Understanding anatomy is the key to successful treatment and prevention of musculoskeletal injuries. This blog is a crash course in basic musculoskeletal anatomy.
What Are Bones?
There are 206 bones in the adult skeleton. A fracture is a break in a bone. The treatment of a fracture depends on many factors: age and health of the patient, location of the fracture, and the amount of displacement.
Displacement is the amount of separation between the broken pieces. Some fractures are minimally displaced. Others are very displaced. “Setting” a fracture is also called a reduction. If a fracture is widely displaced, typically a reduction is performed in some fashion. Sometimes a fracture can be reduced or “closed” with just manual traction and manipulation. A common example of this is a fracture of the distal radius (wrist fracture). Usually, the fractured extremity is then immobilized in a sling, splint or cast. Sometimes the reduction is performed surgically and the fracture is stabilized with pins, rods, screws or plates.
If the broken bone comes through the skin, it is called an open fracture (also known as a compound fracture). When that happens, the risk of an infection is much higher and surgery is almost always performed on an urgent basis.
Bone is not like cement. Bone is a biologically active tissue with a blood supply. When a bone does not heal, that is called a non-union. A bone that heals crooked is called a malunion. Factors that affect healing include smoking, medical problems (such as diabetes), the amount of associated soft tissue injury, and the amount of displacement.
What Are Joints?
There are 230 joints in the adult human body. A joint is simply the articulation or meeting between two bones. Articular cartilage is the bearing surface of a joint. Joints are usually stabilized by surrounding ligaments.
When a joint comes fully out of position, it is called a dislocation. When it comes partially out of position, it is called a subluxation. If a joint dislocated and stays stuck out of position, it needs to be set, or reduced. Often this can be done with just traction and relaxation. When a joint dislocates, it is more likely to keep dislocating. This is called joint instability.
Commonly injured joints include the shoulder, elbow, small joints of the hand, hip and knee cap joint. Therapy, bracing or surgery may be necessary to treat an unstable joint that keeps dislocating or subluxating.
What is Cartilage?
Articular cartilage is the bearing surface of a joint. It is normally white and smooth, like a cue ball, but slightly soft. Cartilage has no nerves or blood vessels in it, so unfortunately when it is damaged, cartilage is a tissue that cannot repair itself, like most other tissues can. Cartilage damage may occur from acute trauma or from overuse and degeneration over time.
Arthritis is a disease of cartilage. There are many different types of arthritis. The most common type of arthritis is osteoarthritis. We still do not understand the underlying cause of osteoarthritis.
Cartilage injuries may be treated non-operatively or with surgery, depending on many factors. Once full-blown arthritis develops, a joint replacement may be the best option for a symptomatic patient. A joint replacement involves putting new bearing surfaces in a joint damaged by arthritis. We use different metals and plastics to do this.
What is a Meniscus?
The meniscus is a specialized structure unique to the knee joint. Once thought to be irrelevant, we now know that the meniscus is an extremely important structure that provides cushion to the knee joint and also stability. There are two in each knee (medial and lateral). Medial is inside, lateral is outside.
Meniscus tears are very common and can be related to trauma or wear and tear degeneration. Not all tears cause symptoms. Patients with symptomatic tears usually present with pain on the side of the knee where the tear is. The most common complaints are pain and clicking.
Treatment can be non-surgical or surgical, depending on several factors (level of symptoms, age, presence of arthritis). Surgery involves either a repair or a trimming (meniscectomy). A repair is done when the tissue is healthy and has a good chance of healing. A menisectomy, or, more accurately, a partial meniscectomy is the most common procedure in orthopaedic surgery. It is done arthroscopically and the recovery is usually quick. However, meniscal loss is associated with the development of arthritis, so we make an attempt to do repairs in younger, active patients whenever possible. When patients say they have “torn cartilage,” they usually mean a torn meniscus, but the meniscus is a totally distinct structure from articular cartilage.
What is the Labrum?
The labrum is a specialized structure unique to both the shoulder and hip. It is a circular structure that goes around the perimeter of the shoulder socket (glenoid) or hip socket (acetabulum). The labrum serves multiple functions, including helping to stabilize the joint. It is often torn when the joint is dislocated. It can also tear from degeneration over time. Surgically, it can be repaired or trimmed, much like the meniscus. The labrum, like the meniscus, has nerves and blood vessels, which explains why it hurts when it is torn and why it can heal on its own or with surgery.
What is Muscle?
There are 640 muscles in the human body. Muscle injuries are extremely common and can result from a single trauma or overuse. Such injuries are called strains. Muscle tissue can heal on its own, although scar may form at the injury site. Most muscle injuries are treated conservatively without surgery.
What is a Ligament?
Ligaments are structures that connect a bone to another bone. They help stabilize joints.
Ligament injuries are called sprains and vary in severity from I to III. A Grade III sprain of a ligament implies a complete tear. Some ligaments will heal on their own with proper non-operative treatment. Common examples are the medial collateral ligament (MCL) of the knee and lateral ligaments of the ankle (associated with common ankle sprain). Some ligaments do not heal well. The best example is the anterior cruciate ligament of the knee (ACL).
When surgery is performed, an injured ligament can either be repaired or reconstructed. A repair is when the two ends are sewn directly end to end or the end of the ligament is attached directly to bone. A reconstruction is undertaken when it is felt that a repair will not work (most ACL tears are treated with a reconstruction). Typically, a tissue graft is used to replace the native ligament. The graft can be taken from the patient’s own body (autograft) or from a cadaver (allograft).
What is a Tendon?
A tendon is a structure than connects a muscle to a bone. Tendon injuries are called strains. Inflammation of a tendon is called tendinitis. Degeneration is called tendinosis.
Tendon injuries are very common. Commonly affected tendons include the rotator cuff tendons (of which there are four4), distal biceps tendon at the elbow, quadriceps and patellar tendons at the knee and Achilles’ tendon at the ankle.
There are a wide range of treatments for tendon problems, including medication, physical therapy, braces, injections (cortisone, platelet-rich plasma), and surgery. Acute, complete tendon ruptures are often treated with surgery, which is usually a direct repair of the tendon back to the bone where it tore off.
Nathan Endres, MD, is an orthopaedic surgeon at the University of Vermont Medical Center and assistant professor at UVM. He is fellowship trained in sports medicine, shoulder surgery and orthopaedic trauma. He is a former ski racer and member of the United States Ski and Snowboard Assocation (USSA) physician pool.