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Pre-operative radiograph (A) On low extremity standing scanogram, left knee shows severe valgus alignment. (B) on anteroposterior weight-bearing radiograph, left knee shows severe valgus osteoarthritis with lateral dislocation of the patella (C) on lateral radiography, patella was not seen. (D) On skyline view, patella is dislocated laterally.
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Roentgenograms showed severe valgus deformity and severe osteoarthritis with patella dislocation of the left knee along with complete loss of lateral compartment joint space (Fig. 1).
(A) Distal femur was resected with 3  valgus to the right angle to the mechanical axial on the coronal plane (B) graphic shows asymmetry of extension gap after bone resection and ligament release.
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Patella was hypoplastic while femoral grove for patella was absent (Fig. 2).
White arrow shows absence of distal femoral groove, and an asterisk shows patella hypoplasia.
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To reduce extensive lateral soft tissue release for gap balancing and relocation of the patella, authors cut distal femur with valgus 3  to the right angle to mechanical axis (Fig. 3).
(A) A custom spacer with a navigation tracker attached was placed the resected tibia with the knee in 90  flexion with maintaining the tension by manual traction. (B) parallel line to the proximal tibial resection plane was displayed on the monitor, and was marked on the cut surface of distal femur.
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With the knee flexed to 90  and maintaining the tension by traction, spacer blocks of extension gap thickness with computer trackers were placed on the tibial cutting surface (Fig. 4A). When parallel line to the proximal tibial resection plane was displayed on the monitor, the surgeon marked a line on the cut surface of distal femur (Fig. 4B).
After the extensor realignment, patella tracked centrally in the patellofemoral groove located centrally throughout the range of motion, and the hip was flexed 90  and passive knee flexion against gravity was 90 .
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Additionally, the medial aspect of capsule and vastus medialis obliquus were brought over the top of the inverted V-shaped pedicle and secured in position with a double row of sutures.3 After the repair was complete, the patella tracked centrally in the patellofemoral groove, the hip was flexed 90 , and passive knee flexion against gravity was 90  (Fig. 5).
Immediate post-operative radiograph (A) Anteroposterior fluoroscopy showed well positioned implant and mediolateral symmetry (B) lateral fluoroscopy showed a patella on the front of femur that had not seen on the preoperative lateral radiography.
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Immediate post-operatively, reduction of patella was confirmed with fluoroscopy (Fig. 6).
At post-operative 1 year (A) On low extremity standing scanogram, left lower extremity shows a restoration of alignment with 3  residual valgus, but it is within an acceptable range. (B) weight bearing AP view, patella was located on front of femur (C) at post-operative 1 year, patella was seen well on the weight bearing lateral view. (D) on skyline view, patella was placed in the groove of the femoral component with minimal lateral displacement.
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However, radiography showed minimal patellar lateral displacement (Fig. 7).