The meniscus is an important structure for maintaining the physiological function of the knee joint, and its absence will lead to cartilage degeneration and osteoarthritis, and it has become a consensus that the meniscus should be preserved and repaired as much as possible in the treatment of meniscal injuries [1]. However, not all damaged meniscus can be repaired [2]. In cases where the meniscus is completely destroyed, unrepairable, or has been removed, meniscal reconstruction is of great importance to restore knee function. The most popular meniscus reconstruction technique is allograft meniscus transplantation [1]. The clinical application of allogeneic meniscus transplantation has been reported abroad [1-3], but only animal experiments and reviews have been published in China [4, 5], and no clinical meniscal transplantation has been reported in the literature. We performed allograft meniscus transplantation in two patients in 2006, and our preliminary report is as follows and discusses the issues in the literature.
1. Clinical data
1.1 General information
Case 1, female, 48 years old, had pain in the left knee after a sprain for 7 years. He had swelling and limitation of flexion and extension of the knee joint. Physical examination: pressure pain in the medial joint space was obvious, and McMurry’s sign was positive. Joint mobility (0 for knee extension, negative for hyperextension, positive for flexion): 5 degrees of extension (with pain), 120 degrees of flexion (with significant pain). X-ray of the left knee showed: basically normal lower extremity force lines, slightly narrowed medial joint space, and sharp intercondylar spine. MRI of the left knee: Grade III injury to the medial meniscus, with a large portion of the posterior horn body missing. Treatment: Arthroscopic medial allograft meniscus transplantation.
Case 2, male, 29 years old, with pain and popping after right knee sprain and joint instability for 2 years. Physical examination: pressure pain in the medial joint space. Positive anterior drawer sign, Lachman test and axial shift test, and positive McMurry sign. Joint mobility: extension -5 degrees (with pain), flexion 135 degrees (with pain). X-ray of the left knee: no significant bony abnormalities. MRI of the left knee: anterior cruciate ligament rupture, medial meniscus grade III injury, and posterior horn body part missing. Treatment: arthroscopic medial allograft meniscus transplantation, reconstruction of the anterior cruciate ligament with four semitendinosus tendons and thin femoral muscle.
1.2. Allogeneic meniscus harvesting, preparation and storage
From legally obtained donor donor (cadaver and non-tumor amputated limb), donor serological test index according to domestic blood donor requirements: HIV, HBsAg, HCV and syphilis seronegative; age < 50 years. The meniscus with a small amount of marginal synovial membrane and the attached proximal tibial bone were excised under aseptic conditions. Soft tissues were removed, blood was removed by high-pressure rinsing, ultrasonic cleaning, degreased and then sterilized by 3-layer aseptic vacuum packaging and irradiation (performed by the PLA Academy of Military Medical Sciences, with a radiation source of drill 60 and radiation equivalent of 25 kGy) to meet the national standard for sterilization of in vivo implants. Bacteria test specimens were sterilized together in the same package to confirm the sterility of the product before use. The vacuum-encapsulated sterilized meniscus was stored at -80°C. Donor records are created for follow-up.
1.3.3 Arthroscopic meniscus transplantation procedure
1.3.1. Allograft meniscus size matching and preparation
The size of the tibial plateau on the affected side of the recipient was measured by X-ray and CT scan, and a donor meniscus of the same sex, side and age was selected, the size of which was 10% larger than that of the recipient. The allograft medial meniscus was made into a complete meniscus with an 8 mm diameter bone peg at the anterior and posterior corner stops on the operating table, and a non-absorbable suture was drilled through the middle of the bone peg for backup (Figure 1).
1.3.2. Arthroscopic exploration and cleaning
Continuous epidural anesthesia was applied with the affected limb in a supine position with the thigh fixed at the end of the surgical bed and the lower leg subluxated. A conventional arthroscopic incision is made medially and laterally in front of the knee (the medial incision is slightly larger to facilitate placement of the allograft medial meniscus) to explore the ligament, meniscus and cartilage lesions (Figure 2). The synovial membrane and fat at the anterior and posterior corners of the affected meniscus are cleared, and the completely broken meniscus stump is arthroscopically excised to its junction with the synovial rim, preserving approximately 2 mm of the meniscus circumference until punctate bleeding occurs. The proximal end of the medial collateral ligament was cut off from the femoral condyle to improve the arthroscopic view, and was postoperatively re-fixed with screws.
1.3.3. Allograft meniscus implantation
To create the posterior meniscal tract, a guide pin was drilled through the medial incision with a locator from the medial tibial tuberosity to the center of the posterior meniscal tract, and a 9 mm hollow drill was used to create the tract. For the anterior meniscus tract, a guide pin is drilled through the medial incision into the center of the anterior meniscus area, and a 9 mm hollow drill is used to create the blind canal tract. The blind canal tract is drilled from the medial side of the tibial tuberosity into the anterior horn with a locator and slightly enlarged. The sutures for the anterior and posterior horn bone pegs were led out through the prepared anterior and posterior horn bone tract to the medial tibial tuberosity by guiding wires, and the anterior and posterior horn sutures were tightened and the transplanted meniscus was implanted in place through the medial incision (Figure 3), allowing the anterior and posterior horn bone pegs of the allograft meniscus to enter the anterior and posterior horn bone tract. The meniscus was sutured posteriorly with 2 stitches using a total internal vertical suture (Fastfix, Smith-Nephew, USA). The other parts were sutured with an inside-out vertical suture, and the anterior horn could also be sutured with an outside-in equal suture until the meniscus was securely fixed, and the anterior and posterior horn bone peg sutures were knotted medially to the tibial tuberosity for fixation. Arthroscopic confirmation of the correct position and good fixation of the transplanted meniscus was performed (Figure 4).
1.4. Postoperative rehabilitation program
After 1 week of postoperative plaster fixation, quadriceps isometric contraction training was started. 6 weeks weight-bearing was avoided on the affected limb, and progressive weight-bearing exercises were started from 6 to 12 weeks. Joint mobility exercises were performed under the protection of knee brace, and the plan was as follows: 2 weeks after surgery, complete extension of the knee and small-angle flexion without rotational load were started, and the flexion was limited to 60 for 6 weeks. At 12 weeks after surgery, the knee was flexed more than 90° without weight-bearing, and the walking function was basically restored; at 18 weeks after surgery, the knee was flexed more than 120°, and the walking function was completely restored; at 24 weeks after surgery, activities such as jogging were gradually started; at 36 weeks after surgery, the motor function was gradually restored.
2 .Results
There was no surgical side injury in the two patients, and there was no obvious wound exudate. In the early stage, the knee was slightly swollen, and the circumference of the knee joint was 36 cm and 41 cm before surgery and 39 cm and 45 cm after surgery. 6 weeks after surgery, the swelling basically disappeared. The joint pain score was 8 and 6 preoperatively and 3 and 2 postoperatively. At 12 weeks postoperatively, the knee mobility of case 1 (recorded as before) was 0. in extension and 100. in flexion. Case 2 knee mobility was 0. extension and 90. flexion. In case 1, the medial joint space increased from 2 mm before surgery to 3 mm after surgery, and in case 2, it was similar to that before surgery.
3, Discussion
3.1. Repair of meniscus injury and its difficulties
The meniscus has important biomechanical functions, including stabilizing the joint, transmitting load, reducing stress, absorbing shock, improving joint lubrication and cartilage nutrition, improving tibiofemoral joint adaptability and joint motion coordination, etc. It is an indispensable part of the normal function of the knee joint. Severe injury or absence of the knee meniscus will lead to joint instability, cartilage degeneration and osteoarthritis [1]. Therefore, treatment of meniscal injuries should preserve and suture repair the meniscus as much as possible. However, not all damaged menisci can be repaired. Because healing is difficult due to the lack of blood supply to the proximal 2/3 of the free edge of the meniscus, and because meniscal injuries are too severe or delayed to heal, the meniscus should be reconstructed to reduce knee pain due to meniscal loss, avoid or reduce degenerative changes in the cartilage and subchondral bone, and restore the mechanical balance of the knee joint in those individuals who are unable to preserve the meniscus or have had it removed [6].
3.2 Selection of a knee meniscal reconstruction substitute
Prostheses for meniscus reconstruction can be made of polytetrafluoroethylene, silicone, carbon fiber, dacron and resorbable polylactic acid and polyacetic acid, whose softness, creep and physiological function are still difficult to meet the requirements of human meniscus [7]. Tissue-engineered meniscus is currently in the experimental stage, such as the use of synthetic collagen scaffolds for fibrocartilage cells to grow into, and many other issues such as its durability and biocompatibility have not yet been solved [8]. Autologous meniscal graft materials, including patellar ligament, quadriceps tendon, Achilles tendon, semimembranosus muscle, fat pad, cartilage membrane, and synovial tissue have been used as meniscal replacements, with unsatisfactory results [8]. Allogeneic meniscus grafts have also been reported in studies [6]. However, it is extremely difficult to achieve an exact match between its morphology, size and structure with the host. The allogeneic meniscus is the most studied and applied meniscus replacement material, and although there may be problems such as disease transmission, many studies have provided a sound theoretical basis for its application [2, 3], and it is currently recognized as the best choice for meniscus reconstruction [2, 3]. This method was used in the present group of cases.
3.3. Storage of homogeneous meniscus
There are four common methods of preserving allogeneic meniscus: fresh preservation, cryopreservation, deep cryopreservation, and freeze-drying. Fresh meniscus can preserve the activity of fibrocartilage cells, but all donor cells will be replaced by recipient cells after meniscus transplantation, and the morphological and biochemical properties of the transplanted meniscus will not be improved by the surviving cells. Therefore, there is no significant superiority of fresh allogeneic meniscus [1, 3]. Moreover, it is rarely used because of its antigenic nature, short preservation time, great difficulties in donor discovery, harvesting, transportation, size matching, and possible transmission of disease. Freeze-dried meniscus can be preserved for a long time, but it destroys the original structural components, which easily leads to matrix degeneration, meniscal wrinkling and irregular remodeling after transplantation [3], and is not used much at present. Cryogenic frozen and deep cryopreserved meniscus are currently the most used, especially the deep cryopreserved meniscus has satisfactory clinical use [1]. Therefore, this method was used to preserve the allograft meniscus in this group of cases.
3.4. Surgical indications for allograft meniscus transplantation
The indications for surgery of allograft meniscus transplantation are not uniformly defined, and the more commonly used indications are: patients aged 20 to 50 years old with severe meniscal damage that cannot be repaired and the meniscus must be removed; knees with early osteoarthritic manifestations in the missing meniscus; and knee degeneration that has a tendency to worsen despite the absence of clinical symptoms [6]. Contraindications include: severe degeneration of knee cartilage (grade III and IV), severe destruction of subchondral bone, significant bone redundancy formation at the joint edges, flattening and deformation of the femoral condyles, significant joint instability, improper force lines in the lower limbs, infection and other contraindications to surgical procedures.
With the development of meniscus transplantation technology, the indications and contraindications for surgery have also changed. Some studies have confirmed that meniscal transplantation for the treatment of chronic degenerative meniscal injuries has also achieved good results [10]. Meniscus transplantation can be performed in conjunction with reconstruction of joint stability in unstable knees. Meniscal transplantation can also be performed simultaneously with osteotomy orthopaedics in cases of lower limb force line malalignment [1].
Meniscus transplantation can be performed by both incisional and arthroscopic surgery. Although arthroscopic surgery is slightly more difficult to perform, it is less traumatic to the joint, has a faster postoperative recovery, and facilitates rehabilitation exercises. Therefore, arthroscopic surgery was used in this group of cases.
3.5. Short-term results and problems of allogeneic meniscus transplantation
The current study confirmed that after allogeneic meniscus transplantation host synovial cells can chemotaxis and migrate into the transplanted meniscus, change into fibrocartilage cells and show matrix reconstruction function, and the transplanted meniscus can heal with the joint capsule and replace part of the function of the diseased meniscus, which can relieve knee pain and other symptoms and improve the function of the knee joint in the short term [11]. The preliminary report of our 2 cases is not enough to draw final conclusions, but technically speaking, it currently shows preliminary satisfactory recent clinical results.
Regarding the immune rejection of allogeneic meniscus grafts. Since the meniscus is mainly composed of collagen fibers and most of the tissue has no blood vessels growing into it, making it shielded from most of the immune system, and the immunogenicity is further reduced by cryopreservation, the existence of immune reaction cannot be excluded, but it does not affect the clinical outcome after meniscus transplantation [1,3]. In this group of cases, the wound healing was good, there was no obvious exudate, and the postoperative immunological indexes were in the normal range, which initially showed that the immune reaction caused by the allogeneic meniscus did not lead to significant adverse clinical effects.
Allogeneic meniscus transplantation has not yet become a standard treatment, but in the current situation where there are many difficulties in the treatment of severe meniscus injuries, this technique is widely valued and may become an important method for the treatment of severe meniscus injuries or defects.