Duck gait or wobble gait is a common sign of congenital medullary dislocation. In unilateral dislocation, lameness appears, while in bilateral dislocation, the pelvis tilts forward when standing, the hips are shrugged back, the waist is convex, the abdomen is bulged, and it is called duck gait or wobble gait because it sways from side to side when walking, and it is easy to fall when walking slightly fast. In clinical practice, attention should be paid to the differential diagnosis. 1, juvenile type proximal spinal muscular atrophy: this disease is also known as (Kugelberg-welander, progressive muscular atrophy), for autosomal dominant disease. Juvenile onset, mainly manifested as proximal muscle atrophy of the extremities, symmetrical distribution, similar to myopathy, but with muscle bundle tremor, electromyography for neurogenic damage, muscle pathology for group atrophy, consistent with loss of innervation. 2, chronic polymyositis: no genetic history, slower progression, symptoms often ebb and flow, the degree of muscle weakness is more pronounced than myasthenia. There is often pain and tenderness and increased blood sedimentation. Serum muscle enzymes are normal or mildly elevated, muscle pathology is consistent with the changes of myositis, and corticosteroid treatment is more effective. 3, myasthenia gravis: myasthenia gravis is aggravated after exercise and reduced after rest, without muscle atrophy and pseudo-muscular hypertrophy. Anticholinesterase agent treatment is effective. Electromyography and muscle biopsy help to identify. 4, ankylosing muscular dystrophy: the disease is rare, autosomal dominant inheritance. It can develop at any age, mostly involving small muscles of the distal hands and feet first, without pseudohypertrophy, early often manifesting as weakness of the distal limbs, occasionally meeting muscle, eye muscle or pharyngeal muscle weakness. The progression is slow, with gradual onset of myotonicity and muscle atrophy. Muscle atrophy is mainly in the distal extremities, and can develop into the facial muscles, bite muscles, temporal muscles and sternocleidomastoid muscles, so the patient’s face is long and thin, with an axe face and goose neck. Some patients may have slurred speech and swallowing difficulties. Most patients have cataracts, hair loss, sexual dysfunction, infertility and mental retardation. Paralysis and myocardial damage with normal or mildly elevated serum enzymes may occur in late stages. Electromyography and muscle pathology help to differentiate.