You perform exercises, you try to maintain your fitness. So, except for muscles, you have to concern about your joints during your workout sessions. Joint stability is a key component for keeping your mobility. Obviously, Joint stability means its ability to perform actions with great coordination of the neuromuscular system. It is vital to get a sound knowledge about joints structure, how they maintain stability with high mobility.

Joint structure and Classification

A joint is basically defined as a connection between two bones. It is clear that you can’t move your body segments without joints. Joints can be classified using joint structure, joint mobility, and range of motion. First, let’s starts with structural classification. It is the most common and easiest way to clarify this topic.

There are three types of joints,

  • Cartilaginous joint (Amphiarthrodial joint)
  • Fibrous joint (Synathrodial joint)
  • Synovial joint (Diarthrodial joint)

Cartilaginous joints

This is the type which is characterized by cartilage between the bones and no joint cavity as well as stability is high and mobility is less. These two subtypes of these cartilaginous joints. They are primary cartilaginous joints(synchondrosis) and secondary cartilaginous joints(symphysis)

Primary cartilaginous joints are made from hyaline cartilage. You can refer to epiphyseal plates (can be temporary) and 1st sternocostal joint (can be permanent) as examples.

The articular surfaces of the secondary cartilaginous joint covered with cartilage and fibrocartilage. These are really strong joints with the greatest stability among all three joint types and very limited movements. Pubic symphysis, Manubriosternal joint, and anterior intervertebral joints of the spine are the best examples for study the science of fibrocartilaginous joints.

Fibrous joints

Fibrous joints are the most stable joints which are largely fibrous in structure. These are immovable joints. And also, they haven’t a joint cavity like cartilaginous joints. We are able to identify three subtypes named Sutures, Syndesmosis, and gomphosis.

  • Sutures-between skull bones
  • Syndesmosis (joined by a strong interosseous membrane)-Joint between radius and ulna, Joint between radius and ulna.
  • Gomphosis- Tooth in its socket

Synovial joints

The most common joint type in your body. The two bone ends are covered by hyaline cartilage. Also, the joint cavity is containing the synovial fluid. There is a synovial membrane in a synovial joint. The fibrous capsule is reinforced by ligaments. Synovial joints have rich blood and nerve supply. These are the most mobile joints and least stable joints.

It is ideal to get a brief overview of synovial joint classification.

  • Ball and socket joints-multi axial joints (Shoulder joint, Hip joint)
  • Hinge joints-uniaxial joints (Elbow joint)
  • Plane joints- These are non-axial joints and relative gliding and rotational movements can be seen
  • Saddle joints-Biaxial joints (trapezio-metacarpal joint)
  • Condylar joints/Ellipsoid joint -Biaxial joints (Wrist joint)
  • Pivot joints-uniaxial joints (Atlantoaxial joint)

Factors affecting the synovial joint stability

As I mention before, we have to discuss the synovial joints here since they are the most mobile joints.  Generally, it is accepted that ligaments, muscles, and shapes of the bone ends affect joint stability. But Studies are done under each of the main joints like the hip, shoulder, knee joint for investigating the major factors. It is so significant since these joints are responsible for weight-bearing and mobility of the body.

Shoulder joint

The shoulder joint is a ball and socket variety joint so it allows you to move your arm in multiple directions. The shoulder joint is the most mobile joint among all the synovial joint and shoulder dislocation is a common condition in the community. Actually, the shoulder joint is a complex of joints. But we mainly focus on the stability of the glenohumeral joint which is made by the articulation of the glenoid cavity of the scapula and head of the humerus. So, the following factors can be identified as the stabilization factors of the shoulder joint.

  • The coracoacromial arch (Coraco-acromial ligament, coracoid process)
  • Rotator cuff muscles which are surrounding the glenohumeral joint
  • Glenoid cavity is very shallow and the glenoidal labrum helps in deepening the glenoid fossa.
  • Stability is also provided by the muscles attaching the humerus to the pectoral girdle, the long head of the biceps brachii, and the long head of the triceps brachii.
  • Atmospheric pressure also stabilizes the joint.
  • Ligaments including the capsular ligament, glenohumeral ligaments, coracoclavicular ligament

Knee joint

The knee joint is the largest and most complex joint. Which has three articulations between femur, tibia, and patella. Two condylar joints can be seen in two condylar joints between the condyles of the femur and tibia and one saddle joint between the femur and the patella.

Structurally, Knee is a week joint as its articular surfaces are not congruent. The tibial condyles are too small and shallow to hold the large, convex, femoral condyles.

Except common stabilizing factors, , following factors mainly contribute to increase the stability of knee joint,

  1. The cruciate ligaments maintain the forward and backward stability
  2. The collateral ligaments maintain side to side stability
  3. the iliotibial tract also stabilizes the knee joint.
  4. Muscles and other ligaments also play a vital role in stabilizing the knee joint

During the higher range of motion actions in sports, most of the time ligaments are damaged but they protect the knee from dislocations.

Hip joint

The hip joint is another ball and socket joint which also can work as a multiaxial joint but joint mobility is quite less than the shoulder joint. But the hip joint is unique since it has great stability as well as mobility. As the femur has a long neck, a fairly wide range of motion is possible. Let’s find out what are the key stabilizing factors of the hip joint.

  1. Depth of the acetabulum
  2. Tension and strength of ligaments
  3. Strength of the surrounding muscles
  4. Length and the obliquity of the neck of the femur
  5. Atmospheric pressure

We can also discuss synovial joint stability and mobility according to the close-packed position and loose-packed position of the joints.

Close packed position of a synovial joint

This is the most congruent position of joint surfaces of a joint. Joint surfaces are tightly compressed and they have a maximal area of contact. So, no further movement is possible since joint surfaces are locked. This is the highest joint stability position

Open packed position of a synovial joint

In this position, articulating surfaces are not congruent. There is a partial contact between joint surfaces. When it comes to the stability of the joint, this is the least stabilizing position, and also joint has the highest mobility.

Credits for featured image: People photo created by freepik –

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