RECONSTRUCTION 2023, Jan, 08 | 12:00 am

Minimally Invasive Subvastus Approach for Total Knee Arthroplasty

P ITFALLS

  • Examine the preoperative lateral radiograph carefully for patella baja as these patients are poor candidates for any minimally invasive total knee approach because it is very difficult to translate the patella laterally.

     

  • Patients with marked preoperative stiffness or prior open knee surgery should be operated on with the minimally invasive subvastus approach only by surgeons with substantial experience in the procedure.

     

  • Patients with poor skin quality, such as those with diabetes mellitus or rheumatoid patients on steroids, are at risk for wound healing problems after any minimally invasive total knee approach (Fig. 2).

 

Minimally Invasive Subvastus Approach

 

Indications

  • Primary total knee arthroplasty for patients and surgeons interested in saving the entire quadriceps tendon insertion on the patella in an effort to speed the return of quadriceps muscle function after surgery (Fig. 1).

    Examination/Imaging

  • The ideal candidate for minimally invasive subvastus total knee arthroplasty (MIS TKA) has good flexion (100°) and a minimal flexion contracture (10°). Moderate varus or valgus deformity (up to 15°) can be dealt with effectively with the typical medial or lateral soft tissue balancing techniques used in standard open knee arthroplasty.

     

     

     

     

    Controversies

    • Several approaches for minimally invasive total knee arthroplasty have been described, and controversy about which is best continues. In several prospective, randomized trials, the minimally invasive subvastus approach has been demonstrated to be better than the standard medial parapatellar arthrotomy, better than the so-called quad-sparing approach, and better than the mini-medial parapatellar approach with respect to earlier straight leg raising, better 10-day and 30-day flexion, and patient satisfaction (Aglietti

    et al., 2006; Faure et al., 1993; Roysam and Oakley, 2001).

     

    FIGURE 1

     

     

     

    FIGURE 2

     

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    Minimally Invasive Subvastus Approach

     

    • The skin should be examined to ensure integrity; multiple prior skin incisions make a minimally invasive approach less desirable.

      Treatment Options

      • The mini-midvastus approach is a viable, straightforward alternative to the minimally invasive subvastus approach. In that approach, the arthrotomy is brought to the superior pole of the patella and then splits the vastus medialis in line with its oblique fibers. That portion of the quadriceps that inserts from the superior pole to the midpole of the patella is by definition detached with this approach.

      • The so-called quad-sparing approach involves a short medial arthrotomy that extends to the superior pole of the patella much like old open medial meniscectomy approaches. This approach is most often done with a curious set of instruments that mandate cutting from the side, or making partial cuts, blind cuts, or freehand finishing cuts. That portion of the quadriceps that inserts from the superior pole to the midpole of the patella is by definition detached with this approach.

      • The mini-medial parapatellar approach is a straightforward approach that involves simply shortening the extent of the arthrotomy that is done proximal to the patella. The patella is not everted during the procedure. If difficulty is encountered during the procedure, this approach can quickly be converted to a standard medial parapatellar approach. That portion of the quadriceps that is divided above the superior pole down to the midpole of the patella is by definition detached with this approach.

       

    • Female patients in general are easier than male patients in part because they typically require smaller components and have more inherent laxity in the soft tissues, which makes exposure and component placement more straightforward.

    • Plain radiographs are examined for the presence of patella baja, which is a relative contraindication to any minimally invasive total knee approach. On the lateral radiograph, any large osteophytes that would hinder exposure are noted. The size of the components are templated.

    • Advanced imaging techniques such as magnetic resonance imaging or computed tomography are not required for the typical patient.

      Surgical Anatomy

    • The vastus medialis obliquus (VMO) inserts at a 50° angle (relative to the long axis of the femur) and extends all the way to the midpole of the patella on the medial side (Fig. 3).

      • The muscle belly of the VMO is more medial and extends more distally than most surgeons think. It is important to truly identify the inferior border of the VMO in order to preserve the entire quadriceps.

      • The triangular portion of tendon that extends from the midpole of the patella along the inferior edge

         

         

         

        FIGURE 3

         

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        Minimally Invasive Subvastus Approach

         

        of the VMO and back to the superior pole of the patella should be preserved with care.

  • Blood vessels crossing in the subvastus space beneath the VMO and on top of the intermuscular septum are generally small until the dissection is carried far proximal (more than 15 cm proximal to superior

    pole of the patella). In most cases, dissection in the subvastus space rarely extends more than 5 cm proximal to the superior pole of the patella.

    Positioning

     

    P EARLS

    • Surgeons should start with a traditional 6- to 8-inch incision and then shorten the incision length over time. While many female patients can readily be operated on with a 3.5-inch incision or less, some male patients—particularly those whose knee implants will be at the large end of the spectrum— are better served with a slightly longer incision.

    • The arthrotomy is made along the inferior edge of the VMO down to the midpole of the patella. Do not be tempted to cheat this superiorly as that will hinder, not help, the ultimate exposure. Always bring the arthrotomy to the midpole or equator of the patella on the medial side.

       

    • If the patella does not slide easily into the lateral gutter, typically it is because a portion of the medial patellofemoral ligament remains attached to the patella. That occurs if the proximal limb of the arthrotomy is made in too horizontal a fashion rather than at the 50°/130° angle that parallels the VMO. By releasing that tight band of tissue, the patella will translate laterally without substantial difficulty.

     

  • The patient is positioned supine on the operating table with a thigh-high tourniquet placed as far proximal as possible.

  • The leg is elevated, and then the knee is maximally flexed, before inflating the tourniquet to allow maximal excursion of the quadriceps during the procedure.

  • Our preference is to avoid the use of any limb-positioning devices. Instead, we use two assistants. The leg can then be maneuvered precisely by the surgeon during surgery. Specifically, the foot can be held by the surgeon’s hip, small movements of which can then flex or extend the knee slightly or add an external rotation force to the limb that facilitates exposure.

  • To maximize visualization of the anterior portion of the distal femur (for femoral sizing or to ensure you will not notch the femur), the knee should be brought out into a more extended position. By positioning the knee in 30–60° of flexion (instead of 90°), the tension in the entire extensor mechanism is relaxed and a good view of the anterior distal femur is obtained.

    Portals/Exposures

  • The incision starts at the superior pole of the patella, ends at the top of the tibial tubercle, and measures

    3.5 inches (8.8 cm) in extension (Fig. 4). The medial skin flap is elevated to clearly delineate the inferior border of the VMO muscle. The fascia overlying the VMO is left intact as this helps maintain the integrity of the muscle belly itself throughout the surgery.

  • The anatomy is very consistent. The inferior edge of the VMO is always found more inferior and more medial than most surgeons anticipate. The muscle fibers of the VMO are oriented at a 50° angle (or

     

     

    P ITFALLS

    • Some previous descriptions of the subvastus approach suggest that the arthrotomy be made in an L-shaped configuration (90° angle between proximal and distal extent), but visualization is much improved if the proximal limb of the arthrotomy is done obliquely along the inferior border of vastus medialis such that the angle of the medial flap is 130°.

     

     

    Minimally Invasive Subvastus Approach

     

    FIGURE 4

     

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    130° relative to the long axis of the limb), and the VMO tendon always attaches to the midpole of the patella. It is very important to preserve this edge of tendon down to the midpole (Fig. 5). That is where the retractor will rest so that the VMO muscle itself is protected throughout the case.

    • The arthrotomy is made along the inferior edge of the VMO down to the midpole of the patella (Fig. 6). At the midpole of the patella, the arthrotomy is directed straight distally along the medial border of the patellar tendon.

       

       

       

       

      FIGURE 5 FIGURE 6

       

      Instrumentation

      • Two 90° bent Hohmann retractors are very useful for this procedure and are recommended highly. The 90° angle proves excellent in safely and efficiently retracting the quadriceps and patella laterally; the tapered tip slides effectively into place to protect the medial and lateral collateral ligaments during femoral and tibial preparation.

      • A large Kocher clamp is clipped in place along the medial soft tissue sleeve just superior to the medial meniscus and is left in place for the entire procedure as a retractor to facilitate visualization of the medial side (see Fig. 8).

       

  • A 90° bent Hohmann retractor is placed in the lateral gutter and rests against the robust edge of VMO tendon that was preserved during the exposure

    (Fig. 7). Surprisingly little force is needed to completely retract the patella into the lateral gutter. The knee is then flexed to 90°, providing good exposure of both distal femoral condyles (Fig. 8).

     

     

     

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    Minimally Invasive Subvastus Approach

     

    FIGURE 7

     

     

     

    FIGURE 8

     

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    P ITFALLS

    • Care must be taken to protect the muscle and skin during guide placement and bone cutting. Bringing the knee into some extension eases the tension on the extensor mechanism and skin, thus decreasing the risk to those structures.

     

    Minimally Invasive Subvastus Approach

     

    Procedure

    Step 1

    • The distal femur is cut with a modified low-profile intramedullary resection guide. Bringing the knee out to 60° of flexion better exposes the anterior portion of the distal femur (Fig. 9).

    • Two 90° bent Hohmann retractors are placed medially and laterally to protect the skin and the collateral ligaments.

      Instrumentation/ Implantation

      • Low-profile instruments specifically designed for contemporary small-incision surgery are available from most major orthopedic implant manufacturers and facilitate the ability to position the knee ideally during surgery.

       

      Step 2

    • The proximal tibia is cut next, and by doing so, more room is made for subsequently sizing and rotating the femoral component (the most difficult part of any MIS TKA).

    • Three retractors are placed precisely to get good exposure of the entire surface of the tibia.

      • A pickle-fork retractor posteriorly provides an anterior drawer and protects the neurovascular structures.

      • Two bent Hohmann retractors medially and laterally protect the collateral ligaments and define the perimeter of the tibial bone (Fig. 10).

       

       

       

       

       

      FIGURE 9

       

      FIGURE 10

       

       

      P ITFALLS

      • Through a small incision, there is a tendency to place the tibial cutting guide in varus and internal rotation. Extra attention should be paid to the position of the tibial tubercle and the long axis of the tibial shaft during guide positioning.

         

      • Because the patella has not been everted, the patellar tendon is often more prominent anteriorly than with a standard arthrotomy and thus at risk for iatrogenic damage with the saw blade during tibial preparation.

       

       

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      Controversies

      • Some surgeons have suggested making the tibial cut in-situ (without anterior subluxation) as a way to decrease soft tissue damage at the time of TKA. To date no information supports or refutes that contention. There is little doubt, however, that it is safer to cut the tibia if it subluxed anteriorly, visualized directly and protected with retractors medially, laterally and posteriorly.

       

      Minimally Invasive Subvastus Approach

       

      FIGURE 11

       

  • The tibial resection is carried out with an extramedullary guide optimized for small-incision surgery (Fig. 11).

    • The tibia is cut in one piece using a narrow but thick saw blade that fits the captured guide.

       

      P EARLS

      • Before making the femoral cuts, the knee should brought into some extension to clearly visualize the anterior cortex and ensure that femoral notching will not occur.

         

      • Bent Hohmann retractors can be placed deep to the collateral ligaments medially and laterally on the femoral side and protect those structures during the resection of the posterior condyles.

       

    • The narrow blade is more maneuverable in the smaller guide and provides better tactile feedback for the surgeon to detect when the posterior and lateral tibial cortices have been cut.

      Step 3

  • The femoral sizing and rotation guide is thin enough that it can be pinned to the distal femur and the knee can still be brought out to 60° of flexion to visualize the anterior femur for accurate sizing

    (Fig. 12).

    • At 60° of flexion, a retractor is placed anteriorly and the surgeon can see under direct vision that the femoral cortex will not be notched.

    • Clearing some of the synovium overlying the anterior femoral cortex helps ensure that femoral sizing is accurate (Fig. 13).

       

       

       

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      Minimally Invasive Subvastus Approach

       

      FIGURE 12

       

       

       

      FIGURE 13

       

       

      P ITFALLS

      • Accurate sizing and rotation of the femoral component is often a challenge with any minimally invasive total knee approach. Surgeons should spend an extra minute or two during the initial part of the surgery to ensure that they are happy with the femoral size and rotation. Use ancillary landmarks (transepicondylar axis; Whiteside’s line) to check rotational position.

       

      • Femoral rotation is confirmed by referencing the surgeon’s choice of the posterior condyles, Whiteside’s line, or the transepicondylar axis, each of which can be defined with this subvastus approach.

         

         

         

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        Minimally Invasive Subvastus Approach

         

        FIGURE 14 FIGURE 15

         

        Instrumentation/ Implantation

        • Sizing and rotation guides specifically made for contemporary small-incision total knee surgery are necessary (Fig. 16).

         

  • After the femoral and tibial cuts are made, the surgeon can carry out final ligament releases and check flexion and extension gap balance in whatever fashion is desired (Fig. 14). The final preparation of the tibia and femur is then done (Fig. 15).

    Step 4

     

    P EARLS

    • When a patellar cutting guide is used, the trial components should be removed as then the entire limb can shorten, which takes tension off the extensor mechanism and allows easier access to the patella for preparation.

     

  • Patellar preparation with this surgical approach is left until the end. Cutting the patella is not required for exposure, and by preparing the patella last, the risk of inadvertent damage to the cut surface is minimized.

  • The patella cut is done freehand or with the surgeon’s choice of cutting or reaming guides.

     

     

     

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    FIGURE 16

     

     

    P EARLS

    • Cement is applied to the entire undersurface of the femoral implant rather than to the bone surface itself in most cases.

       

    • Special attention is paid to removing excess cement from the distal lateral surface of the femur as this area is difficult to see after the patella is cemented in place.

     

    Minimally Invasive Subvastus Approach

     

    Step 5

    • The modular tibial tray is cemented first, then the femur, and finally the patella.

    • The tibia is subluxed forward with the aid of the pickle-fork retractor, and the medial and lateral margins of the tibia are exposed well with 90° bent Hohmann retractors (Fig. 17). Care is taken to remove excess cement from around the tibial baseplate, particularly posterolaterally.

    • The femur is exposed for cementing by placing bent Hohmann retractors on the medial and lateral sides above the collateral ligament insertions on the femur.

       

       

       

      FIGURE 17

       

       

       

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      Minimally Invasive Subvastus Approach

       

      FIGURE 18

       

      A third retractor is placed under the VMO where it overlies the anterior femur. The femoral component is then cemented. Special attention is paid to removing excess cement from the distal lateral surface of the femur as this area is difficult to see after the patella is cemented in place.

  • At this point the final tibial insert can be placed or a trial insert can be used at the surgeon’s discretion (Fig. 18).

  • The patella is cemented last. After the cement has hardened, the knee is put through a range of motion and final balancing and patellar tracking are assessed.

    Step 6

  • The tourniquet is deflated so that any small bleeders in the subvastus space can be identified and coagulated.

  • The closure of the arthrotomy starts by reapproximating the corner of capsule to the extensor mechanism at the midpole of the patella (Fig. 19). Then four interrupted 0 Vicryl sutures are placed along the proximal limb of the arthrotomy (Fig. 20).

    • These sutures can usually be placed deep to the VMO muscle itself and grasp either fibrous tissue or the synovium attached to the distal or undersurface of the VMO instead of the muscle itself.

    • These first four sutures are most easily placed with the knee in extension but are then tied with the knee at 90° of flexion (Fig. 21).

     

     

     

     

     

    Minimally Invasive Subvastus Approach

     

     

     

     

     

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    FIGURE 19

     

    FIGURE 20

     

    FIGURE 21

     

     

     

     

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    Minimally Invasive Subvastus Approach

     

    FIGURE 22

     

     

    P EARLS

    • To avoid overtightening the medial side and creating an iatrogenic patella baja postoperatively, the arthrotomy is closed with the knee in 90° of flexion.

       

    • Skin staples are used, not a subcuticular suture (Fig. 23). More tension is routinely placed on the skin during MIS TKA surgery than in standard open surgery, and our experience suggests the potential for wound healing problems is magnified if the skin is handled multiple times as is the case with a running subcuticular closure.

     

  • A deep drain is placed in the knee joint, and the distal/vertical limb of the arthrotomy is closed with multiple interrupted 0 Vicryl sutures placed with the knee in 90° of flexion. The skin is closed in layers (Fig. 22).

     

     

     

     

    FIGURE 23

     

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    P EARLS

    • All patients are sent home from the hospital with a double-length 6-inch wide Ace wrap that they are instructed to use if the knee begins to swell. Because of the rapid return of quadriceps function, some patients will exercise to excess in the first 7–14 days after surgery. If the knee swells, they are instructed to use the Ace wrap, elevate and ice the knee overnight, and then restart their exercise program at a lower intensity 48 hours later.

     

    Minimally Invasive Subvastus Approach

     

    Postoperative Care and Expected Outcomes

    • Patients are instructed to begin weight bearing as tolerated early after surgery and to actively pursue full extension and maximal knee flexion.

    • In our experience, patients are independent with daily activities an average of 7 days after surgery; able to discard crutches, climb stairs, and be off all opioid medication by 14 days after surgery; and able to discard a cane by 21 days.

 

 

 

P ITFALLS

  • A subgroup of patients with this approach will become very, very active early after surgery and are prone to then have the knee swell and become erythematous. If those patients see their primary care physician, many times they will be put on oral antibiotics for a presumed infection when in fact the knee is merely irritated from the extreme activity. All of our patients are instructed to call us first before seeing another physician for knee swelling. Patients with early swelling are treated with the Ace wrap and ice protocol outlined in the Pearls section above.

 

 

Evidence

Aglietti P, Baldini A, Sensi L. Quadriceps-sparing versus mini-subvastus approach in total knee arthroplasty. Clin Orthop Relat Res. 2006;(452):106-11.

 

Sixty patients were randomized to a mini-subvastus or a so-called quad sparing technique. The mini-subvastus patients had slightly earlier active straight leg raising and better 10 day and 30 day flexion. There were no differences noted at the 3 month followup.

 

Boerger TO, Aglietti P, Mondanelli N, Sensi L. Mini-subvastus versus medial parapatellar approach in total knee arthroplasty. Clin Orthop Relat Res. 2005;440:82-7.

 

In a matched retrospective review of 120 patients, the mini-subvastus approach was found to be technically more demanding than a traditional medial parapatellar approach but resulted in less blood loss, less postoperative pain, faster straight leg raising and better early flexion.

 

Chang CH, Chen KH, Yang RS, Liu TK. Muscle torques in total knee arthroplasty with subvastus and parapatellar approaches. Clin Orthop Relat Res. 2002;(398):189-95.

 

Functional recovery after total knee arthroplasty was faster after a subvastus approach than after a medial parapatellar approach as measured by isometric and isokinetic muscle strength. The peak torque was greater and the hamstring to quadriceps peak torque ratio was greater after the subvastus approach.

 

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Minimally Invasive Subvastus Approach

 

Faure BT, Benjamin JB, Lindsey B, Volz RG, Schutte D. Comparison of the subvastus and paramedian surgical approaches in bilateral knee arthroplasty. J Arthroplasty. 1993;8:511-6.

 

A randomized trial of 20 bilateral knees showed the subvastus approach provided better early strength, required fewer lateral releases and was preferred by patients 4 : 1 over the medial parapatellar approach.

 

Gore DR, Sellinger DS, Gassner KJ, Glaeser ST. Subvastus approach for total knee arthroplasty. Orthopedics. 2003;26:33-5.

 

The subvastus approach is shown to preserve the entire extensor mechanism, reduce lateral release rates, preserve the patella blood supply and is widely applicable by simply subluxing the patella instead of trying to evert it.

 

Hoffman AA, Plaster RL, Murdock LE. Subvastus (Southern) approach for primary total knee arthroplasty. Clin Orthop Relat Res. 1991;(269):70-7.

 

The benefits of the subvastus approach are outlined and highlight the fact that it is a valuable technique for contemporary total knee arthroplasty.

 

Pagnano MW, Meneghini RM. Minimally invasive total knee arthroplasty with an optimized subvastus approach. J Arthroplasty. 2006;21(4 Suppl):22-6.

 

The mini-subvastus approach is shown to be reliable, reproducible and efficient even when applied to a broad group of typical total knee patients.

 

Pagnano MW, Meneghini RM, Trousdale RT. Anatomy of the knee in reference to quadriceps sparing TKA. Clin Orthop Relat Res. 2006;(452);102-5.