Minimal Incision Total Knee Arthroplasty: the Mini-Midvastus Approach

RECONSTRUCTION 2023, Jan, 08 | 12:00 am

Minimal Incision Total Knee Arthroplasty: the Mini-Midvastus Approach

Introduction

Innovative techniques and alteration in instrument design have facilitated the safe and accurate placement of a total knee arthroplasty (TKA) while utilizing a smaller skin incision. Among these techniques is the mini-midvastus approach.
This technique was developed to minimize the surgical insult of TKA and to allow for an earlier return of function.
The decision to proceed with the mini-midvastus TKA is dependent on the surgeon, the patient, technical factors, and the available instrumentation.
The mini-midvastus TKA is a highly successful operation, rewarding for both the surgeon and patient when performed on the correct individual.

P EARLS
- Patient selection is an important variable because a large, stiff, severely deformed knee may present signiﬁcant difﬁculties to the operative team.
- The surgeon should be experienced with standard TKA and well rehearsed in the surgical technique. Additionally, surgical assistants should be educated regarding the principles of the minimally invasive surgery and appropriate retractor placement.
Indications
Indications
- Significant pain and/or disability arising from an underlying arthritic condition of the knee
- Significant arthritic pain and/or disability refractory to nonoperative conservative measures
Requirements for this approach
- A surgeon with a thorough understanding and technical mastery of standard TKA
- Assistant(s) familiar with minimally invasive technique and appropriate retractor placement
- Minimally invasive instrumentation to facilitate a smaller operative window
Despite no absolute contraindications to the mini-midvastus TKA, there are relative contraindications. The surgical procedure is notably more challenging in
- Men with substantial quadriceps muscle mass
- A patient with significant obesity (body mass index
  - 40)
- The presence of a severe coronal plane deformity
- A flexion contracture of 25°
- Passive flexion of 80°
- Severe patella baja
- Significant scarring of the quadriceps mechanism
  
  Examination/Imaging
Preoperative evaluation includes first and foremost a complete history and physical exam.
Radiographic evaluation

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Mini-Midvastus TKA

Standard anteroposterior (AP) and lateral knee radiographs
A flexed posteroanterior knee radiograph
A Merchant’s view knee radiograph
A standing AP full-length extremity film, from the hip to the ankle (may be obtained if alignment is questionable)

Surgical Anatomy

The vastus medialis obliquus (VMO) inserts onto the medial border of the patella and the quadriceps tendon (Fig. 1A).
The VMO is innervated by the terminal branches of the saphenous nerve, which is a branch of the femoral nerve (Fig. 1B). It can be safely dissected

4.5 cm from its patellar insertion without risk of denervation to the muscle distally (Cooper et al., 1999).
If additional exposure is required, the remaining fibers of the VMO may be split bluntly to the level of the vastoadductor membrane and adductor magnus tendon without risk of neurovascular injury (see

Fig. 1A).

Nerve to vastus medialis from femoral nerve

Vastus medialis obliquus (VMO)

Quadriceps

tendon

Patella

Infrapatellar branch of saphenous nerve

A B

FIGURE 1

172

P EARLS

Ipsilateral supports are especially helpful when operating with minimal assistance.

P ITFALLS
Avoid hyperflexion when possible, as this not only tightens the extensor mechanism but also limits exposure.
Avoid excessive retraction at all times. Assistants must retract only where needed and avoid retraction in portions of the wound not being addressed at that moment, thus maintaining a “mobile window.”

Mini-Midvastus TKA

Positioning

The patient is positioned supine on a standard operating room table.
A sandbag is placed under the drapes at the level of the ankle to facilitate holding the knee flexed at approximately 70–90°. In Figure 2, note that the bump is placed across from the contralateral ankle, allowing for a resting position of the operative extremity at less than 70–90° of flexion. A padded tourniquet is placed high on the operative thigh.
A bump may be placed under the ipsilateral pelvis to facilitate internal rotation of the operated knee, preventing external rotation of the knee during the procedure.
In addition, an ipsilateral nonsterile lateral support placed at the level of the thigh may be used so the lower extremity remains upright without being held by an assistant.

P EARLS
- In patients with vascular disease or a history of thrombophilia, a tourniquet is not used.
- There is rarely a need to create a lateral flap of subcutaneous tissue. This is generally
  
  performed only as the initial step in improving patellar tracking.
- Patellar eversion is avoided at all times to circumvent undue tension at the tibial tubercle and the resultant peeling of the patellar tendon from
the underlying bone.

Portals/Exposure
An Esmarch bandage is utilized to exsanguinate the limb.
- The tourniquet is most commonly inflated to 250 mm Hg.
- In larger patients the tourniquet is inflated to 275 mm Hg, but rarely greater than 300 mm Hg.
Skin incision landmarks include the borders of the patella and the tibial tubercle.
- A longitudinal incision is made at the junction of the middle and medial thirds of the patella. The incision begins 1 cm above the superior pole of the patella and ends at the proximal half of the tibial tubercle on the medial side (Fig. 3).
- Skin incisions range in length from 8.5 to 12 cm and are made with the knee in full extension.
Soft tissue dissection is carried down to the inferior-most aspect of the quadriceps tendon, patella, and patellar tendon. A medial subcutaneous flap is created, exposing the VMO and the medial patellar retinaculum.
A medial arthrotomy is performed.
- The arthrotomy begins at the superior pole of the patella and ends at the level of the tibial tubercle (Fig. 4).
- The VMO is identified and a 1-cm oblique split is made sharply in line with the muscle fibers at the level of the superior pole of the patella.
  
  Mini-Midvastus TKA
  
  FIGURE 2
  - The muscle fibers are not cut; additional splitting of the VMO is performed bluntly with a finger, gently separating the muscle fibers approximately 2–4 cm.
    
    173
    
    Superior patella
    
    Tibial tubercle
    
    FIGURE 3 FIGURE 4
    
    174
    
    Mini-Midvastus TKA
With the knee in extension, a partial excision of the infrapatellar fat pad is performed. This assists with release of the patellar tendon and allows for better mobilization of the patella.
A small synovial window is created just superior to the femoral trochlea for easy visualization of the anterior femoral cortex. The majority of the suprapatellar pouch is preserved except in cases of severe inflammatory disease.
Subperiosteal dissection is carried around the medial pretibial border, releasing the meniscotibial attachments.
If a large patella is present, a preliminary patellar cut is performed, resecting approximately 8 mm of bone. This facilitates exposure at the lateral side of the knee.
The patella is laterally dislocated during knee flexion.

Procedure

Step 1: Distal Femoral Bone Cut
The knee is flexed to 70°. The lateral meniscus is released from its anterior attachment and the anterior cruciate ligament is transected.
A thin, bent Hohmann retractor is placed laterally around the margin of the femoral condyle, medial to the lateral meniscus. This retractor is often self-maintaining and helps keep the patella in the laterally dislocated position. Another thin, bent Hohmann retractor is placed medially, exposing the medial femoral condyle.
The AP axis (Whiteside’s line) is marked on the trochlear groove with electrocautery.

P EARLS
- A thumb placed at the proximal tibial crest can act as a lateral buttress for the extramedullary tibial alignment guide.
- A proximal tibial cutting guide designed to accommodate overlying skin avoids excessive retraction and skin irritation.
- If at any stage signiﬁcant tension is present at the skin edges, the surgeon should not hesitate to lengthen the incision.
A 9.5-mm drill is used to enter the femoral canal just anterior to the insertion site of the posterior cruciate ligament (PCL). After drilling, the canal is suctioned of all marrow contents, potentially decreasing the risk for fat embolization.
An intramedullary alignment rod attached to an AP axis guide, set at 5° of valgus relative to the anatomic axis, is inserted. Valgus angle can vary depending on the patient’s anatomy.
A Journey MIS Distal Cutting Block (Smith and Nephew, Memphis, TN) is then mounted and pinned into place with two headless pins (Fig. 5).
- The intramedullary rod is removed. The distal femoral cut is then made.
- An additional 2 mm of distal femoral bone may be resected if there is a preoperative flexion contracture of 15–20°.
  
  175
  
  P ITFALLS
  - During placement of retractors, excessive tibial external rotation, which is often employed in the standard TKA, must be avoided as it decreases visualization of the lateral compartment by rotating the lateral tibial plateau under the femur.
  Mini-Midvastus TKA
  
  Step 2: Proximal Tibial Resection
  - The knee is flexed to approximately 90°.
  - Thin, bent Hohmann retractors are placed medially and laterally. The medial retractor is essential for protection of the medial collateral ligament (MCL).
  - Overhanging anteromedial osteophytes are then removed with a ronguer to facilitate placement of the tibial resection guide directly on the proximal medial tibia.
  - An extramedullary tibial alignment guide is placed parallel to the tibial crest. The second metatarsal acts as a reference point distally.
    - In varus knees, resection is aimed at taking 11 mm from the lateral side.
    - In valgus knees, resection is aimed at taking 9 mm from the medial side. The guide is then pinned at two locations.
  - Once the guide is pinned in place, an Aufranc retractor is placed posteriorly to draw the tibia anteriorly and to protect the posterior neurovascular structures (Fig. 6).
    - The tibia is subluxed (minimally) anterior without any external rotation.
    - Retractors are maintained in a neutral position to minimize soft tissue tension.
      
      FIGURE 5 FIGURE 6
      
      176
      
      Mini-Midvastus TKA
The proximal tibial resection is then performed.
- Medial bone resection is accomplished with the saw blade working in the anterior-to-posterior direction.
- Lateral bone resection is accomplished with the saw blade working in the medial-to-lateral direction.
  
  P EARLS
  - The leg may be extended to 70° to aid in placement of the sizing stylus.
  - A smaller anatomically shaped cutting guide accommodates a small incision and avoids the need for aggressive retraction. In addition, cutting block edges should be rounded to reduce soft tissue irritation and trauma.
  - Rigid saw blades with a narrow body that fans at the distal tip are used to prevent tissue injury from saw blade excursion and to facilitate accurate bone cuts.
  Step 3: Femoral Sizing, Rotation, and
  
  Additional Femoral Bone Cuts
A Journey Rotation/Sizing Guide (Smith and Nephew,

Memphis, TN) is placed against the posterior femoral condyles with care taken to ensure the guide is properly placed and seated. The guide is then pinned with two short pins (Fig. 7).
- For varus knees, the posterior condyles are used as the primary reference for rotation.
- For valgus knees, the anteroposterior axis (Whiteside’s line) is the primary alignment landmark.
The sizing stylus is then attached to the rotation/ sizing guide and positioned on the anterior cortex (Fig. 8).
The rotating/sizing guide is then removed and pin holes are used to position a Journey Femoral A-P (5 in 1) Cutting Block (Smith and Nephew, Memphis, TN) of the appropriate size. The 5-in-1 cutting guide is then pinned into position with attention paid, once again, to rotation (Fig. 9).
A thin, bent Hohmann retractor is placed deep into the MCL to avoid damage to this structure.
The femoral cuts are then performed in the following order: (1) anterior cut, (2) first anterior chamfer, (3) posterior condyles, (4) posterior chamfer, and (5) second anterior chamfer.
The posterior condylar bone is easily removed with a half-inch curved osteotome.

Step 4: Alignment and Gap Check
With laminar spreaders placed laterally and then medially, the medial and lateral menisci are removed, as well as the PCL.
In addition, the posterior femoral condyles are checked for retained osteophytes; if present, these are removed with a curved osteotome.
Spacer blocks are placed in extension and then flexion, to ensure symmetric resection spaces and levels.

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Mini-Midvastus TKA

FIGURE 7

FIGURE 8

FIGURE 9

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Mini-Midvastus TKA
Alignment rods may be attached to the spacer blocks to ensure appropriate alignment.
- On the femoral side, the alignment rod should pass approximately 2 cm medial to the anterior superior iliac spine.
- On the tibial side, the alignment rod should pass over the center of the ankle and point to the second metatarsal.
  
  P EARLS
  - Using an asymmetric tibial tray facilitates appropriate placement of the tray and avoids tibial component overhang posterolaterally.
  Step 5: Tibial Base Plate Preparation
The knee is then flexed to 120° and an Aufranc retractor is placed posteriorly. This is the only time

prior to final component insertion that hyperflexion is employed.
At this point, remaining tibial bone posterolaterally and posteromedially can be resected.
An appropriately sized tibial component is pinned in place with one pin.
The proximal tibia may then be drilled and punched to accept the definitive prosthesis, or this step can wait until component trialing has been performed and tibial component rotation confirmed.

P EARLS
- Utilizing a trial component designed to allow femoral box preparation rather than a standard box cutting guide saves a step and allow more accurate mediolateral placement of the femoral component.
- Erring laterally with femoral component positioning helps to optimize patellar tracking.
Step 6: Final Femoral Preparation and

Patellar Preparation
With the trial tibial baseplate pinned in place, a

femoral trial component designed to allow femoral box preparation is positioned. The femoral box is then prepared with a reamer followed by a box osteotome. A cam is placed in the box of the femoral component to allow smooth trialing.
An initial trial reduction with a variety of polyethylene inserts is performed. An assessment of coronal plane stability is performed in extension and at 90° of flexion.
The patellar cut is then performed. This is either a primary final cut or a finishing cut, depending on whether or not a preliminary cut was performed earlier in the procedure. A freehand technique is used.
This is followed by patellar sizing and drilling of three peg holes.
Finally, the patellar trial is placed and the lateral margin of the patella chamfered with an oscillating saw, which potentially minimizes lateral retinacular impingement.

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Mini-Midvastus TKA

Step 7: Final Trialing
- With all trial components in place, a final assessment of stability is performed in both extension and 90° of flexion.
  
  P EARLS
  - Occasionally, sclerotic bone is drilled with a 2.0-mm drill bit to enhance cement interdigitation.
  - An asymmetric tibial baseplate with a modiﬁed posterolateral edge is used, facilitating clearance of the lateral femoral condyle during insertion and decreasing posterolateral overhang.
  - When implant insertion is anticipated to be relatively easy, two bags of cement are mixed simultaneously. When implant insertion is anticipated to be more challenging, one bag of cement is mixed for the tibial component and the second bag of cement is mixed separately for the femoral and patellar components.
  - Deflating the tourniquet prior to polyethylene insertion allows for better visualization of bleeding vessels at the back of the knee and more thorough hemostasis.
- Soft tissue releases are performed until satisfactory balance is achieved.
- Patellofemoral tracking is observed and, if necessary, a lateral retinacular release is performed.
  
  Step 8: Component Insertion and Cementing
- Following removal of all trial implants, the bone surfaces are washed with normal saline under pulsatile pressure.
- A bone plug is fashioned and impacted into the femoral hole at the intercondylar notch.
- Final tibial preparation requires anterior subluxation. This may be achieved by flexion of 90° or hyperflexion if necessary (Fig. 10). Thin, bent Hohmann retractors are placed medially and laterally, and an Aufranc retractor is placed posteriorly in preparation for tibial component insertion.
- After insertion of the tibial baseplate, excess bone cement is removed.
  - The removal of cement from the posterior tibia is aided by placing the knee in extension and applying traction.
  - A small curved curette is swept posteriorly along the tibial component, removing cement at the bone-implant interface.
    
    FIGURE 10
    
    180
    
    Mini-Midvastus TKA
A two-prong PCL retractor is placed at the posterior femur, elevating the distal femur away from the tibial baseplate. The femoral component is then inserted and malleted into position with the knee at 90° of flexion. Extruded cement is removed from the intercondylar notch and the condylar margins.
A trial liner is inserted and the knee is placed in extension. Extruded cement at the anterior femoral cortex is easily removed at this time.
The patellar component is placed and clamped into position.
While the cement is curing, excess cement is removed and the wound is irrigated with normal saline under pulsatile pressure.
When the cement is hard, the tourniquet is deflated and bleeding is controlled with electrocautery.
The definitive polyethylene insert is then inserted with the knee held in 30° of flexion. The knee is once again copiously lavaged with normal saline and two drains are placed in the lateral gutter.

Step 9: Closure and Dressing
The capsular arthrotomy is closed with 0 Vicryl suture in a simple, interrupted or figure-of-8 stitch. The VMO split and the perimuscular fascia are closed with 0 Vicryl suture in a simple, interrupted stitch. Three to five stitches are usually sufficient.
The deep subcutaneous layer is closed with 0 Vicryl and the superficial subcutaneous layer is closed with 3-0 Vicryl suture. The skin is closed with staples (Fig. 11A and 11B).
Wounds are dressed with a povidone-iodine (Betadine)–soaked pervious tape followed by 4  8 gauze pads.
The entire extremity is then wrapped in bulky Jones foam from the ankle to the proximal thigh. A Cyrocuff cold unit is then placed over the anterior knee and secured into place with elastic wraps from the ankle to the proximal thigh.

Postoperative Care and Expected Outcomes
All patients are started on a continuous passive motion machine on the first postoperative day. Machines are started at 0–80° and advanced as tolerated. Weight bearing as tolerated is also begun on the first postoperative day. The Cyrocuff is used for the duration of the patient’s hospital stay.

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Mini-Midvastus TKA

A B

FIGURE 11

All patients receive warfarin (Coumadin) and calf pumps for thromboembolism prophylaxis. The Coumadin is continued for 6 weeks after surgery.
A patient-controlled epidural is continued until postoperative day 2 along with a femoral nerve block. Thereafter, the patient is maintained on oral analgesics.
Patients are typically discharged on postoperative day 3 or 4.
As of June 2008, the senior author (SBH) has performed over 1000 mini-midvastus TKAs. It is now used in the majority of the primary TKAs he performs.

Initial research on this technique involved a comparative study of 40 TKAs performed using a standard technique with 40 minimal incision TKAs using the mini-midvastus technique as described in this chapter (Haas et al., 2004). There were no preoperative differences between the groups. Postoperatively, patients’ motion returned faster in the mini-midvastus group. Mean flexion for the mini-midvastus group at 6 and 16 weeks was 114°

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Mini-Midvastus TKA

and 122°, respectively, compared with 95° and 110° for the standard TKA group. At 1 year, the mini-midvastus group retained higher mean flexion angles of 125° versus 116° in the control group.

Knee Society scores were also higher in the mini-midvastus group. There were no differences in radiographic alignment or complications.
A more recent retrospective analysis of 335 consecutive patients (391 knees) undergoing mini-midvastus TKA yielded similar results (Haas et al., 2006), as have additional recently published studies (Laskin, 2005; Laskin et al., 2004; Parentis et al., 1999).
- When used for the appropriate patient by an educated operative team with the correct instruments, the mini-midvastus TKA can be safely and effectively performed.
The use of smaller, well-designed instruments permits less surgical dissection while avoiding excessive soft tissue retraction.
Lateral patellar dislocation instead of patellar eversion avoids stress at the patellar tendon insertion while not compromising exposure.
This approach provides excellent visualization while limiting dissection of the quadriceps tendon.
We have found this technique to enhance patient recovery, reduce pain, and improve cosmesis without compromising the radiographic positioning of the implants or the clinical results.

Evidence

Cooper RE Jr, Trinidad G, et al. Midvastus approach in total knee arthroplasty: a description and a cadaveric study determining the distance of the popliteal artery from the patellar margin of the incision. J Arthroplasty. 1999;14:505-8.

The innervation of the distal vastus medialis obliquus muscle was explored in ﬁve cadaver specimens. The muscle could be denervated only by splitting the muscle ﬁbers to the point of attachment to the vastoadductor membrane/adductor magnus tendon. The authors concluded that the approach is safe, without signiﬁcant risk of nerve injury. (Level IV evidence)

Haas SB, Cook S, et al. Minimally invasive total knee replacement through a mini midvastus approach: a comparative study. Clin Orthop Relat Res. 2004;(428):68-73.

Forty consecutive mini-midvastus TKAs were compared to a matched group of standard-approach TKAs. Compared to the standard group, patients in the mini-midvastus group gained motion faster, had better motion at 6 weeks and at 1 year, and had higher Knee Society scores. (Level II evidence)

Haas SB, Manitta MA, et al. Minimally invasive total knee arthroplasty: the mini midvastus approach. Clin Orthop Relat Res. 2006;(452):112-6.

In a review of 391 consecutive mini-midvastus TKAs at a single institution, range of motion at 6 weeks was 111°, at 3 months was 121°, and at 1 and 2 years was 125°. Postoperative Knee Society scores were greater than 95 in all patients. There was no increase in rate of complications with this approach. (Level IV evidence)

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Mini-Midvastus TKA

Laskin RS. Minimally invasive total knee arthroplasty: the results justify its use. Clin Orthop Relat Res. 2005;(440):54-9.

A mini-midvastus capsular incision was used in 100 patients undergoing primary TKA. Patients were followed up for a minimum of 2 years after surgery. The exposure yielded excellent results clinically and radiographically, with restoration of stability and motion. The length of the skin incision varied from 8 to 15 cm with a mean of

10.5 cm. Using the limited exposure did not result in implant malpositioning. (Level IV evidence)

Minimal Incision Total Knee Arthroplasty: the Mini-Midvastus Approach

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