Trochlea Fractures

A Trochlea fracture (specifically Laugier's fracture) is an isolated coronal shear fracture of the joint surface of the trochlea. It does not involve the columns (unless associated with complex fractures).

• Extremely Rare. Represents less than 1% of distal humerus fractures.
• Demographics: Young males (high energy) or Osteoporotic females.
• Pathoanatomy: The trochlea is the "spool" of the elbow. It provides intrinsic stability (constrained joint). Loss of the trochlea allows the ulna to slide medially/laterally or dislocate.

• Trochlea: A spool-shaped structure covered in cartilage through an arc of 300 degrees.
• Sulcus: The central groove articulates with the trochlear notch of the ulna.
• Medial Ridge: More prominent than lateral ridge. Provides valgus stability.
• Center of Rotation: The axis of rotation passes through the center of the trochlea (and capitellum).
• Articular Contact: The ulna articulates with the trochlea in both flexion and extension. Loss of the trochlea results in rapid ulnar migration and instability.

• Watershed: The trochlea is supplied by small vessels entering via the medial capsule and non-articular areas.
• Fracture: The fracture is intra-articular and separates the bone from its blood supply (like an iceberg). High risk of AVN/Non-union.
• Posterior Comminution: Indicates disruption of the posterior vascular supply.

• Ulnar Nerve: Runs immediately posterior to the medial epicondyle. Must be identified and protected (or transposed) in any medial approach.
• Medial Antebrachial Cutaneous Nerve (MABCN): At risk during the superficial dissection. Injury causes painful neuroma.

• Flexor-Pronator Mass: Originates from the medial epicondyle. Must be elevated or split to access the anterior aspect of the trochlea.
• Triceps: Inserts on the olecranon, but its medial border covers the posterior aspect of the medial column.

the primary fracture is an anterior coronal-plane shear of the articular surface (the "wafer" of cartilage and subchondral bone). Modifier B means there is, in addition, comminution of the posterior aspect of the condyle/column - the back wall behind the shear fragment is broken rather than intact.

1. It strips the blood supply. The trochlea's vessels enter posteriorly and through the non-articular medial margin. Posterior comminution disrupts this posterior vascular pedicle, so the articular fragment is rendered largely avascular - hence the higher rates of AVN and non-union with modifier B.
2. It removes the buttress for fixation. Anterior-to-posterior headless compression screws work by compressing the shear fragment against an intact posterior cortex/column that acts as the backstop. If the posterior wall is comminuted, there is nothing to compress against - screws alone pull the fragment into the defect, lose purchase, and fail. The construct must be changed.

• Dubberley A (no posterior comminution): the posterior buttress is intact - headless compression screws (anterior-to-posterior, countersunk) are usually sufficient.
• Dubberley B (posterior comminution): anticipate the need to rebuild or bypass the missing back wall - a posterior/medial column buttress plate (often with bone graft) to support the articular reconstruction, lower the threshold for a wider exposure, and counsel the patient on the substantially higher risk of AVN, non-union and secondary surgery. Where the joint is unreconstructable in a low-demand elbow, this is the pattern that tips toward total elbow arthroplasty.

• Fall on outstretched hand (FOOSH) with elbow slightly flexed and in varus?
• Direct blow?
• Pain, swelling, inability to move elbow.

• Swelling: Medial sided bruising (Ecchymosis).
• Palpation: Tenderness over medial column.
• ROM: Block to flexion/extension implies a mechanical block (loose fragment).
• Neurology: CHECK ULNAR NERVE. Tardy ulnar nerve palsy is a late complication, but acute neuropraxia is common from the blow.

• AP: Often looks normal or shows a faint "flake" medially.
• Lateral: The Diagnostic View. Look for:
  • Double Arc Sign (Two semi-circles).
  • Superior migration of the fragment.
  • "Chewed up" appearance of the joint line.

• Absolute Requirement.
• 2D Views:
  • Coronal: Shows the shearing nature and size of the fragment.
  • Sagittal: Shows posterior comminution (Dubberley B).
• 3D Reconstruction:
  • Essential for preoperative planning of screw trajectory.
  • Determine if you can screw Front-to-Back (easier) or need Back-to-Front (harder).

• The trochlea is a spool (the sulcus) flanked by a tall medial ridge and a smaller lateral ridge. The greater sigmoid (trochlear) notch of the ulna wraps around this spool through nearly its full flexion-extension arc.
• This bony interlock - not the ligaments - is the primary restraint to varus, valgus and axial (medial/lateral) translation of the ulna at the elbow. The medial collateral ligament resists valgus and the lateral ulnar collateral ligament resists varus/posterolateral rotatory instability, but they act on an intact bony fulcrum. The trochlea is the keystone; the ligaments are the guy-ropes.
• Because the articulation is highly congruent (a constrained ginglymus/hinge), even small losses of trochlear height or width change the geometry the ulna tracks on.

• Remove or displace the trochlear spool and the ulna has nothing to sit in - it migrates medially or laterally and can frankly subluxate or dislocate, regardless of whether the collateral ligaments are intact. This is why a competent MCL/LUCL does not protect a trochlea-deficient elbow.
• On a true AP radiograph this manifests as the drop sign / widened ulnohumeral interval - a radiographic surrogate for the lost bony containment.

• It explains why reconstruction is strongly preferred over excision: excising the trochlea removes the joint's primary stabiliser. Fragment excision is therefore reserved for a small fragment (under one-fifth of the articular surface) that is not contributing to containment; excising a larger trochlear fragment leaves an unstable, incongruent elbow.
• It explains why an unreconstructable trochlea in a low-demand elbow is treated with total elbow arthroplasty (a linked/semi-constrained implant re-creates the lost bony constraint) rather than excision arthroplasty.