ACL associated injuries: how often do secondary structures also tear?

When a patient tears their anterior cruciate ligament (ACL), the focus naturally falls on the ACL itself. Yet a large body of evidence now suggests that ACL associated injuries may actually be more frequent than previously thought. Prof. Etienne Cavaignac and the SANTI Study Group set out to quantify exactly how frequently three other structures, the medial meniscal ramp lesion (MMRL), the lateral meniscus root tear (LMRT), and the anterolateral ligament (ALL) tear, occur alongside an ACL injury, and to identify which patients are most at risk of sustaining all four injuries at once.

The findings, drawn from a prospective case series of 602 patients, are striking. For a full breakdown of the methodology and results, the complete study, Epidemiology of Combined Injuries of the Secondary Stabilizers in ACL-Deficient Knees: Medial Meniscal Ramp Lesion, Lateral Meniscus Root Tear, and ALL Tear: A Prospective Case Series of 602 Patients With ACL Tears From the SANTI Study Group, is available to consult directly.

What structures are at risk alongside an ACL tear?

To make sense of the study’s findings, it helps to understand what these three structures actually do.

• The medial meniscal ramp lesion (MMRL) refers to a tear at the posterior attachment of the medial meniscus, a crescent-shaped cartilage pad on the inner side of the knee. The menisci act as shock absorbers and help stabilise the joint.
• The lateral meniscus root tear (LMRT) involves the attachment point of the outer meniscus. A root tear can dramatically alter how load is distributed across the knee.
• The anterolateral ligament (ALL) is a small but important ligament on the outer side of the knee that controls rotational stability. Its involvement in ACL injuries has attracted growing research interest over the past decade.

Each of these structures contributes to what surgeons call secondary stabilisation of the knee. When the ACL fails, these secondary stabilisers take on a greater share of the mechanical load. Understanding whether they are torn at the time of ACL injury changes how surgery should be planned. For the precise diagnostic protocols used in this study, refer to the full publication.

The prevalence of combined ACL meniscus and anterolateral ligament injuries: what the numbers show

The study enrolled 602 patients over 15 years of age who underwent primary ACL reconstruction between January 2019 and June 2021. The results on the frequency of secondary stabiliser injuries in anterior cruciate ligament tears are telling.

The table below shows how frequently each injury combination was found across the 602 patients in the study

Injury pattern	Number of patients	% of total cohort (n=602)
Isolated ACL tear only	147	24%
ACL + ALL	265	44%
ACL + ALL + MMRL	80	13.28%
ACL + ALL + LMRT	36	6%
ACL + MMRL	34	6%
ACL + LMRT	16	2.65%
ACL + MMRL + LMRT	3	0.5%
All four (tetrad injury)	21	3.5%

The headline figure is clear: 76% of patients had at least one additional injury alongside their ACL tear. The ALL was by far the most commonly co-injured structure, present in more than half of all cases when combined injuries are tallied. These figures on the prevalence of medial meniscal ramp lesion, lateral meniscus root tear and ALL tear in ACL injuries had not previously been established in a cohort of this size. The full paper discusses how each structure was identified and the protocols used to standardise assessment.

Risk factors for combined meniscal and ALL injuries in ACL reconstruction patients

One of the study’s most valuable contributions is the identification of which patient profiles carry a higher risk of sustaining multiple injuries simultaneously.

Using multivariate logistic regression (a statistical technique that isolates the effect of each variable independently), the authors found that younger age is a significant risk factor for tetrad injury.

For each additional year of age, the odds of sustaining all four injuries decreased by 7% (adjusted odds ratio 0.93; 95% CI, 0.88–0.99; P = .028). In practical terms, young, active patients who tear their ACL are more likely to have injured their menisci and ALL at the same time.

The study also found that identifying an LMRT more than doubled the likelihood of also finding combined MMRL and ALL injuries (odds ratio 2.11; 95% CI, 1.09–3.12; P = .031). This has a direct implication for surgical practice: once one associated injury is confirmed, the search for others should become even more thorough. The detailed statistical analysis behind these figures is available in the complete study.

What this means for surgical planning and patient care

The practical implication of these findings is straightforward: a systematic, meticulous exploration of the knee at the time of ACL reconstruction is not optional. Since isolated ACL injury accounts for only one in four cases, assuming the knee has suffered only one structural failure is a clinical risk.

The study’s authors recommend that surgeons specifically look for:

• MMRL during arthroscopic exploration of the posteromedial compartment
• LMRT assessed at the posterior horn of the lateral meniscus
• ALL tear identified preoperatively by ultrasound (as done in this study)

Failing to address a co-existing injury at the time of ACL surgery may compromise knee stability and long-term outcomes, particularly rotational control. If you wish to understand the full surgical decision-making framework that informed this research, the complete paper offers detailed guidance.

Conclusion & Findings

This study fundamentally reframes how clinicians should think about ACL injuries. Rather than viewing the torn ACL as the sole problem, the evidence from over 600 patients firmly positions it as the primary finding in what is, more often than not, a multi-structure injury. Younger patients are at heightened risk of sustaining combined lesions, and the identification of one associated injury should prompt a thorough search for others.

If you found this summary useful, explore Prof. Cavaignac‘s other published scientific studies, which cover a wide range of topics in knee surgery with the same rigour and attention to clinical detail.