Intraoperative identification and bone grafting of a chronic pelvic discontinuity

Background

Pelvic discontinuity presents unique treatment dilemmas and is one of the most difficult problems encountered during revision total hip arthroplasty (THA). This clinical entity is often chronic secondary to osteolysis, resulting in significant acetabular bone loss, but can also be seen in acute acetabular fractures, most notably in the elderly population, and following iatrogenic fracture during THA. Pelvic discontinuity involves separation of the ilium superiorly from the ischiopubic segment inferiorly. Multiple surgical techniques exist for treating this condition, including cup-cage construct, hemispheric acetabular component with posterior column plating, pelvic distraction, and a custom triflange construct. While the techniques and outcomes of all these procedures are described in subsequent chapters, this chapter will discuss how to identify a pelvic discontinuity and subsequently use a bone graft to fill cavitary defects of varying sizes and appropriately recreate the hip center of rotation.

Intraoperative identification

While a pelvic discontinuity is most frequently identified preoperatively with a mix of plain radiographs and computed tomography scans, a surgeon must be able to identify this entity intraoperatively in cases of iatrogenic fracture. Failure to identify a pelvic discontinuity will almost certainly result in failure of the acetabular reconstruction ( Fig. 11.1 ).

Risk factors for iatrogenic fracture leading to acute pelvic discontinuity include osteoporotic bone, excessive under-reaming, forcible impaction, and elliptical monoblock uncemented components impacted into a hemispheric bed. If an audible crack is heard or the cup is not able to be impacted , the surgeon should consider an iatrogenic fracture and remove the cup. Visual inspection for fracture lines should be performed, and intraoperative flat plate radiographs should be considered for the evaluation of fracture propagation. Once the implant has been removed, the inferior aspect of the ischium is stressed. Movement between the superior and inferior aspects of the acetabulum indicates a pelvic discontinuity. Additional detail on the treatment of acute pelvic discontinuities can be found in Chapter 10 .

Chronic pelvic discontinuities can be subtle and require careful inspection and identification by the treating surgeon. Typically, chronic pelvic discontinuities extend from the anteroinferior region of the acetabulum in the posterosuperior direction toward the greater sciatic notch. The senior author’s preferred technique for the management of chronic pelvic discontinuity is acetabular distraction and reconstruction with or without the use of modular, porous metal augments.

The first step is to define the discontinuity with a Cobb elevator. Meticulous, careful dissection should be performed as most chronic discontinuities have a deficient medial wall. Aggressive tissue dissection with the Cobb elevator can result in catastrophic complications, including visceral and vascular injury – this should be avoided. The pelvic discontinuity should be debrided superficially to prevent destabilization. The goal of chronic pelvic discontinuity is not to achieve an anatomic reduction and rigid fixation but rather to span the discontinuity with a porous cup with or without porous metal augments to reconstruct the deficient columns. The cup will act as an internal plate to stabilize the pelvic discontinuity. The complete technique is described in Chapter 22 .

A lamina spreader is the authors’ preferred instrument for identifying a pelvic discontinuity. It is placed inside of the acetabulum and opened to put tension on the anterosuperior and posteroinferior columns ( Fig. 11.2 ). If the cavitary bone defect is too large, as in many Paprosky IIIA and IIIB defects, a porous metal augment is placed for primary support, and the acetabulum is distracted through the augment. Alternatively, Steinmann pins can be placed into the ischium and ilium, and a modified lamina spreader is used to distract the acetabulum ( Fig. 11.3 ). Once distracted, the surgeon will then sequentially ream until the anterosuperior and posteroinferior columns are engaged.

Bone graft options