Knee arthroscopy is the most common orthopaedic operation worldwide. Current guidelines do not recommend thromboprophylaxis in patients undergoing knee arthroscopy, due to uncertainty about the risk-to-benefit ration in this setting. Although symptomatic or fatal VTE is uncommon in this setting, the ever-increasing volume of surgery has the potential to substantially increase the overall burden of VTE in patients.
The present results demonstrated that the incidence of DVT in patients undergoing knee arthroscopy was 7.7%, which indicated DVT with subsequent PE cannot be discounted as a potentially life-threatening complication associated with this surgery. A number of studies have investigated the risk of DVT after knee arthroscopy(2, 11-13).
Our study showed that for knee arthroscopy, the incidence of DVT in patients without anticoagulation was 7.4%, which is very close to the result of Delis et al.(14). The incidence of non-symptomatic DVT is very high (19/21, 90.5%), which was similar to those of sun et al.(15), so adequate attention should be paid to the latent DVT, and it is not reliable to diagnose the occurrence of DVT solely by clinical symptoms.
In contrast, the incidence of DVT in the anticoagulation group was 7.9%, which indicated that the use of LMWH may not reduce the probability of DVT in patients within three days after knee arthroscopy. In some previous studies, it was shown that thromboprophylaxis was not recommended after arthroscopic surgery. A recent systematic review suggested that they against routine use of thromboprophylaxis even after anterior cruciate ligament reconstruction surgery(16). Among patients undergoing knee arthroscopy, short-term use of LMWH is not recommended to prevent the formation of DVT in patients without risk factors according to our study. Kessler noted that it is suitable to use LMWH for five to seven days after knee arthroscopy(17). Another randomized controlled trial has revealed that prophylaxis should last seven to ten days(18), as other studies have shown poor results for short-term preventive treatment of only three to six days(19, 20). Although LMWH did not increase the risk of perioperative bleeding, it was not a protective factor to prevent the formation of postoperative DVT in three days.
Different types of surgery are associated with varying degrees of DVT risk. In general, the complexity of arthroscopic surgery, especially when combined with arthroscopic assisted ligament reconstruction, has been considered as a risk factor for the development of DVT(15). In addition, the early immobilization of the affected limb after ligament reconstruction may have an effect on the overall probability of DVT. In this study, however, there was no detectable difference in the incidence of DVT between simple knee surgery and ligament reconstruction, which is consistent with the results reported by Maletis et al.(21). Interestingly, the odds ratio (OR) of DVT in patients with ACL reconstruction accompanied by PCL reconstruction (OR=1) was smaller than that in patients with simple ACL reconstruction (OR=1.8) or PCL reconstruction (OR=1.3) in our study. We analyzed the reason is that the patients underwent ACL reconstruction combined with PCL reconstruction may seek more NSAIDs postoperatively. NSAIDs can not only relieve postoperative pain, thus enabling patients to start functional exercise earlier, but also it has been shown to inhibit platelet aggregation, which may be an important reason to explain this result. However, more prospective studies are needed to further clarify the effect of NSAIDs on DVT formation.
Tourniquet times >60 minutes was identified as another procedure-related risk factor for the development of VTE. The stasis induced by tourniquet, combined with the non-occlusive vascular damage that the patients may experience during the operation, could lead to VTE. Although tourniquet duration was longer than 90 minutes in almost all patients (95.2%, 20/21) with DVT, a longer tourniquet duration was not found as an independent factor for DVT in our study. Likewise, Camporese et al.(22) did not found the relationship between VTE and tourniquet time. We suspect that a longer tourniquet time may only be representative of a more complicated case, and the complexity of the operation is the real risk factor for VTE.
The increased density of D-dimers and fibrinogen degradation products, which aggravate hypercoagulation states and enhance secondary fibrinolysis activity. D-dimer generally assumed to tend to decline to a normal level within three to ten days after tissue injury, and has a high sensitivity for predicting the formation of postoperative DVT. Although D-dimer is affected by pregnancy, trauma, tumor, and surgery, our study excluded possible influencing factors except for surgery, we tried our best to minimize its effects. D-dimer is a sensitive but non-specific marker of DVT, so the positive result of D-dimer cannot be used for diagnosis, on the contrary, the possibility of thrombosis can be excluded when D-dimer is negative(23). Our results also demonstrated that for every unit increase in D-dimer, the probability of patients suffering from DVT increased by 3.7 times, so anticoagulation is necessary for patients with high D-dimer after knee arthroscopy. Meanwhile, D-dimer provides a characteristic of quick and convenient. It can also be used as a routine examination to screen the formation of DVT in hospitals without ultrasound or venography, and unnecessary examination can be avoided for some low-risk patients.
Our research still has some limitations. First of all, because the study population was limited to patients who remained in the hospital after the surgery, which probably underestimates the incidence of DVT, since patients who left the hospital likely did not develop DVT but were excluded from the study population. Secondly, although ultrasonography has been used as the main monitoring method for DVT, it has low sensitivity in patients without symptoms of DVT, especially during the early period postoperative, which may also reduce the incidence of DVT in this study. Thus, ultrasonography alone is not sufficient to provide a reliable assessment for assessing the presence of DVT, even though it is considered as having sensitivity and specificity equivalent to venography. Furthermore, this study was a retrospective study with a limited sample size, which cannot fully incorporate the risk factors that may affect the formation of DVT. Therefore, the conclusions of this study need to be further verified by a larger sample size and multi-center randomized controlled study.