The prevalence of venous thromboembolism after hip and knee replacement surgery

Our study was conducted in the orthopaedic unit of the Mater Misericordiae Hospital (“the Mater Hospital”), North Sydney, NSW. This is a 195-bed private hospital affiliated with the University of Sydney.

All hospital patients who had THR, TKR or bilateral TKR during the period 1 April 1995 to 31 December 2001 were included in the study. Twenty-two orthopaedic surgeons were involved with performing these procedures during the study period.

In the majority of cases, the same physician who saw the patient before admission treated the patient for any postoperative medical complications.

All patients were given chemical and physical prophylaxis.

Chemical prophylaxis. Patients were given either low-molecular-weight heparin (LMWH) or warfarin, according to the surgeon’s preference. Administration of LMWH (once-daily subcutaneous enoxaparin 40 mg or dalteparin 5000 IU) or warfarin orally, to achieve an INR of 2.0–3.0 in 48 hours) was begun on the night of the operation and continued throughout the hospital stay of 6–7 days.

No aspirin, anti-inflammatory drugs or preoperative anticoagulants were used.

Physical prophylaxis. Full-leg graduated compression elastic stockings were worn postoperatively. From June 1996 (15 months after the beginning of the study), all patients were given intermittent pneumatic calf compression from the time of admission and wore the apparatus at all times they were in bed until they were fully ambulant 3–4 days after surgery. This technique was not readily available before June 1996.

For all patients at the Mater Hospital who had THR, TKR or bilateral TKR during the study period, bilateral ultrasonography of the veins of both legs, from groin to lower calf, was performed on Day 7 postoperatively, or sooner if clinically indicated. There were no exclusions.

Both legs were examined. Deep veins imaged were the axial veins (common femoral, superficial femoral, popliteal, peroneal and posterior tibial veins) and extra-axial veins (gastrocnemius and soleus veins).

The common femoral veins were interrogated by doppler ultrasound to elicit phasic response (normal variation in waveform with breathing and talking), confirming patency of the common and external iliac vessels.

The patient was required to sit or, preferably, stand. The thigh vessels were examined with the patient supine, and the popliteal fossae and calves with legs dependent.

Early imaging was performed with a Diasonics 2D Gateway device (Aliso Viejo, Calif, USA) and, from February 2000, a GE Logiq 9 device (Milwaukee, Wis, USA) with a 5.0 MHz/60 matched-impedance convex-linear-array probe, using similar but up-dated technology.

All vessels were imaged in B mode (cross-sectional ultrasound), compressed by probe and interrogated by doppler imaging as appropriate.

Six-view planar aerosol ventilation scans and six-view Tc 99m MAA (macroaggregated albumin) perfusion lung scans were performed on patients showing any signs or symptoms of PE.

If calf DVT (in the posterior tibial, peroneal, gastrocnemius or soleus veins) was found at Day 7, the patient was given therapeutic doses of LMWH (subcutaneous enoxaparin 1 mg/kg or dalteparin 100 IU/kg 12-hourly) or warfarin (to maintain an INR of 2.0–3.0), according to the preference of the surgeon, for a further 7 days.

On Day 14, a second bilateral ultrasound scan was performed on patients with previous thrombi who were available for testing at the Mater Hospital. (Patients who lived too far away to return to the hospital had arrangements made with their local doctor to organise a scan elsewhere and provide follow-up.)

If the second scan showed that the calf thrombus was the same size, was smaller, or had disappeared, LMWH or warfarin was stopped and the patient was instructed to take 100 mg of aspirin daily for 1 month, unless there were contraindications. If the thrombus had increased in size, therapeutic doses of LMWH or warfarin were continued for a further week, when the ultrasound scan was repeated on Day 21.

If the third ultrasound scan showed the calf thrombus was shrinking, LMWH or warfarin was stopped and aspirin given, as above. If the thrombus had grown by Day 21, warfarin was begun in patients who had previously been taking LMWH (LMWH was stopped once the INR was between 2.0 and 3.0), and was continued in the 12% of patients already taking warfarin. Warfarin treatment was then continued for 3–6 months, or until the DVT had disappeared.

If proximal DVT (in the popliteal, superficial femoral or common femoral veins) was found on ultrasonography on Day 7, LMWH and warfarin were used as described above for the extending calf DVT. A V/Q scan was also performed on these patients.

Patients with symptoms and signs suggestive of PE (eg, chest discomfort, arrhythmia or hypoxia) had a chest x-ray and V/Q scan as a primary investigation, with computed tomographic pulmonary angiography performed if the diagnosis was uncertain. If PE was diagnosed, warfarin was used in the same way as described for the extending calf DVT or the proximal DVT. Follow-up ultrasonography and V/Q scans were done as necessary.

The total number of patients included in our study was 5999. Of the preoperative medical disorders, cardiac disease was the most common, followed by respiratory disease, then renal disease.

Forty-eight per cent of the patients were men (mean age, 67 years; range, 19–100 years). Among the 19% of men who had DVT, the mean age was 68 years (range, 26–100 years); the mean age of men without DVT was 67 years (range, 19–100 years).

The mean age of female patients was 69 years (range, 17–100 years). Among the 17% of women with DVT, the mean age was 72 years (range, 32–100 years); the mean age of women without DVT was 66 years (range, 17–100 years).

Follow-up ultrasonography at Day 14 postoperatively was performed in the 528 (49%) patients with DVT who were able to return as outpatients for follow-up or (in rare cases) were still inpatients. The behaviour of thrombi was similar for THR, TKR and bilateral TKR patients, with thrombi extending (in spite of appropriate treatment) in 7%–10% of patients, unchanged in 7%–13%, shrinking in 48%–60%, and resolved in 25%–30%.

Twenty (17%) of the 115 patients with symptomatic in-hospital PE had proximal DVT, 63/115 (54%) had calf DVT, and 30/115 (27%) had no DVT on ultrasonography during their in-hospital stay of 7 days. This does not show that calf DVT causes PE, but does show that many symptomatic in-hospital pulmonary emboli are associated with either calf DVT or no DVT at all.

Risk of any DVT after different types of surgery. The risk of DVT was greater after TKR than THR (odds ratio [OR], 3.64; 95% CI, 3.12–4.26; P < 0.001), and much greater after bilateral TKR than THR (OR, 6.17; 95% CI, 4.97–7.66; P < 0.001). The risk was also greater after bilateral TKR than TKR (OR, 1.69; 95% CI, 1.39–2.07; P < 0.001). The cumulative risk of DVT for two TKRs in the one patient, weeks or months apart, was greater than for bilateral TKR.

Risk of thigh DVT after different types of surgery. Thigh DVT was much more likely after THR than either TKR (OR, 4.19; 95% CI, 2.59–6.77; P < 0.001) or bilateral TKR (OR, 6.89; 95% CI, 2.88–16.47; P < 0.001).

The question of whether calf DVT is clinically significant is fundamental to the decision as to whether pre-discharge imaging for DVT should be done. It should only be done if the benefits outweigh the disadvantages. Venography, the method used in previous research studies, is not suitable for routine evaluation, especially in large studies like ours. It is time-consuming, uncomfortable, and can cause thrombosis and allergic reactions.

Ultrasonography is safe, comfortable and accurate, but to justify its routine use one would have to feel that DVT (which, in our case, mostly means calf DVT) is a serious enough disorder to warrant detection and treatment. DVT can cause postphlebitic syndrome, but little is known about the prevalence or severity of this condition after calf DVT. The other complication of DVT is PE, but it is not known whether calf DVT can actually cause PE.

Presumably, if PE occurs without any DVT being found in the leg, the PE has either come from the pelvis, or a thrombus from the leg has completely embolised to the lung. However, if a patient has calf DVT and PE, it is possible there may have been an additional thrombus in the pelvis or thigh that embolised completely, leaving the patient with PE and calf DVT. We believe it is also possible, especially when there is extensive calf DVT, that some of the calf thrombus may become detached and cause PE with residual calf DVT.