ELSEVIER Bone Vol. 18, No. 5 May 1996:405M10 In Vivo Measurement of Human Tibial Strains During Vigorous Activity D. B. BURR, I C. MILGROM, 2 D. FYHRIE, 3 M. FORWOOD, 4 M. NYSKA, 2 A. FINESTONE, 2 S. HOSHAW, 3 E. SAIAG, 5 and A. SIMKIN 2 I Departments of Anatomy and Orthopedic Surgery, Biomechanics and Biomaterials Research Center, Indiana University School of Medicine, Indianapolis, IN, USA 2 Hadassah University Hospital, Hebrew University Medical School, Ein Kerem POB, Jerusalem, Israel 3 Bone and Joint Center, Henry Ford Hospital, Detroit, MI, USA 4 Department of Anatomical Sciences, University of Queensland, Brisbane, Queensland, Australia 5 Research and Development, Israeli Defense Forces, Military POB, Israel Our understanding of mechanical controls on bone remod- eling comes from studies of animals with surgically im- planted strain gages, but in vivo strain measurements have been made in a single human only once. That study showed that strains in the human tibia during walking and running are well below the fracture threshold. However, strains have never been monitored in vivo during vigorous activity in people, even though prolonged strenuous activity may be re- sponsible for the occurrence of stress fractures. We hypoth- esized that strains >3000 microstrain could be produced on the human tibial midshaft during vigorous activity. Strains were measured on the tibiae of two subjects via implanted strain gauges under conditions similar to those experienced by Israeli infantry recruits. Principal compressive and shear strains were greatest for uphill and downhill zigzag running, reaching nearly 2000 microstrain in some cases, about three times higher than recorded during walking. Strain rates were highest during sprinting and downhill running, reaching 0.050/sec. These results show that strain is maintained below 2000 microstrain even under conditions of strenuous activity. Strain rates are higher than previously recorded in human studies, but well within the range reported for running animals. (Bone 18:405-410; 1996) Key Words: Strain; Stress fracture; Exercise; Bone; Biomechanics. Introduction In vivo strain measurements in humans have been made only once on the tibia of a normal subject. 6 The work of Lanyon et al. showed that strains in the human tibia during walking (ca. -400 microstrain) and running (ca. +850 microstrain) are well below the fracture threshold. Yet, stress fractures occur with repeated high strain or stress loading, suggesting that momentary high strains or strain rates may occur during some vigorous activities. Human strains have never been monitored in vivo during vigor- ous activity, even though prolonged strenuous activity may be responsible for the occurrence of stress fractures. We hypoth- Address.for correspondence and reprints: David B. Burr, Ph.D., Depart- ment of Anatomy, MS 259, Indiana University School of Medicine 635 Barnhill Dr., Indianapolis, IN 46227. E-mail: dburr@indyvax.iupui.edu esized that strains >3000 microstrain could be produced on the human tibial midshaft during vigorous activity, and chose to measure strains under conditions similar to those experienced by Israeli infantry recruits who have a high incidence of tibial stress fractures. The primary goal of these preliminary experiments was to measure, on a limited number of subjects, strains produced during physical activities mimicking those done by Israeli infan- try recruits. Secondary objectives were to work out details of the strain gauging methodology for use on humans and to demon- strate the efficacy and safety of the strain gauging techniques on humans. Materials and Methods Measurement of strains on the human tibia were completed at the Hadassah University Hospital and Hebrew University in Jerusa- lem, on two members of the research team in May 1994. Two unstacked, 45 °, rosette strain gauges (Micromeasurements EA- 06-015-RJ-120, Measurements Group, Inc., Raleigh, NC) were bonded to the medial tibial cortex at midshaft and also 2 cm distal in two members of the research team (D.B.B., age 42, and C.M., age 49) under sterile surgical conditions. The area around the distal tibia was anesthetized by a local injection of 5 mL of 1% lidocaine and 7.5 mL of 0.25% Marcaine (Astra, Sobertalje, Sweden) to the skin, subcutaneous tissue, and periosteum of the tibia. A 5 cm longitudinal incision was made through the skin just posterior to the posteromedial border of the tibia. The skin was mobilized and the subcutaneous incision made directly over the medial border of the tibia. The periosteum was incised lon- gitudinally for 3 cm and elevated gently. Hemostasis of the tibia was achieved by using electrocautery and by applying Avitne (Medchem Products, Inc., Woburn, MA) to the bone's surface. When there was no evidence of bleeding, the tibia was cleaned and degreased with alcohol, and the bone surface was scored with a stainless-steel bone punch. Ethylene-oxide sterilized ro- sette strain gauges with 34 gauge wires (Phoenix Wire, Inc., South Hero, NH) soldered to their leads were attached using half of a dose pack of Howmedica polymethyl methacrylate (PMMA). PMMA was spread over the site where the gauges were to be mounted, and the strain gauges were applied with thumb pressure through a Teflon sheet for 10 min or until the PMMA had hardened. PMMA that extruded from beneath the gauge was trimmed. Bonding with PMMA provides strain mag- nitudes within 2% of those collected using cyanoacrylate-bonded © 1996 by Elsevier Science Inc. 405 8756-3282/96/$15.00 All rights reserved. PII $8756-3282(96)00028-2