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To compare T1ρ relaxation times of the medial and lateral regions of the patella and femoral trochlea at 6 and 12 months following anterior cruciate ligament reconstruction (ACLR) on the ACLR and contralateral extremity. Greater T1ρ relaxation times are associated with a lower proteoglycan density of articular cartilage. This study involved 20 individuals (11 males, 9 females; mean ± SD age 22 ± 3.9 years, weight 76.11 ± 13.48 kg, and height 178.32 ± 12.32 cm) who underwent a previous unilateral ACLR using a patellar tendon autograft. Magnetic resonance images from both extremities were acquired at 6 and 12 months post‐ACLR. Voxel by voxel T1ρ relaxation times were calculated using a 5‐image sequence. The medial and lateral regions of the femoral trochlea and patellar articular cartilage were manually segmented on both extremities. Separate extremity (ACLR and contralateral extremity) by time (6 months and 12 months) analysis of variance tests were performed for each region (P< 0.05). For the medial patella and lateral trochlea, T1ρ relaxation times increased in both extremities between 6 and 12 months post‐ACLR (medial patella P= 0.012; lateral trochlea P= 0.043). For the lateral patella, T1ρ relaxation times were significantly greater on the contralateral extremity compared to the ACLR extremity (P= 0.001). The T1ρ relaxation times of the medial trochlea on the ACLR extremity were significantly greater at 6 (P= 0.005) and 12 months (P< 0.001) compared to the contralateral extremity. T1ρ relaxation times of the medial trochlea significantly increased from 6 to 12 months on the ACLR extremity (P= 0.003). Changes in T1ρ relaxation times occur within the first 12 months following ACLR in specific regions of the patellofemoral joint on the ACLR and contralateral extremity.

Context:Accurate, efficient, and reliable measurement methods are essential to prospectively identify risk factors for knee injuries in large cohorts.Objective:To determine tester reliability using digital photographs for the measurement of static lower extremity alignment (LEA) and whether values quantified with an electromagnetic motion-tracking system are in agreement with those quantified with clinical methods and digital photographs.Design:Descriptive laboratory study.Setting:Laboratory.Patients or Other Participants:Thirty-three individuals participated and included 17 (10 women, 7 men; age 21.7 ± 2.7 years, height 163.4 ± 6.4 cm, mass 59.7 ± 7.8 kg, body mass index 23.7 ± 2.6 kg/m2) in study 1, in which we examined the reliability between clinical measures and digital photographs in 1 trained and 1 novice investigator, and 16 (11 women, 5 men; age 22.3 ± 1.6 years, height 170.3 ± 6.9 cm, mass 72.9 ± 16.4 kg, body mass index 25.2 ± 5.4 kg/m2) in study 2, in which we examined the agreement among clinical measures, digital photographs, and an electromagnetic tracking system.Intervention(s):We evaluated measures of pelvic angle, quadriceps angle, tibiofemoral angle, genu recurvatum, femur length, and tibia length. Clinical measures were assessed using clinically accepted methods. Frontal- and sagittal-plane digital images were captured and imported into a computer software program. Anatomic landmarks were digitized using an electromagnetic tracking system to calculate static LEA.Main Outcome Measure(s):Intraclass correlation coefficients and standard errors of measurement were calculated to examine tester reliability. We calculated 95 limits of agreement and used Bland-Altman plots to examine agreement among clinical measures, digital photographs, and an electromagnetic tracking system.Results:Using digital photographs, fair to excellent intratester (intraclass correlation coefficient range 0.70–0.99) and intertester (intraclass correlation coefficient range 0.75–0.97) reliability were observed for static knee alignment and limb-length measures. An acceptable level of agreement was observed between clinical measures and digital pictures for limb-length measures. When comparing clinical measures and digital photographs with the electromagnetic tracking system, an acceptable level of agreement was observed in measures of static knee angles and limb-length measures.Conclusions:The use of digital photographs and an electromagnetic tracking system appears to be an efficient and reliable method to assess static knee alignment and limb-length measurements.

Context:Decreased sagittal-plane motion at the knee during dynamic tasks has been reported to increase impact forces during landing, potentially leading to knee injuries such as anterior cruciate ligament rupture.Objective:To describe the relationship between lower extremity muscle activity and knee-flexion angle during a jump-landing task.Design:Cross-sectional study.Setting:Research laboratory.Patients or Other Participants:Thirty recreationally active volunteers (15 men, 15 women: age 21.63 ± 2.01 years, height 173.95 ± 11.88 cm, mass 72.57 ± 14.25 kg).Intervention(s):Knee-flexion angle and lower extremity muscle activity were collected during 10 trials of a jump-landing task.Main Outcome Measure(s):Simple correlation analyses were performed to determine the relationship between each knee-flexion variable (initial contact, peak, and displacement) and electromyographic amplitude of the gluteus maximus (GMAX), quadriceps (VMO and VL), hamstrings, gastrocnemius, and quadriceps : hamstring (Q : H) ratio. Separate forward stepwise multiple regressions were conducted to determine which combination of muscle activity variables predicted each knee-flexion variable.Results:During preactivation, VMO and GMAX activity and the Q : H ratio were negatively correlated with knee-flexion angle at initial contact (VMO: r −0.382, P .045; GMAX: r −0.385, P .043; Q : H ratio: r −0.442, P .018). The VMO, VL, and GMAX deceleration values were negatively correlated with peak knee-flexion angle (VMO: r −0.687, P .001; VL: r −0.467, P .011; GMAX: r −0.386, P .043). The VMO and VL deceleration values were negatively correlated with knee-flexion displacement (VMO: r −0.631, P .001; VL: r −0.453, P .014). The Q : H ratio and GM activity predicted 34.7 of the variance in knee-flexion angle at initial contact (P .006). The VMO activity predicted 47.1 of the variance in peak knee-flexion angle (P .001). The VMO and VL activity predicted 49.5 of the variance in knee-flexion displacement (P .001).Conclusions:Greater quadriceps and GMAX activation and less hamstrings and gastrocnemius activation were correlated with smaller knee-flexion angles. This landing strategy may predispose an individual to increased impact forces due to the negative influence on knee-flexion position.