summary Larsen's Syndrome is a rare genetic disorder caused by mutations in filamin B and carbohydrate sulfotransferase 3 deficiency, that presents with characteristic findings of ligamentous hyperlaxity, abnormal facial features, cervical kyphosis, and multiple joint dislocations. Diagnosis is made based on family history associated with typical radiographic and clinical features. No commercially available diagnostic test exists due to the variety of genetic mutations. Treatment is usually open reduction for joint dislocations and early posterior spinal fusion for cervical kyphosis to prevent neurological deterioration. Epidemiology Incidence estimated to be 1 in 100,000 live births Etiology Genetics autosomal dominant (AD) and recessive (AR) inheritance patterns AD linked to a mutation of the gene encoding filamin B AR linked to carbohydrate sulfotransferase 3 deficiency Associated conditions orthopaedic manisfestations hand deformities dislocations hips knees (usually bilateral) shoulders elbows (radial head) scoliosis clubfeet cervical kyphosis may present with extremity weakness secondary to myelopathy caused by hypoplasia of the cervical vertebrae Presentation Symptoms patients have normal intelligence Physical exam hypotonia uncommon but may be due to cervical compression abnormal facial features flattened nasal bridge hypertelorism prominent forehead hands long cylindrical fingers that do not taper wide distal phalanx at the thumb elbows bilateral radial head dislocations may be present knees look for bilateral knee dislocations foot deformities equinovarus eqinovalgus clubfeet Imaging Radiographs recommended AP and lateral of cervical spine during first year of life prior to any intubation to avoid iatrogenic spinal cord injury AP pelvis and lateral of hips ultrasound if less than 3 months findings hypoplasia of vertebrae cervical kyphosis with subluxation hip dislocation MRI recommended cervical kyphosis myelopathy Treatment Cervical kyphosis operative posterior cervical fusion indications patients with significant kyphosis but no neurologic deficits recommended to be performed during the first 18 months of life to prevent neurological deterioration anterior/posterior cervical decompression and fusion indications cervical kyphosis with neurologic deficits Hip dislocations nonoperative closed reduction under anesthesia indications may be attempted but rarely successful operative open reduction of hip dislocation indications failed closed reduction decreased range of motion secondary to contractures around hip unilateral hip dislocation bilateral hip dislocation controversial if considering, perform early and only once Knee dislocations nonoperative closed reduction and casting indications may be attempted but rarely successful operative open reduction with femoral shortening and collateral ligament excision indications knee dislocations that remain unstable after closed reduction