In a SLAP lesion, the upper (superior) portion of the labrum is injured. This upper area is also where the biceps tendon attaches to the labrum. A SLAP tear occurs both in front (anterior) and behind (posterior) of this attachment point.

Introduction

In the shoulder, the superior labral complex is made up of the biceps tendon and a meniscus-like tissue called the labrum. Together, these components help stabilize the shoulder joint during overhead activities. In the mid-1980s, the labral complex was identified as a possible source of shoulder pain and dysfunction in throwing athletes. Since then, numerous reports have provided a better understanding of this complex structure and helped orthopedic surgeons properly treat these “SLAP” lesions.

The cartilage ring provides additional support to the shoulder joint by helping to hold it in place. A labrum tear occurs when part of this ring is broken, frayed or torn.

SLAP injuries are usually caused by falling onto an outstretched arm, repeated throwing, or traumatic shoulder dislocations. Damaging force, whether all at once or over time, causes this stable anchoring complex to loosen and become painful.

The shoulder joint (humeral head) is like a golf ball placed on a golf tee, which is the glenoid fossa. If the labrum is torn, it is more difficult for the humerus to stay in the socket. The end result is that the shoulder joint becomes unstable and prone to injury.

Because the biceps tendon attaches to the scapula through the labrum, labral tears can occur when you put extra pressure on the biceps muscle, such as when throwing a ball. Tears can also result from pinching or compression of the shoulder joint when the arm is raised above the head.

Causes of a SLAP lesion

SLAP lesions, or lesions of the upper anterior portion of the glenoid labrum, can be caused by a variety of factors. The main causes include acute trauma, repetitive movements, anatomical abnormalities and joint instability.

Acute trauma, such as a direct fall onto the shoulder or violent impact, can result in a tear of the labrum at its junction with the biceps brachii tendon, thereby causing a SLAP injury. These traumatic events can place excessive force on the shoulder joint, damaging the labrum and compromising its stabilizing function.

Sports or work activities that involve repetitive movements of the shoulder, such as throwing in baseball or throwing motions in athletes, may also contribute to the development of a SLAP injury. Repetition of these movements can cause progressive wear of the labrum, increasing the risk of tearing and injury.

Congenital or acquired anatomical abnormalities may also play a role in the development of a SLAP lesion. Some individuals may have anatomical defects, such as an abnormal shape of the glenoid fossa or poor healing of the labrum, that predispose them to this injury. These abnormalities can compromise the stability of the shoulder joint, thereby increasing susceptibility to labrum injuries.

Shoulder joint instability, whether congenital or acquired from previous injuries, is also a common cause of SLAP injury. Chronic joint instability can place additional stress on the labrum, increasing the risk of tearing and injury.

  1. Acute Trauma: Sudden trauma, such as a direct fall on the shoulder, a sports collision, or an accident, can cause a tear of the upper labrum of the shoulder.
  2. Repetitive arm movements: Activities that involve repetitive movements of the arm overhead, such as throwing in certain sports like baseball or softball, can contribute to labrum wear and SLAP injury.
  3. Shoulder Instability: Chronic shoulder instability, where the head of the humerus may move abnormally within the joint, increases the risk of developing a SLAP injury.
  4. Degenerative processes: Natural aging and degenerative processes can weaken the labrum over time, increasing susceptibility to injury.
  5. Throwing Sports: Athletes participating in throwing sports, such as baseball, softball, or tennis, are at particular risk for SLAP injury due to the repetitive movements involved in these activities.
  6. Heavy Lifting Activities: Heavy lifting activities, especially those involving raising the arm above the head with heavy loads, can contribute to wear and tear of the labrum and the development of SLAP injury.
  7. Anatomical factors: Some individuals may have anatomical factors predisposing to a SLAP injury, such as an abnormal shape of the acromion (part of the shoulder blade) or variations in shoulder structure.
  8. Poor exercise technique: Poor exercise technique, especially during movements that place heavy strain on the shoulder, can contribute to the occurrence of a SLAP injury.

Symptoms of a SLAP injury

Symptoms of a SLAP injury can vary depending on the severity of the injury and how it affects shoulder function. Here are some of the most common symptoms associated with a SLAP injury:

Pain : Pain is one of the most common symptoms of a SLAP injury. It is usually felt deep in the shoulder and may be described as a dull or stabbing pain. The pain may be exacerbated by certain activities, such as raising your arm above your head or performing rotating movements.

Locking or blocking sensation : People with a SLAP injury may feel a locking or blocking sensation in the shoulder when they try to raise their arm or move it in certain directions. This sensation may be due to joint instability caused by the labrum injury.

Muscle weakness : A SLAP injury can lead to muscle weakness in the affected shoulder, especially during specific movements. The muscles surrounding the shoulder may not function properly due to joint instability or pain, which can limit the shoulder’s range of motion and strength.

Crepitus or clicks : Some people with a SLAP injury may hear or feel crepitus or click sensations when they move their shoulder. This may be due to abnormal friction of the joint surfaces due to instability caused by the labrum injury.

Restriction of mobility : A SLAP injury can cause restriction of shoulder mobility, especially when raising the arm above the head or moving it in certain directions. This mobility limitation may be due to pain, joint instability, or a combination of both.

Shoulder instability : A SLAP injury can also lead to a feeling of shoulder instability, where the person feels like the shoulder is likely to dislocate or dislocate during certain activities. This instability may be accompanied by pain and muscle weakness.

Pathophysiology of a SLAP lesion

The pathophysiology of a SLAP (Superior Labral Anterior to Posterior) lesion of the shoulder involves an alteration of the labrum, a cartilaginous structure located in the shoulder joint. This injury can result from a variety of factors and cause changes to the shoulder, affecting its stability and causing symptoms. Here is an overview of the pathophysiology associated with SLAP injury:

  1. Labrum Tear: SLAP injury usually involves a tear of the labrum, the portion of cartilage that surrounds the glenoid socket of the scapula. This tear can occur as a result of acute trauma, overuse, or age-related degenerative processes.
  2. Traumatic Mechanisms: Acute trauma, such as a fall on the shoulder or a collision, can cause a tear of the labrum. The impact forces the joint into extreme positions, potentially leading to tears.
  3. Overuse or Repetitive Movements: Repetitive overhead arm movements, often associated with throwing sports like baseball, can contribute to progressive wear and tear of the labrum. This can create cumulative microtrauma leading to the SLAP injury.
  4. Shoulder Instability: Chronic shoulder instability, where the head of the humerus does not remain securely in the joint, can cause abnormal stress on the labrum, promoting tears.
  5. Compression and Pinching: Certain specific movements, such as forced abduction of the arm or rotational movements, can compress and pinch the labrum, contributing to its wear and tear.
  6. Deficient Healing Processes: The labrum has a limited ability to heal itself due to its limited blood supply. Therefore, a labrum tear can persist and lead to chronic problems.
  7. Abnormal Humeral Head Displacement: When unstable, the head of the humerus may move abnormally within the joint, generating inadequate forces on the labrum and thus contributing to the injury.
  8. Inflammatory Response and Pain: Tearing the labrum triggers an inflammatory response, causing pain and discomfort. Nerves in the area may be stimulated, causing symptoms such as pain, numbness, or a feeling of blockage.

The mechanism of injury in the case of a SLAP (Superior Labral Anterior to Posterior) lesion of the shoulder is often complex and can vary depending on several factors, including the type of physical activities performed, the movements repetitive stress, trauma and individual anatomical characteristics. Let us explore in detail the main mechanisms involved in the occurrence of SLAP injury.

Mechanism of injury

  1. Acute Trauma: A common mechanism of SLAP injury is acute trauma, such as a direct fall onto the shoulder or a violent collision. In such incidents, the force applied to the shoulder can cause abnormal movements of the humeral head, thereby putting the superior labrum in a vulnerable position. Tearing may occur as a result of this trauma, compromising the integrity of the labrum.
  2. Repetitive Throwing Motions: Athletes involved in throwing sports, such as baseball, softball, or tennis, are particularly susceptible to developing a SLAP injury due to repetitive overhead arm movements. Throwing movements exert significant pressure on the shoulder, repeatedly straining the labrum. Over time, these repeated stresses can contribute to wear and tear of the labrum and eventually injury.
  3. Compression and Pinching: Certain specific movements, such as forced abduction of the arm or rotational movements, can result in compression and pinching of the superior labrum between the humeral head and the glenoid fossa. This mechanism can damage the labrum and lead to a SLAP lesion.
  4. Shoulder Instability: Chronic shoulder instability, where the head of the humerus has excessive mobility in the joint, can contribute to SLAP injury. This instability may result from previous trauma, ligamentous laxity, or other anatomical abnormalities. An unstable humeral head can exert abnormal forces on the labrum, leading to a tear.
  5. Deficient Healing Processes: The labrum has limited vascularity, which means it has limited healing capacity. In the event of a tear, the ability of the labrum to regenerate is restricted. Degenerative processes and lack of adequate healing may contribute to the persistence of the SLAP lesion.
  6. Shoulder Hyperextension: Certain movements, such as shoulder hyperextension, can also contribute to SLAP injury. When the occiput and cervical vertebrae are extended posteriorly, this can place additional pressure on the shoulder structures, including the labrum.
  7. Improper Exercise Technique: Improper exercise technique, particularly during lifting movements or intensive upper extremity training, can result in inappropriate stresses on the shoulder, contributing to the development of a SLAP injury.
  8. Anatomical Factors: Some individuals may have anatomical factors predisposing to a SLAP injury, such as an abnormal shape of the acromion or variations in shoulder structure. These anatomical features may increase the vulnerability of the labrum to injury.

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