Effect of Microvascular Disease on Re-amputation Risk after Unilateral Amputation due to Diabetes or Peripheral Arterial Disease: A Retrospective Cohort Study.

OBJECTIVE

The aim of this study was to evaluate the association between manifestations of microvascular disease (MVD) and other factors on re-amputation risk within 12 months following incident unilateral lower extremity amputation.

METHODS

This was a retrospective cohort study of 8 924 patients with first unilateral transmetatarsal, transtibial, or transfemoral amputation secondary to diabetes and or peripheral arterial disease, identified through a Veterans Affairs database. Re-amputation was defined as any subsequent ipsilateral soft tissue or bony revision or amputation to a higher level. The presence of MVD was determined using a composite variable that required the involvement of each subcomponent (neuropathy, nephropathy, and retinopathy), and also by evaluating each of the subcomponent MVD variables separately. Twenty-nine additional risk factors were evaluated in relation to the primary outcome of re-amputation. A competing risk analysis estimated the cumulative incidence of re-amputation. The effect of risk factors on re-amputation risk was estimated by computing subdistribution hazard ratios (sub-HRs) with 95% confidence intervals (CIs).

RESULTS

The twelve month re-amputation risk was 38.0% (transmetatarsal), 27.2% (transtibial), and 14.1% (transfemoral). The combined MVD variable was not significantly associated with re-amputation risk. However, re-amputation after transmetatarsal amputation was significantly elevated in patients with retinopathy, leukocytosis, or those who were on kidney dialysis, with the highest risk in those with all three (sub-HR 2.2, 95% CI 1.8 - 2.6). Similarly, for transtibial patients, the risk was higher in the presence of retinopathy, leukocytosis, and kidney dialysis, and in those with a prior ipsilateral revascularisation and those on warfarin. The highest risk was observed in those with all factors present (sub-HR 2.1, 95% CI 1.6 - 2.7).

CONCLUSION

This study identified an important association between the pre-amputation diagnosis of retinopathy and risk for subsequent failure of primary healing and need for re-amputation. Presence of retinopathy should be considered when evaluating potential failure of healing during amputation level decisions.