d. Knee Pathologies

What is the vicious cycle in Genu Varum (bow-legged) deformity?

Deformity →

increased medial joint loading →

greater loss of joint space →

greater tibial adduction →

increased strain on LCL →

increased medial joint load

What management strategies are used for Genu Varum?

• High tibial (wedge) osteotomy

• valgus knee brace

• lateral wedge insole

• gait modification

• decrease walking speed

• strengthen glute max & TFL

How much does varus torque increase at the knee during walking in Genu Varum, and how does it affect arthritis risk?

20% increase in varus torque → 6-fold increase in risk of medial compartment arthritis

What are the detrimental effects of Genu Valgum (knock-kneed)?

• ACL stress

• MCL & medial capsule stress

• patellar mal-tracking

• lateral compartment osteoarthritis (OA)

• possible knee replacement surgery

What are some potential causes of Genu Valgum?

• Previous injury

• genetic predisposition

• high BMI

• ligament laxity

• weak hip abductors

• excessive foot pronation

What defines Genu Recurvatum?

Knee hyperextension >10 degrees beyond neutral

what is normal knee hyperextension?

5-10° beyond neutral

How does gravity affect the knee in normal hyperextension?

• Gravity creates a slight extension torque that helps lock the knee in hyperextension, allowing the quadriceps to relax

• This is opposed by passive tension in the:

  • posterior capsule

  • knee flexors

  • gastrocnemius

What causes Genu Recurvatum?

• Posterior structure laxity

• Chronic overpowering/excessive knee extensor torque due to poor postural control

• Neuromuscular disease (spastic quads or paralyzed/weak knee flexors)

What is Jumper’s Knee (Patellar Tendinopathy)?

Chronic pain in the patellar ligament, common in athletes who do repetitive explosive jumping

• no inflammation so it is a “-osis” or “-opathy,” not “-itis”

Which athletes are most commonly affected by Jumper’s Knee?

Basketball and volleyball players (those who perform explosive and repetitive jumping)

• Chase Budinger couldn’t chase or jump the volleyball or basketball ‘cause his patellar tendon/lig took a fall

What extrinsic factors contribute to Jumper’s Knee?

• Training intensity

• Playing surface

• Footwear

What intrinsic factors contribute to Jumper’s Knee?

• patellar hypermobility

• patella alta

• male gender

• Strength

• endurance

• flexibility

• skill level

• tendon elasticity

• body weight & height

How much force can the patellar ligament experience during landing from a jump?

Up to 7x body weight

What biomechanical factors help disperse kinetic injury when landing a jump?

• DF rate and magnitude

• eccentric activation of quadriceps and PFs

What does PFPS stand for?

Patellofemoral Pain Syndrome

What is Patellofemoral Pain Syndrome (PFPS)?

• Diffuse peripatellar or retropatellar pain with insidious onset

• spread-out pain around and behind patella. not sharp

• worse with

  • squatting

  • stair climbing

  • prolonged sitting with knees flexed (movie goers sign)

What activities worsen PFPS pain?

• Squatting

• Stair climbing

• Prolonged sitting with knees flexed (movie goers sign)

What are some causes of Patellofemoral Pain Syndrome?

• Genetic

• Neurologic

• Neuromuscular

• Biomechanical factors

• GNNB = Good Night, Night Bitch PFPS

How does a biomechanical cause contribute to PFPS?

Abnormal patellar tracking in the trochlear groove increases stress on the articular cartilage and innervated subchondral bone → leading to pain

• Abnormal patellar tracking causes uneven pressure in the knee joint, irritating the cartilage and the bone underneath, which leads to pain in PFPS

What degenerative change can occur in PFPS?

Softening of the cartilage, called Chondromalacia Patella

what is Chondromalacia Patella?

softening and breakdown of the cartilage on the underside of the kneecap, causing knee pain and irritation

• Chondro- = cartilage

• -malacia = softening

How should someone with PFPS be instructed to squat?

Keep the knees behind the toes to decrease the moment arm for the quadriceps and increase the moment arm for the hip extensors, shifting force transmission to the hips

Why is keeping the knees behind the toes important in squatting with PFPS?

It decreases the external moment arm for the quads and increases it for the hip extensors, reducing stress on the patellofemoral joint

What is the common mechanism of injury for meniscal tears?

Forceful axial rotation of the femoral condyles over a flexed and weight-bearing knee, pinching and dislodging the meniscus

Which meniscus is more commonly injured and why?

medial meniscus

• because axial rotation + valgus force stresses the MCL and posterior-medial capsule, which are connected to the medial meniscus

Can meniscal tears be acute or degenerative?

Yes, meniscal tears can be either acute or degenerative

What contributes to degenerative meniscal tears?

Repetitive WB activities in knee flexion cause wear and tear on the posterior aspect of the meniscus

What are some risk factors for degenerative meniscal tears?

• Age over 60

• male gender

• repetitive kneeling

• squatting

• stair climbing

• 60 y.o. M bending his knees → meniscal tears

What can degenerative meniscal tears lead to if untreated?

Osteoarthritis (OA)

What is a meniscectomy?

Surgical removal of the torn portion of the meniscus

What is a potential consequence of a partial meniscectomy?

Increased risk of osteoarthritis

due to less coverage and shock absorption for the articular cartilage

What percentage of ACL injuries occur through non-contact mechanisms?

About 70%

Non-contact ACL injuries happen without a direct hit

They occur during:

• sudden stops

• sharp turns

• awkward landing (from a jump)

• twisting or bending beyond normal

What are common non-contact mechanisms of ACL injury?

• Injuries that happen without a direct hit or collision to the body part involved

• Ex:

• Landing from a jump

• Quickly decelerating

• Quick pivoting over a single planted foot

What biomechanical factors contribute to ACL injury?

• Strong quad activation over a slightly flexed knee

• Valgus collapse

• Excessive ER + planted foot

  • Femur IR on fixed tibia

• Knee IR + Ext + Valgus

• Excessive Hyperextension + Planted foot

What other injuries commonly occur with ACL tears?

• Bone

• cartilage

• menisci

• MCL injuries

What is the "Terrible Triad" (Unhappy Triad) of the knee?

• ACL tear

• MCL tear

• medial meniscus tear

Why is the MCL often not surgically repaired after an ACL injury?

Because it has a good blood supply from the capsule, allowing it to heal well without surgery

What are the rehab precautions for meniscus repair vs meniscectomy?

Meniscus repair requires non-weight bearing (NWB), while

Meniscectomy does not have weight bearing precautions

Why are female athletes more likely to tear an ACL than male athletes? And by how much more?

• Females tend to land with greater knee valgus alignment and less trunk, hip, and knee flexion

• they use a quad-dominant landing that strains the ACL by pulling the tibia anteriorly

• 3-5x more likely

What strategies reduce ACL injury risk in female athletes?

• Increasing trunk, hip, and knee flexion during landing

• landing with knees behind the toes to shift force from quads to hamstrings and hip extensors;

  • hamstrings pull posteriorly on tibia, decreasing ACL strain

Why should isolated quad contractions in the last 30-40 degrees of knee extension be avoided early after ACL surgery?

Because the line of pull of the quads on the tibia creates a rotary (anterior translation) force that stresses the ACL

Because they pull the tibia forward, creating high anterior shear force that stresses the healing ACL graft

What type of exercises are preferred early in ACL rehab for strengthening quads?

Closed-chain femoral-on-tibia exercises through moderate degrees of knee flexion that co-activate quads and hamstrings

What degree of knee flexion is recommended early after ACL surgery and why?

>70 degrees

• ACL tension from isolated quad contraction is near zero at this angle

  • aka Quad contraction causes almost no ACL tension here

• hamstrings can pull the tibia posteriorly to unload ACL force

What happens to quad force on the tibia at 80 degrees of knee flexion?

The quads line of force is almost parallel to the tibia,

producing less anterior translation force