RECONSTRUCTION 2023, Jan, 08 | 12:00 am

Cancellous Patellar Bone Grafting in Revision Total Knee Arthroplasty

P ITFALLS

  • Correct rotational positioning of the femoral and tibial components is a prerequisite for a successful outcome.

     

  • Patellar bone grafting in the setting of component malposition will result in gradual lateral subluxation of the patellar shell construct.

 

Cancellous Patellar Bone Grafting

 

Indications

  • Patellar bone grafting is indicated in severe patellar bone deficiency, which precludes adequate fixation of another patellar implant. This accounts for approximately 10% of revision total knee arthroplasty cases.

  • Cancellous patellar bone grafting provides potential for restoration of bone stock, facilitates patellar tracking, improves quadriceps leverage, and is cosmetically appealing.

    Treatment Options

    • Structural bone grafting of the patella

    • Patellar resection arthroplasty

    • Gull-wing osteotomy

    • Porous metal baseplate

    • Crossed Kirschner wires for cemented fixation of the patellar component

    • Patellectomy should be avoided.

     

    Examination/Imaging

  • Examination of the extremity should include:

    • Skin—assessment of location and shape of scars, health of skin

    • Alignment

    • Stability—anteroposterior and varus/valgus

    • Neurovascular examination

    • Range of motion assessment

    • Extensor mechanism integrity, presence of an extensor lag

  • Radiographs

    • Anteroposterior and lateral views of the knee are obtained.

    • Preoperatively, it is helpful to radiographically assess whether the magnitude of patellar bone loss preclude fixation of another patellar implant.

      • Merchant’s views are particularly helpful in assessing the status of the current patellar component as well as the magnitude of patellar bone loss.

      • Figure 1 shows a Merchant’s radiograph demonstrating lateral subluxation of the patella with lucency noted at the cement-bone interface of the patellar component. The amount of remaining patellar bone would preclude fixation of another patellar component.

        Surgical Anatomy

  • The remaining patellar remnant consists of a shell of anterior cortex and variable amounts of patellar rim. In Figure 2A and 2B, the remnant consists of a shell of anterior cortex with an intact patellar rim and cavitary bone stock deficiency.

  • Typically, there is a pseudomeniscus of scar tissue as well as peripatellar fibrotic tissue on the undersurface of the quadriceps tendon.

     

     

     

    FIGURE 1

     

     

     

     

    471

     

    Cancellous Patellar Bone Grafting

     

    A

     

     

     

    Quadriceps tendon

     

    Patellar tendon

     

    Patellar remnant

     

    FIGURE 2 B

     

    472

     

    Cancellous Patellar Bone Grafting

     

    Positioning

  • Patients are positioned in the supine position on the operating room table.

  • A tourniquet can be placed high on the patient’s thigh based on surgeon preference.

  • The leg is prepped and draped free using an extremity drape.

     

    P EARLS

    • Extension of the approach proximally and distally can make identification of the appropriate planes easier when elevating skin flaps.

       

      P ITFALLS

    • Local peripatellar tissue constitutes the basis of cancellous patellar bone grafting, and one should resist the temptation to remove these tissues during exposure.

     

    Portals/Exposures

  • The previous midline anterior surgical incision should be used and extended as required for the revision arthroplasty.

    • If the patient has multiple anterior incisions, select the most lateral (if feasible); otherwise, the bridge between incisions is more likely to become avascular.

  • Soft tissues should be handled carefully to minimize trauma to the skin edges.

  • Minimize skin ischemia by elevating full-thickness flaps off of the musculotendinous layer.

  • The knee is opened with a medial parapatellar arthrotomy.

  • Two marking sutures are placed at the superomedial pole of the patella to facilitate accurate repair of the extensor mechanism.

  • To mobilize the patella, adhesions in the suprapatellar pouch, lateral gutter, and infrapatellar area need to be released.

    • Retain the pseudomeniscus of scar tissue and most of the peripatellar fibrotic tissue on the undersurface of the quadriceps tendon as well as tissue on the remaining patella.

    • The polyethylene insert can be removed to decrease tension on the extensor mechanism and simplify mobilization of the patella.

  • Femoral and tibial components are assessed. Careful evaluation of femoral and tibial component rotational position is mandatory. Revision of femoral and/or tibial components is completed prior to patellar bone grafting.

     

    P EARLS

    • If there is inadequate local soft tissue, a free tissue flap can be obtained from either the suprapatellar pouch or the fascia lata in the lateral gutter of the knee joint.

     

    Procedure

    Step 1

  • The patellar shell is prepared by removing all fibrous

    membrane in the crevices of the remaining patellar bone.

  • The most reliable tissue for a local soft tissue flap lies on the undersurface of the quadriceps tendon.

 

473

 

Cancellous Patellar Bone Grafting

 

  • The flap is created by elevating the tissue from proximal to distal from the undersurface of the tendon (Fig. 3A and 3B). The base of the tissue is left firmly attached to the superior aspect of the patella.

  • The tissue flap is then turned down and sewn into the periphery of the pseudomeniscus/peripatellar fibrous tissue and the remaining patellar rim.

  • A watertight closure is achieved using multiple interrupted nonabsorbable size 0 sutures.

  • A small purse-string opening is left in one portion of the tissue flap repair to facilitate delivery of bone graft into the patellar defect.

 

 

 

 

A

 

 

 

Local soft tissue flap

 

Quadriceps tendon

 

Patellar remnant

 

 

FIGURE 3 B

 

474

 

 

P EARLS

  • In the absence of locally available cancellous autograft, cancellous allograft bone can be used.

 

Cancellous Patellar Bone Grafting

 

Step 2

  • Cancellous autograft is harvested from the metaphyseal portion of the femur during femoral preparation of the revision implant.

  • The bone graft is morselized into small fragments of approximately 5–8 mm in height and width (Fig. 4).

  • This fragment size allows tight impaction of the bone graft into the patellar shell–tissue flap construct.

  • The bone graft is then tightly impacted through the opening of the fascial flap into the patellar bone defect.

  • Sufficient bone is added so that the final patellar construct has a height of between 20 and 25 mm.

    Step 3

  • The tissue flap is then closed completely to contain the bone graft within the patellar shell (Fig. 5A and 5B).

  • The adequacy of the suture repair is examined to ensure that the tissue flap securely contains the impacted bone graft.

  • The peripatellar arthrotomy site is provisionally repaired with several sutures or towel clips to mold the patellar construct in the femoral trochlea as the knee is placed through the full range of motion.

  • The tourniquet is released and bleeding is controlled. The wound is irrigated.

  • The medial parapatellar arthrotomy is closed, followed by closure of the subcutaneous tissue and skin.

  • The limb is immobilized in a well-padded plaster splint.

     

     

     

    FIGURE 4

     

     

     

    Cancellous Patellar Bone Grafting

     

    A

     

    475

     

     

     

    Patellar bone graft construct

     

    B

    FIGURE 5

     

    476

     

    Cancellous Patellar Bone Grafting

     

    Postoperative Care and Expected Outcomes

  • Surgical drains are removed on the first postoperative morning.

  • Antibiotic prophylaxis is provided for the first 24 hours following surgery.

  • Deep venous thrombosis prophylaxis is individualized based on the patient risk profile. Generally low-risk patients receive multimodal prophylaxis consisting of acetylsalicylic acid 325 mg orally twice daily, antiembolism stockings (TEDS), and foot pumps. High-risk patients receive coumadin for 6 weeks with a target international normalized ratio of 1.7–2.2.

  • Postoperative rehabilitation is the same as the usual protocol after revision knee arthroplasty.

    • Patients are mobilized on postoperative day 1 with physiotherapy.

    • The knee is immobilized in a well-padded plaster splint until the second morning after surgery. Then the splint is removed and a light dressing applied to the knee. Active and active-assisted knee range of motion is then started with no restrictions.

    • We use a progressive weight-bearing protocol starting with 40 pounds weight bearing for the first postoperative week. The patient then progresses to 80 pounds in the second week and 120 pounds in the third week. Full weight bearing with the use of a cane is started 4 weeks after surgery. This is continued until the first clinical follow-up at 3 months.

  • The initial case series that described the technique and early clinical results reported:

  • Improved postoperative Knee Society pain and function scores.

  • Restoration of patellar bone stock with incorporation of the bone graft and progressive remodeling of the construct.

    • Figure 6A shows a postoperative Merchant’s radiograph of the patella–bone graft construct.

    • Figure 6B shows a Merchant’s radiograph 16 months after patellar bone grafting. There has been molding and remodeling of the construct against the femoral trochlea.

  • Complications included:

    • Arthrofibrosis requiring manipulation

    • Tibiofemoral instability requiring reoperation to increase polyethylene thickness

 

 

 

A B

FIGURE 6

 

 

 

477

 

Cancellous Patellar Bone Grafting

 

A

FIGURE 7

B

 

  • Femoral component loosening requiring revision of the femoral component

  • Once patellar bone stock is restored using this technique, it is possible to insert a new patellar component at the time of subsequent revision surgery.

  • Figure 7A shows a Merchant’s radiograph taken 6 years after patellar bone grafting. The patient underwent surgery for revision total knee arthroplasty for aseptic loosening of the femoral component. At the time of the revision, patellar bone stock was sufficient to allow resurfacing with a new patellar component.

  • Figure 7B shows a Merchant’s radiograph 1 year after revision total knee arthroplasty with a stable patellar component in satisfactory position.