Patient specific instrumentation (PSI) for orthopedic surgery

A patient specific instrument assembly for guiding a surgical tool on a patient's tibia during a knee replacement surgery, the patient specific instrument assembly comprising:

• an extra-medullary portion at a distal end of the patient specific instrument assembly, the extra-medullary portion having a pair of spaced apart malleoli clamping elements for engaging respective one of a lateral and medial malleoli of the patient, the malleoli clamping elements having a size and/or relative position that is patient-specific for engaging respective one of the lateral and medial malleoli of the patient,
• an elongated rod connected at a distal end to the extra-medullary portion, the elongated rod configured to extend in a direction along a mechanical axis of the patient's tibia,
• an upper mounting portion at a proximal end of the patient specific instrument assembly, the upper mounting portion including a base body connected to a proximal end of the elongated rod and a resection cutting guide, the resection cutting guide having:
• a saw slot for receiving a saw of the surgical tool, the saw slot being operable to guide the saw along a resection plane transverse to the mechanical axis of the patient's tibia;
• and
• an abutting surface on a bone abutting side of the resection cutting guide, the abutting surface adapted to abut an anterior surface of the patient's proximal tibia;
• wherein the resection cutting guide is made of a plastic or metallic material produced by additive manufacturing.