C-Arm in Shoulder Surgery: Optimal Placement, Views, and Applications

Where Should the C-arm be Placed for Shoulder Surgery?

For optimal visualization during shoulder surgery, C-arm placement is highly dynamic and procedure-specific, but generally involves achieving oblique anterior-posterior (AP) and lateral views of the glenohumeral joint, scapula, and humeral head to guide instrument placement, implant positioning, and confirm reduction.

Understanding the C-Arm and Its Role in Shoulder Surgery

The C-arm is a mobile fluoroscopic X-ray system that provides real-time, dynamic imaging during surgical procedures. Its C-shaped arm allows for rotation around the patient, enabling multiple projection angles without repositioning the patient. In shoulder surgery, the C-arm is an indispensable tool for:

• Visualizing bony anatomy: Confirmation of fracture reduction, joint alignment, and the precise position of the humeral head relative to the glenoid.
• Guiding instrument placement: Ensuring accurate drilling, reaming, and placement of guide wires, pins, and screws.
• Confirming implant position: Verifying the orientation, depth, and stability of anchors, plates, screws, and prosthetic components (e.g., glenoid and humeral components in arthroplasty).
• Assessing joint stability: Dynamic assessment of joint congruity and range of motion under fluoroscopy.

Key Anatomical Considerations for C-Arm Positioning

Effective C-arm placement hinges on a thorough understanding of shoulder anatomy and biomechanics. The goal is to obtain clear, unobstructed views of specific structures without superimposition.

• Glenohumeral Joint: The articulation between the humeral head and the glenoid fossa of the scapula. This is often the primary focus.
• Scapula: Especially the glenoid, acromion, and coracoid processes, which serve as landmarks and attachment points.
• Humerus: The proximal humerus, including the head, surgical neck, and greater/lesser tuberosities.
• Clavicle: Important for procedures involving the acromioclavicular (AC) joint or proximal clavicle fractures.

Patient positioning (e.g., beach chair or lateral decubitus) significantly influences the initial setup and required C-arm adjustments.

General Principles of C-Arm Placement for Shoulder Procedures

While specific views vary, fundamental principles guide C-arm placement to ensure optimal fluoroscopic imaging:

• Oblique Anterior-Posterior (AP) View (True AP or Grashey View):

  • Purpose: Provides a clear, non-superimposed view of the glenohumeral joint space.
  • Technique: The C-arm is typically angled approximately 30-45 degrees obliquely from the patient's affected side, directed towards the glenohumeral joint. This angling projects the humeral head directly over the glenoid, separating it from the overlying spine and other posterior structures.
  • Adjustments: Minor caudal or cephalad tilt (often 5-15 degrees) may be necessary to align the X-ray beam perpendicular to the joint line, especially in the beach chair position.

• Lateral View (Scapular Y View or Axillary View):

  • Purpose: Essential for assessing anterior-posterior displacement, glenoid version, and humeral head position in the sagittal or axial plane.
  • Scapular Y View: Achieved by positioning the C-arm so that the X-ray beam is parallel to the plane of the scapula, typically requiring a significant oblique angle (e.g., 60-90 degrees from the true AP) relative to the patient's torso. This view projects the humeral head centered within the "Y" formed by the acromion, coracoid, and scapular body.
  • Axillary View: Often obtained by placing the C-arm superiorly and directing the beam inferiorly through the axilla, or by abducting the arm and placing the detector plate superiorly with the source inferiorly. This view is crucial for assessing glenoid bone loss, anterior/posterior instability, and humeral head translation.

• Dynamic Adjustments: The C-arm position is rarely static. Surgeons will often request slight tilts (cephalad/caudal) or rotations (oblique) to optimize the view of specific structures during different stages of the surgery.

Specific Placement for Common Shoulder Surgeries

The precise C-arm positioning is tailored to the surgical objective:

• Rotator Cuff Repair/Acromioplasty:

  • Focus: Visualization of the acromion, subacromial space, and humeral head.
  • Placement: Often requires AP and slightly caudal or cephalad oblique views to confirm acromial decompression or anchor placement in the greater tuberosity.

• Shoulder Arthroplasty (Total Shoulder Arthroplasty - TSA, Hemiarthroplasty - Hemi, Reverse Total Shoulder Arthroplasty - rTSA):

  • Focus: Critical for accurate glenoid and humeral component positioning.
  • Placement:
    • Glenoid Component: Requires precise AP and lateral (axillary or scapular Y) views to ensure correct version (angle relative to the scapular plane) and inclination (angle relative to the superior-inferior axis) of the glenoid component, minimizing impingement and optimizing stability.
    • Humeral Component: AP views are used to assess stem alignment in the humeral shaft and the appropriate depth of insertion.
  • Dynamic Assessment: Fluoroscopy is used throughout reaming, broaching, and trial component placement to avoid malposition.

• Fracture Fixation (Proximal Humerus, Glenoid, Clavicle):

  • Focus: Confirming fracture reduction and hardware placement.
  • Placement: Requires multiple views (AP, lateral, obliques) to assess fracture fragment alignment in all planes and ensure screws or plates are appropriately positioned, not impinging on soft tissues or articular surfaces. The C-arm may be rotated around the shoulder to get "perfect circles" of screw heads, indicating perpendicularity.

• Shoulder Instability (Labral Repair, Capsular Shift):

  • Focus: Confirming anchor placement in the glenoid rim and assessing joint reduction.
  • Placement: AP and axillary views are crucial for verifying the position of suture anchors and ensuring the humeral head is concentrically reduced within the glenoid.

Optimizing Image Quality and Safety

Effective C-arm use also involves considerations for image quality and radiation safety:

• Minimizing Radiation Exposure (ALARA Principle):

  • Collimation: Restricting the X-ray beam to the area of interest reduces scatter and patient dose.
  • Pulse Fluoroscopy: Using pulsed rather than continuous fluoroscopy significantly reduces radiation.
  • Distance: Maximizing the distance between the X-ray source and the patient, and the patient and the image intensifier (while maintaining image quality), helps reduce dose.
  • Protective Gear: All personnel in the operating room should wear lead aprons, thyroid shields, and lead glasses.

• Avoiding Obstructions: Surgical instruments, drapes, and the surgeon's hands can obstruct views. Careful positioning of the C-arm and the surgical field is necessary.

• Patient Positioning: Ensuring the patient is stably and appropriately positioned is critical for repeatable and clear imaging.

The Collaborative Approach

Successful C-arm utilization in shoulder surgery is a collaborative effort. The surgeon communicates the desired view and the anatomical structures they need to visualize. The radiologic technologist manipulates the C-arm, and the scrub technologist or circulating nurse assists with clearing the field and adjusting drapes. This dynamic interaction ensures that the surgeon receives the necessary real-time imaging to perform the procedure safely and effectively.

In conclusion, the precise placement of the C-arm for shoulder surgery is a nuanced process, demanding a deep understanding of shoulder anatomy, surgical objectives, and the principles of fluoroscopy. Its accurate and judicious use is paramount for achieving optimal surgical outcomes and ensuring patient safety.