Edward C. Weber

Vacuum phenomenon: Clinical relevance

Vacuum phenomenon (VP) is an anatomical entity of potential confusion in the diagnosis and evaluation of joint pathology. Observation of this phenomenon has been demonstrated on basic radiographs, computed tomography, and magnetic resonance imaging. Although VP is most often associated with degenerative joint disease, it is observed with other pathologies. Two problematic scenarios can occur: a false‐positive diagnosis of serious pathology instead of benign VP and a false‐negative diagnosis of benign VP with a more serious underlying process Despite this potential for confusion, criteria for distinguishing VP from other causes of joint pain and for evaluating a suspected case of VP have not been fully established. We reviewed the literature to determine underlying mechanism, symptomology, associated pathologies, and clinical importance of VP. The formation of VP can be explained by gas solubility, pressure–volume relationships, and human physiology. CT, GRE‐MRI, and multipositional views are the best imaging studies to view VP. Although most cases of VP are benign, it can be associated with clinical signs and symptoms. VP outside the spine is an underreported finding on imaging studies. VP should be on the differential diagnosis for joint pain, especially in the elderly. We have proposed criteria for diagnosing VP and generated a basic algorithm for its workup. Underreporting of this phenomenon shows a lack of awareness of VP on the part of physicians. By identifying true anatomic VP, we can prevent harm from suboptimal treatment of patients. Clin. Anat. 27:455–462, 2014.

Anterior Cruciate Ligament Tear

An objective index of anterior cruciate ligament (ACL) tears based on posterior cruciate ligament (PCL) shape has been introduced. The PCL shapes on magnetic resonance imaging (MRI) were measured in 67 patients (31 normal ACL, 31 torn ACL, and five partial ACL tears, all confirmed by arthroscopy). All of the measurements were performed in a blinded manner, without previous knowledge of the MRI or arthroscopy diagnosis. The index consisted of the ratio B/A, with B equaling the length of the line between the posterior inferior tibia1 and the superior anterior femoral attachment of the PCL, and A equaling the maximum perpendicular distance from this line to the PCL. All measurements were performed twice, and the mean was used for statistical significance. The average index ratio was 5.4 and 3.9 for normal ACL and torn ACL, respectively. Using a cutoff value of 4.75, the sensitivity of the index was 87% and the specificity was 84%. An objective and reproducible index measurement of PCL shape for normal and injured ACL has been established. It provides additional information for both orthopaedic surgeons and radiologists in the diagnosis of ACL injury. A prompt, accurate diagnosis is essential in the management of acute ligamentous injury of the knee. Often, the physical examination is compromised by pain, muscle spasm, and knee effusion. With the advent of magnetic resonance imaging (MRI), the evaluation of acute knee ligamentous injury has been facilitated. For anterior cruciate ligament (ACL) injury, the MRI has a specificity of 70-92%, and sensitivity of 70-96%.2*s The appearance of the ACL on MRI may occasionally be equivocal, and it is not possible to confirm or establish the diagnosis of ACL injury. Recently, a few authors have included the presence of various posterior cruciate ligament (PCL) shapes and angulation on MRI as diagnostic signs in the diagnosis of ACL However, these signs were described based on subjective analysis, without accurate objective measurements. The purpose of this study is to provide an objective measurement of the PCL configuration on MRI for both the ACL intact and ACL torn knees.