Structural bone allograft versus titanium trabecular augment in management of Paprosky type III acetabular defects in total hip arthroplasty: A pilot study

INTRODUCTION

Total hip arthroplasty (THA) remains the gold-standard intervention for cases with advanced hip arthritis that significantly compromise daily functional capacity. The demand for THR continues to rise globally, with approximately 89,000 procedures performed in the UK and over 250,000 in the US in 2012 alone. Data from the National Joint Registry indicate a sustained increase in THR procedures over time, attributable to population aging and the broadening of surgical indications.^[1] Consequently, the incidence of revision THA has risen in parallel, frequently presenting greater technical challenges—especially in scenarios characterized by substantial acetabular bone loss.^[2]

Acetabular bone loss can result from various etiologies, including post-infectious sequelae, trauma, or chronic inflammatory arthritis, complicating both primary and revision surgeries.^[3] The severity and configuration of bone loss are commonly categorized using the American Academy of Orthopedic Surgeons classification or the Paprosky system, both of which serve as essential frameworks for guiding reconstructive decision-making.^[4] Restoring acetabular integrity during revision THA is a technically demanding task, especially when primary mechanical stability cannot be achieved using hemispheric cups alone. In such scenarios, additional reconstructive options become necessary.

A range of surgical techniques has evolved to address varying degrees of acetabular deficiency. These include impaction grafting with cemented cups, structural bone allografting, modular porous metal augments, cage and ring constructs, and more complex combinations such as cup-cage or triflange reconstructions.^[5,6] Structural allografts are advantageous for young cases as they restore bone stock and support uncemented components during bone ingrowth. However, concerns regarding graft resorption, loosening, and infection persist.^[6] Porous metal augments, by contrast, provide immediate mechanical stability and promising initial integration, though their long-term performance, particularly in infected fields, remains under investigation.^[6,7]

Accordingly, the present study aimed to compare radiological and clinical outcomes of structural bone allografts versus trabecular titanium augments in the reconstruction of Paprosky type III acetabular defects during THA.

MATERIALS AND METHODS

Radiological outcome assessment

Radiological follow-up was performed using standard anteroposterior and lateral hip radiographs at each follow-up interval [Figures 1 and 2]. Evaluations focused on bony ingrowth, signs of loosening or subsidence, periprosthetic fracture, and dislocation. Radiolucent lines around the acetabular component or augment were assessed using DeLee and Charnley’s criteria.^[8] Acetabular component migration and hip center position were analyzed using the method of Callaghan et al.^[9]

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Figure 1:

Sequential pelvic radiographs of the right hip demonstrating (A) a suspected Paprosky type III acetabular defect (arrow) preoperatively, (B) immediate post-operative placement of a trabecular titanium augment in proper position(arrow) (C) maintained augment position at 6 weeks postoperatively, (arrow) and (D) stable appearance of the titanium augment at final follow-up with restored hip center &bone ingrowth (arrow).

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Figure 2:

Sequential imaging of the right hip showing (A) pre-operative computed tomography (coronal view) revealing an acetabular defect, (B) immediate post-operative radiograph with structural allograft in place, (the arrow) (C) 6-week post-operative radiograph showing a metal augment, (the arrow) and (D) final post-operative radiograph demonstrating the structural allograft with restored hip center and bone ingrowth (arrow).

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Bone ingrowth was defined radiographically according to the criteria described by Engh et al.,^[10] including the absence of radiolucent lines, presence of trabecular continuity across the implant–bone interface, and absence of component migration on serial imaging. Stable fixation was confirmed when at least three of these features were observed on sequential radiographs.

RESULTS

There were no statistically significant differences between the Allograft and Titanium Augment groups in terms of age, sex distribution, or the presence of individual risk factors (all P > 0.05), indicating comparable general characteristics [Table 1].

There was no significant difference in pre-operative HHS between the groups (P = 0.657). However, the Titanium Augment group showed significantly higher HHS at 6 weeks (P < 0.001) and 1 year (P = 0.001), with a borderline difference at 6 months (P = 0.056), indicating better early and long-term functional outcomes [Table 2].

Both groups showed statistically significant improvement in HHS across all post-operative time points compared to pre-operative values (P < 0.001). In addition, significant differences were observed between consecutive periods within each group, indicating continuous functional improvement over time [Table 3].

There were no statistically significant differences between the Allograft and Titanium Augment groups in terms of complications, operative time, blood loss, bone ingrowth, restoration of the acetabular center, or signs of loosening (all P > 0.05), indicating comparable surgical and radiological outcomes between the two techniques [Table 4].

DISCUSSION

Acetabular revision arthroplasty for complex defects remains among the most technically demanding orthopedic surgical interventions. A major limitation in the current literature is the lack of clear differentiation between severe bone loss cases (e.g., Paprosky type III or pelvic discontinuity) and less complex defects, which complicates the interpretation of surgical outcomes.^[11]

The primary aim of revision arthroplasty is to achieve a stable and durable reconstruction, while secondary goals include restoring bone stock, anatomical hip center, and correcting leg-length discrepancies. Cementless options, such as high hip center placement and jumbo cups, may offer stability but fail to restore anatomy or bone stock. Structural bone grafting can address both goals but requires adequate host bone support and often necessitates cage reinforcement for long-term success.^[12]

In cases of pelvic discontinuity with significant bone loss, trabecular metal (TM) constructs have revealed promising short- and mid-term outcomes. Tantalum-based modular porous augment supports both cemented and uncemented components and is available in various configurations to address diverse defect patterns. Their bone-like porosity enhances biological fixation through osteoconduction and osseointegration. Titanium trabecular augments, in particular, offer intraoperative flexibility and mechanical stability, making them a reliable alternative to allografts in appropriate cases.^[13]

Several studies support the clinical efficacy of titanium augments. Xiao et al.^[14] reported favorable long-term radiological and clinical outcomes using porous titanium augments in Paprosky type III defects without pelvic discontinuity. The HHS improved from a mean of 32.1 (range: 17–58) preoperatively to 85.3 (range: 63–98) at final follow-up. Whitehouse et al.^[15] reported a 10-year survival rate of 92% in 40 hips with Paprosky type II–III defects, while Lochel et al.^[16] reported a similar rate of 92.5% in 53 hips. Jenkins et al.^[17] documented a 97% 10-year survival rate in the largest series of 58 Paprosky type III hips.

Mahmoud et al. and Borland et al.^[18,19] found that mixing titanium augmentation with cemented cups yielded mid-term survivorship rates of 95.8% and 97.2%, respectively, at median follow-ups of 5 years and 60.1 months. Furthermore, titanium augments offer versatility in shape and size, allowing for tailored reconstructions and improved intraoperative handling.^[20,21] In contrast, allografts – although effective in restoring bone stock and the hip center – demonstrate lower survivability, with a 55% success rate at 7 years when used in weight-bearing zones.^[22,23]

Titanium augmentation has also been evaluated in the presence of pelvic discontinuity. Abolghasemian et al.^[24] documented aseptic loosening in two such cases using TM shells for type III defects. Jenkins et al.^[17] observed a 97% 10-year survivability rate in 58 revisions using TM shells, with pelvic discontinuity contributing to one of the failures. Abolghasemian et al.^[24] performed cup-cage constructs in 26 hips with pelvic discontinuity and standard cages in 19 hips. Taunton et al.^[25] reported a 95% implant survival rate using custom triflange components in 57 cases over 65 months of follow-up, while De Martino et al.^[26] found an 82.7% survivorship rate across 579 hips using the same design in a systematic review, despite a 29% complication rate.

Chang et al.^[27] reported that combining structural allografts with TM hemispherical cups achieved successful graft incorporation and improved clinical outcomes in Paprosky type III defects. The modified HHS improved from a mean of 29.7–84.1 at final follow-up (P < 0.05). Titanium augments have also demonstrated superior bone ingrowth and implant stability while preserving host bone, with favorable remodeling reported by Issack and Meneghini et al.^[21,28] Short- and mid-term outcomes with titanium implants have been favorable, showing advantages such as ease of insertion and resistance to resorption.

However, structural allografts still offer unique benefits, particularly in restoring bone stock for future revisions and converting uncontained defects to contained ones. Allograft incorporation is typically observed within 12–17 months postoperatively,^[29] with full remodeling reported as early as 18 months. Structural allografts have been widely used for Paprosky type III defects, especially when combined with metal mesh to convert segmental defects into contained ones suitable for impaction grafting.^[30,31] Despite this, technical challenges remain, including difficulty restoring the hip center and risks of cup malposition and aseptic loosening.

Reports have described the use of femoral heads or distal femoral condyles as sources for structural allografts. These grafts are commonly employed for superior segmental defects, although long-term follow-up data indicate loosening rates of 20–30% at 10 years.^[32-34]

This study has several limitations that should be acknowledged. The relatively small sample size limits statistical power, reducing the ability to detect rare complications or subtle radiographic and clinical differences between the treatment groups. Consequently, the statistical precision and generalizability of the findings are restricted, and the results should be interpreted as preliminary. The single-center design may introduce center-specific biases related to surgical technique, implant choice, and postoperative care protocols. Although efforts were made to standardize surgical procedures, variations in surgeon preferences and case-specific factors could have influenced the outcomes. In addition, the follow-up period, while adequate for evaluating short- and mid-term outcomes, may not fully capture long-term implant survivorship, graft incorporation, or delayed complications such as loosening or failure. Another limitation is the absence of formal effect-size or minimal clinically important difference (MCID) analyses, as the study was primarily designed as a pilot to assess feasibility and identify preliminary comparative trends. Therefore, future large-scale, multicenter, and adequately powered randomized trials with predefined MCID and effect-size analyses are warranted to validate these findings and better define their clinical significance.

CONCLUSION

Trabecular titanium augments demonstrated superior early and mid-term functional outcomes compared with structural bone allografts in the management of Paprosky type III acetabular defects during THA. These preliminary findings warrant confirmation in larger, multicenter studies with sufficient power to evaluate long-term outcomes and complication rates.