Knee Anatomy: Locating the Knee Centre and Key Landmarks

How to Find Knee Centre?

Locating the "knee centre" is not about finding a single, universally defined anatomical point, but rather identifying specific landmarks or an approximate axis of rotation that serves as a reference for anatomical, biomechanical, or clinical purposes.

Understanding the "Knee Centre" Concept

The term "knee centre" can refer to different points or axes depending on the context of its use. Unlike a fixed bony landmark, the knee joint's primary function is a complex hinge mechanism, and its axis of rotation shifts slightly throughout its range of motion. Therefore, "finding the knee centre" typically involves identifying:

• Anatomical Midpoint: An approximate central point within the knee joint space or relative to the patella.
• Biomechanical Axis of Rotation: The theoretical pivot point around which the tibia and femur move during flexion and extension. This is often approximated by a specific bony landmark.
• Clinical Measurement Point: A standardized reference point used for specific assessments, such as goniometry (measuring joint angles), limb length discrepancies, or Q-angle measurements.

Essential Anatomical Landmarks for Knee Centre Identification

Accurate identification of the knee centre relies heavily on a thorough understanding of the surrounding bony landmarks. These can be palpated (felt) through the skin.

• Patella (Kneecap): The large, triangular bone located at the front of the knee. Its midpoint or apex (bottom tip) are common reference points.
• Tibial Tuberosity: The prominent bony bump located on the front of the tibia, approximately 2-3 inches below the patella. It serves as the insertion point for the quadriceps tendon.
• Femoral Condyles: The two rounded prominences at the end of the femur that articulate with the tibia.
  • Medial Femoral Condyle: On the inner side of the knee.
  • Lateral Femoral Condyle: On the outer side of the knee.
• Tibial Plateau: The flat top surface of the tibia that articulates with the femoral condyles. The space between the femoral condyles and the tibial plateau forms the joint line.
• Fibular Head: A distinct bony knob located on the lateral (outer) side of the lower leg, just below the knee joint line and slightly posterior to the tibia.

Practical Methods for Locating the Knee Centre

The specific method for finding the "knee centre" depends on your objective.

Method 1: General Anatomical Midpoint

This method aims to find the approximate center of the knee joint for general reference.

• Patient Position: Have the individual sit on a chair or table with their knee bent to approximately 90 degrees, with their foot flat on the floor or supported. This position helps relax the quadriceps and makes landmarks more accessible.
• Palpation:
  1. Locate the Patella: Gently place your fingers over the kneecap.
  2. Identify the Joint Line: Carefully move your fingers just above and below the patella, feeling for the soft depression between the femur and tibia. This is the joint line. You can often feel the edges of the femoral condyles and tibial plateau.
  3. Find the Midpoint: The general anatomical "centre" can be considered the midpoint of the patella, or the approximate centre of the joint line, directly behind the patella.

Method 2: Biomechanical Axis of Rotation (for Goniometry)

When measuring knee joint range of motion (goniometry), the axis of the goniometer is aligned with the knee's axis of rotation for flexion and extension.

• Patient Position: Often supine (lying on back) or seated with the knee exposed.
• Locating the Axis: The approximate axis of rotation for knee flexion/extension is typically located at the lateral femoral epicondyle. This is a prominent bony projection on the lateral side of the femur, just above the joint line.
  1. Palpate the Lateral Femoral Condyle: Feel for the large, rounded prominence on the outer side of the knee.
  2. Move Superiorly: Slide your fingers slightly superior (upwards) and anterior (forwards) from the most prominent part of the lateral femoral condyle. You will feel a distinct, smaller bony projection – this is the lateral femoral epicondyle.
• Application: When using a goniometer, the fulcrum (pivot point) of the goniometer is placed directly over this landmark.

Method 3: Clinical Measurement Points

Certain clinical measurements use specific "knee centre" references.

• Leg Length Measurement: For anatomical leg length, the measurement is typically taken from the Anterior Superior Iliac Spine (ASIS) to the medial malleolus (inner ankle bone), passing through the midpoint of the patella.
• Q-Angle Measurement: This angle reflects the pull of the quadriceps muscle on the patella. It involves three points: the ASIS, the midpoint of the patella, and the tibial tuberosity.

Importance of Accurate Knee Centre Identification

Precise identification of knee landmarks and the conceptual "centre" is crucial for various applications:

• Exercise Prescription and Performance: Ensuring proper joint alignment during exercises like squats, lunges, and leg presses helps optimize muscle activation and minimize undue stress on the knee joint.
• Injury Prevention: Understanding the mechanics of the knee and its rotational axis aids in identifying movement patterns that could lead to injury.
• Rehabilitation: Accurate goniometry allows clinicians to objectively measure and track improvements in joint range of motion following injury or surgery.
• Biomechanics Research: Precise landmarking is essential for collecting reliable data on human movement, aiding in the development of safer equipment and training protocols.
• Orthotics and Prosthetics: Custom-fitting devices like knee braces or prosthetic limbs requires exact measurements relative to the knee's anatomical and functional axes.

Tips for Effective Palpation

• Relaxation: Ensure the individual whose knee you are examining is relaxed. Tensed muscles can obscure bony landmarks.
• Gentle but Firm Pressure: Use enough pressure to feel the bone without causing discomfort.
• Comparative Palpation: Whenever possible, compare findings to the opposite knee to identify any asymmetries or confirm landmarks.
• Anatomical Knowledge: A strong understanding of the underlying anatomy is paramount. Visualize the bones and their relationships.
• Practice: Like any skill, palpation improves with repeated practice.

Limitations and Considerations

• Individual Variation: Anatomical structures can vary slightly between individuals in terms of size and prominence.
• Soft Tissue Interference: Adipose tissue (fat) and large muscle masses can make palpation more challenging.
• Joint Pathology: Swelling, effusion (fluid accumulation), or deformities due to injury or disease can alter the feel of landmarks.
• Dynamic vs. Static: The knee's axis of rotation is not perfectly fixed but undergoes slight translation (shifting) during movement. Static palpation provides an approximation.

By understanding the various interpretations of "knee centre" and mastering the palpation of key anatomical landmarks, fitness professionals and students of kinesiology can gain valuable insights into knee joint mechanics, leading to more effective and safer practice.