Classification
- Type: Synovial plane (modified — the patella glides within the trochlear groove)
- Degrees of freedom: 2 (superior-inferior glide during knee flexion/extension; medial-lateral glide and tilt)
- Region: Knee complex (functions with the anatomy/joints/tibiofemoral joint)
Articular Surfaces
- Posterior patella (convex, with a central ridge): The patella's posterior surface has a vertical central ridge that divides it into medial and lateral facets. The lateral facet is larger. The articular cartilage of the patella is the thickest in the body (up to 6–7 mm), reflecting the enormous compressive forces it sustains. A small "odd facet" on the extreme medial border contacts the medial femoral condyle only in deep knee flexion (>135°).
- Femoral trochlear groove (concave): A V-shaped groove on the anterior distal femur between the medial and lateral condyles. The lateral wall is higher and steeper than the medial — this bony buttress prevents lateral patellar displacement. A shallow trochlear groove (trochlear dysplasia) predisposes to patellar dislocation.
Movements and ROM
| Movement |
Description |
Mechanism |
| Inferior glide |
Patella tracks inferiorly during knee flexion |
Pulled by the patellar tendon as the quadriceps lengthens |
| Superior glide |
Patella tracks superiorly during knee extension |
Pulled by the quadriceps tendon |
| Lateral tracking |
Slight lateral movement during early flexion |
Influenced by the Q-angle and lateral retinacular pull |
| Tilt |
Patella tilts medially/laterally |
Imbalance between medial (VMO) and lateral (VL + retinaculum) forces |
Contact areas change with flexion angle. At 0° flexion, the patella sits above the trochlear groove (no contact). At 30°, the inferior pole enters the groove. At 60°, the middle facets contact. At 90°, the superior facets contact. At 135°, the odd facet contacts the medial condyle. Patellofemoral compression increases with flexion — reaching 6–8 times body weight during deep squatting.
Capsular Pattern
Not applicable in the traditional sense. The patellofemoral joint does not follow a classical capsular pattern. Restriction presents as decreased patellar mobility (hypomobility in one or more glide directions) rather than a proportional ROM pattern.
Resting Position
- Full knee extension
- Patella sits above the trochlear groove; freely mobile; can be glided medially, laterally, superiorly, and inferiorly
Close-Packed Position
- Full knee flexion
- Patella maximally compressed into the trochlear groove
End-Feels
Assessed as patellar glide mobility rather than movement end-feels:
- Normal: The patella should glide approximately one-quarter to one-half of its width in each direction (medial, lateral, superior, inferior)
- Restricted: Decreased excursion with a firm capsular or retinacular end-feel
- Hypermobile: Excessive excursion (>one-half patellar width), especially laterally — indicates lateral retinacular laxity or VMO weakness
Ligaments
Medial Patellofemoral Ligament (MPFL)
- Attachments: Medial femoral epicondyle → medial patellar border
- Function: The primary restraint against lateral patellar displacement (provides approximately 50–60% of the total medial restraining force). Rupture of the MPFL is present in virtually all traumatic patellar dislocations.
- Injury mechanism: Lateral patellar dislocation — the MPFL tears as the patella dislocates laterally over the lateral femoral condyle. Most commonly occurs during a pivoting movement with the knee slightly flexed and a valgus force.
- Condition link: Patellar dislocation, recurrent patellar instability
Lateral Retinaculum
- Attachments: ITB and vastus lateralis → lateral patellar border
- Function: Provides lateral soft tissue support. In many patients, the lateral retinaculum is the problem rather than the solution — chronic tightness pulls the patella laterally, producing lateral tracking and patellar tilt.
Patellar Tendon (Ligament)
- Attachments: Inferior patellar pole → tibial tuberosity
- Function: Transmits quadriceps force to the tibia for knee extension. Technically a ligament (bone to bone) but universally called the patellar tendon.
Mobilization Techniques
Hands-on instruction is required. The descriptions below provide clinical reference detail for understanding and supervised practice. They are not a substitute for instructor-led technique training. Correct hand placement, force dosage, and tissue response interpretation require hands-on coaching and feedback.
Full patellar mobilization technique descriptions are included in
anatomy/joints/tibiofemoral — see the Patellar Mobilizations section. The key techniques (medial, lateral, superior, inferior patellar glides) are described there in full Option B detail with hand placement, grading, and clinical reasoning.
General Contraindications
- Absolute: Patellar fracture, acute patellar dislocation (refer for reduction), active infection
- Relative: Patellar subluxation (do not mobilize laterally — this worsens lateral tracking), significant joint effusion (ballotable patella — address effusion first; patellar testing is unreliable with effusion)
Muscles Acting on the Patella
- anatomy/muscles/quadriceps — the four quadriceps muscles insert via the quadriceps tendon onto the superior patella; the patella is a sesamoid bone within this tendon
- Vastus medialis oblique (VMO): The medial patellar stabilizer — its oblique fibers pull the patella medially, counteracting the lateral pull of the VL and ITB. VMO weakness is the most important modifiable factor in patellofemoral syndrome.
- Vastus lateralis (VL): The largest quadriceps muscle; its pull is primarily superior and slightly lateral
- Rectus femoris: Pulls the patella superiorly; biarticular (hip flexion + knee extension)
- Vastus intermedius: Deep; pulls the patella straight superiorly
Conditions Affecting This Joint
- conditions/patellofemoral-syndrome — anterior knee pain worsened by stairs, squatting, and prolonged sitting ("theater sign"); lateral patellar tracking, VMO weakness, tight lateral retinaculum; the most common knee condition in young adults
- Patellar dislocation — lateral dislocation (virtually always lateral); MPFL rupture; valgus + flexion + rotation mechanism; recurrence rate >40% after first dislocation
- Chondromalacia patellae — softening and fibrillation of the patellar articular cartilage; graded I–IV; produces anterior knee pain and crepitus
- Patellar tendinopathy ("jumper's knee") — inferior pole tenderness worsened by eccentric loading (jumping, landing, stairs)
- conditions/osteoarthritis — patellofemoral OA produces crepitus and anterior knee pain; often coexists with tibiofemoral OA
Clinical Notes
- VMO is the key to patellofemoral rehabilitation. The VMO provides the only medial pull on the patella. Its timing and strength relative to the VL determine patellar tracking. In patellofemoral syndrome, the VMO is often delayed in activation (fires after the VL rather than simultaneously), allowing the lateral structures to pull the patella off-track during the first 20–30° of knee flexion. Rehabilitation targets VMO activation timing and strength.
- The Q-angle determines patellar tracking mechanics. The Q-angle (ASIS → patella center → tibial tuberosity) reflects the lateral pull of the quadriceps vector on the patella. Normal: males 10–15°, females 15–20°. Increased Q-angle (wide pelvis, femoral anteversion, tibial external torsion, pes planus) increases lateral patellar tracking force.
- Patellofemoral compression increases dramatically with flexion angle. 0° = 0x body weight; 30° = 0.5x; 60° = 3x; 90° = 6x; full squat = 8x. This is why patients with patellofemoral pain are worse with stairs (60–90° loading), squatting, and prolonged sitting with knees bent.
- Patellar mobility testing always precedes tibiofemoral mobilization. A hypomobile patella prevents normal tibiofemoral mechanics. Always assess and restore patellar mobility first before performing tibiofemoral anterior or posterior glides.
Key Takeaways
- VMO weakness and delayed activation is the primary modifiable factor in patellofemoral syndrome — rehabilitation must target VMO timing and strength.
- Patellofemoral compression reaches 6–8 times body weight in deep flexion — this explains why stairs, squatting, and prolonged sitting worsen symptoms.
- Patellar mobility must be restored before tibiofemoral mobilization — a stuck patella prevents normal knee mechanics.
- The MPFL is the primary restraint against lateral dislocation — it ruptures in virtually all first-time patellar dislocations.
