Crescent fractures are represented by a spectrum of morphological fracture patterns, sharing a common mechanism of injury. We propose three distinct types according to the extent of Sacroiliac (SI) joint involvement and the size of the crescent fragment, which enables a pragmatic choice of surgical approach and stabilisation technique.

Crescent fractures are fracture dislocations of the SI joint in which there is variable amount of disruption of the SI ligaments extending proximally as a fracture of the posterior iliac wing. We identified three groups of Crescent fractures according to the extent of SI joint involvement, relationship of the fracture line to the S1 and S2 nerve root foramina on anteroposterior and outlet plain radiograph views, and CT films. Type I involves the less than inferior third of the SI joint with a large posterior iliac fragment left attached to the sacrum. This is best approached anteriorly for stabilisation. Type II has between one-third to two-thirds involvement of the SI joint and is treated according to Helfet's technique. Type III has a very small crescent fragment left attached to the sacrum and the inferior two-thirds of the SI joint is disrupted. This is treated with percutaneous SI screws, but will need anterior open reduction in delayed presentations. Based on this, we treated sixteen patients and followed them for at least two years. There were four Type I, four Type II and eight Type III fractures. Fifteen had anatomical reduction and stabilisation of the SI joint with good functional results. Delayed referral, the presence of significant soft tissue injury posteriorly and infected external fixator pins.

From our experience we would like to propose this functional classification of crescent fractures which we find useful in making a choice of surgical approach and stabilisation technique to achieve satisfactory reduction and stabilisation of sacroiliac joint.