Gaining Surgical Exposure in Total Knee Arthroplasty

Introduction

The importance of adequate exposure in revision total knee arthroplasty (TKA) is critical to successful and safe surgery. Even a healthy native knee has a relatively limited soft-tissue envelope; the compromised knee is unforgiving and requires patience and meticulous technique to adequately visualize important structures, access implants, and provide a safe environment to ensure a successful outcome for the patient.

First and foremost, appropriate planning and handling of soft tissues are necessary to give the incision the best chance to heal. Beyond taking previous surgeries into account, the surgeon should consider other risk factors for wound complications in patients undergoing TKA. These include diabetes, autoimmune and inflammatory diseases such as rheumatoid arthritis, renal failure, lupus, and human immunodeficiency virus (HIV). Patients with a history of chronic corticosteroid use should raise the surgeon’s concern for wound healing issues.

Without adequate and wide exposure, removing implants safely and inspecting and treating underlying bony defects is extremely difficult. Further, inadequate exposure commonly leads to increased loss of bone stock during removal of implants. Extensile exposure of the knee in the revision setting allows the surgeon to perform the procedure more quickly, preserve bone stock, and balance the knee. Extensile exposure also assists the surgeon in avoiding intraoperative fracture and devastating complications such as knee instability, extensor mechanism disruption, and wound breakdown.

The revision knee surgeon has multiple options available to expose the knee and safely perform surgery. Choosing the correct extensile exposure technique is dependent on appropriate preoperative evaluation and planning as well as experience. The following sections are meant to aid the revision knee surgeon in decision-making and give specific tips and tricks for performing extensile exposures to the knee.

Preoperative Assessment

One of the most important elements of revision knee surgery is to have a clear understanding of the reason for revision. This may include infection, aseptic loosening, component malposition, arthrofibrosis, instability, or bearing wear. Radiographs of the knee should be obtained to assist in preoperative planning. Views include bilateral weight-bearing anteroposterior, lateral, patellar, merchant, and sunrise views of the affected knee. Long-leg alignment radiographs from the hip to ankle are also helpful in planning the type of revision and the need for corrective releases and bone cuts. In general, radiographs should be evaluated for implant type and component positioning, component rotation, the presence of hardware other than arthroplasty implants that may need to be removed, and bony defects that will need to be addressed intraoperatively. In addition, the patella should be assessed for maltracking, signs of extensor mechanism disruption, and position (i.e., baja or alta).

Preoperative range of motion can be predictive of how challenging exposure may be in the revision setting. In general, a knee with less than 80 degrees of flexion may need an extensile exposure technique. The surgeon should note the location of previous incisions, noting any previous infections and, particularly, wound healing problems. If patients suffered from wound complications in the past, further inquiry is necessary to determine the possible causes (e.g., infection, poor blood glucose control, steroid use) and whether adjustments can be made in order to lower the risk of future wound complications. It is also important to know when previous incisions were made, which plays a role in the amount of scarring the surgeon can expect to encounter.

Management of Previous Incisions

Prior incisions should be noted during the preoperative assessment and considered in preoperative planning. As a general rule, a single previous TKA midline incision can be incorporated and modified as needed during revision TKA ( Fig. 7.1 ). For infected cases or those with hypertrophic scarring, the previous scar may be excised.

Whenever possible, one should utilize and incorporate previous incisions. If not, maintain at least a 6-cm skin bridge to decrease the risk of skin necrosis. Another factor to consider is the most recent incision and whether it healed without complication. Because blood supply to the skin originates from the medial aspect of the knee via the descending saphenous branch of the medial geniculate artery, using the most lateral previous longitudinal incision if multiple are present will decrease the risk of devascularizing the superficial skin over the knee. Deeper subcutaneous flaps may then be created to aid in the exposure ( Fig. 7.2 ). The cutaneous blood supply around the knee progresses from deep to superficial; therefore, development of full-thickness skin flaps are paramount (i.e., maintaining skin, dermis, and fat as one layer) to preventing skin necrosis ( Fig. 7.3 ).

If transverse scars are present, attempts should be made to bisect the incision at least 60 degrees, or as close to 90 degrees as possible. Crossing an old incision at an acute angle creates a peninsula of skin with tenuous blood supply, at risk for skin necrosis.

Intraoperative Principles of Exposure

Exposure in revision TKA with a medial parapatellar arthrotomy with thorough intraarticular release and sound surgical technique is crucial and in the vast majority of cases provides the surgeon with sufficiently wide exposure. In a review of 126 revision TKAs, Della Valle et al. found that a standard medial parapatellar arthrotomy approach was adequate in providing exposure in 111 (92%) of cases.

Initial exposure begins with the knee in flexion to maintain some tension on the skin, a long incision that follows the patient’s prior scar, and development of full-thickness skin flaps. This allows for preservation of maximal blood supply as described previously. During exposure, one should excise old scar(s) below the level of the dermis, as these can be a harbor of bacteria. Mobilizing the extensor mechanism by removing all fibrous adhesions from the suprapatellar pouch as well as the medial and lateral gutters aids in soft-tissue excursion. This includes any adherent fibrous tissue from the dorsal aspect of the quadriceps tendon proximal to the patella.

Next, flex and externally rotate the tibia. This delivers both the anteromedial and posteromedial tibia, making it easier to create a robust medial flap of the deep structures, including the retinaculum, deep medial collateral ligament (MCL), and semimembranosus bursa. The medial release can be performed all the way to the mid-coronal plane without destabilizing the knee. This step reduces stress on the tubercle and the extensor mechanism by relative lateral displacement, which obviates the need to evert the patella and decreases the risk of patellar tendon disruption.

Further mobilization of the distal extensor mechanism must be performed safely. To do this, the fibrous tissue/scarring between the inferolateral tendon and anterolateral tibia must be identified and debrided while protecting the patellar tendon by orienting the knife parallel to the tendon. The scar tissue on the lateral aspect of the patella is also gently released to relax the fibrotic fat pad, allowing subluxation of the patella. A lateral release can be performed to increase exposure but may not be necessary. If there is concern for peeling of the patellar tendon during exposure or subluxation, a pin can be placed in the distal tendon to stabilize it. This helps prevent further peeling. It also serves as a constant reminder that the tendon is at risk and that additional care should be taken to avoid further disruption. Another alternative is to make two or three longitudinal incisions in the fibrotic fat pad while staying deep to the tendon, known as the “mango peel,” to relax adhesions and aid in excursion of the patellar tendon.

Following the medial exposure and mobilization of the extensor mechanism, a medial, lateral, and peripatellar synovectomy should be performed to create more space again for revision work and lessen tension on the soft tissues. Usually, the plane between the extensor and the synovium can be created bluntly on the lateral side. Often, the lateral aspect of the tibia is the most difficult to expose due to the extensor mechanism being scarred and in the way. By placing a retractor over the lateral aspect of the tibia early in the procedure, the soft tissues will progressively relax over time and make retraction easier. The plane between the retinaculum and medial soft tissue can be found bluntly. Care should be taken while excising the synovium to avoid cutting into the capsule or extensor mechanism. Peripatellar synovial overgrowth should be excised to allow for increased subluxation of the patella.

In the majority of revision TKAs, these techniques provide adequate exposure and allow for safe implant removal. If extensile exposure is necessary, additional techniques may be utilized.