Fig. 1

a Animal position during surgery: to standardize the knee position during the surgery, mice were placed on a custom made fixture (Plaster of Paris) with a pre-shaped body groove and a support rim for the right knee. Both ankle and groin were strapped down with 0.6 mm cords (green) to align the thigh and calf into the support rim (blue), creating a 90° knee angle position. b Schematic of the surgery model: PB = patellar bone, VL = vastus lateralis, RF = rectus femoris, VM = vastus medialis, FC = femoral condyles, TT = tibial tuberosity, TH = tibial head, EP = epiphyseal plate. The corresponding post-operative macro image (c) shows the graft in-vivo: the tibio-patellar cerclage (TPC, white suture, yellow in the schematic) is a bone-to-bone cerclage whose function is to directly bypass the function of the patellar tendon, thus to transfer the tensile force of the quad-muscle onto the joint (functionally: knee extension). Additionally, a tibio-musculotendinous cerclage (TMC, green suture) facilitates the construct and due to its more proximal insertion, framing the patellar bone, it is meant to reduce the luxation of the patellar bone. The two graft sutures (blue sutures) are stitched through the graft and the corresponding tendon stump to keep the graft in place. The long free suture ends of both cerclages are placed subcutaneously far away from the construct to reduce tissue granulation. (* indicates the India ink which was used to mark the central full-thickness defect used for a different study). d Macro image after sacrifice: the graft is elevated on a backing, the whole construct is covered with a layer of connective scar tissue. Both graft suture knots are visible underneath (#) and the graft shows proximal and distal continuity within the patello-tibial construct