We retrospectively reviewed the charts and radiographs of 43 patients who underwent acetabular revision for a Type IIIA acetabular defect with a porous tantalum acetabular shell and augment from January 1, 2002, to January 1, 2009. All surgeries were performed by the two senior authors (SMS, WGP) at Central Dupage Hospital (Winfield, IL, USA) or the Rush University Medical Center (Chicago, IL, USA). We identified patients from an operating room database retrieval system using the standard current procedural terminology codes for revision THA. Forty-three hips (42 patients) underwent acetabular revision with porous tantalum acetabular components and modular augments for Type IIIA acetabular defects during the aforementioned time period. This approach was indicated for (1) acetabular defects with severe superior and lateral bone loss; (2) compromising stability of a standard hemispherical component; and where (3) preparation of a large or jumbo cup would result in excessive bone loss from the anterior column and loss of stability. A relative contraindication of this approach during the study period was very young (< 35 years old) age in which multiple future revision surgeries are anticipated. In these patients, to preserve and possibly restore acetabular bone, a distal femoral allograft reconstruction was considered. Four patients died from diseases unrelated to THA before the minimum 2-year followup. Three patients were lost to followup. This left 36 patients with 37 hip revisions. The mean age at the time of surgery was 60 years (range, 36–80 years). The reason(s) for revision were aseptic loosening of the acetabular component (31), second-stage reconstruction after infection (five), and revision of a failed chronically dislocated hemiresurfacing arthroplasty (one). Four patients had pelvic discontinuity that was treated with distraction as previously described by the senior authors (WGP, SMS). Minimum followup of the cohort was 26 months (mean, 60 months; range, 26–106 months). We had prior Institutional Review Board approval.
We used a posterior approach to the hip in all cases and antibiotics were withheld until definitive cultures were obtained. On removal of fibrous tissue and complete exposure of the acetabular defect, we sequentially used hemispheric reamers at the native hip center until both the anterior and posterior columns were engaged. With a trial acetabular component in place, trial augments were positioned, usually in the posterior superior quadrant as is typically required for Type IIIa defects. We then contoured the bone and/or the tantalum augment with a reamer and/or barrel burr to optimize the surface contact area. With a trial acetabular component in place, the tantalum augment was secured to the bone with multiple 6.5-mm screws. We then packed the augment with morselized fresh-frozen cancellous allograft mixed with viable autograft reamings if available. The portion of the augment to contact the acetabular component was coated with polymethylmethacrylate (PMMA). The acetabular component (either a modular or revision porous tantalum metal shell) was then firmly impacted against the native bone and the PMMA-covered portion of the augment. The revision porous tantalum shell offers the theoretical advantages over the modular component of a lower modulus of elasticity, increased ability to obtain screw fixation by drilling directly through the tantalum shell, and locked screws with greater pull out strength through cementation of the screw holes. The revision acetabular shell was used in 15 reconstructions when the surgeon believed the bone quality was particularly poor, additional screw fixation was required, and in all of the patients with pelvic discontinuity. We placed multiple screws (a minimum of two but as many as five depending on the quality of bone and availability of fixation) through the acetabular component into host bone. The largest femoral head possible for the size of the acetabular component was used to minimize the risk of instability (usually 36 or 40 mm). Even in the setting of abductor deficiency, in which the benefits of a larger femoral head are not as appreciated, we avoided placing constrained liners to minimize stress at the host bone-component interface before ingrowth [2
Postoperatively, we placed all patients in an abduction brace and followed posterior THA precautions with touch-down weightbearing for 12 weeks before being advanced to weightbearing as tolerated without a brace. Patients were mobilized on postoperative Day 1. Physiotherapy was directed to concentrate on simple ambulation, activities of daily living, and maintaining posterior hip precautions for the first 12 weeks. At 12 weeks, the therapists began weaning the patient from assisted ambulatory devices and initiated more aggressive strengthening of core musculature, hip abductors, and hip flexors. All patients were counseled preoperatively that they may always have some limp and require a cane for balance. At 6 months postoperatively, patients were cleared to return to most activities with recommendations to avoid repetitive impact (jumping), heavy lifting, and deep/exaggerated hip positions.
Routine followup consisted of clinic visits at 2, 6, and 12 weeks followed by 3, 6, 12 months, and then annual afterward. An AP pelvis, AP hip, and Lowenstein lateral hip radiographs were obtained at every followup visit. Our radiology technicians are well trained and experienced at standardizing hip and pelvic radiographs. All films are printed to true size and then evaluated by the technician and the treating surgeon. The printed radiographs are superimposed with prior films to evaluate for gross deviation in sizing and rotation. Evaluation of the appearance of radiographic landmarks such as the obturator foramen or measurements such as the distance of the pubic symphysis to the coccyx allow for estimation and consistency of pelvic rotation in multiple planes. Measurement of the known size of the prosthetic femoral head confirms appropriate and consistent sizing of the radiographs. Beginning at the 6 months postoperatively, Harris hip scores (HHS) are obtained through the history and physical examination performed by the treating surgeon.
Radiographs were reviewed and the results documented by the treating surgeon (WGP, SMS) at each clinic visit in the medical records. For the purpose of this study an additional investigator (DJD) also reviewed the immediate postoperative and the most recent available radiographs for each patient. Loosening was defined radiographically as a change in the component abduction angle of greater than 10° or a change in the horizontal or vertical position of greater than 6 mm after correcting for magnification. These parameters are based on previously published studies from our and other institutions and allow for some variance in xray rotation and magnification to minimize a false-positive diagnosis of aseptic loosening [4
]. There was no interobserver variability in the radiographic diagnosis of aseptic loosening of the acetabular components.