Mid-term results of revision surgery using double-trabecular metal cups alone or combined with impaction bone grafting for complex acetabular defects

Because of good to excellent prognosis, primary total hip arthroplasty (THA) is an effective treatment for advanced hip diseases [1]. The failure rate requiring reoperation after primary THA is up to 12% at 10-year follow-up [2, 3]. With the younger tendency and the rising life expectancy of patients undergoing THA, the amount of revision surgery following THA is expected to increase in the near future [4]. The restoration of the native hip center of rotation (COR) plays an important role in primary THA and revision THA [5, 6]. Various types of treatments and implants for the reconstruction of acetabular bone defects have been developed recently [2, 7]. On account of advantages in biomechanics and biocompatibility, trabecular metal (TM) augments and TM cup were increasingly used in revision THA [8].

Bone grafting was required to reconstruct the complex periacetabular bone defects [9]. The technique of impacting bone grafting (IBG) would take the place of the bulk grafts gradually because of low osseointegration potential of bulk grafts [10]. Furthermore, it has been reported that the revision THA using structural bone graft without reinforcement devices can lead to a poor result [11]. Regardless of the method used, the proper anchoring would be hindered in severe acetabular bone defects [10]. Some researchers suggested that the technique of using custom-made implants in combination with TM component was a reliable option to deal with complex acetabular defects [7, 12]. However, there is no gold standard for the treatment of complex periacetabular bone defects, and acetabular revision for severe bone defects is still a challenging surgery [11, 13]. In order to increase the function results after reconstruction of acetabular bone defect, new treatment options of using IBG and other revision devices were recommended [14].

In the present study, we extended the use of double-trabecular metal (double-TM) cups alone or combined with IBG to revision surgery in patients with Paprosky III acetabular defect without pelvic discontinuity. The purpose of the current study was to compare and analyze the clinical and radiological outcomes of these two methods for revision surgery in complex acetabular defects. We hypothesized that using double-TM cups alone or combined with IBG were dependable techniques to manage Paprosky III acetabular defects without pelvic discontinuity.

A total of 18 cases out in 21 patients in this group were followed up at last, with a follow-up rate of 85.7%. The median operative time and blood loss volume during the operation were 210 (IQR 201 to 240) min and 950 (IQR 900 to 1013) ml, respectively. There was no significant difference between these two methods in terms of age (p = 0.229), sex (p = 0.606), BMI (p = 0.155), previous surgeries (p = 0.796), and follow-up period (p = 0.286) (Table 1). No patients experienced infection and nerve palsy after the revision surgery. Complications of dislocation were treated with closed reduction and bracing, and delayed wound healing was treated with prolonged wound dressing. The dislocation rate of acetabular revision (33.3%) was higher than revision THA (8.3%). Trendelenburg-positive was showed in 2 (11.1%) hips at the last follow-up. No patients underwent re-revision surgery for any reasons at the last follow-up (Table 2).

For all patients, the mHHS significantly improved from an average preoperative value of 44.1 (rang 35 to 50) to 73.7 (rang 68 to 85) at the last follow-up, and mHHS was good in 2 (11.1%) hips, fair in 15 (83.3%) hips, and poor in 1 (5.6%) hip. The average preoperative UCLA score was 2.6 (rang 2 to 4), which improved significantly to 7.3 (range 7 to 8) at the last follow-up. The average SF-36 scores improved significantly at the last follow-up, especially in bodily pain category. The mean LLD decreased significantly from 24.2 mm (range 20 to 32 mm) preoperatively to 5.8 mm (range 3 to 9 mm) at the last follow-up. However, there was no significant difference between these two methods in terms of mHHS, UCLA, SF-36, LLD, and COR at the last follow-up (p > 0.05) (Table 3). No hips were outside the Lewinnek [20] acetabular cup abduction and anteversion safe range. We discovered bone graft incorporation in all hips one year after the revision operation. Asymptomatic grade-1 heterotopic ossifications were found in 3 (16.7%) patients who received no advanced treatment. No failure for acetabular loosening or metal failure was found at the last follow-up.

Acetabular revision that involves complex bone defects presents a complex and challenging procedure for the arthroplasty surgeon. Multiple surgical reconstruction options have been described for acetabular revision, including jumbo cup component, IBG combined with a cemented cup, metal mesh, bulk autograft, or allograft combined with hemispherical cups, cup-cage construct, and TM augments and hemispherical cups [2, 7]. Using jumbo cup is a straightforward method to reconstruct Paprosky III acetabular defect with a good survival rate of 96% at 15 years of follow-up [9]. However, the host bone would be widely removed when a jumbo cup was used, and it would be difficult to reconstruct with the residual bone stock at the second revision surgery. To fill the bone defects adequately and maximize the contact with the host bone, custom-made implants are one option to address large bone defects in revision surgery [27]. TM components could provide strong initial stability and promote a deep bony ingrowth with the design of high porosity and low modulus of elasticity [26]. Currently, some studies have been carried out to evaluate the effects of a novel treatment strategy of double-cup technique applied to manage Paprosky III acetabular defects without pelvic discontinuity, and double-TM cups reconstruction was considered a credible way for acetabular revision according to their short-term results [7, 12]. In a word, there are multiple options for acetabular revision recently, but with no clear optimal treatment described.

We used double-TM cups alone or combined with IBG to performed revision surgery and achieved good mid-term clinical and radiological results in patients with Paprosky III acetabular defects without pelvic discontinuity. Clinically, patients receiving double-TM cups showed a considerable improvement in a variety of functional scores. Double-TM construct was associated with an average of a 29.6-mHHS and a 4.7-UCLA increase between preoperative and the last follow-up. In this study, the average mHHS score of 73.7 points at the last follow-up was similar to the previous research results with double-cup technique [7, 12] (Table 2). Furthermore, the improvement in the mHHS of double-TM construct is similar to the improvement achieved with alternative treatment options. For example, porous tantalum shells and augments have a reported average postoperative mHHS of 81 [13]. Custom triflange acetabular component and uncemented jumbo cups have a reported average postoperative mHHS of 76.2 and 78.5, respectively [28].

Radiographically, restoring the hip COR to an anatomic position is important to re-create normal biomechanics and decrease joint reactive force and to improve the wear resistance and longevity of the acetabular construct [5, 6]. In our present study, we have used double-TM cups alone or combined with IBG to achieve a reduction of the migration of hip COR. Despite the large and complex of acetabular bone defects, we wished the postoperative ratio of position of COR in surgical site/contralateral site to be more close to 1. The results of our study showed the hip COR was corrected to be more similar with contralateral site and there was no significant difference between these two methods (Table 3). It is vitally important, in fact, that surgeons should pay more attentions to achieving initial stability of implants, biologic ingrowth, and normal anatomical structure in acetabular revision [4].

In revision surgery with large acetabular defects, the complications rate is also an important issue. The complication incidence (33.3%) of our present study was higher than that of what Loppini et al. reported (18.8%) [12] but was similar to that of what Webb et al. reported (40%) [7] (Table 2). Our complication rate, however, was similar to alternative treatment options. Custom triflange acetabular component have a reported complication rate of 29% [28]. The dislocation rate of revision THA ranged from 14 to 21% [29]. Among the reported complication of our study, dislocation was the most common (16.7%). The dislocation rate of our study was similar to the treatment option with augments for complex bone defects [30], but reporting was heterogeneous across studies. Revision surgery using cementless jumbo cups, reinforced cages and rings, and custom triflange acetabular component have a dislocation rate of 8.3%, 7.2%, and 11%, respectively [28, 31]. Furthermore, we found the dislocation rate for acetabular revision (33.3%) was higher than that for revision THA (8.3%). It has been demonstrated that patient-derived factors, surgical factors, or both influences the rate of THA dislocation [32]. We believe the previous surgery and posterolateral surgical approaches are risk factors for dislocation following revision THA. The procedure of enhanced posterior soft tissue repair could reduce the dislocation rate [32]. Similarly, the malposition of the acetabular cup and femoral head size are common surgical factors for dislocation in revision THA [32]. With the help of preoperative 3D simulation and model, complex revision THA could be managed with moderate to high accuracy and satisfied clinical outcomes [26]. Larger femoral heads could reduce the rate of dislocation, so all patients in our study were applied with 32-mm heads. Currently, several studies have reported that dual mobility bearing articulations have low rates of dislocation after revision THA [32, 33]. Therefore, detailed preoperative evaluation, reasonable surgical procedure and components, and postoperative assessment are the keys to reduce the dislocation after revision THA.

Due to the large and complex acetabular bone defects, a gap exists between the socket and the host bone during revision THA. Undoubtedly, poor quality of acetabular bone bed would cause reconstruction failure. Currently, IBG combined with acetabular components was widely used in revision THA when significant bone defects exist [17]. The technique of IBG would take the place of the bulk grafts gradually because of low osseointegration potential of bulk grafts [10]. One of the major benefits of IBG is the ability to restore bone stock. Garcia-Cimbrelo et al. [34] have reported that IBG contributed to restore acetabular bone stock and anatomic hip COR, and had good results in the last follow-up. However, autografts were difficult to widely use because of donor shortage and donor site morbidity. By the technique of creeping substitution, vascularization and incorporation occurred in impacting allografts [35]. But some studies showed poor outcomes in revision THA with structural bone grafts without reinforcement devices [11]. Therefore, many authors recommended the combined application of other revision devices to gain good to excellent clinic and radiographic outcomes [14]. In our present study, eight (44.4%) patients underwent reconstruction with double-TM cups combined with IBG, and we found bone graft incorporation in all hips 1 year after the revision surgery. In terms of the clinical and radiological assessments after revision surgery, there was no significant difference between the method of double-TM cups alone and the method of double-TM cups combined with IBG at the last follow-up. Therefore, this reconstruction method of double-TM cups combined with IBG frequently allows the surgeons to restore the anatomic hip COR and improve the biomechanics of the hip in revision surgery.

Furthermore, the cost of revision THA is usually an important issue, especially in patients of large and complex bony defects. Usage of TM augments, cup-cage, or custom triflange implant brings great financial burden to patients, particularly in developing countries. Although the charge standard and medical reimbursement policy of different areas and countries are different, it is comparable in one institution of a country. In our institution, the cost of double-TM cups with/without bone graft was less than the use of one TM cup with augments or with the cup-cages components, or with custom triflange construct. Therefore, we have reconstructed Paprosky III acetabular defects with double-TM cups alone or in combination with IBG, and the results revealed good to excellent mid-term clinical function with less cost finally in our present study.

We acknowledge limitations of our study. First, our present study was retrospectively designed with relatively small sample size. It was hard to obtain a larger number of patients who underwent rare and uncommon acetabular reconstruction with double-TM cups alone or combined with IBG from a single institution. Second, the mixed pathology of patients could contribute to inconsistent results. Likewise, the implants of femur revision in this series were not identical. We chose implants according to the anatomy and requisite during the operation. Finally, the relatively short to mid-term follow-up period also could contribute to inferior results. Further study with longer follow-up are needed to determine the long-term results of the use of double-TM cups with/without IBG for complex acetabular reconstruction.

In summary, acetabular revision surgery with double-TM cups alone or combined with IBG can achieve similar outcomes in terms of their clinical and radiological results. Therefore, there is no doubt that these two methods are practical and reliable techniques to reconstruct complex acetabular bone defects. Nevertheless, the overall complications rate was still a challenging technique. To avoid high complications, detailed preoperative design and nearly anatomic construction should be performed.