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BACKGROUND Patients with incidentally found musculoskeletal lesions are regularly referred to orthopaedic oncology. Most orthopaedic oncologists understand that many incidental findings are nonaggressive and can be managed nonoperatively. However, the prevalence of clinically important lesions (defined as those indicated for biopsy or treatment, and those found to be malignant) remains unknown. Missing clinically important lesions can result in harm to patients, but needless surveillance may exacerbate patient anxiety about their diagnosis and accrue low-value costs to the payor. QUESTIONS/PURPOSES (1) What percentage of patients with incidentally discovered osseous lesions referred to orthopaedic oncology had lesions that were clinically important, defined as those receiving biopsy or treatment or those found to be malignant? (2) Using standardized Medicare reimbursements as a surrogate for payor expense, what is the value of reimbursements accruing to the hospital system for the imaging of incidentally found osseous lesions performed during the initial workup period and during the surveillance period, if indicated? METHODS This was a retrospective study of patients referred to orthopaedic oncology for incidentally found osseous lesions at two large academic hospital systems. Medical records were queried for the word "incidental," and matches were confirmed by manual review. Patients evaluated at Indiana University Health between January 1, 2014, and December 31, 2020, and those evaluated at University Hospitals between January 1, 2017, and December 31, 2020, were included. All patients were evaluated and treated by the two senior authors of this study and no others were included. Our search identified 625 patients. Sixteen percent (97 of 625) of patients were excluded because their lesions were not incidentally found, and 12% (78 of 625) were excluded because the incidental findings were not bone lesions. Another 4% (24 of 625) were excluded because they had received workup or treatment by an outside orthopaedic oncologist, and 2% (10 of 625) were excluded for missing information. A total of 416 patients were available for preliminary analysis. Among these patients, 33% (136 of 416) were indicated for surveillance. The primary indication for surveillance included lesions with a benign appearance on imaging and low clinical suspicion of malignancy or fracture. A total of 33% (45 of 136) of these patients had less than 12 months of follow-up and were excluded from further analysis. No minimum follow-up criteria were applied to patients not indicated for surveillance because this would artificially inflate our estimated rate of clinically important findings. A total of 371 patients were included in the final study group. Notes from all clinical encounters with orthopaedic and nonorthopaedic providers were screened for our endpoints (biopsy, treatment, or malignancy). Indications for biopsy included lesions with aggressive features, lesions with nonspecific imaging characteristics and a clinical picture concerning for malignancy, and lesion changes seen on imaging during the surveillance period. Indications for treatment included lesions with increased risk of fracture or deformity, certain malignancies, and pathologic fracture. Diagnoses were determined using biopsy results if available or the documented opinion of the consulting orthopaedic oncologist. Imaging reimbursements were obtained from the Medicare Physician Fee Schedule for 2022. Because imaging charges vary across institutions and reimbursements vary across payors, this method was chosen to enhance the comparability of our findings across multiple health systems and studies. RESULTS Seven percent (26 of 371) of incidental findings were determined to be clinically important, as previously defined. Five percent (20 of 371) of lesions underwent tissue biopsy, and 2% (eight of 371) received surgical intervention. Fewer than 2% (six of 371) of lesions were malignant. Serial imaging changed the treatment of 1% (two of 136) of the patients, corresponding to a rate of one in 47 person-years. Median reimbursements to work up the incidental findings analyzed was USD 219 (interquartile range USD 0 to 404), with a range of USD 0 to 890. Among patients indicated for surveillance, the median annual reimbursement was USD 78 (IQR USD 0 to 389), with a range of USD 0 to 2706. CONCLUSION The prevalence of clinically important findings among patients referred to orthopaedic oncology for incidentally found osseous lesions is modest. The likelihood of surveillance resulting in a change of management was low, but the median reimbursements associated with following these lesions was also low. We conclude that after appropriate risk stratification by orthopaedic oncology, incidental lesions are rarely clinically important, and judicious follow-up with serial imaging can be performed without incurring high costs. LEVEL OF EVIDENCE Level III, therapeutic study.