This study involved a consecutive series of patients who underwent acetabular reconstruction using TM augments (Zimmer Inc., Warsaw, IN) as a support for impaction bone grafting and cemented acetabular cups from February 2004 through March 2008. The follow-up period was at least 2 years. We present all the cases in which this technique was used in our department, including those during the period with the learning curve. Independently trained research assistants collected the data prospectively.
At our unit, during the inclusion period 70 hip revision procedures were performed every year, giving 280 procedures over the 4 years. Two-thirds of these procedures were performed for acetabular problems. In the 180 acetabular revision procedures performed in the time period, 24 patients (13 men) met the criteria of massive aseptic acetabular bone loss to warrant this technique. The mean age was 62 (24–87) years. The patients had undergone between 1 and 4 previous surgeries before the procedure.
Patients were assessed 6 weeks or less before surgery and at 12 weeks and 1 year. They were assessed annually thereafter. Median follow-up was 61 (32–81) months. None of the patients were lost to follow-up, but the 2-year postoperative questionnaire was completed by 21 of the 24 patients.
All the patients were operated by or under the direct supervision of the senior authors (NTB and JPH). A posterior approach was used in all cases. The existing cup was explanted, and the interface membrane removed and acetabulum cleaned. The acetabular defect was then quantified according to Paprosky grading (Paprosky et al. 1994
) and recorded. There were 15 Paprosky grade 3A defects and 9 grade 3B defects.
Sequential gentle acetabular reaming was carried out to identify the best fit. The TM augments are available in different sizes and shapes, making it easier for the surgeon to choose the correct size of implant. The appropriate size and number of augments were then chosen for the defect ().
Wedge type trabecular metal augment.
The augment was tested with the trial cup to ensure best cover and support. It was secured with one or two 6.5-mm screws. In all but 1 case, a single wedge-shaped augment was used. In that particular case, a wedge-shaped augment was used in conjunction with a disc-shaped augment for a medial wall defect.
Morsellised allograft from donor femoral head was then packed around and over the augment and secured in place using an appropriate-sized acetabular reamer in reverse. A low-profile Exeter cup (Stryker, Berkshire, UK) was selected to give at least 2–3 mm of cement mantle. Cement was inserted on top of the morsellised graft and pressurized. The Exeter cup was then cemented in place on top of the impacted graft. Femoral revision was then carried out as required in 7 of the 24 patients. Antibiotics and thromboprophylaxis were prescribed as per out unit protocol.
Patients were mobilized with partial weight bearing with crutches for 6 weeks, followed by transition to full weight bearing as tolerated over the following 6 weeks. By 3 months, all patients were allowed full weight bearing.
Patients completed questionnaires preoperatively and at each postoperative assessment. Hip status was assessed using the Western Ontario and McMaster Universities’ (WOMAC) questionnaire (Theiler et al. 2002
) Scores for pain, function, and stiffness were transformed to a 0- to 100-point scale, with 0 indicating extreme pain/functional disability/stiffness and 100 indicating no pain/functional disability/stiffness. This method has been widely reported (Wright et al. 2004
, Wylde et al. 2008
, Lingard et al. 2009
). Generic health was assessed using the SF-36 version 2 health survey (Ware 2000
) with its 10 components ranging from 0 to 100 with 100 being best. Postoperatively, satisfaction data were recorded using a validated measure of satisfaction (Mahomed et al. 1998
). This questionnaire includes 4 questions asking about satisfaction with the overall outcome, pain relief, ability to perform activities of daily living, and ability to participate in leisure activities. Responses are given on a 4-point Likert scale, which ranges from very satisfied to very dissatisfied. In addition to validated questions, the patients were also asked whether they would undergo the operation again and how much the surgery had improved their quality of life. The responses were given on a 5-point Likert scale that ranged from “a great improvement” to “the quality of my life is worse”.
Standard AP pelvis and lateral hip radiographs were obtained. The radiographs were all digital images and each radiograph was calibrated for measurement using the head size of the prosthesis. Preoperative radiographs, radiographs taken immediately postoperatively, and the most recent follow-up radiographs were analyzed ( and ).
Preoperative failed THR with acetabular bone loss.
The preoperative radiographic analysis included classification of bone defects using the Paprosky classification, measurement of the abduction angle of the existing cup (in the case of revisions), and the position of the existing cup (in the case of revisions). Teardrop sign is a reliable and a constant feature seen on AP radiographs of the pelvis. We used this key landmark to determine the position of the cup. A horizontal line was marked along the inferior border of the 2 teardrops on an AP pelvic radiograph, a vertical line bisecting the ipsilateral teardrop was then marked, and the point of intersection was noted. The horizontal (x-) and vertical (y-) distance from this intersection point and the most inferior point of the rim of the cup gives the position of the cup in relation to the teardrop. For the purposes of this study, we assumed that the ideal cup position is where the inferior most point of the rim of the cup lies adjacent to the teardrop (i.e. the vertical and horizontal distance are 0 mm). This assumption was made on the basis of this being the anatomical position of the cup within the acetabulum.
The postoperative radiographic analyses included measurement of the abduction angle and acetabular component position using the methodology described above. The most recent follow-up radiographs were also assessed for (1) evidence of bony ingrowth or lucency around the TM augments or disc and (2) quality of the cement mantle (i.e. evidence of cup loosening from comparative radiographs). Migration of the acetabular component was determined by calculating the difference between the cup position (x- and y-axes) at the most recent follow-up and the radiograph taken immediately postoperatively.
In order to determine whether the data followed a normal distribution, the Kolmogorov-Smirnov test was used. If p < 0.05, non-parametric tests rather than parametric tests were used. To compare continuous variables, paired t-tests were used for parametric data and the Mann-Whitney U test was used for variables not having a Gaussian distribution. All the tests were 2-tailed and the 5% significance level was used throughout. The chi-square test was used to compare categorical data. Statistical analyses were performed using SPSS software version 11.
The patients were not entered into a clinical trial; no formal ethics approval was therefore required. All procedures were performed by a trained consultant orthopaedic surgeon.