PMC Tear

The posteromedial corner of the knee is a complex structure composed of multiple ligaments, tendons, and soft tissues that work together to stabilize the knee joint during movement. The key components of the PMC include:

• Superficial Medial Collateral Ligament (sMCL): This ligament is one of the primary stabilizers of the knee, preventing the tibia (shinbone) from shifting outward under stress. It helps resist valgus forces, which push the knee inward.
• Deep Medial Collateral Ligament (dMCL): Located beneath the superficial MCL, this structure reinforces the medial side of the knee and provides additional resistance to excessive movement.
• Posterior Oblique Ligament (POL): A crucial stabilizing ligament that controls excessive knee rotation and prevents posterior (backward) shifting of the tibia.
• Semimembranosus Tendon and Its Expansions: The semimembranosus muscle, part of the hamstrings, has tendon expansions that integrate with the PMC structures, assisting with dynamic knee stability.
• Oblique Popliteal Ligament: This ligament extends across the back of the knee, reinforcing the posteromedial capsule and providing additional resistance against rotational forces.

Each of these components works together to ensure proper knee function, and damage to the PMC can lead to significant instability if left untreated.

Common causes include:

• Direct trauma to the inner knee, such as a collision during contact sports (football, rugby, soccer).
• Hyperextension injuries, which may occur when an athlete lands awkwardly after a jump or experiences sudden, forced knee extension.
• Twisting motions with a planted foot, common in basketball, skiing, and martial arts, leading to rotational stress on the ligaments.
• Falls that apply excessive inward or backward force to the knee, particularly in high-impact activities.
• Multiligament knee injuries, where the PMC is damaged alongside the MCL, PCL, or anterior cruciate ligament (ACL) due to a severe impact.

A PMC injury often presents with significant pain and instability on the medial (inner) side of the knee. Patients may experience:

• Pain and swelling localized to the inner and back portions of the knee.
• A feeling of knee instability, particularly when pivoting, twisting, or walking on uneven ground.
• Difficulty bearing weight due to instability or pain.
• Limited range of motion, particularly with full knee extension.
• A sensation of the knee “giving out”, especially when changing direction quickly.
• Bruising or tenderness along the medial joint line.

Symptoms vary depending on the severity of the injury, and they can worsen if the injury is left unaddressed.

A thorough medical history, clinical examination and imaging studies are required to accurately diagnose a PMC injury. Dr. David Gazzaniga is an orthopedic surgeon and sports medicine expert who employs various diagnostic methods, including:

• Medical history includes a discussion of the circumstances that caused the injury.
• Physical Examination that includes tests of knee stability, and a gait examination including standing alignment, and specific tests for PMC injuires.
• Imaging Studies:
  • X-rays may be used to rule out fractures or bone avulsions, where ligaments pull a piece of bone away from its attachment site.
  • MRI is the gold standard for evaluating soft tissue damage, helping to identify the extent of ligament tears and structural damage.
  • Ultrasound imaging can sometimes be used to assess ligament integrity, particularly for superficial structures like the MCL.

Accurate diagnosis is essential to understanding the full extent of the injury and guiding appropriate medical decisions.

If left untreated or inadequately rehabilitated, a PMC injury can result in chronic knee instability and long-term complications, including:

• Persistent knee instability, leading to difficulty with physical activity and daily movements.
• Increased risk of further knee injuries, particularly to the ACL, MCL, or PCL.
• Early-onset knee osteoarthritis, due to abnormal joint mechanics and chronic instability placing excess stress on the cartilage.
• Loss of full knee function, limiting athletic performance and overall mobility.
• Recurrent knee “giving out” episodes, making routine activities, such as walking downstairs or pivoting, challenging.

A posteromedial corner (PMC) injury is a complex and often underdiagnosed condition that affects the inner and back portion of the knee joint. Since the PMC includes multiple ligamentous and soft tissue structures essential for knee stability, injuries in this region can significantly affect mobility and function.

Prompt recognition and accurate diagnosis using clinical assessments and imaging are crucial for guiding appropriate management strategies. When improperly treated, PMC injuries can lead to chronic instability and long-term complications, emphasizing the need for careful evaluation by an orthopedic specialist. Understanding the complexity of PMC injuries helps in making informed decisions regarding recovery, rehabilitation, and long-term knee health.