What is the term of the external covering of the bone that contains osteoblasts and blood vessels?

Bone flap (vascularized bone, osseous–periosteal flap)

Bone is vascularized through endosteal and periosteal sources (Fig. 22.22). The complex blood supply of bone is based on nutrient vessels entering the bone directly and through vascular connections between muscles and bone, typically where the muscle has a large bony origin or insertion. Vascularized bone is useful in muscles suitable for microvascular transplantation or in those muscles designed for transposition when the vascular attachments to bone are distal to the point of rotation. The commonly transferred bones include the fibula based on the peroneal artery, iliac crest based on the deep circumflex iliac artery (Fig. 22.23), the scapula based on the circumflex scapula or thoracodorsal arteries (Fig. 22.24), and the radius based on the radial artery (Fig. 22.25). The calvarial osseous flap based on the superficial temporal artery or occipital artery with partial- or full-thickness bone is also useful for reconstructing facial anomalies and deformities (Fig. 22.26).82–85

The use of periosteum and part of the cortical bone as an osseous–periosteal flap is being widely used for nonunion of the bone and small bone defects. The genicular osseous–periosteal flap, also known as the medial femoral condyle flap, based on the articular branch of the descending genicular artery and vein with periosteum and a thin (0.5 to 1.0 mm) layer of outer cortical bone, was first reported by Sakaiet al. to treat fracture nonunion (Fig. 22.27).86 Further applications of this flap with or without skin and cartilage expanded to reconstructing small bone defects, avascular necrosis of the bone and other complex defects of the hand.87–89

There is no widely accepted classification of bone flaps alone. Perhaps it is due to the complexity of the vasculature to each bone. One of the most widely used, the fibula, has vascular supply from the branches of the anterior tibial artery supplying the head, neck, and epiphysis while the peroneal artery gives rise to multiple arcuate vessels along the fibula and a nutrient vessel in the mid third of the fibula bone (Fig. 22.28). Thus, depending on the portion of the fibula bone being harvested, the pedicle of the bone flap can differ not only in anatomical region but also in type of vascular supply to the bone. The fibula bone flap with or without the skin (fasciocutaneous) flap is frequently used for segmental bone defects especially after mandibular resection, long bone resection and for pelvis reconstruction (seeFig. 22.23).90 The fibular bone including the head and epiphyseal growth plate is used in patients who need further growth of the long bone such as reconstruction after sarcoma resection of the proximal humerus.91,92

6.23.2 Periosteum for Human Phalanx Model

The periosteum is known to have three roles: (1) a source of osteocytes/chondrocytes that differentiate from pluripotent undifferentiated mesenchymal cells, (2) a scaffold for the proliferation of osteocytes/chondrocytes, and (3) a source of growth factors.12

Histologically, the periosteum consists of a superficial thick fibrous layer and a deep thin cambium layer. In the cambium layer, a large number of osteoblasts (pleuripotent undifferentiated mesenchymal cells), which stain eosinophilically with toluidine blue, are present, and they differentiate into osteocytes and chondrocytes. The periosteum is involved in bone growth (appositional growth) through the proliferation and differentiation of osteoblasts, and increases bone thickness and strength.13 Also, the thickness of the cambium layer and the number of cells in it are known to markedly reduce with age, with decreases in the capacity for bone growth.12,14

Recently, more detailed research has been conducted on the periosteum, and the structure of the periosteum has been reported to differ as regards the diaphysis and the metaphysis. The metaphysial periosteum has a thick cambium layer with a large number of cells in it, and shows no structural changes associated with aging. The diaphysial periosteum, on the other hand, is thinner than the metaphysial periosteum, and both the thickness of the cambium layer and the number of cells in it have been reported to decrease markedly with age.15

Periosteal Pocket Versus Bone Seat and Tie-Down Holes

A custom-fit bone seat and tie-down holes may be drilled in the traditional fashion into the parietal bone to recess and immobilize the R/S. Historically, older devices with thicker R/Ss necessitated such drilling to reduce the height of the internal device, making it less obtrusive under the skin and protecting it from trauma. However, current R/Ss are 30% to 40% thinner than the previous generation and do not cause the same cosmetic deformity or increased susceptibility to damage as did their predecessors. In addition, the parietal bone is often only 1 mm thick in young children, preventing truly functional recessing into a bone seat. Drilling of the seat and bone holes may also expose dura and has resulted in a variety of reported complications, including cerebrospinal fluid (CSF) leak, subdural hematoma, epidural hematoma, lateral sinus thrombosis, and large cerebral infarcts.59-63

In addition, use of a full bone seat with intraosseous tie-down sutures prolongs the procedure by 10 to 30 minutes and has not prevented migration of the R/S. In 1998, Roland et al. reported 22 cases of R/S migration.64 A decade later, Davids et al. reported that 60% of their rare but serious complications were associated with R/S migration.65 A 2009 review of the U.S. Food and Drug Administration Manufacturer and User Facility Device Experience (MAUDE) database revealed that 6 of the most recent 100 complications of all types and degrees involved migration of the R/S.66

The periosteal pocket technique was described in 2009, following an anatomic study of 40 half heads and a prospective controlled study of 227 consecutive procedures that demonstrated no migrations. In this technique, a tight subperiosteal pocket customized to the size of the R/S was dissected over the parietal bone between the temporoparietal suture anteriorly and the lambdoid suture posteriorly. The mouth of the pocket was then puckered with pericranial sutures. This technique shortens the time for placing the R/S and obviates the need for a bony seat and tie-downs.56,67

THE PERIOSTEUM

The periosteum is a dense, fibrous connective tissue sheath that covers the bones. The outer layer, made up of collagen fibers oriented parallel to the bone, contains arteries, veins, lymphatics, and sensory nerves. The inner layer contains osteoblasts (i.e., cells that generate new bone formation). Repetitive stress can stimulate the inner layer of the periosteum to create bone outgrowths, called spurs. This often occurs at the heel when the plantar fascia is short.

The periosteum weaves into ligaments and the joint capsule. Stretching of the periosteum provides mechanoreceptor information about joint function at these junctions.

The periosteum also blends with the tendons, forming the tenoperiosteal junction (Figure 6-11), where the muscle pulls on the bone during joint movement. The sensory nerves in the periosteum are sensitive to tension forces. The tenoperiosteal junction is a common site of soft tissue injury. An acute tear or cumulative microtearing of the periosteum can result in random orientation of the collagen in the area, leading to the development of abnormal cross-fiber links and adhesions. Massage can address this abnormal fibrotic development at the tenoperiosteal junction. Friction is used to introduce small amounts of controlled inflammation, which results in an active acute healing process. With appropriate healing and rehabilitation, a more functional outcome is achieved.

Periosteal Reaction

Periosteal reaction is of various types with none being pathognomonic of any particular tumour; rather, the type helps to indicate the aggressiveness of the lesion. A thick, well-formed, solid periosteal reaction (Fig. 40.4A and B) indicates a slow rate of growth but not necessarily a benign lesion, since it may be seen with grade 2 chondrosarcoma. A laminated periosteal reaction (seeFig. 40.1B) indicates subperiosteal extension of tumour, infection or haematoma. Lesions demonstrating periodic growth may show a multilaminated pattern (seeFig. 40.4C). A Codman triangle indicates the limit of subperiosteal tumour in a longitudinal direction (seeFig. 40.4D). Vertical (sunburst spiculation or ‘hair-on-end’) types of periosteal reaction are seen with the most aggressive tumours such as osteosarcoma (seeFig. 40.4E) and Ewing sarcoma (seeFig. 40.4F). However, the most rapidly growing lesions may not be associated with any radiographically visible periosteal response because mineralisation of the deep layer of periosteum can take 2 weeks.

40.3.1.2 Periosteum-Derived Mesenchymal Progenitors

Periosteum is a source of progenitors with osteogenic and chondrogenic differentiation potential [46]. Lineage tracking analyses demonstrated the contribution of periosteal progenitors to new bone formation in fracture healing models [47]. TE bone product for the reconstruction of jaw defects was developed from autologous periosteal cells [23,24,48,49]. A sample of periosteum tissue (~ 1 cm2) was minced, enzymatically digested, and the cells were expanded for 1-4 passages prior to the preparation of TE bone products [23,24,49]. In addition, periosteal progenitors were reported to reach at least 30 population doublings in culture [50], suggesting their potential for the treatment of more extensive bone defects requiring large cell numbers.

6.3.3 Soft tissue grafts

Periosteum and perichondrium grafts are biomembranes with two layers, an outer fibrous layer and an inner cambium, or osteogenic, layer. Perichondrium lines developing bone, and when vascularized, becomes periosteum, or the nonjoint lining of bone. There is no significant difference between the repair mechanisms of both grafts, but periosteum is more readily available. Since periosteum favors chondrocyte and osteocyte growth, it is an option for full-thickness articular cartilage defects. Prior to graft use, the lesion must be cleaned, and the defect must be expanded to full thickness and at least 1 mm deep into the subchondral bone. Once the graft is implanted, two types of cells guide the repair procedure. The periosteal chondrocyte precursor cells promote chondrogenesis, whereas the bone marrow stem cells from the subchondral bone can promote chondrogenesis and osteogenesis. However, though initial outcomes were promising, long-term results were inconsistent, with graft calcification being a major concern (Alfredson & Lorentzon, 2001; Carranza-Bencano et al., 1999; Mara et al., 2011; Ritsila et al., 1994; O’Driscoll, 1999).

While all of the treatment options mentioned have shown some success, all have their respective disadvantages (Table 6.1). The common disadvantages that arise are mechanical inadequacies, lack of chondrogenesis, lack of lateral integration, and fibrous tissue in-growth, all of which allow for short-term success but almost always lead to failure in the long term. Therefore, recent attempts have involved TE in order to provide a mechanically relevant, hyaline-like cartilage that can maintain its properties for the long term.

Table 6.1. The advantages and disadvantages of current treatments for articular cartilage damage

The periosteal component

When the periosteum is lifted from the underlying cortical bone, whether it be by trauma, tumour or pus, it responds by laying down bone. This is an activation of the normal process of bone formation. This component is always most in evidence in a fracture on the side with the least tissue disruption. It does not entail endochondral ossification and results from activity of osteoblasts in the inner cambium (Latin: bark) layer of the periosteum. Periosteal new bone formation is stimulated by movement and is abolished by rigid internal fixation. In osteosarcoma (a primary tumour of bone), the periosteum is lifted by the tumour and new bone may form under the elevated periosteum giving rise to the radiological sign called Codman’s triangle.

Removal of the Canal Skin

The periosteum and canal skin are elevated from the bone as far as the annular ligament (Fig. 9-5). Care should be taken not to elevate the ligament and the remnant of the middle fibrous layer. The dissection is superficial to the fibrous layer of the remnant in such a way that the remnant is de-epithelialized in continuity with the canal skin, if possible. It is often easier to begin the final removal and de-epithelialization by starting anterosuperiorly, using a cup forceps (Fig. 9-6). Removal of the canal skin and de-epithelialization are continued inferiorly and posteriorly. The periosteum and canal skin are removed from the ear and kept moist in Tis-U-Sol irrigating solution.

In elevating the periosteum and the canal skin, one works perpendicular to the annular ligament and remnant, keeping the instrument on the bone at all times, until the dissection is completed to the level of the remnant. The dissection is continued parallel to the annular ligament to avoid elevating it and the remnant (Fig. 9-7).

Periosteal reactions

The periosteum adheres to the external surface of bone, and contains many blood vessels that penetrate and supply the bone. It is capable of producing new bone. In the young growing animal, adhesion of the periosteum to bone is loose, and reaction to trauma is more pronounced and occurs faster than in the adult. Periosteal reactions are due to either trauma or a disease process, and they may be first seen radiographically after 7–10 days. There are different types of periosteal reaction, in order of increasing aggressiveness (Fig. 2-2): smooth, lamellar or onion skin, palisading, spiculated or sunburst, and amorphous. Smooth periosteal reaction is a non-aggressive type of new bone formation and is characterized by a solid, continuous (of pillar-like, longitudinal or undulating) appearance, but always with smooth contours. It is commonly seen with trauma (subperiosteal hematoma) or benign processes. The other types of periosteal reaction are included in the interrupted category, and are considered aggressive. Lamellar periosteal reaction represents multiple layers of new bone formation along a cortex and may be seen with trauma, infection or, less likely, neoplasia. With the spiculated type, new bone radiates from the cortex. This pattern may be associated with osteomyelitis, malignant tumor, or a healing fracture with motion present. Amorphous new bone is unorganized, non-functional bone laid down in the soft tissues next to a bone and may be seen with trauma, infection, or neoplasia. Although type of periosteal reaction can help to grade aggressive versus benign bone lesions, it should not be relied upon for diagnosis, as other features of the lesion are more reliable (see below).