Arthroplasty is one of the most successful examples of renovations in surgery that have dramatically improved the quality of life for patients with end-stage arthritis. Minimally invasive surgery (MIS) has matured over the past 20 years, and MIS TKA, with a surgical incision of less than 5 inches, is a new form of total knee arthroplasty that is in its early stages of development. With the development of specialized surgical instruments for MIS TKA, the application of computer-aided positioning technology, the standardization of operator techniques, and the advent of robotic surgical techniques, MIS TKA has matured and represents the latest technology in this field.
1. Advantages of MIS TKA
MIS TKA does not involve the knee extension device or the suprapatellar capsule. If a minimally invasive technique is performed to incise the joint capsule, invasion of the knee extensor, the suprapatellar capsule, and the use of a restrictive incision to exenter the patella are not truly minimally invasive techniques. MIS TKA has unique advantages over conventional TKA: ① Less invasive surgical debridement, minimal invasion of the anatomical structures of the important knee extensor mechanism, greater postoperative knee stability, and better recovery of joint function. The postoperative knee is more stable and the joint function is better restored. ② Minimal skin incision scarring to meet the cosmetic requirements of the patient. (iii) Reduced intra- and postoperative blood loss. ④Decreased pain level. ⑤ Early functional movement of the knee joint is possible. ⑥Shortened hospitalization time and reduced medical costs. ⑦ The advantages of more obvious early efficacy and less surgical sequelae.
2. Indications for MIS TKA
The indications for MIS TKA are mainly for patients who are undergoing initial knee replacement. Specific requirements include a knee with a range of motion of 110° or greater (10° or less for knee flexion deformity and 125° or greater for flexion), 10° or less for knee valgus deformity and 15° or less for knee valgus deformity. Minimally invasive surgery is contraindicated in patients with a combination of reduced bone mass and inflammatory osteoarthritis. MIS TKA should be avoided if possible in overly obese patients (over 180 pounds), not only with regard to weight alone, but also with regard to excessive knee circumference. For patients who are too old or have important organ problems, MIS TKA is not advocated due to the long duration of minimally invasive surgery.
3. Surgical techniques for MIS TKA
All the preoperative preparations are required to be more perfect. In addition to routine radiographic examination, 3D reconstruction of the knee joint with CT is performed if necessary to understand the condition of the knee joint, femur and tibia, and then to develop the best surgical plan. The surgical approach and the specific method of operation used for MIS TKA varies slightly from one academic to another, but currently the surgical approach can be divided into medial and lateral knee approaches. Since most of the traditional TKA surgical approaches use the medial knee approach, MIS TKA also started and developed from the medial knee approach, including surgical techniques and surgical instruments, which are all designed around this approach. Therefore, only after the operator has mastered and gained insight into the medial knee approach should he/she attempt to perform MIS TKA using the lateral knee approach.
3.1 Medial knee approach
The conventional TKA approach is usually the one that produces damage to the medial femoral muscle. In active knee extension, the medial femoral muscle is the only muscle in the quadriceps group that prevents the patella from shifting laterally. Therefore, care must be taken to protect the innervation of the medial femoral muscle when performing MIS TKA, and interference with this muscle should be avoided as much as possible, including avoiding making incisions in the tendon to which it attaches to the patella.
3.1.1 Medial Parapatellar Approach:
This approach is a modified Insall approach, which 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 joint capsule starts from the medial aspect of the patella at the superior pole of the patella and follows the medial edge of the patella to the end of the patellar ligament at the upper tibia (see Figure 1). 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 (see Figure). 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 sparing approach (QS):
This 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, and is therefore highly recommended by many scholars. Among these approaches, the more commonly used is the subvastus approach (see figure). The procedure is as follows: an anterior mid-knee skin incision, approximately 8 to 14 cm in length, is made at the midpoint of the medial patellar border and the joint capsule is incised down to the superior 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 bluntly separated along the medial border of the medial femoral muscle, 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 (Midvastus Approach).
Engh et al. first proposed the medial femoral approach (see Figure), which combines the advantages 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 14 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 full separation of the medial femoral muscle belly 2 cm 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 surgical approach
Once proficiency in the lateral approach to the knee for MIS TKA is achieved, the surgeon can determine additional indications for MIS TKA. The use of a lateral knee incision for MIS TKA is particularly advantageous compared to a medial incision. A major advantage 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, since the medial aspect of the knee is not exposed, 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 superior lateral and superior medial knee arteries can also be avoided. The release of the tense lateral support band is more easily accomplished through the lateral approach. In MIS TKA with internal knee valgus, precise tibial osteotomy is easier to perform through the lateral approach. The lateral approach also allows precise adjustment of the iliotibial bundle through the tibial tuberosity osteotomy.
The disadvantage of the lateral approach is the difficulty in reaching the posterior medial soft tissue attachment portion of the tibia due to the tibial tuberosity being approximately 7 mm off the lateral tibial midline. Another disadvantage is that the operator is much less familiar with this approach than with the traditional medial approach and the operation is relatively unfamiliar.
3.3 MIS TKA osteotomy and prosthesis mounting operation
3.3.1 Tria surgical approach
Tria is performed with the Nexgen LPS Flex Knee (Zimmer, Warsaw, IN) system using the QS method without damaging the medial femoral muscle, which allows the knee to be osteotomized 2 mm more than other types of prostheses during the posterior femoral osteotomy, increasing the knee flexion gap and facilitating the performance of minimally invasive techniques. Once inside the knee joint, the subpatellar Hoffa fat pad is removed to expose the knee structure. The patella is replaced first, followed by insertion of a positioning rod into the medullary cavity of the femur and osteotomy of the distal femur from the medial aspect of the femur. The tibia is osteotomized from the medial side of the tibial plateau using an intramedullary positioning rod.
After measuring the knee extension gap and balancing the soft tissues to ensure that the gap after knee osteotomy is 20 mm. in the extension position and adjusting the position and degree of rotation of the medial and lateral knees, the femur is precisely osteotomized in the anterior-posterior direction and in the oblique plane, and the posterior femoral condyle is kept in a 3° externally rotated position. The rotational alignment of the tibia is determined with reference to the tibial cross-section, the box osteotomy of the femur and the talar center of the ankle joint. After completion of the osteotomy, a trial mold of the prosthesis was installed to check the joint alignment, range of motion, patellar trajectory, flexion and extension gaps, and ligament soft tissue balance. The tibial prosthesis is fixed with bone cement first, followed by the femoral prosthesis and finally the patellar prosthesis, and the polyethylene tibial liner is placed.
3.2.2 Bonutti surgical approach
Bonutti draws on the advantages of the position used during knee arthroscopy, where the affected limb is placed on a lower limb support brace with the lower leg draped, using gravity to increase the knee gap, making it easier for the operator to observe the soft tissues at the back of the joint and thus perform soft tissue balancing.
Using a support frame, a circular support bar is padded behind the affected knee, maintaining a position of 20-30° hip flexion and 90-100° knee flexion. A skin incision of approximately 6-12 cm in length is made through the medial femoral muscle approach to the anterior medial aspect of the knee. The medial femoral oblique muscle is cut approximately 2 cm, and the joint capsule is incised to expose the joint cavity. The tibial osteotomy is performed first, followed by the femoral osteotomy. The osteotomy is performed with the knee joint in flexion and extension, and the osteotomy is relatively easy to perform. After the femoral prosthesis of the knee is placed, the tibial side of the prosthesis is then placed and the rotational alignment is adjusted. The tibial plateau is prepared in this position for fixation of the tibial prosthesis. The joint space is maintained using the module and a soft tissue balancing operation is performed to make both sides of the knee symmetrical. Next, the patellofemoral articular surface is osteotomized and the patellofemoral prosthesis is fixed. The rest of the procedure is similar to conventional TKA.
3.2.3 Vince procedure
The Vince method uses an inferior quadriceps approach for the joint capsule incision. The advantage of the Vince method is that surgeons already familiar with traditional TKA do not have to specialize in osteotomy techniques; the disadvantage is that the skin and soft tissues are stretched too much.
3.2.4 Robotic system
The use of a robot system for surgical operations can significantly improve the precision of the procedure. Robotic systems were developed in conjunction with navigation systems and are available as Robodoc and Caspar systems. Their preoperative 3D finite element analysis and simple and straightforward design offer significant advantages over navigation systems.
The robotic system can operate in areas that are difficult for the surgeon to reach, loosening soft tissues and determining the depth of the osteotomy site, thus having the ability to avoid damage to ligaments, nerves, and vascular system. The operation does not require an intramedullary positioning guide. In addition, the robotic system does not use a saw to remove the bone surface, but uses a grinding method with an error of 0.25 mm or less, ensuring that more bone tissue is retained on the osteotomy surface and that the osteotomy surface is flatter, which facilitates the application of biologic fixation techniques for non-cemented joint prostheses.
The disadvantage of the robotic system is that the operation takes more time and costs more; moreover, the operator needs longer professional training to be proficient in operating the system.
4.Postoperative rehabilitation measures of MIS TKA
The postoperative rehabilitation measures for MIS TKA are to allow the patient to move around 2 hours after surgery. To facilitate the patient’s movement, there is no need to perform knee braking measures. The plasma drain can be removed on the second postoperative day, antibiotics are applied to prevent infection, and measures to prevent deep vein thrombosis are used, all of which are the same as the postoperative measures for conventional TKA.
5.Treatment effect of MIS TKA
MIS TKA can obtain good early results. (1) The surgical blood loss is reduced. in 58 cases of MIS TKA reported by Tria, the average surgical time is 110 minutes; the average blood loss is 200 cc, which is half of the blood loss of traditional TKA surgical operation. (2) The postoperative knee pain index was reduced, and the reliance on pain medication was significantly lower. (2) Early recovery of knee function was significantly faster in the MIS TKA group than in the conventional TKA; three months after surgery, the knee could be flexed to an average of 116° in the MIS TKA group, compared with an average of 97° in the conventional TKA; at one year after surgery, joint mobility had reached 125° (110°-135°) in the MIS TKA group, compared with 116° (95°-130°) in the conventional group. 95° to 130°).
Computer navigation-assisted MIS TKA increases the precision of the surgical operation. The conventional TKA is about 75%, while the computer-guided MIS TKA is 84% and the robotic MIS TKA is 95%, based on an angular deviation of less than 3° after knee arthroplasty.
MIS TKA may also be inferior to conventional TKA in terms of joint alignment and soft tissue balance, as well as trauma due to excessive skin traction.
6. Outlook
Although it is still too early to judge the long-term results of using MIS TKA, the early apparent efficacy, especially with the advantages of less surgical trauma, early mobility, and fewer surgical sequelae, has given impetus to the development of this technique.MIS TKA is characterized by aestheticization of the surgical incision, minimization of anatomical damage, and new operating techniques. The smaller surgical incision requires a change in the surgical approach and the specialization of surgical instruments. New operating techniques require the development of appropriate knee prostheses and computer-assisted techniques, thus changing the traditional model of knee replacement. MIS TKA should be performed with proper selection of surgical indications, preoperative CT scan of the knee to determine the condition of the knee joint, femur and tibia, gentle operation to minimize soft tissue damage, complete removal of excess cement from the margins, and minimization of surgical complications. Operators need to be trained in the specialized surgical skills necessary to perform MIS TKA proficiently.
With the development and development of MIS TKA surgical instruments, standardization of surgical operations, and, aided by computer technology-based navigation systems, the development and application of surgical techniques in MIS TKA has resulted in more precise MIS TKA operations and more minimal damage to joint structures and surrounding soft tissues, achieving no early clinical failures or complications. With the development of standardization, the possibility of eventually making MIS TKA a mainstream surgical direction in the future is great.