Naegele believes that the condition is due to congenital causes, his theory being based upon the following facts: 1. The complete fusion of the sacrum with the femur, and the absence of all traces of secondary anchylosis. 2. Arrest of development of either lateral half of the sa crum, diminution in the size of the corresponding innominate bone, and in the length of the synostosis, as compared with the synchondrosis on the opposite side. 3. The fact that synostoses and deformities in other bones may also be the result of congenital anomalies, and that congenital synostosis is usually added to a malformation of the united bones, which consists especially in arrest of development. 4. The close resemblance between pelves of this type. 5. The absence of every other cause or external influence which could have produced this deformity.
Martin believes that there is first an inflammatory process, then fusion of the femur and sacrum occurs, with induration of the surrounding bone, and the anchylosis preventing the further development of adjacent parts would cause the deviation of the bones, in proportion as these con tinue to grow. Hohl proved that there might be in these cases entire absence or imperfect development of the centre of ossification of the alas of the sacrum. Now if the centre is wanting only in the first sacral ver tebra, the latter is supplied by the increased development of the centre in the second vertebra. If the centres for the second and third are want ing, there results, necessarily, atrophy of the corresponding side of the sacrum, and in consequence, gradual formation of the obliquely-oval pel vis, without our being able to recognize at any point in the pelvis patho logical change.
Simon-Thomas concludes as the result of a series of observations that: 1. In every oblique-oval pelvis anchylosis should be regarded as the pri mary change, the result of a previotis inflammation, which may occur at any time, even in foetal life. 2. Inflammation may occur primarily in the sacroiliac joint, in consequence either of internal causes or trauma tism, or it may develop secondarily, in consequence of some affection of the neighboring joints (the articulations of the lumbar vertebrae or the hip). 3. If anchylosis occurs after puberty, when the pelvic bones have reached their complete development, simple atrophy of the adjacent bony parts results, the deformity becoming more complete according as the anchylosis takes place late. 4. After the original disease, which caused the anchylosis, has been cured, the traces of a pre-existing joint may be so completely effaced as no longer to be recognized on superficial exami nation. 5. Other deformities, besides anchylosis, such as obliquity, and contraction of the pelvic canal, flattening of the lateral wall, diminished size of the greater sacro-sciatic notch, scoliosis of the lumbar vertebra, etc., are secondary lesions, which ought to be attributed, partly to atro
phy of the bones, partly to the unequal pressure supported by the two lateral halves of the pelvis, and partly to the necessity of re-establishing the lost equilibrium.
Litzmann opposes these views, and tries to prove that the anchylosis is secondary, being the result of excessive pressure applied at the cotyloid cavity, when the weight of the body is thrown habitually upon one leg. Olshausen agrees with this writer. Schroeder believes that the anchylosis is secondary to inflammation of the joint. This inflammation may be of an acute suppurative form, often associated with caries of the neighbor ing bones. If the inflammation takes place after the bones have fully developed, the shape of the pelvis is not changed; in these cases anchylo sis is not generally complete, and we always see osseous bridges extend ing between the bones. If the inflammation occurs in infants, before the alm of the sacrum are formed, the result of the synostosis is an arrest of development of the alm at the point which it had attained when the in flammation occurred. When the other alm attains its normal size, the weight of the body is unequally distributed, so that the anchylosed side is exposed to more pressure than the healthy side. If the inflammation occurs during intrauterine life, congenital anchylosis results, with marked contraction of the alas of the sacrum on the affected side, and, in conse quence of this, arrested development and obliquity of the pelvis. This obliquity is not due to ancbylosis alone, but solely to the contraction of the ale of the sacrum on the corresiSonding side, whereby the weight of the body is thrown more upon the femur of the affected side, so that the cotyloid cavity approaches the promontory, and the syrnphysis is displaced to the opposite side. It follows from the preceding that the synostosis does not necessarily result from atrophy of the aim, but is easily explained in other ways. Oblique deformity, not anchylosis, is the distinguishing feature of these pelves; this may result from hip-disease, amputation of the thigh, or old dislocation. Is anchylosis ever the primary condition? Spiegelberg thinks not. Ho denies the existence of a congenital failure of development, because the sacroiliac articulation is formed before any osseous centres exist in the sacral aim, and because all oblique pelves in which anchylosis exists are already more developed than in the foetus at term. If anchylosis occur early, it may prevent the growth of the bones around the joint. When synostosis does not take place until after the complete development of the two bones, there is a partial, but not a complete, disappearance of the, joint.