Kinematics

Principles of Kinematics As a PTA, you apply the principles of kinematics frequently. Whether you are attempting to improve passive ROM, teaching patients a home exercise program with active ROM, or performing joint mobilizations, kinematics plays a key factor in your decision making. It may have been awhile since you reviewed the concepts of osteokinematics and arthrokinematics, so let’s discuss some key points.

Osteokinematic Motion Osteokinematic motion is the physiologic or bone movement that you visually identify as flex/ext, abd/add, and IR/ER. These movements are produced by concentric or eccentric muscle contractions via levers within the body and occur in the cardinal planes of motion. Osteokinematic movement results in either the proximal segment moving on a fixed distal segment (squatting against a wall) or the distal segment moving on a relatively fixed proximal segment (knee extension while sitting). Osteokinematic motion can also be classified as open or closed kinematic chain. Open Chain: Isolates muscle groups, focuses local, and is not global. Typically, the distal segment is free to move in space (non-weightbearing) and limb movement only occurs distal to the moving joint. Closed Chain: Utilizes multiple muscle groups and provides compressive forces (axial loading) and kinesthetic and proprioceptive feedback. The distal segment is commonly fixed or stabilized on a supportive surface. Most importantly, co-contraction of muscles with closed chain activities reduces shear forces.

Arthrokinematic Motion Arthrokinematic motion is the accessory or joint surface movement that takes place intrinsically within the joint. Thus, arthrokinematic motion accompanies osteokinematic motion through 1) rolling (e.g. femur rolls on the tibia like a tire), 2) gliding and sliding (e.g. the pure translatory motion on the humeral head on the glenoid cavity at 170 degrees of abduction), and 3) spinning (e.g. the humerus spinning for internal rotation like a top). These are also the motions we take into consideration when applying joint mobilizations to a patient.

Convex-Concave Rule Arthrokinematics follows the convex-concave rule also referred to as a male and female relationship. The majority of synovial joints have a convex (male) and a concave (female) surface. The aforementioned rule states that the convex surface glides/slides in a direction opposite to the movement of the bony lever shaft, while the concave surface glides/slides in the same direction to the moving shaft of the bony lever.

KNOWLEDGE CHECK: A patient is sitting on the edge of a treatment table and extending his knee. According to the convex-concave rule, which of the following is true? The tibia is both rolling and gliding anteriorly The tibia is rolling anteriorly but gliding posteriorly The femur is rolling and gliding posteriorly The femur is rolling and gliding anteriorly Feedback: The tibia is the moving concave surface, and slide occurs in the same direction as movement of the bone. Remember that osteokinematic or angular motions are the visual movements of the bone, while the arthrokinematic, or accessory movements, are the translator movements occurring between joint surfaces

Patient is a 21 y.o. female referred to physical therapy following the diagnosis of right shoulder pain. She is currently on scholarship with the swim team and participates in the 800 and 1500 meter events (long distance). Pt. denies history of injury and describes the idiopathic pain as slowly becoming worse over several months. Anterolateral right shoulder pain was subjectively rated at a 2/10 at rest and 7/10 at worst. Right shoulder pain increases with overhead movement, especially when she tries to perform a freestyle stroke. The pt. described the pain as “sharp” when performing overhead movements and “achy” at rest after practice. The evaluating PT determined the patient has inferior and posterior capsular tightness accompanied by moderate anterior laxity. Matt—can you make this a box that they can access (maybe by clicking a button?) on all the following screens? All the questions that follow relate to this patient. The box doesn’t have to look like this or anything, I just put this here as a marker between the previous question and the other set.

KNOWLEDGE CHECK: What osteokinematic motion best reproduces the patient’s complaints of sharp pain? Shoulder flexion Shoulder external rotation Shoulder internal rotation Shoulder extension Feedback: shoulder flexion, or elevation of the humerus, is “overhead motion”

KNOWLEDGE CHECK: Applying the convex-concave rule, which of the following are true of normal shoulder kinematics? (Check all that apply) Shoulder flexion is accompanied by inferior glide of humeral head Shoulder flexion is accompanied by superior glide of the humerus Shoulder internal rotation is accompanied by posterior glide of the humeral head Shoulder internal rotation is accompanied by anterior glide of the humerus Feedback: The humeral head (convex surface) glides opposite the direction of movement of the humerus

KNOWLEDGE CHECK: Given the patient information, and considering kinematic principles, what is the BEST application of a joint mobilization technique? Inferior glides in shoulder extension Inferior glides in loose-packed position Anterior glides in neutral rotation Anterior glides in internal rotation Feedback: Gliding inferiorly in the loose-packed position will allow for stretching of the tight inferior capsule. Anterior glides would be contraindicated due to an already lax anterior capsule.

Summary Kinematics plays a huge role in manual-based therapy. Understanding the role of kinematics can be a key factor when determining treatment approaches. Always use critical thinking skills and the basics of kinematics to guide your decisions.