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Total Knee Arthroplasty. 06/06/2006. Dr. Rami Eid. Introduction. TKA is one of the most successful and commonly performed orthopedic surgery. The best results for TKA at 10 – 15 yrs. compare to or surpass the best result of THA. Indications for Knee Arthroplasty. Indications for TKA.
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Total Knee Arthroplasty 06/06/2006 Dr. Rami Eid
Introduction • TKA is one of the most successful and commonly performed orthopedic surgery. • The best results for TKA at 10 – 15 yrs. compare to or surpass the best result of THA.
Indications for TKA • Relieve pain caused by osteoarthritis of the knee (the most common). • Deformity in patients with variable levels of pain: • Flexion contracture > 20 degrees. • Severe varus or valgus laxity.
Osteoarthritis • American College of Rheumatology classification criteria: Knee pain and radiographic osteophytes and at least 1 of the following 3 items: • Age >50 years. • Morning stiffness <=30 minutes in duration. • Crepitus on motion.
Contraindications for TKA • Recent or current knee sepsis. • Remote source of ongoing infection. • Extensor mechanism discontinuity or severe dysfunction. • Painless, well functioning knee arthrodesis. • Poor health or systemic diseases (relative contraindications).
Indications: Younger patients with unicompartmental disease instead of HTO. Elderly thin patient with unicompartmental disease (shorter rehabilitation, greater ROM) Contraindications: Flexion contracture >= 5 degrees. ROM < 90 degrees. Angular deformity >= 15 degrees. Cartilaginous erosion in the weight-bearing area of the opposite compartment. Unicondylar Knee Arthroplasty
Patellar Resurfacing • Indication for leaving the patella unresurfaced: • Congruent patellofemoral tracking. • Normal anatomical patellar shape. • No evidence of crystalline or inflammatory arthropathy. • Lighter patient.
Classification 1 3 1- Cruciate retaining 2- Cruciate substituting 3- Mobile bearing 4- Unicondylar 4 2
Kinematics • The TRIAXIAL motion of the knee: • Articular geometry • Ligamentous restraints
Degrees of Freedom • Constrained Prostheses • Non-constrained Prostheses • Intermediated Prostheses
Constrained Prostheses • Hinged implants. • One degree of freedom.
Non-constrained Prostheses • Ideal implants. • 5 degrees of freedom. • Intact ligamentous system.
Intermediated Prostheses • Anterior-posterior stability. • Two types: • FREEMAN (a cylinder in a non conforming trough). • INSALL (posterior stabilized knee).
Intermediated Prostheses Freeman Insall
Longitudinal Alignment Of Knee • Tibial components are implanted perpendicular to the mechanical axis. • Femoral component is implanted in 5 – 6 degrees of valgus.
Longitudinal Alignment Of Knee • Posterior tibial tilt is about 5 – 7 degrees. • Usually depend on the articular design. Anatomic tilt 5 degrees
Rotational Alignment Of Knee • Create a rectangular flexion space. • External rotation of the femoral component 3 degrees.
PCL retaining prostheses: Better ROM (roll-back, flat tibial surface). More symmetrical gait (stair climbing). Less femoral bone resection is required. PCL needs to be accuracy balanced. PCL substituting prostheses: Easier surgical exposure. See-saw effect prevention. Lower tibial polyethylene contact stress Posterior tibial component displacement. Patella clunk syndrome. PCL-retention or PCL-substitution ?
Patellofemoral Joint • The patella acts to lengthen extensor lever arm. • This arm is greatest at 20 degrees of flexion.
Patellofemoral Joint • Changes in the patellar area of contact can leads to eccentric loading of the patellofemoral joint.
Patellofemoral Joint • Limb with larger Q angle has a greater tendency for lateral subluxation. • Preventing subluxation: • Prosthetic component. • Vastus medialis (in early flexion).
Polyethylene Issues 1- Dished polyethylene avoids the edge loading. (as PCL substitution) 2- Minimal polyethylene thickness >= 8 mm to avoid higher contact stress.
Preoperative Evaluation • Soft tissue defects around the knee. • Vascular status to the limb. • Extensor mechanism. • Preoperative range of motion. • Standing (AP) view, a lateral view of the knee, and a skyline view of the patella.
Surgical Preparation • Administer a dose of a 1st generation cephalosporin (or vancomycin, clindamycin) • Avoid pressure on peripheral nerves.
Surgical Approaches • Medial parapatellar retinacular approach. • Subvastus approach. • Midvastus approach.
Subvastus approach: Intact extensor mechanism. Decreasing pain. More limited. Postoperative hematoma. Midvastus approach: Preserve genicular a. to the patella. Contraindication in limited preoperative flexion. Postoperative hematoma. Surgical Approaches
Surgical Approaches • Lateral parapatellar retinacular approach: • In valgus knees. • Improve patellar tracking and ligamentous balancing.
Bone Preparation – Tibial Resection • The guide is aligned with the anterior tibial tendon and first web space of the toes.
Varus Deformity • 1st Osteophytes must be removed. • 2nd Release the deep MCL. • 3rd Release semimembranosus and pes anserinus insertion. • 4th release posterior capsule and PCL.
Valgus Deformity • 1st Remove all osteophytes. • 2nd release lateral capsule. • 3rd • Lesser deformity: release Iliotibial band. • Greater deformity: release LCL +/- PCL. • Valgus deformity + flexion contracture >> release posterior capsule.
Flexion Contracture • Extension gap < Flexion gap >> more distal femoral bone cut, posterior capsule release. • Flexion gap < Extension gap >> larger tibial insert.