Patient selection and physical examination of the patient who is a candidate for a standard medial parapatellar arthrotomy in revision total knee arthroplasty (TKA) are discussed. Step-by-step surgical techniques for the standard medial parapatellar arthrotomy are described, including surgical “pearls” describing ways to increase the exposure without extension to further extensile approaches.
A standard medial parapatellar arthrotomy is claimed to be used in most revision TKAs. However, adequate exposure in the strict standard medial parapatellar arthrotomy may be affected by several factors, including the cause of revision surgery, the condition of skin and soft tissue around the knee, the range of motion (ROM), and the change of the normal knee anatomy.
The following sequential procedures are useful for increasing the surgical exposure in revision TKA using a standard medial parapatellar arthrotomy:
Excision of thickened synovium and fibrous tissues and lysis or débridement of scarred tissue in both medial and lateral gutters
Débridement of scarred tissue beneath the extensor mechanism, including scarred tissue at the patellar tendon, around the patella, and at the quadriceps tendon
Release of the lateral retinaculum to increase patellar mobility
Subperiosteal peel of the distal femur to increase visualization of the distal femur
Extensile arthrotomy if the exposure is still limited
Revision TKA under inadequate exposure may cause intraoperative complications ranging from skin problems to avulsion of the patellar tendon from the tibial attachment, which is a catastrophic problem. Avoidance of these complications by careful evaluation of the tension of the capsule and surrounding tissues is mandatory.
If a revision TKA is indicated, the extension of the standard surgical approach is based on several factors, including the cause of revision surgery, the condition of the skin and soft tissue around the knee, the range of motion (ROM), and the change of the normal knee anatomy. Selection of the skin incision usually relies on the prior incisions, but options for capsular arthrotomy may range from a standard medial arthrotomy to an extensile arthrotomy based on proper surgical visualization.
A medial arthrotomy of the knee is defined as a capsular incision located medial to the patella and the patellar tendon and includes the medial parapatellar arthrotomy, the midvastus arthrotomy, and the subvastus arthrotomy. In revision surgery, the term medial arthrotomy usually refers to the medial parapatellar arthrotomy, which is considered the workhorse of capsular incisions. In fact, the medial parapatellar arthrotomy provides better versatility for further extensile arthrotomy. Therefore, this chapter describes the surgical technique of the standard medial parapatellar arthrotomy in revision TKA.
Indication and Contraindications
In general, a standard medial parapatellar arthrotomy provides adequate exposure in most cases of revision TKA. However, it is common that slight extension of the arthrotomy to the quadriceps snip is performed. Therefore, a strict medial parapatellar arthrotomy in revision TKA may not facilitate adequate visualization in all knees.
A strict medial parapatellar arthrotomy in revision TKA should be indicated for patients whose knee profiles are not much different from those of the virgin knees. Patients may have implant loosening or knee instability with well-preserved ROM ( Fig. 6.1 ). On the physical examination, patients should have a single or a few prior skin incisions with normal soft tissue appearance. The affected knee should have a good passive ROM, which is usually greater than 100 degrees. These findings reflect good extensor mechanism mobility, which facilitates patellar eversion or patellar subluxation. In these conditions, adequate visualization of both femur and tibia can be accomplished according to the strict capsular incision. In addition, I propose that the positive finding of a ballottable patella due to chronic knee effusion represents a large suprapatellar pouch that facilitates extensor mechanism mobility.
In contrast, the presence of multiple prior skin incisions with poor blood supply and soft tissue mobility is a relative contraindication for a strict medial parapatellar arthrotomy. These patients usually have limited knee ROM. The radiograph may demonstrate a patella baja or distortion of the normal knee anatomy. Common diagnoses in these cases include multiple revised knee, periprosthetic infection, previous resection arthroplasty, and painful knee after TKA.
At the preoperative evaluation, the patellar mobility test ( Fig. 6.2 ) is useful for evaluation of mediolateral mobility of the patella. The positive test indirectly represents good mobility of the extensor mechanism, which will allow a strict medial parapatellar arthrotomy providing adequate exposure.
Spinal or epidural anesthesia is preferred, with planning for a longer operative time than that of primary TKA. The patient is in the supine position, and the tourniquet cuff is properly prepared with low-pressure inflation. The surgical draping is made in similar fashion to the preparation for primary TKA. Fixing of a solid bump to stabilize the foot when the knee is flexed to 90 degrees is useful; however, this technique cannot be done in a knee with limited flexion. Syringes for joint fluid collection and sterile containers for tissue frozen sections and tissue cultures are prepared.
The skin incision is usually made using the prior skin incision with slight extension to the normal tissue. The skin incision is 15 to 25 cm long, with the proximal end extending approximately 6 to 10 cm above the superior pole of the patella and the distal end extending to the medial border of the tibial tubercle ( Fig. 6.3 , A ). The prior skin incisional hard scar may be excised as needed.
Subcutaneous dissection of both medial and lateral sides is made at a level just below the fascial layer in order to maintain skin viability (see Fig. 6.3 , B ). If the fascia is difficult to identify, a thick skin flap should be made to avoid compromise of the arterial supply to the skin.
Further dissection is made until the border between the medial quadriceps tendon and the muscle fibers is identified at the proximal end (see Fig. 6.3 , C ) and the border between the medial patellar tendon and the medial tibial capsule is identified at the distal end (see Fig. 6.3 , D ).
The skin incision should be made with the knee in flexion, so that the tension and the elasticity of the skin and soft tissue will provide unassisted skin retraction.
Slightly extending the incision beyond the prior skin and subcutaneous incision into the normal tissue at the proximal end provides a relevant identification of the muscle and tendon junction, preventing unintentional incision of the arthrotomy into the muscle fibers.
In the knee with multiple prior skin incisions, choose the most lateral longitudinal skin incision that seems appropriate for revision TKA.
If a prior transverse skin incision cannot be avoided, it should be incised in perpendicular fashion.
After normal quadriceps tendon at the proximal end is identified, the standard medial parapatellar arthrotomy incision is made from 6 to 8 cm above the superior patellar pole ( Fig. 6.4 , A ) to the medial border of the tibial tubercle (see Fig. 6.4 , B ). The thickened synovium and fibrous tissue, which obstruct visualization of the suprapatellar pouch, are excised with a scalpel or an electrocautery ( Fig. 6.5 ). The knee is then fully extended, and the medial tibial capsule is subperiosteally released from the proximal tibia to expose the proximal medial tibia and the medial tibial metal tray to the posteromedial corner around the semimembranosus insertion. This release provides tibial external rotation with relaxed tension on the extensor mechanism ( Fig. 6.6 ). Similarly, the lateral tibial capsule is released from the proximal tibia to expose the lateral tibial tray in order to visualize the lateral border of the tibial component ( Fig. 6.7 ). The thickened synovium and fibrous tissue at the medial and lateral gutter are excised to increase intraarticular visualization and to increase knee flexion. Additional débridement of the hard, scarred tissue at the medial and lateral gutters is made as needed.