Minimally Invasive Total Knee Arthroplasty Technique

Updated: Jun 17, 2021
  • Author: Derek F Amanatullah, MD, PhD; Chief Editor: Erik D Schraga, MD  more...
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Technique

Minimally Invasive Approaches to Total Knee Arthroplasty

In a minimally invasive total knee arthroplasty (MIS-TKA), the midline skin incision is approximately twice the length of the patella (ie, 6-14 cm), and a parapatellar arthrotomy is performed (see the image below).

Minimally invasive total knee arthroplasty (MIS-TK Minimally invasive total knee arthroplasty (MIS-TKA). Midline skin incision is performed. Mini-incision is approximately twice length of patella, 6-14 cm (blue); conventional incision is longer (red extensions).

For varus knees, a curvilinear medial skin incision extending from the superior pole of the patella to the tibial joint line provides better exposure. For valgus knees, a curvilinear lateral skin incision extending from the superior pole of the patella to the tibial joint line provides better exposure. [24] If necessary, a second lateral incision may be made from the lateral femoral epicondyle to just above the Gerdy tubercle. [7]

A limited (or mini-) medial parapatellar arthrotomy is favored (see the image below). This familiar approach facilitates a natural transition from conventional TKA to MIS-TKA. [4] MIS-TKA limits the proximal extension into the quadriceps tendon to 2-4 cm and still allows sufficient lateral subluxation of the patella. [30] Patellar eversion should be avoided, and the infrapatellar fat pad may be retained to limit anterior knee pain and potential wound complications. [31, 32, 33, 34]  Because of the unique incisions of specific MIS procedures, converting to the standard medial parapatellar arthrotomy can be problematic and may require an entirely new incision.

Minimally invasive total knee arthroplasty (MIS-TK Minimally invasive total knee arthroplasty (MIS-TKA). Parapatellar (ie, medial parapatellar, midvastus, subvastus, or lateral) arthrotomy is performed to access knee joint and perform arthroplasty.

Other options for the arthrotomy include the midvastus, subvastus, and lateral approaches. [6, 35, 36, 37]

A midvastus (or midvastus split) approach involves cutting 1-3 cm of the vastus medialis obliquus (VMO). [17] However, the VMO is the only muscle that prevents lateral displacement of the patella when the knee is actively extended. [20]  A prospective study found that the midvastus approach does not afford a better gait pattern than conventional TKA does at 8 weeks postoperatively. [38]  A study comparing MIS techniques found no difference between the medial parapatellar and midvastus approaches in terms of patellar tracking and anterior knee pain. [39]

A subvastus arthrotomy avoids disturbing the quadriceps mechanism but may make it difficult to evert the patella. However, with satisfactory dissection and smaller instrumentation, patellar translation alone is sufficient. A retrospective study found that the subvastus approach provides adequate exposure and excellent early recovery in valgus native knees. [40] However, employing this technique also requires proper patient selection, in that it becomes increasingly difficult to retract the quadriceps tendon laterally in larger and more muscular patients. [30]  

The quadriceps-sparing technique is essentially a subvastus approach with no patellar translation; it necessitates modified instrumentation. Both the subvastus approach and the quadriceps-sparing approach often provide limited visibility of the lateral tibial condyle and have longer learning curves for the surgeon. [31]  A retrospective study comparing the quadriceps-sparing and medial parapatellar approaches found no clinical or radiographic differences at a minimum follow-up of 5-years, demonstrating no apparent long-term benefits to the more challenging quadriceps-sparing approach. [33]

A randomized, double-blind study by Tomek et al compared a quadriceps-sparing subvastus approach with the medial parapatellar approach. [41] The investigators found that the quadriceps-sparing approach yielded no significant advantages over the medial parapatellar approach in terms of either time to recovery of knee function or opioid utilization. However, patients who underwent the quadriceps-sparing procedure reported slightly lower mean pain scores at rest on postoperative day 1 and during activity on postoperative day 3.

Another randomized study, by Wegrzyn et al, compared the gait of patients 2 months after a subvastus approach or a standard medial parapatellar approach and found no differences between the groups with respect to outcome scores, activity scores, patient milestone diary of activities, isometric quadriceps strength, or gait parameters. [42]

The lateral approach is a newer technique for MIS-TKA that involves an incision through the iliotibial band. It often requires computer navigation and has been associated with a higher incidence of postoperative complications. [43]  A disadvantage of a lateral arthrotomy is the reduced access to the tibia and the posteromedial soft-tissue attachments that results from the position of the incision approximately 7 mm lateral to the tibial tubercle. [20]  Potential advantages of the lateral approach include the following [7] :

  • It obviates the need for an intramedullary guide for femoral component positioning
  • It does not violate the quadriceps mechanism
  • It permits eversion of the patella
  • It does not dislocate the knee joint

Although the limited skin incision and arthrotomy hinder simultaneous visualization of every component of the joint, the mobile window concept allows all portions of the joint to be visualized during MIS-TKA—but not at the same time. Accordingly, the surgeon must be vigilant to avoid placing undue stress on the soft tissue through aggressive retraction.

MIS-TKA is facilitated by 10-35° of knee flexion. [44] In addition, gravity can be used to assist in visualizing the knee joint and minimizing soft-tissue trauma through what is known as the suspended leg technique. By flexing the hip to 20-30° and allowing the knee to flex to 90-100° of flexion, the target portion of the knee can be manipulated into the surgical field.

Familiarity with techniques of soft-tissue and bony manipulation is essential for a successful MIS-TKA, but the specific techniques used may vary, depending on the surgical approach used. [23]

Patellar capsular release enhances the lateral mobility of the patella and the exposure of the anterior knee joint. Subluxation or retraction of the patella results in minimal postoperative quadriceps dysfunction as compared with the complete patellar eversion used in conventional TKA. [45, 34] Joint dislocation is avoided during bone cuts to prevent capsular damage, which affects postoperative recovery. Progressive bone cuts increase the volume of available surgical space through which to operate. They may be done in either of the following sequences [6, 20] :

  • First the tibia, then the femur, and finally the patella
  • First the patella (if it is to be resurfaced), then the distal femur, then the tibia, and finally the remaining femur

Even when this tactic is used, however, surgeons may need to complete bone cuts freehand and remove bone piecemeal after the initial osteotomy.

After the procedure, the patient should be followed at the same time intervals that would be appropriate for a conventional TKA. Clinical and radiographic examinations should be done at 2 weeks, 6 weeks, 3 months, and 6 months and then yearly for the life of the TKA to monitor for aseptic loosening and late infection.

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Complications

The more difficult surgical approaches required for MIS-TKA are associated with a prolonged surgical learning curve. This learning curve can affect operating time, as well as infection rate. [46, 47, 48]  In addition, the limited visibility inherent in MIS-TKA exacerbates the technical difficulty of performing accurate osseous cuts and can result in cement retention. Otherwise, the complications of MIS-TKA are similar to those of conventional TKA. Infection, aseptic loosening, implant malposition, and arthrofibrosis remain potential complications.

To prevent deep venous thrombosis (DVT), as well as pulmonary embolism (PE), patients should be on an appropriate anticoagulation regimen, as recommended by the American Academy of Orthopaedic Surgeons (AAOS). At present, there does not appear to be a consensus among orthopedic surgeons regarding the choice of a pharmacologic agent for prophylaxis. A retrospective study of 113 patients found no difference in thromboembolic events or bleeding complications among MIS-TKA and conventional TKA patients treated postoperatively with either enoxaparin or rivaroxaban. [49]

Lateral skin numbness due to intraoperative injury of the infrapatellar branch of the saphenous nerve is expected after TKA and has an impact on patient satisfaction. [50] A clinical study by Tanavalee et al found no difference in skin numbness between MIS-TKA and conventional TKA; this result was explained by the cadaveric finding that all branches of the infrapatellar branch of the saphenous nerve appear to cross the midline from medial to lateral between the superior pole of the patella and the tibial tubercle. [51]

MIS-TKA does not result in any improvement in component survivorship. Attempts to determine whether it yields any significant improvements in postoperative knee function or long-term component longevity have yielded conflicting reports. [52, 53]

MIS-TKA may not actually be atraumatic to the knee. One study found that serum levels of creatinine phosphokinase (CPK), myoglobin, aldolase, lactate dehydrogenase (LDH), glutamic oxaloacetic transaminase, and creatinine were equal in conventional TKA and MIS-TKA soft tissues. [54] Another study found no differences between conventional TKA and MIS-TKA with regard to preoperative and postoperative C-reactive protein (CRP) or interleukin (IL)-6 levels. [14]

As a result of the high cost of the new instruments required, the significant potential for complications, and the substantial learning curve, MIS-TKA is currently recommended only for high-volume surgeons who receive specialized training. [24]

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