Agnes G. d’Entremont

A non-invasive, 3D, dynamic MRI method for measuring muscle moment arms in vivo: demonstration in the human ankle joint and Achilles tendon.

Muscle moment arms are used widely in biomechanical analyses. Often they are measured in 2D or at a series of static joint positions. In the present study we demonstrate a simple MRI method for measuring muscle moment arms dynamically in 3D from a single range-of-motion cycle. We demonstrate this method in the Achilles tendon for comparison with other methods, and validate the method using a custom apparatus. The method involves registration of high-resolution joint geometry from MRI scans of the stationary joint with low-resolution geometries from ultrafast MRI scans of the slowly moving joint. Tibio-talar helical axes and 3D Achilles tendon moment arms were calculated throughout passive rotation for 10 adult subjects, and compared with recently published data. A simple validation was conducted by comparing MRI measurements with direct physical measurements made on a phantom. The moment arms measured using our method and those of others were similar and there was good agreement between physical measurements (mean 41.0mm) and MRI measurements (mean 39.5mm) made on the phantom. This new method can accurately measure muscle moment arms from a single range-of-motion cycle without the need to control rotation rate or gate the scanning. Supplementary data includes custom software to assist implementation.

Effect of opening-wedge high tibial osteotomy on the three-dimensional kinematics of the knee

Although it is clear that opening-wedge high tibial osteotomy (HTO) changes alignment in the coronal plane, which is its objective, it is not clear how this procedure affects knee kinematics throughout the range of joint movement and in other planes. Our research question was: how does opening-wedge HTO change three-dimensional tibiofemoral and patellofemoral kinematics in loaded flexion in patients with varus deformity?Three-dimensional kinematics were assessed over 0° to 60° of loaded flexion using an MRI method before and after opening-wedge HTO in a cohort of 13 men (14 knees). Results obtained from an iterative statistical model found that at six and 12 months after operation, opening-wedge HTO caused increased anterior translation of the tibia (mean 2.6 mm, p < 0.001), decreased proximal translation of the patella (mean -2.2 mm, p < 0.001), decreased patellar spin (mean -1.4°, p < 0.05), increased patellar tilt (mean 2.2°, p < 0.05) and changed three other parameters. The mean Western Ontario and McMaster Universities Arthritis Index improved significantly (p < 0.001) from 49.6 (standard deviation (sd) 16.4) pre-operatively to a mean of 28.2 (sd 16.6) at six months and a mean of 22.5 (sd 14.4) at 12 months. The three-dimensional kinematic changes found may be important in explaining inconsistency in clinical outcomes, and suggest that measures in addition to coronal plane alignment should be considered.

What Clinimetric Evidence Exists for Using Hip-specific Patient-reported Outcome Measures in Pediatric Hip Impingement?

BackgroundPatient-reported outcomes (PROs) are an increasingly popular research tool used to evaluate the outcomes of surgical intervention. If applied appropriately, they can be useful both for disease monitoring and as a method of assessing the efficacy of treatment. Many disorders can lead to impingement in children and adolescents, but it is not clear if any PROs have been validated to evaluate outcomes in these populations.Questions/purposesWe performed a systematic review of the literature to answer the following research questions: (1) Which hip-specific PROs are used in pediatric populations with impingement? (2) What clinimetric evidence exists for the use of these specific PROs in this population?MethodsWe performed two systematic searches of three databases (Medline, EMBASE, and Ovid All EBM Reviews). The first search aimed to identify specific PROs that have been applied to pediatric impingement populations. The second search aimed to find clinimetric evaluations of the PROs from the first search in this population.ResultsWe found six hip-specific PROs applied in pediatric impingement: Harris Hip Score, modified Harris Hip Score, Iowa Hip Score, Merle d’Aubigné Hip Score, Hip Outcome Score, and Non-arthritic Hip Score. However, we found no papers validating any of these PROs in this population. Furthermore, we found no papers validating any of these PROs in any pediatric population.ConclusionsA number of adult PROs have been applied in pediatric impingement disorders without evidence of validation in any pediatric population. Further work to develop and validate a hip-specific pediatric PRO is required.

Fundamental Concepts in Evidence-Based Medicine

Evidence-based medicine (EBM) practitioners consciously, deliberately, and consistently use the best current evidence to make patient care decisions. The evidence derives from clinical research, where randomized controlled trials (RCTs) are the best evidence. However, RCTs may not be appropriate in some situations, particularly in surgery, and important evidence may be obtained from other well-designed types of studies. Ideally, evidence synthesized in a methodologically correct way can help clinicians to make optimal treatment decisions in cross talk with the individual patient, taking into account the clinical situation and circumstances and patient values.

Biomechanical Considerations in Arthritis of the Hip

Biomechanics plays a role in the etiology of hip arthritis and in its treatment. It is surprising how little is known about hip biomechanics, given the prevalence of hip arthritis, the importance of biomechanics to many types of arthritis, and how much more is known about the biomechanics of other joints. Overall, it is clear that many hip conditions reduce joint range of motion. The evidence does not appear clear whether these reductions in range of motion are due to bony impingement or soft tissue changes. Models predict that hip disorders change contact pressure as would be predicted intuitively, and that surgical procedures like osteotomies have the desired effect on contact pressure. However, there is very limited experimental evidence to back up these predictions or quantify them reliably.