The Correlation between Mechanobiology and Fracture Healing; Osteosynthesis, Biomaterial Optimization and TRIZ Design Principles to Develop Ameliorative Implants for Reconstruction of Median Osteochondrotomy of the Sternum.

The application of stainless-steel wire is still the "standard of care" and is believed to be the "gold standard" after trans-sternal thoracotomy. To overcome postoperative instability and surgical wound infection there had been the development of a variety of circumferential, Hemi-circular, and surface on-lay implant designs to enhance bone healing of the sternum particularly in compromised patients. This fundamental descriptive theoretical research study probes into biology and effects of mechanical environment on fracture healing in general and various types of ossifications that may occur during healing of the sternum. Following surgical anatomy of the sternum, the biology of fracture (osteotomy) healing, an update on the conventional and newer biomaterials, and role of 3D printing in custom additive manufacturing of the surgical implants have been discussed in detail. There is discussion on design principles and structural optimization in-line with patient-specific and patient-appropriate osteosynthesis. In support, the Teorija Rezhenija Izobretatelskikh Zadatch engineering principles have been applied to improve implant design in the face of the current strategies to relieve some of the recalcitrant deficiencies underlying the mechanics of the most favored implant for the reconstruction of the sternum. Several scientific domains of the engineering design principles and fracture healing processes have been connected leading to four newly conceptualized prototype designs for the reconstruction of the sternum. In conclusion, despite increased knowledge of the fracture healing process there are limited means to mitigate the adverse mechanical environment experienced by the healing sternum. There are uncertainties how to transfer the well-known facts of tissue strain during healing from the experimental platform to the operating table at the time of fracture fixation and reconstruction of the sternum for its optimal healing.

Rationale and Options for Choosing an Optimal Closure Technique for Primary Midsagittal Osteochondrotomy of the Sternum. Part 1: A Theoretical and Critical Review of Functional Anatomy, Biomechanics, and Fracture Healing.

The sternum is central in binding the bilateral costal structures to form the anterior wall of the thorax. The airtight subatmospheric pressure cavity of the thorax during respiration and episodes of cough produces significant dynamic forces acting perpetually on its walls, influencing functions of the contained viscera. The embryonic development of the sternum concurs with that of the heart and parts of the pectoral girdle. Any imperfection of the sternum, whether congenital or iatrogenic, can significantly compromise the normal physiology of the thoracic wall and cardio-respiratory systems. Midsagittal osteochondrotomy (division) of the sternum is a necessary step to access the mediastinum for an open cardiac procedure. To return the thorax to its normal function, it is imperative that surgeons have thorough working knowledge of the surgical anatomy of the sternum and the biomechanics of an intact and disrupted thoracic wall. Patient-based outcome measures of an index cardiac surgery can only be considered conclusive if the divided sternum heals over time to have full benefit of the surgery. Here, the essential topographical anatomy and embryology of the sternum, thoracic biomechanics, fracture biology, and surgical access to the mediastinum are reviewed to provide a better understanding of the performance and importance of the healed sternum.

Rationale and Options for Choosing an Optimal Closure Technique for Primary Midsagittal Osteochondrotomy of the Sternum, Part 2: A Theoretical and Critical Review of Techniques and Fixation Devices.

The intact one-piece sternum is indispensible to the thorax for its normal physiological biomechanics. To overcome tri-planar forces acting on the sternum following midsagittal osteochondrotomy, it must be reconstructed using an optimal technique to withstand distraction loads of normal respiration and violent cough. It should be fixed rigidly to reconstitute the anterior coronal column of the axial skeleton to maintain erect posture and prevent kyphosis. Sterile or infective non-union of the sternum compromises the physical endurance of patients and has an immense psychological effect. From an engineering perspective, there is no substantially proven gold standard technique to fix a divided sternum. Stainless steel wire applied in various configurations to a variety of shapes and sizes has become an acceptable standard of care due to its long-standing history and cost-effectiveness. Recently there has been a proliferation of innovative techniques to deal with primary and failed union of the sternum in an effort to prevent mechanical failure and serious deep surgical wound infection progressing to mediastinitis. Among the newer implant designs, the ones currently in use are shaped like clamps and clasps to compress the sternal halves together as well as alphabet-shaped mini-plating systems. In this section of the review series, mechanisms, pros and cons of currently available implants to reconstruct the bisected sternum, and external support systems considered necessary in high-risk clients are discussed.

Rationale and Options for Choosing an Optimal Closure Technique for Primary Midsagittal Osteochondrotomy of the Sternum. Part 3: Technical Decision Making Based on the Practice of Patient- Appropriate Medicine.

The topographic anatomy of the sternum is similar in a healthy population. However, in a clinical subset of patients with comorbidities such as diabetes mellitus, chronic obstructive pulmonary disease, high body mass index, chronic renal disease, or age-related osteoporosis, there are significant changes in the normal physiology that may influence overall patient outcome following trans-sternal intrathoracic surgery. These changes can create technical difficulties in reconstructing the bisected sternum and adversely affect the biomechanics of the thoracic wall, forcing difficult surgical choices with regard to implant options and increasing the cost of an otherwise routine cardiac surgery. A thorough preoperative surgical and technical planning is essential to avert perioperative complications such as failure of wound healing, non-union of the sternum, and life-threatening mediastinitis. Patient expectations need to be explored and the patients should be well informed so that they can make knowledgeable choices regarding their illness and surgical interventions. They should also be given a probable prognosis to provide psychological support. Within the realm of clinical methodology, the concept of patient-appropriate medicine is introduced to direct attending team to become aware of overall health of its patient. The inclusion of a clinical biomechanical engineer as a surgical team member is recommended to perform patient-specific finite element analysis to select an optimal implant to fix the sternum. To help assess the overall benefit-risk profile objectively, an absolute therapeutic index has been proposed.