Factor V Leiden and the risk of proximal venous thrombosis after total hip arthroplasty

The Journal of Arthroplasty Vol. 13 No. 2 1998

Factor V L e i d e n a n d t h e Risk of P r o x i m a l V e n o u s T h r o m b o s i s After Total Hip Arthroplasty Steven T. Woolson, MD, James L. Zehnder, MD, and William J. Maloney, MD

Abstract: Deep vein thrombosis (DVT) remains a major cause of morbidity in

patients undergoing total hip arthroplasty (THA). Despite postoperative DVT prophylaxis, 20-50% of THA patients still develop DVT. Currently, there is no accurate way of predicting which patients will develop DVT despite standard prophylaxis. The presence of factor V Leiden is the most common cause of inherited DVT risk. It has been postulated that patients who have factor V Leiden and are subjected to thrombogenic stressors such as THA would have an increased risk of thrombosis. The factor V Leiden genotype of 36 patients who developed proximal DVT after surgery and 45 control patients who had THA but did not develop DVT was determined. All patients had had prophylaxis against thrombosis using intermittent pneumatic compression alone or in combination with warfarin or aspirin. Surveillance for proximal DVT was performed on all patients prior to discharge by duplex ultrasound. The 2 groups were similar in age, sex, and type of operation. Three of 36 study patients who had developed DVT (8%) and 2 of 45 control patients who had not developed DVT (4%) were heterozygotes for factor V Leiden; these prevalences were not statistically different. Heterozygosity for factor V Leiden is not associated with DVT prophylaxis failure in patients undergoing THA. Key words: hip arthroplasty, complications, deep vein thrombosis, thrombosis risk factors.

Deep vein thrombosis (DVT) is a c o m m o n complication following a total hip or knee arthroplasty, with an overall prevalence of 2 0 - 5 0 % and a 10-20% prevalence of proximal thrombosis despite p r o p h y laxis with low-molecular-weight heparin, warfarin, or intermittent p n e u m a t i c compression [1]. At present, no screening tests are available to determine w h i c h patients u n d e r g o i n g total hip arthroplasty (THA) have a higher risk of developing thrombosis despite prophylaxis. Recently, a s y n d r o m e associated with resistance to the natural anticoagulant activated protein C has been described [2]. The molecular basis for this

resistance is a m u t a t i o n in the factor V gene called factor V Leiden [3]. Factor V Leiden is the most c o m m o n cause of an inherited risk for v e n o u s t h r o m b o e m b o l i c disease yet identified. It has been postulated that patients w h o have resistance to activated protein C (or w h o test positive for factor V Leiden) and are subjected to other t h r o m b o g e n i c stressors w o u l d have an increased prevalence of thrombosis [4].

Materials and Methods The factor V Leiden status of 81 patients w h o had u n d e r g o n e primary or revision THA was retrospectively determined. All patients had had p r o p h y laxis against DVT using intraoperative and postoperative i n t e r m i t t e n t p n e u m a t i c c o m p r e s s i o n with sequential thigh-high compression sleeves

From the Departments of Pathology and Medicine (Hematology), Stanford University Medical Center, Stanford, California.

Reprint requests: Steven T. Woolson, MD, 1220 University Drive, Menlo Park, CA 94025. Copyright © 1998 Churchill Livingstone. 0883-5403/1302-001355.00/0

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(Kendall, Mansfield, MA) and graduated elastic stockings. Twenty-six of the 81 patients also received adjunctive oral aspirin or low-dose warfarin either because a prospective randomized trial of DVT prophylaxis was being done or because the patients had a prior history of DVT or pulmonary embolism. Both wartarin and oral aspirin were begun on the night prior to surgery and were continued only during hospitalization unless a proximal thrombus was found. The dosage of aspirin was 650 mg twice daily by mouth, and warfarin dosages were titrated to prolong the prothrombin time to 1.3-1.5 times the control value or an international normalized ratio (INR) between 2 and 3 after an initial 10-rag dose given the night prior to surgery. All study patients were treated with heparin followed by 3 months of low-dose warfarin following the diagnosis of proximal thrombosis. All patients had predischarge surveillance for proximal DVT between postoperative days 5 and 7 using compression duplex ultrasound, which was shown to have 89 % sensitivity and 100% specificity in comparison to ascending venography at our institution [5]. Of a total of 49 patients who had had a proximal thrombosis detected after THA by 1 of us (S.T.W.) between 1984 and 1996, 36 (73%) were contacted and agreed to have their factor V Leiden status determined. These 36 patients constituted the study group. Forty-five patients who had undergone THA between 1985 and 1996 and had had negative findings on surveillance ultrasound tests prior to

discharge were randomly chosen to constitute the control group. The demographic and surgical data for these 2 groups, including the age, weight, height, sex, prior history of DVT, preoperative diagnosis, type of surgery (primary, revision), surgical time, type of femoral component fixation (cemented vs cementless), type of anesthesia (regional or general), type of DVT prophylaxis, and preoperative and postoperative hematocrit, were compared (Table 1 ).

Factor V Leiden Assay Genomic DNA was isolated from patient leukocytes (QIAamp Blood Kit, Qiagen, Valencia, CA) collected in ethylenediaminetetra-acetate tubes. A 267-bp fragment of the factor V gene flanking the factor V Leiden mutation site at position 1691 was amplified as described by Bertina et al. [3] with the following modifications: 50 IxL of a mixture containing 10 mmol/L Tris-HC1, pH 8.3, 50 mmol/L KC1, 1.5 mmol/L MgC12, 0.001% gelatin, 1.25 U of Taq DNA polymerase, 150-500 ng genomic DNA, and 12.5 pM concentrations of each primer was heated to 80°C, then 0.8 mmol/L final concentration of each nucleoside triphosphate was added. The mixture was heated to 95°C for 3 minutes and then subjected to 30 cycles of 94°C (1 minute), 55°C (1 minute), and 72°C (1 minute), followed by 72°C for 7 minutes, using a microprocessor-controlled thermal cycler (Perkin-Elmer, Norwalk, CT). The 267-bp am-

Table 2. Demographic Information

No. of patients Average age (y) Average height (cm) Average weight (kg) Sex (M/F) History of prior DVT/PE (yes/no) Type of surgery (primary/revision) Average surgical time (minutes) Femoral component fixation (cemented/cementless) Type of anesthesia (regional/general) Average preoperative Hct ( % ) Average postoperative Hct (%) Type of DVT prophylaxis IPC alone IPC + LDW IPC + ASA Preoperative diagnosis OA Hip fracture ON Misc

Study Group

Control Group

36 69 I71 76 19117 9•27 (25%)

45 66 170 76 19126 4/41 (9%) 34/11 104 17128 34111 37.6 30.9

2818

106 26/10 15/21 37.5 34.0

Significance (P Value)

.2 .7 .8 .4 .07 >.9999 .8 .003 .003 .9 .0006

22 9 5

33 8 4

.5* .5* .5*

32 (78%) 2 0 2

35 (89%) 4 2 4

NS NS NS NS

*Chi-square test. DVT, deep vein thrombosis; PE, pulmonary embolism; Hct, hematocrit; IPC, intermittent pneumatic compression; LDW, low-dose warfarin; ASA, acetylsalicylic acid; OA, osteoarthritis; ON, osteonecrosis; Misc, miscellaneous.

Factor V Leiden and Thrombosis After THA plification product was digested with MnlI for 60 minutes at 37°C, and the resulting fragments were separated by electrophoresis in a 3% agarose gel. Under these conditions, wild-type factor V (1691 G) yields a 167-bp fragment and factor V Leiden (1691A) yields a 200-bp fragment. On this basis, patients can be classified as wild type for factor V (only a 167-bp band is visualized), heterozygous for factor V Leiden (167- and 200-bp fragments are present), or h o m o z y g o u s for factor V Leiden (only a 200-bp band is present).

Statistical Analysis The data were analyzed by the 2-tailed Fischer's exact test or the unpaired t-test to assess statistical significance of patient demographics and factor V Leiden prevalence b e t w e e n DVT and control patients.

Results As s h o w n in Table 1, the statistically signi:~icanr differences b e t w e e n the study and control groups included the use of general anesthesia, the use of a c e m e n t e d femoral c o m p o n e n t , and a higher postoperative hematocrit, all of which had a higher prevalence in the study group. There was a trend toward a higher prevalence of a history of DVT or p u l m o n a r y embolism in study patients (Fisher's exact tests, P = .07, chi-square P = .05). Three of the 36 study patients (8%) and 2 of the 45 control patients (4%) tested positive for factor V Leiden. The prevalence of factor V Leiden in these groups was not significantly different (P = .65 by 2-tailed Fischer's exact test; chi-square P = .47) (Table 2).

Discussion Postoperative DVT remains an important clinical problem for patients undergoing THA despite the u s e of prophylactic regimens. Total hip arthroplasty is a thrombogenic procedure with a DVT prevalence in excess of 50% of patients not given prophylaxis [1[. Effective prophylaxis (warfarin, adjusted-dose unfractionated heparin, low-molecu-

T a b l e 2. P r e v a l e n c e of Factor V L e i d e n Factor V Leiden

Study Group

Control Group

Significance (P Value)

Positive Negative

3 (8%) 33

2 (4%) 43

.65

•

Woolson et al.

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lar-weight heparin, or intermittent pneumatic compression) is associated with a risk reduction of 5 0 - 8 0 % [1]; however, 1 0 - 2 0 % of patients treated with effective prophylaxis by 1 of these methods still develops proximal DVT. Identification of risk factors that would predict the failure of prophylactic measures could allow more aggressive prophylaxis for this select group and is an important consideration in the m a n a g e m e n t of these patients. Deficiencies of natural anticoagulants (antithrombin, protein C, protein S) clearly increase the risk of u n p r o v o k e d venous thrombosis [6]; however, inherited deficiencies of these proteins are rare and therefore unlikely to be a frequent cause of the failure of DVT prophylaxis in patients undergoing joint arthroplasty. Recently, a n o t h e r lesion in the protein C pathway, factor V Leiden, was described. This is a m u t a t i o n in the factor V gene that does not affect factor Va's ability to promote clot formation but does inhibit the ability of activated protein C to inactivate factor Va [7-9]. The p h e n o t y p e of individuals with factor V Leiden is similar to that of individuals with natural anticoagulant deficiencies (eg, r e c u r r e n t venous thrombosis often occurring before age 40). Individuals w h o are h o m o z y g o u s for factor V Leiden have b e e n estimated to have a 50-fold increased risk, whereas heterozygotes have a 10-fold increased risk of venous thrombosis. In contrast to natural anticoagulant deficiencies, which are rare, however, factor V Leiden is a relatively c o m m o n point mutation, present at a prevalence of approximately 3 - 5 % in the U.S. population. Because of the relatively high prevalence of factor V Leiden and its associated higher risk of venous thromboembolic disease, we postulated that factor V Leiden could be a risk factor for hip arthroplasty patients, resulting in a higher prevalence of postoperative DVT than in patients w i t h o u t the mutation, despite the use of standard DVT prophylaxis regimens. Diagnosis of the factor V Leiden defect can be made in 2 ways. A plasma assay is available that measures the resistance of the individual's plasma to a standard a m o u n t of added activated protein C. Alternatively, the factor V genotype m a y be determ i n e d by isolating genomic DNA from patient leukocytes, amplifying the DNA flanking the factor V Leiden m u t a t i o n site, and t h e n determining the genotype by MnlI restriction fragment length. Our laboratory and others have recently compared these 2 methods [10-13]. The plasma assay has the advantage of simplicity, but the first-generation plasma assay has only a 50% sensitivity for factor V Leiden heterozygotes [12,13]. Using the plasma

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assay w o u l d therefore lead to a significant underestimation of factor V Leiden prevalence in our p o p u lation. We therefore chose to use the molecular m e t h o d to definitively identify the factor V genotype in our patient population. Other investigators have recently reported no increase in postoperative DVT in orthopaedic surgery patients w h o had activated protein C resistance by the plasma assay [i4], also supporting the conclusion that factor V Leiden/ activated protein C resistance is not an important cause of failure of standard DVT prophylaxis in joint arthroplasty patients. We f o u n d no difference in the prevalence of the factor V Leiden m u t a t i o n b e t w e e n hip arthroplasty patients w h o had developed postoperative DVT and those w h o had not. The only differences b e t w e e n the study and control groups were in the percentage of c e m e n t e d versus cementless femoral c o m p o n e n t fixation, the postoperative hematocrit, and the type of anesthesia. The last difference reflects findings reported in a prior study of the risk of proximal DVT in patients having THA w h o were treated with intermittent p n e u m a t i c compression alone, w h e r e the prevalence of prior DVT was significantly higher in patients w h o had general anesthesia (l 1%) t h a n in patients w h o had regional (4%) anesthesia (P = .02) [15]. We believe that the other 2 factors were not relevant to the risk of proximal DVT and are therefore inconsequential differences. The underlying causes of failure of prophylaxis in hip arthroplasty patients r e m a i n to be identified. It is possible that the t h r o m b o g e n i c stimulus of this procedure is of sufficient m a g n i t u d e that relatively subtle defects in the anticoagulant m e c h a n i s m are overshadowed. In this regard, it will be of interest to study the prevalence of factor V Leiden and postoperative DVT in general surgery patients, w h e r e the t h r o m b o g e n i c stress is less and defects in the natural anticoagulant system m a y be m o r e evident.

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