Arthroscopic medial patellofemoral ligament reconstruction for recurrent patellar dislocation: short-term clinical results


 The present study aimed to introduce a novel technique to reconstruct medial patellofemoral ligament (MPFL) via arthroscopy for recurrent patellar dislocation. A retrospective review of a prospectively collected registry was undertaken. A total of 34 patients (35 knees) who underwent arthroscopic reconstruction of MPFL from December 2017 to August 2019 were identified. Kujala score, Tegner score, Lyscholm score, patellar tilt, and congruence angle were recorded preoperatively and postoperatively. The occurrences of patient satisfaction, complications, and recurrent dislocation were recorded. The cohort consisted of both genders equally, and the mean age was 21.0±7.8 years, the mean body mass index was 22.5±3.5, and the mean follow-up time was 21.8±5.6 months. The patellar tiltdecreased from 46.4±19.3° to 12.5±16.9° (P < 0.001), the congruence angle decreased from 46.4±19.3° to 12.5±16.9° (P < 0.001), Kujala score improved from 55.1±4 to 88.7±4.4 (P < 0.001); Tegner score improved from 1.3±0.4 to 3.7±1.1 (P < 0.001), and Lyscholm score improved from 55.5±3.9 to 89.1±4.8 (P < 0.001). Among them, 30 (88.2%) patients fully recovered to normal pain-free daily life, 24 patients (70.6%) returned to sports, 32 patients were satisfied with surgery, and no redislocations were encountered. MPFL reconstruction via arthroscopy improves the knee joint function in patients with recurrent patellar dislocation and is a safe and effective surgical treatment for recurrent patellar dislocation.

Recurrent patellar dislocation is often multifactorial and therefore, the diagnosis and treatment become challenging.
Furthermore, MPFL is the most important static structure that maintains the medial stability of patella 10 . A previous biomechanical study suggested that MPFL contributes to maintaining patellar stability of 50-60% in knee flexion within 0-30°range [11][12][13] . A magnetic resonance imaging (MRI) study showed that 98.6% of patients with acute patellar dislocation had MPFL rupture 14 . Therefore, MPFL reconstruction has become the gold standard for the treatment of recurrent patellar dislocation.
Femoral trochlear dysplasia is an major risk factor for recurrent patellar dislocation 5,6,9,15,16 . Severe femoral trochlear needs to be corrected by trochleoplasty. Increased tibial tubercle-trochlear groove (TT-TG) distance is another risk factor for patellar dislocation 7,17 . Increased TT-TG distance leads to abnormal patella track and increases the risk of patellar dislocation risk. When the TT-TG distance is >20 mm, the abnormality needs to be treated with anteromedial tibial tubercle transfer. In addition, lateral retinaculum release significantly reduces the pressure on the lateral side of the patellofemoral joint 18,19 .
Recent studies have shown that isolated MPFL reconstruction exhibits satisfactory clinical outcomes on patients with femoral trochlear dysplasia, abnormal TT-TG distance, and Caton index [20][21][22][23] . A large number of surgical techniques have been used to treat recurrent patellar dislocation. At present, the surgical treatment usually uses open incisions to establish the patella and femoral bones tunnel for MPFL reconstruction, which has disadvantages such as large surgical incisions, slow recovery, and obvious postoperative wound scars. Arthroscopy is used to loosen the lateral retinaculum and treat the intraarticular cartilage damage, reducing the surgical incisions and achieving early recovery 24 . Gao et al. 25 made a window through the joint capsule under arthroscopy to expose the inner edge of the patella and reconstruct the MPFL patella insection. The insection of the femoral tunnel needs to be located by C-arm fluoroscopy, which has the disadvantages of the prolonged operation time, inaccurate positioning, and exposure of patients and medical staff to ionizing radiation. In the present study, accurate positioning was achieved by locating the MPFL femoral insection by arthroscopy, and the MPFL femoral tunnel was reconstructed via arthroscopy. Therefore, the purpose of this study was to evaluate the short-term clinical outcomes of MPFL reconstruction under arthroscopy in the treatment of recurrent patellar dislocation. Herein, we hypothesized that MPFL reconstruction under arthroscopy achieves good clinical outcomes and significantly improves the Kujala score, Tegner score and Lysholm score, as well as the postoperative patella tilt and congruence angle.

Results
The cohort was followed up for an average of 21.8±5.6 (13-32) months, and the last follow-up time point was September 2020. The average TT-TG distance measured by CT before the operation was 17.7±4. At the last follow-up, no further dislocation was found in the patient. Table 1 summarizes the

Discussion
This study is the first report of arthroscopic reconstruction of MPFL. The results showed that arthroscopic reconstruction of MPFL in the treatment of recurrent patellar dislocation could achieve satisfactory therapeutic effects in a short period. A total of 34 patients were followed up for an average of 21 months. None of the patients had re-patella dislocation. The preoperative and postoperative comparison showed that the knee joint function score, patella inclination angle, and fit angle were significantly improved.
After an acute dislocation of the patella, conservative treatment is usually given priority, including physical therapy and fixation of the patella support band. Some studies have found that the incidence of recurrence of patellar dislocation after acute patellar dislocation is 10-50% 26  The contracture of the lateral retinaculum is one of the factors for the outward movement of the patella. By loosening the lateral retinaculum, the pressure on the lateral patella can be relieved and the dislocation of the patella corrected 29 . Therefore, it has become an auxiliary surgery for the treatment of dislocation of the patella. However, a randomized controlled study by Malatray et al. 30 concluded that for patients undergoing MPFL reconstruction for recurrent patellar dislocation, lateral retinaculum release is not required. Song et al. 31 found that excessive loosening of the lateral retinaculum can leads to iatrogenic patella instability, especially for patients without lateral retinaculum contracture.
Therefore, it is necessary to screen patients with contracture of the lateral support belt and then allow a moderate release. The lateral support band loosening under arthroscopy reduces surgical trauma, helps early recovery, and avoids excessive loosening. In conclusion, arthroscopic reconstruction of MPFL can significantly improve the knee function of patients with recurrent patellar dislocation, and is a safe and effective surgical method for the treatment of recurrent patellar dislocation. follow-up for >1 year. Subsequently, patients treated with combined tibial tuberosity transfer were excluded from the study. Moreover, this study was approved by the Hospital Ethics committee of the First Affiliated Hospital of Shenzhen University. All the participants had surrendered informed consent preoperatively. As for participants under the age of 18 years, informed consent had been obtained from a parent and/or legal guardian. All methods were carried out in accordance with relevant guidelines and regulations.

Methods
Kujala, Tegner, and Lyscholm scores were evaluated before the operation. The standard anterior lateral view of knee flexion at 30°and computed tomography (CT) examination of the knee joint was performed before the operation. TT-TG distance, patella tilt, and congruence angle were measured by CT. Knee joint MRI was performed before the surgery to confirm lateral dislocation of the patella and MFPL rupture. Then, the CT examination of the knee was performed to assess the bone tunnel position postoperatively.
Surgical technique. All procedures were performed by the same senior surgeon. First, the adductor tubercle and medial femoral condyle on the medial side of the femur were touched; then, the midpoint of the two was taken as the MPFL femoral insection, the skin was marked, and the Kirschner wire was located (Figure 2A). A 0.5-1 cm incision was made on the upper inner edge of the patella to bluntly subsequently, the anchor tail was pulled to confirm that the anchor is stable( Figure 2B). The knee arthroscopy anterolateral and anteromedial approaches were applied to clean up the synovial tissue in the joint. The tension of MPFL was explored in the state of flexion and extension of the knee joint, followed by an arthroscopic exploration of patellofemoral joint matching( Figure 3A). Next, the cartilage damage of the patellofemoral joint was explored, freshening and microfracture operations and a depth of about 5 cm was drilled under the arthroscope. The allogeneic tendon was woven into a diameter of 6 mm as the MPFL graft, the fold anchor line was fixed on the inner side of the patella, and soft tissue was used to cover the reconstruction of the MPFL patella insection( Figure 2C). The MPFL graft is penetrated into the femoral side bone tunnel through a subcutaneous canal, the tendon is tightened at 30°of knee flexion, and the patellofemoral joint matching is monitored by arthroscopy within the range of motion of the knee joint, and the tension of the MPFL is adjusted ( Figure 3B). The 6-mm interface screw fixes the MPFL femur insection ( Figure 4B). The MPFL femoral side was pressed by elastic bandage compression bandage to prevent subcutaneous hematoma formation, and the cotton legs were fixed to prevent thrombosis in lower limbs. 2 weeks. The full range of knee motion was achieved within 2 months. Partial weight-bearing and full weight-bearing started at 2 weeks and 4 weeks after surgery, respectively. The knee brace was fixed for 3 months, which started to return to sports 6 months post-surgery.
Statistical analysis. The data were analyzed using SPSS19.0 and expressed as mean±standard deviation. The imaging evaluation and functional score were compared as the preoperative and postoperative differences by paired t-test. P < 0.05 indicated statistically significant difference.