In vitro hip testing in the International Society of Biomechanics coordinate system

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.

Standardization of hemipelvis alignment for in vitro biomechanical testing

“…Past studies, where a reference frame was defined for other bone segments (tibia, and vertebra), reported errors of the order of 1–3°, comparable to the present one. Only few studies expressly defined a reference frame for the human pelvis in vitro . Comparisons with the present study are difficult, as the reproducibility of such references has only seldom been quantified.…”

“…To the Authors’ knowledge, this is the second study in which a reference frame for the hemipelvis was derived from the reference frame of the whole pelvis. In fact, van Arkel and Jeffers developed a procedure to apply the ISB reference frame to the whole pelvis before bisecting it, and then apply the same reference when the hemipelvises were used for in vitro testing . They found that after bisection, the hemipelvis had a misalignment compared to the original whole pelvis.…”

“…Despite the considerations above, only a few studies can be found where a suitable reference frame is defined for the pelvis and hemipelvis . It is very important to underline that hemipelvic specimens are frequently adopted for in vitro purposes .…”

“…Recently van Arkel and Jeffers described an in vitro method to align a hemipelvic specimen, based on the reference frame recommended by the International Society of Biomechanics (ISB) . The proposed procedure requires first aligning the whole pelvis, using four landmarks; the authors propose a procedure to dissect the specimen to obtain two hemipelvises which preserve the same alignment previously identified for the whole pelvis.…”

Capsular Ligament Function After Total Hip Arthroplasty

“…The hips were mounted into a 6-degrees-of-freedom testing rig (Fig. 2) using an established protocol 24 . This rig adopted the International Society of Biomechanics coordinate system 25 and allowed either for flexionextension or abduction-adduction torques to be applied through pulleys with hanging weight couples, or for these axes to be fixed at specific angular positions with screw clamps 19,22 .…”