HEREDITARY ONYCHO-OSTEODYSPLASIA (Nail-Patella Syndrome) In 1820, Chatelain described a patient with congenital anomalies of the nails, Elbows and knees, the earliest report of nail dystrophy associated with skeletal dysplasia. In 1897, Little quoted a description by Sedgwick of a family of which 18 Members of four generations had no thumbnails and no patellae, thus suggesting the hereditary nature of this disorder. Involvement of the elbows in this hereditary defect reported by Wrede, in 1909, and Firth 1912. A detailed study of this triad of anomalies was made by Osterreicher, in 1931. Turner, in 1933, observed flaring of the iliac crests and prominence of the anterior superior iliac spines in some of' the affected patients." Fong, in 1946 during routine pyelography, noted conical bony projections on the dorsolateral aspects of the ilia, which he termed iliac horns, however, he did not associate them with any syndrome." A few years later, these iliac horns were observed in association with knee, elbow, and nail anomalies by other authors. Thus iliac horns were established as an important constituent of this syndrome. The popular name of "nail patella syndrome" has been applied to this triad of anomalies, but Love and Beiler, in 1957, coined the more correct term of hereditary osteo-onychodysplasia." And other terms applied to this condition are hereditary onycho-osteodysplasia" and hereditary onycho-osteoarthrodysplasia. Incidence The exact incidence of this syndrome is not known. Mino et al., in 1948, collected over 100 cases from the literature. Duncan and Souter, in 1963, found reports in the world literature of 44 families exhibiting the syndrome; the whole series comprised over 400 affected persons, details being available for only 252 of them. In 1960, Duthie and Hecht reported one case among 800 boys examined at a boys summer camp.

Inheritance Onycho-osteodysplasia is transmitted as a simple dominant autosomal character. As the gene is not sex linked, either males or females can transmit the condition. The gene displays complete penetrance, variable expressivity, and marked pleomorphism, meaning that the individual who possesses the gene is always affected. Various combinations of nail, elbow, pelvic, and knee involvement may be present, and the gene is capable of producing a variety of anomalies affecting structures derived from different embryonic germ layers. There Is definate linkage of the gene locus of the nail-patella gene and that of the ABO blood groups. The syndrome in a given family will be transmitted in association with only one of the genes A, B, or O. Clinical Features Nail Dystrophy. The commonest anomaly of the syndrome, the dystrophy becomes less severe in the more ulnar digits (Fig.2-92 E and F), The little finger is very occasionally affected. Abnormalities of the toenails have been noted in some cases. The thumbnail may be absent, bifid, or show hemiatrophy (the ulnar side of the nail is usually the absent part). In a very rare instance, the nail of the index finger may also be absent. The nails may be decreased in length and show numerous longitudinal cracks. Bony abnormalities of the digits have not been demonstrated. Mesodermal tissues of the fingers appear to be involved to some extent.

The terminal pulp may extend round from the volar aspect onto the dorsal surface. The dorsal skin creases over the distal interphalangeal joints may be absent or poorly developed. There may be laxity of the ligaments of metacarpophalangeal and Interphalangeal joints. Knee Dysplasia. This abnormality manifest as absence or hypoplasia of patella (Fig. 2-92 C to K). The hypoplastic patella may be ovoid, triangular, or irregular in shape and may arise from several ossific centers. The patella may be located more distally than in the normal knee superimposed on both the femoral and lateral tibial condyles. The presenting complaint may be recurrent dislocation of the patella, caused by hypoplasia Of the lateral femoral condyle, varying degrees of genu valgum are usually present. The medial femoral condyle is frequently large and prominent. The medial tibial plateau may slip downward and miedially, or even may be grooved. The medial margin of the proximal tibial metaphysis tends to sweep upward and medially in a characteristic arc. Elbow Dysplasia. The carrying angle of the elbow joint is increased. There is hypoplasia of the lateral side of the elbow joint involving not only the capitellum and

lateral condyle, but also the radial head (Fig 2-92 A to D. The radial head may articulate normally with the capitellum, or there may be subluxation or dislocation posteriorly. There may be a pointed exostosis of the lateral aspect of the coronoid process. Range of motion of the elbow joints is usually limited. Pelvic Dysplasia. "Iliac horns" and flaring of the iliac crests with prominence of the anterior superior iliac spines are the two types of pelvic abnormalities encountered. Iliac horns, one of the most common characteristic features of onycho-osteodysplasia, may be visible, palpable, or impalpable, according to their size (Fig. 2-93). Secondary centers of ossification may occur at their tips. They are Present quite early in life. When outflaring of the iliac crests with prominence of the anterior superior iliac Spines is present with the iliac horns, the appearance of the pelvis has been likened to that of an elephant's ear. Other purely coincidental anomalies may be found in association with the foregoing main lesions, such as clubfoot, congenical dislocations of the hip, spina bifida, congenital contracture of the little finger, abnormal pigmentation of the iris, renal dysplasia, and PIummer-Vinson Syndrome (dysphagia, hypochromic anemia, and koilonychia.

Figure 2-93. Hereditary

Onycho-osteodysplasia.

Roentgenogram of the pelvis and upper femora

Showing bilateral iliac horns. Note the severe valgus

Deformity of femoral necks.

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