Immediate Weight Bearing Versus Protected Weight Bearing in Supracondylar Distal Femur Fractures: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Immediate Weight Bearing Versus Protected Weight Bearing in Supracondylar Distal Femur Fractures (NCT03167099), a randomized na study. The primary outcome is Time to Distal Femur Fracture Healing by Radiographic Evidence.

2. Clinical Question

3. Trial Design

This was a prospective, randomized study with a parallel-group design and no masking. The registry record lists the study as completed and identifies West Virginia University as the sponsor. The listed phase is NA. Enrollment was 53. The record gives a start date of 2015-04 and a primary completion date of 2018-10.

Participants were assigned to full or partial weight bearing following fixation of a distal femur fracture. The brief summary describes the full-weight-bearing approach as immediate weight bearing on a fracture fixed with a primary locking plate, either a distal condylar locking plate or a LISS. The comparator arm description identifies partial weight bearing as standard of care. Further details about how assignment was generated or concealed are not reported in the registry record.

The primary outcome was time to radiographic evidence of fracture healing, reported as a mean with a standard deviation. Its stated timeframe was up to 12 weeks. Radiographs were assessed for bridging of 3 or 4 cortices during follow-up office visits. The record also lists time to ambulation and time of participation in physical therapy as secondary outcomes. Although 16 outcome measures are listed, results for only 2 secondary outcomes are identified as posted. Detailed results for those secondary outcomes are not included in the record details.

The registry record lists no analysis entries, while it does post group summaries and a comparison for the primary outcome. The trial’s original sample-size rationale, full statistical analysis plan, allocation procedures, and any interim analyses are not reported in the registry record. The planning illustrations associated with the posted comparison are separate from the trial’s own design assumptions.

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

Analysis population for the primary outcome, as defined in the registry: Radiographic evidence not available for 4 subjects in each arm.

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 Time to Distal Femur Fracture Healing by Radiographic Evidence, measured over up to 12 weeks.

The primary endpoint is time to distal femur fracture healing by radiographic evidence. It is a continuous measure expressed in months, and the registry record reports a mean and standard deviation for each arm. The stated observation timeframe was up to 12 weeks. At follow-up office visits, radiographs were assessed for bridging of 3 or 4 cortices, as described in the record.

Time to radiographic healing provides a way to describe how long participants took to reach a defined imaging finding. Using a continuous time measure retains information about the timing of healing rather than reducing the result to a simple healed-or-not-healed category at one assessment. That general advantage depends on the outcome being assessed consistently and on the follow-up information being sufficiently complete. Details about radiograph assessment procedures, assessor blinding, and how time was assigned when visits did not coincide with healing are not reported in the registry record.

The reported mean was 1.75 months in the full-weight-bearing group and 2.15 months in the partial-weight-bearing group. The comparison is presented as partial minus full weight bearing, yielding a mean difference of 0.4 months. These summaries describe the participants with posted radiographic outcome data; the record notes that radiographic evidence was unavailable for 4 subjects in each arm. The endpoint is an imaging-based measure and should not be taken to represent every aspect of recovery or function. The registry record separately lists time to ambulation and time of participation in physical therapy as secondary outcomes.

7. Results Posted in the Registry

• Partial Weight Bearing: mean 2.15 versus 1.75 on control; difference 0.40 (95% CI -0.04 to 0.84), standardized effect d = 0.52; z-test p = 0.076.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is continuous: each observation is a time to radiographic fracture healing, expressed in months. A mean summarizes the center of a group’s observed values, while a standard deviation describes their spread around the mean. These answer different questions. A mean difference compares the group averages; it does not describe every participant’s course or the full shape of the outcome distribution.

The comparison is oriented as partial weight bearing minus full weight bearing. In the posted results, the group means are 2.15 and 1.75 months, respectively, and the mean difference is 0.4 months. A positive value under this orientation means the partial-weight-bearing group’s mean was larger. Keeping the contrast direction explicit is important: reversing the subtraction would reverse the sign, without changing the underlying group means.

A confidence interval gives a range of values reasonably compatible with the data under the statistical method used. In general, a narrower interval indicates greater precision, while a wider interval leaves more uncertainty about the size and direction of the effect. The interval for this comparison includes values below and above zero. Zero represents no mean difference under the stated contrast. That span means the posted data do not pin down the direction of the underlying mean difference with high precision. A confidence interval is not a guarantee that the true effect lies within its limits, nor does it show the probability that a particular effect is true.

The unadjusted p-value is 0.076. In general, a p-value describes how unusual data at least as inconsistent with a null hypothesis would be if that null hypothesis and the test’s assumptions held. It is not the probability that the null hypothesis is true, and it does not measure the clinical importance of an effect. The record calls this value unadjusted; it does not report whether the trial’s own analysis included other adjustments, what test was prespecified, or what threshold was intended for primary inference. The 0.05 significance level listed for planning illustrations should not be mistaken for a reported trial analysis rule.

Means and standard deviations are commonly used to describe continuous outcomes, but interpretation can depend on the distribution of the data and the analysis method. General statistical practice may use methods that account for skewness or other departures from assumptions. The registry record does not report the distribution of healing times, diagnostic checks, or a detailed analysis method, so no claim can be made about whether such issues were assessed. The posted comparison should be understood using the information actually recorded rather than an assumed model.

Random allocation is intended, in general, to make comparison groups similar on average with respect to both measured and unmeasured characteristics. It does not ensure identical groups, particularly in a small trial. The record identifies the design as randomized, but details of sequence generation, concealment, stratification, and implementation are not reported in the registry record. No masking was used. That fact may be relevant to care and outcome assessment, but the record does not say whether radiograph readers or other assessors were masked.

Missing outcome data also affect interpretation. Radiographic evidence was unavailable for 4 subjects in each arm. Equal counts of missing evidence do not, by themselves, establish that the missingness has no effect on the comparison. In general, bias can arise if outcome availability is related to the outcome or differs in relevant ways between participants with and without measurements. The reasons for missing evidence and the handling of those cases are not reported in the registry record. The participant counts attached to the primary outcome are 22 and 23; the record does not state a fuller analysis population definition.

There are 16 listed outcome measures, and the record identifies 2 posted secondary outcomes. Testing multiple outcomes can raise a multiplicity question: when many hypotheses are examined, the chance of at least one small p-value can increase. Statistical approaches to multiplicity depend on the prespecified outcome hierarchy and analysis plan. Those details are not reported in the registry record, so it is not possible to determine how secondary outcomes or multiple analyses were intended to be handled. The multiplicity concern does not change the numerical primary comparison, but it limits what can be inferred from a selective set of reported results.

The sample-size illustrations are planning calculations based on the observed effect, rather than a report of the trial’s original design. Their stated assumptions are a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation, with the effect to detect set to a stated fraction of the observed effect. In general, such calculations estimate the participants needed under those assumptions to have a specified chance of detecting an effect of the chosen size if it exists. They do not show the probability that this completed study detected its true effect. The original sample-size justification and any trial-specific planning assumptions are not reported in the registry record.

10. Confidence Intervals and Precision

The estimated mean difference is 0.4 months, with partial weight bearing minus full weight bearing as the direction of comparison. The confidence interval extends from below zero to above zero. It therefore allows for a range of possibilities that includes no mean difference, as well as a difference in either direction. The interval is the most direct posted indication of uncertainty around the estimated contrast.

The unadjusted p-value is 0.076. A p-value and a confidence interval are related summaries, but they do not answer exactly the same question: the interval conveys a range of effect sizes compatible with the analysis, while the p-value summarizes compatibility with a particular null hypothesis under the test assumptions. Neither quantity describes the clinical importance of the observed difference. The record does not report the trial’s prespecified statistical decision threshold or detailed inferential method.

The observed group standard deviations were 0.63 months and 0.87 months. These indicate that individual healing times varied around their respective group means. The participant counts contributing to the reported summaries were 22 for full weight bearing and 23 for partial weight bearing. The record also notes unavailable radiographic evidence for 4 subjects in each arm. These counts and the missing measurements are relevant context for judging how much information underlies the estimate.

Precision is not the same as validity. A confidence interval can quantify sampling uncertainty under an analysis while leaving unanswered questions about missing outcomes, measurement, or analysis choices. Here, the interval does not tightly identify a single direction or magnitude, and the registry record does not document enough analysis detail to resolve all those other uncertainties. The result is best read as an estimate with substantial room for uncertainty, rather than as proof of no difference or proof of a difference.

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 sample-size figures are planning illustrations based on the observed effect, not the trial’s original design assumptions. For this continuous-outcome comparison, the figures are participants per arm, not total events. The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect used for each illustration is a stated fraction of the observed effect.

The 80% power column gives the number of participants per arm that the planning calculation indicates would be needed to have an 80% chance of detecting the chosen effect under those assumptions, if that effect were present. The 90% power column uses a higher target chance of detecting the chosen effect, and therefore gives a larger planning requirement. These are conditional planning quantities, not guarantees about a future study’s result.

The rows consider planning for 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. As the target effect becomes smaller, the calculations require more participants per arm to detect it at the same power target. This is a general feature of planning for smaller differences: they are harder to distinguish from random variation, all else being equal.

For example, planning for 100% of the observed effect corresponds to 58 participants per arm for 80% power and 77 for 90% power. Planning for 75% corresponds to 102 and 136, and planning for 50% corresponds to 229 and 306, respectively. These calculations are not observed power for the completed trial. The registry record does not report the trial’s original sample-size justification or its own design assumptions.

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 = 0.400; pooled standard deviation σ = 0.762.
2. n = 2 × (1.96 + 0.842)² × 0.762² / 0.400² = 57.0, rounded up to 58 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 <- 0.4                      # observed difference in means
sigma <- 0.762290001581831                     # 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(3167099)
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 = 58 (80% power), 77 (90% power)
 75% of observed effect: n per arm = 102 (80% power), 136 (90% power)
 50% of observed effect: n per arm = 229 (80% power), 306 (90% power)
power.t.test: 58 
Simulated power at n = 58 per arm: 0.799 (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 16 outcome measures and identifies 2 posted secondary outcomes. The primary endpoint is time to radiographic healing. Having multiple outcomes can be useful when a trial examines several aspects of recovery, but it also raises the question of how the analyses were prioritized and whether any adjustment for multiple testing was planned. The registry record does not report a multiplicity strategy, a detailed hierarchy of outcomes, or the analysis plan needed to evaluate those choices.

The primary comparison is described with an unadjusted p-value of 0.076. The record does not explain what, if any, adjustments were made elsewhere in the analysis, or whether this is the prespecified primary analysis. A single unadjusted p-value should not be treated as if it accounts for all outcomes or analyses. Nor can it be determined from the record whether the posted outcome results represent all analyses that were planned.

Radiographic evidence was unavailable for 4 subjects in each arm. The record does not state why these measurements were unavailable, whether the absences occurred for similar reasons, or how missing outcomes were treated in the primary comparison. In general, missingness can affect a result if participants without outcome measurements differ in relevant ways from those with measurements. Equal numbers missing in each arm do not demonstrate that the groups’ missing outcomes are comparable.

The primary outcome summaries include 22 participants in the full-weight-bearing arm and 23 in the partial-weight-bearing arm. The record does not specify whether the analysis was intention-to-treat, per protocol, or based on another population definition. It also does not describe imputation, sensitivity analyses, or procedures for handling incomplete follow-up. Those details are not reported in the registry record.

Consequently, the posted estimate can be described, but the extent to which it is robust to missing data or multiplicity cannot be determined from the record. The absence of analysis details should not be filled in by assuming a particular approach.

14. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: failure of fixation (3.8%), fracture from fall (3.8%), nonunion (3.7%), fall unknown source (3.7%).

The registry record reports serious adverse events for 2 of 26 participants at risk in the full-weight-bearing arm and 2 of 27 at risk in the partial-weight-bearing arm. It reports other adverse events for 0 of 26 at risk in the full-weight-bearing arm and 1 of 27 at risk in the partial-weight-bearing arm. These are descriptive counts and denominators as recorded; they do not by themselves establish whether an event was caused by the assigned weight-bearing approach.

Deaths are reported as 3 in the full-weight-bearing group and 7 in the partial-weight-bearing group. The record does not provide enough detail to interpret causes, timing, relationship to treatment, or whether the deaths overlap with reported adverse-event categories. The counts should therefore be presented as registry safety information without attributing them to the intervention.

Serious-event terms listed among the leading terms include Failure of Fixation and Fracture from fall, each reported as 3.8%, and Nonunion and Fall unknown source, each reported as 3.7%. The record does not provide arm-specific counts for these terms in the information available for this comparison. Adverse-event summaries are not a substitute for the primary healing-time analysis, and these data alone do not establish a safety difference between groups.

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

The posted primary result describes mean time to radiographic fracture healing of 1.75 months with full weight bearing and 2.15 months with partial weight bearing. The mean difference, calculated in the stated direction of partial minus full weight bearing, is 0.4 months. The group means therefore place the partial-weight-bearing mean later, but the confidence interval spans values on both sides of no difference. The estimate is not sufficiently precise to establish a clear direction or magnitude of the underlying contrast.

This result does not establish that the approaches are equivalent. Showing equivalence or noninferiority generally requires a prospectively stated margin and an analysis designed to test that claim. Such a margin and analysis plan are not reported in the registry record. Conversely, the observed difference alone does not establish that one approach produces faster healing in a broader population. Randomized assignment supports a comparative design, but the posted evidence still has uncertainty and incomplete outcome information.

The endpoint is radiographic healing, not a complete measure of recovery. The record lists time to ambulation and time of participation in physical therapy as secondary outcomes, but detailed secondary results are not included in the information. The primary result therefore does not answer every question about function, rehabilitation, or the experience of participants.

The record reports serious adverse events, other adverse events, and deaths, but these counts should not be interpreted as causal treatment effects without further detail. The registry information does not establish that weight-bearing assignment caused or prevented any particular event. Taken together, the posted results allow a careful description of the observed group summaries and their uncertainty; they do not support a broad claim about effectiveness or safety.

16. Why This Trial Matters Statistically

This trial addresses a statistical question that arises when comparing two post-operative care strategies: whether the average time to an imaging-defined outcome differs between randomized groups. Its parallel randomized design provides a framework for comparing full and partial weight bearing while reducing, in general, the risk that treatment choice alone reflects patient characteristics. The record identifies randomization but does not provide the procedures used to implement it.

The central statistical lesson is the distinction between the observed estimate and its precision. The observed mean difference is 0.4 months, but its confidence interval extends on both sides of zero. Reporting only the two group means would conceal this uncertainty; reporting only a p-value would also provide an incomplete account of the likely range of effects. The group standard deviations add context about variation in healing times, while the interval focuses on uncertainty in the mean contrast.

The trial also illustrates why incomplete outcomes and analysis transparency matter. Radiographic evidence was unavailable for 4 subjects in each arm, and the registry record does not explain the reasons or analysis handling. With a continuous endpoint based on follow-up imaging, the pattern of missing assessments can affect how confidently the posted comparison is interpreted. The absence of a reported analysis plan also limits conclusions about prespecification, multiplicity, and analysis populations.

Finally, planning illustrations based on the observed effect are not evidence of the completed study’s power. They show how planning requirements change when the target effect is smaller, under stated assumptions. Separating those illustrations from the trial’s own unreported design assumptions helps prevent a retrospective calculation from being mistaken for a prospective justification. The record is useful for seeing how estimate, uncertainty, missingness, and planning assumptions each contribute to statistical interpretation.

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 primary endpoint has missing radiographic evidence for 4 subjects in each arm. The reasons for the missing evidence and its handling in the analysis are not reported in the registry record. This leaves uncertainty about whether the posted means represent a comparable outcome population and whether missingness could influence the estimate.

The registry record does not report detailed methods for random-sequence generation, allocation concealment, radiograph assessment, or masking of outcome assessors. The study itself is listed as unmasked. It is not possible to determine from the record whether imaging assessment was protected from knowledge of assigned group.

The record lists 16 outcome measures, but identifies 2 posted secondary outcomes and provides no detailed multiplicity plan or complete statistical analysis plan. It also does not define the analysis population or describe sensitivity analyses. These omissions limit assessment of prespecification and robustness.

The primary outcome is measured by radiographic bridging of 3 or 4 cortices during follow-up office visits, with a timeframe of up to 12 weeks. The record does not specify how the time of healing was assigned between visits or provide further details about measurement procedures. The posted result therefore cannot answer questions about all dimensions of recovery, and the secondary outcomes are not detailed in the information.

The sample-size rationale for the trial, recruitment and eligibility details beyond the stated condition, and any interim analyses are not reported in the registry record. The enrollment figure and posted outcome summaries are not a substitute for those design details. The result should be interpreted as a limited registry comparison, with uncertainty about missing data, analysis choices, and outcome assessment.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Immediate Weight Bearing Versus Protected Weight Bearing in Supracondylar Distal Femur Fractures — NCT03167099.
• Registry record last updated 2022-08-05; status last verified 2022-06.
• Results first posted 2022-08-05.
• 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

NCT03167099 is a completed prospective randomized parallel-group study sponsored by West Virginia University. It compared full with partial weight bearing after fixation of closed supracondylar distal femur fractures. The study was unmasked, and enrollment was 53.

The primary endpoint was time to distal femur fracture healing by radiographic evidence, measured in months over a timeframe of up to 12 weeks. Mean healing time was 1.75 months in the full-weight-bearing group and 2.15 months in the partial-weight-bearing group. The posted mean difference was 0.4 months, with an unadjusted p-value of 0.076 and a confidence interval spanning zero. Radiographic evidence was unavailable for 4 subjects in each arm.

The record also lists time to ambulation and time of participation in physical therapy as secondary outcomes. Detailed statistical methods, the trial’s original sample-size rationale, missing-data handling, and a multiplicity plan are not reported in the registry record. The primary comparison is therefore best read as an estimate with substantial uncertainty and limitations in the available analysis detail.