What pertinent clinical history should be obtained for a patient whose knee MRI reveals a medullary infarct of the distal femoral diaphysis?

Clinical History for Medullary Infarct in Distal Femoral Diaphysis

Obtain a detailed history of corticosteroid use, alcohol consumption, and underlying conditions associated with hypercoagulability or lipid disorders, as these are the primary risk factors for bone infarction. 1

Essential Risk Factor Assessment

Medication History

• Document current and past corticosteroid therapy, including dose (daily prednisolone ≥30 mg markedly increases risk), duration, and indication, as steroid therapy is one of the most common causes of osteonecrosis 1, 2
• Inquire about chemotherapy or radiation therapy exposure, both of which are established risk factors for bone infarction 1, 2
• Ask about cyclosporine use, which may reduce risk when used as a steroid-sparing agent 2

Substance Use and Metabolic Factors

• Quantify alcohol consumption history, as alcoholism is a major risk factor for both epiphyseal and metadiaphyseal osteonecrosis 1, 2, 3
• Screen for dyslipidemia and hyperlipidemia, which are common etiological factors in bone infarction 2, 3
• Calculate body mass index, as BMI >24 kg/m² is associated with worse outcomes in osteonecrosis 2

Underlying Medical Conditions

• Review history of HIV infection, as HIV patients have increased risk and may have asymptomatic multifocal disease 1, 2
• Ask about hematologic disorders including lymphoma, leukemia, blood dyscrasias, hemoglobinopathies, and hypercoagulability states 1, 2
• Document history of Gaucher disease or Caisson disease (decompression sickness) 1, 2
• Inquire about systemic lupus erythematosus, which is mentioned as a possible cause in the literature 3
• Ask about renal transplantation and dialysis duration, as prolonged dialysis before transplant increases risk 2

Symptom Characterization

Pain Assessment

• Determine if the patient has pain over the affected area, as approximately 30% of bone infarctions are symptomatic despite being traditionally considered asymptomatic 3
• Characterize pain as dull or aching if present, which is the typical pattern when metadiaphyseal infarcts become symptomatic 3
• Note that metadiaphyseal bone infarctions do not lead to subchondral fracture or secondary osteoarthritis, explaining their generally benign long-term course 1

Functional Impact

• Assess for any limitation in weight-bearing or mobility, though this is less common with diaphyseal infarcts compared to epiphyseal osteonecrosis 1

Multifocal Disease Screening

Bilateral and Multifocal Involvement

• Ask about pain or symptoms in other locations, particularly the contralateral femur, as bone infarctions are multiple and symmetrical in 60% of cases 3
• Screen for hip, knee, ankle, or shoulder pain, as patients with metadiaphyseal infarcts often have concurrent epiphyseal osteonecrosis (present in >50% of cases) that may be unrecognized 1, 3
• Document that femoral head osteonecrosis is bilateral in 70-80% of nontraumatic cases, and multifocal osteonecrosis commonly involves hip (68%), knee (44%), ankle (17%), and shoulder (15%) 1, 2

Trauma History

• Explicitly ask about recent or remote trauma to the affected limb, though post-traumatic forms of metadiaphyseal bone infarction are not described in the literature 3
• Distinguish from traumatic causes, as the absence of trauma history supports the diagnosis of idiopathic bone infarction 3

Age and Demographics

• Note patient age, as bone infarction typically affects adults in the third to fifth decades of life (mean age 49 years in one series) 3
• Document that age >40 years is associated with increased risk of complications in epiphyseal osteonecrosis, though this is less relevant for metadiaphyseal lesions 1, 2

Associated Conditions to Exclude

• Rule out arteriopathies and cytosteatonecrosis, which are mentioned as possible causes in the literature 3
• Consider that the true prevalence of osteonecrosis is vastly underestimated because many patients are asymptomatic, especially with metadiaphyseal cases 1

Critical Clinical Pitfalls

• Do not assume the lesion is isolated; actively search for multifocal disease through systematic questioning about other joint pain, as 77% of bone infarctions are located around the knees and frequently coexist with epiphyseal osteonecrosis 1, 3
• Recognize that conventional radiographs miss approximately 28% of bone infarctions (18 of 65 lesions in one series), so negative imaging elsewhere does not exclude multifocal disease 3
• Understand that metadiaphyseal infarcts have benign long-term sequelae compared to epiphyseal osteonecrosis, which helps guide prognostic discussions 1