A cohort study of 4,190 patients treated with low-intensity pulsed ultrasound (LIPUS): findings in the elderly versus all patients

Abstract

Background: Patient age is one of many potential risk factors for fracture nonunion. Our hypothesis is that older patients (≥ 60) with fracture risk factors treated with low-intensity pulsed ultrasound (LIPUS) have similar heal rate (HR) to the population as a whole. We evaluate the impact of age in conjunction with other risk factors on HR in LIPUS-treated patients with fresh fracture (≤ 90 days old).

Methods: The Exogen Bone Healing System is a LIPUS device approved in 1994 to accelerate healing of fresh fracture. After approval, the FDA required a Post-Market Registry to assess performance. Patient data collected from October 1994 until October 1998 were individually reviewed and validated by a registered nurse. Four distinct data elements were required to report a patient: date fracture occurred; date treatment began; date treatment ended; and a dichotomous outcome of healed v. failed, by clinical and radiological criteria. Data were used to calculate two derived variables; days to treatment (DTT) and days on treatment (DOT). Every validated fresh fracture patient with DTT, DOT, and outcome is reported.

Results: The validated registry had 5,765 patients with fresh fracture; 73% (N = 4,190) are reported, while 13% of patients were lost to follow-up, 11% withdrew or were non-compliant, and 3% died or are missing outcome. Among treatment-compliant patients, HR was 96.2%. Logistic estimates of the odds ratio for healing are equivalent for patients age 30 to 79 years and all age cohorts had a HR > 94%. Open fracture, current smoking, diabetes, vascular insufficiency, osteoporosis, cancer, rheumatoid arthritis, and prescription NSAIDs all reduced HR, but older patients (≥ 60) had similar HRs to the population as a whole. DTT was significantly shorter for patients who healed (p < 0.0001).

Conclusions: Comorbid conditions in conjunction with aging can reduce fracture HR. Patients with fracture who used LIPUS had a 96% HR, whereas the expected HR averages 93%. Time to treatment was significantly shorter among patients who healed (p < 0.0001), suggesting that it is beneficial to begin LIPUS treatment early. Older patients (≥ 60) with fracture risk factors treated with LIPUS exhibit similar heal rates to the population as a whole.

Figure 1

Summary of the effect of patient age on heal rate (%). The heal rate (HR) for each decade in shown, together with the upper and lower 95% confidence interval (CI) for each HR estimate. The HR is significantly higher than the overall HR only in patients age 20–29 years of age (p < 0.003); the HR did not differ significantly by age among patients older than age 30.

Figure 2

Effect of age and BMI on heal rate (HR). HR shows a decreasing trend with increasing weight, but HR tends to cluster by age, except in obese patients more than 60 years old. This suggests that BMI generally has more impact on HR than does patient age.