Quantification of the effects of respiration and parallax on inferior vena caval filter position

The parallax effect in the evaluation of range of motion in lumbar total disc replacement

BACKGROUND

Range of motion (ROM) has been shown to influence clinical outcomes of total disc replacement (TDR). While the parallax effect in image acquisition has been shown in the literature to influence the accuracy of a variety of measurements, this concept has not been investigated in the assessment of ROM analysis following TDR. We performed an evaluation of the influence of radiograph beam angle on "by hand" and on "gold standard" flexionextension ROM measurements in lumbar total disc replacement. The purpose of this study is to determine (1) the influence of X-ray beam angle on index level angle (ILA) measurements in lumbar TDR using the keel method, and (2) whether the out-of-plane radiographic beam effects cause a difference between true and calculated range of motion.

METHODS

Eight blinded orthopaedic surgeons used the keel method to calculate ROM measurements from radiographs of a flexible Sawbones model (Pacific Research Laboratories, Inc., Vashon, Washington) implanted with a ProDisc-L device (Synthes Spine, West Chester, Pennsylvania). Radiographs were obtained at beam angles of 0°, 5°, 10°, and 15° in the sagittal plane from the device center. Calculations were compared to measurements obtained by a validated digitized software method (Quantitative Motion Analysis, QMA, Medical Metrics, Inc., Houston, Texas). Inter- and intraobserver precision and accuracy were determined.

RESULTS

Compared with QMA, the radiographic keel method had an average error of 3.7°. No significant effect of variation in beam angle on interobserver precision (N = 16, P = .92) or accuracy (N = 16, P = 0.86) or intraobserver precision (N = 8, P = .09) or accuracy (N = 8, P = 0.07) of ROM measurements was identified. Repeat testing with QMA also revealed no effect of parallax and resulted in nearly identical ROM measurements.

CONCLUSIONS

Accuracy and precision of the keel method to determine ROM from index level angle measurements after TDR was not affected by increases in X-ray beam angles up to 15° from the device center.

CLINICAL RELEVANCE

Our study demonstrates that range of motion measurements are not influenced by parallax effect when using the keel method to determine index level angle measurements in lumbar total disc replacement.

Computed tomography imaging of vena cava filter complications: a pictorial review

Caval filters are widely used in the prevention of pulmonary embolism. Filters have proved to be effective, but the complication rate is not negligible. Computed tomography (CT) provides a complete evaluation of the filter, including both caval and extracaval complications. In this review, we describe the normal CT aspect of cava filters, the classification of complications and their CT findings. Technical considerations for adequate CT imaging are also highlighted.

Does cervical spinal cord injury induce a higher incidence of complications after prophylactic Greenfield inferior vena cava filter usage?

PURPOSE

To determine whether acute cervical spine injury represents a risk factor for complications from prophylactic placement of current generation Greenfield inferior vena cava (IVC) filters.

MATERIALS AND METHODS

A retrospective chart review performed during a 7-year period identified 11 patients with acute cervical spinal cord injuries who underwent prophylactic Greenfield IVC filter insertion. Specific complications evaluated included symptomatic pulmonary embolism (PE), migration, filter base diameter changes, caval perforation, and thrombosis. The amount of migration and changes in filter base dimension were compared statistically with a control population of IVC filter patients (n = 16) without cervical spine injuries.

RESULTS

Filter migration (> 10 mm) was the most common complication (46%). Migration usually is caudally directed (64%), may occur early (36% moved > 10 mm within a 30-day period), and is often asymptomatic. The prevalence of filter migration greater than 30 mm was 27%. The average amount of migration for the subpopulation under study was greater than that seen with the control population (P < .05). No statistically significant change in filter base size occurred. The study population also had rates of PE (9%-18%), caval perforation (9%), and IVC thrombus formation (18%) that were higher than the rates in historical controls. The majority of patients with these complications received vigorous pulmonary toilet (46%), including "quad coughs" or cardiopulmonary resuscitation (18%).

CONCLUSIONS

Acute cervical spinal cord injury and the associated supportive care may be associated with an increased risk for caudal IVC filter migration, IVC perforation, caval thrombosis, and PE.