Radiation Therapy for Heterotopic Ossification Prophylaxis Acutely After Elbow Trauma: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Radiation Therapy for Heterotopic Ossification Prophylaxis Acutely After Elbow Trauma (NCT00991887), a randomized na study. The primary outcome is Mayo Elbow Performance Score.

2. Clinical Question

3. Trial Design

The registry record describes a randomized, double-blind, parallel-group trial of radiation therapy after elbow trauma. Enrollment is listed as 48. The record lists elbow fracture as the condition and identifies Wake Forest University Health Sciences as the sponsor. The phase is listed as not applicable.

Participants were assigned to radiation therapy or no radiation therapy after surgery. The intervention arm description specifies that radiotherapy would be administered no later than 72 hours postoperatively. The control arm description says participants would not receive radiation therapy after surgery. The registry record does not provide further detail about the radiation regimen, the surgical procedures, or how randomization was implemented.

The primary outcome was the Mayo Elbow Performance Score at six months. The reported arm summaries include 24 participants in the no-radiation group and 21 in the radiation group. The record does not explain why these outcome denominators differ from the enrollment figure, or whether that reflects missing measurements, exclusions, or another reason.

The study status is listed as terminated. The start is recorded as 2005-09 and primary completion as 2009-08. The reason for termination and the original planned study duration are not reported in the registry record. The record does not report the trial’s original sample-size justification, the planned analysis population, or a detailed statistical analysis plan. The listed design features establish the broad comparison, but do not identify how blinding was maintained or whether the primary outcome analysis followed the randomized assignment for every participant.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Patients with elbow trauma treated with radiation therapy in the prevention of post-traumatic heterotopic ossification. Subjects are randomized to either radiation therapy or no radiation therapy.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Mayo Elbow Performance Score, measured over 6 month.

The primary endpoint is the Mayo Elbow Performance Score at six months, reported as a mean with a standard deviation. The registry description says the score is based on a 100-point scale, with higher scores indicating better function. It assesses pain, stability, function, and motion, and classifies results as excellent, good, fair, or poor according to score ranges.

A functional score can provide a continuous summary of several aspects of elbow status. Reporting the mean allows comparison of the groups’ average scores, while the standard deviation describes the spread of individual scores around each group mean. These summaries do not show how many participants fell into each qualitative score category, nor do they give the distribution of scores or the proportion meeting a particular functional threshold. Those details are not reported in the registry record.

The endpoint measures function, not the registry’s hypothesized need for surgical excision of heterotopic ossification. Although the hypothesis mentions excision, the record lists only one outcome measure, the six-month score. Consequently, the posted endpoint directly addresses a between-group comparison of function at that time point; it does not establish the number of excisions or provide a direct estimate of that hypothesized outcome.

7. Results Posted in the Registry

• Radiation Therapy (XRT): mean 69.00 versus 66.00 on control; difference 3.00 (95% CI -9.28 to 15.28), standardized effect d = 0.14; z-test p = 0.632.

8. Statistical Interpretation

9. Statistical Methods Explained

The posted outcome is continuous: each participant’s Mayo Elbow Performance Score is a numerical value, and the group results are summarized by means and standard deviations. The comparison is the difference between the radiation group mean and the no-radiation group mean. The reported direction is radiation therapy compared with no radiation therapy, so a positive difference means the radiation group has the higher average score. Because higher scores indicate better function, the sign has that descriptive interpretation, without establishing a causal or clinical conclusion by itself.

What does a mean difference describe?

In general, a mean difference expresses how far apart two group averages are in the endpoint’s units. Here, the difference is reported as 3.0 units. It does not imply that every participant’s score changed by that amount, nor does it describe the spread of individual responses. Means can be useful for a group-level summary, but may conceal variation or differences in the shape of the score distributions. The registry record does not report individual scores or distributional summaries beyond the standard deviations.

Why report standard deviations?

In general, a standard deviation describes how dispersed observations are around their group mean. The posted standard deviations are 23.0 for no radiation therapy and 19.0 for radiation therapy. A standard deviation is not the same as a standard error: the former describes variation among participant scores, while the latter describes uncertainty in an estimated group mean. Standard deviations alone do not establish whether the score distributions are approximately symmetric or whether extreme values influence the means. Those distribution details are not reported in the registry record.

What does the confidence interval add?

In general, a confidence interval gives a range of values that are compatible with the observed data under the statistical model and its assumptions. The interval for the unadjusted mean difference extends from -9.276 to 15.28. Because it includes zero and values in both directions, the estimate is not precise enough to determine the direction of the mean difference from this comparison alone. A confidence interval is not a guarantee that the true value lies inside its particular endpoints, and it does not communicate the probability that the treatment effect is a particular value.

What does the p-value mean?

In general, a p-value measures how unusual data at least as inconsistent with a specified null hypothesis would be if that hypothesis and the test assumptions were true. The unadjusted p-value is 0.632. It is not the probability that the null hypothesis is true, and it does not measure the probability that the result arose “by chance.” It also does not quantify the clinical importance of the estimated difference. Interpretation should consider the estimate and confidence interval, not the p-value in isolation.

Why call this comparison unadjusted?

The reported comparison is an unadjusted recalculation from the posted summary statistics. It does not account for baseline characteristics, stratification variables, or other covariates. The registry record does not report an adjusted model, a sponsor-authored inferential analysis, or a detailed statistical plan. It is therefore not possible to confirm whether an adjusted analysis was planned or performed, or what methods it would have used. The unadjusted comparison answers a limited descriptive question about the recorded group summaries.

How do trial design features affect interpretation?

Random allocation is intended, in general, to make assigned groups comparable at the start of a trial, while blinding can reduce some forms of bias in treatment delivery or outcome assessment. The registry record lists randomized allocation and double masking, but does not explain the procedures used to implement either feature. The parallel design means the record describes separate groups rather than a within-participant comparison. These design labels are relevant context, but do not supply the missing details about enrollment, follow-up, analysis, or outcome availability.

Finally, the displayed planning calculations are illustrations based on the observed effect and stated assumptions, not the trial’s own design calculations. They should not be confused with the observed outcome comparison or used to infer what the trial was originally designed to detect. The original design assumptions and sample-size justification are not reported in the registry record.

10. Confidence Intervals and Precision

The estimated unadjusted mean difference is 3.0 units, with a 95% confidence interval from -9.276 to 15.28. The interval communicates substantial uncertainty about the size and direction of the difference. It includes zero, so the posted data are compatible with no mean difference, and it also includes values indicating lower or higher average scores in the radiation group. The interval does not isolate a narrow range around the estimate.

In general, the width of a confidence interval reflects both the amount of information in the data and variability in the outcome, together with the statistical method and its assumptions. The posted arm summaries have standard deviations of 23.0 and 19.0, and outcome counts of 24 and 21. The registry record does not report the missing-outcome process or whether the participants with posted scores represent all randomized participants. That context matters when assessing how broadly the interval can be interpreted.

The confidence interval is not a range containing every individual participant’s score, and it is not a prediction interval for a future participant. It concerns the group mean difference estimated under the comparison method. Nor does an interval that crosses zero prove that the groups are equivalent: an equivalence conclusion would require a prespecified equivalence margin and an analysis designed for that question. Such a margin and analysis are not reported in the registry record.

The point estimate should therefore be read alongside the interval rather than as a precise measure of the effect. The interval allows appreciable differences in either direction, so this comparison does not resolve whether the mean scores differ or how large any underlying difference may be.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. They use a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is set as the stated fraction of the observed effect. The displayed scenarios consider 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. For each scenario, separate columns give the participants per arm for 80% power and for 90% power.

In plain terms, the 80% power column gives the planning number per group under which the assumed effect would have an 80% chance of producing a statistically significant result under the planning model, if the assumed effect and other assumptions were correct. The 90% power column applies the corresponding higher target for detecting that assumed effect. The reported planning figures are 787 and 1,053 participants per arm for 100% of the observed effect; 1,399 and 1,872 for 75%; and 3,146 and 4,212 for 50%, respectively.

Smaller effects are harder to distinguish from random variation, so the planning calculations require more participants per arm as the assumed effect becomes smaller. These figures are illustrations based on the observed effect and the stated planning assumptions. They are not observed power. The registry record does not report the original sample-size justification or the assumptions used to plan the trial, so the illustrations should not be read as a reconstruction of that original design.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = 3.000; pooled standard deviation σ = 21.233.
2. n = 2 × (1.96 + 0.842)² × 21.233² / 3.000² = 786.4, rounded up to 787 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- 3                      # observed difference in means
sigma <- 21.2334751069221                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(991887)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 787 (80% power), 1,053 (90% power)
 75% of observed effect: n per arm = 1,399 (80% power), 1,872 (90% power)
 50% of observed effect: n per arm = 3,146 (80% power), 4,212 (90% power)
power.t.test: 787.4 
Simulated power at n = 787 per arm: 0.801 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry record lists one outcome measure, the six-month Mayo Elbow Performance Score, and reports no secondary outcomes. It does not report a multiplicity plan or explain whether additional outcomes were collected but not entered in the registry. With only the posted primary outcome available, the record does not allow assessment of how multiple endpoints or multiple analyses may have affected interpretation.

The record does not describe how missing outcome data were handled. It does not report whether participants without a six-month score were excluded, whether any values were imputed, or whether sensitivity analyses were performed. The enrollment figure is 48, whereas the endpoint summaries list 24 participants in the no-radiation group and 21 in the radiation group. The reason for this difference is not reported in the registry record. It would be inappropriate to assume that all participants were followed, that missingness was random, or that the posted groups include every randomized participant.

The analysis population is also not reported in the registry record. In particular, the record does not say whether the comparison followed intention-to-treat, per-protocol, or another population definition. It does not provide participant flow, exclusions after randomization, or reasons for any exclusions. These omissions limit the ability to evaluate whether the arm summaries preserve the randomized comparison.

The record lists randomized allocation and double masking but does not report a detailed statistical analysis plan. The planned handling of baseline imbalances, any interim analyses, and the multiplicity strategy are not reported in the registry record. The posted unadjusted recalculation should therefore be interpreted as a comparison of the recorded summary statistics, not as confirmation that a prespecified analysis was followed. The registry record also does not report how protocol deviations or outcome-assessment issues were addressed.

14. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 1% reporting threshold.

Most frequent non-serious adverse event terms

The registry record reports zero serious adverse events among 24 participants at risk in the no-radiation group and zero among 21 at risk in the radiation group. It also reports other adverse events among 4 participants at risk in the no-radiation group and 8 at risk in the radiation group. The record does not list serious adverse-event terms. Death counts are not reported in the registry record.

These are counts of affected participants as recorded, not a complete description of event type, timing, severity, or relationship to treatment. The record does not provide a comparative statistical analysis of the adverse-event counts, nor does it explain how adverse events were collected or defined. A count of zero serious adverse events in the posted data does not establish that no serious events occurred outside the recorded observation or reporting process.

The other-adverse-event counts should not be interpreted as proof of a treatment effect or as a measure of overall safety. Without details on event categories, follow-up, and missing safety data, the counts provide only a limited registry summary. The registry hypothesis referred to safe administration, but no separate inferential safety result is reported.

15. What the Result Does, and Does Not, Mean

The posted data describe a six-month functional outcome comparison between randomized groups. The mean Mayo Elbow Performance Score was 69.0 with radiation therapy and 66.0 with no radiation therapy; the unadjusted difference was 3.0 units. The 95% confidence interval, from -9.276 to 15.28, spans zero and values in both directions. The unadjusted p-value is 0.632. Taken together, the estimate is uncertain and does not establish a clear direction or precise magnitude for the difference in average scores.

This is not a finding of equivalence. The registry record does not report an equivalence margin or an equivalence analysis. Nor does the result show that the groups had identical outcomes: the observed means differ, while the confidence interval indicates uncertainty about the underlying difference. The score summarizes function across pain, stability, function, and motion, but the record does not provide component-level results or score-category counts.

The registry hypothesis also addressed the number of patients requiring surgical excision of heterotopic ossification. That outcome is not posted among the registry’s outcome measures, so the functional-score comparison cannot answer that question. The adverse-event summary provides counts but no statistical safety analysis, detailed event descriptions, or death counts. It is not a complete assessment of safety.

Interpretation is further limited by the absence of reported detail on missing data, analysis populations, the original sample-size justification, and the reason for termination. Those omissions mean the posted summaries cannot establish how fully the outcome data represent all randomized participants or whether the reported comparison matches the trial’s original analysis plan. The result should be read as an uncertain summary of the recorded six-month scores, not as a definitive conclusion about treatment efficacy or safety.

16. Why This Trial Matters Statistically

This trial is statistically instructive because it pairs a modest observed difference in group means with a confidence interval that spans a range of potentially important directions and sizes. The point estimate alone can appear straightforward, but the uncertainty interval makes clear that the data do not provide a precise estimate of the group difference. Interpreting the estimate and its precision together is more informative than treating a p-value as a verdict.

The record also illustrates why the target outcome matters. The stated hypothesis concerned both safe acute administration and reducing the need for surgical excision, while the only posted outcome measure is a functional score at six months. The outcome available for statistical interpretation does not directly measure every part of the research question. This distinction prevents an endpoint result from being stretched to answer an unreported clinical outcome.

Another important issue is the gap between enrollment and the reported endpoint denominators. Without participant-flow information or a missing-data explanation, readers cannot determine how the available scores relate to the randomized groups as a whole. Randomization is valuable, but interpreting its benefits requires knowing how participants were handled after assignment and which participants contributed to the analysis.

Finally, the planning illustrations show how sample-size requirements depend on the assumed effect and power target, but they are not evidence about the trial’s actual design rationale. The original design assumptions are not reported. Separating such planning calculations from observed results helps avoid confusing a hypothetical future study design with the evidence generated by this trial.

17. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The registry record lists the trial as terminated, but does not give a reason. It does not report whether termination affected recruitment, follow-up, or outcome collection. Enrollment is listed as 48, while the primary outcome summaries include 24 participants in the no-radiation group and 21 in the radiation group. The record does not explain this discrepancy, and no participant-flow account is available in the registry record.

The intervention description states that radiation therapy was to be given no later than 72 hours postoperatively, but the radiation dose, delivery details, and treatment adherence are not reported in the registry record. Further details about surgical care and outcome assessment are also not reported. Although the design is listed as double-blind, the record does not identify who was masked or how masking was maintained.

The six-month Mayo Elbow Performance Score is the only posted outcome measure. The registry hypothesis referred to surgical excision of heterotopic ossification, but no such outcome result is reported. The record does not provide component scores, score categories, baseline scores, or longer-term outcome summaries. It also does not report a detailed analysis plan, missing-data methods, analysis population, or sponsor-authored inferential analysis.

Safety information is limited to serious and other adverse-event counts. Event descriptions for serious events are absent, deaths are not reported in the registry record, and the method and duration of safety surveillance are not described. Taken together, these omissions constrain interpretation of the functional comparison and prevent a complete assessment of the broader hypothesis and safety context.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Radiation Therapy for Heterotopic Ossification Prophylaxis Acutely After Elbow Trauma — NCT00991887.
• Registry record last updated 2022-04-21; status last verified 2017-09.
• Results first posted 2017-09-21.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

21. Record Summary

NCT00991887 is a randomized, double-blind, parallel-group trial sponsored by Wake Forest University Health Sciences. It compares radiation therapy administered no later than 72 hours after surgery with no radiation therapy after surgery in patients with elbow trauma. The registry lists elbow fracture as the condition, enrollment of 48, and a terminated status.

The only posted outcome measure is the Mayo Elbow Performance Score at six months. The mean was 66.0 in the no-radiation group and 69.0 in the radiation group; the unadjusted mean difference was 3.0, with a 95% confidence interval from -9.276 to 15.28 and an unadjusted p-value of 0.632. The interval is compatible with differences in either direction and does not provide a precise estimate. The registry record does not report the reason for termination, the original sample-size justification, missing-data methods, or a result for surgical excision of heterotopic ossification.