Table 4.
Cox Regression Estimates of the Association between Risk Factors and Hazard of Death within One Year.
| Patient Characteristic | Hazard Ratio (95% CI) | p Value |
|---|---|---|
| Age | 1.00 (0.98–1.03) | 0.75 |
| Male (Ref: Female) | 0.41 (0.20–0.83) | 0.01 |
| Non-white (Ref: White) | 0.68 (0.33–1.37) | 0.28 |
| Ambulatory status at index (Ref: Ambulatory) | ||
| Ambulatory with assistance | 3.76 (1.11–12.78) | 0.03 |
| Non-ambulatory | 3.65 (0.78–17.03) | 0.10 |
| Living situation (Ref: Home) | ||
| Other | 0.44 (0.08–2.37) | 0.34 |
| Medical history | ||
| Stroke (Ref: No) | 0.45 (0.10–1.98) | 0.29 |
| Coronary artery disease (Ref: No) | 2.97 (1.31–6.71) | 0.01 |
| Myocardial infarction (Ref: No) | 1.91 (0.86–4.26) | 0.11 |
| Congestive heart failure (Ref: No) | 3.51 (1.64–7.51) | 0.001 |
| Hyperlipidemia (Ref: No) | 0.90 (0.45–1.80) | 0.76 |
| Atrial fibrillation (Ref: No) | 2.32 (0.78–6.86) | 0.13 |
| Chronic obstructive pulmonary disease (Ref: No) | 1.98 (0.78–5.05) | 0.15 |
| End-stage renal disease (Ref: No) | 5.35 (2.51–11.43) ‡ | <0.001 |
| Malignancy (Ref: No) | 1.46 (0.62–3.46) | 0.39 |
| Smoking status (Ref: Never) | ||
| Former | 0.61 (0.27–1.35) | 0.22 |
| Current | 1.09 (0.31–3.78) | 0.89 |
| Medications | ||
| Statin (Ref: No) | 1.59 (0.66–3.87) | 0.30 |
| Antiplatelet (Ref: No) | 1.00 (0.47–2.13) | 1.00 |
| Anticoagulation (Ref: No) | 0.73 (0.30–1.78) | 0.49 |
| Dual antiplatelet (Ref: No) | 1.85 (0.85–4.03) | 0.12 |
| Optimal medical therapy (Ref: No) | 1.32 (0.63–2.73) | 0.46 |
| Non-invasive vascular testing | ||
| Abnormal waveform—femoral (Ref: Multiphasic) | 0.93 (0.11–7.77) | 0.95 |
| Abnormal waveform—popliteal (Ref: Multiphasic) | 1.57 (0.49–5.04) | 0.45 |
| Abnormal waveform—ankle (Ref: Multiphasic) | 1.35 (0.62–2.94) | 0.45 |
| ABI (Ref: 0.8–1.4) | ||
| 0.5–0.8 | 1.55 (0.44–5.42) | 0.50 |
| ≤0.5 | 0.82 (0.19–3.60) | 0.79 |
| Invalid | 3.48 (1.17–10.36) | 0.03 |
| Toe pressure (Ref: ≥30 mm Hg) | ||
| <30 mm Hg | 2.56 (0.78–8.42) | 0.12 |
| 0 mm Hg | 2.61 (0.89–7.68) | 0.08 |
| Angiographic findings Patent genicular arteries (Ref: 4 or 5) |
||
| ≤3 | 0.54 (0.21–1.39) | 0.20 |
| WIfI 1-year amputation risk (Ref: Very/low risk) | ||
| Moderate/high risk | 3.88 (0.84–17.80) | 0.08 |
| Amputation type (Ref: Toe) | ||
| Transmetatarsal | 1.86 (0.68–5.05) | 0.23 |
| Below-knee | 0.97 (0.38–2.46) | 0.95 |
| Through- or above-knee | 1.26 (0.49–3.24) | 0.63 |
| Indication (Ref: Dry gangrene) | ||
| Any infection | 0.40 (0.17–0.96) | 0.04 |
| Nonhealing wound or rest pain | 0.78 (0.24–2.57) | 0.68 |
| Infection (Ref: None) | 1.29 (0.52–3.22) | 0.58 |
| Partially open or open (Ref: Closed) | 0.99 (0.40–2.45) | 0.99 |
| Revascularization prior to or concomitant to index amputation (Ref: No) | 0.81 (0.36–1.80) | 0.60 |
| Revascularization after index amputation (Ref: No) | 0.51 (0.16–1.65) | 0.26 |
| Debridement after index amputation (Ref: No) | 0.51 (0.12–2.12) | 0.35 |
| UHRA | 1.87 (0.80–4.37) | 0.24 |
N = 203 index amputations (ankle disarticulation excluded). N in estimation sample may be smaller due to case-wise deletion of missing data and/or small cells. CI, confidence interval; ABI, ankle-brachial index; WIfI, wound, infection, and ischemia index. All variables measured at index. Parameter estimates are from Cox regression models controlling for amputation type, sex, race, and age. All other patient characteristics were included in models for each one separately due to the small sample size. ‡, remains significant after Bonferroni correction for 35 tests (implies lowering p < 0.05 to p < 0.0014).