Meniscus tears are a source of discomfort for a significant number of patients. The can affect both younger and older people, depending on the type of tear and usually symptoms include painful clicking, popping, locking, catching, and the knee giving way. In functional terms, meniscus tears lead to decreased walking endurance and balance performance.
The human menisci are C-shaped or semi-circular fibro-cartilaginous structures with bony attachments on the tibia bone. The menisci are essential for joint stability, shock absorption, distribution of contact forces, joint lubrication, and proprioception.
Meniscal tears can be classified as acute or degenerative. Acute tears are common in younger population, usually due to an excessive amount of force applied to a normal knee and meniscus. This is different from a degenerative tear, which is mostly met in the older population and results from repetitive normal forces acting upon a worn down meniscus.
Tears can also be described based on their orientation. They can be vertical longitudinal, vertical radial, horizontal, oblique or complex/degenerative. A degenerated tear, is typically presenting in patients over the age of 30 and has often an insidious onset of symptoms with no known traumatic event.
Meniscal tears happen mostly when the meniscus is losing its elastic properties and undergoes permanent deformity.
With vascular penetration of less than one third of its total surface, healing potential in the setting of chronic meniscal degeneration remains low. To create an effective treatment plan, a good understanding of the tissue properties is essential. The most important property for meniscus healing is viscoelasticity.
Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like water, resist shear flow and strain linearly with time when a stress is applied. That means that the same material can have two very different responses to a force depending on how fast the force was applied! It seems that faster strain rates cause more elastic responses, whereas slower strain rates cause more fluid-like behaviour. Also, if you apply a constant force to a viscoelastic material, then the displacement increases over time. When this force is released, the elastic properties that allow it to return to each previous position are reduced and it takes time for the material to recover to its initial configuration.
What that practically means, is that if you are sitting with your knees bent at an angle higher than 90 degrees for a long time, and feel pain rising up, it is because the elastic properties of your meniscus are reduced. That also applies for slow forces applied on your meniscus, especially if the load is quite high (eg. cycling, weightlifting).
To begin the healing process, the elastic properties of the meniscus need to be enhanced. A typical exercise rehabilitation program starts with low load, fast paced exercises in the full pain free range of motion and the load increases gradually according to each person’s symptoms.
If you have any questions or think you need a knee assessment, get in touch and we can book you in for an initial assessment with our experienced Physiotherapists. Or book online.
References:
Ferry, J.D., 1980. Viscoelastic properties of polymers. John Wiley & Sons.
Herrlin, S., H?llander, M., Wange, P., Weidenhielm, L. and Werner, S., 2007. Arthroscopic or conservative treatment of degenerative medial meniscal tears: a prospective randomised trial. Knee Surgery, Sports Traumatology, Arthroscopy, 15(4), pp.393-401.
Howell, R., Kumar, N.S., Patel, N. and Tom, J., 2014. Degenerative meniscus: pathogenesis, diagnosis, and treatment options. World journal of orthopedics, 5(5), p.597.
Mordecai, S.C., Al-Hadithy, N., Ware, H.E. and Gupte, C.M., 2014. Treatment of meniscal tears: an evidence based approach. World journal of orthopedics, 5(3), p.233.
Shemesh, M., Asher, R., Zylberberg, E., Guilak, F., Linder-Ganz, E. and Elsner, J.J., 2014. Viscoelastic properties of a synthetic meniscus implant. journal of the mechanical behavior of biomedical materials, 29, pp.42-55.
Smith, N.A., Parsons, N., Wright, D., Hutchinson, C., Metcalfe, A., Thompson, P., Costa, M.L. and Spalding, T., 2018. A pilot randomized trial of meniscal allograft transplantation versus personalized physiotherapy for patients with a symptomatic meniscal deficient knee compartment. The bone & joint journal, 100(1), pp.56-63.
Mordecai, S.C., Al-Hadithy, N., Ware, H.E. and Gupte, C.M., 2014. Treatment of meniscal tears: an evidence based approach. World journal of orthopedics, 5(3), p.233.