RECONSTRUCTION 2023, Jan, 08 | 12:00 am

Revision of Failed Unicompartmental Knee Arthroplasty

P ITFALLS

  • As in revision total knee arthroplasty (TKA), the etiology of failure of the primary procedure must be identified to ensure the successful outcome of the revision (Knight et al., 1997).

 

Revision of Failed UKA

 

Indications

  • Symptomatic failure of the index UKA due to polyethylene wear, component loosening, persistent pain, and sepsis

  • Symptomatic progression of osteoarthritis in an un-resurfaced compartment

    Examination/Imaging

    Controversies

    • The role of revision to another UKA is controversial. Theoretical indications could include early component loosening without bone loss, or late isolated polyethylene insert exchange for wear in an otherwise well-functioning knee.

    • Exact indications for the use of augments, grafts, or stemmed components are subjective.

     

  • The knee must be evaluated methodically to determine the cause(s) of failure of the UKA as in revision of a TKA.

  • Plain radiographs should include anteroposterior (Fig. 1A), lateral (Fig. 1B), and “sunrise” views of the knee and standing hip-to-ankle films of the lower extremity (Fig. 2A).

    Treatment Options

    • Isolated polyethylene insert exchange may be considered for late wear of a well-fixed and positioned modular UKA. The implant should have a good track record, the new insert should be of high-quality polyethylene, and the opposite compartment cartilage should be in good condition.

    • Revision to another UKA may be considered if the cause for failure is identified and can be corrected with another UKA. Thus the indications for the initial UKA must still be present.

    • If there is any concern regarding the appropriateness of a lesser procedure, conversion to TKA should be performed.

     

  • To predict the components and techniques that may be needed, the anticipated line of resection below the level of the implant and medial defect is drawn perpendicular to the mechanical axis of the tibia (see Fig. 2A). In Figure 2B, “A” is the distance from the lateral plateau to the line drawn perpendicular to the mechanical axis from the medial bone defect.

 

 

84°

 

90°

 

 

A B

FIGURE 1

 

291

 

 

 

 

 

Revision of Failed UKA

 

6°

 

84°

 

A

90°

 

 

A = distance from lateral plateau to the line drawing perpendicular to mechanical axis from the medial bone defect

 

A B

FIGURE 2

 

  • Regardless of the cause of failure, a revision to a TKA has a more predictable outcome than revision to another UKA. The re-revision rate after revision to another UKA is three times higher than that after revision to TKA (Lewold et al., 1998).

  • If a primary UKA is revised to a TKA, the risk of re-revision is not higher compared to the risk of revision of primary TKA (Lidgren et al., 2005).

 

  • If the distance is less than 10 mm from the tibial joint line of the unaffected compartment, then standard bone resections and components will likely suffice.

  • If the defect is 10–15 mm, the surgeon can choose among metal, bone graft, or cement to reconstruct the deficiency.

  • For large defects (15 mm), a metal augment or structural bone graft will likely be needed (Springer et al., 2006).

 

292

 

Revision of Failed UKA

 

Surgical Anatomy

  • As in all knee arthroplasty surgery, the medial collateral ligament (MCL) should be protected with a blunt curved Hohmann retractor during tibial and femoral component removal and bone resections.

  • All principles of revision knee arthroplasty surgery apply.

     

    P EARLS

    • Subcutaneous tissue should be meticulously dissected down to the fascia layer to preserve blood supply.

       

    • The medial and posteromedial tibia should be dissected carefully from the overlying soft tissue to protect the MCL while allowing forward subluxation.

       

      P ITFALLS

    • Damage to the extensor mechanism, MCL, or remaining proximal tibia can occur from overly aggressive efforts at exposure and component removal.

     

  • A unique aspect of revision UKA surgery is the challenge of determining optimum femoral rotation in the presence of the deficient posterior medial (or lateral) condyle.

  • Whiteside’s line and the transepicondylar axis are good methods to set femoral rotation since the posterior condylar axis is distorted by bone loss.

    Positioning

  • Supine position with tourniquet use as in TKA.

    Portals/Exposures

  • The usual principles of revision knee surgery exposure apply.

  • A medial parapatellar arthrotomy is most commonly used. Skin incisions should incorporate previous incisions, and, if multiple, the most lateral incision takes priority, extended proximally or distally as required.

     

    P EARLS

    • Cement in the lug hole can be removed with a curved curette or pencil-tipped high-speed burr.

       

    • All-polyethylene tibial components can be removed by cutting the cement-implant interface and then addressing the polyethylene peg and cement.

       

      P ITFALLS

    • The interface between the posterior flange of the femoral component and cement on the posterior condyle of the femur can be difficult to access, but should be carefully addressed to avoid the risk of fracture of the condyle (see Fig. 5).

     

    Procedure

    Step 1: Removal of UKA Components

  • The principles of component removal are identical to

    those of revision TKA, with the priorities being minimizing bone loss and protecting the surrounding soft tissue envelope.

    • Exposure to the knee is obtained (Fig. 3A), and the polyethylene insert is removed (Fig. 3B).

    • The interface between prosthesis and cement should be clearly identified.

  • A thin-blade oscillating saw or flexible osteotome can be used to disrupt the interface between the implant and the bone cement (Fig. 4).

  • A straight osteotome can be used to disrupt the prosthesis-cement interface at the posterior part of the femoral condyle (Fig. 5).

  • The femoral and tibial components should be removed with minimal force to avoid damage to the underlying bone. Figure 6 shows the bone defect after UKA component removal.

 

 

 

293

 

Revision of Failed UKA

 

A B

 

 

FIGURE 3

 

FIGURE 4

 

 

 

FIGURE 5 FIGURE 6

 

 

 

 

 

 

Whitesides’s line

 

Medial epicondyle

 

Bone defect

 

Lateral epicondyle

 

 

A

FIGURE 7

Trans-epicondylar axis

 

Revision of Failed UKA

 

B

Posterior condylar axis

 

294

 

 

P EARLS

  • Whiteside’s line, the transepicondylar axis, and the tibial bone cut can be used to determine the femoral component rotation in the presence of posterior bone deficiency (Fig. 7A and 7B).

     

  • The distal femoral bone cut is straightforward using standard instruments at the desired depth and degree of valgus orientation. Distal femoral augmentation is rarely required.

     

  • The tibial bone cut should be measured approximately 10 mm from the lateral plateau. The tibial bone resection should be at 90° to the anatomic axis, with the desired degree of posterior slope.

     

  • Avoid excessively deep tibial resection (below the level of the fibular head) with the use of augments or grafts as indicated.

     

  • A bed of healthy, nonsclerotic bone is needed for stable cement fixation.

 

Step 2: Femoral and Tibial Bone Preparation

  • Depth of bone resections should be referenced from

    the intact condyle or plateau. The orientation and depth of femoral and tibial resections should be as in primary TKA.

  • The retention or substitution of the posterior cruciate ligament is dependent on the surgeon’s preference.

  • Flexion and extension gap balancing is done by spacer or trial components, again following standard techniques of knee arthroplasty.

    Step 3: Revision Grafting

  • Assess the bone defect(s) to determine the need for bone graft, metal augments, or stemmed implants.

    • If the defect is contained, autogenous bone graft

      can be packed into the defect.

    • For larger uncontained defects, options include the use of the resected intact tibial plateau as an autograft, metal wedge or step augments, or, for severe deficiencies, a structural allograft.

  • In the revision of more contemporary designs of UKA, the revision procedures were straightforward and the bone deficiencies were not challenging (Levine et al., 1996; McAuley et al., 2001). Figure 8A and 8B shows a minimal bone defect (arrow) on the femoral condyle after anteroposterior bone cuts were done.

 

 

 

 

 

 

Minimal bone defect on femoral condyle after antero-posterior bone cuts were done

 

Revision of Failed UKA

 

A B

FIGURE 8

 

295

 

 

P ITFALLS

  • There is a tendency to try to avoid the need for medial reconstruction by an overly deep or varus tibial cut. Alignment and bone preservation must be priorities.

 

  • A modular stem can be used when reconstructing large defects to bypass the defect as a load-sharing device (Fig. 9). If the bone defect is large (15 mm from the lateral plateau), metal augments and stems may be used.

 

Controversies

  • The relative indications for the various techniques of reconstruction of the medial tibial deficiency (autograft, allograft, cement, or metal augments) are subjective.

 

 

FIGURE 9

 

 

P EARLS

  • The femoral bone defects are easily addressed and rarely need stemmed implants or formal augmentation.

     

    P ITFALLS

  • Excessive tibial resection (15 mm or below the fibular head) in an attempt to simplify the procedure may actually complicate it.

     

  • Tibial dimensions diminish rapidly with deeper resection, making size-matching the femoral component challenging and producing the potential need for a thicker polyethylene insert than may be available.

 

 

 

296

 

Instrumentation/ Implantation

  • Revision instruments and implants must always be available to deal with planned or unanticipated deficiencies.

 

Revision of Failed UKA

 

Step 4: Trial Component Insertion

  • The trial components should be put in to confirm flexion and extension gap balance and patellar tracking (Fig. 10A), after which the final components are inserted (Fig. 10B).

  • Bone surfaces must be meticulously prepared for cementation as in any primary or revision TKA.

    Postoperative Care and Expected Outcomes

  • The postoperative protocol for rehabilitation should be similar to that for a primary TKA.

 

 

 

A B

FIGURE 10