Plating of an acute pelvic discontinuity

Background

Periprosthetic pelvic discontinuity is the loss of continuity between the superior and inferior hemipelvis involving the floor and both columns of the acetabulum because of either fracture or bone loss. The prevalence of pelvic discontinuity is challenging to assess; however, most series report the incidence at between 1% to 5% in revision total hip arthroplasty (THA). It is usually chronic in nature, associated with pathologic bone loss, and associated with failed THA. Acute pelvic discontinuity (APD) encountered in the setting of primary and revision THA is much less common and can also be challenging to manage.

The most common cause of APD is iatrogenic, occurring during overzealous acetabular preparation, impaction of the acetabular implant, or removal of well-fixed implants ( Fig. 10.1 ). ^, Postoperative traumatic periprosthetic fractures of the acetabulum can result in APD, and although extremely rare, the incidence is expected to increase. Risk factors for APD include female sex, rheumatoid arthritis, osteoporosis, poor bone quality, history of pelvic radiation, press-fit uncemented acetabular components (especially elliptical designs), acetabular under- or over-reaming, and revision acetabular surgery. ^{, ,}

Unlike chronic pelvic discontinuity, the majority of acute cases are associated with more modest bone loss, better bone quality, relatively mobile hemipelvises amenable to reduction, and favorable biology/healing potential. As such, anatomic reduction and compression plating of the discontinuity, followed by revision of unstable acetabular components, is the mainstay of treatment of APD ( Fig. 10.2 ). ^{, , , ,} APD associated with massive bone loss (failing THA, multiple revisions) or unfavorable biology (malignancy, pelvic radiation) are best managed with techniques reserved for chronic pelvic discontinuity as described in the respective chapters of this textbook.

Premise: This technique is based on the use of compression plating to facilitate bone-to-bone healing of the discontinuity in the setting of normal bone metabolism, adequate bone stock, and favorable biology for fracture healing associated with APD. Restoration of pelvic/column stability is combined with a revision of an unstable acetabular component using highly porous cementless fixation, which has been shown to have superior outcomes than cemented or other nonbiologic (cages/rings) techniques. ^,

Diagnosis and evaluation of APD

The largest available series reports a 0.4% incidence of iatrogenic intraoperative acetabular fractures, occurring more often in revision THA and associated with patient and surgical factors. ^{, ,} Surgeons must maintain a high index of suspicion for intraoperative fractures, especially APD, because of the relative rarity and significant consequences if missed. Several observations can alert the surgeon to the possibility of an intraoperative APD, including unexpected medialization of the reamers; unexplained failure of the shell to become stable; unexpected medialization; and a change in pitch during impaction of the shell. Full exposure of the acetabulum, visualization of the entire fracture, and testing column stability are essential to identifying APD. Intraoperative radiographs should be considered if the diagnosis is equivocal. We prefer the Unified Classification System (UCS) to classify and guide management for all periprosthetic fractures, although other acetabular-specific classification systems can be used. The large majority of intraoperative iatrogenic APD are B2 (unstable prosthesis/good bone stock) in the UCS classification, appropriately managed with compression plating and cup revision. The classification and management of acetabular periprosthetic fractures apart from APD are beyond the scope of this chapter.

Iatrogenic intraoperative APD may go unrecognized, leading to the diagnosis on postoperative radiographs or in the early postoperative period (pain) ( Fig. 10.3 ). ^, Non-operative management of UCS B2 fractures is associated with poor outcomes and should only be reserved for those medically unfit for revision surgery. ^, If non-operative management is chosen in cases with a non-displaced fracture and a stable appearing shell, close clinical and radiographic follow-up must be done to monitor for a change in position of the cup or fracture displacement and protected weight-bearing is recommended for a period of time postoperatively.

Although they represent only about 10% of THA periprosthetic fractures, trauma-related acetabular fractures can be a cause of APD ( Fig. 10.4 ). These injuries can be an indicator of a high-energy mechanism, and patients should be managed as per Advanced Trauma Life Support protocols. ^, Most acute traumatic APD periprosthetic fractures are transverse or t-type. ^{, ,} There is some evidence for the non-operative treatment of acute traumatic APD for non-displaced B1 fractures; however, displaced B1 or B2 fractures must be addressed surgically in medically fit patients. ^,

A detailed review of the radiographic evaluation of pelvic discontinuity can be found in Chapter 3 . The evaluation of APD requires, at minimum, an AP pelvis, AP and lateral hip, and Judet view pain radiographs. ^{, ,} Markers of APD include a visible fracture line though the pelvis, translation/rotation of the inferior relative to the superior portion of the pelvis, asymmetry of the obturator rings, and medial migration of the inferior hemipelvis (and/or implant) disrupting Köhler’s line ( Fig. 10.5 ). Computed tomography (CT) with modern metal suppression, thin cut, and reformatted protocols can aid in the diagnosis of APD and in the determination of the fracture pattern, bone loss, and operative planning. ^,

Lastly, the importance of a thorough history, physical exam, and comprehensive preoperative evaluation cannot be overstated. The history of the affected joint and any previous operative reports, implant stickers, and serial radiographs should be obtained and reviewed when possible.

Surgical technique