Can Vascular Injury be Appropriately Assessed With Physical Examination After Knee Dislocation?

BACKGROUND:
Knee dislocations are rare injuries with potentially devastating vascular complications. An expeditious and accurate diagnosis is necessary, as failing to diagnose vascular injury can result in amputation; however, the best diagnostic approach remains controversial.

QUESTIONS/PURPOSES:
We asked: (1) What patient factors are predictors of vascular injury after knee dislocation? (2) What are the diagnostic utilities of palpable dorsalis pedis or posterior tibial pulses, and the presence of an ankle-brachial index (ABI) of 0.9 or greater?

METHODS:
A database at a Level I trauma center was queried for patients with evidence of knee dislocation, demographic information (age at the time of injury, sex, Injury Severity Score, BMI, mechanism of injury), and the presence of open injury were recorded. One-hundred forty-one patients underwent screening at initial presentation, of whom 26 (24%) underwent early vascular exploration based on an abnormal physical examination. One-hundred five (91%) of the remaining 115 patients were available at a minimum followup of 6 months (mean, 19 ± 10 months). In total, 31 unique patients were excluded, including 10 patients (7%) who were lost to followup before 6 months. Among the 110 patients who met inclusion criteria, the mean age and SD was 37 ± 13 years, and the Injury Severity Score was 15 ± 9. There were 71 males (65%). Logistic regression was used to determine independent correlates of vascular injury. The vascular examination was reviewed for the presence of a palpable pulse in the dorsalis pedis artery, the presence of a palpable pulse in the posterior tibial artery, and whether the ABI in the dorsalis pedis was 0.9 or greater. Contingency tables were generated to assess the sensitivity, specificity, and accuracy of physical examination maneuvers. The physical examination was collectively regarded as "normal" when both pulses were palpable and the ABI was 0.9 or greater. The initial physical examination as just described was considered the diagnostic test being evaluated in this study; "positive" tests were evaluated by and confirmed at vascular surgery, and 6 months clinical followup without symptoms or progressive signs of vascular injury confirmed the absence of injury in the remainder of the patients. Contingency tables were generated again to assess the sensitivity, specificity, and accuracy of the combined physical examination.

RESULTS:
Increased BMI (odds ratio [OR], 1.077; 95% CI, 1.008-1.155; p = 0.033) and open injuries (OR, 3.366; 95% CI, 1.008-11.420; p = 0.048) were associated with vascular injury. No single physical examination maneuver had a 100% sensitivity for ruling out vascular injury. A normal physical examination (palpable pulses and ABI ≥ 0.9) had 100% sensitivity for ruling out vascular injury.

CONCLUSIONS:
Increased BMI and the presence of open dislocation are associated with a greater risk for vascular injury after knee dislocation. The combination of a palpable dorsalis pedis and posterior tibial pulse combined with an ABI of 0.9 or greater was 100% sensitive for the detection of vascular injury based on clinical followup at 6 months.

LEVEL OF EVIDENCE:
Level III, diagnostic study.