ACL injuries in teenagers: what parents need to know

ACL injuries in children and adolescents have risen faster than in any other age group in Australia. Between 2000 and 2015, the rate of ACL reconstruction in Australians aged 5 to 14 rose by close to eight per cent every year, a steeper rise than in adults, and the reason this has become a common conversation in the rooms rather than an unusual one.

If your child has injured their knee, this page covers what the injury means, why the decision is different in a growing skeleton, and what the realistic timeline looks like.

Why the numbers have risen

Part of it is better recognition and better imaging. Most of it is not. Young athletes now specialise in one sport earlier, train year-round with fewer off-season breaks, and play at higher intensity for more months of the year. The peak rates in Australia fall in males aged 20 to 24 and females aged 15 to 19, and adolescent girls carry a higher rate than boys of the same age.

Recognising it

The history is usually characteristic: a non-contact pivot, landing or sudden change of direction; often an audible pop; the knee swells within a few hours; and the child cannot continue playing. Swelling that appears quickly after a knee injury is significant and should be assessed, even if the pain settles over the following days.

Not every unstable knee in a teenager is an ACL rupture. Kneecap dislocation produces a similar story and needs to be distinguished, as does a physeal (growth plate) injury, which is specific to skeletally immature patients.

What is different about a growing skeleton

The growth plates sit close to where the tunnels for an ACL graft are drilled. In a child with significant growth remaining, a standard adult reconstruction technique risks injuring the growth plate, which can cause a limb length difference or an angular deformity. Several techniques exist to avoid this, including physeal-sparing and partial transphyseal methods. The choice depends on the child’s skeletal maturity, which is assessed clinically and radiologically rather than from their birthday.

The older advice was to delay reconstruction until skeletal maturity and manage the child in a brace. That advice has largely reversed, because the delay was found to be associated with further meniscal and cartilage damage from repeated giving-way episodes. The current approach in most cases is to reconstruct, using a technique appropriate to the child’s skeletal age, rather than to wait.

The re-injury problem

This is the part that parents need to hear clearly. Young athletes who return to pivoting sport after ACL reconstruction have the highest rate of second ACL injury of any group, either a rupture of the graft or a tear of the other knee. Most of these happen in the first year back.

Two things reduce that risk, and both require patience:

• Not returning early. Re-injury rates fall substantially with each month of delay up to about nine months after surgery. A return at six months because the season is on is a poor trade.
• Meeting objective criteria before returning. Strength symmetry, hop testing and movement quality, measured rather than assumed. In published cohorts, patients who failed those criteria re-injured at around 38 per cent; patients who passed them almost never did.

A supplementary procedure called lateral extra-articular tenodesis, performed at the same time as the reconstruction, has been shown to reduce graft failure in high-risk patients, with young age and return to pivoting sport two of the main risk factors. Whether it is appropriate is discussed on a case-by-case basis.

The timeline parents should plan for

• Weeks 0–2: settle the knee, restore full extension, reduce swelling. Assessment and MRI.
• Weeks 2–6: pre-operative rehabilitation. A strong, straight, quiet knee going into surgery produces a better result coming out of it.
• Surgery, then a structured programme of roughly nine to twelve months.
• Return to pivoting sport at nine months at the earliest, and only after passing the testing.

Realistically, that means a season is lost. It is worth saying so at the start rather than allowing a family to build a plan around a return that is not safe.

Prevention, for the sibling and the team

Neuromuscular warm-up programmes, such as the FIFA 11+ and the netball and football equivalents, reduce ACL injury rates meaningfully in adolescent athletes when they are done consistently. They take about fifteen minutes and require no equipment. If your child plays a pivoting sport and their club does not run one, that is a conversation worth having with the coach.

Getting seen

A knee that swells quickly after a twisting injury in a young athlete should be assessed. A GP referral is required for the Medicare rebate. Dr Mooney consults at Orthopaedics 360 in Eastwood, and in Mount Gambier and Naracoorte.

If you are not sure how urgent it is, the hip and knee self-check takes a few minutes and points you to the right next step. A recent knee injury with swelling, giving way or loss of movement is seen as a priority.