The Knee Flashcards
Which side of the distal femur has more contact with the patella?
Lateral (medial has more contact with tibia than patella)
Which tibial condyle is longer?
medial
Because the tibia is vertical and the femur is slightly oblique, what angle to they create in standing at the knee?
~185° (slight valgus)
What knee angle is considered genu valgum?
> 185°
What angle is considered genu varum?
< 175°
Describe the mechanical axis between the hip and ankle in both normal standing & single-leg standing. How might this be relevant for a patient that demonstrates genu varum/valgum?
- hip is aligned directly over the ankle in the absence of anatomical dysfunction
- mechanical axis shifts medially in SLS, since the hips shift position
- the shifting axis in SLS combined with genu valgum/varum can overload supporting structures in the knee
What connective tissue makes up knee menisci?
fibrocartilage
Contrast the shapes of the medial vs lateral meniscus.
lateral is o-shaped, medial is c-shaped
What are the beginning and end of the meniscus called?
anterior and posterior horns
What are the 3 zones of the knee meniscus? Describe their blood supply, respectively.
- red zone: outer third, receives blood from capsular arteries
- red-white zone: middle third, poor blood supply
- white zone: central third, poor blood supply
What portion of the knee menisci is separated from the capsule? What is its blood supply?
posterior lateral corner of the lateral meniscus is separated from the capsule by the popliteus tendon & is relatively avascular.
List 6 attachments of the lateral knee meniscus to nearby structures.
- anteriorly to medial meniscus (transverse ligament)
- to the patella via thickening of anterior capsule (patellomeniscal ligament)
- posteriorly to the popliteus
- posteriorly to the posterior cruciate ligament (PCL)
- medial femoral condyle (meniscofemoral ligament)
- edge of the capsule (coronary ligaments)
List 6 attachments of the medial knee meniscus to nearby structures.
- edge of the capsule (coronary ligaments)
- anteriorly to lateral meniscus (transverse ligament)
- to the patella via thickening of anterior capsule (patellomeniscal ligament)
- posteriorly to semimembranosus muscle
- anterior horn attaches to the anterior cruciate ligament (ACL)
- posterior horn attaches to the posterior cruciate ligament (PCL)
Which knee meniscus is more mobile?
lateral meniscus
Describe the muscular attachments that can create movement of the knee menisci.
popliteus contractions can move the lateral meniscus, semimebranosus contractions can move the medial meniscus
List 4 functions of the knee menisci.
- increase contact area of femoral condyles on the tibial plateau
- assist with joint glide
- limit hyperextension
- provide cushion & support to the weight-bearing surfaces
Describe the innervation of the knee menisci.
nociceptors & joint mechanoreceptors (pain and proprioception can be altered after injury)
Describe the 3 regions of the lateral compartment of the knee and the reinforcing structures associated with each.
Anterior region: supported laterally by the lateral retinaculum
Middle region: reinforced by the distal ITB
Posterior region: reinforced by the arcuate complex
Describe the 2 layers of the lateral retinaculum. Which portion of the lateral knee compartment does the retinaculum reinforce?
- Superficial oblique layer: runs from the ITB to the lateral border of the patella & patellar tendon
- Transverse layer: undersurface of ITB to lateral patellar border
- reinforces the lateral portion of the anterior region of the lateral compartment
What 3 structures comprise the arcuate complex of the knee?
- lateral collateral ligament (LCL)
- arcuate ligament (reinforced by biceps femoris tendon)
- popliteus tendon
What are the attachments of the arcuate ligament of the knee?
posterior lateral femoral condyle to posterolateral tibia
What motions does the lateral collateral ligament of the knee restrain?
varus angulation of the tibia & excessive lateral rotation of the tibia
Describe how the contribution to knee stability provided by the LCL changes depending upon knee position.
- provides ~55% of the resistance to varus stress in 5° of flexion
- 69% with 25° flexion
(posterior structures are on slack in flexed position)
The posterior third of the medial compartment of the knee is reinforced by what two soft tissue structures?
- posterior oblique ligament (thickening of medial capsular ligament)
- semimembranosus muscle
What is the posterior oblique ligament of the knee and what are its attachments?
- thickening of the medial capsular ligament
- from the adductor tubercle of the femur to the tibia and posterior capsule
- also attaches to the semimembranosus tendon sheath and oblique popliteal ligament
What are 3 functions of the posterior oblique ligament?
- reinforces the posteromedial aspect of the knee joint
- provides resistance to valgus forces near full extension
- provides support as the knee moves into flexion (semimembranosus attachment)
Describe how the contribution to knee stability provided by the MCL changes depending upon knee position.
- provides ~57% of the resistance to valgus stress in 5° of flexion
- 78% with 25° flexion
In addition to the MCL, what intra-articular ligamentous structure plays a supportive role in resisting valgus forces on the knee?
PCL (MCL/PCL tear results in the greatest valgus of any ligament injury combination)
Describe the divisions and attachments of the MCL
- divided into superficial and deep layers (bursa in between)
- deep layer is divided into meniscofemoral and meniscotibial ligaments
- superficial layer connects the medial femoral condyle and the tibia below pes anserine (also semimembranosus and vastus medialis)
Describe the general blood supply to the MCL
rich blood supply, so it heals well following injury
Describe the main soft tissue structures that support both the medial and lateral posterior knee joint capsule.
- Laterally: arcuate popliteal ligament & popliteus
- Medially: semimembranosus tendon (and its expansion) & oblique popliteal ligament (medially)
Describe the soft tissue structures associated with lateral knee joint capsule
lateral retinaculum, LCL is loosely attached to the capsule fibers and runs to the head of the fibula, dividing the biceps femoris tendon
Why are the ACL and PCL called “cruciate” ligaments?
the form a cross in the sagittal plane, providing joint stability
What is the blood supply to the ACL? PCL?
both are supplied by the genicular arteries (anastamosis/branches from of popliteal artery)
Describe the innervation of the ACL & PCL.
both innervated by branches from the tibial nerve
Aside from providing mechanical stability, what other two roles do the ACL and PCL play in knee joint function?
- via mechanoreceptors (Ruffini corpuscles, Pacinian corpuscles, Golgi tendon organs), they give the brain information about the location of the joint in space and stresses that the joint is undergoing
- mechanoreceptors and free nerve endings provide “preparatory” information to enhance muscular responses to provide dynamic stabilization
What are the proximal and distal attachments of the ACL?
lateral femoral condyle (posteromedial corner) to area anteromedial to the intercondylar eminence (anterior tibial plateau)
Is the ACL taut in knee flexion or knee extension? What does this mean for clinical testing for ACL tears?
trick question: both
- the ligament is divided into the anterior medial bundle (tight in flexion) & the posterior lateral bundle (tight in full extension through 20° of flexion)
- if anterior medial bundle is torn, but posterior lateral bundle is intact, Anterior Drawer test can be positive.
The ACL provides 85% of resistance to anterior tibial translation in what degree(s) of knee flexion?
30° of knee flexion
In addition to anterior tibial translation, what other movements of the tibia does the ACL also check?
medial/internal rotation, hyperextension, and secondary support against varus/valgus forces
What is the most common mechanism for ACL injury?
deceleration force in slight flexion combined with medial or lateral tibial rotation
The ACL can be damaged when a deceleration force in slight knee flexion is combined with either medial or lateral tibial rotation. Why both types of rotation?
Medial tibial rotation: ACL winds around PCL
Lateral tibial rotation: ACL stretches over the lateral condyle, creating strain
How do knee muscles contribute to & relieve strain on the ACL?
- quads can generate anterior tibial translation near full extension
- hamstrings and soleus can create posterior tibial translation
Describe the attachments of the PCL.
travels from the medial femoral condyle (lateral aspect) to posterior tibial plateau
The PCL provides most of it’s resistance to posterior tibial translation in what general knee position?
flexion (anterolateral bundle makes up 95% of PCL)
What are the two divisions of the PCL?
anterolateral bundle (95%) and posteromedial bundle (5%)
The anterolateral bundle of the PCL is taut in what general knee position?
flexion
The posteromedial bundle of the PCL is taut in what general knee position?
extension
The PCL provides 95% of resistance to posterior tibial translation in what degree(s) of knee flexion
30°-90° of knee flexion
The PCL doesn’t check posterior tibial translation as much in ranges close to knee extension. What 3 are secondary restraints against posterior translation in extension?
- MCL
- Popliteus
- The posterior capsule
Following a PCL rupture, the greatest posterior tibial translation will occur in what degree(s) of knee flexion? Why?
70°-90°of knee flexion; the secondary restrains (MCL, popliteus, posterior capsule) are on slack
What is the most common mechanism of PCL injury?
hyperflexion (PCL is most taut in flexion)
Direct tibial posterior translation injuries (e.g. dashboard injury) results in injury to what knee structures?
secondary structures like MCL, poplietus, and posterior capsule rather than PCL
Aside from posterior tibial translation, at 90° of knee flexion, the PCL plays a secondary role in resisting what other movement(s)?
secondary resistance to tibial external rotation, varus and valgus forces
The PCL provides secondary resistance to tibial external rotation in knee flexion. What other structure(s) provide(s) this resistance?
posterolateral corner (when both posterolateral corner & PCL are torn, increased tibial ER is seen in varying degrees of knee flexion)
How do the hamstring muscles affect strain on the PCL?
- contraction of the semimembranosus, semitendinosus, and biceps femoris produce posterior tibial translation in non-weightbearing and directly increase strain on PCL
In addition to the hamstrings, what 5 other muscles contribute to knee flexion?
- popliteus
- gastrocnemius
- sartorius
- gracilis
- tensor fascia lata (via ITB)
What action of the knee do the sartorius, gracilis, and tensor fascia lata all have in common?
knee flexion
The tensor fascia lata produces knee flexion in what position?
when the knee is already flexed
The knee flexors are all two-joint muscles except which two?
short head of biceps femoris and popliteus
In addition to knee flexion, what action of the knee do the popliteus, gracilis, sartorius, semimembranosus, and semitendinosus all have in common?
tibial medial/internal rotation (in knee flexion)
When the knee is in flexion, what 5 muscles produce tibial medial/internal rotation?
- popliteus
- gracilis
- sartorius
- semimembranosus
- semitendinosus
In addition to knee flexion, what action of the knee do the biceps femoris and tensor fascia lata have in common?
tibial lateral/external rotation (in knee flexion)
When the knee is in flexion, what 2 muscles produce tibial lateral/external rotation?
- biceps femoris
2. tensor fascia lata (via ITB)
What 3 muscles insert at the pes anserinus?
- sartorius
- gracilis
- semitendinosus
What secondary forces on the knee do the semimembranosus, semitendinosus, medial head of gastrocneumius, sartorius, gracilis all have in common?
they all create varus knee movement / check valgus forces
What 5 muscles can help check valgus forces on the knee?
- semimembranosus
- semitendinosus
- gracilis
- sartorius
- medial head of gastrocnemius
What secondary forces on the knee do the biceps femoris, lateral head of gastrocnemius, and popliteus all have in common?
they all create valgus knee movement / check varus forces
What 3 muscles can help check varus forces on the knee?
- biceps femoris
- lateral head of gastrocnemius
- popliteus
What is the screw home mechanism?
the tibia laterally/externally rotates at end-range knee extension & must medially/internally rotate to “unlock” and initiate knee flexion
During the squat and leg press, posterior shear forces / PCL strain are greatest in what degree(s) of knee flexion?
83°-105° of flexion
Contrast anterior shear / ACL strain forces in weight-bearing vs non-weight bearing exercise
no anterior shear / ACL strain in weight-bearing exercises like squats & leg presses; anterior shear develops in 40°-0° of knee flexion during exercises like knee extension (peaks in the last 10 degrees)
During knee extension exercises, when are forces on the ACL the greatest?
anterior shear force starts at 40° of knee flexion and peaks in the last 10 degrees to extension
To avoid anterior shear / ACL strain during knee extension exercises, what ROM should be avoided?
0°-40° of flexion
Describe the changes in the amount of contact between the patella and the femur as the knee moves through flexion.
- in full extension, the patella is loosely sitting in the trochlear groove; only the inferior pole is in contact with the femur
- the patella contacts the femur both medially and laterally by 20° of flexion
- contact area increases with further flexion, and by 45°, the middle of the patella is in contact with the femur
- by 90°, the upper third of the patella is in contact with the femur
- after 90°, the patellar contact shifts inferiorly and laterally, loading the odd facet
What are the 2 biomechanical factors that contribute to patellofemoral joint compression?
contact area size & force generation
What % of bodyweight are patellofemoral compressive forces in walking, jogging, and standing from a chair, respectively?
walking = 50% BW jogging = 3-4x BW sit-stand = 6.7x BW
Why do patellofemoral compression forces increase beyond 90° of knee flexion?
odd and lateral facets engage, but total contact area decreases
The medial facet of the patella bears the greatest compressive load in what degree(s) of knee flexion?
up to 70° of knee flexion
In knee flexion beyond 90°, what structure helps to dissipate patellar contact forces?
quadriceps tendon comes into contact with femoral groove
What 3 structural abnormalities can cause instability of the patella?
- shallow trochlear groove
- less prominent lateral femoral condyle (trochlear dysplasia)
- laxity of patellar soft tissue tethers
What is trochlear dysplasia?
less prominent lateral femoral condyle that causes patellar instability
What soft tissue structure provides the most resistance to lateral patellar movement?
medial patellofemoral ligament (60%)
The lateral patellofemoral ligament provides a tether between which two structures?
the patella & the ITB
What two lines make up the Q-angle?
ASIS to midpoint of the patella & midpoint of patella to tibial tuberosity
What are considered normal Q-angles for men and women?
men: 10°-15°, women: 15°-20°
What Q-angle is generally considered structurally abnormal? Why is this clinically relevant?
> 20°; can place a patient at risk for excessive lateral patellar forces
How can exercises be designed to minimize excessive patellofemoral compressive forces?
avoiding terminal 30° of knee extension during nonweight-bearing exercise & avoiding greater than 90° of flexion during weight-bearing exercise
If a patient presents with anterior knee pain, but their patellofemoral examination is negative, what other structure should be tested?
PCL (can be a source of anterior knee pain - check patient history for instances of potential trauma, i.e. old injuries)
What can the timing of knee joint swelling following injury tell you about the structures involved?
immediate swelling can be internal joint trauma or hemarthrosis; delayed onset of hours or days indicates a synovial fluid response
What are the Ottawa Knee Rules and how are they implemented?
- age> 55
- isolated tenderness of the patella (no other bony tenderness)
- tenderness of fibular head
- inability to flex the knee to 90°
- inability to bear weight both immediately & in the ER (4 steps, limping is okay)
- if any of these are present, refer for imaging (x-ray)
- if not, no imaging is necessary
- 100% sensitivity for fracture
If a patient complains of knee pain that is “shooting”, “burning”, or travels up/down the leg, what other areas may be involved?
hip, spine, and S.I. may be involved
If a patient with knee pain is between 5-17 years old and presents with a largely negative knee examination, what diagnosis should be considered? What other clinical findings would support this diagnosis?
Slipped Capital Femoral Epiphysis / Legg-Calve-Perthes
- (+) FABER
- Limited hip IR
- Excessive hip ER
What disease commonly causes bilateral knee pain and swelling?
Lyme Disease (deer tick bite)
In a patient with knee pain, what other areas should be screened?
lumbar spine, SIJ, hip, and ankle
Describe the performance and grading of the Knee Effusion measurement technique described in the monograph. How reliable is this method?
- push medial knee swelling proximally
- sweep from mid-thigh to lateral knee
- observe the return of swelling
- grading:
0: no swelling returns
Trace: small amount returns
1+: returns with lateral sweep
2+: returns without lateral sweep
3+: swelling does not move at all
- kappa 0.75
What did Lynch & Logerstedt et al discover about the relationship between knee joint effusion and quadriceps muscle activation?
Although saline injections diminish quad muscle function, Lynch et al found that quad activation failure(“inhibition”) was not seen in even very large knee joint effusions following ACL rupture
How is voluntary activation of the quadriceps affected in patients with ACL injury and/or anterior knee pain?
voluntary activation can be as much as 10%-12% less (can be seen on both involved and uninvolved limbs)
What are the 2 types of factors that can lead to passive resistance to knee joint motion? How are they distinguished during the physical examination?
external & internal; therapist end feel
What are 3 external factors that can lead to passive resistance to knee joint motion?
- capsular tightness
- scarring
- loss of musculotendinous flexibility
What are 3 internal factors that can lead to passive resistance of knee joint motion?
- bony or meniscal block
- loose body
- component of surgery (e.g. poorly placed graft or ill-fitting prosthesis)
Why might both a soft & a firm end feel for knee flexion be considered “normal”?
it depends on hip position:
- if hip is flexed, knee flexion end feel should be soft (soft tissue approximation of calf & thigh
- if hip is extended, knee flexion end feel should be firm (anterior muscle tension)
What end feel for knee extension is considered “normal”? How does the leg position affect the limiting structures?
- end feel for knee extension should be firm
- it depends on hip position:
- if hip is extended, knee extension is limited by the capsule & ligaments
- if hip is flexed, knee extension is limited by muscle
What are the landmarks for measuring knee ROM?
- axis: lateral epicondyle
- stationary arm: midline of femur
- moving arm: lateral malleolus