KNEE
Are current thrombo-embolic prophylaxis guidelines applicable to unicompartmental knee replacement? C. A. Willis-Owen, K. M. Sarraf, A. E. Martin, D. K. Martin From Sportsmed SA, Stepney, Australia
C. A. Willis-Owen, MA, MFSEM, FRCS (Tr & Orth), Consultant Orthopaedic Surgeon Queen Mary’s Hospital, Department of Orthopaedic Surgery, Frognal Avenue, Sidcup, Kent DA14 6LT, UK. K. M. Sarraf, BSc(Hons), MBBS, MRCS, Specialist Registrar in Trauma and Orthopaedic Surgery Chelsea and Westminster Hospital, 369 Fulham Road, London SW10 9NH, UK. A. E. Martin, Research Assistant D. K. Martin, MS(Orth), FRACS, FAOrthA, Consultant Orthopaedic Surgeon Sportsmed SA, 32 Payneham Road, Stepney, South Australia 5069, Australia. Correspondence should be sent to Mr C. A. Willis-Owen; e-mail:
[email protected] ©2011 British Editorial Society of Bone and Joint Surgery doi:10.1302/0301-620X.93B12. 27650 $2.00 J Bone Joint Surg Br 2011;93-B:1617–20. Received 31 May 2011; Accepted after revision 16 August 2011
Symptomatic and asymptomatic deep-vein thrombosis (DVT) is a common complication of knee replacement, with an incidence of up to 85% in the absence of prophylaxis. National guidelines for thromboprophylaxis in knee replacement are derived from total knee replacement (TKR) data. No guidelines exist specific to unicompartmental knee replacement (UKR). We investigated whether the type of knee arthroplasty (TKR or UKR) was related to the incidence of DVT and discuss the applicability of existing national guidelines for prophylaxis following UKR. Data were collected prospectively on 3449 knee replacements, including procedure type, tourniquet time, surgeon, patient age, use of drains and gender. These variables were related to the incidence of symptomatic DVT. The overall DVT rate was 1.6%. The only variable that had an association with DVT was operation type, with TKR having a higher incidence than UKR (2.2% versus 0.3%, p < 0.001). These data show that the incidence of DVT after UKR is both clinically and statistically significantly lower than that after TKR. TKR and UKR patients have different risk profiles for symptomatic DVT. The risk-benefit ratio for TKR that has been used to produce national guidelines may not be applicable to UKR. Further research is required to establish the most appropriate form of prophylaxis for UKR.
Unicompartmental knee replacement (UKR) has been considered to be applicable for up to 48% of patients presenting with osteoarthritis of the knee.1 UKR remains controversial among knee surgeons. Although more cost effective and associated with lower rates of infection and better outcome scores, UKR has a significantly higher revision rate.1-6 Little data exists on the incidence of thromboembolic complications following UKR. Symptomatic and asymptomatic deep-vein thrombosis (DVT) is one of the most common complications of lower limb arthroplasty, with an incidence of between 41% and 85% in the absence of prophylaxis.7,8 Symptomatic DVT can cause considerable morbidity and can lead to pulmonary embolism (PE), which may be fatal. There is no agreement as to what degree of prophylaxis is appropriate.9 Many countries have developed guidelines for DVT prophylaxis for lower limb arthroplasty and these have proved controversial.10-21 Data from TKR are extrapolated to apply to ‘knee arthroplasty’ without offering guidance specific to UKR. Where no specific guidance exists, these national guidelines are often applied to UKR patients.
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The purpose of this study was to investigate whether the type of knee arthroplasty (TKR versus UKR) is related to the incidence of DVT. Multivariate analysis was used on a prospectively gathered dataset to investigate the factors related to DVT in a large cohort of patients undergoing primary knee replacement with modern prophylactic measures.
Patients and Methods At our specialist private orthopaedic hospital, data regarding every surgical procedure carried out were prospectively collected and stored in a database. The variables of patient age and gender, procedure type (TKR versus medial UKR), tourniquet time, use of drains and surgeon (eight consultant surgeons contributed data, including DKM) were recorded. Post-operative complications were recorded for every patient using a mandatory standardised form. Operating surgeons were audited on their collection of complication data and faced various penalties for any incomplete records. Patients undergoing knee replacement did so under general, regional or combined anaesthesia as clinically indicated. A tourniquet was used in all patients. TKR was carried out using 1617
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a medial parapatellar or subvastus approach with LCS (DePuy Orthopaedics Inc., Johnson & Johnson, Raynham, Massachusetts), PFC (DePuy Orthopaedics), Scorpio (Stryker Orthopaedics, Mahwah, New Jersey), or Triathlon (Stryker Orthopaedics) implants. UKR was performed using a mini medial parapatellar approach using Preservation (DePuy Orthopaedics) or Oxford (Biomet Ltd, Bridgend, United Kingdom) implants. Patients were assessed pre-operatively for risk factors for thromboembolic events and were considered to be at high risk if they had any of the following: a history of DVT or PE; obesity (body mass index > 30); varicose veins; hormone replacement therapy; the oral contraceptive pill; prothrombotic states (protein S or C deficiency; antithrombin III deficiency; activated protein C resistance; lupus anticoagulant, antiphospholipid antibody, or factor V Leiden mutation); nephrotic syndrome; polycythaemia; paraproteinaemia; or malignancy. Those who were not at risk were given enoxaparin (low-molecular-weight heparin) 20 mg once daily subcutaneously starting approximately 12 hours post-operatively until discharge from hospital, then aspirin 300 mg orally daily until six weeks after surgery. Patients at risk were given enoxaparin 20 mg twice daily subcutaneously until discharge from hospital, then aspirin 300 mg orally daily until six weeks after surgery. Both groups were mobilised on the first post-operative day, instructed to wear above-knee thromboembolic deterrent stockings for six weeks, and advised to perform foot and ankle exercises while in bed. This regime was devised in collaboration with physicians and haematologists, and in the light of available literature and general consensus in Australia at the start of the study period.22-26 It does not reflect current national guidelines. During their inpatient stay all patients were assessed daily by nursing and medical staff for the signs and symptoms of DVT. Any patient with a suspicion of DVT underwent duplex ultrasound scanning by a specialist radiologist. Before discharge, patients were counselled by an orthopaedic nurse on the signs and symptoms of DVT and encouraged to contact the hospital to arrange a duplex ultrasound scan if they had any concerns. Three aspects of duplex ultrasonography were used to identify a DVT: obstruction of flow, loss of compressibility, and visible thrombus within the lumen of the vein.27 Patients who did not attend their follow-up appointments were contacted by telephone to ascertain the reason, and if they were receiving treatment elsewhere, details of that treatment were sought. Thus, we believe we have a relatively accurate and complete prospectively collected record of patients with symptomatic DVT. This dataset provides no information on asymptomatic DVT. Statistical analysis. Data regarding all primary knee replacements carried out between 2002 and 2008 were gathered and analysed using the statistical software package ‘R’ version 2.9.1 (The R Project for Statistical Computing, Murray Hill, New Jersey). Binomial generalised linear
Table I. Patient demographics for each group (TKR, total knee replacement; UKR, unicompartmental knee replacement) with significance testing using two-tailed Fisher’s exact tests and unpaired t-tests. TKR (n = 2369) Gender (male:female) 1099:1270 Mean age (yrs) 64.5 (29.6 to 92.8) (range) Mean tourniquet time 76.1 (40.0 to 185.0) (mins) (range) Use of drains 2302:67 (with:without)
UKR (n = 1080)
p-value
511:569 0.63 61.5 (29.1 to 93.6) < 0.0001 75.0 (40.0 to 170.0) 0.16 1051:29
0.91
models were fitted to the data, incorporating a range of putative predictor variables and a binary outcome measure (proven post-operative DVT present or absent). Putative predictors included age, gender, surgeon identity and surgical procedure (TKR or UKR). All patients with a confirmed DVT were identified, and this provided the basis for a binary outcome measure. Those with incomplete data were removed prior to model fitting. This led to the removal of only three patients. Testing was carried out using generalised linear modelling fitting a binomial model (logit). A pvalue < 0.05 was considered statistically significant.
Results Data were available for 3449 patients, 2369 TKRs and 1080 UKRs. Demographic details are shown in Table I. The UKR group had a mean age of three years less than the TKR group, and this was statistically significant (p < 0.001). There were no statistically significant differences between the groups with regard to tourniquet time, surgeon identity, gender or use of a drain. There was a suspected DVT in 511 patients (14.8%), all of whom had a duplex scan. Clinical suspicion of DVT was approximately 3.3 times more common after TKR (448 out of 2369 cases, 18.9%) than after UKR (63 out of 1080 cases, 5.8%). There were 54 confirmed DVTs in total, giving an overall rate of 1.6%, with 51 in the TKR group (2.2%) and three in the UKR group (0.3%). Generalised linear modelling was used to assess the incidence of DVT against the recorded variables. The only putative variable to attain significance was the operation type, with an incidence of 0.3% in the UKR group versus 2.2% in the TKR group (p < 0.001) (Table II). Longer tourniquet times were not associated with a significantly higher incidence of DVT (p = 0.63). Discussion There have been many studies in the literature comparing the clinical outcomes of TKR with UKR, but few have compared the incidence of DVT between the two groups. A systematic study of UKR for the treatment of unicompartmental osteoarthritis reported that although there was no overall difference in the rate of complications between TKR and UKR, DVTs appeared to be reported THE JOURNAL OF BONE AND JOINT SURGERY
ARE CURRENT THROMBO-EMBOLIC PROPHYLAXIS GUIDELINES APPLICABLE TO UNICOMPARTMENTAL KNEE REPLACEMENT?
Table II. Significance testing using generalised linear modelling Variable
Deep-vein thrombosis
Non-deep-vein thrombosis
Mean tourniquet time 78.4 (45 to 129) 75.6 (40 to 185) (mins) (range) Mean age (yrs) (range) 62.9 (38 to 82) 63.5 (29 to 93) 17.0:1 2.2:1 Operation group (TKR:UKR)* Gender (male:female) 1.2:1 0.9:1 Incidence of DVT for each surgeon
p-value 0.63 0.30 0.0003 0.33 0.57
* TKR, total knee replacement; UKR, unicompartmental knee replacement
more often following TKR than after UKR.28 Other studies comparing TKR and UKR revealed similar results, with no statistically significant difference in the incidence of DVT.29,30 Our data demonstrate that the incidence of DVT after UKR is clinically and statistically significantly lower than after TKR. Furthermore, this effect is not accounted for by the duration of surgery as measured by the tourniquet time. There is a much controversy about the effect and duration of tourniquet use on the development of symptomatic or asymptomatic DVT in knee replacement.31-34 Our findings are at odds with a number of small studies that have showed an effect of duration of surgery33 and the use of tourniquet31-33 on the incidence of DVT, but are in agreement with the results of a prospective multicentre doubleblind study in UKR patients.34 Our study has a number of limitations. It is not possible to be certain that all episodes of DVT were detected by our data collection procedure; however, the purpose of this work was to study symptomatic DVT. The incidence of symptomatic DVT is similar to that reported in the literature for specialist elective units,7-20,28-34 suggesting that we have not missed a significant number of DVTs. The type of anaesthesia provided to our patients varied but records of which techniques (regional versus general) used were not available. This is a potentially confounding factor, as regional anaesthesia is associated with a lower incidence of DVT.35-38 However, we have no reason to believe that the anaesthetic technique differed between groups. We have not recorded the incidence of DVT without prophylaxis and draw no conclusions regarding this. Similarly, we have not recorded the incidence of asymptomatic DVT; however, the clinical significance of these events is still debated.18,20,22,39 We scanned fewer patients in the UKR group than in the TKR group. It may be argued that this contributed to the lower incidence of confirmed DVT in the UKR group, but the same strict clinical criteria for suspicion of DVT were used in both groups. In addition, UKR patients tended to have a shorter length of stay (by approximately two days) than TKR patients. Thus the window of opportunity for VOL. 93-B, No. 12, DECEMBER 2011
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detecting DVT during the hospital stay in this group was smaller. This may have contributed to our lower scanning rate; however, all patients were warned of the symptoms of DVT and encouraged to contact us if there was concern after discharge, and a significant number of patients presenting in this manner were included in the data. The mean age of the UKR group was three years less than that of the TKR group. There are conflicting data with regard to the relationship between age and the incidence of DVT. Some studies have shown that increasing age is a contributing factor for the development of symptomatic DVT,40-42 but several other studies in arthroplasty patients have not recorded this association.43-46 A three-year mean age difference in unlikely to have accounted for a significant proportion of the observed difference in our study. We did not store detailed data on the potential confounding factors or comorbidities, such as pre-existing venous disease, previous history of DVT, genetic thrombophilic states, previous fracture or malignancy. These factors are thought to be associated with an increased risk of DVT in patients undergoing joint replacement. A study by Kim and Kim47 indicated that factors such as advanced age, hypertension, tourniquet time, severity and duration of the operation, among others, have little relevance to the incidence of DVT after TKR. However, it identified that factors such as obesity, prolonged post-operative immobilisation, previous venous disease and hyperlipidaemia had a direct effect on increasing the incidence of DVT. It is possible that our TKR group contained more high-risk patients than the UKR group, so this, rather than the nature of the procedure, may account for some of the increased rate of DVT. Thus we cannot ascribe the incidence of DVT to the surgical procedure alone. However, we have demonstrated that typical patients undergoing TKR have a statistically significantly higher incidence of DVT than typical patients undergoing UKR. Studies involving rare events such as symptomatic DVT despite prophylaxis require large numbers of subjects to detect small effects. Many of the limitations of our study could be addressed by a carefully designed prospective study or by the collection of data regarding such complications linked with the national joint registry. Our data show that TKR and UKR patients have different risk profiles for symptomatic DVT although the same prophylactic regimen is used for both groups. In light of these results the risk-benefit ratio for TKR that has been used to produce national guidelines for thromboembolism prophylaxis may not be applicable to UKR. Further research is required to establish the most appropriate form of prophylaxis for this specific group of 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.
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