Joints
Knee joint
Two incongruent surfaces made to fit by the menisci. The largest joint in the body, and the one that draws its stability almost entirely from ligaments and muscles instead of from bony shape.
- Joint type
- Compound pivot hinge (trochoginglymus): femorotibial and femoropatellar, two degrees of freedom
- Body region
- Knee
- Latin name
- Articulatio genus
Movements, axes and normal values
| Movement | Plane | Axis | Normal range | End feel |
|---|---|---|---|---|
| Flexion | sagittal | transverse, moving posteriorly during the movement | 0-140 degrees | soft (soft tissue) |
| Extension | sagittal | transverse | 0 degrees; up to 10 degrees of hyperextension is normal | hard-elastic (ligaments) |
| External rotation of the tibia | transverse | longitudinal through the medial tibial condyle | 0-40 degrees, only at 90 degrees of flexion | elastic |
| Internal rotation of the tibia | transverse | longitudinal through the medial tibial condyle | 0-10 to 30 degrees, only at 90 degrees of flexion | elastic |
- Close-packed position
- Full extension with external rotation of the tibia
- Resting (loose-packed) position
- 25 degrees of flexion
- Capsular pattern
- Flexion far more limited than extension, in a ratio of about 10 to 1
- Arthrokinematics
- In the open chain the concave tibia moves over the convex femoral condyles: roll and glide go the same way. In the closed chain the convex femur moves over the tibia and they run in opposite directions. In the last 20 degrees of extension the tibia rotates outwards about 10 degrees because the medial condyle is longer: the screw-home mechanism, which locks the knee in standing. The popliteus unlocks it again.
- Stability
- Anterior cruciate ligament against anterior translation of the tibia, posterior cruciate against posterior translation, collateral ligaments against valgus and varus, menisci for load distribution and congruence, and the quadriceps with the hamstrings as active stabilisers.
- Palpation
- Joint line medially and laterally at 90 degrees of flexion, patella with its borders, tibial tuberosity, pes anserinus medially below the joint line, head of the fibula laterally with the common peroneal nerve around it.
- Clinical
- Anterior cruciate ligament rupture with the classic rotational trauma; meniscal injury with locking; patellofemoral pain syndrome; knee osteoarthritis; iliotibial band friction syndrome laterally.
- Source
- Kapandji, Physiologie articulaire deel 2; Neumann, Kinesiology of the Musculoskeletal System; Magee, Orthopedic Physical Assessment
Clinical tests
- Lachman test
- Anterior drawer test
- McMurray test
- Valgus and varus stress test
- Posterior drawer test
- Posterior sag sign
- Pivot shift test
- Fluctuation test for effusion
- Ottawa knee rules
- Joint line tenderness
- Noble compression test