The internal surface of the capsule invested by its synovial membrane corresponds to the cotyloid ligament, to the neck and a portion of the head of the femur. The external is covered anteriorly by the reetus femoris, psoas, and iliaeus muscles, internally by the obturator externus and peetineus; posteriorly it lies upon the quadratus .femons, pyriformis, and obturator interims, and superiorly the glutams minimus adheres very closely to it.
The capsule of the hip-joint, although stronger, is not so long or so loose as that of the scapulo-humeral articulation, neither is it pierced by any tendon.
Synovial membrane.—To facilitate descrip tion, let us commence at the greatest circum ference of the head of the femur. From this point the synovial membrane passes outwards over the neck of the bone as far as the attach ment of the capsular ligament; from the bone it is reflected on to the deep surface of this ligament, along which it passes to the line of its attachment to the os innominatum and transverse ligament : along that line it is re flected again on to the Margin of the aeetabu 'um over the cotyloid ligament into the cavity, which it completely lines, and from which it is carried by the round ligament, which it invests, to the head of the femur.
A rterics.—The hip-joint is supplied with blood by branches from the obturator artery, derived from the internal iliac or from the in ternal circumflex branch of the femoral. These are distributed, some in the fat and cellular tissue, filling the excavation at the bottom of the aeetabulum, whilst others ramify on the ligamentum teres, and are conducted by it to the head of the femur. It not unfrequently occurs that the joint receives blood from both these sources.
Nerves.—These are derived from the obtu rater, which uniting with the deep division of the anterior crural cause the pain to be referred to the knee in some diseases of the hip-joint.
illations.—The motions of this joint are mostly performed by the femur upon the os innominatum, and consist of flexion, exten sion, abduction, adduction, cireumduction, and rotation.
In slight flexion the head of the femur revolves upon its axis in the cotyloid cavity ; the anterior portion of the capsular liga ment being relaxed, whilst the posterior is rendered proportionally tense. If this motion be augmented to any considerable extent, the capsular ligament is relaxed to a greater degree anteriorly, whilst posteriorly, in consequence of the distance between its two points of attach ment being increased, it is very tense, and ren dered convex by being stretched over the head of the femur, which is now very prominent in this situation, resulting from the altered re lations between it and the acetabulum. The anterior part of the head of the femur is placed against the deepest portion of the aectabulum, whilst its broad articulating surface situate above the depression for the round ligament is directed backwards, where the acetabulum is too shallow to receive it completely ; it there fore forms a projection in this situation, a pro jection which, in my opinion, ought rather to be attributed in this instance to the natural formation of the parts than to any displacement of the head of the bone.
NVIten excessive flexion is combined with adduction, the head of the femur glides from before backwards, and from within outwards in the aeetabulum ; its anterior portion is con cealed in this cavity, whilst its posterior emerging lies against the capsular ligament, considerably increasing its tension. To pro
duce these motions muscles of great power are employed ; in some these agents are not con fined merely to onejoint, but have two oppo site functions to perform, being flexors of one joint at the same time that they extend another.
In abduction, when the lower extremity of the femur is separated from the median line, its head is naturally directed downwards, its inferior portion being forced against the capsular ligament ; therefore when the motion is carried to any great extent the ligament is liable to rupture, and allow the head of the femur to escape over the internal lip of the acetabulum into the obturator foramen.
In adduction the same occurs as in abduc tion, but in an inverse direction, with this ex ception, that as the motion cannot be carried so far, and as in this case the head of the femur is opposed to the deepest portion of the acetabulum, dislocation cannot occur. Simple adduction, unaccompanied by any flexion of the joint, is very limited. Let any one, while standing in the erect pos ture, approximate his knees, it will be found that the utmost he can do is to bring them very near to each other, but that lie cannot press them as melt Other ; if, however, the hipjoints have been previously very slightly flexed, then the knees may be easily pressed against each other, and the adduction may be carried to a much greater extent, so as to cross the legs. It is limited by the ligamenturn tcres and the external and anterior part of the capsular liga ment.
Circurnduction combining the four preceding is a compound movement, in which the inferior extremity describes a cone, the apex of which is at the joint ; the head of the femur in the course of this motion successively assumes the several situations already described.
In rotation outwards the head of the femur is directed forwards and inwards, the anterior surface of the neck looks outwards, the pos terior inwards resting on the brim of the ace tabulum ; the capsular ligament is put upon the stretch on its inner side. Any sudden jerk or violence when in this position is liable to produce dislocation upwards upon the pubis.
In rotation inwards the bone assumes the contrary direction, and the capsular ligament and ligament= teres are equally put upon the stretch. In this case dislocation may occur either upon the dorsum of the ilium or into the sciatic notch. For this motion we have but few muscles, this position being produced merely by the tensor vaginw femoris and anterior fibres of the gluteus medius muscles. The disparity between the number of muscles influencing the motions of rotation outwards and inwards is very striking, but this may be attributed to the direction of the aeetabulum from within out wards and forwards naturally tending to pro duce rotation inwards. Consequently before, the opposite motion can be effected there is this inequality to be overcome, and hence the disparity between the muscles.
( H. Hancock.)