44


PART I FOUNDATION CONCEPTS


end-feel feels springy at the end of the range because the joint capsule or ligaments are limiting any further movement into the range of motion. An example of a capsular end-feel is the resistance to movement felt at the end of wrist fl exion. An empty end-feel is any joint motion that is limited by pain rather than by any physical resistance from body structures. Although there may be inconsistencies with the ratings of joint end-feels by clini- cians, a joint that is limited or exceeds range-of-motion norms and displays atypical end-feels should be evaluated further for impairments and dysfunction.


ARTHROKINEMATICS


During human movement, both the joint surfaces and the bony shafts must achieve appropriate interplay for the entire limb or trunk segment to move in correct alignment without placing abnormal stress on or incur- ring damage to joint structures. This interaction between the two joint surfaces is called arthrokinematic motion and takes place during the osteokinematic movement of the entire bone. In contrast to osteokinematic motion, arthrokinematic or accessory motion is not under vol- untary control. During these accessory movements, one joint surface is stable, while the opposing surface moves on the steady surface. The specifi c arthrokinematics that occur at any joint depend on the shape of the joint sur- faces, the integrity of the periarticular structures, and the performance of the muscles. A tight joint capsule or a malfunctioning neuromuscular unit can impede the arthrokinematic motion in a joint and ultimately prevent optimal joint movement that is functional and symptom- free. When the arthrokinematic motion is decreased, the joint is considered hypomobile. If there is exces- sive motion between the joint surfaces, which can occur because of overstretched ligaments or damage to the joint surfaces, the joint can be classifi ed as a hypermobile joint.


General Concepts


To provide therapeutic interventions related to joint dys- function (i.e., joints that are hypomobile or hypermobile), it is necessary to understand basic concepts that apply to joints and their arthrokinematic motion. These concepts include understanding the relationship between joint surfaces and movement when the joints are in various positions and the types of movement that occur between the joint surfaces.


Close-Packed Position


The position, shape, and size of joint surfaces often cor- relate with the degree of arthrokinematic movement between them. A close-packed position is the posi- tion of the joint where the surfaces are congruent and in maximal contact with each other. Often this position occurs at the extreme ends of range of motion where the


ligaments and joint capsule are taut and under tension. The position tends to be one of marked stability with little or no movement or joint play between surfaces; the surfaces are compressed. While standing with the knee in full extension, the joint is locked and there is little to no movement between the femur and the tibia; this is the joint’s close-packed position.


Loose-Packed Position


In a loose-packed position, the joint ligaments and capsule are slack, and joint play between surfaces is increased compared with the closed-pack position. The surfaces are incongruent and tend to be the least congru- ent in the mid-range of the available range of motion. All positions of a joint other than the close-packed position are considered to be loose-packed positions. Joint sur- faces in a loose-packed position should display an ade- quate amount of joint accessory or joint play movement if arthrokinematic motion is to accompany the osteokine- matic movement of a body segment during general body motion. While sitting with the knee in a loose-packed position of fl exion, the tibia can rotate medial and lateral in relation to the femur. In full knee extension, there is little to no tibial rotation at the knee joint. The position of a joint where there is the least amount of congruency and where the joint structures have the least amount of tension is called the resting position of the joint. Typi- cally, the resting position is near the mid-range of the available range of motion of the joint.


Types of Arthrokinematic Motion


During movement of body segments, articular surfaces of synovial joints move in one or a combination of the following ways: roll, glide (slide), and spin. This section explores the general concepts of these accessory move- ments and their contribution to overall joint function. The chapters related to individual joints describe the spe- cifi c arthrokinematic movements that occur during each of the osteokinematic motions for that particular joint.


Clinical Connection 2.6


Joint restrictions resulting in decreased range of motion can be the result of restrictions in the arthrokinematic motion between joint surfaces. Increasing the passive arthrokinematic motion through manual joint mobilization techniques plays an important role in gaining overall range of motion and function of the joint. To address impairments related to the arthrokinematic motion at a joint, the clinician must fi rst grasp an understanding of basic fundamental concepts related to movement between joint surfaces.


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