NORMATIVE DATA AND THE EFFECT OF GRAFT CHOICE ON ISOKINETIC KNEE MUSCLE STRENGTH IN PAEDIATRIC PATIENTS FOLLOWING ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION: A RETROSPECTIVE STUDY

Return to sport (RTS) criteria after an anterior cruciate ligament reconstruction (ACLR) is typically based on functional tests results and knee strength recovery. Patients aim to reach a limb symmetry index (LSI) of 90% and hamstrings-to-quadriceps (H/Q) ratios of 0.5–0.8. While attaining these postoperative objectives, the risk of re-injury has risen to 30%. Therefore, comparing peak isokinetic torque data to normative data in addition to the aforementioned metrics may add to the current assessment of postoperative strength deficits and readiness to RTS. Strength deficits are typically directly related to the location of the graft harvested. Due to the paucity of studies that compare postoperative outcomes in pediatric patients who either received a hamstring tendon autograft (HTA), quadriceps tendon autograft (QTA), or a patellar tendon autograft (PTA), graft choice remains dependent on the operating surgeon's preference and patients individual needs. The primary objective of this study was to generate normative data from the non-injured knee flexors and extensors isokinetic strength parameters of 13- to 18-year-old patients. The secondary objective was to determine the effects of graft choice on postoperative knee strength and patient-reported outcomes. A retrospective chart review was conducted including patients aged 13–18 years that underwent primary ACLR and performed a standardized bilateral isokinetic knee strength assessment between June 1st 2017 and March 1st 2022 at our institution. Anthropometric data, ACL-RSI and Pedi-IKDC scores, and isokinetic knee strength testing results at 6 to 7 months postoperatively were collected. Normative data calculated using patient's non-operated knee average peak torque relative to body mass at 60 deg/sec, 180 deg/sec, and 300 deg/sec in flexion and extension. Using the norms measured, Z-scores were calculated and compared between grafts. ANOVAs were performed to compare postoperative strength results and patient-reported outcomes between grafts. A total of 286 patients were included in this study. The mean age of patients in the cohort was 15.78& 1.26 years and 63% of the cohort was female. Males and patients with higher BMI had greater average relative peak torque at all three speeds in flexion and extension (p<0.05). HTAs were associated to significantly greater knee extension strength at 60 deg/sec on the operated side (p=0.0001 vs QTA, p=0.007 vs PTA). Patients having received a HTA normalized their average relative peak torque to a greater extent than patients having received a QTA (–0.51 vs −0.78, p=0.0002) or PTA (–0.51 vs −0.97, p=0.008) in flexion at 60 deg/sec. The HTA (n=167) were associated to significantly higher LSI in extension at all three speeds (p<0.05) than QTA (n=45) and PTA (n=55). QTA were associated to a significantly higher LSI in flexion at 60 deg/sec than HTA (p=0.01). ACL-RSI and Pedi-IKDC scores were not significantly different between the three autograft groups (p≥0.05). The postoperative pediatric ACLR knee strength norms calculated can be used as clinical reference values for patients awaiting RTS clearance. Additionally, our findings suggest that HTAs lead to greater and more normal postoperative knee average peak torque relative to body mass and LSI compared to QTAs and PTAs.