ANATOMY OF JOINTS AND BACK
There are different types of arthritis, and they may affect different parts of the body like the shoulder bone, backbone, elbow, hand and wrist, hip, knee and toe. To understand how these diseases affect the various joints, it is very necessary to know their anatomy.
THE SHOULDER
The two main shoulder bones are the humerus and the scapula (shoulder blade). The end of the scapula, called the glenoid, meets the head of the humerus to form a glenohumeral cavity that acts as a flexible ball-and-socket joint.
The joint cavity is cushioned by articular cartilage covering the head of the humerus and the face of the glenoid. The scapula extends up and around the shoulder joint at the tear to form a roof called the acromion and around the shoulder joint at the front to form the coracoid process.
The nature of the onset of the shoulder pain and its behaviour of precipitating by acute or repeated trauma helps to find out the cause. Stiffness accompanies pain in intrinsic disorders of the shoulder.
The joint is stabilized by a ring of fibrous cartilage surrounding the glenoid called the labrum.
Ligaments connect the shoulder bones, and tendons join the bones to the surrounding muscles.
The biceps tendon attaches the biceps muscle to the shoulder and helps to stabilize the joint.
Four short muscles originate on the scapula and pass around the shoulder, where their tendons fuse to form the rotator cuff.
THE KNEE
The knee bones, the femur and the tibia meet to form a hinge joint. The joint is protected in front by the patella (kneecap). The joint is cushioned by articular cartilage that covers the ends of the tibia and femur, as well as the underside of the patella. The lateral meniscus and media meniscus are pads of cartilage that further cushion the joint, acting as shock absorbers between the bones.
Ligaments help to stabilize the knee. The collateral ligaments run along the sides of the knee and limit sideways motion. The anterior cruciate ligaments, or ACL, connect the tibia to the femur at the centre of the knee. Its function is to limit the rotation and forward motion of the tibia. (A damaged ACL is replaced in a procedure known as ACL Reconstruction.) The posterior cruciate ligament, or PCL (located just behind the ACL), limits the backward motion of the tibia.
These components of the knee, along with the muscles of leg muscles, work together to manage the stress the knee receives while walking, running and jumping. Common symptoms with problems in and around the knee are pain, limping and insecurity on walking. Anterior knee pain, particularly in young women, suggests patellofemoral problems, but localized anterior pain may be due to peri-articular problems. Diffuse knee pain usually results from arthritis of the knee or hip. Locking of the knee suggests an intra-articular loose body or torn meniscus.
THE ELBOW
The elbow is a hinge joint comprising the humerus, ulna and radius.
The unique positioning and interaction of the bones in the joint allow for a small amount of rotation and hinge action. This rotation is easily noticed during activities such as hand-to-mouth eating motions.
The primary stability of the elbow is provided by the ulnar collateral ligament on the medial (inner) side of the elbow.
However, one of the most common injuries of the elbow occurs on the lateral, or outer, side of the elbow–called Lateral Epicondylitis or Tennis Elbow.
THE HAND AND WRIST
The hand comprises many small bones called carpals, metacarpals and phalanges. The two bones of the lower arm–the radius and the ulna–meet at the hand to form the wrist.
The hand comprises many small bones called carpals, metacarpals and phalanges. The two bones of the lower arm–the radius and the ulna–meet at the hand to form the wrist.
THE HIP
Pain in the region of the hip may arise from the hip joint, bursae, tendon insertions, sacroiliac joints, bone of the femur or pelvis, intrapelvic viscera, abdominal wall or the lumbar spine and its associated nerve roots.
Patients often use the expression ‘hip pain’ to refer to pain anywhere from the iliac crest and buttock to the greater trochanter and thigh. As locating the exact site of pain helps determine the cause, it is important to the painful area. Pain due to hip-joint disease is usually felt in the groin but sometimes in the buttock, over the greater trochanter, in the thigh or at the knee. Soft tissue lesions around the hip and lumbar spine disease also commonly present with pain in these regions, but in most cases, the source of pain can be determined with careful attention only.
THE PARTS OF THE SPINE AND THEIR WORKING
The lumbar spine comprises the last five vertebrae of the spine. To better understand how the parts of the spine affect each other, sometimes focus is made on a spinal segment. A spinal segment is composed of the following:
• Two vertebrae.
• The intervertebral disc between the two vertebrae.
• The two nerve roots that leave the spinal cord, one from each side.
The vertebrae are the bones of the spine. Their function is to provide support and protection to the spinal cord. Each vertebra comprises a large round piece of bone called the body attached to a bony ring. When the vertebrae are stacked one on the other, they form a column on a skinny tube in the back. The tube formed by the rings in the back is where the spinal cord and nerves run. The facet joints allow the vertebrae to be linked like a chain. They provide mobile connections between each vertebra, which shift and slide as the back is bent or twisted. An intervertebral disc sits between each vertebra. The disc is a large, round ligament that connects the vertebrae.
Understanding the anatomy of the vertebrae and the spinal segment in cross-section is helpful. A look at the disc in cross-section reveals that it comprises two parts. The annulus is the outer ring. It is the strongest part and is responsible for connecting the vertebrae. The nucleus pulposus is the soft, inner portion responsible for the spine’s shock absorption properties. The spine’s nerve roots carry information between the lower extremities and the brain. The nerve roots are sometimes the cause of low back pain as well. Pain in the low back and one or both legs may occur when the nerve roots are irritated or pinched by the disc or bone spurs.