11.1.1 Principal Indications

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  Medial hemiarthroplasty

  
  
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  Allo-arthroplasty

  
  
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  Intra-articular fractures

  
  
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  Partial synovectomy

11.1.2 Positioning and Incision

The patient is placed in the supine position. After optional application of a tourniquet as far proximally on the thigh as possible, the leg is draped to allow free movement. The longitudinal parapatellar incision begins at the tibial tuberosity and runs in a slight curve along the medial border of the patellar ligament to the proximal pole of the patella ( Fig. 11.1 ). After flexing the knee to approximately 30°, the subcutaneous tissue is divided. The medial retinaculum and fascia over vastus medialis are exposed parallel to the skin incision ( Fig. 11.2 ).

In the mini subvastus approach, a right-angled incision is made in the medial retinaculum distal to the vastus medialis tendon, with one limb of the incision extending to the medial tibial plateau medial to the patella and patellar tendon, and the other running at the lower border of the vastus medialis toward the intermuscular septum. There, the muscle is dissected bluntly from the septum and the underlying joint capsule ( Fig. 11.3 ).

The mini midvastus approach involves splitting the vastus medialis where it meets the patella ( Fig. 11.4 ). The transverse incision begins at the proximal medial pole of the patella. Fascia and muscle are divided in the line of their fibers over a distance of 2–4 cm to avoid denervation of the distal part of the muscle.

The quadriceps-sparing approach is a parapatellar approach that ends at the proximal medial pole of the patella and can be extended as far as the quadriceps tendon if necessary. As in the midvastus approach, the transverse insertion of the vastus medialis muscle is divided from the medial border of the patella as far as its proximal pole ( Fig. 11.5 ).

The joint capsule is split in a proximal direction beneath the vastus medialis muscle as far as the suprapatellar recess ( Fig. 11.6 ). To expose the joint, the patella can be lateralized (not everted) with the attached vastus medialis.

11.1.3 Exposure of the Knee Joint

No further dissection is required for exposure of the medial joint compartment. The tibial plateau and femoral condyle are readily accessible by moving the soft tissue window with the knee in various degrees of flexion.

If the entire joint is to be visualized, the tibial plateau is exposed subperiosteally from the medial side, proximal to the tibial tuberosity. Hoffa′s infrapatellar fat pad and the deep infrapatellar bursa remain attached to the patellar ligament. This allows the patella to be moved laterally without tension with reduced knee flexion. Two Langenbeck retractors are now inserted laterally, the tips of which are supported on the lateral femoral condyle. They hold the patella in a lateralized position while the knee is flexed cautiously to 70–80° ( Fig. 11.7 ). This tenses the vastus medialis increasingly over the distal femur, and vastus medialis can tear if the knee is flexed with excessive force, especially with the midvastus approach.

11.1.4 Wound Closure

Hemostasis is ensured after release of the tourniquet. The joint capsule and divided retinaculum are sutured. In the midvastus approach, the superficial muscle fibers and the muscle fascia are also sutured.

11.1.5 Note

In the minimally invasive approaches, the connection between the quadriceps tendon and vastus medialis is always preserved. This avoids the patella′s tendency to postoperative lateralization, and quadriceps function is maintained. During flexion and extension, the joint incision moves proximally or distally like a mobile window, depending on which part of the joint is to be exposed.

In principle, the quadriceps-sparing approach is the least traumatic for the muscles but can be used only in thin patients.

If a bicondylar knee prosthesis is to be inserted via the minimally invasive approach, smaller instruments are required. In the case of contracted knees, greater axial misalignment, muscular or obese patients, or revision surgery, it is advisable to extend the incision to the conventional anteromedial parapatellar approach ( Fig. 11.8 ).

11.2.1 Principal Indications

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  Allo-arthroplasty

  
  
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  Synovectomy

  
  
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  Arthrodesis

  
  
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  Extension of minimally invasive approaches

11.2.2 Positioning and Incision

The patient is placed in the supine position with the leg extended and draped to allow free movement. The skin incision begins 5 cm proximal to the superior border of the patella, approximately in the center, curves distally 1 cm medial to the medial border of the patella, and then runs to the tibial tuberosity medial to the patellar ligament.

If exposure of the pes anserinus or medial collateral ligament is required, the skin incision may be extended for another 5 cm distally ( Fig. 11.8 ). The subcutaneous tissue is now dissected anteriorly and posteriorly, after which the infrapatellar branch of the saphenous nerve is identified ( Fig. 11.9 ).

11.2.3 Exposure of the Knee Joint

The medial patellar retinaculum is incised 2 cm medial to the border of the patella. The joint capsule is then bluntly dissected from the retinaculum and the quadriceps tendon with scissors ( Fig. 11.10 ). A stay suture is placed in the extensor apparatus of the knee joint at the level of the proximal border of the patella to allow for proper closure of the retinacula. The quadriceps tendon is then split several millimeters lateral to the insertion of vastus medialis. The joint capsule is opened about 2 cm proximal to the medial joint cavity. When dividing the synovial joint capsule distally, account has to be taken of the insertion of the anterior horn of the meniscus ( Fig. 11.11 ). The patella can now be retracted laterally and rotated by 180°. If dislocation and rotation of the patella in a lateral direction are not possible, the incision of the quadriceps tendon and the joint capsule should be extended further proximally. In repeat operations, it occasionally proves necessary to detach scar tissue in the area of Hoffa′s infrapatellar fat pad and the lateral joint capsule to make complete dislocation and rotation of the patella possible. Then the knee is flexed to 90°, which permits clear exposure of the medial and lateral femoral condyle, the intercondylar fossa with both cruciate ligaments, the medial and lateral meniscus, and the tibial plateau ( Fig. 11.12 ).

11.2.4 Extension of the Approach

To expose the pes anserinus as well as the medial joint capsule as far as the semimembranosus corner, the incision is extended 5 cm distally from the tibial tuberosity. The skin incision in the proximal region is the same as for the medial parapatellar approach.

After splitting the subcutaneous tissue, the infrapatellar branch of the saphenous nerve is first identified and retracted with a nerve loop. The medial arthrotomy is typically performed via the retinacula 2 cm medial to the internal border of the patella. Subsequently, the layer below the infrapatellar branch is undermined, the nerve is elevated, and beneath it the fascia and the insertion of the superficial part of the pes anserinus are incised. If necessary, the incision may be extended proximally into the quadriceps tendon ( Fig. 11.13 ). The knee joint can now be flexed to 90° by hinging down the operating table. In this position, the fascia with the tendons of the superficial part of the pes anserinus can readily be dissected in a posterior direction so that the medial knee joint capsule is clearly exposed. When detaching the superficial part of the pes anserinus from the tibia, care should be taken to spare the underlying attachment of the medial collateral ligament.

If necessary, the posterior portion of the knee joint can also be inspected from the medial side. The knee joint capsule is opened obliquely behind the posterior medial collateral ligament, and a Langenbeck retractor is inserted ( Fig. 11.14 ). This incision generally affords a good overview of the posteromedial corner of the medial meniscus, the posterior joint capsule, and the deep portions of the medial collateral ligament. If exposure of the tibial attachment of the posterior cruciate ligament is required, the incision of the capsule may be extended in a medial direction on the femur, a portion of the medial gastrocnemius head being transected at the same time ( Fig. 11.15 ). The tendon of adductor magnus must not be damaged during this incision. The overlying articular nerve of the knee and the branches of the medial superior genicular artery must likewise be spared.

11.2.5 Anatomical Site

( Fig. 11.16 )

The so-called posteromedial joint corner or semimembranosus corner has special significance for the function of the knee joint. The posterior portion of the medial knee joint capsule is dynamically stabilized by the semimembranosus. Semimembranosus has five insertions whose direction is dependent on the flexion of the knee joint. The reflected part runs beneath the medial collateral ligament to the tibia and guards against external rotation on flexion. The direct medial attachment to the tibia causes contraction of the posterior capsule in the extended position. The oblique popliteal ligament is a radiation of the semimembranosus tendon into the posterior joint capsule. Two other fiber tracts radiate into the posterior medial collateral ligament (posterior oblique ligament) on one hand, and into the aponeurosis of the popliteus muscle on the other.

Arthrotomies of the posteromedial portion of the joint may be performed both anterior and posterior to the posterior medial collateral ligament. This femorotibial ligament is closely connected to the posteromedial corner of the medial meniscus. The posterior horn of the meniscus is stabilized by this ligament. Additional dynamic stabilization of this ligament is provided by branches of the semimembranosus tendon.