Arthrokinematics: An Important Biomechanical Concept

Today I am going to cover a topic that I did not learn until PT school.  I feel as though the topic of arthrokinematics is important for health and fitness professionals to know because it explains why and how to mobilize basically any synovial joint in the human body.  It is obvious that a manual therapist or orthopedic specialist would find it necessary to obtain this knowledge, but I can also make the case that a fundamental background would benefit the fitness professional as well.  Arthrokinematics is defined as the study of the motions that occur within joint spaces during bone movements.   Most of the joints that we as PT’s or fitness professionals are interested in fall under the category of synovial joints.  Some examples of synovial joints are the knee, ankle, hip, wrist, elbow, shoulder, joints of the foot and hand, and all of the facet joints of the spine.  By definition, synovial joints, differ from other joints because of they are enclosed by a joint capsule which is filled with synovial fluid (basically a lubricating fluid that is necessary for movement).  Please see image at right for visual.

In general, joints in the body are in a convex/concave relationship, which allows for greater surface area for the bones to contact each other; increasing joint stability, dissipating compression forces, and providing more guidance for movement.  These convex/concave relationships govern the rules for arthrokinematics.  Before we get to the “convex/concave” rule for synovial joint movement, we need to know the accessory movements that are available.

The three accessory movements include: Roll, Glide, and Spin

An example of roll would be during a soccer kick or a lateral raise.  Both the tibia and the humerus roll superiorly during the kick and concentric portion of the exercise respectively.  An example of spin is at the humeroradial joint during pronation and supination.  Here, the radius spins about a fixed humerus.  There is negligible roll or glide during spin.  An example of glide would be at the facet joints of the vertebral column. During a toe touch stretch, for example, the superior vertebra glides superiorly on the fixed inferior.  The opposite is true during extension of the spine.  Please see picture for visual of glide.  The facet joints in the picture are underneath the black arrows.  Note how the articular surfaces of the vertebrae are approximated during extension.

If the two articulating surfaces are convex/concave, the rule can apply.  The convex/concave rule for arthrokinematics has two parts.

1. If a convex surface moves upon a fixed concave surface, the roll and glide are in opposite directions. (ex. femur rolling and gliding upon a fixed tibia during a squat or deadlift)

2. If a concave surface moves upon a fixed convex surface, the roll and glide are in the same direction. (ex. tibia rolling and gliding on a fixed femur during a leg extension)

Lets take a look at a few more examples.  Elbow during bicep curl=ulna rolling and gliding in same direction upon a fixed humerus.  Hip abduction= femur rolling superiorly and gliding inferiorly upon a fixed acetabulum (hip bone).  Close kinetic chain ankle dorsiflexion/ plantarflexion as in a squat=tibia/fibula rolling and gliding in the same direction upon a fixed talus.

Starting to get the idea?

With a little anatomy knowledge (or by taking a quick look in any atlas), we can easily conclude the shape of the articulating surfaces, and thereby understand which way to mobilize.  Furthermore, it is important to understand when to use this principle.  Arthrokinematics should only be used with joint mobilization in mind.   It is not necessary to increase muscular extensibility, but performing both together can save time.  Joint mobilization is used to increase the ROM of the inert or non-contractile structures surrounding the joint, namely the joint capsule and ligaments.

I think it is easy to understand how increasing joint play is important and how this can be used in rehabilitation of injuries.  Specifically injuries that have left patients with decreased range of motion due to immobilization.  But how does this apply to healthy athletes or clients looking to increase their range of motion?  Below are a few examples of how using an exercise band can increase range of motion using the principle of arthrokinematics.  I am by no means suggesting that static stretching should be eliminated.  Remember, joint mobilization does not facilitate muscle lengthening.  But, there are times when both can be used simultaneously.   These examples are some of the more relevant because lack of hip extension and ankle dorsiflexion ROM is quite common.

Please click the link below to view :

Talocrural Joint Mobilization with Tibial Glide

Half Kneeling Hip Flexor Stretch with Femoral Glide

Rectus Femoris Emphasis

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