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Understanding Knee Joint, Its Structure, 6 Causes of Knee Joint Pain

Understanding Knee Joint and its Structure

Knee joint Comprises Of:-

  • Bones- Femur, Tibia and Patella.1
  • Cartilages- Medial and Lateral Menisci.
  • Ligaments- Medial and Lateral Cruciate Ligaments, Medial and lateral Collateral Ligaments, Patellar Ligaments, and Oblique Popliteal Ligament.

Understanding Knee Joint

How Are The Three Bones Positioned In Knee Joint?

Femur lies on the top of tibia forming a main compartment of the knee joint, and patella lies in front of the knee joint.

Where Is Patella Located In Knee Joint?

The patella is a flat bone. Back (posterior) surface of patella articulate with femur and forms an anterior compartment of the knee joint. The tendon of the quadriceps femoris muscle adheres and covers anterior surface of the patella.

Where Are The Cartilaginous Menisci Situated In Knee Joint?

Two cartilaginous menisci are shaped like “C” lies on inner and outer side of upper flat surface of tibia. Fibrocartilaginous menisci are crescentic in shape. Outer border is convex and thick, while inner border is concave and thin.

What Is The Function Of Cartilaginous Menisci?

The cartilaginous menisci are fastened to superior or upper surface of tibia and lies between tibia and femur. The surface of the cartilaginous menisci is smooth and allows effortless movements of knee joint between tibia and femur. The outer thick portion of the menisci are well vascularized and heal completely following tear. Inner portion of the menisci are poorly vascularized and do not heal well, may at time ends in necrosis. Menisci assist in smooth flexion and extension movement of knee joint. Menisci also acts as a shock absorber when acute pressure changes occur within knee joint.

Which Are The Knee Joint Ligaments?

Ligaments are divided as extra-capsular ligaments and intraarticular ligaments.

Extra-Capsular (external) Ligaments

  • Patellar Ligament.
  • Medial Collateral Ligament (MCL).
  • Lateral Collateral Ligament (LCL).
  • Oblique Popliteal Ligament.
  • Arcuate Ligament.

Intra-Articulate Ligaments

  • Anterior Cruciate Ligament (ACL).
  • Posterior Cruciate Ligament (PCL).
  • Posterior Menisci-Femoral Ligament. 

What Are The Causes Of Knee Joint Pain?

6 Causes of knee joint pain are-

  1. Inflammation of Soft Tissues-
    • Bursitis
    • Synovitis
    • Tendinitis
  2. Injuries-
    • Bones- Fracture of tibia, femur, patella or fibula and Dislocation of knee joint and patella.
    • Tear-
      • Ligament
      • Muscles
      • Cartilages-menisci
  3. Knee Joint Disease-
    • Arthritis
    • Infection
    • Cancer Tumor
  4. Loose Body In The Joint-Fragments of:
    • Bones
    • Cartilages
    • Soft tissue
  5. Muscle Disease-
    • Spasm
    • Myalgia
  6. Pinch Nerve
    • Obturator Nerve
    • Femoral Nerve

What is Bursitis?

Bursa is a sac of natural lubricant fluid enclosed in a cyst that lies between bone and tendon or bone and muscles.2 Bursa prevents injuries of the tendon or muscles resulting from persistent friction of tendon or muscles over hard surface of bone. There are several bursas around knee joint protecting several tendons from friction injuries. Inflammation of bursa is known as bursitis. Bursitis is observed following knee joint surgery or injuries. Bursitis is very painful condition. Most common bursitis resulting in severe knee joint pain is ”housemaid’s knee” and ”preacher’s knee.” A ”Baker’s cyst” is a bursitis observed as a tender swelling over the back of the knee.

What is Tendinitis?

Inflammation of tendons is known as Tendinitis. Tendinitis is seen following trauma or injury to the tendon.3 Tendons and ligaments are occasionally damaged following sports injury, accidental injury, fall or surgical trauma. Tendinitis is very painful condition, mostly observed during joint movement, muscle contraction or direct pressure on tendon. Tendinitis is caused by irritation and inflammation of one or more tendons. Injured tendon may heal with scar tissue and become tight band of fibrous tissue. In few cases non-inflamed tendon could be painful as in Illiotibial band syndrome.

What Is Iliotibial Band Syndrome?

Iliotibial ligament is attached to pelvic bone and outside of knee joint over tibia. Sports injury of runners and contact sports participants often causes soft trauma of the Iliotibial tendon. Tendon injury heals with minor scarring of muscles and tendons. Tendon becomes very tight with scar tissue causing shortening of the tendon. The disease is very painful and known as an iliotibial band syndrome. Pain is on the outside of knee joint unlike patellar tendinitis and Osgood Schlatter disease.

What Is Patellar Tendinitis?

Patellar tendinitis causes pain in front of the knee joint.4 Patellar tendon is the distal end of quadriceps muscles. Patellar tendon is attached to anterior surface patella and tibia. Runners, skiers, cyclists and participants of contact sports often suffer with inflammation of the patellar tendon. Inflammation is caused by continuous contraction and friction between patella bone and patellar tendon. Pain often is mistaken for the patellar dislocation.

What is Osgood Schlatter Disease?

Tendon of the quadriceps muscles spreads over patella and attaches to anterior surface of patella and tibial bone below patella. Overuse of quadriceps muscles causes irritation of the tendon below patella. Continuous vigorous use of irritated tendon and quadriceps muscles causes pain over the tibial attachment and eventually results in inflammation of tendon. Symptoms are more common in young patients and examination indicates lump below knee joint. Disease is known as Osgood Schlatter disease. Patellar tendinitis and Osgood Schlatter disease may be misdiagnosed as Patella-Femoral Pain Syndrome.

What is Patella-Femoral Pain Syndrome?

Patella-femoral pain syndrome is also known as Patellar Chondromalacia. Pain is more predominant over the top of the patella near femur bone. Pain is caused by friction between patella and femur bone because of minor misalignment. Disease is seen in older patients secondary to degenerative patellar disease. Similar pain is also observed in patellar dislocation.

What is Patellar Dislocation?

Patellar dislocation is either partial or complete. Partial dislocation is also known as patellar subluxation. Area over Knee Cap (patella) is extremely painful and swollen. Examination may or may not indicate displaced patella. Patellar displacement is seen in complete dislocation of patella. Displacement of patella is not seen when patella is partially subluxated. Dislocated patella or kneecap in most cases lies on outside of knee. Patellar dislocation often follows tear of knee joint ligaments. Symptoms of Patellar Dislocation are often same as symptoms of Anterior Cruciate Ligament (ACL) or Posterior cruciate Ligament (PCL) injury.

What is Anterior Cruciate Ligament (ACL) injury?

Femur and tibia are fastened to each other by anterior and posterior cruciate ligament. Ligaments prevent subluxation and dislocation as well as hyperextension of knee joint. Anterior Cruciate Ligament (ACL) injury is often seen in athletes involved in contact sports. Ligaments may be partially or completely torn following overstretched knee joint in hyperextension. Ligament also tears following direct high-speed impact of the leg above the knee joint. Condition is extremely painful. Complete tear may be associated with partial dislocated knee joint.

What is Posterior Cruciate Ligament (PCL) Injury?

The posterior cruciate ligament (PCL) is one of the four major ligaments that lies within the knee joint. PCL is a tough ligament. PCL functions to prevent posterior subluxation of tibia over femur bone. PCL also prevents lateral shift of patella. PCL injury is observed in younger patients during contact sports resulting in partial or complete tear of ligaments. PCL tear is also observed in older patients suffering with degenerative knee diseases. Degenerative diseases cause degeneration of meniscus, ligaments and bones resulting in laxity of knee joint space. Slack knee joint of older patients occasionally hyper-extends while walking on rough uneven surface, and results in tear of PCL. PCL may follow subluxation of knee joint and patella. PCL and ACL tear may be associated with Meniscus tear.

What is Meniscus Tear?

Meniscus is a “C” shaped cartilage that adheres to tibia and participates in knee joint activities all the time. Meniscus tear is observed in all ages. Tear is common among younger patient involved in vigorous training for jogging, cycling, skiing and contact sports. Professional sports and vigorous training results in rapid wear and tear of knee joint structures and cartilages of meniscus. Forceful knee joint activities creates rapid changes in shearing forces within knee joint, which may result in meniscus tear. Meniscus tear is also common among elderly population secondary to degeneration of the cartilage. Meniscus tear causes severe pain with joint movements. Symptoms of meniscus tear are often same as loose body syndrome.

What Is Loose Body Syndrome?

Loose body syndrome is very painful condition. Pain is observed following any movements of knee joint. Loose body may be a fragment of bone, cartilage or soft tissue. This is common in older patients suffering with degenerative knee disease. Very rarely a loose body could be a foreign body such as fragments of bullets or metal accidentally introduced into knee joint. Loose body syndrome may be associated with degenerative knee joint arthritis.

What is Knee Joint Arthritis?

Arthritis is an inflammatory disease of knee joint. Most common arthritis causing knee joint pain is rheumatoid arthritis, osteoarthritis, psoriatic arthritis, gout and pseudogout.

  • OsteoarthritisOsteoarthritis is most common type of degenerative arthritis of knee joint. Wear-and-tear with aging affects bones, cartilages and tendon causing severe pain. Osteoarthritis may be precondition for dislocation, meniscus tear and ligamental tear in older population.
  • Rheumatoid Arthritis- Rheumatoid arthritis is second most common arthritis of knee joint caused by autoimmune disease. Pain is moderate to severe and responds to treatment.
  • Gout- Gout of knee joint is a rare disease. Gout is caused by increased concentration of uric acid in knee joint.
  • Pseudogout- Pseudogout of knee joint is more common than gout. Pseudogout is caused by deposition of crystals of calcium in joint fluid.
  • Psoriatic Arthritis- Psoriatic arthritis is observed in 30% of patients suffering with psoriasis. Pain is often moderate to severe.

Watch 3D Video of Knee Joint Rheumatoid Arthritis:


What is Septic Arthritis?

Septic arthritis is seen following knee joint infection. Knee joint is swollen, painful and red. Septic arthritis is often seen after trauma, surgery and septicemia. Patient often has fever.

How Severe Is Pain Caused By Cancer Tumor Of Knee Joint?

Cancer tumor spread in knee joint could be benign or malignant. Knee joint cancer or metastatic bone tumor is very rare. Knee joint contains bones, cartilages and tendons. Malignant cancer of bone (Osteosarcoma), cartilage (Chondrosarcoma) or tendon (Fibrosarcoma) may occur within knee joint even though it is very rare. Benign tumor like lipoma is common mostly localized over posterior compartment of knee joint. Pain caused by spread of malignant cancer is extremely severe than benign cancer like lipoma. Malignant cancer spreads rapidly and causes severe intractable pain.

How Can A Muscle Disease Cause Knee Joint Pain?

Spasm of muscles around knee can cause severe pain and is often misdiagnosed as knee joint pain. Fatigue muscles often induce pain with flexion and extension of knee joint. Diseases such as fibromyalgia, myofascial disease and muscle tear affecting muscles close to knee can imitate pain similar to knee joint pain.

What Are The Pinch Nerve Pains Of Knee Joint?

Structures of knee joint receive sensory nerve from obturator, femoral and tibial nerve. All or any one of the three nerves can be pinched along its course to knee from spinal cord. Nerves may be pinched secondary to disk herniation, bulge disk, spinal stenosis or foraminal stenosis within spinal canal. Nerve could be pinched outside spinal canal along its course to knee joint by hematoma, abscess or tumor. Pain may be wide spread along the course of the nerve or localized depending on where the nerve is pinched. Pain is excruciating and continuous.


Also Read:

Pramod Kerkar, M.D., FFARCSI, DA
Pramod Kerkar, M.D., FFARCSI, DA
Written, Edited or Reviewed By: Pramod Kerkar, M.D., FFARCSI, DA Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:April 18, 2023

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