The Effect Of Increasing Femoral Head Size On The Force Required For Dislocation

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Materials Science

Background:

• Alternative bearings enable larger femoral head use in total hip arthroplasty (THA).
• Intraoperative assessment of hip stability is crucial for successful THA outcomes.

Purpose of the Study:

• To evaluate the impact of increasing femoral head size on the force and range of motion (ROM) required for dislocation during intraoperative assessment in THA.

Main Methods:

• Ten cadaver hips underwent THA using a standard posterior approach.
• Components were implanted, and the extremity was subjected to a custom jig simulating intraoperative assessment.
• ROM to dislocation and torque were recorded for femoral head sizes ranging from 28mm to 44mm.

Main Results:

• A significant increase in torque (p<0.0001) and ROM (p<0.0001) to dislocation was observed with larger femoral head sizes.
• Least square means for torque ranged from 2.07 to 3.65 N*m, and ROM ranged from 43.5° to 59.5° as head size increased from 28mm to 44mm.
• Significant differences in ROM were found between nonadjacent head sizes (e.g., 28mm vs. 44mm).

Conclusions:

• Increasing femoral head size in THA confers greater stability during intraoperative assessment.
• Larger head sizes increase both the ROM prior to dislocation and the force required for dislocation.
• Femoral head size is a key factor influencing total hip implant stability.