CH. 10 Structure & Function of the Knee

CH. 10 Structure & Function of the Knee

Objectives

• Describe the primary supporting structures of the knee.
• Describe factors that contribute to excessive lateral tracking of the patella.
• Explain how patellofemoral joint compression force is increased or decreased relative to the depth of a squatting position.
• Describe the biomechanical consequence associated with hamstring tightness.
• Explain the principles of active and passive insufficiency about multiarticular muscles of the knee.
• Describe the combined movements at the hip and knee that promote the most effective force production in the hamstrings and rectus femoris.

Overview

• The knee consists of the tibiofemoral joint and the patellofemoral joint.
• Motion at the knee occurs in two planes: sagittal and transverse (IR and ER).
• Most activities require the knee to move simultaneously in both planes.
• The knee is relatively unstable because it lacks a deep concave socket; therefore, strong ligaments and muscles are required for stabilization, making the soft tissues vulnerable to injury.

Components of the Knee

• Bones
• Menisci: Make the knee stable and deeper the cavity of the tibia.
• Muscles
• Ligaments
• Bursae

Osteology - Distal Femur

• Medial and lateral condyles articulate with the medial and lateral condyles of the tibia.
• The intercondylar notch is located on the posterior-inferior aspect of the distal femur, which separates the medial and lateral condyles. Forms a passageway for the anterior and posterior cruciate ligaments.
• Medial and lateral epicondyles are palpable bony projections on the medial and lateral femoral condyles and serve as attachments for the medial and lateral collateral ligaments of the knee.

Proximal Tibia

• Medial and lateral condyles of the tibia are smooth and shallow for articulation with the condyles of the femur.
• Intercondylar eminence: double-pointed projection of bone separating the medial and lateral condyles of the tibia.
• Serves as an attachment for the anterior and posterior cruciate ligaments and medial and lateral meniscus.
• Tibial tuberosity: protrusion of bone located on the anterior aspect of the proximal tibia, which serves as a distal attachment for the quadriceps muscle.

Proximal Fibula & Patella

• The fibula is a long, slender bone that courses along the lateral shaft of the tibia.
• The fibular head is the rounded superior portion of the fibula that articulates with the superior-lateral aspect of the tibia. This articulation forms that proximal tibiofibular joint.
• The patella is also known as the kneecap.
• Small, plate-like bone embedded within the quadriceps tendon.
• The patella exists within the quadriceps tendon; it is highly mobile and is at risk for abnormal gliding or subluxation.
• The base or superior pole of the patella accepts the quadriceps tendon.
• The apex or inferior pole accepts the proximal side of the patellar tendon.
• The patella glides superior inferior and move side to side.

Arthrology

• Tibiofemoral joint
  • Essential to the forward progression of the leg. Connective tissues surrounding it guide movements but also stabilize the articulation, as well as absorb and transmit forces
  • Surrounding musculature as another critical element of stability and shock absorption across the knee
• Patellofemoral joint
  • Protects the delicate structures within the knee and improves the moment arm for the quadriceps, thereby improving the extensor torque-producing potential of this muscle group.
  • Protect structures under the knee cap

Normal Alignment

• The articulation between the femur and tibia does not typically form a straight line.
• The femur usually meets the tibia to form a lateral angle of 170-175 degrees, which is normal genu valgum.
• Less than 170 degrees is excessive genu valgum (knock-kneed).
• Greater than 180 degrees is genu varum (bow-legged).

GENU VALGUM & VARUM

• Excessive genu valgum (knock-knee): < 170 degrees
• Genu varum (bow-leg): > 180 degrees

Supporting Structures

• Anterior and posterior cruciate ligaments
  • The predominant anterior-posterior direction of the cruciate ligaments stabilizes the knee against the shear forces that occur while walking or running.
• Anterior cruciate ligament (ACL): often injured during sporting events such as soccer, football, or skiing activities that generate a combination of large rotational, side-to-side, and hyperextension forces
• Posterior cruciate ligament (PCL): injured less often but may be ruptured along with the ACL
• Surgery is generally required to repair a ruptured cruciate ligament
  • Prevent motion of the patella forward and back
  • Less injured

Primary Functions of Anterior & Posterior Cruciate Ligaments

• ACL
  • Resists anterior translation of the tibia relative to a fixed femur (open-chain).
  • Resists posterior translation of the femur relative to a fixed tibia (closed-chain).
  • Resists extremes of knee extension.
  • Resists valgus and varus deformations and excessive horizontal plane rotations.
  • Tibia still anterior
  • ACL prevent tibia from moving forward
• PCL
  • Resists posterior translation of the tibia relative to a fixed femur (open-chain).
  • Resists anterior translation of the femur relative to a fixed tibia (closed-chain).
  • Resists extremes of knee flexion.
  • Resists valgus and varus deformations and excessive horizontal plane rotations.
  • Femur still posterior
  • PCL prevent tibia from moving backwards

Anterior Cruciate Ligament

• Runs from the anterior tibia to the posterior femur.
• Prevents anterior tibial displacement.
• Tight during extension.
• Starts on the front of the tibia and ends on the back of the femur.

Posterior Cruciate Ligament

• Runs from the posterior tibia to the anterior femur.
• Prevents posterior tibial displacement.
• Tight during flexion.

Guideline for ACL Reconstruction

• Many protocols for post-operative ACL reconstruction limits active or forceful knee extension.
• Rationale: Activation of the quadriceps at ranges from 40 degrees of flexion to 0 degrees of extension produces anterior shear forces that pull the tibia anterior relative to the femur.
• Motions that maximally challenge the integrity of the new graft, such as heavily resisted, end-range (open-chain) knee extension exercises, are often avoided in early stages of rehab.
• Instead, co-contraction of the muscles about the knee such as short-arc quads are beneficial.
• Avoid genu knee extension.

Extensor Lag

• After surgery or injury, patients have considerable difficulty in getting quads to perform the last degrees of active knee extension.
• Occurs when passive knee extension is greater than active knee extension.
• A common rationale is quadriceps inhibition from swelling.
• Too much inflammation, edema, and pain can’t get knee extension.

Medial & Lateral Collateral Ligaments

• Primary frontal plane stabilizers of the knee, protecting against forces that produce excessive genu valgus.
• MCL: resists valgus-producing forces at the knee.
• LCL: resists varus-producing forces at the knee.
• Both ligaments are taut in full extension; assist with locking the knee.
• Valgus = valgum, Cause meniscus tear.

VALGUS AND VARUS PRODUCING FORCES TO COLLATERAL LIGAMENT

• Medial collateral ligament resists valgus-producing force.
• Lateral collateral ligament resists varus-producing force.

Medial & Lateral Menisci

• Crescent-shaped fibrocartilaginous discs located at the top of the medial and lateral condyles of the tibia.
• Absorb compressive forces across the knee caused by muscular contraction and the body weight.
• Deepen the articular surface of the knee, facilitating the arthrokinematics and further stabilizing the joint.
• The medial meniscus is firmly attached to the tibia, which is more commonly torn.
• MRI is the preferred method to confirm diagnosis.
• Almost work like a labrum, reduce forces.

Meniscal Tear

• Results from traumatic injury.
• The injury will involve twisting of the knee while it is in a semi flexed position with the foot planted on the ground or hyperflexion injury.
• Characterized by joint line pain and tenderness, swelling, loss of range of motion, complaint of “catching” or “locking” within the joint, and feelings of instability.
• Tear in outer-third of meniscus is more likely to heal spontaneously since that portion is vascular.
• Outer meniscus have high blood supply
• Deep or full tear have no blood supply and cannot repair itself.
• No bloody supply

Posterior Capsule

• Prevents hyperextension of the knee.
• Arcuate popliteal ligament and oblique popliteal ligament
• Knee that demonstrates marked hyperextension is referred to as genu recurvatum – a condition that strains the posterior capsule and many other structures.
• Not strong enough ligaments

Popliteal Space

• Area behind the knee.
• Contains nerves and blood vessels.
  • Tibial nerve
  • Common peroneal nerve
  • Popliteal artery and vein
• Diamond-shaped fossa.
  • Superomedial: Semitendinosus and Semimembranosus
  • Superolateral: Biceps femoris
  • Inferior: Medial and lateral heads of gastrocnemius

Kinematics

• 2 degrees of freedom
  • Flexion & extension = sagittal plane
  • Internal & external (axial rotation) = horizontal plane
• Joint allows approximately 40 degrees of rotation.

Bursa

• Suprapatellar – between quad tendon and femur
• Prepatellar - between the skin and the patella
• Infrapatellar (superficial) - between the skin and patellar tendon
• Deep infrapatellar - between patellar tendon and tibia
• Do not regenerate once is gone

Screw Home Mechanism

• The medial femoral condyle is larger than the lateral condyle.
• As extension occurs, the articular surface of the lateral condyle is used up while ~1/2” remains medially; therefore, the medial condyle must glide posteriorly to use all its articular surface as it rolls into extension.
• With knee extension in open/closed chain, it externally rotates about 10-15 degrees – assists in locking the knee.
• Medial femoral condyle is larger than the lateral
• Medial condyle femoral have to continue moving to allow rotation

Patella Ratio

• Patella’s position in relation to the femur is expressed as a ratio of patella tendon length divided by the greatest diagonal length of the patella.
• Normal: patella is roughly equal in length to the patella tendon.
• Alta: Patella is placed in an elevated position, which delays patella engagement of the trochlea until an increased angle of flexion occurs. Greatly increases the risk of dislocation.
• Baja: Most often results from soft tissue contracture and hypotonia of the quadriceps muscle following surgery or trauma to the knee.
• Just know patella is mobile

Q-Angle

• Overall line of force of the quadriceps relative to the knee.
• Goniometry: axis - midpoint of knee; stationary arm – pointed toward ASIS; moving arm – pointed toward tibial tuberosity
• Q-angle is normally 13 to 15 degrees, which reflects the normal genu valgus posture of the knee.
• The larger the Q-angle, the greater is the lateral force applied to the patella when the knee flexes during weight bearing.
• Women have a slightly greater Q-angle than men.
• Normal genu valgum 170-175
• The bigger the Q angle it can track patella laterally
• Proximal medial shaft of the tibia

Pes Anserine

• “Goose foot” (Latin)
• Muscle group:
  • Sartorius
  • Gracilis
  • Semitendinosus
• Each has a different proximal attachment.
• Common distal attachment: Anterior medial aspect of proximal tibia
• Proximal medial shaft of the tibia = PMS
• Lateral tracking of patella is because VL is tight (Stronger) and VMO hypotonic (weaker)

Arthrokinematics

• Open-chain: Flexion
  • Rule #2
  • Roll and slide posteriorly
• Open-chain: Extension
  • Rule #2
  • Roll and slide anteriorly
• Closed-chain: Flexion
  • Rule #1
  • Roll posteriorly and slides anteriorly
• Closed-chain: Extension
  • Rule #1
  • Roll anteriorly and slides posteriorly

Positioning the Ankle to Change the Biomechanics of the Knee

• Ankle plantarflexed = increases knee extension
• Ankle dorsiflexed = increases knee flexion
• Genu recurvatum = knee hyperextension, is caused by excessive plantar Flexion.
• Gastrocnemius is tight so is limiting their dorxiflexion.
• Stretch calf to release tightness

Knee Extensor Muscles (Quadriceps)

• Rectus femoris: bipennate muscle is the only true antagonist to the hamstrings
• Vastus lateralis: largest, and strongest of all quadriceps muscles. The line of pull is directed laterally, which explains why abnormal tracking of patella occurs most commonly in the lateral direction.
• Vastus medialis: divides into two fiber groups: vastus medialis longus and vastus medialis oblique.
• VMO approaches the patella 50–55-degree angle to the midline, which provides a medially directed pull on patella that counteracts the lateral pull of vastus lateralis.
• Vastus intermedius: deepest muscle
• Medially to patella

Stretching the Rectus Femoris

• To optimally stretch rectus femoris, the hip must be extended, and the knee flexed.
• Clinicians must pay attention to any anterior tilting of the pelvis. It essentially puts the hip in a flexed position.
• It is corrected by strong activation of the abdominals to stabilize the pelvis

Excessive Lateral Tracking of the Patella

• Normally, patella tracks within the intercondylar groove without excessive deviation either medially or laterally.
• Excessive lateral tracking of the patella increases pressure and friction within the patellofemoral joint
• May result in pain, inflammation, and joint degeneration. In severe cases, it may dislocate.
• Knee pain have almost no VMO or atrophy
• Weakness of medialis knee cap is going out

Increased Compression Within the Patellofemoral Joint During a Deep Squat

• Joint pain is one of the most common clinical conditions of the knee
• A common feature of this impairment is the inability of the patellofemoral joint to tolerate large compression forces
• Clinicians recommend that patients with patellofemoral joint pain avoid or limit squatting to reduce excessive compression and wear and tear of the posterior side of the patella.

Knee Flexor Muscles

• Semimembranosus
• Semitendinosus
• Biceps femoris – long and short heads
• Gracilis and sartorius
• Gastrocnemius and plantaris
• Popliteus: unlocks the knee And flex the knee

Effective Stretching of the Hamstring Muscles

• Put the knee into an extended position and incorporate varying amounts of hip flexion
• To improve the effectiveness of this stretch, the individuals can be instructed to actively contract the muscles that stabilize the pelvis into an anterior tilt

Synergy Between Rectus Femoris and Hamstrings

• Running or jumping
• Simultaneous action of hip extension and knee extension.
• The rectus femoris is being stretched simultaneously while hamstrings are activated for hip extension, all while the quadriceps are active to complete knee extension.
• Vice versa, hamstrings are actively shortened at the hip but stretched at the knee
• Study active and passive insufficiency

Table 10.4 Movement Combinations That Promote Effective and Ineffective Force Production

• Effective
  • Hip flexion and knee flexion
  • Hip extension and knee extension
  • Hamstrings and rectus femoris can work synergistically and maintain a proper length-tension relationship
• Ineffective
  • Hip flexion and knee extension
    • Rectus femoris becomes actively insufficient
    • Hamstrings become passively insufficient
  • Hip extension and knee flexion
    • Rectus femoris becomes passively insufficient
    • Hamstrings becomes actively insufficient

Internal and External Rotators

• The ability to perform rotation of the knee for either group is almost negligible when the knee is near full extension but maximal when the knee is flexed to 90 degrees
• Active length-tension relationship
• The strength of the internal rotator muscles of the knee outweighs the strength of the external rotator muscles
• IR muscles > ER muscles

Muscles

• Internal rotators of the knee
  • Semimembranosus
  • Semitendinosus
  • Gracilis
  • Sartorius
  • Popliteus deep to gastrocnemius
• External rotators of the knee
  • Biceps femoris - long head
  • Biceps femoris – short head

Common Knee Presentations

• Genu valgum = knock knees (distal segment is lateral to proximal)
• Genu varum = bowlegs (distal segment is medial to proximal)
• Genu recurvatum = hyperextension
• Patellar tendonitis (jumper’s knee): patellar tendon, jumping sports
• Osgood Schlatter’s disease:
  • Overuse, adolescents, pull on tibial epiphysis at tibial tuberosity. Often accompanied with pain and enlargement of tibial tuberosity
  • Avolcion fraction on tibial tuberosity
  • Growing pains
  • Quads get elongated and pulled on tibial tuberosity

Common Knee Pathologies

• Baker’s cyst (popliteal cyst): Synovial hernia or bursitis of the posterior knee
• Patellofemoral pain syndrome: Diffuse anterior knee pain, abnormal patellar alignment, tracking, biomechanical
• Chondromalacia patella: Softening of articular cartilage of posterior patella, abnormal tracking of patella

Common Knee Pathologies

• Prepatellar bursitis (housemaid’s knee): Constant pressure on knees, carpet layers
• Terrible triad: Tears of ACL, MCL, and medial meniscus

Common Patterns of Joint Restriction

• Decreased knee extension/ knee flexion contracture: Tightness of knee flexors, posterior capsule
• Decreased superior migration of patella: Weakness of knee extensors
• Functional limitations: Produces forward flexed posture during gait or standing
• Muscle fatigue
• May lead to tightness of hip flexors and low back

Quiz Questions!

• The primary ligament involved in resisting large valgus-producing forces at the knee is the:
  • a) Medial collateral ligament
• You notice that a patient is ambulating with a bow-legged appearance. You know that this is indicative of:
  • b) Genu varus

Quiz Questions!

• Which of the following describes the primary sagittal plane function of the anterior cruciate ligament?
  • c) Resists anterior translation of the tibia relative to a fixed femur
• Which of the following muscles is NOT associated with the pes anserinus?
  • b) Rectus femoris

Quiz Questions!

• Which of the following statements best describes genu recurvatum?
  • b) A knee that displays marked hyperextension
• A muscle that courses anterior to the medial-lateral axis of rotation of the knee is able to perform?
  • b) Knee extension

References

• Mansfield, P. J., & Neumann, D. A. (2024). Essentials of kinesiology: for the physical therapist assistant (4th edi.). Elsevier
• Mansfield, P. J., & Neumann, D. A. (2019). Essentials of kinesiology: for the physical therapist assistant (3rd ed.). Mosby, Inc.
• Dutton, M. (2012). Orthopaedics for the physical therapist assistant. Jones & Barlett Learning, LLC