After anterior cruciate ligament (ACL) reconstruction, the bone tunnels drilled to secure the graft can gradually widen over time. This phenomenon, known as ACL tunnel widening, is one of the most commonly cited reasons for performing revision surgery in two stages: first filling the tunnels with bone graft, then reconstructing the ligament several months later. But this approach significantly lengthens the patient’s journey, requiring two operations, two anaesthetics and an extended rehabilitation period.
A large-scale study led by Prof. Cavaignac and the SANTI Study Group challenges this practice. Entitled Influence of Preoperative Tunnel Widening On the Outcomes of a Single Stage–Only Approach to Every Revision Anterior Cruciate Ligament Reconstruction: An Analysis of 409 Consecutive Patients From the SANTI Study Group and published in The American Journal of Sports Medicine, this research analyses the clinical outcomes of 409 patients who all underwent single-stage revision, regardless of the degree of tunnel enlargement. The findings invite a rethink of the two-stage approach. For the full dataset and statistical analyses, consult the complete study.
What is tunnel widening after ACL reconstruction?
During anterior cruciate ligament reconstruction, the surgeon drills two tunnels into the bone, one in the tibia and one in the femur, to anchor the new graft. In the months or years that follow, these tunnels can enlarge. The term ACL tibial tunnel widening refers specifically to the tibial tunnel, though the phenomenon can affect both tunnels.
Several mechanisms explain this tunnel widening after ACL reconstruction. Among them, the windscreen wiper effect plays a significant role: the graft performs repetitive micro-movements inside the tunnel, progressively eroding the bone wall. Tunnel widening and the windscreen-wiper effect in ACL graft failure are recognized mechanisms.
When revision surgery becomes necessary, the presence of widened tunnels (diameter of 12 mm or above) presents a technical challenge: how can a new graft be securely fixed in compromised bone? The conventional answer is a two-stage procedure. Prof. Cavaignac’s study explores an alternative.
How the study was conducted: 409 patients analysed
The study included 409 consecutive patients who underwent ACL revision surgery, with a mean follow-up of 69.6 months (approximately five and a half years). Every patient was operated on in a single surgical stage using an outside-in drilling technique, which allows the surgeon to create new tunnels whilst avoiding the old ones.
The researchers then compared two groups based on preoperative radiographs:
| Group | Criterion | Number of patients |
| Group A | Both tunnels below 12 mm | 111 |
| Group B | At least one tunnel 12 mm or above | 247 |
Outcomes were assessed across several parameters: knee stability, validated functional scores (IKDC, KOOS, Lysholm, Tegner, ACL-RSI), graft re-rupture rates and reoperation rates. The complete study details the methodology and statistical analyses used.
Results that support single-stage revision
The results are clear-cut. Across all 409 patients, the side-to-side anteroposterior laxity difference (the abnormal forwards-backwards play of the knee) dropped from 7.7 mm before surgery to just 1.2 mm at two years. This improvement, which was statistically significant (p < 0.001), reflects restored stability.
Mean functional scores (IKDC, KOOS) all exceeded the thresholds for the Patient Acceptable Symptom State, the level at which patients consider themselves satisfied with the condition of their knee.
The most striking finding: no significant difference was observed between Group A (narrow tunnels) and Group B (widened tunnels) on any of the measured criteria:
- Knee stability
- Graft rupture rate
- Reoperation rate unrelated to graft rupture
- Functional scores (IKDC, KOOS, Lysholm, Tegner, ACL-RSI)
In other words, preoperative ACL tunnel widening did not negatively affect the outcomes of single-stage surgery.
What this means for patients awaiting ACL revision
This study provides strong evidence in favour of a simplified treatment pathway. If the outside-in technique delivers excellent results even when tunnels are widened, the indication for two-stage surgery could be reconsidered in many cases.
For the patient, the potential benefits of a single-stage approach are tangible:
- One surgical procedure instead of two
- A single period of anaesthesia and hospitalisation
- A shorter overall recovery time
- A quicker return to daily activities and sport
Of course, every situation remains individual, and the surgical decision depends on numerous factors assessed by the operating surgeon. But with 409 patients and a mean follow-up of nearly six years, this study represents one of the largest series published on the subject.
Conclusion & Findings
This study from the SANTI Study Group, led by Prof. Cavaignac, provides robust evidence that revision anterior cruciate ligament reconstruction can be performed in a single surgical stage without compromising outcomes, even when the tunnels are widened. We encourage you to explore Prof. Cavaignac’s other published scientific studies, which continue to advance evidence-based knee surgery.
If you are facing the prospect of ACL revision surgery, Prof. Cavaignac is a surgeon who combines scientific rigour with clinical expertise to offer each patient tailored care informed by the latest evidence.