#Dislocation# is a rare complication of hip disease, and is most likely to occur during the stage of adduction with inversion. It has been known to take place during sleep, apparently from spasmodic contraction of muscles. In the dorsal dislocation, which is the most common form, adduction and inversion are exaggerated, the trochanter projects above and behind Nélaton's line, and the head of the bone may be felt on the dorsum ilii. It is a striking fact that after dislocation has occurred there is less complaint of pain or of startings than before, and passive movements may be carried out which were previously impossible.
#Diagnosis of Hip Disease.#--The diagnosis is to be made not only from other affections of the joint, but also from morbid conditions in the vicinity of the hip, as in any of these the patient may seek advice on account of pain and a limp in walking. The patient should be stripped, and if able to walk, his gait should be observed. He is then examined lying on his back, and attention is directed to the comparative length of the limbs, to the attitude of the limbs and pelvis, and to the movements at the hip-joint, especially those of rotation. When there is any doubt as to the diagnosis, the examination should be repeated at intervals of a few days. In children, there are three non-febrile conditions attended with a limp and with shortening of the limb, which may be mistaken for hip disease,--_congenital dislocation_, _coxa vara_, and _paralysis following poliomyelitis_--but in all of these the movements are not nearly so restricted as they are in disease of the joint.
In tuberculous disease of the _sacro-iliac joint_, while the pelvis may be tilted, and the limb apparently lengthened, the movements at the hip are retained. In tuberculous disease of the _great trochanter_, or of either of the _bursæ_ over it, while there may be abduction, eversion, impairment of mobility, and swelling in the region of the trochanter followed by abscess formation, the movements are less restricted than in disease of the joint.
In _psoas abscess_ associated with spinal disease, or in _disease of the bursa underneath the psoas_, the limb is flexed and everted, there may be lordosis, and the patient may limp in walking, but the movements at the hip are restricted only in the directions of extension and inversion, while in hip disease they are restricted in all directions.