Joint Anatomy and Arthrokinematics for Physiotherapy Assessment

1) Joint structure and what it predicts about motion

Joint types: what moves, what limits

In assessment, joint anatomy is not “background knowledge”; it predicts which motions should be available, which should be limited, and what kind of end-feel and accessory motion you should expect. A useful mental model is: shape + surface congruency + capsule/ligaments + intra-articular structures determine range, stability, and arthrokinematics.

• Synovial joints: designed for movement; have articular cartilage, synovial fluid, and a capsule. Motion is guided by joint surface geometry and restrained by capsule/ligaments.
• Fibrous joints (e.g., syndesmosis): minimal motion; stability prioritized. Symptoms often relate to stress at the ligamentous connection rather than classic capsular restriction.
• Cartilaginous joints (e.g., symphysis): small motion with load distribution; symptoms often load-related and may show limited “spring” rather than large ROM loss.

Capsule: the “envelope” that shapes passive range

The capsule is a continuous sleeve that becomes taut in predictable directions. When the capsule is the primary limiter (e.g., adhesive capsulitis), passive ROM tends to reduce in a characteristic proportion (capsular pattern). When the capsule is not the limiter, restrictions are often direction-specific and inconsistent (non-capsular pattern).

Ligaments: direction-specific restraints and proprioceptive drivers

Ligaments limit motion in specific directions and often become taut near end-range. They also contribute to joint position sense. Clinically, a ligament-dominant limitation often presents as: pain or apprehension in a specific direction, sometimes with relatively preserved motion elsewhere, and a firm end-feel that appears earlier than expected.

Labrum and menisci: depth, congruency, and load distribution

• Labrum (e.g., shoulder, hip): deepens the socket and increases stability without sacrificing too much motion. Labral compromise may present as catching, clicking, or pain with combined movements (e.g., flexion-adduction-internal rotation at the hip), and may alter the “centering” of the joint during motion.
• Menisci (knee): improve congruency and distribute load. Meniscal issues can produce joint line tenderness, mechanical symptoms, and a non-capsular limitation (often more pronounced in flexion than extension, or vice versa, depending on the tear and swelling).

Articular surface shape: the built-in guide rails

Surface geometry strongly influences expected arthrokinematics. For example, a convex head on a concave socket tends to require gliding opposite the direction of osteokinematic motion to maintain congruency; a concave surface moving on a convex surface tends to glide in the same direction as the bone motion. This is a clinical shortcut for predicting which accessory glide might be limited when a patient cannot reach a certain range.

2) Arthrokinematics essentials applied to major joints

Key terms you must be able to “see” during movement

• Roll: multiple points on one surface contact multiple points on the other (like a tire rolling). Roll alone would displace the joint surfaces.
• Glide (slide): a single point on one surface contacts multiple points on the other. Glide maintains congruency and prevents impingement or translation.
• Spin: rotation around a fixed axis with the same point contacting the same point (or near-same) on the opposing surface.

Most functional joint motions combine roll and glide; pure spin is less common but important (e.g., radial head during pronation/supination; hip flexion has a substantial spin component).

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Convex–concave rule (clinical version)

Use this to choose which accessory glide to test or mobilize when a specific osteokinematic motion is limited.

• Convex moving on concave: roll and glide occur in opposite directions.
• Concave moving on convex: roll and glide occur in the same direction.

Clinical caution: this rule predicts the dominant glide direction, but real joints have coupled motions, variable axes, and soft-tissue constraints. Use it as a starting hypothesis, then confirm with accessory testing and symptom response.

Shoulder complex (glenohumeral focus)

Expected arthrokinematics: During shoulder elevation (abduction/flexion), the humeral head must remain centered on the glenoid. This requires a balance of superior roll with inferior glide (convex humeral head on concave glenoid).

• Abduction: superior roll + inferior glide.
• External rotation: posterior roll + anterior glide (dominant direction depends on plane and tensioning).
• Internal rotation: anterior roll + posterior glide.

Common presentation of altered arthrokinematics: reduced inferior or posterior glide can present as painful or limited elevation with a “pinch” sensation, early scapular substitution, or a firm capsular end-feel. Example: reduced posterior glide may limit internal rotation and contribute to altered humeral head centering during elevation, sometimes perceived as anterior shoulder discomfort.

Hip

The hip is a deep ball-and-socket with strong capsuloligamentous support. Arthrokinematics are similar to the shoulder (convex femoral head on concave acetabulum), but the capsule is thicker and often a major limiter.

• Flexion: primarily spin with associated glide; limitations often reflect capsular tightness, posterior soft tissue, or anterior impingement depending on symptom location and end-feel.
• Internal rotation: anterior roll + posterior glide (dominant accessory limitation often felt as reduced posterior glide).
• External rotation: posterior roll + anterior glide.

Example: limited hip internal rotation with a firm end-feel and reduced posterior glide may show up as toe-out gait, difficulty with pivoting, or anterior hip discomfort in flexion/adduction tasks.

Knee (tibiofemoral and patellofemoral essentials)

The knee is guided by menisci, cruciates, and the geometry of the femoral condyles. Arthrokinematics differ depending on whether the tibia is moving on the femur (open chain) or the femur on the tibia (closed chain).

• Open-chain knee extension (concave tibia on convex femur): tibia rolls and glides anteriorly.
• Open-chain knee flexion: tibia rolls and glides posteriorly.
• Terminal extension “screw-home”: tibial external rotation (or femoral internal rotation in weight-bearing) contributes to locking; loss may present as difficulty achieving the last degrees of extension.

Patellofemoral tracking: patella glides superiorly with knee extension and inferiorly with flexion; it also tilts and rotates subtly. Swelling, retinacular tightness, or altered femoral rotation can change tracking and provoke anterior knee pain.

Ankle (talocrural) and subtalar

Talocrural joint behaves like a mortise-and-tenon hinge with a convex talus moving in the concave tibiofibular mortise (in open chain). Dorsiflexion commonly requires posterior glide of the talus relative to the tibia.

• Dorsiflexion (open chain): talus rolls anteriorly and glides posteriorly.
• Plantarflexion (open chain): talus rolls posteriorly and glides anteriorly.

Example: reduced posterior talar glide often presents as limited dorsiflexion, early heel rise in gait, compensatory pronation, or knee valgus during squat/landing tasks.

Subtalar joint contributes to inversion/eversion and foot adaptability. Restrictions may present as reduced pronation/supination capacity and altered load distribution rather than a single “missing” plane of motion.

Elbow and forearm

• Humeroulnar: primarily hinge; capsular restriction often affects flexion/extension with a firm end-feel.
• Proximal radioulnar: radial head spins within the annular ligament during pronation/supination. Loss of spin or pain with compression can indicate joint irritation or ligament involvement.

Cervical spine (facet-guided motion)

Cervical motion is largely guided by facet orientation and coupled motions. Rather than applying a single convex–concave rule, think in terms of facet glides and symptom reproduction with segmental accessory testing. For example, limited opening/closing glide can present as restricted rotation/side-bending to one side with localized end-range pain.

3) Clinical implications: capsular vs non-capsular patterns

What a capsular pattern suggests

A capsular pattern is a proportional limitation of passive ROM typical of capsular involvement (e.g., inflammation, fibrosis). It suggests the capsule is the primary limiter rather than a single structure.

Important: patterns vary across sources and individuals. Use capsular patterns as a hypothesis generator, then verify with end-feel, accessory motion, irritability, and symptom reproduction.

What a non-capsular pattern suggests

A non-capsular pattern is a limitation that does not match the expected capsular proportion. It suggests a specific structure or mechanical issue such as:

• Internal derangement (e.g., meniscus, loose body): disproportionate loss, locking/catching, variable end-feel.
• Ligament sprain: pain/apprehension in a specific direction with relatively preserved other motions.
• Muscle/tendon limitation: pain on resisted testing, stretch pain, and a more elastic end-feel.
• Impingement or bony block: hard end-feel, abrupt stop, pain in combined positions.

End-feel as a decision aid (paired with symptom response)

• Firm capsular: typical of capsular tightness; often consistent and reproducible.
• Hard: bony approximation or osteophyte; consider joint degeneration or structural block.
• Empty: pain prevents reaching end-range; indicates high irritability or acute inflammation.
• Springy block: suggests internal derangement (e.g., meniscal involvement) when consistent with history and other findings.

4) Practical assessment flow by region: AROM → PROM → end-feel → accessory motion screening

This flow links what you see (AROM) to what the joint allows (PROM), then to what stops it (end-feel), and finally to the likely arthrokinematic driver (accessory motion). Keep the sequence consistent to reduce bias.

Step-by-step template (use for any joint)

1. AROM: observe range, quality, symptom location, substitutions, and willingness to move.
2. PROM: compare available range to AROM; note symptom onset, resistance onset, and whether limitation is pain-dominant or stiffness-dominant.
3. End-feel: categorize and compare side-to-side; determine if it matches the suspected tissue behavior.
4. Accessory motion screening: test the glide/spin most relevant to the limited osteokinematic motion; compare mobility and symptom reproduction.

Clinical reasoning shortcut: If a motion is limited and painful at end-range, ask: “Which accessory glide should accompany this motion?” Then screen that glide to confirm whether it is restricted, painful, or both.

Shoulder (glenohumeral-focused flow)

• AROM: elevation (flexion/abduction), external rotation (arm at side), hand-behind-back (functional IR). Note scapular substitution and painful arc behavior.
• PROM: reassess ER/IR and elevation in a controlled plane (often scapular plane). Compare symptom onset vs resistance onset.
• End-feel: capsular firm end-feel with global limitation suggests capsular involvement; sharp pinch/hard stop in specific positions suggests impingement or bony constraint.
• Accessory screening: inferior glide (elevation), posterior glide (IR and elevation mechanics), anterior glide (ER). Determine whether restriction reproduces symptoms or simply feels stiff.

Example (altered arthrokinematics): Patient cannot reach overhead without anterior shoulder discomfort. PROM elevation is limited with a firm end-feel. Accessory testing shows reduced inferior glide and/or posterior glide. This supports a hypothesis of reduced humeral head centering contributing to painful elevation.

Hip (flow)

• AROM: flexion, extension, abduction, internal/external rotation (seated or prone). Watch pelvic substitution and trunk lean.
• PROM: focus on internal rotation and flexion/adduction positions if symptoms suggest anterior hip involvement; compare symptom behavior.
• End-feel: firm capsular end-feel with early resistance often indicates capsular restriction; hard end-feel in flexion/adduction may suggest bony impingement.
• Accessory screening: posterior glide (often relevant for flexion and IR), anterior glide (extension/ER), inferior glide (general mobility). Note whether glide limitation matches the most limited osteokinematic direction.

Knee (flow)

• AROM: flexion/extension in open chain; note lag, pain location, and willingness to load.
• PROM: assess end-range extension carefully; compare flexion range and symptom irritability.
• End-feel: empty end-feel may reflect high irritability/effusion; springy block may suggest internal derangement when consistent.
• Accessory screening: tibiofemoral anterior/posterior glides (related to extension/flexion mechanics), patellar glides/tilt (if anterior knee symptoms). Consider that swelling can globally reduce accessory motion.

Example (altered arthrokinematics): Patient lacks terminal extension after injury. PROM extension is limited with a firm-to-springy end-feel. Accessory testing shows reduced anterior tibial glide (open chain) and reduced patellar superior glide. This supports a mechanical limitation affecting the last degrees of extension.

Ankle (talocrural-focused flow)

• AROM: dorsiflexion/plantarflexion; add functional dorsiflexion (e.g., knee-to-wall) to observe compensations.
• PROM: confirm dorsiflexion limitation with knee flexed and extended to differentiate gastrocnemius contribution vs joint restriction.
• End-feel: firm capsular end-feel is common with talocrural stiffness; empty end-feel suggests irritability.
• Accessory screening: posterior talar glide (key for dorsiflexion), anterior talar glide (plantarflexion). Compare symptom response and mobility side-to-side.

Example (altered arthrokinematics): Reduced dorsiflexion during squat with heel lift. PROM dorsiflexion limited even with knee flexed. Posterior talar glide is restricted and may reproduce anterior ankle pinching, supporting a talocrural arthrokinematic restriction.

Elbow/forearm (flow)

• AROM: flexion/extension; pronation/supination with elbow at 90°.
• PROM: compare end-range pain vs stiffness; note whether limitation is isolated to pronation or supination.
• End-feel: firm capsular end-feel for hinge restriction; pain-limited empty end-feel in acute irritation.
• Accessory screening: humeroulnar distraction and glides as appropriate; radial head spin/glide for pronation/supination limitation.

Cervical spine (flow)

• AROM: rotation, side-bending, flexion/extension; observe coupled motion and symptom distribution.
• PROM: gentle overpressure to assess end-range behavior and irritability.
• End-feel: firm end-feel is common; empty end-feel suggests high irritability.
• Accessory screening: segmental PA glides and facet opening/closing glides guided by the direction of limitation and symptom reproduction.

Quick mapping: limited motion → likely accessory to screen