1. One human trait which has been difficult to explain genetically is congenital dislocation of the hip.
2. An individual does not inherit congenital dislocation of the hip, but does inherit a primary defect, or hip dysplasia, which produces anatomical and physiological alterations of the joint called "flat socket". Only secondarily does actual dislocation occur, and dislocation need not necessarily occur.
3. Primary hip dysplasia is due to a genetic background.
4. Roentgenographic consanguinity studies are essential for a true genetic investigation of hip dislocation.
5. There is no "dislocation" gene.
6. There is a "hip dysplasia" gene.
7. The gene involved is not a recessive gene, but is a dominant gene.
8. The trait of hip dysplasia cannot be sex linked, because it is observed to pass from father to son.
9. Dysplasia of the hip without dislocation is a distinct clinical and roentgenographic entity, and should be included in textbooks in the chapter on classical dislocation, because the two entities have the same genetic etiology.
10. Dysplasia of the hip without dislocation occurs more frequently and may be more disabling than classical dislocation.
11. Acclivity of the roof of the acetabulum is the primary anatomical feature of a dysplastic acetabulum or flat socket.
12. Hip dysplasia refers not only to the acetabulum, but also to all joint-forming parts of the hip joint.
13. Primary hip dysplasia can lead much more easily to complete dislocation in the female than in the male.
14. Primary hip dysplasia with dislocation on one side is frequently associated with dysplasia without dislocation on the opposite side.
15. Hip joint instability and incongruity between the head and socket are the physiological and anatomical expressions of hip dysplasia without dislocation.
16. Primary hip dysplasia may remain asymptomatic for many years; in some individuals it may never be expressed clinically.
17. The extreme disability observed in some individuals is caused by traumatic arthritis of the hip joint resulting from mechanical factors of instability and incongruity.
18. The patient may gain relief of pain and disability by conservative treatment and surgical measures.
19. The geneticist and the surgeon have a tremendous opportunity for cooperative investigation.