Stem Cell-Based Tissue Engineering for Bone Repair - Tissue Engineering: Computer Modeling, Biofabrication and Cell Behavior - page 3

determined that the bone marrow stroma contains fibroblast-like stem cells that also
possess osteogenic potential [ 4 ]. These cells are referred to as bone marrow stromal
cells (BMSC), though their exact location in-vivo is yet to be determined [ 4 ].
Both mesenchymal and embryonic stem cells have been investigated as os-
teogenic sources for stem cell repair of bone defects. The findings from these studies
will be outlined further in this chapter.
2.2 Clinical Therapies for Fracture Repair
Although there are many treatment options for bone repair, the extent and quality
of repair that occurs from these strategies is inconsistent. Physiological impairment
of fracture healing can be caused by pathologies such as osteoporosis, osteogenesis
imperfecta, or defects in the mechanical stability or vascular supply of the bone at
the time of fracture [ 5 ]. In all of these cases, nonunion fractures are likely to develop.
Nonunions are fractures that fail to heal naturally 6-8 months after the time
of fracture. In the human population, approximately 10 % of fractures fail to
heal naturally [ 5 ]. Risk factors for nonunions include smoking, aging, anemia,
diabetes, use of anti-inflammatory drugs, infection, and lack of calcium and
vitamin D in the diet. The main symptom of a nonunion is persistent pain
at the breakage site, and can be conclusively diagnosed with x-ray, magnetic
resonance, or computed tomography imaging [ 5 ].
Currently, nonsurgical treatment of nonunions involves the application of a bone
stimulator. The stimulator uses ultrasonic or electromagnetic waves to stimulate
healing [ 5 , 6 ]. However, the patient must be diligent in wearing the external de-
vice for 20 minutes to 2 hours every day. Because of this, the rate and quality of
fracture healing is highly dependent on consistency of use [ 6 ].
Surgical treatments of nonunions include bone grafts, internal fixation, and ex-
ternal fixation [ 7 , 8 ]. For bone grafting procedures, the bone for the graft is usually
taken from the rim of the pelvis or iliac crest of the patient [ 8 ]. However, these pro-
cedures can be very painful and have low bone yield. As well, the use of bone grafts
alone does not provide any initial stability to the defect [ 8 ].
In defects where mechanical stability is required, internal or external fixation is
used [ 7 , 8 ]. For internal fixation, metal plates and screws are attached to the outside
of the bone, or rods are placed inside the bone canal to confer additional mechanical
stability to the fracture [ 8 ]. This type of fixation can also be combined with bone
grafts.
External fixation involves a rigid frame positioned outside of the defective limb
that is attached to the internal bone by pins or wires [ 8 ]. Distraction osteogenesis
(also called the Ilizarov method) can be used with external fixation to stretch the