الفهرس 
BIOMECHANICS OF TOTAL KNEEOnly 14 pages are availabe for public view
 |  | from | 143 |  |  |
| | | from | 143 | | |
Abstract
Traditional TKA is an effective, well-documented, and widely accepted surgical solution for patients with severe arthritis .Patient dissatisfaction related to postoperative pain, stiffness, and long difficult rehabilitation persist even with modern implant designs.127
The median parapatellar approach with patellar eversion has been the gold standard for most orthopedic surgeons because of ease of visualization and the ability to accurately align the components. However, this approach has led to prolonged rehabilitation and postoperative pain because of the significant disruption of the quadriceps mechanism during the procedure. Other approaches which have been more quadriceps sparing have been described in the literature, including the sub-vastus and mid-vastus approaches.53
The standard sub-vastus approach was found to be superior to the median parapatellar in terms of need for post-operative analgesia and improved quadriceps function as demonstrated by the ability to straight leg raise in the early post-operative period.128
Recently, various authors have reported superior clinical results and decreased costs using minimally invasive techniques for total knee arthroplasty. 103
The principles of MIS-TKA is as follows:
(1) minimal interruption of the vascular supply in the knee region;
(2) minimal dissection of muscles, tendons, and ligaments;
(3) minimal loss of blood;
(4) minimal pain to the patient.46
The minimal incision approach is less invasive, which minimizes soft
tissue dissection, but can be converted to a standard approach if necessary. Critical to this minimally invasive approach is patient selection, because all cases may not be performed with limited dissection. The ideal patient would have a fixed angular deformity of less than or equal to 10 degrees varus or greater than or equal to 15 degrees valgus; less than or equal to 10 degrees flexion contracture; and greater than 90-degree arc of motion. 77
The major approaches for MIS-TKA are mini-parapatellar , mini-midvastus, mini-subvastus, quadriceps-sparing and mini-lateral approaches. The mini-midvastus and the mini-subvastus techniques violate the extensor mechanism more than the quadriceps-sparing approach. The mini-midvastus splits the muscle, and this usually extends proximally by the end of the operation with the possibility of denervating the distal portion of the muscle. The mini-subvastus lifts the entire extensor mechanism over the anterior portion of the femur and often avulses the vessels in the septum leading to a postoperative hematoma that often is mistakenly interpreted as an element of medial swelling. The quadriceps-sparing technique involves significantly less dissection and decreases the possibility of postoperative swelling and vastus medialis weakness. The mini-lateral technique preserves V.M.O completely with less post-operative rehabilitation time but needs a learning curvs as it is the least familiar. 105
The major differences between the standard approach and minimally invasive approach is patellar eversion and dislocation of the tibiofemoral joint. The surgical technique for the traditional group includes eversion of the patella with the knee kept in flexion for most of the operation. Standard retraction methods allow a full view of the entire knee. This technique, combined with a full dislocation of the tibiofemoral joint, affords excellent exposure and allows the use of larger instruments. However, the traditional technique requires additional soft tissue dissection and tension. Patellar eversion twists the patellar tendon and places it on stretch. This represents potential trauma to the patellar tendon and peripatellar tissues, as can be witnessed by the tendency for the patellar tendon to avulse from its tibial insertion.6
The MIS technique uses a patellar subluxation and does not twist the patellar tendon. Dislocation of the tibia is avoided. The instruments are downsized, and the sequence of the operation is altered to take advantage of the relaxing effect of the osteotomies. Leg positioning and dynamic retraction are used to minimize soft-tissue dissection and tension.6
The benefits of minimal-incision surgery include less surgical dissection, less blood loss and pain, an earlier return to function, and a smaller scar.5
Patients who received the mini-incision required less pain medication and had greater ROM in the first postoperative days compared to patients that had the standard incision. These benefits were achieved with a minimal increase in tourniquet time and only a few minor wound healing problems.18
The mini-incision technique also affords fewer visual clues. This can impair a surgeon’s ability to assess proper component positioning, soft tissue balancing, and protection of important structures (medial collateral ligament, popliteus tendon, and patella). The mini-incision also makes it difficult to visualize the lateral tibial plateau, seat stemmed tibial implants, avoid internal rotation of the tibial and femoral components, and to remove loose bony fragments, uncapped bone, or retained cement. In addition, the need for aggressive retraction to compensate for the mini-incision can lead to problems with wound healing, and the potential for avulsion of the extensor mechanism and posterior cruciate ligament Future improvements in implantation instruments, advances in prosthetic design, may help compensate for the problems associated with MIS-TKA.129