Surgical techniques 2022, Dec, 21 | 12:00 am

Revision Total Knee Arthroplasty With Femoral Bone Loss: Metal Augments

 

 

Revision Total Knee Arthroplasty With Femoral Bone Loss: Metal Augments

Gwo-Chin Lee

 

DEFINITION

  • The number of revision TKA procedures performed is projected to increase at an annual rate of 19.3%.8

  • Femoral bone defects are uncommon in primary TKA but are very common in revision knee surgery.

  • Modular femoral augments are useful for moderate-sized bony defects, allowing the surgeon to maximize bone–prosthesis contact while restoring the joint line or posterior condylar offset.

  • Improvements in prosthesis design and biomaterials have increased the usefulness and versatility of metal augments in addressing larger bone defects.

     

     

  • A systematic approach to preoperative planning, intraoperative evaluation, and reconstruction is essential in addressing femoral defects using augments.

    ANATOMY

  • The most common form of bone defect encountered at the time of revision surgery is bone loss from the distal and posterior femur (Table 1).

  • Aside from “filling the defect,” it is important to restore the femorotibial joint line and the posterior condylar offset. Significant alterations in either or both will be detrimental to the function of the prosthesis.

  • The joint line typically lies 25 mm distal to the femoral epicondyles, and the posterior femoral condyles are offset an average of 25.8 mm from the posterior cortex of the femur.2

    PATHOGENESIS

  • In unoperated knees, bone loss on the femoral side can be caused by previous osteochondral defects, avascular necrosis,

     

    Type

    Description

    Illustration

    Reconstruction

    I

    Intact metaphyseal bone. Minor bone

     

    Cement or morselized bone graft

     

    defect not compromising component

     

     

     

    stability.

     

     

     

    Unicondylar: metal augments or femoral head allograft

    Bicondylar: metal augments ± distal

    femoral allograft for bicondylar bone loss

    Deficient metaphyseal bone that compromises a major portion of either condyle, requiring a structural bone graft, hinged implant, or custom component

    III

    Defects <5 mm: cement or bone graft

    Defects >5 mm but <10 mm: metallic augments (distal or posterior) with or without bone grafting

    Damaged metaphyseal bone. Cancellous bone loss necessitating cement fill, augments, or bone graft to restore reasonable joint line level.

    Defects can involve one condyle (IIA) or both condyles (IIB).

    II

    Anderson Orthopedic Research Institute Classification for Femoral Bone Defects

    Table 1

     

     

     

     

     

     

    B

     

    FIG 1 • A. AP radiograph of a knee with severe deformity that has resulted in severe bone loss. B. Massive bone loss was encountered during revision

    A surgery with severe osteolysis.

     

     

    severe valgus or varus deformity, posttraumatic arthritis, and Charcot arthropathy (FIG 1A).

    • During revision surgery, osteolysis secondary to wear debris and bone loss secondary to removal of well-fixed components or a cement mantle are the most common causes of femoral bone defects (FIG 1B).

    • Rarely, earlier trauma resulting in severe angular deformity may require the use of augments for joint reconstruction and restoration of limb alignment.

      NATURAL HISTORY

    • Untreated bone defects in the native knee can lead to progressive joint collapse, ligamentous laxity, and progressive bone loss.

    • Osteolytic lesions caused by wear debris can progress and lead to loss of implant support and eventual component loosening.

    • Intraoperative mismanagement of defects can lead to subop-timal fixation, significant alterations in knee kinematics, instability, and early implant failure.

      PATIENT HISTORY AND PHYSICAL FINDINGS

    • A complete history and physical examination must be performed before any revision knee surgery is undertaken. The details of the index arthroplasty with regard to pain relief and the interval to failure should be recorded. In addition, problems during the postoperative period such as falls or operative wound complications should be probed.

    • Patients with loose femoral components often present with painful TKAs. Pain often occurs at start-up, arising from the seated position, and with stair climbing. These patients often may complain of swelling and effusions within the knees.

    • An AP radiograph of the pelvis and a careful back and hip examination should be performed to rule out coexistent spinal or hip disorder as the cause of the patient’s knee pain.

      IMAGING AND OTHER DIAGNOSTIC STUDIES

    • Plain radiographs of the knee, including standing AP, lateral, and Merchant views of the affected knee, should be reviewed.

 

For patients with deformity, the entire length of the affected bone should be visualized.

  • In revision cases, serial radiographs may help assess the progression of osteolysis, radiolucent lines, and implant migration.

  • CT scans of the knee permit assessment of component rotation and can assess the size and location of osteolysis more ac-curately.4 Recently, MRI also has been shown to be effective in quantifying osteolytic defects.9

  • Blood studies, including a complete blood count with differential, sedimentation rate, and C-reactive protein, should be obtained to rule out infection.

  • Nuclear medicine studies including bone scan (to detect a loose prosthesis) and indium and sulfur colloid scans (to detect the presence of infection) also can be helpful in the preoperative workup.

  • Aspiration should be done when there is any suspicion of infection. The synovial fluid should be evaluated and cultured for the presence of microoorganisms.

    DIFFERENTIAL DIAGNOSIS

  • Infection

  • Arthritis of the hip and spine

  • Flexion instability

  • Patellar maltracking and extensor mechanism dysfunction

  • Tibial component loosening

  • Periprosthetic fractures

    NONOPERATIVE MANAGEMENT

  • Unless the patient has obvious signs of component malposi-tioning, loosening, fracture, or infection, a trial of conservative treatment aimed at strengthening the quadriceps musculature with emphasis on the vastus medialis oblique muscle should be the cornerstone of nonoperative treatment.

  • Patients who have evidence of early osteolysis on plain radiographs but have no clinical symptoms or pain should be encouraged to obtain serial radiographs annually to check for progression of the lesion(s).

  • No consensus has been reached regarding when it is appropriate to revise or perform bone grafting in an asymptomatic knee with radiographic evidence of osteolysis.

 

SURGICAL MANAGEMENT

  • A systematic approach is required to reconstruct bone defects successfully during revision surgery.

    Preoperative Planning

  • Thorough preoperative planning is the key to a successful reconstruction.

  • Review of radiographs and CT scans and careful templating allow anticipation of problems that could be encountered during surgery (FIG 2A,B).

  • Most bone loss can be addressed by the use of metal augments and a long-stem prosthesis (FIG 2C).

  • For larger osteolytic lesions, special wedges, femoral heads, and allografts must be ordered in advance so they are available during reconstruction.

  • In all cases of revision, stemmed and constrained implants (or sometimes a hinged prosthesis) must be considered and must be available.

    Positioning

  • The standard position for patients undergoing revision TKA is supine.

  • Care is taken to drape out a wide surgical field in case a more extensile approach is necessary. A sterile tourniquet applied on the surgical field may be helpful.

    Approach

  • The knee is approached via the standard medial parapatel-lar approach.

  • Protection of the patellar tendon during this phase of the operation is crucial.

  • An extensive synovectomy and débridement of the medial and lateral gutters are critical for decompression of the joint.

  • The patella usually is not everted during revision TKA.

  • In knees with severe ankylosis, techniques such as the quadriceps snip, lateral release, and tibial turbercle osteotomy are helpful for exposure. The surgeon must know the implications of each of these releases and repair or reconstruct them properly at the end of the procedure.

  • The bone defect is addressed by the use of cement (smaller lesions), metal augments, or structural grafts. The critical issues are to restore joint line, achieve appropriate alignment, and attain ligamentous balancing. Reconstruction also aims at restoring a stable platform for positioning and fixation of the components.

     

     

     

     

     

     

     

    C

     

    FIG 2 • A,B. AP and lateral radiographs of the knee before revision surgery. Large osteolytic defects involving both the femur and the tibia are visible. Careful preoperative planning is required to be able to address bone loss encountered at the time of arthroplasty. C. Most cases of knee revision with bone loss can be addressed with the use of a long-stem prosthesis and metal

    A B augments.

     

     

    TECHNIQUES

     

    METAL AUGMENTS

    • Modular metal augments allow for restoration of distal, posterior, and even metaphyseal femoral defects.

    • For most systems, the largest femoral augments allow for restoration of 8 to 10 mm of bone defect. The use of cemented stacked augments for filling defects up to 30 mm has been reported.5

    • Most revision systems have intramedullary systems that allow bone cuts to be made relative to a press-fit intramedullary rod.

    • The distal femoral cut is freshened to provide a stable platform for the new prosthesis.

    • Next, the size of the femoral component is selected. Preoperative templating can give clues to the proper

     

    component size. Traditionally, the femoral component is upsized to better fill the flexion gap (TECH FIG 1A).

    • Determining proper femoral component rotation is critical to a successful reconstruction. The femoral component should be set parallel to the transepicondylar axis of the femur (TECH FIG 1B). Other secondary guides include the proximal tibia and the femoral intercondylar line.

      • Malrotation of the femoral component also can exaggerate the severity of bone loss.

    • The rest of the reconstruction varies according to the revision knee system being used, but should follow a systematic approach. In some systems, the trial components

       

       

       

       

       

       

       

      TECHNIQUES

       

       

       

      TECH FIG 1 • A. Sizing the femoral component is an important part of the revision process. B. Assessing the appropriate rotation using transepicondylar axis and Whiteside’s line. Note the distortion of the posterior condylar line as a result of bone loss. C. Some implants have trials with slots, which allows for more precise sizing and preparation for modular augments. D. Femoral trial

      D with augments and stem in place.

       

      have slots that allow bone cuts to be made for more precise fitting of the modular augment (TECH FIG 1C).

      • A stemmed trial femoral component with the necessary augments is assembled and inserted. Trialing should focus on the overall stability of the knee in extension

        and flexion, and also on patellofemoral tracking (TECH FIG 1D).

    • The definitive prosthesis is assembled and cemented into place in the standard fashion.

       

      BONE CEMENT

      • Indicated for use in small, preferably contained, bony defects up to 5 mm in depth

      • Limitations include its low modulus of elasticity and that it does not restore bone stock

      • Following removal of the existing prosthesis, all surfaces are thoroughly débrided. There is a membrane that often forms between the old bone–cement interface. Areas of bony sclerosis should be débrided to punctate bleeding with the aid of a high-speed burr.

         

    • The femur is prepared with the revision instrumentation specific to the implant system, paying attention to joint line restoration, rotation, and restoration of the posterior condylar offset. The use of stemmed implants allows for distribution of joint stresses and almost always is required in cases of revision surgery with bone loss.

    • The new femoral component is cemented into place separately, and the cement is allowed to harden under direct vision.

       

      MORSELIZED AUTOGRAFT OR ALLOGRAFT

      • Indicated for use in larger contained defects, especially in younger patients. The main advantage of this technique is that it allows for restoration of bone stock.

      • Limitations: cannot be used for uncontained defects, and does not restore a stable platform capable of supporting the prosthesis

      • Using a curette or a high-speed burr, the host bone is débrided to create a favorable environment for graft incorporation.

        • Visible defects are packed with morselized auto- or allograft.

        • A bone tamp may be used to pack the bone chips tightly.

    • Prepare the femur using the revision instrumentation particular to the system being used.

    • Once the femur is prepared, insert a stemmed trial femoral component, with or without wedges, onto the femur.

    • Before final impaction of the trial component, tightly pack the bone chips around the stems and the posterior condyles. Impacting the trial prosthesis into place will effectively shape the new distal femur.

    • The new stemmed femoral component is cemented separately to minimize the chance of component malposition.

       

       

      TECHNIQUES

       

      STRUCTURAL ALLOGRAFTS (FEMORAL HEMICONDYLE)

      • Structural allografts are indicated for large, uncontained defects involving one femoral condyle. The attachments of the collateral ligaments are preserved by a thin shell of bone following removal of the femoral implant.

      • The host bone–allograft interface is prepared as previously described.

      • Gently, using a hemispherical acetabular reamer, the bony defect is reamed to accept a femoral head (TECH FIG 2A).

         

         

         

        Reamer

    • Using the corresponding female resurfacing reamer, a femoral head allograft is reamed to remove all cartilagi-nous debris (TECH FIG 2B).

    • The femoral head is coupled to the bony defect and secured using two threaded Steinmann pins inserted from proximal to distal (TECH FIG 2C).

    • The distal femur then is prepared using the instrumentation particular to the system being used.

    • The femoral head allograft is fixed to the host bone using 4.5-mm short-thread cancellous screws inserted from proximal to distal (TECH FIG 2D).

    • Finally, a stemmed femoral component is cemented into place.

       

      Lateral epicondyle

       

      Tibia

       

      A B

       

       

       

      Femoral head allograft

       

      Medial epicondyle

       

      Steinmann pins

       

      Tibia

       

      Lateral epicondyle

       

      Tibia

       

      C D

      TECH FIG 2 • A. A hemispherical reamer is used to prepare the host surface. B. Using the matching female reamer, the cartilage of the femoral head allograft is denuded to cancellous bone. C. The graft is provisionally fixed using two threaded Steinmann pins. D. The allograft is fixed definitively using two short-thread 4.5-mm cancellous screws from proximal to distal before implantation of the prosthesis.

       

      DISTAL FEMORAL ALLOGRAFT

      • Indicated for massive osteolytic defects involving both distal condyles and distal femoral metaphysis. It allows for restoration of bone stock while preserving the collateral ligament insertions.

      • In cases in which a distal femoral allograft may be required, preoperative sizing of the host femur and the allograft is crucial.

        • Comparing radiographs of the allograft to the host femur (may size against an unoperated side if available) improves fit and decreases the chances of mismatch.

      • The native femur is prepared to accept the allograft by carefully preserving the collateral ligament attachments (TECH FIG 3A).

         

    • The allograft is then shaped to allow for intussusception (bone within bone) into the native femur. It is important to obtain a secure fit of the allograft during this step (TECH FIG 3B).

    • Using traditional distal femoral cutting guides, the femur is prepared to accept a stemmed prosthesis (TECH FIG 3C–E).

    • Demineralized bone matrix is used to line the host–allo-graft interface. This allows the filling of gaps and also provides a barrier against cement intrusion (TECH FIG 3F).

    • A stemmed femoral implant is cemented into place (TECH FIG 3G,H).

       

       

       

       

       

       

       

      TECHNIQUES

       

       

       

       

       

       

       

       

       

       

      TECH FIG 3 • A. Severe bone loss encountered during surgery. Because the collateral ligaments were still intact, use of structural allograft to reconstitute bone was deemed appropriate. B. The allograft is cut to the approximate size needed to fit the defect. C–E. The rest of the cuts are performed using standard instruments to obtain a well-shaped structural graft. The prepared graft is produced to fit the defect exactly. F. Demineralized bone matrix can be used in the interface between allograft and host. G,H. The long stem implant is then cemented over

      G H the allograft.

       

      PEARLS AND PITFALLS

      Preoperative planning

       

      Exposure

       

      Bone loss

      • Comprehensive preoperative evaluation including workup for infection and other causes of knee pain (hip and spine) should be performed in all patients undergoing revision TKA.

      • CT scans of the knee are helpful in assessing component rotation and quantify the degree of bone loss.

      • Preoperative templating is critical for successful reconstruction. Be prepared.

      • Removal of preexisting components is a common cause of bone loss during revision TKA.

      • Careful exposure of the implants with attention to the interface between the posterior phalanges of the prosthesis and the host bone will prevent unnecessary bone loss.

      • Small contained bony defects can be addressed with either cement or morselized bone graft.

      • Metal augments are useful for augmenting distal and posterior femoral defects measuring less than 1 cm and with good structural support.

      • Proper sizing of the femoral component, the use of offset stems, and correct component rotation can minimize smaller defects.

      • Large structural and uncontained femoral defects involving one or both femoral condyles require augmentation with allografts.

       

       

      Reconstruction

       

      Trial components

       

      Fixation

      • The host bone should be thoroughly débrided to optimize the interface between the native bone and the allograft bone or cement.

      • Restoration of the joint line and the posterior condylar offset is crucial to the overall success of the revision process. Failure to restore posterior offset can lead to motion loss.6

      • When using metallic augments, the decision to use distal femoral augments is made early in the procedure. Revision instrumentation will key off these augments for subsequent bone cuts.

      • When using distal femoral allografts, prepare the allograft by first removing the epicondyles and making a provisional cut on the anterior cortex of the allograft. This will allow the allograft to be impacted into the host bone.

      • Whether cementing or press-fitting the stem, the trial femoral component should be assembled using a stem, which confers axial and rotational stability to the femoral trial.

      • Using a marking pen, trace out the anterior phalange of the revision femoral component once a satisfactory trial has been achieved. This will provide a guide to fixation of the definitive prosthesis (FIG 3).

      • An intraoperative radiograph can help assess the overall alignment of the implants and their position in relation to the tibiofemoral joint.

      • Each component should be cemented separately to prevent inadvertent changes in component position.

      • During final impaction of the definitive prosthesis, pay attention to its position in relation to the position of the trial components. Overimpaction of the implants may lead to fracture, loss of fixation of structural bone grafts, and alterations in the flexion and extension gaps.

       

       

       

       

      FIG 3 • Using a marking pen, the trial prosthesis is traced following a satisfactory trial of all the components. This tracing will provide a guide to the depth of seating for the definitive prosthesis.

       

      POSTOPERATIVE CARE

  • Early motion is instituted for most patients using a continuous passive motion (CPM) machine set from 0 to 60 degrees immediately following surgery.

  • For patients who have had extensive procedures, a well-padded Robert Jones dressing is applied following the operation. Immobilization is maintained for 24 to 48 hours.

  • Following revision TKA, patients usually are allowed to bear weight as tolerated on the prosthesis.

  • Alterations of weight-bearing status and limitations on knee flexion generally result from other procedures performed at the time of arthroplasty, such as tibial tubercle osteotomy, quadriceps snip, or V-Y turndown.

    OUTCOMES

  • Overall, the survivorship of revision femoral components using metal wedges with or without structural augments is 79.4% at 8 years.5

  • For knees with small, contained cavitary defects requiring only cement or morselized graft, the 10-year survivorship approaches that of primary knee arthroplasty.6

  • Modular femoral augments used for reconstruction of type

    II defects have an 11-year survival rate of 92%. It is not

    uncommon to see nonprogressive radiolucent lines surrounding metallic augments.9

  • Femoral revisions augmented with structural allografts have a 10-year survival rate of 75%.3

    COMPLICATIONS

  • Traditional complications following revision TKA include infection, wound complications, and loosening.

  • Patellar maltracking and extensor mechanism dysfunction also can occur, especially if there is component malrotation.

  • Knee instability can result from an imbalance in the flexion and extension gaps.

  • Resorption of large structural allografts leading to subsequent implant loosening has been described.

 

REFERENCES

  1. Banks SA, Harman MK, Bellemans J, et al. Making sense of knee arthroplasty kinematics: news you can use. J Bone Joint Surg Am 2003;85A(Suppl 4):64–72.

  2. Bellemans J, Banks S, Victor J, et al. Fluoroscopic analysis of the kinematics of deep flexion in total knee arthroplasty. J Bone Joint Surg Br 2002;84:50–53.

  3. Clatworthy MG, Balance J, Brick GW, et al. The use of structural allograft for unconstrained defects in revision total knee replacement: A minimum 5 year review. J Bone Joint Surg Am 2001;83A:404–411.

  4. Gonzalez MH, Mekhail AO. The failed total knee arthroplasty: Evaluation and etiology. J Am Acad Orthop Surg 2004;12:436–446.

  5. Hockman DE, Ammeen D, Engh GA. Augments and allografts in revision total knee arthroplasty: usage and outcome using one modular revision prosthesis. J Arthroplasty 2005;20:25–41.

  6. McAuley JP, Engh GA, Ammeen DJ. Revision of failed unicompart-mental knee arthroplasty. Clin Orthop Relat Res 2001;392:279–282.

  7. Patel J, Masonis JL, Guerin J, et al. The fate of augments to treat type-2 bone defects in revision knee arthroplasty. J Bone Joint Surg Br 2004;86B:195–199.

  8. Saleh KJ, Rand JA, McQueen DA. Current status of revision total knee replacements: how do we assess results. J Bone Joint Surg Am 2003;85A:18–20.

  9. Vessely MB, Frick MA, Oakes D, et al. Magnetic resonance imaging with metal suppression for evaluation of periprosthetic osteolysis after total knee arthroplasty. J Arthroplasty 2006;21:26–31.

  10. Werle JR, Goodman SB, Imrie SN. Revision total knee arthroplasty using large distal femoral augments for severe metaphyseal bone deficiency: a preliminary study. Orthopedics 2002;25:325–327.