| Background Anterior cruciate ligament injury is a common kind of sports injury and anterior cruciate ligament reconstruction is the main treatment method currently.The purpose of this operation is to restore the stability of the knee and help patients finally return to sports.However,the current return-to-sport tests and criteria do not well in preparing patient to sports and the exact kinematic mechanism of returning to sport is not clear.SNQ(Signal to Noise Quotient)is a new imaging index,which is widely used in the evaluation of graft maturity after ACL reconstruction,and it may have potential application value in the evaluation of return-to-sport after ACL reconstruction.In addition,the high-speed dual-planar fluoroscopic imaging system is an exquisite equipment for kinematics evaluation of the knee,which can accurately evaluate the kinematics of patients after anterior cruciate ligament reconstruction,identify the kinematic differences between patients with and without ability to return to play,and explore the specific mechanism of return-to-sport.Objectives 1.To compare the ATTD(Anterior Tibial Translation Difference),the SNQ in the distal,median and proximal areas of the graft between patients return-to-sport and not return-to-sport after anterior cruciate ligament reconstruction.To analyze the diagnostic performance for return-to-sport of these indexes and possible cutoff values.2.To identify the 6-DOF(Degree Of Freedom)kinematic difference of the knees during flat walking between patients who have returned to sport after anterior cruciate ligament reconstruction and those who had not.To find out the biomechanical mechanism affecting return-to-sport after anterior cruciate ligament reconstruction.Methods 1.Subjects enrolled: From May 2020 to March 2021,a total of 87 patients diagnosed with primary ACL rupture,who planned to undergo arthroscopic anatomic single-bundle ACL reconstruction with autologous hamstring tendon were enrolled.All patients was full informed consent when they were enrolled in the study.The baseline information such as age,sex,height,weight,BMI and left/right were recorded by case report cards.2.Anterior cruciate ligament reconstruction and postoperative rehabilitation: All the patients were treated with single-bundle hamstring tendon anatomic anterior cruciate ligament reconstruction and provided with postoperative rehabilitation exercise teaching and rehabilitation education.All the patients received the standard postoperative rehabilitation process and outpatient follow-up in 2 weeks,1 month,3months and 6 months after operation respectively.3.Return-to-sport tests and other assessments: The subjects were followed up again in the outpatient department 9 months after surgery for return-to-sport test.IKDC and ACL-RSI questionnaires were filled in and hop test was performed.At the same time,the difference of anterior tibial translation difference of each subject was measured by Ligs knee measuring instrument and recorded in the case report card(anterior tibial translation difference = anterior tibial translation of the operated knee-anterior tibial translation of the contralateral knee).Based on the evaluation results,subjects were divided into two groups according to the return-to-sport criteria adopted in this study.4.MRI evaluation of the knee: Nine months after surgery,MRI of the operated knee was obtained.The SNQ in the distal,median and proximal areas of each graft was calculated.The difference of SNQ between the return-to-sport group and the not return-to-sport group was compared.ROC curves were drawn to compare the effect of SNQ of different parts in predicting return-to-sport and determine the best cut-off value.5.Reconstruction of 3D model of knee joint based on CT: Random number table method was used to select 15 cases in the return-to-sport group and 15 cases in the not return-to-sport group.All the selected subjects were examined with CT of the operated knee to establish 3D CT model of knee joint.6.Knee kinematics image collection: All the 30 subjects were enrolled to walk on a treadmill at 1m/s on flat ground,and a high-speed dual-planar fluoroscopy imaging system was used to collect kinematics images of a complete gait cycle.7.Registration and 6-DOF kinematics analysis of knee joint: The 3D model of knee joint and the kinematics image of knee joint were imported into Rhino software respectively,and the working environment was established.The6-DOF spatial data of femur and tibia at corresponding time points were calculated and analyzed.Results 1.Imaging evaluation of return-to-sport after anterior cruciate ligament reconstruction based on SNQ of grafts from MRI A total of 82 patients completed a 9-month postoperative follow-up.According to the criteria determined by this study,there were 53 cases in the return-to-sport group and 29 cases in the not return-to-sport group.There was no significant difference in anterior tibial translation difference between the two groups under 90 N forward force(0.37±0.41 mm VS0.52±0.36 mm,P = 0.081).However,under the 120 N and 150 N forward force,the ATTD in the return-to-sport group was significantly smaller than that in the not return-to-sport group(1.54±0.28 mm VS 1.91±0.44 mm,P < 0.001;2.08±0.66 mm VS 2.63±0.78 mm,P <0.001).There was no significant difference in distal graft SNQ between the return-to-sport group and the not return-to-sport group(6.51±3.98 VS 7.93±4.12,P = 0.131),but the mid-graft SNQ and proximal graft SNQ of the return-to-sport group were significantly lower than those of the not return-to-sport group(13.45±5.15 VS 17.75±5.75,P = 0.131).P = 0.001;17.15±4.85 VS 19.55±5.05,P = 0.038).Among the ROC curves,ATTD(120N)had the largest area under the curve,and its AUC was 0.75(0.634,0.866).The optimal cut-off value of this index was 1.635.Under this index,the sensitivity and specificity of predicting not return-to-sport patients were 82.8% and 62.3% respectively.The AUC of SNQ(middle region)was 0.713(0.599,0.827),and the optimal cut-off value of this index was 14.57.Under this index,the sensitivity,specificity and Yoden index for predicting not return-to-sport patients were 75.9%,60.4%,and 0.363.2.Comparison of 6-DOF kinematics of the knee joint between the return-to-sport group and the not return-to-sport group after anterior cruciate ligament reconstruction based on DFIS In the whole supporting phase of gait cycle,the distance of tibia forward to femur in the not return-to-sport group was larger than that in the return-to-sport group(0.964±0.038 mm VS 0.764±0.038 mm,P = 0.001).The maximum tibial forward distance in the not return-to-sport group was greater than that in the return-to-sport group(3.03±0.59 mm VS 3.64±0.42 mm,P = 0.003).In coronal medial-lateral translation,the tibia moved laterally relative to the femur more in the not return-to-sport group than in the return-to-sport group(1.61±0.048 mm VS 0.77±0.048 mm,P < 0.001).The downward movement distance of tibia relative to femur in the not return-to-sport group was larger than that in the return-to-sport group(-3.09±0.049 mm VS-2.67±0.049 mm,P < 0.001).The maximum downward displacement of tibia in the not return-to-sport group was larger than that in the return-to-sport group(-6.34±0.77 mm VS-4.37±0.73 mm,P < 0.001).In sagittal flexion and extension movement,the knee flexion angle of the not return-to-sport group was lower than that of the return-to-sport group(6.72±0.072° VS 8.34±0.072°,P <0.001).In coronal varus and valgus movement,the knee varus angle in the not return-to-sport group was larger than that in the return-to-sport group(-0.396±0.025° VS-0.006±0.025°,P < 0.001).In horizontal rotation movement,the external rotation angle of the knee joint in the not return-to-sport group was larger than that in the return-to-sport group(1.80±0.053° VS 1.768±0.053°,P < 0.001).Conclusion At 9 months after ACL reconstruction,35.4% of patients were still unable to return to sport.Compared with the return-to-sport group,the anterior tibial translation difference of the knee joint in the not return-to-sport group was larger at 120 N and 150 N,and the SNQ of MRI in the middle and proximal parts of the grafts was larger.Anterior tibial translation difference under 120 N and 150 N forward force,SNQ(middle)and SNQ(proximal)could be used as indicators for predicting patients who failed to return to sport with good sensitivity and specificity.In terms of kinematics,the not return-to-sport group showed obvious knee joint forward,lateral and rotational instability in the flat walking support phase,which may be an important reason affecting the failure of return to sport. |
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