Although knee arthroplasty has been performed for more than 100 years, it really became an extremely important surgical procedure in the field of orthopedics after the 1970s, namely, artificial knee arthroplasty. It is now one of the main surgical procedures for the treatment of severe knee pathologies. It is the tireless pursuit of orthopaedic surgeons that has led to the considerable gains we have now made in surgical technique, endograft design, and clinical decision making in total knee arthroplasty. Some complex total knee arthroplasties, such as: stiff knees, fixed internal and external knee rotations and severe deformities can also be performed with good surgical results. Related reports of their overall prosthetic 10-15 year survival rate of about 85-90% are encouraging. In this new phase, we should demand more from total knee arthroplasty.
Surgical options
The surgical selection of total knee arthroplasty is something that every orthopaedic surgeon must master. The increasing proportion of elderly people in China has increased the incidence of knee osteoarthritis, a local degenerative change of the knee joint. Early conservative treatment of the lesion is effective, and when non-operative results are poor, such as in patients with joint dysfunction, cartilage damage and severe degenerative arthritis, choosing the appropriate surgical approach is the key to treatment. Currently, for younger patients with osteoarthritis (40-60 years old), a more recognized phased approach is generally used. That is, less invasive procedures are used first, followed by more invasive procedures. From arthroscopy to osteotomy to unicondylar knee arthroplasty and finally total knee arthroplasty.
The typical clinical presentation of unicompartmental arthritis is pain and pressure in the affected compartment, often accompanied by joint rales, bone formation, angular deformity, and laxity of the collateral ligaments due to articular cartilage wear. Non-surgical treatment (e.g., modifications of activity patterns, NSAIDs, articular chondroprotective agents, intra-articular injections, bracing) is effective in mild cases. Surgical treatment options for unicompartmental arthritis include osteotomy, unicondylar knee replacement, and total knee replacement. Knee unicondylar replacements have been used to treat unicompartmental tibiofemoral arthritis for more than 30 years.
Despite early reports of poor outcomes, with improvements in endosseous implants, case selection, and surgical technique, unicondylar knee replacement has now evolved into a safe and reliable surgical procedure for the treatment of unicompartmental tibiofemoral arthropathy. Compared to total knee replacement, unicondylar replacement offers lower costs, shorter hospital stays, greater postoperative mobility, better recovery outcomes, and higher patient satisfaction. To ensure the efficacy of unicondylar replacement, proper case selection, superb surgical technique, and avoidance of overcorrection of deformities are necessary. This approach is indicated for patients with limited pain, good mobility, and simultaneous imaging of a single tibiofemoral arthritis. TKA is recommended for tibiofemoral arthritis with significant deformity, reduced ROM, or bicompartmental arthritis.
Although total knee arthroplasty has shown effectiveness in reducing pain and improving knee function in the treatment of advanced osteoarthritis patient population, its survival after prosthesis implantation has not been confirmed. Therefore, in middle-aged and active patients, the surgical approach should be chosen more carefully. The most appropriate age for initial total knee arthroplasty is around 65 years of age, at which age there is no significant activity and all physical indicators are normal, and a second revision surgery is generally not required based on the current life expectancy of the prosthesis.
Knee mobility
Knee mobility (ROM) is an important factor in the success of TKA surgery. The main factors affecting knee mobility after TKA are surgical and non-surgical factors. Currently, surgical factors are considered to be the most important factors affecting knee mobility after TKA, including the selection of the prosthesis, the position of the joint line, the correct and reasonable osteotomy, and the reconstruction of the soft tissue balance. There is still much debate about these factors in current research. However, the clarification of these factors can provide surgeons with some theoretical basis to pay attention to the operation points and improve the operation skills during the surgery.
Selection of prosthesis
The choice of prosthesis is crucial for the patient. The right prosthesis not only provides a better postoperative and functional recovery of the knee, but also reduces the difficulty of surgery to a great extent. For the material of the prosthesis, alloys are used for the distal femur and proximal tibia, and the liner is made of polyethylene polymer. Cobalt and titanium alloys are the two most commonly used metals in artificial knee joints today. These two materials have good properties in terms of fatigue strength, modulus of elasticity, and wear resistance, which, combined with advanced manufacturing processes, have resulted in knee prostheses that are increasingly long-lived and better adapted to the normal structure of the human body. Artificial knee prostheses have evolved over the decades from the earliest hinged, bicompartmental, tricompartmental, and restricted condyle prostheses to today’s movable liner prostheses and unicondylar prostheses, which have made excellent advances in the mobility, stability, and longevity of artificial knee prostheses.
The original hinged prosthesis is now used primarily for knee revision, tumors and severe knee disease due to low mobility and high loosening rates. The early production of artificial joint prostheses caused a high rate of surgical failure due to a lack of understanding of design, materials, biomechanics and immaturity in the manufacturing process. At this stage, the above problems have been studied in depth and a certain theoretical basis has been developed, especially in terms of prosthesis materials, manufacturing processes and new understanding of biomechanics, which allows for more satisfactory results in total knee arthroplasty.
Prosthesis design
In total knee arthroplasty, the positioning of the prosthetic component is the main factor affecting its longevity. The fundamental purpose of component alignment is to reconfigure the normal mechanical axis of the lower extremity to obtain a balanced, stable knee joint. Alignment is critical to the weight-bearing aspects of the knee joint, not only to the articular surfaces, but also to the alignment between the prosthesis and the osteotomy surfaces. The size and shape of the distal femoral prosthesis is equally important in order to obtain as close a resemblance to the normal structure as possible. The shape, position, size and positioning of the femoral component are also relevant to the mechanics and longevity of the prosthesis. Although there is some controversy regarding the design of knee prostheses and the adjustment of lower extremity force lines in surgery, the theoretical basis and ultimate goal of alignment between prosthetic components is the same.
Early knee prosthesis designs attempted to exactly mimic the alignment of the normal knee, including a 9° inversion of the femoral component and a mild inversion and backward tilt of the tibial component, but this was clinically proven to be a faulty alignment, primarily because only one state of knee alignment was considered. In fact, the balance of the joint is constantly changing during the dynamic motion of the knee. This requires that we consider this factor not only in the prosthesis design, but also in the intraoperative placement of the knee components and the amount of osteotomy that should be planned in detail before surgery.
Femoral alignment, tibial alignment, valgus alignment, sagittal and rotational alignment, and even patellar alignment in patellar replacements play a critical role in total knee arthroplasty and influence the short and long-term success of the procedure. For the surgeon, knowledge of the basic anatomical relationships and variations of the knee joint is necessary to reconstruct the lower extremity force lines. Equally important are the principles of positioning of the prosthetic component, surgical instrumentation and surgical technique.
Intraoperative management of the soft tissue balance is also an important factor in the stability and function of the postoperative knee. The stability of the joint depends on the inherent restriction of the prosthesis itself and the stability provided by the attachment of the ligaments, capsule and muscles surrounding the knee joint. The restriction of the prosthesis itself is mechanical stability, while the stability provided by the reconstruction of the lower extremity force lines and the balance of the soft tissues is biological stability. Biological stability plays a more important role in terms of function and long-term results. At the same time, in the quest for lower loosening and improved range of motion of the knee joint, prosthesis designs are becoming smaller and more precise.
This low restrictive prosthesis is more dependent on the balance of the soft tissues surrounding the knee in order to ensure its stability after surgery. Proper management of the posterior cruciate ligament is an important part of balancing the soft tissues. There are three general views regarding the posterior cruciate ligament in total knee arthroplasty, namely, to preserve the posterior cruciate ligament, not to preserve the posterior cruciate ligament, and to decide whether to preserve it based on pathology. Physicians who retain the posterior fork believe that this ligament is one of the strongest ligaments in the knee and provides intrinsic stability to the knee. Proponents of not preserving the posterior cruciate ligament believe that it can lead to eventual joint degeneration.
Posterior cruciate ligament: cut, or leave?
Pathologically, the pathology of the knee determines whether to preserve the posterior cruciate ligament. In patients without significant internal or external rotation or flexion deformity, the contracture is mild and may be considered for retention. However, in patients with significant valgus and flexion deformities, preservation of the posterior cruciate ligament makes it more difficult to adjust the soft tissue balance around the knee and accelerates the wear of the polyethylene liner. In certain conditions, such as rheumatoid arthritis or the end stage of knee degeneration due to previous high tibial and distal femoral osteotomies or traumatic arthritis, removal of the cruciate ligament may allow for better knee mobility.
Conversely, in younger patients without more severe deformities, preservation of the posterior cruciate ligament with as much normal knee structure as possible provides not only anterior-posterior stability, but also stability of the flexion gap.
Perioperative management
Perioperative management has received increasing attention in recent years in total knee arthroplasty. Patients are concerned about the potential complications of anesthesia, pain, and blood transfusion. Over the past decade, our research and innovations in perioperative transfusion management and analgesia have led to a significant increase in patient satisfaction with the procedure. Although there is some debate about certain theories, the advances in management have been more significant, most notably regarding the management of postoperative pain. Orthopedic surgery is considered the most painful of surgical procedures, and postoperative pain after total knee replacement is one of the biggest concerns for patients. Early postoperative activity and ambulation are dependent on better analgesic protocols.
In addition, joint fibrosis and decreased postoperative activity are directly related to pain and also increase the incidence of pulmonary and vascular complications. The current effective and widely accepted approach for postoperative analgesia after total knee arthroplasty is multimodal analgesia. This approach effectively combines a multi-gradient analgesic regimen of preoperative patient education, early application of prophylactic analgesics, anesthetic techniques, surgical techniques, intraoperative periarticular local injections, and postoperative analgesic medications. Of these, intraoperative local periarticular injections are the core of the multimodal analgesic protocol, which allows for acute pain control, early functional exercise and improved patient satisfaction primarily after knee arthroplasty. Although it is unlikely that total pain-free pain can be achieved after total knee arthroplasty, continued research in this area will bring us closer to this goal.
Minimally Invasive Total Knee Arthroplasty
As patients demand better results and surgeons continue to innovate in surgical techniques, total knee arthroplasty is becoming more and more minimally invasive. Minimally invasive, of course, does not only mean that the skin incision is reduced, but more importantly, that the surgical technique minimizes the trauma to the entire knee extension device. This idea was originally intended to reduce the surgical incision and wound aesthetics, but is now centered on reducing intraoperative trauma and speeding up the postoperative recovery process, which encompasses a range of techniques for the entire knee replacement procedure, including minimally invasive surgical techniques, appropriate surgical instruments and prosthesis design, and computer-aided navigation techniques.
Starting in the early 1990s, with the success of minimally invasive unicondylar knee replacement, surgeons began to explore minimally invasive techniques for total knee arthroplasty. At present, the quadriceps-preserving incision is the most classic in total knee replacement, which does not damage the structure of the quadriceps muscle, while preserving the normal shape of the suprapatellar capsule and patella, and does not damage the quadriceps muscle and tendon, which control the knee bending movement, with the characteristics of less trauma, less bleeding, and faster recovery. Minimally invasive surgery has become a trend in surgery, and while surgical techniques and tools are improved, the design of the prosthesis should be continuously improved to achieve a truly minimally invasive total knee replacement. The use of computer-aided positioning technology, standardization of surgeon techniques, and robotic surgical systems have led to the maturation of minimally invasive total knee arthroplasty, representing the latest technology and trends in this field.