Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

Featured on Channel NewsAsia

Knee Replacement

Basics
Description
  • Total knee arthroplasty resurfacing of the articular surfaces of the knee with metal and interposed plastic liner is a highly effective treatment for patients with disabling knee arthritis.
  • The components are shaped to conform to the previous joint geometry.
  • Classification is by involved compartment.
    • Medial compartment (tibial femoral)
    • Lateral compartment (tibial femoral)
    • Patellofemoral
Epidemiology
Incidence
  • 61% of total knee replacements occur in females .
  • In 2003, 418,000 surgeries were performed in the United States .
    • The number of knee replacements performed per year continues to rise.
    • Patients had an average age of 67 years at the time of replacement.
Risk Factors
  • Trauma
  • Meniscectomy
  • Obesity
Etiology
  • Osteoarthritis: Often idiopathic
  • Posttraumatic: Athletic injuries, falls, motor vehicle accidents
  • Inflammatory arthritis: Rheumatoid arthritis, pseudogout, or gout
Associated Conditions
  • Many patients have associated hip arthritis.
  • Foot and ankle arthritis with and without severe deformity is common in patients with rheumatoid arthritis.
Diagnosis
Signs and Symptoms
  • Signs:
    • Effusions
    • Medial joint line tenderness
    • Varus (osteoarthritis) or valgus (rheumatoid arthritis)
    • Deformity
    • Limp
  • Symptoms:
    • Pain
    • Start-up pain
    • Swelling
    • Catching
    • Giving way
History
Pain not responsive to medications
 
Physical Exam
  • The knee is examined for signs of osteoarthritis, including:
    • Effusions
    • Joint line tenderness (suggests meniscal disorder)
    • Areas of tenderness
    • ROM
    • Gait disruption
Tests
Lab
  • When infectious causes are considered, the C-reactive protein and ESR are useful tests.
  • Serum uric acid levels are determined if the clinician suspects gouty arthritis.
Imaging
  • Plain radiographs are the 1st step in imaging.
    • Standing AP view of both knees: Can detect subtle loss of the articular cartilage thickness.
    • Lateral view: Can assess for arthritic changes in the patellofemoral joint.
  • MRI can be used to detect meniscal tears, synovial proliferative disorders such as PVNS, and cartilage loss.
Diagnostic Procedures/Surgery
Arthrocentesis is an easy and effective method for screening for septic arthritis and gout or pseudogout.
 
Pathological Findings
  • The common denominator in all forms of arthritis is breakdown of the articular cartilage with loss of the proteoglycan and gradual loss of thickness.
  • As the cartilage thins, the joint deformity increases, and patients often experience the painful sensation of bone rubbing on bone.
Differential Diagnosis
  • Arthritis
  • Infections: Septic arthritis or osteomyelitis
  • Patellofemoral syndrome or patellofemoral instability
  • Meniscal tears
  • Tumors
Treatment
General Measures
  • Patients with knee arthritis first should be treated with nonoperative means, including NSAIDs, pain medicines, ambulatory aids, braces, and intra-articular injections.
  • Patients <50 years old should be considered for realignment surgery or arthroscopy.
  • After failure of nonoperative treatments and an extensive discussion of surgical risks and expectations, the patient may elect to proceed with surgery.
  • Patients are prepared for knee replacement with a careful medical examination.
    • They may consider autologous blood donation.
    • NSAIDs and, if medically safe, blood thinners are halted 6-7 days before the procedure.
Special Therapy
Physical Therapy
  • The focus of this integral component of care after knee replacement is on the following:
    • ROM (attaining 0-110° within 4-8 weeks)
    • Quadriceps strengthening
    • Full weightbearing
Medication
  • After knee reconstruction, adequate narcotic analgesics are necessary to allow patients to participate fully in physical therapy.
  • Most patients do not require long-term analgesics, although intermittent courses of NSAIDs may be used for minor aches and pains about the knee.
Surgery
  • Knee replacement can be partial or total.
    • Partial or unicompartmental replacement:
      • Can be performed through a smaller incision
      • Is indicated if only 1 compartment of the knee has arthritis and the cruciate ligaments are functioning
      • Can be performed for the medial or lateral compartments of the knee
      • Patellofemoral compartment replacement is being developed.
    • Total knee replacement:
      • Is performed through a midline incision over the knee
      • Bony cuts are made with the use of specialized jigs to obtain correct alignment.
      • The components are cemented onto the bone or are press fit (the bone then will grow into the pores).
      • The articular surface of the patella also may be resurfaced.
      • The actual joint articulation is between metal and high-density polyethylene.
  • Two replacement designs are available.
    • In 1 design, the PCL is retained.
    • In the other, the PCL is excised.
      • A peg is built into the polyethylene liner of these knee replacement designs.
  • Computer-assisted surgery is under development.
    • Allows for alignment to be checked precisely intraoperatively
    • May allow for improvements in component placement
  • After surgery, all patients should be treated with low-molecular-weight heparin or Coumadin to prevent DVT.
    • In the hospital, mechanical prophylaxis and early mobilization also should be used.
Follow-up
Disposition
Issues for Referral
Severe pain, swelling, redness, or instability after surgery
 
Prognosis
  • The long-term results of total knee replacement are excellent.
    • ~91% of knee replacements are functioning well at 10 years.
    • At 20 years, 78% are functioning well.
  • Newer prosthetic designs have shown a 96% survival rate at 8-year follow-up.
  • No differences have been found in the results of cruciate-retaining and cruciate-sacrificing total knee designs.
  • 1 study has shown a 95% survival rate for unicompartmental replacement at 10 years, but that arthritic changes slowly continued in the knee.
Complications
  • Infection
  • Aseptic loosening
  • Polyethylene wear and osteolysis
  • Patellofemoral problems:
    • Subluxation
    • Dislocation
  • Periprosthetic fracture:
    • Femoral
    • Tibial
    • Patellar
  • Tendon ruptures:
    • Quadriceps
    • Patellar
  • DVT and pulmonary embolus
  • Medical complications:
    • Heart attack
    • Pneumonia
    • Urinary infection
    • Death
  • Stiffness
  • Numbness around the incision
  • Pain
  • Pes bursitis
Patient Monitoring
  • After surgery, patients are followed at 1-month intervals until they attain a functional ROM, after which they are followed once a year.
  • Plain radiographs are used to monitor the metal and cement interfaces with the bone and to check for polyethylene wear.
Miscellaneous
Codes
ICD9-CM
  • 714.0 Rheumatoid arthritis
  • 7715.96 Osteoarthritis of the knee
Patient Teaching
Early on, patients must perform their ROM exercises rigorously to attain functional ROM and to prevent contractures.
 
Activity
  • To ensure the longevity of the replacement, patients must modify their activities.
  • Activities can be grouped as follows:
    • Good activities:
      • Walking
      • Bicycling
      • Golf
      • Swimming
    • Bad activities:
      • Running
      • Racquetball
      • Heavy lifting
      • Singles tennis
FAQ
Q: How long will a knee replacement last?
A: At the 10-year follow-up, ~91% of total knee replacements are functioning well. At 20 years, this number is reduced to 78%.
 
Q: When should I get a knee replacement?
A: Knee replacement is indicated for patients with severe arthritis of the knee and degenerative changes. Patients must have made extensive attempts at nonoperative treatment and be ready to take the risks of major surgery. Patients also must be ready to change their lifestyle and stop activities (e.g., running) that may lead to failure of the knee replacement.

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