Subjects
This retrospective study was approved by the ethics committee of Shenzhen Second People’s Hospital, and all patients gave informed consent preoperatively. Patients who underwent primary ACL reconstruction using anterior tibialis tendon allografts in our department from March 2010 to June 2013 were reviewed. Patients were included if they met the following criteria: 1) 18 years of age or over; 2) primary ACL surgery; 3) no concomitant ligament injury; 4) unilateral ACL injury; 5) no previous surgery on the effected knee, 6), no chondral lesion worse than Outerbridge grade 2; 7) clinically and magnetic resonance imaging (MRI) confirmed ACL rupture.
Exclusion criteria included: 1) damage of multiple ligaments or injury of articular cartilage; 2) radiographic evidence of Kellgren-Lawrence over grade or osteoarthritis and/or severe osteoporosis; 3) bilateral ACL injuries; 4) partial ACL rupture; 5) concomitant total or subtotal meniscectomy; 6) young patients with unclosed growth plates.
Overall, there were 78 patients met the inclusion criteria in total. The time between injury and surgery ranged from 3 day to 12 months. All patients underwent initial surgery with ACL reconstruction. There were 32 cases with meniscus injury and the menisci were sutured, shaped, or resected according to the type of injury. All of the surgeries were performed by one senior surgeon. And all of the patients were randomly divided into two groups, the STDB reconstruction group (N=42) and the STSB reconstruction group (N=36).
Surgical procedure
Allograft Preparation
The anterior tibialis tendon allografts (Bone Tissue Engineering Library, Shanxi, China) were prepared on a back table after thawing in 37°C normal saline. Length of the tendon was measured and doubled on itself, then the ends of tendon are whip stitched for about 35 mm with No. 2 Fiberwire suture (Arthrex, Naples, FL). The STDB group separated the allograft (24 to 30 cm) into AM and PL bundles with a mean length of 12 to 15 cm (Fig. 1), while in STSB group, the allograft (24 to 30 cm) was folded. After weaving, the graft was clamped at either end on the preparation board with 10 lb of tension. The tendon allograft is kept moist until implantation. According to our experience, the anterior tibialis tendon allograft regularly provide a folded diameter over 9 mm.
Surgeries were performed on patients in a supine position with the affected knee flexing at an angle of 90° to cause the lower leg to naturally droop beside the bed. Epidural anesthesia was given. A tourniquet was applied around the upper thigh. A routine external anterior approach under arthroscopy was performed in order to confirm the diagnosis of torn ACL.
Construction of femur tunnel: The knee was explored by arthoscopy according to convention procedures to identify the diagnosis (Fig. 2A). Both the lateral intercondylar ridge and the lateral bifurcate ridge are important bony landmarks for the femoral attachments of the ACL, and the femoral tunnel was created in the center of the lateral bifurcate ridge but should not surpass the lateral intercondylar ridge. It was drilled through the AM portal with a cannulated reamer using a freehand technique at 120° of the knee (Fig. 2B).
Creation of tibial tunnels: In the STDB group, the tibial AM tunnel was placed in the anterior part of the footprint and the tibial PL tunnel was in the posterior part of the footprint (Fig. 2C). Both tibia and femoral drills were selected according to the graft diameter. Traction stitches of AM and PL bundles were passed through the end of the Kischner wire. Then, the wire was brought from the tibial tunnels out of the femoral tunnel. The two grafts were introduced to the tibial and femoral tunnels with traction stitches. The AM bundle was positioned in the AM tunnel and the PL bundle was in the PL tunnel. The femoral side secured was by flipping over the Endobutton. After that, the two bundles of the grafts were tightened in the tibial ends. Two hydroxyapatite interference screw with a diameter of 1 mm larger than the graft were screwed into the two tibial tunnels in 90° flexion of the knee, respectively (Fig. 2D). In the STSB group, the tibial tunnel was reamed through the AM surface of the tibia at the level of the tibial tubercle, passing through the landmarks of the center of the ACL remnant (Fig. 2E). The graft was first introduced into the tibial tunnel with a guide wire, and then pulled directly into the femoral tunnel and fixed on the femoral side by flipping over the Endobutton (Fig. 2F). On the tibial side, manually tighten the graft and fix it at 30° knee flexion by a door-shaped nail (2.3 mm Kirschner’s needle). The fixation was then strengthened by using a hydroxyapatite interference screw with a diameter of 1 mm larger than the graft.
Neither impingement nor cartilage damage was observed under arthroscopy in all patients.
Postoperative treatment and rehabilitation
Cefoxitin 1g bid was taken during postoperative 48 hours to prevent infection for all patients. The affected limb was wrapped with cotton pad for 72 hours. Three-dimensional computed tomography (3D CT) were performed immediately after surgery to evaluate the bone tunnel and fixation, and magnetic resonance imaging (MRI) was applied to check the ligament healing at postopertive 3, 6, 12 and 24 months.
Same postoperative rehabilitation plan was applied to both groups. The affected limb was immobilized with adjustable support. Patients were allowed to walk with crutches and while protected by knee braces (the specific walking time was based on whether the meniscus was sutured) at the second day after operation. Patients were encouraged to flex their knees from 0 to 90° within 2 to 4 weeks, reach 120° within 6 to 8 weeks. However, they were instructed not to flex the knee over 120° in the 3 month postoperative period. The braces were worn for at least 2 months. Patients were allowed to swim and ride a bicycle 6 months after the operation, begin jogging 10 months after the operation, and participate in strenuous exercise 18 months after the operation [17].
Observation indicators
Knee function was assessed by International Knee Documentation Committee (IKDC), Lysholm, and Tegner scores before operation and at follow-up in all patients. The Lachman test and pivot shift test were performed to assess the knee joint stability. A positive Lachman test is defined as: with the knee flexed 20°-30°, the tibia is displaced anteriorly relative to the femur with either a soft endpoint or greater than 4 mm of displacement. The pivot shift test is considered positive if the proximal tibia subluxes anteriorly on the distal femur at about 30° of flexion.
Statistical analysis
Data were expressed as mean ± standard deviation (SD) and analyzed by SPSS 18.0 software (SPSS Inc., Chicago, IL, USA). Independent samples t-test and χ2 test were done on the general data of patients. Preoperative and postoperative IKDC, Lysholm, Tegner scores, and KT-3000 measurements were tested for Mann Whitney U rank. P <0.05 was considered statistically significant.