Research Horizons


Identifying a Common Contracture Phenotype for BPBI and CP

Orthopaedic Surgery | Top Scientific Achievement
2023 Research Discoveries (A) Microendoscopic probe consisting of two 20-guage needles inserted into biceps muscle while mounted on a handheld microscope (B) allows visualization of sarcomeres in real time as depicted from the unaffected and affected muscles in a subject with BPBI (C,D, respectively) and a subject with CP (E,F, respectively).

While brachial plexus birth injuries (BPBI) and cerebral palsy (CP) are distinct conditions that cause specific neurological challenges, the phenotype defining muscle contractures for both conditions are characterized by reduced functional muscle length and strength.  

A study led by first author Sia Nikolaou and corresponding author Roger Cornwall, MD, suggests this commonality is present, which challenges existing hypotheses that contractures are caused by a relative excess of muscle strength.  

With a lack of understanding of the physiology of these contractures, there are no curative treatments for BPBI or CP contractures. This study compared muscle phenotypes for BPBI and CP contractures to test if they were linked to deficiencies in muscle length. The team conducted elbow flexion strength testing in 10 human subjects over 6 years of age with either BPBI or CP. Researchers measured peak torque and impulse along with sarcomere length in each subject’s bilateral biceps brachii muscles using needle microendoscopy.   

The team found peak torque and impulse were significantly lower on the affected side compared to the unaffected side, and that sarcomere length was longer in affected muscles compared to unaffected. The longer sarcomeres indicate overstretched muscles, consistent with a deficit in muscle length. These results were similar between subjects with BPBI and CP. These findings suggest that contracture treatments should focus on lengthening affected muscles rather than weakening them. 

This study helped to challenge prevailing beliefs that muscle contractures in patients with BPBI or CP were caused by a relative excess in muscle strength,” Cornwall says. Given that current treatments often focus on reducing strength in impacted muscles, this research can lead to beneficial shifts in how we understand and treat contractures in these patients.” 

The next steps for this line of research include investigating the broader concept of myobrevopathy, or disorders of short muscles, and the mechanisms surrounding the regulation of muscle length. 

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Publication Information
Original title: Brachial plexus birth injury and cerebral palsy lead to a common contracture phenotype characterized by reduced functional muscle length and strength
Published in: Frontiers in Rehabilitation Sciences
Publish date: Aug. 16, 2022
Read the study

Research By

Sia Nikolaou, PhD
Sia Nikolaou, PhD
Division of Orthopaedics
Roger Cornwall, MD
Roger Cornwall, MD
Clinical Director, Division of Pediatric Orthopaedics