This was a prospective randomized controlled trial and was approved by the hospital’s ethics review committee and registered at the national clinical registration center.
Participants
Patients who underwent single-bundle ACLR in our department between September 2018 and July 2019 and meet the criteria were included in the study. All patients were randomly assigned to the all-inside ACLR group or the standard ACLR group using the random number table method. The sample size was determined via power analysis. The inclusion criteria for participants were history of trauma and MRI showing ACL discontinuity or hyperintense signal, age 18–45 years, body mass index (BMI) of 18–28, and informed consent and signed relevant documents. The patients were excluded if they had any of the following: injured > 12 months ago; combined collateral ligament, posterior cruciate ligament, cartilage injury of more than 3 degrees and a meniscus grade III injury; history of ACLR surgery; generalized ligament laxity; severe underlying diseases or uncooperative follow-up; and bilateral ACL injury.
Clinical evaluation
The Tegner, International Knee Documentation Committee (IKDC), and Lysholm scores were recorded at postoperative months 3, 6, and 12 to assess functional recovery. At postoperative month 12, a GNRB arthrometer (Genourob, France) was used to assess knee laxity. Arthrometer measurement was performed as follows, under knee flexion of 30°and at 134-N load, the tibia anterior movement of the ACLR and normal contralateral knee was measured separately. The difference is obtained by subtracting the two measurements. The measurement was repeated three times and the value with the greatest difference was taken. The greater the anterior laxity, the more relaxed the knee joint. Data collectors and patients were not aware of the surgical approach. Only the surgeon was aware of the grouping. The study procedure is indicated in Fig. 1.
MRI analysis
The signal/noise quotient (SNQ) of the proximal, middle and distal regions of interest (ROI) of the intra-articular graft was measured using 3.0-T MRI (Extremity 18 3 T Tim Coil, SIEMENS, Germany) at postoperative months 3, 6, and 12 to observe the graft maturity law. All patients were required to rest for 60 min before measurement. Using fat-suppressed proton density (FS-PD) sequence. Thickness was 3 mm. Repetition time (TR) was 3140 ms. Echo time (TE) was 36 ms. Flip angle was 150°. Scan time was 118 s. Matrix was 320 × 256. Field of view (Fov) was 160 mm. From a sagittal image (Pd-tse-fs-sag) to select the interface that clearly showed graft and quadriceps tendon ROI. The graft ROI was located at the proximal (near the femoral tunnel), distal (near the tibial tunnel), and the middle (between them) regions. The ROI for the quadriceps tendon was located 2 cm above the patellar attachment point [14]. The signal value of the point 2 cm anterior to the tibial tuberosity was used as the background signal. The area of ROI signal measurement was controlled at 10-sq.mm (with an allowable error of ≤ 0.5-sq.mm). The MRI-based graft SNQ is used widly to assess graft maturity [15]. A higher SNQ indicates lower graft maturity. Graft SNQ was calculated using the following formula.
Graft SNQ = (Graft ROI mean signal value − Quadriceps tendon ROI mean signal value) / Background mean signal value.
The MRI scan was perform at a single magnet for all patients, and the whole process was completed by a fixed, blinded radiologist. The location of the proximal, distal, and middle ROI have been presented in Fig. 2.
Surgical techniques
All operations were performed by Prof. W Li who is an experienced orthopedic trauma surgeon specializing in sports medicine. The patient was placed in the supine position after lumbar anesthesia, with the lower leg hanging over the edge of the bed. A subpatellar anteromedial and anterolateral approach was used to perform knee arthroscopy, and a planing knife was used to clean the subpatellar fat pad and synovial membrane. The injury was explored, the ACL tibial and femoral stumps were cleaned, and the posterior edge of the lateral wall of the intercondylar socket of the femur was exposed. Using an anteromedial approach, the entry point was prepped using a microfracture cone and marked slightly posteriorly above the midpoint of the lateral wall of the resident’s crest.
The all-inside reconstruction technique was performed via an anteromedial approach using an inverted drill (Arthrex, USA) to drill a 2-cm hole in the femoral bone tract in a retrograde fashion (Fig. 3). Standard reconstruction was also performed via an anteromedial approach using an ordinary drill to drill the bone tract in a prograde fashion, with the size of the bone tract depending on the diameter of the grafted tendon. For creating the tibial tunnel, both reconstruction techniques used an internal port that was located at the center of the C-shaped stop of the ACL tibia and an external port located approximately 3 cm medially to the tibial tuberosity. For the all-inside reconstruction technique, the tibial tunnel was drilled using an inverted drill (Arthrex, USA), and the drill wing was opened to enlarge the tract in a retrograde fashion to a depth of approximately 2 cm. For the standard reconstruction technique, a guide pin was first placed and the full-length tibial tunnel was drilled along the guide pin.
The autologous tendons were collected for graft preparation before drilling the tunnel. The size of the graft was used to determine the size of the tunnel. Both techniques were performed by making an oblique incision on the skin at approximately 3 cm medial to the tibial tuberosity to expose the semitendinosus and gracilis tendon, and the tendon was retrieved using a tendon retriever. All-inside reconstruction involved only a single harvest of the semitendinosus tendon, and the extracted tendon was double-folded to create a four-stranded single-bundle structure (Fig. 3) The ends of the graft tendon were connected with an adjustable TightRope (Arthrex, USA). The diameter and length of the graft were recorded intraoperatively. The prepared grafted tendon was entered through the arthroscopic port, and the retraction cord guided the grafted tendon through the femoral tunnel. The adjustable steel plate was then attached outside the bone cortex and fixed by tightening and knotting it. Next, the tibial guide cord was tractored to the tibial tunnel along with the lead on the other side of the grafted tendon, and the traction tibial guide cord pulled the tendon lead out, pulling the tendon into the tibial tunnel. Standard reconstruction involved harvesting the semitendinosus and gracilis tendon, folding them in half to prepare a four-stranded single-bundle structure, and attaching an adjustable steel plate to one end of the graft tendon, and securing it with an ordinary traction wire at the other end. The graft end with an adjustable steel plate was guided through the tibial tunnel to the femoral tunnel, and the steel plate was then stuck outside the femoral cortex and fixed by knotting it. Another graft end on the tibial side was fixed with an absorbable interference screw (DePuy Mitek, USA).
For standard ACLR, the graft was tightened using the traction rope after placement, and the knee was stretched and flexed 10 times. Finally, the knee was tightened at 15 degrees of flexion and fixed with an interference screw. For all-inside ACLR, only the adjustable loop was tightened and knotted outside the tibial tunnel when the knee was flexed at 15 degrees. After the graft was completely fixed, it was confirmed via arthroscopy that the tendon provided no torsion, the tension was good, and there was no impact between the graft and the femoral condyle. The joint cavity was flushed, and the incisions were sutured and bandaged, and the affected limb was fixed with a straight leg brace. The patient was then returned to the ward.
Postoperative rehabilitation
The rehabilitation protocol for both groups was the same. The patient was gradually weight-bearing on the affected limb from the third day to the first week postoperatively. From weeks 2 to 4, the patient practiced knee flexion with a goal of 90 degrees. During postoperative week 4, the use of crutches was stopped, and full weight-bearing was achieved. During postoperative month 3, the knee was flexed to 130 degrees, and squatting exercises against the wall were started. Flexibility and technique training was started in postoperative month 4, and patients returned to \to non-contact sports activities at postoperative month 6 and to pivoting sports including competitive, confrontational, physical contact sports at postoperative month 9.
Statistical analyses
Power analysis was used to determine the sample size (α err prob = 5%, 1-β err prob = 80%). IBM SPSS 21.0 statistical software was applied to outcomes data analysis. The measurement data were expressed as mean ± standard deviation (M ± SD). For comparison between two independent groups, the data met the normal distribution criteria using independent samples t-test and Pearson correlation analysis. The data did not meet the normal distribution using Mann–Whitney U-test and Spearman correlation analysis. A p value of < 0.05 was considered statistically significant.