Abstract
Many innovative experiments are designed to answer research questions about hip biomechanics, however many fail to define a coordinate system. This makes comparisons between studies unreliable and is an unnecessary hurdle in extrapolating experimental results to clinical reality. The aim of this study was to present a specimen mounting protocol which aligns and registers hip specimens in the International Society of Biomechanics (ISB) coordinate system, which is defined by bony landmarks that are identified by palpation of the patient׳s body. This would enable direct comparison between experimental testing and clinical gait analysis or radiographic studies. To represent the intact hip, four intact synthetic full-pelves with 8 full-length articulating femora were assembled and digitised to define the ISB coordinate system. Using our proposed protocol, pelvis specimens were bisected into left and right hemi-pelves and femora transected at the mid-shaft, and then mounted in bone pots to represent a typical experimental setup. Anatomical landmarks were re-digitised relative to mechanical features of the bone pots and the misalignment was calculated. The mean misalignment was found to be less than 1.5° flexion/extension, ab/adduction and internal/external rotation for both the pelves and femora; this equates to less than 2.5% of a normal range of hip motion. The proposed specimen mounting protocol provides a simple method to align in vitro hip specimens in the ISB coordinate system which enables improved comparison between laboratory testing and clinical studies. Engineering drawings are provided to allow others to replicate the simple fixtures used in the protocol.
Highlights
The aim of this study is to provide a method to register the International Society of Biomechanics (ISB) body reference frames to bones before bisecting the pelvis and transecting the femur, and restore the same coordinate system when the specimen is installed in the experimental fixtures
The mean 7standard deviation misalignment after using the drilling guides to mount the specimens into a bone pot in the ISB pelvic reference frame was: 1.571.6° adduction, 0.5 71.1° internal rotation and À 0.6 71.7° flexion
Some authors recommend alternative coordinate systems to the ISB system based on anatomical landmarks that have the smallest inter-specimen variance (Cristofolini, 1997; Yoshioka et al, 1987)
Summary
In the past 10 years, many research labs have developed new methods to study hip joint biomechanics including: digital image correlation (Dickinson et al, 2012, 2011), roentgen stereophotogrammetric analysis (Dy et al, 2008; Myers et al, 2011), digital variable resistance transducers (Safran et al, 2011; Smith et al, 2011), real-time contact-pressure measurement (Lee et al, 2015; Rudert et al, 2014), fluid infusion devices (Cadet et al, 2012; Dwyer et al, 2014), optical tracking motion analysis (Lopomo et al, 2010; Signorelli et al, 2013), 3D digital reconstructions combining CT scans and motion tracking (Dwyer et al, 2014; Incavo et al, 2011), combined use of in-vitro and finite element modelling (Anderson et al, 2008; Dickinson et al, 2011; Elkins et al, 2011), custom built rigs in servo-hydraulic actuators/materials testing machines (Dickinson et al, 2012; Elkins et al, 2011; Ito et al, 2009; Song et al, 2012; van Arkel et al, 2015a, 2015b) and six-degreesof-freedom robotic load/torque actuators (Colbrunn et al, 2013; Smith et al, 2014).
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