Tornetta Rockwood Adults 9781975137298 FINAL VERSION

18

SECTION ONE • General Principles

to achieve absolute stability using lag screw fixation and locking neutralization plates report excellent clinical outcomes; how- ever, callus was noted in 78% of the fractures, emphasizing the challenge of achieving absolute stability. 218 DELAYED UNION AND NONUNION Delayed healing and hypertrophic nonunion may occur if frac- tures are unstable, allowing excessive motion at the fracture site. Conversely, with an overly stiff fixation construct in the set- ting of a residual fracture gap, an atrophic nonunion may result. In the case of hypertrophic nonunion, the interfragmentary motion may be at a level that disrupts the healing tissue. The upper limit of interfragmentary motion for natural bone healing is unknown; however, it is likely to be greater than the 0.2 to 1 mm of motion, which is thought to be optimal for cal- lus formation. Animal studies show healing in the presence of fracture site motion as great as 6 mm, albeit slower than with smaller amounts of motion. 55 In vivo monitoring of tibia fractures treated with fracture braces confirms healing with interfragmentary motion of 4 mm. 185 When motion is exces- sive, additional cartilaginous tissue is deposited at the fracture to control the motion. This results in increasingly wide callus formation. When the fracture strain exceeds the allowable strain for the healing tissue, the process is disrupted and more tissue is deposited to stabilize the fracture. If the fracture does not heal, a typical hypertrophic nonunion with a large amount of callus but no fracture bridging will develop. Nonunions or delayed unions also result after fixation with overly stiff implants in the setting of a residual fracture gap. The current emphasis on biologic fracture plating limits the ability to compress individual fracture fragments, resulting in resid- ual fracture gaps after the fracture is stabilized. A fracture with a residual gap stabilized with a stiff construct will not allow adequate fracture motion to stimulate callus formation and an atrophic nonunion may result. 88 Clinically, the use of locked plates to stabilize distal femur fractures using biologic tech- niques results in a nonunion rate of nearly 20% (Fig. 1-19). 33,147

A

B

healed sheep tibia osteotomies stabilized with compression plates failed through the original fracture site at 48 weeks in one-third of specimens. 207 Because of this slow healing process, early plate removal after direct bone healing risks refracture through the original fracture site (Fig. 1-17). Currently, it is rec- ommended that plate removal be delayed for up to 2 years after surgery to allow adequate time for complete union. 112 The technical ability of the surgeon to obtain an environment of absolute stability is limited. 39,157 In the original description of primary bone healing, Perren et al. used two orthogonal plates to compress a sheep tibia osteotomy in an attempt to obtain absolute stability. 169 They found predominantly direct contact healing under the plates, but gap healing at the cortex opposite the plates, indicating the difficulty in obtaining adequate com- pression despite an optimized fracture model. These findings have been reproduced in more recent compression plating ani- mal studies (Fig. 1-18). 39,171 Modern clinical studies attempting Figure 1-17.  Plating of clavicle fracture. A: After 12 months, the state of primary bone healing is largely invisible on radiographs, as perios- teal callus is not expected. B: Refracture occurred 9 days after plate removal through the original fracture site.

Figure 1-18.  Compression plating of an ovine tibia osteotomy 39 shown by radiograph ( A ) and photograph ( B ) of dissected tibia at week 9 after fixation. C: Torsion testing resulted in refracture involving the osteot- omy. D: The micro-CT illustrates gap healing with transversely oriented osteons at one cortex, and primary bone healing at the opposing cortex. (Reprinted with permission from Bottlang M, Tsai S, Bliven EK, et al. Dynamic Stabilization of Simple Fractures With Active Plates Delivers Stronger Healing Than Conventional Compression Plating. J Orthop Trauma . 2017;31(2):71–77. ) A, B C, D

Copyright © 2020 Wolters Kluwer Health, Inc. Unauthorized reproduction of this content is prohibited.

LWBK1698-C01_p001-042.indd 18

05/12/18 8:38 PM