The treatment of isolated medial knee compartment osteoarthrosis remains contentious. Surgical options include tibial osteotomy, unicompartmental replacement (UKR) or total knee replacement (TKR). UKR is considered to be less invasive, quadriceps sparing and may be seen either as a temporising measure or as the definitive treatment.1 Pearse et al have reported on the New Zealand experience of revision of UKR to TKR.2 This study is commendable due to the high capture rate (98%) and as such may allow for more definitive conclusions to be drawn from the dataset. The authors have examined the sample population with respect to the incidence of revision from a UKR to either another UKR or TKR. During the ten year study period 4283 patients underwent primary UKR. Of these 236 required revision to either a TKR (215) or to another UKR (36). These three cohorts provided the basis for comparison of outcome between revised patients and the primary TKR cohort. The authors found a lower Oxford knee score at six months in the revised group to TKR compared with either the primary TKR or primary UKR cohorts. This is perhaps not surprising. In some regards this is perhaps an unfair comparison as it is accepted that recovery from revision surgery, no matter how technically straightforward, represents a second insult to the soft tissues of the knee and is therefore slower than after primary surgery.
Proponents of UKR argue that it achieves better pain relief than tibial osteotomy, that revision of such a device is technically easier than revision TKR and a number of reports from specialist centres document > 90% ten year survival.3,4 In 2008 the NJR data set for England and Wales recorded over 60,000 primary knee replacements of all types with less than 10% of these being unicompartmental which is similar to that documented in the NZ registry.5 Pearse et al2 have found that time to failure was worryingly early after re-revision. Specifically, the authors found that the mean age at the time of re-revision for the failed UKR patients was 62 years, approximately six years younger than both the primary UKR and TKR groups, respectively. Early failure of such revised components will place additional burdens upon an already stretched arthroplasty service with an increasingly ageing population and greater numbers of cases being performed year on year.
Crucial to the arguments for and against the use of this device, especially in the younger age group, is the perceived difficulty with revision. The report from the NZ registry when examining the orthopaedic community as a whole found in almost a third of cases the surgeon was required to use revision components. This was presumably to address medial column insufficiency. This worrying finding is also very much at odds with selected work which claims that such surgery is an ‘easy’ revision and can be accomplished without revision components.6 It is intuitive to presume that revision of a failed medial component with a 7o anteroposterior slope will require an augment irrespective of the size of the previously use polyethylene thickness. It is imperative that the treating surgeon should be familiar with these potential per-operative pitfalls and counsel the patient that such revision surgery is not simple and may require a constrained device with possible reduction in its longevity. It is this group which demands close long term surveillance. This is against a background of clear evidence of long term success for minimally constrained total knee replacements.7 It is further possible that UKR may prejudice against long term success of a revised total knee component and that the sum survival of the UKR and revised component may not exceed a primary TKR. The patient will have been exposed to a second operation with all its attendant risks. Additionally, previous studies have confirmed that there is a poorer recovery from revision surgery in terms of functional outcome and quality of life for both hip and knee arthroplasty.8 This is clearly reflected in the current paper but lack of longer term outcome for these subgroups limits further interpretation.
This excellent work has highlighted the early demographics for revision of UKR in a national study. It should serve to raise the less specialist surgeons’ awareness of the requirement for revision components at the second operation. The early failure of these devices warrants closer scrutiny and this may have applicability in the UK setting. I look forward to an age matched prospective comparative study of survivorship between primary TKR and revised UKR with particular emphasis on the younger group.
1. Hanssen AH, Stuart M, Scott RD, Scuderi GR. Surgical Options for the Middle-Aged Patient with osteoarthritis of the knee Joint. Instr Course Lect 2001;50:499-511.
2. Pearse AJ, Hooper GJ, Rothwell AG, Frampton C. Survival and functional outcome after revision of a unicompartmental to a total knee replacement: The New Zealand National Joint Registry. J Bone Joint Surg [Br] 2010;92-B:508-12.
3. Svard UC, Price AJ. Oxford medial unicompartmental knee arthroplasty: a survival analysis of an independent series. J Bone Joint Surg [Br] 2001;83-B:191-4.
4. Martin JG, Wallace DA, Woods DA, Carr AJ, Murray DW. Revision of unicondylar knee replacements to total knee replacement. The Knee 1995;2:121-5.
5. No authors listed. National Joint Registry for England and Wales, 6th Annual Report. 2009.
6. Aleto TJ, Berend ME, Ritter MA, Faris PM, Meneghini RM. Early failure of unicompartmental knee arthroplasty leading to revision. J Arthroplasty 2008;23:159-63.
7. Roberts VI, Esler CN, Harper WM. A 15-year follow-up study of 4606 primary total knee replacements. J Bone Joint Surg [Br] 2007;89-B:1452-6.
8. Deehan DJ, Murray JD, Birdsall PD, Pinder IM. Quality of life after knee revision arthroplasty. Acta Orthop 2006;77:761-6.
Deehan D, Consultant Orthopaedic Surgeon
The Freeman Hospital, Newcastle-upon-Tyne, United Kingdom