Orphanet Journal of Rare Diseases | Longitudinal Study of Joint Range of Motion in Children with Spinal Muscular Atrophy Receiving Disease-Modifying Treatment

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This article presents the first systematic assessment of joint range of motion (ROM) trends in children aged 0-8 years with spinal muscular atrophy (SMA) undergoing disease-modifying treatment (DMT). It reveals a continuous decline in knee extension ROM, while elbow and wrist joint ROM remain stable. The study emphasizes the importance of regular monitoring of knee ROM and provides practical recommendations for clinical rehabilitation management.

 

Literature Overview
This article, titled 'Course of joint range of motion in children with spinal muscular atrophy receiving disease-modifying treatment,' published in the Orphanet Journal of Rare Diseases, reviews and summarizes the longitudinal changes in joint ROM among children with SMA who receive disease-modifying treatment (DMT). It reports a mean annual decrease of 3° in knee extension ROM over a 3-year follow-up period, while elbow and wrist joint ROM remain stable. The study also documents the use of rehabilitation interventions, including orthoses, stretching exercises, and standers, offering clinical insights for monitoring and intervention.

Background Knowledge
Spinal Muscular Atrophy (SMA) is an autosomal recessive disorder caused by mutations in the SMN1 gene, with disease severity correlated with SMN2 copy number. Untreated SMA patients often experience reduced joint ROM, leading to contractures that impair daily functions such as standing, grasping, and feeding. With the increasing use of DMTs, including Nusinersen, Risdiplam, and Onasemnogene abeparvovec, patients' survival and motor function have significantly improved, yet changes in joint ROM have not been systematically assessed. This study fills that gap by presenting the first systematic evaluation of joint ROM progression in a large prospective cohort, analyzing knee, elbow, and wrist joints across different age groups, and incorporating rehabilitation intervention data to inform clinical management. Challenges include accurately measuring joint ROM in young children and controlling for variability in treatment and intervention protocols. The study addresses these by implementing a standardized operating procedure (SOP) and regular training, enhancing measurement reliability and offering methodological guidance for future studies.

 

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Study Methods and Experiments
The study employed a prospective observational cohort design, enrolling 39 children with SMA who initiated DMT within 18 months of symptom onset and were followed for 3 years. ROM measurements included knee extension, elbow extension, and wrist deviation, taken bilaterally using a standardized goniometer and averaged. The researchers developed a standardized operating procedure (SOP) to ensure consistency and conducted training every 6 months. Data were analyzed using linear mixed models (LMM) with age as the time variable, allowing for non-linear trends to evaluate changes in joint ROM over time.

Key Findings and Insights

• Knee extension ROM decreased by approximately 3° annually over the 3-year follow-up, indicating progressive contracture risk even with DMT.
• Elbow and wrist joint ROM remained relatively stable, suggesting DMT may better preserve ROM in these joints compared to the knee.
• Some children (8 cases) showed improvement in knee extension ROM after initial restriction (<0°), highlighting significant inter-individual variability.
• Stander use increased only after age 2, while knee ROM decline occurred primarily before that, suggesting intervention timing may lag behind clinical needs.

Research Implications and Future Directions
This study is the first to systematically document joint ROM changes in a prospective cohort of SMA children receiving DMT, providing critical evidence for clinical rehabilitation. Future research should investigate the impact of different treatment regimens on joint ROM and consider additional joints (e.g., ankle) and structural changes such as fat infiltration. The study recommends standardized ROM assessments of knee extension every 6 months to enable early detection and timely intervention.

 

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Conclusion
This study systematically assessed joint ROM changes in children with SMA receiving DMT and found progressive decline in knee extension ROM, while elbow and wrist joints remained stable. These findings suggest that, although DMTs significantly improve motor function, knee contractures still pose a risk requiring enhanced monitoring and rehabilitation. The study also highlights the importance of early prevention, particularly within the first year of life, to prevent ROM decline. In addition, the mismatch between intervention timing and clinical progression indicates a need to optimize rehabilitation strategies for more precise joint protection. This article provides new evidence for clinical rehabilitation practices and may help improve long-term outcomes.

 

I L B Oude Lansink, J W G Gorter, W L van der Pol, B Bartels, and A Beelen. Course of joint range of motion in children with spinal muscular atrophy receiving disease-modifying treatment. Orphanet Journal of Rare Diseases.