Copyright © 2009 by The Journal of Bone and Joint Surgery, Inc.
Commentary & Perspective
Commentary & Perspective by
Ronald W. Lindsey, MD*,
University of Texas Medical Branch, Galveston, Texas
Posted November 2009
The medical community has long recognized that patients who sustain acute
spinal injuries are at substantial risk for venous thromboembolism, which includes
deep venous thrombosis and pulmonary embolism. Studies have established not only
that the basis for this risk can be attributed to Virchow's triad of stasis,
hypercoagulability, and intimal injury1 but also that variations in
some hemostatic factors and fibrinolytic systems have been specifically implicated
as potential sources for venous thromboembolism susceptibility following spinal
cord injury. Although the substantial morbidity and mortality associated with
venous thromboembolism in patients with spinal trauma have been well established,
and although a consensus exists among spine surgeons that prophylaxis is essential,
the optimal selection, initiation, and duration of mechanical and/or pharmacological
prophylaxis remain elusive. In fact, evidence-based practice guidelines for prophylaxis
against venous thromboembolism after acute spinal injuries (with or without injury
to the spinal cord) are nonexistent.
Spinal trauma, as compared with other elective and nonelective orthopaedic
conditions that warrant the use of early preventive measures against venous thromboembolism,
is associated with a number of special considerations that pose a challenge to
the development of meaningful treatment standards and recommendations. The level
and/or type of spinal injury, the nature and extent of concomitant spinal cord
injury, the associated other organ injuries, the optimal time to initiate therapy
and the duration of that therapy, and the influence of surgery (anticipated or
recent) are just a few of the factors that complicate the decision-making with
regard to thromboembolic prophylaxis in these patients. Moreover, establishing
how best to select and apply the various types of currently approved mechanical
and pharmacological modalities to any protective regimen further compounds the
issue of prophylaxis against venous thromboembolism. Finally, aside from effectively
decreasing the prevalence of deep venous thrombosis and pulmonary embolism, the
current inability to accurately determine which prophylaxis-related complications
are related to traumatic injury to the spine and which are related to acute injury
to the spinal cord suggests that the development of evidence-based recommendations
for prophylaxis against venous thromboembolism will be extremely challenging.
Ploumis et al. have performed a meta-analysis of the electronically available
literature on thromboprophylaxis in patients with acute spinal injuries (with
and without spinal cord injury) to determine the optimal preventive regimen.
Clearly, apart from a large, randomized, well-controlled, multicenter prospective
study, this paper may provide the most credible guidelines to date on this issue.
Their methodology included querying all major databases; their study selection
process required not only the utilization of preventive measures but also the
use of an objective deep venous thrombosis or pulmonary embolism diagnostic test
as well as randomization and control for heparin-based pharmaceutical agents.
All papers were graded in accordance with their level of evidence with regard
to the primary research question, and only studies that met at least 50% of the
validity criteria were included in the analysis of unfractionated heparin as
compared with low-molecular-weight heparin. The data were grouped according to
the following categories: (a) control (no prophylaxis), (b) all mechanical methods,
(c) vitamin K antagonists, (d) non-vitamin K antagonists, (e) mechanical plus
pharmacological prophylaxis, (f) early prophylaxis (initiated within two weeks
after spinal cord injury), and (g) late prophylaxis (initiated more than two
weeks after spinal cord injury). All patients receiving unfractionated heparin
were grouped together as "heparin"; all patients receiving low-molecular-weight heparin were grouped as
such. Finally, similar data were pooled, and the pooled data were analyzed. Although
489 articles were identified, only twenty-one studies met the inclusion criteria.
The level of evidence of the studies varied greatly; only a few constituted
randomized trials. In addition, most of the literature pertained to patients
with spinal cord injuries. However, the authors were still able to provide meaningful
insight into some questions while highlighting the issues that continue to elude
us. The risk for deep venous thrombosis is higher in patients with spinal cord
injury; mechanical measures may be as effective without supplemental pharmacological
agents; vitamin K antagonists appear to be more effective (than non-vitamin K
antagonists) for pulmonary embolism; and, in patients with acute spinal cord
injury, low-molecular-weight heparin (as opposed to unfractionated heparin) is
more effective prophylactically for deep venous thrombosis, while similar in
effect with regard to pulmonary embolism. Furthermore, low-molecular-weight heparin
(compared with unfractionated heparin) is associated with less bleeding. However,
with regard to the patient with acute spinal cord injury, this paper (and the
literature) does not recommend when to initiate pharmacological prophylaxis,
nor does it recommend the duration of treatment. Ultimately, the study recommends
that clinicians approach these decisions on the basis of clinical experience,
expertise, and patient-specific risk factors.
The authors should be applauded for their comprehensive and methodologically
sound review of the subject. They have, undoubtedly, strengthened and refined
our existing knowledge regarding prophylaxis against venous thromboembolism in
patients with spine injuries. However, they have also demonstrated that the existing
literature is too heterogeneous and the clinical issues are too complex to resolve
without additional data from future prospective, randomized, controlled clinical
trials dedicated to answering only one question at a time.
*The author did not receive any outside funding or grants in support of his research for or preparation of this work. Neither he nor a member of his immediate family received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.
Reference
1. Virchow RLK. Thrombose und Embolie. Gefässentzündung und septische Infektion. Gesammelte Abhandlungen zur wissenschaftlichen Medicin. Frankfurt am Main: Von Meidinger und Sohn; 1856. p 219-732. Translation in: Matzdorff AC, Bell WR. Thrombosis and embolie. Canton, Massachusetts: Science History Publications; 1998. p 1846-56.
|
