Duchenne muscular dystrophy (DMD) progressively weakens and deforms the muscles and joints of the lower limbs, leading from clumsiness and toe walking in early childhood to loss of independent walking in later childhood or adolescence. It does this by causing structural damage within muscle fibres, which are gradually replaced by fat and fibrous tissue, especially around the hips, thighs, and calves.
Disease mechanism and lower limb focus
Duchenne muscular dystrophy is caused by mutations in the dystrophin gene, leading to absence or severe reduction of dystrophin, a protein that stabilises muscle cell membranes during contraction. Without dystrophin, repeated muscle use in walking, running, and standing produces micro‑injury, calcium overload, inflammation, and progressive degeneration of muscle fibres in the lower limbs. Over time, muscle cells in the hips, thighs, and calves are replaced with fat and connective tissue, making the muscles weaker and less elastic while sometimes appearing larger from the outside.
Pattern of muscle weakness in the legs
Weakness in Duchenne muscular dystrophy typically starts in the proximal lower limb muscles (hip and thigh) before affecting distal muscles (leg and foot). Early in the course of the disease, children struggle with movements that require strong hip and thigh power, such as rising from the floor, climbing stairs, running, and jumping. As the disease progresses, more distal muscles around the knee and ankle become involved, leading to difficulty with walking on uneven surfaces, controlling foot placement, and maintaining stability during stance and gait.
Hip and thigh involvement
The hip extensors and abductors, as well as thigh muscles such as the quadriceps, are among the first lower limb muscles to weaken. Weak hip extensors make it hard to straighten the trunk over the hips, so children compensate with lumbar lordosis (excessive inward curve of the lower back) and a forward lean when standing and walking to keep the centre of gravity over the feet. Weak hip abductors and thigh muscles contribute to a waddling gait with excessive side‑to‑side trunk sway, reduced walking speed, and rapid fatigue, especially when walking longer distances or on inclines.
Lower leg muscles and pseudohypertrophy
In contrast to the wasting seen at the hips and thighs, the calf muscles, especially the posterior compartment (gastrocnemius and soleus), often look enlarged, a feature known as pseudohypertrophy. Imaging and histological studies show that this enlargement is largely due to replacement of normal muscle with fat and fibrous tissue, with only scattered true hypertrophied fibres remaining. This tissue transformation shortens the effective muscle–tendon unit of the plantar flexors, contributing to toe walking and difficulty bringing the heel fully to the ground.
Gait deviations and functional consequences
Because the lower limbs are affected before the upper limbs, early functional problems are most obvious in walking and standing. Typical gait features include toe walking, a wide base of support, increased lumbar lordosis, and a waddling or Trendelenburg pattern due to hip abductor weakness and calf tightness. As weakness and contractures worsen, stride length shortens, cadence decreases, and children rely more on compensatory trunk motions and hand support (for example, using Gowers’ manoeuvre to stand), until eventually continuous independent walking is no longer possible.
Contractures and deformities of the lower limb
Contractures—permanent shortening of muscles and surrounding soft tissues—are a hallmark of Duchenne muscular dystrophy and particularly affect the lower limbs. In the legs, contractures commonly develop in the gastrocnemius–soleus complex, hamstrings, and hip flexors, which restrict ankle dorsiflexion, knee extension, and hip extension. These contractures lock the lower limbs into equinus (ankle plantarflexion), knee flexion, and hip flexion postures, further worsening toe walking, crouched stance, and difficulty standing upright or transferring.
Impact on posture, balance, and falls
Lower limb weakness and deformity profoundly affect posture and balance control in Duchenne muscular dystrophy. To compensate for hip and trunk weakness, children shift their pelvis forward and exaggerate lumbar lordosis, which moves their centre of mass over the feet but reduces dynamic stability and increases energy expenditure. Reduced ankle range of motion and calf tightness limit the ability to use normal ankle strategies for balance, so children have trouble recovering from small perturbations and are more prone to frequent falls and apparent clumsiness.
Progression to loss of ambulation
Studies and clinical observations show that loss of lower limb function usually occurs before significant loss of upper limb function. As hip, thigh, and lower leg muscles deteriorate and contractures advance, walking distance gradually decreases, stair climbing becomes impossible, and sit‑to‑stand transfers require increasing use of external support until independent ambulation is lost, often in late childhood or early adolescence despite modern management. After this point, further weakness in residual lower limb muscles and fixed deformities reinforce wheelchair dependence and limit standing programmes, with secondary effects on bone health and spinal alignment.
Role of lower limb management
Because lower limb involvement drives much of the disability in Duchenne muscular dystrophy , orthopaedic and physiotherapy management focus heavily on the legs. Key strategies include daily stretching (especially of the gastrocnemius–soleus complex, hamstrings, and hip flexors), night‑time ankle–foot orthoses, standing frames, and guided exercise to preserve range of motion, delay contractures, and maintain walking ability for as long as possible. When conservative measures are insufficient, lower limb orthopaedic surgery (for example, tendon lengthening) may be considered to improve limb alignment, standing tolerance, and the efficiency of remaining gait.
Overall, Duchenne muscular dystrophy affects the lower limb by selectively weakening proximal leg muscles first, altering gait and posture, promoting calf pseudohypertrophy and contractures, destabilising balance, and ultimately leading to loss of independent walking despite targeted supportive care.