Tuesday 11- 12 Bossone – Office HoursKnee ImplantsBiomechanics – how we exert forces, the moments that we exert from the body and on the body- sport motions, understand and optimize motion to output- artificial organs/joints/automotive crashes/solid to fluid mechanics/tissue engineeringknee joint- femur, tibia, patella – 3 main bones- fibula- not a load baring bone, transfers load from the ankle upward2 main joints- tibio (tibia and femur)/patello (patella and femur) skin / muscle/ joint capsule (hematic seal that holds synovial fluid that lubricates joint area) - all bones are covered by articular cartlidge (3-5 mm) - the bone just under the cartilage is called subcondial bone distal- further away from headproximal – towards your head, closer to headmedial – towards the midlinelateral – outside of the body Knee Stabilizers – - static – stabilizes knee when your not moving - ligament- dynamic – activietly stabilizing knee – muscles- fibular collateral ligament (lateral collateral ligament)- tibular collateral ligament ( medial collateral ligament)ACL – ligament that restrains anterior drop- rupturing an acl you have an unconstrained motion in the knee- also has rotary stabilization - needs to have surgery if completely rupturedknee has six degrees of freedom – ability of a body to move about a given axis any object can have max 6 degrees of freedom (3 axis/lateral and rotational movement on each axis) - more mobility/lose stability - limited mobility – more stability - rotation - extension - abductions- adduction - flexionCommon Conditions that lead to TKR- Osteoarthritis o Primary (idiopathic) – wearing of cartilage over time o Secondary – post traumatic arthritis- Rheumatoid Arthritis o Immune disorder, body attacks itself, autoimmune diseaseIndications for surgery- Bones begin to rub against each other due to cartridge degeneration - bone spurs/exposed bone – form around the joint/ ligaments start to weaken- pain causes people to alter weight (limp) to compensate for the change in structure/pain- this alters the ligaments/muscles strengths and function around the joint – overall weakens the jointMore common than hip OA80% are above the age of 7555+ more likely in women, before its equal chancesMore likely with: Increased age/obesity/gender-female/trauma/infections/ repetitive occupational traumaStages of OA1. pain2. loss of function*usually when implant occurs3. stiffness4. swelling5. deformity – bow legged ness sometimes (genuvadus???) 6. crepitus – creaky noises from knee when moved before an implant, some solutions are- 1st try non pharmacologic solutions: weight loss/physical therapy/knee braces- pharmacologic therapy – glucosamine sulphate/NSAIDS/proteoglycan (absorbs water and cushions)- steroids – FDA limits its to four/year – limits proteoglycan productionArthroscopy – Minimally invasive surgery/go through a port with a tube. The cartridge starts looking like a carpet when it starts to wear out. The tube removes/shaves fuzzy cartilage out and makes it smooth Osteotomy – less popular nowAltered cartilage caused by pain in knee – remove a wedge in the tibia to alter the pressure points on the tibia plateau Knee Replacement Partial and Total depending on current condition of the kneeTHeophilus Gluck – performed the first knee athroplasty Implant designs- UNCONSTRAINEDo Cruciate retaining/sparing – posterior/anterior ligaments o Cruciate substituting (posterior stabilized – PS knee) * most commonly usedo Mobile bearing prosthesis – tibial tray is supposed to move to allow for another degree of freedom – thought more flexibity would allow for more load sharing – not always the caseo Constrained– hinge - the medial side of a knee replacement is larger than the lateral side- screw home mechanism – 20 degrees causes rotational and lateral movement in the joint. The geometry prvides stability to a knee when walking- on a hinge joint – all rotation is occurring on a single axel – uniaxilur 6/27/13Unconstrained TKR design-- 3 parts – tibial tray on surface of tibia/section in femur/plastic inset that slides into tibial tray- Purpose of stem- interacts with stop of femur piece Criteria for Materials used in TKR- - Biocompatible - come up with list of materials that satisfy conditions/choose the best - cement less fixation relies on bone DESIGN PROCESS- prevalence of the issue/how many people are affected/is their a need for a solution- design need- identify list of clinical needs/conditions of problem- come up with criteria to meet that need - make up designs to meet criteria, test designs, final product of design cycleBEST MATERIAL DESING- groove in center of implant allow for tracking/alignment- robotic knee surgery has become more popular- reduces times/minimally invasive/more precise- CT scans generate personalized replacement designs (specific to to each patient)R – radius of curvature1/R = AC *shows how curved something isTKR don’t have the same R all the way aroundUnicentric designs- stationary axis of rotation Polycentric – moving axis of rotation/moves at knee rotates and glidesTechnical goals of Knee Replacements- Restoration of mechanical alignments- Preservations of joint line- Balance ligaments- 1. Coronal Plane- 2. Sagittal Plane- Maintaining or restoring normal Q – angle- Angle of the line of action of force of the quadriceps muscle group-Tendons connect muscle and bone- hip joints- epiphysis/ diaphysis/ metaphysicship replacement failures1. chronic pain2. unequal leg lengthsKNEE JOINT: What are two joints in the knee?Tibial femular jointPatella femular jointWhat is the screw home mechanism in the knee joint?Rotation between the tibia and the femur in the last 20 degress of rotation. It locks in place with the last 20 degrees of motion and allows the knee to move. What are the four static stabilizers of the knee?- ACL, PCL, medial, lateralWhat is the q angle?Angle of line of action of force of the quadriceps and the longitudinal axis of the tibia. 3 types of knee arthroplasty:1. constrained, unconstrained, moving platformunconstrained – posterior stabilized kneetwo bones in the hip joint: pelvis and femurwhat is the pelvis part of the hip joint called?Accetabulum (socket of the the ball and socket joint)Metallic shell- into the hip boneInsert of liner which is polyethelene or ceramicFemoral component of the hip implant is femoral stem that goes into femur. Femoral head –