Introduction

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  This chapter reviews posterolateral rotary instability of the elbow.

  
  
• ▪
  

  Elbow instability may significantly limit a patient’s function and ability to perform sports and activities of daily living.

  
  
• ▪
  

  Posterolateral rotary instability has become more frequently and accurately recognized because of improved understanding of elbow anatomy, biomechanics, diagnostic physical exam techniques, and treatment options.

  
  
• ▪
  

  Imaging modalities are serving a more important role in the diagnosis of posterolateral elbow instability.

  
  
• ▪
  

  Surgical reconstruction may be required in chronic or subtle posterolateral rotatory instability (PLRI) cases. Outcomes after surgery provide satisfactory results in most patients.

Introduction

• ▪
  

  This chapter reviews posterolateral rotary instability of the elbow.

  
  
• ▪
  

  Elbow instability may significantly limit a patient’s function and ability to perform sports and activities of daily living.

  
  
• ▪
  

  Posterolateral rotary instability has become more frequently and accurately recognized because of improved understanding of elbow anatomy, biomechanics, diagnostic physical exam techniques, and treatment options.

  
  
• ▪
  

  Imaging modalities are serving a more important role in the diagnosis of posterolateral elbow instability.

  
  
• ▪
  

  Surgical reconstruction may be required in chronic or subtle posterolateral rotatory instability (PLRI) cases. Outcomes after surgery provide satisfactory results in most patients.

Epidemiology

Posterolateral rotatory instability of the elbow was originally described by O’Driscoll et al in 1991 ( ). Since that time, several studies have demonstrated that the majority of posterolateral elbow instability cases result from a traumatic mechanism of injury that includes a combination of axial loading, valgus stress, and rotational force ( ). This combined loading pattern results in posterior subluxation of both the radial head and ulna from the humerus with rotation of the semilunar notch away from the trochlea ( ). A recent systematic review by found that 67 of 71 (94%) patients identified a traumatic cause as the source of their lateral elbow instability. Atraumatic causes include chronic cubitus varus malunion, which has been described as an uncommon cause of chronic attenuation of stabilizing ligaments in the lateral elbow and subsequent posterolateral instability ( ). Similarly, posterolateral instability may result from iatrogenic causes such as corticosteroid injections, arthroscopic procedures, or open procedures that place the primary stabilizers at risk of injury (e.g., aggressive debridement for extensor carpi radialis brevis tendinosis).

Anatomy

Appreciating elbow anatomy is very important in understanding the mechanism of injury and pathology associated with elbow instability in general as well as specifically with regard to PLRI. Elbow stability is maintained by both static and dynamic stabilizers. Static stability is provided by the bony articulations between the radiocapitellar, ulnohumeral, and proximal radioulnar joints as well as capsuloligamentous structures. The bony articulations provide stability at the extremes of motion, at either less than 20 degrees or greater than 120 degrees of elbow flexion ( ). The soft tissue restraints provide primary stability throughout the remainder of the elbow’s arc of motion ( ).

The major soft tissue static stabilizer in the lateral elbow is the Y-shaped lateral collateral ligament (LCL) complex. This complex is composed of the radial collateral ligament, the accessory LCL, the annular ligament, and the lateral ulnar collateral ligament (LUCL) ( Fig. 27.1 ). Some authors have suggested that these components of the LCL complex may be more accurately described to be thickenings of the capsule (similar to the glenohumeral ligaments in the shoulder) rather than discrete and separate structures ( ). The LUCL has been described to be the most important primary stabilizer against valgus stress (Anakwe et al, 2011, 2014; ).

Lateral elbow ligamentous anatomy.

The medial collateral ligament complex is composed of three bundles: the anterior bundle, posterior bundle, and transverse bundle ( Fig. 27.2 ). The anterior bundle is the primary stabilizer to valgus stress with the elbow in extension. The anterior capsule is also important in stabilizing the elbow in extension. The posterior bundle is tight in flexion and is the main stabilizer in flexion. The transverse ligament, however, is not a significant factor in elbow stability. The role the medial collateral ligament plays in PLRI depends on the extent and mechanism of injury.

Medial elbow ligamentous anatomy.

The elbow also has dynamic stabilization. Dynamic stability is provided by musculotendinous structures surrounding the elbow that function throughout elbow range of motion. This stability depends on the neuromuscular control about the joint. The biceps, triceps, and other muscles create compressive forces across the joint during flexion, extension, and rotation motion ( ).

Mechanism

Posterolateral rotatory instability injuries are commonly a result of an injury mechanism that involves a combination of axial load, valgus stress, and rotation on the outstretched upper extremity. The level of energy involved and the position of the hand, elbow, and shoulder during impact determine the type of injury sustained. PLRI is most commonly associated with an injury sustained while the upper extremity starts in extension and supination at the time of contact with the floor with subsequent axial load and valgus force applied to the elbow by the body weight of the falling patient ( Fig. 27.3 ). This position places the elbow in a less stable position and more vulnerable to injury compared with a stable flexed and pronated position.

Mechanism of elbow injury involving hyperextension, axial compression, and internal rotation.

described that the injury mechanism progresses across the elbow in a three-stage stepwise fashion from the lateral to the anterior and the anterior to the medial sides of the elbow. First, the LUCL is disrupted, then the anterior and posterior aspects of the capsule are torn, and finally the medial ulnar collateral ligament (MUCL) is disrupted. This pattern is referred to as the circle of Horii ( Fig. 27.4 ). The primary cause of posterolateral instability is injury to the LUCL. If the MUCL is intact, then the coronoid may not completely dislocate and may become displaced proximal to the humerus. This is a “perched” type of elbow instability injury. To have a complete posterolateral dislocation, then the combination of the LUCL, capsule, and MUCL is expected to be disrupted.

Elbow instability progresses from lateral to medial involving the lateral ulnar collateral ligament (LUCL) capsule and medial ulnar collateral ligament (MUCL).

The categorization of elbow instability may be subdivided into simple or complex. Simple elbow dislocations have no associated fracture and account for approximately 60% of dislocations. Complex elbow dislocations have an associated fracture present at the time of injury ( ). A “terrible triad” injury is a type of complex elbow dislocation involving injury of three structures: disruption of the LUCL as well as a fracture of the coronoid process and radial head or neck ( ).