Diagnosing pedal osteomyelitis: testing choices and their consequences

To compare the efficacies and cost-effectiveness of four strategies for the management of suspected pedal osteomyelitis in the setting of vascular impairment: 1) therapeutic trial of short-term antibiotics for presumed cellulitis without osteomyelitis (short); 2) technetium bone scanning followed by either short-term therapy if negative or either a biopsy or aggressive long-term intravenous therapy if positive (scan); 3) bone biopsy followed by long-term intravenous therapy if positive or short-term therapy if negative (biopsy); and 4) immediate long-term intravenous antibiotics for presumed osteomyelitis (long).

Decision analysis and cost-effectiveness analysis with sensitivity analyses. The main outcomes states are amputation and the resource expenditures associated with bone scans, biopsies, and therapies.

The authors obtained estimates of test accuracy from literature review and summarized them using newly developed meta-analytic techniques.

The optimal decision depends heavily on the estimated probability of osteomyelitis at presentation. At very low probabilities, the short-term strategy is preferred. When the probability of osteomyelitis is from 2% to 8%, the lowest amputation rate occurs when one does a diagnostic scan. From 8% to 50%, the best outcomes follow biopsy. At probabilities higher than 50%, the preferred strategy is long-term antibiotics. However, the differences in outcomes are quite small even when osteomyelitis is a virtual certainty.

Over the whole range of prior probabilities, the short-term strategy is the least expensive. At very low probabilities, it dominates the other strategies. When the likelihood of osteomyelitis is higher (10-20%), scanning results in outcomes and cost-effectiveness ratios comparable to those of immediate biopsy and is less invasive. When the probability of osteomyelitis is 50%, biopsy is quite cost-effective compared with all the other strategies (cost-effectiveness ratio = $15,502 per amputation averted) and is preferred to the scan strategy. When the confidence that a patient has osteomyelitis is very high (> 90% probability), the improved outcomes associated with long-term antibiotics are achieved with little additional expense and with favorable cost-effectiveness ratios compared with those of the other strategies.