Offering a closer look at the emergence and evolution of locking plates, these authors provide a thorough review of the literature to gauge the effectiveness of this fixation for first MPJ arthrodesis, calcaneal fractures and distal tibia fractures.
Plates and screws have been in use for bone healing to facilitate osteosynthesis since 1886.1 Researchers have studied these techniques of promoting primary bone healing with rigid stable internal fixation.
The founders of the Swiss American Study of Internal Fixation standardized the use of plates in the 1950s.2 The principles set forth by the American Orthopedic group included direct fracture exposure with anatomic reduction and rigid internal fixation.2 These conventional plating systems and methods have relied on the compressive force of the plate-to-bone interface to provide a stable construct. Ideally, the rigidity with this technique will lead to primary bone healing with no callus formation.
For many years, all the focus has been on the mechanical stability of the bone. Over the past 30 years, this philosophy has changed to addressing the “biology” of the fracture. More and more, attention and priority have shifted to the soft tissue envelope and the vascularity of the injury.
The amount of compression needed at the plate-to-bone interface to obtain stability diminishes the periosteal blood supply. This decreased blood to the injured bone has the potential to cause bone necrosis, delayed union or non-union of the bone, and an increased risk of infection and sequestration.3,4 The torque that surgeons use to insert the screws generates an axial preload and results in friction between the plate-bone interface. Accordingly, one must adequately contour the plate to sit directly against the bone. Within the plate, the screws can still toggle so authors have recommended bicortical screw fixation to prevent this toggling motion.5,6 Since this technique relies on the compression of the plate to bone for stability, good bone quality is required for solid fixation.
Primary bone healing can occur when strain levels at the fracture site are less than 2 percent. The definition of strain is the change in the length of the fracture gap divided by the length of the original fracture gap.7 Strain levels between 2 and 10 percent produce callus formation with bone healing, referred to as secondary bone healing. Strain levels greater than 10 percent result in no bone healing.7
That said, stable internal fixation usually provides less than 2 percent strain, resulting in primary bone healing.7 In contrast, splints, casts, intramedullary nails, bridging plates and external fixation usually lead to strain levels of 2 to 10 percent, leading to secondary bone healing with callus formation.7 Perren noted that “tissues cannot be produced under strain conditions which exceed the elongation at time of tissue rupture.”8
Plate-screw-bone constructs can act as either load-sharing or load-bearing devices. Neutralization plates function as load-sharing devices, neutralizing the effects of bending, rotation and axial forces on the fracture site.9,10 These plates cross a fracture that is already reduced and compressed with lag screws. In contrast to this are load-bearing buttresses and antiglide plates. These plates act as counter shear forces at the fracture site by converting the shear strain to axial compression forces.
As the demand to preserve the surgical site “biology” increased in priority and minimally invasive and indirect bridging fixation became popular, locking plate technology emerged. Locking plates are also essential for stable fixation in osteopenic or pathologic bone, and are less compressive to the periosteal blood supply of the bone. The locking of the screw to the plate controls axial orientation and creates a single-beam construct that is very stable. This single-beam construct functions when there is no motion between the components of the beam (the plate and screws) and the bone. This construct is four times stronger in comparison with the load-sharing constructs in which motion occurs between each individual component of the screw-plate configuration.11 Load-bearing plates require ideal circumstances of “good” bone to be able to permit enough screw torque to utilize single beam constructs.12
These single-beam constructs act as fixed angle devices, which enhance fracture fixation in circumstances of comminuted fractures or in instances of poor bone quality since bone to plate compression is not necessary for stability. The locking plate construct converts shear stress to compressive stress at the screw to bone interface. Therefore, the strength of fixation in locking plates is equal to the sum of all the screw-bone interfaces. This differs from the non-locking plates in which the strength of the fixation depends on each individual screw’s axial stiffness or pullout resistance.13
Locking plates act as “internal external fixators” due to the inherent angular and axial stability, and because of their close proximity to the bone and fracture site.12 The screw lengths for locking plates are 10 to 15 times shorter than for external fixators, thus greatly increasing fixation rigidity. The fixation rigidity is a direct function of the screw material, length and diameter as well as the material and dimensions of the plate.
Acting as “internal fixators,” locking plates do not rely on plate to bone compression or friction forces to obtain stability, which allows the preservation of the local blood supply to the bone. This preservation of the local blood supply in theory leads to more rapid bone healing, decreased bone resorption, decreased incidence of delayed or non-union, and secondary loss of reduction. This also avoids stress shielding below the plate, preventing local bone necrosis and infection.14-16
The mechanical principles for fracture fixation offer completely different biological environments for bone healing between locked plates and compression plates. The compression plate creates an environment that promotes primary bone healing through absolute stability and anatomic reduction. Since locking plates function as internal fixators, they provide an environment conducive to secondary bone healing. The choice of fixation often depends on the fracture pattern, fracture location and quality of the bone. Initially, surgeons reserved locking plates for indirect fracture reduction, osteoporotic bone and comminuted fractures.
In foot and ankle surgery, there has been an increase in locking plate use for trauma, reconstruction and elective surgeries. These plates have anatomic site-specific designs that increase ease of use. There has also recently been a push for immediate weightbearing due to the stability of locking plates. This in theory leads to decreased morbidity.
Hyer and colleagues compared four plate constructs for the fixation of first metatarsophalangeal joint (MPJ) arthrodesis.17 The four groups received a static plate, a static plate with a lag screw, a locked plate or a locked plate with a lag screw respectively. Researchers found no significant difference in the time to fusion or rate of fusion between static and locked plates with or without a lag screw.
Hunt and coworkers also looked at different types of fixation for a first MPJ arthrodesis.18 They compared a locking plate to a non-locking plate. There were 73 feet in the locking plate group and 107 feet in the non-locking plate group. Locked plates were associated with higher non-union rates. The authors suggested the reason for the lower union rate with locked plating included a diminished ability to obtain sufficient inter-fragmentary compression with the locked plate design and the inferior rigidity of the titanium plate used in this study in comparison to a stainless steel plate.
In an analysis of locking fixation in the first metatarsocuneiform joint, Saxena and colleagues compared the outcomes of two different fixation constructs for the Lapidus bunionectomy.19 The study compared 19 patients with crossed lag screws to 21 patients with a locking plate with a plantar lag screw. Other than fixation, the only interventional difference pertained to postoperative weightbearing, in which those receiving the plate initiated full weightbearing on the operated foot at four weeks postoperative in comparison to six weeks for those with crossed screws. The authors found no statistically significant differences related to postoperative complications between the two fixation groups. The authors concluded that the Lapidus bunionectomy fixated with a locking plate and a plantar lag screw allows earlier weightbearing in comparison to crossed lag screws without a difference in complications.
Sorenson and colleagues also assessed the success of a locked plate for the Lapidus fusion.20 In 19 out of 21 feet, surgeons used an interfragmentary screw with plates in the other two. It is also worth noting that 16 out of 21 feet received bone marrow aspirate. The findings denoted an average of 6.95 weeks to radiographic fusion, an average of two weeks to ambulation and a 9.52 percent rate of asymptomatic malunion. There was also a 0 percent rate of delayed union or non-union, a 0 percent rate of revision, and a rate of hardware removal of 4.76 percent.
In a cadaveric study, Scranton and coworkers looked at two different constructs for the first metatarsocuneiform joint arthrodesis.21 This study compared a locking compression plate to crossed screws. Researchers tested each modality on five cadaveric limbs. The plate proved to be a more rigid construct.
Cottom and coworkers performed a slightly different study of locking plates on the first metatarsocuneiform arthrodesis.22 They compared a low profile locking plate with a compression screw versus the same locking plate with a plantar interfragmentary screw. There were five cadaveric limbs in each group. The mean ultimate load of the locking plate with a plantar interfragmentary screw was statistically greater than the locking plate with an intra-plate compression screw.
Klos and colleagues compared a medial locking plate with a compression screw versus two crossed screws for the fixation of a first metatarsocuneiform joint arthrodesis.23 Each group consisted of four cadaveric limbs. Under cyclic loading conditions, the construct using a medial locking plate with an adjunct compression screw was superior to the construct using two crossed screws.
Gruber and coworkers also compared two types of fixation for a first metatarsocuneiform arthrodesis: a dorsomedial locking plate with a lag screw and crossed screws. Each group consisted of five cadaveric limbs. The researchers found no difference in rigidity between the two groups.24
Granata and colleagues studied the locking plate fixation success of the talonavicular joint.25 The authors analyzed two lag screws in seven cadaveric limbs versus one lag screw and a locked compression plate in six cadaveric limbs. In their biomechanical model, a dorsal locked compression plate with one retrograde screw was more effective at limiting the 3D motion across the talonavicular joint in comparison with the traditional construct of two lag screws.25
Abbasian and colleagues analyzed three types of fixation for a calcaneal osteotomy: a lateral locking plate, a headless screw or a headed screw.26 In 67 osteotomies, 17 had fixation using a headed screw, 18 received a headless screw and the remaining 32 had lateral plate fixation. Overall, 47 percent of the headed screws, 11 percent of the headless screws and 6 percent of the lateral plates required removal to address symptoms that physicians suspected were due to the hardware. There was a 10 percent rate of wound complications in the lateral plate cohort. The incidences of local wound complications and radiological delayed union were higher in the group fixated with lateral locking plates. There was no significant difference in union rate among the three types.
In an analysis of locking plates on calcaneal fractures, Hyer and colleagues performed a two-year retrospective analysis of 17 calcaneal fractures treated with locking plates.27 Weightbearing began at approximately four to five weeks. Serial radiographic analysis occurred throughout the two years of the study. The authors concluded that early weightbearing could begin in patients with calcaneal fractures if surgeons employed locking plates for the fractures.
Blake and coworkers performed a biomechanical analysis of a locking and a non-locking plate on a cadaveric calcaneal fracture model.28 Surgeons created a Sanders IIB type calcaneal fracture in 10 matched pairs of cadaveric calcanei. Each pair had fixation with the same calcaneal reconstruction plate using either locking or non-locking screws in the same hole pattern. Specimens had axial loading for 1,000 cycles through the talus followed by load to failure. Statistical comparisons occurred between the locking and non-locking constructs on the displacements during cyclic loading as well as construct stiffness and load achieved at selected fragment displacements. Researchers found no mechanical advantage to locking technology for calcaneal fractures in their model.
Redfern and coworkers also compared a locking plate and non-locking plate for calcaneal fractures in five cadaveric limbs each.29 In a cadaver model of Sanders type IIB calcaneal fractures, locking plate fixation did not provide a biomechanical advantage over traditional non-locking plate fixation.
Eckel and colleagues analyzed four different lateral plate constructs for distal fibula fractures.30 Researchers divided 40 fresh frozen lower extremities into four groups. Simulating Weber B distal fibula fractures with an osteotomy, the study authors stabilized the fracture with one of four plate systems: a standard one-third tubular plate with an interfragmentary lag screw; a locked compression plate with a lag screw; a low-profile locking plate with a lag screw; or a non-locking plate. Researchers applied controlled monotonic bending and cyclic torsional loading, and quantified bending stiffness, torsional stiffness and fracture site motion. They found no significant differences in plate performance.
In a cadaveric model, Kim and colleagues compared a locking and conventional plating system for the fixation of the distal fragment of a distal fibula fracture.31 Overall, the data indicated that a locking plate construct with two distal unicortical screws was mechanically equivalent to standard plating with three distal screws. In addition, fixation with the standard plates depended on bone mineral density whereas the locking plate fixation was independent of bone mineral density. The authors state that the clinical implication of this study was that locking plates may be advantageous in patients with the most severe osteoporosis.
Another study by Ozkaya and coworkers analyzed the treatment of distal tibial fractures with locking and non-locking plates through a minimally invasive approach.32 In their study, 43 patients with closed fractures of the distal tibia metaphysis received either a stainless steel non-locking plate or a titanium locking plate. Minimally invasive medial plating with titanium locking plates resulted in prolonged secondary healing both in comminuted and simple fracture patterns in comparison to conventional stainless steel non-locking plates. Researchers utilized no free interfragmentary lag screws in this study.
Ahmad and colleagues analyzed percutaneous locked plating for fractures of the distal tibia.33 They reviewed 18 patients treated with locking plates. They found that distal tibial locking plates have high fracture union rates, minimum soft tissue complications and good functional outcomes. The literature shows similar fracture union and complication rates in locking and non-locking plates.
O’Neil and coworkers compared two types of fixation for a tibiotalocalcaneal arthrodesis.34 Researchers tested an intramedullary nail with a lag screw against a locking plate with a lag screw with six cadaveric limbs in each group. The locking plate construct showed higher final rigidity than the intramedullary nail construct.
After analysis of all of these studies, it appears that the best construct is a free interfragmentary screw coupled with a locking plate. This offers the most rigid construct with compression across the fracture or fusion site. Locking plate technology also affords early weightbearing of the operative extremity. This may decrease post-surgical morbidity in patients over the long term, specifically decreasing the incidence of deep venous thrombosis. Further study is needed to determine this. Locking plates seem to be a viable option in foot and ankle trauma and reconstruction cases without increasing complications.
Dr. DeCarbo is a fellowship trained foot and ankle surgeon in private practice at the Orthopedic Group in Pittsburgh. He is a faculty member with the Monongahela Valley Foot and Ankle Reconstructive Fellowship in Monongahela, Pa. Dr. DeCarbo is a Fellow of the American College of Foot and Ankle Surgeons.
Dr. Pappas is a Fellow with the Monongahela Valley Foot and Ankle Reconstructive Fellowship in Monongahela, Pa. He is an Associate of the American College of Foot and Ankle Surgeons.
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18. Hunt KJ, Ellington JK, Anderson RB, et al. Locked versus non locked plate fixation for hallux MTP arthrodesis. Foot Ankle Int. 2011; 32(7):704-709.
19. Saxena A, Nguyen A, Nelsen E. Lapidus bunionectomy: early evaluation of crossed lag screws versus locking plate with plantar lag screw. J Foot Ankle Surg. 2009; 48(2):170-179.
20. Sorensen MD, Hyer CF, Berlet GC. Results of lapidus arthrodesis and locked plating with early weight-bearing. Foot Ankle Spec. 2009; 2(5):227-233.
21. Scranton PE, Coetzee JC, Carreira D. Arthrodesis of the first metatarsal joint: a comparative study of fixation methods. Foot Ankle Int. 2009; 30(4):341-345.
22. Cottom JM, Rigby RB. Biomechanical comparison of a locking plate with intraplate compression screw versus locking plate with plantar interfragmentary screw for Lapidus arthrodesis: a cadaveric study. J Foot Ankle Surg. 2013; 52(3):339-342.
23. Klos, K, Gueorguiev B, Muckley T, et al. Stability of medial locking plate and compression screw versus two crossed screws for lapidus arthrodesis. Foot Ankle Int. 2010; 31(2):158-163.
24. Gruber F, Sinkov VS, Bae SY, et al. Crossed screws versus dorsomedial locking plate with compression screw for first metatarsocuneiform arthrodesis: a cadaver study. Foot Ankle Int. 2008; 29(9):927-930.
25. Granata JD, Berlet GC, Ghotge R, et al. Talonavicular joint fixation: A biomechanical comparison of locking compression plates and lag screws. Foot Ankle Spec. 2014; 7(1):20-31.
26. Abbasian A, Zaidi R, Guha A, et al. Comparison of three different fixation methods of calcaneal osteotomies. Foot Ankle Int. 2013; 34(3):420-425.
27. Hyer CF, Atway S, Berlet GC, Lee TH. Early weight bearing of calcaneal fractures fixated with locked plates: a radiographic review. Foot Ankle Spec. 2010; 3(6):320-323.
28. Blake MH, Owen JR, Sanford TS, et al. Biomechanical evaluation of a locking and non-locking reconstruction plate in an osteoporotic calcaneal fracture model. Foot Ankle Int. 2011; 32(4):432-436.
29. Redfern DJ, Oliveira ML, Campbell JT, et al. A biomechanical comparison of locking and non-locking plates for the fixation of calcaneal fractures. Foot Ankle Int. 2006; 27(3):196-201.
30. Eckel TT, Glisson RR, Anand P, et al. Biomechancial comparison of four different lateral plate constructs for distal fibula fractures. Foot Ankle Int. 2013; 34(11):1588-1595.
31. Kim T, Ayturk UM, Haskell A, et al. Fixation of osteoporotic distal fibula fractures: a biomechanical comparison of locking versus conventional plates. J Foot Ankle Surg. 2007; 46(1):2-6.
32. Ozkaya U, Parmaksizoglu AS, Gul M, et al. Minimally invasive treatment of distal tibial fractures with locking and non-locking plates. Foot Ankle Int. 2009; 30(12):1161-1167.
33. Ahmad MA, Sivaraman A, Zig A, et al. Percutaneous locking plates for fractures of the distal tibia: our experience and a review of the literature. J Trauma Acute Care Surg. 2012; 72(2):E81-7.
34. O’Neill PJ, Logel KJ, Parks BG, et al. Rigidity comparison of locking plate and intrameduallary fixation for tibiotalocalcaneal arthrodesis. Foot Ankle Int. 2008; 29(6):581-586.
For further reading, see “Point-Counterpoint: Are Locking Plates Necessary For First MPJ Fusion?” in the June 2011 issue of Podiatry Today.