A. Diez-Perez, R. Güerri, X. Nogues, E. Caceres, M. Peña, L. Mellibovsky, P. Hansma

Bone mechanical properties at a tissue level are likely a key element of bone quality. Current techniques for the assessment of these properties require invasive bone sampling. We developed a minimally invasive microindentation technique suitable for use in clinics.Women with osteoporotic fracture and age-paired controls without fractures were measured. Secondary osteoporosis and treatment with bone acting drugs were exclusion criteria. The commercial (1) Bone Diagnostic Instrument (2,3) was positioned over the midpoint of the tibia with an adjustable arm that included an micropositioner. After anesthetizing the area, the head of the instrument was vertically placed until the probe penetrated the skin and soft tissue covering the bone. The operator scraped the periosteum and a measurement sequence was initiated (precycles to find the surface of the bone and 20 test cycles to a maximum force of order 11 N at 2 Hz as described previously (3)). Measurement was repeated 3 to 5 times. Sometimes 2 operators took measurements to check for operator effect. Data were processed by analysis software (1) and corrected to compensate for minor variations (± 7%) in the maximum force. Patients experienced minor discomfort only during local anesthesia. Indentation Distance Increase (IDI) Creep Indentation Distance (CreepID) First Indentation Distance (FirstID) and Total Indentation Distance (TotalID) were measured. A t-test was used to analyze cases vs. controls. ERB approval and written informed consent were obtained. Thirteen cases (eleven hip, two multiple vertebral) (age 80.6 (5.5)) and six controls (79.8 (7.9) yrs.) were measured. Results shown as mean (SD). Interobserver CV ranged from 8.7% (MIDI) to 21.3% (FirstID). Cases and controls showed statistically different (in microns) MIDI (19.98 (7.35) vs. 11.75 (0.73) p =0.0008) CreepID (6.65 (1.89) vs. 4.14 (0.76) p=0.0003) FirstID (36.9 (9.08) vs. 23.96 (3.83) p=0.0002) and TotalID (52.35 (12.26) vs. 33.48 (3.85) p=0.0001). Testing time was 10 minutes per case approximately.

We conclude that in vivo microindentation is a reproducible and convenient measure of bone tissue mechanical properties and performs well in discriminating fracture from non-fracture cases with suitable variability. This technique opens new possibilities of measuring bone strength at the tissue level in patients. Grant FIS 07/358

1. Active Life Technologies, Santa Barbara CA. 2. Rev Sci Instrum 2006;77:075105. 3. Rev Sci Instrum 2008;79:064303

Disclosures: None

Attachments

Microindentation in Fracture Cases and Controls