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Clinical indications for CT angiography in lower extremity trauma

Patterson, Joseph T. MD; Fishler, Thomas MD; Bohl, Daniel D. MPH; Piper, Greta L. MD; Leslie, Michael P. DO

doi: 10.1097/BCO.0000000000000397
Resident Research

Background: Missed vascular injuries in lower extremity trauma may lead to a preventable lower extremity amputation. CT angiography (CTA) is an accurate and expedient, but costly and potentially harmful, test for vascular injury in lower extremity trauma. Specific physical examination findings and injury patterns may be predictive of detection of a vascular injury by CTA and could guide CTA use in lower extremity trauma.

Methods: This was a retrospective review of consecutive trauma patients at an academic level 1 trauma center who underwent CTA of a lower extremity from January 2006 through December 2012. The positive predictive values of injury pattern and physical examination signs for CTA detection of a vascular injury and vascular intervention, adherence to published guidelines for CTA use, and CTA-related adverse events were assessed.

Results: Diagnostic CTA studies demonstrated a vascular injury in 55.6%. A vascular intervention followed in 13.9%, while 5.6% of studies led to a contrast-related adverse event. The positive predictive value of a CTA affecting treatment was significantly higher in the presence of high-risk injuries and hard examination findings than in the presence of low-risk injuries and soft examination findings (84.6%, 95% CI [54.6–98.1%] vs. 16.7%, 95% CI [3.6–41.1%]). Palpable pulses and ankle brachial index (ABI)>0.9 led to observational management without complications, regardless of CTA findings or other signs of vascular injury.

Conclusions: The utility of CTA is improved by assessing the pretest positive predictive value of vascular injury from injury pattern and physical examination. The Eastern Association for the Surgery of Trauma guidelines may miss some vascular injuries in patients with high-risk injuries and normal ABI. CTA is not indicated in lower extremity trauma when physical examination and injury pattern do not suggest a vascular injury.

aUniversity of California San Francisco, Department of Orthopaedic Surgery, San Francisco, CA

bSonoran Orthopaedic Trauma Surgeons, Scottsdale, AZ

cYale University School of Medicine, Department of Orthopaedics and Rehabilitation, New Haven, CT

dNew York University Langone Medical Center, Department of Surgery, New York, NY

Financial Disclosure: Dr. Fishler discloses a current or past financial relationship with Styker and Smith and Nephew. The other authors have no disclosures. The authors report no conflicts of interest in regard to this work.

Manuscript was a podium presentation at 30th Annual Orthopaedic Trauma Association Meeting. Polytrauma section. Tampa, FL. 2014 October 17.

Correspondence to Joseph T. Patterson, MD, 500 Parnassus Ave, MU-302 West, San Francisco, CA 94143 Tel: +415-353-2808; fax: +415-353-2248; e-mail: joseph.patterson@ucsf.edu.

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INTRODUCTION

Missed vascular injuries in lower extremity trauma may lead to a preventable lower extremity amputation. Computed tomography angiography (CTA) is an accurate and rapid diagnostic tool for detecting vascular injuries in lower extremity trauma, including arterial laceration, transection, dissection, thrombotic occlusion, pseudoaneurysm, arteriovenous fistula, and intimal flaps.1–5 Timely identification of such injuries by lower extremity CTA facilitates early intervention and may prevent amputation. Although lower extremity CTA is sensitive and specific for detecting these injuries, the cost, radiation exposure, and delay of care associated with lower extremity CTA limit its as a screening test for vascular injury in the trauma setting.1–6

Knowledge of when lower extremity CTA is likely to detect a lower extremity vascular injury, and when CTA is likely to affect treatment, would improve the utility of CTA as a confirmatory diagnostic tool in suspected lower extremity vascular injury. To this purpose, we describe the positive predictive values (PPV) of specific physical examination findings and injury patterns for predicting CTA detection of a vascular injury as well as the PPV of these examination and injury findings for vascular repair in lower extremity trauma patients.

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MATERIALS AND METHODS

This study was performed with approval from the Yale University Human Investigations Committee. A retrospective review was performed of consecutive trauma patients at a level 1 trauma center who underwent CTA of a lower extremity in the emergency department for suspected vascular injury between January 1, 2006, and December 31, 2012. The inclusion criteria were age over 16 yr, trauma activation, penetrating or blunt injury, injury site between inguinal crease or gluteal folds proximally and malleoli of the tibia and fibula distally, and CTA evaluation of suspected vascular injury of the involved lower extremity. Electronic medical records were reviewed by a panel of three for patient demographics, Glasgow Coma Scale (GCS), injury mechanism and pattern, Abbreviated Injury Scale, Injury Severity, Score and diagnostic vascular studies performed including ankle-brachial index (ABI), Doppler ultrasonography (DUS), and CTA. Subsequent vascular surgery or transcatheter intervention for the suspected vascular injury was noted. Physical examination findings of “hard signs”, “soft signs”, or no physical examination signs of ischemia or vascular injury on evaluation in the emergency department as previously-defined (Table 1).7,8 Injury patterns previously associated with a greater incidence of vascular injury were classified as “high-risk” (Table 2).4 Open combined tibial and fibular fractures were included as additional high-risk injury patterns not previously described.

TABLE 1

TABLE 1

TABLE 2

TABLE 2

Lower extremity CTA was considered negative in the absence of a vascular injury in the study report or with isolated findings of vessel spasm without other evidence of injury. CTA was considered to disagree with management if a positive CTA was contradicted by subsequent conventional angiography without intervention, vascular surgical or transcatheter intervention were performed despite a negative CTA, or if no intervention was performed after a positive CTA. A CTA study was considered ordered against practice guidelines when no signs of a vascular injury were present on physical examination and ABI was >0.9 or DUS was negative.8–10 Adverse events of CTA were defined as allergic contrast reaction and anaphylaxis, or contrast-induced nephropathy (25% or 0.5 mg/dL increase in serum creatinine from baseline within 48-72 hr of CTA intravenous contrast administration).11

The PPV of “any exam finding”, “any soft exam finding”, and “any hard exam finding” of CTA detection of a vascular injury and of subsequent vascular intervention were calculated among all patients. PPV of single examination findings also were calculated for specific examination findings with ≥10 occurrences. Additional PPV were calculated for “any exam finding”, “any soft exam finding”, and “any hard exam finding” stratified by low-risk or high-risk injury patterns. Vascular surgery or transcatheter intervention rates between patients with and without examination findings suggestive of lower extremity vascular injury were compared by Fisher’s exact test.

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RESULTS

Demographics of 72 trauma patients with a suspected vascular injury who met inclusion criteria are summarized in Table 3. Of 72 CTA studies, 40 (55.6%) were positive for some abnormal finding. Ten (13.9%) of the CTA studies led to a vascular intervention: nine (12.5%) patients underwent surgical repair or bypass and one (1.4%) received anticoagulation for an intimal injury. All patients who underwent vascular intervention had a positive CTA in addition to a pulseless foot or ABI<0.9. No patients with a positive CTA but palpable pulses or ABI>0.9 received underwent vascular intervention. Notably, five (36%) of 11 patients with soft signs of vascular injury, an ABI>0.9, and a high-risk pattern received treatment for a vascular injury detected by CTA. No patients with a negative CTA received treatment.

TABLE 3

TABLE 3

No patients underwent angiography after a negative CTA study. Conventional angiography uniformly agreed with all CTA findings. Surgical exploration of one CTA finding of peroneal artery discontinuity revealed a small (<1 mm) but intact peroneal artery. Two (2.7%) patients without either hard or soft signs of vascular injury were found to have a vascular injury detected by CTA, both of whom received no additional intervention and were discharged home without documented complication.

The PPV of physical examination findings for detection of a vascular injury by CTA and subsequent vascular intervention are shown in Table 4. The PPV of a CTA affecting treatment was significantly higher in the presence of high-risk injuries and hard-examination findings than in the presence of low-risk injuries and soft-examination findings (84.6%, 95% CI [54.6–98.1%] vs. 16.7%, 95% CI [3.6–41.1%]).

TABLE 4

TABLE 4

Lower extremity CTA was ordered in compliance with published guidelines in 53 (73.6%) trauma patients with suspected lower extremity vascular injury and was obtained against published recommendations and institutional protocol in three patients (4.2%) with no documented signs of vascular injury on physical examination and ABI>0.9 or negative DUS. None of these patients had a vascular injury detected on CTA or received treatment. CTA was obtained against published recommendations in 16 patients (22.2%) with signs of vascular injury and ABI>0.9 or negative DUS; three patients had positive CTA findings and one was started on anticoagulation therapy for an intraluminal hematoma of the popliteal artery.

CTA agreed with management in 95.8% of cases. Six of 72 (8.3%) limbs were amputated secondary to a vascular injury detected by CTA within 5 days of presentation. Four of 72 (5.6%) patients experienced contrast-induced nephropathy, all of whom recovered with supportive management.

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DISCUSSION

Lower extremity CTA is a costly and nephrotoxic diagnostic test that may delay the care of trauma patients with a suspected lower extremity vascular injury. However, CTA is a useful diagnostic test to confirm or rule out a suspected lower extremity vascular injury. In this series, physical examination and injury pattern were predictive of CTA detection of a vascular injury as well as subsequent vascular intervention for that injury by surgical or transcatheter methods.

The potential negative effects of CTA must be weighed against the expected clinical benefit for this population. Radiation exposure from lower extremity CTA (2.8-9.3 mSv whole body effective dose) is lower than conventional angiography (11.0-36.2 mSv; reference, 21.0–40.2 mSv for trauma screening chest/abdomen/pelvis).6,12–14 Adverse contrast-related events are reported in 4-6% of lower extremity CTA studies.6,15 Delays of care include approximately 6-10 min of scan time if added to trauma CT chest/abdomen/pelvis imaging and additional transport and preparation time for studies performed in isolation. Based on our data, CTA may be an appropriate and useful diagnostic addition to a screening trauma CT of the chest, abdomen, pelvis, head, brain, and cervical spine when physical examination and injury pattern have a high positive predictive value for detection and treatment of a vascular injury. We have summarized our interpretation of these findings in a clinical decision tool (Table 5) that may be helpful when deciding whether to order a CTA in a traumatized lower extremity.

TABLE 5

TABLE 5

The rate of positive findings on CTA is higher in our series than previously reported (56% compared to 25-44%). Conversely the rate of additional intervention was lower than previously described (25% compared to 40-86%).2,3,16,17 The higher utilization of CTA and lower rate of intervention may reflect institutional variance in practice as well as ordering of 26.4% of CTA studies against institutional guidelines.

A number of research groups and trauma associations have published indications for CTA in lower extremity trauma. The Western Trauma Association guideline for management of a mangled extremity provides a level 3 recommendation for the use of CTA as a confirmatory diagnostic test for vascular injury when ABI<0.9.10 The same guideline also recommends CTA as a primary screening test at the time of initial trauma CT screening independent of physical examination findings, ABI, or DUS results.10 Redmond et al. 8 described lower extremity CTA as a diagnostic test for vascular injury in the presence of arterial hemorrhage, distal ischemia, or ABI<0.9 with positive DUS.8 The Eastern Association for the Surgery of Trauma protocol, followed at our study site, recommends that patients with ABI>0.9 be discharged without further imaging, and the Eastern guidelines as well as Franz et al. advocate exploration without CTA in the presence of hard signs of vascular injury independent of injury pattern.9,18 Universal to these recommendations is that lower extremity CTA is not recommended in the absence of physical signs of vascular injury and ABI was >0.9 and/or DUS was negative.8–10 Our results support these recommendations.

One-third of patients in this series with soft signs of vascular injury, an ABI>0.9, and a high-risk pattern underwent subsequent vascular intervention. CTA studies in these patients were performed against the recommendation of Eastern Association for the Surgery of Trauma9 and the recommendations of Redmond et al. 8 by those recommendations, these patients would be discharged without CTA and their injuries would consequently be missed. We suggest that a high-risk injury pattern warrants a CTA to rule out vascular injury even in the presence of a normal ABI.

Physical examination findings alone may not be sufficient as a screening tool to undertake surgical or endovascular exploration of a potential vascular injury in a lower extremity trauma patient without diagnostic imaging confirmation.1,4,19,20 Examination findings in conjunction with an ABI>0.9 and DUS are sufficient to rule out vascular injury without CTA angiography (negative predictive values 96-100% and 99-100%, respectively).1,21–24 Clinical algorithms that advocate the use of ABI or DUS as screening tools before ordering a CTA study suggest that CTA is inappropriate when ABI and/or DUS are negative and physical examination is not suggestive of a vascular injury.2,3,7,8,10,16

This study has limitations, including the biases inherent to a retrospective case series of patients who received an intervention, without comparison to subjects who did not receive the intervention. We did not capture patients with signs of a vascular injury or high-risk injury pattern who did not receive a CTA, nor did we capture vascular injuries that were explored operatively without a preceding CTA. As a result, only the PPV (not the sensitivity, specificity, and negative predictive values) of physical examination findings could be calculated. DUS was not routinely performed and ABI not consistently documented and therefore neither were incorporated into our analysis. CTA was used as the reference standard for these analyses as opposed to open surgical or endovascular confirmation of injury. Patients discharged with a negative CTA may have experienced sequelae of a missed vascular injury.

In summary, CTA is useful for guiding clinical management of a suspected lower extremity vascular injury in a trauma patient, and the utility of CTA is improved by assessing the pretest PPV of vascular injury from injury pattern and physical examination. We have shown that CTA is not indicated in lower extremity trauma when physical examination fails to demonstrate signs of vascular injury. Published recommendations for the use of CTA in this setting are variable and may lead to missed injuries. Injury patterns at high risk for vascular injury with normal ABI may warrant CTA to rule out occult vascular injury. Real-world compliance with publication recommendations for the use of CTA in lower extremity appears moderate-to-high.

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Key Points

  • Injury mechanism and physical signs predict CTA detection as well as treatment of lower extremity vascular injuries in trauma patients.
  • Eastern Association for the Surgery of Trauma guidelines for CTA indications may miss some vascular injuries that merit surgical or transcatheter intervention.
  • CTA adds no diagnostic value in lower extremity trauma when no signs of vascular injury are present.
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Keywords:

CT angiography; CTA; lower extremity; vascular injury

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