ACL reconstruction in children and teens may take longer to fully heal than previously thought.
This article summarises findings from the study Knee Anterior Laxity and Graft Maturation After Transphyseal Anterior Cruciate Ligament Reconstruction, which highlights the relationship between ligament healing and knee laxity following surgery in skeletally immature patients.
ACL tears are increasingly common in children and adolescents involved in sports. The goal of reconstructive surgery is to restore knee stability and prevent long-term complications like meniscal injuries or early osteoarthritis. However, the biological healing of the graft, known as ligamentisation, remains poorly documented in young populations.
This prospective study conducted from 2017 to 2019 sheds light on how the anterior cruciate ligament graft matures over time in children. The research focused on 50 patients aged 9 to 16 who underwent transphyseal ACL reconstruction, a surgical technique that crosses the growth plates without affecting bone development. The graft used was a segment of the patient’s own semitendinosus tendon.
Before surgery, patients presented with a side-to-side difference in knee anterior laxity of 2.78 mm (a common sign of ACL deficiency). Postoperatively, measurements taken at 6, 12, and 24 months showed a progressive reduction in laxity, with values dropping to 1.59 mm, 1.80 mm and 1.30 mm, respectively. These improvements were statistically significant, indicating a good functional restoration of knee stability.
It is important to note that these results were consistent across both sexes and age groups, reinforcing the robustness of the surgical technique used.
MRI scans assessed graft healing using the Signal-to-Noise Quotient (SNQ) and the Howell classification, two standard tools to quantify tissue regeneration and ligament quality. The study revealed that SNQ values remained stable between 6 and 12 months post-op, with significant improvement only observed between 12 and 24 months (P=0.008). This confirms that graft maturation (meaning the transformation of the tendon into a ligament-like structure) is delayed in younger patients.
Surprisingly, there was no clear correlation between MRI signals and clinical knee laxity, suggesting that imaging alone may not be sufficient to determine readiness for returning to sport.
Even if the knee feels stable during movement tests at 6 or 12 months, the biological quality of the graft may still be insufficient. This is a crucial message for clinicians, patients and families: the feeling of "normal" knee function can be misleading.
The study advocates for a conservative approach when planning a return to sport. Decisions should not rely solely on the absence of laxity or on time passed since surgery. Instead, they must include a combination of clinical evaluation, imaging findings, and functional testing.
Professor Etienne Cavaignac, orthopaedic surgeon at Toulouse University Hospital and expert in ACL reconstruction, stresses the need for a tailored follow-up plan to reduce the risk of reinjury in young athletes.
This study shows that in children and adolescents, ACL graft maturation is a delayed process, with significant healing occurring only after one year post-op. Knee laxity may improve earlier, but that does not mean the graft is biologically ready. These findings highlight the importance of cautious and evidence-based return-to-sport protocols in young patients.
For expert surgical care and long-term follow-up, we strongly recommend consulting Professor Étienne Cavaignac, a leader in paediatric ACL reconstruction.
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