What type of corrosion is most likely to occur with stainless steel plates and screws used for internal fixation in a patient with closed fractures?

Fretting Corrosion is the Most Likely Type of Corrosion in Stainless Steel Plates and Screws

Fretting corrosion is the most likely type of corrosion to occur with stainless steel plates and screws used for internal fixation of radius and ulna fractures. 1

Mechanism of Fretting Corrosion in Orthopedic Implants

• Fretting corrosion occurs at the interface between the screw heads and plate holes due to micromotion between these components during physiological loading 1
• This micromotion disrupts the protective passive oxide layer (chromium oxide) that normally forms on stainless steel surfaces, exposing the underlying metal to the corrosive physiological environment 2
• The cyclic loading of the implant during normal daily activities creates the conditions for fretting, which then initiates the corrosion process 3
• Even minimal micromotion (as little as 100 μm of direct contact) can trigger significant corrosion reactions in stainless steel implants 3

Comparison with Other Types of Corrosion

• Crevice corrosion: While crevice corrosion can occur in stainless steel implants, studies show it typically requires specific conditions such as hypertonic saline environments or pre-existing damage to the passive layer 1, 4
• Galvanic corrosion: This would require two dissimilar metals in contact, which is not the case in standard stainless steel plate and screw constructs that use components made of the same alloy 2
• Erosion corrosion: This type requires a flowing fluid with abrasive particles, which is not typically present in the internal environment surrounding orthopedic implants 2

Evidence Supporting Fretting as Primary Mechanism

• In-vitro studies demonstrate that cyclic loading of plate-screw constructs leads to immediate electrochemical potential changes indicative of fretting corrosion 1
• Clinical retrievals of stainless steel implants commonly show corrosion patterns consistent with fretting at the screw-plate interface 1
• Research has shown that fretting can initiate within just 2 seconds (2 cycles) of micromotion in stainless steel implants in physiological solutions 3
• The term "mechanically assisted crevice corrosion" (MACC) is now used to describe the combined mechanism where fretting initiates and accelerates crevice corrosion in orthopedic implants 5, 6

Clinical Implications

• Fretting corrosion can lead to:

  • Release of metal ions and debris into surrounding tissues 2
  • Potential hypersensitivity reactions in susceptible patients 2
  • Implant loosening and mechanical failure in severe cases 2
  • Adverse local tissue reactions that may compromise fracture healing 5

• The risk of fretting corrosion is influenced by:

  • Implant design and manufacturing quality 6
  • Patient factors such as activity level and bone quality 3
  • Surgical technique, including proper plate contouring and screw tightening 1

Prevention Strategies

• Newer stainless steel alloys with higher nitrogen content show improved resistance to fretting corrosion 2
• Proper implant selection and surgical technique to minimize micromotion between components 1
• In patients with known metal hypersensitivity, alternative materials such as titanium alloys may be considered 2

While all four types of corrosion can theoretically occur in orthopedic implants, the evidence strongly supports fretting corrosion as the primary and initiating mechanism in stainless steel plate and screw constructs used for internal fixation of fractures.