BACKGROUND: Limb compression bandages, such as Unna boots, successfully treat 30% to 60% of venous leg ulcers. The authors of this study attempted to create a simple model to predict which patients’ ulcers will heal using this therapy.
POPULATION STUDIED: All patients were drawn from a dermatology skin ulcer clinic. A training group of 260 consecutive patients with chronic venous leg ulcers was used to develop predictive models. Venous ulcers were defined as wounds in the “gaiter area” of the limb from the mid-calf to 1 inch below the malleolus. All patients had lower leg edema and cutaneous evidence of venous disease. second group of 219 patients enrolled in the control arm of 2 randomized controlled trials testing skin allograft versus compression was used to validate the rule. Ulcers in this study were at least 4 weeks old and between 0.5 and 200 cm2 in area.
STUDY DESIGN AND VALIDITY: This was a cohort study for developing and validating a clinical decision rule. Prognostic models were created with 10 risk factors and statistically analyzed for their ability to correctly predict wound healing. The models were simplified by dropping prognostic factors one by one from the model, as long as the ability to predict healing was not affected. All of the models were evaluated by measuring the area under the receiver-operating characteristic (ROC) curve. By definition, an area closer to 1 indicates a better ability to distinguish which ulcers will heal. An area of 0.5 indicates a worthless test or rule. The most accurate model from the training group was evaluated using the validation group.
OUTCOMES MEASURED: The primary outcome measure was the ability of a model to predict wound healing within 24 weeks as measured by the area under the ROC curve.
RESULTS: Overall, 65% of ulcers from the training group and 56% of ulcers from the validation group healed by 24 weeks. All of the candidate models had areas under the ROC curve greater than 0.80, meaning that the model discriminated between ulcers that did and did not heal more than 80% of the time. The simplest model, which gave a score of 1 point for a wound area greater than 5 cm2 (measured by a template) and 1 point for wound age greater than 6 months, correctly predicted healing 87% of the time. Ulcers with a score of 0 healed in 95% of the validation group, while ulcers with a score of 1 healed in 73% of the validation group.
This simple rule accurately predicts which venous stasis ulcers will heal in 6 months using compression bandages. Score 1 point for a wound older than 6 months and 1 point if the area of the wound is greater than 5 cm2 as measured by a template. Ulcers with a score of 0 are 95% likely to heal, while those with a score of 2 are only 37% likely to heal. Patients whose ulcers rate a score of 0 can be treated with compression bandages and are unlikely to need referral. Whether newer therapies will add benefit for patients with a score of 1 or 2 is unknown. Early referral of patients with ulcers with a score of 2 will likely depend on local practice.