Fine thread versus coarse thread. A comparison of the maximum holding power

Area of Science:

• Orthopedic biomechanics
• Surgical implant design
• Bone fixation materials

Background:

• Traditional cancellous bone screws are designed for long bones but are ill-suited for smaller anatomical regions like the hand and foot.
• Fine machine screws present an alternative fixation option due to their dimensions being more appropriate for hand and foot bone structures.
• Understanding the comparative biomechanical holding power of different screw types is crucial for optimizing osteosynthesis in orthopedic surgery.

Purpose of the Study:

• To biomechanically compare the axial pull-out strength of fine machine screws against conventional cancellous and cortical screws.
• To evaluate screw performance in both synthetic (polyurethane foam) and natural (bovine cancellous bone) bone models.

Main Methods:

• A biomechanical study was conducted using polyurethane foam and bovine cancellous bone as test materials.
• Tested screw types included a 4 mm cancellous screw, 3.5 mm and 2.7 mm cortical screws (both pretapped and self-tapping), and 2.2 mm, 1.6 mm, and 1.2 mm fine machine screws.
• Axial extraction force was applied to screws inserted according to manufacturer instructions, and holding power was measured.

Main Results:

• The 4 mm cancellous bone screw demonstrated superior holding power in both test materials.
• In bovine cancellous bone, 2.2 mm fine machine screws showed no significant difference in holding power compared to 3.5 mm cortical screws.
• Fine machine screws exhibited superior performance relative to their thread diameter in cancellous bone, attributed partly to debris impaction.

Conclusions:

• Fine machine screws provide significant biomechanical holding power in cancellous bone, comparable to larger cortical screws, making them suitable for hand and foot osteosynthesis.
• The design of fine machine screws, particularly their thread dimensions and the impaction effect, contributes to their enhanced performance in spongy bone.
• This study supports the use of fine machine screws as an effective fixation option in orthopedic procedures involving small bone structures.