Although RUS is the most common congenital functional disorder of the elbow joint (Siemianowicz, Wawrzynek, & Besler, 2010), it is considered a rare disease (National Institutes of Health, 2012). In most cases, RUS is an isolated defect involving only one limb. Bilateral RUS is usually familial and affects males more than females. In a small number of cases, evidence of an autosomal-dominant inheritance pattern is found (Elliott et al., 2010, Spritz, 1978). Approximately one third of persons with RUS have associated skeletal, cardiac, renal, neurologic, or gastrointestinal anomalies (Wurapa, 2012).
The elbow joint is identifiable at 35 days after conception. The radius begins to chondrify at 41 days and the ulna at 44 days after conception. The radius and ulna are connected proximally and share a common perichondrium. In utero insults may interrupt the normal radioulnar differentiation and segmentation, resulting in a spectrum of congenital proximal forearm abnormalities (Elliott et al., 2010). The affected forearm is usually fixed in pronation, because pronation is the normal fetal position (James & Heiden, 2001).
Various researchers have described and categorized congenital RUS. The simplest classification system is one that describes two general types: fusion of the radius and ulna at their proximal border or fusion distal to the proximal radial epiphysis (Pediatric Orthopedic Society of North America [POSNA], 2013). The original description of RUS by Cleary and Omer (1985) listed four types: fibrous synostosis, bony synostosis, RUS associated with posterior radial head dislocation, and RUS associated with anterior dislocation of the radius.
RUS also may develop as a result of an operatively treated forearm fracture. Persons who sustain high-energy, comminuted open fractures are at increased risk for the development of RUS. This complication also may occur as a result of soft tissue injury, reconstructive procedures, injury to the interosseous membrane, and any trauma causing hematoma formation between the radius and ulna. Whereas congenital RUS affects only the proximal forearm, posttraumatic RUS may present anywhere along the forearm (Bergeron, Desy, Bernstein, & Harvey, 2012).
The functional arc of forearm rotation is 100 degrees. Most activities of daily living can be performed with an arc of 60 degrees (Sardelli, Tashjian, & MacWilliams, 2011). Persons whose forearms are fixed at greater than 60 degrees pronation have more problems than do those with approximately 20-degree fixed pronation (POSNA, 2013). As occurred with the patient in this case study, congenital RUS is usually recognized when children are 18 to 60 months of age. Parents or teachers observe activity limitations such as difficulty holding pencils, crayons, and spoons; difficulty with shirt buttons, coat buttons, or belts; the inability to rotate baseball gloves into position to catch a ball; difficulty accepting objects into an open palm; difficulty with brushing hair and teeth; or difficulty using eating utensils and getting a cup to the mouth (Wurapa, 2012). Less commonly, affected persons are noted to have an abnormal carrying angle, shortening of the forearm, or flexure contractures. Pain is not a presenting symptom, but it may develop during adolescence when progressive radial subluxation can occur. The delay in diagnosis is attributed to the lack of requirement for forearm rotation in infants and the use of compensatory shoulder and wrist motion (James & Bednar, 2010).
J Pediatr Health Care. 2014;28(4):357-360. © 2014 Mosby, Inc.