Knee Flashcards
Normal genu valgum
- Slight medial angulation of the femur, horizontal tibial articular surface
- Knee forms an angle on the lateral side of 170-175 (5-10 degrees of genu valgum)
Excessive genu valgum
15 degrees)
Genu varum
> 180 degrees in frontal plane
Three compartments of the knee
- Medial compartment (medial tibial plateau, meniscus, femoral condyle)
- Lateral compartment
- Patellofemoral compartment
^ Used to describe OA and TKA/ partial KA
Mismatch of surfaces of femur and tibia
Large convex femoral condyle
Smaller tibial plateaus
Meniscus function
“Gaskets” to improve joint congruity and stability
Shock absorption –> disperse load on articular cartilage to a wider surface area
Meniscus injury increases OA risk
Deform in weight bearing
Mobile: Move with the tibia. Lateral moves more than medial (more tears occur in medial)
Medial vs. lateral tibial plateau
Medial: Concave
Lateral: Mostly flat (Slightly concave)
Femoral condyles - medial vs. lateral
Lateral condyle is steeper
Femoral groove is aka trochlea
Thickest hyaline cartilage in the body?
Patella
Makeup of menisci
Fibrocartilage (like labrum, IVD)
- Large water content
Anchored in the intercondylar area
Coronary ligaments
Vascular and nerve supply to menisci
- Inner 2/3 poorly vascularized, not innervated
- Outer 1/3: Vascular, innervated
Medial meniscus
- C shaped
- Less mobile than lateral
- Attachments: Joint capsule, MCL, ACL at anterior horn, Semimembranosus at posterior horn
Attaches to MCL via menisco-tibial/ coronary ligaments
- Body’s center of mass usually runs through medial compartment –> more tears
- Varus malalignment is more common with degeneration (increases medial stress) –> more tears
Lateral meniscus
- O shaped
- More mobile (weaker capsular attachments)
- No attachment to LCL
- Attachments: PCL, Popliteus, medial mensicus (via transverse ligament in anterior knee)
Tears in lateral are less common than tears in medial
Meniscal Tear special tests
Thessaly
McMurray
Apley
Palpation for tenderness (more posterior than you think, along jt line)
None of these tests are great
Thessaly test
For meniscus tear
- Pt stands on one leg
- Pt flexes knee to 20 degrees, rotates body over knee
- Repeat rotation 3 time in each direction
Positive: Joint-line pain and possibly a sense of locking or catching
McMurray’s Test
For meniscus tear
- Pt in supine
- Grasp heel and flex knee to EROM, using other hand to palpate jt line
- Medial meniscus: ER tibia as knee is extended
- Lateral meniscus: IR tibia as knee is extended
Positive: Audible or palpable thud or click
Apley’s Test
For meniscus tear
- Pt in prone
- Knee flexed to 90 degrees
- Load menisci and twist (this is part 2 of test)
Part 1: distraction of tibia and twist
Swelling inside joint capsule
Effusion
Joint capsule and reinforcing ligaments
Anterior: Major contribution from medial and lateral patellar retinaculum
Posterior: Reinforced by oblique popliteal ligament and the arcuate popliteal ligament
Lateral: LCL, ITB, lateral patellar retinaculum, biceps, popliteal tendon
Medial: Patellar tendon to posterior capsule. MCL, medial patellar retinaculum
Posterior-medial capsule reinforces by pes
Synovial lining of capsule
- Provides nourishment and lubrication to joint
- Highly vascular and innervated
- Lines capsule, except it wraps around cruciate ligaments and excludes them
–> Cruciates are intracapsular but extrasynovial
Plica
Thickening and fold of synovial lining
- Remnants of synovial septa
- Loose, pliant, elastic fibrous CT
- Passes back and forth over femoral condyles as knee moves
- Only issue when irritated
3 plica:
- Infrapatellar
- Suprapatellar
- Mediopatellar (most problems)
Knee Bursae
- Limit friction between muscles, bones, ligaments
- Suprapatellar/ prepatellar bursa gets inflamed with direct trauma or lots of kneeling
- Subpopliteal bursa distends in popliteal space with trauma or effusion
Popliteal cyst
Side effect of joint effusion
- Produces outpouching of synovium in popliteal space
AKA Baker’s cyst
Effusion
- Pressure evenly distributed at 15-20 degrees of knee flexion
Limits knee flexion - no limit to knee extension ROM
–> Quad atrophy and shut down
Vascular supply to cruciate ligaments
Poor (especially ACL)
ACL
- From posteromedial aspect of lateral femoral condyle to anterior intercondylar region of tiba
- Prevents: Anterior tibial translation, rotation, varus/valgus forces in extension, hyperextension
2 bundles: Anterior medial and Posterior lateral
- Extension: Both taught
- Flexion: P-L bundle on slack
Mechanism of ACL injury
Most are non-contact
- often deceleration or landing from a jump
- knee in 20-30 degrees flexion (ACL almost lax)
- Hyperextension, falls, contact mechanisms also possible
Other structures often damaged:
- Menisci, articular cartilage, MCL, lateral side complex, PCL
- Bone bruises usually seen on MRI (LFC and lateral tibial plateau)
ACL Tear special tests
Lachman’s
Anterior drawer
Others: Pivot shift, lelli’s test
Lachman: Supine, knee flexed 15 degrees
Ant. Drawer: Supine, knee flexed 90 degrees
PCL
- Broader and thicker than ACL
- Lateral side of medial femoral condyle to posterior intercondylar area of tibia
- Two bundles (Anterior lateral and posterior medial)
- Knee flexion - complex twisting and changes in length and orientation
Tension is greatest between 90 and 120 degrees of flexion
Mechanism of PCL injury
- Fall onto front of knee, with ankle in full PF
- Dashboard injury
- Contact sports
Other structures are injured 50% of the time
PCL Tear special tests
Posterior Drawer
Posterior Sage sign/ Godfrey’s test (Supine, legs at 90/90)
Intercondylar Notch Width and cruciate tears
- Size of cruciate ligaments is = size of intercondylar notch
- Smaller notch, smaller ligaments, easier to tear
- Notch width doesn’t correlate with height/ weight
- Males have larger notches than females, on average
MCL and LCL
- Both tight in extension, relatively lax in flexion (Distance between attachment sites is smaller in flexion)
- Taught in external rotation of tibia
MCL
- Flat and broad
- Attachments to medial meniscus
- Two components: Superficial and deep fibers (tears usually begin in deep fibers)
- Limits valgus or abduction force
Proxmal tears: More stiff, but faster healing
Valgus/ Varus Stress Test
For MCL/ LCL
- Pt in supine
- test in full extension and 30 degrees flexion
Block hip rotation with hand
- if test is positive in extension, there is damage to jt capsule
LCL
- Cord like
- No meniscal attachment
- Posterior to IT band, anterior to biceps
- Attaches to fibular head
- Limits varus or ADD force. Stressed in figure 4 position (lateral capsule is also important in resisting varus force)
Only way to get isolated LCL sprain - forced figure 4 mechanism
Lateral side complex
Resistance to varus stress is provided by 6 structures
- LCL
- Biceps tendon
- Lateral capsule
- ITB
- Lateral gastroc
- Popliteal
- Injuries to complex are usually in combo with ACL/PCL, need surgery
Knee joint motion
Average: 5-0-145
Axis of rotation: 2 cm above fibular head
Axis of rotation migrates posteriorly with flexion
OKC: Tibia glides posterior (Flex) and anterior (Ext)
CKC: Femur glides anterior and rolls posterior (flex), or glides posterior and rolls anterior (ext)
Screw Home Rotation of knee
- Locking knee into extension requires 10 degrees of tibial ER
- Conjunct rotation
- Driven by: Shape of medial femoral condyle, passive tension in ACL, slight lateral pull of quads
- Condyle shape most important
When moving into flexion, popliteus unlocks knee by IR tibia
CKC: Locking = IR of femur
Tibial Rotation
IR: 30
ER: 40
Limited rotation in extension (ligaments are tight, close packed)
Rotation is maximal at 90 degrees flexion
Occurs around axis that closely approximates course of PCL
Menisci distort with femoral condyles in WB, not really in non WB
Two muscles that attach to AIIS
- Rectus femoris
- Vastus intermedius
Osgood Schlatter’s Disease/ Sinding-Larsen Johansson Disease
Traction apophysitis
- Osgood: Tibial tubercle
- SLJ: Distal pole patella
Rehab: Activity modification, patellar tendon strap, maintain LE flexibility
Jumper’s Knee (Patellar Tendinopathy)
Inflammatory/ Degenerative condition of patellar tendon
- Usually proximal tendon
- Distal tendonitis can occur in distance runners
Treatment: Eccentric exercises
Popliteus
Lateral femur, fibular head, and LM - courses medially to posterior tibia
OKC: Internally rotates tibia
CKC: Externally rotates femur
Attaches to Lateral Meniscus to move it out of the way as knee begins to flex
IT Band
TFL and Glut Max –> Gerdy’s tubercle on proximal tibia
- Resists varus stress at knee
- Fibers connecting to patella can influence tracking of patella
- Knee flexion 20: Assists knee flexion (depends where joint is relative to joint axis)
ITB Syndrome
- Irritation at LFC
- Repetitive injury
- Stress and friction –> inflammation
Rehab:
- TFL, ham and quad flexibility
- Hip and knee control
- Inflammation care
Structures resisting anterior tibial translation
ACL
Hamstrings, capsule, MCL, LCL
Structures resisting posterior tibial translation
PCL,
Quads, Capsule, LCL
Patella: Patellar tendon length
Normal ratio is 1:1
Patella baja: Low riding patella
Patella alta: High riding
–> Associated with instability
Patellofemoral congruence
- Most mobile in extension (quads relaxed)
- Compression increased posteriorly and laterally with increased force through joint
- Most stable in the trochlear groove (in flexion)
Medial patellar stabilization provided by:
VMO
Medial retinaculum
Steep lateral femoral condyle
Medial Patellofemoral Ligament
Lateral Pull of patella is a result of
Large q angle
Tight lat. retinaculum/ ITB
Increased force IR
Weak VMO
