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    Management of Patellar Maltracking During Revision Total Knee Arthroplasty

    A 70-year-old woman presents with worsening right knee pain and new onset knee “buckling” and instability 11 years after primary total knee arthroplasty. Radiographs show progressive displacement and maltracking of her patella, with possible patellar component dissociation. What is the best way to approach her revision surgery?

    Authors

    Blair S. Ashley, MD, and Andrew M. Star, MD

    Introduction

    Total knee arthroplasty (TKA) is a successful operation, with satisfaction rates ranging from 85% to 92%. [1-4] However, persistent anterior knee pain remains a complaint of many unhappy patients, the causes of which are often multifactorial and poorly understood and include technical and patient factors: [5,6]

    Technical Factors

    • Component malrotation
    • Patellar maltracking
    • Patellofemoral overstuffing

    Patient Factors

    • Obesity
    • Quadriceps weakness
    • Pathologic gait patterns

    Complications related to the patellofemoral joint can be difficult to diagnose and manage. Utilization of advanced imaging, such as 2D and 3D computed tomography (CT) scans, have been helpful adjuncts in assessing component position, which may impact patellar tracking. [7,8] Patellar tracking is affected by overall limb alignment, implant type, implant position, and soft tissue tensioning, often making surgical correction of maltracking a challenge for the treating surgeon.

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    When a patient presents with persistent anteromedial knee pain and possible symptoms of patella maltracking, it is imperative for the surgeon to do a thorough preoperative workup to diagnose the problem so that the patient can be adequately counseled about the spectrum of revision options, as well as the likelihood of success with revision surgery.

    Case Presentation

    A 70-year-old woman with rheumatoid arthritis presents with increasing instability and frequent episodes of feeling that her right knee is “giving way.” She had undergone right primary total knee arthroplasty (TKA) 12 years prior. Although she never felt significant pain relief after the TKA, she did not notice difficulty with standing from a seated position or navigating the stairs until after a long bike ride approximately 1 year ago.

    Physical Exam

    • Height: 5 feet, 7 inches; weight: 177 pounds; BMI: 28
    • Alert and oriented x3, with no apparent distress
    • Well-healed midline incision
    • No effusion
    • Right knee range of motion: 0° to 125°
    • Stable to varus and valgus stress
    • Tender to palpation anteromedially, particularly with flexion
    • Mild weakness with knee extension, but no extensor lag
    • Normal distal lower extremity neurovascular exam

    Laboratory Tests

    • Serum erythrocyte sedimentation rate: 10 mm/hr
    • Serum C-reactive protein: <5 mg/L
    • Synovial fluid cell count: 569 white blood cells (20% neutrophils)
    • Synovial fluid alpha defensin test negative; cultures negative

    Imaging

    Figure 1. Preoperative radiographs from 2008.

    Figure 2. Postoperative radiographs from 2009 after the index procedure.

    Figure 3. Followup radiographs from 2020 obtained for the workup of worsening anteromedial pain.

    Figure 4: Axial view from a CT scan of the right knee shows that the femoral component is internally rotated approximately 4° relative to the transepicondylar axis (a) and that the tibial component is internally rotated approximately 15° relative to the tibial tubercle (b).

    Diagnosis

    Patellar maltracking with concomitant patellar component dislocation and possible femoral component malrotation

    Treatment

    There are several considerations for the management of this patient:

    • Based on serial radiographs, it is apparent that patellar subluxation is progressing and that the component may be dissociated from the bone.
    • The CT scan shows that the posterior condylar angle of the femur is 4° of internal rotation.
    • The femoral and tibial components appear well fixed based on the available radiographs and CT scan.
    • Management options range from a soft tissue release and patellar and polythene exchange to a revision of all components with revision components and possible augments.

    We discussed these treatment options with the patient and emphasized that the final decision would be made intraoperatively after inspection of the components. The patient verbalized her understanding and then gave informed consent for right revision TKA, including possible revision of 1 or all components and soft tissue release.

    Surgical Procedure

    • A midline incision was made through the prior incision and dissection was carried down to the fascia.
    • Prior to making the arthrotomy, a mass was noted in the soft tissues and dissected. It revealed a portion of the dissociated patellar button.
    • A standard medial parapatellar arthrotomy was made. The patella was everted and the remainder of the button was identified. The patella was recut and the polyeythlene pegs were removed using a burr.
    • Patellar tracking, femoral rotation, and tibial rotation were evaluated. The femoral component appeared internally rotated compared with the transepicondylar axis; thus, the decision was made to revise all components.
    • The well-fixed femur and tibia were removed using a combination of flexible osteotomes and a saw.
    • Once all components were removed, the residual cement was removed and the soft tissues and canals were debrided. Samples of the synovium, tibial bone, and femoral bone were sent for culture and pathology.
    • We proceeded to ream the tibial canal to accommodate a 16-mm stem included in the revision system we had selected (Attune revision system, DePuy Synthes; Warsaw, Indiana). Using a burr, we removed the sclerotic metaphyseal bone prior to broaching for the 45-mm tibial sleeve. We ultimately chose a size 5 mobile-bearing tibial tray.
    • We then turned our attention to the femur, which we reamed for a size 16 x 60-mm press-fit stem and broached for a sleeve. The femoral alignment was contoured with the saw to better externally rotate the femoral component, promoting patellar tracking. A size 5 femur was utilized.
    • The patella was measured to accommodate a 35, which enabled medialization of the component without overhang. A limited lateral release was performed using the bovie.
    • All components were cemented with antibiotic-loaded cement on the bone surfaces, but the press-fit stems and sleeves were left devoid of cement.
    • Intraoperatively, the range of motion was 0° to 130° and was stable in extension, mid-flexion, and flexion, with excellent patellar tracking.

    Figure 5. Postoperative radiographs immediately following revision surgery.

    Discussion

    Patellar maltracking is a frequent source of persistent anteromedial knee pain, frustrating patients and surgeons following TKA. Identifying patients at risk for maltracking is an important part of preoperative planning. In this case report, the patient’s coronal valgus deformity placed her at risk for maltracking problems. [9] Other preoperative radiographic risk factors to consider include patellar shift more than 3 mm, patellar tilt, lateral facet thinning, and lateral patellofemoral arthritis. [9,10]

    Intraoperatively, anatomic landmarks can be used to assess component position and optimize patellar tracking; for example, using the transepicondylar axis to guide femoral rotation and the tibial tubercle to optimize tibial component rotation. Slight lateralization of the femoral and tibial components and medialization of the patellar component are desired.

    The tightness of the lateral retinaculum can also be assessed by various methods, including the “towel clip test,” [11,12] the vertical patellar test, [12] and the “no thumb technique.” [13] Release of the lateral retinaculum using an inside-out technique and further release of the iliotibial band using a pie-crusting technique can be employed if maltracking persists after confirming appropriate component rotation. [14,15]

    Multiple methods have been described to assess component rotation postoperatively, including radiographs, 2D CT scans, and 3D CT scans. [7,8] Berger et al [8] developed helpful parameters using 2D CT scans, showing that:

    • Small amounts of combined femoral and tibial component internal rotation, ranging from 3° to 8°, correlated with lateral tracking and patellar tilting
    • Moderate combined internal rotation (3° to 8°) correlated with patellar subluxation
    • Large of amounts of combined internal rotation (7° to 17°) correlated with early patellar dislocation or late patellar prosthesis failure

    Ideally, components should have a combined external rotation of 0° to 10°. [8] Our patient had a combined internal rotation of 19°, which put her at risk for patellar dislocation and late prosthesis failure, as observed. Her history of the knee always being painful, but then getting acutely worse, in conjunction with serial radiographs raised suspicion for component failure and dissociation. Similarly, her history of difficulty with moving from sitting to standing and navigating stairs reinforced the associated quadriceps weakness or dysfunction that can occur with patellofemoral maltracking.

    During revision, it is important for surgeons to be critical of component position so that they do not attempt to correct the problem only with soft tissue procedures, rather than revising all the components if necessary, despite it being a more invasive and time-consuming procedure.

    Surgical Pearls

    • Patients should be evaluated preoperatively for factors placing them at increased risk for patellar maltracking.
    • Anatomic landmarks should be used intraoperatively to assess component rotation, and patellar tracking should be critically evaluated. Soft tissue releases alone cannot compensate for component malposition.
    • If patellar maltracking is suspected postoperatively, it is imperative to obtain advanced imaging to assess component rotation prior to proceeding to revision.

    Author Information

    Blair S. Ashley, MD, and Andrew M. Star, MD, are from The Rothman Institute at Thomas Jefferson University Hospital, Philadelphia, Pennsylvania.

    Adult Reconstruction Section Editor, Rothman Institute Grand Rounds

    P. Maxwell Courtney, MD

    Disclosures: The authors have no disclosures relevant to this article.

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