Understanding your Diagnosis: The anatomy of knee pain
In a typical consultation with an orthopaedic specialist, volumes of medical information can spill across the doctor’s desk and into the patient’s lap in as little as fifteen minutes. In SkyGen’s ‘Understanding your Diagnosis’ series, prospective patients are encouraged to arm themselves with a general understanding of the anatomy within their joints in order to improve the quality and depth of the conversations held between patients and clinicians.
The knee is a seemingly complex yet robust joint, strong enough to withstand the significant weight of the human torso and the masses of laptop bags, backpacks, suitcases, dependent children and text books alternately affixed to its frame.
The knee’s strength and flexibility, its two most impressive attributes, are critical to our capacity for transportation, physical activity and productivity.The size, structure and density of the bones comprising the knee joint lend it significant strength and load-bearing capacity whilst the knee’s arrangement of cartilage, menisci, ligaments and tendons support its flexibility and integrity throughout its full range of motion.
To learn more about the components of the knee joint, how it functions and how it can deteriorate, patients (and undergraduate medical students) often start by asking the following questions:
Which bones are the femur, tibia and fibula?
The large femur bone is located in the centre of the upper leg compartment, commonly referred to as the thigh. The femur articulates with (connects and pivots around) both the pelvis (at the top) and primarily the tibia (at the knee). The sharp front edge of the tibia bone (the largest bone below the knee) is the bone of your shin and is built to resist quite a beating from coffee tables and bed frames, whilst the fibula (sometimes incorrectly called the fibia) is a thinner bone which sits next to the tibia and stabilises the knee and provides additional motion at the ankle joint. The lowest point of each fibula is responsible for the bony bump of the outer ankle. The tibia has a similar point at its lowest tip forming the medial (inner) ankle.
What are medial and lateral condyles?
Both the femur and tibia have articulating condyles. Essentially, condyles are the smooth faces of the bones that fit together to provide articulation or motion within the knee joint. There are two condyles on each bone which have a small separation between them. The condyles of the femur look a little like the knuckles of your index and middle finger when bent, except the condyles have a very smooth surface coating them called articular cartilage. The term ‘medial’ means closer to the midline (usually interchangeable with the word ‘inner’) and ‘lateral’ refers to parts of the body further away from its midline (often interchangeable with the word ‘ outer’).
What is a lateral and medial meniscus?
Each meniscus (plural: menisci) within the knee is made of an organic shock-absorbing material called fibrocartilage. Contrary to popular belief, the menisci are not full discs separating the femur and tibia, but rather fill in most of the gap around where the bones touch and articulate. The menisci allow the heavy load carried by the femur to be distributed evenly around the condyles of the tibia. Even small tears in the menisci can cause clicking and locking within the knee joint and certain, often larger tears can cause knee instability, pain and severely reduced mobility.
What is articular cartilage?
The articular cartilage is the smooth, slippery, organic coating wrapped over the condyles of the femur and tibia, allowing the knee to move freely without friction or discomfort. Unfortunately, cartilage can become damaged by a variety of causes including traumatic accidents, high impact activities and wear and tear over time. People who are restricted to wheelchairs and hospital beds for long periods of time even experience cartilage damage, supporting the theory that there is a particular window of activity in which the cartilage actually maintains itself naturally without intervention.
What is an articular cartilage defect?
An articular Cartilage defect is a measured and categorised diagnosis of cartilage damage, often given a grade based on the guidelines of the International Cartilage Repair Society (ICRS). These give a good indication of the damage in terms of depth, described below:
Grade 0: Normal, healthy, undamaged cartilage
Grade 1: A soft spot or blistering on the cartilage surface
Grade 2: Small/minor tears in the cartilage
Grade 3: Tears or lesions in the cartilage are deeper than 50% of the cartilage thickness
Grade 4: The damaged cartilage exposes the bone beneath it
Further to the grading system, the severity of lesions, blisters and tears are dependent on their size (area) and location. The cartilage covering the joint surfaces is thicker in some places and shallower in others and some locations, irrespective of thickness are more susceptible to pain than others i.e. a small, shallow defect in one area could cause far more pain than a large, grade 3 or 4 lesion in another area.
How do ligaments support the knee joint?
There are a number of ligaments that support the knee joint and damage or deterioration to any of these supportive structures can lead to significant knee pain and subsequent joint damage.
On either side of the knee (medial and lateral), there is a ligament that attaches the femur to the bones of the lower leg. These are called the collateral ligaments.
The medial collateral ligament, like the lateral collateral ligament, stabilises the knee and prevents side-to-side movement, ensuring that the condyles of the knee ‘track’ properly, articulate and pivot around each other optimally without causing inflammation or pain.
The medial collateral ligament attaches the lower inside (medial) edge of the femur to the upper medial edge of the tibia (shin bone) and is susceptible to injuries and tears during forceful twisting or direct hits to the outer side of the knee – commonplace in tackling and contact sports. These types of injury often require rehabilitation with physical therapy and often this repair can be accelerated and outcomes improved with stem cell-driven regenerative medicine.
The lateral collateral ligament attaches the lower lateral edge of the femur to the thin bone running alongside the tibia, the fibula. When it tears or detaches following a traumatic blow to the inner side of the leg or accidental twisting of the knee, the result is as debilitating as a tear to the medial collateral ligament, a knee joint without the supportive outer ligaments effectively ‘taping’ the outer edges of the bones together.
Deep inside the knee joint, two cruciate ligaments ‘crisscross’ against each other attaching the two largest bones of the leg, the femur and tibia. Each cruciate ligament is a strong band of fibrous tissue named according to the side of the tibia
The frontal/anterior cruciate ligament (ACL) protrudes from the front of the tibia running backwards behind the knee to the rear/posterior side of the base of the femur. The ACL prevents your tibia from sliding forwards and dislocating from underneath the femur.
A tear to the anterior cruciate ligament is considered one of the worst and most painful knee injuries. Although the collateral ligaments provide important support and integrity at the knee, the ACL is critical to the femur’s ability to safely sit on the tibia without dislocating. ACL injuries and tears often require some form of surgical of regenerative medical treatment (or a combination of both) in order to restore its tensile (pulling) and attachment strength.
The rear/posterior cruciate ligament (PCL) runs from the rear of the tibia, around the inner side of the ACL and firmly attaches to the base of the femur. The PCL prevents the femur from slipping over and in front of the tibia and is considered to be stronger and less prone to injury than the ACL. Additionally, a tear to the PCL is often far less debilitating than a tear to the ACL, rarely requiring more than non-surgical physical therapy and/or regenerative medicine.
What role does the kneecap (patella) play in knee stability?
The patella is a free-floating bone, suspended in front of the knee joint by a tendon (above) and a ligament (below). The tendon, called the quadriceps tendon, facilitates extension of the knee by connecting the quadriceps muscles to the patella which is then attached to the shin via the patellar ligament (also sometimes called a tendon even though it attaches bone to bone).
In a healthy knee joint, the patella glides and ‘tracks’ along a shallow groove at the end of the femur ensuring that the contraction of the quadriceps pulls the front of the shin forward and preventing the tendon from falling to either side of the knee.
In certain disorders of the knee’s ligaments and tendons, collectively referred to as ‘tendonopathies’, the patella is pulled off track leading to inflammation and joint pain. These disorders are common in bodybuilders and running athletes where extremes of contractile force are repeatedly pulled over the knee joint, critically depending on proper alignment of the patella.
Where can I learn more about my knee injury and joint treatment options?
The best place to air your concerns and questions about the treatment of your knee pain is in the consultation room with your orthopaedic specialist. Make sure never to leave a consultation with unanswered questions or treatment options that you’re not happy with. Often, obtaining second and third opinions is the best way to develop your own understanding of your knee pain and the range of treatments now available through surgery and non-surgical alternatives.
*Please read: Although the information provided on this page may describe a particular patient experience and/or outcome, readers must understand that each patient presents with a unique medical history and may be recommended a different treatment/surgery by their surgeon to that described above. Individual results may vary between surgery centre/hospital, surgeon, surgery type and patient. Although SkyGen agrees to share all updates from patients at their request, SkyGen does not endorse any physical activities attempted by patients following surgery which do not follow the explicit instructions provided by their surgeon. SkyGen encourages all patients to discuss the risks of such activities with medical professionals before attempting these themselves.