Latarjet Procedure: Screw Types, Sizes, and Fixation Principles

What Screws Are Used in Latarjet?

The Latarjet procedure primarily utilizes two or three screws, typically 3.5mm to 4.5mm in diameter, to secure the transferred coracoid bone block to the anterior glenoid rim, most commonly employing cancellous or cortical screws, often cannulated, to achieve stable fixation for recurrent anterior shoulder instability.

Understanding the Latarjet Procedure

The Latarjet procedure is a well-established surgical technique used to address recurrent anterior glenohumeral (shoulder) instability, particularly when there is significant bone loss from the anterior glenoid (shoulder socket) or a large bony defect on the humeral head (Hill-Sachs lesion). Unlike soft tissue-only repairs (e.g., Bankart repair), the Latarjet procedure is a bone-block transfer, involving the osteotomy (cutting) of a portion of the coracoid process (a hook-like projection from the scapula), along with its attached conjoint tendon, and its transfer to the anterior aspect of the glenoid. This transferred bone block effectively extends the glenoid articular surface, providing a bony buttress against anterior dislocation, and the conjoint tendon acts as a dynamic sling to further stabilize the joint when the arm is abducted and externally rotated.

The Role of Screws in Latarjet

The success of the Latarjet procedure hinges on the secure and stable fixation of the transferred coracoid bone block to the native glenoid. This fixation is critical for promoting bony union (osteointegration) between the graft and the glenoid, which is essential for long-term stability and prevention of re-dislocation. Screws are the primary means of achieving this rigid internal fixation. Their role is to compress the coracoid graft against the glenoid, providing immediate mechanical stability and creating an optimal environment for bone healing.

Types of Screws Used

The choice of screws can vary based on surgeon preference, patient bone quality, and specific surgical technique, but certain types are standard:

• Cancellous Screws vs. Cortical Screws:
  • Cancellous Screws: These screws have a coarser thread pitch and deeper threads, designed for optimal purchase in cancellous (spongy) bone, which is abundant in the coracoid and glenoid. They are often preferred for their ability to compress the bone graft effectively.
  • Cortical Screws: These screws have a finer thread pitch and shallower threads, designed for dense cortical (compact) bone. While the primary fixation is in cancellous bone, some surgeons may use cortical screws for their strength or if bone quality dictates.
• Cannulated vs. Non-Cannulated Screws:
  • Cannulated Screws: These screws feature a hollow shaft, allowing them to be inserted over a guide wire (K-wire). This "over-the-wire" technique enhances precision in screw placement, allowing the surgeon to confirm ideal positioning before final screw insertion, minimizing the risk of malpositioning or neurovascular injury. They are widely used due to their precision.
  • Non-Cannulated Screws: These are solid screws inserted without a guide wire. While still effective, they may require more meticulous freehand drilling.
• Self-Tapping vs. Non-Self-Tapping Screws:
  • Self-Tapping Screws: These screws have a cutting flute at their tip, allowing them to create their own thread as they are driven into the bone, eliminating the need for a separate tapping step. This can streamline the surgical process.
  • Non-Self-Tapping Screws: These require a separate tapping instrument to create the screw threads in the bone before the screw is inserted.
• Screw Material:
  • Stainless Steel: A traditional and widely used material, known for its strength and biocompatibility.
  • Titanium: Increasingly popular due to its excellent biocompatibility, lower artifact on MRI scans, and good strength-to-weight ratio.
• Screw Head Type: Screws typically have a low-profile head or are designed to be countersunk (flush with the bone surface) to minimize soft tissue irritation.

Screw Size and Number

• Diameter: The most commonly used screw diameters range from 3.5 mm to 4.5 mm. This size provides sufficient strength for bone fixation while minimizing the risk of fracturing the relatively small coracoid graft.
• Length: Screw length is determined intraoperatively based on the thickness of the coracoid graft and the depth required for adequate purchase into the glenoid. Typical lengths range from 25 mm to 40 mm. The goal is bicortical purchase (engaging both sides of the bone) in the glenoid to maximize stability, without penetrating too far posteriorly and risking neurovascular structures.
• Number: The vast majority of Latarjet procedures utilize two screws for fixation. In some cases, or for specific anatomical variations, three screws may be used to enhance stability, particularly if the bone block is larger or bone quality is compromised.

Fixation Principles and Biomechanics

The screws employed in Latarjet are typically used in a lag screw technique. This involves drilling a glide hole in the near cortex (coracoid graft) that is larger than the screw's major diameter, and a pilot hole in the far cortex (glenoid) that matches the screw's minor (core) diameter. As the screw is tightened, it draws the coracoid graft firmly against the glenoid, creating interfragmentary compression. This compression is biomechanically advantageous as it:

• Increases the friction between the bone surfaces, enhancing immediate stability.
• Reduces the gap between the bone fragments, promoting primary bone healing (direct osteointegration) rather than healing via callus formation.
• Distributes stress more evenly across the bone-screw interface.

Potential Complications Related to Screw Fixation

While screws are essential for the procedure's success, their use is not without potential complications, which a knowledgeable fitness professional or kinesiologist should be aware of for post-operative management:

• Screw Prominence or Irritation: If a screw head is not adequately countersunk or if it protrudes, it can irritate surrounding soft tissues, potentially causing pain or discomfort.
• Screw Loosening or Back-out: Though rare with proper technique, screws can loosen over time, leading to graft instability or failure of union.
• Screw Breakage: Extremely rare, but can occur due to excessive stress or material fatigue.
• Neurovascular Injury: Incorrect screw length or trajectory can risk injury to vital neurovascular structures located posterior to the glenoid, such as the axillary nerve or posterior circumflex humeral artery. This underscores the importance of precise surgical technique and imaging guidance.
• Non-union or Malunion: While screws aim to prevent this, inadequate fixation can contribute to the failure of the coracoid graft to fully integrate with the glenoid.

Post-Operative Considerations and Rehabilitation

For fitness enthusiasts, trainers, and kinesiologists, understanding the surgical fixation is crucial for guiding rehabilitation. The initial post-operative period focuses on protecting the screw fixation and the healing bone graft. Early range of motion is often carefully controlled to avoid undue stress on the repair. As bone healing progresses, the screws provide the necessary stability for gradual progression to strengthening exercises. While the screws are generally left in permanently, they may be removed in rare cases if they cause persistent symptoms.

Conclusion

The selection and precise placement of screws are fundamental to the success of the Latarjet procedure. Typically, two or three cannulated cancellous or cortical screws of 3.5mm to 4.5mm diameter are employed to achieve stable compression and facilitate bony union of the coracoid graft to the glenoid. This robust fixation is the cornerstone for restoring shoulder stability and enabling a successful return to activity for individuals suffering from complex anterior shoulder instability.