RECONSTRUCTION 2023, Jan, 08 | 12:00 am

Monoblock Total Knee Arthroplasty*

P ITFALLS

  • Relative contraindications relate to the difficulty in obtaining exposure for tibial insertion:

     

    • Preoperative valgus deformities greater than 20°, particularly with associated stiffness

       

    • Patella baja, in which tibial exposure is difficult

       

    • Obese and well-muscled patients, who may also provide some difficulty at the time of tibial insertion

       

  • Cases with significant preoperative ligamentous laxity in which a constrained prosthesis may be required may be better treated with modular components.

     

  • Limited sizes and polyethylene thicknesses exist with some monoblock tibial systems.

     

  • “Mini”-approaches can make exposure and insertion of a monoblock tibial component more difficult.

 

Monoblock TKA

 

Indications

  • Monoblock tibial components are suitable for use in almost all patients with degenerative joint disease requiring total knee arthroplasty (TKA).

  • Cemented monoblock components remain the “gold standard.”

    • When using an uncemented component, proximal tibial bone quality must be adequate for press-fit impaction and stable ingrowth.

    • In cases with poor quality bone, a cemented technique should be used.

      Examination/Imaging

  • A standard knee-focused musculoskeletal physical examination is required.

  • Rule out any of the previously mentioned relative contraindications to monoblock use.

  • Plain radiographs

    • A standard weight-bearing knee series with anteroposterior (AP), 45° posteroanterior, lateral, and sunrise (Merchant’s) patellar views are required.

    • A full-length standing view is of benefit when significant deformity exists.

      Surgical Anatomy

      Controversies

      • Though indications for modular tibial exchange are limited, this option does not exist for monoblock tibias, and thus the entire tibial component must be removed and revised.

      • All tibial monoblock components are not the same:

        • Extensive long-term experience exists with traditional all-polyethylene and metal-backed monoblock components.

        • Limited short-term clinical studies have been performed to support the use of current porous metal implants.

       

  • Adequate exposure to the proximal tibia is essential in this procedure.

  • Medial soft tissue structures are released in a full-thickness subperiosteal manner, including the deep medial collateral ligament (MCL) and semimembranosus, which allows the tibia to be subluxed forward.

    Positioning

  • Patient is placed supine on the operating table.

  • A tourniquet is placed high on the affected thigh (Fig. 1).

     

     

     

    187

     

     

    P EARLS

    • A bolster can be placed to aid with foot stability at 90° of flexion (see Fig. 1).

       

      P ITFALLS

    • Ensure that knee flexion is not limited by the drapes or positioning, as this will compromise the exposure required for implantation.

     

    Monoblock TKA

     

    FIGURE 1

    Portals/Exposures

    • An anterior midline incision is made (Fig. 2).

    • A mini-medial parapatellar approach (Fig. 3) is used. Aspects of this approach include:

    Equipment

    • A large sandbag or horizontal bolster is fixed to the table and supports the foot at 90° of flexion.

     

    • Removal of a portion of the retropatellar fat pad and release of the lateral patellofemoral ligaments

    • Subperiosteal dissection of medial soft tissue structures

    • Release of the semimembranosus

    • Cruciate ligament release

       

       

       

      FIGURE 2 FIGURE 3

       

       

       

      188

       

       

      P EARLS

      • Release of posteromedial structures allows the tibia to be subluxed anteriorly without compromising the medial stability of the knee.

         

        P ITFALLS

      • Failure to obtain adequate exposure can result in malposition, malalignment, or failure to fully seat the tibial component.

       

      Monoblock TKA

       

      FIGURE 4

      Controversies

      • Alternative mini-approaches can be used, including quad-sparing, midvastus, or subvastus approaches, but in all cases adequate exposure for tibial implantation is required.

       

      • Rotational subluxation of the knee is achieved, with the tibia anterior and externally rotated with respect to the femur. The knee is flexed with medial soft tissue stripping, including the semimembranosus, for exposure and bent Hohmann retractor in place (Fig. 4).

      • The semimembranosus and capsule are further released from the posteromedial tibia.

         

        P EARLS

        • When addressing a varus knee, releases are performed prior to bone cuts.

           

        • In valgus knees, bone cuts are performed prior to lateral soft tissue releases, which aids with exposure to the lateral compartment.

           

          P ITFALLS

        • Failure to protect the collateral ligaments, popliteus tendon, and patellar tendon during bone cuts

         

        Procedure

        Step 1

      • Following exposure, the tibial cut is made at 90° to

        the anatomic axis using an extramedullary tibial cutting guide (Fig. 5). The MCL and patellar tendon are protected.

      • Standard femoral and patellar cuts are made, which aid in relaxing the soft tissues for improved tibial exposure.

      • Remaining meniscal tissue is excised.

      • Varus-valgus balancing is performed and may require appropriate soft tissue releases.

      • A spacer block is inserted in flexion followed by extension, confirming symmetric soft tissue tension with rectangular and equal flexion and extension gaps.

      • Alignment rods are used to verify that a neutral mechanical axis has been achieved.

         

        189

         

         

         

        Monoblock TKA

         

        FIGURE 5

         

         

        P EARLS

        • Multiple landmarks are used to achieve appropriate tibial rotation, including:

           

          • Junction of the medial and middle thirds of the patellar tendon

          • Tibial crest

          • Center of the ankle joint

             

            P ITFALLS

        • Inadequate exposure, particularly in the posterolateral corner, may lead to internal rotation during positioning of the tibial trial baseplate.

         

        Step 2

        • Tibial exposure is obtained with hyperflexion, external rotation, an anterior drawer moment on the proximal posterior tibia, and downward pressure on the distal femur.

        • The tibial trial component is inserted (Fig. 6). Note the exposure of the posterolateral corner, allowing appropriate sizing and rotation.

           

           

           

          FIGURE 6

           

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          Monoblock TKA

           

      • The remaining trial components are inserted.

      • Appropriate soft tissue balancing is reassessed, including:

    • Range of motion

    • Gap balancing

      • Varus-valgus

      • Flexion-extension

    • Patellar tracking

      • Necessary adjustments or soft tissue releases are made.

        Step 3

      • The trial polyethylene component is removed.

         

        P EARLS

        • Insert the tibial component before inserting the patellar button (if patellar resurfacing is performed) as the extra space provided allows for better tibial exposure.

           

        • We do not routinely use a posterior retractor on the tibia, but this can be helpful in some cases when there is difficulty exposing the tibia.

           

        • Posterior retractors must be carefully placed directly against the posterior cortex.

           

          P ITFALLS

        • Care must be taken in rotational exposure of the tibia as this should not be a forceful maneuver. If difficulty exists, further skin, posteromedial, or capsular release may be required.

           

        • Aggressive maneuvers for exposure can result in tibial fractures especially in osteoporotic bone.

         

      • Tibial stem site lug holes are drilled (Fig. 7).

      • Trial components are removed.

      • Bony surfaces are irrigated and dried.

      • When a posterior cruciate–substituting component is used, the femoral component is inserted prior to tibial insertion as the post on the tibial polyethylene component blocks femoral component insertion.

    • Figure 8A shows a posterior stabilized uncemented monoblock component prior to insertion.

    • In Figure 8B, the component is secured to a front-loading insertion device.

      • With a posterior cruciate–retaining system, the tibial component is inserted followed by the femoral component as this leaves more room for tibial subluxation, and there is no tibial post to block femoral insertion.

       

       

       

      FIGURE 7

       

       

       

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      Monoblock TKA

       

      A B

      FIGURE 8

       

      • The tibial component is inserted in a cemented or uncemented manner.

      • For uncemented tibial component insertion, surface cement is applied to the porous metal base but not the lug holes (Fig. 9).

      • For cemented tibial component insertion, the knee is hyperflexed, externally rotated, and brought forward away from the cemented femoral component (Fig. 10). Note the clearance required to insert the tibial component without damaging the femoral component.

 

 

 

FIGURE 9 FIGURE 10

 

192

 

Monoblock TKA

 

Step 4

  • Complete tibial component seating is confirmed, particularly with press-fit uncemented components. In Figure 11, the tibial component is fully seated following insertion, and the knee is stable in both the varus-valgus and AP planes.

  • Flexion and extension gap balancing, range of motion, and varus-valgus balancing are once again reassessed prior to closure.

     

    P ITFALLS

    • Incomplete seating of the tibial component

       

    • Proximal tibial fracture due to aggressive impaction of an uncemented component

       

    • Failure to achieve appropriate balancing and stability

     

  • Drains are inserted at the surgeon’s discretion.

  • Fibrin glues or sprays may be applied to decrease postoperative bleeding.

  • The tourniquet is released and hemostasis is obtained.

  • A meticulous layered interrupted closure is performed (Fig. 12).

     

     

     

     

     

     

    FIGURE 11

     

     

    FIGURE 12

     

     

     

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    B

     

     

    Monoblock TKA

     

    A

    FIGURE 13

     

    Complications

    • Standard TKA complications may be encountered after monoblock TKA insertion.

    • Specific to the use of an uncemented component, there is also a risk of:

      • Tibial fracture at the time of insertion

      • Loosening

      • Migration

     

    Postoperative Care and Expected Outcomes

    • AP (Fig. 13A) and lateral (Fig. 13B) images confirm position and alignment.

    • Routine postoperative care with full weight bearing is instituted.

    • Continuous passive motion and reinfusion drains may be used at the surgeon’s discretion.

    • Standard thromboprophylaxis and antibiotic protocols are followed.

Evidence

Gioe TJ, Sinner P, Mehle S, Ma W, Killeen KK. Excellent survival of all-polyethylene tibial components in a community joint registry. Clin Orthop Relat Res.

2007;(464):88-92.

 

A 99.7% survival at 14.3 years, with wear or osteolysis as the end point, was reported using an all-polyethylene design in patients with an average age of 77. Estimated cost savings were $729 per case.

 

Gioe TJ, Stroemer ES, Santos ER. All-polyethylene and metal-backed tibias have similar outcomes at 10 years: a randomized level I [corrected] evidence study. Clin Orthop Relat Res. 2007;(455):212-8.

 

A study demonstrating equivalent outcomes with an all-polyethylene tibial component compared with a metal-backed modular component at 10 years. (Level I evidence)

 

Keating EM, Meding JB, Faris PM, Ritter MA. Long-term followup of nonmodular total knee replacements. Clin Orthop Relat Res. 2002;(404):34-9.

 

Faris PM, Ritter MA, Keating EM, Meding JB, Harty LD. The AGC all-polyethylene tibial component: a ten-year clinical evaluation. J Bone Joint Surg Am. 2003;85:489-93.

 

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Monoblock TKA

 

These authors reviewed their extensive experience with all nonmodular tibial components, and the subset that were of an all-polyethylene design. In their system, a lower survival rate was noted for all-polyethylene (68.11%) compared with metal-backed tibial components at 10 years. They pointed out that a flat, nonconforming tibial surface was used, and that longevity of monoblock components may be design specific.

 

Pagnano MW, Levy BA, Berry DJ. Cemented all polyethylene tibial components in patients age 75 years and older. Clin Orthop Relat Res. 1999;(367):73-80.

 

This study reviewed the results of all-polyethylene tibial components in elderly patients receiving TKAs. Survival of the index TKA at 14 years was 100%, with symptomatic aseptic loosening as the end point.

 

Ranawat AS, Mohanty SS, Goldsmith SE, Rasquinha VJ, Rodriguez JA, Ranawat CS. Experience with an all-polyethylene total knee arthroplasty in younger, active patients with follow-up from 2 to 11 years. J Arthroplasty. 2005;20(7 Suppl 3):7-11.

 

Good clinical results were demonstrated at midterm follow-up in this younger, active patient population, with an average age of 57, receiving an all-polyethylene tibial component. There was one infection and one posttraumatic loosening; no cases of osteolysis or aseptic loosening were noted.

 

Rodriguez JA, Baez N, Rasquinha V, Ranawat CS. Metal-backed and all-polyethylene tibial components in total knee replacement. Clin Orthop Relat Res. 2001;(392):174-83.

 

This comparison of metal-backed modular tibial components to an all-polyethylene component showed superior durability with the nonmodular design. Best-case rate of survival was 75% for the modular design versus 96% with the all-polyethylene tibia.

 

Siffri PC, Cushner FD. Short term results of total knee arthroplasty utilizing a cemented trabecular metal tibial monoblock. Poster presentation, AAOS meeting, Chicago, 2006.

 

Tsao AK. Minimum two-year results in uncemented trabecular metal tibial baseplates. Paper presented at the ABJS meeting, Lexington, 2007.