INDICATIONS OF A PARTIAL KNEE REPLACEMENT

The Indications

Physical Signs

  1. Pain sever enough to justify joint replacement.
  2. Flexion deformity less than 15%.

Intra Operative Signs

  1. Presence of intact ACL.
  2. Satisfactory appearance of the central articular cartilage of the lateral compartment.
 

Radiographic Signs

  1. Full-thickness cartilage loss with estimated bone-on-bone contact in the medial compartment.
  2. Full thickness cartilage preserved in the lateral compartment.
  3. Intact articular surface at the back of the tibial plateau.
  4. Intra-articular versus deformity manually correctable (in 20° flexion).

Common Discussions

a) Age

Old age is not a contraindication as UKA has had a lower morbidity and the recovery is more rapid than with a TKA. If the patient will outlive his prosthesis, a UKA is to be recommended as it is easier to revise than a TKA if the indications are met.

 

b) Activity level

UKA achieve better kinematics than TKA post-operatively and therefore is a less invasive procedure with expeditious rehabilitation.

 

c) Weight

Obese patients are not a contraindication to the use of a UKA. 

d) Patellafemoral osteoarthritis

This is not a contraindication for UKA and the SKAR indicated that only one out of 699 knees required revision due to patellofemoral degeneration.

e) Other indications

As the knee joint fails in one compartment and possibly the other, it is not necessary to implant a total knee prosthesis as the unicompartmental knee replacement can be implanted in the newly failed compartment. This does not mean that the unicompartmental knee replacement initially implanted failed, but that the progression can be addressed with another less invasive procedure.

Contraindications for Partial Replacements

There are many occasions where the surgeon is confronted by patient-specific problems not conforming to any textbook, requiring alternative treatment modalities.(Not everything is discussed or mentioned and specific patients can elect to accept the risks if out of the normal range of indicators). Generalised inflammatory disease in a contraindication which means that the pathological process is not limited to a single compartment. Anatomical contraindications for a mobile unicompartmental knee replacement:

  1. Damaged or absent ligaments (cruciate or collateral)
  2. Varus not correctable
  3. Medial/Lateral subluxation not correctable or stress views
  4. Failure to demonstrate bone on bone wear
  5. Flexion deformity >15°
  6. Flexion room <100°
  7. Lateral wear or defect centrally
  8. Previous valgus high tibial osteotomy

Post operative period

  • Pain control varies according to surgeon’s/anaesthetist’s preference.
  • Blood loss is minimal as a tourniquet is used intra-operatively.

Rehabilitation

  • Range of Motion (ROM) – before leaving the hospital 0°-90°
  • Immediate ambulation.
  • Recovery 6 weeks for good ROM and virtually no pain although it can take longer in individual patients experiencing stiffness, pain and swelling remaining evident in excess of 3 months.

Principles of the Unicompartmental Knee Arthroplasty (UKA)

The mobile and fixed bearing varieties of the UKR has different indications and different wear patterns. It has been proven that the mobile bearing has a longer life span if the indications are met.

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