Preoperative imaging of cervical pedicles: comparison of accuracy of oblique radiographs versus axial CT scans.

In spite of concerns about safety during their insertion, cervical spine pedicle screws have demonstrated biomechanical superiority over lateral mass screws in several biomechanical studies. One of the concerns for placement of cervical pedicle screws is their small size. Preoperative planning with computed tomography to assess pedicle width has been shown to be extremely accurate and is recommended by several authors. To date there has been no study assessing the accuracy of oblique radiographs for pedicle measurement. We sought to compare accuracy of the oblique radiographic measurements of cervical pedicle width with axial CT scan measurements. Five fresh-frozen human cadaveric cervical spines C3-C7 were studied. Thin cut 1.25 mm computed tomography axial cuts were made through the pedicle isthmus. Oblique radiographs at 35 degrees , 45 degrees , and 55 degrees angles were taken of the right and left pedicles of each specimen using a standardized technique. Each radiograph contained a pin of known length to correct for magnification. All pedicles were again measured and corrected for magnification using the standard pin. Corrected oblique radiograph measurements were compared to CT for each specimen. The outer pedicle width was measured and agreed upon by consensus. The radiograph measurements were on average significantly larger than CT measurements for the pedicles indicating that the pin standard did not completely correct magnification. Plain radiographic data failed to reveal that one oblique angle was favorable to another in terms of magnification or precision. Plain radiographs at oblique angles do not provide accurate measurements of subaxial cervical pedicles at 35 degrees , 45 degrees , or 55 degrees angles. We recommend that thin cut axial CT scans be obtained on all patients prior to transpedicular fixation in the cervical spine.

Evaluation of periprosthetic lucency after total ankle arthroplasty: helical CT versus conventional radiography.

BACKGROUND: Osteolysis after total ankle arthroplasty (TAA) has become a major concern regarding long-term implant survival. The primary goal of this study was to determine whether CT was more sensitive than plain films in detecting the presence and extent of periprosthetic lucency. A secondary goal was to determine whether lack of syndesmotic fusion was associated with more extensive lucency. METHODS: Seventeen patients (19 ankles) who had TAA between 2001 and 2003 were consecutively recruited and evaluated as part of a prospective study. Plain radiographs and helical CT with metal-artifact minimization were obtained. Evidence of lucent lesions and syndesmotic fusion was compared using the different imaging techniques. RESULTS: Of the 19 ankles imaged, a total of 29 lesions were detected by CT, whereas plain radiographs detected 18 lesions. CT detected 21 lesions less than 200 mm(2), of which plain radiographs detected only 11. The mean size of the lesions detected on CT was over three times larger than the size on plain radiographs. With the small sample size used, there were no statistically significant differences between ankles with and without fusion of the syndesmosis and the extent (p = 0.84) and location (p = 0.377) of lucency. CONCLUSION: CT is a more accurate method for early detection and quantification of periprosthetic lucency than plain radiographs. Accurate evaluation of lucent lesions may identify patients at high risk for lack of syndesmotic fusion with subsequent loosening and implant failure.

Extracapsular placement of distal tibial transfixation wires.

BACKGROUND: Treatment of tibial plafond fractures with external fixation may involve use of transfixation wires within the periarticular region. Pin track infections that develop along wires placed intracapsularly may lead to joint infection. To our knowledge, there have been no previous investigations assessing the circumferential reflection of the ankle capsule or the potential for communication between the distal tibiofibular joint and the tibiotalar joint. The purpose of this study was to define these anatomic entities to provide guidelines for safe extracapsular placement of distal tibial wires. METHODS: Twelve fresh-frozen cadaveric ankles and three ankles of living human volunteers were utilized for this study. High-resolution magnetic resonance imaging was performed on each ankle after pressurized distention of the joint capsule with gadolinium solution. The perpendicular distance from the subchondral bone at the joint line to the capsular synovial reflection was measured with use of a verified technique. The cadaveric ankles were sectioned, the capsular synovial reflections were measured by investigators who were blinded to the imaging results, and the corresponding measurements were compared. RESULTS: The anterolateral capsular synovial region displayed the most proximal reflection in all specimens (mean, 9.3 mm; maximum, 12.2 mm). The anteromedial region displayed less reflection (mean, 3.3 mm; maximum, 5.5 mm). All posteromedial and posterolateral synovial reflections were 12.2 mm from the subchondral surface of the plafond avoids penetration of the capsule. The distal tibiofibular joint communicates with the tibiotalar joint and thus should not be penetrated, to ensure extracapsular placement of the wires.

Imaging of football injuries to the upper extremity.

Imaging of football players is unique in many ways. Familiarity with mechanisms of injury, position of the player, and the need for rapid diagnosis and reporting will help radiologists when dealing with these athletes. Although plain radiographs are typically the first imaging modality used, MR imaging has become the cornerstone on which diagnoses and treatment decisions are based. As these athletes become stronger, faster, and more skilled, the ability to accurately assess their injuries becomes even more important, and understanding of the challenges that these patients present becomes critical.

Throwing injuries of the upper extremity.

The overhead throwing motion is a complex sequence of maneuvers that requires coordinated muscle activity in the upper and lower extremities. The shoulder and elbow are subject to multidirectional forces and are particularly vulnerable to injury during specific phases of the overhead throwing motion. Ligamentous, tendinous, neural, and osseous pathology that may occur in the shoulder or elbow of an overhead-throwing athlete will be discussed, with an emphasis on the role of MR imaging and MR arthrography.

MRI findings in Little Leaguer's shoulder.

Little leaguer's shoulder, a stress injury of the proximal humeral physis, should be considered in the differential diagnosis for an adolescent baseball player with shoulder pain, especially if the player is pitching regularly in a competitive environment. While roentgenographs may or may not be helpful, depending on the duration and severity of the injury, we report the MRI appearance of a case of little leaguer's shoulder. We found MRI helpful in diagnosing injury to the growth plate that was radiographically occult; furthermore, we were able to document the patient's progress with a follow-up MRI examination, which showed improvement with treatment.