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. 2010 Dec;92 Suppl 2(Suppl 2):12-22.
doi: 10.2106/JBJS.J.00780.

Effects of construct stiffness on healing of fractures stabilized with locking plates

Michael Bottlang  1 , Josef Doornink, Trevor J Lujan, Daniel C Fitzpatrick, J Lawrence Marsh, Peter Augat, Brigitte von Rechenberg, Maren Lesser, Steven M Madey
Affiliations

Effects of construct stiffness on healing of fractures stabilized with locking plates

Michael Bottlang et al. J Bone Joint Surg Am. 2010 Dec.
No abstract available

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Figures

Fig. 1
Fig. 1
The stiffness and interfragmentary motion of locked-plate constructs was assessed. a: Generic 4.5-mm plate and screws. b: Diaphyseal fixation with a conventional plate (CP) or a locking plate (LP). c: Axial loading and assessment of resulting interfragmentary motion (ds) at the near and far cortices.
Fig. 2
Fig. 2
a: Conventional (CP) and locked-plate (LP) constructs were comparably stiff and were approximately one order of magnitude stiffer than external fixators (ExFix)-. b: Axial loading caused plate bending and asymmetric gap closure, whereby interfragmentary motion (IFM) at the near cortex was minimal. c: Near-cortex motion in response to 400-N simulated toe-touch loading remained below 0.1 mm, which is considered insufficient to promote secondary bone-healing.
Fig. 3
Fig. 3
Periosteal callus measurement at six months postoperatively in a study of patients yielded examples of deficient callus formation (≤20 mm2) and bridging callus (247 mm2). The callus size distribution illustrates that 37% of all fractures had formed no or very little callus (≤20 mm2) at six months.
Fig. 4
Fig. 4
Far-cortical-locking concept. a: Far-cortical-locking screws lock into the plate and the far cortex. The screws have a reduced midshaft diameter to retain a controlled motion envelope (Δd) in the near cortex, which increases the screw's working length. b: Analogous to external fixators, far-cortical-locking constructs derive a low stiffness from elastic flexion of the screw shafts. c: Flexion of far-cortical-locking screws within the near-cortex motion envelope induces parallel motion at the fracture gap.
Fig. 5
Fig. 5
a: Far-cortical-locking (FCL) constructs exhibit a biphasic stiffness profile, similar to that of Ilizarov external fixators. The primary stiffness was 88% lower than that of the standard locked-plate (LP) construct, enabling interfragmentary motion at reduced postoperative loading. At elevated loads, far-cortical-locking stiffness increases as a result of the additional support of screws at the near cortex. (Reprinted from: Bottlang M, Doornink J, Fitzpatrick DC, Madey SM. Far cortical locking can reduce stiffness of locked-plate constructs while retaining construct strength. J Bone Joint Surg Am. 2009;91:1988.) b: The elastic shaft of far-cortical-locking screws allows evenly distributed load sharing between screws and effectively prevents the stress risers seen at the end-screw of standard locked-plate constructs.
Fig. 6
Fig. 6
Evaluation of fracture-healing with locked-plate (LP) and far-cortical-locking (FCL) constructs in an ovine fracture-healing model. a: Postoperative radiographs depicting 3-mm-gap tibial osteotomy sites stabilized with locked-plate and far-cortical-locking constructs. b: Tibiae treated with far-cortical-locking constructs healed to be 54% stronger with torsional testing and tolerated 156% more energy to failure than tibiae treated with standard locking plates.
Fig. 7
Fig. 7
Radiographic, computed tomography (CT), and histological evaluation of the tibiae after the sheep was killed at nine weeks after surgery. The locked-plate (LP) constructs suppressed callus formation at the near cortex, where gap motion is minimal, leading to partial nonunions in three of the six sheep. The far-cortical-locking (FCL) constructs induced more callus formation, symmetric callus, and reliable bridging in all six sheep.
Fig. 8
Fig. 8
a: Periarticular far-cortical-locking (FCL) construct, whereby far-cortical-locking screws are used only in the diaphyseal segment and metaphyseal fixation is performed with a standard locked-plate technique. b: Quasi-physiologic loading of cadaveric femora along the mechanical axis to assess construct stiffness, durability, and residual strength was done with this setup.
Fig. 9
Fig. 9
a: In response to loading at one times body weight, standard periarticular locking constructs (the locked-plate [LP] group) induced asymmetric fracture motion. Near-cortex motion remained below 0.1 mm, which is considered insufficient to promote secondary bone-healing. Under the same load, far-cortical-locking (FCL) constructs induced essentially parallel motion, sufficient to promote secondary bone-healing. b: While far-cortical-locking screws reduced construct stiffness by 81%, the far-cortical-locking constructs remained as strong as the locked-plate constructs.
See this image and copyright information in PMC

References

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