Treatment of periprosthetic acetabular fractures after previous hemi- or total hip arthroplasty

Periprosthetic acetabular fractures are severe complications of hemi- (HA) or total hip arthroplasty (THA), and are on the rise in terms of occurrence and recognition [1‐5]. As the function of implants in hip replacement is based on the bone–cement or bone–prosthesis fixation, a fracture that interrupts this fixation presents a challenging situation. In the presence of osteoporosis, even a fall from a standing position can lead to comminuted acetabular fractures with poor prognosis [6‐10]. Different management approaches for stabilization of the acetabular component using dual plates and cages have been described in the literature. In the case of a structural bone defect, allograft treatment has been attempted [11‐16].

Nevertheless, the results of revision surgery in HA or THA with acetabular discontinuity are poor, and conservative treatment may not be an adequate alternative [17‐20]. Lower limb extension may seem to be an option, but in terms of limited physiologic tolerance in elderly patients, such treatment depicts a considerable health risk due to prolonged immobilization [21, 22]. Therefore, acetabular implants favoring stable fixation and immediate postoperative mobilization with full weight-bearing are thought to be the solution. For this purpose, a custom-built roof-reinforcement plate was designed in an attempt to provide sufficiently stable fixation at the intact iliac bone, in order to allow for early postoperative full weight-bearing in periprosthetic acetabular fractures (Fig. 1a, b). The purpose of this article is to provide a description of the novel implant and describe the surgical technique.

The designed plate by itself has an outer diameter of 50 mm and an inner diameter of 48 mm, which perfectly fits cemented cups of 46 mm. On the cranial side, the cage is extended by a fin to provide sufficient fixation at the intact iliac bone by means of eight angle-stable 3.5-mm screws aimed in different directions. The inner ring is outfitted with another seven holes for 3.5-mm angle-stable screws to provide stabilization for the anterior and posterior column, as well as the acetabular roof. As reaming of the fractured acetabulum is performed up to 52 mm, only one size is necessary for all cases. According to preoperative planning based on CT scans, left and right implants are needed due to the fin of the cage (Fig. 1a, b).

(Fig. 2, 3, 4, 5, 6, 7)

Between 2010 and 2014, 7 patients suffering from a periprosthetic fracture were treated using the roof-reinforcement plate. At the time of surgery, the average age of these 7 patients was 80 years (range 65–91 years). Previously, 5 patients had undergone HA and 2 THA. All except one patient with HA had a transverse fracture; the one exception had a T-fracture. Of the two patients with THA, one showed an anterior column fracture in combination with a fracture of the quadrilateral plane; the other patient had a central dislocation of the acetabular components without fracture of the two columns. Postoperatively, all patients were allowed for full weight-bearing. Only 5 patients were available for follow-up (FU), two had died in the meantime. FU of the single patients was performed after 3, 6, 6, 15, and 24 months postoperatively. At this time, X‑rays in 4 patients and a CT scan in one were available. In all patients, bony consolidation could be proven, without any signs of loosening (Fig. 8). All patients except one were able to reach their preinjury mobility level. The patient who did not reach the former mobility level had to use a cane, which he did not need before surgery. Of the remaining 4 patients, 2 used a cane, one a walking frame, and one did not use a walking aid at all.

Compared to the increasing number of acetabular fractures in the elderly, patients with periprosthetic acetabular fractures are still not very common. Considering a time period of almost 4 years in two level I trauma centers, the authors can report only on 7 patients. Due to the advanced age of the patients, with an average age of 80 years, only 5 were available for FU. Two patients had died in the meantime. In a group of patients with such advanced age it is sometimes difficult to follow-up for a long time period. The authors are aware that this is a limitation of this paper.

In the literature it is reported that the typical acetabulum fracture in osteoporotic bone conditions involves the anterior column associated with a fracture of the quadrilateral plane [5]. This seems to be different with periprosthetic fractures. Only one of the 7 patients showed the described fracture type, whereas among the other 6, a transverse fracture was found in 5 patients and a T-fracture in one. Concerns are reported in the literature regarding stable fixation of the acetabular component, recommending additional cables or plates [5, 10]. The design of the described roof-reinforcement plate is such that all the stability is provided by fixation of the fin of the cage at the intact iliac bone by eight multidirectional angle-stable screws. Additional stability is provided by up to seven angle-stable screws through upper, anterior, and posterior holes of the ring. The stability of fixation allows immediate postoperative full weight-bearing, at least in most cases. Fixation of a fractured anterior column can be performed by anterior screws, but this does not enhance primary stability of the cage. The results of a series of 30 consecutive patients of the same age (average 79 years) suffering from acetabulum fractures without previous prostheses have shown that the stability provided by the fixation described above was sufficient for early full weight-bearing (paper under review). No loosening signs were found in any case. New and modern titanium fixators with multidirectional interlocking screws inserted by a minimally invasive procedure might be an alternative [24]; however, in the authors’ experience, in periprosthetic fractures the quadrilateral plane is commonly destroyed and associated with a dome fragment of the acetabulum. Furthermore, due to advanced head protrusion in the case of HA, the bone of the quadrilateral plane is thin and of very poor quality, rendering stable fixation even with the new plates difficult.

In summary, this report demonstrates that this custom-built roof-reinforcement plate is a beneficial addition to the treatment spectrum for elderly patients with previous hip replacement, especially for patients with periprosthetic acetabular discontinuity after THA and HA. Early mobilization with full weight-bearing within the first 10 days after surgery can be achieved, at least in most cases. However, short- and long-term results from higher numbers of cases are needed in order to draw conclusions on the mechanical behavior of this custom-made reconstructive implant over time.