Medial Parapatellar Approach
Medial Parapatellar Approach
The medial parapatellar approach3 is the workhorse approach to the knee. Extended to its full length, it allows excellent access to most structures.
Portions of the incision can be used to gain access to the suprapatellar pouch, the patella, and the medial side of the joint. When a straight, midline, longitudinal skin incision is used in conjunction with a medial parapatellar capsular approach, the incision offers an exposure large enough for total knee arthroplasty.
Minimally invasive approaches have been described for the insertion of total knee replacements where the patella is not dislocated. Such approaches may significantly reduce the damage done to the extensor mechanism by the surgery and reduce the amount of postoperative scarring that occurs in the suprapatellar pouch. Such approaches, however, limit visualization of the distal femur, making accurate positioning of implants more difficult. Additional imaging, especially computer-assisted surgery, may be helpful if these approaches are used for total knee replacement.
The uses of the medial parapatellar approach include the following:
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Ligamentous reconstructions
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Patellectomy
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Drainage of the knee joint in cases of sepsis
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Open reduction and internal fixation of distal femoral fractures when a medial plate is to be used
Medial meniscectomy, removal of loose bodies and anterior cruciate reconstruction is nearly always carried out using arthroscopic approaches.
Position of the Patient
Place the patient in a supine position on the operating table. The approach can be made with or without the use of a tourniquet. Operating without a tourniquet slows the surgical approach, but bleeding points are easy to pick up in the superficial surgical dissection. If you are using a tourniquet, it will need to be removed prior to closure of the wound to allow you to obtain hemostasis of the wound. If you are using a tourniquet, exsanguinate the leg by applying a compressive bandage or by elevating the limb for 5 minutes; then, inflate a tourniquet (Fig. 10-9).
Place a sandbag on the table in such a position that it supports the heel when the knee is flexed to 90 degrees. This sandbag will help maintain the knee in a flexed position during joint replacement surgery. Position a table support on the outer aspect of the upper thigh to prevent the leg from
falling into abduction when the knee is flexed.
Landmarks and Incision
Landmarks
Palpate the patella. Run fingers down to the patellar ligament (ligamentum patellae) which runs from the inferior border of the patella and is palpable to its insertion into the tibial tubercle.
Incision
Internervous Plane
There is no internervous plane in this approach, even when the incision is extended superiorly into the intermuscular plane between the vastus medialis and rectus femoris muscles. Because both of these muscles are supplied by the femoral nerve well proximal to this dissection the intermuscular plane is safe for knee surgery.
Superficial Surgical Dissection
Divide the subcutaneous tissues in the line of the skin incision, ensuring hemostasis. Develop a medial skin flap to expose the quadriceps tendon, the medial border of the patella, and the medial border of the patellar tendon. Enter the joint by cutting through the joint capsule. Begin on the medial side of the patella, taking care to leave a cuff of capsular tissue medial to the patella and lateral to the quadriceps muscle to facilitate closure. Divide the quadriceps tendon in the midline to enter the suprapatellar pouch. Finally, complete the capsule incision by dividing the fibrous tissue on the medial aspect of the patellar tendon. The capsular incision will almost certainly also cut through the synovium, since the capsule and synovium are intimately related.
Retract the fat pad, or excise it, as dictated by the exposure requirements. As the joint line is approached, care should be taken not to damage the anterior insertion of the medial meniscus unless the approach is being used for joint replacement surgery (Figs. 10-10 to 10-12).
Deep Surgical Dissection
If the approach is to be used for reconstruction of a fracture of the medial femoral condyle retract the patella laterally and the cut edge of the knee joint capsule medially to expose the anterior and medial aspects of the condyle.
If the approach is to be used for total joint replacement dislocate the patella laterally and rotate it 180 degrees; then, flex the knee to 90 degrees (Fig. 10-13; see Fig. 10-9). Try to avoid avulsion of the patellar ligament from its insertion on the tibia as the patella is dislocated, because reattaching the tendon to the bone is difficult. If the patella does not dislocate easily, it can be given added mobility by extending the skin incision superiorly over the interval between the rectus femoris and vastus medialis muscles. Continue the dissection deeper, splitting the quadriceps tendon farther just lateral to its medial border (see Fig. 10-13).
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Figure 10-9 Position of the patient for the medial parapatellar approach. Begin with the straight leg position, and then flex the knee for the deeper dissection.
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Figure 10-10 Make a longitudinal, straight, midline incision.
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Figure 10-11 Make a medial parapatellar capsular incision.
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Figure 10-12 Continue the incision through the joint capsule and along the patellar ligament and quadriceps tendon to gain access to the joint.
In the case of revision surgery, the suprapatellar pouch is reduced in size or may actually be obliterated. Careful sharp dissection through the scar tissue may significantly improve the mobility of the patella, which allows greater flexion of the knee and eversion of the patella.
In those rare cases in which the patella still does not dislocate,
carefully remove the patellar ligament attachment with an underlying block of bone. The bone makes subsequent reattachment easier (Fig. 10-14). Be aware that the tibial components of many knee replacements incorporate a central peg that makes reattachment of a bone block impossible if a screw is to be used. In such cases, a staple fixation may be indicated.
When the patella is dislocated and the knee is flexed fully, this incision provides the widest possible exposure of the entire knee joint.
Dang
Nerves
The infrapatellar branch of the saphenous nerve often is cut during this approach. The major danger in cutting the nerve is the development of a postoperative painful neuroma. Because the area of anesthesia produced usually is not troublesome, do not repair the nerve if it is cut. Instead, resect it and bury its end in fat to decrease the chances that a painful neuroma will form (see Figs. 10-32 and 10-35).
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Figure 10-13 Dislocate the patella laterally, and flex the knee to 90 degrees.
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Figure 10-14 Detach the patellar ligament attachment with an underlying block of bone.
Muscles and Ligaments
If the patellar ligament becomes avulsed from its insertion on the tibia, it is difficult to reattach. Postoperative mobilization of the knee is delayed and residual stiffness is common.
How to Enlarge the Approach
Local Measures
Superior Extension. Extend the approach proximally between the rectus femoris and vastus medialis muscles. Then, split the underlying vastus intermedius muscle to expose the distal two-thirds of the femur. Stay in the distal third of the thigh; more proximally, the branches of the femoral nerve may become involved, resulting in partial denervation (see Anteromedial Approach to the Distal Two-thirds of the Femur in
0).Inferior Extension. Mobilize the upper part of the attachment of the patellar ligament to the tibia or remove the patellar ligament with an
underlying block of bone. This extension may be useful in dealing with complex intra-articular fractures of the knee joint. (See the section detailing the lateral approach to the distal femur for combined use in repair of the cruciate ligament.)