To summarize the current knowledge on vascular complications and deep venous thrombosis (DVT) prophylaxis after anterior cruciate ligament (ACL) reconstruction.

A systematic review was conducted according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses statement. MEDLINE, EMBASE, Cochrane, Web of Science, CINAHL, PubMed publisher, and Google scholar medical literature databases were searched up to November 10, 2015. Any arthroscopic surgical method of primary or revision intra-articular ACL reconstruction of all graft types in humans was included. A risk of bias assessment was determined.

Fourty-seven studies were included in the review. Pseudaneurysms were the most frequently reported arterial complication after ACL reconstruction, irrespective of graft type or method of graft fixation with an incidence of 0.3%. The time to diagnosis of arterial complications after ACL reconstruction varied from days to mostly weeks but even years. After ACL reconstruction without thromboprophylaxis, the incidence of DVT was 9.7%, of which 2.1% was symptomatic. The incidence of pulmonary embolism was 0.1%. Tourniquet time > 2 h was related to venous thromboembolism. Thromboprophylaxis is indicated in patients with risk factors for venous thromboembolism.

After ACL reconstruction, the incidence of arterial complications, symptomatic DVT and pulmonary embolism was 0.3%, 2.1% and 0.1% respectively. Arterial complications may occur with all types of arthroscopic ACL reconstruction, methods of graft fixation as well as any type of graft. Patients considered to be at moderate or high risk of venous thromboembolism should routinely receive thromboprophylaxis after ACL reconstruction.

Vascular complications after anterior cruciate ligament (ACL) reconstructions cause serious morbidity and potential mortality[1]. They can be categorized in arterial and venous thromboembolic complications. The incidence of arterial complications after ACL reconstruction is unknown[1]. Case reports have been published using various techniques of ACL reconstruction[1].

Venous thromboembolism (VTE) after ACL reconstruction may present clinically as symptomatic or asymptomatic deep venous thrombosis (DVT), pulmonary embolism (PE) and postthrombotic syndrome[1-3]. The incidence of VTE after ACL reconstruction varies from 0.2%-14%[1,2,4-11]. The variable incidence of VTE after ACL reconstruction depends on the diagnostic methods of DVT (clinical parameters, venography, ultrasound or magnetic resonance venography), the heterogeneity of patient demographics (age, risk factors, surgical time, concomitant surgery, tourniquet time and postoperative mobilisation) and DVT prophylaxis[1,12]. Deep venous thrombosis may cause pulmonary embolism which may be fatal in its immediate course or may result in pulmonary hypertension in the long term[1,13]. The postthrombotic syndrome may cause serious morbidity and affects 23% of limbs 2 years after DVT, 35%-69% and 49%-100% at 3 and at 5-10 years respectively[1,4,14]. ACL reconstruction ranks number 6 of most performed orthopedic operations[15]. However uniform evidence-based clinical practice guidelines for DVT prophylaxis after ACL reconstruction are lacking[1,2,16].

A thorough understanding of the incidence, risk factors and potential methods for prevention of vascular complications after ACL reconstruction is critical to optimize patient safety[17]. This systematic review presents the current knowledge of arterial complications, VTE and thromboprophylaxis after arthroscopic ACL reconstruction. The review will highlight the incidence, types and risk factors of arterial complications and VTE after ACL reconstruction as well as the current recommendations for DVT prophylaxis.

The reporting in this systematic review was conducted according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement[18].

The most important finding of the present study is that after ACL reconstruction, the incidence of arterial complications, symptomatic DVT and PE was 0.3%, 2.1% and 0.1% respectively. The incidence of 0.3% of arterial complications may be overestimated considering the fact that only case reports have been published in the literature. However, the pooled incidence of DVT after ACL reconstruction without thromboprophylaxis was 9.7%, of which 2.1% of patients was symptomatic.

Pseudaneurysms were the most frequently reported arterial complication after ACL reconstruction, irrespective of graft type or method of graft fixation. Pseudoaneurysms differ from true aneuryms in that they do not contain all the layers of an artery. They resemble organized hematomas that have internal arterial flow[1]. A direct arterial trauma by a drill bit, shaver, hardware or fixation device for ACL reconstruction may cause a pseudoaneurysm. This condition usually presents with repeated hemarthrosis and a pulsatile mass within days to weeks after ACL reconstruction. Their growth may lead to neuropraxia and DVT due to compression of nerves and nearby veins, respectively[1]. Patients with poor collateral development may have severe ischemia and poor prognosis, even leading to amputation[1,35,38].

Krupp et al[60] analysed the safety of femoral cross-pin in ACL reconstruction. They concluded that insertion angle, not tunnel drilling method, influenced saphenous nerve and femoral artery/vein injury at risk[60]. Post et al[61] studied the relative position of the neurovascular structures at risk when drilling bicortical screws for tibial fixation in ACL reconstruction[45]. Arthroscopic tibial tunnels were made in cadaver human knees using lateral X-rays for accurate positioning. A 4.5 mm bicortical drill hole was placed perpendicular to the tibial surface 1 cm distal to the tibial tunnel. The distances from the posterior tibial drill exit point to the nearby neurovascular structures were measured with a caliper. The closest structure to the exit point was the bifurcation of the popliteal artery/vein (11.4 ± 0.6 mm). The next closest was the anterior tibial vein (11.7 ± 1.6 mm). The closest any individual hole came to a neurovascular structure was 3.5 mm from the anterior tibial vein. They concluded that bicortical screw and spiked washer fixation of soft tissue ACL grafts appears to be relatively safe[45,61]. Curran et al[58] performed an in vitro study comparing 2 techniques for ACL tibial fixation with a bicortical screw. They concluded that aiming the screw towards the fibula reduced the risk of vascular injury compared to screws drilled perpendicular to the cortex. Other possible recommendations to prevent neurovascular damage are the use of a drill bit stop for bicortical screws or a single cortex fixation on the tibia without compromising stability of fixation[1]. The incidence of arterial complications in the present review (0.3%)[45] was updated in a consecutive series of 1961 ACL reconstructions with hamstring autografts and bicortical tibia fixation by the same authors[1]. The incidence was reduced from 0.3% to 0.15% after the safety measures were applied as suggested by Janssen et al[1] and Curran et al[58].

A high level of suspicion, with clinical symptoms of painful pulsating mass and sensory deficits in lower leg and foot, is mandatory in detecting these potentially devastating lesions. The differential diagnosis should include compartment syndrome and DVT[47]. Doppler examination and intact dorsal pedal and posterior tibial pulses are unreliable in diagnosing arterial lesions after ACL reconstruction[47]. Contrast-, CT- or MRI- angiographies are the diagnostic tools of choice[45,46]. Surgical exploration and vascular repair (or ligation/embolization of the feeding vessel) remain standard management[45,46]. An immediate surgical exploration is imperative in limiting neurological damage[1,45,46].

A meta-analysis of DVT after knee arthroscopy without thromboprophylaxis found an overall DVT rate of 9.9% (3.1%-17.9%) when routine screening using ultrasound or contrast venography was used[13]. Proximal DVT rate was 2.1% (0%-4.9%)[13,62]. Proximal DVT may progress to PE, however the clinical significance of distal DVT remains questionable[62-64]. Sun et al[29] found that the total incidence of VTE, diagnosed with venography on the third day after arthroscopic knee surgery, was 14.9%, of which only 3.7% were symptomatic. Delis et al[14] found 50% of the DVT patients to be completely asymptomatic. They also examined the history of DVT if treated (aspirin in calf DVT, heparin-warfarin in proximal DVT)[13]. Following early diagnosis, total clot lysis was documented in 50% and partial clot lysis in the remaining 50%, within 118 d median follow-up. Segmental venous reflux developed in at least 75% of the legs sustaining thrombosis. A previous thrombosis or the presence of two or more risk factors for thromboembolism significantly increased the incidence of DVT. No symptoms or signs of PE were documented[13,14].

The current review showed that after ACL reconstruction without thromboprophylaxis, the incidence of DVT was 9.7%, of which 2.1% was symptomatic. The incidence of PE was 0.1%. These findings are similar to the conclusions by Erickson et al[3]. They described an 8.4% rate of DVT after ACL reconstructions in patients without postoperative thromboprophylaxis (73% was asymptomatic), while the rate of symptomatic PE was 0.2%[3]. Maletis et al[11] described symptomatic DVT in 0.2% of 16192 primary and revision ACL surgeries. However, the authors did not specify the use of thromboprophylaxis[11]. Cullison et al[10] and Adala et al[6] found comparable rates of DVT of 1.5% and 1.8% respectively using prospective pre- and postoperative ultrasonography in patients without VTE risk factors. The authors recommended that thromboprophylaxis is not necessary in the absence of risk factors in patients younger than 45 years of age with early postoperative mobilization[6]. In a study of 282 Chinese patients, the incidence of DVT was 12.1% after ACL reconstruction. Tourniquet time > 2 h and concomitant PCL reconstructions were risk factors for DVT[8]. Ye et al[4] found that the incidence of DVT was 14%, diagnosed by unilateral venography on the third day after ACL reconstruction. Proximal DVT occurred in 16.7% of DVT patients. None of the DVT patients developed PE. The authors recommended thromboprophylaxis in female patients and patients older than 35 years[4]. The described variable incidence of VTE after ACL reconstruction depends on the diagnostic methods of DVT (clinical parameters, venography, ultrasound or magnetic resonance venography) and the heterogeneity of patient demographics (age, risk factors, surgical time, concomitant surgery, tourniquet time and postoperative immobilization).

The use of a tourniquet improves operative visualisation during arthroscopic ACL reconstruction[65,66]. Various authors reported that tourniquet time in excess of 90 min increased the rates of VTE[8,17,30,67]. Smith et al[65] published a meta-analysis of tourniquet assisted arthroscopic knee surgery. There was no difference in complication rate if tourniquet time exceeded 60 min. Hirota et al[22,25] quantified pulmonary emboli after tourniquet release in patients during ACL reconstruction (extramedullary) vs total knee arthroplasty (intramedullary procedure)[13]. They chose these two groups for having more than 60 min tourniquet time and detected pulmonary emboli in all patients after release of the tourniquet using transesophageal echocardiography with a peak at 30-40 s postrelease[13]. The amount of emboli was defined as percentage of total emboli formed in relation to the right atrial area. This percentage returned to baseline levels 2 min after tourniquet release in the ACL group. They found a significant linear correlation between the amount of emboli and duration of tourniquet inflation in the ACL group. In comparison, the total knee arthroplasty group had a significant larger amount of emboli (4-5 fold) with no return to baseline levels during the assessment period. No patient in either group showed signs of PE[13,22,25]. In a recent systematic review, Papalia et al[66]. concluded that a tourniquet can be used safely, provided that the inflation pressure is not excessive and tourniquet time is less than 2 h.

Asymptomatic pulmonary emboli occur in all patients with ACL reconstructions after tourniquet release[1,13]. Furthermore, PE may occur as a result of proximal DVT[13,24,50,52]. Hetsroni et al[30] analysed 418323 arthroscopic knee procedures and found an incidence of 0.03% for symptomatic PE. Risk factors were female sex, age, history of cancer and prolonged operating time (> 90 min). In spite of improved prevention and treatment of PE, the mortality is still estimated to be 20%-30%[68]. It is the third most common cardiovascular cause of death, with 2/3 of the death occurring within the first few hours as a result of severe hemodynamic and respiratory disturbances[53,68,69]. Janssen et al[1,13] found an incidence of fatal PE of 0.05% in a consecutive series of 1961 arthroscopic ACL reconstructions[1]. Risk factors were preexistent coagulopathy, oral contraceptive medication and delay in DVT diagnosis.

Thromboprophylaxis after ACL reconstruction remains controversial[1,9,16,27,50,52,59,70,71]. Geerts et al[59] reviewed the evidence-based literature for thromboprophylaxis in knee arthroscopy and only recommend prophylaxis with Low Molecular Weight Heparin in patients with risk factors for VTE (Grade 2B level of evidence). Risk factors in their study were history of DVT, age ≥ 40 years, surgical time > 60 min. and a complicated/prolonged procedure[59]. Additional risk factors for VTE after ACL reconstruction in other studies on VTE were smoking, oral contraceptive use or hormone replacement, BMI > 30 kg/m², chronic venous insufficiency, cancer and thrombophilic conditions[1,12,14,30,52,59,64,72]. In a randomized controlled trial, Marlovits et al[20] concluded that extended duration of thromboprophylaxis with enoxaparin by an additional 20 d significantly reduced venographically detected DVT after ACL reconstruction without an increase in major bleeding compared to enoxaparin limited to in-hospital thromboprophylaxis for 3-8 d. The authors found a 41.2% incidence of DVT for discharged patients who had a placebo as postdischarge thromboprophylaxis in contrast to 2.8% in the thromboprophylaxis group. Risk factors for DVT were age over 30 years, prolonged immobilization and surgical time[20]. It should be noted that their mean surgical time as a teaching hospital (> 2 h) as well as their hospital stay of 3-8 d do not reflect most current ACL surgery practices with early discharge and mobilization. A Cochrane systematic review on interventions for preventing VTE in adults undergoing knee arthroscopy reported that no strong evidence was found to conclude that thromboprophylaxis is effective to prevent VTE in people with unknown risk factors for thrombosis[20,68,70]. This is confirmed by other recent studies on DVT prophylaxis after ACL reconstruction and knee arthroscopic procedures[2,17,64]. It is now common practice in a surgical setting to use a risk-assessment model, such as the one developed by Capriani et al[20]. Patients considered to be at moderate or high risk of VTE should routinely receive thromboprophylaxis[1]. However, recommendations for the best type and duration of prophylaxis after ACL reconstruction still need to be defined[5]. In spite of the scientific effort to date, no recommendations for routine thromboprophylaxis in ACL reconstruction can be provided in the absence of risk factors for VTE[1,13]. Further investigation is required to analyse actual incidence and severity of venous thromboembolism as well as the efficacy-to-bleeding tradeoff for routine thromboprophylaxis after ACL reconstruction in patients without risk factors for VTE[1,13].

This systematic review has several limitations. In the search for the available knowledge on vascular complications, studies of various level of evidence were included. Another weakness of this review is the inclusion of studies with small population size. Both the quality and limited amount of studies for specific research questions may limit the level of evidence for this review. Although strict and adapted for various study types, the risk of bias assessment of the Cochrane Library and the classifications of “low”, “questionable” and “high” risk of bias for the studies may limit the strength of evidence. One might argue that a “low” risk of bias RCT study is of higher level of evidence than a “low” risk of bias prospective cohort study. Another weakness of this study is that only articles in English were included. Additional relevant articles published in languages other than English could contribute to the level of evidence presented in this review.

The clinical relevance of this review is that patients undergoing ACL reconstruction may be informed that vascular complications can occur with any type of reconstruction and that thromboprophylaxis should be prescribed in patients with risk factors for VTE.

After ACL reconstruction, the incidence of arterial complications, symptomatic DVT and PE was 0.3%, 2.1% and 0.1% respectively. Arterial complications may occur with all types of arthroscopic ACL reconstruction, methods of graft fixation as well as any type of graft. Patients considered to be at moderate or high risk of VTE should routinely receive thromboprophylaxis after ACL reconstruction.