Patellofemoral Arthroplasty

Key Concepts

Patellofemoral arthroplasty (PFA) is indicated for a specific subset of patients with degenerative arthritis whose pattern of symptoms localizes to the anterior knee and occurs primarily during activities that load the knee in flexion. This may include climbing up and down stairs, rising from a seated position, squatting, kneeling, and/or navigating uneven surfaces.
Outcomes of PFA can be optimized with proper surgical indications, appropriate implant selection, and meticulous surgical technique.
PFA can be considered a definitive procedure for older patients with isolated patellofemoral arthritis. This may offer advantages over total knee arthroplasty (TKA) such as decreased blood loss, shorter hospital stay, and improved range of motion. PFA can also be utilized as an “interim” procedure for relatively young patients with advanced symptomatic patellofemoral arthritis and early tibiofemoral arthritis who wish to postpone TKA (Figure 49.1).

Surgical Indications

Isolated, advanced, primary patellofemoral degenerative arthritis
Patellofemoral arthritis with trochlear dysplasia
- These patients have a relatively low reported rate of progression of tibiofemoral arthritis and are well suited for PFA.
- Patellofemoral malalignment is common in this population and may be addressed by way of implant selection and positioning or with concomitant bony or soft tissue realignment procedures.
Posttraumatic patellofemoral arthritis
Radiographic evidence of patellofemoral joint space narrowing
- Patients with “normal” low-flexion-angle axial radiographs exhibit inferior results versus those with visible patellofemoral joint space narrowing.
Failure of a comprehensive nonoperative management program

Contraindications

Moderate or advanced tibiofemoral chondromalacia
Inflammatory arthritis
- PFA can be considered if there is no clinical or radiographic evidence of synovitis or inflammatory arthropathy in the operative knee.
Post septic arthritis
Morbid obesity
Significant coronal plane malalignment (>5°-10° varus/valgus)
Significant patella baja (<0.8 Caton-Deschamps Index)
Significant flexion contracture (>5°-10°)

Figure 49.1 ▪ Preoperative AP, lateral, and Merchant radiographs (A-C) and postoperative AP and Merchant (D and E) radiographs of a 50-year-old woman with advanced patellofemoral arthritis who underwent PFA. Progression of tibiofemoral arthritis occurred 12 years post PFA (F) and subsequent conversion to TKA was performed (G-J).

Imaging

Radiographs: Standing anteroposterior (AP), posteroanterior (PA) flexion, lateral, Merchant, and long-leg standing hip-to-ankle radiographs (Figure 49.2).
Magnetic resonance imaging (MRI) may be necessary to rule out significant (grade 3-4) tibiofemoral chondromalacia (Figure 49.3).
Computed tomography (CT) may assist with preoperative planning, specifically regarding the need for concomitant tibial tubercle osteotomy (TTO) in the setting of significant lateral patellar subluxation/dislocation (Figure 49.4).

Figure 49.2 ▪ AP (A), PA flexion (B), lateral (C), Merchant (D), and hip-to-ankle standing radiographs (E) of a 58-year-old woman demonstrating isolated patellofemoral arthritis with neutral mechanical axis.

Figure 49.3 ▪ Axial (A) and coronal (B) MRI confirms isolated patellofemoral disease.

Surgical Technique

Choice of implant: Most patients with isolated patellofemoral degenerative arthritis have trochlear dysplasia and exhibit internal rotation of the distal femur. The authors prefer an implant that utilizes an onlay design owing to belief that it provides a more reproducible outcome for these patients than an inlay design (Figure 49.5). The inlay prosthetic design typically matches the patient’s anatomy and therefore is better suited for patients with posttraumatic arthritis or those with low-grade or no trochlear dysplasia (Figure 49.6).

Figure 49.4 ▪ CT confirms high-grade trochlear dysplasia (A), and the patient required tibial tubercle osteotomy and medial patellofemoral ligament reconstruction in addition to PFA (B).

Figure 49.5 ▪ Axial CT (A) and intraoperative photograph (B) of an inlay component that required conversion to an onlay PFA (C) due to persistent “J sign”.

Preoperative Planning

Trochlear component: Consider anteroposterior and medial-lateral sizing. In the setting of patella alta, ensure that the proximal extent of the prosthesis is adequate for proper tracking. If there is no apparent engagement of the patella in the trochlea on lateral radiograph, consider tibial tubercle distalization, either staged or in conjunction with PFA. If the patella is tracking or subluxating laterally, in general, a trochlear component with a wider proximal geometry will be less likely to require a combined realignment procedure.
Patellar component: For extensive patellar wear resulting a very thin patella, consider leaving the patella unresurfaced or performing a staged bone grafting procedure (Figure 49.7).

Figure 49.6 ▪ Surgical (A) and Merchant radiographic (B) images of an inlay prosthesis in a patient with no evidence of patellofemoral malalignment. (From Cannon A, Stolley M, Wolf B, Amendola A. Patellofemoral resurfacing arthroplasty: literature review and a description of a novel technique. Iowa Orthop J. 2008;28:42-48.)

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