Ortho Kinematics: Understanding Bone Movement, Planes, and Importance

What is Ortho Kinematics?

Ortho kinematics, often used interchangeably with osteokinematics, is the study of the gross, observable movements of bones in space relative to the three cardinal planes of the body. It describes the motion of the shafts of bones rather than the subtle movements of joint surfaces.

Understanding Ortho Kinematics: The Basics

Kinematics is the branch of mechanics that describes motion without considering the forces that cause it. When we add "ortho" (referring to bones) or "osteo" (also referring to bones), we focus specifically on the macroscopic movement of the bony levers of the human body. This field is fundamental to understanding how we move, perform exercises, and recover from injuries.

Key Principles of Ortho Kinematics:

• Planes of Motion: All human movement occurs within or across three cardinal planes, each perpendicular to the others:
  • Sagittal Plane: Divides the body into left and right halves. Movements include flexion and extension (e.g., bicep curl, squat).
  • Frontal (Coronal) Plane: Divides the body into front and back halves. Movements include abduction and adduction (e.g., lateral raise, side bend).
  • Transverse (Horizontal) Plane: Divides the body into upper and lower halves. Movements include rotation (e.g., trunk rotation, pronation/supination).
• Axes of Rotation: Each plane of motion has a corresponding axis of rotation, which is an imaginary line around which the movement occurs.
  • Medial-Lateral Axis: Corresponds to the sagittal plane (e.g., shoulder flexion/extension occurs around this axis).
  • Anterior-Posterior Axis: Corresponds to the frontal plane (e.g., hip abduction/adduction occurs around this axis).
  • Vertical (Longitudinal) Axis: Corresponds to the transverse plane (e.g., spinal rotation occurs around this axis).

Common Ortho Kinematic Terminology:

• Flexion: Decreasing the angle between two bones.
• Extension: Increasing the angle between two bones.
• Abduction: Moving a limb away from the midline of the body.
• Adduction: Moving a limb towards the midline of the body.
• Internal (Medial) Rotation: Rotating a limb towards the midline.
• External (Lateral) Rotation: Rotating a limb away from the midline.
• Pronation: Rotation of the forearm or foot inward.
• Supination: Rotation of the forearm or foot outward.

Ortho Kinematics vs. Arthrokinematics

It's crucial to distinguish ortho kinematics (or osteokinematics) from arthrokinematics, as both are vital for complete movement analysis.

• Ortho Kinematics (Osteokinematics): Describes the gross movement of the bones themselves. For example, when you perform a bicep curl, the forearm (radius and ulna) moves relative to the upper arm (humerus). This is an observable, measurable movement of the limb.
• Arthrokinematics: Describes the specific movements of the joint surfaces within the joint capsule. These are subtle, involuntary motions that accompany larger osteokinematic movements and are essential for normal, pain-free range of motion. The three primary arthrokinematic motions are:
  • Roll: New points on one surface meet new points on the opposing surface (like a tire rolling on the road).
  • Slide (Glide): One point on a surface contacts new points on the opposing surface (like a car skidding).
  • Spin: One point on a surface rotates around a fixed axis on the opposing surface (like a top spinning).

While ortho kinematics tells us what the limb is doing, arthrokinematics explains how the joint allows that movement to occur efficiently. Both must be present and coordinated for healthy, functional movement.

The Importance of Ortho Kinematics in Movement Analysis

Understanding ortho kinematics provides the foundational language and framework for analyzing human movement, critical for fields ranging from exercise science to clinical rehabilitation.

• Exercise Prescription and Performance: It allows fitness professionals to select appropriate exercises that target specific muscle groups by understanding the joint actions involved. For example, knowing that a squat involves hip, knee, and ankle flexion/extension helps in proper form coaching.
• Injury Prevention: Deviations from ideal ortho kinematic patterns can indicate muscle imbalances, poor motor control, or compensatory movements, increasing injury risk. Recognizing these patterns is key to corrective exercise.
• Rehabilitation and Assessment: Physical therapists and other clinicians use ortho kinematic principles to assess range of motion (e.g., using a goniometer), identify limitations, and design interventions to restore functional movement after injury or surgery.
• Biomechanics Research: It forms the basis for more advanced biomechanical analyses, including kinetic studies (forces causing motion) and electromyography (muscle activation).
• Sport-Specific Training: Analyzing the ortho kinematic movements involved in a sport (e.g., a golf swing, a baseball pitch) allows for targeted training to improve performance and reduce the risk of overuse injuries.

Applying Ortho Kinematics in Practice

For anyone involved in human movement, from the casual exerciser to the seasoned clinician, ortho kinematics offers a vital lens through which to view and optimize physical activity.

• For Fitness Enthusiasts: Understanding basic joint movements helps in performing exercises with correct form, maximizing effectiveness, and minimizing injury risk. For instance, knowing that a deadlift involves hip extension helps you focus on driving through the glutes and hamstrings.
• For Personal Trainers and Coaches: It's the bedrock of exercise selection, progression, and regression. It enables precise cueing ("flex your knees," "abduct your arm") and effective analysis of client movement patterns.
• For Clinical Professionals (PTs, OTs, Chiropractors): Ortho kinematics informs diagnostic assessments, goal setting for rehabilitation, and the development of therapeutic exercise programs. It's used to measure objective changes in joint range of motion over time.

Conclusion

Ortho kinematics is an indispensable concept in exercise science and kinesiology, providing the fundamental language to describe and analyze the gross movements of the human body. By understanding how bones move in planes and around axes, we gain critical insights into exercise mechanics, functional movement, injury prevention, and rehabilitation strategies. It serves as the macroscopic view that complements the microscopic understanding provided by arthrokinematics, together offering a comprehensive picture of human motion.