Bilateral distal femoral sclerosis in older women: a likely benign pattern

Design

Retrospective descriptive imaging series with age-matched controls

Population

30 women, mean age 76.7, with bilateral distal femoral sclerotic lesions

Primary outcome

Radiographic, CT, MRI and histological features

Effect

Lateral predominance in 73%; fat-signal marrow on MRI; fat necrosis with dystrophic calcification on histology

A retrospective series in European Radiology (7 October) describes 30 women, mean age 77, with sclerotic lesions in both distal femurs on knee radiographs, after excluding known skeletal disorders. Two musculoskeletal radiologists assessed 60 radiographs, 13 CTs and 10 MRIs, and one histological sample from a similar tibial lesion was reviewed.

The changes were exclusively or mainly lateral in about three-quarters of knees and linear, nodular, popcorn-like or mixed in shape, with near-perfect agreement between readers (kappa 0.88 or more). On MRI the lesions showed a reticular, fibrous-looking pattern following the trabeculae within marrow of fat signal on T1 and T2. The sampled lesion showed necrotic fat cells with dystrophic calcification, without osteonecrosis or extensive new bone. Blood tests did not differ from age-matched controls.

Bilateral sclerotic marrow lesions in an older woman often prompt a bone scan, MRI or biopsy to exclude metastasis or a cartilage tumour. This pattern, if recognised, may spare some of that. The evidence is a small descriptive series with one histological specimen, so a lesion with any aggressive feature, pain or a cancer history still needs standard workup.

• Consider a benign fat-necrosis pattern when an older woman has symmetrical, mainly lateral distal femoral sclerosis without aggressive features.
• Look for fat-signal marrow with a reticular trabecular pattern on MRI, which supports the benign interpretation.
• Compare both knees; bilateral, symmetrical change favours this pattern over metastasis.
• Work up any lesion with cortical destruction, periosteal reaction, soft-tissue mass, pain or a known primary cancer in the usual way.
• Describe the pattern in the report so the referrer is not prompted towards unnecessary biopsy.

Why it matters

Recognising a benign pattern on knee radiographs can prevent a cascade of scans and a biopsy in older women.

Don't overread it

This is a 30-patient descriptive series with one histological sample; it describes a pattern rather than proving it is always benign.

The statistics, in plain English

A kappa of 0.88 or more means the two radiologists almost always agreed on the lesion's shape, so the pattern is reproducible. It does not measure how often the pattern is correctly separated from malignancy.

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