Knee Rotation: Understanding Internal, External, and Clinical Significance

What is the Internal and External Rotation of the Knee?

The knee joint, while primarily known for its hinge-like action of flexion and extension, also possesses a crucial, albeit more subtle, capacity for internal (medial) and external (lateral) rotation, particularly when it is in a flexed position.

Introduction to Knee Anatomy & Kinesiology

The knee is the largest joint in the human body, formed by the articulation of the femur (thigh bone), tibia (shin bone), and patella (kneecap). Classed as a modified hinge joint (or ginglymus joint), its primary movements are flexion (bending) and extension (straightening). However, its complex anatomy, including the condyles of the femur and the menisci, allows for a limited degree of rotational movement, which is vital for dynamic activities and overall knee health.

Understanding Knee Rotation

Knee rotation refers to the turning of the tibia relative to the femur around its longitudinal axis. This rotational capability is significantly greater when the knee is flexed (bent), as the collateral ligaments (medial and lateral) become taut in full extension, restricting rotation. When the knee is flexed to approximately 20-30 degrees or more, the ligaments are less taut, allowing for greater rotational freedom.

Internal (Medial) Rotation of the Knee

Definition: Internal rotation of the knee describes the movement where the anterior (front) aspect of the tibia rotates inward, towards the midline of the body, relative to the femur. If you were standing and bent your knee slightly, internal rotation would involve pointing your toes inward without moving your hip.

Anatomy (Muscles Involved): The primary muscles responsible for internal rotation of the knee are:

• Pes Anserinus Group: This collective term refers to the conjoined tendons of three muscles that insert on the medial (inner) aspect of the tibia:
  • Semitendinosus: One of the hamstring muscles.
  • Semimembranosus: Another hamstring muscle, lying deep to the semitendinosus.
  • Sartorius: The longest muscle in the body, running obliquely across the anterior thigh.
  • Gracilis: A long, slender muscle on the medial side of the thigh.
• Popliteus: A small, triangular muscle located on the posterior (back) aspect of the knee. It plays a critical role in "unlocking" the fully extended knee by internally rotating the tibia (or externally rotating the femur) to initiate flexion.

Functional Significance: Internal rotation is crucial for:

• Stabilizing the knee during weight-bearing activities.
• Controlling movements that involve pivoting or cutting, especially when combined with flexion.
• Deceleration during running and jumping.

External (Lateral) Rotation of the Knee

Definition: External rotation of the knee describes the movement where the anterior (front) aspect of the tibia rotates outward, away from the midline of the body, relative to the femur. Using the same example, external rotation would involve pointing your toes outward without moving your hip.

Anatomy (Muscles Involved): The primary muscle responsible for external rotation of the knee is:

• Biceps Femoris: The lateral (outer) hamstring muscle. It has two heads (long and short) and inserts onto the head of the fibula and lateral condyle of the tibia.
• Tensor Fasciae Latae (TFL) via the Iliotibial (IT) Band: While primarily a hip abductor and flexor, the TFL, through its connection to the IT band, can exert a rotational force on the tibia, contributing to external rotation, particularly in certain positions.

Functional Significance: External rotation is crucial for:

• Dynamic stabilization during complex movements.
• Propulsion and power generation in activities like kicking or pushing off.
• Absorbing rotational forces during impact or changes in direction.

The Role of Knee Position in Rotation

It is critical to reiterate that the amount of internal and external rotation available at the knee is highly dependent on the degree of knee flexion.

• Full Extension: At full extension, the knee is in its most stable, "locked" position. The femoral condyles are maximally congruent with the tibial plateau, and the collateral ligaments are taut, virtually eliminating rotation.
• Flexion: As the knee flexes, the ligaments loosen, and the congruency between the femoral and tibial articular surfaces decreases, allowing for increased rotational freedom. The greatest range of rotation typically occurs between 20 and 90 degrees of flexion.

Clinical Significance and Functional Implications

Understanding knee rotation is paramount for exercise professionals, clinicians, and athletes due to its implications for:

• Injury Prevention: Abnormal or excessive rotational forces are common mechanisms for knee injuries, particularly anterior cruciate ligament (ACL) tears, which often occur during non-contact pivoting or landing movements involving combined knee flexion and rotation.
• Sport-Specific Movements: Many athletic activities, such as cutting in basketball, pivoting in soccer, throwing in baseball, or skiing, demand precise control over knee rotation to generate power, change direction, and maintain stability.
• Rehabilitation: Post-injury rehabilitation programs often focus on strengthening the muscles that control knee rotation to restore stability, improve proprioception, and prevent re-injury.
• Exercise Prescription: Awareness of knee rotation helps in designing exercises that safely train the knee's full range of motion while avoiding positions that place undue stress on the joint. For example, exercises involving deep squats or lunges may be modified if an individual has limitations or pain with rotational movements.
• Gait and Biomechanics: During walking and running, small degrees of knee rotation occur naturally to accommodate foot placement and ground reaction forces, contributing to efficient and shock-absorbing movement.

Conclusion

While the knee's primary functions are flexion and extension, its capacity for internal and external rotation is a sophisticated biomechanical feature that significantly contributes to its overall function, stability, and adaptability. This secondary movement, primarily available in a flexed knee, is crucial for dynamic activities, injury prevention, and the complex interplay of forces throughout the lower kinetic chain. A comprehensive understanding of knee rotation is essential for optimizing movement, enhancing athletic performance, and promoting long-term knee health.