Basic Science Measured loads on a vertebral body replacement during sitting Antonius Rohlmann, PhD*, Thomas Zander, PhD, Friedmar Graichen, PhD, Marcel Dreischarf, MSc, Georg Bergmann, PhD Julius Wolff Institut, Charit e—Universit€ atmedizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany Received 9 January 2011; revised 25 March 2011; accepted 15 June 2011 Abstract BACKGROUND CONTEXT: Sitting is frequently assumed to cause high spinal loads because people with sedentary work often suffer from low back pain. It is assumed that the posture while sitting, as well as several seat parameters, also affects the spinal loads. PURPOSE: To measure the loads on a spinal implant for different upper body inclinations, backrest declinations, seat heights, types of seat, and arm positions. STUDY DESIGN: Loads on a vertebral body replacement during sitting were measured in five patients with telemeterized implants. METHODS: The telemeterized vertebral body replacement measures all six load components. It was implanted into five patients suffering from compression fractures of a lumbar vertebral body. Loads were measured when the patients were sitting on a stool and inclining their upper body between 15  flexion and 10  extension in steps of 5  ; on a chair with an adjustable backrest that allowed declination angles between 108  and 180  ; on an office chair while the seat height was varied between 40 and 60 cm in steps of 5 cm; and successively on seven different types of seats. The effect of the arm position was also studied. RESULTS: The resultant implant force was increased on the average by 48% for 15  flexion and decreased by 19% for 10  extension of the trunk. When sitting on a chair with an adjustable backrest, the loads decreased with an increasing backrest declination angle. The seat height had in most cases only a minor effect on implant loads. In comparison to sitting on a stool, the loads were reduced when sitting on a bench (7%) or a stool with a padded wedge (9%), a knee stool (19%), a chair (35%), and an office chair (41%). Sitting on a physiotherapy ball increased the loads by 7%. Placing the hands on the thighs reduced the implant loads on the average by 19% in comparison to arms hanging on the sides. CONCLUSION: Spinal loads can be reduced by leaning against the backrest, placing the arms on the armrest or the thighs, and by decreasing the flexion angle of the upper body. Ó 2011 Elsevier Inc. All rights reserved. Keywords: Sitting; Load measurement; Vertebral body replacement; Telemetry; Spinal loads Introduction High spinal loads and keeping a constrained posture over a long period are reasons for back pain [1,2]. People with sedentary work often suffer from low back pain. Sitting is frequently assumed to cause high spinal loads. However, sitting can vary by several factors, such as type of seat (eg, chair, physiotherapy ball, and knee stool), pos- ture (eg, relaxed, erect, upper body inclined, and leaned against the backrest), and the positioning of the arms (eg, on the thighs, armrests, a table, and hanging them lat- erally). In addition, the inclination of the pelvis and thus the lordosis of the lumbar spine may differ strongly during sitting. Some types of seats assist certain pelvis inclina- tions, which are alleged to reduce spinal load or are consid- ered to prevent back pain. These types include, for example, physiotherapy balls, modern office chairs with a tiltable backrest that permit changing the shape of the back [3], and chairs with alternating microrotatory move- ments of the seat [4]. FDA device/drug status: Not applicable. Author disclosures: AR: Research Support (Staff/Materials): SpineLab, Switzerland (D); Grants: Epionics (B), Heraeus Medical (D). TZ: Nothing to disclose. FG: Nothing to disclose. MD: Nothing to disclose. GB: Research Support (Staff/Materials): Zimmer Inc. (E). The disclosure key can be found on the Table of Contents and at www. TheSpineJournalOnline.com. * Corresponding author. Julius Wolff Institut, Charit e—Universit€ ats- medizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany. Tel.: (49) 30-450559083; fax: (49) 30-450559980. E-mail address: antonius.rohlmann@charite.de (A. Rohlmann) 1529-9430/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.spinee.2011.06.017 The Spine Journal 11 (2011) 870–875