Duchenne muscular dystrophy (DMD) is a genetic disorder resulting in the progressive degeneration and weakness of muscles. The condition is caused by mutations in the gene that produces dystrophin, a protein necessary for maintaining the integrity of muscle fibers. Without dystrophin, muscles gradually become damaged and replaced by fat and fibrous tissue, leading to a decline in function. This muscle deterioration manifests through significant changes in posture, which evolve as the disease advances.
Early Postural Indicators
Some of the earliest signs of Duchenne muscular dystrophy involve distinct postural adjustments that children use to compensate for growing muscle weakness. One characteristic indicator is the Gowers’ sign. This maneuver is observed when a child attempts to stand up from a seated or lying position on the floor. Due to weakness in the large muscles of the hips and thighs, the child will use their hands and arms to push off the floor and then “walk” their hands up their legs to extend their torso into an upright position.
Another prominent early sign is a waddling gait. This walking pattern develops because the muscles around the hips are too weak to stabilize the pelvis during movement. To compensate, the child sways from side to side, tilting their hips to lift the leg and swing it forward, creating a distinctive waddling motion.
Progressive Spinal Curvature
As DMD progresses, weakness in the trunk muscles leads to significant changes in spinal alignment. Initially, many boys develop a pronounced lumbar lordosis, an exaggerated inward curve of the lower back often described as a “swayback” posture. This postural change is a compensatory mechanism to maintain balance. Weakness in the abdominal muscles and the hip extensors causes the pelvis to tilt forward, and the boy must arch his back to keep his center of gravity stable and remain upright.
This lordosis is often most apparent while the child is still able to walk. As muscle weakness intensifies and the child transitions to using a wheelchair, scoliosis frequently emerges or accelerates. Scoliosis is a sideways curvature of the spine, which can develop rapidly once daily walking ceases due to increasing weakness and asymmetry in the trunk and postural muscles. Severe scoliosis can become a serious health concern, as the twisting and curving of the spine can compress the chest cavity and impair respiratory function.
Joint and Limb Positioning
Beyond the spine, the progressive replacement of muscle tissue with inelastic connective and fatty tissue affects the limbs, leading to joint contractures. A contracture is the tightening or hardening of muscles and tendons, which results in a limited range of motion and can lead to fixed, abnormal joint positions. This process occurs because the fibrotic tissue that replaces healthy muscle does not have the same elasticity.
In DMD, contractures commonly affect several key joints. One of the earliest is the equinus deformity at the ankle, caused by the shortening of the Achilles tendon. This pulls the heel up and forces the foot downward, leading to a persistent toe-walking gait. Flexion contractures are also common at the hips and knees, where the joints become bent and difficult to straighten, further compromising mobility and complicating seating and daily care.
Management of Postural Changes
Managing the postural effects of Duchenne muscular dystrophy is a continuous process aimed at preserving function and enhancing quality of life. Physical therapy forms a foundational part of this care, with a focus on regular stretching routines to maintain the existing range of motion in the joints and slow the progression of contractures.
To supplement physical therapy, bracing and orthotics are often employed. Devices such as Ankle-Foot Orthoses (AFOs) are frequently prescribed. These braces are worn, often at night, to hold the ankle in a neutral position, providing a sustained stretch to the calf muscles and Achilles tendon to counteract the development of equinus deformity.
As mobility decreases and wheelchair use becomes necessary, proper seating and positioning become important. Standard wheelchairs are often inadequate, necessitating customized seating systems designed to support an individual’s specific postural needs. These systems incorporate specialized cushions and supports to maintain spinal alignment and help prevent the worsening of scoliosis. In cases where scoliosis becomes severe and threatens respiratory health, surgical intervention, such as spinal fusion surgery, may be recommended.