Eight-point score predicts osteonecrosis after femoral neck screws in under-65s

Design

Retrospective multicentre prognostic study

Population

1,012 adults aged 18 to 65 with femoral neck fractures fixed with three cannulated screws

Primary outcome

Osteonecrosis of the femoral head at 2 years or more

Effect

4% (scores 0 to 3) vs 42% (scores 6 to 8); AUC 0.80 vs 0.70 for Garden

A retrospective study from three Chinese centres in Clinical Orthopaedics and Related Research (published 22 September) included 1,012 adults aged 18 to 65 whose femoral neck fractures were fixed with three cannulated screws, all followed for at least two years. Osteonecrosis of the femoral head developed in 21%.

Five preoperative features were retained in the FNF-ON8 score: age 45 or over (1 point), displacement (3), comminution (1), a superior subcapital fracture line (2) and an inferior subcapital fracture line (1). Osteonecrosis occurred in 4% of patients scoring 0 to 3 and 42% of those scoring 6 to 8. The score discriminated better than the Garden classification (AUC 0.80 vs 0.70), and among displaced fractures a score of 6 or more still carried about five times the odds.

In a young patient, the choice between head preservation and arthroplasty, and the intensity of follow-up imaging, hinge on osteonecrosis risk. The score uses only the injury radiographs and age, so it can inform consent before surgery. It has not been externally validated and was derived with one fixation method, so treat it as an aid to counselling, not a decision rule.

• Record age, displacement, comminution and the position of the fracture line on preoperative imaging in under-65s with femoral neck fractures.
• Use a high score to frame consent discussions about osteonecrosis risk and the possibility of later arthroplasty.
• Consider closer imaging follow-up for patients scoring 6 or more after head-preserving fixation.
• Reassure low scorers that their osteonecrosis risk in this cohort was about 4%, while continuing routine follow-up.

Why it matters

It gives a number to a risk that otherwise rests on the Garden grade and the surgeon's impression.

Don't overread it

The score was derived and tested in the same retrospective cohort with one implant; it needs external validation before guiding treatment choice.

The statistics, in plain English

An AUC of 0.80 means that, given one patient who developed osteonecrosis and one who did not, the score ranks them correctly about 80% of the time, against 70% for the Garden grade. A negative predictive value of 0.96 at the low threshold means a score below 4 rarely missed osteonecrosis in this cohort.

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