Total Knee Arthroplasty: Medial Parapatellar and Extensile Approaches
Michael R. Dayton, MD
Giles R. Scuderi, MD
Dr. Dayton or an immediate family member serves as a paid consultant to or is an employee of Exactech, Inc. and Smith & Nephew; has received research or institutional support from Exactech, Inc. and Stryker; and serves as a board member, owner, officer, or committee member of the American Academy of Orthopaedic Surgeons and the American Orthopaedic Association. Dr. Scuderi or an immediate family member has received royalties from Biomet and Zimmer; is a member of a speakers’ bureau or has made paid presentations on behalf of Biomet, Convatec, Medtronic, Pacira, and Zimmer; serves as a paid consultant to or is an employee of Acelity, Biomet, Medtronic, Pacira, and Zimmer; has stock or stock options held in Force Therapeutics; has received research or institutional support from Pacira; and serves as a board member, owner, officer, or committee member of Operation Walk USA.
This chapter is adapted from Incavo SJ, Dayton MR, Exaltacion JJF: Total knee arthroplasty via the medial parapatellar approach, in Flatow E, Colvin AC, eds: Atlas of Essential Orthopaedic Procedures. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2013, pp 341-344 and Seidenstein A, Scuderi S, Scuderi GR: Revision total knee arthroplasty via quadriceps snip, in Flatow E, Colvin AC, eds: Atlas of Essential Orthopaedic Procedures. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2013, pp 359-362.
A standard anterior midline skin incision with a medial parapatellar arthrotomy continues to be the most widely used method of exposure for total knee arthroplasty (TKA). The extensor mechanism of the knee, which is composed of the quadriceps muscle and tendon, patella, and patellar tendon, comprises a complex interaction of structures providing continuity for effective knee function. Proper preservation of the extensor mechanism is vital to successful recovery in TKA. The main advantage of the anterior approach to the knee is that it provides excellent visualization and access to the distal femur, proximal tibia, and patella. Although not extensile in the classic sense, it is more extensile than most approaches for TKA.
INDICATIONS
The medial parapatellar approach for TKA is indicated for both primary and revision TKA cases. Variations in pathologic morphology may include varus or valgus deformity, patella alta or patellar infera, and previous tibial or femoral osteotomy. It can be used regardless of preoperative range of motion. Patients of short stature, obese patients, and patients with muscular lower extremities are ideal candidates for this approach. The tissue along the medial course of the patella and knee capsule is sufficiently thick to provide a satisfactory closure following TKA. The approach is straightforward to perform and efficiently exposes the knee joint.
Indications for the medial parapatellar approach may also include the option for medial imbrication (advancement) of the arthrotomy if necessary for lateral patellar subluxation. Furthermore, should the patellar tendon be excessively thin or insufficient, a side-to-side repair of this structure can be achieved.
This approach has evolved over time, generally owing to the popularization of “minimally invasive” surgical approaches. In general, long incisions have been decreased from the traditional hands-breadth proximal to the patella extending distally past the tibial tubercle. Excellent exposure can usually be achieved by shortening the incision from 4 cm proximal to the superior pole of the patella to 1 cm proximal to the tibial tubercle. Lateral eversion of the patella is no longer considered necessary in all cases of knee replacement and has been frequently replaced by simple lateral subluxation of the patella. With lateral subluxation instead of eversion the chance of avulsion of the patellar tendon from the tibia is greatly diminished. Enthusiasm for the so-called less invasive approaches to the knee has considerably decreased because of the feeling that limited surgical exposure achieved may result in less than optimal component placement or inadvertent soft-tissue damage.
A distinct feature of the medial parapatellar approach is the capacity for extensile exposure. In the setting of revision or a profoundly ankylosed knee, a modification of anterior exposure may be necessary. The quadriceps snip has evolved from more traditional surgical techniques, such as the V-Y quadriceps turndown described by Coonse and Adams and Insall’s patellar turndown.1,2,3 In 1988, Insall discovered that by extending the medial arthrotomy proximally and transecting the quadriceps tendon laterally, greater exposure was achieved. This observation led to the use of the quadriceps snip (Figure 1) as a means of exposing the tight knee in primary and
revision TKA.1,4 The quadriceps snip should be the first-line workhorse approach for revision TKA because it allows exposure of the tight knee without risking tibial tubercle avulsion or patellar tendon rupture.1 Even in the case of primary TKA, extensive scarring of the extensor mechanism may require more than a simple medial parapatellar approach. In patients with quadriceps contracture and limited flexion, modification of the standard medial parapatellar may be necessary to avoid compromise of the extensor mechanism and facilitate proper flexion and exposure for TKA. After arthrotomy via a standard medial parapatellar approach, the knee should be passively flexed and lateral subluxation of the patella attempted. If the exposure is insufficient or an inordinate amount of tension is placed on the patellar tendon, the quadriceps snip is indicated and should be performed at this point in the procedure.
revision TKA.1,4 The quadriceps snip should be the first-line workhorse approach for revision TKA because it allows exposure of the tight knee without risking tibial tubercle avulsion or patellar tendon rupture.1 Even in the case of primary TKA, extensive scarring of the extensor mechanism may require more than a simple medial parapatellar approach. In patients with quadriceps contracture and limited flexion, modification of the standard medial parapatellar may be necessary to avoid compromise of the extensor mechanism and facilitate proper flexion and exposure for TKA. After arthrotomy via a standard medial parapatellar approach, the knee should be passively flexed and lateral subluxation of the patella attempted. If the exposure is insufficient or an inordinate amount of tension is placed on the patellar tendon, the quadriceps snip is indicated and should be performed at this point in the procedure.
 FIGURE 1 Illustrations of the quadriceps snip. A, A standard medial parapatellar arthrotomy with proximal transection of the quadriceps tendon in an oblique fashion into the fibers of the vastus lateralis. B, With release of the quadriceps tendon proximally, the patella is subluxated laterally, and the joint is exposed. |
CONTRAINDICATIONS
Medial Parapatellar
Previous skin incisions oriented longitudinally and lateral to that through which a medial parapatellar approach would be performed are a relative contraindication. Narrow skin bridges pose considerable risk of skin necrosis. Incisions 4 cm or less from a previous incision should be avoided. If skin bridges of 4 cm or less must be used for the arthroplasty, close attention to wound healing is mandatory. Hospital discharge may need to be delayed in such a case. If skin necrosis develops, soft-tissue coverage should be obtained expeditiously, prior to wound breakdown.
Specific circumstances may require alternative approaches to the medial parapatellar arthrotomy. Previous surgery using a lateral approach may compromise the blood supply to the patella. As the patella is supplied by the midpatellar vessels in the middle one-third of the anterior surface—with the vessels entering the apex behind the tendon—disruption of more than one supply may compromise the patella. Specifically, the upper one half of the patella is supplied only by the midpatellar vessels. Cadaver studies have shown absence of vascular filling after medial arthrotomies done too close to the patella, and also after radical fat pad excision, lateral release too close to the patella, and cautery of the prepatellar vessels.
ALTERNATIVE APPROACHES
Surgical approaches that vary from the medial parapatellar approach must be able to satisfactorily allow
soft-tissue releases that correctly align the knee (Table 1). While allowing appropriate tissue releases, the approach must also avoid undesirable loosening or attenuation of tissue in areas already weakened by disease.
soft-tissue releases that correctly align the knee (Table 1). While allowing appropriate tissue releases, the approach must also avoid undesirable loosening or attenuation of tissue in areas already weakened by disease.
Subvastus Approach
Although the original description of this technique dates back to 1929, it has been recently used with increasing popularity as described by Hoffman.5 Similar indications exist for this approach as for the medial parapatellar. Theoretical advantages include decreased patellar subluxation and vascular devitalization. This remains a topic of debate. Disadvantages include the potentially increased technical difficulty, particularly in muscular patients and in short individuals.
Midvastus Approach
The midvastus approach emerged in popularity in the 1990s. This technique, theoretically combining advantages of the medial parapatellar and subvastus approaches, divides the vastus medialis obliquus (VMO) in line with the fibers in their midsubstance.6 A unique feature of this approach, in contrast to the medial parapatellar, is the lack of disruption of the vastus medialis insertion into the quadriceps tendon. Another theoretical advantage of this muscle splitting approach with regard to healing potential is that the quadriceps tendon receives its nutrition mainly from the overlying paratenon and soft tissue and takes more time to heal. Medial capsular advancement may be difficult to perform with this approach at the time of closure. Compared with the subvastus approach, however, this option allows easier eversion and lateral displacement of the patella. Both of these techniques are relatively contraindicated in muscular and short patients, patients with previous high tibial osteotomy, previous revision surgery, or aggressive ossific osteoarthritis.
Lateral Parapatellar
This approach is most commonly used in the presence of valgus knee deformity, where lateral intra-articular adhesions or contractures may be present.7 This approach may also be useful when lateral retinacular release is necessary. Laterally based dissection avoids the attenuation of medial tissue that accompanies medial exposure. The lateral tissue, however, is considerably thinner in the capsule, potentially hampering the integrity of the capsular closure. This is a more technically demanding exposure, particularly given the inconsistency with which valgus knees may present. Anatomy is reversed with this approach, and difficulty may be encountered with medial patellar reflection even in the primary total knee setting since the tibial tubercle is lateral to the midline of the tibia. Medial patellar reflection may also be difficult in the setting of revision TKA.
TECHNIQUE
Medial Parapatellar
Room Setup/Patient Positioning
The patient is placed in the supine position, with a bump under the ipsilateral hip if excessive lower extremity external rotation is present. A device to alternately hold the foot in flexion and extension may be helpful. Application of a proximal thigh tourniquet is standard, and routine prep and drape should allow full exposure of relevant anatomy and landmarks, including tibial tubercle, patella, and distal quadriceps.
Instruments/Equipment/Implants
The medial parapatellar approach generally does not require specific instrumentation or equipment. Some retraction tools, however, may be very helpful. A bent Hohmann is useful for lateral tissue distraction whether the patella is everted or not. A marking tool may be helpful to note the extent of the arthrotomy from the medial side of the quadriceps tendon and medial border of the patella (ensuring at least 5 mm from the medial patellar edge) distally to the medial border of the patellar tendon. This is to ensure reapproximation in identical points at time of closure. In cases of a tight extensor mechanism, a pin through the patellar tendon and into the proximal tibia may be helpful to avoid avulsion of the former from its attachment into the tibial tubercle. If extremely tight, however, the surgeon should not hesitate to employ the use of an extensile technique.
Surgical Technique
With the knee in extension, the anterior skin incision is marked 4 cm proximal to the patella to 1 cm distal to the tibial tubercle (Figure 2, A). The knee is placed in the flexed position for the skin incision (Figure 2, B). Often, with the knee flexed, the entire length of the marked skin incision is not entirely necessary because of the stretching of the skin. Enough proximal incision should be used to provide exposure of at least 2 to 3 cm of the quadriceps tendon. The dissection should occur through the fat just deep to the muscle fascia to minimize disruption to the skin blood supply (Figure 3). Medial and smaller lateral full thickness skin flaps are developed. The arthrotomy is then started 2 to 3 cm proximal to the patella curving along the medial patella and then parallel to the patellar ligament to the tibial tubercle. The arthrotomy should maintain a 5 mm cuff of soft tissue lateral to the vastus medialis insertion and medial to the patella and patellar ligament (Figure 4).
The knee is then extended and the proximal medial tibia is exposed by elevating the medial capsular flap and deep MCL from the bone to the mid coronal plane for most cases (Figure 5). If more medial release is required
this can be continued further to the posteromedial corner of the knee joint. The anterolateral tibia is exposed by retracting the patellar ligament anteriorly (Figure 6). The patella can then be subluxated laterally (Figure 7) or everted (Figure 8) when the knee is flexed with care being taken to not place undue tension on the patellar tendon insertion. A Hohmann retractor is placed under the lateral meniscus after the anterior portion of this has been cut. If additional lateral exposure is desired after patellar eversion, the patellofemoral ligament can be cut in its midsubstance with gentle retraction by the lateral retractor (Figure 9).
this can be continued further to the posteromedial corner of the knee joint. The anterolateral tibia is exposed by retracting the patellar ligament anteriorly (Figure 6). The patella can then be subluxated laterally (Figure 7) or everted (Figure 8) when the knee is flexed with care being taken to not place undue tension on the patellar tendon insertion. A Hohmann retractor is placed under the lateral meniscus after the anterior portion of this has been cut. If additional lateral exposure is desired after patellar eversion, the patellofemoral ligament can be cut in its midsubstance with gentle retraction by the lateral retractor (Figure 9).
TABLE 1 Results for Various Arthrotomy Techniques Versus Medial Parapatellar Approach | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
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