Isolated fractures of the ischium are rare and quite often do not involve the weight bearing portion of the pelvis. Avulsion fractures of the ischium can occur with acute hamstring injuries. The majority of fractures of the ischium are associated with acetabular fractures that affect the posterior column. The obturator foramen is a fixed ring structure. A fracture in one part of the ring will almost always lead to a fracture of the ischiopubic ramus.
The ischium is one of three bones that contribute to formation of the hemipelvis. The ischium is composed of a body and ramus. The body contains the posterior one third of the acetabulum. The ramus extends ventrally to connect to the inferior pubic ramus. The ramus of the ischium is where the ischial tuberosity is found. The posterior ischium contains the lesser sciatic notch and a portion of the greater sciatic notch. The ischial spine separates the greater sciatic notch (cephalad) from the lesser sciatic notch.
The ischial tuberosity serves as a point of attachment for many muscles. It is where all of the hamstrings originate except for the short head of the biceps femoris muscle. The quadratus femoris, inferior gemellus, obturator internus, obturator externus, and a portion of the adductor magnus muscles originate from the tuberosity. The sacrotuberous ligament attaches from the sacrum to the ischial tuberosity and, in conjunction with the sacrospinous ligament, stabilize the pelvis from rotational deformity. The sacrospinous ligament runs from the ischial spine to the sacrum.
The blood supply to the ischium mainly is from the obturator artery and the internal pudendal artery. There are numerous nutrient foramina along the ischial tuberosity where these vessels enter the bone with the soft tissue attachments.
Patients typically present with pain in the absence of deformity. Patients may be able to ambulate or be completely obtunded in the polytrauma patient. The mechanism of injury usually dictates the degree of associated injuries.
Any fracture in the pelvic should raise the clinical suspicion for associated injuries. A comprehensive physical examination is warranted in these situations per the ATLS protocol. After physical examination, plain radiographs should include AP pelvis, inlet, outlet and Judet views. Isolated ischial fractures are rare and a CT may be warranted to evaluate the acetabulum.
Isolated ischial fractures that are caudad to the acetabulum are not involved with weight bearing and do not require fixation for ambulation. There are some instances where open reduction and internal fixation is indicated.
- Open fractures
- Vascular injury
- Posterior wall fractures (relative)
- Posterior column fractures (relative)
- Hamstring avulsion of the tuberosity (relative)
The ischium is approached posteriorly most commonly through a Kocher Langenbeck approach.
Complications include infection, neurovascular injury, bowel or bladder injury.