Porous Tantalum for Patellar Reconstruction in Revision Total Knee Arthroplasty

P ITFALLS

• Not recommended in patients who have or are suspected to have an active infection of the knee.

   

• Not indicated in patients who have very poor peripatellar blood supply that may inhibit healing of the porous tantalum patellar shell.

 

Porous Tantalum for Patellar Reconstruction

 

Indications

• Patients noted to have a loose or absent patellar component at or prior to revision of a failed knee replacement procedure in whom marked patellar bone loss precludes use of a cemented total knee arthroplasty (TKA).

  Examination/Imaging

  Controversies

  • There are no data confirming long-term fixation using a porous tantalum patella in TKA (Nelson et al., 2003).

   

• Although there are no specific examination maneuvers or tests to evaluate the extent of patellar bone loss in patients who have undergone previous TKA, the examination includes the standard evaluation of the knee, including range of motion, ligamentous stability testing, and patellar tracking, which can be evaluated throughout the range

  of motion.

  Treatment Options

  • Patellectomy is an option in cases of severe patellar bone loss. However, outcomes after revision TKA in which a patellectomy is performed have been shown to be poor (Nelson et al., 2003; Parvizi et al., 2002).

  • Patelloplasty, which involves removal of the patellar button and leaving the patellar bone stock without resurfacing, leads to inferior results compared to revision of the patella (Barrack et al., 1998).

  • Bone grafting of the remaining patellar shell may be done using the technique described by Hanssen (2001).

   

• The decision regarding a tantalum shell and evaluation of patellar bone loss will ultimately be made intraoperatively at the time of revision surgery; however, preoperative radiographs will help determine the extent of patellar osteolysis.

  • Plain radiographs should be taken in anteroposterior, lateral, and Merchant’s views.

  • The extent of patellar osteolysis is best appreciated on the lateral (Fig. 1*) and Merchant’s views.

  • Preoperative radiographs will also reveal any additional surgical concerns. The preoperative lateral radiograph in Figure 2 demonstrates a periprosthetic patella fracture.

• Computed tomography scanning is valuable in assessing femoral and tibial osteolysis where component artefact is more likely to obscure the extent of bone loss.

  Surgical Anatomy

• The patella is the largest sesamoid bone in the body and lies within the extensor mechanism of the

  knee joint.

  • The average thickness of the patella is 23 mm in females and 26 mm in males.

  • Restoration of the patellar thickness is important for normal extensor mechanism function.

     

    *Figure 1 from Nelson CL, Lonner JH, Lahiji A, et al. Use of a trabecular metal patella for marked patella bone loss during revision total knee arthroplasty. J Arthroplasty. 2003;18(Suppl 1):37-41.

     

     

     

     

     

    Porous Tantalum for Patellar Reconstruction

     

     

     

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    FIGURE 1

     

    FIGURE 2

     

     

• The patella increases the functional lever arm of the quadriceps muscle by transmitting the forces across the knee joint at a greater distance from the axis of rotation.

• The patella is anchored and stabilized over the anterior aspect of the knee by the quadriceps and patellar tendons in the proximal-distal axis and by the medial and lateral retinacula in the medial-lateral axis. Figure 3 illustrates the force vectors acting on the patella from the extensor mechanism as well as the lateral and medial retinacula.

• The patellar blood supply is provided by the geniculate arteries, which form an anastomotic ring around the patella (Scapinelli, 1967). This ring lies less than 1 cm from the peripheral border of the patella.

  • Lateral retinacular release, when necessary, should be performed 1–2 cm away from the lateral patellar border.

     

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    P EARLS

    • We use two paint rollers secured to the table such that the proximal one will hold the knee hyperflexed, and the second is placed more distally such that the knee can be held at approximately 90° of flexion during the procedure.

       

    • A 3-L saline bag or a roll of surgical towels may be placed under the operative-side buttock to give a gentle tilt to the pelvis. This produces slight internal rotation of the operative leg and makes the resting position of the leg more natural for the procedure.

     

     

     

    Porous Tantalum for Patellar Reconstruction

     

    Quadriceps

     

     

    Lateral retinaculum, vastus lateralis, and

    iliotibial tract

     

    Equipment

    • Leg positioning devices exist to hold the knee in varying degrees of flexion that can be utilized depending on surgeon preference.

     

    FIGURE 3

     

    Medial retinaculum and vastus medialis

     

    Patellar tendon

     

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    Porous Tantalum for Patellar Reconstruction

     

    Positioning

    • Position the patient supine on the operating table.

    • Place a tourniquet on the proximal thigh of the operative leg.

    • Use a leg positioner or “paint roller” secured to the operating table to hold the knee in flexion during the procedure.

       

      P EARLS

      • We leave a 2- to 5-mm rim of retinaculum attached to the patella as we curve our arthrotomy incision around the medial aspect of the patella. This helps to give a more anatomic closure.

         

      • We mark the quadriceps tendon with methylene blue on both sides of the arthrotomy to assure an anatomic repair.

         

      • The repair should be performed with the same degree of knee flexion as was present during the original arthrotomy.

         

        P ITFALLS

      • In multiple revision situations where there are previous incisions over the front of the knee, the lateral-most skin incision should be utilized to preserve the blood supply to the skin, which travels from medial to lateral anteriorly.

       

      Portals/Exposures

    • There are several standard approaches to the knee for purposes of reconstruction and revision (medial parapatellar, lateral parapatellar, subvastas, midvastus).

      • The medial parapatellar approach is our preferred approach for revision surgery.

      • This approach is extensile and can be modified using a quadriceps snip, tibial tubercle osteotomy, or quadriceps turndown to optimize exposure.

    • In the case of revision TKA, the previous skin incision is most often used to prevent skin necrosis that may be caused by a separate incision that creates a skin bridge between the new and any previous incisions.

      • When there is more than one prior incision, it is generally recommended that the most lateral longitudinal incision that allows satisfactory

        exposure be used.

         

    • The remainder of the approach is dictated by surgeon preference.

      • We use a medial parapatellar incision into the knee in primary and revision cases, as it provides a safe and extensile approach to the knee joint.

        Instrumentation

        • Use two sharp towel clips, one proximally at the superior pole placed through the quadriceps tendon, and one at the inferior pole through the patellar tendon, to stabilize the patella during the procedure.

         

      • For revision TKA, we start by making a long midline anterior skin incision that begins approximately 4 cm proximal to the superior pole of the patella and is taken distally to 4 cm below the inferior pole.

      • We make our deep incision in line with the quadriceps tendon fibers proximally and carry it around the medial aspect of the patella, then extend it distally parallel to the patellar tendon. We leave a 2- to 5-mm cuff of tissue around the patella for later repair.

    • At the time of patellar revision, the patella along with the extensor mechanism is everted to expose the backside of the patella.

    • This is most easily done with the knee in full extension as it takes the tension off the extensor mechanism.

       

       

      P EARLS

      • We recommend erring toward using a larger diameter porous tantalum shell. This may decrease the risk of insetting the shell and creating a stress riser at the inferior or superior pole, which may lead to avulsion fractures.

         

      • We recommend deflating the tourniquet to confirm punctate patellar bleeding prior to implantation of the shell.

         

      • We recommend fixation with #2 FiberWire sutures in conjunction with a drill and straight Keith needles to facilitate passage of sutures.

         

        P ITFALLS

      • Excessive reaming of the patella compromises the strength of the remaining shell with creation of stress risers at the superior and/ or inferior poles.

       

      Procedure

      Step 1

      • Once adequate exposure of the knee is achieved and the patellar component is exposed via eversion of the extensor mechanism, the previous implant is removed.

  • In cases of severe bone loss, the patellar button is usually loose and is easily removed.

  • If this is not the case, then the button may be sawed off at the level of the pegs using a reciprocating saw. The remaining pegs and cement can be ground out from the patella using a high-speed burr.

  • In the case of a well-fixed, cementless patellar component with osteolysis, removal may require sectioning of the metal baseplate with a

    metal-cutting burr or a diamond wheel.

    • At this point, the remaining rim of patellar bone must be reamed using an appropriately sized spherical reamer that corresponds to the radius of the porous tantalum shell to be implanted

    (Fig. 4A† and 4B).

     

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    Porous Tantalum for Patellar Reconstruction

     

    †Figures 4A, 5, and 6A from Nasser S, Poggie RA. Revision and salvage patellar arthroplasty using a porous tantalum implant. J Arthroplasty. 2004;19:562-71.

     

     

     

    A B

    FIGURE 4

     

    Instrumentation/Implantation

    • Depending on the implant manufacturer, there may be more than one diameter of porous tantalum shell available, as well as different thickness options.

    • Selection of the shell diameter should be based on remaining patellar bone stock (erring to the larger diameter shell).

    • Thickness of the component should be chosen such that

    the component most closely replicates the normal thickness of the patella (26 mm in males and 23 mm in females), unless the thickness of the contralateral native patella is known.

     

     

     

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    P EARLS

    • When suturing down the shell via the peripherally placed holes, use a crossing star pattern to ensure even tensioning of the implant to the underlying soft tissues.

     

    Porous Tantalum for Patellar Reconstruction

     

    Step 2

    • Next, trial the component by tying down the shell using several sutures to the surrounding soft tissues.

    • Check the tracking of the implant to ensure good alignment within the femoral trochlea.

      Instrumentation/ Implantation

      • Use a small (1.6- or 2.0-mm) drill to facilitate passage of the sutures through the remaining patellar bone.

      • Use straight Keith needles to pass sutures through drill holes and soft tissues.

       

    • Once the desired positioning is achieved, place #2 or #5 nonabsorbable braided sutures through the peripheral holes provided on the porous tantalum shell and into the quadriceps tendon and remaining patellar bone.

      • Figure 5 shows the porous tantalum shell with the peripheral holes numbered in a crossing star pattern to depict the order in which the sutures should be tied down.

         

         

         

        FIGURE 5

         

         

         

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        Porous Tantalum for Patellar Reconstruction

         

        A

         

         

         

         

        P EARLS

        • After the bearing surface has been cemented into the porous tantalum shell, check the patellar tracking.

           

        • Use either a lateral retinacular release or medial retinacular reefing to optimize tracking of the patellar component.

         

        B

        FIGURE 6

         

  • Figure 6A shows the sutures being placed through the peripheral holes on the porous tantalum shell and through the patella and quadriceps tendon.

  • Figure 6B shows the porous tantalum shell after suture placement.

     

     

     

    FIGURE 7

     

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    Porous Tantalum for Patellar Reconstruction

     

    Step 3

    • The porous tantalum shell is manufactured to accept the standard three-prong all-polyethylene bearing surface.

    • The polyethylene bearing surface corresponding to the femoral component of the revision hardware should be utilized whenever possible.

    • Cement the polyethylene bearing surface into the porous tantalum shell using standard cementation and compression techniques. Figure 7 shows the porous tantalum shell and polyethylene bearing surface after completion of fixation to the remaining patellar bone and extensor mechanism.

      Step 4

    • Irrigate the knee and the finished components thoroughly using a pulse lavage device.

    • Close the arthrotomy with heavy Vicryl sutures in an interrupted fashion.

    • The skin and subcutaneous tissues are closed using Vicryl and staples.

    • A drain may be used at the surgeon’s preference.

     

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    P ITFALLS

    • Early outcome studies have shown a potential increased risk of patellar avulsion fractures at the superior or inferior pole, which may require additional revision surgery.

     

    Porous Tantalum for Patellar Reconstruction

     

    Postoperative Care and Expected Outcomes

    • Asandard physical therapy regimen as would be instituted after primary TKA is recommended.

  • Include continuous passive motion machines immediately postoperatively, range-of-motion exercises, gait training, and conditioning exercises.

• The dressings are removed on the second postoperative day, and the staples are removed 2 weeks after surgery.

 

 

 

A B

 

 

 

C FIGURE 8A

 

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Controversies

• There may be a role for a protected physical therapy regimen postoperatively, which avoids active-resisted knee extension exercises to potentially decrease the occurrence of patellar avulsion fractures.

 

Porous Tantalum for Patellar Reconstruction

 

• Follow-up radiographs are used to assess component stability, fixation, tracking, and alignment.

• Anteroposterior (Fig. 8A), lateral (Fig. 8B), and Merchant’s view (Fig. 8C) radiographs are recommended postoperatively, between 4 and 12 weeks after surgery, and then based upon surgeon preference.

• We perform radiographs immediately postoperatively, at 6 weeks, 6 months, and 1 year, and then biennially.