Thursday, October 16, 2008

Changed Biomechanics of Knee after meniscus injury & effect of meniscus repair on knee Mechanics.

1. Posterior root of Medial meniscus: A vital area for knee
Injuries to posterior root of the medial meniscus are becoming increasingly recognized as a factor that can cause rapidly progressive arthritis.
2. Biomechanical changes after partial or total meniscus removal
Shoemaker SC et al studied the role of the meniscus in the anterior-posterior stability of the loaded anterior cruciate-deficient knee and effects of partial versus total excision on cadaver knee in 1986. The effects of progressive removal of the menisci on the anterior-posterior force-versus-displacement response of the anterior cruciate-deficient knee were studied in fresh cadaver specimens at 20 degrees of flexion without and with tibial-femoral contact force (joint load).
The findings are as follows:
1. In the absence of joint load, removal of the medial meniscus increased total anterior-posterior laxity and subsequent lateral meniscectomy produced an additional 10 per cent increase.
2. When a bucket-handle tear of the medial meniscus was removed, the application of joint load caused the tibia to displace (subluxate) forward on the femur. Subsequent removal of the remainder of the medial meniscus and complete lateral meniscectomy both produced additional smaller anterior tibial subluxations.
3. Changes in total anterior-posterior laxity due to progressive meniscectomy in the loaded knee were dependent on both the amount of applied anterior-posterior force and the level of compressive force.
3. Changes of contact area i.e. load bearing area after meniscectomy
The role of the meniscus in load transmission across the knee has long been a subject of debate. Baratz ME et al examined the biomechanical consequences of the operative treatments for bucket-handle and peripheral meniscal tears.
Contact areas and instantaneous intraarticular pressure distributions were measured in two groups of human cadaver knees.
In Group I, consisting of 4 knees, Baratz ME et al created a bucket-handle tear involving the inner one-third of the meniscus, followed by partial, and then total meniscectomy.
In Group II, consisting of 3 knees, Baratz ME et al created a 2 cm peripheral tear of the posterior meniscal horn, followed by open repair, arthroscopic repair, segmental, and then total meniscectomy.
Knees were tested in an Instron testing machine after each procedure to peak local contact stresses (PLCS) at various knee angulations with calibrated amount of exerted force.
Findings:
1. After partial meniscectomy, contact areas decreased approximately 10% and PLCS increased approximately 65%. After total meniscectomy, contact areas decreased approximately 75%, and PLCS increased approximately 235%.
2. PLCSs and contact areas were found to be the same using either repair technique.
4. Effect of meniscus repair on knee biomechanics:
Injuries to posterior root of the medial meniscus are becoming increasingly recognized as a factor that can cause rapidly progressive arthritis. Allaire R et al reported Biomechanical consequences of a tear of the posterior root of the medial meniscus are similar to total meniscectomy. This study demonstrated significant changes in contact pressure and knee joint kinematics due to a posterior root tear of the medial meniscus. Yet root repair was successful in restoring joint biomechanics to within normal conditions.

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