Ultrasound spots DVT after knee, hip arthroplasty

May 30, 2004

Surveying post-arthroscopic patients with ultrasound can effectively detect asymptomatic deep venous thrombosis (DVT) and potentially cut down on warfarin treatment, according to researchers from Singapore and Canada.

"It is standard practice at our institution to perform duplex ultrasound of the venous system prior to discharge," wrote Dr. Kuang-Ying Yang and colleagues in a poster presentation at the 2004 American Academy of Orthopedic Surgeons (AAOS) meeting in San Francisco. "However, (ultrasound's) role in routine postoperative surveillance for DVT is not well defined. We report the effectiveness of our screening program in the management of thromboembolism." Yang is from Singapore General Hospital; his co-authors are from the London Health Sciences Centre at the University of Western Ontario.

This retrospective review covered 1,766 total hip (879) or knee (887) arthroplasties performed over a two-year period at the Canadian center. High-resolution color duplex Doppler sonography was performed four to five days after surgery, using an electrical focused linear-array transducer and 5-MHz probes. The standard prophylaxis included in-patient warafin, and aspirin up to six week after discharge.

"The entire deep venous system, from proximal common femoral vein down, and beyond the trifurcation of the popliteal vein in the calf, was evaluated for compressability at 1-cm intervals," the authors explained. The scan was considered positive if the area of interest was not fully compressible.

According to the results, there were 162 abnormal scans in 1,510 patients, who were followed up for three months. There were 76 cases of acute DVT, of which only 20% were symptomatic. After discharge, 11 patients had DVT for an overall DVT rate of 5%. The majority of cases (77%) were proximal. Distal DVT was found with ultrasound in 17% of the cases; 6% were a combination of proximal and distal.

There was one case of fatal pulmonary embolism and three non-fatal cases. The risk factors for DVT in these patients were as follows:

Mean age of 66.5 years

70 years and over had significantly higher risk (p=0.001)

Knee revision surgery

Primary hip surgery

Body mass index (BMI) of 31.8 or higher

The authors cautioned that the high number of proximal DVT cases could be due to ultrasound's lack of sensitivity for detecting distal DVT. However, they stressed that because the clinical diagnosis of DVT is highly unreliable, duplex sonography offers a simple and inexpensive way to follow up on arthroscopy patients.

In addition, the authors concluded that extended use of warafin can be avoided in 95% of patients who exhibit a less than 1% chance of developing late DVT based on ultrasound results.

These results dovetail with previous research that has reported middling to good results with ultrasound post-arthroplasty. A group from Chang Gung Memorial Hospital in Taiwan considered ultrasound to be a "reasonably good alternative to venography in the diagnosis of DVT after total knee arthroplasty." However, in their series of 55 patients, venography did slightly better, finding 32 cases of DVT compared to 23 with sonography (Chang Gung Medical Journal, January 2004, Vol. 27:1, pp. 16-21).

Another group from Pamela Youde Nethersole Eastern Hospital in Hong Kong used Duplex ultrasonography to follow 88 patients after total hip or knee arthroplasty. Based on ultrasound follow-up results, patients with distal thrombus, but no propagation, were considered stable and observed clinically. Eighteen months later, none showed proximal propagation or postthrombotic symptoms (International Orthopedics, February 5, 2003, Vol. 27:3, pp. 168-171).

By Shalmali Pal
AuntMinnie.com staff writer
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