Muscles, Tendons & Ligaments - Oh My!

What makes a joint stable?

Understanding soft tissues in the body is crucial, as these structures play a significant role in musculoskeletal health and are frequently involved in canine chiropractic care. Soft tissues are a broad category of non-bony structures in the body that encompass a variety of tissues with different functions and characteristics.

These tissues are called “soft” because they are pliable and relatively deformable compared to the hard, rigid bones of the skeleton. Soft tissues include: muscles, tendons, ligaments, fascia, cartilage, tendinous sheaths, bursae and adipose tissue. For the this Tuesday email we will focus on muscles, tendons and ligaments. We will circle back around to the other components of soft tissue in a future email.

Let’s begin with the mighty muscle. Muscles are an integral part of the musculoskeletal system and serve several key functions in the body. They are composed of bundles of muscle fibers that contract to produce movement, stabilize joints, and maintain posture.

Muscles can be further classified as skeletal (voluntary muscles attached to bones), smooth (involuntary muscles found in organs like the digestive tract), and cardiac (involuntary muscles of the heart).

1. **Movement:** Muscles are primarily responsible for generating force and facilitating movement of the body. Skeletal muscles are attached to bones via tendons, and when they contract, they pull on the bones, causing joint movement. This enables our pets to perform a wide range of activities, from simple tasks like walking and sitting to more complex movements like running and jumping.

2. **Posture and Stability:** Muscles also play a vital role in maintaining proper posture and stability. They help support the spine and other skeletal structures, preventing excessive stress on joints and ensuring that the body remains in a balanced position. This is particularly relevant in chiropractic care, as spinal alignment is essential for overall health.

3. **Protection of Organs:** Some muscles, like the abdominal muscles, help protect internal organs by providing a strong muscular wall around them. These muscles contribute to core stability and are crucial for activities like jumping into and out of the car and playing chase at the park.

4. **Heat Generation:** Muscles generate heat as a byproduct of their contractions. This thermogenic activity is essential for maintaining body temperature, especially in cold environments.

5. **Metabolism:** Muscles are metabolically active tissues. They consume energy (calories) both during activity and at rest. This metabolic activity can have implications for weight management and overall health.

6. **Joint Stabilization:** Muscles surrounding joints act as dynamic stabilizers, helping to prevent excessive joint movement and protecting them from injury. Proper muscle function is essential in maintaining your dog’s joint health.

7. **Blood Circulation:** Muscle contractions also assist in moving blood through the veins, particularly in the extremities. This aids in returning blood to the heart and plays a role in circulatory health.

8. **Respiration:** Muscles, including the diaphragm and intercostal muscles, are involved in the process of breathing. They contract and relax to expand and contract the lungs, facilitating inhalation and exhalation.

9. **Facial Expression:** Muscles in the face enable a wide range of facial expressions and communication through non-verbal cues, although muscles contribute to the verbal communication of growling and barking too.

In second place we have tendons. Tendons play a crucial role in musculoskeletal health. Tendons are dense, fibrous connective tissues that connect muscle to bone. They transmit the force generated by muscle contractions to the bones, allowing for movement of the joints. Tendons are critical for proper joint function and stability.

1. **Muscle to Bone Attachment:** Tendons serve as the bridge between muscles and bones. They anchor muscles to specific points on bones, allowing for the transmission of force generated during muscle contractions to the bones. This connection is essential for movement and joint function. Without tendons, muscles would not be able to move bones, and the skeletal system would be immobile.

2. **Stability and Joint Function:** Tendons help stabilize joints by maintaining proper alignment and preventing excessive movement. They act as dynamic stabilizers during joint motion, ensuring that joints move smoothly and within their intended range of motion. This stability is critical for joint health and injury prevention.

3. **Energy Storage:** Tendons have a unique property called “elastic recoil.” When muscles contract, tendons can store and release energy, which is particularly important in activities like running and jumping. This energy storage and release mechanism enhance the efficiency of muscle function and movement.

4. **Shock Absorption:** Tendons help absorb and distribute the shock generated during physical activities. They reduce the impact forces transmitted to the bones and joints, protecting them from excessive stress and potential injury.

5. **Collagen Structure:** Tendons are primarily composed of collagen, a strong and flexible protein. Collagen provides the structural integrity and tensile strength needed for tendons to withstand the forces placed upon them during muscle contractions and joint movements.

6. **Joint Health:** Tendons play a role in joint nutrition and lubrication. They are associated with synovial sheaths that provide lubrication to reduce friction between the tendon and surrounding tissues, ensuring smooth movement.

Lastly, we have the infamous ligaments.  Ligaments are strong, flexible bands of connective tissue composed mainly of collagen fibers. They are found throughout the body, connecting bones to other bones across joints. Unlike tendons, which connect muscles to bones, ligaments do not contract but instead serve to stabilize and support joints.

1. **Joint Stability:** Ligaments are primarily responsible for providing stability to joints. They act like strong ropes that hold bones together, preventing excessive or abnormal joint movements. This stability is essential for maintaining proper joint alignment and preventing dislocations or subluxations.

2. **Limiting Range of Motion:** While allowing for a certain degree of movement in a joint, ligaments also limit the range of motion to prevent hyperextension or hyperflexion. This limitation helps protect your canine’s joint from injuries that could occur with extreme movements.

3. **Proprioception:** Ligaments contain sensory receptors known as proprioceptors. These receptors provide feedback to the nervous system about joint position and movement. This information is crucial for maintaining your animal‘s balance, coordinating muscle contractions, and preventing overstretching or injury to ligaments.

4. **Joint Lubrication:** Some ligaments are associated with synovial sheaths, which produce synovial fluid. This lubricating fluid helps reduce friction between ligaments, tendons, and other structures within the joint, ensuring smooth movement.

5. **Shock Absorption:** Ligaments, particularly those found in weight-bearing joints (like elbows and knees/stifles), play a role in absorbing and distributing shock. This helps protect the joint surfaces and adjacent tissues from excessive forces during activities like running or jumping.

6. **Guiding Joint Movement:** In some joints, ligaments guide and direct the motion of bones during joint movement. For example, the cruciate ligaments in the knee/stifle help control anterior-posterior movement of the tibia and femur.

The stability of a joint is the result of a complex interplay between muscles and ligaments, as well as other factors like tendons, cartilage, and the joint’s bony structure. The specific percentage of stability attributed to muscles versus ligaments can vary depending on the joint in question, its location in the body, and individual differences.

However, as a general guideline, it is commonly accepted in the field of biomechanics and musculoskeletal physiology that the primary source of joint stability comes from the muscles surrounding the joint. I have heard that it could be as high as 80% of a joints stability comes from the muscles. Muscles are dynamic structures that can contract and relax to control and stabilize joint movement actively. They provide real-time adjustments to joint position and are particularly essential in maintaining joint stability during movement and in various functional activities.

Ligaments, on the other hand, provide passive stability to joints by limiting excessive joint motion. They act as strong, fibrous bands that connect bone to bone and are more effective at preventing extreme or unnatural movements rather than actively controlling joint position. Ligaments are like structural reinforcements, and they play a crucial role in preventing dislocations or subluxations.

The specific balance between muscle and ligament contribution to joint stability varies among individuals and breeds and depends on factors such as muscle strength, joint integrity, and proprioceptive control. In some joints, such as the shoulder, hip, and knee, muscle strength and coordination play a predominant role in stability. In others, like the sacroiliac joint in the pelvis, ligaments play a significant stabilizing role due to their configuration and function. 

Understanding the function of soft tissue is essential for providing comprehensive canine chiropractic care that promotes musculoskeletal health which leads to overall well-being in our animal companions.