1016/j.nmd.2006.12.002.
17. Paleg GS, Smith BA, Glickman LB. Systematic review and evidence-based clinical recommendations for dosing of pediatric supported standing programs. Pediatr Phys Ther. 2013;25(3):232–247. doi:10.1097/PEP.0b013e318299d5e7.
18. Galasko CS, Williamson JB, Delaney CM. Lung function in Duchenne muscular dystrophy
. Eur Spree J. 1995;4(5):263–267.
19. Townsend EL, Bibeau C, Holmes TM. Supported standing in boys with Duchenne muscular dystrophy
. Pediatr Phys Ther. 2016;28(3):320–329. doi:10.1097/PEP.0000000000000251.
20. Houde S, Filiatrault M, Fournier A, et al Deflazacort use in Duchenne muscular dystrophy
: an 8-year follow-up. Pediatr Neurol. 2008;38(3):200–206. doi:10.1016/j.pediatrneurol.2007.11.001.
21. Moxley RT III, Pandya S, Ciafaloni E, Fox DJ, Campbell K. Change in natural history of Duchenne muscular dystrophy
with long-term corticosteroid treatment: implications for management. J Child Neurol. 2010;25(9):1116–1129. doi:10.1177/0883073810371004.
22. Angelini C. The role of corticosteroids in muscular dystrophya critical appraisal. Muscle Nerve. 2007;36(4):424–435. doi:10.1002/mus.20812.
Keywords:Copyright © 2019 Academy of Pediatric Physical Therapy of the American Physical Therapy Association
ambulatory assessment; contracture; DMD; Duchenne muscular dystrophy; gastrocnemius; muscular dystrophy; North Star heel cord; NSAA; range of motion; ROM