Total derangement or dislocation of the stifle joint is a serious injury usually caused by severe direct or indirect trauma to the knee.
The type of dislocation observed depends upon the direction and location of the inciting trauma. Luxation of the stifle joint is not a very common injury because of the many soft tissue structures that interact to provide stability for the joint. These structures include the cranial and caudal cruciate ligaments along with the medial and lateral collateral ligaments. In addition, some support may also be derived from the quadriceps muscle and patella tendon cranially and the oblique poplitcal muscle, hamstring muscles, and the gastroenemius muscle, caudally. In many cases, fractures may accompany dislocations. Other structures are also likely to be injured including the menisci, joint capsule, popliteal artery, and peroneal nerve. Vascular integrity and neurologic function must be carefully evaluated as these complications usually are the limiting factor in the outcome of the injury.
Successful treatment of a stifle joint luxation must allow the animal to regain functional use of the limb. Good results achieved by a variety of methods support the notion that various techniques, which maintain reduction and stability, can be successful clinically. Initial maintenance of reduction and stability encourages well-organized periarticular collagen formation to provide long term joint stability. Closed reduction maintained with external coaptation, open reduction with extraarticular or intraarticular ligament reconstruction with transarticular external skeletal fixation and open reduction with transarticular pinning have been successful methods of treatment for stifle joint luxations. Although successful return to function has been reported following use of these techniques, some authors recommend stifle joint arthrodesis as the primary surgical treatment because of the severe general disruption sustained by the periarticular soft tissues at the time of injury. Based upon my experience, the results of surgical reduction and stabilization are generally good to excellent, and primary arthrodesis should only be attempted after attempts at reconstruction fail.
Because of the relatively infrequent occurrence of stifle joint luxation, only a few articles have appeared over the last several years comparing the results of various techniques of surgical intervention. It is generally agreed that it is difficult to accurately achieve and maintain reduction by closed methods alone. To provide a stable environment for healing of the soft tissues leading to well organized collagen formation and long term joint stability, surgical intervention is recommended.
A standard lateral parapatella approach and lateral arthrotomy is used to gain access to the stifle joint and allow inspection of the intraarticular and periarticular soft tissue damage. Because ligaments can appear to be grossly intact while having lost any load carrying ability, all ligaments should be inspected while undergoing stress palpation. Numerous different combinations of ligament damage have been reported with rupture of both cruciate ligaments and one of the collateral ligaments occurring most frequently. Interestingly, despite severe ligamentous and soft tissue damage, there is usually minimal, if any, gross articular damage observed at surgery. Remnants of the damaged cruciate ligament or ligaments should be removed and partial meniscectomy performed in animals with meniscal tears or avulsions. It is at this point that the various options available to this surgeon to achieve and maintain reduction and stability come into play.
In one technique, although the collateral ligaments are assessed for damage, they are not repaired; and reduction is achieved and maintained by placement of a transarticular pin while the stifle joint is held in a functional angle of approximately 135-140 degrees. While the technique is generally effective in cats and small dogs, transarticular pinning is not an especially rigid fixation. Distal pin migration and bending of the pin where it crosses the joint occur frequently, and failure of the technique may be due to reliance upon the transarticular pin to provide most of the stability of the fixation. It is quick, inexpensive, and easy to perform compared to other techniques, however, and may be the technique of choice in debilitate or muli-trauma patient in which anesthesia time should be limited. The authors of the technique conclude, however, by mentioning that better success would be achieved when the pin is used to maintain reduction while additional fixation in the form of a transarticular external skeletal fixators is used to provide sufficient rigidity to allow adequate healing of periarticular soft tissues. Such additional fixation would absolutely be necessary when repairing stifle luxations with this technique in medium and large sized dogs.
In another technique, the stifle luxation is maintained in reduction with multiple extraarticular sutures while transarticular external skeletal fixation is used to provide rigid fixation. In this technique, damaged collateral ligaments are repaired and extraarticular suture stabilization is performed for the damaged cruciate ligaments. Extraarticular stabilization is considered technically easier and may avoid further soft tissue disruption and instability of the joint when compared to intraarticular ligament reconstruction techniques. Transarticular external skeletal fixation augments joint stability while the tissues progress through the stages of inflammation and repair. Consistently, good to excellent functional results have been achieved in cats and all sizes of dogs with this surgical protocol.
My own personal preference is to use extraarticular stabilizing sutures and transarticular external skeletal fixation for medium and large sized dogs. In small dogs and cats, extraarticular stabilization and external coaptation consisting of a modified Bobby Jones bandage have consistently resulted in good to excellent results. While the majority of animals experience a loss of stifle joint range of motion in extreme flexion, the loss of flexion does not seem to interfere with clinical limb function. The development of mild to moderate degenerative joint changes has been observed radiographically. However, there does not appear to be a correlation between radiographic changes and functional limb use. The periarticular bone formation observed may be induced by the inciting trauma and not by post-operative instability or abnormal joint mechanics.
In conclusion, stifle joint luxation is an uncommon injury resulting from severe trauma. With proper surgical treatment, good to excellent clinical results and a return to normal or near-normal function can be expected in the majority of patients.