Minimally Invasive Total Knee Arthroplasty Technique
- Author: Derek F Amanatullah, MD, PhD; Chief Editor: Erik D Schraga, MD more...
Minimally Invasive Approaches to Total Knee Arthroplasty
In 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).
A curvilinear medial skin incision extending from the superior pole of the patella to the tibial joint line provides better exposure for varus knees. A curvilinear lateral skin incision extending from the superior pole of the patella to the tibial joint line provides better exposure for valgus knees. If necessary, a second lateral incision may be made from the lateral femoral epicondyle to just above the Gerdy tubercle.
A limited median parapatellar arthrotomy is favored (see the image below). This familiar approach facilitates a natural transition from conventional TKA to MIS-TKA. MIS-TKA limits the proximal extension into the quadriceps tendon to 2-4 cm and still allows sufficient lateral subluxation of the patella. Patellar eversion should be avoided. Because of the unique incisions of specific minimally invasive procedures, converting to a standard median parapatellar arthrotomy can be problematic and may require an entirely new incision.
Other options for the arthrotomy include the midvastus, subvastus, and lateral approaches.[6, 17, 18, 19] A midvastus approach involves cutting 1-3 cm of the vastus medialis obliquus (VMO). However, the VMO is the only muscle that prevents lateral displacement of the patella when the knee is actively extended.
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. 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.
A randomized, double-blind study by Tomek et al compared a quadriceps-sparing (QS) subvastus approach to TKA with medial parapatellar arthrotomy (MPPA). The investigators found that the QS technique yielded no significant advantages over the MPPA technique in terms of either time to recovery of knee function or opioid utilization; however, QS patients 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 arthrotomy or an MPPA 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. There was a marginally higher speed of stair ascent in the subvastus arthrotomy.
The lateral approach is a newly described technique for MIS-TKA that involves an incision through the iliotibial band. It often requires computer navigation. Advantages of the lateral approach include the following :
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
A possible disadvantage of the 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.
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 flexion. 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 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.
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. 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, 13] :
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 6 weeks, 3 months, and 6 months and then yearly for the life of the TKA to monitor for aseptic loosening and late infection.
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.[24, 25, 26] 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.
MIS-TKA is unlikely to 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.
MIS-TKA may not actually be atraumatic to the knee. One study found that serum levels of creatinine phosphokinase, myoglobin, aldolase, lactate dehydrogenase, glutamic oxaloacetic transaminase, and creatinine were equal in conventional TKA and MIS-TKA soft tissues. 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.
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.
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