Introduction

Leg Position
Appropriate leg position is crucial when performing minimally invasive total knee arthroplasty. During the procedure, the knee is flexed to 70–90°. Hyperflexion is used only intermittently for specific portions of the case, such as insertion of the tibial component. To aid in holding the leg, a sandbag is placed across from the contralateral ankle when positioning the patient on the table.

Incision
With the leg fully extended, a longitudinal incision measuring 9.5 to 12 centimeters (33/4 to 43/4 inches) is made over the anterior aspect of the knee along the medial border of the patella. The incision extends approximately from the middle of the tibial tubercle to the proximal extent of the patella to one finger’s breath proximal to the patella.

Arthrotomy
Begin 5 millimeters medial to the tibial tubercle and extend dissection around the medial border of the patella. The arthrotomy is extended up to the proximal border of the patella. The supra-patella pouch is identified, separated from the underside of the tendon and preserved. The distal extent of the vastus medialis (VMO) is identified and the orientation of the fibers is determined. An oblique cut is made to the VMO and the muscle fibers are then spread bluntly for approximately 2 centimeters. (Figure 1)

Exposure
With the leg extended, the patella is retracted laterally. The fat pad is excised both medially and laterally leaving a small amount of fat deep under the patella tendon. The patella tendon proximal to the tubercle is dissected from the tibia. The anterior horn of the medial meniscus is divided and dissection is carried around the proximal medial tibia using electrocautery and a boxed osteotome. A thin bent Hohmann retractor is placed on the proximal medial tibia. The proximal soft tissue attachments extending around the proximal medial tibia are released in the standard fashion. A small window is made along the anterior surface of the distal femur with the use of electrocautery to reference the anterior cortex. (Figure 2)

Note: In patients with tight extensor mechanism (usually larger, muscular patients or those with abundant patella osteophytes), the patella is cut at this time.
(See Patella Preparation)