From a consideration of the above series of cases, the following points may be emphasized:

1. Age apparently was not an important factor in the etiology of this type of dislocation, as the age distribution ranged from seventeen to seventy-five, although it may be noted that three of the four patients were over fifty.

2. The type of trauma seemed not to be a constant factor. In Case 1 and possibly Case 2, the trauma was direct, applied to the latenal side of the knee. In Cases 3 and 4, indirect violence from a slip and fall was responsible.

3. The diagnosis of a traumatic dislocation of the knee is usually obvious at inspection. The diagnosis of an irreducible dislocation, however, depends upon one characteristic sign, —a more or less deep transverse groove or depression along the medial joint line. This sign may be obscured by excessive swelling or obesity; but, even in these cases, it becomes evident when closed reduction is attempted and only partial reduction is secured. Roentgenograms are of no great help, as the hindrance to reduction is a soft-tissue obstruction rather than bone obstruction.

4. Pathological changes were identical in all four cases except for the sprain fracture of the tip of the intercondyloid eminence found in Case 3, and the loosening or dislocation without gross tearing of the medial meniseus in Case 2.

5. Treatment naturally falls into three categories, —non-operative, operative, and postoperative.

In non-operative treatment, it would appear that attempts at closed reduction should only be made in the absence of a visible transverse groove along the medial joint line and when, consequently, the true diagnosis is in doubt. In this series of cases, all attempts at close reduction proved to be unsuccessful.

In operative treatment, before actual reduction of the dislocation, the joint should be thoroughly inspected for any additional pathological changes, such as a torn or displaced medial meniscus or loose fracture fragments. Although, in the cases here reported, no fragments were encountered, in another case, the dislocation itself was readily reduced by closed reduction, but check roentgenograms demonstrated a loose fracture fragment in the joint, which required subsequent operative removal.

The problem of postoperative fixation after complete ruptures of the cruciate and lateral ligaments is one about which considerable difference of opinion appears to exist; various periods of immobilization, ranging from four weeks to a year, have been recommended. A somewhat prolonged period might be justified in carrying out conservative treatment of a complete rupture of the medial collateral ligament. In these cases, however, an efficient repair of the collateral ligament (which usually proved to have been avulsed from its attachment rather than ruptured in the middle) has been performed, and the lateral instability of the knee thereby corrected. Admittedly, the cruciate ligaments are also torn, but complete immobilization of the knee from six to ten weeks, if carried out immediately after injury, results in excellent healing and stability of the knee without the necessity of any surgical repair of these ligaments themselves.

It is most important, however, that the plaster-fixation be applied with the knee in maximum adduction to relieve the medial collateral ligament of any strain. Inclusion of the foot in some inversion for the first few weeks is also desirable. It is important that the cast be snug-fitting at all times in order to prevent the development of any lateral wobble in the knee during healing. Consequently, one or more changes of the plaster are necessary to counteract any looseness which may result from subsidence of swelling and shrinking of the muscles.

Lastly, it is important to institute setting-up quadriceps exercises as soon as possible after the operation, and to ensure use of the leg muscles by early ambulation, long before the actual removal of the cast. If these simple principles are carried out, an excellent functional result from a severe injury may reasonably be anticipated regardless of the age of the patient.