Pelvic discontinuities consist of a lack of continuity between the superior hemipelvis and inferior hemipelvis. While typically encountered in failed total hip arthroplasties (THAs) with massive bone loss, acute pelvic discontinuities may also occur during primary THAs due to excessive acetabular reaming or impaction of press-fit acetabular components. A thorough history and physical examination are paramount, but radiographic analysis remains the cornerstone of such a diagnosis. Indications of a pelvic discontinuity include a visible fracture line, obturator ring asymmetry, and medial migration of the inferior hemipelvis with disruption of Kohler’s line [1].

Many classifications have been proposed to describe periprosthetic bone loss in revision THAs. Paprosky et al.’s [2] is the most commonly utilized scheme, but the American Academy of Orthopedic Surgeons (AAOS) [3] also has a classification scheme available. In the Paprosky classification, there is no specific classification for a pelvic discontinuity. However, they can occur with type IIC or IIIB defects. Based upon the AAOS classification, pelvic discontinuities are considered a type IV defect [3]. Berry et al. [1] further subclassified these type IV defects into three subtypes: type IVa (association with cavitary or mild segmental bone loss), type IVb (large segmental or a combined defect), and type IVc (any lesion on a previously irradiated acetabulum).

The true epidemiology of pelvic discontinuities after primary THA is difficult to assess. However, most literature suggests that the incidence is between 1 and 5% [4–6]. The Mayo Clinic reported an incidence of 0.9% in 3505 revisions [7]. Given the fact that primary and revision THAs are projected to increase by 174% and 137%, respectively, by the year 2030 [8], it is likely that pelvic discontinuities will continue to be an increasing burden.

There are several risk factors that may predispose patients to an intraoperative pelvic discontinuity. Those factors include:

There are a few scenarios that deserve special attention. Postmenopausal women have a particularly increased risk of acute pelvic discontinuity given their smaller acetabuli and lower bone density [12]. In addition, the use of press-fit acetabular component is a risk factor for pelvic discontinuities. While Springer et al. [11] highlighted the risk of an intraoperative pelvic discontinuity due to over-reaming of the acetabulum, others have shown an increased risk of fracture with under-reaming and impaction of uncemented acetabular components [12, 13].

There are several preventative measures that may reduce the risk of pelvic discontinuity during a primary THA. Foremost, a safe and adequate exposure of the acetabulum is essential. The importance of such an exposure is highlighted by the fact that cup malpositioning is more common in obese patients where exposure is often compromised [14]. In addition, patients with poor bone quality (i.e., postmenopausal females with osteoporosis) deserve special attention to avoid overly aggressive placement of retractors.

Once an adequate exposure is obtained, the surgeon must carefully ream the acetabulum, taking into account the preoperative templating, sharpness of the reamers, quality of the host bone, and particular implant system being utilized. Over-reaming can lead to major defects, particularly when the acetabulum is reamed asymmetrically. In some scenarios, the surgeon may consider line-to-line reaming to minimize aggressive impaction of the acetabular component. If an uncemented acetabular component is impacted and an adequate press-fit is not obtained, the surgeon should remove the acetabular component to ensure that a discontinuity was not inadvertently created. Intraoperative imaging in orthogonal planes should also be considered if suspicion for an intraoperative fracture exists.

While a thorough history and physical examination are important, most pelvic discontinuities are diagnosed on imaging studies. All patients should have a basic set of radiographs including an anteroposterior (AP) pelvis, AP hip, and a lateral hip. With these views, the anterior column can be evaluated via the iliopectineal line, while the posterior column can be evaluated via with ilioischial line (Fig. 12.1). A disruption in either of these lines is concerning for a pelvic discontinuity. Judet radiographs are often very helpful, including an iliac oblique and obturator oblique [15]. Martin et al. [16] recently showed that radiographic indicators of a pelvic discontinuity include either a fracture line identified on two orthogonal views (i.e., AP pelvis and true lateral radiograph or both Judet views) or a fracture line identified on one view (AP pelvis, Judet view, or true lateral radiograph) associated with evidence of pelvic rotation or pelvic asymmetry (Fig. 12.1). The above criteria was accurate in diagnosing 94% of pelvic discontinuities without advanced imaging. Moreover, the combination of an AP pelvis, a lateral hip, and Judet views led to an accurate diagnosis in nearly all cases.

However, advanced imaging, particularly thin-cut (i.e., 1 mm) computerized tomography (CT) scans are playing an increasing role in both the diagnosis and management of patients with pelvic discontinuities. When compared to radiographs, CT scans incrementally allow for assessment of remaining columnar bone, as well as amount of remaining superior dome, anterior wall, and posterior wall. Three-dimensional reconstructions are increasingly useful for the diagnosis of a pelvic discontinuity as well [17]. Contemporary higher quality CT scans have been available through the use of metal artifact reduction sequences (MARS) . Additional techniques can lead to more precise evaluation. Recently, Fehring et al. [18] reported a novel technique where CT scans were reformatted into 45° Judet views. This allowed for an increase in the sensitivity of diagnosing pelvic discontinuities by 18%.

The treatment of an intraoperative pelvic discontinuity primarily depends on when the discontinuity is recognized. If noted intraoperatively, pelvic discontinuities should be treated operatively (as noted below). However, if only appreciated postoperatively, then a discussion must occur between the patient and the surgeon to discuss management options. Nonoperative management is reserved for frail patients who cannot tolerate a second operative procedure.

The surgical treatment of pelvic discontinuities is demanding given the fact that both fracture and implant fixation must be addressed. The first goal is to restore a biomechanically continuous pelvic ring connecting the superior and inferior aspects of the pelvis (and thus acetabulum). The second is to obtain a stable reconstruction based on rigidly fixed implants.