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High rate of mechanical failure seen with locking plates for femoral neck fractures
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Failure rates neared 37% in patients with femoral neck fractures treated with posterolateral femoral locking plates, according to a study presented at the American Academy of Orthopaedic Surgeons 2012 Annual Meeting.
“Locking plate constructs resulted in inferior outcomes with a high rate of mechanical failure, especially amongst displaced fractures,” study investigator Marschall B. Berkes, MD, of the Hospital for Special Surgery in New York City, said during his presentation. “We believe that this construct is too stiff, preventing micromotion, thus placing the burden entirely on the implant, leading to these failures. We would not recommend its use for femoral neck fractures, instead favoring more flexible constructs.”
New construct
Berkes, under the guidance of his mentor, Dean G. Lorich, and colleagues previously studied other fixation methods in their quest to curtail femoral shortening and loss of reduction. They found good results using length-stable fixation, which required intraoperative compression and fixation with fully-threaded screws, but femoral shortening and differences in offset led them to consider a new posterolateral femoral locking plate with a fixed-angle construct.
Berkes and colleagues conducted a minimum 1-year follow-up of 18 patients with femoral neck fractures fixed with posterolateral femoral locking plates and compared the findings to a historical control group with a similar mean age, gender distribution and percentage of displaced fractures who were treated with length-stable fixation. Indications for operation with the locking plate included femoral neck fractures in patients younger than 65 years, displaced fractures in patients older than 65 years who remained physically active and any minimally or nondisplaced fracture regardless of age, Berkes said.
This postoperative AP radiograph of the hip shows broken locking screws, loss of reduction and screw perforation into the joint.
Source: Berkes MB
During procedures, surgeons used guide wires to assist placement of the locking plate construct in a preliminary position. Partially-threaded screws were placed across the fracture site for intraoperative compression, Berkes said. The reduction was then locked into place using 5-mm locking screws through the plate after which partially-threaded screws were exchanged for fully-threaded screws, he added. Then a calcar and a shaft screw were placed.
Postoperative radiographs were used to assess the quality of reduction and were compared to radiographs taken at a minimum of 6 months to assess for femoral neck shortening. Other outcome measures were collected at a minimum of 1-year follow-up including Harris hip score, hardware-related complications and reoperation.
Failures
Although 17 of the 18 patients in the locking plate group achieved anatomic reduction, investigators found the group had lower union rates and Harris hip scores and higher reoperation and complications rates than the control group.
The average Harris hip scores at follow-up were 67.9 for the locking plate group vs. 84.7 for the control group, according to the study abstract. Patients in the locking plate group who achieved bony union showed average displacements of 0.78 mm inferiorly and 1.62 mm medially, and had an average increase of 2.41° varus.
The researchers found seven cases of failure in the locking plate group with screw breakage and varus collapse as the main culprits of failure. They also found one instance of screw breakage with a stable bony collapse that resulted in malunion and one fracture of the most distal screw that required a revision open reduction and internal fixation.
“This mode of mechanical failure suggests to us that this fixation was simply too rigid to allow for femoral neck union, inhibiting micromotion and preventing the healing process from occurring,” Berkes said. “Looking further into this, we feel there may be some role of fracture comminution and/or fracture site resorption that occurs, creating a situation where the lack of direct bony contact with the locking plate construct prevents any sort of motion at the fracture site. This load would then be transferred entirely to the metal, and at that point becomes a race between bony union and mechanical failure.”
He added, “We would submit to you that some degree of autodynamization may be necessary, which is simply not afforded by the locking plate construct.” – by Renee Blisard Buddle
Reference:
- Berkes MB, Little MT, Lazaro LE, et al. Outcomes following internal fixation of femoral neck fractures with a novel locking plate implant. Paper #185. Presented at the American Academy of Orthopaedic Surgeons 2012 Annual Meeting. Feb. 7-11. San Francisco.
For more information:
- Marschall B. Berkes, MD, can be reached at the Hospital for Special Surgery, 535 E. 70th St., New York, NY; 212-606-1000; email: berkesm@hss.edu.
- Disclosure: Berkes has no relevant financial disclosures.