The biomechanics of reverse anatomy shoulder replacement--a modelling study

Area of Science:

• Orthopedic biomechanics
• Prosthetic joint design
• Shoulder arthroplasty

Background:

• Reverse anatomy shoulder prostheses are increasingly used for arthritic shoulders with severe rotator cuff arthropathy.
• The biomechanical aspects of these prostheses remain incompletely understood.

Purpose of the Study:

• To investigate the biomechanical properties and functional outcomes of the DELTA reverse shoulder prosthesis.
• To analyze joint contact forces and impingement during standardized activities.

Main Methods:

• Adaptation of a 3D biomechanical shoulder model to simulate the DELTA reverse prosthesis geometry.
• Modification of muscle configurations to represent pathology and computation of joint contact forces.
• Utilizing a contact detection algorithm to identify prosthesis-scapula impingement.

Main Results:

• The reverse design significantly increases deltoid moment arm (42%) for arm elevation, compensating for rotator cuff dysfunction.
• It restores joint stability by altering joint contact force envelopes and managing shear forces.
• The study confirmed impingement between the prosthesis and scapula, predicting bone notches, though optimization may reduce but not eliminate this issue without affecting stability.

Conclusions:

• Reverse shoulder prostheses offer significant advantages for irreparable rotator cuff arthropathy by enhancing deltoid function and stability.
• Impingement and potential bone notching are critical challenges that necessitate optimized fixation and design modifications.
• Further optimization of reverse designs is crucial for maximizing patient functionality while mitigating associated complications.