Bilateral distal femoral sclerosis in older women: a benign pattern to recognise

Design

Retrospective imaging series with age-matched controls

Population

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

Primary outcome

Imaging pattern, interobserver agreement and histological correlation

Effect

Lateral predominance in 73% of knees; κ ≥ 0.88; fat necrosis with dystrophic calcification on histology

Musculoskeletal radiologists reviewed knee radiographs from 2018 to 2023 and identified 30 women (mean age 76.7) with bilateral sclerotic lesions in the distal femur, excluding known bone disorders. They had 60 radiographs, 13 CTs, 10 MRIs and one histological specimen.

The sclerosis was lateral or mainly lateral in 73% of knees and central in the rest, with linear, nodular, popcorn-like or mixed morphology; two readers agreed almost perfectly (κ ≥ 0.88). On MRI, a reticulonodular fibrous-looking pattern followed the trabeculae within fat-signal marrow. A biopsied similar tibial lesion showed necrotic fat cells with dystrophic calcification, without osteonecrosis. Clinical and laboratory findings matched age-matched controls, and no lesion had aggressive features.

The authors propose a distinct benign pattern. That rests on 30 women and one specimen, so it is a pattern to recognise, not a proven rule.

In practice, symmetrical bilateral sclerosis with these features, fatty marrow and no aggressive signs in an older woman may reasonably be reported as likely benign, with comparison to prior films rather than reflex biopsy or serial imaging.

• Recognise bilateral, mainly lateral, linear or popcorn-like distal femoral sclerosis in older women.
• Check MRI for a reticular pattern within fat-signal marrow and absence of aggressive features.
• Consider reporting it as likely benign rather than recommending biopsy.
• Investigate further if the lesion is unilateral, enlarging, painful or has aggressive features.

Why it matters

Recognising a benign symmetrical pattern can spare older women biopsies and repeat scans.

Don't overread it

Thirty patients and a single specimen describe a pattern; they do not prove every such lesion is benign.

The statistics, in plain English

A kappa of 0.88 or more means two radiologists almost always agreed on location and morphology, which suggests the pattern is reproducible. It does not measure how often the pattern is benign.

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