TM is a biomaterial made of porous tantalum that has a 3D structure and is highly porous (Figure 1). TM has a porosity similar to that of cancellous bone, encouraging ingrowth (Bobyn et al. 1980, Cohen 2002, Unger et al. 2005). The elastic modulus of TM is more similar to that of cancellous and cortical bone than is the elastic modulus of other commonly used metals (O’Keefe et al. 1999). The coefficient of friction against bone is higher than other porous coatings such as sintered beads and fibers.

The high coefficient of friction increases the grip on the bone, and may be more effective in preventing early failure than other structures that have been used in the past as a support for impaction bone grafting.

Impaction grafting of acetabular defects in conjunction with meshes has been shown to have mixed outcomes: 12% failure at 10 years (van Haaren et al. 2007) and 28% failure at 7 years (van Egmond et al. 2011). As TM augments are very stable mechanically, we hypothesized that using an augment to fill a defect first and then to perform impaction grafting on top would provide more stability to the subsequently cemented cup than a mesh and bone graft would.

We report our experience with TM augments to improve stabilization of impaction grafts and subsequently cemented cups in revision cases in a tertiary referral practice.

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 (Figure 2).

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”.

The outcomes of the use of impaction bone grafting in conjunction with mesh vary. Reports have shown a failure rate of up to 28% after 7 years (van Haaren et al. 2007). It should be stressed that while our short-term results are good, the long-term results may be no better than with using a mesh.

The combination of augments and cemented cups may also be attractive when considering potential failure. Failing uncemented metal-backed cups will result in friction and wear between the augment and the cup, thus generating a lot of wear from metal debris. This is probably not the case when there is failure with cemented cups.

We used TM augments to restore segmental bony defects before using a compact morsellised bone grafting technique and a cemented socket. This technique allowed us to place the augment in the required alignment for the defect, as it did not determine the final alignment of the socket. We obtained satisfactory short-term results, both clinically and radiographically. The sequential radiographs showed no statistically significant changes in cup inclination and migration over the postoperative period. This indicates that the TMT augment provides a good bed for incorporation of the bone graft into the acetabular bone and the augment.

Re-revision was required in 1 of 24 hips because of severe pain after a fractured augment, 13 months after the revision surgery. We believe that the failure occurred because of the stress going through the augment, accentuated by a relatively open (high-abduction-angle) position of the acetabular component. We have since modified our technique, with a deliberate attempt to keep the acetabular component relatively closed.

The use of TM augments is gaining popularity in the management of bone loss in acetabular reconstruction. The TM augment is used to fill the defect and is packed with morsellised bone graft. The reconstruction is then completed using a cementless cup or a cemented cup. In a study using TM augments and cementless cup, Nehme et al. (2004) reported good early to medium-term results. Similarly, in a series of 28 hips with a Paprosky type IIIA defect and 13 hips with a type IIIB defect, Sporer and Paprosky (2006) found no failures after aseptic loosening. Weeden and Schmidt (2007) also reported no revisions for aseptic loosening when reviewing 43 Paprosky type IIIA or type IIIB acetabular revisions at a mean follow-up time of 3 years. Lakstein et al. (2009) found an 8% failure rate at 4 years on average when TM cups (Zimmer) without augments were used in patients with < 50% host bone contact.