- Design
- Retrospective cohort with penalised logistic regression, minimum 6-year follow-up
- Population
- 581 patients after primary hamstring-autograft ACL reconstruction
- Primary outcome
- ACL graft rerupture
- Effect
- OR 1.28 per degree of slope (95% CI 1.10–1.47); OR 0.91 per year of age (0.87–0.95)
This retrospective cohort followed 581 patients for at least six years after primary ACL reconstruction with hamstring autograft, some with lateral extra-articular tenodesis. There were 38 graft reruptures.
Each extra degree of posterior tibial slope raised the odds of rerupture by about 28%, and each extra year of age lowered them by about 9%. The relative effect of slope did not change with age. But because young patients start from a much higher baseline, the absolute numbers diverged sharply: with a slope of 15 degrees, predicted rerupture risk was about 37% at 18 and about 4% at 45.
The authors estimated that predicted risk fell below 10% at about age 27 for a 12-degree slope and about 35 for a 15-degree slope. Those thresholds come from a model fitted to a modest number of events, so treat them as a guide rather than a rule.
In practice, a steep slope in a teenager is a different problem from the same slope in a 45-year-old. Slope-reducing osteotomy and added lateral procedures carry their own costs, and this study supports concentrating them on young patients with steep slopes.
- Measure posterior tibial slope on a lateral radiograph before primary ACL reconstruction.
- Weigh age and slope together when counselling about rerupture risk.
- Consider augmentation or slope-correcting surgery mainly for young patients with steep slopes.
- Do not apply the age thresholds rigidly; they come from a model with 38 events.
- Record slope in the operation note so revision surgeons have it.
Why it matters
It turns a single slope cut-off into an age-adjusted judgement about who needs more than a standard reconstruction.
Don't overread it
Retrospective, single-system cohort with few events; the age thresholds are estimates, not validated cut-offs.
The statistics, in plain English
An odds ratio of 1.28 per degree means each extra degree multiplies the odds by about 1.3, so three degrees roughly doubles them. Absolute risks such as 36.6% are model predictions, not observed rates, and with only 38 reruptures the uncertainty around them is wide.
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