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About Orthopaedic Surgery

Knee

Anatomy | Meniscus Injuries | Ligament Injuries
Patellar Disorders | Arthritis | Total Knee Replacement
Total Knee Surgery/Computer Assisted Surgery

Anatomy
The function of the knee requires a large range of motion and the ability to resist the great forces placed on it. The requirement for motion is met by the shape of the bones of the knee: the round end of the thigh bone (femur) rolls on the relatively flat top of the leg bone (tibia) so that the knee flexes from totally straight to over 150 degrees of flexion. The second requirement is met by the strong ligaments which prevent side-to-side motion (medial and lateral collateral ligaments) and front to back motion (anterior and posterior cruciate ligaments). The mismatch in the ends of the bones of the knee is improved by the medial and lateral menisci (knee cartilages). The ends of the femur and tibia are covered by the joint cartilage (different from the menisci), which provides a smooth gliding surface for joint motion. top

Meniscus Injuries (Torn Cartilages)
Meniscal tears occur when excessive motion of the knee places stress on these cushions between the femur and tibia. This can be from forced extension, flexion, side-to-side, or rotational motions. The tearing may be minor and have no mechanical effect on the normal gliding of the knee, or it my be greater and cause catching, popping, and even locking of the knee so that it will not extend completely.

The examination of a knee with a torn cartilage may reveal swelling, popping and joint tenderness, but the swelling may subside rapidly. If there is a suspicion of a torn meniscus, a magnetic resonance imaging study may be ordered, since plain x-rays don't show the menisci. If there is only minor tearing, nothing more than time for the inflammation of the injury to subside and rehabilitation of the muscles of the thigh and leg may be required. If there is a large tear which affects the mechanical function of the knee, surgical excision of the torn fragment by arthroscopic surgery may be required. top

Ligament Injuries
If the knee is subjected to forces which exceed the strength of the ligaments, there may be complete or incomplete rupture of one or more ligaments. The medial collateral ligament is injured when a force is applied to the lateral, or outside, aspect of the knee, causing a stretching of the ligament. The anterior cruciate ligament is injured when the knee is subjected to forces which flex, extend, or rotate the knee excessively, and often is injured in concert with a collateral ligament injury, or even a posterior cruciate ligament injury. The posterior and lateral collateral ligaments are infrequently injured. Any of these ligament injuries may be associated with a meniscus tear (see meniscus injuries).

If instability is not severe, knee ligament injuries can be treated by rehabilitation and, if needed, a brace to prevent instability during activity. If there is significant instability, especially in the case of an anterior cruciate or combined ligament injury, surgical reconstruction may be needed. It is not possible to restore anterior cruciate ligament function by simply repairing it-substitution of the ligament with either a graft from the patellar tendon, or with hamstring tendons is required. These grafts can be taken from the patient's knee or a tendon from a cadaver donor can be used. Whichever procedure is used, appropriate rehabilitation is essential for satisfactory function of the reconstructed knee, and return to vigorous activity is not recommended for 6 to 12 months after surgery.

In the case of the commonly injured anterior ligament, the optimum treatment is reconstruction using arthroscopic techniques, which minimize the trauma and the time required for rehabilitation. Other knee ligaments require open repairs or reconstructions to restore satisfactory function. top

Patellar Disorders
A common source of knee pain is the patella, or kneecap. It is a bone which acts rather like a guide for the tendon of the quadriceps muscle, which is the muscle in the thigh which straightens the knee. The quadriceps tendon attaches to the top and the patellar tendon to the bottom of the patella, which glides in a groove in the end of the thighbone as the knee bends and straightens. If the patella is not supported well by its restraining ligaments, &/or the groove in the femur is not well formed, the patella may have excessive mobility and become inflamed, causing pain in the front of the knee which is often accompanied by swelling, popping, and giving way of the knee. This instability may also result in roughness of the cartilage of the patella-femoral joint, or such roughness can occur in the absence of instability, often after trauma to the front of the knee. Most often, it occurs for no apparent reason.

After the cause of patella-femoral pain is determined, the initial treatment is based on strengthening the muscles which control the patella, particularly the quadriceps muscle. Properly done weight training, bicycling, and swimming are important tools in the rehabilitation of the knee with patellar pain. Knee supports of various types can also be useful. If these measures are not successful, surgical treatment to improve patellar stability or decrease the forces between the patella and femur may be performed. In the case of patellar subluxation, the kneecap usually slips off the femur laterally. Correction of this condition can often be accomplished by simply releasing the tight ligaments on the lateral side of the patella, but sometimes may require additional tightening up of the medial ligaments, or even moving the bony attachment of the patellar tendon toward the medial side of the knee.
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Arthritis
The two most common types of arthritis are osteoarthritis and rheumatoid arthritis. Both can be progressive diseases. They cause degeneration of the joint cartilage, along with painful roughening and deformity of the joint surfaces. Both types may ultimately require total knee replacement. However, some osteoarthritic knees can be treated with bone realignment (osteotomy). Several things can cause arthritis. The first is a fracture, which results in a deformed joint surface. Another cause is post-traumatic changes from injured knee cartilages or ligaments. Finally, several types of inflammation of the joint may cause arthritis. top

Total Knee Replacement
Sometimes arthritis of the knee causes enough pain and stiffness to interfere with daily activities. In this case, replacement of the joint surfaces with a total knee replacement prosthesis can be performed. In most total knee designs, the end of the thighbone (femur) is cut off and replaced by a "metal femoral prosthesis" (substitute). There are two ways to stabilize the hardware. One is with cement. The other option is to let the bone grow into the surface of the part. This option requires a specially designed prosthesis. The upper end of the leg bone (tibia) is removed and replaced with a tibial component, which is similarly fixed to the bone.

Total knee replacement is a major surgical procedure. There may be potential complications, such as: infection, blood clots in the legs, stiffness of the knee, and other medical problems. Intensive rehabilitation is required to restore motion and strength to the knee. Long-term follow up is necessary to evaluate the knee for the potential problems, such as: loosening, infection, or breakage of the prosthesis. Patients with total joints will need to take antibiotics before dental or urological procedures. This will minimize the chance of infection caused by bacteria introduced into the blood during the procedure. top

Total Knee Surgery/Computer Assisted Surgery
One of the most significant advances in total knee surgery has been in the accuracy of component placement and the restoration of balance in the surrounding muscles and ligaments. This has been accomplished by utilizing computer navigation. Computer assistance allows a level of precision that is not possible in stand techniques.

The principles of computer-assisted surgery (CAS) are very straightforward. A similarity can be drawn between CAS and aircraft navigation. Computers assist in providing accurate timely positional information allowing for informed decision making. In the same manner that a pilot can bring the aircraft to a safe landing in poor visibility, the surgeon can position the parts of the total knee in a precise manner making the slightly needed corrections as the operation progresses. Timely information provided by computer analysis is now available during the procedure.

Infrared technology is utilized to produce a moving digital model of your joint that is used during the operation. There is no need for either x-rays or CT scans, therefore no radiation exposure is involved. The digital model is then used to guide the position of the bone cuts, sizing of the components, and ultimate placement of the total knee. Surgical instruments the computer can see are incorporated into the operation thus allowing the cuts and placement of the total knee components to be monitored and controlled within fractions of a millimeter. Once a bone cut is made the bone bed surface can be computer evaluated to allow refinement if needed. This allows for correction of potential misalignment. Real-time data is used to modify the procedure to ensure accuracy. This is quite different than traditional non-CAS surgery where the total knee components are evaluated after the surgery is done utilizing x-ray.

Accuracy of placement and the balancing of the tissues around the total knee are very important to its longevity or lifespan. This is critical in today's medicine where total knee patients have a greater life expectancy. Mechanical wear and loosening are increased by inaccurate component placement. These problems can require future revision surgery, which may be more complicated.

Computer assisted surgery is the next big advancement in total knee surgery. Northern Rockies Orthopaedics with Dr. Schutte is the Center of Computer Navigated Total Knee Surgery in western Montana.top

NOTE: The information on this site is informational only and is not intended to be medical advice. NO ANSWERS TO MEDICAL QUESTIONS WILL BE GIVEN BY E-MAIL OR OTHER CORRESPONDENCE. Contact your physician for advice about specific medical conditions.

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