[Non traumatic posterior instability in primary total knee replacement and its revision]

Area of Science:

• Orthopedic surgery
• Biomedical engineering

Background:

• Dislocation is a rare but challenging complication following total knee arthroplasty (TKA).
• Tibiofemoral instability, particularly when flexion and extension gaps are asymmetric and collateral ligaments are compromised, increases dislocation risk.

Observation:

• A case of posterior dislocation of a posterior-stabilized prosthesis occurred spontaneously without trauma.
• The patient exhibited significant varus instability and a positive anterior drawer test with tibial internal rotation, precluding conservative management.

Findings:

• Initial revision with a constrained condylar prosthesis failed to resolve instability, indicating insufficient constraint for severe asymmetric flexion instability.
• Subsequent implantation of a rotating-hinge prosthesis successfully eliminated further dislocation episodes and instability.

Implications:

• Severe asymmetric instability in TKA may necessitate advanced prosthetic solutions beyond standard constrained implants.
• Careful assessment of ligamentous integrity and joint line mechanics is crucial for preventing TKA dislocation.