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Arthroscopy of Knee
For knee disease

Arthroscopy is a procedure most often performed on the knee joint and requires the use of a device called an arthroscope. An arthroscope is a tubular instrument approximately 5 mm. (1/8 inch) in diameter, which contains fiberoptics and lenses to convey a cold light into a joint and return an image to a small television camera. The image is displayed on a monitor screen in the operating room. The arthroscope is used for both diagnosis and treatment.

Anatomy and Physiology

  • The knee is a complex mechanism formed by the joining of bones, ligaments, muscles and protective cartilage (Figure 1)
  • Bones
    1. Femur. The femur or thighbone extends from the hip to the knee and forms the upper aspect of the knee
    2. Tibia. The tibia is the major bone in the lower leg, sometimes called the shinbone. The tibial plateau is the portion of the tibia that forms the lower aspect of the knee
    3. Fibula. The fibula is a slightly shorter bone that runs parallel and along the outside of the tibia
    4. Patella. The small bone in front of the knee: the kneecap
  • Major ligaments
    1. Medial collateral ligament---limits inward bending of the knee. This ligament extends from the lower end of the femur on the medial side (inside) of the knee to the tibia
    2. Lateral collateral ligament---limits outward bending of the knee. This ligament extends from the lower end of the femur on the lateral side (outside) of the knee to the fibula
    3. Anterior cruciate ligament--- This is a rope like ligament that runs from the center of the femur to the anterior aspect (front) of the tibia. It is a major stabilizer of the knee that prevents the femur from rotating and sliding back on the tibia (Figure 2)
    4. Posterior cruciate ligament--- This is a rope like ligament that runs from the center of the femur to the to the posterior aspect (back ) of the tibia. It works to stabilize the knee by preventing the femur from rotating and sliding forward on the tibia
  • Muscles
    1. The quadriceps muscle ends in the patellar tendon that covers the patella
    2. The hamstring muscles strengthen the back of the knee
  • Cartilage
    1. Smooth white cartilages cushion the knee, line the surface of the femur, tibia and patella within the joint
    • Menisci are C-shaped cartilages sandwiched between the femur and tibia, one on the inside (medial meniscus) and one on the outside side of the knee (lateral meniscus)
  • Synovium is a special tissue that lines all motion joints and produces a lubricating fluid
  • Knee function
    1. The knee is not just a simple hinged joint that bends backward (flexion)
    2. It also has a rotary motion that locks the femoral condyles into the tibial plateau on straightening (extension) the leg
    3. On extension of the knee, the ligaments become tight and convert the knee into a rigid locked structure
    4. The knee unlocks on flexion allowing the increased range of motion seen as the lower leg swings backward
Figure 1 - Anatomy of the knee
Figure 2 - Arthroscopic view of the anterior and posterior cruciate ligaments

Pathology

There are four diseases of the knee that are amenable to treatment using an arthroscope

  • Degenerative changes in the femoral or tibial articular cartilages
    1. This occurs with the aging process or with repetitive minor injury to the joint. (Figure 3A)
    2. Occasionally, a piece of the cartilage may break off and become a loose body in the joint
  • Tears of the menisci (usually the medial meniscus) of the joint due to a sudden twisting of the joint with the foot planted, or with repeated deep knee bends (Figure 4A)
  • Tears in the ligaments, most particularly the anterior cruciate ligament, can occur from twisting and falling or from a direct blow to the kneecap
  • Degenerative changes in the patellar (kneecap) cartilage may cause the surface to become rough, (Figure 5A) or mechanical injury to the patella may damage the cartilage limiting joint movement or cause the patella to be off center with uneven wearing
Figure 3a - The cartilage of the femur is roughened and eroded by wear. Figure 3b - The cartilaginous surface of the femur has been shaved with a shaver and is further smoothed with a small warming device.
Figure 3c - (punch hole femur) Because the cartilage is almost gone, small puncture holes are placed into the bone to stimulate growth of new cartilage. Figure 4a - The medial meniscus is fragmented.
 
Figure 5a - Rough cartilage surface due to degenerative change.

History and Exam

  • Pain
    1. Acute pain, particularly after an injury, is most likely a result of injury to the collateral or cruciate ligaments or the menisci
    2. Gradual onset of pain, particularly, in the older patient is indicative of degenerative changes within the joint
    3. Pain or tenderness located at the joint line indicates a tear of the meniscus
  • Swelling
    1. Swelling developing within hours after an injury suggests a cruciate ligament tear
    2. Swelling of the knee developing later after injury may be associated with a tear of the menisci
    3. Gradual onset of swelling without recent injury suggests degenerative changes in the cartilage or meniscus
  • Locking or abnormal joint mobility
    1. The knee may lock in partial flexion due to tears of the menisci and cruciate ligaments or from loose tissue in the joint (joint mouse)
    2. Excessive mobility of the knee occurs when there is a tear in the ligaments, most commonly the anterior cruciate ligament

Tests

  • Plain X-rays of the knee in both the anterior-posterior (front to back) and lateral (side to side) views are taken to determine if there is a fracture or degenerative changes in the joint, such as a loss of joint space or irregularity of the joint surface. An additional anterior-posterior X-ray with the patient standing may show additional problems with the joint space not seen when stress is not applied
  • CT (computerized tomography) may be helpful to pinpoint a questionable fracture
  • MRI (magnetic resonance imaging) is now the method of choice for evaluating the non-bony (soft) tissues of the knee. This is particularly useful in determining injuries to the menisci, the presence of loose bodies of cartilage, and irregularities of the joint surface

Surgical Procedure

  • The arthroscope is inserted through a small incision (port) in the skin. Fluid is inserted through another port to distend the joint and clear away any blood that may result
  • Working instruments such as scissors or knife are inserted through a third port
  • The orthopedist works with the arthroscope in one hand and manipulates a working instrument with the other while looking inside of the joint on the monitor
  • To correct degenerative femoral or tibial cartilages
    1. A small rotary shaver is used to smooth out the rough surface of a degenerated cartilage. A small heating tool may also be used to further smooth the surface (Figure 3B-above)
    2. When the cartilage is completely worn from the joint surface, small holes may be punctured into the bone to stimulate growth of new cartilage (Figure 3C-above)
    3. Grasping forceps are used to remove loose bodies or other loose debris
  • To correct tears of the menisci (usually the medial meniscus) of the knee
    1. When the menisci are torn near their center where the blood supply is poor, the injured portion is usually trimmed or smoothed. (Figure 4B)
    2. Damage to the menisci at the outer edge can usually be repaired since the blood supply is much better
  • Repair of a tear of the anterior cruciate ligament
    1. Fortunately, a ruptured anterior cruciate ligament can now be repaired through the use of an arthroscope
    2. The damaged ligament is replaced by grafting a strip of the patellar tendon in its place
    3. The central third of the patellar tendon is removed with an attached block of bone at each end
    4. Using a drill guide, drill holes are placed in the tibia and femur near the site where the original ligament was attached
    5. The graft is then pulled through the holes and held in place with screws
  • Patellar injury
    1. Patellar cartilage damage is usually treated in the same manner as femoral or tibial cartilage with a small rotary shaver. (Figure 5B)
    2. Malalignment of the patella is corrected by cutting tissue bands on either side of the patellar tendon thus allowing the tendon to be released and realign correctly
Figure 4b - The meniscus is trimmed. Figure 5b - A rotary shaver is used to smooth the patellar surface.

Complications

  • Stiffening or fixation of the joint (ankylosis)
  • Occasionally the delicate instruments may break within the joint. Usually the piece is found and removed at the time of arthroscopy. Rarely, repeat surgery is required
  • Failure of ligament reconstruction
  • Infection
  • Hemorrhage in the joint
  • Injury to nerves or vessels that pass beside the joint
  • Deep venous clotting (thrombosis) with the possibility of the clot going to the lungs (pulmonary embolus), which can cause severe difficulty in breathing and possible death

Postoperative Care

  • It is best to elevate and ice the knee to minimize pain and swelling
  • Crutches are used for several days

After Care

  • Contact the doctor for:
    1. Bleeding
    2. Uncontrolled pain
    3. Elevated temperature
    4. Marked redness or drainage
    5. Numbness
    6. Shortness of breath
  • Exercise the muscles around the knee. Occasionally physical therapy may be needed