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Increased risk of failure following revision total knee replacement in patients aged 55 years and younger J. B. Stambough, J. C. Clohisy, R. L. Barrack, R. M. Nunley, J. A. Keeney From Washington University in St. Louis, Department of Orthopaedic Surgery, Saint Louis, Missouri, United States
The aims of this retrospective study were to compare the mid-term outcomes following revision total knee replacement (TKR) in 76 patients (81 knees) < 55 years of age with those of a matched group of primary TKRs based on age, BMI, gender and comorbid conditions. We report the activity levels, functional scores, rates of revision and complications. Compared with patients undergoing primary TKR, those undergoing revision TKR had less improvement in the mean Knee Society function scores (8.14 (–55 to +60) vs 23.3 points (–40 to +80), p < 0.001), a similar improvement in UCLA activity level (p = 0.52), and similar minor complication rates (16% vs 13%, p = 0.83) at a mean follow-up of 4.6 years (2 to 13.4). Further revision surgery was more common among revised TKRs (17% vs 5%, p = 0.02), with deep infection and instability being the most common reasons for failure. As many as onethird of patients aged < 55 years in the revision group had a complication or failure requiring further surgery. Young patients undergoing revision TKR should be counselled that they can expect somewhat less improvement and a higher risk of complications than occur after primary TKR. Cite this article: Bone Joint J 2014; 96-B:1657–62
J. B. Stambough, MD, Resident, Orthopaedic Surgery J. C. Clohisy, MD, Professor in Orthopaedic Surgery - Daniel C. and Betty B. Viehmann Distinguished Professorship in Orthopaedic Surgery R. L. Barrack, MD, Professor in Orthopaedic Surgery Charles F. and Joanne Knight Professor of Orthopaedic Surgery R. M. Nunley, MD, Associate Professor, Orthopaedic Surgery J. A. Keeney, MD, Assistant Professor, Orthopaedic Surgery Washington University in St. Louis, 660 South Euclid Ave, Campus Box 8233, Saint Louis, Missouri 63110, USA. Correspondence should be sent to Dr J. B. Stambough; e-mail: [email protected] ©2014 The British Editorial Society of Bone & Joint Surgery doi:10.1302/0301-620X.96B12. 34486 $2.00 Bone Joint J 2014;96-B:1657–62. Received 24 May 2014; Accepted after revision 28 August 2014
Kurtz et al1 report an expected doubling of the number of revision TKRs being required by the year 2015 and have estimated that > 900 000 primary TKRs and 100 000 revision TKRs will be undertaken in patients aged ≤ 55 years in the United States by the year 2030. Any increase in primary TKR can be anticipated to contribute to the revision burden. Several factors may contribute to an increased risk of revision surgery in younger patients. These include the combined effects of higher levels of activity and longer periods of function on polyethylene wear and osteolysis, the failure of individual components and increased exposure to systemic infection. Reports using data from national registries have identified younger patients as being at a substantially increased risk of revision surgery following primary TKR.2-4 Community-based registries have previously reported increased revision rates among younger men, with cementless fixation and unicompartmental replacement comprising a higher risk of revision surgery.5 Schroer et al6 have reported that most contemporary TKR revisions occur within five years after the index replacement and Williams et al7 reported reduced overall satisfaction in patients aged < 50 years after TKR. Recently, Baker et al8 demonstrated that
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diminished operative success is associated with increased poor patient-reported satisfaction scores. Finally, Aggarwal et al9 reported a rate of survival of 71% (95% CI = 60.7% to 83.0%), six years post-operatively with revision as the endpoint, in patients aged ≤ 50 years of age, with higher rates of aseptic failure. The aims of this study were to compare the mid-term outcome after revision TKR in patients aged < 55 years with a matched group of patients undergoing primary TKR.
Patients and Methods After obtaining ethical approval for the study, we identified patients aged < 55 years from our joint replacement registry who had required revision TKR > four years after the primary procedure. We considered all revision TKRs undertaken between January 1996 and December 2008 performed by one of five surgeons (including RLB, JCC, RMN) in which an exchange of both femoral and tibial components was performed. Patients were also included in the study if they had required further surgery including a further revision procedure or had died. In all, 77 patients (81 knees) met these criteria. The demographic details which were recorded from the medical records of each 1657
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Table I. Demographic data for revision and primary total knee replacement groups (mean with range, as applicable) Demographics
Primary n = 81 knees, 76 patients
Revision n = 81 knees, 77 patients
p-value
Age (yrs) Follow-up (yrs) BMI (kg/m2) Females Pre-operative diagnosis (%) Inflammatory arthritis Rheumatoid Lupus Psoriatic Osteonecrosis Comorbidities Cardiac Diabetes Pulmonary
48.7 (26 to 55) 4.8 (2.0 to 13.9) 33.9 (14.9 to 54.9) 53
48.5 (25 to 55) 4.6 (2.0 to 13.1) 33.9 (19.3 to 54.2) 53
0.85* 0.68* 0.91* 1.00
10 (12) 8 (10) 1 (1) 0 (0) 1 (1)
10 (12) 6 (8) 2 (2) 1 (1) 1 (1)
1.00† 0.80† 1.00† 1.00† 1.00†
12 (14) 15 (18) 13 (16)
13 (16) 19 (23) 11 (13)
0.84† 0.68† 0.78†
BMI, body mass index * Two-tailed t-test † Fisher exact test
Table II. Pre-operative indication for initial revision in the revision total knee replacement (TKR) group Revision diagnosis/failure mechanism (n = 81 TKRs)
n (%)
Aseptic loosening Infection Instability Arthrofibrosis/stiffness Wear/osteolysis Pain Malalignment Periprosthetic fracture Liner dislodgement
26 (32) 14 (17) 13 (16) 11 (14) 7 (9) 6 (7) 2 (2) 1 (1) 1 (1)
patient included the age at the time of revision surgery, gender, BMI, comorbidities, previous surgery to the knee, the indication for revision, and the revision procedure performed. Patients who had not returned for a routine evaluation were contacted and asked to return for follow-up assessment (12 patients, 15%). The mean follow up was 4.6 years (2 to 13.4). A separate search of the registry was performed to identify an historical comparison group of patients who had undergone primary TKR and were aged ≤ 55 years during the same time frame. This group was matched for age, gender, body mass index (BMI) and comorbidities. Gender was matched exactly, the mean age was matched to within five years, and the mean BMI was to within 5 kg/m2. Further matching involved the pre-operative diagnosis, with an equal number of patients in each group having an inflammatory arthritis (Table I). Patients were matched through a blinded process, irrespective to outcome, by an author not involved in patient care (JBS). The distribution of gender (53 women and 28 men) and the mean BMI (33.9 kg/m2,14.9 to 54.9) were the same in both groups (Table I). Using World Health Organization criteria,10 62% of patients were considered obese (BMI > 30 kg/m2). In the revision TKR group, overall ten knees (12%) had inflammatory arthritis, with six having rheumatoid arthritis
(8%), two with systemic lupus (2%), and one each with psoriatic arthritis and primary osteonecrosis (1% each). The most common pre-operative indications in the revision group were aseptic loosening (26 knees, 32%), infection (14 knees, 17%), instability (13 knees, 16%) and stiffness (11 knees, 14%) (Table II). Revisions performed for infection were two-staged, with survival being recorded following the second stage. All revisions were approached through a standard medial arthrotomy. A total of 66 revision TKRs (32%) were performed using constrained components, including one rotating hinge, and 18 (22%) included patellar resurfacing. Both the femoral and tibial components were cemented in all revisions. In all, 67 revisions (83%) involved hybrid fixation with more extensive metaphyseal cement to augment cementless fixation, and antibiotics were included in the cement in 60 revisions (74%). Function was assessed using the University of California Los Angeles (UCLA) Activity Scale11 and the Knee Society knee function score12 obtained pre-operatively and at the most recent follow-up. The post-operative complications and requirement for further surgery were noted from the medical records. Failure was identified from the medical notes and confirmed with available radiographs in all cases of aseptic loosening or osteolysis leading to revision. FemTHE BONE & JOINT JOURNAL
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Table III. Mean (range) clinical activity score profiles for the primary and revision total knee replacement groups pre-operatively (pre-op) and post-operatively (post-op) Activity scores
Primary n = 81 knees, 76 subjects
Revision n = 81 knees, 77 subjects
p-value*
UCLA pre-op UCLA post-op UCLA mean improvement KS function pre-op KS function post-op KS function mean improvement
3.48 (1 to 9) 4.71 (2 to 10) 1.37 (–2 to +7) 45.64 (20 to 80 66.62 (20 to 100) 23.30 (–40 to +80)
3.26 (1 to 9) 4.13 (1 to 10) 1.15 (–2 to +9) 45.96 (5 to 100) 50.69 (5 to 100) 8.14 (–55 to +60)
0.29 0.09 0.52 0.91 < 0.001 < 0.001
UCLA, University of California Los Angeles Activity Score; KS, Knee Society function subscore * Two-tailed t-test
oral and tibial radiolucent lines were measured by the method described by Bach et al.13 A further revision of any type, including exchange of the tibial polyethylene insert, was considered a failure. Statistical analysis. A two-tailed t-test was used to assess continuous variables, including age, length of follow-up, BMI, and UCLA activity and Knee Society function scores in both groups. Categorical variables, including preoperative diagnosis, comorbidities, surgical complications, cause of failure and rates of revision were assessed with Fisher’s exact test. Hazard ratios (HR) with 95% confidence intervals (CI) were used when comparing the incidence of failure between groups. For subgroup analysis between septic and aseptic revisions, a log-rank test was used to compare survival (time to failure = second revision). Statistical analysis was carried out with GraphPad Prism 6.04, (La Jolla, California)for log-rank testing and calculating Hazard Ratios. Statistical significance was set at p ≤ 0.05.
Results In the revision group, the mean change in UCLA activity score was 1.15 points (–2 to +9) and the mean Knee Society functional subscore improved by 8.14 points (–55 to +60). In the primary TKR group, the mean change in UCLA activity score was 1.37 points (–2 to +7) and the mean Knee Society functional subscore improved by 23.3 points (–40 to +80). Although the difference in UCLA activity scores was not clinically or statistically significant (p = 0.52, two-tailed t-test), the improvement in Knee Society subscore was significant (p < 0.001, two-tailed t-test) (Table III). In all, 14 revision TKRs (17%) were re-revised at a mean of 3.6 years (0.2 to 11.7) post-operatively compared with four revisions (5%) in the primary TKR group occurring at a mean of 7.4 years (3.6 to 14.9) post-operatively. This difference in the rate of revision between the two groups was statistically significant (p = 0.02, two-tailed t-test). There was an equal distribution of men and women in the revision group who required re-revision, with a trend towards a higher rate in men (14 knees in seven men, seven women, 25% vs 13%, p = 0.18, two-tailed t-test). Infection was the most common cause of failure in both groups, affecting six knees (43%) in the revision group and three (50%) in the primary TKR group. However, the difference in the overall re-revision rate did not reach significance with the number VOL. 96-B, No. 12, DECEMBER 2014
of patients available (7% vs 2%, p = 0.28, two-tailed t-test) (Table IV). Those who had undergone an initial revision TKR for infection had a significantly increased risk of requiring a further revision for infection compared with all other indications for revision (HR 3.86, 95% CI 1.84 to 8.08, p = 0.003, two-tailed t-test). Half the failures in patients undergoing revision TKR for infection occurred within the first post-operative year, generally at about three months post-operatively, with persistent infection involving the same organisms (coagulase-negative staphylococci in two knees and Staphylococcus aureus in the other). The later-presenting failures of revision TKR for infection were caused by recurrent coagulase-negative staphylococci in two knees, but in the remaining knee the culture failed to identify an organism. Failure of primary TKR due to infection occurred later, 3.5 and 7.4 years post-operatively, respectively. Aseptic loosening was the second most common indication for initial revision TKR, although its overall relative risk for further revision surgery in the revision group was 0.45 (95% CI 0.12 to 1.67, p = 0.23, two-tailed t-test). This was not statistically significant when compared with other indications for revision. When the diagnoses of septic and aseptic revision were separated in the revision group, there was no significant difference between the overall rate of revision (log-rank test, p = 0.249) and time to failure (log-rank test, p = 0.341) between the subgroups (Fig. 1). Furthermore, we found no significant differences in demographic variables, including mean age (p = 0.267, two-tailed t-test), mean BMI (p = 0.975, two-tailed t-test), gender (p = 0.359, two-tailed t-test) or inflammatory arthritis as the underlying diagnosis (p = 0.761, two-tailed t-test), between septic and aseptic revisions in the revision group. There was no difference in the mean UCLA activity score pre- (p = 0.161, two-tailed t-test) or post-operatively (p = 0.489, two-tailed t-test) between the two subgroups. There was, however, a significant difference in pre-operative Knee Society function scores (p = 0.032, two-tailed t-test) that was not found post-operatively (p = 0.53, two-tailed t-test). When aseptic loosening was the indication for the initial revision, the likelihood of further revision was less than half that of the knees revised for infection (HR 0.416, 95% CI 0.128 to 1.346, p=0.143, two-tailed t-test). No statistical difference in failure rates was seen for those with inflammatory arthritis
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Table IV. Details of the 14 patients in the revision total knee replacement (TKR) group who required re-revision Pre-operative diagnosis
Reason for failure
BMI (kg/m2)
Time to re-revision (mths)
Aseptic loosening
Aseptic Loosening
40.86
79.3
Aseptic loosening Aseptic loosening
Aseptic Loosening 25.9 Extensor Mechanism 37.85 Failure Instability 28.06 Infection 28.96 Infection 19.34 Recurrent Infection 25.63 Recurrent Infection 43.67 Recurrent Infection 22.64 Recurrent Infection 49.44
22.9 7.7 7.3 7.3 0.2 17.4 20.3 1.9 65.9
Component Failure Instability
25.14 30.58
3.5 91.7
None
Maltracking Periprosthetic fracture Instability
Osteolysis/Wear
36.84
140.6
None
Painful TKR
Recurrent Hemarthrosis
30.88
130.4
Number Gender
Ethnicity
Age at revision
1
F
Caucasian
51
2 3
M F
Caucasian Caucasian
51 55
4 5 6 7 8 9 10
M F M F F F F
Caucasian Caucasian Caucasian Caucasian Caucasian Caucasian Caucasian
55 54 25 50 52 36 51
11 12
M M
Caucasian Caucasian
43 54
Hepatobiliary, smoking Depression Cardiac, gastrointestinal, depression None Hypertension Hepatobiliary, renal None Hypertension Haematological Cardiac, diabetes, smoking, depression None Inflammatory arthritis
13
M
47
14
M
African American Caucasian
45
Comorbidities
Instability Aseptic loosening Arthrofibrosis Infection Infection Infection Infection
Aseptic Revisions
100
Survival (%)
Septic Revisions
50 p = 0.341
0 0
150 50 100 Time to revision (mths)
complications in the revision group included wound dehiscence (three knees, 4%), prolonged wound drainage (two knees, 2%) and painful hardware (one knee, 1%). Dehiscence and drainage were managed with open irrigation and debridement. The painful hardware involved screws and cerclage wires used to repair an osteotomy of the tibial tubercle which was used during the original revision TKR. In the primary group there were 11 complications (13%), most being limitation of movement requiring manipulation, comprising 91% of all complications (ten knees). One patient developed a painful and recurrent haematoma requiring irrigation and debridement one month postoperatively. There was no significant difference in complication rates between the two groups (p = 0.83, two-tailed t-test).
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Fig. 1 Kaplan–Meier analysis showing no significant difference (log-rank test, 95% CI 0.135 to 1.988, p = 0.341) in survival after revision total knee replacement (TKR) with aseptic and septic subgroup analysis.
between the revision and primary TKR groups (p = 0.222, two-tailed t-test). Overall, 13 complications (16%) not requiring a change of components occurred in the revision group. Seven knees (9%) had < 90º of flexion, and these patients underwent a manipulation under anaesthesia. This was the most common complication not requiring further surgery in the revision group. Two of these patients required additional open procedures, including synovectomy and retinacular release to address persistent limitation of movement. Other
Discussion Patients between 45 and 55 years of age are the fastestgrowing group undergoing TKR.14,15 They are anticipated to have higher rates of revision than those patients aged > 65 years, either because of higher activity levels or a cumulative risk of failure over lifespan of the prosthesiss.7,16-18 Because of the higher risk for revision surgery, it is important for both surgeons and patients to understand the unique features of this younger population and their impact on the prosthetic joint. By understanding the causes of failure in revision TKR, we can improve our approach to treatment and manage expectations in order to optimise results. There were several limitations to this study. First was the selection bias inherent to retrospective case-control studies. The standard outcome tools for the assessment of patients undergoing revision surgery changed during the 13-year period of the study. Some patient-reported clinical and functional outcome measures were not available for the THE BONE & JOINT JOURNAL
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whole duration of the study, notably for the level of pain reported by patients. The methods of assessing function were applied consistently throughout the study. Ghanem et al19 reported limitations with the validity of data when limited data points are assessed following revision TKR. A second confounding variable was the use of different designs of implant and surgical techniques for both groups during the course of the study. The variability in surgical practice makes it difficult to assess the potential influence of implant design or surgical technique, including fixation strategy, implant constraint and the choice of bearing surfaces, on functional outcome or survival. Furthermore, not being able to verify the alignment of the components radiologically owing to inconsistent archiving of the images hindered our ability to make definitive statements about the causes of failure. A final limitation was the study design. Including both septic and aseptic revisions in the revision TKR cohort potentially acted to confound our results. Subgroup analysis between the two revealed a significant difference in preoperative knee function subscores. Nevertheless, because this difference was eliminated after revision TKR, it suggests that the two groups may reach a similar level in terms of pain, activity and function despite disparate causes for the initial revision. In spite of these limitations, we believe that the reported functional instruments used and the midterm follow-up data provide an understanding of revision TKR which can be broadly applied in these patients. More younger women are seeking TKR than men, with the literature suggesting a > 300% increase in those aged 45 to 55 years between 2000 to 2008.20,21 Our revision group confirmed this trend, with a higher proportion of women (65%) also undergoing TKR. We noted a trend for higher risk of re-revision among men, similar to limited evidence suggesting higher failure rates for revision and primary TKR among men of all ages.5 Our results also demonstrate that, compared with primary TKR, revisions are associated with smaller improvements in function and higher failure rates at mid-term follow-up. These observations are consistent with the limited results available in the literature.2,3,22,23 Previous authors have reported good to excellent functional outcomes in younger patients undergoing primary TKR for either osteoarthritis or rheumatoid arthritis.24-28 Without consideration of age stratification, Baker et al22 reported lower functional activity levels within the first year after surgery for revision TKR compared with primary TKR. Our results in younger patients are consistent with this trend, with similar activity levels between patients undergoing primary and revision procedures but less functional recovery attained, as determined by the Knee Society subscore. To date, there have been few studies that highlight the reasons for failure of revision TKR among patients aged < 55 years. Earlier studies including patients of all ages suggested that the two most common indications for revision are aseptic loosening and infection.6,9,16 In patients aged < 55 years with osteoarthritis, Odland et al29 reported a 16% revision rate for aseptic loosening and osteolysis ten VOL. 96-B, No. 12, DECEMBER 2014
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years post-operatively in a group of 59 patients (67 knees). Aseptic loosening was the leading indication for revision TKR, suggesting that this may be due to increased demands on the prosthesis. The 17% incidence of mid-term re-revision TKR in our patients highlights the challenges in preventing early failures from mechanisms other than wear in younger patients. Our findings suggest a similar time to failure of the revision in younger patients (mean 3.6 years). The higher re-revision rate for infection in the first year after surgery is also consistent with other reports.30 Schwarzkopf et al31 have suggested that more resistant organisms may be found in patients referred to specialised tertiary referral centres, which might be a contributing factor in early failures among those undergoing revision for infection at our institution and at other centres. In our study, 16% of patients in the revision group and 13% of those in the primary group had a complication of surgery that did not require revision. Most complications in both groups were related to a limited range of movement of the knee. Baier et al32 recently reported that approximately one-third of patients (19 out of 78 knees, 28%) undergoing revision TKR have some complication, and 26% (18 knees) had a re-operation within five years of surgery. Although limited movement requiring manipulation was the most common complication in both our revision (9%) and primary groups (12%), young patients undergoing revision were not at a higher risk of this complication than other patients undergoing primary TKR. Maloney33 reported an 11% incidence (24/214 knees) of arthrofibrosis, defined as < 90º flexion, within two months following primary TKR in patients of all ages. Among 33 patients (38 knees) aged < 40 years, Mont et al34 found that 24% (nine knees) required manipulation following primary TKR. Because the decision to proceed with manipulation or other surgery to address limited movement may be influenced by other factors, it is possible that our study under-reports the impact of limited movement in these patients. Revision TKR is a generally effective procedure when performed in patients aged < 55 years. However, we found that as many as one-third of patients may experience either a post-operative complication or early failure of a revision procedure, and these concerns are more likely to have a substantial impact on their future quality of life. As the number of both primary and revision TKRs being performed substantially increases in young patients, additional studies will be needed to assess improvements in activity, function and satisfaction, and to limit the adverse impact of limited movement, instability and infection. Young patients undergoing revision TKR should be counselled that they can expect somewhat less improvement and a higher risk of complication than occur after primary TKR. The authors would like to thank W. J, Maloney, MD and R. S. J. Burnett, MD (FRCSC) for allowing the inclusion of their patients. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. This article was primary edited by G. Scott and first proof edited by J. Scott.
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References 1. Kurtz S, Ong K, Lau E, Mowat F, Halpern M. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg [Am] 2007;89-A:780–785. 2. Harrysson OL, Robertsson O, Nayfeh JF. Higher cumulative revision rate of knee arthroplasties in younger patients with osteoarthritis. Clin Orthop Relat Res 2004;421:162–168. 3. Himanen AK, Belt E, Nevalainen J, Hämäläinen M, Lehto MU. Survival of the AGC total knee arthroplasty is similar for arthrosis and rheumatoid arthritis; Finnish Arthroplasty Register report on 8,467 operations carried out between 1985 and 1999.Acta Orthop 2005;76:85–88. 4. Julin J, Jämsen E, Puolakka T, Konttinen YT, Moilanen T. Younger age increases the risk of early prosthesis failure following primary total knee replacement for osteoarthritis; a follow-up study of 32,019 total knee replacements in the Finnish Arthroplasty Register. Acta Orthop 2010;81:413–419. 5. Gioe TJ, Novak C, Sinner P, Ma W, Mehle S. Knee arthroplasty in the young patient: survival in a community registry. Clin Orthop Relat Res 2007;464:83–87. 6. Schroer WC, Berend KR, Lombardi AV, et al. Why are total knees failing today? Etiology of total knee revision in 2010 and 2011. J Arthroplasty 2013;28(8Suppl):116– 119. 7. Williams DP, Price AJ, Beard DJ. The effects of age on patient-reported outcome measures in total knee replacements. Bone Joint J 2013;95-B:38–44. 8. Baker PN, Rushton S, Jameson SS, et al. Patient satisfaction with total knee replacement cannot be predicted from pre-operative variables alone: A cohort study from the National Joint Registry for England and Wales. Bone Joint J 2013;95B:1359–1365. 9. Aggarwal VK, Goyal N, Deirmengian G, et al. Revision total knee arthroplasty in the young patient: is there trouble on the horizon? J Bone Joint Surg [Am] 2014;96A:536–542. 10. James PT, Leach R, Kalamara E, Shayeghi M. The worldwide obesity epidemic. Obes Res 2001;(9Suppl4):228S–233S. 11. Amstutz HC, Thomas BJ, Jinnah R, Kim W, Grogan T, Yale C. Treatment of primary osteoarthritis of the hip. A comparison of total joint and surface replacement arthroplasty. J Bone Joint Surg [Am] 1984;66-A:228–241. 12. Insall JN, Dorr LD, Scott RD, Scott WN. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res 1989;248:13–14. 13. Bach CM, Biedermann R, Goebel G, Mayer E, Rachbauer F. Reproducible assessment of radiolucent lines in total knee arthroplasty. Clin Orthop Relat Res 2005;434:183–188. 14. Kurtz SM, Lau E, Ong K, et al. Future young patient demand for primary and revision joint replacement: national projections from 2010 to 2030. Clin Orthop Relat Res 2009;467:2606–2612. 15. Singh JA, Vessely MB, Harmsen WS, et al. A population-based study of trends in the use of total hip and total knee arthroplasty, 1969-2008. Mayo Clin Proc 2010;85:898–904. 16. Koh IJ, Cho WS, Choi NY, Kim TK; Kleos Korea Research Group. Causes, risk factors, and trends in failures after TKA in Korea over the past 5 years: a multicenter study. Clin Orthop Relat Res 2014;472:316–326.
17. McCalden RW, Robert CE, Howard JL, et al. Comparison of outcomes and survivorship between patients of different age groups following TKA. J Arthroplasty 2013;28(8Suppl):83–86. 18. Wainwright C, Theis JC, Garneti N, Melloh M. Age at hip or knee joint replacement surgery predicts likelihood of revision surgery. J Bone Joint Surg [Br] 2011;93B:1411–1415. 19. Ghanem E, Pawasarat I, Lindsay A, et al. Limitations of the Knee Society Score in evaluating outcomes following revision total knee arthroplasty. J Bone Joint Surg [Am] 2010;92-A:2445–2451. 20. Dunbar MJ, Howard A, Bogoch ER, Parvizi J, Kreder HJ. Orthopaedics in 2020: predictors of musculoskeletal need. J Bone Joint Surg [Am] 2009;91-A:2276–2286. 21. No authors listed. Canadian Joint Replacement Registry (CJRR) 2007 annual report - hip and knee replacements in Canada. Ottawa: Canadian Institute for Health Information; 2008. 22. Baker P, Cowling P, Kurtz S, et al. Reason for revision influences early patient outcomes after aseptic knee revision. Clin Orthop Relat Res 2012;470:2244–2252. 23. Hartley RC, Barton-Hanson NG, Finley R, Parkinson RW. Early patient outcomes after primary and revision total knee arthroplasty; a prospective study. :J Bone Joint Surg [Br] 2002;84-B:994–999. 24. Diduch DR, Insall JN, Scott WN, Scuderi GR, Font-Rodriguez D. Total knee replacement in young, active patients; long-term follow-up and functional outcome. :J Bone Joint Surg [Am] 1997;79-A:575–582. 25. Duffy GP, Trousdale RT, Stuart MJ. Total knee arthroplasty in patients 55 years old or younger. 10- to 17-year results. Clin Orthop Relat Res 1998;356:22–27. 26. Gill GS, Chan KC, Mills DM. 5- to 18-year follow-up study of cemented total knee arthroplasty for patients 55 years old or younger. J Arthroplasty 1997;12:49–54. 27. Keeney JA, Eunice S, Pashos G, Wright RW, Clohisy JC. What is the evidence for total knee arthroplasty in young patients? : a systematic review of the literature. Clin Orthop Relat Res 2011;469:574–583. 28. Lonner JH, Hershman S, Mont M, Lotke PA. Total knee arthroplasty in patients 40 years of age and younger with osteoarthritis. Clin Orthop Relat Res 2000;380:85–90. 29. Odland AN, Callaghan JJ, Liu SS, Wells CW. Wear and lysis is the problem in modular TKA in the young OA patient at 10 years. Clin Orthop Relat Res 2011;469:41– 47. 30. Portillo ME, Salvadó M, Alier A, et al. Prosthesis failure within 2 years of implantation is highly predictive of infection. Clin Orthop Relat Res 2013;471:3672–3678. 31. Schwarzkopf R, Oh D, Wright E, Estok DM, Katz JN. Treatment failure among infected periprosthetic patients at a highly specialized revision TKA referral practice. Open Orthop J 2013;7:264–271. 32. Baier C, Lüring C, Schaumburger J, et al. Assessing patient-oriented results after revision total knee arthroplasty. J Orthop Sci 2013;18:955–961. 33. Maloney WJ. The stiff total knee arthroplasty: evaluation and management. J Arthroplasty 2002;17(4Suppl1):71–73. 34. Mont MA, Sayeed SA, Osuji O, et al. Total knee arthroplasty in patients 40 years and younger. J Knee Surg 2012;25:65–69.
THE BONE & JOINT JOURNAL
Increased risk of failure following revision total knee replacement in patients aged 55 years and younger J. B. Stambough, J. C. Clohisy, R. L. Barrack, R. M. Nunley, J. A. Keeney From Washington University in St. Louis, Department of Orthopaedic Surgery, Saint Louis, Missouri, United States
The aims of this retrospective study were to compare the mid-term outcomes following revision total knee replacement (TKR) in 76 patients (81 knees) < 55 years of age with those of a matched group of primary TKRs based on age, BMI, gender and comorbid conditions. We report the activity levels, functional scores, rates of revision and complications. Compared with patients undergoing primary TKR, those undergoing revision TKR had less improvement in the mean Knee Society function scores (8.14 (–55 to +60) vs 23.3 points (–40 to +80), p < 0.001), a similar improvement in UCLA activity level (p = 0.52), and similar minor complication rates (16% vs 13%, p = 0.83) at a mean follow-up of 4.6 years (2 to 13.4). Further revision surgery was more common among revised TKRs (17% vs 5%, p = 0.02), with deep infection and instability being the most common reasons for failure. As many as onethird of patients aged < 55 years in the revision group had a complication or failure requiring further surgery. Young patients undergoing revision TKR should be counselled that they can expect somewhat less improvement and a higher risk of complications than occur after primary TKR. Cite this article: Bone Joint J 2014; 96-B:1657–62
J. B. Stambough, MD, Resident, Orthopaedic Surgery J. C. Clohisy, MD, Professor in Orthopaedic Surgery - Daniel C. and Betty B. Viehmann Distinguished Professorship in Orthopaedic Surgery R. L. Barrack, MD, Professor in Orthopaedic Surgery Charles F. and Joanne Knight Professor of Orthopaedic Surgery R. M. Nunley, MD, Associate Professor, Orthopaedic Surgery J. A. Keeney, MD, Assistant Professor, Orthopaedic Surgery Washington University in St. Louis, 660 South Euclid Ave, Campus Box 8233, Saint Louis, Missouri 63110, USA. Correspondence should be sent to Dr J. B. Stambough; e-mail: [email protected] ©2014 The British Editorial Society of Bone & Joint Surgery doi:10.1302/0301-620X.96B12. 34486 $2.00 Bone Joint J 2014;96-B:1657–62. Received 24 May 2014; Accepted after revision 28 August 2014
Kurtz et al1 report an expected doubling of the number of revision TKRs being required by the year 2015 and have estimated that > 900 000 primary TKRs and 100 000 revision TKRs will be undertaken in patients aged ≤ 55 years in the United States by the year 2030. Any increase in primary TKR can be anticipated to contribute to the revision burden. Several factors may contribute to an increased risk of revision surgery in younger patients. These include the combined effects of higher levels of activity and longer periods of function on polyethylene wear and osteolysis, the failure of individual components and increased exposure to systemic infection. Reports using data from national registries have identified younger patients as being at a substantially increased risk of revision surgery following primary TKR.2-4 Community-based registries have previously reported increased revision rates among younger men, with cementless fixation and unicompartmental replacement comprising a higher risk of revision surgery.5 Schroer et al6 have reported that most contemporary TKR revisions occur within five years after the index replacement and Williams et al7 reported reduced overall satisfaction in patients aged < 50 years after TKR. Recently, Baker et al8 demonstrated that
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diminished operative success is associated with increased poor patient-reported satisfaction scores. Finally, Aggarwal et al9 reported a rate of survival of 71% (95% CI = 60.7% to 83.0%), six years post-operatively with revision as the endpoint, in patients aged ≤ 50 years of age, with higher rates of aseptic failure. The aims of this study were to compare the mid-term outcome after revision TKR in patients aged < 55 years with a matched group of patients undergoing primary TKR.
Patients and Methods After obtaining ethical approval for the study, we identified patients aged < 55 years from our joint replacement registry who had required revision TKR > four years after the primary procedure. We considered all revision TKRs undertaken between January 1996 and December 2008 performed by one of five surgeons (including RLB, JCC, RMN) in which an exchange of both femoral and tibial components was performed. Patients were also included in the study if they had required further surgery including a further revision procedure or had died. In all, 77 patients (81 knees) met these criteria. The demographic details which were recorded from the medical records of each 1657
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Table I. Demographic data for revision and primary total knee replacement groups (mean with range, as applicable) Demographics
Primary n = 81 knees, 76 patients
Revision n = 81 knees, 77 patients
p-value
Age (yrs) Follow-up (yrs) BMI (kg/m2) Females Pre-operative diagnosis (%) Inflammatory arthritis Rheumatoid Lupus Psoriatic Osteonecrosis Comorbidities Cardiac Diabetes Pulmonary
48.7 (26 to 55) 4.8 (2.0 to 13.9) 33.9 (14.9 to 54.9) 53
48.5 (25 to 55) 4.6 (2.0 to 13.1) 33.9 (19.3 to 54.2) 53
0.85* 0.68* 0.91* 1.00
10 (12) 8 (10) 1 (1) 0 (0) 1 (1)
10 (12) 6 (8) 2 (2) 1 (1) 1 (1)
1.00† 0.80† 1.00† 1.00† 1.00†
12 (14) 15 (18) 13 (16)
13 (16) 19 (23) 11 (13)
0.84† 0.68† 0.78†
BMI, body mass index * Two-tailed t-test † Fisher exact test
Table II. Pre-operative indication for initial revision in the revision total knee replacement (TKR) group Revision diagnosis/failure mechanism (n = 81 TKRs)
n (%)
Aseptic loosening Infection Instability Arthrofibrosis/stiffness Wear/osteolysis Pain Malalignment Periprosthetic fracture Liner dislodgement
26 (32) 14 (17) 13 (16) 11 (14) 7 (9) 6 (7) 2 (2) 1 (1) 1 (1)
patient included the age at the time of revision surgery, gender, BMI, comorbidities, previous surgery to the knee, the indication for revision, and the revision procedure performed. Patients who had not returned for a routine evaluation were contacted and asked to return for follow-up assessment (12 patients, 15%). The mean follow up was 4.6 years (2 to 13.4). A separate search of the registry was performed to identify an historical comparison group of patients who had undergone primary TKR and were aged ≤ 55 years during the same time frame. This group was matched for age, gender, body mass index (BMI) and comorbidities. Gender was matched exactly, the mean age was matched to within five years, and the mean BMI was to within 5 kg/m2. Further matching involved the pre-operative diagnosis, with an equal number of patients in each group having an inflammatory arthritis (Table I). Patients were matched through a blinded process, irrespective to outcome, by an author not involved in patient care (JBS). The distribution of gender (53 women and 28 men) and the mean BMI (33.9 kg/m2,14.9 to 54.9) were the same in both groups (Table I). Using World Health Organization criteria,10 62% of patients were considered obese (BMI > 30 kg/m2). In the revision TKR group, overall ten knees (12%) had inflammatory arthritis, with six having rheumatoid arthritis
(8%), two with systemic lupus (2%), and one each with psoriatic arthritis and primary osteonecrosis (1% each). The most common pre-operative indications in the revision group were aseptic loosening (26 knees, 32%), infection (14 knees, 17%), instability (13 knees, 16%) and stiffness (11 knees, 14%) (Table II). Revisions performed for infection were two-staged, with survival being recorded following the second stage. All revisions were approached through a standard medial arthrotomy. A total of 66 revision TKRs (32%) were performed using constrained components, including one rotating hinge, and 18 (22%) included patellar resurfacing. Both the femoral and tibial components were cemented in all revisions. In all, 67 revisions (83%) involved hybrid fixation with more extensive metaphyseal cement to augment cementless fixation, and antibiotics were included in the cement in 60 revisions (74%). Function was assessed using the University of California Los Angeles (UCLA) Activity Scale11 and the Knee Society knee function score12 obtained pre-operatively and at the most recent follow-up. The post-operative complications and requirement for further surgery were noted from the medical records. Failure was identified from the medical notes and confirmed with available radiographs in all cases of aseptic loosening or osteolysis leading to revision. FemTHE BONE & JOINT JOURNAL
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Table III. Mean (range) clinical activity score profiles for the primary and revision total knee replacement groups pre-operatively (pre-op) and post-operatively (post-op) Activity scores
Primary n = 81 knees, 76 subjects
Revision n = 81 knees, 77 subjects
p-value*
UCLA pre-op UCLA post-op UCLA mean improvement KS function pre-op KS function post-op KS function mean improvement
3.48 (1 to 9) 4.71 (2 to 10) 1.37 (–2 to +7) 45.64 (20 to 80 66.62 (20 to 100) 23.30 (–40 to +80)
3.26 (1 to 9) 4.13 (1 to 10) 1.15 (–2 to +9) 45.96 (5 to 100) 50.69 (5 to 100) 8.14 (–55 to +60)
0.29 0.09 0.52 0.91 < 0.001 < 0.001
UCLA, University of California Los Angeles Activity Score; KS, Knee Society function subscore * Two-tailed t-test
oral and tibial radiolucent lines were measured by the method described by Bach et al.13 A further revision of any type, including exchange of the tibial polyethylene insert, was considered a failure. Statistical analysis. A two-tailed t-test was used to assess continuous variables, including age, length of follow-up, BMI, and UCLA activity and Knee Society function scores in both groups. Categorical variables, including preoperative diagnosis, comorbidities, surgical complications, cause of failure and rates of revision were assessed with Fisher’s exact test. Hazard ratios (HR) with 95% confidence intervals (CI) were used when comparing the incidence of failure between groups. For subgroup analysis between septic and aseptic revisions, a log-rank test was used to compare survival (time to failure = second revision). Statistical analysis was carried out with GraphPad Prism 6.04, (La Jolla, California)for log-rank testing and calculating Hazard Ratios. Statistical significance was set at p ≤ 0.05.
Results In the revision group, the mean change in UCLA activity score was 1.15 points (–2 to +9) and the mean Knee Society functional subscore improved by 8.14 points (–55 to +60). In the primary TKR group, the mean change in UCLA activity score was 1.37 points (–2 to +7) and the mean Knee Society functional subscore improved by 23.3 points (–40 to +80). Although the difference in UCLA activity scores was not clinically or statistically significant (p = 0.52, two-tailed t-test), the improvement in Knee Society subscore was significant (p < 0.001, two-tailed t-test) (Table III). In all, 14 revision TKRs (17%) were re-revised at a mean of 3.6 years (0.2 to 11.7) post-operatively compared with four revisions (5%) in the primary TKR group occurring at a mean of 7.4 years (3.6 to 14.9) post-operatively. This difference in the rate of revision between the two groups was statistically significant (p = 0.02, two-tailed t-test). There was an equal distribution of men and women in the revision group who required re-revision, with a trend towards a higher rate in men (14 knees in seven men, seven women, 25% vs 13%, p = 0.18, two-tailed t-test). Infection was the most common cause of failure in both groups, affecting six knees (43%) in the revision group and three (50%) in the primary TKR group. However, the difference in the overall re-revision rate did not reach significance with the number VOL. 96-B, No. 12, DECEMBER 2014
of patients available (7% vs 2%, p = 0.28, two-tailed t-test) (Table IV). Those who had undergone an initial revision TKR for infection had a significantly increased risk of requiring a further revision for infection compared with all other indications for revision (HR 3.86, 95% CI 1.84 to 8.08, p = 0.003, two-tailed t-test). Half the failures in patients undergoing revision TKR for infection occurred within the first post-operative year, generally at about three months post-operatively, with persistent infection involving the same organisms (coagulase-negative staphylococci in two knees and Staphylococcus aureus in the other). The later-presenting failures of revision TKR for infection were caused by recurrent coagulase-negative staphylococci in two knees, but in the remaining knee the culture failed to identify an organism. Failure of primary TKR due to infection occurred later, 3.5 and 7.4 years post-operatively, respectively. Aseptic loosening was the second most common indication for initial revision TKR, although its overall relative risk for further revision surgery in the revision group was 0.45 (95% CI 0.12 to 1.67, p = 0.23, two-tailed t-test). This was not statistically significant when compared with other indications for revision. When the diagnoses of septic and aseptic revision were separated in the revision group, there was no significant difference between the overall rate of revision (log-rank test, p = 0.249) and time to failure (log-rank test, p = 0.341) between the subgroups (Fig. 1). Furthermore, we found no significant differences in demographic variables, including mean age (p = 0.267, two-tailed t-test), mean BMI (p = 0.975, two-tailed t-test), gender (p = 0.359, two-tailed t-test) or inflammatory arthritis as the underlying diagnosis (p = 0.761, two-tailed t-test), between septic and aseptic revisions in the revision group. There was no difference in the mean UCLA activity score pre- (p = 0.161, two-tailed t-test) or post-operatively (p = 0.489, two-tailed t-test) between the two subgroups. There was, however, a significant difference in pre-operative Knee Society function scores (p = 0.032, two-tailed t-test) that was not found post-operatively (p = 0.53, two-tailed t-test). When aseptic loosening was the indication for the initial revision, the likelihood of further revision was less than half that of the knees revised for infection (HR 0.416, 95% CI 0.128 to 1.346, p=0.143, two-tailed t-test). No statistical difference in failure rates was seen for those with inflammatory arthritis
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Table IV. Details of the 14 patients in the revision total knee replacement (TKR) group who required re-revision Pre-operative diagnosis
Reason for failure
BMI (kg/m2)
Time to re-revision (mths)
Aseptic loosening
Aseptic Loosening
40.86
79.3
Aseptic loosening Aseptic loosening
Aseptic Loosening 25.9 Extensor Mechanism 37.85 Failure Instability 28.06 Infection 28.96 Infection 19.34 Recurrent Infection 25.63 Recurrent Infection 43.67 Recurrent Infection 22.64 Recurrent Infection 49.44
22.9 7.7 7.3 7.3 0.2 17.4 20.3 1.9 65.9
Component Failure Instability
25.14 30.58
3.5 91.7
None
Maltracking Periprosthetic fracture Instability
Osteolysis/Wear
36.84
140.6
None
Painful TKR
Recurrent Hemarthrosis
30.88
130.4
Number Gender
Ethnicity
Age at revision
1
F
Caucasian
51
2 3
M F
Caucasian Caucasian
51 55
4 5 6 7 8 9 10
M F M F F F F
Caucasian Caucasian Caucasian Caucasian Caucasian Caucasian Caucasian
55 54 25 50 52 36 51
11 12
M M
Caucasian Caucasian
43 54
Hepatobiliary, smoking Depression Cardiac, gastrointestinal, depression None Hypertension Hepatobiliary, renal None Hypertension Haematological Cardiac, diabetes, smoking, depression None Inflammatory arthritis
13
M
47
14
M
African American Caucasian
45
Comorbidities
Instability Aseptic loosening Arthrofibrosis Infection Infection Infection Infection
Aseptic Revisions
100
Survival (%)
Septic Revisions
50 p = 0.341
0 0
150 50 100 Time to revision (mths)
complications in the revision group included wound dehiscence (three knees, 4%), prolonged wound drainage (two knees, 2%) and painful hardware (one knee, 1%). Dehiscence and drainage were managed with open irrigation and debridement. The painful hardware involved screws and cerclage wires used to repair an osteotomy of the tibial tubercle which was used during the original revision TKR. In the primary group there were 11 complications (13%), most being limitation of movement requiring manipulation, comprising 91% of all complications (ten knees). One patient developed a painful and recurrent haematoma requiring irrigation and debridement one month postoperatively. There was no significant difference in complication rates between the two groups (p = 0.83, two-tailed t-test).
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Fig. 1 Kaplan–Meier analysis showing no significant difference (log-rank test, 95% CI 0.135 to 1.988, p = 0.341) in survival after revision total knee replacement (TKR) with aseptic and septic subgroup analysis.
between the revision and primary TKR groups (p = 0.222, two-tailed t-test). Overall, 13 complications (16%) not requiring a change of components occurred in the revision group. Seven knees (9%) had < 90º of flexion, and these patients underwent a manipulation under anaesthesia. This was the most common complication not requiring further surgery in the revision group. Two of these patients required additional open procedures, including synovectomy and retinacular release to address persistent limitation of movement. Other
Discussion Patients between 45 and 55 years of age are the fastestgrowing group undergoing TKR.14,15 They are anticipated to have higher rates of revision than those patients aged > 65 years, either because of higher activity levels or a cumulative risk of failure over lifespan of the prosthesiss.7,16-18 Because of the higher risk for revision surgery, it is important for both surgeons and patients to understand the unique features of this younger population and their impact on the prosthetic joint. By understanding the causes of failure in revision TKR, we can improve our approach to treatment and manage expectations in order to optimise results. There were several limitations to this study. First was the selection bias inherent to retrospective case-control studies. The standard outcome tools for the assessment of patients undergoing revision surgery changed during the 13-year period of the study. Some patient-reported clinical and functional outcome measures were not available for the THE BONE & JOINT JOURNAL
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whole duration of the study, notably for the level of pain reported by patients. The methods of assessing function were applied consistently throughout the study. Ghanem et al19 reported limitations with the validity of data when limited data points are assessed following revision TKR. A second confounding variable was the use of different designs of implant and surgical techniques for both groups during the course of the study. The variability in surgical practice makes it difficult to assess the potential influence of implant design or surgical technique, including fixation strategy, implant constraint and the choice of bearing surfaces, on functional outcome or survival. Furthermore, not being able to verify the alignment of the components radiologically owing to inconsistent archiving of the images hindered our ability to make definitive statements about the causes of failure. A final limitation was the study design. Including both septic and aseptic revisions in the revision TKR cohort potentially acted to confound our results. Subgroup analysis between the two revealed a significant difference in preoperative knee function subscores. Nevertheless, because this difference was eliminated after revision TKR, it suggests that the two groups may reach a similar level in terms of pain, activity and function despite disparate causes for the initial revision. In spite of these limitations, we believe that the reported functional instruments used and the midterm follow-up data provide an understanding of revision TKR which can be broadly applied in these patients. More younger women are seeking TKR than men, with the literature suggesting a > 300% increase in those aged 45 to 55 years between 2000 to 2008.20,21 Our revision group confirmed this trend, with a higher proportion of women (65%) also undergoing TKR. We noted a trend for higher risk of re-revision among men, similar to limited evidence suggesting higher failure rates for revision and primary TKR among men of all ages.5 Our results also demonstrate that, compared with primary TKR, revisions are associated with smaller improvements in function and higher failure rates at mid-term follow-up. These observations are consistent with the limited results available in the literature.2,3,22,23 Previous authors have reported good to excellent functional outcomes in younger patients undergoing primary TKR for either osteoarthritis or rheumatoid arthritis.24-28 Without consideration of age stratification, Baker et al22 reported lower functional activity levels within the first year after surgery for revision TKR compared with primary TKR. Our results in younger patients are consistent with this trend, with similar activity levels between patients undergoing primary and revision procedures but less functional recovery attained, as determined by the Knee Society subscore. To date, there have been few studies that highlight the reasons for failure of revision TKR among patients aged < 55 years. Earlier studies including patients of all ages suggested that the two most common indications for revision are aseptic loosening and infection.6,9,16 In patients aged < 55 years with osteoarthritis, Odland et al29 reported a 16% revision rate for aseptic loosening and osteolysis ten VOL. 96-B, No. 12, DECEMBER 2014
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years post-operatively in a group of 59 patients (67 knees). Aseptic loosening was the leading indication for revision TKR, suggesting that this may be due to increased demands on the prosthesis. The 17% incidence of mid-term re-revision TKR in our patients highlights the challenges in preventing early failures from mechanisms other than wear in younger patients. Our findings suggest a similar time to failure of the revision in younger patients (mean 3.6 years). The higher re-revision rate for infection in the first year after surgery is also consistent with other reports.30 Schwarzkopf et al31 have suggested that more resistant organisms may be found in patients referred to specialised tertiary referral centres, which might be a contributing factor in early failures among those undergoing revision for infection at our institution and at other centres. In our study, 16% of patients in the revision group and 13% of those in the primary group had a complication of surgery that did not require revision. Most complications in both groups were related to a limited range of movement of the knee. Baier et al32 recently reported that approximately one-third of patients (19 out of 78 knees, 28%) undergoing revision TKR have some complication, and 26% (18 knees) had a re-operation within five years of surgery. Although limited movement requiring manipulation was the most common complication in both our revision (9%) and primary groups (12%), young patients undergoing revision were not at a higher risk of this complication than other patients undergoing primary TKR. Maloney33 reported an 11% incidence (24/214 knees) of arthrofibrosis, defined as < 90º flexion, within two months following primary TKR in patients of all ages. Among 33 patients (38 knees) aged < 40 years, Mont et al34 found that 24% (nine knees) required manipulation following primary TKR. Because the decision to proceed with manipulation or other surgery to address limited movement may be influenced by other factors, it is possible that our study under-reports the impact of limited movement in these patients. Revision TKR is a generally effective procedure when performed in patients aged < 55 years. However, we found that as many as one-third of patients may experience either a post-operative complication or early failure of a revision procedure, and these concerns are more likely to have a substantial impact on their future quality of life. As the number of both primary and revision TKRs being performed substantially increases in young patients, additional studies will be needed to assess improvements in activity, function and satisfaction, and to limit the adverse impact of limited movement, instability and infection. Young patients undergoing revision TKR should be counselled that they can expect somewhat less improvement and a higher risk of complication than occur after primary TKR. The authors would like to thank W. J, Maloney, MD and R. S. J. Burnett, MD (FRCSC) for allowing the inclusion of their patients. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. This article was primary edited by G. Scott and first proof edited by J. Scott.
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