Haemodynamic assessment in simulated operative positions before knee arthroplasty can be useful in deep vein thrombosis prediction

Abstract

Purpose

During knee arthroplasty, the leg is placed in several forced positions, which are mainly uncomfortable for all tissue structures in the region, including the vascular structures. Veins have a weaker quality of the wall structure than arteries, so during the forced position morphological and haemodynamic consequences are expected mainly in the venous system. Conditions of safe aseptic environment for the arthroplasty are in collision with routine intra-operative analysis of local haemodynamics in real time. This is the reason why we have no insight into the haemodynamic and morphological changes at the time in which the initiation of deep vein thrombosis (DVT) occurs. For this reason we created the hypothesis that the monitoring of the occurrence and detection of potential DVT risks can be achieved pre-operatively using echosonograms in simulated operative positions, and then compare them with the cases of postoperative DVT.

Methods

This research was conducted as a prospective, analytical, minimally manipulative and observational clinical study in the period January 2011 to October 2013. In the preoperative period we made ultrasound and colour-Doppler examinations of deep veins in simulated operative position (full extension 0°, semiflexion 30–60°, flexion 90° and maximal flexion 90°+). The target vein was the posterior tibial vein in the distal third of calf. During the operation we took a note of anaesthesia duration and forced positions duration. After the operation we were looking for ultrasound signs of DVT in a follow-up period of six weeks. The sample was made from 91 patients selected for knee arthroplasty: 56 women and 35 men patients of average age 67.46 years. The oldest patient was 81, and the youngest 48. Average body mass index was 26.98 (±2.20) kg/m². After initial ultrasound, the sample was divided into two groups according to vein flow velocity. Patients who had a flow velocity lower than 10 cm/s in any of the forced positions were in the investigated group (N-b, n = 38), and patients who had more favourable haemodynamics in forced positions were in the control group (N-a, n = 53). Patients underwent arthroplasty without tourniquet, and the operative, postoperative and anaesthesiological protocol was the same for all the patients.

Results

Friedman’s test results point out significant differences of posterior tibial vein flow velocity in four simulated positions (0°, 30–60°, 90°, 90°+). Overview of the median value of the posterior tibial vein flow velocity points out reduction of the posterior tibial vein flow velocity in the third and fourth simulated positions. Average range values were lowest in simulated position 90°+. Relative risk for the DVT occurrence was 21.6 % higher in the group of patients with flow velocity lower than 10 cm/s with statistical significance. The incidence of DVT was higher in women (22.85 %) than in men (14.28 %). There was one (1.09 %) case of pulmonary embolism (PE) presented as segmental PE.

Conclusions

We believe that preoperative ultrasound analysis performed during the simulation of operative positions is a useful pre-operative test that can identify patients at risk of developing postoperative DVT. We would recommend that during surgery procedure to minimise forced position of knee flexion.