Humeroradial and Humeroulnar Synostosis

► [Fusion between humerus and radius and humerus and ulna, respectively]

Both these anomalies are less common than radioulnar synostosis. Congenital, isolated humeroulnar synostosis is exceedingly rare. Acquired cases of humeroulnar fusion taking the form of bony bridging between contiguous foci of heterotopic calcification are well known (Hastings and Graham 1994). From a clinical standpoint, both humeroradial and humeroulnar synostosis imply fixed flexion of the forearm, usually near 90° (Fig. 5.28).

Both sporadic and genetic cases of humeroradial synostosis are encountered. The genetic forms are characterized by bilateral involvement and lack of the distal ulnar malformations (longitudinal deficiency of ulna) that are common in the sporadic cases (Hunter et al. 1976). Fusion of all three bones articulating at the elbow joint can also occur sporadically, in association with upper limb oligo-ectro-syndacty-ly (Hersh et al. 1989). Three entities of humeroradial synostosis can be delineated: (a) autosomal dominant ankylosis of the elbow as part of a systemic disorder causing multiple synostoses with brachy-mesophalangism (facio-audio-symphalangism syndrome); (b) autosomal recessive humeroradial synostosis (OMIM 236400) with dysgenesis of the ulna but without oligodactyly as part of a syndromal disorder; (c) autosomal recessive humeroradial synostosis with great variability within families (nonger-minal, uni- or bilateral) as part of the ulnar malformation and oligodactyly (SC phocomelia syndrome). Consanguinity is frequent in the families of patients who have inherited this condition as a recessive trait (Keutel et al. 1970).

In multiple synostoses syndrome (facio-audio-symphalangism syndrome, OMIM 186500), a disorder with an autosomal dominant mode of inheritance and with variable expression, multiple progressive joint fusions with onset in early childhood at the proximal interphalangeal joints (proximal sympha-langism) and progression to the carpal, tibio-tarsal, and tarsal articulations are typically encountered. Ankylosis of other joints, including the middle-ear ossicles (otosclerotic deafness), cervical vertebrae, hips, and radiohumeral joints, develops with age (da Silva et al. 1984; Herrman 1974). Affected patients show a broad, tubular (hemicylindrical) nose without alar flare (Maroteaux et al. 1972). Linkage to 17q21-q22 has been demonstrated (Krakow et al. 1998). The detection of mutations in the Noggin gene both in familial autosomal dominant multiple synos-toses syndrome and in families with proximal sym-phalangism indicates that these are allelic disorders (Gong et al. 1999). Roberts-SC phocomelia syndrome (OMIM 268300) manifests with limb reduction defects (absent, hypoplastic, bowed, and deformed long and short tubular bones, missing rays), fused thin ribs with abnormal rib number, and platyspondyly with reduced intervertebral spaces. Camptodactyly and clinodactyly are occasional features (Herrmann et al. 1969). The phenotype of what originally was considered to be a separate entity, SC phocomelia, is milder, with longer survival (Hunter et al. 1976; Pfeiffer and Braun-Quentin 1994). Humeroradial synosto-sis can also occur in association with an unusual type of multiple synostosis syndrome (humeroradial syn-ostosis/multiple synostosis syndrome, OMIM 236410) that involves carpal, tarsal, and phalangeal joints, with apparent agenesis of the distal phalanges of the postaxial digits (Richieri-Costa et al. 1986). Additional findings in this constellation include plagiobrachy-cephaly, prominent forehead, broad nasal root, small ears with hypoplastic lobes, and normal mental development. Based on parental consanguinity, autosomal recessive inheritance has been suggested. Bilateral humeroradial synostosis, with fixed flexion of the elbow, is constant in Antley-Bixler syndrome (trapezoidocephaly/synostosis, OMIM 207410), which is probably an autosomal recessive disorder. The

Congenital Humeroradial Synostosis

syndrome also displays craniosynostosis with brachy-cephaly and frontal bossing, midface hypoplasia, choanal atresia, depressed nasal bridge, dysplastic ears, stenotic external auditory canals, bowed femurs, joint contractures, narrow chest with gracile ribs, arachnodactyly, clubfoot, carpo-tarsal synostosis, and long bone fractures (Antley and Bixler 1975). Humeroradial synostosis, together with brachy-cephaly, mild syndactyly, and broad thumbs and toes, also occurs with Pfeiffer syndrome (acrocephalosyn-dactyly, OMIM 101600) (Martsolfet al. 1971).Humero-radio-ulnar synostosis has been noted in association with distal humeral bifurcation and tridactylous ectrosyndactyly (Gollop and Coates 1983; Leroy and Speeckaert 1984).

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