Table 1.

Bone Strain Index reproducibility and clinical studies.

Topic	Author	Year	Patients no.	Main findings
In vivo reproducibility	Messina et al.	2020	30	BSI in vivo reproducibility of Total Femur (CoV = 3.89%, reproducibility = 89.22%) was better compared to that of Femur Neck (CoV = 4.17%, reproducibility = 88.46%).
Prediction of vertebral re-fracture (multicentric retrospective study)	Messina et al.	2020	234	BSI hazard ratio (95% CI) of incident re-fracture for each unit increase was 1.372 (1.038–1.813), p-value = 0.0261, proportionality test p-value: 0.5179.
Bone geometry and structural indexes in Mastocytosis (retrospective study)	Ulivieri et al.	2020	96	Tryptase showed a statistically inverse correlation with Lumbar Spine BMD (r = −0.2326; p = 0.0226) and with TBS (r = −0.2801; p = 0.0057) and a direct correlation with Lumbar BSI (r = 0.2759; p = 0.0065). In the multivariate regression model only the Lumbar BSI remained statistically significant in systemic Mastocytosis (p = 0.0064) and non-systemic Mastocytosis (p = 0.0338).
Prediction of vertebral re-fracture (multicentric retrospective study)	Ulivieri et al.	2020	143	The hazard ratio of re-fracture for each unit increase of BSI, BMD and TBS were, respectively, 1.201, 0.231, and 0.034. BSI resulted in being the nearest to the statistical significance to predict a re-fracture, with greater values associated with higher re-fracture risk.
DXA parameters response to Teriparatide (retrospective study)	Messina et al.	2020	40	In the entire population, the ameliorations after therapy regarded BSI (-13.9%), TBS (5.08%), BMD (8.36%). Significant HSA variations were shown only at the femoral shaft, but of very small entity [FS_BMD (0.23%), FS_CSA (−0.98%), FS_SEC_MOD (−2.33%) and FS_BR (1.62%)].
In vivo reproducibility	Messina et al.	2020	150	BSI best reproducibility value was observed in the group with BMI between 25 and 30 kg/m2 (CoV 1.97%, reproducibility 94.5%), while the worst was in the group with BMI > 30 kg/m2 (CoV 3.96%, reproducibility 89.0%). BSI reproducibility progressively worsened from lower BMI to higher BMI, but the amount of this reduction was never statistically significant.
In vitro reproducibility and soft tissue thickness influence	Messina et al.	2019	Phantom based study	The highest value of BSI reproducibility was 98.3% (1-cm soft tissue thickness, HD-mode), whereas the lowest one was 96.1% (6 cm soft tissue thickness, HD-mode). Variations between scans with superimposed 0–6 cm thickness of soft tissue were between 0.76% and 1.46% for BMD, and between 1.03% and 1.57% for BSI.
DXA derived parameters in haemophilic patients (retrospective study)	Ulivieri et al.	2018	70	A reduced bone mass was present at the femoral neck in 55.7%, at total femur in 18.6%and at the lumbar spine in 54.3% of patients. Lumbar spine BMD, TBS and lumbar BSI did not correlate with HJHS (Hemophilia Joint Health Score). HSA bone geometric parameters correlated negatively with HJHS.
Clinical observational retrospective study	Ulivieri et al.	2018	125	A low fracture risk seems to be related to a low carboxy-terminal cross-linking telopeptide of type I collagen level. In contrast, a positive Romberg test, together with compromised BSI, appears to be strictly connected with fragility fractures characterizing the pathway leading to fracture in postmenopausal women.