JBJS

Of Mice and Men: Temporal Comparison of Femoral Shaft Fracture Healing After Intramedullary Nailing: Retrospective Observational Study of Modified Radiographic Union Scores for Tibia

J Bone Joint Surg Am. 2025 Jul 10;107(16):1841-1847. doi: 10.2106/JBJS.24.01304.

ABSTRACT

BACKGROUND: Researchers employ murine fracture models to study bone healing, but the temporal relationship between mouse and human fracture healing is poorly understood. The hypothesis of this study was that it was possible to quantify specific post-fracture time frames corresponding to the stages of endochondral ossification in both mice and humans.

METHODS: Radiographs of mice and human femoral fractures treated with intramedullary stabilization were reviewed. The study included 330 human femoral fractures (OTA/AO 32A, B, or C injuries) that ultimately healed without complications in patients aged 18 to 55 years and 309 surgically created midshaft femoral fractures in 3-month-old C57BL6/J mice. Multiple orthopaedic surgeons assessed the radiographs using the Modified Radiographic Union Score for Tibia (mRUST). A 4-parameter log-logistic curve was fit to describe fracture healing over time, with 3 parameters allowed to vary: Y∞ (mRUST score at time = ∞), k (healing rate in [1/log(time)]), and X0.5 (time to half-healing).

RESULTS: The values (and 95% confidence interval) for the mice were Y∞ = 14.70 (14.54 to 14.87), k = 4.54/log(days) (4.30 to 4.77), and X0.5 = 11.77 days (11.56 to 11.98). For the humans, the values were Y∞ = 16.78 (16.21 to 17.36), k = 1.37/log(days) (1.28 to 1.45), and X0.5 = 91 days (83 to 99). All parameters differed significantly between the mice and humans (p < 0.05).

CONCLUSIONS: Using mRUST scoring and mathematical modeling, we were able to quantify and compare the temporal progression of fracture healing in mice and humans.

CLINICAL RELEVANCE: These data are relevant for designing and/or interpreting fracture healing studies of mice and humans to promote rational translation of fracture research between species.

PMID:40833385 | PMC:PMC12344732 | DOI:10.2106/JBJS.24.01304

The Future Is Mobile: Pilot Validation Study of Apple Health Metrics in Orthopaedic Trauma

J Bone Joint Surg Am. 2025 Jun 4;107(16):1825-1832. doi: 10.2106/JBJS.24.00842.

ABSTRACT

BACKGROUND: Surgeons often lack objective data on patient functional outcomes, particularly as compared with the patient's baseline. The present study aimed to determine whether gait parameters recorded on Apple iPhones provided longitudinal mobility data following lower-extremity fracture surgery that matched clinical expectations. We hypothesized that iPhones would detect the mobility changes of injury and early recovery, correlate with patient-reported outcome measures, and differentiate nonunion.

METHODS: This cross-sectional study included 107 adult patients with lower-extremity fractures who owned iPhones and had at least 6 months of follow-up. Participants shared Apple Health data and completed Patient Reported Outcomes Measurement Information System (PROMIS) surveys. The primary outcome was the daily step count. Four other gait-related parameters were analyzed: walking asymmetry, double support, walking speed, and step length. Mixed-effects models compared mobility parameters at pre-injury, immediate post-injury, and 6-months post-injury time points. Correlations between mobility parameters and PROMIS surveys were assessed. A mixed-effect model evaluated the relationship between step count recovery and surgery for nonunion.

RESULTS: There was a 93% reduction in daily step count from the pre-injury period to the immediate post-injury period (95% confidence interval [CI], -94% to -93%). Other gait parameters also showed increased impairment from pre-injury to post-injury. At 6 months, step count improved sixfold relative to the immediate post-injury period but remained 52% below baseline (95% CI, -55% to -49%). PROMIS Physical Function correlated moderately with step count (r = 0.42; 95% CI, 0.25 to 0.57) and weakly with other gait parameters. Patients with a known nonunion had a 55% slower recovery of step count than those without a nonunion (95% CI: 44% to 66%).

CONCLUSIONS: Apple Health mobility parameters captured changes in mobility following lower-extremity fracture and throughout the subsequent recovery period. These metrics distinguished between patients with and without nonunions, demonstrating their potential usefulness as objective, real-world functional outcome measures. These "digital biomarkers" may aid clinical decision-making and research and could be utilized for the early identification of patients at risk for poor outcomes.

LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

PMID:40833368 | PMC:PMC12354133 | DOI:10.2106/JBJS.24.00842

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