Clinical Biomechanics of the Knee: Part 2

Clinical Biomechanics of the Knee: Part 2

This section of the presentation discusses the clinical biomechanics of the knee, focusing on tibiofemoral alignment, the patellofemoral joint, and associated kinematics, as well as clinical implications for movement and injury risk.

Objectives

The session aims to elaborate on the following objectives:

  1. Tibiofemoral Alignment: Understanding how it affects knee movement during activities and injury risk.

  2. Functional Activities: Requirements of the knee for Activities of Daily Living (ADLs) and other functional actions.

  3. Kinematic Roles: Exploring the arthrokinematics and osteokinematics of the knee in movement and interventions for knee injuries.

  4. Patellofemoral Joint: Examining its role within the knee complex and functionality within specific activities.

Tibiofemoral Alignment

Tibiofemoral alignment is assessed to observe the relationship between the femur and tibia. Two methods of measurement in clinical settings include:

  • Tibiofemoral Angle: Measured during X-rays, this angle represents the alignment between the femur and tibia, ranging from 0 to 180 degrees. The normal range is between 170 to 175 degrees.

    • Genu Valgum: Defined as an angle less than 165 degrees, resulting in knees that appear to be knocked-kneed. This condition increases compressive forces on the lateral side and tensile forces on the medial side.

    • Genu Varum: Occurring at angles greater than 180 degrees, this condition leads to bow-leggedness, increasing medial compressive forces and tensile forces laterally.

Effects of Aging and Degenerative Changes

As individuals age, variations in the tibiofemoral angle can increase either towards varus or valgus configurations. Pathological changes due to conditions like osteoarthritis may result in pain and functional limitations, affecting activities such as walking and climbing stairs.

Measuring the Q Angle

The Q angle is another clinical measure - it is formed by:

  • A line from the anterior superior iliac spine (ASIS) through the mid-patella.

  • A line from the mid-patella to the tibial tuberosity.

In males, the normal Q angle ranges from 8 to 14 degrees (greater angles suggest a valgus alignment, lesser indicate varus). For females, the norm extends from 15 to 17 degrees. Caution is necessary as inter-rater reliability can be poor in clinical measurements.

Osteokinematics of the Knee Joint

The primary motions at the knee include:

  • Flexion: Normal range is 130 to 140 degrees.

  • Extension: Including hyperextension, with normal limits between 5 to 10 degrees. Excess hyperextension is termed genu recurvatum, which could cause discomfort.

  • Internal and External Rotation: Measured at 90 degrees of flexion, with normal external rotation observed between 30 to 40 degrees and internal rotation between 10 to 30 degrees.

Functional Requirements for Flexion

Despite needing a maximum of 130 degrees for full flexion, functional performance shows:

  • Only about 70 degrees is necessary for normal gait.

  • Approximately 82 degrees for transferring on/off the toilet or climbing stairs.

  • Around 90 degrees for rising from a seated position and 115 degrees for activities requiring deeper flexion, like squatting or landing.

Arthrokinematics Associated with the Knee Joint

Understanding arthrokinematics is important for both open-chain and closed-chain movements:

  • Open Chain (Tibia moving on Femur):

    • Extension involves an anterior roll and glide.

    • Flexion corresponds to a posterior roll and glide.

  • Closed Chain (Femur moving on Tibia):

    • Extension involves an anterior roll with a posterior glide.

    • Flexion results in a posterior roll and anterior glide.

Joint Mobilizations

When performing joint mobilizations, gliding techniques are employed. For instance:

  • To enhance knee extension, an anterior glide of the tibia is executed.

  • For improved flexion, a posterior glide is implemented. This understanding is crucial when addressing restrictions in movement.

Screw Home Mechanism

The screw home mechanism is essential in the last five degrees of knee extension. It involves the external rotation of the tibia, aided by structures such as:

  • Anterior movement of the menisci.

  • Tension in the anterior cruciate ligament (ACL).

  • Lateral pull from the quadriceps.

This mechanism plays a vital role during gait, aligning the foot and tibia during the stance phase, and requires unlocking the knee for flexion, which is managed by the popliteus muscle.

Patellofemoral Joint Anatomy

The patella is classified as a true sesamoid bone placed within the quadriceps and patellar tendon. Its importance lies in enhancing the mechanical advantage of the quadriceps, allowing for effective knee extension by decreasing required force.

  • The posterior side of the patella is covered with hyaline cartilage, facilitating smooth movement through the femoral groove.

  • Common issues with the patella include maltracking, which can stem from inadequate muscle recruitment or tightness in adjoining soft tissues.

  • The patellofemoral joint is subject to high compressive forces during functional activities, potentially leading to anterior knee pain.

Patella Facets

Anatomically, the patella has:

  • Base: Superior aspect where the quadriceps tendon attaches.

  • Apex: Inferior section of the patella.

  • Facets:

    • The medial facet is flattened/convex.

    • The lateral facet is larger with a round shape and vertical edge separating it from the medial aspect.

    • The odd facet is located more medially and is vital in tracking with femoral contact.

Contact Points During Flexion

The contact of the patella with the femur at varying flexion angles is critical:

  • At full extension, the patella has no contact with the femur.

  • Initial contact occurs between 10-20 degrees of knee flexion at the patella's inferior aspect.

  • At 90 degrees of flexion, all medial and lateral facets contact the femur.

  • In deep flexion (135 degrees), contact is limited to the odd and lateral facets, increasing the potential for patellofemoral pain during activities like deep squats.

Patellofemoral Joint Compression Forces

The patellofemoral compression increases with knee flexion:

  • At full extension, minimal compression is noted, even during quad contractions.

  • At foot strike (gait), with knee flexed at 10-15 degrees, there's about 50% body weight on the patellofemoral joint.

  • This increases to over three times body weight at 60 degrees of flexion and can reach as much as eight times body weight during deep squats.

Stabilizers of the Patellofemoral Joint

The stability of the patellofemoral joint relies on numerous structures, both passive and active:

Passive Stabilizers Include:

  • Medial and Lateral Retinaculums.

  • Medial Patellofemoral Ligament.

  • Lateral Wall of the Femoral Groove.

Active Stabilizers Include:

  • Vastus Medialis Oblique (VMO) and Vastus Lateralis.

  • Iliotibial (IT) Band.

  • Quadriceps Tendon and Patellar Tendon.

While these stabilizers are essential for proper patellofemoral mechanics, excessive tightness or restriction may hinder patellar movement. Maintaining the elasticity of these structures is critical for functional outcomes.

Conclusion

This comprehensive overview of knee biomechanics highlights the intricate relationships between bone angles, joint mechanics, and pathological states, as well as the significance of understanding these elements in clinical practice for effective diagnosis and management of knee-related issues.

Thank you for attending this presentation on Clinical Biomechanics of the Knee.