Mechanical Influence of Surrounding Soft Tissue on Bone Regeneration Processes: A Bone Lengthening Study

Abstract

Bone lengthening is a bone regeneration technique with multiple clinical applications. One of the most common complications of this treatment is the lack of adaptation of the surrounding soft tissue to their extension. A better understanding of the mechanobiology of the tissues involved in distraction osteogenesis would allow better control of the clinical cases. Bone lengthening treatments were performed in vivo in the metatarsus of Merino sheep, measuring the distraction forces by means of an instrumented fixator. The tissue relaxation after distraction was analyzed in this study. A viscoelastic model was also applied to distraction data to assess the mechanical behavior of the tissues during the distraction phase. Tissue relaxation is similar to other bone regeneration processes which do not imply surrounding soft tissue extension, e.g. bone transport. The effects of this tissue on distraction forces are limited to the first minutes of distraction and elongations above 4% of the original length with the protocol applied. Moreover, the surrounding soft tissue initially loses some of its viscoelasticity and subsequently suffers strain hardening from day 5 of distraction until the end of the distraction phase, day 15. Finally, anatomical changes were also evidenced in the elongated limb of our specimens.

Mechanobiology of Bone Consolidation During Distraction Osteogenesis: Bone Lengthening Vs. Bone Transport

“…18 Functional limb length discrepancy could also induce temporal deformities according to literature, 20,37 which could affect the loading capacity of the treated limb up to the development of compensation mechanics. In particular, limb deformity was visually manifested in our specimens by a rotation in the sagittal plane of the hoof, as reported in Bla´zquez-Carmona et al 4 Regardless of the dissimilarities in the MGRF values in the HI limb, BL (blue curves) and BT (red curves) treatments seem to share a similar pattern in the GRF shape to the control data (green data), as shown in Fig. 4.…”

“…Concerning the BL group, discomfort derived from distraction in long bones is suggested to be a significant factor in the gait disturbances, which has been shown to persist during the consolidation phase and restrain functional weight-bearing. 20,58 This side effect could gain significance with the elongation percentage, about 12.5% of the original bony length in our study, which intensifies the damages caused by the stretching of the surrounding soft tissues, 4,20,39 and a lowering of the nerve conductivity. 18 Functional limb length discrepancy could also induce temporal deformities according to literature, 20,37 which could affect the loading capacity of the treated limb up to the development of compensation mechanics.…”

“…38,39,47 The standard treatment applies directly a gradual distraction to the bony fragments resulting from a single osteotomy until the clinically required elongation is achieved. 4 Bone transport (BT) is another reconstructive approach based on DO to handle specific orthopedic diseases, such as non-unions or bone defects, especially infections. 7,17,34,35 This technique is based on the progressive transport of a bony segment, normally osteotomized from the original bone, toward the infected/diseased bony fragment, which is generally removed in a surgery.…”

“…7,34 The main difference between BT and BL is the preservation of the limb's original length, avoiding potential problems derived from the elongation of the surrounding soft tissues. 4,18,34 One of the major limitations of these bone regeneration processes is the length of time required for the consolidation phase until the regenerated tissue is ossified and stabilized enough to disassemble the corresponding fixation. 39,47 To prevent premature removal, daily clinical monitoring has traditionally been based on qualitative techniques, including manual examinations or radiological evaluation of the callus bridging.…”

Enhancing the Efficiency of Distraction Osteogenesis through Rate-Varying Distraction: A Computational Study

“…During the consolidation phase, an axial compressive load of 500 N was applied to the model. This load represents the It has been experimentally shown that callus tissues exhibit time-dependent viscoelastic behavior under distraction loads [26,28,29]. After a distraction load was applied, the stresses within the distraction gap relaxed at an exponential rate.…”