pouch in the knee, or on one or other side of the olecranon in the elbow.  In most instances the patient has carefully observed his own symptoms, and is aware not only of the existence of the loose body, but of its erratic appearance at different parts of the joint.  This feature serves to differentiate the lesions from a torn medial meniscus in which the pain and tenderness are always in the same spot.  As the body usually contains bone, it is recognisable in a skiagram.

[Illustration:  FIG. 169.—­Multiple Cartilaginous Loose Bodies from Knee-joint.]

There are two methods of removing the body; the first and simpler method is applicable when the body can be palpated, usually in the supra-patellar pouch; it is preferably transfixed by a needle and can then be removed through a small incision; otherwise, the joint must be freely opened and explored, firstly to find the body and further to remove it.

The characters of this type of loose body are remarkably constant.  It is usually solitary, about the size of a bean or almond, concavo-convex in shape, the convex aspect being smooth like an articular surface, the concave aspect uneven and nodulated and showing reparative changes, healing over of the raw surface, and the new formation of fibrous tissue, hyaline cartilage and bone, the necessary nutriment being derived from the synovial fluid (Fig. 167).  The body is sometimes found to be lodged in a defect or excavation in one of the articular surfaces, usually the medial condyle of the femur, from which it is readily shelled out by means of an elevator.  It presents on section a layer of articular cartilage on the convex aspect and a variable thickness of spongy bone beneath this.

The origin of these bodies is one of the most debated questions in surgical pathology; they obviously consist of a portion of the articular surface of one of the bones, but how this is detached still remains a mystery; some maintain that it is purely traumatic; Konig regards them as portions of the articular surface which have been detached by a morbid process which he calls “osteochondritis dessicans.”

Multiple Chondromas and Osteomas of the Synovial Membrane.—­In this rare type of loose body, the surface of the synovial membrane is studded with small sessile or pedunculated tumours composed of pure hyaline cartilage, or of bone, or of transition stages between cartilage and bone.  They are pearly white in colour, pitted and nodular on the surface, rarely larger than a pea, although when compressed they may cake into masses of considerable size.  With the movements of the joint many of the tumours become detached and lie in the serous exudate excited by their presence.  They are found also in the diverticula of the synovial membrane, in the shoulder in the downward prolongation along the tendon of the biceps, in the hip in the bursal extension beneath the psoas.