Peter M. Bonutti, MD
Bonutti Orthopedic Clinic, Effingham, IL.

Introduction
Surgical techniques used in performing Total Knee Arthroplasty (TKA) have been essentially unchanged for over 20 years. The patient is positioned supine and a 20-30 cm (8-12 inch) incision is made with the leg extended. The patella is then everted and the knee is flexed with retractors used to expose the arthrotomy site. While this extensive exposure aids in aligning the knee, enhancing visualization of landmarks and allowing the use of bulky instruments to complete the bone preparation for implants, it imposes significant trauma to the quadriceps mechanism and soft tissue.

A Minimal Incision Total Knee Arthroplasty (MIN TKA) procedure has been developed utilizing the new Suspended Leg Technique. The patient's leg is placed in a leg holder and flexed over the edge of a surgical table allowing the weight of the leg to distract the joint and push tissue away. Sterile draping is possible and a mobile, sterile field is created that allows sequential flexion and extension as needed. The surgeon can be in a sitting or standing position during the procedure.

Materials and Methods
Twenty consecutive patients were evaluated utilizing the suspended leg approach for MIN TKA: Twelve female, eight male. Patient ages ranged from 56-87, weight averaged 210 lbs (110 - 270 lbs).

The patient's leg was flexed and suspended over a table. Unique sterile draping technique and surgical heads were utilized and an incision was made two times the patellar length - 6.5-12 cm with the knee in flexion. VMO split was utilized and the patella was retracted (not everted) laterally using special retractors to expose the joint.

Special downsized instrumentation were used to performed extramedullary tibial and intramedullary femoral alignment with an anterior referencing system.

The knee was sequentially flexed and extended to expose either the tibia or the femur and allow appropriate releases.

With the leg suspended, enhanced exposure of the posterior joint was obtained and simplified retraction of the patella laterally was allowed with reduced damage to the quadriceps mechanism. Implant trailing and ligament balancing were especially enhanced in flexion allowing gravity to distract the leg to evaluate true collateral ligament balancing both in flexion / extension and through rotation. (Note, when the leg is flexed in a traditional leg holder, the posterior femur impacts against the posterior tibia and one does not obtain a true anatomic ligament balancing).

The patella was then rotated 90° only in full extension to expose the patella for resurfacing. Then a tricompartmental total knee replacement (Scorpio - Stryker) was cemented in position, patella tracking and ligament balancing was once again evaluated through range of motion and the knee was closed in flexion.

Incision length averaged 9 cm in extension or 12 cm in knee flexion (range 9.0-14.0 cm). Tourniquet time averaged 55 minutes.

No exclusions were made based on preoperative ROM, contractures, stiffness, or degree of deformity.

Results
Post-operative radiographs showed good alignment and position. Exceptions included two femoral components in slight flexion, one tilted patella, and one notched femur.
Postoperatively, 90° flexion was obtained by 18 of 20 patients by the third postoperative day. Discharge average was third postoperative day.

Discussion
Total Knee Arthroplasty techniques are evolving with minimal incision arthroplasty posing several potential advantages including: 1) limited incision; 2) reduced trauma to the extensor mechanism; 3) improved posterior joint exposure; 4) enhanced collateral ligament balancing in flexion.

MIN TKA with the Suspended Leg Technique uses the knee in flexion during the bulk of the procedure through an incision that is two times the patellar length or approximately 9 cm. With the knee in flexion landmarks are easier to expose, the skin is stretched, and the patella can easily be retracted laterally utilizing a VMO snip of 1 cm. Superior capsulotomy is simplified and the quadriceps mechanism is elevated rather than released during the exposure. Sequential flexion or extension of the knee allows exposure of the joint and progressive relaxation of the retractors, either medially or laterally allows enhanced exposure as needed to the joint. Elevation of the quadriceps mechanism permits satisfactory exposure of the anterior joint without extensive damage to the quadriceps mechanism.

The limited incision technique can be performed with a standard leg holder similar to arthroscopic knee approach with the hip in slight flexion and novel sterile draping technique to ensure a mobile sterile field. This approach can be used for Arthroscopy to Unicompartmental to Total Knee Arthroplasty. It may be considered a universal positioning for knee surgery. Computer Assisted Navigation may assist in optimizing alignment and bone cuts.

Conclusion
Although these results are preliminary, the Suspended Leg Technique may be a viable option for MIN TKA. The technique is evolving, and there is a definite learning curve. Improved instrumentation should reduce the risk of complications. Further study and evaluation of the Suspended Leg Technique is recommended, but may be a future direction for minimally invasive total knee arthroplasty.