What is LET and how has it improved ACL reconstruction outcomes?

If you have been told you need ACL reconstruction, or if you have looked into the topic at all, you may have come across the term LET. It sounds technical, and the acronym does not help — but the concept behind it is straightforward, and the evidence supporting its use in certain patients is now compelling.

What does LET stand for?

LET stands for lateral extra-articular tenodesis. It is a supplementary procedure performed at the same time as ACL reconstruction, not instead of it. While the ACL graft reconstructs the torn ligament inside the knee joint, LET adds a secondary restraint on the outside of the knee to address rotational instability — a component of instability that the ACL graft alone does not fully control in some patients.

The goal of LET is to reduce the risk of graft failure and re-rupture, particularly in patients who are at the highest risk of that happening.

The anatomy: what LET actually does

The ITB — the iliotibial band, a thick band of connective tissue running down the outside of the thigh — provides the raw material for a LET. A strip of the ITB is harvested from its lower end, tunnelled beneath the lateral collateral ligament, and fixed to the outer surface of the tibia at a bony landmark called Gerdy's tubercle. This creates a new restraint on the lateral side of the knee that limits how far the tibia can rotate inward — the motion that places the ACL graft under the greatest stress during pivoting and cutting movements.

The pivot shift phenomenon — the giving way sensation that characterises ACL deficiency — is driven largely by this rotational instability. By controlling tibial rotation more effectively, LET reduces the forces that would otherwise load the graft and potentially cause it to fail.

A procedure with a long history

LET is not a new idea. Lateral extra-articular procedures were described in the orthopaedic literature decades ago and were used widely in the 1970s and 1980s. They were largely set aside when intra-articular ACL reconstruction became the standard, partly because the early versions were used alone (without an ACL graft) and partly because the evidence base for the combined approach was not yet established.

The procedure has been revived over the past decade, not as a fashion, but because high-quality evidence began to catch up with clinical intuition. We now have Level 1 randomised controlled trial data to guide when and for whom LET should be used.

The STABILITY trial

The landmark piece of evidence is the STABILITY trial, a large, well-designed randomised controlled trial that compared ACL reconstruction alone versus ACL reconstruction with LET in young, active patients returning to pivoting sport. The results were striking.

In the trial, patients who received LET alongside their ACL reconstruction had a graft failure rate of approximately 11% at two years, compared with approximately 25% in those who had ACL reconstruction alone. That represents a roughly 50% reduction in graft failure in a population that is already at high risk.

These are not minor differences. For a young athlete, a re-rupture is not just a setback — it carries significant risks to long-term knee health, extended time away from sport, and a further operation. Any procedure that meaningfully reduces that risk deserves serious consideration.

The STABILITY trial showed roughly a 50% reduction in graft failure rates in high-risk patients who received LET alongside ACL reconstruction.

Who benefits most from LET?

LET is not recommended for every ACL patient. The evidence supports its use most strongly in patients who have several of the following characteristics:

Age under 25. Younger patients have higher re-rupture rates across the board, and the absolute benefit of LET is greatest in this group.

High-level athletes returning to pivoting sport. Football, basketball, netball, soccer, rugby — any sport involving cutting, jumping, and directional change. The rotational demands are highest in these activities.

High-grade pivot shift pre-operatively. The pivot shift test assesses rotational instability. Patients with a more pronounced pivot shift are at greater risk of ongoing instability after standard ACL reconstruction, and benefit more from the addition of LET.

Generalised ligament laxity. Patients who are naturally more flexible throughout their joints tend to place greater demands on the ACL graft, and the additional rotational control provided by LET is particularly valuable.

Contralateral ACL injury. A history of ACL tear in the opposite knee suggests an underlying susceptibility that warrants a more robust reconstruction approach.

What does the procedure involve?

LET adds a relatively small amount to the overall operation. It is performed through a separate small incision on the outer side of the knee and typically takes approximately 15 to 20 additional minutes. A carefully measured strip of ITB is prepared, routed beneath the lateral collateral ligament, and fixed with a small bone anchor or interference screw. The rest of the ACL reconstruction — graft harvest, tunnel drilling, and fixation — proceeds as normal.

The recovery timeline is not significantly altered by the addition of LET. Patients follow the same rehabilitation protocol, and the presence of the lateral construct does not restrict the rehabilitation programme in any meaningful way.

Does LET cause stiffness or limit movement?

This is one of the most common concerns raised about LET, and the evidence is reassuring. Studies, including the STABILITY trial data, have not shown a significant loss of knee range of motion in patients who received LET compared with those who did not. The procedure is performed with the knee in a neutral position, and the ITB strip is fixed at a tension that controls rotation without limiting normal joint movement.

Clinical experience supports this: patients who have LET performed alongside their ACL reconstruction do not, as a rule, experience more stiffness than those who have ACL reconstruction alone.

Does LET interfere with the ACL graft?

No. The ACL graft is an intra-articular structure — it sits inside the knee joint. LET is entirely extra-articular, sitting on the outside of the joint capsule. The two procedures address different components of instability and do not interfere with one another anatomically or biologically.

Is LET right for every ACL patient?

No, and this is important. Older patients with lower functional demands, or those with isolated ACL tears who are not returning to high-level pivoting sport, may not need LET. The decision is made on an individual basis, weighing up age, activity level, the severity of pre-operative instability, and the patient's goals. Adding a procedure that carries its own small risks is only worthwhile when the expected benefit is clear.

Dr Mooney's approach

LET is used selectively in this practice, based on the indications outlined above. For a young, active patient returning to pivoting sport with a high-grade pivot shift, the evidence supports its routine addition. For an older patient with lower demands, ACL reconstruction alone is typically appropriate. Every patient is assessed individually, and the decision is made in the context of their specific situation, goals, and the clinical findings at consultation.