Introduction

Modular tantalum augments have been introduced to manage severe bone defects in hip and knee revision surgery. The porous surfaces of tantalum augments are intended to enhance osseointegration and a number of studies have documented their excellent biocompatibility. However, the characteristics of tantalum augment osseointegration on human ex vivo specimens from re-revision procedures have not been reported so far.

Introduction: Periprosthetic fractures have long been recognized as one of the major complications after hip resurfacing arthroplasty. Both biomechanical factors and pathological changes of bone tissue might hypothetically influence its occurrence. We analyzed retrieved femoral remnants to identify possibly different fracture modes.

Material and Methods: 83 hips revised for periprosthetic fracture (134.5 days in situ±159.2) were analyzed macroscopically, contact radiographically and histologically. Most cases (80.7%) were treated for advanced stages of osteoarthritis. Hips with preoperative femoral head necrosis were not included. 49 (59.0%) patients were men (57.8 years old±8.5) and 34 (41.0%) women (55.1 years old±10.0; p=.3445). Occurrence of reactive changes and of avascular necrosis in addition to amount of osteonecrosis were used as the major histological criteria for classification of the fracture as acute biomechanical, acute postnecrotic or chronic.

Statistical analyses were performed using statistical software. Probability of Type I error was set to 5% (alpha=0.05).

Results: 37 (44.6%) femoral neck fractures (83.9 days±87.7) occurred earlier than the remaining 46 (55.4%) head fractures (174.1 days±89.7; p=.0129). 50(60.2%) remnants revealed complete osteonecrosis and were thus classified as acute postnecrotic fractures, 29 (34.9%) chronic fractures were characterized by finding of pseudoarthrosis or preformed callus and the remaining 4 (4.8%) were classified as acute mechanic. Acute mechanic fractures (17.5 days±8.0) failed earlier than both acute postnecrotic (146.3 days±181.7; p=.0049) and chronic (130.8 days±120.6; p=.0017) fractures.

Osteonecrosis was found in 81 (97.6%) hips revised after fracture (p< .0001). The vertical size of avascular necrosis in hips after acute postnecrotic fracture (21.1mm±8.5) was bigger (p< .0001) than in both chronic (7.3mm±7.3) and acute mechanic (0.9 mm±1.2) fractures.

Even though 33 (66.0%) of 50 patients with acute postnecrotic fracture were men (p=.0237), no significant differences between males and females were found with respect to age of patients (p=.3445) or duration of prosthesis implantation (p=.1232).

Conclusion: We analyzed hips revised for periprosthetic fracture after the resurfacing arthroplasty. Three distinct fracture modes of this complication could have been identified morphologically. Osteonecrosis secondary to the hip resurfacing arthroplasty appeared to be causative for more than a half of all fractures in present cohort. Mechanical and biomechanical factors related to the procedure might have possibly influenced the occurrence of both postnecrotic fractures and cases with vital reactive changes of tissues neighbouring the fracture line.

The proposed classification may help to understand causes of periprosthetic fractures after hip resurfacing arthroplasty.

The idea of resurfacing the femoral head instead of removing it has been attractive for a long time.

Unfortunately the results have been invariably poor if compared with contemporary available conventional hip prosthesis. In the last decade metal on metal technology with very accurate manufacturing made hip resurfacing a viable option. The main complication of this operation is early failure due to femoral neck fracture. This event is still incompletely understood and probably multi-factorial. Accurate placement of the femoral component to avoid notching the femoral neck, cementing technique to avoid over-penetration of the cement, small implantation forces and careful soft tissue handling to minimize the damage to the bone vascularity are thought to be the main issues. The ideal candidates for this operation are young and active patients because they have good bone quality and will take advantage of the improved performances that hip resurfacing can offer.

Unfortunately young men are also the group of patients at higher risk for the formation of heterotopic ossifications.). To prevent this complication radiotherapy was administered in a single dose of 6 Gy with two opposite fields of 18 MV generally the first post operative day. When we started to perform hip resurfacing we did not consider changing our protocol. Between March 2004 and May 2005, 55 hip resurfacings were performed using the ASR implant (DePuy) by a single surgeon (LM). Most males under the age of 60 received radiotherapy. There were 4 femoral neck fractures in the 23 male patients who received radiotherapy (17.3 %) and 1 fracture in the 32 patients who did not receive radiotherapy (3.1 %, Chi-square test: p= 0.07). All the fractures occurred between the 90th and the 120th postoperative day. No fractures were reported in the 12 women included in this study. What arouse our attention was the unacceptably high number of femoral neck fractures. The learning curve alone could not explain what was happening. At first the radiotherapy was not considered at all as factor but errors in the surgical technique were looked for. The clue came from the observation that there were no women in the fracture group in spite of the fact that the surgical technique was the same and also in spite of the fact that women should be at higher risk due to poorer bone quality as shown in the literature. This led us to check the incidence of fractures in the radiotherapy and in the non radiotherapy group. At this stage things became quite clear. Subsequently the histology of the specimen was re-examined with regard to this factor. Bone necrosis of the femoral head in the patients who underwent radiotherapy was much more pronounced then in other failures which show different degrees of necrosis. In conclusion there are strong indications that radiotherapy of the femoral head should not be performed in combination with hip resurfacing.