Standard anterior medial parapatellar knee arthrotomy

Stepwise procedure

1. Position
   • Place the patient supine on a radiolucent table.
   • Position the knee near the end of the table so it can flex to at least 90 degrees.
   • A thigh support or bolster may be used. Apply a proximal thigh tourniquet if indicated.
   • Prep and drape the entire limb so the knee can be flexed and extended during the operation.
2. Surface marking and skin incision
   • Identify the patella, patellar tendon, tibial tubercle, medial border of the patella, and joint line.
   • Make a longitudinal anterior midline incision, centered on the knee. Length depends on the required exposure.
   • Make the incision with the knee flexed when practical, as this allows the skin and subcutaneous tissue to fall aside and facilitates exposure.
   • Incorporate a usable previous midline scar if present. With several previous scars, preserve skin vascularity and plan the incision carefully.
3. Subcutaneous dissection
   • Divide subcutaneous tissue in line with the skin incision.
   • Develop full-thickness medial and lateral skin flaps only as much as required. Maintain a thick medial flap, staying just superficial to the extensor mechanism.
   • Be aware that the infrapatellar branch of the saphenous nerve is variable and vulnerable in anteromedial dissection. Injury may cause anteromedial numbness or a painful neuroma.
4. Identify the extensor mechanism
   • Identify the quadriceps tendon superiorly, patella centrally, patellar tendon inferiorly, and the medial retinaculum and vastus medialis medially.
   • Plan the arthrotomy so that a cuff of tissue remains for secure repair.
5. Perform the medial parapatellar arthrotomy
   • Begin proximally in the quadriceps tendon, just medial to the patella and adjacent to the vastus medialis.
   • Leave a small cuff, approximately 3-4 mm, of tendon/retinaculum attached to the vastus medialis for later repair.
   • Continue the incision distally along the medial margin of the patella.
   • Curve the incision around the inferomedial pole of the patella and extend it distally along the medial border of the patellar tendon.
   • Continue onto the anteromedial tibia as needed, commonly about 3-4 cm distal to the joint line.
6. Enter and expose the joint
   • Open the capsule and synovium in line with the retinacular incision.
   • Evacuate fluid or blood if present and obtain cultures before irrigation or antibiotics when infection is suspected, where clinically appropriate.
   • Flex the knee and gently laterally sublux or evert the patella according to the necessary exposure. Do not force patellar eversion.
   • Release tight lateral patellofemoral synovium or plicae only if needed for safe exposure.
   • Preserve the patellar tendon and avoid unnecessarily aggressive fat-pad excision or lateral release, particularly when patellar blood supply may already be compromised.
7. Extend exposure if required
   • Elevate the anteromedial capsule and, when indicated for medial compartment or tibial exposure, elevate the deep medial collateral ligament subperiosteally from the proximal tibia toward the posteromedial corner.
   • For a stiff knee or inadequate exposure, first reassess positioning, soft-tissue releases, and the need for a larger incision.
   • Extensile options such as quadriceps snip, V-Y quadricepsplasty, or tibial tubercle osteotomy are separate advanced procedures and should not be routine.
8. Intra-articular inspection or procedure
   • Systematically inspect the suprapatellar pouch, patellofemoral joint, medial and lateral compartments, intercondylar notch, cruciate ligaments where relevant, menisci, articular surfaces, and posterior recesses.
   • Complete the procedure indicated, then remove debris and irrigate thoroughly.
9. Closure
   • Restore the patella to its normal position and check patellar tracking through knee flexion and extension.
   • Repair the capsule, medial retinaculum, and quadriceps tendon securely with interrupted or running heavy absorbable/nonabsorbable sutures according to the operation.
   • Re-approximate the tissue cuff left on the vastus medialis and ensure no gap or undue tension in the arthrotomy repair.
   • Close subcutaneous tissue and skin in layers. Use a drain only when indicated by the specific operation.

Key technical points

• Do not force patellar eversion. If exposure is limited, increase the skin incision, release tethering tissue appropriately, or use an indicated extensile approach.
• Protect the extensor mechanism. Avoid extending the arthrotomy into or damaging the patellar tendon.
• Protect skin perfusion. Avoid thin skin flaps and excessive retraction, especially in revision surgery or scarred knees.
• Protect the infrapatellar saphenous nerve branch during medial superficial dissection.
• Retain a repairable medial cuff during the proximal arthrotomy. Inadequate closure can lead to medial retinacular failure and patellar maltracking.
• Before closure, assess patellar tracking and ensure that closure does not over-tighten the medial side.