Tilted lateral radiographs in the evaluation of intra-articular distal radius fractures.

The anatomy of the distal radius confounds the assessment of fracture displacement of the lunate facet. Since reduction of the articular surface is paramount to obtaining good clinical results, this study was designed to evaluate whether a radiograph taken 22 degrees from true lateral (forearm held at a 22 degrees angle from the horizontal film cassette) would enhance the accuracy of measuring displacement. Fifteen lunate facet fractures of varying depression were produced in 7 fresh cadaveric wrists. Posteroanterior (PA), standard lateral, and 22 degrees tilted lateral radiographs were obtained of each fracture pattern. Four observers reviewed the films and measured the depression of the fragments from their anatomic position. Measurement error from actual depression averaged 1.1 mm when the evaluators evaluated the 22 degrees lateral and PA films, 1.5 mm for the standard lateral and PA views, and 0.8 mm for the standard lateral, 22 degrees lateral, and PA radiographs (combined group). The decrease in measurement error obtained from all 3 groups was statistically significant. The results of this study suggest that the 22 degrees tilted lateral, either in combination with the standard lateral radiograph or just with the PA view, may help the hand surgeon better understand the intra-articular depression of lunate facet fractures of the distal radius.

Obex/nucleus gracilis position: its role as a marker for the cervicomedullary junction.

Traditionally, the decussation for the pyramids has been the designated marker for the cervicomedullary junction. With Chiari malformations abnormal caudal migration of posterior fossa structures occurs, resulting invariably in a low position of the caudal poles of the cerebellar tonsils (i.e. tonsillar heterotopia) and a low position of the cervicomedullary junction. Since there is considerable variability in normal caudal tonsillar position and because the pyramidal decussations are difficult to image, diagnostic confusion may exist when the cerebellar tonsils reside in an intermediately low position. This study utilized anatomic specimens to establish the normal morphologic relationship between the position of the obex/nucleus gracilis (O/NG) and the pyramidal decussations; the former consistently lies 5-6 mm rostral to the latter. Having established that anatomic relationship, the O/NG position was then used to assess the cervicomedullary junction position in a radioanatomic survey of normal brain MR examinations. This analysis established a mean O/NG position 10-12 mm above the plane of the foramen magnum. The O/NG position was then evaluated in patients with low tonsillar position. This analysis revealed, as expected, that patients with Chiari II malformation exhibited tonsillar and O/NG positions well below the plane of the foramen magnum. It also distinguished between two additional groups of patients with less florid MR findings. These include patients who exhibit minimally low cerebellar tonsils but essentially normal O/NG position; these patients should be considered normal expressing only minor variation of tonsillar position. The remaining patients exhibit evidence of both intermediately low tonsillar and low O/NG positions, suggesting an underlying anomaly of both tonsil and brainstem development.(ABSTRACT TRUNCATED AT 250 WORDS)