Although the number of total hip arthroplasties (THAs) being performed in the United States is increasing, revision THAs are more common.1 Many acetabular revisions can be successfully performed with standard or jumbo cementless acetabular cups, but major osseous deficiencies typically require reconstruction with a cage or cup/cage that bridges gaps in the pelvis and obtains fixation of the arthroplasty components.2,3 Cages and rings have been combined with all-polyethylene acetabular components (ie, all-polyethylene cups, or APCs) to reconstruct pelvic bone defects, but complications, including APC dissociation (Figure 1) and postoperative instability, can occur despite stable fixation of cage to pelvis.4 The incidence of dislocations with pelvic reconstruction rings using APCs has been reported to be 11%.4 If an APC has to be replaced because of wear, then major surgery may be required to extract the worn cup and cement a new cup in its place.
In this article, we describe a technique in which a metal, multihole acetabular shell is cemented into the cage or ring construct, avoiding some of the complications associated with traditional techniques by permitting use of a variety of liners.
Materials and Methods
We retrospectively reviewed the cases of all of Dr. Bolanos’ patients who underwent acetabular revision THA with cage reconstruction between February 1, 1998 and October 9, 2006. During this period, we were cementing a modular metal shell into the cage instead of an APC or polyethylene liner. All patients who underwent revision THA with cage reconstruction during the study period were included. Bone defects were treated with structural or morselized bone allograft. Every reconstruction involved use of an antiprotrusio cage or ring secured to the pelvis with screws, and a multihole acetabular shell cemented into place with a polyethylene liner applied. Elevated rims, lateralized liners, and constrained liners were used as needed to optimize stability. Femoral components were retained. Cage size was based on matching the osseous deficiencies. Shell size was determined by the inner diameter of the corresponding cage. Liner size was based on matching the shell and femoral head. During this period, none of the patients had other reconstructive techniques, such as trabecular metal augmentation, in combination with a modular acetabular shell, cup/cage reconstruction, or custom triflange components.
Patients engaged in protected weight-bearing ambulation for 3 months after surgery and were then permitted full, unrestricted activity. The primary outcome was mechanical failure of the reconstruction, or reoperation (Table). All reconstructions in this series consisted of acetabular revisions for aseptic loosening.
Surgical Technique
Six consecutive cases of pelvic discontinuity and 7 cases of segmental acetabular bone loss required use of cages or rings. Reconstruction cages were used to secure fixation to the ilium and ischium. With the technique described in this article, we used screws with rounded, prominent heads rather than flat heads between the cup and the cage or ring (Synthes, 6.5 mm) to ensure adequate cement mantle. The rounded screw heads were left prominent to approximate the function of cement pegs found on APCs. Screws were placed into the anterior, superior, medial, and posterior aspects of the cage to ensure adequate cement mantle between cup and cage. This was confirmed with trial placement of the cup into the cage before cementation and observation of the uniformity of the space between cup and cage. Trial placement also confirmed that the screws did not interfere with appropriate positioning of the cup. A multihole, metal acetabular cup was then cemented in the cage or ring such that cement extruded around the shell and into the holes of the cup and the cage, securing the cup to the cage. Use of a multihole, metal shell resulted in excellent cement fixation because the multiple holes created multiple circumferential cement pegs. Various liner options could then be used to optimize stability of the reconstruction. In some cases, excessive cement extruded into the interior aspect of the shell and hardened before curettage. If the excess cement could interfere with complete seating/locking of the liner, then a high-speed burr was used to easily remove cement (Figure 2). Polyethylene liners were then inserted into the shell. Femoral reconstruction was then performed, if needed, and stability of the arthroplasty checked. This technique allows the surgeon to then select from a variety of polyethylene liners as needed to optimize stability. Liners with elevated rims, lateralized liners, and constrained liners could be interchangeable options with this technique.
Results
Thirteen patients with major osseous deficiencies of the pelvis were treated using this technique. At mean follow-up of 64.2 months (range, 3-133 months), 10 of the 13 patients had favorable outcomes without further surgery. One patient developed recurrent aseptic loosening that required re-revision, another patient developed recurrent instability that required acetabular liner and femoral head exchange, and a third patient with poor balance fell multiple times. This patient’s ninth fall resulted in dissociation of the acetabular shell from the cage (Figure 3), treated with placement of another cemented multihole metal shell with a standard liner. As dislocations recurred, the liner was changed to a constrained liner (Figure 4). The patient did not have any further dislocations or other hip-related problems. Integrity of cemented shell-cage fixation was maintained in 12 of the 13 patients at final follow-up.
