Is It an ACL or MCL Tear? How to Tell and What to Do Next

27 Nov 2025

ACL (anterior cruciate ligament) and MCL (medial collateral ligament) tears are common knee ligament injuries that can cause pain, swelling, and knee instability. Understanding the differences between these injuries is crucial for timely diagnosis, effective treatment, and a safe return to activity. Dr Foo Gen Lin, an experienced orthopaedic surgeon specialising in sports injuries and hip preservation, explains what sets ACL and MCL tears apart.

What Are ACL and MCL Injuries?

blog_Is It an ACL or MCL Tear? How to Tell and What to Do Next

The ACL and MCL are key ligaments that stabilise the knee joint:

ACL (anterior cruciate ligament): located inside the knee, it controls forward movement and provides rotational stability. ACL tears often occur during sudden pivoting, jumping, or abrupt stops.
MCL (medial collateral ligament): found along the inner side of the knee, it prevents excessive inward bending and protects the joint from side impacts. MCL injuries are usually caused by direct blows to the outer knee.

Both ligaments are essential for maintaining knee stability, especially during sports or physical activity. Injuries to these ligaments can lead to long-term problems if not properly diagnosed and treated.

Key Differences Between ACL and MCL Tears

Feature	ACL Tear	MCL Tear
Symptoms	Popping sound at injury, rapid swelling, knee “giving way,” instability	Pain and tenderness on the inner knee, stiffness, swelling, usually stable
Common Causes	Sudden twisting, abrupt stops, awkward landings, rapid direction changes	Direct impact to the outer knee (e.g., tackles, collisions, falls)
Diagnosis	Lachman test, MRI to confirm tear, X-ray to rule out fractures	Valgus stress test, MRI to confirm tear, X-ray to rule out fractures
Treatment & Recovery	Partial tears may heal conservatively; full tears usually require surgery; rehab 9–12 months	Most MCL tears heal without surgery; mild tears recover in 4–8 weeks; severe tears may take 3+ months

Symptoms to Watch For

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ACL Tear Signs:

Audible “pop” at the time of injury
Rapid swelling within hours
Feeling of instability or knee “giving way”

MCL Tear Signs:

Pain along the inner knee
Swelling and stiffness
Knee generally remains stable

Early recognition of these symptoms is key to preventing further damage and ensuring optimal recovery.

Diagnosis of ACL and MCL Injuries

Accurate diagnosis typically involves:

Clinical examination: Lachman test for ACL, valgus stress test for MCL
Imaging: MRI to confirm ligament damage and assess meniscus/cartilage involvement; X-ray to rule out fractures

Prompt assessment by an orthopaedic surgeon is essential for determining the best treatment approach.

Treatment and Recovery Options

Non-surgical care: Rest, ice, compression, elevation (RICE), bracing, and physiotherapy are first-line treatments for both ACL and MCL injuries.
MCL tears: Mild injuries often heal in 4–8 weeks without surgery. Severe tears may require 3+ months of rehab.
ACL tears: Partial tears may respond to conservative care, but complete tears usually require reconstructive surgery. Recovery post-surgery typically takes 9–12 months.

A personalised rehabilitation plan helps restore knee stability, strength, and mobility, reducing the risk of re-injury.

When to See an Orthopaedic Specialist

When to See an Orthopaedic Specialist for an ACL or MCL tear

Seek medical attention if you experience:

Sudden knee trauma or a popping sound
Persistent pain, swelling, or stiffness
Difficulty bending, straightening, or bearing weight
A feeling that your knee may give way

Recovering from an ACL or MCL tear requires accurate diagnosis, effective treatment, and guided rehabilitation. At Core Clinic, Dr Foo Gen Lin provides expert evaluation and personalised treatment plans, working alongside Dr Wang Ming Chang—the only doctor in Singapore with dual specialist accreditation in Sports Medicine and Family Medicine. Together, they offer a comprehensive, multidisciplinary approach to help patients regain knee stability, reduce pain, and return to their active lifestyle safely. Book a consultation today to receive expert care and a tailored recovery plan for your knee injury.

Featured Contributor:

Apex Sports Clinic
As passionate athletes, we intimately understand the anguish and frustration that injuries can inflict, and our primary commitment is to facilitate your swift return to the sports you love.

With a collective experience exceeding 15 years, the Apex team has been dedicated advocates for athletes, assisting them in preventing, overcoming, and conquering injuries. We've invested countless hours in rigorous training and education to ensure we are exceptionally equipped to provide you with the highest care and support.

Our practice specialises in both non-surgical and surgical treatments for sports injuries, including knee ligament injuries, shoulder dislocations, and hip labral tears. We also handle emergencies like acute fractures and injuries and chronic joint conditions like osteoarthritis. With our experienced medical team and evidence-based approach, we provide personalised care to help patients recover and improve musculoskeletal health.

Connect with Apex Sports Clinic on their w ebsite.