Bones

The human skeleton (Fig. 36-1) has 206 separate bones. The bony framework of the human body is divided into the axial skeleton, which consists of 80 bones that make up the skull, vertebrae, and ribcage, and the appendicular skeleton, which consists of 126 bones that make up the limbs. Each upper extremity is composed of 32 bones, and each lower extremity is composed of 31 bones. Bones are classified according to shape as long, short, flat, and irregular. The humerus in the upper arm, radius and ulna in the forearm, femur in the thigh, and tibia and fibula in the lower leg are long bones.

The end of a long bone is referred to as the epiphysis, and the shaft is referred to as the diaphysis. Thin plates of cartilage are found in the ends of long bones. In immature bone this is the area of growth and elongation. In mature bone these plates are ossified and do not grow (Fig. 36-2). The bones in the hand and foot are short bones. The scapula and patella are examples of flat bones. The vertebrae are irregular bones.

The cortex (outer layer) of bone is compact, hard connective tissue. This cortical osseous tissue surrounds porous, spongy, cancellous tissue. The innermost substance is bone marrow and is classified as either red or yellow according to its location and function (see Fig. 36-2).

The red marrow is found in the ends of long bones, porosities of cancellous bone, and flatter bones, such as the skull, sternum, and pelvic bones. This type of marrow is responsible for erythropoiesis, which is the formation of red blood cells and certain white blood cells. Yellow marrow is found in the medullary canals, or shafts of long bones, and has a higher adipose content.

Periosteum, a strong fibrous membrane, covers bone, except at joints. The blood supply and innervation penetrate periosteum and enter the bone through structures known as Volkmann canals. Lengthwise, lamellar structures, referred to as haversian canals, provide weight-bearing strength and passage for additional blood supply (Fig. 36-3). The inner aspect of bone is lined with endosteum, which is tissue similar to periosteum. In small children this layer contains osteoclasts that destroy bone to enlarge the marrow cavity for circumferential growth.

Bone healing

Broken bones heal by a process referred to as union. Union of bones takes place in a series of steps (Fig. 36-4):

1. Hematoma formation. Blood accumulates in the area of break or injury. The inflammatory process ensues, and extravascular blood converts from liquid to a semisolid clot. Active phagocytosis removes necrotic tissue and debris.

2. Callus formation. Fibrin cells form a network around the injured area. The damaged periosteum is stimulated to generate osteoblasts, forming new bony substance referred to as osteoid. Minerals begin to accumulate in the network, forming a collagen callus. A callus is visible on radiograph within 1 to 2 weeks of injury.

3. Calcification process. Calcification begins and establishes support of the injury. Connective tissue proliferates across the site and is usually completely calcified within 6 weeks.

4. Remodeling phase. Excess cellular material is resorbed, and the bone resumes its preinjury strength and configuration. This remodeling phase is enhanced by stress and exercise. Depending on the site and severity of the injury, complete remodeling can take 6 months to 1 year to complete.

Cartilage

Cartilage, a smooth, relatively firm, compressible connective tissue, cushions most articular surfaces at the ends of bones. It does not have a direct blood supply and is devoid of lymphatics and nerves. Cartilage derives its nutrition from synovial fluid and maintains a high water content except in pathologic states.

Joints

Bones give stability, but the body must bend and flex for locomotion. The ends of bones come together at joints. The articular cartilage and construction of the joint prevent bones from scraping against each other. Tough, fibrous connective tissue forms the outside capsule of the joint, and a finer membranous lining secretes synovium, which is similar to egg albumin. The synovial fluid contains macrophages and white blood cells that keep the joint free of debris and bacteria that could interfere with mobility.

Joints are classified by variations in structure that permit movement (Fig. 36-5). The hip and shoulder are ball-and-socket joints; the knee, ankle, elbow, and phalangeal joints of the fingers are hinged; the wrist is a condyloid joint; and the thumb is a saddle joint. The proximal and distal bone ends are held securely in place by the joint capsule attached to both bone shafts and by ligaments.

Ligaments

Ligaments are bands of flexible, tough fibrous tissue that join the articular surfaces of bones and cartilage. They become strong when the parallel configuration of their collagen fiber is oriented against the forces applied to them (e.g., the cruciate ligaments stabilize the knee joint). Ligaments are avascular and heal slowly. They do not readily reattach to bone when torn and are prone to subsequent reinjury.

Muscles

The human body has hundreds of muscles. Muscles are all the contractile tissues of the body and are classified as smooth (involuntary), branching (cardiac), or striated skeletal (voluntary). Muscles have a rich arterial supply because they require oxygen to perform many functions, and they have a multilevel venous drainage system because they perform as the venous pumps for resaturation by the lungs. They contract when an electrochemical impulse from the brain crosses the myoneural junction, causing fibers to shorten. Groups of muscles work together (i.e., contract simultaneously to bring about body movement).

Skeletal muscle is the largest category of muscle tissue. There are more than 600 skeletal muscles in the human body. Skeletal muscle constitutes approximately 23% of small female body weight and 40% of larger male body weight. Each muscle fiber is a single cell that ranges in length from 0.04 to 3 inches (1 to 80 mm). The fibers are bound together into fascia-covered bundles referred to as fasciculi. Several fascia-bound fasciculi constitute a skeletal muscle and contract in response to signals mediated by the nervous system and neurotransmitters, such as acetylcholine.

The peripheral attachment is referred to as the origin. The distal attachment is referred to as the insertion.

Tendons

Tendons are bands of extremely strong, flexible fibrous tissue that attach muscle bundles to the periosteum of bones (see Figs. 36-1 and Fig. 36-31). They are encased in the synovial membrane sheath of movable joints.

Instrumentation

Each orthopedic procedure must have the correct instrumentation for that particular bone, joint, tendon, or other structures the surgeon will encounter. An instrument used on a hip procedure is not appropriate for a hand procedure. Orthopedic instruments are heavy—often large and bulky, resembling carpentry tools—but also delicate. Each instrument has a specific purpose and requires special care and handling. Orthopedic instruments can be divided into categories by functional design.

Exposing instruments

To expose a bone or joint, special retractors and elevators are used (Fig. 36-6). Retractors are contoured to fit around the bone or joint without cutting or tearing muscles. Periosteal elevators are semi-sharp instruments used to strip periosteum from bone without destroying its ability to regenerate new bone. They are used for blunt dissection.

Grasping instruments

Grasping instruments are required to hold, manipulate, or retract bone. Bone-holding forceps should be selected appropriately for the size of the bone in the surgical field. Bone hooks are used for retraction and leverage (Fig. 36-7). Heavy clamps are needed to hold smaller bones or grasp a joint capsule, such as a meniscus clamp for fibrocartilage in the knee.

Dissecting and debulking instruments

Cutting instruments are used to remove soft tissue around bone; to cut into, cut apart, or cut out portions of bone; and to smooth jagged edges of bone. The surgeon’s armamentarium includes osteotomes, gouges, chisels, curettes, rongeurs, reamers, bone-cutting forceps, meniscotomes, rasps, files, drills, and saws (Fig. 36-8). These have sharp edges. Extra care should be taken not to nick or damage cutting edges; they should always be protected on the instrument table and during cleaning, sterilizing, and storing. Fitted sterilizable cases (Fig. 36-8, E), trays, foam towels, or canvas cases are used to keep sets together by sizes (e.g., osteotomes, gouges, chisels, curettes), as well as to protect cutting edges.

Cutting instruments must be sharp. Osteotomes, chisels, gouges, and meniscotomes can be sharpened by operating room (OR) personnel with handheld hones or a honing machine designed for this purpose. Most manufacturers provide a service for sharpening and repairing instruments. Curettes, rongeurs, and reamers should be returned for sharpening. Small drill bits and saw blades usually are disposable (Fig. 36-9).

Measuring devices

Rulers, calipers, depth gauges, and flexible devices for measuring angles are important for the appropriate sizing of implants and selective bone cutting. Measurements of bone diameter are performed when selecting a joint prosthesis (Fig. 36-10).

Materials and equipment used frequently

The items discussed in this section are used frequently in many orthopedic procedures.

Special considerations in orthopedic surgery

Both internal direct-current stimulators and external pulsating electromagnetic field or electrical capacitor devices are used to stimulate bone and neural regeneration, revascularization, epiphyseal growth, and ligament maturation.

General considerations

Indications for orthopedic surgery

Preoperative assessment of an acute or a chronic disability affecting the musculoskeletal system of an extremity includes evaluation of the extent of bony or soft tissue involvement with or without concomitant neurovascular compromise.

Assessment for signs and symptoms of neurovascular impairment in an extremity includes the six Ps: Pallor, Pulses, Pain, Paresthesia, Puffiness, and Paralysis. The six Ps are assessed postoperatively and monitored until support devices, such as castor splints, are removed from the surgical site.

Adult orthopedic surgery is usually necessitated by trauma or by a degenerative disease process. Surgical procedures on the following major anatomic classifications of structures are discussed in this chapter:

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