Knee: Menisci, Ligaments, Patellofemoral Mechanics, and Movement Patterns

Stability and Tracking Demands: How to Think About the Knee

The knee is a large load-bearing joint with relatively incongruent bony surfaces. It relies on passive restraints (menisci, ligaments, capsule) and dynamic control (quadriceps/hamstrings/hip strategy) to manage two constant demands: (1) tibiofemoral stability during flexion/extension and rotation, and (2) patellofemoral tracking during knee bending under load. Clinically, symptoms often cluster around either a tracking/load tolerance problem (patellofemoral or tendon) or a stability/shear problem (ligament/meniscus), though overlap is common.

1) Landmarks for Knee Assessment (Stability + Tracking Orientation)

Joint Lines (Medial and Lateral)

Why they matter: The tibiofemoral joint line approximates where meniscal tissue sits and where tibiofemoral compression/shear is perceived. Joint line tenderness and symptom reproduction with twisting/compression behaviors can support meniscal involvement (not diagnostic alone).

• Medial joint line: commonly symptomatic with medial meniscus behaviors and MCL-related irritation (MCL is close to medial meniscus/capsule).
• Lateral joint line: consider lateral meniscus behaviors; also be mindful of lateral structures (ITB region) that can refer discomfort near the lateral joint line.

Patella Borders (Superior/Inferior, Medial/Lateral) and Facets

Why they matter: Patellar border sensitivity, crepitus with compression, and pain with loaded knee flexion often relate to patellofemoral load tolerance and tracking. Comparing medial vs lateral facet sensitivity can help you hypothesize where contact pressure may be higher during functional tasks.

• Inferior pole: relevant for patellar tendon and inferior pole patellar pain patterns.
• Medial/lateral borders: guide observation of tilt and glide tendencies during quadriceps contraction and knee flexion.

Tibial Tuberosity

Why it matters: The tibial tuberosity is the distal attachment of the patellar tendon. Local tenderness, thickening, and pain with jumping/landing or resisted knee extension can indicate patellar tendinopathy or tendon irritability.

Fibular Head

Why it matters: The fibular head is a key lateral landmark for the LCL attachment region and biceps femoris insertion. It also helps you orient lateral knee symptoms that may be mistaken for “joint line pain.” Palpation here can help differentiate lateral ligamentous irritation from lateral meniscal behaviors.

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2) Arthrokinematics in Flexion/Extension and Patellar Tracking Concepts

Tibiofemoral Motion: Flexion/Extension With Rotation Coupling

In weight-bearing tasks (squat, step-down), the femur moves on the tibia. In open-chain tasks (seated knee extension), the tibia moves on the femur. Clinically, what matters most is that knee flexion/extension is rarely “pure hinge”: small rotations occur and are controlled by the menisci and ligaments.

• Menisci as load managers: they increase contact area, reduce peak stress, and help guide motion. Symptoms often appear when compression is combined with rotation (pivoting, deep squat with twist).
• ACL/PCL as shear controllers: they resist anterior/posterior translation and help guide rolling/gliding during motion—especially near end ranges and during deceleration.
• MCL/LCL as varus/valgus controllers: they resist frontal-plane opening and contribute to rotational restraint (especially MCL with tibial external rotation control).

Patellofemoral Mechanics: Tracking as a Load Distribution Problem

Patellar tracking is best framed as how contact pressure is distributed across the patellofemoral joint during knee flexion under load. The patella acts as a pulley for the quadriceps, increasing the knee extensor moment arm. As knee flexion increases, patellofemoral contact generally increases, and symptoms often emerge when tissue load tolerance is exceeded.

• Key idea: “Maltracking” is rarely a single structural fault; it is often a movement strategy + tissue irritability interaction.
• Common clinical contributors: reduced tolerance to compressive load (patellofemoral joint), quadriceps capacity deficits, hip strategy that increases dynamic valgus, and task dosing (stairs/running/jumping volume).

Practical Observation: Tracking During a Controlled Knee Bend

Step-by-step:

1. Position the patient standing with feet hip-width, hands lightly on support if needed.
2. Ask for a slow mini-squat to ~30–45° knee flexion, then return.
3. Observe: knee path over the foot, speed control, and whether pain appears on descent, ascent, or both.
4. Repeat with a slight change in task: slower tempo, reduced depth, or wider stance to see if symptoms change (helps infer irritability and load sensitivity).

Interpretation cues: pain that increases with depth and improves when depth is reduced suggests compressive load sensitivity; pain that spikes with speed/impact suggests rate-of-loading sensitivity (often tendon or high-irritability patellofemoral states).

3) Typical Clinical Patterns (What Symptoms Tend to Do)

Patellofemoral Pain (PFP): Load-Related Anterior Knee Features

• Common behavior: diffuse anterior/retropatellar pain with stairs (especially down), squatting, running hills, prolonged sitting with knees flexed.
• Often sensitive to: increased knee flexion angle under load, high repetition, and poor single-leg control strategies (knee drifting medially, trunk sway).
• Helpful differentiators: pain is usually not sharply localized to a single point like a tendon; swelling is typically minimal; mechanical locking is not typical.

Practical example: A patient reports pain 3/10 at the start of a run that becomes 6/10 on downhill sections and improves when they shorten stride and reduce downhill volume. This supports a patellofemoral load tolerance issue with sensitivity to higher compressive demand and braking forces.

Patellar Tendinopathy: Focal Load-Rate and Energy Storage Sensitivity

• Common behavior: focal pain at inferior pole of patella or along patellar tendon, worse with jumping/landing, sprinting, rapid deceleration, or repeated squats.
• Warm-up phenomenon: symptoms may ease as activity continues, then flare later or next day depending on irritability.
• Palpation clue: localized tenderness and thickening compared with the other side (not required, but supportive).

Practical example: Pain is minimal during slow cycling but spikes during drop jumps and quick direction changes. This points toward tendon energy-storage demands rather than general patellofemoral compression intolerance.

Ligament Sprain Considerations: Instability and Protective Guarding

Ligament-related presentations often involve a clear mechanism (twist, valgus collapse, hyperextension) and a sense of giving way or apprehension. Early on, swelling and guarding can limit exam quality.

• MCL: medial pain after valgus stress; tenderness along medial joint line/medial femoral condyle region; pain with side-to-side cutting early.
• LCL: lateral pain after varus stress; tenderness near fibular head region; discomfort with lateral cutting.
• ACL: pivoting injury, rapid swelling, instability with deceleration/pivot; avoid aggressive testing in high-irritability acute presentations.
• PCL: posterior force mechanism (e.g., dashboard-type), posterior knee discomfort, difficulty with downhill or deceleration tasks.

Meniscal Symptom Behaviors: Compression + Rotation Sensitivity

Meniscal symptoms are best described by behavior patterns rather than a single “positive test.” Many meniscal tears are asymptomatic; clinical relevance depends on irritability and mechanical behavior.

• Common behavior: joint line pain with twisting, pivoting, deep squat, or rising from a deep squat; intermittent catching sensations.
• Mechanical red flags: true locking (inability to fully extend) or recurrent blocked motion episodes suggest a mechanical component and warrant timely escalation.
• Effusion pattern: swelling may increase after provocative load (especially deep flexion + rotation tasks).

Practical example: Pain is minimal walking straight but sharp when turning quickly on the planted foot; deep squat produces a pinch at the medial joint line and a sense of catching. This supports a compression-rotation sensitive pattern consistent with meniscal involvement (while still considering other causes).

4) Functional Tests and Gentle Special Test Selection (Based on Acuity)

Functional Tasks: Squat and Step-Based Screens

Use functional tasks to identify where symptoms appear (angle, speed, load), how movement is controlled, and what modifications reduce symptoms. Keep the first exposure submaximal.

Squat (Bilateral)

Step-by-step:

1. Start with a mini-squat to ~30° knee flexion.
2. Progress depth only if symptoms remain acceptable.
3. Note pain location (anterior vs joint line), onset angle, and whether pain is worse on descent (eccentric control) or ascent (concentric demand).
4. Modify: reduce depth, slow tempo (3 seconds down), or widen stance; note changes.

Step-Down (Eccentric Control and Patellofemoral Load)

Step-by-step:

1. Use a low step initially (10–15 cm).
2. Ask the patient to tap the heel to the floor slowly and return.
3. Observe knee alignment over the foot, pelvic drop, trunk lean, and symptom reproduction.
4. Modify: reduce step height, add hand support, or cue “sit back” to redistribute load.

Interpretation cues: anterior knee pain that increases with step height and improves with support suggests load tolerance issues; marked wobble and loss of control suggests capacity/coordination deficits contributing to symptoms.

Single-Leg Squat or Single-Leg Sit-to-Stand (Only if Tolerated)

Use when: symptoms are low irritability and the patient can control the task safely. This is a high-demand screen for dynamic valgus strategies and quadriceps/hip capacity.

Gentle Special Test Selection Based on Acuity

Choose tests that match the suspected tissue and the current irritability. In acute/high-irritability knees, prioritize observation, swelling assessment, and gentle end-feel checks over aggressive torsion tests.

Decision Pathway: Link Findings to Likely Irritability and Next Steps

Use this pathway to connect (A) symptom behavior, (B) functional tolerance, and (C) exam findings to a practical plan.

1) Screen for urgent features (same-day/rapid referral considerations if present):  true locking, major instability/giving way with falls, large rapid effusion, inability to weight-bear, suspected fracture, systemic red flags.  If present → protect, refer/escalate.  If absent → proceed.  2) Identify dominant pain location + behavior:  A) Anterior pain with squat/steps/sitting → consider patellofemoral load intolerance.  B) Focal inferior pole/tendon pain with jumping/sprinting → consider patellar tendinopathy.  C) Joint line pain with twist/deep flexion + catching → consider meniscal behavior.  D) Clear trauma + instability/apprehension → consider ligament sprain.  3) Grade irritability (guides test selection and dosing):  High: pain easily provoked, night/rest pain, significant swelling, marked ROM loss/guarding.  Moderate: pain with functional load, settles within hours, mild swelling, partial ROM limits.  Low: pain only with higher loads, minimal swelling, full/near-full ROM.  4) Choose next steps based on irritability + pattern:  High irritability → reduce load/ROM depth, emphasize symptom-calming strategies, gentle ROM, isometrics, protected function; defer aggressive special tests.  Moderate irritability → graded exposure to functional tasks (squat/step), tempo control, isometrics progressing to isotonic strength; monitor 24-hour response.  Low irritability → progress capacity (strength + power as appropriate), single-leg control, task-specific retraining (stairs/running/jumping), and higher-level functional testing.  5) Re-test a key functional task (e.g., step-down) after a small modification:  If pain decreases with reduced depth/hand support/tempo → supports load sensitivity and guides dosing.  If instability/catching persists despite modifications → consider further investigation or referral based on severity and function.

Quick Mapping: Finding → Likely Interpretation → Action

• Pain increases with deeper knee flexion under load; improves with shallower range: patellofemoral compressive load sensitivity → reduce depth temporarily, build tolerance with controlled tempo and graded exposure.
• Focal tendon pain with fast SSC (stretch-shortening cycle) tasks; tolerates cycling: tendon energy-storage sensitivity → start with isometrics/isotonics, delay plyometrics, manage jump/landing volume.
• Joint line pain + twist sensitivity + intermittent catching: meniscal behavior → avoid repeated torsion early, use symptom-guided ROM/loading; escalate if true locking or persistent mechanical block.
• Instability/apprehension after trauma; swelling/guarding limits exam: ligament sprain consideration → protect, brace/crutches if needed, gentle testing only, reassess when irritability reduces; refer if significant laxity suspected.