Osteoarthritis is the most common cause of long-term disability in most people after age 65, and the knee is the most commonly involved site. Eighty percent of people with knee osteoarthritis have limitations in motor function, and 25% of these patients have difficulty with activities of daily living. The annual economic cost of osteoarthritis in the United States is estimated at $6 billion. Total knee arthroplasty (TKA) is an important treatment, but it is often accompanied by severe pain after surgery and during postoperative recovery. Most patients require an assistive device for at least 6 weeks or longer until the muscle incisions involved have healed. They also face several months of frequent physical therapy and narcotic analgesics. This is why it is an ongoing research effort by orthopedic surgeons to reduce post-operative pain and obtain better knee function in knee replacement patients.
Minimally invasive total knee arthroplasty (MISTKA) and its development over the last 10 years have many advantages over traditional total knee arthroplasty. Minimally invasive total knee arthroplasty is usually associated with less postoperative pain, shorter hospital stays, faster recovery of quadriceps muscle strength, and reduced reliance on assistive devices. Minimally invasive total knee arthroplasty is performed with a shorter incision typically 8-12 cm (depending on the individual patient) and avoids damage to the quadriceps tendon, compared to the 14-16 cm incision used in conventional TKA. Standard total knee arthroplasty involves patellar dislocation and valgus; with minimally invasive total knee arthroplasty, the patella is displaced without valgus and no damage to the extensor apparatus is done.
The concept of MIS has caused much controversy among orthopaedic surgeons and among patients during its introduction for more than a decade, so there is no generally accepted method of defining MIS in total knee arthroplasty.MIS qualification is based on incisional sizing only, and the aim of minimally invasive is to reduce arthroplasty loss to ensure quadriceps function and knee stability. Our study found that MISTKA can compromise the knee extension device by avoiding valgus patellar approach.MISTKA several surgical approaches: traditional medial knee approach: transmedial femoral approach (MidvastusApproach), submicro medial femoral approach (SubvastusApproach), quadriceps preserved approach ( QuadricepsSparing (QS) and lateral knee approaches. In our study, we found that the mini medial femoral approach (SubvastusApproach) has a shorter recovery time for patients, less intraoperative bleeding, and reduced knee extension device injuries.
1. Advantages of the minimally invasive knee
The MISTKA operation does not invade the knee extensor device and does not involve the suprapatellar capsule. If a minimally invasive technique is performed to manipulate the joint capsule, invasion of the knee extensor device, the suprapatellar capsule and the use of a restrictive incision to externally rotate the patella are not truly minimally invasive techniques. The main concerns of patients undergoing TKA are postoperative knee pain and the time required to restore joint function, as well as the long term function of the joint. Traditional TKA provides relief from knee pain, but is a challenge for some patients to return to activities of daily living and often requires a long period of time for postoperative recovery. proponents of MISTKA generally agree that it allows for faster patient recovery time, less intraoperative bleeding, less soft tissue damage, more pain relief, better skin repair appearance, and better functional recovery of the patient’s knee after surgery. Critics emphasize the possible long-term complication outcomes associated with MISTKA (e.g., lower survival rates) and the length of the learning curve. Despite the rapid rise of MIS and the promotion of total knee arthroplasty, some surgeons are unsure if MISTKA is a reasonable surgical approach. Then faster recovery time with the promise of less postoperative pain and the ability to reduce unsightly scars with MIS can inspire orthopedic surgeons and patients to improve and explore minimally invasive knee techniques.
As a new technique, MISTKA has unique advantages over conventional TKA, although there are differences in operating methods and surgical instrumentation among surgeons, and postoperative follow-up and evaluation of outcomes are both short and small.
①Smallest extent of surgical debridement trauma, minimal damage to the anatomical structure of the important knee extensor device, no loss of knee extensor device, no patella exostosis, more stable knee joint after surgery, and better recovery of joint function.
②Minimize skin incision scar to meet the patient’s cosmetic requirements.
③Reduced intraoperative and postoperative blood loss.
④Decreased pain level.
⑤The knee joint can be functionally active early.
⑥Shortened hospitalization time and reduced medical costs.
⑦The advantages of more obvious early efficacy and less surgical sequelae. If, MISTKA is only the concept of aesthetics with a small skin incision alone, and its therapeutic effect is not as good as traditional TKA, or the postoperative period is accompanied by more complications, then MISTKA loses the significance of developing applications.
2.Indications for MISTKA
The indications for MISTKA are mainly for patients who receive knee replacement for the first time.
3. Surgical approach for MISTKA
A detailed preoperative evaluation is performed. In addition to routine X-ray examination, vascular ultrasound examination of both lower extremities and bone density examination, 3D reconstruction of the knee joint is performed if necessary to understand the condition of the knee joint, femur and tibia and to formulate the best surgical plan. Depending on the patient’s condition and the characteristics of the knee joint, the surgical approach and the specific operation methods used for MISTKA are slightly different, and the current surgical approach can be divided into medial and lateral approaches to the knee joint. They are described below.
3.1 Medial knee approach
The medial knee approach is the traditional TKA approach. In knee extension, the medial femoral muscle prevents the patella from shifting laterally. Therefore, care must be taken to protect the nerve of the medial femoral muscle when performing MISTKA.
3.1.1 MedialParapatellarApproach:
This approach has the characteristics of simple incision, easy to grasp, clear exposure of the operative area, away from the vascular nerve, and safe operation. The incision of the articular capsule starts from the medial aspect of the patella at the superior pole of the patella and runs along the medial edge of the patella to the end of the patellar ligament at the upper tibia. If the knee cavity is not adequately exposed, the joint capsule incision can be extended 2-4 cm above the patella to the medial 1/3 of the quadriceps tendon. This incisional approach causes interference with the knee extension device due to injury to the quadriceps and suprapatellar capsule, which may cause chronic quadriceps atrophy and thus slower postoperative recovery than other approaches.
3.1.2 Quadriceps preservation approach (QuadricepsSparing, QS):
The quadriceps-sparing approach is considered to be the most physiologically correct approach because it does not interfere with the knee extension device, has less postoperative pain, and increases muscle strength more quickly. The more commonly used of these approaches is the subvastusapproach to the medial femoral muscle. The procedure is as follows: an anterior mid-knee skin incision, approximately 8-10 cm in length, is made at the midpoint of the medial patellar border and the joint capsule is incised down to the superior border of the tibial tuberosity. The lower extremity is rotated internally, the medial femoral muscle is lifted upward, and the patella is incised medially from the midpoint of the medial patellar border for 2 cm, then the medial femoral muscle is separated bluntly along the medial border of the muscle gap, and after release, the patella is pulled laterally. This approach is limited by the patient’s own conditions (obesity, short femur, strong muscles, joint hypertrophy, etc.), and its inward transverse incision is prone to neurovascular injury, and is influenced by the design of the tibial side prosthesis of the traditional knee prosthesis system.
3.1.3 Medial femoral approach (MidvastusApproach).
The medial femoral approach is characterized by a combination of good exposure of the medial parapatellar incision and good protection of the extensor structures by the inferior quadriceps incision, but this approach may damage the innervation from the lateral to the medial femoral muscles. The procedure is as follows: an anterior mid-knee skin incision, approximately 8 to 12 cm in length, incision of the deep fascia and after appropriate separation, flexion of the knee, incision of the parapatellar support band and joint capsule from the medial superior pole of the patella downward to the top of the tibial tuberosity, and a full 2 cm separation of the medial femoral muscle belly inward and upward, release of the patella and external displacement of the patella. This approach is not suitable for patients with excessive obesity, knee flexion less than 90°, and overly strong quadriceps.
3.2 Lateral knee approach
One of the main advantages of using the lateral knee incision for MISTKA over the medial incision is the complete preservation of the quadriceps muscle, which allows for immediate postoperative rehabilitation of the medial femoral muscle; another advantage is the maintenance of control of the patella medially, limiting the tendency of the patella to shift outward. In the lateral approach, the infrapatellar branch of the saphenous nerve and the medial articular branch of the saphenous nerve accompanying the descending branch of the middle knee artery can be completely protected from injury. The disadvantage of the lateral approach is the difficulty in reaching the posterior medial soft tissue attachment portion of the tibia because the tibial tuberosity is approximately 7 mm off the lateral tibial midline. Another disadvantage is the relative unfamiliarity of the operator’s operation. A randomized controlled study by Bonutti et al. compared the MISsubvastus and midvastus approaches to bilateral total knee replacement and they showed no differences.
3.3 MISTKA osteotomy and prosthesis fitting operation
3.3.1 Tria surgical approach
The NexgenLPSFlexKnee (Zimmer, Warsaw, IN) system was used to perform MISTKA using the QS method without damaging the medial femoral muscle, which allows for 2 mm more osteotomy than other types of knee prostheses during the posterior femoral osteotomy, resulting in a larger flexion gap in the knee joint and facilitating the performance of minimally invasive techniques.
3.2.2 Bonutti surgical approach
By using gravity to increase the knee gap, the operator can easily observe the soft tissues at the back of the joint, thus making it easier to perform soft tissue balancing.
3.2.3 Vince procedure
This method of joint capsule incision uses a subfemoral approach to the quadriceps muscle. The joint replacement operation is much the same as that of conventional TKA. The advantage of the Vince method is that surgeons already familiar with the operation of conventional TKA do not have to specialize in osteotomy techniques; the disadvantage is that the skin and soft tissues are stretched too much.
4.Postoperative rehabilitation measures of MISTKA
Post-operative rehabilitation measures of MISTKA can be carried out in stages. 0-1 days after surgery: eliminate swelling, reduce pain, early isometric exercises, joint mobility exercises, avoid muscle atrophy and joint adhesions. 2 days after surgery: drainage removal. 2-4 days after surgery: strengthen joint mobility and muscle strength exercises, 5-7 days after surgery: weight-bearing and proprioceptive exercises, improve joint control and stability, gradually improve gait. 2 weeks-1 month after surgery: strengthen joint mobility, strengthen muscle strength and joint stability, and restore the ability to perform all activities of daily life.
5.Treatment effect of MISTKA
MISTKA can obtain good early results.
(1) Less blood loss during surgery. The average operation time is 70 minutes; the average blood loss is 200ml, which is half of the blood loss of traditional TKA operation.
(2) The postoperative knee pain index was reduced, and the dependence on pain medication was significantly reduced.
(3) Early recovery of knee function was significantly faster in the MISTKA group than in the conventional TKA; three months after surgery, the knee could be flexed to an average of 110° in the MISTKA group, compared with an average of 90° in the conventional TKA; at one year after surgery, the joint mobility had reached 120° (110°-135°) in the MISTKA group, compared with 100° (95°-130°) in the conventional group. 95° to 130°).
6. Development of minimally invasive total knee arthroplasty
The smaller surgical incision for total knee arthroplasty requires a change in the surgical approach and the specialization of surgical instruments. The new operating techniques require the development of suitable knee prostheses and computer-assisted technology, thus changing the traditional model of knee replacement. With the development of computer technology-based navigation systems, surgical techniques have been developed and applied in MISTKA, resulting in more precise MISTKA operations and more minimal damage to joint structures and surrounding soft tissues, achieving no early clinical failures and complications. Computer-aided design technology has been successfully introduced into the clinical application of artificial knee joints. With the help of software, a virtual joint identical to the patient’s knee can be simulated on a computer, and the model can be used to find the most suitable prosthesis for that patient in a database of joint prostheses and what modifications to the procedure are needed at the time of surgery. The use of computer-aided technology can help the determination of soft tissue balance on both sides in prosthetic arthroplasty evolve from empirical estimation to computerized quantitative testing, greatly improving the accuracy of the procedure. Although computer navigation technology is still in the developmental stage, with the development of science and technology, it is believed that computer-assisted technology and minimally invasive knee technology will be perfectly integrated.