In recent years, unicompartmental knee arthroplasty (UKA) has received renewed attention. The minimally invasive technique not only allows the patient to regain motor function as soon as possible, but also reduces the incidence of complications. Patients with unicompartmental knee degeneration and good stability are the best candidates for this procedure. The use of Quadriceps-sparing QS has greatly advanced the development of UKA.
The QS technique preserves the function of the quadriceps and can be converted to a total knee arthroplasty TKA if necessary. This surgical instrumentation is simple to learn and increases both the efficiency of the operating room and the familiarity of the surgical team. In the last four years, 343 patients have undergone UKA with this technique and only 5 patients (1.5%) have undergone revision, with good knee function, high satisfaction and high prosthesis survival rates.
Over the past 25 years, unicondylar knee replacement (UKA) has gained recognition from different people. When UKA was first introduced into the clinic in the 1870s, it gained widespread popularity among surgeons because of its low bone cut and ease of revision. This also coincided extremely well with other surgical approaches at the same time, such as the surface replacement of the hip joint, which not only preserved its own bone tissue but also offered the possibility of other further surgery if necessary.
However, at that time there was a lack of surgical instruments and little was known about the choice of indications and the design of the prosthesis. These problems led to a high failure rate of the early surgery, which was completely abandoned in the United States in the 1990s, but European surgeons continued their work, advancing the surgical technique and refining the choice of indications1,2.
During the same period, with the development of sports medicine and other disciplines, orthopaedic surgeons increasingly recognized the potential significance of reducing surgical trauma and introduced the concept of minimally invasive surgery (MIS). 1991,Repicci and Romanowski3 applied the UKA minimally invasive technique in clinical practice, and in 1998, Albrektsson and Carlsson designed the MG Uni ( Zimmer, Inc, Warsaw, IN) for clinical use, which is mainly a minimally invasive technique for intramedullary localization of UKA.
Modern UKA has satisfactory results with long-term survival rates exceeding 94%. This high survival rate, low complications and refinement of surgical instrumentation led to the formation of the simplified ground UKA minimally invasive technique in 2000, which was further developed as the OS-TKA technique. This technique, in particular, is suitable for UKA.
Patient selection
The most important factor in improving the long-term success rate of UKA is appropriate patient selection. Patient selection is, of course, multifaceted and includes factors such as age, physical examination, x-ray performance and personality.
For the joint replacement surgeon, the age of the patient is the most problematic issue. As the population grows, more and more young people are presenting prematurely with severe osteoarthritis. This segment of the population wants good knee function and short recovery times, and UKA technology offers physicians the option of treating younger patients, even those with limited osteoarthritis in the elderly.
UKA is supposed to be “the first knee for younger patients and the last knee for older patients” (A.J. Tria, Jr, personal communication, 2001). This statement means that patients younger than 60 years of age will need another revision after joint replacement, whereas patients older than 80 years of age will only need a single replacement. Patients between the ages of 60-80 are better candidates for TKA, only a point that is very familiar to most orthopedic surgeons.
On physical examination, the knee should have good range of motion, good joint stability, and little angular deformity. This is because extensive soft tissue release is not possible due to the limited exposure of the minimally invasive technique. Therefore this procedure requires better normal soft tissue stability, and soft tissue contractures and stiffness are not recommended for this procedure. uka relies on normal ligaments to stabilize the joint, and normal collateral and cruciate ligaments are essential for proper joint function after arthroplasty. No old damage to the ligaments is allowed, especially for a mobile prosthesis. Because the UKA has only a limited thickness and relies on normal ligament function, it can only correct limited angles of flexion contracture and valgus deformity, generally limited to 10 degrees.
The pain in the affected knee is confined to the affected joint space, figuratively referred to as “one-finger pain”, and severely affects the patient’s lifestyle. Diffuse pain, especially patellofemoral pain, is a relative contraindication. TKA should be chosen over UKA if patellofemoral arthropathy is confirmed, such as a positive half-squat test or stair climb test, and UKA should be avoided for severe retropatellar friction.
X-rays are very important in the selection of UKA. The degree of degeneration of the involved joint space must be carefully observed to exclude lesions of the contralateral joint space and patellofemoral joint. In general, moderate joint degeneration is the best choice, while inflammatory arthritis is a contraindication. This is because in inflammatory arthritis, all other intersegments are potentially at risk for further degeneration.
Other intervertebral compartments with small bone fragments are acceptable. Excessive tibial subluxation or narrowing of the intercondylar fossa is a sign of joint instability and these cases are more suitable for TKA. a posterior anterior radiograph (skier’s view) in the flexed knee position is very good at detecting posterior tibial wear and is useful for unicondylar replacement of the lateral joint. This postural x-ray is often missed in routine x-rays.
One of the greatest advantages of UKA is that the normal ligaments and structures of the contralateral compartment are preserved, consistent with normal kinematics and normal sensation and function of the affected knee. However, this is also the biggest disadvantage of this procedure. Because so much normal structure is present in the joint, it is a potential factor for post-arthroplasty pain.
Among all of the operator’s procedures, there have been several failed patients with unexplained pain in the contralateral joint space that could not be resolved by arthroscopic surgery or conservative treatment. This unexplained pain caused headaches for UKA surgeons. It is therefore recommended to avoid giving this type of surgery to patients who are eager to relieve their pain and are quite fussy.
Surgical technique
Approach
The medial and lateral approaches are available for UKA. Image 1 shows the skin incision for the lateral approach. The one detailed below is the medial interarticular compartment UKA, as surgery of this lateral compartment is more common.
The skin incision extends from the middle of the tibial tuberosity up to 1 cm above the superior pole of the patella. the medial parapatellar arthrotomy, too, is extended to the superior pole of the patella. To reduce the tension on the medial soft tissues, the medial joint capsule can be incised horizontally and transversely at the middle of the medial femoral condyle. However, injury to the quadriceps muscle should be avoided. If some patients have a low medial quadriceps head stop, then the medial head must be freed from the patellar stop. A true subquadriceps approach can also be applied, and that requires more proximal capsule and subcutaneous freeing. The posterior patellar fat pad needs to be removed (Figure 2) and then the deeper layer of the medial collateral ligament is separated along the edge of the medial tibial plateau up to the stop of the semimembranosus tendon.
The knee is straightened and the lateral joint space and patellofemoral joint are examined (Figure 3). If the articular cartilage of the two joints mentioned above has a degree I or II cartilage injury, UKA can be continued; if it is degree III or more, or if the patellofemoral joint has a buttress injury, the procedure is changed to TKA.
Femoral osteotomy
The femoral locator insertion point should be positioned 0.5-1 cm medial to the deepest point of the glide sulcus and 1 cm anterior to the posterior cruciate ligament stop (Figure 4). After drilling, the appropriate intramedullary locator is selected. Because the ideal aim of UKA is a mild undercorrection of the knee valgus angle, the locator should be angled less than 1 degree from the femoral tuberosity valgus angle (e.g., femoral valgus angle of 6 degrees, femoral locator of 5 degrees). The osteotomy angle of the femur does not affect the entire lower extremity force line of the UKA, but the selection of an appropriately angled positioner will ensure a more parallel osteotomy of the femur and tibia and improve the longevity of the prosthesis.
The long bar of the femoral locator should be inserted along the long axis of the femur, with the tip of the bar as far as possible along the posterior aspect of the bone cortex to ensure a neutral knee plane of flexion of the femoral prosthesis (Figure 5). The patella can often be pulled laterally with the force of one finger in a flexed knee at 70 to expose sufficient field of view for surgery. The loose cartilage of the medial condyle should be removed beforehand so as not to interfere with the positioner fitting into the femoral condyle.
After the locator is fully placed, three gold nails fix the osteotomy block to the femoral condyle (Figure 6 the first gold nail is fixed). Because the ideal UKA requires a 6 mm distal femoral osteotomy, a medial gap or lateral gap osteotomy should be performed using a lateral femoral locator. A standard 10 mm medial locator can also be used to fix the gold nail in the most distal row of holes of the osteotomy block and then move the block to the nearest row of holes to also achieve an osteotomy of 6 mm.
After osteotomy of the distal femur, the patella and glide groove can be protected using the intramedullary gang on the locator (Figure 7). The superior edge of the osteotomy should be located on the tidal line of the femur.
Figure 1 Skin incision for a single replacement of the lateral joint.
Figure 2 The patella is lifted and the fat pad is removed.
Figure 3 Turning up the patella to examine the patellar cartilage injury.
Figure 4 The anteromedial aspect of the intercondylar fossa is used as the medullary opening point.
Figure 5 Femoral locator and 6-mm osteotomy block are installed.
Figure 6 Fixation of the osteotomy block.
Tibial osteotomy
Any of the available extramedullary tibial locators can be used to perform a suitable tibial osteotomy. The authors are used to applying the minimally invasive tibial locator of the MG-Uni. It is very simple yet achieves the desired reproducible results. The purpose of the tibial osteotomy is to place the prosthesis in a neutral sagittal position with a coronal position parallel to the normal tibial plateau.
To achieve this, the distal end of the locator should be placed 1 cm medial to the center of the ankle joint and 1 cm distal to the medial tibial tuberosity. This allows the locator to be positioned 1 cm medial to the tibial force line and parallel to the tibial force line (Figure 8). The osteotomy block is fixed at the proximal tibia and the thickness and inclination of the osteotomy is determined. The ideal thickness of the osteotomy is 4 mm, bearing in mind that the polyethylene spacer provided by UKA has a small selection of thicknesses, and in some patients with severe bone defects, the tibia should be osteotomized as little as possible (Figure 9).
During osteotomy, the medial collateral ligament should be carefully protected using a warp plate, and special care should be taken when osteotomizing horizontally to the posterior cortex. Special care should be taken to avoid osteotomies under the anterior cruciate ligament. Vertical osteotomies should be made parallel to the anterior-posterior axis of the tibia and can be achieved by leaving the foot in a neutral position. The osteotomy should be located medial to the ACL stop and extend posteriorly to just below the lateral edge of the medial femoral condyle.
The cut bone block is pulled using a kocher clamp and the cut platform is removed intact by gently cocking it upward and inward using a bone knife (Figure 10). If the bone block is ruptured, the posterior portion is held in abeyance and removed until the femoral osteotomy is complete.
Femoral finishing
After completion of the femoral tibial force line osteotomy, the next step focuses on the selection of the prosthesis size. Bend the knee 90 degrees and place the femoral size osteotome with the front just reaching the osteotomy margin, never exceeding the osteotomy margin to avoid patellar impingement. The left and right are slightly smaller than the osteotomy margin. When the tibia is in neutral position and the knee is flexed at 90 degrees, the femoral osteotome will also be in the proper rotation angle on its own, again confirming the line of force. The internal and external positions are adjusted to confirm that the femoral prosthesis is positioned centrally between the tibial osteotomy and the femoral condyle (Figure 11).
Once the size and position are determined, the osteotome is firmly anchored and femoral finishing begins. The anchor hole is first drilled and then the osteotomy is performed in all directions (Figure 12). Special care is taken to protect the medial collateral ligament during the osteotomy. The bone block is removed, taking care to hyperflex the knee and pulling the posterior bone block forward to avoid the bone block slipping into the posterior joint space (Figure 13).
Figure 7 Removal of the femoral bone block and installation of the patellar retractor.
Figure 8 Placement of the tibial locator.
Figure 9 Fixation of the osteotomy block and interception of the tibia.
Figure 10 Complete removal of the tibial plateau.
Figure 11 Femoral osteotome is installed so that the osteotome is located in the center of the osteotomy surface of the femur and parallel to the tibial plateau.
Figure 12 Drilling of the femoral fixation hole and osteotomy.
Meniscectomy and local anesthesia for analgesia
After the osteotomy is completed and the bone is removed, the posterior joint space is further cleared. External rotation of the tibia can facilitate this step. A calf fixator can also be utilized to facilitate the maneuver and can be fixed to the desired different angles of knee flexion and rotation (Figure 8). After external rotation of the tibia, the meniscus is removed using two Kocher clamps and pulling forward (Figure 14). All the tissue remaining in the posterior joint space can be easily removed.
After clearing the joint, the authors prefer to inject a mixture of 20 ml of bupivacaine and 10 mg of morphine around the posterior joint capsule, at the site of meniscectomy, to facilitate postoperative analgesia (Figure 15). This approach provides good postoperative analgesia and facilitates early ambulation and postoperative recovery. Early and extensive continuous passive motion can also be performed to reduce the risk of joint adhesions.
Tibial refinement
With the lower leg in the internally rotated position, measurement and refinement of the tibial size is completed. A posterior lateral meniscal retractor can be used at this point to facilitate visualization of the entire surface of the tibial plateau (Figure 16). The annular sizer is placed on the osteotomy surface of the tibial plateau under direct vision and a prosthesis as large as possible as the size of the tibial plateau is selected. Avoid being too large, but being too small also tends to cause undermining of the prosthesis. If the posterior edge of the tibia cannot be seen straight on, a depth gauge can be used to help determine the position of the posterior edge of the tibial plateau (Figure 17). The tibial prosthesis trial mold is placed and secured, and the tibial fixation hole is drilled, at which point the tibia can be internally rotated to facilitate manipulation (Figure 18).
Figure 13 Removal of the bone block from the posterior femoral condyle.
Figure 14 The meniscus is pulled forward using Kocher forceps and removed.
Figure 15 Local analgesic injection.
Figure 16 Placement of a lateral retractor to facilitate visualization of the intact tibial plateau.
Figure 17 Measurement of the size of the tibial plateau. Figure 18 Drilling of tibial fixation holes.
Mounting the trial mold
The knee is hyperflexed, rotated in neutral position, and the femoral trial mold is installed under direct vision (Figure 19). Flex the knee 90 degrees and install the spacer trial mold. If the osteotomy is appropriate, the 8mm or 10mm shim trial die will achieve the correct force line and ligament balance. At this point, the range of motion of the joint, force lines and ligament tightness are checked to ensure good joint function. A 2mm laxity of the medial collateral ligament allows for good joint function, mechanical requirements and a long life4.
A 2mm ligament tension tester can be used to test the laxity of the medial collateral ligament (Figure 20).
Bone cement fixation of the prosthesis
After the prosthesis trial mold is completed, if the surgeon is satisfied with the choice of prosthesis, then the prosthesis is prepared for fixation. The joint cavity is thoroughly flushed and the joint surface is dried with dry gauze. It is important to use bone cement in the soft state, as this minimally invasive technique leaves very little room for post-cleaning capsule cement. As with all joint replacement procedures, continuous fixation technique and the surgical team’s proficiency in the procedure are important in order to achieve consistent cement fixation technique and fixation results.
When the cement appears soft, the cement is injected into the fixation air of the tibia and the tibial prosthesis is placed. When placing the tibial plateau, the tibial plateau is placed at a low posterior and high anterior angle using a bone tool, squeezing the cement mostly anteriorly (Figure 21). The prosthesis is fixed with gentle blows using a fixation tool, avoiding violent hammering to avoid fracture of the tibial plateau (Figure 22). The cement is scraped off posteriorly using a cement scraper, with special attention to the cement directly behind the prosthesis. The great advantage of a metal tibial prosthesis is that it allows complete removal of excess cement, whereas an all-polyethylene prosthesis does not.
The femoral prosthesis is then inserted with hyperflexion of the knee to avoid impingement with the tibial prosthesis. The prosthesis is gently driven in to clean up any surrounding spillage of cement, particularly around the posterior femoral condyle (Figure 23). The intercondylar fossa is then confirmed to be free of impingement and the polyethylene spacer is finally placed (Figure 24).
Figure 19 Installation of tibial and femoral trial molds.
Figure 20 Measurement of joint tension using a 2-mm tension tester in the extended position.
Figure 21 Placement of the tibial prosthesis with a posterior downward tilt to squeeze the cement posteriorly to the anterior.
Figure 22 Gently striking fixation.
Figure 23 Femoral prosthesis is placed with percussion fixation.
Figure 24 Placement of polyethylene spacer.
The tourniquet is then loosened to stop the bleeding completely, the joint is flushed, drainage is placed, and the incision is sutured. Drains are optional and are routinely placed in the authors’ unit to reduce postoperative pain and blood accumulation in the joint. The length of the incision averaged 9 cm (Figure 25). Postoperative radiographs showed typical lateral UKA (Figure 26, 27) and medial UKA (Figure 28, 29).
Surgical traps
Potential pitfalls of the UKA arise in four main areas: exposure, osteotomy, soft tissue management, and refinement. The main difficulty in exposure is the inadequate mobility of the patella, which requires excessive stretching of the quadriceps and is detrimental to the subsequent steps. Therefore, during incision of the joint capsule, all medial fascia and hypertrophic synovial membrane that restrict patellar mobility should be separated. Sometimes, as in the simplified subtrochanteric approach, it is necessary to release a little bit of the joint capsule and fascial tissue posteriorly. Rather than reluctantly operating through an inadequately exposed field of view, it is better to release a little of the soft tissue such as the joint capsule.
As mentioned above, the locator should be placed correctly to ensure that the osteotomy is indeed made and the line of force is correct. It is important to make sure that the osteotomy block is close to the bone and that obstructions such as bone redundancy and remnant cartilage must be removed before setting the nail. Note that inadequate osteotomy of the distal femur can result in an undersized femoral prosthesis. Reducing the posterior angle of the tibial osteotomy can correct small flexion contractures, a technique often used in TKA.
It is important to realize that the more inward the field of view is exposed, the more likely it is to lead to tibial inversion due to the placement of the tibial locator in the deviated and internally rotated position. The anterior-posterior axis of the locator must be parallel to the anterior-posterior axis of the tibia. The thickness of the tibial osteotomy relies primarily on bony landmarks rather than ligamentous tension. Old ligament injuries and contractures can lead to incorrect osteotomies, and unlike TKA, UKA has a more limited chance of saving errors.
Ligament balancing in UKA surgery is relatively easy, but is necessary. Internal rotation correction should aim to leave a little mild internal rotation, and only then can prosthetic balancing within the soft tissue be achieved. Some patients with old medial collateral ligament injuries have overfilled the medial structures in an attempt to tighten them, resulting in valgus. It is better to leave a mild degree of medial laxity than to overcorrect for valgus and avoid pain and early joint degeneration in the lateral joint space. Moderate or greater medial laxity should be converted to TKA to facilitate ligament balancing and prosthesis selection.
Finally, hemostasis within the joint after removal by joint cleaning, cement fixation of the prosthesis, and free body is important but sometimes very difficult due to limited exposure. A small scraping spoon and angled scrapers are essential. Often, direct vision is difficult due to overtightening of the joint, and the posterior view of the joint can be improved by increasing the posterior tilt angle of the tibial osteotomy to widen the flexion gap. Calf fixators to hold the calf and tibial prosthesis in an externally rotated position can improve direct visualization and clearance of the posterior joint capsule, and this technique should also become routine for minimally invasive techniques.
Postoperative Rehabilitation
The postoperative management of the UKA minimally invasive procedure is very simple. Drainage is placed according to the decision of the surgeon. Postoperative pain is minimal due to the intraoperative injection of local anesthetic. A wide range of continuous knee motion is possible immediately after surgery and gait exercises should be performed as soon as the anesthesia subsides. Our patients are routinely discharged one day postoperatively. Many rehabilitation measures are performed after discharge. assisted walking is discontinued after 1-2 days and tolerable gait and strength training is performed. light work is started after 1-2 weeks and moderate work is performed after one month. Light physical activity can be started at the same time, and full strength golfing can be performed 6 weeks after surgery.
Results
UKA has become a reliable and predictable surgical procedure. Applying the traditional approach and instrumentation, many surgeons have outperformed the TKA.4 The superiority of the UKA is due to the large knee flexion angle, good joint function, and high patient satisfaction. Compared to conventional UKA, minimally invasive surgical UKA is comparable in terms of operative time, lower extremity force lines, soft tissue balance and fixation, with similar short-term clinical results and no difference in long-term outcomes.
We have performed UKA on 343 patients over the past 4 years, applying the techniques described above. the surgical technique was very proficient, with an average tourniquet time of 25 minutes (Figure 30). 2 (0.6%) patients underwent revision surgery because of infection. 1 (0.3%) patient was returned because of lateral joint degeneration, and this patient should have undergone TKA for the first surgery. 2 (0.6%) patients Two patients (0.6%) underwent revision because of unexplained contralateral joint pain. No patient was repaired for a loose prosthesis, and one patient was reoperated for a fixed free body. 7 patients (2%) underwent arthroscopic surgery for a meniscal tear, and 2 of these patients were repaired. Postoperative X-rays showed fairly satisfactory force lines and prosthetic fixation in all patients, and no patient had an unresolved failure factor.
Figure 25 Length of the incision.
Figure 26 Orthopantomogram of the lateral UKA.
Figure 27 Lateral slice of the lateral UKA.
Figure 28 Orthopantomogram of the medial UKA.
Figure 29 Lateral slice of medial UKA.
Figure 30 Tourniquet time for the first 37 UKA procedures with increasingly shorter subsequent procedures.
Conclusion
Over the past 5 years, the minimally invasive technique of UKA has gained worldwide popularity, providing a powerful tool for joint surgeons worldwide due to its advantages of less pain, less trauma, and faster recovery. the QS surgical instrumentation is a reliable system with strong bone cutting reversibility, powerfully improving surgical efficiency in the operating room, and can be easily converted to TKA when necessary. these features, combined with proper patient selection efficient surgical technique, avoidance of possible surgical pitfalls and rapid postoperative recovery, return the patient to a satisfactory, long-lasting, highly functional knee.