Rethinking Exoskeleton Simulation-Based Design: The Effect of Using Different Cost Functions.

Designing an exoskeleton that can improve user capabilities is a challenging task, and most designs rely on experiments to achieve this goal. A different approach is to use simulation-based designs to determine optimal device parameters. Most of these simulations use full trajectory tracking limb kinematics during a natural gait as a reference. However, exoskeletons typically change the natural gait kinematics of the user. Other types of simulations assume that human gait is optimized for a cost function that combines several objectives, such as the cost of transport, injury prevention, and stabilization. In this study, we use a 2D OpenSim model consisting of 10 degrees of freedom and considering 18 muscles, together with the Moco optimization tool, to investigate the differences between these two approaches with respect to running with a passive knee exoskeleton. Utilizing this model, we test the effect of a full trajectory tracking objective with different weights (representing the importance of the objective in the optimization cost function) and show that when using weights that are typically used in the literature, there is no deviation from the experimental data. Next, we develop a multi-objective cost function with foot clearance term based on peak knee angle during swing, that achieves trajectories similar (RMSE=7.4 deg) to experimental running data. Finally, we investigate the effect of different parameters in the design of a clutch-based passive knee exoskeleton (1.5 kg at each leg) and find that a design that utilizes a 2.5 Nm/deg spring achieves an improvement of up to 8% in net metabolic energy. Our results show that tracking objectives in the cost function, even with a low weight, hinders the simulation's ability to change the gait trajectory. Thus, there is a need for other predictive simulation methods for exoskeletons.

Lower Extremity Kinematic and Kinetic Characteristics as Effects on Running Economy of Recreational Runners.

PURPOSE: This study aimed to determine associations between running economy (RE) and running sagittal plane kinematic and kinetic parameters. METHOD: A total of 30 male recreational runners (age: 21.21 ± 1.22 yr, V̇O 2max : 54.61 ± 5.42 mL·kg -1 ·min -1 ) participated in two separate test sessions. In the first session, the participant's body composition and RE at 10 and 12 km·h -1 were measured. In the second session, measurements were taken for the sagittal plane of hip, knee, and ankle angles and range of motion (ROM), as well as ground reaction force. RESULTS: Moderate correlations were found between lower energy costs at 12 km·h -1 and smaller hip flexion at toe-off ( r = 0.373) as well as smaller peak hip flexion during stance ( r = 0.397). During the swing phase, lower energy costs at 10 km·h -1 were moderately correlated with smaller peak knee flexion and smaller knee flexion and extension ROM ( r = 0.366-0.443). Lower energy costs at 12 km·h -1 were moderately correlated with smaller peak hip and knee flexion as well as knee extension ROM ( r = 0.369-0.427). In terms of kinetics, there was a moderate correlation between higher energy costs at 10 km·h -1 and larger peak active force, as well as larger peak braking and propulsion force ( r = -0.470-0.488). Lower energy costs at 12 km·h -1 were moderately to largely correlated with smaller peak impact and braking force ( r = 0.486 and -0.500, respectively). Regarding the statistical parametric mapping analysis, most outcomes showed associations with RE at 10 km·h -1 , including knee flexion (42.5%-65.5% of the gait cycle), ankle plantarflexion (32.5%-36% of the gait cycle), active force (30.5%-35% of the stance phase), and propulsion force (68%-72.5% of the stance phase). Lower energy costs at 12 km·h -1 were correlated with smaller hip flexion (5.5%-12% and 66.5%-74%) and smaller knee flexion (57%-57.5%) during the running gait cycle. CONCLUSIONS: This study indicates that biomechanical factors are associated with RE in recreational runners. To design effective training methods to improve RE, coaches and runners should focus on the sagittal plane kinematics of the hip, knee, and ankle, as well as lower vertical and horizontal kinetic parameters.

Comparing risk assessment methods for work-related musculoskeletal disorders with in vivo joint loads during manual materials handling.

The validity of observational methods in ergonomics is still challenging research. Criterion validity in terms of concurrent validity is the most commonly studied. However, studies comparing observational methods with biomechanical values are rare. Thus, the aim of this study is to compare the Ovako Working Posture Analysing System (OWAS) and the Rapid Entire Body Assessment (REBA) with in vivo load measurements at hip, spine, and knee during stoop and squat lifting of 14 participants. The results reveal that OWAS and REBA action levels (AL) can distinguish between different in vivo load measurements during manual lifting. However, the results also reveal that the same OWAS- and REBA-AL do not necessarily provide equal mean values of in vivo load measurements. For example, resultant contact force in the vertebral body replacement for squat lifting ranged from 57% body weight (%BW) in OWAS-AL1 to 138%BW in OWAS-AL3 compared to 46%BW in REBA-AL0 and 173%BW in REBA-AL3. Furthermore, the results suggest that the performed squat lifting techniques had a higher risk for work-related musculoskeletal disorders than the performed stoop lifting techniques.

Infection in osteotomy around the knee: Incidence, management and outcomes in a high-volume case series.

PURPOSE: Current evidence around the management of osteotomy-related infection is insufficient to robustly underpin the expert statements formulated by a recent European consensus statement. We present a review of a large case series in a high-volume osteotomy practice to contribute to the understanding of the incidence, management and outcome of infection in this subspecialty area. METHODS: Analyses of two prospectively collected databases for all osteotomy around the knee and infections related to osteotomy were performed, along with a review of hospital readmission data to capture all osteotomy-related infections. Clinical notes were reviewed to assess patient demographics, incidence of infection, how infection was managed and clinical outcome. RESULTS: In a series of 822 osteotomies in 755 patients, there were 21 (2.8%) cases of suspected infection. Twelve (1.6%) were contemporaneously deemed 'superficial' and nine confirmed 'deep' infections (1.2%). Deep infections were all successfully managed with wound debridement, with or without plate removal, depending on union and time from initial surgery. One of these infections was noted during a revision procedure, but no revision was carried out as a direct result of infection, no external fixation was required and no infected nonunions were experienced. CONCLUSION: All of the cases in this series were managed successfully with debridement ± removal of the plate, without the need for revision or external fixation. Any potential signs of infection around an osteotomy, especially in the case of medial high tibial osteotomy, should raise awareness for deep infection and the need for further surgery due to the limited overlying soft tissue cover. This evidence supports the recent European Society of Sports Traumatology, Knee Surgery and Arthroscopy algorithm. LEVEL OF EVIDENCE: Level IV, case series.

Low-value MRI of the knee in Norway: a register-based study to identify the proportion of potentially low-value MRIs and estimate the related costs.

OBJECTIVES: The objective of this study is to investigate the proportion of potentially low-value knee MRI in Norway and to provide an estimate of the related costs. DESIGN: Register study based on conditional data extraction and analysis of data from Control and Reimbursement of Healthcare Claims registry in Norway. SETTING: MRI in public specialist healthcare with universal health coverage (Norway). PARTICIPANTS: 48 212 MRIs for 41 456 unique patients and 45 946 reimbursement claims. OUTCOME MEASURES: Proportion of MRIs of the knee that (1) did not have a relevant tentative diagnosis prior to the knee MRI, (2) did not have a relevant alternative image of the knee before the MRI or (3) did not have a relevant code from the specialist care within 6 months after the MRI, and those that had combinations of 1, 2 and 3. Estimated costs for those that had combinations of 1, 2 and 3. RESULTS: Very few patients (6.4%) had a relevant diagnosis code or prior imaging examination when having the MRI and only 14.6% got a knee-related diagnosis code from the specialist care within 6 months after the MRI. 21.8% of the patients had knee X-ray, CT or ultrasound within 6 months before the MRI. Between 58% and 85% of patients having knee MRIs in Norway have no relevant examinations or diagnoses six months prior to or after the MRI examination. These examinations are unlikely to benefit patients and they correspond to between 24 108 and 35 416 MRIs at a cost of €6.7-€9.8 million per year. CONCLUSION: A substantial proportion of MRIs of the knee in Norway have no relevant examinations or diagnoses before or after the MRI and are potentially of low value. Reducing low-value MRIs could free resources for high-value imaging, reduce waiting times, improve the quality of care and increase patient safety and professional integrity.

Forty-Six Years of Technological Innovation in Musculoskeletal Medicine: An Analysis of a Patent Database (1973 to 2018).

BACKGROUND: Technological innovation in orthopaedics is key to advancing patient care. As emerging technologies near maturity, clinicians must be able to objectively assess where and when these technologies can be implemented. Patent databases are an underappreciated resource for quantifying innovation, especially within orthopaedic surgery. This study used a patent database to assess patent activity and relative growth of technologies in musculoskeletal medicine and orthopaedics over a period of 46 years. METHODS: A total of 121,471 patent records were indexed from Lens.org , a patent database. These patents were grouped into subspecialty clusters and technology clusters using patent codes. Five-year (2014 to 2018), 10-year (2009 to 2018), and 30-year (1989 to 2018) compound annual growth rates were calculated and compared for each cluster. RESULTS: Annual patent activity increased from one patent in 1973 to 4,866 patents in 2018. Of the eight subspecialty clusters, the largest number of patents were related to 'Inflammation' (n = 63,128; 40.57%). The 'Elbow', 'Shoulder', and 'Knee' clusters experienced increased annual patent activity since 2000. Of the 12 technological clusters, the largest number of patents were related to 'Drugs' (n = 55,324; 39.75%). The 'Custom/patient-specific instrumentation, 'Computer Modeling', 'Robotics', and 'Navigation' clusters saw growth in the average annual patent activity since 2000. DISCUSSION: Innovation, as measured by patent activity in musculoskeletal medicine and orthopaedics, has seen notable growth since 1973. The 'Robotics' cluster seems poised to experience exponential growth in industry investment and technological developments over the next 5 to 10 years. The 'Diagnostics', 'Computer Modeling', 'Navigation', and 'Design and Manufacturing' clusters demonstrate potential for exponential growth in industry investment and technological developments within the next 10 to 20 years.

Gait and strength assessment following surgical repair by intramedullary nailing of isolated tibial shaft fracture.

The objective of the study was to evaluate the long-term strength and gait outcomes after intramedullary nailing of isolated tibial diaphyseal fractures. This retrospective cohort study was conducted at an academic Level I trauma center. Fifteen participants with isolated tibial diaphyseal fractures (OTA/AO 42) at least 2 years postoperative from intramedullary nailing (IMN) provided informed consent. The average age was 40 ± 14 (range, 24-69); there were nine men and six women. Knee flexion-extension strength data were collected. Temporal-spatial, kinematic, and kinetic gait parameters were measured and compared to historic control data. Participants completed the SF-36 and shortened musculoskeletal function assessment questionnaires. The mean length of follow-up between surgery and gait analysis was 6 ± 2 years. The fractured limb demonstrated deficits in quadriceps strength between 9.8% and 23.4% compared to the unaffected limb. Temporal-spatial parameters revealed slower walking speed, shorter stride length, decreased cadence, and shorter single-limb support time in the fractured limb. Altered kinematic and kinetic findings included a knee extension shift during stance, with an increased knee flexor moment demand and decreased total knee power during loading and midstance. These findings represent deficits in concentric and eccentric knee extensor activity. Additionally, the fractured limb demonstrated decreased ankle dorsiflexion during stance and diminished ankle push-off power. Long-term outcomes after IMN of tibial diaphyseal fractures demonstrate decreased quadriceps strength and altered gait parameters that may have implications to the high incidence of knee and ankle pain in the fractured limb.

Lower-extremity kinematics and kinetics differ based on drop vertical jump variation: An assessment of methodology for a return-to-play protocol using motion analysis.

BACKGROUND: The drop vertical jump (DVJ) is commonly used in return-to-play evaluations to assess movement quality and risk during a dynamic task. However, across biomechanics literature, a multitude of DVJ variations have been used, influencing the generalizability and potential interpretation of the reported findings. RESEARCH QUESTION: The purpose of this study was to identify differences in lower extremity kinematics and kinetics between DVJ variations that differ based on horizontal jump distance, verbal instructions, and the use of a jump target. METHODS: A single-group repeated measures design was used in a laboratory setting. Twenty participants were tested, and three-dimensional angles and moments of the pelvis, hip, knee, and ankle were computed. Wilcoxon signed rank tests were performed to determine differences between DVJ variations. RESULTS: Reduced knee flexion at initial contact and greater knee extensor moments across the descent phase were observed with increased horizontal jump distance. Additionally, both verbal instructions and a jump target influenced movement strategies at the pelvis, hip, and knee. Ground reaction forces were found to be similar across conditions and jump height following the first landing increased with a target. SIGNIFICANCE: Although subtle, the biomechanical differences observed between task variations emphasize the importance of standardizing motion analysis protocols for research and clinical decision-making. Given the findings of the current study, the authors recommend using the Half Height variation in patients treated for a knee injury as it will likely be the most indicative of movement quality.

Within- and between-day reliability and repeatability of neuromuscular function assessment in females and males.

The study evaluated the reliability and repeatability of the force and surface electromyography activity (EMG) outcomes obtained through voluntary and electrically evoked contractions of knee extensors in females (n = 18) and males (n = 20) and compared these data between sexes. Maximal isometric voluntary contractions (iMVCs) of knee extensors associated with electrical stimulation of the femoral nerve were performed over 4 days (48-h interval), with the first day involving familiarization procedures, the second involving three trials (1-h interval), and the third and fourth involving just one trial. The intraclass correlation coefficient (ICC), coefficient of variation (CV), and repeatability of outcomes from within- and between-day trials were determined for each sex. Females presented lower maximal voluntary force during iMVC (iMVCForce) and associated vastus lateralis EMG activity (root mean square, RMSVL), force evoked by potentiated doublet high-frequency (Db100Force) and single stimuli (Qtw), and M-wave amplitude than males (P ≤ 0.01, partial eta squared ≥0.94). Voluntary activation (VA) and RMSVL/M-wave amplitude did not differ between sexes. iMVCForce, VA, Db100Force, Qtw, and M-wave amplitude were the most reliable outcomes in within-day trials, with similar results between sexes (ICC > 0.62; CV < 6.4%; repeatability: 12.2%-22.6%). When investigating between-day trials, the iMVCForce, VA, Db100Force, and Qtw were the most reliable (ICC > 0.66; CV < 7.5%; repeatability: 13.2%-33.45%) with similar results between sexes. In conclusion, females presented lower iMVCForce and evoked response than males. Although reliability and repeatability statistics vary between trials, data (e.g., from EMG or force signal), and sexes, most of the outcomes obtained through this technique are reliable in females and males.NEW & NOTEWORTHY Although reliability and repeatability of knee extensors vary according to the type of neuromuscular function outcome (e.g., from force or EMG responses), the trial intervals (i.e., hours or days), and the sex of the participant, most force and EMG outcomes obtained through these neuromuscular assessment protocols present ICC > 0.75, very good CV (<10%), and repeatability <25% in within- and between-day trials in both sexes.

Ultrasound assessment of medial crural cutaneous nerve and infrapatellar branch and of the saphenous nerve: establishing a safety zone for preventing nerve injury in knee surgery and injections.

PURPOSE: Our study aimed to illustrate the positional relationship of the two branches of the saphenous nerve: the infrapatellar branch of the saphenous nerve (IPBSN) and medial crural cutaneous nerve (MCCN), as well as the anatomical landmarks using high-resolution ultrasound (HRUS) to help prevent iatrogenic nerve injury. METHODS: We used HRUS to explore the positional relationships among the anatomical landmarks, IPBSN, and MCCN in 40 knees of 20 participants. The distances from these branches to key reference points were recorded. Using the ultrasound caliper mode, we measured the depth from the skin surface to the nerves at four distinct points. RESULTS: The average distances between IPBSN and medial border of patella (MBP) and IPBSN and medial border of patellar ligament (MBPL) were 47 ± 7 mm and 42 ± 9 mm, respectively. MCCN showed mean distances of 94 ± 9 mm and 96 ± 9 mm to MBP and MBPL, respectively. The mean distance from the upper edge of pes anserine to IPBSN at the patellar apex (PA) level was 24 ± 10 mm and to MCCN was 34 ± 9 mm. CONCLUSION: We used high-resolution ultrasound to evaluate IPBSN and MCCN and their positions relative to anatomical landmarks. The study results offer valuable insights into the course of these nerves, which can help establish a safety zone to prevent accidental nerve injuries during knee surgeries and injections.

Elite vs. Experienced Male and Female Trail Runners: Comparing Running Economy, Biomechanics, Strength, and Power.

ABSTRACT: Besson, T, Pastor, FS, Varesco, G, Berthet, M, Kennouche, D, Dandrieux, P-E, Rossi, J, and Millet, GY. Elite vs. experienced male and female trail runners: comparing running economy, biomechanics, strength, and power. J Strength Cond Res 37(7): 1470-1478, 2023-The increased participation in trail running (TR) races and the emergence of official international races have increased the performance level of the world best trail runners. The aim of this study was to compare cost of running (Cr) and biomechanical and neuromuscular characteristics of elite trail runners with their lower level counterparts. Twenty elite (10 females; ELITE) and 21 experienced (10 females; EXP) trail runners participated in the study. Cr and running biomechanics were measured at 10 and 14 km·h-1 on flat and at 10 km·h-1 with 10% uphill incline. Subjects also performed maximal isometric voluntary contractions of knee and hip extensors and knee flexors and maximal sprints on a cycle ergometer to assess the power-torque-velocity profile (PTVP). Athletes also reported their training volume during the previous year. Despite no differences in biomechanics, ELITE had a lower Cr than EXP (p < 0.05). Despite nonsignificant difference in maximal lower-limb power between groups, ELITE displayed a greater relative torque (p < 0.01) and lower maximal velocity (p < 0.01) in the PTVP. Females displayed shorter contact times (p < 0.01) compared with males, but no sex differences were observed in Cr (p > 0.05). No sex differences existed for the PTVP slope, whereas females exhibited lower relative torque (p < 0.01) and velocity capacities (p < 0.01) compared with males. Although not comprehensively assessing all determining factors of TR performance, those data evidenced level and sex specificities of trail runners in some factors of performance. Strength training can be suggested to lower level trail runners to improve Cr and thus TR performance.

Morphological assessment of cartilage and osteoarthritis in clinical practice and research: Intermediate-weighted fat-suppressed sequences and beyond.

Magnetic resonance imaging (MRI) is widely regarded as the primary modality for the morphological assessment of cartilage and all other joint tissues involved in osteoarthritis. 2D fast spin echo fat-suppressed intermediate-weighted (FSE FS IW) sequences with a TE between 30 and 40ms have stood the test of time and are considered the cornerstone of MRI protocols for clinical practice and trials. These sequences offer a good balance between sensitivity and specificity and provide appropriate contrast and signal within the cartilage as well as between cartilage, articular fluid, and subchondral bone. Additionally, FS IW sequences enable the evaluation of menisci, ligaments, synovitis/effusion, and bone marrow edema-like signal changes. This review article provides a rationale for the use of FSE FS IW sequences in the morphological assessment of cartilage and osteoarthritis, along with a brief overview of other clinically available sequences for this indication. Additionally, the article highlights ongoing research efforts aimed at improving FSE FS IW sequences through 3D acquisitions with enhanced resolution, shortened examination times, and exploring the potential benefits of different magnetic field strengths. While most of the literature on cartilage imaging focuses on the knee, the concepts presented here are applicable to all joints. KEY POINTS: 1. MRI is currently considered the modality of reference for a "whole-joint" morphological assessment of osteoarthritis. 2. Fat-suppressed intermediate-weighted sequences remain the keystone of MRI protocols for the assessment of cartilage morphology, as well as other structures involved in osteoarthritis. 3. Trends for further development in the field of cartilage and joint imaging include 3D FSE imaging, faster acquisition including AI-based acceleration, and synthetic imaging providing multi-contrast sequences.

Assessment of the Effectiveness of Knee Joints Treatment With the Use of 90 Y : Prospective Ultrasound and Clinical Analysis.

PURPOSE: The purpose of this prospective study was to assess the effectiveness of knee joints treatment by radiosynoviorthesis with the use of 90 Y based on ultrasound and clinical analysis. MATERIALS AND METHODS: Ninety-seven patients were qualified for treatment from October 2016 to June 2017, and observation period lasted until December 2017. Bioethics Committee of the Medical University of Silesia approved this study. The effectiveness of knee joints treatment with the use of 90 Y was based on 927 ultrasound measurements of fluid and 927 synovial thickness in 3 sites of the suprapatellar recess, 309 assessments of patient's disability documented in Lequesne questionnaire, 309 assessments of pain on visual analog scale, as well as 103 overall self-assessment. Statistical methods were used to process the results. RESULTS: A reduction in fluid was found in 62.14% of the knees; synovial thickness reduction was observed in 97.09% of all knees. The greatest benefit from the therapy was experienced by patients complaining of morning stiffness lasting more than 15 minutes (in 85.71% of joints). There was reduction in pain at rest in 94.52% of knee joints and in 80.39% of joints with pain while walking. At the second follow-up visit after treatment, the percentage of improvement in self-assessment was 74.76%. CONCLUSIONS: Statistically significant decreases in the amount of fluid and thickness of the synovial membrane as well as the level of disability and the intensity of pain after radiosynoviorthesis 90 Y treatment were demonstrated.

Moving orthopaedic procedures out of the operating theatre:Outpatient needle arthroscopy can reduce cost & waste, and increase inpatient capacity compared to conventional knee arthroscopy.

BACKGROUND: Needle arthroscopy (NA) is an emerging technique that could streamline pathways, facilitate timely care, and reduce service burden. The primary aim was to assess the practical and economic viability of an outpatient NA service. Secondary aims were to assess the relative costs and benefits compared to a conventional arthroscopy (CA) service. METHODS: This service feasibility study was conducted between 2021-2022 in a high-volume national treatment centre. A NA pathway was established for patients with chronic soft tissue pathology or early degenerative knee disease. The pathway was evaluated in terms of: i) cost; ii) efficiency, and iii) waste production, and an assessment was conducted of the patient-related and service-related effects. RESULTS: The cost of the NA pathway was £1555.20 per patient, compared to £2,351.53 for CA. Time to management was 45 days for NA versus 180 days for CA. The NA pathway involved two hospital attendances, whereas CA required a minimum of three. NA cases produced 1.4 kg of non-recyclable waste compared to 5.0 kg produced by CA. For every two cases managed by NA instead of CA, capacity for one additional obligate-inpatient procedure was created. CONCLUSIONS: The NA pathway offers a technically and economically viable approach for the management of refractory knee symptoms in the context of chronic soft tissue or early degenerative disease. NA placed less demand on hospital resources, produced two-thirds less non-recyclable waste, and is amenable to a one-stop clinic approach. Clinical studies focused on objective and patient-reported outcome measures are required to assess clinical efficacy.

A Health-Impact Assessment of an Ergonomic Measure to Reduce the Risk of Work-Related Lower Back Pain, Lumbosacral Radicular Syndrome and Knee Osteoarthritis among Floor Layers in The Netherlands.

Sand-cement-bound screed floor layers are at risk of work-related lower back pain, lumbosacral radicular syndrome and knee osteoarthritis, given their working technique of levelling screed with their trunk bent while mainly supported by their hands and knees. To reduce the physical demands of bending of the trunk and kneeling, a manually movable screed-levelling machine was developed for floor layers in the Netherlands. The aim of this paper is to estimate the potential health gains of working with a manually movable screed-levelling machine on the risk of lower back pain (LBP), lumbosacral radicular syndrome (LRS) and knee osteoarthritis (KOA) compared to traditional working techniques. This potential health gain was assessed using the epidemiological population estimates of the Population Attributable Fraction (PAF) and the Potential Impact Fraction (PIF), combined with work-related risk estimates for these three disorders from systematic reviews. The percentage of workers exceeding these risk estimates was based on worksite observations among 28 floor layers. For LBP, 16/18 workers were at risk when using traditional working techniques, with a PAF = 38%, and for those using a manually movable screed-levelling machine, this was 6/10 with a PIF = 13%. For LRS, these data were 16/18 with a PAF = 55% and 14/18 with a PIF = 18%, and for KOA, 8/10 with a PAF = 35% and 2/10 with a PIF = 26%. A manually movable screed-levelling machine might have a significant impact on the prevention of LBP, LRS and KOA among floor layers in the Netherlands, and health-impact assessments are a feasible approach for assessing health gains in an efficient way.

Attention to Detail: The Effect of Fluoroscopic Parallax on Limb Alignment Assessment During Corrective Osteotomy.

BACKGROUND: The accuracy of a corrective osteotomy is dependent on many factors. One error rarely considered is using noncentered fluoroscopic imaging to assess intraoperative alignment. This study quantified the coronal alignment error produced by visual parallax per interval changes in vertical and horizontal positioning of the C-arm and alignment rod during intraoperative evaluation. METHODS: Unilateral hip, ankle, and knee fluoroscopic images were obtained from a single intact cadaveric specimen. A center-center fluoroscopic image was obtained by moving the C-arm appeared in the center square of the nine-box grid. With the base of the C-arm stationary, the radiograph generator/intensifier portion of the C-arm was translated medially until the target bone appeared on the edge of the fluoroscopic image. RESULTS: One hundred eight images were obtained. Measurement error increased by an average of 14% per 10 mm of horizontal C-arm offset. Minimal effect was seen if the obtained image was within 5 mm of the true center; however, once 55 mm of offset was reached, all experimental conditions resulted in at least 10 mm of parallax error. CONCLUSION: Our results demonstrate that small variations in C-arm positioning can create statistically significant inaccuracies when assessing limb alignment using intraoperative fluoroscopy.

Intraoperative Assessment of Gap Balancing in Total Knee Arthroplasty Using Navigation with Joint Stability Graphs.

The purpose of this study was to assess continuous gaps in the replaced knee throughout the full range of motion (ROM) after total knee arthroplasty (TKA) using a joint stability graph, and to analyze the gap laxity in the mid-flexion range. Ninety-three TKAs were performed using imageless navigation with a joint stability graph. While positioning guides for each respective cut, the surgeon can safely preview the resection's impact for the resulting joint gaps and control the soft tissue balance at the knee flexion of 0° (extension) and 90° (flexion). The gaps between the femoral component and insert were evaluated throughout the full ROM using the joint stability graph. The mechanical axis (MA) and change of joint line height were radiographically evaluated. Posthoc power analyses using a significant α value of 0.05 were performed on the proportion of the mid-flexion instability as a primary outcome to determine whether the sample had sufficient power. The power was determined to be sufficient (100%). The flexion-extension gap differences in each medial and lateral compartment and the mediolateral gap differences in flexion and extension were all ≤3 mm. None of the knees had mid-flexion instability, which is defined by a peak mid-flexion gap that is 3 mm greater than the smaller value of flexion or extension gap. The average MA was well corrected from varus 11.4° to varus 1.0° postoperatively. The proportion of postoperative well-aligned knees (MA ≤ 3°) was 87.1%. The joint line height was well preserved (14.7 vs. 14.8 mm, p = 0.751). The joint stability graph in TKA using the navigation can effectively evaluate the continuous gap throughout the ROM, including the mid-flexion range. Mid-flexion instability was uncommon in primary TKAs with appropriate alignment and proper preservation of the joint line. The Level of evidence for the study is IV.

Mid-flexion laxity could be identified with continuous flexion-arc gap assessment in patients with a large preoperative convergence angle.

PURPOSE: To analyze the incidence of intraoperative mid-flexion laxity using continuous flexion-arc gap assessment, risk factors for mid-flexion laxity, and clinical results in navigation-assisted total knee arthroplasty (TKA). METHODS: Ninety posterior-stabilized TKAs were performed under navigation guidance for patients with degenerative arthritis and varus deformity. Intraoperatively, the gap between the trial femoral component and insert was evaluated in the navigation system with continuous flexion-arc gap assessment. Each medial and lateral gap at flexion (90°) and extension (0°) were made to be less than 3 mm. Mid-flexion laxity was determined when the gap in the flexion range between 15° and 60° was 3 mm or more. The proportion of knees with mid-flexion laxity was investigated. The factors affecting mid-flexion laxity were identified in terms of demographics, preoperative convergence angle, and change in joint line height and posterior femoral offset. The Knee Society Score and Western Ontario and McMaster Universities Osteoarthritis Index were evaluated. RESULTS: There were 31 cases (34.4%) of lateral mid-flexion laxity (average peak mid-flexion gap = 3.7 mm). The other 59 cases did not show mid-flexion laxity. The preoperative convergence angle was the only significant factor affecting lateral mid-flexion laxity (odds ratio = 1.466, p = 0.002). There were no significant differences in the clinical results between the groups with and without mid-flexion laxity. CONCLUSIONS: The continuous flexion-arc gap assessment was useful in evaluating mid-flexion laxity using navigation-assisted TKA. The preoperative convergence angle, reflecting soft-tissue laxity, can be a practical and simple radiographic finding for predicting lateral mid-flexion laxity. LEVEL OF EVIDENCE: IV.

Knee flexor strength and symmetry vary by device, body position and angle of assessment following ACL reconstruction with hamstring grafts at long-term follow-up.

PURPOSE: Persistent deficits in knee flexor strength following harvest of semitendinosus and gracilis for anterior cruciate ligament reconstruction are inconsistent in the literature. Variation in methodology, including measuring torque at higher knee flexion angles may partially explain these discrepant findings. The objective of this study was to determine whether positioning (seated vs supine), consideration of peak or joint-angle-specific torque or device (Isokinetic Dynamometer vs NordBord Hamstring Dynamometer) impact the magnitude of knee flexor strength differences between limbs. METHODS: Participants (n = 31, 44.2 ± 10.7 years,) who were at 14 ± 4.4 years follow-up for unilateral ACL reconstruction with semitendinosus/gracilis grafts completed the ACL Quality of Life outcome and an assessment including isokinetic concentric knee extensor and flexor strength in seated and supine with peak torque and torque at 60° (T60) and 75° (T75) knee flexion measured, followed by an eccentric Nordic Hamstring Curl. RESULTS: Isokinetic concentric knee flexor torque was reduced in supine relative to seated, on the reconstructed limb against the unaffected, and at higher degrees of knee flexion relative to peak torque (T60 and T75 against peak torque). Limb symmetry varied by methodology (F(6,204) = 8.506, p = 0.001) with reduced symmetry in supine T75 against all measures (71.1 ± 16.5%, p < 0.05), supine T60 against seated peak torque (82.7 ± 14.2%, p < 0.05), and the NordBord was lower than seated peak torque that was not statistically significant (83.9 ± 12.8%, n.s.). Knee extensor peak (r2 = 0.167 (F(1,27) = 5.3, p = 0.03) and Nordic curl eccentric torque (r2 = 0.267, F(2,26) = 4.736, p = 0.02) were predictors of ACL-QoL score, although a combined model did not improve over Nordic torque alone. CONCLUSION: Limb symmetry cannot be assumed in clinical practice across differing assessment methods for knee flexor strength as deficits are greatest in the supine position with torque measured at 75° knee flexion. Isokinetic knee extensor and eccentric knee flexor torque during the Nordic hamstring curl were predictors of ACL-QoL scoring and should be considered alongside patient-reported outcomes for patients following ACL reconstruction with hamstring grafts. LEVEL OF EVIDENCE: Level IV.

Assessment of reporting practices and reproducibility potential of a cohort of published studies in computational knee biomechanics.

Reproducible research serves as a pillar of the scientific method and is a foundation for scientific advancement. However, estimates for irreproducibility of preclinical science range from 75% to 90%. The importance of reproducible science has not been assessed in the context of mechanics-based modeling of human joints such as the knee, despite this being an area that has seen dramatic growth. Framed in the context of five experienced teams currently documenting knee modeling procedures, the aim of this study was to evaluate reporting and the perceived potential for reproducibility across studies the teams viewed as important contributions to the literature. A cohort of studies was selected by polling, which resulted in an assessment of nine studies as opposed to a broader analysis across the literature. Using a published checklist for reporting of modeling features, the cohort was evaluated for both "reporting" and their potential to be "reproduced," which was delineated into six major modeling categories and three subcategories. Logistic regression analysis revealed that for individual modeling categories, the proportion of "reported" occurrences ranged from 0.31, 95% confidence interval (CI) [0.23, 0.41] to 0.77, 95% CI: [0.68, 0.86]. The proportion of whether a category was perceived as "reproducible" ranged from 0.22, 95% CI: [0.15, 0.31] to 0.44, 95% CI: [0.35, 0.55]. The relatively low ratios highlight an opportunity to improve reporting and reproducibility of knee modeling studies. Ongoing efforts, including our findings, contribute to a dialogue that facilitates adoption of practices that provide both credibility and translation possibilities.