Surgical Procedure

Lateral Exposure

TKA can be performed through a lateral skin incision in at least two ways. One is simply a modification of the more standard median parapatellar approach; namely, a lateral incision is made. However, the capsular incision is made after medial undermining and is made in a manner identical to those described in discussions that follow. This lateral skin and medial capsular exposure may have some theoretical advantages with regard to skin healing, sensation, and potential neuromata formation. It is also used to better protect the main capsular closure because this is not directly under the skin incision. The surgeon may feel that the advantages are purely conjecture and are outweighed by the potential disadvantages of a more difficult exposure. Even if the surgeon prefers this approach, its use in patients with obesity would definitely be more difficult. Here the presence of a medial or even a lateral skin flap involves a much more troublesome exposure ( Fig. 7.3 ).

A lateral skin incision paired with a lateral parapatellar arthrotomy may be considered, especially in the presence of severe valgus deformity. This may have some advantages for skin healing and skin innervation. It may also maintain both superior medial and inferior medial blood supplies to the patella and the general integrity of the medial tissues to obviate certain problems of lateral patellar subluxation.

In this approach special attention to the patellar tendon and more difficult access to the distal end of the femur can be anticipated because of the relative lateral position of the tibial tubercle. This point appropriately introduces an exposure wherein a lateral parapatellar incision is combined with a small tibial tubercle osteotomy. The approach was described for facilitating lateral collateral and other lateral soft tissue release in patients with severe valgus deformity. True lateral parapatellar approaches have a presumed advantage of effecting good lateral retinacular release and providing direct exposure for a lateral collateral release or pie-crusting technique.

Medial Exposure

Medial exposure of the knee joint for TKA may be done through a variety of skin incisions ranging from centrally oriented, straight longitudinal ones to curved incisions directed as far medially as the medial femoral condyle and/or epicondyle. Almost anything in between, straight or curved, may be used as well (see Fig. 7.1A–C . If the very unusual expectation of needing some type of auxiliary lateral incision were to be considered, then a more medially positioned skin exposure may be appropriate to allow an adequate 8-cm skin bridge. The alternative option is to plan a full thickness skin and subcutaneous tissue flap to allow access to the lateral retinaculum and capsule.

In the case of morbid or super obesity a strong argument can be made for a straight midline incision, because it can be very difficult to evert the subcutaneous and skin tissue flap in these patients. An asymmetrical collection of the subcutaneous mass in anything other than a midline incision in the patient with obesity presents a major obstacle, first to exposure and second to approaching the knee with the prosthetic instruments (see Fig. 7.3 ). Often in those patients where the subcutaneous tissue is actually a barrier to the procedure, this layer can be mobilized from the fascia on the lateral side of the knee to allow this layer and the patella to actually “tuck” under the more superficial layer and remove the soft tissue block.

Medial exposures involve midline or slightly medial incisions in both the quadriceps and patellar tendons and are typically considered the “standard” median parapatellar incision. Another approach is the subvastus or “southern” form of incision that avoids any cut in the quadriceps mechanism directly ( Fig. 7.4A–C ). This medial approach proceeds along the inferomedial border of the vastus medialis muscle. Its obvious advantage would be the avoidance of direct surgical trauma to the extensor mechanism. Its disadvantages include some tendency to less extensive exposure and the fact that at the time of closure the capsular layer just anterior and proximal to the medial collateral ligament is quite thin and closure can be incomplete. This drawback would have to be considered in terms of adequate exposure in the especially difficult cases or in those with obesity and/or proximal tibial deformity such as what occurs after proximal tibial osteotomy. A variation of this approach is the midvastus split that follows this approach and extends about 1 to 2 cm proximally. It does involve a slight split of the vastus muscles in line with the muscle fibers ( Fig. 7.4D and E ).

The medial parapatellar approach, for most orthopedic surgeons in the United States, is a very familiar one that gives relatively good and easy exposure for a given length of incision even in the more difficult cases. This is because of the relatively lateral position of the tibial tubercle and the longitudinal incision in the quadriceps mechanism. This latter point allows the respective medial and lateral aspects of the quadriceps musculature to fall to each side, thus facilitating overall exposure. Its possible disadvantage includes considerations of patellar circulation, especially if extensive lateral release is to be performed; possible failure of the superior medial capsular repair; and development of lateral patellar subluxation. Compromise of the patellar circulation with the possibility of inducing avascular necrosis of the patella is an infrequent complication but is a valid concern in the event of patellar fracture. It is possible to dissect the lateral superior geniculate vessels to the patella if an extensive lateral release is required to preserve the blood supply. Preservation of the fat pad is also a consideration to preserve patellar circulation if an extensive lateral release is anticipated.

Full discussion of the approaches and the pertinent anatomy can be found in most orthopedic surgical approach textbooks. The following discussion is in the context of a medial arthrotomy and difficult cases where the greater level of exposure involves techniques for handling the quadriceps mechanism.

Tibial Tubercle Osteotomy and Quadriceps Turn Down

In patients who have a stiff preoperative knee with limited flexion, or those with patella baja, mobilization of a contracted anterior extensor mechanism may need to be incorporated into the exposure to allow adequate flexion of the knee and mobilization of the patella. This can be more important in the patient who is morbidly obese. Occasionally, despite excellent attempts to achieve adequate surgical exposure, the surgeon is unable to do so or they find themselves relatively more compromised than desired. The situation is usually simplified by “disconnecting” the quadriceps mechanism. This disconnection may be accomplished either proximally or distally and may be viewed as analogous to trochanteric osteotomy during exposure of the hip.

Proximal Quadriceps Tendon

The quadriceps snip, which extends a standard median parapatellar approach across the proximal quadriceps tendon, can be done easily and often does not require a more extensive dissection. A 45-degree angle cut in line with the vastus lateralis muscle is performed ( Fig. 7.5A ).

A more extensile exposure is the Coonse-Adams turn down, which facilitates exposure in some especially difficult cases ( Fig. 7.5B–C ). Performance of this technique requires subcutaneous dissection along the proximal lateral aspect at the capsular plane or, more accurately, the plane of the quadriceps tendon and the vastus lateralis. An oblique incision is then made across the lateral portion of the quadriceps muscle and is directed in a distal lateral direction. This incision will generally allow sufficient mobilization of the lateral extensor tissues. One may question the adequacy of circulation remaining to the patella and the basic requirements for protection of the repair of this incision postoperatively. It can be noted immediately that the tissue involved in the repair is strong and that it should provide a scaffold for strong suturing techniques. In consideration of this approach one is directed to the report concerning the use of this auxiliary incision as part of a V-Y quadricepsplasty.

In comparison to a tibial tubercle osteotomy, which is described in the next section, the Coonse-Adams turn down does not provide as great a degree of extensor mechanism mobilization. However, it may be easier to perform and to repair.

Tibial Tubercle Osteotomy

Osteotomy of the tibial tubercle offers wide exposure, but it has potential drawbacks. The surgeon has to be primarily concerned about the possibility of postoperative avulsion, that is, failure of fixation. This fact is of special concern in knee arthroplasty surgery because immobilization in extension by bracing postoperative protection will affect the knee motion and outcome. Avulsion is a realistic concern, as the patient setting is typically one in which flexion is limited from the beginning. If poor bone quality compromises fixation, then the surgeon may prefer a proximally extended exposure option.

A specific technique of tibial tubercle osteotomy is shown in Fig. 7.6 . Efforts are made to achieve a suitably thick piece of bone without undermining the residual strength of the proximal tibial area. The bone fragment is made long enough to provide room for two or three fixation screws, and provision is attempted for contouring the bone proximally so that there is a step cut that will prevent proximal migration as long as the fragment remains opposed to the tibial base. The osteotomy can also be contoured to anteriorize the extensor mechanism and realign the patellar tendon for lateral subluxation of the mechanism if needed. The fragment is elevated using a bone saw with a thin blade. Fascia and muscle that attach to the fragment laterally are maintained in continuity as well as possible.

If fixation is to be achieved by screws, then predrilling these holes along with tapping and countersinking before osteotomizing the tubercle fragment can be done as long as the surgeon plans to avoid the baseplate keel. However, if there is a planned change for antero-medialization of this fragment, this should not be done. These maneuvers protect the resulting fragment, ensuring that it is large enough to receive the screws and that no damage will occur during drilling or tapping of the screws. The fragment is reapplied with AO malleolar screws (4.5-mm lag screws). These automatically provide a lag effect without proximal over-drilling. Furthermore, location of the distal cortex is relatively easier owing to the pointed shape of the screw tips and the self-tapping nature of the screw threads. Alternatively, or in combination, fixation may be achieved by wiring as shown in Fig. 7.7 .

Fixation can be augmented by placing a screw and washer proximal to the tibial tubercle fragment. This practice provides a post that is an obstacle to proximal migration failure. Additionally, fixation can be further enhanced by the use of at least one heavy ligament suture, which is restrained by a screw head or staple distally, or the use of a bone anchor. As with trochanteric fixation at the hip, the best opportunity for this approach is at the time of original surgery and not as a revision procedure. Therefore the tubercle is securely reattached by whatever number of screws, wires, sutures, or staples are required. Any bulky, prominent hardware can be removed after the tubercle is healed.

Postoperative management of both the tibial tubercle osteotomy and the Coonse-Adams turn down is described in the postoperative rehabilitation section. Briefly, patients protect such repairs with removable knee immobilizer splints. They are permitted active flexion to tolerance out of the splint and very gentle passive flexion that is commonly done with gravity-assisted knee bending. Also, they can dangle the extremity with instruction to the therapist to perform no forced flexion or extension against resistance. For patients who have had a V-Y type of turn down, there is initial permission to do straight leg raising exercises with the knee immobilizer in place, but they are not permitted to perform active knee extension out of the splint for the first 6 weeks after surgery.

Exposure Details

The details of exposure discussed in this section are particular to the general anteriomedial exposure. This section reflects the personal opinions and experience of the original and current authors so that the true novice should have a minimal number of questions remaining about a technique that works. The technique has evolved from a large operative experience, where a great emphasis has been placed on technical facility, a proper combination of speed, efficiency, gentleness of tissue handling, accuracy of hemostasis, and care in the accuracy of ligament balance and bone cutting. Efficiency in the operative procedure to decrease time of open exposure of the knee has also been shown to decrease complications and infection. The development of the smooth performance of an operation, without wasted time and with good facility, becomes worthwhile when the technically difficult cases are approached.

Capsular Exposure

Fig. 7.8A illustrates a relatively straight, very slightly medially positioned incision; a longitudinal midline approach is used in patients with obesity (see Fig. 7.1A ). A slightly curved, relatively more medially positioned incision is used when tightening of the medial collateral ligament is planned (see Fig. 7.1C ).

Incision length should avoid the traumatic stretching incisional margins, especially at the inferior apex, to avoid any wound healing issues. Relatively larger incisions are particularly indicated in patients with obesity.

Except when large, subcutaneous venous varicosities are encountered, no major bleeding points are present down to the level of the capsule. Once the capsular area is well defined, the two- or three-member team may focus its attention on hemostasis in the subcutaneous region.

On incising the subcutaneous fat in the suprapatellar region, one is directed to identify the deep fascia that overlies the fat investing the quadriceps tendon ( Fig. 7.8B ). The purpose of making this identification relates principally to wound closure, because specific repair of this deep fascia can be accomplished and provides strength and good approximation while avoiding strangulation of large amounts of subcutaneous fat with sutures. The fat underlying this fascia leads directly to the quadriceps tendon. Also, the identification of this deep fascia improves understanding of the tissue planes as they relate to the exposure of the medial aspect of the joint capsule.

Exposure is carried deeper to the level of the quadriceps tendon in the proximal one-third of the wound, to the capsular tissue over or adjacent to the patella in the middle one-third, and distally to the periosteum over the anteromedial flare of the tibia ( Fig. 7.8C ). Specifically, incision into the prepatellar bursa at the anterior aspect of the knee or into the paratenon overlying the patellar tendon itself is avoided.

Definition of the capsular plane is performed next from distal to proximal ( Fig. 7.8D ). As dissection proceeds from the area of the distal, medial aspect of the capsule and the medial tibial flare, it comes to a soft tissue plane, which is superficial to the level of the quadriceps tendon. This is because the fascia overlying the quadriceps tendon, which was mentioned earlier and which has been incised, is in the proximal aspect of the wound, superficial to the level of dissection. In the distal aspect it is the layer contiguous with the distal capsule and actual periosteum. Incising this fascia proximally puts the surgeon at a deeper level in the proximal aspect of the wound than in the distal aspect. As the distal plane of dissection is taken proximally, it is necessary to incise this fascia to connect the two levels of dissection ( Fig. 7.8D , inset).

Sufficient medial capsular space is uncovered to allow the medial capsular incision adjacent to the patella and enough edge to effect good repair at the time of closure. Enough exposure of the anterior extracapsular surface of the patella to allow the use of any patellar fixation clamps or cutting jigs needed in the procedure can be done at this stage. In the patient with obesity this layer can be mobilized in a full thickness layer of skin and subcutaneous tissue to allow the fascial layer to sublux below without tethering to allow exposure.