The Journal of Arthroplasty xxx (2014) xxx–xxx

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Revision of Unicompartmental Knee Arthroplasty Versus Primary Total Knee Arthroplasty Johnathan D. Craik, MRCS a, Sherif A. El Shafie, MRCS b, Vinay K. Singh, FRCS orth a, Roy S. Twyman, FRCS orth a a b

Epsom and St Helier University Hospitals NHS Trust, UK The Elective Orthopaedic Centre, Epsom, UK

a r t i c l e

i n f o

Article history: Received 7 July 2014 Accepted 24 October 2014 Available online xxxx Keywords: revision unicompartmental arthroplasty knee Oxford

a b s t r a c t The risk of revision following unicompartmental arthroplasty (UKA) is greater compared with primary total knee arthroplasty (TKA). Some surgeons report that UKA revision is straightforward with outcomes comparable to TKA. We reviewed all Oxford medial UKAs and TKAs performed at our institution over a five year period. Patient reported outcomes were compared between revised UKAs, successful UKAs and primary TKAs. Out of 546 Oxford medial UKAs, twenty-nine (5.3%) were revised at a mean of 25 months. The commonest indications for revision were aseptic loosening and progression of osteoarthritis. Ten patients (34%) required augments, stemmed implants or bone grafts. Outcomes following revision were poorer than those following successful UKA and primary TKA, and were a consequence of poor pre-operative function rather than the complexity of surgery. © 2014 Elsevier Inc. all rights reserved.

Medial unicompartmental knee arthroplasty (UKA) is an effective treatment option for patients with isolated compartment arthritis. Benefits of this procedure over total knee arthroplasty (TKA) include superior kinematics, quicker recovery time, greater patient satisfaction, and preservation of bone stock [1–5]. It is also argued that in cases of UKA failure, revision is relatively straightforward with similar outcomes compared with primary TKA [6–8]. The study reviews the experience of a large orthopaedic unit in the Southeast of England to determine the indications for medial UKA revision and the difficulties encountered during surgery, and compares patient reported outcomes with those following primary total knee arthroplasty. Methods A prospective database of patient reported outcomes was reviewed for all medial UKAs performed at our institution between August 2006 and October 2011. Patients requiring UKA revision were identified from the hospital database and the UK National Joint Registry. Patient outcomes following successful primary UKA (not requiring revision), UKA revision and primary TKA were compared using Oxford knee scores, EQ5D scores and health visual analogue scores. The indications for revision and the requirement for bone grafting, stems and augments were identified from peri-operative imaging and clinical notes.

The Conflict of Interest statement associated with this article can be found at http:// Reprint requests: Johnathan D Craik, MRCS, Department of Orthopaedics, Epsom General Hospital, Dorking Road, Epsom, Surrey, KT18 7EG.

Outcome scores between the groups were compared using the Students t-test and χ2 test for continuous and categorical variables respectively. Statistical analysis was performed using Microsoft Office Excel 2008 (Mac OSx 10.6.8). A P value of less than 0.05 was considered significant.

Results During the study period, 518 patients underwent medial UKA (546 knees, Oxford phase 3; Biomet UK Ltd, Swindon, UK) and 6753 patients received primary TKA. Baseline demographics, follow-up and revision rates are shown (Table 1). Of the 546 medial UKAs, 29 (5.3%) patients required revision surgery at a mean of 25 months. The revision rate for primary TKAs performed over the same period was significantly lower at 0.8% (57 cases, P b 0.01) at a mean interval of 19 months. There were no differences between the groups with regard to operative side. None of the patients who required revision of their medial UKA underwent simultaneous bilateral surgery. Final outcome scores for all patients following primary TKA, successful primary UKA, and revision UKA surgery were recorded at a mean follow-up of 20 months. Of the 29 patients requiring UKA revision, 25 patients were revised to TKA and 4 were revised to UKA or additional patello-femoral joint arthroplasty. 22 patients (76%) had complete outcome data at a mean follow-up of 26 months. There was no association between UKA failure and patient gender (P = 0.27) or BMI (P = 0.48). The primary reasons for revision were aseptic loosening (9 cases), progression of osteoarthritis (9 cases), persistent pain (6 cases), infection (2 cases), poly-dislocation (2 cases) and peri-prosthetic fracture (1 case). 10 patients (34%) required augments, stemmed implants or bone grafts. 0883-5403/© 2014 Elsevier Inc. all rights reserved.

Please cite this article as: Craik JD, et al, Revision of Unicompartmental Knee Arthroplasty Versus Primary Total Knee Arthroplasty, J Arthroplasty (2014),


J.D. Craik et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx

Table 1 Baseline Demographics, Follow-Up, and Revision Rates for Both Unicompartmental and Total Knee Arthroplasty Groups.

UKA TKA P value

Total Patients

Complete Follow-Up

Mean Follow-Up

Mean Age

Mean BMI

Male:Female Ratio


518 6753

334 (64%) 4495 (67%)

20 months 20 months

66 71 b0.01

30.0 30.6 b0.01

1.05 0.56 b0.01

29 (5.3%) 57 (0.8%) b0.01

At the time of primary UKA, there were no significant differences in pre-operative Oxford knee, Eq5D and health visual analogue scores between successful UKA patients and those eventually requiring revision (P values N 0.05). However prior to revision surgery, Oxford knee and Eq5D scores had become significantly poorer (Figs. 1 & 2). In addition pre-revision Eq5D scores were significantly worse compared with patients treated with primary TKA (Fig. 2). There were no significant differences in mean pre-operative or post-operative health visual analogue scores between patients requiring revision surgery and either successful UKA or primary TKA (Fig. 3). When comparing the improvements in scores following surgery, patients with successful medial UKA had a greater improvement in Oxford knee scores (P = 0.04) compared with those undergoing revision surgery (Table 2). However there were no other significant differences in improvements in scores with surgery between the groups.

Discussion These results demonstrate that the risk of early revision surgery in patients following medial UKA is significantly greater compared with primary TKA. Patients requiring revision surgery have worse prerevision functional scores when compared with the pre-operative scores of those undergoing primary total knee arthroplasty. In addition, despite comparable improvements in scores between the groups with surgery, a relatively poorer function in the revision UKA group persists. The results also demonstrate that revision UKA surgery is not always straightforward and additional measures to compensate for loss of bone stock are often required. However the requirement for these additional measures does not seem to influence outcome. As a result the poorer outcomes observed in revision UKA patients appear to be as a consequence of worse pre-revision function rather than the intricacies of surgery. One could therefore argue that in cases where patient function is deteriorating following UKA, expediting revision surgery may be of interest to ensure better function in the long term. The increased risk of early failure following UKA compared with TKA is demonstrated by several national joint registries with revision rates of

Fig. 1. Mean pre-operative/revision and post-operative Oxford Knee Scores. Error bars represent 95% confidence intervals.

between 4.3% to 6.3% at 3 years [9–12]. It is important to recognise however that this increased revision rate may be influenced by the perceived ease of UKA revision compared with TKA revision surgery. In addition, the younger patient cohort, who is simultaneously more likely to undergo UKA as well as being more active, may confound these results. Patients undergoing UKA may also have greater post-operative expectations that could influence decisions towards revision surgery. One survey of 7230 patients demonstrated that those receiving UKA were generally less satisfied than those following TKA which highlights this point [13]. Nonetheless our results indicate that pre-operative Eq5D scores in patients requiring revision surgery are significantly poorer than those undergoing primary TKA, which would not be fully explained by patient expectations alone. Some authors have argued that in cases of failed medial compartment arthroplasty, revision surgery offers similar outcomes to TKA [6–8]. In addition it has been suggested that the use of augments, stems and bone graft is not required in cases where the indications for surgery were progression of disease in other compartments [14]. However our results do not support these conclusions and warn against the temptation to relax patient selection criteria in light of the above claims. Several other studies also report that a significant proportion of patients require stems, augments and bone grafts during revision with rates ranging from 17% to 67% [3,15–19]. The mean interval to revision surgery for failed medial compartment arthroplasty in our cohort was 25 months. This is consistent with other studies performed over a similar time period reporting intervals of between 19 and 28 months [15–17]. However differences exist in the literature with regard to the primary cause of failure. Aseptic loosening and progression of osteoarthritis accounted for the vast majority of failures in our study. In contrast, Rancourt et al identified that 61.9% of patients requiring revision of failed UKA was secondary to progression of arthritis, with only 12.7% due to aseptic loosening [17]. This difference may be explained by variations in patient selection or volume of surgical practice which has been shown to be a key factor in the success of UKA [20].

Fig. 2. Mean pre-operative/revision and post-operative Eq5D Scores. Error bars represent 95% confidence intervals.

Please cite this article as: Craik JD, et al, Revision of Unicompartmental Knee Arthroplasty Versus Primary Total Knee Arthroplasty, J Arthroplasty (2014),

J.D. Craik et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx


Acknowledgements The authors would like to acknowledge the contributions of Mr Joshua Jacobs, Ms Grace Beer and Ms Zoe Beer for their help with collecting the data for this study. References

Fig. 3. Mean pre-operative/revision and post-operative health visual analogue scores. Error bars represent 95% confidence intervals.

Table 2 Mean Improvements in Scores.


Revision UKA

Successful UKA

P Value


P Value

11.9 0.283 5.4

15.3 0.311 6.9

0.04 0.39 0.98

15.0 0.299 10.2

0.07 0.51 0.94

P values represent significance of difference relative to revision UKA patients.

A limitation of this study is that it was not possible to obtain complete outcome data for the entire patient cohort. Nonetheless our overall patient numbers are large and are representative of the experience from a single orthopaedic unit. These results are therefore likely to be more representative of general, high-volume orthopaedic units as opposed to outcomes from implant design centres that have been difficult to reproduce.

Conclusion Revision UKA surgery is associated with poorer outcomes compared with primary TKA and appears to be a consequence of poorer preoperative function. The commonest indications for revision surgery are aseptic loosening and progression of arthritis and a high proportion of patients will require additional surgical measures to compensate for loss of bone stock. An appreciation of these results is important for appropriate patient selection for UKA and pre-operative counselling.

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Please cite this article as: Craik JD, et al, Revision of Unicompartmental Knee Arthroplasty Versus Primary Total Knee Arthroplasty, J Arthroplasty (2014),

Revision of unicompartmental knee arthroplasty versus primary total knee arthroplasty.

The risk of revision following unicompartmental arthroplasty (UKA) is greater compared with primary total knee arthroplasty (TKA). Some surgeons repor...
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