ABSTRACT
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.
Subject(s)
Achilles Tendon , Ankle Joint , Imaging, Three-Dimensional/methods , Magnetic Resonance Imaging/methods , Movement , Muscle, Skeletal , Achilles Tendon/anatomy & histology , Achilles Tendon/physiology , Adult , Animals , Ankle Joint/anatomy & histology , Ankle Joint/physiology , Biomechanical Phenomena , Equipment Design , Female , Humans , Imaging, Three-Dimensional/instrumentation , Magnetic Resonance Imaging/instrumentation , Male , Middle Aged , Models, Biological , Movement/physiology , Muscle, Skeletal/anatomy & histology , Muscle, Skeletal/physiology , Phantoms, Imaging , Rotation , Sheep , Young AdultABSTRACT
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.
