Dislocation of rotating hinge total knee prostheses. A biomechanical analysis.

Area of Science:

• Orthopedic biomechanics
• Biomaterials engineering

Background:

• Symptomatic instability and implant dislocation are known complications of rotating hinge total knee prostheses.
• Understanding the biomechanical factors influencing implant stability is crucial for improving patient outcomes.

Purpose of the Study:

• To investigate the relationship between the central rotational stem design (length and taper) and the stability of rotating hinge total knee implants.
• To identify specific design characteristics associated with increased implant laxity and dislocation.

Main Methods:

• Biomechanical analysis of seven rotating hinge total knee implant designs from different manufacturers.
• Measurement of stem lengths and tapers.
• Assessment of tilting laxity through distraction testing to determine dislocation thresholds.

Main Results:

• Implant designs featuring shorter and/or more tapered central rotational stems exhibited greater tilting, laxity, and instability.
• Specific designs showed varying dislocation resistance, with one requiring significantly less distraction before failure.
• Implant stability was directly correlated with stem length and inversely correlated with stem taper.

Conclusions:

• The study confirms that shorter stem length and greater taper are associated with increased instability and laxity in rotating hinge knee implants.
• These findings underscore the critical role of stem geometry in preventing symptomatic instability and dislocation.