1.1 Joint Kinematics and Arthrokinematic Principles
Key Takeaways
Osteokinematics describes motion of bones. Arthrokinematics describes relative motion at joint surfaces, including roll, glide and spin.
In the Kaltenborn model a convex surface rolls and glides in opposite directions. A moving concave surface rolls and glides in the same direction. Identify the moving partner and test the model prediction clinically.
Close-packed and resting positions describe typical differences in joint play and passive restraint. Choose an actual comfortable assessment or treatment position based on the joint and presentation.
Near knee extension, the tibia normally rotates externally relative to the femur in a classic open-chain example. The reciprocal description for a fixed tibia is femoral internal rotation.
Kinetic-chain labels describe distal constraints. Exercise angle, resistance and muscle activity determine loads more specifically than the label alone.
Joint Kinematics and Arthrokinematic Principles
Name the joint, the moving bone, the reference bone and the position before describing motion. The same joint motion can be expressed relative to either bone. A description of relative movement does not automatically prescribe a treatment.
Whole-Bone and Joint-Surface Motion
Osteokinematics describes gross movement, such as knee flexion in the sagittal plane. Joint motion can include simultaneous components. A goniometer can quantify a selected gross angle but does not measure the relative movement of the cartilage surfaces.
Arthrokinematics describes motion between the surfaces. In idealized roll, successive points on one surface meet successive points on the other. In idealized glide, a point on one surface slides past successive points on the other. Spin is rotation about an axis through the contact region, as illustrated by the radial head during forearm rotation. Real joints can combine these components. Joint play is the small passive motion examined with an external force, such as distraction or glide. It is one aspect of accessory motion, alongside surface motion that accompanies an active task.
| Dominant rotational freedoms in a simplified model | Example | Named movements |
|---|---|---|
| One | Humeroulnar hinge or proximal radioulnar pivot | Flexion and extension at the hinge, or forearm rotation at the pivot |
| Two | Metacarpophalangeal joint | Flexion and extension, and abduction and adduction |
| Three | Glenohumeral or hip joint | Flexion and extension, abduction and adduction, and internal and external rotation |
These are classifications of dominant rotations. A three-dimensional description of one bone relative to another can report three rotations and three translations even when some components are small or coupled.
Convex–Concave Model and Glide Selection
In the Kaltenborn model, a convex surface rolling in one direction on a fixed concave surface is paired with glide in the opposite direction. A concave surface rolling on a fixed convex surface is paired with glide in the same direction. The model helps organize an assessment of joint play. Measured in vivo kinematics reflect more than idealized surface shape.
| Setup | Model interpretation |
|---|---|
| Convex humeral head moves on the glenoid in abduction | Superior roll pairs with inferior glide. An inferior glide is one direction to assess if clinically appropriate. |
| Concave tibial surface moves on the femur in open-chain extension | Anterior roll and anterior glide of the tibia in the simple sagittal model. |
| Convex femoral surface moves on the fixed tibia during squat descent | Posterior roll pairs with anterior glide in the simple sagittal model. The knee can also translate and rotate in three dimensions. |
| Convex talar dome moves in a stabilized mortise during dorsiflexion | Anterior roll pairs with posterior talar glide in the model. If the tibia moves over a fixed talus, describe the motion relative to that setup. |
Worked assessment. A patient with limited shoulder abduction has been cleared for mobilization. Inferior humeral glide is a model-based hypothesis to assess. Check irritability and other restrictions and reassess the task after treatment. A small adhesive capsulitis trial found a posterior glide produced more improvement in external rotation than an anterior glide. That result illustrates why measured response and clinical context matter. In vivo studies also report small translations of the humeral head centre that depend on the task and coordinate system. Surface glide in a model and translation of the head centre are different descriptions.
Coupled Knee Rotation and Moving Axis
Near terminal extension, the screw-home mechanism describes coupled axial rotation. With the femur fixed, the tibia typically rotates externally relative to the femur. The same relative rotation can be described as femoral internal rotation with the tibia fixed. At the start of flexion the relative direction reverses. The popliteus can contribute to tibial internal rotation in open chain or femoral external rotation on a fixed tibia. Articular shape, ligament tension, muscle action and loading affect the amount and timing. Walking does not necessarily reproduce the unloaded pattern at each phase.
A joint's instantaneous axis of rotation describes its local rotational motion at a particular time. In a planar analysis the corresponding instantaneous centre can change location as the joint moves. A curve through successive centres is a centrode. In the Reuleaux construction, perpendicular bisectors of displacement lines between corresponding landmarks estimate a centre over a small finite movement. Very small movements can amplify measurement error. In three dimensions a helical axis can describe rotation with translation along the axis. An unusual estimate is not a specific test for a meniscal tear or ligament injury.
Packed and Resting Positions
In a conventional close-packed position, joint play is reduced as passive restraint increases and the joint surfaces fit more closely. In a resting or loose-packed position, passive slack can make joint play easier to assess. These are practical descriptions. Joint fluid volume, tissue state and symptoms can change the available play and the position the patient tolerates.
| Joint | Conventional example |
|---|---|
| Humeroulnar | Full extension with the forearm supinated is a close-packed example. About 70° elbow flexion and slight supination is a reference resting position in the Kaltenborn method. |
| Tibiofemoral | Near full extension is a conventional close-packed example. Some flexion is a common starting position when assessing joint play if appropriate. |
| Talocrural | Dorsiflexion engages the wider anterior talar dome. Slight plantarflexion can provide a starting position for testing play if tolerated. |
The actual resting position is found by examination. For an acutely painful or effused knee, support a tolerable position and assess the injury. Studies with simulated effusion show that pressure varies with angle and injected volume. A specific angle cannot be inferred from the presence of fluid. A comfortable resting position can be useful for symptom-oriented mobilization after safety screening. A movement-specific position can be appropriate when assessing or treating mobility and when the tissues can tolerate it.
Patterns of Passive Restriction
A capsular pattern is a traditional description of several passive movements being restricted in a recognizable relationship. Shoulder adhesive capsulitis commonly has loss in multiple planes with marked restriction of passive external rotation. Hip osteoarthritis commonly restricts internal rotation and flexion. A painful or stiff knee can lose flexion and extension. The amount and order vary. Compare sides, test with appropriate positioning, and interpret with symptoms, end feel and relevant diagnostic criteria. Neither a pattern nor its absence identifies a single structure or disease.
Open and Closed Kinetic Chains
In an open-chain task the distal segment can move relative to its surroundings, as in seated knee extension against an ankle weight. In a closed-chain task the distal segment is constrained by the environment, as with feet supported on the floor during a squat. Load can be added to either. A closed-chain constraint often couples several joints. Both tasks can involve co-contraction, joint compression and shear. What matters clinically is the actual load, range, resistance placement, tissue status and desired task.
For example, in vivo measurements found that a squat and active knee flexion–extension could both strain the ACL. The Aspetar ACL reconstruction guideline allows appropriately selected limited-range open-chain knee extension from week 4, alongside closed-chain training, with attention to symptoms and individual restrictions. A chain label alone does not establish graft load or readiness for that exercise.
After immobilization, a patient has limited glenohumeral abduction and is cleared for mobilization. Which glide direction does the Kaltenborn model suggest assessing?
Inferior glide of the humeral head on the glenoid
Superior glide of the humeral head on the glenoid
Anterior glide of the humeral head on the glenoid
Posterior glide of the humeral head on the glenoid
In the simplified model of open-chain knee extension, the tibia moves and the femur is fixed. Which roll and glide are predicted?
The femur rolls anteriorly and glides posteriorly on a fixed tibia.
The tibia rolls anteriorly and glides anteriorly on the fixed femur.
The tibia rolls anteriorly and glides posteriorly on the fixed femur.
The femur rolls posteriorly and glides anteriorly on a fixed tibia.
A patient has an acutely painful, effused knee after trauma. While assessing the injury and arranging further evaluation as indicated, how should the knee be supported?
Force full extension because the close-packed position always minimizes pressure.
Set 90° flexion because that angle is always the resting position.
Support a comfortable position without forcing a preset angle.
Place it in maximal flexion to unload all passive restraints.
After a healed ankle fracture, a patient is cleared for manual therapy and has limited dorsiflexion. With the lower leg stabilized, which talar glide does the simplified model suggest assessing?
Anterior glide of the calcaneus on the cuboid
Distal glide of the cuboid on the navicular
Anterior glide of the talus within the mortise
Posterior glide of the talus within the mortise
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