Customized patient-specific orthopaedic surgical instrument and method for preparing a patient's femur

1. An orthopaedic surgical instrument comprising:

a customized patient-specific 5-in-1 cutting block having a plurality of cutting guides including a first chamfer cutting guide, a second chamfer cutting guide, an anterior cutting guide, a posterior cutting guide, and a distal cutting guide, the cutting block comprising:

a keel including a distal segment extending from an anterior end to a posterior end, an anterior segment extending proximally from the anterior end of the distal segment, and a posterior segment extending proximally from the posterior end of the distal segment,

a plurality of ribs extending medially and laterally from the distal segment, the anterior segment, and the proximal segment of the keel, each rib including a first end coupled to the keel, a cantilevered second end, and a bone-facing surface extending from the first end to the second end of each rib,

a pair of pin guides sized to receive bone fixation pins to secure the cutting block to a patient's femur, wherein both of the pair of pin guides extend through the keel,

wherein each bone-facing surface of each rib has a customized patient-specific negative contour configured to receive a portion of a corresponding positive contour of the patient's femur, and

wherein the plurality of ribs cooperate to define the plurality of cutting guides, each cutting guide including a slot having an open outer end defined between corresponding cantilevered second ends of adjacent ribs.

2. The orthopaedic surgical instrument of claim 1 , wherein each of the first chamfer cutting guide and the second chamfer cutting guide include medial and lateral slots.

3. The orthopaedic surgical instrument of claim 1 , wherein:

the first chamfer cutting guide includes a first slot aligned with a second slot, and

the second chamfer cutting guide includes a third slot aligned with a fourth slot.

4. The orthopaedic surgical instrument of claim 1 , wherein the distal cutting guide has medial and lateral slots.

5. The orthopaedic surgical instrument of claim 4 , wherein the distal cutting guide includes a first slot aligned with a second slot.

6. The orthopaedic surgical instrument of claim 1 , wherein each of the anterior cutting guide and the posterior cutting guide have medial and lateral slots.

7. The orthopaedic surgical instrument of claim 1 , wherein the keel includes a customized patient-specific negative contour configured to receive a portion of a corresponding positive contour of a surface defining a patient's intercondylar notch.