Clavicles with Lateral Hooks

► [Handlebar clavicles]

This characteristic shape of the clavicle, involving an excessive upward convexity of its lateral portions (Igual and Giedion 1979), is a minor radiologic feature inconsistently found in a group of skeletal dysplasias and malformation syndromes (Fig. 2.41). Traditionally described in individuals with thrombo-

Handlebar Clavicles
Fig. 2.41. Osteogenesis imperfecta in a 16-year-old boy. Bilateral handlebar configuration of the clavicles and diffuse osteoporosis are apparent. The numbers refer to the measured values of d (see text for explanation). (From Oestreich 1981)
Handlebar Clavicles
Fig. 2.42. Brachial plexus palsy in a 7-year-old child with right brachial plexus palsy since birth. Note handlebar configuration of the right clavicle. The left clavicle is not affected. The numbers refer to the measured values of d (see text for explanation). (From Oestreich 1981)

cytopenia-radial aplasia syndrome (TAR syndrome, OMIM 27400),handlebar clavicles also occur in several other disorders, notably chromosome 8 trisomy syndrome (including mosaics), diastrophic dysplasia (OMIM 222600), and Holt-Oram syndrome (OMIM 142900) (Oestreich 1981). Long clavicles with lateral hooks are occasionally found in multiple pterygium syndrome (Escobar syndrome, OMIM 265000), an autosomal recessive disorder with multiple pterygia (neck, axilla, elbow, popliteal, fingers, intercrural); short stature; limb defects (camptodactyly,syndactyly, talipes equinovarus, rocker-bottom feet); characteristic facies (ptosis of eyelids, down-slanting palpebral fissures, hypertelorism, epicanthal folds, micro-gnathia, down-turned corners of the mouth, sad expression, low-set ears); genital anomalies (cryp-torchidism, absence of labia majora); and muscu-

loskeletal anomalies (multiple flexion contractures, scoliosis, kyphosis, vertebral fusions, rib anomalies, absent patella). Inconstant features include rib segmentation anomalies, tall vertebrae, radial head and hip dislocation, diaphragmatic hernia, and cardiac defects (Escobar et al. 1978; Hall et al. 1982; Jones 1997).

An association of bilateral microtia, short stature, absent patellae, and peculiar facies, the so-called ear-patella-short stature syndrome (Meier-Gorlin, OMIM 224690), was originally found in two female sibs (Cohen et al. 1991). Additional features included complete elbow dislocation, slender ribs and long bones, abnormal glenoid fossa, clavicles with lateral hooks, clinodactyly, flat epiphyses, and delayed bone age (Meier and Rothschild 1959; Gorlin et al. 1975; Gorlin 1992; Hurst et al. 1988).

In most, if not all, of the congenital malformation syndromes featuring handlebar clavicles there is also some degree of ipsilateral upper limb reduction deformity. First rib anomalies and smallness of the scapulae can be associated (Oestreich 1981).

The clavicular hooks can also be acquired defects, most typically in the context of disorders with weakened muscles of the ipsilateral limb, such as persistent brachial plexus injury after birth trauma (Fig. 2.42) or other neuromuscular disorders. It is believed that the effects of muscular imbalance, specifically of the deltoid and pectoralis major, acting either during intrauterine life or at any time after birth, may account for the development of the lateral clavicle hooks (Oestreich 1981).

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