Management strategies for pelvic discontinuity

Intraoperative assessment

How should an intraoperative diagnosis of PD be performed? Karachalios tells us that this can be performed with the assistance of a Cobb elevator. Gentle pressure should be applied to either the anterior or the posterior column of the inferior hemipelvis in an anteroposterior direction. An observation of movements between the superior and posterior acetabulum is a confirmation of the existence of a PD. In chronic cases, however, bone loss can be severe and accompanied by fibrous tissue (ie, a stable fibrous nonunion); as a result, movements and fracture lines may not be visible. Under such circumstances, meticulous and careful debridement of the scar tissues will be necessary for a definitive classification of the bone defects.

Postoperative assessment

Plain x-rays are currently used as a standard method in assessing postoperative construct stability, osseointegration, and fracture healing [9]. Radiographic finding of a persistent and progressive radiolucency at the bone-implant interface indicates failure of bone ingrowth into the acetabular components, and porous surface shedding, fragmentation, and debonding of the porous coating are suggestive of interface instability and loosening. Rotational migration of the component (usually vertically), changes in screw position, screw fracture, and circumferential radiolucency around an acetabular screw are indicative of construct failure [9]. Depending on the findings, further CT scans may be necessary and early re-revision surgery should be planned. On the other hand, a nonunion of a PD does not necessarily mean a construct failure [9].

Managing acute pelvic discontinuity

As mentioned previously, in acute PD, the gaps between superior and inferior acetabulum are usually smaller and the bones should still have good vascularity. Together, they translate into a generally good healing potential [1, 4, 5]. In case of good bone stock, the previous cup should be removed and the fracture inspected. Internal fixation using compression plates and screws, along with a hemispheric highly porous acetabular component is usually a good option for acute pelvic discontinuity [1, 9]. In case of poor bone stock, other more rigid fixations such as cup-cage construct and double plating in combination with bone grafts have been suggested to achieve absolute stability. The goal of the treatment is to stabilize the discontinuity via compression, thereby promoting fracture healing and implant bone ingrowth [1, 9].

There are situations when an acute PD may be treated nonoperatively. A final decision for nonoperative or operative treatment should be based on the pre- and intraoperative assessment of implant stability and patient needs. In older patients with low functional demands and stable implants (see Figure 2), a nonoperative treatment may be a good option. For unstable implants, reduction and plate internal fixation combined with revision of the acetabular component have been suggested and bone grafts may be indicated [1, 9, 17].

Managing chronic pelvic discontinuity

A chronic PD develops progressively, has larger gaps between the bones, is often filled with fibrous tissue, and bone edges are atrophic, sclerotic, and avascular. The healing potential of chronic PD is generally poor, resembling that of an atrophic fibrous nonunion [1–4, 12]. The stepwise goals in treating this very challenging condition are: 1) identify and confirm the problem, 2) remove the scar tissue until clean bone edges are achieved, 3) reestablish the continuity of the superior and inferior hemipelvis with implants, and if necessary, bone grafts, and 4) achieve a sound, stable reconstruction [2].
To achieve the best possible results, careful planning is necessary and the whole surgical team should be prepared for unfavorable and/or unexpected scenarios. This means that a variety of implant removal tools, various implants, and graft materials should be at hand to accommodate unplanned techniques. The surgical approach should be chosen according to the surgeon’s experience, although most surgeons prefer the posterior approach because it allows for excellent exposure to visualize the acetabulum, a badly damaged acetabular socket, the posterior column, and ilium [1, 5]. In addition, a posterior approach would also allow, when necessary, for an intraoperative decision to perform an extended trochanteric osteotomy, which provides an even wider exposure and acetabular visibility [1].

The best result of a PD reconstruction is a secure fixation of the acetabular component to the pelvis and stabilizing the hemipelvis to promote subsequent bone ingrowth [1, 9]. Several reconstruction techniques that have been described with good results are presented below.

Cages and rings with graft

Historically, massive bulk allograft used with a cemented liner in the setting of chronic PD had a 45% failure rate [18, 19]. In contrast, among a subset of reconstructions where a roof-reinforcement ring was used in addition to the allograft, seven of eight hips were stable at an average of 7.5 years [18]. Since then, reconstruction cages and rings have been extensively used to reconstruct severe acetabular bone defects and PD. Structural or morselized bone allografts were used to fill the acetabular defect and then a cage or ring, cemented in an appropriate orientation, was used to protect the grafted area until the allograft would be incorporated into host bones by creeping substitution [9]. The reconstruction principle for such an impaction grafting technique is a combination of mechanical and biological fixation, with the cement providing the mechanical strength and the bony ingrowth providing the biological fixation [9]. Several manufacturers have developed various ilioischial or nonilioischial (onlay or inlay) spanning cages and rings. However, despite reports of early satisfactory outcomes, many of these devices were later withdrawn due to subsequent mid- and long-term failures (Figure 3) [20–22].

Internal fixation with acetabular reconstruction

In treating chronic PD in patients with good bone stock and good healing potential, compression plates and multiple screws can be used in combination with a cementless acetabular cup to stabilize the discontinuity. Both single plating (of the anterior or posterior columns) and double plating (of both the anterior and posterior column) through a combined ilioinguinal and posterior approach have been suggested [1, 2, 23].

Acetabular distraction with cementless acetabular cup

Instead of compressing the fracture line in a PD, Sporer et al [19] described a method of acetabular distraction in which the defect is expanded. Briefly, after the original acetabular component is removed, you proceed to debride all the scar tissues to the point that punctate bleeding occurs and viable host bones are uncovered. With the help of a laminar spreader or a Cobb elevator, the discontinuity is mobilized and the defect pulled apart and expanded (note: this can often be difficult), and a cementless acetabular cup can then be implanted. In this method, the initial reconstruction stability is provided by the compression force of the bone edge of the distracted PD (ie, elastic recoil of the pelvis) on the implant [19, 24]. In case of large bone defect, porous tantalum augments may be filled into the defect, secured to the host bone with screws, and the acetabular component can then be impacted into place, using polymethylmethacrylate cement as the fixation agent for the augment-cup interface. It is believed that the initial mechanical stability provides the stability for bone ingrowth into the prosthesis both superiorly and inferiorly and achieves biological fixation [5, 9, 19]. The current literature on the results of distraction is limited, even though the initial result was encouraging [1, 9].

Tantalum cementless acetabular cups with augments

The surface property of highly porous tantalum is similar to that of trabecular bones and has been demonstrated to allow excellent osseointegration in canine studies [25]. Unlike the cage constructs that rely only on mechanical stability of the metal of the cage and the strength of the screw fixation to the host bones, highly porous trabecular tantalum implants allow bony ingrowth and osseointegration, providing a basis for long-term stability [24, 26]. In addition, porous tantalum has a high coefficient of friction against cancellous and cortical bone, which contributes to initial stability [26]. Some porous metal acetabular designs also allow the placement of screw holes anywhere in the cup for fixation to the host bones (eg, ilium, pubic, and ischial rami) by using a high-speed burr [5]. In combination with augments, highly porous tantalum implants have been used in both acute and chronic PD, especially in those with good bone stock (Figures 4 and 5) [26]. Early and midterm outcomes are encouraging, leading to an expansion of the indication for their use (Figure 6) [20, 27].