Surgical Approach

See alsoVideo 10-1 .

The most commonly used skin incision for primary TKA is an anterior midline incision. Variations may be considered, but in general most incisions will compromise the infrapatellar branch of the saphenous nerve and result in an area of numbness on the outer aspect of knee. This should be discussed with the patient before surgery. There are many variations on the approach to the knee deep to the subcutaneous level of dissection.

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  Make a medial parapatellar retinacular incision with the knee in flexion to allow the subcutaneous tissue to fall medially and laterally, which improves exposure ( Figure 10-1 ).

  
  

  
  

  
  

  

  
  
  
  
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  If a preexisting anterior scar on the knee is in a usable position, incorporate it into the skin incision. If multiple previous incisions are present, choose the most lateral usable incision because the blood supply to the skin of the anterior knee tends to come predominantly from the medial side. Previous direct medial and lateral incisions and transverse incisions can generally be ignored.

  
  
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  Make the skin incision long enough to avoid excessive skin tension during retraction, which can lead to areas of skin necrosis.

  
  
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  Keep the medial skin flap as thick as possible by keeping the dissection just superficial to the extensor mechanism.

  
  
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  Extend the retinacular incision proximally the length of the quadriceps tendon, leaving a 3- to 4-mm cuff of tendon on the vastus medialis for later closure.

  
  
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  Continue the incision around the medial side of the patella, extending 3 to 4 cm onto the anteromedial surface of the tibia along the medial border of the patellar tendon.

  
  
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  Expose the medial side of the knee by subperiosteally elevating the anteromedial capsule and deep medial collateral ligament off the tibia to the posteromedial corner of the knee ( Figure 10-2 ).

  
  

  
  

  
  

  

  
  
  
  
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  Extend the knee, and evert the patella to allow a routine release of the lateral patellofemoral plicae. In obese patients, if eversion of the patella is difficult, develop the lateral subcutaneous flap further so that the patella can be everted underneath this tissue. Alternatively, the patella can be subluxated laterally if this provides adequate exposure ( Figure 10-3 ).

  
  

  
  

  
  

  

  
  
  
  
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  Flex the knee and remove the anterior cruciate ligament and the anterior horns of the medial and lateral menisci, along with any osteophytes that may lead to component malposition or soft tissue imbalance. The posterior horns of the menisci can be excised after the femoral and tibial cuts have been made. If a PCL-substituting prosthesis is to be used, the PCL can be resected at this time or can be removed later in the procedure along with the box cut made in the distal femur for the PCL-substituting femoral component.

  
  
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  With PCL substitution and PCL retention, subluxate and externally rotate the tibia. External rotation relaxes the extensor mechanism, decreases the chance of patellar tendon avulsion, and improves exposure.

  
  
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  Expose the lateral tibial plateau by a partial excision of the infrapatellar fat pad and retraction of the everted extensor mechanism with a levering-type retractor placed adjacent to the lateral tibial plateau.

  
  
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  During all maneuvers that place tension on the extensor mechanism, especially knee flexion and patellar retraction, pay careful attention to the patellar tendon attachment to the tibial tubercle. Avulsion of the patellar tendon is difficult to repair and can be a devastating complication.