KNEE Structured oral examination question7: Revision knee replacement

EXAMINER: Have a look at these images and tell me what you can see. (Figure 3.7.)

CANDIDATE: These are AP and lateral radiographs of failed left total knee replacement. The implants appear to be loose with widespread osteolysis and bone loss in the femur and tibia. The tibial base plate is in varus and extended. There is notching of the anterior cortex of femur. There is calcification of soft tissues including the popliteal vessels. I would like to see immediate postoperative and most recent radiographs for comparison. The radiographs are suggestive of infection until proven otherwise.

EXAMINER: Good. You investigate this patient and come up with a diagnosis of aseptic loosening. The patient is keen to consider single-stage revision surgery. What are your concerns with regards to these radiographs?

CANDIDATE: I am concerned about several factors, namely:

   The state of the collateral ligaments ( stability ).

 Soft tissues and vascular status of the limb.  The extensive bone loss.

The collateral ligaments are likely to be dysfunctional and especially the MCL therefore a constrained knee replacement may be required. The soft tissues appear contracted and calcified which may lead to wound complications. The bone loss will require bone graft, augmented or stemmed implants.

EXAMINER: Are you aware of any classification system for bone loss around knee arthroplasty?

CANDIDATE: The most commonly used classification system is that of the Anderson Orthopaedic Research Institute (AORI) which classifies the femur (F) and tibia (T) separately as follows:

Type 1 – Intact metaphyseal bone with minor defects which will not compromise the stability of a revision component.

Type 2 – Damaged metaphyseal bone. Loss of cancellous bone in the metaphyseal segment which will need to be filled with cement, augments or a bone graft at revision in order to restore the joint line. Defects can occur in one femoral condyle or tibial plateau (2A) or in both condyles or plateaux (2B).

Type 3 – Deficient metaphyseal bone. Bone loss which comprises a major portion of either condyle or plateau. These defects are occasionally associated with detachment of the collateral or patellar ligaments and usually require longstemmed revision implants with bone grafts or a custom-made hinged prosthesis.

Engh G. Bone defect classification. In GA Engh, CH Rorabeck (Eds), Revision Total Knee Arthroplasty. Baltimore, MD: Lippincott Williams and Wilkins, 1997 , pp. 63–120.

EXAMINER: You mentioned that a constrained implant may be required. What are the levels of constraints?

CANDIDATE: The constraint ladder within knee implant design includes:

PCL retaining (cruciate retaining or CR). Rotating platform more constrained due to conformity. #

PCL substituting (posterior stabilized or PS).

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Unlinked constrained condylar implant (varus–valgus constrained or VVC) provides anteroposterior and varus– valgus stability (substitute for deficient collaterals), e.g. constrained condylar knee (LCCK, NexGen), TC3.

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Linked, constrained condylar implant (rotating-hinge knee or RHK). Rarely indicated. Used for global instability ( total collateral disruption/recurvatum) and severe distal femoral bone loss, osteolysis/fracture.

EXAMINER: What are the indications of PCL substituting posterior stabilized (PS) implants?

CANDIDATE: Some of the indications of PCL sacrificing implants are:

 Previous patellectomy.  Rheumatoid arthritis.  Post-traumatic osteoarthritis with stiffness.

 Previous HTO and large deformity.  Over-released PCL.

EXAMINER: What are the advantages of PS over CR ( cruciate retaining) design?

CANDIDATE: The advantages are:

 Conforming surfaces allowing roll-back.

 No component slide.

 Provides a degree of VVC.

 The cam–post mechanism improves anterior–posterior stability.

 Facilitates any deformity correction.

 UsesmorecongruentjointsurfacesthanCR,whichreduceswear.

 Better range of motion.

 Technically easier than CR and reproducible.  Higher degree of flexion.

EXAMINER: Are you aware of any current literature regarding performance of PS and CR implants?

CANDIDATE: There are limited studies in the literature comparing the outcomes of the two designs. Most of the studies are characterized by a small number of patients, different outcome measures, poor randomization and comparing designs of different manufacturers. Range of motion appears to be the only common outcome parameter. A meta-analysis by Jacobs et al. showed a difference in range of motion and reproduction angle favouring posterior stabilized designs over PCL retention designs 1 year postoperatively. However, it is uncertain whether this observation is of clinical relevance. It seems that in patients with functional PCL the decision as to which design is chosen depends largely on the favour and training of the surgeon.

Jacobs WC, Clement DJ, Wymenga AB. Retention versus removal of the posterior cruciate ligament in total knee replacement. Act Orth 2005;76(6):757–768.

EXAMINER: (Going back to the radiographs.) What are the principles of management of bone loss in revision knee replacement in this patient?

CANDIDATE: The options of management of the extensive bone loss are:

1. The use of cement, either alone or combined with screws and mesh.
2. The use of bone grafting with structural or morsellized graft.
3. The use of modular augmentation of the components with wedges or blocks of metal. Recent studies show modular porous-coated press-fit metaphyseal sleeves may be used to fill AORI type 2 and 3 defects and provide for stable ingrowth. 4. The utilization of custom-made, tumour or hinge implants.

The method of reconstruction and the materials for revision surgery are largely dependent on the potential for future further revision and the life expectancy, functional demand and comorbidities of the patient. In this patient who is reasonably young restoration of bone stock is preferable, because of likelihood of further revision surgery