JOT - 2026-07-16 - Journal Article
Is the use of retrospectively collected radiographic scores an accurate method to determine time to union? A retrospective clinical cohort.
Schlauch AM, Zakusylo A, Schaffer N, Mauffrey C, Hellwinkel JE, Ricci WM
Topics
Key Takeaway
Retrospectively determined radiographic time to union after tibial IMN overestimates predicted TTU by 34.2 days, with an IQR:median ratio of 0.9 indicating low accuracy.
Summary Depth
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Summary
This study evaluated whether retrospectively scored mRUST values from uncontrolled-interval radiographs accurately capture time to union (TTU) in tibial IMN patients. mRUST ≥12 defined union; IQR:median ratio quantified accuracy across 89 patients. Observed median TTU was 96 days (IQR:median 0.9, low accuracy), overestimating a cohort-derived predicted TTU of 61.8 days by 34.2 days; the interval between the last pre-union radiograph and confirmed union had an IQR:median of 1.1, the largest source of variability.
Key Limitation
The predicted TTU is derived from the same cohort's mRUST data rather than an independent prospective dataset, creating circularity in the accuracy comparison.
Original Abstract
OBJECTIVES
To evaluate the accuracy of time to union (TTU) in a cohort of patients after intramedullary nailing (IMN) of tibial shaft fractures where radiographic union was measured retrospectively with uncontrolled intervals between radiographs.
METHODS
Design: Retrospective cohort.
SETTING
A single Level I academic Trauma Center.
PATIENT SELECTION CRITERIA
Included were adult patients (18 years and older) treated with IMN for an acute tibial shaft fracture (OTA/AO 42A, 42B, 42C) between January 2020 to January 2025 with at least 6 week and 12-week post-operative radiographic evaluations. Patients who required a reoperation to promote union were excluded.
OUTCOME MEASURES AND COMPARISONS
The modified radiographic union scores for tibial fractures (mRUST) were determined at each post-operative radiographic follow-up. The observed TTU was defined as the days from IMN to radiographic union (defined as mRUST ≥ 12). Cohort median time intervals were determined for: the time from IMN to the radiograph immediately prior to union; the time between the radiograph prior to union and union, and the TTU. The inter-quartile range to median ratio (IQR:median) was calculated for these intervals to normalize the time interval ranges and was used to define accuracy. Accuracy was defined as follows: low accuracy =
IQR
median ≥0.5; moderate accuracy =
IQR
median 0.2-0.5; and high accuracy =
IQR
median ≤0.2. A predicted TTU for the cohort was calculated by considering all mRUST scores from the entire cohort over time to estimate the time at which 50% of the population would be expected to achieve radiographic union. This was a way to account for the changing nature of mRUST scores with time in between clinical visits. To determine if the observed TTU over- or underestimated the predicted TTU, the predicted TTU was compared to the observed TTU by taking the difference between the two.
RESULTS
89 patients with a mean age of 43.1 years (SD = 13.7 years) and 65.9% male were included. The median observed TTU was 96 days (mean 208.6, SD 363.8 days) with an
IQR
median of 0.9, indicating low accuracy. The median time from surgery to the radiograph immediately prior to union was 47 days (mean 58.7, SD 37.3 days) with an
IQR
median of 0.4 (moderate accuracy). The median time between the radiograph immediately prior to union and union was 49 days (mean 150, SD 358 days) with an
IQR
median of 1.1 (low accuracy). The predicted TTU was 61.8 days. The observed TTU over-estimated TTU by 34.2 days.
CONCLUSIONS
In patients treated with tibial IMN, retrospectively determining radiographic time to union (TTU) with uncontrolled interval radiographic evaluations was an inaccurate method to determine TTU. The observed TTU over-estimated a predicted TTU by 34.2 days. These findings highlight the inaccuracy of retrospectively determined TTU in orthopaedic clinical cohorts.
LEVEL OF EVIDENCE
Level III.