Do "Anatomic" Distal Ulna Plating Systems Fit the Distal Ulna Without Causing Soft Tissue Impingement?

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Anatomy

Background:

• Distal ulna fracture fixation plates often lead to extensor carpi ulnaris (ECU) tendon irritation and necessitate removal.
• The anatomical proximity of the ulna articular cartilage and the ECU tendon creates a narrow space, increasing impingement risk.

Purpose of the Study:

• To define the safe zone for distal ulna plate application.
• To determine if wrist and forearm positioning influences the risk of ECU tendon impingement.

Main Methods:

• Four different distal ulna plates (Acumed, Medartis, Skeletal Dynamics, Synthes) were applied to 12 cadaveric specimens.
• The safe zone was measured in terms of angular arc and circumferential distance.
• Impingement was assessed across various wrist positions (flexion, extension, neutral, pronation, supination).

Main Results:

• The safe zone for distal ulna plate placement is characterized by a 92° arc and a 15 mm perimeter.
• Cumulative ECU impingement varied significantly by plate: Acumed (0%), Synthes (22%), Skeletal Dynamics (31%), and Medartis (68%).
• Impingement was most frequently observed in the supination position, with a clear hierarchy of impingement risk: Medartis > Skeletal Dynamics > Synthes > Acumed.

Conclusions:

• The mobility of the ECU tendon poses an impingement risk with ulnarly placed distal ulna plates.
• Intra-operative assessment, particularly in supination, is crucial for evaluating plate impingement.
• Plate-specific considerations include mandatory contouring for Medartis, Acumed's limitations in far-distal fractures, Synthes' suitability for proximal fractures, and Skeletal Dynamics' versatility.