Here is an article on meniscal injuries.
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What are Meniscal Injuries?
The knee joint, classified as a hinge joint, is one of the largest and most complex joints supporting the human body.
The importance of this specific joint to everyday activities is indisputable. For any adult with a healthy knee joint, walking, running, and squatting are tasks that require little effort. Since the knee is used so frequently, it is vulnerable to injuries, overuse and degeneration.
Meniscal injuries are the leading causes of disability directly related to the knee. A meniscal injury refers to tearing any of the two menisci of the knee. A meniscus is commonly described as a rubbery, crescent-shaped piece of cartilage that functions as the main shock-absorber in the knee joint. This structure chiefly cushions the two main bones making up the knee joint: the thigh bone and the shin bone.
When someone says they are suffering from a torn cartilage of the knee, they are referring to a meniscal injury.
Meniscal tears can occur in many ways. The most common for those that are active is a result of strong or forceful twisting motions. There are other ways that a meniscus injury can occur and I will go through those in a later article. A meniscal tear is classified based on its gross appearance and on its location along the meniscus. The different descriptions are thoroughly discussed in the succeeding articles.
A meniscal injury commonly occurs with other injuries of the knee, such as tearing of the anterior cruciate ligament. A meniscal injury is a knee injury that occurs in a wide variety of individuals. Although athletes engaged in contact sports are more widely recognized as at risk for meniscal injury, anyone can suffer from a meniscus tear at any age.
The meniscus weakens with age as well. For this reason, older adults may suffer from a meniscus injury even when they initially only had a minor knee injury. A meniscal injury is typically manifested by acute knee pain, swelling of the knee joint, and locking of the knee. These signs and symptoms may not be life threatening, but without the right interventions, meniscal injuries may significantly disrupt daily activities, reduce function, cause pain, and lead to reduced quality of life.
The understanding and appreciation of the menisci with regard to the biomechanics of the knee has drastically changed since Sutton described these structures as of no use in the 1960s. Given the limited understanding about its importance to knee biomechanics, the meniscus was commonly completely removed once its integrity was in doubt. Today, the menisci are regarded as vital structures of the knee. Along with this development, the diagnosis, treatment and rehabilitation of meniscal injury has radically changed through the years. These articles aim to introduce the basic concepts of a meniscal injury, focusing on its treatment and rehabilitation through exercise.
More and more research and client feedback supports the importance of an effective exercise program in the recovery of a meniscus injury in order to regain function, decrease pain, overcome knee catching, improve knee movement and increase knee strength. It must be noted a meniscus injury exercise program involves a lot more than just strengthening and stretching in order to make a full recovery. In the following articles we will go into the components in more detail.
Anatomy of the Knee and the Menisci
A meniscus is a rubbery wedge-shaped cartilage that cushions the thigh bone and the shin bone. Before thoroughly discussing this vital structure of the knee, it is essential to understand the anatomy of the knee joint. What structures make up one of the largest joints in the human body? How do these structures support the movements involving the lower extremities?
Overview of the Knee Joint
The knee joint is recognized as the largest joint in body. Similar to the elbow joint, the knee joint is classified as a hinge joint. A joint is the point where two or more bones meet to allow movement. A hinge joint is a type of joint where a bulging outward part of one bone fits into an inward curved-like surface of another bone. This specific type of joint only allows motion in one plane or a backward and forward motion. To be concise, hinge joints are so named as they resemble the hinges that allow the pivoting of a part, such as a door, on a motionless frame.
Let’s look at an overview of the knee joint. The knee joint consists of four bones and a broad network of ligaments, or structures that connect bones to other bones, and muscles.
Bones of the Knee Joint
The knee may appear like a non-complex joint, but it mainly consists of four bones:
The femur, or the thigh bone, is the largest bone in the lower extremity. It is attached by ligaments and a capsule to the tibia, which is commonly called the shin bone.
Running parallel to the tibia is the fibula. The patella, also known as the knee cap, is a flat triangular-shaped bone found at the front of the knee joint.
These bones are covered by a protective structure, called the articular cartilage. The cartilage is inherently designed to decrease the frictional forces every time the bones of the knee move. The major movements of the knee joint occur between the femur, the tibia, and the patella.
Ligaments of the Knee
The stability of the knee is largely attributed to the ligaments. There are four main ligaments found in the knee joint:
- anterior cruciate
- posterior cruciate
- medial collateral
- lateral collateral
The cruciate ligaments are found within the knee, whereas the collateral ligaments are found on the inner and outer areas of the knee.
Among these ligaments, the anterior cruciate ligament, or ACL, must be discussed further. Meniscal tears commonly occur in association with an ACL disruption, specifically on the lateral side of the knee (New England Musculoskeletal Institute, 2011). Injuries involving the menisci occur with ACL tears up to 70% of the time (Write State Physicians, 2012). The ACL forms a cross right in the middle of the knee. It runs from the front of the shin bone to the back of the femur. The ACL functions to inhibit the tibia from making excess forward motion. Twisting motions are the most common causes of ACL injuries.
The articular cartilage is a smooth tissue that encloses the ends of bones making up the knee joint. In the knee, the articular cartilage facilitates gliding of the bones of the knee without causing damage or excessive friction to the surfaces.
The menisci protect the articular cartilage of the knee from sustaining excessive pressure on one surface area on the joint’s surface. In the absence of the menisci, the forces applied to the knee are not effectively transmitted. The pressure is applied more intensely on one region, a condition that will eventually lead to wearing and tearing of the articular cartilage, as seen in osteoarthritis.
Knee Joint Capsule
The joint capsule of the knee is described as a thick and tough structure that surrounds the entire knee joint.
A synovial membrane that lines the inside of the capsule produces the synovial fluid, which functions as a lubricant. The knee joint capsule is further reinforced by the surrounding ligaments.
Each knee joint is comprised of two menisci, the wedge- or crescent-shaped structures found between the two major bones of the knee: the thigh bone and the shin bone. The upper surfaces of the menisci are in contact with the round prominences of the thigh bone; the lower surfaces of the menisci make contact with the plateaus of the shin bone. In cross section, the menisci are triangular in shape.
The C-shaped medial meniscus lies in the inner edge of the superior surface of the tibial bone. It is found on the inside part of the knee.
The lateral meniscus found on the outer edge of the knee is almost circular in shape. Compared to the medial meniscus, the lateral meniscus covers a wider portion of the tibial plateau surface.
Reports showed that the medial meniscus does not demonstrate direct connection to any muscles in the lower extremity (Bhagia, 2012).
Function of Menisci
These fibrocartilages function as effective shock absorbers of the knee. The menisci efficiently spread out the forces that are transmitted across the knee joint, making them crucial structures in maintaining the correct distribution of weight between the tibia and femur. The back or the posterior parts of the menisci absorb most of the pressure every time the knee bends (Orthogate, 2011).
Mobility of the Menisci
Both the medial and lateral menisci are anchored to the other supporting structures of the knee. Despite the attachments, the menisci are mobile. The degrees of their mobility are not the same, however. It was found that the medial meniscus is only half as mobile as the lateral meniscus (Baker, 2011). The excursion or mobility of the lateral meniscus is thought to exceed more than 10 millimeters. The greater mobility displayed by the lateral meniscus is explained by its looser attachment to the capsule.
The posterior horn of the medial meniscus has the greatest risk for disruption (Baker, 2011). Its vulnerability to injury may be attributed to the fact that this part of the medial meniscus has the least degree of mobility.
Water and Collagen Component
Water is the major component of the meniscus, comprising 70% of the total wet weight of the fibrocartilage (Athanasiou & Sanchez-Adams, 2009). At dry weight, collagen, specifically type 1 collagen, makes up 75% of the total weight of the meniscus. Collagen is a group of insoluble fibroproteins that form the structures supporting and connecting the tissues. Type 1 collagen fibers are arranged in circumferential direction to endure the tensile strength of the meniscus during weight bearing and for shock absorption. It is approximated that there are nearly 30 types of collagen in the body.
For any bodily tissue, an adequate blood supply is essential to repair and healing. The lesser the blood supply, the slower the healing time or the poorer the prognosis. The circulating blood distributes the nutrients and elements required for healing; thus, it is important to be familiar with the blood supply to the menisci to understand a meniscus injury’s potential response to treatment and rehabilitation.
The meniscal blood supply is limited to its outer edges or margins. The remaining areas lacking blood supply obtain the nutrients required for repair from the synovial fluid, a lubricating fluid found in the cavities of joints. Areas lacking blood supply rely on the process of passive diffusion and mechanical pumping to receive the said nutrients.
Arnoczky suggested a classification system that aims to categorize meniscus lesions with regard to the meniscal blood supply. As an overview, the red zone obtains sufficient supply of blood and the white zone does not.
- Red-red tear – The red-red tear occurs in the red zone, recognized as a blood-rich area. This is found on meniscus’ outer border. In this type of tear, both sides obtain functional supply of blood, a condition that promotes good healing.
- Red-white tear – The red-white tear includes the outer rim and the middle part of the meniscus. In this type, one end of the tear receives adequate blood supply and the other is in the area that lacked sufficient supply of blood.
- White-white tear – The white-white tear is completely found in the middle part of the meniscus, an area where blood supply is lacking. As a consequence, repair and healing is not favorable.
Let’s wrap up the article right here. I will be back later the in week with another article on the meniscus.
Later this week, I will be releasing the Meniscus Tear Solution:
Rick Kaselj, MS
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