Article Figures & Tables
Figures
- Fig. 1
Summary of native (top row) and prosthetic (bottom row) patellofemoral kinematics. (A) Patellar tracking between 0° and 90°. The native patella translates medially in early flexion and translates laterally in further flexion. The patella tracks more medially following total knee arthroplasty (TKA). (B) Frequency-of-contact map showing patellofemoral contact between 0° and 90°. The distal patella initiates contact and, with increasing flexion, the contact area migrates more proximally (adapted and redrawn from reference 5 with permission of Elsevier). (C) Patellar tilt before and after TKA. The patellar tilt appears to be increased following TKA, particularly between 10° and 45° (reproduced from reference 4 with permission of Springer). L = lateral; M = medial; P = proximal.
- Fig. 2
Anteroposterior, axial and sagittal photographs of Triathlon (Stryker), Sigma (DePuy Synthes) and Genesis II (Smith & Nephew) femoral components. Modern components share common features, such as proximal extension of the trochlea, raised lateral trochlear flange, lateralized groove and deepened trochlea. L = lateral; M = medial.
- Fig. 3
“Overstuffing” may be a factor contributing to anterior knee pain. It can occur when the size of the femoral or patellar component is greater than the amount of bone that was resected. AP = anteroposterior.
- Fig. 4
Alignment of the femoral component. The femoral component is placed in 3° external rotation compared to the posterior condylar axis.
- Fig. 5
Alignment of the tibial component. The tibial component is placed in external rotation; various landmarks, such as the tibial tubercle or ankle joint, can be used. The centre of the ankle corresponds to the medial and middle thirds of the space between the malleoli.
- Fig. 6
Centred (A) and medialized (B) patellar button placement. The latter may allow a reduction in lateral patellar shear forces.
- Fig. 7
Patellar clunk is thought to be secondary to the catching of proliferative fibrous tissue at the junction of the distal quadriceps tendon and the superior pole of the patella.
- Fig. 8
The intercondylar box ratio of a femoral component (A/B). Implants with a decreased ratio (< 0.7) are associated with decreased patellar clunk. Reproduced from reference 54 with permission of the British Editorial Society of Bone & Joint Surgery.
Tables
- Table 1
Summary of techniques to avoid patellofemoral complications after total knee arthroplasty
Complication Technique for avoidance Patellar maltracking or instability Femoral component design: extended and deepened trochlear groove
Femoral component rotation (3° external rotation compared to posterior condylar axis)
Tibial component rotation (central third of tibial tubercle)
Place patellar button in medialized position
Lateral patellar facetectomyPatellar clunk Use femoral component with low intercondylar box ratio
Avoid substantial changes in joint line height, decreased patellar thickness or use of small patellar button
Maintain posterior femoral condylar offsetPatellar avascular necrosis Avoid unnecessary lateral retinacular release
Avoid excessive patellar reamingPatellar fracture Use all-polyethylene patellar component
Avoid excessive patellar resection when resurfacingAnterior knee pain Attempt to minimize any of the above issues
Select appropriately sized femoral and patellar components; preoperative templating to avoid patellofemoral offset changes
Circumferential patellar denervation
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