We hypothesised that the anterior and posterior walls of the body of the first sacral vertebra could be visualised with two different angles of inlet view, owing to the conical shape of the sacrum. Six dry male cadavers with complete pelvic rings and eight dry sacrums with K-wires were used to study the effect of canting (angling the C-arm) the fluoroscope towards the head in 5° increments from 10° to 55°. Fluoroscopic images were taken in each position. Anterior and posterior angles of inclination were measured between the upper sacrum and the vertical line on the lateral view. Three authors separately selected the clearest image for overlapping anterior cortices and the upper sacral canal in the cadaveric models. The dry bone and K-wire models were scored by the authors, being sure to check whether the K-wire was in or out.

In the dry bone models the mean score of the relevant inlet position of the anterior or posterior inclination was 8.875 (standard deviation (sd) 0.35), compared with the inlet position of the opposite inclination of –5.75 (sd 4.59). We found that two different inlet views should be used separately to evaluate the borders of the body of the sacrum using anterior and posterior inclination angles of the sacrum, during placement of iliosacral screws.

Cite this article: Bone Joint J 2015;97-B:705–10.

Crescent fracture dislocations are a well-recognised subset of pelvic ring injuries which result from a lateral compression force. They are characterised by disruption of the sacroiliac joint and extend proximally as a fracture of the posterior iliac wing. We describe a classification with three distinct types. Type I is characterised by a large crescent fragment and the dislocation comprises no more than one-third of the sacroiliac joint, which is typically inferior. Type II fractures are associated with an intermediate-size crescent fragment and the dislocation comprises between one- and two-thirds of the joint. Type III fractures are associated with a small crescent fragment where the dislocation comprises most, but not all of the joint. The principal goals of surgical intervention are the accurate and stable reduction of the sacroiliac joint. This classification proves useful in the selection of both the surgical approach and the reduction technique. A total of 16 patients were managed according to this classification and achieved good functional results approximately two years from the time of the index injury. Confounding factors compromise the summary short-form-36 and musculoskeletal functional assessment instrument scores, which is a well-recognised phenomenon when reporting the outcome of high-energy trauma.