Lumbosacral lesions associated with pelvic ring injuries.

In pelvic ring injuries, an anterior lesion is usually combined with a lesion of the posterior ring segment. A fracture of the sacrum is the most common type of posterior lesion. Its severity ranges from a stable minimal compression fracture of the ala of the sacrum to a displaced fracture with complete loss of stability. The fracture line commonly involves the first and second sacral foramina, exiting the bone distally through its free border and proximally just lateral to the articular process of S1. This study shows that in a number of cases the proximal fracture line passes through or medial to the articular process of S1. Consequently, displacement of the involved hemipelvis causes no damage to the lumbosacral junction if the fracture line passes lateral to the articular process of S1. However, any displacement of the mobile hemipelvis must injure the lumbosacral junction with the latter fracture pattern if the fracture line passes through or medial to the articular process of S1. We found an injury of the lumbosacral junction in 6% of all of our pelvic ring injuries and in 38% of those with an unstable vertical sacral fracture. One kind of these lesions, the locked dislocation of the L5/S1 joint, was shown to inhibit reduction of a displaced sacral fracture. Furthermore, these lesions may be responsible for some of the lumbosacral pain frequently persisting after pelvic ring injuries.