Introduction

Pulmonary embolism (PE) represents one of the most frequent and dangerous complication in patients undergoing a surgical procedure [76, 81]. Approximately 500,000 cases of deep vein thrombosis (DVT) and PE occur in the United States each year. In about 20% of cases, the initial clinical manifestation of venous thromboembolism (VTE) is sudden death due to PE. Of those patients who suffer a massive PE, 70% die within the first hour of symptom onset [2, 64, 66].

Because patients with recent surgery have a 22-fold increased risk of postoperative VTE, a large research effort has been directed toward identifying the safest and most effective prophylaxis after surgery [44, 49].

Obviously, thromboembolic risk is not the same in all patients, and it can vary greatly depending on the kind of surgery. To appropriately target prophylaxis against thromboembolism, surgical procedures and patients at risk must first be identified and categorized into levels of risk [20, 40, 67] (Table 1).

Table 1 Levels of thromboembolism risk in surgical patients without prophylaxis (modified from Clagett et al., Geerts et al., and Nicolaides et al. [19, 40, 67]) (DVT deep vein thrombosis, PE pulmonary embolism, VTE venous thromboembolism)
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The patients at greatest risk for VTE are those undergoing major lower extremity orthopedic surgery, and those who have experienced major trauma or spinal cord injury [6, 8, 10, 15, 19, 20, 24, 28, 30, 39, 44, 67, 84].

For instance, the incidence of DVT in patients who underwent hip and knee surgery without prophylaxis ranges from 48 to 80% [6, 25, 46, 63, 65, 66, 80, 90, 94]. In a prospective study of 443 patients with major trauma who did not receive any thromboprophylaxis, the incidence of DVT, using routine bilateral contrast venography, was 58%. Among trauma subgroups, the expected high rates of DVT were seen in patients with lower extremity (69%) and spine (62%) fractures and in patients with major head injuries (54%) [39]. Other less invasive procedures, such as knee arthroscopy, also pose a risk [26].

For any kind of surgery, certain patient characteristics have been identified as risk factors for VTE. These include: increasing age; prolonged immobility; stroke or paralysis; previous VTE; cancer and its treatment [33, 54, 59]; trauma (especially fractures of the pelvis, hip, or leg); obesity; varicose veins; cardiac dysfunction; pregnancy; and oral contraceptive use or estrogen replacement therapy [19, 43]. These are often present in combination in a hospitalized population. For surgical patients, the incidence of VTE is affected by pre-existing factors and by factors related to the procedure itself [19, 20, 40, 64, 67, 79, 87].

It is therefore appropriate to perform a prophylaxis in surgical patients. Table 2 summarizes some advice regarding the risk of VTE.

Table 2 Regimens to prevent VTE (modified from the Sixth ACCP Consensus Conference on Antithrombotic Therapy, 2001 [40]) (LMWH low-molecular-weight heparin, ES elastic stockings, IPC intermittent pneumatic compression, LDUH low-dose unfractionated heparin)
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Pharmacological prophylaxis to prevent thromboembolic events has become standard practice in high-risk patient groups. The gold standard is low-molecular-weight heparin (LMWH). The major advantages of LMWH are improved efficacy and safety, longer half-life and reduced need for laboratory monitoring [71].

If these recommendations are well known for general orthopedic surgery, especially in elective hip and knee and trauma procedures, little has been published about the problem of DVT and it prophylaxis for spinal surgery.

Despite being generally considered as a sub-speciality of orthopedic or neuro-surgery, spine surgery has developed significantly over the last 20 years, to become an independent surgical speciality. It includes many surgical procedures for a variety of pathologies, and involves a highly heterogeneous class of patients. A careful analysis in terms of thromboembolic risks is therefore required in each individual case.

Three main variables need consideration:

  1. 1.

    Patient-related variables, such as age, gender (oral contraceptive use or hormonal substitutive therapy), bed rest, obesity and concomitant pathologies (hypertension, diabetes, varicose veins)

  2. 2.

    Disease-related variables, such as trauma, tumor, deformity, degenerative pathology, and finally

  3. 3.

    Surgery-related variables, such as approach (anterior, posterior, combined), positioning, instrumentation, operating time, and location (cervical, thoracic, lumbar spine)

There is no unique risk factor, because spinal surgery does not take one single form; it is therefore not possible to suggest a standardized thromboprophylaxis for spinal surgery, as can be done for hip and knee surgery. Moreover pharmacological prophylaxis has never met the approval of spine surgeons, due to the possibility of hemorrhagic complications [10, 16, 25, 32, 37, 47, 82, 85, 91, 92, 94].

For more on this subject, the interesting paper by Janku et al. published in 1996 [53] is worth a review. Janku and co-workers conducted a study into the practice of prevention of venous thromboembolism among orthopedic surgeons in the United States, based on a questionnaire mailed to 5000 randomly selected practising surgeons. They found that the low rate of incidence of venous thrombosis and the risks related to the use of anticoagulants, which can lead to hematoma and cauda equina syndrome in patients undergoing elective spinal surgery, appeared to discourage pharmacologic prophylaxis. Elective spinal procedures were carried out by 383 of the surgeons, each of whom estimated dealing with, on average, 37 such cases per year. Only 21% of surgeons used prophylaxis in all patients, a further 21% used it only in risk cases, and 58% of surgeons did not employ any kind of prophylaxis.

The figure of 58% using no kind of prophylaxis is high, considering that the onset of an epidural hematoma with its potentially tragic complications (not always reversible even after an immediate revision and decompression) or a deep hematoma with a consequent infection and hardware removal, represent a failure of treatment and a source of disability in the patient. Among those who did use some form of prophylaxis, the most frequent method was mechanical (elastic compressive stockings, intraoperative compressive pumps).

Up to now, no precise indications have been published relating to VTE prophylaxis in spinal surgery, with spine surgeons having to rely on generic recommendations from general orthopedic surgery and neurosurgery [1, 3, 13, 69, 77].

We performed a literature review concerning this topic in order to better understand and quantify the incidence of VTE and its prophylaxis in spinal surgery.

Literature review

Historically, the first contribution was published by Uden [88] in1979. Out of 1229 patients who underwent Harrington correction and fusion for idiopathic scoliosis, there were eight DVT cases (0.0065%), with one fatal PE, which occurred between the 12th and 34th postoperative day.

Subsequently three papers were published by Ferree and co-workers on a limited number of cases. In the first paper [36], 86 patients were studied with preoperative and postoperative ultrasonography of the lower extremities to identify acute DVT. Postoperative DVT developed in five of them (6%), and there were two decompressions (one breast cancer); one discectomy; one posterior fusion (previous thrombophlebitis); and one anterior fusion (oral contraceptive use). None of the patients developed symptoms of PE.

In the second paper [35], 185 posterior surgery patients were studied. Elastic compression stockings (ECS) were used for prophylaxis in 74 patients (ECS group); and intermittent pneumatic compression (IPC) was used in the remaining 111 patients (IPC group). The results were: three cases of DVT following laminectomy (4% of 84 total laminectomy patients; 8% of 40 ECS group laminectomy patients), and one case of DVT in the fusion group (1% of 101 total fusion patients; 3% of 34 ECS group fusion patients).

The last of the Ferree studies [34] reviewed 60 consecutive patients undergoing lumbar laminotomy for herniated disc (n=51) or laminectomy for spinal stenosis (n=9); compression stockings were the method of prophylaxis. Three patients (5%) developed postoperative calf DVT (ultrasonography detection); one was a 43-year-old man without risk factors in the herniated disc group; one was a 67-year-old woman (L4–S1 laminectomy for stenosis); and one was a 75-year-old woman (decompressive laminectomy) affected by breast cancer.

In the Dearborn et al. study [29], 318 major spinal reconstructive procedures, excluding discectomies and cervical spine cases, were considered. There were seven cases of PE, six of which occurred among 97 patients undergoing combined anterior and posterior spinal procedures (6.1%). Only one patient had a clinical PE after posterior procedure. The overall clinical PE rate in combined-approach patients was 6%, significantly greater than the rate in patients undergoing posterior surgery alone. PE occurred in two patients with negative ultrasound examinations, and none of the patients with PE had clinical signs or symptoms of DVT before embolization.

The higher risk of PE after combined anterior-posterior spinal fusions indicates that retraction and manipulation of the great vessels may lead to stasis or intimal damage that can predispose to clot formation.

A multicentric retrospective study of thromboembolic complications after lumbar disc surgery involving 16,656 patients from 50 French neurosurgical units was published in 1993 [31]. No prophylaxis was used in 62.2% of the patients; subcutaneous heparin was employed in 6% of patients, LMWH was used in 25.8% of patients, and in 6% oral anticoagulants were used. Two major groups were identified: group A (10,351 patients), without prophylaxis, and group B (6305 patients), with some kind of prophylaxis. There were 105 VTE complications (0.63% of all surgical patients), with 94 cases of DVT and 11 of PE. In group A there were 63/10,351 cases of DVT (0.609%) and 5/10,351 cases of PE (0.048%); in group B there were 31/6305 cases of DVT (0.492%) and 6/6305 cases of PE (0.095%).

Kozak and O’Brien [58], in a series of 69 simultaneous combined anterior (left-sided, retroperitoneal approach to the lower lumbar spine) and posterior fusions between January 1984 and November 1986 for primary low-back pain or persistence of pain following previous lumbar surgery, reported an incidence of 3/69 cases of DVT (4.34%) and 2/69 (2.89%) cases of nonfatal pulmonary embolism.

More recently, two papers coming from East Asia have been published. The first of these [70] concerned 110 patients who underwent posterior spinal surgery: 54 cervical; 7 thoracic; and 49 lumbar, without any type of prophylaxis.

No patients showed clinical signs of DVT or PE. However, 17 patients (15.5%) showed venographic evidence of DVT; 16 of these had distal thrombi, and only one had a proximal thrombus. DVT was venographically evident in 3 (5.6%) of the 54 patients who underwent cervical procedures, and in 13 (26.5%) of the 49 patients who underwent lumbar procedures.

In the study by Lee et al. [60], which was based on 313 patients, no specific anti-thrombotic prophylaxis was used in any patient before or after surgery. All patients were examined with duplex ultrasonography in both lower extremities between the 5th and 7th postoperative days, to ensure that any asymptomatic thrombi were not missed. Only one patient had a clinically symptomatic DVT; four patients were noted to have results compatible with DVT. The overall incidence of thrombotic complication without any form of prophylaxis was 1.3% (4/313) and the incidence of symptomatic DVT was 0.3% (1/313).

Smith et al. [83] studied 317 patients in whom prophylaxis was done with compressive stockings and sequential-pneumatic-compression thigh-length cuffs. Duplex ultrasonography was performed in 126 patients (40%) to screen for the presence of asymptomatic thrombosis.

DVT developed in 1 of the 126 patients who had been evaluated with duplex ultrasound, 16 days after the operation and 10 days after discharge, and in 1 of the 191 who had not been so evaluated,15 days after the operation, after discharge from the hospital. The operation in both patients had involved a left-sided, lateral, retroperitoneal exposure of the caudal lumbar and lumbosacral discs.

A fatal PE developed in one of the patients who had not been evaluated with ultrasound, 8 days after the operation (anterior decompression and arthrodesis with anterior instrumentation) for a severe burst fracture of the second lumbar vertebra.

Wood et al. [95] published in 1997 a study on 136 patients in whom a mechanical prophylaxis was used (thigh-high sequential-pneumatic-compression wraps or pneumatic foot-compression wraps).

Investigations using Doppler ultrasound revealed one ultrasound positivity in a 49-year-old woman who had undergone anterior spine T11–L3 fusion and posterior T4–L3 fusion on the 6th postoperative day, and one case of subclinical PE (3rd postoperative day) in a 33-year-old woman, who was a smoker and was obese, and had undergone a posterior L3–L5 fusion.

West and Anderson [93] carried out a prospective study on 41 adult patients (>18 years old) undergoing major spinal surgery using pedicular or segmental instrumentation (including six cases of anterior surgery): 14 operations were for spinal deformity; 16 for trauma; and 11 for degenerative spine disease.

No preoperative or intraoperative thrombotic prophylaxis was used. After surgery, all patients were placed in compression stockings until the patient was able to walk well. One day before discharge the patients underwent noninvasive testing to rule out DVT of the lower extremities (color Doppler). Six patients (14%) were found to have results compatible with DVT, of whom three were trauma patients (two paraplegic); two had been operated for spinal deformity; and one for degenerative spine disease. If we eliminate the two patients who had paraplegia secondary to trauma, the incidence of DVT changes to 4/39, or 9.8%.

Rokito et al. [78], in 370 major reconstructive spinal procedures on 329 patients, reported one case of DVT (0.3% of incidence) on the 16th day in a patient with high co-morbidity (obesity, diabetes, hypertension, bed rest, anterior retroperitoneal approach), in whom only mechanical prophylaxis was used.

Benz et al. [12] found an incidence of 1 case of PE in 68 patients operated on for decompression or decompression combined with fusion in patients aged over 70 years. One case of non-fatal PE in a 57-year-old woman affected by cauda equina tumor (neurinoma) at the L2 and L3 levels, who underwent tumor resection with L1–L5 posterolateral fusion and spinal instrumentation, was found in a report by Arai et al. [7].

Knop et al. [57] described three cases of fatal PE and six of DVT and non-fatal PE in a group of 682 patients who underwent surgical repair for thoracolumbar injuries.

Andreshak et al. [5] investigated 150 lumbar spine surgery procedures in which the patients were placed in intraoperative sequential-pneumatic-compression devices and divided into an obese and a non-obese group. In the obese group (55 patients), there was 1 case of fatal PE out of 55 procedures, which occurred in a 62-year-old man on the 3rd postoperative day; and there was 1 case of DVT in the non-obese group (95 patients).

Stolke et al. [86] reported 1 case of fatal PE in 412 primary surgeries and 69 reoperations in lumbar disc macro- and microsurgery.

Fujita et al. [38] studied 169 spinal fusions in adult patients of more than 60 years of age; there was 1 case of PE and 2 of DVT in 169 patients.

Brown and Eismont [14] reported 1 case of DVT in 98 patients undergoing anterior correction for scoliosis, while Ramirez and Thisted [74] found an incidence of pulmonary embolism of 0.1% among 28,395 patients undergoing lumbar discectomy. Patients undergoing lumbar discectomy are generally considered at low risk for thromboembolism [48].

Finally, four isolated cases of arterial thromboembolism were reported as a consequence of compression and occlusion of the common left iliac artery during anterior lumbar interbody fusion [45, 56, 61, 75].

Table 3 summarizes the most important studies found in the literature, divided by type of study. The gold standard for these types of studies, represented by a prospective, randomized, controlled study, is impossible because of ethical and health issues.

Table 3 Literature review listed by type of study (ECS elastic compressive stockings, PC pneumatic compression)
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Conclusions

Prophylaxis for VTE is an area that has received intense study in certain contexts [27], but less than adequate coverage in others. A Scottish study documented fatal PE in surgical patients over a 1-year period: 56% of the patients who died of PE had not received prophylaxis, despite having major risk factors and with no contraindications to standard antithrombotic regimens [42].

The true incidence of thromboembolic complications in spinal surgery remains unknown [17]. The question is whether the incidence of DVT in spinal surgery is sufficient to consider any type of prophylaxis. Because insufficient data exist, it is not possible to suggest a standardized prophylactic regimen; elastic compression alone or combined with pharmacological prophylaxis seem both to be efficacious. For patients at risk, prophylaxis with both measures is strongly recommended [40].

Methods of prophylaxis include pharmacologic [10, 21, 22, 23, 37, 41, 62, 68, 73, 89], mechanical [9, 11, 92], and combinations of these. Anticoagulation has not gained wide acceptance by spinal surgeons: the possibility of epidural hematoma and catastrophic neurologic injury makes the morbidity of anticoagulation potentially worse in spinal surgery patients than in total joint replacement patients.

Major bleeding was significantly increased with the preoperative regimen, but not with the postoperative regimen of LMWH. Recent studies revealed that LMWH beginning within 2 h preoperatively or 6 h postoperatively decrease the risk of venous thrombosis equally [1, 3, 47, 50, 51, 52, 55, 63, 72] and should be helpfully employed in spinal surgery.

We think that the problem of VTE and its prophylaxis should be more extensively investigated in controlled studies specifically for complex modern spinal surgery in order to formulate some guidelines for the sake of patient health and safety and to address surgeons’ uncertainty in this matter.