Osteoarthritis is a degenerative joint disease that affects animals and humans. It is characterised by the destruction of the articular cartilage in a joint. Osteoarthritis is a painful, chronic condition that affects people and dogs’ mobility and quality of life.

A recent study of mice with induced injury to the articular cartilage in their knee (stifle) joints demonstrated the important role that the menisci plays in protecting the cartilage, stabilising the stifle joint and in so doing slowing the progression of osteoarthritis.

What is the meniscus in dogs?

Dogs have a medial (inner) mensicus and a lateral (outside) meniscus in their stifle. These menisci are C-shaped discs that are deeply concaved with thick outer borders. In large breed dogs, they can measure up to 8 mm. Menisci are comprise of fibrocartilage and are covered by synovial membrane. They are located between the femoral and tibial condyles and are attached by meniscal ligaments.

The role of menisci is two-fold. Firstly, it stabilises the joint by providing a congruous articulating surface between the femur and tibia. Providing such a surface reduces contact stresses on the tibeal plateau.

The second role of the menisci is to protect the articular cartilage of the joint. The articular cartilage is a thin fibrous connective tissue on the articulating surface of bones in synovial joints. It is comprised of chondrocytes, the death of which result in osteoarthritis. With synovial (joint) fluid, articular cartilage allows for frictionless movement of joint surfaces.

The menisci play a role in governing fluid flow to the articular cartilage. Prior to cartilage to cartilage contact, the menisci is thought to be loaded with fluid which increases the fluid pressure in the cartilage. Increased pressure stiffens the tissue and protects the chondrocytes from injurious strain as the joint is loaded.

How does the menisci reduce the risk of osteoarthritis?

The study with mice sought to evaluate how the meniscus protects the articular cartilage and reduces the risk of osteoarthritis onset and progression as measured by chondrocyte death.

The study randomly divided 39 mice into six (6) groups as follows:

• Loaded, meniscus intact, no cartilage injury
• Loaded, meniscus intact, cartilage injury
• Loaded, meniscus removed, no cartilage injury
• Loaded, meniscus removed, no cartilage injury
• Not loaded, meniscus removed, no cartilage injury
• Not loaded, meniscus removed, cartilage injury

For the purpose of the study, the meniscus was surgically removed and the cartilage injury was incurred surgically with a scalpel.

The stifle was loaded by electrically stimulating the knee extensor muscles to 80% of the maximum muscle contraction to establish contact with the two articular surfaces. The study involved 15 contractions every 30 minutes for a total period of 240 minutes. Measurements of chondrocyte death were taken before loading and every 30 minutes up to 240 minutes post loading.

Results

Chondrocyte (cell) death increased with increased time and number of joint loading cycles. In the loaded group with the meniscus removed and cartilage injury, cell death increased significantly and steadily from 90 minutes resulting in 45% cell death at the end of the 240 minute observation period. This compares with 14.5% cell death in the loaded group with intact meniscus and cartilage injury.

The percentage of cell death also increased over time at the site of the cartilage injury. In the group with the meniscus removed cell death around the injury site was 70% versus 30% in the group with an intact meniscus at the injury site. This finding indicates that an intact meniscus helps to reduce cartilage cell death and prevent further damage to the collagen fibrils and maintain the integrity of the fibrillar network.

Discussion

This study found that the menisci helped reduce the percentage of cartilage cell death in joints with intact cartilage. In this study, when the meniscus was removed, cell death was nearly doubled.

In subjects with cartilage injury and intact meniscus, the percentage of cell death when the joint is loaded was similar to that of the control groups where the joint was not loaded, the meniscus was removed and the cartilage was injured.

These findings show the role the meniscus plays in protecting even injured joints from contact stresses. It evenly distributes stresses across the articulating surfaces and mediates fluid flow to the articular cartilage. It is through the process of evenly distributing stresses that appears the meniscus protects chondrocytes from necrosis (death) and the onset of osteoarthritis.

There are some limitations to this study that should be noted. Firstly, it is not clear if the findings in mice can be extrapolated to canines or other animals. Secondly, the articular cartilage damage was incurred surgically. This type of injury does not accurately reflect the chronic, degenerative injuries that are observed in dogs with osteoarthritis in the stifle.

Tips for maintaining healthy stifle joints in dogs

This study shows that loading healthy stifle joints with intact menisci and no cartilage damage resulted in less than 10% chondrocyte death over the course of the observation period. Therefore, preventing cartilage and menisci damage is key to preventing osteoarthritis in dogs.

Here are some tips for maintain healthy joints.

Avoid overloading joints

This study showed that even in healthy joints, overloading the joint resulted in some cartilage damage which over time will lead to cartilage degeneration and osteoarthritis. Overloading can occur in several ways including

Obesity

The dog being overweight stresses joints unnecessarily. Stresses on joints increase when an overweight dog performs weight bearing exercise like walking.
For more please see https://www.fullstride.com.au/blog/obesity-and-osteoarthritis-in-dogs

Repetitive activity

Repetitive activities where the dog has insufficient rest or is not adequately prepared or conditioned for the task. Repetitive activities may include chasing and retrieving a ball, running up and down stairs, jumping up and down on furniture or out of a car. Dog sports also include repetitive tasks like jumping, retrieving, and heeling on one side only.

The risk with performing repetitive tasks is that joints can be stressed directly by the task. For example the stress on a shoulder joint from jumping out of a car.

Joints can also be overloaded from imbalances in muscle recruitment and activation. Muscular imbalances may be caused when muscles are fatigued and the dog recruits other muscle groups as compensation. Imbalances can also occur when a set of muscle become stronger over time through conditioning than contralateral muscles. When muscle groups are not exerting comparable forces then joints can be loaded abnormally.

For more please see https://www.fullstride.com.au/blog/repetitive-strain-injury-in-dogs-and-how-to-treat-it

Address potential joint injury early

While only the periphery of the meniscus has blood supply, which is considered a requirement for healing, human and animal studies of meniscus injury have shown that even in the absence of blood supply the meniscus is capable of healing. In a study of 198 people with meniscal repairs that extended into the zone with no blood supply, 80% were asymptomatic at a designated follow up point.

The chance of healing increases if the tear occurs in or close to the vascularised zone. Other factors that influence healing is the tear pattern and shape, and the presence of other injury (such as cruciate ligament injury) in the stifle joint. As the meniscus plays such an important role in protecting articular cartilage, addressing any potential tear early helps protect the dog from the onset of osteoarthritis.

Diet and hydration

Feeding the dog a diet rich in vitamins and minerals is essential to support cell regeneration and healing. An abundance of food based nutrients allows dogs to perform optimally without fatiguing and contributes to strong musculoskeletal structure. Ensuring dogs are well hydrated is also essential for maintaining well lubricated soft tissues (muscles, tendons, ligaments, and connective tissue) that contribute to proper joint function.

These tips for maintaining healthy stifle joints can help prevent the onset of osteoarthritis and keep dogs moving freely without pain into their senior years.

Full Stride provides canine massage treatments including passive range of motion, stretching and remedial exercises. Treatments are offered in the dog’s home (within a service area) and at a treatment room on the north side of Brisbane.

If you are looking for a SAENA certified canine massage practitioner outside of Brisbane please see https://www.saena.com.au/listings/landing

Until next time, enjoy your dogs.

Sources:

Abusara, Z, Andrews, S.H.J, Von Kossell, M & Herzog, W. 2018 “Menisci protect chondrocytes from load-induced injury” Scientific Reports, September 2018

Evans, H & de Lahunta, A, 2013, Miller’s Anatomy of the Dog (4th ed), Elsevier Saunders, Missouri.

Kainer, Robert A & McCracken, Thomas O 2003, Dog Anatomy: A Coloring Atlas, Telon New Media, Wyoming USA.

Starke, C, Kopf, S, Petersen, W, & Becker, R. 2009 “Meniscal Repair”, Arthroscopy:The Journal of Arthroscopy and Related Surgery Vol 25, No 9 (September) 2009 pp 1033-1044