BIOMECHANICS 2010 BIOMECHANICS CHAPTER XVIII KNEE JOINT

KNEE JOINT : STRUCTURE The knee is the lower extremity joint connecting the femur, fibula, patella, and the tibia. Since in humans the knee supports nearly the entire weight of the body, it is the joint most vulnerable both to acute injury and the development of osteoarthritis. Patella  The patella or kneecap is a thick, triangular bone which articulates with the femur and covers and protects the knee joint. It is the largest sesamoid bone in the human body. It is attached to the tendon of the quadriceps femoris muscle, which contracts to extend/straighten the knee. The vastus intermedialis muscle is attached to the base of patella.

KNEE JOINT : STRUCTURE Medial Collateral Ligament [MLC] : - resists forces acting from the outer surface of the knee- valgus forces. Lateral Collateral Ligament [LCL] : - It resists impacts from the inner surface of the knee- varus forces. Anterior Cruciate Ligament [ACL] : - prevents the tibia moving forward. It is most commonly injured in twisting movements. Posterior Cruciate Ligament [PCL] : - This ligament travels from the posterior surface of the tibia to the anterior surface of the femur and in doing so wraps around the ACL.

LOADS ON THE KNEE JOINT Tibial component lossening related to the load imbalance between medial and lateral surface of the tibia varus alignment: load imbalance ↑ à stress ↑ à tibial component loosening on the medial side à wear on the medial side ↑ à need for metal-backing on the tibial component    valgus aligment: wear on the lateral side ↑

LOADS ON THE KNEE JOINT Normal Varus deformity Adduction moment increase → Load asymmetry → Need for the proper limb alignment for TKR

LOADS ON THE KNEE JOINT Medial & Lateral load distribution Load imbalnce ↑ à Stress ↑ à Tibial component lossening on the medial side à Wear on the medial side ↑   Need for TKR(Total Knee joint Replacement) on the tibial component

TOTAL KNEE JOINT REPLACEMENT [TKR] Total Knee replacement is a surgery to replace worn or damaged parts of the knee joint. The surface of the diseased joint are removed and replaced with an artificial joint. This surgery can relieve pain and improve movement in knee joint.   May need a total knee replacement if; ○ Other treatments such as medicine, steroid injections and physical therapy, no longer stop knee pain or help movement of the joint. ○ The pain or poor movement in knee prevents you from doing your normal activities.

TKR Normal Knee Joint A Worn Knee Joint Knee is a hinge joint where the end of the thigh bone (femur) meets the top of the large bone in lower leg (tibia). A healthy knee has smooth cartilage that covers the ends of the bones. The two bones glide smoothly as you bend your knee. The muscle and ligaments around the knee joint support your weight and help move the joint smoothly when you walk. The smooth cartilage layers can wear down on the ends of the bones. The cartilage can wear down as you age or from injury, arthritis, or a side effect from certain medicines. When the bone surface and cartilage wear down, they become rough, like sandpaper. As you move your leg, the bones grind and you have pain and stiffness.

TKR

ARTIFICIAL KNEE JOINT 2. Tibial component: 1.Femoral component: The metal femoral component curves around the end of the thighbone and has an interior groove so the kneecap can move up and down smoothly against the bone as the knee bends and straightens 2. Tibial component: The tibial component is a flat metal platform with a polyethylene cushion. The cushion may be part of the platform (fixed) or separate (mobile) with either a flat surface (PCL-retaining) or a raised, sloping surface (PCL-substituting). 3. Patellar component:   The patellar component is a dome-shaped piece of polyethylene that duplicates the shape of the kneecap anchored to a flat metal plate.