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Distal femur: dynamization of plating
S44 Injury, Int. J. Care Injured 49S1 (2018) S44–S48 Volume 49 Supplement 1 June 2018 ISSN 0020-1383
Contents lists available at ScienceDirect
Injury Plating of Fractures: current treatments and complications Guest Editors: Peter Augat and Sune Larsson
j o u r n a l h o m e p a g e : w w w. e l s e v i e r . c o m / l o c a t e / i n j u r y
Distal femur: dynamization of plating Utku Kandemira,* a
Department of Orthopaedic Surgery, University of California, San Francisco, California, USA
K E Y W O R D S
A B S T R A C T
Dynamization Distal femur Fracture Plating Nonunion Delayed union
With advances in osteosynthesis technology providing improved stability of fixation and better outcomes, surgical treatment has become the standard of care for distal femur fractures. Pre-contoured distal femoral locking plates are the most commonly used implants for fixation. However, healing problems such as delayed union, failure of fixation, and /or nonunion are not uncommon. The fixation construct being “too stiff” is a commonly quoted reason when nonunion/failure of fixation occurs on distal femur fractures fixed with a plate. A flexible fixation construct allowing controlled axial micromotion could help stimulate the bone healing. In order to achieve this goal, plating construct stiffness can be modified by several methods. © 2018 Elsevier Ltd. All rights reserved.
Introduction Distal femur fractures are relatively uncommon fractures, estimated to be about 0.4% of all fractures and 6% of all femur fractures [1,2]. More than half of all distal femur fractures occur in the elderly and this is expected to increase with the aging population [3]. With advances in osteosynthesis technology providing improved stability of fixation and better outcomes, surgical treatment of distal femur fractures has become the standard of care [4–6]. The primary goal of surgical treatment is to provide optimal mechanical fixation that allows for an early range of motion and to achieve healing without loss of alignment and fixation. It has been noted that strain at the facture site is critical for a successful healing process. Excessive axial strains as well as shear strain between fracture fragments may both be detrimental to bone healing [7–9]. At the same time, a moderate amount of strain is necessary to stimulate callus formation [7–9]. Strain is related to fracture gap and interfragmentary motion which in turn depends on stiffness of fixation construct. While the ideal value of stiffness i.e. the balance between the stability and motion at fracture site, to achieve uneventful and timely fracture healing for a specific fracture pattern and bone characteristics is yet to be determined, it has been shown that construct stiffness can be modified by the surgeon by choosing implant material, screw type, position of screws or position of the plate [10]. In a simple fracture pattern with anatomic reduction a stiffer construct may be preferable (stainless steel implant with hybrid or locking screws) [8]. On the other hand, in a comminuted fracture pattern, a less stiff construct allowing for more micromotion with fatigue life long enough to for the plate
to survive until fracture healing may provide better outcome (e.g. titanium implant with locking screws) [8,11–14]. Rigid fixation constructs aim to provide absolute stability at the fracture site. The healing occurs with primary/direct healing consisting intramembranous healing and osteonal /haversian remodeling without formation of callus. This is preferred type of healing for intraarticular fractures and may be for simple fractures patterns at the metaphysis and diaphysis. Flexible fixation constructs provide relative stability. The healing occurs with secondary/indirect healing which consists of both intramembranous and endochondral ossification with formation of callus. This is commonly applied for comminuted fractures and fractures at the metaphysis and diaphysis. In summary, stability at the fracture site dictates the type of healing. Regarding fixation with plates, compression plating and neutralization plating after anatomic reduction of simple fractures are examples of rigid fixation construct. On the other hand, bridge plating of a comminuted diaphyseal or metadiaphyseal fracture is an example of flexible fixation construct. In the setting of distal femur fractures, if there is an extension of the fracture into the knee joint, anatomic reduction and rigid fixation of the intraarticular component of the fracture providing absolute stability is necessary [9]. The healing of the intraarticular component is usually not problematic. When the supracondylar metadiaphyseal component of the fracture is comminuted, plate fixation is a bridging construct providing relative stability. On the other hand, both rigid and flexible fixation constructs providing relative stability could be applied for simple fracture patterns at the metadiaphyseal part of the distal femur. Dynamic construct vs. static/fixed construct
* Corresponding author at: Department of Orthopaedic Surgery, University of California San Francisco, 2550 23rd St., Bldg.9, 2nd Floor, San Francisco, CA 94110, USA E-mail address: [email protected] (U. Kandemir). 0020-1383/© 2018 Elsevier Ltd. All rights reserved.
Dynamic fixation construct usually refers to fixation with intramedullary nail when interlocking screws are placed in a
U. Kandemir / Injury, Int. J. Care Injured 49S1 (2018) S44–S48
dynamic hole through the nail in a length stable fracture pattern (such as transverse fracture pattern where the length will not change with loading) in contrast to static locking when interlocking screws are placed through round holes. Most of the contemporary femoral and tibial intramedullary nail designs have an oblong hole with an option of placing the interlocking screw in dynamic mode. All static nailing constructs and most of the plating constructs (except anatomic reduction and compression fixation) have some micromotion at the fracture site in torsional and bending stress. While nailing constructs are extremely stiff under axial loads, plating constructs tend to bend under axial loads due to their position outside the mechanical loading axis. This bending results in closing of the fracture gap at the far cortex and a lack of micromotion at the near cortex of the plate. The rationale behind dynamic plating constructs is that a more uniform motion along the longitudinal bone axis is introduced at the fracture site which in turn provides stimulation of bone healing. The typical plating constructs are static and not dynamic in the longitudinal axis of the bone even when a bridging construct is applied for a comminuted fracture. Recently, dynamic constructs for plating were introduced with modifications of the bone-screw or plate screw interfaces [22,40–42]. These dynamic designs allow more and controlled motion at the fracture site without compromising the longitudinal stability of fracture fixation. Far locking screw, dynamic locking screw, active plates are examples of these modifications. Dynamization While the term dynamic describes the condition at the time of fixation, dynamization is usually reserved for the modification of original fixation on follow up. When there is delayed healing or nonunion, dynamization may help in order to stimulate bone healing through an increase of compressive axial motion and loading of the bone. Dynamization of nailing constructs has been previously described and applied [15,16]. The goal is to convert a static construct into a dynamic construct which can be achieved either by exchanging static interlocking screws with an interlocking screw in dynamic mode or removing all interlocking screws on one side of the fracture altogether if there is no concern of rotational instability. Dynamization of a plating construct may be helpful to achieve bone healing before failure of fixation occurs in cases of delayed healing and nonunion. This can be achieved by modifying the fixation construct from a stiff construct to a more flexible construct. The stiffness can be modified to allow more motion at the fracture site by removing screws close to fracture site and/or exchanging locking screws with nonlocking screws as much as possible without compromising the overall construct stability. Evaluation of the cause(s) of delayed healing or nonunion is critical. Dynamization is obviously not a good option when the cause of the delayed healing or nonunion is instability of the fixation construct and may results in catastrophic failure. Fixation constructs in distal femur fractures Implant choices available for the fixation of distal femur fractures include intramedullary nails and plates [17]. Pre-contoured distal femoral locking plates are the most commonly used implants [4,11,18,19] allowing for locking, non-locking or hybrid (combination of locking and non-locking) screw fixation. However, healing problems such as delayed union, failure of fixation, and/or nonunion occur in up to 23% of patients [12,20,21]. Numerous, previous studies clearly demonstrated that type of implant and fixation construct influence biomechanical performance [2,6,12,17,22–29]. While it is not exactly clear how rigidity of implant or fixation construct affects failure, the amount of rigidity
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of the fixation construct has been associated with healing problems and failure of fixation [4,12,13,30–32]. Multiple factors influence the mechanical strength of a distal femoral locking plate construct including the fracture pattern, bone quality, quality of reduction, implant design (number of periarticular screws, geometrical shape, thickness of plate), implant material, length of plate, the position of plate (offset vs. contact to bone), screw type (size, locking vs. nonlocking, unicortical vs. bicortical), and screw configuration. Other than the fracture pattern and bone quality, the rest of the factors are under the surgeon’s control and can be modulated [4,10,33]. Dynamic construct or dynamization as a solution to nonunion/failure of fixation of distal femur fractures The evaluation of any delayed healing and nonunion should include a detailed investigation of the host and biological factors such as smoking and metabolic and endocrine abnormalities [34,35] in addition to the detailed analysis of fixation mechanics. The restoration of the mechanical axis and alignment is of utmost importance in order to achieve the best outcome [30]. The fixation construct being “too stiff” is a commonly quoted reason when nonunion/failure of fixation occurs on distal femur fractures fixed with a plate [4,12,13,30–32]. Stiffness of a plating construct is the amount of displacement in response to applied force. A stiffer construct will have less motion at the fracture site compared to a more flexible construct. A flexible fixation construct allowing axial micromotion will help stimulate the bone healing. On the other hand, a fixation construct too flexible allowing too much axial motion or bending, torsional, or shear motion at fracture site will prevent bone healing and result in delayed union or nonunion [36]. It should be noted that, while a stiffer construct may not seem to help for healing, it might provide a longer fatigue life before failure, which translates into more time for healing. Strain levels should also be considered while choosing screw configuration in a given fixation construct [37]. Increased strain levels in the bone around the screws, specifically the screws closer to the fracture site, are critical in failure of fixation with loosening. In healthy bone under axial loading, decreased working length and increased plate rigidity are associated with lower strain levels. In osteoporotic bone, spacing of screws within the plate on each side of fracture decreases strain levels. In case of no load sharing contact at fracture site such as significant comminution, increasing working length to make the construct more flexible increases the strain levels around the screws [37]. Options to modify the plating construct stiffness Options for modifying plating construct stiffness are shown in Table 1. Implant design The specific shape of the implant is associated with construct stiffness. This has been reported in biomechanical studies comparing different types of locking plates used for fixation of distal femur fractures [17]. The thickness and the width of the plate are correlated with stiffness. All other parameters being equal, a thicker distal femoral locking plate will result in a stiffer fixation construct. Implant material Most of the currently used plates are alloys of stainless steel or titanium. As modulus of elasticity of titanium is lower, the same design stainless steel plate will provide stiffer fixation construct compared to the titanium plate of the same design. Not all stainless steel alloys and titanium alloys used for manufacturing the plates are the same. The ingredients of alloy may be modified to achieve a stiffer or less stiff plate.
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Table 1 Options to modify the plating constructs stiffness 1.
3.
4.
5.
(b)
Implant design a.
2.
(a)
Shape
b.
Thickness
c.
Width
Implant material a.
Modification of stainless steel alloy
b.
Modification of titanium alloy
c.
Carbon fiber reinforced polyetherketone
Fixation construct a.
Nonlocking only fixation
b.
Very far fixation: increased working length
Screw-bone or plate-screw interface a.
Far cortical locking
b.
Dynamic locking screw
c.
Active locking plate
Modification of construct: dynamization a.
Removal of screws crossing fracture site (if there are any) (Fig. 2)
b.
emoval of screws that are closer to fracture site (Fig. 3)
c.
Exchange of locking screws to nonlocking screws (Fig. 4)
d.
Exchange of bicortical screws closer to fracture site to unicortical screws (Fig. 5)
While titanium plates seems more attractive in fixation of distal femur fractures, the clinical results have not been shown to be superior to stainless steel plates [21]. With the reports of fixation construct being “too stiff” as a cause of failure of fixation, recently, plates made of carbon fiber reinforced polyetherketone were designed [38] and approved for clinical use in distal femur fractures [40]. They are claimed to have comparable fatigue life to stainless steel and titanium plates and less stiffness, which could potentially provide better construct stiffness for bony healing. Fixation construct The type of screws used influence construct stiffness. Using conventional screws only at the diaphysis will provide a less stiff construct compared to when locking screws are used. On the other hand, the use of only conventional screws may compromise the fixation especially in osteoporotic bone and failure of fixation with loosening at bone screw interface and pull-out of the plate may happen. This type of failure could be minimized by using longer plates especially in non-osteoporotic bone. Another option to decrease the stiffness across the fracture site is to increase the distance between proximal and distal points of fixation across the fracture site. This increase in working length will allow more motion across the fracture site and may be preferred especially for comminuted fractures [33].
Fig. 1. Radiographic imaging (X-rays and CT scan) is shown of a patient 9 months after (a) open reduction and (b) internal fixation. The patient presented with persistent and worsening pain associated with weight bearing localized at distal thigh and above knee and no pain in resting position. As a treatment option of the delayed union/nonunion, this patient could benefit from dynamization methods as simulated in Figs. 2–5.
Far cortical locking, dynamic locking screw, and active locking plates are examples of modifications of screw-bone or plate-screw interface delivering symmetric motion. Far cortical locking consists of partially threaded locking screws that lock into the plate and far cortex allowing motion at the level of the screw hole at the near cortex. Improved healing rates have been reported with this design modification [22]. The same can be achieved using near cortical slots with regular locking screws [41]. The dynamic locking screw is a locking screw consisting of two elements, the sleeve with the thread and the pin with the locking head. Both connected in a way that allows movement within the screw without movement in the bone-screw interface or at plate screw interface [41]. Active locking plate provides controlled axial dynamization by elastic suspension of locking holes within the plate [42]. Modification of fixation construct: dynamization When there is delayed healing or nonunion, a process similar to dynamization of nailing constructs, could be considered by modification of fixation construct by several methods (Fig. 1): • • •
Screw-bone or plate-screw interface Modifications of the fixation points or the type of screws used in the shaft affect primarily the bending stiffness. Modifications of the screw-bone or plate-screw interface at the level of the diaphysis induce axial motion without causing any shear or failure of fixation i.e. controlled axial micromotion. This type of modifications can also help with more homogenous circumferential bony healing as stress shielding of the near (lateral) cortex occurs compared stronger bone healing on the far (medial) side of the fracture when fixed locking screw constructs is used. [20]. Faster and stronger healing with these types of modifications compared to standard locking plate construct is associated with lower risk of fixation failure due to the reduced load sharing duration of the fixation construct.
•
Removing the screws closer to the fracture site thus increasing the distance without fixation (working length) [33,43]. Exchanging the locking screws closer to the fracture site with nonlocking screws. Exchanging the bicortical screws closer to the fracture site with unicortical screws. Removal of screw(s) crossing the fracture site at the supracondylar area (not the ones crossing the intraarticular fracture site) in cases that was placed with original fixation will eliminate the stiffness across the fracture site [44,45].
• Dynamization of the plating construct may provide the necessary stimulus for healing and avoid failure of fixation. Assessment of a fixation construct as too stiff while it actually is too flexible would be a major mistake and will results in quick failure. A pitfall in dynamization is that the fatigue life of the plate might be shortened with dynamization unless bony contact occurs unloading the plate.
U. Kandemir / Injury, Int. J. Care Injured 49S1 (2018) S44–S48
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Fig. 2. Dynamization by removal of screws crossing fracture site.
Fig. 4. Exchange of locking screws to nonlocking screws.
Fig. 3. Removal of screws that are closer to fracture site.
Figs 5. Exchange of bicortical screws closer to fracture site to unicortical screws.
Intramedullary nailing Intramedullary nailing nails designed specifically for distal femur fractures with multiple interlocking screws in different planes commonly provides adequate fixation for distal femur fractures. Intramedullary nails provide an extremely large axial stiffness by the position of the nail at the center of the load axis [46,47]. Micromotion in distal femur nailing is typically generated by off axis loading resulting in bending and/or twisting of the nail. The prerequisite for distal femur nailing thus is that the fracture pattern should be amenable for fixation with IMN, providing some inherent rotational stability. The amount of the bone of the supracondylar fragment may be the limiting factor if 3 or 4 interlocking screws in multiple planes cannot be placed at the distal fragment. Summary Healing problems are not uncommon in treatment of distal femur fractures. Most common type of implant used for fixation is distal femoral locking plate. The stiffness of the fixation construct may be related to failures. The construct stiffness can be modulated with interplay of multiple parameters at the time of original fixation. When delayed healing or nonunion occurs, dynamization of plating should be considered if the stiffness of the construct is deemed to be the problem.
Disclosure The author reports no conflicts of interest. Acknowledgment The authors of this manuscript express their thanks to the Osteosynthesis and Trauma Care Foundation for the sponsorship of the publication of this Supplement in Injury. References [1] Court-Brown CM, Caesar B. Epidemiology of adult fractures: a review. Injury 2006;37(8):691–7. [2] Meyer RW, Plaxton NA, Postak PD, et al. Mechanical comparison of a distal femoral side plate and a retrograde intramedullary nail. J Orthop Trauma 2000;14(6):398–404. [3] Arneson TJ, Melton LJ 3rd, Lewallen DG, et al. Epidemiology of diaphyseal and distal femoral fractures in Rochester, Minnesota, 1965–1984. Clin Orthop Relat Res 1988;234:188–94. [4] Beltran MJ, Gary JL, Collinge CA. Management of distal femur fractures with modern plates and nails: state of the art. J Orthop Trauma 2015;29(4):165–72. [5] Stover M. Distal femoral fractures: current treatment, results and problems. Injury 2001;32(Suppl 3):SC3–13. [6] Zlowodzki M, Williams S, Zardiackas LD, et al. Biomechanical evaluation of the less invasive stabilization system and the 95 degree angled blade plate for the internal fixation of distal femur fractures in human cadaveric bones with high mineral density. J Trauma 2006;60:836–840.
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[7] Augat P, Burger J, Schorlemmer S, et al. Shear movement at the fracture site delays healing in a diaphyseal fracture model. J Orthop Res 2003;21:1011–1017. [8] Hak DJ, Toker S, Yi C, et al. The influence of fracture fixation biomechanics on fracture healing. Orthopedics 2010;33(10):752–755. [9] Perren SM. Evolution of the internal fixation of long bone fractures. The scientific basis of biological internal fixation: choosing a new balance between stability and biology. J Bone Joint Surg Br 2002;84(8):1093–110. [10] Kandemir U, Augat P, Dipl-Ing SK, Dipl-Ing FW, von Oldenburg Dipl-Ing G, Schmidt U. Implant material, type of fixation at the shaft and position of plate modify biomechanics of distal femur plate osteosynthesis. J Orthop Trauma 2017;31(8):e241–e246. [11] Henderson CE, Kuhl LL, Fitzpatrick DC, et al. Locking plates for distal femur fractures: is there a problem with fracture healing? J Orthop Trauma 2011;25(Suppl 1):S8–14. [12] Henderson CE, Lujan TJ, Kuhl LL, et al. 2010 Mid-America Orthopaedic Association Physician in training award: healing complications are common after locked plating for distal femur fractures. Clin Orthop Relat Res 2011;469:1757–1765. [13] Rodriguez EK, Boulton C, Weaver MJ, et al. Predictive factors of distal femoral fracture nonunion after lateral locked plating: a retrospective multicenter casecontrol study of 283 fractures. Injury 2014;45(3):554–9. [14] Rodriguez EK, Zurakowski D, Herder L, et al. Mechanical construct characteristics predisposing to non-union after locked lateral plating of distal femur fractures. J Orthop Trauma 2016;30(8):403–408. [15] Litrenta J, Tornetta P 3rd, Vallier H, Firoozabadi R, Leighton R, Egol K, Kruppa C, Jones CB, Collinge C, Bhandari M, Schemitsch E, Sanders D, Mullis B. Dynamizations and exchanges: and indications. J Orthop Trauma 2015;29(12):569–73. [16] Swanson EA, Garrard EC, Bernstein DT, O’Connor DP, Brinker MR. Results of a systematic approach to exchange nailing for the treatment of aseptic femoral nonunions. J Orthop Trauma 2015;29(1):21–7. [17] Schmidt U, Penzkofer R, Bachmaier S, et al. Implant material and design alter construct stiffness in distal femur locking plate fixation: a pilot study. Clin Orthop Relat Res 2013;471(9):2808–2814. [18] Gangavalli AK, Nwachuku CO. Management of distal femur fractures in adults: an overview of options. Orthop Clin North Am 2016;47(1):85–96. [19] Gwathmey FW Jr, Jones-Quaidoo SM, Kahler D, et al. Distal femoral fractures: current concepts. J Am Acad Orthop Surg 2010;18(10):597–607. [20] Lujan TJ, Henderson CE, Madey SM, et al. Locked plating of distal femur fractures leads to inconsistent and asymmetric callus formation. J Orthop Trauma 2010;24:156–162. [21] Ricci WM, Streubel PN, Morshed S, et al. Risk factors for failure of locked plate fixation of distal femur fractures: an analysis of 335 cases. J Orthop Trauma 2014;28(2):83–9. [22] Bottlang M, Lesser M, Koerber J, et al. Far cortical locking can improve healing of fractures stabilized with locking plates. J Bone Joint Surg Am 2010;92:1652–1660. [23] Haidukewych G, Sems SA, Huebner D, et al. Results of polyaxial locked-plate fixation of periarticular fractures of the knee. J Bone Joint Surg Am 2007;89:614–620. [24] Higgins TF, Pittman G, Hines J, et al. Biomechanical analysis of distal femur fracture fixation: fixed-angle screw-plate construct versus condylar blade plate. J Orthop Trauma 2007;21:4–6. [25] Ito K, Hungerbühler R, Wahl D, et al. Improved intramedullary nail interlocking in osteoporotic bone. J Orthop Trauma 2001;15(3):192–196. [26] Otto RJ, Moed BR, Bledsoe JG. Biomechanical comparison of polyaxial-type locking plates and fixed-angle locking plates for internal fixation of distal femur fractures. J Orthop Trauma 2009;23:645–652. [27] Wähnert D, Hoffmeier K, Froeber R, et al. Distal femur fractures of the elderly: different treatment options in a biomechanical comparison. Injury 2011;42:655–659.
[28] Wähnert D, Hoffmeier KL, von Oldenburg G, et al. Internal fixation of type-C distal femoral fractures in osteoporotic bone. J Bone Joint Surg Am 2010;92:1442–1452. [29] Zlodowski M, Williamson S, Cole PA, et al. Biomechanical evaluation of the less invasive stabilisation system, angled blade plate, and retrograde intramedullary nail for the internal fixation of distal femur fractures. J Orthop Trauma 2004;18:494–502. [30] Augat P, Simon U, Liedert A, et al. Mechanics and mechanobiology of fracture healing in normal and osteoporotic bone. Osteoporos Int 2005;16(Suppl 2):36–43. [31] Vallier HA, Hennessey TA, Sontich JK, et al. Failure of LCP condylar plate fixation in the distal part of the femur. A report of six cases. J Bone Joint Surg Am 2006;88(4):846–53. [32] Vallier HA, Immler W. Comparison of the 95-degree angled blade plate and the locking condylar plate for the treatment of distal femoral fractures. J Orthop Trauma 2012;26(6):327–32. [33] Stoffel K, Dieter U, Stachowiak G, et al. Biomechanical testing of the LCP: how can stability in locked internal fixators be controlled? Injury 2003;34(Suppl 2):B11–9. [34] Brinker MR, O’Connor DP, Monla YT, Earthman T. Metabolic and endocrine abnormalities in patients with nonunions. J Orthop Trauma 2007;21(8):557–70. [35] Holick MF. Vitamin D deficiency. N Engl J Med 2007;357(3):266–81. [36] Uhthoff HK, Poitras P, Backman DS. Internal plate fixation of fractures: short history and recent developments. J Orthop Sci 2006;11(2):118–26. [37] MacLeod AR, Simpson AH, Pankaj P. Age-related optimization of screw placement for reduced loosening risk in locked plating. J Orthop Res 2016;34(11):1856–1864. [38] Bagheri ZS, Tavakkoli Avval P, Bougherara H, Aziz MS, Schemitsch EH, Zdero R. Biomechanical analysis of a new carbon fiber/flax/epoxy bone fracture plate shows less stress shielding compared to a standard clinical metal plate. J Biomech Eng 2014;136(9):091002. [39] Hak DJ, Mauffrey C, Seligson D, Lindeque B. Use of carbon-fiber-reinforced composite implants in orthopedic surgery. Orthopedics 2014;37(12):825–30. [40] Gardner MJ, Nork SE, Huber P, Krieg JC. Stiffness modulation of locking plate constructs using near cortical slotted holes: a preliminary study. J Orthop Trauma 2009;23(4):281–7. [41] Döbele S, Horn C, Eichhorn S, Buchholtz A, Lenich A, Burgkart R, Nüssler AK, Lucke M, Andermatt D, Koch R, Stöckle U. The dynamic locking screw (DLS) can increase interfragmentary motion on the near cortex of locked plating constructs by reducing the axial stiffness. Langenbecks Arch Surg 2010;395(4):421–8. [42] Bottlang M, Tsai S, Bliven EK, von Rechenberg B, Klein K, Augat P, Henschel J, Fitzpatrick DC, Madey SM. Dynamic stabilization with active locking plates delivers faster, stronger, and more symmetric fracture-healing. J Bone Joint Surg Am 2016;98(6):466–74. [43] Märdian S, Schaser KD, Duda GN, Heyland M. Working length of locking plates determines interfragmentary movement in distal femur fractures under physiological loading. Clin Biomech (Bristol, Avon) 2015;30(4):391–6. [44] Märdian S, Schmölz W, Schaser KD, Duda GN, Heyland M. Interfragmentary lag screw fixation in locking plate constructs increases stiffness in simple fracture patterns. Clin Biomech (Bristol, Avon) 2015;30(8):814–9. [45] Oh JK, Hwang JH, Lee SJ, Kim JI. Dynamization of locked plating on distal femur fracture. Arch Orthop Trauma Surg 2011;131(4):535–9. [46] Augat P, Penzkofer R, Nolte A, Maier M, Panzer S, v Oldenburg G, Pueschl K, Simon U, Bühren V. Interfragmentary movement in diaphyseal tibia fractures fixed with locked intramedullary nails. J Orthop Trauma 2008;22(1):30–6 [47] Penzkofer R, Maier M, Nolte A, von Oldenburg G, Püschel K, Bühren V, Augat P. Influence of intramedullary nail diameter and locking mode on the stability of tibial shaft fracture fixation. Arch Orthop Trauma Surg 2009;129(4):525–31.
Contents lists available at ScienceDirect
Injury Plating of Fractures: current treatments and complications Guest Editors: Peter Augat and Sune Larsson
j o u r n a l h o m e p a g e : w w w. e l s e v i e r . c o m / l o c a t e / i n j u r y
Distal femur: dynamization of plating Utku Kandemira,* a
Department of Orthopaedic Surgery, University of California, San Francisco, California, USA
K E Y W O R D S
A B S T R A C T
Dynamization Distal femur Fracture Plating Nonunion Delayed union
With advances in osteosynthesis technology providing improved stability of fixation and better outcomes, surgical treatment has become the standard of care for distal femur fractures. Pre-contoured distal femoral locking plates are the most commonly used implants for fixation. However, healing problems such as delayed union, failure of fixation, and /or nonunion are not uncommon. The fixation construct being “too stiff” is a commonly quoted reason when nonunion/failure of fixation occurs on distal femur fractures fixed with a plate. A flexible fixation construct allowing controlled axial micromotion could help stimulate the bone healing. In order to achieve this goal, plating construct stiffness can be modified by several methods. © 2018 Elsevier Ltd. All rights reserved.
Introduction Distal femur fractures are relatively uncommon fractures, estimated to be about 0.4% of all fractures and 6% of all femur fractures [1,2]. More than half of all distal femur fractures occur in the elderly and this is expected to increase with the aging population [3]. With advances in osteosynthesis technology providing improved stability of fixation and better outcomes, surgical treatment of distal femur fractures has become the standard of care [4–6]. The primary goal of surgical treatment is to provide optimal mechanical fixation that allows for an early range of motion and to achieve healing without loss of alignment and fixation. It has been noted that strain at the facture site is critical for a successful healing process. Excessive axial strains as well as shear strain between fracture fragments may both be detrimental to bone healing [7–9]. At the same time, a moderate amount of strain is necessary to stimulate callus formation [7–9]. Strain is related to fracture gap and interfragmentary motion which in turn depends on stiffness of fixation construct. While the ideal value of stiffness i.e. the balance between the stability and motion at fracture site, to achieve uneventful and timely fracture healing for a specific fracture pattern and bone characteristics is yet to be determined, it has been shown that construct stiffness can be modified by the surgeon by choosing implant material, screw type, position of screws or position of the plate [10]. In a simple fracture pattern with anatomic reduction a stiffer construct may be preferable (stainless steel implant with hybrid or locking screws) [8]. On the other hand, in a comminuted fracture pattern, a less stiff construct allowing for more micromotion with fatigue life long enough to for the plate
to survive until fracture healing may provide better outcome (e.g. titanium implant with locking screws) [8,11–14]. Rigid fixation constructs aim to provide absolute stability at the fracture site. The healing occurs with primary/direct healing consisting intramembranous healing and osteonal /haversian remodeling without formation of callus. This is preferred type of healing for intraarticular fractures and may be for simple fractures patterns at the metaphysis and diaphysis. Flexible fixation constructs provide relative stability. The healing occurs with secondary/indirect healing which consists of both intramembranous and endochondral ossification with formation of callus. This is commonly applied for comminuted fractures and fractures at the metaphysis and diaphysis. In summary, stability at the fracture site dictates the type of healing. Regarding fixation with plates, compression plating and neutralization plating after anatomic reduction of simple fractures are examples of rigid fixation construct. On the other hand, bridge plating of a comminuted diaphyseal or metadiaphyseal fracture is an example of flexible fixation construct. In the setting of distal femur fractures, if there is an extension of the fracture into the knee joint, anatomic reduction and rigid fixation of the intraarticular component of the fracture providing absolute stability is necessary [9]. The healing of the intraarticular component is usually not problematic. When the supracondylar metadiaphyseal component of the fracture is comminuted, plate fixation is a bridging construct providing relative stability. On the other hand, both rigid and flexible fixation constructs providing relative stability could be applied for simple fracture patterns at the metadiaphyseal part of the distal femur. Dynamic construct vs. static/fixed construct
* Corresponding author at: Department of Orthopaedic Surgery, University of California San Francisco, 2550 23rd St., Bldg.9, 2nd Floor, San Francisco, CA 94110, USA E-mail address: [email protected] (U. Kandemir). 0020-1383/© 2018 Elsevier Ltd. All rights reserved.
Dynamic fixation construct usually refers to fixation with intramedullary nail when interlocking screws are placed in a
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dynamic hole through the nail in a length stable fracture pattern (such as transverse fracture pattern where the length will not change with loading) in contrast to static locking when interlocking screws are placed through round holes. Most of the contemporary femoral and tibial intramedullary nail designs have an oblong hole with an option of placing the interlocking screw in dynamic mode. All static nailing constructs and most of the plating constructs (except anatomic reduction and compression fixation) have some micromotion at the fracture site in torsional and bending stress. While nailing constructs are extremely stiff under axial loads, plating constructs tend to bend under axial loads due to their position outside the mechanical loading axis. This bending results in closing of the fracture gap at the far cortex and a lack of micromotion at the near cortex of the plate. The rationale behind dynamic plating constructs is that a more uniform motion along the longitudinal bone axis is introduced at the fracture site which in turn provides stimulation of bone healing. The typical plating constructs are static and not dynamic in the longitudinal axis of the bone even when a bridging construct is applied for a comminuted fracture. Recently, dynamic constructs for plating were introduced with modifications of the bone-screw or plate screw interfaces [22,40–42]. These dynamic designs allow more and controlled motion at the fracture site without compromising the longitudinal stability of fracture fixation. Far locking screw, dynamic locking screw, active plates are examples of these modifications. Dynamization While the term dynamic describes the condition at the time of fixation, dynamization is usually reserved for the modification of original fixation on follow up. When there is delayed healing or nonunion, dynamization may help in order to stimulate bone healing through an increase of compressive axial motion and loading of the bone. Dynamization of nailing constructs has been previously described and applied [15,16]. The goal is to convert a static construct into a dynamic construct which can be achieved either by exchanging static interlocking screws with an interlocking screw in dynamic mode or removing all interlocking screws on one side of the fracture altogether if there is no concern of rotational instability. Dynamization of a plating construct may be helpful to achieve bone healing before failure of fixation occurs in cases of delayed healing and nonunion. This can be achieved by modifying the fixation construct from a stiff construct to a more flexible construct. The stiffness can be modified to allow more motion at the fracture site by removing screws close to fracture site and/or exchanging locking screws with nonlocking screws as much as possible without compromising the overall construct stability. Evaluation of the cause(s) of delayed healing or nonunion is critical. Dynamization is obviously not a good option when the cause of the delayed healing or nonunion is instability of the fixation construct and may results in catastrophic failure. Fixation constructs in distal femur fractures Implant choices available for the fixation of distal femur fractures include intramedullary nails and plates [17]. Pre-contoured distal femoral locking plates are the most commonly used implants [4,11,18,19] allowing for locking, non-locking or hybrid (combination of locking and non-locking) screw fixation. However, healing problems such as delayed union, failure of fixation, and/or nonunion occur in up to 23% of patients [12,20,21]. Numerous, previous studies clearly demonstrated that type of implant and fixation construct influence biomechanical performance [2,6,12,17,22–29]. While it is not exactly clear how rigidity of implant or fixation construct affects failure, the amount of rigidity
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of the fixation construct has been associated with healing problems and failure of fixation [4,12,13,30–32]. Multiple factors influence the mechanical strength of a distal femoral locking plate construct including the fracture pattern, bone quality, quality of reduction, implant design (number of periarticular screws, geometrical shape, thickness of plate), implant material, length of plate, the position of plate (offset vs. contact to bone), screw type (size, locking vs. nonlocking, unicortical vs. bicortical), and screw configuration. Other than the fracture pattern and bone quality, the rest of the factors are under the surgeon’s control and can be modulated [4,10,33]. Dynamic construct or dynamization as a solution to nonunion/failure of fixation of distal femur fractures The evaluation of any delayed healing and nonunion should include a detailed investigation of the host and biological factors such as smoking and metabolic and endocrine abnormalities [34,35] in addition to the detailed analysis of fixation mechanics. The restoration of the mechanical axis and alignment is of utmost importance in order to achieve the best outcome [30]. The fixation construct being “too stiff” is a commonly quoted reason when nonunion/failure of fixation occurs on distal femur fractures fixed with a plate [4,12,13,30–32]. Stiffness of a plating construct is the amount of displacement in response to applied force. A stiffer construct will have less motion at the fracture site compared to a more flexible construct. A flexible fixation construct allowing axial micromotion will help stimulate the bone healing. On the other hand, a fixation construct too flexible allowing too much axial motion or bending, torsional, or shear motion at fracture site will prevent bone healing and result in delayed union or nonunion [36]. It should be noted that, while a stiffer construct may not seem to help for healing, it might provide a longer fatigue life before failure, which translates into more time for healing. Strain levels should also be considered while choosing screw configuration in a given fixation construct [37]. Increased strain levels in the bone around the screws, specifically the screws closer to the fracture site, are critical in failure of fixation with loosening. In healthy bone under axial loading, decreased working length and increased plate rigidity are associated with lower strain levels. In osteoporotic bone, spacing of screws within the plate on each side of fracture decreases strain levels. In case of no load sharing contact at fracture site such as significant comminution, increasing working length to make the construct more flexible increases the strain levels around the screws [37]. Options to modify the plating construct stiffness Options for modifying plating construct stiffness are shown in Table 1. Implant design The specific shape of the implant is associated with construct stiffness. This has been reported in biomechanical studies comparing different types of locking plates used for fixation of distal femur fractures [17]. The thickness and the width of the plate are correlated with stiffness. All other parameters being equal, a thicker distal femoral locking plate will result in a stiffer fixation construct. Implant material Most of the currently used plates are alloys of stainless steel or titanium. As modulus of elasticity of titanium is lower, the same design stainless steel plate will provide stiffer fixation construct compared to the titanium plate of the same design. Not all stainless steel alloys and titanium alloys used for manufacturing the plates are the same. The ingredients of alloy may be modified to achieve a stiffer or less stiff plate.
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Table 1 Options to modify the plating constructs stiffness 1.
3.
4.
5.
(b)
Implant design a.
2.
(a)
Shape
b.
Thickness
c.
Width
Implant material a.
Modification of stainless steel alloy
b.
Modification of titanium alloy
c.
Carbon fiber reinforced polyetherketone
Fixation construct a.
Nonlocking only fixation
b.
Very far fixation: increased working length
Screw-bone or plate-screw interface a.
Far cortical locking
b.
Dynamic locking screw
c.
Active locking plate
Modification of construct: dynamization a.
Removal of screws crossing fracture site (if there are any) (Fig. 2)
b.
emoval of screws that are closer to fracture site (Fig. 3)
c.
Exchange of locking screws to nonlocking screws (Fig. 4)
d.
Exchange of bicortical screws closer to fracture site to unicortical screws (Fig. 5)
While titanium plates seems more attractive in fixation of distal femur fractures, the clinical results have not been shown to be superior to stainless steel plates [21]. With the reports of fixation construct being “too stiff” as a cause of failure of fixation, recently, plates made of carbon fiber reinforced polyetherketone were designed [38] and approved for clinical use in distal femur fractures [40]. They are claimed to have comparable fatigue life to stainless steel and titanium plates and less stiffness, which could potentially provide better construct stiffness for bony healing. Fixation construct The type of screws used influence construct stiffness. Using conventional screws only at the diaphysis will provide a less stiff construct compared to when locking screws are used. On the other hand, the use of only conventional screws may compromise the fixation especially in osteoporotic bone and failure of fixation with loosening at bone screw interface and pull-out of the plate may happen. This type of failure could be minimized by using longer plates especially in non-osteoporotic bone. Another option to decrease the stiffness across the fracture site is to increase the distance between proximal and distal points of fixation across the fracture site. This increase in working length will allow more motion across the fracture site and may be preferred especially for comminuted fractures [33].
Fig. 1. Radiographic imaging (X-rays and CT scan) is shown of a patient 9 months after (a) open reduction and (b) internal fixation. The patient presented with persistent and worsening pain associated with weight bearing localized at distal thigh and above knee and no pain in resting position. As a treatment option of the delayed union/nonunion, this patient could benefit from dynamization methods as simulated in Figs. 2–5.
Far cortical locking, dynamic locking screw, and active locking plates are examples of modifications of screw-bone or plate-screw interface delivering symmetric motion. Far cortical locking consists of partially threaded locking screws that lock into the plate and far cortex allowing motion at the level of the screw hole at the near cortex. Improved healing rates have been reported with this design modification [22]. The same can be achieved using near cortical slots with regular locking screws [41]. The dynamic locking screw is a locking screw consisting of two elements, the sleeve with the thread and the pin with the locking head. Both connected in a way that allows movement within the screw without movement in the bone-screw interface or at plate screw interface [41]. Active locking plate provides controlled axial dynamization by elastic suspension of locking holes within the plate [42]. Modification of fixation construct: dynamization When there is delayed healing or nonunion, a process similar to dynamization of nailing constructs, could be considered by modification of fixation construct by several methods (Fig. 1): • • •
Screw-bone or plate-screw interface Modifications of the fixation points or the type of screws used in the shaft affect primarily the bending stiffness. Modifications of the screw-bone or plate-screw interface at the level of the diaphysis induce axial motion without causing any shear or failure of fixation i.e. controlled axial micromotion. This type of modifications can also help with more homogenous circumferential bony healing as stress shielding of the near (lateral) cortex occurs compared stronger bone healing on the far (medial) side of the fracture when fixed locking screw constructs is used. [20]. Faster and stronger healing with these types of modifications compared to standard locking plate construct is associated with lower risk of fixation failure due to the reduced load sharing duration of the fixation construct.
•
Removing the screws closer to the fracture site thus increasing the distance without fixation (working length) [33,43]. Exchanging the locking screws closer to the fracture site with nonlocking screws. Exchanging the bicortical screws closer to the fracture site with unicortical screws. Removal of screw(s) crossing the fracture site at the supracondylar area (not the ones crossing the intraarticular fracture site) in cases that was placed with original fixation will eliminate the stiffness across the fracture site [44,45].
• Dynamization of the plating construct may provide the necessary stimulus for healing and avoid failure of fixation. Assessment of a fixation construct as too stiff while it actually is too flexible would be a major mistake and will results in quick failure. A pitfall in dynamization is that the fatigue life of the plate might be shortened with dynamization unless bony contact occurs unloading the plate.
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Fig. 2. Dynamization by removal of screws crossing fracture site.
Fig. 4. Exchange of locking screws to nonlocking screws.
Fig. 3. Removal of screws that are closer to fracture site.
Figs 5. Exchange of bicortical screws closer to fracture site to unicortical screws.
Intramedullary nailing Intramedullary nailing nails designed specifically for distal femur fractures with multiple interlocking screws in different planes commonly provides adequate fixation for distal femur fractures. Intramedullary nails provide an extremely large axial stiffness by the position of the nail at the center of the load axis [46,47]. Micromotion in distal femur nailing is typically generated by off axis loading resulting in bending and/or twisting of the nail. The prerequisite for distal femur nailing thus is that the fracture pattern should be amenable for fixation with IMN, providing some inherent rotational stability. The amount of the bone of the supracondylar fragment may be the limiting factor if 3 or 4 interlocking screws in multiple planes cannot be placed at the distal fragment. Summary Healing problems are not uncommon in treatment of distal femur fractures. Most common type of implant used for fixation is distal femoral locking plate. The stiffness of the fixation construct may be related to failures. The construct stiffness can be modulated with interplay of multiple parameters at the time of original fixation. When delayed healing or nonunion occurs, dynamization of plating should be considered if the stiffness of the construct is deemed to be the problem.
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