Flatfoot kinematics and coordination during bilateral heel rises: Effects of knee angle variation.

There is little age- and sex-specific objective data concerning anterior knee translation in school-aged children. We aimed to establish age- and sex-specific baseline data for anterior knee translation of the knee in girls and in boys in grades 5 to 12. We also investigated whether a correlation exists between anterior knee translation and global joint laxity in girls in grades 5 to 12. A sample of convenience from a local school was used. Fifteen boys and 15 girls were randomly chosen from each grade, 5 to 12, to undergo anterior translation measurements with the KT2000 knee ligament arthrometer at 15, 20, and 30 lb of force. In addition, Beighton scores and bone age were determined. Anterior knee translation decreased with age in both girls and boys. Girls had greater anterior knee translation and end-point compliance than age-matched boys. In girls, there was a positive correlation between increased global joint laxity and increased anterior knee translation at 20 and 30 lb. However, hyperextension of the knee by itself was not a predictor of greater anterior translation. Anterior translation of the knee showed age and sex variation in school-aged children. These data are important in establishing a foundation of baseline data to understand sex differences in ligament development and function and to help guide injury prevention strategies. Level II diagnostic study.

Unicompartmental knee arthroplasty (UKA) in anterior cruciate ligament deficiency (ACLD) has been debated for decades after the development of highly cross-linked polyethylene. This study aims to evaluate the effect of posterior tibial slope on restoring adequate knee stability and flexion after UKA in patients with ACLD. A total of 15 fresh cadaveric knees were divided into three groups: intact ACL, partial ACLD, and complete ACLD. Fixed-bearing UKAs including 3-D-printed tibial inserts with the slopes ranging from 3° to 12° were performed using computer-assisted navigation. Blinded evaluation of knee motion and anterior knee translation with knees flexed 20° and 90° was conducted using KT-arthrometry and stress radiography. A 1° slope increase translated the knees anteriorly by 0.85 mm and 0.76 mm in 20° and 90° of knee flexion for a complete ACLD ( R = 0.7 and 0.8, respectively, p < 0.001) compared to 0.5-0.6 mm for the normal and partial ACLD groups, respectively. Setting a slope of 5-8° of UKA for an intact ACL maintained both the stability and the motion of native knees. No significant changes of knee translation and flexion ability were observed after leveling the slopes at 5-7° and 5-6° for partial and complete ACLD, respectively ( p > 0.05 for all comparisons). In conclusion, UKA in complete ACLD knees is challenging since 1° of slope change nearly doubles the degree of knee translation compared to ACL-intact knees. The optimum posterior tibial slopes for fixed-bearing UKA patients with partial and complete ACLD are 5-7° and 5-6°, respectively.

Relationship between muscle strength and knee pain in knee osteoarthritis patients

The purpose of this retrospective study was to evaluate the influence of physiologic posterolateral rotatory laxity on anterior cruciate ligament (ACL) reconstruction in terms of anterior knee stability and clinical outcomes. We retrospectively studied 113 patients who had undergone ACL reconstruction between June 2004 and August 2008. Patients were categorized into three groups according to the degree of tibial external rotation at 90° of knee flexion: Group 1 (<40°), Group 2 (40° to 50°), and Group 3 (≥50°). Ligament stability was determined with use of the Lachman test, the pivot-shift test, and KT-2000 arthrometer testing. Function was assessed with use of the Lysholm score and the International Knee Documentation Committee (IKDC) score. Clinical outcomes were determined from data obtained before surgery and at the twenty-four-month follow-up visit. We observed differences in postoperative knee translation between the groups (p < 0.001). A post hoc test showed increased mean knee translation in Group 3 compared with Groups 1 and 2. The degree of external rotation at 90° was positively correlated with anterior knee translation (r = 0.428; p = 0.007). However, there was an inverse correlation with the Lysholm knee scores (r = -0.146; p = 0.015) and IKDC scores (r = -0.205; p = 0.003). The stability and functional scores after ACL reconstruction had a negative correlation with the degree of external rotation of the tibia at 90° (physiologic posterolateral rotatory laxity). After ACL reconstruction, patients with ≥ 50° of tibial external rotation had increased anterior translation and worse functional outcomes in comparison with those who had < 50° of tibial external rotation.

Background/Objectives: This study aimed to provide preliminary normative data on intersegmental coordination patterns during heel rises at different knee joint positions and across various phases and periods. Methods: Twelve 21-year-old university students from the same cohort performed heel rises in knee-extended and knee-flexed conditions. Shank and foot kinematics were recorded using the VICON Oxford Foot Model, and intersegmental coordination was analyzed using a modified vector coding technique. Results: The results showed that coordination patterns varied significantly between the ascending and descending phases and across the early, middle, and late periods. In the early ascending phase, knee extension exhibited in-phase coordination (shank external rotation with hindfoot inversion), resembling propulsion-related coordination in gait, whereas knee flexion displayed greater anti-phase coordination between hindfoot plantar flexion and forefoot dorsiflexion. The middle and late periods demonstrated heel-rise-specific patterns, with coordination shifting from proximal to distal dominance. Knee flexion altered the coordination between the shank and hindfoot and between the hindfoot and forefoot in the sagittal plane compared to that during knee extension. Conclusions: These findings suggest that the knee position influences intersegmental coordination during heel rises, and the present results provide reference values that can enable future diagnostic validation and comparative studies in pathological populations.

1) To evaluate the effects of a 12-wk high-intensity knee extensor and flexor resistance training program on strength, pain, and adherence in patients with advanced knee osteoarthritis and varus malalignment and 2) to generate pilot data for change in dynamic knee joint load, patent-reported outcomes, and self-efficacy after training. Fourteen patients (48.35 +/- 6.51 yr) with radiographically confirmed medial compartment knee osteoarthritis and varus malalignment of the lower limb were recruited from a surgical waiting list for high tibial osteotomy. Participants completed a high-intensity isokinetic resistance training program three times per week for 12 wk. Knee extensor and flexor strength were assessed every third week, whereas pain and adherence were recorded at every training session. The external knee adduction moment during the gait, the 6-min-walk test, the Knee Injury and Osteoarthritis Outcome Score (KOOS), and the Arthritis Self-Efficacy Scale (ASES) were also evaluated before and after training. Significant improvements in knee extensor and flexor strength were observed without increases in pain during or after training. Adherence to the high-intensity program was high. No significant changes were observed for dynamic knee joint load or the KOOS. There was a significant increase in the function subscale of the ASES only. These findings suggest that patients with advanced knee osteoarthritis and malalignment can experience substantial gains in strength after a high-intensity resistance training program without concomitant increases in pain, adverse events, or compromised adherence. These findings provide support for future clinical trials with longer-term outcomes.

Background: The regulation of muscle force is a vital aspect of sensorimotor control, requiring intricate neural processes. While neural activity associated with upper extremity force control has been documented, extrapolation to lower extremity force control is limited. Knowledge of how the brain regulates force control for knee extension and flexion may provide insights as to how pathology or intervention impacts central control of movement.Objectives: To develop and implement a neuroimaging-compatible force control paradigm for knee extension and flexion.Methods: A magnetic resonance imaging (MRI) safe load cell was used in a customized apparatus to quantify force (N) during neuroimaging (Philips Achieva 3T). Visual biofeedback and a target sinusoidal wave that fluctuated between 0 and 5 N was provided via an MRI-safe virtual reality display. Fifteen right leg dominant female participants (age = 20.3 ± 1.2 years, height = 1.6 ± 0.10 m, weight = 64.8 ± 6.4 kg) completed a knee extension and flexion force matching paradigm during neuroimaging. The force-matching error was calculated based on the difference between the visual target and actual performance. Brain activation patterns were calculated and associated with force-matching error and the difference between quadriceps and hamstring force-matching tasks were evaluated with a mixed-effects model (z > 3.1, p < 0.05, cluster corrected).Results: Knee extension and flexion force-matching tasks increased BOLD signal among cerebellar, sensorimotor, and visual-processing regions. Increased knee extension force-matching error was associated with greater right frontal cortex and left parietal cortex activity and reduced left lingual gyrus activity. Increased knee flexion force-matching error was associated with reduced left frontal and right parietal region activity. Knee flexion force control increased bilateral premotor, secondary somatosensory, and right anterior temporal activity relative to knee extension. The force-matching error was not statistically different between tasks.Conclusion: Lower extremity force control results in unique activation strategies depending on if engaging knee extension or flexion, with knee flexion requiring increased neural activity (BOLD signal) for the same level of force and no difference in relative error. These fMRI compatible force control paradigms allow precise behavioral quantification of motor performance concurrent with brain activity for lower extremity sensorimotor function and may serve as a method for future research to investigate how pathologies affect lower extremity neuromuscular function.

Background: Previous studies have stated that closely matching the size of the anterior cruciate ligament (ACL) insertion site footprint is important for biomechanical function and clinical stability after ACL reconstruction. However, the ACL varies widely regarding the area of femoral insertion, tibial insertion, and midsubstance of ACL, and reconstructing the insertion site area with a uniform diameter graft can result in a cross-sectional area that is greater than that of the midsubstance of the native ACL. Therefore, understanding the effect of relative graft size in ACL reconstruction on knee biomechanics is important for surgical planning. Purpose: To assess how the percentage of femoral insertion site affects knee biomechanics in single- and double-bundle ACL reconstruction. Study Design: Controlled laboratory study. Methods: A total of 14 human cadaveric knees were scanned with magnetic resonance imaging and tested using a robotic system under an anterior tibial load and a combined rotational load. In total, 7 knee states were evaluated: intact ACL; deficient ACL; single-bundle ACL reconstruction with approximate graft sizes 25% (small), 50% (medium), and 75% (large) of the femoral insertion site; and double-bundle reconstruction of approximately 50% (medium) and 75% (large) of the femoral insertion site, based on the ratio of the cross-sectional area of the graft to the area of the femoral ACL insertion site determined by magnetic resonance imaging. Results: Anterior tibial translation was not significantly larger than the intact state in single-bundle and double-bundle medium graft reconstructions (P > .05) and was significantly greater in the single-bundle small graft reconstruction (P < .05). Anterior knee translation in single-bundle medium graft and large graft reconstructions was not statistically different (P > .05). In contrast, the anterior tibial translation for double-bundle large graft reconstruction was significantly smaller than for double-bundle medium graft reconstruction at low flexion angles (P < .05). The single-bundle small graft force was significantly different from the intact ACL in situ force (P < .05). The graft force with double-bundle large reconstruction was significantly greater than that with the double-bundle medium reconstruction (P < .05) but was not significantly different from that of the intact ACL (P > .05). Conclusion: Knee biomechanics with a single-bundle small graft tended to be significantly different from those of the intact knee. In the kinematic and kinetic data for the single- and double-bundle medium graft reconstruction, only the anterior translation at full extension for the single-bundle reconstruction was significantly different (lower) from that of intact knee. This was a time zero study. Clinical Relevance: This study can provide surgeons with guidance in selecting the graft size for ACL reconstruction.

Controlled laboratory study, cross-sectional data. To investigate isometric knee flexion and extension strength, failure of voluntary muscle activation, and antagonist cocontraction of subjects with knee osteoarthritis (OA) compared with age-matched asymptomatic control subjects. Quadriceps weakness is a common impairment in individuals with knee OA. Disuse atrophy, failure of voluntary muscle activation, and antagonist muscle cocontraction are thought to be possible mechanisms underlying this weakness; but antagonist cocontraction has not been examined during testing requiring maximum voluntary isometric contraction. Fifty-four subjects with knee OA (mean +/- SD age, 65.6 +/- 7.6 years) and 27 similarly aged control subjects (age, 64.2 +/- 5.1 years) were recruited for this study. Isometric knee flexion and extension strength were measured, and electromyographic data were recorded, from 7 muscles crossing the knee and used to calculate cocontraction ratios during maximal effort knee flexion and extension trials. The burst superimposition technique was used to measure failure of voluntary activation. Knee extension strength of subjects with knee OA (mean +/- SD, 115.9 +/- 6.7 Nm) was significantly lower than for those in the control group (152.3 +/- 9.6 Nm). No significant between-group difference was found for failure of voluntary muscle activation, or the cocontraction ratios during maximum effort knee flexion or extension. These results demonstrate that the reduction in isometric extension strength, measured with a 90 degrees knee flexion angle, in subjects with knee OA is not associated with increased antagonist cocontraction.

The purpose of this study was to examine the influence of short hamstring muscles (hamstrings) on gravitational torque of the leg (GT) and on knee extension and knee flexion concentric isokinetic torque. Fifteen non-disabled men (ages: 18 to 37 years) with clinically short hamstrings(passive straight-leg-raising ≤ 65°) were measured for the GT in two positions: 1) seated position that included a passive stretch of the hamstrings, and 2) supine position that did not include a passive stretch of the hamstrings. Subjects performed three trials of maximal concentric knee extension and flexion in the seated position under four randomly ordered conditions(60°·s $^{-1}$ with seated GT, 60°·s $^{-1}$ with supine GT, 180°·s $^{-1}$ with seated GT, and 180°·s $^{-1}$ with supine GT). One-way ANOVA analysis showed that the GT measured while seated(36.00 ± 9.58 Nm) was greater than the GT measured while supine (21.00 ± 3.90 Nm) (P &lt; 0.001). The greater GT while seated was explained by the sum of the passive hamstring torque and the true GT. Knee flexion peak torque, knee flexion average torque, and the hamstring/quadriceps average torque ratios were decreased at 60°·s $^{-1}$ (P ≤ 0.023) using the seated GT compared to using the supine GT. The same torque characteristics did not differ significantly for knee flexion at 180°·s $^{-1}$ , or for knee extension at either isokinetic speed. We concluded that hamstring passive torque contributed to greater GT in the seated position, which caused invalid knee flexion torque measurements when tested at 60°·s $^{-1}$ . This evidence supports weighing the leg supine in order to remove hamstring passive torque and to ensure valid knee concentric isokinetic torque measurements when testing at 60°·s $^{-1}$ .

Klemola, SE, Gorman, BT, Welch, N, and Kung, SM. Isokinetic knee extension and flexion strength in female athletes at 20 and 40 weeks after bone-patellar tendon-bone anterior cruciate ligament reconstruction. J Strength Cond Res 39(9): e1075-e1080, 2025-Despite females' higher anterior cruciate ligament (ACL) injury risk, research assessing the rehabilitation of knee extensor and flexor strength after an ACL reconstruction (ACLR) with a bone-patellar tendon-bone (BPTB) graft in female athletes is limited. The purpose of this study was to investigate the restoration of knee extension strength in female athletes after ACLR with a BPTB graft, along with knee flexion strength, limb symmetry index (LSI), and return to sport (RTS) status. Eighty-nine 16-30-year-old female athletes who underwent a BPTB ACLR were eligible for analysis. Participants completed isokinetic knee extension and flexion strength testing at 20 ± 5 (T1) and 40 ± 5 (T2) weeks post-ACLR using an isokinetic dynamometer. Changes in peak knee extension and flexion torques, and LSI values were assessed in the injured and noninjured limbs from T1 to T2. RTS status was recorded at T2. Two-way repeated measures ANOVA analyzed peak extension and flexion torques and paired t-tests analyzed LSI. Statistical significance was set at p ≤ 0.05. Compared with the injured limb, the noninjured limb demonstrated a higher peak extension torque at T1 ( p < 0.0001) and T2 ( p < 0.0001) and a higher peak knee flexion torque at T1 only ( p = 0.004). Peak knee extension ( p < 0.0001) and flexion ( p = 0.03) torque LSI were significantly higher at T2 than at T1. Despite significant improvements in knee extension and flexion strength, a deficit in the injured limb's knee extensor strength remained at 40 weeks postsurgery, which highlights the need for female athletes to prioritize strengthening the injured limb's knee extensors during rehabilitation, especially before returning to training and/or competition.

The effect of load magnitude on three-dimensional patellar kinematics in vivo

Prosthetic alignment is an important factor in the overall fit and performance of a lower-limb prosthesis. However, the association between prosthetic alignment and control strategies used by persons with transfemoral amputation to coordinate the movement of a passive prosthetic knee is poorly understood. This study investigated the biomechanical response of persons with transfemoral amputation to systematic perturbations in knee joint alignment during a level walking task. Quantitative gait data were collected for three alignment conditions: bench alignment, 2 cm anterior knee translation (ANT), and 2 cm posterior knee translation (POST). In response to a destabilizing alignment perturbation (i.e., the ANT condition), participants significantly increased their early-stance hip extension moment, confirming that persons with transfemoral amputation rely on a hip extensor strategy to maintain knee joint stability. However, participants also decreased the rate at which they loaded their prosthesis, decreased their affected-side step length, increased their trunk flexion, and maintained their prosthesis in a more vertical posture at the time of opposite toe off. Collectively, these results suggest that persons with transfemoral amputation rely on a combination of strategies to coordinate stance-phase knee flexion. Further, comparatively few significant changes were observed in response to the POST condition, suggesting that a bias toward posterior alignment may have fewer implications in terms of stance-phase, knee joint control.

Intertrial reliability of work measurements was studied in 19 men with a partial medial meniscal tear (ME group) and in 10 men with no history of knee injury (control group). Three maximal voluntary concentric contractions of the muscles involved in knee extension (KE) and knee flexion (KF) were performed on a dynamometer at 30 degrees and 180 degrees/s using a preloading protocol. The subjects moved their legs through an arc of 90 degrees, and the work produced in the constant-velocity phase between 70 and 20 degrees of KE was computed for each trial. In ME group subjects able to perform three consecutive contractions (n = 12-14), high intertrial intraclass correlation coefficients (ICCs) were found (ICCs = .86-.92), except for KE work measurements at 180 degrees/s (ICC = .67). In the control group subjects, high ICCs were obtained for KE work measurements (ICCs = .87 and .95), whereas the low ICCs obtained for KF work measurements (ICCs = .64 and .79) increased to .86 and .93 when the first trial was removed. In both groups, a significant increase was found over the trials for KF measurements at 180 degrees/s and KE measurements at 30 degrees/s, but work measurements were shown to peak at the second trial. The results of this study suggest that the work produced on the second trial reflects a subject's maximal capacity. [Durand A, Malouin F, Richards CL, Bravo G. Intertrial reliability of work measurements recorded during concentric isokinetic knee extension and flexion in subjects with and without meniscal tears.

Mobility limitations, including a decrease in walking speed, are major issues for people with autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS). Improving our understanding of factors influencing walking speed in ARSACS may inform the development of future interventions for gait rehabilitation and contribute to better clinical practices. The objective of the study was to identify the factors influencing the self-selected walking speed in adults with ARSACS. The dependent variable of this cross-sectional study was the self-selected speed and the factors (independent variables) were age, sex, balance, balance confidence, knee flexion and extension cocontraction indexes, lower limb coordination, passive range of motion of ankle dorsiflexion, knee and hip extension, and global spasticity. Multiple regression models were used to assess the relationships between walking speed and each factor individually. Six factors were significantly associated with walking speed and thus included in regression models. The models explained between 42.4 and 66.5% of the total variance of the self-selected walking speed. The factors that most influence self-selected walking speed are balance and lower limb coordination. In order of importance, the other factors that also significantly influence self-selected walking speed are ankle dorsiflexion range of motion, lower limb spasticity, knee extension range of motion, and confidence in balance. Balance and lower limb coordination should be targeted in rehabilitation interventions to maintain walking ability and functional independence as long as possible. The six factors identified should also be included in future studies to deepen our understanding of walking speed.