JBJS | Prevention of Deep-Vein Thrombosis after Total Hip Arthroplasty. Comparison of Warfarin and Dalteparin*

The Journal of Bone & Joint Surgery, Volume 79, Issue 9

Articles | September 01, 1997

Prevention of Deep-Vein Thrombosis after Total Hip Arthroplasty. Comparison of Warfarin and Dalteparin*

CHARLES W. FRANCIS, M.D.†, ROCHESTER; VINCENT D. PELLEGRINI, JR., M.D.‡, HERSHEY, PENNSYLVANIA; SAARA TOTTERMAN, M.D.†; ALLEN D. BOYD, JR., M.D.†; VICTOR J. MARDER, M.D.†; KRISTIN M. LIEBERT, M.A.†, ROCHESTER, NEW YORK; BERNARD N. STULBERG, M.D.§, CLEVELAND, OHIO; DAVID C. AYERS, M.D.¶, SYRACUSE, NEW YORK; AARON ROSENBERG, M.D.#, CHICAGO, ILLINOIS; CRAIG KESSLER, M.D.**, WASHINGTON, D.C.; NORMAN A. JOHANSON, M.D.††, PHILADELPHIA, PENNSYLVANIA

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Investigation performed at University of Rochester School of Medicine, Rochester; The Milton S. Hershey Medical Center, Hershey; Cleveland Center for Joint Reconstruction, Cleveland; State University of New York Health Science Center at Syracuse, Syracuse; Rush-Presbyterian-St. Luke's Medical Center, Chicago; George Washington University Medical Center, Washington, D.C.; and Temple University School of Medicine, Philadelphia

The Journal of Bone & Joint Surgery. 1997; 79:1365-72

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Abstract

The effectiveness and safety of warfarin were compared with those of a low-molecular-weight heparin (dalteparin) for the prevention of deep-vein thrombosis after total hip arthroplasty in a prospective, randomized, multi-institutional trial. Patients who were older than eighteen years of age and were scheduled to have an elective primary or revision total hip arthroplasty were eligible; 580 patients were randomized, 550 had the operation and received prophylaxis, and 382 had evaluable venograms. Prophylaxis was provided either with warfarin beginning the night before the operation or with dalteparin beginning two hours before the operation and was continued until venography was performed. Bleeding was assessed on the basis of intraoperative blood loss, transfusion requirements, a decrease in hematocrit, and clinically identified bleeding complications.The prevalence of deep-vein thrombosis was found to be significantly lower in the patients who had received dalteparin than in those who had received warfarin (twenty-eight [15 per cent] of 192 patients compared with forty-nine [26 per cent] of 190 patients; p = 0.006). Deep-vein thrombosis occurred in the calf veins of twenty-one patients (11 per cent) who had received dalteparin and of forty-three patients (23 per cent) who had received warfarin; this difference was significant (p = 0.003). Proximal deep-vein thrombosis occurred in ten patients (5 per cent) who had received dalteparin and in sixteen patients (8 per cent) who had received warfarin; however, with the numbers available, no significant difference could be detected (p = 0.185). We also could not detect a significant difference with regard to the intraoperative and postoperative blood loss, the decrease in hematocrit, and the prevalence of major bleeding complications between the two groups; however, the patients who had received dalteparin had a significantly higher prevalence of bleeding complications involving the operative site (p = 0.03), and a significantly greater percentage required postoperative transfusions (p = 0.001).We concluded that preoperative prophylaxis with dalteparin is significantly more effective than that with warfarin in preventing deep-vein thrombosis after total hip arthroplasty. The greater effectiveness of dalteparin must be considered, however, in light of an increased need for postoperative transfusions and an increase in the prevalence of wound-related bleeding complications.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | References

Deep-vein thrombosis is a frequent complication after total hip arthroplasty; in five randomized, prospective studies that included between seventy-three and 310 patients each, it occurred in 40 to 60 per cent of patients who had not received prophylaxis^{1,23,38,39,41}. The clinical consequences, which are often serious and may be life-threatening, include acute symptoms in the lower extremity that can delay rehabilitation, pulmonary embolism, and later development of post-phlebitic syndrome. The treatment of thromboembolic complications poses the additional problems of a substantial risk of bleeding in the postoperative period, the need for readmission to or a prolonged stay in the hospital, inconvenience to the patient, and added cost. The high risk of thromboembolic disease has led to several recommendations that prophylaxis be provided routinely^3,19,28,42. Several prophylactic regimens after total hip arthroplasty, including the use of warfarin^{6,13,14,18,20,21,24,37}, dextran^12,18,21, unfractionated heparin⁴, antithrombin III¹⁵, low-molecular-weight heparin^{5,7,18,24,26,37,40}, and pneumatic compression^14,17,23, have been evaluated in clinical trials. In North America, prophylaxis with warfarin has been used most frequently³².

Prophylaxis with warfarin has several advantages. It can be administered orally, it has been in clinical use for a long time, and it is associated with an acceptably low risk of bleeding complications. In addition, it can be easily continued after the patient has been discharged from the hospital. This is an important consideration as patients are released earlier after the operation than they were in the past and evidence indicates that the risk of deep-vein thrombosis extends for several weeks postoperatively^2,34.

Low-molecular-weight heparin also effectively reduces thromboembolic complications postoperatively with a low risk of bleeding²². Many studies, including large North American trials^5,26,40, have compared low-molecular-weight heparin and unfractionated heparin for prophylaxis after total hip arthroplasty, and the findings have suggested that low-molecular-weight heparin is more effective than unfractionated heparin without increasing the prevalence of bleeding complications³¹. The use of low-molecular-weight heparin for prophylaxis against deep-vein thrombosis is increasing. Three trials, two in North America^24,37 and one in Europe¹⁸, directly compared low-molecular-weight heparin with warfarin in patients having either a total hip or a total knee arthroplasty. In two of these studies^24,37, there was a significantly lower rate of deep-vein thrombosis (p = 0.03 and p < 0.001) in the patients who had received low-molecular-weight heparin than in those who had received warfarin when all patients were considered together. However, when the patients who had had a total hip arthroplasty were considered separately, a significant difference between the rates associated with the two drugs could not be detected in any of the trials.

To investigate further the relative safety and effectiveness of these two commonly used prophylactic regimens, we conducted a prospective, randomized, multi-institutional trial limited to patients having a total hip arthroplasty. The study used an open-label design, but the primary end point for the determination of effectiveness (deep-vein thrombosis as diagnosed with venography) was evaluated by an independent observer who was blinded with regard to the patients' treatment-group assignments. In contrast to previous studies^24,37, both treatments were started preoperatively to maximize their effectiveness.

*Although none of the authors have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article, benefits have been or will be received but are directed solely to a research fund, foundation, educational institution, or other non-profit organization with which one or more of the authors are associated. Funds were received in total or partial support of the research or clinical study presented in this article. The funding sources were Grant HL-30616 from the National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, and a grant from Pharmacia-Upjohn, Kalamazoo, Michigan.

†Vascular Medicine Unit, P.O. Box 610 (C. W. F., V. J. M., and K. M. L.) and Departments of Radiology, P. O. Box 6944 (S. T.) and Orthopaedics, P. O. Box 665 (A. D. B., Jr.), University of Rochester Medical Center, 601 Elmwood Avenue, Rochester, New York 14642.

‡Department of Orthopaedics and Rehabilitation, The Milton S. Hershey Medical Center, P. O. Box 850, Hershey, Pennsylvania 17033.

§Cleveland Center for Joint Reconstruction, St. Vincent Charity Hospital, 2322 East 22nd Street, Suite 102, Cleveland, Ohio 44115.

¶Department of Orthopedic Surgery, State University of New York Health Science Center at Syracuse, 550 Harrison Center, Suite 100, Syracuse, New York 13202.

#Department of Orthopaedic Surgery, Rush-Presbyterian-St. Luke's Medical Center, 1725 West Harrison Street, Suite 1063, Chicago, Illinois 60612.

**Lombardi Cancer Center, Georgetown University Medical Center, 3800 Reservoir Road, N.W., Washington, D.C. 20007.

††Department of Orthopaedic Surgery, Temple University School of Medicine, 3401 North Broad Street, Philadelphia, Pennsylvania 19140.

‡Department of Orthopaedics and Rehabilitation, The Milton S. Hershey Medical Center, P. O. Box 850, Hershey, Pennsylvania 17033.

§Cleveland Center for Joint Reconstruction, St. Vincent Charity Hospital, 2322 East 22nd Street, Suite 102, Cleveland, Ohio 44115.

¶Department of Orthopedic Surgery, State University of New York Health Science Center at Syracuse, 550 Harrison Center, Suite 100, Syracuse, New York 13202.

#Department of Orthopaedic Surgery, Rush-Presbyterian-St. Luke's Medical Center, 1725 West Harrison Street, Suite 1063, Chicago, Illinois 60612.

**Lombardi Cancer Center, Georgetown University Medical Center, 3800 Reservoir Road, N.W., Washington, D.C. 20007.

††Department of Orthopaedic Surgery, Temple University School of Medicine, 3401 North Broad Street, Philadelphia, Pennsylvania 19140.

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TABLE I CLINICAL CHARACTERISTICS OF THE PATIENTS

*The values are given as the mean and the standard deviation.†P = 0.04.‡P = 0.03.

	Intent-to-Treat Population		Patients Who Had at Least One Evaluable Venogram
	Dalteparin	Warfarin	Dalteparin	Warfarin
No. of patients	271	279	192	190
Age* (yrs.)	63 ± 13	63 ± 14	63 ± 14	64 ± 13
Gender (male/female) (no. of patients)	127/144	132/147	92/100	95/95
Race (per cent white)	88	94†	88	95‡
Weight* (kg)	80 ± 19	80 ± 18	80 ± 18	80 ± 18
Type of operation (no. of patients)
Primary/revision	207/64	194/85	151/41	142/48
With cement/without cement	80/191	83/196	52/140	50/140
Duration of operation* (mins.)	161 ± 72	163 ± 62	162 ± 74	160 ± 59
Duration of anesthesia* (mins.)	221 ± 75	225 ± 67	225 ± 77	226 ± 67
General anesthesia/regional anesthesia	183/88	177/102	122/70	113/77
(no. of patients)
Previous thromboembolism	26	25	18	21
(no. of patients)

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TABLE I CLINICAL CHARACTERISTICS OF THE PATIENTS

*The values are given as the mean and the standard deviation.†P = 0.04.‡P = 0.03.

	Intent-to-Treat Population		Patients Who Had at Least One Evaluable Venogram
	Dalteparin	Warfarin	Dalteparin	Warfarin
No. of patients	271	279	192	190
Age* (yrs.)	63 ± 13	63 ± 14	63 ± 14	64 ± 13
Gender (male/female) (no. of patients)	127/144	132/147	92/100	95/95
Race (per cent white)	88	94†	88	95‡
Weight* (kg)	80 ± 19	80 ± 18	80 ± 18	80 ± 18
Type of operation (no. of patients)
Primary/revision	207/64	194/85	151/41	142/48
With cement/without cement	80/191	83/196	52/140	50/140
Duration of operation* (mins.)	161 ± 72	163 ± 62	162 ± 74	160 ± 59
Duration of anesthesia* (mins.)	221 ± 75	225 ± 67	225 ± 77	226 ± 67
General anesthesia/regional anesthesia	183/88	177/102	122/70	113/77
(no. of patients)
Previous thromboembolism	26	25	18	21
(no. of patients)

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TABLE II INTRAOPERATIVE BLOOD LOSS AND REQUIREMENTS FOR TRANSFUSION*

*NS = not significant.†The values are given as the mean and the standard deviation.

	Dalteparin	Warfarin
No. of patients	271	279
Blood loss† (ml)
Day of op.	1381 ± 908	1376 ± 850	NS
Postop. days 1 through 8 (total)	219 ± 183	225 ± 161	NS
Whole-blood transfusions
Day of op.
No. of patients	103	92	NS
Volume† (ml)	772 ± 528	729 ± 485	NS
Postop. days 1 through 8 (total)
No. of patients	54	38	p = 0.039
Volume† (ml)	643 ± 276	614 ± 245	NS
Packed red blood-cell transfusions
Day of op.
No. of patients	84	90	NS
Volume† (ml)	513 ± 280	450 ± 277	NS
Postop. days 1 through 8 (total)
No. of patients	130	86	p < 0.001
Volume† (ml)	605 ± 445	537 ± 446	NS
Maximum decrease in hematocrit† (per cent)	8 ± 5	7 ± 5	NS

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TABLE II INTRAOPERATIVE BLOOD LOSS AND REQUIREMENTS FOR TRANSFUSION*

*NS = not significant.†The values are given as the mean and the standard deviation.

	Dalteparin	Warfarin
No. of patients	271	279
Blood loss† (ml)
Day of op.	1381 ± 908	1376 ± 850	NS
Postop. days 1 through 8 (total)	219 ± 183	225 ± 161	NS
Whole-blood transfusions
Day of op.
No. of patients	103	92	NS
Volume† (ml)	772 ± 528	729 ± 485	NS
Postop. days 1 through 8 (total)
No. of patients	54	38	p = 0.039
Volume† (ml)	643 ± 276	614 ± 245	NS
Packed red blood-cell transfusions
Day of op.
No. of patients	84	90	NS
Volume† (ml)	513 ± 280	450 ± 277	NS
Postop. days 1 through 8 (total)
No. of patients	130	86	p < 0.001
Volume† (ml)	605 ± 445	537 ± 446	NS
Maximum decrease in hematocrit† (per cent)	8 ± 5	7 ± 5	NS

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TABLE III CLINICALLY IDENTIFIED BLEEDING COMPLICATIONS*

*NS = not significant and NA = not applicable. The values are given as the number of patients.†One patient who received dalteparin needed a reoperation, and two needed a tranfusion. Two patients who received warfarin needed a transfusion, and one had a prolonged hospitalization.‡Two patients who received dalteparin needed a transfusion.§One patient who received dalteparin and one who received warfarin needed a transfusion.

	Dalteparin	Warfarin
No. of patients	271	279
Operative site†	12 (4%)	3 (1%)	p = 0.03
Excessive intraoperative bleeding	3	0
Excessive drainage	2	1
Wound hematoma	7	2
Hematuria‡	10 (4%)	8 (3%)	NS
Gastrointestinal-tract bleeding§	7 (3%)	3 (1%)	NS
Hematemesis	2	1
Occult blood in stool	3	2
Occult blood in gastric aspirate	2	0
Ecchymosis at site of injection	2	NA

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TABLE III CLINICALLY IDENTIFIED BLEEDING COMPLICATIONS*

	Dalteparin	Warfarin
No. of patients	271	279
Operative site†	12 (4%)	3 (1%)	p = 0.03
Excessive intraoperative bleeding	3	0
Excessive drainage	2	1
Wound hematoma	7	2
Hematuria‡	10 (4%)	8 (3%)	NS
Gastrointestinal-tract bleeding§	7 (3%)	3 (1%)	NS
Hematemesis	2	1
Occult blood in stool	3	2
Occult blood in gastric aspirate	2	0
Ecchymosis at site of injection	2	NA

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FIG1:: Fig. 1 Graph showing the international normalized ratios (INR) for the patients who received warfarin. Open circles indicate values for the patients who had positive venograms, and closed circles indicate values for those who had negative venograms. Day 0 represents the day of the operation. The differences in the ratios between the patients who had positive and negative venograms were not found to be significant, with the numbers available, on any day. Day 0: p = 0.612; Day 1: p = 0.666; Day 2, p = 0.616; Day 3, p = 0.919; Day 4, p = 0.845; Day 5, p = 0.963; Day 6, p = 0.241; and Day 7, p = 0.335.

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

Patients who were eighteen years of age or older and were scheduled to have a unilateral primary or revision total hip arthroplasty were eligible for the study. The criteria for exclusion included a serum creatinine level of at least 1.7 milligrams per deciliter (150 micromoles per liter); defective hemostasis; documented gastrointestinal or other bleeding within three months before the operation; a cerebral hemorrhage within three months before the operation; an operative procedure involving the eye, ear, or central nervous system within one month before the operation; a known hypersensitivity to heparin; severe hypertension; and a weight of less than forty-one kilograms. Women who were pregnant or breast-feeding also were excluded, as were those who had reproductive potential unless they had had a negative pregnancy test. A patient could be included for only one operative procedure. The trial was approved by the Institutional Review Boards of all participating hospitals, and all patients gave informed consent before enrollment, which occurred between May 1992 and March 1995.

Treatment Regimens

The patients were randomly assigned to receive prophylaxis with either warfarin or low-molecular-weight heparin. The patients assigned to prophylaxis with low-molecular-weight heparin received dalteparin sodium (Fragmin), with the first dose of 2500 international units given subcutaneously within two hours before the operation. A second dose of 2500 international units was given subcutaneously on the evening of the day of the operation, at least six hours after the preoperative dose. The second dose on the day of the operation was omitted if the operation was performed at 4:00 P.M. or later. On the first and subsequent postoperative days until venography was performed, 5000 international units of dalteparin was administered daily as a single dose.

The patients assigned to prophylaxis with warfarin received warfarin sodium (Coumadin), with the first dose administered orally on the evening before the operation. Patients weighing fifty-seven kilograms or less received five milligrams, and those weighing more than fifty-seven kilograms received 7.5 milligrams. The second dose of warfarin was given on the evening of the day of the operation and was administered in the same dose on the basis of body weight. Subsequently, daily doses of warfarin were adjusted to maintain a prothrombin-time index of 1.4 to 1.5, corresponding to an international normalized ratio of approximately 2.5. Aspirin and drugs known to interact with warfarin were avoided if possible, and no other investigational drugs were used concomitantly.

Assessment of Efficacy

Bilateral ascending venography was performed with use of the technique described by Rabinov and Paulin³⁶ at a mean (and standard deviation) of 7 ± 2 days postoperatively, or earlier if there were clinical signs of deep-vein thrombosis. Venographically diagnosed deep-vein thrombosis was the primary end point for determination of efficacy in the study. The criterion for the diagnosis of deep-vein thrombosis was a constant intraluminal filling defect seen in more than one projection. A venogram was considered evaluable if the major deep veins of the lower extremity, including two of the three pairs of calf veins, the popliteal vein, and the superficial femoral vein, could be visualized on two projections. A positive venogram always was considered adequate. The thrombus was classified as distal if it involved the calf veins only and as proximal if it involved the popliteal or a more proximal vein. Patients who had both a proximal and a distal thrombus were classified as having proximal thrombosis. All venograms were evaluated by a radiologist who had no knowledge of the treatment-group assignment. Thrombi involving muscular or superficial veins were recorded but were not considered deep-vein thrombi.

Pulmonary embolism was diagnosed with perfusion-and-ventilation scintigraphy or pulmonary angiography, or both. These studies were done to confirm a diagnosis of embolism in a patient who had clinical findings; they were not performed in patients who did not have signs or symptoms. A positive pulmonary angiogram was a secondary end point for the trial, as was a high-probability lung scan in a patient for whom there was a high clinical suspicion of pulmonary embolism³³. All lung scans and pulmonary angiograms were reviewed by an independent third-party evaluator who did not have knowledge of the treatment-group assignment.

Assessment of Safety

Objective measures of bleeding included intraoperative blood loss as estimated by the anesthesiologist, postoperative blood loss as measured from drains, blood-transfusion requirements, and changes in hemoglobin and hematocrit. Decisions regarding transfusion were based on standard clinical practice and were made by the attending surgeon. Clinically identified bleeding complications were considered major if they were fatal or if they required a transfusion, a reoperation, or a prolonged hospital stay. Wound-related complications and minor bleeding also were recorded.

Statistical Analysis

The sample size of 580 patients (290 in each treatment group) was based on a desire to detect a between-treatment difference in the prevalence of deep-vein thrombosis, assuming a frequency of 25 per cent in association with warfarin and 15 per cent in association with dalteparin. A total of 250 patients were required for each treatment group for a two-tailed comparison of proportions, conducted at a 0.05 level of significance with a power of 0.80. The sample size was set at 580 to accommodate an expected 15 per cent loss of patients due to withdrawal from the study or inadequate venograms. All patients were included in the intent-to-treat population except for those who had never received the medication and those who had received it but had not had the scheduled operation. The per-protocol population was defined as patients in the intent-to-treat population who had at least one evaluable venogram. Comparisons of end points within populations were done with the Cochran-Mantel-Haenszel test, the Wilcoxon rank-sum test, or the Fisher exact test.

Results

Introduction | Materials and Methods | Results | Discussion | References

Of the 580 patients, 288 were randomized to treatment with dalteparin and 292 were randomized to treatment with warfarin. Thirty patients (seventeen who were randomized to treatment with dalteparin and thirteen who were randomized to treatment with warfarin) were excluded from the intent-to-treat population because they had never received the drug (twenty-seven patients) or they had received the drug but the operation had been canceled (three patients). All patients in the intent-to-treat population were included in the per-protocol analysis if they had at least one evaluable venogram. An additional seventy-nine patients who had received dalteparin and eighty-nine who had received warfarin were excluded from the per-protocol analysis because a venogram had not been made (123 patients), the venogram had been misplaced or was missing (fifteen patients), or it had been made but was not evaluable (thirty patients).

The patients were well matched with regard to clinical characteristics (Table I). Both intent-to-treat groups included somewhat more women than men, and there was a significantly greater proportion of white patients among those who were assigned to treatment with warfarin (p = 0.04 in the intent-to-treat population and p = 0.03 in the patients who had evaluable venograms). In the population that had evaluable venograms, forty-one (21 per cent) of the 192 patients who had received dalteparin had a revision operation compared with forty-eight (25 per cent) of the 190 who had received warfarin; however, this small difference is unlikely to have affected the results.

Deep-vein thrombosis developed in twenty-eight (15 per cent) of the 192 patients who had received dalteparin compared with forty-nine (26 per cent) of the 190 who had received warfarin; this difference was significant (p = 0.006). Deep-vein thrombosis was identified in the calf veins of twenty-one (11 per cent) of the 192 patients who had received dalteparin compared with forty-three (23 per cent) of the 190 who had received warfarin; this difference also was significant (p = 0.003). The prevalence of proximal deep-vein thrombosis was lower in the patients who had received dalteparin than in those who had received warfarin (ten [5 per cent] of 192 compared with sixteen [8 per cent] of 190); however, with the numbers available, a significant difference could not be detected (p = 0.185).

A total of twenty-three patients who had received dalteparin and thirteen who had received warfarin had clinical symptoms that were suggestive of deep-vein thrombosis. Venography was performed in twenty-six of these patients and confirmed the diagnosis in only four, indicating a poor correlation between clinical findings of deep-vein thrombosis and a positive venogram.

In the patients who had received warfarin, the international normalized ratio was not increased on the day of the operation, but it increased rapidly thereafter, reaching a maximum on the second postoperative day (Fig. 1). We detected no significant difference, with the numbers available, in the mean international normalized ratio on any postoperative day between the patients who had a positive venogram and those who had a negative venogram.

Bleeding was evaluated in the intent-to-treat groups (patients who had received at least one dose of the drug and had had the operation). This analysis included 271 patients who had received dalteparin and 279 who had received warfarin. We did not detect a significant difference in the measured blood loss between the two groups, either on the day of the operation or in the postoperative period (Table II). We also did not detect a significant difference with regard to the number of patients who required a transfusion or the mean volume of the transfusion on the day of the operation, although both values were somewhat greater for the patients who had received dalteparin. However, fifty-four (20 per cent) of the 271 patients who had received dalteparin required whole-blood transfusion on the first through the eighth postoperative day compared with thirty-eight (14 per cent) of the 279 who had received warfarin; this difference was significant (p = 0.039). There also was a significant difference between the two groups with regard to the number of patients who required transfusion of packed red blood cells on the first through the eighth postoperative day (130 [48 per cent] of the patients who had received dalteparin compared with eighty-six [31 per cent] of those who had received warfarin; p < 0.001).

Major bleeding complications occurred in six patients (2 per cent) who had received dalteparin and in four (1 per cent) who had received warfarin. Of the six patients who had received dalteparin, two had a wound hematoma requiring transfusion, one had a wound hematoma necessitating readmission to the hospital for a reoperation nine days after the prophylaxis with dalteparin had been discontinued, two had hematuria requiring transfusion, and one had gastrointestinal bleeding requiring transfusion. Of the four patients who had received warfarin, two had a wound hematoma requiring transfusion, one had prolonged and excessive drainage from the wound that increased the duration of hospitalization, and one had hematemesis requiring transfusion. There was bleeding at the operative site in twelve (4 per cent) of the patients who had received dalteparin compared with only three (1 per cent) of those who had received warfarin; this difference was significant (p = 0.03) (Table III). Other bleeding complications, including minor bleeding in the gastrointestinal or urinary tract and hematoma at the site of an injection, occurred in sixteen (6 per cent) of the patients who had received dalteparin compared with ten (4 per cent) of those who had received warfarin; however, with the numbers available, we could not detect a significant difference (p = 0.28).

Discussion

Introduction | Materials and Methods | Results | Discussion | References

The results of this prospective, randomized trial demonstrate that dalteparin was more effective than warfarin in preventing over-all deep-vein thrombosis following total hip arthroplasty. Bleeding as determined by measured blood loss or a postoperative decrease in hematocrit was similar in the two groups, but a significantly greater proportion of patients who received dalteparin required transfusion (p = 0.001) and there also was a significantly greater prevalence of bleeding complications related to the operative wound in that group (p = 0.03).

The rates of deep-vein thrombosis were consistent with those reported in previous comparable studies in which warfarin and low-molecular-weight heparin were used. Meta-analyses of between twenty-three and fifty-six published studies performed between 1966 and 1993 revealed rates of identifiable deep-vein thrombosis ranging from 12 to 17 per cent following total hip arthroplasty with use of low-molecular-weight heparin for prophylaxis^25,30,31. In recent large North American randomized trials that included 100 to 1173 patients who had received low-molecular-weight heparin twice daily, the reported rates of deep-vein thrombosis ranged from 21 to 50 per cent^{5,26,37,40,41}. With use of one daily dose of low-molecular-weight heparin after total hip arthroplasty, the rates were 14 to 21 per cent in trials including 195 to 330 patients^18,24,37. Meta-analyses of 139 patients³⁰ and 864 patients²⁵ who had received warfarin revealed rates of 19 and 24 per cent, whereas in recent large single studies comprising 232 to 665 patients the rates ranged from 14 to 23 per cent^14,18,24,37.

In three previous studies^18,24,37, the efficacy and safety of a low-molecular-weight heparin were compared directly with the efficacy and safety of warfarin, but each study had important differences in design compared with the current study. Hull et al.²⁴ reported the results in patients who had had either a total hip or a total knee replacement and had been randomized to treatment either with warfarin beginning on the evening of the day of the operation or with a low-molecular-weight heparin starting eighteen to twenty-four hours postoperatively. In the second study³⁷, the patients were randomized into three treatment groups: fifty anti-factor-X_a units of ardeparin per kilogram of body weight beginning on the evening of the day of the operation and then administered twice daily, fifty anti-factor-X_a units of ardeparin per kilogram of body weight beginning on the evening of the day of the operation and followed by ninety anti-factor-X_a units per kilogram of body weight daily, and five milligrams of warfarin beginning on either the night before or the morning of the operation. In a European study, prophylaxis with nadroparin or coumarin was initiated the day before the operation¹⁸. None of these trials showed a significant difference in the development of deep-vein thrombosis in the patients who had received warfarin compared with those who had received low-molecular-weight heparin; however, two of them^24,37 revealed lower rates of deep-vein thrombosis in the patients managed with low-molecular-weight heparin after a knee replacement and in the combined group of patients who had had knee and hip replacements. Hull et al.²⁴ reported a 23 per cent rate of deep-vein thrombosis (seventy-nine of 340 procedures) and a 3.8 per cent rate of proximal deep-vein thrombosis (thirteen of 340 procedures) in patients managed with warfarin compared with a 21 per cent rate (sixty-nine of 332 procedures) and a 4.8 per cent rate (sixteen of 332 procedures) in patients managed with low-molecular-weight heparin. The RD Heparin Arthroplasty Group³⁷ reported a 14 per cent rate of deep-vein thrombosis or pulmonary embolism (twenty-four of 174 procedures) in the patients who had received warfarin compared with an 8 per cent rate (fourteen of 178 procedures) in the patients who had received low-molecular-weight heparin twice daily and a 14 per cent rate (twenty-four of 171 procedures) in those who had received low-molecular-weight heparin once daily; however, with the numbers available, they detected no significant differences. Our results show a clear difference between the results of the two prophylactic regimens: 15 per cent of the patients who had received dalteparin and 26 per cent of those who had received warfarin had deep-vein thrombosis (p = 0.006). This difference may be due to our use of dalteparin for preoperative prophylaxis and to the larger size of our sample compared with that in the studies of patients managed with ardeparin³⁷ or nadroparin¹⁸.

We found evidence of increased bleeding in the patients who had received dalteparin; a greater proportion of those patients required transfusions, and there was a greater frequency of bleeding at the operative site. More bleeding in association with low-molecular-weight heparin than with warfarin also was reported by Hull et al.²⁴; the rate of major bleeding complications was 1.2 per cent (nine of 721 patients) in the group that had received warfarin compared with 2.8 per cent (twenty of 715 patients) in the group that had been managed with low-molecular-weight heparin (p = 0.04). There also was a higher rate of uncomplicated wound hematomas in the group managed with low-molecular-weight heparin compared with the group managed with warfarin (6.7 per cent [forty-eight of 715 patients] compared with 3.6 per cent [twenty-six of 721 patients]; p = 0.01)²⁴. In the study in which ardeparin was compared with warfarin³⁷, no significant difference could be detected, with the numbers available, between the rates of clinically identified bleeding complications. However, the patients managed with ardeparin had greater blood loss as reflected in the so-called blood-loss index, which combined measures of the difference between the preoperative and postoperative levels of hemoglobin and the requirements for transfusion.

A potential explanation for the higher rate of thrombosis and the lower rate of bleeding complications associated with warfarin in the current study is that our patients were relatively undertreated. The target intensity of anticoagulation with warfarin was an international normalized ratio of 2.5, but the data show that the mean daily international normalized ratio from the first through the seventh postoperative day was less than 2.2 (Fig. 1), somewhat lower than planned. This probably reflects a cautious approach to the regulation of anticoagulants and the preference for undertreatment to avoid bleeding complications in the early postoperative period. Additional analysis of the data, however, showed no evidence that the patients who had deep-vein thrombosis had lower international normalized ratios than those who did not have it, so it is not clear that the lower intensity of anticoagulation contributed to the higher rate of thrombosis.

An important difference between the current study and the North American trials reported previously^24,37 is the use of preoperative prophylaxis. Both warfarin and low-molecular-weight heparin were started postoperatively in the study reported by Hull et al.²⁴, and the RD Heparin Arthroplasty Group³⁷ used low-molecular-weight heparin postoperatively and warfarin preoperatively. The initiation of therapy postoperatively may decrease the rate of bleeding complications, but in the two previous studies^24,37 in which that approach was used the rate was greater with low-molecular-weight heparin than it was with warfarin. The preoperative initiation of low-molecular-weight heparin in the current study may have increased its effectiveness relative to warfarin and thereby may have contributed to the significant difference in the rate of deep-vein thrombosis between the two groups. The preoperative initiation of prophylaxis also may be important because deep-vein thrombosis associated with orthopaedic procedures often occurs on the day of the operation²⁹, and a delay in the initiation of prophylaxis for as long as twenty-four hours postoperatively leaves the patient unprotected during a period of high risk. Preoperative prophylaxis with low-molecular-weight heparin has been evaluated in many studies previously, and the rates of bleeding complications have been found to be either equal to or lower than the rates in the comparison groups managed with warfarin¹⁸, unfractionated heparin^8,11,27,34, dextran^7,9,10, or a combination of heparin and dihydroergotamine¹⁶. However, there have not, to our knowledge, been any studies directly comparing the preoperative with the postoperative use of low-molecular-weight heparin, so the relative safety and effectiveness can only be inferred.

In summary, dalteparin was more effective than warfarin in preventing deep-vein thrombosis following total hip arthroplasty in a trial in which both drugs were begun preoperatively. However, the patients who received dalteparin had a greater need for transfusions in the postoperative period and had significantly more wound-related bleeding complications. The greater efficacy of dalteparin in preventing deep-vein thrombosis must be considered in light of this increase in bleeding complications.

References

Introduction | Materials and Methods | Results | Discussion | References

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Leyvraz, P. F.; Bachmann, F.; Hoek, J.; Buller, H. R.; Postel, M.; Samama, M.; and Vandenbroek, M. D.: Prevention of deep vein thrombosis after hip replacement: randomised comparison between unfractionated heparin and low molecular weight heparin. British Med. J.,303: 543-548, 1991.303543 1991

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TABLE I CLINICAL CHARACTERISTICS OF THE PATIENTS

*The values are given as the mean and the standard deviation.†P = 0.04.‡P = 0.03.

	Intent-to-Treat Population		Patients Who Had at Least One Evaluable Venogram
	Dalteparin	Warfarin	Dalteparin	Warfarin
No. of patients	271	279	192	190
Age* (yrs.)	63 ± 13	63 ± 14	63 ± 14	64 ± 13
Gender (male/female) (no. of patients)	127/144	132/147	92/100	95/95
Race (per cent white)	88	94†	88	95‡
Weight* (kg)	80 ± 19	80 ± 18	80 ± 18	80 ± 18
Type of operation (no. of patients)
Primary/revision	207/64	194/85	151/41	142/48
With cement/without cement	80/191	83/196	52/140	50/140
Duration of operation* (mins.)	161 ± 72	163 ± 62	162 ± 74	160 ± 59
Duration of anesthesia* (mins.)	221 ± 75	225 ± 67	225 ± 77	226 ± 67
General anesthesia/regional anesthesia	183/88	177/102	122/70	113/77
(no. of patients)
Previous thromboembolism	26	25	18	21
(no. of patients)

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TABLE I CLINICAL CHARACTERISTICS OF THE PATIENTS

*The values are given as the mean and the standard deviation.†P = 0.04.‡P = 0.03.

	Intent-to-Treat Population		Patients Who Had at Least One Evaluable Venogram
	Dalteparin	Warfarin	Dalteparin	Warfarin
No. of patients	271	279	192	190
Age* (yrs.)	63 ± 13	63 ± 14	63 ± 14	64 ± 13
Gender (male/female) (no. of patients)	127/144	132/147	92/100	95/95
Race (per cent white)	88	94†	88	95‡
Weight* (kg)	80 ± 19	80 ± 18	80 ± 18	80 ± 18
Type of operation (no. of patients)
Primary/revision	207/64	194/85	151/41	142/48
With cement/without cement	80/191	83/196	52/140	50/140
Duration of operation* (mins.)	161 ± 72	163 ± 62	162 ± 74	160 ± 59
Duration of anesthesia* (mins.)	221 ± 75	225 ± 67	225 ± 77	226 ± 67
General anesthesia/regional anesthesia	183/88	177/102	122/70	113/77
(no. of patients)
Previous thromboembolism	26	25	18	21
(no. of patients)

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TABLE II INTRAOPERATIVE BLOOD LOSS AND REQUIREMENTS FOR TRANSFUSION*

*NS = not significant.†The values are given as the mean and the standard deviation.

	Dalteparin	Warfarin
No. of patients	271	279
Blood loss† (ml)
Day of op.	1381 ± 908	1376 ± 850	NS
Postop. days 1 through 8 (total)	219 ± 183	225 ± 161	NS
Whole-blood transfusions
Day of op.
No. of patients	103	92	NS
Volume† (ml)	772 ± 528	729 ± 485	NS
Postop. days 1 through 8 (total)
No. of patients	54	38	p = 0.039
Volume† (ml)	643 ± 276	614 ± 245	NS
Packed red blood-cell transfusions
Day of op.
No. of patients	84	90	NS
Volume† (ml)	513 ± 280	450 ± 277	NS
Postop. days 1 through 8 (total)
No. of patients	130	86	p < 0.001
Volume† (ml)	605 ± 445	537 ± 446	NS
Maximum decrease in hematocrit† (per cent)	8 ± 5	7 ± 5	NS

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TABLE II INTRAOPERATIVE BLOOD LOSS AND REQUIREMENTS FOR TRANSFUSION*

*NS = not significant.†The values are given as the mean and the standard deviation.

	Dalteparin	Warfarin
No. of patients	271	279
Blood loss† (ml)
Day of op.	1381 ± 908	1376 ± 850	NS
Postop. days 1 through 8 (total)	219 ± 183	225 ± 161	NS
Whole-blood transfusions
Day of op.
No. of patients	103	92	NS
Volume† (ml)	772 ± 528	729 ± 485	NS
Postop. days 1 through 8 (total)
No. of patients	54	38	p = 0.039
Volume† (ml)	643 ± 276	614 ± 245	NS
Packed red blood-cell transfusions
Day of op.
No. of patients	84	90	NS
Volume† (ml)	513 ± 280	450 ± 277	NS
Postop. days 1 through 8 (total)
No. of patients	130	86	p < 0.001
Volume† (ml)	605 ± 445	537 ± 446	NS
Maximum decrease in hematocrit† (per cent)	8 ± 5	7 ± 5	NS

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TABLE III CLINICALLY IDENTIFIED BLEEDING COMPLICATIONS*

	Dalteparin	Warfarin
No. of patients	271	279
Operative site†	12 (4%)	3 (1%)	p = 0.03
Excessive intraoperative bleeding	3	0
Excessive drainage	2	1
Wound hematoma	7	2
Hematuria‡	10 (4%)	8 (3%)	NS
Gastrointestinal-tract bleeding§	7 (3%)	3 (1%)	NS
Hematemesis	2	1
Occult blood in stool	3	2
Occult blood in gastric aspirate	2	0
Ecchymosis at site of injection	2	NA

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TABLE III CLINICALLY IDENTIFIED BLEEDING COMPLICATIONS*

	Dalteparin	Warfarin
No. of patients	271	279
Operative site†	12 (4%)	3 (1%)	p = 0.03
Excessive intraoperative bleeding	3	0
Excessive drainage	2	1
Wound hematoma	7	2
Hematuria‡	10 (4%)	8 (3%)	NS
Gastrointestinal-tract bleeding§	7 (3%)	3 (1%)	NS
Hematemesis	2	1
Occult blood in stool	3	2
Occult blood in gastric aspirate	2	0
Ecchymosis at site of injection	2	NA