Introduction to movement and joints
In this chapter we will present an overview of the different types of joint, their classification and joint movement(s).
Describing movement
To help describe movement, we use the terminology of ‘planes’. There are three planes of movement in the human body (the frontal and sagittal planes are shown in Figure 2.1a):
• Frontal plane – divides the body into anterior and posterior portions. An example of this movement would be lifting your arms and legs out to the side while doing a star jump: your arms and legs would be moving in the frontal plane.
• Transverse plane – divides the body through a line parallel to the floor in the horizontal position. Twisting and rotational movements such as turning your head to look over your shoulder occur in the transverse plane.
• Sagittal plane – divides the body into left and right portions with a line that goes from anterior to posterior. For example, when you are walking, your feet are moving in a sagittal plane.
Directions of movement are described using the terms superior/inferior, anterior/ventral and posterior/dorsal (Figure 2.1b).
What are joints?
The main purposes of the musculoskeletal system are movement and support. It is joints that enable movement. Joint mobility varies greatly and depends on a multitude of factors, such as the type of joint, ligament and muscular tension, and the apposition of connective tissue inside the joint. The structure of the joint dictates the angle and direction of the movement that takes place, but the joint must be sufficiently stable to maintain its integrity. For every joint there is an integral balance between stability and mobility: the more mobile a joint is, the less stable it is, and vice versa.
Figure 2.1
Planes and directions of movement
Joints are not only responsible for allowing movement; they also aid shock absorbency. Some of this shock absorbency is effected by the dynamics of the fluid and cartilage inside the joints (see Chapter 1). It is particularly important in the spine and lower extremities to help in the dissipation of forces that could potentially damage other parts of the body, for example when we run, jump or exercise. The mechanism is similar to shock absorbers in vehicles, which reduce damage or wear caused to the vehicle by the forces of the road.
When examining joints, the two components we are looking for are the ‘quantity’ and the ‘quality’ of the movement. The quantity refers to the range of movement of the joint. Through examination, our aim is to assess the amount of movement the joint can achieve within a particular plane until the movement stops. The limitation of the movement can be caused by pain or muscular contraction, or by the approximation of bone, connective tissue or soft tissue.
When a bony approximation is present, it is felt as a sudden ending of movement through the joint. Bony approximation can be due to natural anatomical approximation of the joint surfaces or to bony hypertrophy, either intra- or extracapsular. A connective tissue cause of the end of range of movement will give a firm end feel but it will also give an element of spring when tensioned. This spring end of range element is caused by the joint capsule or ligaments around the joint. Restriction of a joint movement due to soft tissue approximation gives a much softer end feel, with no definite end to the range of movement. This uncertainty about the exact end of range of movement may be an issue when examining larger patients.
Arthrokinematics
Arthrokinematics or arthrokinematic movement (sometimes also called joint play) refer to the specific simultaneous movements of joint surfaces. These are classed as roll, glide and spin.
• Roll is when one surface of a bone ‘rolls’ across another, similar to a wheel rolling along the ground.
• Glide happens when one articular surface moves parallel to another while keeping the space equal between the two surfaces.
• Spin occurs when one bone/joint surface ‘spins’ on another around a central axis.
The shape of the articular surfaces of the joints helps to dictate how these movements can occur (see ‘Types of joint’ later in the chapter). Individual joints are described in more detail in separate chapters, but a very brief summary of the mechanics of the knee here will serve to illustrate how different movements can occur in one joint.
The knee is classified as a modified hinge joint because the joint allows all the movements of roll, spin and glide. As the knee bends, forces of roll and glide occur as the condyles of the femur articulate with the tibial plateau. These movements are guided by the shape of the meniscus of the knee and the pull of the ligamentous tissues. Spin also occurs as the knee approaches full extension, when the tibia externally rotates (or spins) along its long axis to achieve a close-packed position in knee-joint extension. This is important as the forces involved in achieving this position cause an energy-saving biomechanical tension on the supportive structures of the knee when the person is standing. (We will discuss this in more detail in Chapter 13, The knee.)
Types of joint
Joints can be divided into three types:
• fibrous
• cartilaginous
• synovial.
Fibrous joints
Fibrous joints are strong joints that allow either small ranges of movement or, in some cases, no movement to occur. They can be subdivided into three groups:
• suture – e.g. of the cranial bones in the adult skull (Figure 2.2)
• gomphosis – e.g. the root of a tooth attaching to the bone
• syndesmosis – e.g. tibia and fibula (Figure 2.3).
Suture and gomphosis type joints generally have no movement. Syndesmosis joints (such as between the tibia and the fibula) have a small amount of movement. (We will discuss this further in Chapter 13, The knee.)
Figure 2.2
Sutures of the cranium. The arrow indicates the suture between the frontal and temporal bones
Figure 2.3
The syndesmosis joint of the distal tibia and fibula
Cartilaginous joints
Cartilaginous joints are generally flexible, strong, shock-absorbing joints that have no direct blood supply and no space between the cartilaginous and the skeletal tissues. They are of two types:
• synchondrosis – e.g. first rib and the sternum (Figure 2.4)
• symphysis – e.g. pubic symphysis, vertebral disc and vertebra (Figure 2.5).
Synovial joints
Synovial joints are the most common type of joint in the human body and, when they are healthy, they are generally mobile. The articular part of the skeletal tissue is covered with smooth articular/synovial cartilage. The joint is then supported by ligamentous tissue and a synovial joint capsule. These structures are important in allowing smooth fluid movement of the healthy joint while maintaining the stability and integrity of the joint.
Figure 2.4
The synchondrosis joint between the first rib and the sternum
Figure 2.5
Symphysis joints in the vertebral column
Synovial joints can be subdivided into six different types of joint, according to their shape and structure, which dictate the movement that happens at the joint:
• planar
• hinge
• pivot
• condyloid
• saddle
• ball-and-socket.
Synovial joints are the main joints of the human body and they are the joints which manual therapists will treat most frequently. We will therefore discuss them now in more detail.
Planar joints
Planar joints have articular surfaces which are slightly curved and allow gliding movements to occur. For this reason they are occasionally referred to as ‘gliding joints’. The range of movement within a planar joint is limited. Examples of planar joints are the carpal and tarsal joints in the hands and feet (Figure 2.6).
