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 login to view 4 more bullets scoliosis clubfeet cervical kyphosis login to view 2 more bullets 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 login to view 2 more bullets AP pelvis and lateral of hips login to view 1 more bullet findings hypoplasia of vertebrae cervical kyphosis with subluxation hip dislocation MRI recommended cervical kyphosis myelopathy Treatment Cervical kyphosis operative posterior cervical fusion login to view 3 more bullets anterior/posterior cervical decompression and fusion login to view 2 more bullets Hip dislocations nonoperative closed reduction under anesthesia login to view 2 more bullets operative open reduction of hip dislocation login to view 7 more bullets Knee dislocations nonoperative closed reduction and casting login to view 2 more bullets operative open reduction with femoral shortening and collateral ligament excision login to view 2 more bullets