Structural response of cadaveric ribcages under a localized loading: stiffness and kinematic trends

To improve understanding of structural coupling and deformation patterns throughout the loaded ribcage, the present study reports the force-displacement and kinematic responses under a highly-localized loading condition using three PMHS ribcages (ages 44, 61, and 63 years). The ribcages were quasi-statically loaded locally to a non-failure displacement (nominally 15% of the ribcage depth at the loaded rib level) at approximately 25 unilateral locations and 5-7 geometrically symmetric bilateral locations on the anterior surface of each ribcage, for a total of 94 tests. The translations of 56 points distributed around the anterior, lateral, and posterior portions of the superficial surface of the ribcage were measured while under loading. Each of the first through sixth rib levels was then separated from the remaining ribs, and this "rib ring" structure was individually loaded at the sternum in the anterior-posterior direction. The force when the ribcage was deflected to 8% of its initial depth was normalized to the force at the upper sternum (viz. 81.2±32.2 N). The normalized unilateral force at the costo-chondral junction was found to vary from 0.76±0.29 at rib 1 to 0.15±0.02 at rib 9, while bilateral forces (sum of left and right aspects) varied from 0.92 to 1.11. The rib rings were generally less stiff, ranging from 0.78±0.24 for rib 1 to 0.19±0.01 for rib 6. The deformation patterns under all loading conditions were quantified. In general, bilateral loading produced an approximately symmetric deformation pattern, while unilateral loading resulted in approximately twice as much resultant deformation on the ipsilateral side compared to the contralateral side.