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

Objective Treatment of displaced periprosthetic acetabular fractures in elderly patients. The goal is to stabilize an acetabular fracture independent of the fracture pattern, by inserting the custom-made roof-reinforcement plate and starting early postoperative full weight-bearing mobilization. Indications Acetabular fracture with or without previous hemi- or total hip arthroplasty. Contraindications Non-displaced acetabular fractures. Surgical technique Watson-Jones approach to provide accessibility to the anterior and supraacetabular part of the iliac bone. Angle-stable positioning of the roof-reinforcement plate without any fracture reduction. Cementing a polyethylene cup into the metal plate and restoring prosthetic femoral components. Postoperative management Full weight-bearing mobilization within the first 10 days after surgery. In cases of two column fractures, partial weight-bearing is recommended. Results Of 7 patients with periprosthetic acetabular fracture, 5 were available for follow-up at 3, 6, 6, 15, and 24 months postoperatively. No complications were recognized and all fractures showed bony consolidation. Early postoperative mobilization was started within the first 10 days. All patients except one reached their preinjury mobility level. This individual and novel implant is custom made for displaced acetabular and periprosthetic fractures in patients with osteopenic bone. It provides a hopeful benefit due to early full weight-bearing mobilization within the first 10 days after surgery. Limitations In case of largely destroyed supraacetabular bone or two-column fractures according to Letournel additional synthesis via an anterior approach might be necessary. In these cases partial weight bearing is recommended.


Introductory remarks
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][2][3][4][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][7][8][9][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][12][13][14][15][16].
Nevertheless, the results of revision surgery in HA or THA with acetabular  [17][18][19][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 custom-built roofreinforcement implant
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 anglestable 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).  4 Clinical assessment of pelvic stability 4 Documentation of the patient's preinjury mobility status 4 X-ray of the pelvis and hip with AP and oblique views 4 CT scans of the involved hip in three planes for implant planning 4 Documentation of the sensibility and circulation of the foot 4 General preparations for surgery Instruments and implants 4 Basic set of surgical instruments for pelvic surgery 4 Patient-fitted roof-reinforcement plate 3.5 based on preoperative CT scans 4 Screwdriver hex 2.5 mm with screwdriver bit and helve 4 Screwdriver star drive T15 with screwdriver bit 4 Torque limiter 1.5 Nm 4 3.5-mm hex self-cutting angle-stable screws (L = 10-95 mm) 4 3.5 mm star drive self-cutting anglestable screws (L = 10-95 mm)

Treatment of periprosthetic acetabular fractures after previous hemi-or total hip arthroplasty. Introduction of a new implant Abstract
Objective. Treatment of displaced periprosthetic acetabular fractures in elderly patients. The goal is to stabilize an acetabular fracture independent of the fracture pattern, by inserting the custom-made roof-reinforcement plate and starting early postoperative full weight-bearing mobilization.
Indications. Acetabular fracture with or without previous hemi-or total hip arthroplasty.
Contraindications. Non-displaced acetabular fractures. Surgical technique. Watson-Jones approach to provide accessibility to the anterior and supraacetabular part of the iliac bone. Anglestable positioning of the roof-reinforcement plate without any fracture reduction. Cementing a polyethylene cup into the metal plate and restoring prosthetic femoral components. Postoperative management. Full weightbearing mobilization within the first 10 days after surgery. In cases of two column fractures, partial weight-bearing is recommended.
Results. Of 7 patients with periprosthetic acetabular fracture, 5 were available for follow-up at 3, 6, 6, 15, and 24 months postoperatively. No complications were recognized and all fractures showed bony consolidation. Early postoperative mobilization was started within the first 10 days. All patients except one reached their preinjury mobility level. This individual and novel implant is custom made for displaced acetabular and periprosthetic fractures in patients with osteopenic bone. It provides a hopeful benefit due to early full weight-bearing mobilization within the first 10 days after surgery.
Limitations. In case of largely destroyed supraacetabular bone or two-column fractures according to Letournel additional synthesis via an anterior approach might be necessary. In these cases partial weight bearing is recommended.

Schlüsselwörter
Mobilisierung · Osteoporose · Gewichtsbelastung · Prothese · Azetabulum Surgical technique (. Fig. 2, 3, 4  The triangle of the tensor fascie latae, gluteus medius, and lateral vastus muscle is then identified and opened midway between the anterior spine and greater trochanter. Subsequently, the ridge of the lateral vastus muscle is revealed Fig. 4 8 After exposure of the prosthesis, the leg is brought into second position while dislocating carefully the prosthetic head. Retractors are placed anteriorly, posteriorly, and inferiorly, to optimize visualization of the acetabular fracture. In patients with non-periprosthetic fractures, the capsule is exposed and resected by a T-shape incision. Furthermore, femoral neck osteotomy and acetabular cartilage removal is performed before stepwise socket reaming, starting from 44 up to 52 mm, and implant insertion. In periprosthetic fractures after total hip arthroplasty, the acetabular component is removed with or without all the cement, depending on the type of prosthesis. In case of hemiarthroplasty, only the prosthetic head has to be removed Operative Orthopädie und Traumatologie 2 · 2016 107  Postoperative management 4 Passive and active motion should be exercised up to the onset of pain and intensified step-by-step directly after surgery. 4 Early mobilization with full weightbearing is started within the first few days with use of a walking aid (crutches, walking frame, cane). 4 In cases of destruction of the supraacetabular bone or with two column fractures, postoperative CT scan is recommended in order to check the number of screws positioned in stable bone. Postoperative mobilization depends on this information (full or partial weight-bearing). 4 If the inserted Prolene ® mesh graft leaks, a cement outflow into the pelvis is possible. 4 As joint stability depends on the positioning of the polyethylene cup, increased attention has to be paid during cementing. 4 In the case of poor positioning of the cemented cup, dislocation of the prosthetic head can occur. 4 Deep wound infection should be treated by early surgical debridement and appropriate antibiotic treatment. 4 Incomplete healing of the bone in situations of osteoporosis, partial weight-bearing is recommended.

Results
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 Tfracture. 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 weightbearing. 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.

Discussion
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 Tfracture 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 anglestable screws. Additional stability is provided by up to seven angle-stable screws through upper, anterior, and posterior holes of the ring. The stability of fixa-tion 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.

Conclusion
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 weightbearing 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 custommade reconstructive implant over time.