- •Current thread-lengths available for femoral neck fractures are not ideal to maximize purchase without crossing the fracture.
- •The most common thread-lengths available for larger size lag screws are 16mm, 32mm, and 40mm.
- •The average optimal length of lag screw threads is 33.2 ± 6.7 mm in femoral neck fracture patients to maximize purchase.
- •Men typically have larger femoral heads and can accommodate larger thread-lengths than women (p < 0.001).
- •Lag screws with 26mm thread lengths could improve the overall fixation without crossing the fracture line in 90% of patients.
It is common practice when placing cannulated screws within the femoral head when treating femoral neck fractures to avoid the thread-forms from crossing the fracture line. Despite the widespread use of cannulated screws in internal fixation of femoral neck fractures, there is no study to our knowledge that describes the ideal length of thread-forms.
The purpose of this study is to determine the thread length that will maximize purchase within the femoral head while minimizing risk of crossing the fracture line. Additional analysis was conducted to identify factors associated with the maximal possible length of treads in minimally and non-displaced femoral neck fractures.
We performed a retrospective study of all patients treated for a minimally or non-displaced femoral neck fracture from April 1, 2004 through December 31, 2017. Only patients who had received a pre-operative CT or MRI scan were included. Fixation was then templated using radiographs and the distance from the subchondral bone to the fracture line was then measured.
The study included 127 patients. The average estimated length of lag screw threads was 33.2 ± 6.67 mm, with lower quartile of 29.1 mm and higher quartile of 37.2 mm. The median was 32.0 mm and most frequently encountered estimate was 29 mm. Estimated lag screw size did not differ significantly based on age or BMI, but both height (p < 0.001) and race (0.04) were positively correlated with estimated lag screw size and males had longer measurements compared to females, 37.2 ± 7.0 mm vs 31.4 ± 5.7 mm (p < 0.001), respectively.
In conclusion, we propose an additional lag screw thread form with length 26.0 mm to capture 90% of femoral neck fractures.
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- Hip fractures in the United States: 2008 nationwide emergency department sample.Arthritis Care Res (Hoboken). 2012; 64: 751-757
- The future of hip fractures in the United States. Numbers, costs, and potential effects of postmenopausal estrogen.Clin Orthop Relat Res. 1990; 252: 163-166
- Fractures in the elderly: when is hip replacement a necessity?.Clin Interv Aging. 2011; 6: 1-7
- Optimizing stability in femoral neck fracture fixation.Ortho. 2015; 38: 625-630
- A prospective randomised trial of internal fixation versus arthroplasty for displaced fractures of the neck of the femur. Functional outcome for 450 patients at two years.J Bone Jt Surg Br. 2002; 84: 183-188
- Internal fixation versus hemiarthroplasty versus total hip arthroplasty for displaced subcaptial fractures of the femur - 13 year results of a prospective randomized study.Injury. 2000; 31: 793-797
- Internal Fixation compared with arthroplasty for displaced fractures of the femoral neck. A meta-analysis.J Bone Jt Surg Am. 2003; 85-A: 1673-1681
- Torsion and bending analysis of internal fixation techniques for femoral neck fractures: the role of implant design and bone density.J Orthop Res. 1987; 5: 433-444
- Relationship of mechanical factors to the strength of proximal femur fractures fixed with cancellous screws.J Ortho Trauma. 1996; 10: 248-257
- The biomechanics of screws.Orthop Rev. 1989; 18: 1302-1307
- Holding power of different screws in the femoral head: a study in human cadaver hips.Acta Orthop Scand. 1984; 55: 249-351
- Short versus long thread cannulated cancellous screws for intracapsular hip fractures: a randomised trial of 432 patients.Injury. 2010; 41: 382-384
- Postcranial robusticity in Homo. I: temporal trends and mechanical interpretation.Am J Phys Anthropol. 1993; 91: 21-53
- Length of long bones and their proportion to body height in hindus.J Anat. 1924; : 374-378
- Fracture fixation in the operative management of hip fractures (FAITH): an international, multicentre, randomised controlled trial.Lancet. 2017; 389: 1519-1527
- Use of fully threaded cannulated screws decreases femoral neck shortening after fixation of femoral neck fractures.Arch Orthop Trauma Surg. 2018; 138: 661-667
Published online: January 31, 2019
Accepted: January 30, 2019
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