title: Duration-dependent influence of dynamic torsion on the intervertebral disc: an intact disc organ culture study.
abstract: OBJECTIVE
  Mechanical loading is an important parameter that alters the homeostasis of the intervertebral disc (IVD). Studies have demonstrated the role of compression in altering the cellular metabolism, anabolic and catabolic events of the disc, but little is known how complex loading such as torsion-compression affects the IVD cell metabolism and matrix homeostasis. Studying how the duration of torsion affects disc matrix turnover could provide guidelines to prevent overuse injury to the disc and suggest possible beneficial effect of torsion. The aim of the study was to evaluate the biological response of the IVD to different durations of torsional loading.
  
  
  METHODS
  Intact bovine caudal IVD were isolated for organ culture in a bioreactor. Different daily durations of torsion were applied over 7 days at a physiological magnitude (±2°) in combination with 0.2 MPa compression, at a frequency of 1 Hz.
  
  
  RESULTS
  Nucleus pulpous (NP) cell viability and total disc volume decreased with 8 h of torsion-compression per day. Gene expression analysis suggested a down-regulated MMP13 with increased time of torsion. 1 and 4 h per day torsion-compression tended to increase the glycosaminoglycans/hydroxyproline ratio in the NP tissue group.
  
  
  CONCLUSIONS
  Our result suggests that load duration thresholds exist in both torsion and compression with an optimal load duration capable of promoting matrix synthesis and overloading can be harmful to disc cells. Future research is required to evaluate the specific mechanisms for these observed effects.
authors.affiliation: Tissue and Organ Mechanobiology, Institute for Surgical Technology and Biomechanics, University of Bern, Stauffacherstrasse 78, 3014, Bern, Switzerland. samantha.chan@empa.ch.|Biointerfaces, EMPA, Swiss Federal Laboratories for Materials Science and Technology, St Gallen, Switzerland. samantha.chan@empa.ch.
authors.forename: Samantha C W
authors.initials: SC
authors.lastname: Chan
authors.affiliation: Institute for Biomechanics, ETH Zürich, Zurich, Switzerland.
authors.forename: Jochen
authors.initials: J
authors.lastname: Walser
authors.affiliation: Institute for Biomechanics, ETH Zürich, Zurich, Switzerland.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Ferguson
authors.affiliation: Tissue and Organ Mechanobiology, Institute for Surgical Technology and Biomechanics, University of Bern, Stauffacherstrasse 78, 3014, Bern, Switzerland.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Gantenbein
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000502:physiology*; D019149:Bioreactors; D002417:Cattle; D007403:Intervertebral Disc / Q000502:physiology*; D009924:Organ Culture Techniques / Q000379:methods*
keywords: Bioreactor; Complex loading; Dynamic loading; Intervertebral disc; Organ culture; Torsion