Introduction

Thromboembolic disorders encompass a range of conditions characterized by the formation of blood clots that can occlude vascular pathways, leading to significant clinical consequences. Deep vein thrombosis (DVT) represents a crucial component of this spectrum, where clots primarily develop in the deep veins of the lower extremities1. DVT can manifest as symptomatic, presenting with signs such as swelling, pain, and erythema, or as asymptomatic, where patients remain unaware of the clot’s presence2. Distal DVT, occurring in the veins below the knee, often carries a lower risk of pulmonary embolism (PE) compared to proximal DVT. However, distal DVT can propagate to the proximal thigh veins, potentially leading to PE3. The broader classification, venous thromboembolism (VTE), includes both DVT and pulmonary embolism (PE), the latter being a potentially fatal complication resulting from dislodged clots. The variation within these disorders is essential for proper diagnosis, management, and implementing preventative strategies to mitigate the risk of adverse outcomes.

Anticoagulants, including low molecular weight heparin (LMWH), rivaroxaban, warfarin, apixaban, dabigatran, and unfractionated heparin, utilize distinct mechanisms to prevent thrombosis4. LMWH enhances the activity of antithrombin III, inhibiting thrombin and factor Xa, thereby disrupting the coagulation cascade5. Rivaroxaban and apixaban act as direct factor Xa inhibitors, preventing the conversion of prothrombin to thrombin and subsequently inhibiting thrombus formation6. Dabigatran, a direct thrombin inhibitor, binds to thrombin, blocking fibrin clot formation7. Warfarin inhibits vitamin K epoxide reductase, thereby reducing the synthesis of vitamin K-dependent clotting factors (II, VII, IX, and X)8. Unfractionated heparin exerts its anticoagulant effect by potentiating antithrombin III, leading to the inactivation of multiple coagulation factors, including thrombin and factor Xa9. Each of these agents plays a critical role in regulating hemostasis and preventing thromboembolic complications.

Deep vein thrombosis (DVT) is a well-documented complication following orthopedic surgeries, particularly those involving the lower extremities. The DVT in patients with knee injury varies across the studies. One study found that the incidence of DVT in patients after lower extremity injury or surgery was 0.8%10. Another study reported an overall prevalence of DVT in patients with knee surgeries to be 31.6–37.6% despite anticoagulant therapy11. In severely injured patients, the incidence of DVT remained high despite aggressive thromboprophylaxis, with a rate of 9.4%12. In electrically injured patients, the incidence of DVT was 6.5% but increased to 62% in patients with a Caprini score > 813. While DVT has been extensively studied in the context of total knee arthroplasty and other common knee surgeries14,15,16,17,18,19there is limited research on its occurrence following posterior cruciate ligament (PCL) avulsion fracture surgery—a rare but clinically significant injury.

The PCL (posterior cruciate ligament) is the most robust ligament within the knee. PCL avulsion fractures present a distinct type of PCL injury, which is less frequent than the more typical intra-substance PCL tear20. It commonly occurs in adults due to high-energy mechanisms, such as a direct impact on the tibia when the knee is flexed (e.g., motor vehicle collision) or significant hyperextension (trauma related to sports activities)21. Nevertheless, with an increasing number of individuals participating in sports, these injuries are expected to rise in frequency. There is a consensus that a displaced PCL avulsion fracture should undergo anatomical reduction and fixation. Both open and arthroscopic fixation methods have been documented to yield favorable outcomes22. Heparin and rivaroxaban are commonly used to prevent deep venous thrombosis (DVT) after knee surgery. Several studies have compared the effectiveness of these two drugs. One study found that Rivaroxaban prophylaxis was associated with lower rates of symptomatic VTE, symptomatic DVT, asymptomatic DVT, distal DVT, and proximal DVT compared to enoxaparin23. Another study concluded that there was no difference in the risk of symptomatic VTE during anticoagulant prophylaxis between the two drugs24. It is important to note that anticoagulant therapy after knee arthroplasty was found to be ineffective in preventing VTE25. Overall, while both Heparin and Rivaroxaban are effective in preventing DVT after knee surgery, further research is needed to determine the ideal treatment option.

As one of the knee surgeries, the postoperative anticoagulation regimen and its efficacy for PCL avulsion surgery have not received sufficient attention given the unique nature of PCL avulsion fractures, their associated surgical fixation techniques, and the potential for prolonged post-operative immobilization. Moreover, research in this area is quite limited. This study aims to assess and compare the efficacy of LMWH (Low Molecular Weight Heparin) followed by Rivaroxaban with the absence of anticoagulant treatment in PCL avulsion fracture surgery. By focusing on this specific injury, the study seeks to provide evidence-based recommendations for thromboprophylaxis in this understudied patient population.

Materials and methods

Study design and participants

This quasi-experimental study was conducted at the Yan’An Hospital Orthopedic Trauma Department from February 2020 to January 2024. A total of 37 patients with PCL avulsion fractures were enrolled in the study. Ethical approval was obtained from the Yan’An Hospital Medical Ethics Committee prior to patient enrollment, with the approval number 2024-043-01. All patients were provided with comprehensive information regarding the examinations involved in the study, as well as the potential health risks. Written informed consent was obtained from each participant, who signed the necessary consent forms and relevant documentation prior to enrollment. All methods were performed in accordance with the relevant guidelines and regulations.

During the follow-up period, three patients were lost to follow-up, and one patient did not adhere to the prescribed rivaroxaban regimen. As a result, four patients were excluded from the final analysis. The remaining 33 patients were divided into Group A (n = 16) and Group B (n = 17). The same surgeon performed all surgeries; no additional patients were lost to follow-up. All 33 participants completed the study, ensuring complete data collection for analysis (Fig. 1).

Fig. 1
Fig. 1
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Flow Chart of the patients (N = 37) in this study.

Inclusion criteria were specifically tailored to patients with diagnostic indications and clinical manifestations necessitating PCL avulsion fracture surgery in the orthopedics department. There was no age limitation. Furthermore, the study focused on individuals with specific types of PCL avulsion fractures, namely Type 2, 3a, 3b, and 4. All patients underwent color Doppler Ultrasound for excluding DVT 24 h before the surgery.

Exclusion criteria encompassed patients with diagnosed DVT, meniscus tear grade II, and III26 were excluded. Multi-ligament knee injuries, bilateral cases and chronic cases, Pregnant or lactating woman, heparin allergies, prior anticoagulant therapy, peripheral vascular disease, immunosuppressive drug therapy, active infections, acute thrombophlebitis, neurological disorders affecting the lower extremities were also excluded. This was done to prevent pre-existing medical conditions and acute issues from impacting the study results, focusing on a relatively stable patient population (Table 1).

Table 1 Inclusion and exclusion criteria.
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Sample size

The number of necessary samples was estimated under the assumption that the proportion of development of DVT after PCL surgery would be 1.0% (expected) and 21.9%27 for groups A and B respectively. With a type 1 risk of 10.0% and a type 2 risk of 30.0%, with 70% power, and a dropout rate estimated at 20.0%. The final sample size was estimated at 19 and 19 patients would be necessary for groups A and B respectively. Finally, 16 and 17 patients were enrolled in this study. The sample size was determined using a power analysis for a quasi-experimental study design.

Surgical methods

The same surgeon performed Open Reduction and Internal Fixation (ORIF) reconstruction procedures. The surgeries adhered to standard protocols, including anesthesia induction, establishing the conventional surgical position, routine sterilization, and applying an inflatable tourniquet for hemostasis. Given the fragmented nature of the fracture pieces, anatomical alignment was restored by securing them through the insertion of absorbable Bone Anchor Nails. All patients underwent surgery in the prone position, with spinal or general anesthesia administration. A thigh tourniquet was applied to the operated leg following a knee examination, and it was deflated for procedures lasting longer than 120 min, with an additional 10–15 min if deemed necessary. During the surgical procedures, distinct cases of posterior cruciate ligament (PCL) avulsion fractures of the tibia within the knee joint were encountered (Fig. 2A, B). These cases demonstrated a consistent pattern of PCL insert avulsion, characterized by fracture pieces displaced inward and upward by approximately 2 cm. An incision, approximately 8 cm in length, was made in the popliteal fossa, centered on the positioning point. This facilitated the exposure and protection of the popliteal artery, popliteal vein, and popliteal nerve. The joint capsule was then incised to unveil the insertion point of the tibial intercondylar spinous posterior cruciate ligament. In fracture displacement and avulsion, the distal end of the insertion point underwent expansion and tapping.

Fig. 2
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(A and C) Radiological images of Patient 1’s PCL avulsion fracture before and after the operation, respectively. (B and D) Radiological images of Patient 2’s PCL avulsion fracture before and after the operation, respectively.

One or two composite suture anchors (4.75 mm x 19.1 mm, ARTHREX) with threads were strategically inserted, and protective sutures were utilized to accurately knit and suture the posterior cruciate ligament (Fig. 3 AB, CD). The fractured end was anatomically reduced, and the tension of the cruciate ligament was strictly verified. The joint cavity underwent a thorough cleansing, being flushed with physiological saline. The joint capsule was precisely repaired, and the wound was sutured. Subsequently, a pressure bandage was applied, and the tourniquet was released. A post-operative follow-up X-ray was done to confirm the surgical accuracy (Fig. 2C, D). To further stabilize the lower limb, external fixation with a lower limb brace was initiated.

Fig. 3
Fig. 3
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(A and B) Intraoperative images of Patient 1 using an absorbable bone anchor, while (C and D) Intraoperative images of Patient 2 using the same method. The region indicated by the black arrow corresponds to the fracture fragment.

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Treatment method

The postoperative care and rehabilitation protocol outlined in this study demonstrates a thorough and structured approach to ensuring the well-being and recovery of patients following PCL avulsion fracture surgery. Throughout the hospital stay, the patient was given a non-weight-bearing hinged knee brace with a range of motion from 0° to 30°.

Postoperatively, ice application with a compressive wrap was implemented for 20 min every 3–4 h during the initial 24–48 h to mitigate swelling. Progressive and restrictive exercises targeting the quadriceps and hamstrings commenced 24 h after the operation.

Regarding medical intervention, Group A and Group B patients were provided with the same standard antibiotics, nonsteroidal anti-inflammatory drugs (NSAIDs), and proton pump inhibitors (PPIs). This consistent medication regimen across both groups ensures that the study’s focus on anticoagulation interventions remains isolated and unbiased.

The specifics of the anticoagulation regimen for Group A are precisely defined, with patients receiving a subcutaneous injection of LMWH (Heparinum Natricum Minor Molecularis) 5000 IU starting from the 1st postoperative day and continuing for 1 week. This was followed by an oral form of 10 mg rivaroxaban, an Xa factor inhibitor, for 3 weeks post-surgery28. The structured administration of LMWH and Rivaroxaban is a critical aspect of the study, providing insights into their efficacy and safety in preventing thromboembolic events in the context of PCL avulsion fractures.

In contrast, patients in Group B did not receive these specific anticoagulation interventions, providing a clear basis for comparison.

Sutures were routinely removed 14 days postoperatively in both groups, and no substantial differences were observed. The healing time did not exhibit significant variances between the two groups, and there were no postoperative complications related to active bleeding. A localized ecchymosis at the LMWH injection site was observed in only one case; it was self-limiting, required no intervention, and did not necessitate discontinuation of prophylaxis.

Seven days and 1-month post-operation, all patients underwent color Doppler ultrasound examinations to assess the presence and condition of Deep Vein Thrombosis (DVT) in both lower extremities. All assessments were performed by experienced radiologists blinded to both groups. This approach was employed to minimize potential bias and ensure the consistency and reliability of the imaging results. This postoperative assessment is crucial for understanding the impact of anticoagulation interventions on DVT incidence and severity.

The study’s comprehensive approach to postoperative care, rehabilitation, and medical intervention ensures that all variables are carefully controlled, allowing for a robust examination of the effects of prophylactic anticoagulation in patients with PCL avulsion fractures.

Outcome

Patients’ blood parameters were regularly assessed at 1-, 4-, 7-, and 10-days post-operation. These assessments included Hemoglobin (Hb), Erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), Albumin (ALB), and D-Dimer (D-D) levels. The primary focus was on the imaging index of lower limb thrombosis. Following the surgery, we utilized color Doppler ultrasound to examine the deep veins of the lower limbs, specifically the superficial femoral artery, popliteal vein, and posterior tibial muscle of the calf vein.

Statistical analysis

Statistical analysis was performed using GraphPad Prism 9. Statistical significance was set at 95% confidence and 10% acceptable error levels. The measurement data (Age, Weight, BMI) were expressed with mean standard deviation among groups, presented as “x ± s,” and analyzed with two-sample t-tests or Mann-Whitney U-tests. Count data (gender, side of fracture, causes of injury) were presented as percentages and compared using Fisher’s exact test. A significant level of p < 0.05 was considered.

Results

No statistically significant differences were observed in the patients’ demographic data in groups A and B (Table 2). The two groups were comparable in terms of laboratory indicators before surgery. The two groups had no substantial differences in Hb, ESR, CRP, and D-D, Alb before surgery (Fig. 4).

Table 2 Demographic characteristics of the study patients in two groups (N = 37).
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Fig. 4
Fig. 4
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Comparison of preoperative (Pre-Op) and postoperative (1, 4, 7, and 10 days after operation) levels of CRP, ESR, Hb, Alb, and D-D between the two groups revealed no significant differences. However, in D-D, a significant difference (P < 0.05) was observed in Group B compared to Group A at 7 days after operation and 10 days after operation. CRP refers to C-reactive protein, ESR to erythrocyte sedimentation rate, Hb to hemoglobin, Alb refers to albumin, and D-D to D-Dimer.

In Figs. 1 and 37 patients who underwent surgery for PCL avulsion fractures performed by the same doctor were initially screened during the observation stage. All participants in the study signed the consent form. After screening, they were allocated to two groups: Group A, treated with LMWH followed by Rivaroxaban, and Group B, receiving no anticoagulant intervention. 4 participants were excluded for not meeting the final inclusion criteria (Table 1), resulting in a final cohort of 33 patients (Group A: n = 16; Group B: n = 17).

The ESR, CRP, ALB, Hb, and D-D levels were evaluated preoperatively (Pre-Op) and postoperatively (1, 4, 7, and 10 days after the operation) between the two groups. Figure 4 shows no statistically significant differences in ESR, ALB, CRP and Hb between the two groups (P > 0.05). However, the D-D levels postoperatively were higher in group B compared to group A at 7 and 10 days after the operation (P < 0.05 for both time points).

As indicated in Table 3, the total incidence of Deep Vein Thrombosis (DVT) detected by Color Doppler Ultrasound at 1 month postoperatively in both study groups. Was 6.25% in Group A and 35.29% in Group B (p = 0.041). The incidence of MCVT was 100% in Group A and 60% in Group B (p = 0.166). PTVT was observed in 20% of patients in Group B, while no cases were detected in Group A (p = 0.325). Additionally, one patient (20%) in Group B developed both MCVT and PTVT, whereas no such cases were observed in Group A (p = 0.325). The percentage of DVT-free patients at 1 month postoperatively was 93.75% in Group A and 64.71% in Group B (p = 0.041).

Table 3 The total incidence rate of deep vein thrombosis in color doppler ultrasound in two groups after 1 month (N = 33). An asterisk (*) indicates statistical significance (p < 0.05).
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As presented in Table 4, During the 7 days postoperatively, the incidence of DVT was 6.25% in Group A (1 case of MCVT) and 17.65% in Group B (3 cases: 2 MCVT and 1 PTVT) (p = 0.316). The percentage of DVT-free patients was 93.75% in Group A and 82.35% in Group B (p = 0.041). From 8 days to 1 month postoperatively, no cases of DVT were detected in Group A (0%), while Group B had a DVT incidence of 21.43% (3 cases: 2 MCVT and one combined MCVT and PTVT) (p = 0.078). The percentage of DVT-free patients was 100% in Group A and 78.57% in Group B (p < 0.01).

Table 4 The comparison of color doppler ultrasonography finding in two groups at 7 days and 1 month of post-operative day separately (N = 33).
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Discussion

This study compares LMWH followed by Rivaroxaban with no prophylaxis in post-PCL avulsion fracture surgeries to identify the DVT incidence rate. The primary outcome of the study focused on the occurrence of DVT in patients undergoing PCL avulsion fracture surgery. In addition, among the four excluded patients, three were lost to follow-up, and one did not take rivaroxaban regularly (Fig. 1).

This study utilized a quasi-experimental, real-world evidence design in which patients were assigned to prophylaxis or no prophylaxis groups according to clinical judgment and routine treatment practices, enabling the observation of outcomes in a naturalistic clinical setting. Due to ethical considerations, randomizing patients was not feasible. Patient baseline characteristics were carefully assessed and found to be comparable between groups to minimize confounding factors and enhance the validity of between-group comparisons (Table 2).

Both groups received consistent postoperative care and rehabilitation protocols, ensuring that any observed differences in outcomes are more likely to be attributed to the anticoagulant intervention rather than variations in patient management. Statistical analysis of patient demographics (Table 2), including age, weight, BMI, gender, side of fracture, and causes of injury, demonstrated no statistically significant differences between Group A and Group B.

This study chose low-molecular-weight heparin (LMWH) followed by rivaroxaban due to its well-established benefits over other anticoagulants. LMWH was used initially for its rapid onset, predictable anticoagulant effect, and lower risk of heparin-induced thrombocytopenia (HIT) compared to unfractionated heparin (UFH)29,30. It has been widely recommended in orthopedic procedures due to its effectiveness in reducing early postoperative thrombotic risk without frequent laboratory monitoring31,32. Rivaroxaban was selected for extended prophylaxis because of its proven efficacy, ease of oral administration, and predictable pharmacokinetics. Unlike vitamin K antagonists (VKAs) such as warfarin, rivaroxaban does not require routine International Normalized Ratio (INR) monitoring. It has fewer drug and dietary interactions, making it a more convenient option for long-term use33. Additionally, its once-daily dosing regimen enhances patient adherence compared to other direct oral anticoagulants (DOACs) like apixaban or dabigatran. Previous clinical studies have demonstrated that LMWH followed by rivaroxaban provides effective thromboprophylaxis in orthopedic surgeries, with a comparable or lower risk of bleeding complications34.

The assessment of laboratory parameters, including Hemoglobin (Hb), Erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), Albumin (ALB), and D-D), established baseline comparability between the two groups (Fig. 4). Postoperatively, Group B exhibited higher levels of D-D at 7 and 10 days after the operation, suggesting potential differences in the inflammatory status between the groups and, simultaneously, indicating a heightened risk of hypercoagulability35,36,37.

The study findings suggest that the administration of a combined anticoagulation regimen consisting of LMWH and Rivaroxaban (Group A) was effective in reducing the incidence of DVT, particularly in the long-term postoperative period. During 7 days post-operatively, Group A showed a relatively low DVT incidence of 6.25%, primarily consisting of 1 case of MCVT. In contrast, Group B, which received no anticoagulation therapy, demonstrated a higher DVT incidence of 17.65% (3 cases), including 2 MCVT and 1 PTVT cases. Although the difference in DVT incidence between the two groups was not statistically significant (p = 0.316), the absence of DVT in 93.75% of patients in Group A was significantly higher compared to 82.35% in Group B (p = 0.041) points to an early protective effect of the anticoagulation therapy.

From the 8th day to 1-month post-surgery, Group A exhibited no new cases of DVT, while Group B saw an increase in DVT incidence to 21.43% (3 cases), 2 MCVT and one combined MCVT and PTVT. The difference in DVT rates between the two groups approached significance (p = 0.078), suggesting that while the initial 7 days showed no significant difference in the anticoagulation regimen’s effectiveness, the benefits of continuous prophylaxis with Rivaroxaban became more apparent over time. Furthermore, the absence of DVT in 100% of Group A patients compared to 78.57% in Group B (p < 0.01) highlights the continual protective effect of the LMWH and Rivaroxaban regimen.

Importantly, an additional layer of complexity arises from the revelation that 1 out of 1 and 3 out of 6 patients in Groups A and B were asymptomatic for DVT respectively. The identification of asymptomatic deep vein thrombosis (DVT) in this study highlights the importance of routine screening in high-risk populations, such as patients undergoing PCL avulsion fracture surgery. Asymptomatic DVT, while lacking overt clinical manifestations, poses a significant risk for complications, including pulmonary embolism (PE) and chronic venous insufficiency, if left undetected and untreated38.

Imaging modalities, such as color Doppler ultrasound, play a critical role in early diagnosis39enabling timely initiation of anticoagulation therapy to prevent thrombus progression and mitigate long-term sequelae. These findings suggest the need for heightened clinical vigilance and individualized management strategies to optimize patient outcomes in this population.

These emphasize the covert nature of this condition and the crucial for cautious diagnostic strategies, particularly given the association observed between DVT, regular color Doppler ultrasonography, and the prevalence of asymptomatic DVT and MCVT. These findings contribute to our understanding of DVT epidemiology and emphasize the need for comprehensive diagnostic approaches to enhance early detection and tailored management approaches, considering both symptomatic and asymptomatic presentations.

Mills, Roger et al. (2012) well documented the positive effectiveness of LMWH followed by rivaroxaban in anticoagulation after total joint arthroplasty40 providing us with significant insights. In comparison to the previous study done by Beyer-Westendorf, Jan et al. (2013)41the efficacy and safety of LMWH and Rivaroxaban in 5,061 patients undergoing hip and knee replacement surgery found that, Rivaroxaban is more effective in preventing thrombosis than LMWH. They also suggested that switching from LMWH to Rivaroxaban may be beneficial, which aligns with our research findings. The proportions of DVT in our study were higher, which might be attributed to several factors. Although PCL avulsion surgery is less invasive and has a shorter operative duration than TKA, it often involves prolonged immobilization and restricted weight-bearing during the postoperative period, which are known risk factors for venous stasis and thrombotic events42.

The study’s findings carry implications for clinical practice, suggesting that prophylactic anticoagulation with LMWH followed by Rivaroxaban may play a crucial role in mitigating the risk of DVT following PCL avulsion fracture surgery. The observed protective effect aligns with existing literature supporting anticoagulant prophylaxis in orthopedic procedures. The choice of LMWH and Rivaroxaban as anticoagulant regimens offers a practical approach with manageable side effects, providing clinicians with valuable insights into potential prophylactic strategies.

Despite the valuable insights gained, the study has inherent limitations. Patients with posterior cruciate ligament (PCL) avulsion fractures are relatively uncommon43making it challenging to recruit a large sample size for this study. Its single-center design and relatively small sample size necessitate caution in generalizing the findings. More significantly, the study focused on specific types of PCL avulsion fractures, and further research is needed to explore the generalizability of the findings to other fracture patterns. Multicenter studies involving diverse patient populations and long-term follow-up are essential to validate the results and establish definitive guidelines for anticoagulant prophylaxis in the context of PCL avulsion fractures. Additionally, exploring the cost-effectiveness of LMWH and Rivaroxaban for routine prophylaxis in similar orthopedic settings and the potential benefits of extended anticoagulation therapy would provide valuable insights.

Spinal anesthesia, the standard technique used for all patients in this study, may influence the risk of deep vein thrombosis (DVT) due to its potential effects on venous stasis44. Additionally, the use of a tourniquet during surgery may further increase the risk of DVT45. The potential impact of these factors on DVT risk is acknowledged as a confounding element in this study.

Conclusion

In this study, the combination of LMWH followed by rivaroxaban was associated with a significantly lower incidence of deep vein thrombosis (DVT) (6.25%) compared to no anticoagulation therapy (35.29%) in patients undergoing PCL avulsion fracture surgery. Postoperative D-Dimer levels were also significantly lower in the LMWH-rivaroxaban group 7 and 10 days after surgery. As for ESR, CRP, ALB and Hb levels, no significant differences were observed between the two groups. Asymptomatic DVT cases were identified in both groups, stressing the importance of routine screening in this patient population. These findings highlight the potential role of LMWH and rivaroxaban in reducing thrombotic events following PCL avulsion fracture surgery.