Cutting edge Orthopedics

Knee Dislocations • 39  low incidence of occurrence and high incidence of being missed at initial presentation. These inju- ries are often missed on initial assessment due to spontaneous reduction of the joint, distracting injuries, and absence of abnormality on initial review of plain radiographs. For example, Walker and Kennedy found that the incidence of occult ligamentous knee injuries can be as high as 48% in patients with femur fractures. They point out that the diagnosis of these ligamentous injuries is often delayed by months [4]. Moreover, despite the fact that knee dislocations and bicruciate knee injuries can present after spontaneous reduction, spontaneous reduction does not decrease their morbidity. In a retrospective review of 50 patients with knee dislocations, Wascher and col- leagues found that bicruciate injuries that spontaneously reduced were equivalent to “classic” knee dislocations (three ligaments injured) with regard to injury severity, major vascular injury, and mechanism [5]. The clinical presentation of patients with knee dislocations can often be complicated by pop- liteal artery injuries and injuries to the common peroneal nerve. With regard to MS, it is noted that he has diminished pulses in his right leg. Concomitant popliteal artery injury is a well-estab- lished complication of knee dislocations. In a retrospective study of 245 knee dislocations (241 from a literature review; 4 patients gathered in the study), Green and Allen found the incidence of popliteal artery injury to be as high as 32% [6]. Popliteal artery injury can be a devastating com- plication of these injuries if left untreated. Data from the Lower Extremity Assessment Protocol (LEAP) study of severely injured lower extremities showed that approximately 20% of patients who present to a level one trauma center with a dysvascular limb will need an amputation [7]. This study also demonstrated that this rate rises with increased warm ischemia time. Thus missing these injuries on initial evaluation places patients with knee dislocations at an increasingly high risk for losing their limb. During evaluation of MS in the emergency department, one must obtain either an ankle- brachial index (ABI) examination or computed tomography angiography (CTA) given his knee dislocation. One evidence-based change in the standard of care of these injuries has been the move from routine angiography to selective angiography. Physical examination is the first step in discovering popliteal artery injuries. In a prospective outcome study involving 134 dislocated knees, Stannard and colleagues found that a thorough physical exam had a 90% positive predictive value, with 100% sensitivity and 99% specificity [8]. However, the clinical utility of the protocol set forth by this study, which uses serial physical exams performed by the same surgeon, has been questioned because of the labor-intensive nature of having one person perform multiple serial exams during the initial period after injury. In addition to a thorough physical exam, a quick assessment for vascular injury that can be done at the bedside is the ABI. In a prospective study of 38 patients, with knee dislocations, an ABI of less than 0.90 predicted a vascular injury in 11 patients, with 100% sensitivity and 100% specificity [9]. In the past decade, CT angiography has replaced conventional angiography in detecting vascular injuries in the extremities as a less inva- sive method of detecting these injuries and is a possible screening exam for at-risk limbs or as a diagnostic tool for abnormal ABIs [10]. The preponderance of the published literature indicates that every patient who presents with an obvious knee dislocation, history of a knee dislocation, or physical exam that indicates a knee