What are the causes of a Medial Collateral Ligament (MCL) injury?

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Last updated: May 15, 2025View editorial policy

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From the Guidelines

MCL injuries are primarily caused by direct blows to the outside of the knee, creating valgus stress that stretches or tears the ligament on the inner side of the knee, and prophylactic knee braces have been found to lack sufficient evidence of efficacy in reducing the incidence or severity of these injuries. MCL injuries can occur through various mechanisms, including contact sports tackles, falls during skiing, or sudden changes in direction during activities like soccer or basketball, as well as non-contact mechanisms such as forceful twisting or pivoting motions that place excessive stress on the inner knee 1. Some common risk factors for MCL injuries include:

  • Participation in high-risk sports
  • Previous knee injuries
  • Inadequate conditioning
  • Poor technique during athletic movements The severity of MCL injuries can range from grade I (mild stretching) to grade III (complete tear), with symptoms including inner knee pain, swelling, instability, and difficulty bearing weight. According to the American Family Physician, strength training, conditioning, technique refinement, and flexibility are more important in MCL injury prevention than the use of prophylactic knee braces 1. Therefore, prevention of MCL injuries should focus on proper technique, appropriate protective equipment, and strengthening exercises for the muscles supporting the knee joint, rather than relying on prophylactic knee braces.

From the Research

MCL Injury Causes

  • The medial collateral ligament (MCL) is a major stabilizer of the knee joint and is the most common ligament injured in the knee, particularly in athletes 2, 3, 4, 5.
  • MCL injuries can be caused by minor trauma, which can result in tearing of the superficial portion, or higher energy mechanisms, which can disrupt both the deep and superficial layers 2.
  • The MCL is often injured in conjunction with the anterior cruciate ligament (ACL) 3.
  • MCL injuries can result in valgus instability of the knee and make the patient susceptible to degenerative knee osteoarthritis 5.

Common Causes of MCL Injuries

  • Knee trauma 2, 3, 4, 5
  • Athletic activities 2, 3, 4
  • Valgus forces 5
  • Rotatory forces 5

Diagnosis and Treatment of MCL Injuries

  • History and physical examination are often adequate for diagnosis, but the gold standard for diagnosis is MRI 2.
  • Lesser injuries to the MCL can often be treated conservatively with early rehabilitation, but more significant tears often necessitate surgery 2, 3, 5.
  • Preoperative physical therapy should be completed before surgical management to allow for return of knee range of motion and an attempt at MCL healing 3.

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

Review: Medial collateral ligament injuries.

Journal of orthopaedics, 2017

Research

MCL injuries of the knee: current concepts review.

The Iowa orthopaedic journal, 2006

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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