Faculty Bibliography

Sports injuries of the knee involving the extensor mechanism are common. Specific conditions additionally affect the extensor mechanism in adolescents during growth and maturation, and in older patients as a result of degeneration. Prior to the advent of magnetic resonance (MR) imaging, the specific anatomical-pathological cause of anterior knee pain was often uncertain, with diagnosis limited to clinical examination and conventional radiographic assessment. MR imaging allows for the accurate and specific diagnosis of pathology of the extensor mechanism, impacting on decision making and clinical treatment of such conditions. In this article the anatomy, normal MR appearance, and common pathological conditions of the extensor mechanism of the knee are described.

Encountering an incidental tumor or tumor-like lesion during a routine magnetic resonance imaging (MRI) of the knee is not uncommon. By far, the majority of these lesions are benign and many of them have characteristic appearances on MRI to allow a confident diagnosis. The most common, and some less common, but important incidental lesions will be discussed including bone lesions (bone cysts, subchondral fractures, enchondromas, non-ossifying fibromas, "tug" lesions, osteochondromas, bone infarcts, and prominent red marrow) and soft tissue lesions (synovial hemangiomas, intracapsular chondromas, bursae, synovitis, soft-tissue cysts, hematomas, heterotopic ossification, vascular lesions and normal variants). Gaining familiarity with the MRI appearance of these incidentally encountered lesions will be helpful in avoiding unnecessary additional tests and/or imaging.

Absence of the long head of the biceps tendon is a rare anomaly particularly when it occurs bilaterally. We present the magnetic resonance and arthroscopy findings in a patient with bilateral congenital absence of the long head of the biceps who presented with bilateral shoulder pain. Identification of a shallow or absent intertubercular groove may aid in differentiating congenital absence of the long head of the biceps from a traumatic tendon rupture.

OBJECTIVE: The objectives of this study were to determine the frequency of a third head of the gastrocnemius and to describe the course, morphology, and insertion of the third head as seen on the basis of routine magnetic resonance (MR) imaging of the knee. MATERIALS AND METHODS: This study was a prospective study of 1,039 consecutive knee MR examinations which were performed for symptoms of pain not associated with claudication. The examinations were performed between September 2004 and January 2005 and were evaluated for the presence of an anomalous third head of the gastrocnemius and to determine its origin and course. Examinations were performed on a variety of magnets ranging from 0.2 to 1.5 T. RESULTS: Of the 1,039 knees, 20 (1.9%) demonstrated an anomalous third head of the gastrocnemius which was seen arising near the midline of the posterior distal femur, between the mid and medial aspect, and joining the medial aspect of the lateral head of the gastrocnemius. The size of the third head varied from a thin threadlike muscle to a rather bulky muscle. In all of these patients, the third head coursed lateral to the popliteal vessels, and none coursed between the vessels. One additional case of a third head of the gastrocnemius was seen which joined the medial head of the gastrocnemius. CONCLUSION: A third head of the gastrocnemius joining the lateral head is not an uncommon variant, seen in 1.9% of knee MR examinations. Most are not associated with vascular symptoms

OBJECTIVE: The symptoms and physical findings of intersection syndrome have been well described in the clinical medical literature. However, the magnetic resonance imaging (MRI) findings in patients with intersection syndrome of the forearm have only recently been described in a small number of patients. We review our experience with imaging of intersection syndrome, describe previously unreported MRI findings, and emphasize modifications to MRI protocols for its evaluation. MATERIALS AND METHODS: Institutional review board approval was obtained for this retrospective review of patients with MRI findings consistent with intersection syndrome of the forearm during the period from January 2004 to September 2006. Six patients were identified, three males and three females, with an average age of 39.3 years. The MRI examinations were reviewed to assess signal abnormalities within and adjacent to the first and second dorsal extensor tendon compartments (DETC): tendinosis, peritendinous edema or fluid, muscle edema, subcutaneous edema, and juxtacortical edema. The overall longitudinal extent of signal alterations was measured as well as the distance from Lister's tubercle to the crossover of the first and second DETC. RESULTS: Review of the MRIs showed increased intrasubstance tendon signal suggesting tendinosis in two of the six patients, peritendinous edema or fluid in all six patients, muscle edema in five of the six patients, and subcutaneous edema in three of the six patients. Juxtacortical edema was seen in one patient. Peritendinous edema or fluid extended distally beyond the radiocarpal joint in three of the six patients. The average distance from Lister's tubercle to the crossover of the first and second DETC was 3.95 cm, in keeping with recently published data. CONCLUSION: Intersection syndrome is an uncommon MRI diagnosis. In addition to the previously described MRI findings of edema adjacent to the first or second DETC, possibly with proximal extension and subcutaneous edema, we have identified additional abnormalities: tendinosis, muscle edema, and juxtacortical edema. In addition, our review shows that first and second DETC signal abnormalities in patients with intersection syndrome are not necessarily limited to the site of crossover but can extend distally beyond the radiocarpal joint. As standard wrist protocols may not include the area of intersection between the first and second DETC, coverage may need to be extended to the mid-forearm

OBJECTIVE: The usefulness of MRI in costal cartilage injuries has not been shown. We report the MRI findings in a series of patients with costal cartilage injuries. CONCLUSION: MRI can be a useful technique in the diagnosis of costal cartilage injuries

PURPOSE: To retrospectively evaluate the appearance of lesions of osseous and soft-tissue structures of the glenohumeral joint on magnetic resonance (MR) images after first-time traumatic posterior shoulder dislocation. MATERIALS AND METHODS: The study was institutional review board approved and HIPAA compliant, as appropriate, for the four institutions at which the involved patients were treated. Informed patient consent was obtained, were applicable. Thirty-six male patients (age range, 15-80 years; mean age, 40.2 years) with clinically documented first-time traumatic posterior shoulder dislocation were examined with MR arthrography (18 patients) or conventional shoulder MR imaging (18 patients). Causes of posterior shoulder dislocation were electric shock in one patient, seizure in one patient, and trauma in 34 patients. Hill-Sachs lesions, rotator cuff tears, biceps tendon abnormalities, posterior labrocapsular complex lesions, humeral head translation, and osseous glenoid version angle were evaluated. Spearman rank correlation and Student t test analyses were performed. RESULTS: In 31 (86%) of the 36 patients, a reverse Hill-Sachs lesion was found. Eleven (31%) patients had a reverse osseous Bankart lesion. Twelve full-thickness rotator cuff tears were seen in seven (19%) patients: four supraspinatus tendon, three infraspinatus tendon, and five subscapularis tendon tears. Six (17%) patients had biceps tendon abnormalities. Posterior labrocapsular complex tears were identified in 21 (58%) patients: 10 (48%) with posterior labral sleeve avulsions and 11 (52%) with reverse Bankart lesions. Twenty-seven (75%) patients had a retroverted scaphoglenoid angle (mean, 4.5 degrees ). The mean humeral translation distance relative to the osseous glenoid fossa was -4.8 mm; in 33 (92%) patients, this distance was translated posteriorly. CONCLUSION: The MR appearance of traumatic posterior shoulder dislocation was characterized by reverse Hill-Sachs lesions in 86% of patients and posterocaudal labrocapsular lesions in nearly 60% of patients. Full-thickness rotator cuff tears were seen in approximately 20% of patients

OBJECTIVES: The objective was to retrospectively determine the prevalence and patterns of iliopsoas injuries based on consecutive MRI examinations, correlated with clinical findings. MATERIALS AND METHODS: From 4,862 consecutive MRI examinations of the hips and pelvis, 32 patients with 33 iliopsoas injuries were identified and graded as muscle strain, partial tendon tear, and complete tendon tears. These patients' medical records were reviewed to determine age, gender, and cause of symptoms. RESULTS: The prevalence of iliopsoas tendon and myotendinous injuries was 0.66% (95% CI: 0.44-0.89). There were 18 females and 14 males whose ages ranged from 7 to 95 years (mean, 54 years). The most frequent presenting symptom was hip pain and the most frequent clinical diagnosis, an occult fracture. The most common injuries in patients under 65 years (16 patients) were muscle strains and partial tendon tears, most often due to an athletic injury. The most common injury in patients 65 years and older (16 patients) was a complete tear (8 patients, all females), 2 of which were spontaneous in origin. CONCLUSIONS: Each grade of iliopsoas injury occurred with similar frequency. The more advanced the age of the patient, the more severe the injury. Non-athletic injuries predominated in patients 65 years and older; athletic injuries were the most common cause of iliopsoas injury in patients under 65 years