The stability of total talar prosthesis-How stable to dislocation? Cadaveric study

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Prosthetics research

Background:

• Ankle instability is a common complication following ankle arthrodesis or trauma.
• Total talar prosthesis (TTP) offers a potential solution for severe talar bone loss or destruction.
• Characterizing TTP stability and the impact of implant size is essential for clinical success.

Purpose of the Study:

• To evaluate the ankle stability of total talar prosthesis (TTP) in a cadaveric model.
• To determine the influence of implant size, specifically downsizes implants, on TTP stability.
• To assess the resistance of TTP to dislocation under various stress conditions.

Main Methods:

• Twelve below-knee cadaveric specimens were used, divided into size-matched and 5% downsized TTP implant groups.
• Ankle stability was assessed pre- and post-TTP insertion using fluoroscopy, measuring anterior drawer distance and talar/subtalar tilt angles.
• Dislocation resistance was tested by increasing stress force up to 350 N under varus, valgus, and anterior/subtalar loading.

Main Results:

• TTP insertion led to significant instability under varus and anterior drawer stress compared to native ankles.
• Downsized implants showed significantly greater anterior drawer instability than size-matched implants.
• Anterior dislocation occurred in all cases with downsized implants, unlike other stress conditions where no dislocation was observed.

Conclusions:

• Total talar prosthesis (TTP) demonstrates stability under valgus and subtalar stress.
• Clinicians must be aware of potential anterior instability associated with TTP.
• Careful consideration of implant sizing is recommended to mitigate the risk of anterior dislocation, particularly with downsized components.