Managing Osteolysis in a Well-Fixed Acetabuar Shell
In a presentation from ICJR Australia, Dr. Edwin Su outlines the pros and cons of retaining or revising a well-fixed acetabular shell.
When a patient presents with osteolysis around a well-fixed acetabular shell, the surgeon is faced with a complex decision process and a potentially difficult revision surgery.
At the recent ICJR Australia meeting, Edwin Su, MD, from Hospital for Special Surgery in New York, reviewed this decision process, discussed the pros and cons of retaining or revising the shell, and outlined surgical steps that might influence the final decision.
Dr. Su said the goals of the surgical treatment for these patients are the following:
- Arrest the osteolytic process
- De-bulk the biologic response via a complete synovectomy and removal of wear debris
- Replenish bone stock
- Exchange bearing surfaces and, if possible, increase head size and take advantage of new bearing materials
Retaining the Shell
When a patient has a well-fixed acetabular shell, the surgeon’s impulse typically is to try to retain it. There are pros and cons to this approach, as Dr. Su outlined:
- Shorter surgical time
- Less blood loss
- No bone loss
- Quicker recovery
- Lower cost
- High rate of instability
- Incomplete access to retroacetabular lesions
- Little to no opportunity to reposition components or use newer bearing materials and designs
When reviewing the surgical steps involved in retaining the shell, Dr. Su noted that surgeons must always have implants and instruments ready to do a complete revision, depending on what is discovered during the surgery.
The process of retaining the shell begins by removing the worn liner and assessing component position, condition, and stability. Dr. Su then proceeds to bone grafting retroacetabular lesions, either through screw holes or a “trap door” cut in the bone.
If the shell does not have an intact locking mechanism, it is possible to cement the new liner into place. The shell must be large enough to accommodate the new liner plus at least a 2-mm cement mantle. The shell and liner should be roughened to provide better interface strength.
Studies have shown that the lever-out strength of a cemented liner compares favorably to a modular locking mechanism.
Revising the Shell
In the case of osteolysis and a well-fixed acetabular shell but a lot of wear, the surgeon may decide to revise the patient. Dr. Su said there are also pros and cons to this option:
- Better access to the acetabulum for removing granuloma and filling bone lesions
- Ability to reposition the cup use newer designs and materials
- Disruption of the remaining periacetabular bone
- Longer recovery period due to the time needed for bony ingrowth into the new shell
- More expensive procedure
When comparing isolated acetabular liner exchange with complete acetabular component revision, Lie et al  found the relative risk of re-revision to be 1.8 times greater for isolated liner exchange. They noted that 28% of these re-revisions were done for dislocations and 11% for loosening.
Other studies have also shown high dislocation rates with isolated liner exchange – for example, 25% in a study by Boucher et al  at 5 years of follow-up.
Dr. Su said that studies find increased failure rates if the cup is outside the “safe zone,” which underscores the importance of a complete pre-revision assessment.
Balance of Factors
Dr. Su concluded that whether to retain or to revise the acetabular shell is a question of balancing several factors:
- Is it possible to access the bone lesions?
- What is the position of the existing acetabular component?
- What is the track record of the existing implant – is it known to last or to fail early?
- What is the condition of the acetabular cup?
- Is there enough bone stock in and around the acetabulum to allow revision of the cup?
- Is the existing cup size sufficient to allow cement fixation of a new liner?
- How did the existing implant perform for the patient – did it work well and last a long time, or did it fail shortly after the primary surgery?
Click the image below to watch Dr. Su’s presentation.
- Lie SA, Hallan G, Furnes O, Havelin LI, Engesaeter LB. Isolated acetabular liner exchange compared with complete acetabular component revision in revision of primary uncemented acetabular components: a study of 1649 revisions from the Norwegian Arthroplasty Register. J Bone Joint Surg Br. 2007 May;89(5):591-4.
- Boucher HR, Lynch C, Young AM, Engh CA Jr, Engh CA Sr. Dislocation after polyethylene liner exchange in total hip arthroplasty. J Arthroplasty. 2003 Aug;18(5):654-7.