Acute Knee Dislocations and Their Complications

Dislocations of the knee are true surgical emergencies. They are rare lesions, and opinions vary widely as to their treatment. The end result may be exceedingly good or tragically bad, depending on the extent of injury to the popliteal artery, the peroneal and tibial nerves, and the ligamentous structures about the knee. Knee dislocations are defined in relationship to the tibial displacement with respect to the femoral condyles (Fig 1 not shown). Thus a tibia lying anterior to the femur is an anterior dislocation. Using this terminology there are five main types of dislocations: anterior, posterior, lateral, medial, and rotatory (the irreducible posterolateral dislocation). The largest series of knee dislocations in the literature is the 39 cases reported by Jonasch6 in 1961. Nikolai13 reported a series of 33 cases in 1960. The largest series in the English literature is that of Kennedy,8 who reported on 22 cases in 1963 (Table I).Table I: Summary of LiteratureIt has been said that the paucity of literature on the subject of knee dislocations reflects as much the bad results of treatment as its infrequency of occurrence. We feel that this is an unnecessarily pessimistic outlook, and are reporting 15 cases of knee dislocations, three of which had arterial injury and all of which obtained satisfactory end results. Anatomy of the Popliteal Space. The severity of injury in knee dislocations is directly related to damage of contents of the popliteal space. Injury to the popliteal artery is related to the peculiar anatomy of the region (Fig 2 not shown). The popliteal artery originates at the tendonous hiatus of the adductor magnus muscle, by which it is firmly anchored to the femoral shaft. Within the popliteal space it gives off five arterial branches: paired superior genicular, paired inferior genicular, and unpaired middle genicular arteries. These arise immediately above and below the knee joint and constitute the major collateral system about the knee. In addition, the communicating system is supplied from above by the supreme genicular artery and the descending branch of the lateral femoral circumflex artery. Distally the anastomotic network communicates with the anterior tibial artery by way of the anterior tibial recurrent artery. The popliteal artery passes distally between the heads of the gastrocnemius muscle and then beneath the tendonous arch of the soleus muscle, by which it is held firmly against the underlying bone. At this point the artery ends by division into posterior and anterior tibial arteries, the latter of which passes immediately through the interosseous membrane. Although the popliteal artery is moored snugly at either end, it is not in contact with bone but is stretched like a bowstring across the popliteal space. Any distortion of the skeletal anatomy causes stretching of the popliteal artery. Arterial rupture tends to occur at the point of emergence of a major branch, especially if the artery is tethered by passage through a fibro-osseous canal such as the adductor canal or soleus hiatus. The nerves in the popliteal space are not anatomically fixed as the arteries are, and therefore are less likely to become severed. Hence, injuries to the nerves are usually traction in continuity, from which recovery may occur. Their surgical repair may await determination of spontaneous recovery. Injuries of the Popliteal Artery. All authors writing on the subject of knee dislocations advocate immediate reduction of the dislocation, in the emergency room if necessary, without anesthesia. In most instances the reduction is accomplished quite easily by gentle but sustained traction. Following reduction a very careful, critical evaluation of the circulatory status of the extremity must be carried out. The amount of deformity of the extremity in the emergency room can not be used as an indication of the probability of rupture of the popliteal vessels because the overwhelming force to dislocate the knee joint, and the immediate deformity, has invariably been much greater than is present at the time of examination, when the joint has been returned to at least relative alignment.5,12 The presence of seemingly warm skin over the dorsum of the foot and toes can not be considered as evidence of intact blood supply because this has been found in the presence of complete arterial occlusion.11 The presence of full dorsalis pedis and posterior tibial pulses following reduction does not invariably mean that there has been no injury to the popliteal vessels. Contusion of the artery or severe injury to the intimal and medial layers without the loss of continuity is a common consequence of traction injury, and thrombus formation ensues within a few hours to several days.3,9,11 Case I. A 41-year-old female presented with pain in the left knee. She stated that she fell on an uneven sidewalk while fleeing from an assailant. On examination there was slight medial and anterior-posterior instability of the knee, and the left foot was slightly cooler than the right, but there were good dorsalis pedis and posterior tibial pulses. Over the next three days the pulses markedly diminished, and an arteriogram revealed a block of the popliteal artery (Fig. 3A). An exploration of the knee joint revealed a tear in the posterior capsule of the knee joint, a tear of the medial head of the gastrocnemius muscle and cruciate ligaments, and an intimal tear and thrombosis of the popliteal artery at the level of the adductor canal. A resection of approximately 2 cm of damaged vessel and end-to-end anastomosis was performed. The cruciate ligaments and capsule were not repaired. A postoperative arteriogram showed a patent vessel (Fig. 3B). The extremity was immobilized for six weeks at 20° flexion. Three months after injury the patient was ambulatory with better than 90° knee motion, very slight anterior-posterior instability, and full bounding pulses in the left foot.Fig 3.: A–B. (A) Case 1, arteriogram showing blockage of the popliteal artery three days after injury. (B) Case 1, postoperative arteriogram showing patency of popliteal artery reconstruction.There is considerable debate as to the merits of arteriography in this particular injury. Some feel that it simply adds to delay of operative intervention. Others feel that its value is in accurately localizing the injured area and extent of collateral circulation.2,15 In general we are relying more and more on diagnostic arteriography in dealing with these lesions, but caution that the results of the arteriogram must be critically interpreted, and if any doubt whatsoever arises in its interpretation, the pendulum should swing to open exploration of the area. The method of arterial repair is dictated by the local conditions. In his very thorough review of the literature, Jonasch6 reported 43 cases of knee dislocations with injuries to the popliteal artery. Thirty-six of these patients were treated with closed reduction only, and all thirty-six resulted in amputation. Two patients were treated with ligation, and both resulted in amputation. Four cases of suture repair of the popliteal artery resulted in two amputations, and two with preservation of the limb and good functional results. Another patient treated with a vein graft got a good result. All four of their own cases resulted in amputation. Schum16 is credited with the first successful repair of a torn popliteal artery. This occurred as a result of blunt trauma, and not as a result of a dislocated knee. The importance of adequate debridement of the damaged artery has been stressed by Jones7 and by Moore,10 who recommend removal of 1 cm of apparently normal artery to avoid induction of thrombus formation by minute injuries to the vessel wall. If end-to-end anastomosis is possible after debridement, this is most likely to be successful. Case 2. A 26-year-old male was involved in an auto accident in which he sustained a closed anterior dislocation of the right knee (Fig 4A). A closed reduction was performed in the emergency room without anesthesia. Following reduction the right foot remained cold and pulseless, and demonstrated hypesthesia. An arteriogram showed blockage of the popliteal artery (Fig 4B). At exploration an intimal tear of the artery was found, approximately 1¼ inches of vessel was resected (Fig 4C), and an end-to-end anastomosis performed. The extremity was immobilized for six weeks in 20° of flexion. An arteriogram at six weeks after injury showed a patent vessel with rapid run-off (Fig 4D). The patient has a stable knee with a 10° knee flexion contracture and total of 120° of motion (Fig 4E, 4F).Fig 4.: A–E. (A) Case 2, anterior knee dislocation. (B) Case 2, post reduction arteriogram showing complete blockage of popliteal artery. (C) Case 2, resected portion of damaged popliteal artery measured approximately 1¼If an end-to-end anastomosis is not possible, the best alternative is the use of autogenous vein graft.5,9,11 The saphenous vein of the opposite leg serves better than a vein from the injured extremity, where disruption would lead to increased venous stasis and swelling. In addition to the attractiveness of using a living autogenous material, the vein graft has the advantage of availability and lesser incidence of occlusion than other types of arterial substitutes. The method of suture using continuous 6–0 arterial silk has been repeatedly described in the literature.5,11 Combined injuries involving nerves of the popliteal region present a special problem. Sensory disturbance and paralysis may result, either from concomitant injury of the tibial and peroneal nerves or as a result of ischemia. According to Tibbs,17 loss of cutaneous sensation is the best single index of critical ischemia. Although a pure nerve lesion is easily recognized, it may be difficult to distinguish a pure arterial injury from one involving the nerve as well. This is, of course, of some prognostic significance, since an anesthetic foot is extremely troublesome, even though vascular recovery is complete. Anterior Knee Dislocations. This is the most common type of knee dislocation, and it is this lesion which is most frequently accompanied by injury to the popliteal artery. Kennedy,8 in his cadaver experiments, was able to produce this lesion consistently by hyperextension of the knee, producing rupture of the posterior capsule of the knee and posterior cruciate ligament which allowed the tibia to ride forward on the femur. He also showed that this occurred without complete rupture of the medial and lateral collateral ligaments. We encountered six anterior dislocations (Table II), two of which had arterial injury. All were treated with closed reduction, and repair of the arterial injury when present, but no attempt was made to repair the collateral or cruciate ligaments. After approximately six weeks of immobilization, the extremities were started on a vigorous physical therapy program. All six obtained stable knees with mild anterior-posterior laxity and better than 90° motion.Table II: Summary of Our Experience with 15 Acute Knee DislocationsThe only isolated nerve injury in our series was a result of an anterior dislocation. There was complete recovery of the peroneal nerve palsy after one year, during which time the patient wore a short leg brace. Posterior Knee Dislocations. We have treated four of these lesions, one a severely open dislocation with concomitant open fracture of the patella which was treated with patellectomy and repair of the torn medial and lateral collateral ligaments with staples. Skin coverage required a posterior relaxing incision and skin grafting of the defect created. This patient obtained a stable painless knee with 60° motion from full extension. Another posterior dislocation (Fig 5A) had a concomitant fracture of the anterior tibial plateau. Because of some coolness of the involved foot, an arteriogram was performed which was reassuringly normal (Fig 5B). The knee was explored, the fracture was reduced, and both menisci were removed because of tears in the anterior portion of each. The patient has a stable knee with greater than 90° motion (Fig 5C, 5D).Fig 5.: A–D. (A) Acute posterior knee dislocation with fracture of anterior tibial plateau. (B) Normal arteriogram following reduction of posterior knee dislocation. (C) Patient has full knee extension. (D) Patient has full knee flexion.Two posterior dislocations occurred as a result of football injuries. Both patients were treated with closed reduction and immobilization for approximately six weeks, and now have stable knees with a full range of motion. Medial Knee Dislocations. We have only recently encountered our first complete medial dislocation of the knee. The injury occurred as a result of an automobile accident with severe concomitant local soft tissue injury and an open fracture of the opposite tibia and fibula. Initially the foot was cold and pulseless, but with reduction a dorsalis pedis pulse was obtained. An arteriogram showed an intact popliteal artery and its tibial branches. The medial superior and inferior genicular arteries did not fill because they had been avulsed at the time of injury. The foot, however, remained viable with good circulation, sensation, and dorsalis pedis pulse. After repeated debridements and dressing changes, extensive skin grafting was performed. It is possible that this knee may require bracing or fusion because of instability. Lateral Knee Dislocations. All three of our lateral knee dislocations sustained complete tears of the medial collateral ligament, anterior cruciate ligament, and medial meniscus. Case 3. A 22-year-old male fell while descending the stairs of a football stadium and sustained a lateral dislocation of the left knee (Fig 6A). Following closed reduction good peripheral pulses were obtained, but because of severe instability the knee was explored, and repair of the medial collateral and anterior cruciate ligaments was performed. The medial meniscus was torn at the periphery but was not removed. The knee was immobilized for six weeks and a long leg brace worn for three months. The patient has a full range of motion of the knee with mild instability, and has resumed his position in his college marching band (Fig 6B, 6C).Fig 6.: A–C. (A) Case 3, lateral dislocation left knee. (B) Case 3, full knee extension five months post ligamentous repair of left knee. (C) Case 3, full knee flexion.The other two lateral dislocations were treated with repair of the medial collateral ligament and anterior cruciate ligament and excision of the torn medial meniscus, and obtained stable knees with a full range of motion. We believe repair of the injured ligaments in lateral dislocation is mandatory if a stable knee is to be obtained. Posterolateral Knee Dislocations with Buttonholing of the Medial Femoral Condyle (The Irreducible Posterolateral Dislocation). Posterolateral dislocations of the knee differ from other types of dislocations in several aspects. They have been described extensively by Quinlan,14 Clarke,4 Anderson,1 and others. It is primarily a rotatory dislocation without great displacement, and without associated injuries to the vessels or nerves. It is almost always accompanied by buttonholing of the medial femoral condyle through the medial capsule, and invagination of the medial ligament into the joint. It is irreducible except by operation. According to Quinlan,14 the mechanism of injury is a severe abduction-medial rotation violence to the knee while the knee is not bearing weight. The invagination of the capsule and the prominence of the medial femoral condyle producing a dimple in the skin at the joint line, together with irreducibility of the dislocation, is diagnostic of these posterolateral dislocations. We refer to the invagination of the skin as the “dimple” sign (Fig 7).Fig 7.: The so-called “dimple” sign seen with irreducible posterolateral or rotatory knee dislocations.In our series we encountered one of these lesions which was seen several days after the initial injury. Open reduction was performed, and the medial femoral condyle was found directly below the skin. The opening in the capsule was enlarged, and then reduction was accomplished. Concomitant tear of the anterior cruciate ligament was repaired and a torn medial meniscus excised. Because of skin necrosis, a skin graft was later required in the area where the femoral condyle had been so prominent. The end result was good, and the patient has a stable knee with full range of motion. SUMMARY Although acute knee dislocations are serious injuries with potentially disastrous results, we believe that with immediate reduction, critical evaluation of the vascular status of the extremity, and prompt surgical intervention when indicated, most of these extremities can be saved. We would emphasize the use of diagnostic arteriography, and imaginative use of relaxing incisions and skin grafts to overcome coverage problems in open knee dislocations. Acknowledgments We wish to acknowledge the cooperation of our associates Dr. Joel Fisler, Dr. W. David Francisco, Dr. John Lynch, and Dr. Andreas Grisolia, who contributed individual cases for this study.