This post comes from Fred Nelson, MD, an orthopaedic surgeon in the Department of Orthopedics at Henry Ford Hospital and a clinical associate professor at Wayne State Medical School. Some of Dr. Nelson’s tips go out weekly to more than 3,000 members of the Orthopaedic Research Society (ORS), and all are distributed to more than 30 orthopaedic residency programs. Those not sent to the ORS are periodically reposted in OrthoBuzz with the permission of Dr. Nelson.
Fracture fixation with a plate and screws has been around for a century—and so has the problem of screw loosening. Part of the cause of screw loosening seems to be toggling caused by radial forces arising from plate micromotion. Several decades ago, locked screws were designed to prevent loosening and provide better fixation, but screws still loosen.
Two tests can predict screw loosening associated with bone microfracture and absorption: axial pullout stress and toggling radial stress. Recent studies have investigated two hypotheses: radial stress is a predominant cause of screw loosening, and bone resorption is triggered by high radial stress.
Finite Element Analyses
A finite elemental model was used to replicate fixation of a tibial fracture with a 3-mm gap using either a dynamic compression plate (DCP) or locking compression plate (LCP).1 The model included contact with bone, tension on screw insertion, and the placement of two inner screws and one outer screw on either side of the fracture for an 8-hole plate. Axial loading, torsional loading, and bending were applied. Forces exceeding 55 megapascal (MPa) were considered adequate to cause microfracture, whether by radial or axial force. (For reference, 55 MPa is just about 8,000 pounds per square inch.)
The principal finding was that more bone was damaged by radial than by axial stress in both types of plates. Both plate types had more bone damaged by radial stress at the central two screws than at the two end screws for all bending models.
A separate study evaluated clinical radiographs of fixation for humeral, radial, ulnar, femoral, and tibial shaft fractures. Researchers looked for screw migration or bone absorption of ≥1 mm around the screw. Both DCPs and LCPs were reviewed.
Researchers found that the outer screws loosened only after the inner screws loosened. There were 3 cases of bone loss with no loosening, 17 cases of bone loss with screw displacement, and no cases of screw loosening without bone loss. This strongly suggests that bone loss must occur for loosening to take place and that the earliest screw loosening occurs closer to the facture site.
Taken together, these results imply that the use of larger inner screws and/or the use of a different angle of fixation might reduce bone absorption that leads to loosening. In addition, radial stress testing might be more important than axial testing. Still, LCPs remain superior at resisting axial loading and bending moments, while DCPs remain superior at resisting torsional loading of unstable fractures.
- Feng X, Lin G, Fang CX, Lu WW, Chen B, Leung FKL. Bone resorption triggered by high radial stress: The mechanism of screw loosening in plate fixation of long bone fractures. J Orthop Res. 2019 Jul;37(7):1498-1507. doi: 10.1002/jor.24286. Epub 2019 Apr 8 PMID: 30908687
Trying to educate elderly patients and their family members about how to best treat a femoral neck fracture can be difficult. These patients typically have multiple—and often severe—medical comorbidities that can make even the most “simple” surgery complex and life-threatening. Making such discussions even harder is the lack of Level-I evidence related to treating these common injuries. For severely displaced fractures, the evidence supports performing either a hemi- or total hip arthroplasty on most patients. But the data is much less clear for minimally or nondisplaced fractures.
For these reasons, I was excited to read the study by Dolatowski et al. in the January 16, 2019 issue of JBJS. The authors performed a prospective, randomized controlled trial comparing internal screw fixation to hemiarthroplasty for valgus impacted or nondisplaced femoral neck fractures in >200 patients with a mean age of 83 years. They found that patients who underwent hemiarthroplasty had a significantly faster “up-and-go” test and were significantly less likely to undergo a major reoperation than those who underwent internal fixation. However, patients in the internal-fixation group were less likely to develop pulmonary complications. There were no between-group differences in overall hip function (as evaluated with the Harris hip score) or in the 24-month mortality rate.
This study lends support to what many surgeons tell elderly patients with a nondisplaced femoral neck fracture: a hemi- (or total) arthroplasty will probably provide the lowest risk of needing a repeat operation for the injury, while placing percutaneous screws may decrease the risk of cardiopulmonary complications related to the operation. While these findings may not be surprising, this study provides important Level I data that can help us educate patients and their families so that the best treatment for each individual patient can be determined.
Chad A. Krueger, MD
JBJS Deputy Editor for Social Media
OrthoBuzz occasionally receives posts from guest bloggers. This guest post comes from Matthew Herring, MD in response to a recent study in the Journal of Orthopaedic Trauma.
Low-energy sacral fractures in the geriatric population typically heal over time without operative intervention. Nonoperative treatment usually involves analgesics and progressive rehabilitation. Unfortunately, given the frailty and low physiologic reserves of many in this patient population, these fractures can still take a significant toll. Fracture pain may last for weeks to months; deconditioning occurs secondary to poor mobilization; and many patients are discharged to skilled nursing facilities rather than returning directly home.
Given this associated morbidity, Walker et al.1 asked whether percutaneous transiliac-transsacral screw fixation could offer some benefit in the treatment of sacral fragility fractures. The authors present a retrospective review of 41 elderly patients who were admitted with sacral fragility fractures. All patients first received a trial of nonoperative management, which included analgesia and physical therapy-guided mobilization. If patients were unable to appropriately ambulate secondary to pain, they were offered surgery. Sixteen patients elected surgery, which consisted of transiliac-transsacral screw fixation of the posterior pelvic ring.
After surgery, the operative group reported greater reductions in pain than the nonoperative cohort, and they were more likely to be discharged directly home from the hospital (75% versus 20%). Furthermore, at the time of discharge, 100% of the surgical patients were able to ambulate with physical therapy, compared to only 72% of the nonoperative group. No surgical complications occurred, and the average total surgical time was only 34 minutes.
Sacral fragility fractures can result in significant pain and disability in an already frail population. While these fractures are typically managed conservatively, this study suggests that some patients may benefit from surgical intervention. Percutaneous transiliac-transsacral screw fixation is a relatively low-risk procedure (at least in the normomorphic sacrum). And if a single screw can reduce pain, improve function, and more quickly return geriatric patients to their baseline level of independence, then the risk-benefit calculus would favor surgery, unless specific contraindications are present.
While this study is not powerful enough to rewrite treatment protocols, it does give credence to considering surgical fixation for sacral fragility fractures in those who still struggle after a trial of conservative management, and it makes a strong argument for further investigation.
Matthew Herring, MD is a fellow in orthopaedic trauma at the University of California, San Francisco and a member of the JBJS Social Media Advisory Board.
- Walker, J. Brock, et al. “Percutaneous Transiliac–Transsacral Screw Fixation of Sacral Fragility Fractures Improves Pain, Ambulation, and Rate of Disposition to Home.” Journal of orthopaedic trauma 32.9 (2018): 452-456.
Syndesmotic injuries of the ankle, with or without malleolar ankle fractures, are common. Studies have found that up to 40% of all athletic injuries are ankle sprains and that 5% to 10% of those involve disruption of the tibiofibular syndesmosis. However, despite the frequent occurrence of this injury and related injuries, the best treatment of syndesmotic ankle injuries remains unresolved.
In the October 2015 issue of JBJS Reviews, Jones et al. describe ankle syndesmotic injuries, noting that the normal syndesmosis widening can be up to 1.5 mm, that the syndesmosis helps to prevent excessive fibular motion during locomotion, that clinical examination to diagnose syndesmotic injury is frequently inaccurate, and that initial injury and intraoperative stress radiographs help to confirm the diagnosis. The authors note that effective treatment requires accurate reduction and stable fixation in order to allow the syndesmotic ankle ligament to heal and also to limit syndesmotic motion. This effective treatment provides the best chance for the restoration of stable ankle mechanics. Nonoperative treatment of isolated injuries is appropriate in most cases. However, the timing of weight-bearing remains controversial and the timing of and indications for fixation removal after operative treatment are also unresolved.
After an extensive review and discussion of diagnostic and treatment options, this Critical Analysis Review article provides the following recommendations for ankle syndesmotic injury. There is good evidence that ankle syndesmotic reduction and fixation provides the best results. Similarly, there is good evidence that screw fixation can be achieved with engagement of three or four cortices. There is fair evidence that screw fixation can be metallic or bioabsorbable and that screw fixation and suture button fixation have similar outcomes. There is also fair evidence that syndesmotic injuries with associated malleolar fractures have the worst outcomes. However, there is poor evidence that transsyndesmotic and suprasyndesmotic fixation have similar results. There is also poor evidence that screw removal should be performed after three months.
These recommendations are based on extensive review and analysis and should be helpful in aiding in the treatment of syndesmotic ankle injuries.
Thomas A. Einhorn, Editor