3 Mecánica Atricular

Understanding Joint Functionality

Overview of Articulations

• The discussion begins with an introduction to the topic of articulations, emphasizing the need to expand on previous knowledge regarding joint types—those that allow movement and those that do not.

• The speaker highlights the importance of definitions in understanding various conditions related to joints, such as contusions, dislocations, and fractures.

Definition and Structure of Joints

• A joint is defined as an anatomical segment formed by two or more congruent bone ends. Congruence refers to how one bone can be concave while another is convex, fitting together perfectly.

• Joints are divided into three components: passive part (bones), active part (muscles), and neurovascular apparatus. This classification aids in understanding their functions.

Components of a Joint

Passive Component

• The passive component includes congruent bones, articular cartilage (hyaline cartilage), synovial membrane, synovial fluid, and ligaments which stabilize the joint during movement.

• Ligaments are described as thickened parts of the capsule made from firm connective tissue that stabilizes joints; they should not be confused with tendons.

Active Component

• The active component consists of striated muscles that cross over joints through tendon insertions into bones. Tendons facilitate movement while ligaments provide stability.

Neurovascular Component

• This component includes nerves and blood vessels essential for sensation (e.g., pain perception), proprioception (awareness of body position), and circulation within the joint area.

Importance of Sensation in Joints

• Nerves in joints help detect vibrations, static positions, pain, temperature changes; this sensory feedback is crucial for maintaining posture and preventing injury.

• Conditions like Marfan syndrome can impair pain perception in joints leading to potential complications due to lack of positional awareness.

Synovial Fluid Characteristics

Composition and Function

• Synovial fluid is produced by the synovial membrane; it resembles egg white in consistency. It serves multiple functions including lubrication and nutrient transport within the joint.

• Variability exists in synovial fluid volume across different joints; larger joints like knees contain more fluid compared to smaller ones like interphalangeal joints.

Biological Significance

• Synovial fluid acts as an ultrafiltrate from plasma containing proteins, glucose, hyaluronic acid among other substances vital for joint health.

Understanding Synovial Fluid and Joint Structure

The Role of Mucin in Joint Health

• Mucin is a crucial anticoagulant present in synovial fluid, which prevents coagulation during bleeding within the joint.

• In cases of hemarthrosis (bleeding into the joint), arthrocentesis can be performed after a few days to extract liquid blood rather than clotted blood due to mucin's properties.

• The healing process begins with trauma leading to bleeding, forming a hematoma that eventually organizes into a clot necessary for proper healing. This process is hindered by the presence of mucin in synovial fluid.

• Fractures occurring within the joint (intra-articular fractures) may experience delayed healing because they are exposed to synovial fluid, which slows down clot formation essential for recovery.

• Synovial fluid also contains various cellular components such as red blood cells and white blood cells, which are important for diagnosing joint pathologies through cytochemical analysis. Its density ranges from 1015 to 1017 kg/m³ and has an alkaline pH between 9.4 and 9.7.

Joint Capsule Structure

• The joint capsule is made up of elastic connective tissue that stabilizes the joint structure, reinforced externally by ligaments that provide additional stability.

• Inside the capsule lies the synovial membrane, closely attached to it, where flattened pseudo-endothelial cells produce synovial fluid essential for lubrication and nourishment of cartilage surfaces.

Classification of Joints

• Joints can be classified based on their mobility:

• Diarthrosis: freely movable joints.

• Anfiartrosis: joints with limited movement.

• Sinartrosis: immovable joints.

This classification was expanded upon by Wilson who introduced anfiartrosis as a distinct category alongside diarthrosis and sinartrosis.

Types of Sinartroses

• Sinartroses can further be divided:

• Sincondrosis: immovable joints connected by cartilage (e.g., costosternal joint).

• Sinfibrosis: joined by fibrous tissue; includes sutures (e.g., between parietal bones) characterized as dentate or serrated connections.

The unique characteristics of these types highlight their structural differences and functional implications in human anatomy.

Articulaciones y su Clasificación

Tipos de Articulaciones

• Las vértebras sacras se fusionan en una sola masa a través de sinostosis, similar a la unión entre el occipital y el esfenoides. Se mencionan las anfierartrosis como articulaciones con movimiento limitado.

• La sindesmosis es un tipo de articulación donde los huesos están unidos por tejido conjuntivo, como en la tibio-peroneal distal y la costovertebral (costilla con vértebra).

• Los dientes se colocan en sinartrosis debido al poco movimiento que presentan, aunque hay cierto movimiento imperceptible. Esto contrasta con su clasificación anterior.

• La sínfisis o fibrocartílago une las articulaciones mediante tejido fibrocartilaginoso, como en la sínfisis del pubis y entre cuerpos vertebrales a través de discos intervertebrales.

• Existen diferentes clasificaciones para las articulaciones según distintos autores, lo que puede generar confusión. Se busca homogeneizar estos términos para facilitar el entendimiento.

Clasificación de Diartrosis

• Las diartrosis son articulaciones que permiten gran movimiento; algunos autores utilizan términos variados como esferoidea o enartrosis para describirlas (ejemplo: hombro y cadera).

• Las condíleas pueden ser simples (como el temporo-maxilar) o dobles (como en la rodilla). También se mencionan las artrodías o planas, presentes en las intercarpales e intertarcianas.

• La unión entre vértebras incluye partes articulares que no son visibles desde el cuerpo vertebral. Se discuten varios términos para describir estas uniones.

Movimientos Articulares

• La troclear o bisagra permite movimientos de flexión y extensión, ejemplificada por la cúbito-humeral e interfalángicas.

• La articulación trocoide permite rotación; se menciona específicamente la radiocarpiana proximal durante supinación y pronación del antebrazo.

• Se utiliza una analogía para recordar los términos supinación (palma hacia arriba/súplica) y pronación (palma hacia abajo/propina), aunque aclara que no provienen etimológicamente de esas palabras.

Otras Articulaciones

• La silla de montar se describe entre el trapecio metacarpiano y el primer metacarpiano, así como entre calcáneo y cuboides.

• La sinartrosis es una falsa articulación donde dos segmentos óseos están separados por músculo, ejemplificada por la escápula con la parrilla costal.

Introducción a la Marcha Biomecánica

• Se anticipa una clase sobre semiología del aparato locomotor enfocándose en biomecánica de marcha.

• Definición: marcha es un medio de locomoción donde siempre un segmento del miembro inferior está en contacto con el suelo; nunca ambos miembros inferiores están en el aire simultáneamente durante este proceso.

Understanding Gait Mechanics

The Sound of Walking

• The sound produced by walking is distinctive; it allows one to identify individuals based on their gait without visual confirmation.

• Variations in sound, such as "toc" versus "tox," indicate different walking conditions, like dragging a foot or limited contact due to pain or deformity.

Measuring Step Length and Duration

• Step length is defined as the distance between two consecutive points of support from the same leg, typically measuring around 80 cm.

• Gender and height influence step length; women generally have shorter strides compared to men, while taller individuals tend to have longer steps.

• Normal walking speed ranges from 90 to 120 steps per minute, but cultural differences can lead to variations in this metric.

Foot Support and Angles

• The point of foot support varies; it may be on the toes or heels depending on discomfort or use of orthotics.

• The angle of foot placement (angle de fic) is formed by lines drawn along each foot's axis when standing. This angle typically measures around 32 degrees but can vary pathologically.

Pathological Gait Patterns

• An increased angle of fic can resemble Charlie Chaplin's walk, where feet are exaggeratedly apart. This may occur in certain conditions like flat feet or during pregnancy for stability.

• Conversely, a decreased angle resembles a parakeet's walk with feet closer together, which can also indicate specific pathologies.

Center of Gravity and Energy Efficiency

• The width between feet during standing (base of support) should ideally be between 5 and 10 cm for optimal balance.

• A stable center of gravity minimizes energy expenditure while maximizing movement efficiency. Ideally, this center remains consistent during motion for effective energy use.

• In humans, the center of gravity is located just anterior to the second sacral vertebra and shifts slightly during movement within a range of about 5 cm.

Understanding Gait Efficiency and Mechanics

The Impact of Impairments on Gait

• Efficient gait can be compromised by impairments such as limb shortening, prosthetic use, or joint pain leading to a claudicating gait (limping).

• A claudicating gait results in significant shifts in the center of gravity, which can move 10 to 20 cm laterally and vertically, reducing overall walking efficiency.

Phases of Gait Analysis

• Analyzing gait involves focusing on one limb at a time; for example, examining the right leg's movement through various phases.

• The first phase is "double support posterior of impulse," where both feet are on the ground but one is preparing to push off forward.

Detailed Breakdown of Gait Phases

• The second phase is "oscillation," where the foot moves from back to front without touching the ground.

• The third phase is "double support anterior of reception," occurring when one foot lands while the other prepares for takeoff. This includes a monopodalic support moment.

Joint Positions During Gait

• In the first phase, hip extension occurs with knee semiflexion and plantar flexion at the ankle due to body weight and muscle action.

• During oscillation, hip transitions from extension to neutral and then flexion; this prevents dragging of the foot by allowing dorsiflexion at the ankle.

Importance of Joint Functionality

• In "double support anterior of reception," proper alignment and function of joints are crucial for effective weight transfer during walking.

• If any joint experiences pain or limited function during this phase, it can lead to an abbreviated step length and contribute to a claudicating pattern.