Fig. 4

a Chronic patellar ligament rupture, the patellar ligament ruptured approximately 1.5 cm below the inferior patellar pole, and the termination of the patellar ligament on the tibial tubercle was complete. The patella can be pushed down approximately 4 cm. The ruptured tendon was flocculent, with irregular broken ends and atrophy of patellar ligament. b Preparing for quadriceps tendon V-Y quadricepsplasty. c Patellar displacement distance was measured after patellar ligament connected to patella, then decided the length of quadriceps snip. d After V-Y lengthening of quadriceps femoris tendon. e After opening the capsule articularis genus, we found synovial hyperplasia, degeneration of the medial and lateral menisci, osteophyte formation around the joint, articular cartilage degeneration and wear, and subchondral bone exposure, especially of the medial compartment. We preserved posterior cruciate ligament. f After distal femur and proximal tibia osteotomy was completed. We preserved posterior cruciate ligament. g Installing the prosthesis, bone cement filled bone defect. h The locking suture knots were placed into the patellar tendon with nonabsorbable sutures. The two ends of the same suture pass through adjacent tunnels by Krakow suture technique. The suture was tied over the superior pole of the patella