Total Knee Arthroplasty Dr. Rami Eid 06/06/2006

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 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).

Unicondylar Knee Arthroplasty 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.

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

Classification 1 3 1- Cruciate retaining 2- Cruciate substituting 3- Mobile bearing 4- Unicondylar 2 4

Biomechanics of Knee Arthroplasty

Kinematics The TRIAXIAL motion of the knee: Articular geometry Ligamentous restraints

Degrees of Freedom

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.

Role of PCL – Femoral Roll-Back

Role of PCL – Femoral Roll-Back

PCL-retention or PCL-substitution ? 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 ?

PCL-retention or PCL-substitution ?

Patella Clunk Syndrome

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.

Surgical Technique for Primary TKA

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.

Surgical Approaches Subvastus approach: Midvastus 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 Lateral parapatellar retinacular approach: In valgus knees. Improve patellar tracking and ligamentous balancing.

Bone Preparation – IM Femoral Guide

Bone Preparation – Gap Technique

Bone Preparation – Tibial Resection The guide is aligned with the anterior tibial tendon and first web space of the toes.

Balancing of The Knee

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.

Varus Deformity

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.

Valgus Deformity

Flexion Contracture Extension gap < Flexion gap >> more distal femoral bone cut, posterior capsule release. Flexion gap < Extension gap >> larger tibial insert.

Flexion – Extension Balancing

Computer Assisted Surgery in Total Knee Arthroplasty

Management of Bone Deficiency

Patellofemoral Tracking Internal rotation of tibial component increases the tendency to lateral patellar subluxation. Prosthetic patella should be medially positioned.

Postoperative Management

Roentgenographic Evaluation

Total knee replacement exercise protocol Postoperative day 1 Bedside exercises (e.g. ankle pumps, quadriceps exercises…) Postoperative day 2 Exercises for active ROM and terminal knee extension Gait training with assistive device Postoperative day 3-5 Progression of ambulation on level surfaces and stairs (if applicable) Postoperative day 5 to 4 weeks Stretching of quadriceps and hamstring muscles Progression of ambulation distance

Specific Disorders

Previous HTO Difficult surgical exposure. Lateral ligamentous laxity. Difficult stem placement. Patella infera.

Previous Patellectomy PCL retaining arthroplasty for better results.

Complications of Total Knee Arthroplasty Thromboembolism. Infection. Neurovascular complications. Patellofemoral complications. Periprosthetic fractures.

Patellofemoral Complications Patella clunk syndrome. Patellar component failure. Rupture of patellar ligament.

Periprosthetic Fractures

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