Shoulder Internal Rotation: The Role of the PIGHL, Anatomy, and Clinical Implications

What ligament limits shoulder internal rotation?

The primary ligament limiting shoulder internal rotation is the posterior band of the inferior glenohumeral ligament (PIGHL), a crucial component of the glenohumeral joint capsule that becomes taut as the humerus rotates internally, restricting further movement.

The Primary Limiter: Posterior Band of the Inferior Glenohumeral Ligament (PIGHL)

The glenohumeral joint, commonly known as the shoulder joint, is a highly mobile ball-and-socket joint. While its extensive range of motion is beneficial, it relies heavily on a complex interplay of static and dynamic stabilizers to maintain stability. Among the most critical static stabilizers are the glenohumeral ligaments, thickenings of the fibrous joint capsule.

Specifically, the inferior glenohumeral ligament (IGHL) is a robust, hammock-like structure with distinct anterior and posterior bands. When the arm is abducted (raised away from the body), the IGHL becomes the primary stabilizer against anterior and posterior translation of the humeral head. During internal rotation, particularly with the arm abducted, the posterior band of the inferior glenohumeral ligament (PIGHL) becomes taut, acting as a primary checkrein to limit the extent of this movement.

Understanding Shoulder Internal Rotation

Shoulder internal rotation, also known as medial rotation, is the movement of the humerus (upper arm bone) rotating inwards towards the midline of the body around its longitudinal axis. This movement occurs at the glenohumeral joint.

Key Muscles Involved in Internal Rotation:

• Subscapularis: The largest and most powerful internal rotator, part of the rotator cuff.
• Pectoralis Major: Especially the sternal head, contributes significantly.
• Latissimus Dorsi: A large back muscle that also acts as a powerful internal rotator.
• Teres Major: Often called the "lat's little helper," it synergistically assists in internal rotation.

Internal rotation is a fundamental movement for many daily activities and sports, from throwing a ball to reaching behind your back. Adequate and controlled internal rotation range of motion is vital for shoulder health and function.

Anatomy of the Glenohumeral Joint Capsule and Ligaments

The glenohumeral joint is formed by the articulation of the spherical head of the humerus with the shallow, pear-shaped glenoid fossa of the scapula (shoulder blade). This inherent bony instability is compensated for by soft tissue structures.

• Joint Capsule: A fibrous sac enclosing the joint, providing a sealed environment and contributing to stability. It is relatively lax to allow for large movements but becomes taut at end-ranges of motion.
• Glenohumeral Ligaments (GHLs): These are three distinct thickenings of the anterior and inferior portions of the joint capsule, named based on their position:
  • Superior Glenohumeral Ligament (SGHL): Limits inferior translation of the humeral head when the arm is adducted, and restricts external rotation.
  • Middle Glenohumeral Ligament (MGHL): Limits external rotation, particularly in the mid-range of abduction.
  • Inferior Glenohumeral Ligament (IGHL): The most significant stabilizer when the arm is abducted. It consists of:
    • Anterior Band (AIGHL): Primary restraint to anterior translation and external rotation when the arm is abducted.
    • Posterior Band (PIGHL): Primary restraint to posterior translation and internal rotation when the arm is abducted.
    • Axillary Pouch: The hammock-like inferior portion connecting the two bands.

How the PIGHL Limits Internal Rotation

During internal rotation, the humeral head rotates posteriorly within the glenoid fossa. As this movement approaches its end range, the posterior aspect of the joint capsule, and specifically the posterior band of the inferior glenohumeral ligament (PIGHL), becomes stretched and taut. This tension acts as a physical barrier, preventing further inward rotation and protecting the joint from excessive movement that could lead to instability or injury.

While the PIGHL is the primary ligamentous limiter, other structures also contribute to the overall restriction of internal rotation:

• Posterior Joint Capsule: The entire posterior aspect of the capsule becomes taut.
• Posterior Rotator Cuff Muscles: The infraspinatus and teres minor, being external rotators, become stretched at the end range of internal rotation, contributing to the passive restraint.
• Bony Impingement: In some cases, the greater tuberosity of the humerus may impinge against the posterior rim of the glenoid, providing a bony block to further motion, though this is less common as a primary physiological limiter compared to soft tissue structures.

Clinical Significance and Implications

Understanding the role of the PIGHL and other posterior structures in limiting internal rotation is vital for clinicians and fitness professionals:

• Glenohumeral Internal Rotation Deficit (GIRD): Common in overhead athletes (e.g., baseball pitchers, tennis players), GIRD is a loss of internal rotation range of motion often accompanied by a compensatory increase in external rotation. This imbalance can shift the center of rotation, placing increased stress on anterior structures during throwing and increasing the risk of shoulder impingement, labral tears, and rotator cuff injuries. The PIGHL and posterior capsule often become thickened and tight in these individuals.
• Shoulder Rehabilitation: Assessing and addressing limitations in internal rotation is a key component of rehabilitation programs for various shoulder conditions. Stretching and manual therapy techniques often target the posterior capsule and PIGHL to restore optimal mobility.
• Post-Surgical Considerations: Following certain shoulder surgeries (e.g., posterior labral repair), restricting internal rotation may be critical to protect healing tissues, and the PIGHL's role in this limitation is directly considered.

Assessing Shoulder Internal Rotation

Shoulder internal rotation range of motion is typically assessed with the individual supine (lying on their back) and the arm abducted to 90 degrees. A goniometer is used to measure the angle of rotation. Normal internal rotation range of motion can vary but generally ranges from 70 to 90 degrees with the arm abducted to 90 degrees.

Conclusion

The shoulder joint's remarkable mobility is carefully regulated by a network of ligaments and the joint capsule. For internal rotation, the posterior band of the inferior glenohumeral ligament (PIGHL) stands out as the primary ligamentous restraint. Its integrity and flexibility are crucial for maintaining optimal shoulder mechanics, preventing excessive motion, and mitigating the risk of injury, particularly in activities requiring dynamic shoulder function. A balanced range of motion, supported by healthy ligamentous structures, is fundamental to a resilient and high-performing shoulder.