Medial meniscus posterior root tear (MMPRT) is defined as a radial tear of <10 mm from the MMPR attachment and is reported to disrupt the MM hoop action thereby disrupting knee joint kinematics ^{[1, 2]}. MMPRT is widely known to cause osteonecrosis (ON) and rapid progression of knee osteoarthritis ^{[3, 4]}. Therefore, it is important to properly treat and restore the hoop action. Pull-out suture, suture anchor, and open-wedge high tibial osteotomy (OWHTO) have been widely used for surgical treatment of MMPRT, and relatively good clinical results have been reported ^{[5, 6, 7]}. However, radiologic and arthroscopic findings are not sufficient ^{[5, 6, 7]}. Recently, Ishikawa et al. reported that MMPR-reconstruction is useful for reconstructing the failed hoop function of MM ^[8]. However, the results of MMPR-reconstruction have not been reported, and its usefulness is not yet known. This report describes a case of MMPRT with varus knee treated with MMPR-reconstruction and OWHTO.

A 78-year-old Japanese man was referred to this hospital due to the right popliteal pain. His height was 159 cm, his weight was 59 kg, and his body mass index was 23.3. He had no history of trauma. Orthopedic physical examination of the right knee revealed tenderness from the posteromedial joint line to the popliteal fossa with a mild joint effusion. Ligament instability tests were all negative. The McMurray test was positive for pain but not click. His range of motion (ROM) was restricted to 0–145 degrees because deep flexion exacerbated the pain. The knee injury and osteoarthritis score (KOOS) was 22 points. Imaging studies were performed with plain radiography, including the entire length of the lower limbs with weight-bearing, frontal and lateral views of both knees, and magnetic resonance imaging (MRI). Plain radiography showed no obvious osteoarthritis of the knee, but the mechanical axis percentage was 17%, indicating a varus knee (Fig. 1). MRI showed a giraffe neck sign on T2-weighted coronal imaging and a white meniscus sign on T2-weighted sagittal imaging (Fig. 2). Arthroscopic MMPR-reconstruction using an autogracilis tendon and OWHTO was performed as follows: (1) The presence of MMPRT was confirmed using a probe (Fig. 3). (2) An autologous gracilis tendon was harvested using a diagonal skin incision on the medial side of the tibia. The harvested gracilis tendon was double folded and grafted with a baseball-groove suture at the end. (3) A soft-tissue tunnel was created from the femoral to the tibial side at the outer lesion of the MM, 5 mm from the MMPR edge, using a 3.5 mm 90° hook electrode (Mitek VAPR 3 system, DePuy Mitek), and a 60 °hooked rotary scissors (ACUFEX; Smith and Nephew) (Fig. 4). (4) A tibial tunnel was made from the lateral tibia to the anatomical MMPR attachment using an anterior cruciate reconstruction guide (3M) (Fig. 5). (5) The graft was inserted through a soft-tissue tunnel (Fig. 6). (6) OWHTO was performed using normal procedures to provide a mechanical axis percentage of 62.5% (Fig. 7). (7) The graft was pulled through the tibial tunnel and fixed with an artificial ligament fixture (pull-out button, AI-Medic) (Fig. 8a). The patient was started on partial weight-bearing 2 weeks postoperatively, and he was allowed full weight-bearing 6 weeks postoperatively. His ROM was limited to 90° for the first 4 weeks postoperatively and 130°for 6–12 weeks postoperatively. Full flexion and squatting were allowed beginning 3 months postoperatively. The patient underwent a second look operation and metal removal 1 year postoperatively. The reconstructed MMPR was well engrafted (Fig. 8b), and the area of necrosis showed good fibrocartilage augmentation (Fig. 9). KOOS showed improvement with a score of 91 points, and the patient experienced no pain while performing normal activities.

This report presents, to the best of our knowledge, the first case of MMPR-reconstruction and OWHTO for MMPRT with varus knee. A good clinical result was obtained. Furthermore, the MM hoop was successfully reconstructed and maintained 1 year later at a second look surgery. Pull-out suture, suture anchor, and OWHTO have been widely used for surgical treatment of MMPRT ^{[5, 6, 7]}. Moon et al. treated MMPRT with pull-out repair and reported that the Lysholm score improved from 48.3 points preoperatively to 83.2 points postoperatively, while MM extrusion increased from 3.6 mm preoperatively to 5.0 mm postoperatively ^[9]. Furthermore, Chung et al. reported worsening in Kellgren-Lawrence grade 5 years after pull-out repair ^[10]. Seo et al. reported 11 patients who had a second look surgery after pull-out repair and found none with complete healing. There were five cases of Lax healing, four cases of scar healing, and two cases of failed healing ^[11]. Jung et al. performed a follow-up MRI, on average 30 months after suture anchor repair, and reported that 50% had complete healing, 40% had partial healing, and 10% had no healing ^[7]. They also reported that MM extrusion ranged from 3.9 mm preoperatively to 3.5 mm postoperatively, with no significant improvement ^[7]. In this report, although there are only short-term results available, the patient achieved a good clinical outcome as well as good reconstruction of the hoop. Furthermore, despite extensive ON, good cartilage regeneration was observed. There have been reports of meniscus reconstruction using the peroneus longus tendon after lateral meniscectomy ^[12]. In addition, a study using rabbits reported that the semitendinosus and gracilis were suitable for meniscus reconstruction ^[13]. The outer region of the meniscus and the tendon are both rich in type I collagen ^{[13, 14]}, and it has been reported that the transplanted tendon can replace the meniscus ^[13]. As is well known in anterior cruciate ligament reconstruction, both the semitendinosus and gracilis show good bone tendon healing ^[15]. Furthermore, the varus knee mechanical axis and steep posterior tibial slope (PTS) increase mechanical stress on the MMPR and are reported to be risk factors. In the present case, OWHTO reduced the femorotibial angle and PTS, resulting in a reduced load on the graft. The use of OWHTO in conjunction with MMPR-reconstruction using the gracilis may have resulted in better engraftment.

This report is the first case, to the best of our knowledge, of MMPR-reconstruction and OWHTO for MMPRT with varus knee.

MMPR-reconstruction and OWHTO may be a useful treatment for MMPRT with varus knee.