patellofemoral arthroplasty

A 48-year-old female patient presents with anterior left knee pain. She has had a history of recurrent patellofemoral dislocations as an adolescent that was treated with multiple soft tissue procedures as well as tubercle osteotomy in the past. She underwent patellofemoral arthroplasty 2 years ago (Fig. 7–8) and continues to have anterior knee pain.

 

 

Figure 7–8

 

Which of the following is FALSE regarding patellofemoral arthroplasty?

1. The procedure is best performed in patients with anterior knee pain who have rheumatoid arthritis

2. PF arthroplasty should be avoided in patients with patellar maltracking or malalignment problems unless these problems are corrected preoperatively

3. External rotation of the trochlear component such that it is parallel to the epicondylar axis will improve patellar tracking

4. In the setting of medial or lateral joint-line pain, PF arthroplasty should be avoided

Discussion

The correct answer is (A). Inflammatory arthropathy, which typically affects the joint globally in all three compartments, is a contraindication to unicompartmental knee replacement. Patellofemoral arthroplasty will fail in the setting of patellar

maltracking and therefore should be avoided or the malalignment/malrotation corrected prior to arthroplasty. Newer-generation “onlay” designs of PF arthroplasty have addressed some of the design concerns of the “inlay” implants whereby the trochlear component can be externally rotated to optimize patellar tracking and eliminate some of the concerns of patellar subluxation that occurred with first-generation PF arthroplasty designs. Patellofemoral arthroplasty should not be performed in the setting of medial and lateral disease in the knee as well as flexion contractions. It is possible to combine a medial or lateral UKA or autologous osteochondral grafting to address disease in one other compartment, but in general, the standard of care remains to be total knee arthroplasty if more than one compartment is affected.

The primary reason for failure and revision of first-generation patellofemoral replacement is:

1. Progression of disease in the medial and lateral compartments

2. Infection

3. Osteolysis/loosening

4. Patellofemoral catching and instability

 

Discussion

The correct answer is (D). The initial “inlay” style designs resulted in catching/subluxation of the patella and problems with patellar tracking. Contemporary improvements in trochlear component design with inlay implants implanted parallel to the epicondylar axis, improved radius of curvature, and tracking angles of the components have improved outcomes with respect to patellofemoral tracking. Long-term results of these contemporary designs have not yet been defined.

Which of the following techniques should be AVOIDED when performing patellofemoral arthroplasty?

1. Remove marginal osteophytes in the intercondylar notch

2. Restoration of anatomic patellar thickness

3. Lateralization of patellar component

4. External rotation of the trochlear/femoral component to be perpendicular to the AP axis of the femur

Discussion

The correct answer is (C). As in total knee replacement, the patellar component should be medialized to prevent lateral subluxation of the patella in PF arthroplasty. Other principles of patellar resurfacing should be adhered to including: attention to restoring the patient’s own patellar thickness and external rotation of the femoral component to optimize patellofemoral tracking and to limit the potential for lateral catching and subluxation of the patella. Removal of osteophytes in the intercondylar notch will also improve tracking.

 

Objectives: Did you learn...?

 

The indications for patellofemoral arthroplasty?

 

The causes for revision of patellofemoral arthroplasty?