Irreducible posterolateral knee dislocation resulting from a low-energy trauma

Case Report

Irreducible Posterolateral Knee Dislocation Resulting From a Low-Energy Trauma ¨ rgu¨den, M.D., Hakan Bilbas¸ar, M.D., A. Merter O ¨ zenci, M.D., Mustafa U F. Feyyaz Akyıldız, M.D., and Semih Gu¨r, M.D.

Abstract: A small amount of knee dislocations is included in the irreducible knee dislocations group. In such instance, medial femoral condyle is buttonholed through the gap formed by medial retinacular and capsular structures and this prevents reduction. In this study, we present two cases in which there were irreducible posterolateral knee dislocations resulting from a low-energy trauma. In both cases, dimple sign produced by the invagination of the medial retinacular structures and capsule and ecchymosis medially were noted. Soft tissue invaginated between the trochlea and intercondylar notch was extracted by open reduction. Key Words: Low-energy trauma—Irreducible—Knee dislocation—Dimple sign—Open reduction—Injury mechanism.

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nee dislocation is a rare injury. Although it occurs generally during a high-energy trauma, knee dislocations can also occur after a low-energy trauma.1-3 Most of the diagnosed cases can easily be reduced by closed manipulation. Irreducible knee dislocations are even more rare and usually they are included in the group requiring open reduction.3-10 The medial retinaculum and capsule, which prevent reduction by invaginating within the femorotibial joint cavity, must be extracted from the joint. In this study, we present two cases with posterolateral knee dislocations after low-energy traumas, which cannot be reduced by closed methods. CASE REPORTS Between 1990 and 2002, knee dislocation was diagnosed in 21 knees of 19 patients. Two of them were

From the Faculty of Medicine , Department of Orthopedics and Traumatology, Akdeniz University, Antalya, Turkey. ¨ rAddress correspondence and reprint requests to Mustafa U ¨ niversitesi Tıp Fak¨ultesi, Ortopedi ve Travg¨uden, M.D., Akdeniz U matoloji Anabilim Dalı, 07070 Antalya, Turkey. E-mail: urguden@ akdeniz.edu.tr © 2004 by the Arthroscopy Association of North America 0749-8063/04/2006-3787$30.00/0 doi:10.1016/j.arthro.2004.04.010

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irreducible and required open reduction. One of the patients was a 51-year-old man and the other was a 53-year-old woman. The dislocations of the patients occurred after low-energy traumas. The 51-year-old man was admitted to emergency service 2 hours after the trauma and the 53-year-old woman was admitted 3 hours after the trauma. In their stories, it was reported that the male patient was swimming in the sea while the undulating effect of the wave pushed him forward and his ankle was trapped between the parts of a floating bridge and dislocation occurred while his knee was flexed, abducted, tibia externally and femur internally rotated; the female patient fell during walking after she got stuck, her foot stood still, her knee flexed and came to valgus, her tibia externally and femur internally rotated. There were no neurovascular injuries in the initial examinations of the two patients. In addition to physical examination, it was angiographically proven (as a standard protocol in our clinic) that there was no vascular lesion in the male patient. In the female patient, we believed that there was a little risk for vascular damage because the injury occurred after a low-energy trauma and there was no dramatic displacement in irreducible dislocations. Physical examination findings were further supported by the noninvasive Doppler ultrasonography method in the female patient.

Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 20, No 6 (July-August, Suppl 1), 2004: pp 50-53

IRREDUCIBLE POSTEROLATERAL KNEE DISLOCATION

FIGURE 1.

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Dimple sign on the medial aspect of the knee.

Dimple sign was noted in the physical examinations of the knee joints of both patients (Fig 1). No dramatic displacements were observed in the evaluations of the x-ray films (Fig 2). In the male patient, who could not be taken into operation soon as a result of the logistic problems, anatomic structures preventing reduction were documented by magnetic resonance imaging (Fig 3). Time elapsed until the operation was 4 hours in both cases. Elastic fixation was determined during an attempt for closed reduction in both cases, and it was seen that knees returned to their dislocated position again. This was followed by open reduction to extract the soft tissues within the joint cavity preventing reduction. After the skin and subcutaneous tissues were cut by a median longitudinal incision, it was observed that the medial femoral condyle was just under the subcutaneous tissue and completely extraarticular. The joint cavity was opened by a medial parapatellar arthrotomy. It was noted that the medial retinaculum and capsule buttonholed through the in-

FIGURE 3. Invagination of the medial retinacular structures into the knee joint seen on magnetic resonance imaging.

FIGURE 2. Anteroposterior and lateral direct x-ray views of the posterolateral dislocation.

FIGURE 4. Structures seen in the medial joint cavity during open reduction.

tercondylar notch and prevented reduction (Fig 4). Reduction was achieved after extraction of the medial retinaculum and capsule from the joint cavity. In both cases, it was seen that the medial collateral ligaments and both cruciate ligaments were injured but the posterolateral structures were intact. After closure of the medial parapatellar arthrotomy and the skin incision, extremity was splinted with the knee flexed at 20°. In the x-rays taken after splintage, it was determined that concentric reduction was not achieved in the female patient and fixation was achieved by an external fixator application. There were no necrosis or wound healing problems around the surgical incisions and medially where the dimple sign was observed. No

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neurovascular pathology was detected during follow up. Reconstruction was proposed to the female patient in the subacute phase, but the conservative treatment was applied when she rejected that treatment. The male patient was taken under a reconstruction program in the subacute phase, but the patient moved abroad. DISCUSSION Dislocation of the knee is a rare but serious injury that often results in disruption of the popliteal vessels, the collateral and cruciate ligaments, and the capsule of the knee joint. Most of the diagnosed cases can be reduced by closed methods. Reported publications in the literature regarding the irreducible cases are generally very few in number.3,5-7,9-12 Most of the irreducible knee dislocations are posterolateral dislocations and result from the soft tissue interposition.5-8,10 Clinical and radiologic aspects of posterolateral knee dislocations are quite different from classic knee dislocations. As a result of the lack of the dramatic displacement shown on radiography, the nature and severity of the injuries are not always readily appreciated and the treatment of these dislocations is sometimes delayed.5,6,8 Recognition of this entity in reports in the literature has heightened the awareness of the need for surgical intervention to achieve reduction. The medial collateral ligament and both cruciate ligaments are often injured in these irreducible knee dislocations, but the lateral ligaments and neurovascular structures are usually spared.5-8,10 One of the most consistent and characteristic findings of these injuries is the dimple sign.4-8 Achievement of the reduction early in the irreducible cases will help decrease the risk of skin necrosis medially.5 Skin necrosis medially can occur in cases in which open reduction is delayed.4,10 This period is even more important in cases in which knee dislocation is produced by direct trauma onto the medial aspect of the knee. We believe that the possibility for skin necrosis in our cases was eliminated because of the early open reduction procedure. There is a consensus concerning the formation of irreducible posterolateral knee dislocation that the knee should be in flexion under the effect of the continuing valgus stress. Still, there is no consensus about the position of the tibia, internally or externally rotated, in irreducible dislocations.4-8 When we evaluated the injury mechanism in our cases, we determined that the knees were slightly flexed and were in valgus, tibias externally, femurs internally rotated.

Evidence suggests that knee flexion, valgus stress, and external tibial and internal femoral rotation are important mechanisms in irreducible knee dislocations. The relationship between knee dislocation and neurovascular involvement is a well-known phenomenon and much about this subject is pointed out in the literature.13-18 Shelbourne et al.2 stated that the possibility of vascular involvement is less in low-energy traumas and suggested that these can be evaluated by noninvasive methods. However, McCoy et al.1 stated that possibility of vascular injury is quite high in low-energy knee traumas. Because there is not dramatic displacement in irreducible knee dislocations, no neurovascular injury is reported so far.5-8,10 In dislocations produced by low-energy traumas, further displacement of the knee is prevented by the invaginated medial capsular and retinacular structures in the joint and these lower the risk of arterial injury. The absence of neurovascular injuries in our cases made us believe that neurovascular status in such cases can be evaluated by noninvasive methods without the need for invasive imaging techniques. In conclusion, if a dimple sign is noted in physical examination or an elastic fixation is noted during reduction maneuver, it must be remembered that concentric reduction of such cases can be achieved by open reduction. Because there is no dramatic displacement in irreducible knee dislocations produced by low-energy traumas, we believe that the monitoring of neurovascular status will be sufficient without the need for invasive methods.

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