Technology Interventions to Improve Outcomes After Knee Replacement: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Technology Interventions to Improve Outcomes After Knee Replacement (NCT04482400), a randomized na study. The primary outcome is Objectively Measured (Actigraph) Sedentary Behavior at 2 Months.

2. Clinical Question

3. Trial Design

The registry record describes a randomized, single-masked, parallel-group study. Participants were assigned to either NEAT!2 or MyKneeGuide. Both groups had an app-based intervention and a coaching schedule: biweekly calls for 8 weeks, then monthly maintenance calls between months 2 and 5. This active comparison means that the primary contrast concerns the difference between two technology-supported approaches.

The recorded enrollment is 83. The posted primary outcome summaries include 41 participants in the NEAT!2 group and 38 in the MyKneeGuide group. These outcome counts need not represent every person enrolled; the registry record does not explain the relationship between enrollment, outcome availability, or analysis inclusion. The reasons for any difference in counts are not reported in the registry record.

The study status is completed. The recorded start date is 2020-08-01, and primary completion is recorded as 2024-10-25. The registry lists phase as NA. The purpose described in the record is to examine health outcomes after knee replacement, including physical activity, sedentary behavior, physical function, and pain at 2 and 5 months.

Randomization can help make groups comparable at the point of assignment, but it does not by itself establish that all later measurements are complete or that all analysis choices are unbiased. The registry record does not report the randomization method, allocation concealment details, the masking role, or whether masking was maintained. It also does not report the original sample-size justification or the trial’s planned statistical analysis strategy.

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

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 Objectively Measured (Actigraph) Sedentary Behavior at 2 Months, measured over 2 months.

The primary endpoint is objectively measured sedentary behavior at 2 months, reported as a mean in minutes per day. Actigraph accelerometers are used to measure movement, with sedentary behavior described as less than 100 counts per minute. An objective device-based measure can provide a standardized estimate of time spent at low activity, rather than relying only on participant recollection or judgment.

The endpoint is relevant to the stated study purpose because the interventions are intended to address sedentary time after knee replacement. The primary comparison asks whether the average measured sedentary behavior differs between the two randomized groups at the assessment. It is a continuous outcome: each participant’s measurement can take a range of values, and the group summaries are expressed as means and standard deviations.

The registry lists the primary timeframe as 2 months, while its endpoint description says sedentary behavior was measured with accelerometers between baseline and 3 months. Those descriptions are both retained in the record; the specific measurement schedule within that interval is not reported in the registry record. The reported outcome is a group-level summary and does not, on its own, describe every participant’s activity pattern or establish what caused any difference between groups.

7. Results Posted in the Registry

• MyKneeGuide: mean 638.24 versus 659.52 on control; difference -21.28 (95% CI -54.66 to 12.10), standardized effect d = -0.28; z-test p = 0.211.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Physical Function

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • MyKneeGuide: mean 1,340 versus 1,339 on control; difference 1.37 (95% CI -135.62 to 138.36), standardized effect d = 0.00; z-test p = 0.984.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between MyKneeGuide and the control. The interval gives the range of effects that remain compatible with the data.

WOMAC Pain Subscale

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • MyKneeGuide: mean 3.00 versus 3.05 on control; difference -0.05 (95% CI -1.49 to 1.39), standardized effect d = -0.02; z-test p = 0.946.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between MyKneeGuide and the control. The interval gives the range of effects that remain compatible with the data.

Total Physical Activity Measured by Actigraph Accelerometers

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • MyKneeGuide: mean 1,442 versus 1,532 on control; difference -90.33 (95% CI -308.44 to 127.78), standardized effect d = -0.18; z-test p = 0.417.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between MyKneeGuide and the control. The interval gives the range of effects that remain compatible with the data.

The registry lists secondary outcomes covering physical function, pain, activity measured by accelerometers, adherence to calls, use of the NEAT!2 app, responses to NEAT!2 prompts, and a chair stand test. Numerical group comparisons are posted for physical function, WOMAC pain, and total physical activity. The registry record does not report numerical results for the other listed measures in the information summarized for this analysis.

Across the posted secondary measures, the estimates do not show a clear and precise separation between the randomized groups. Their confidence intervals include zero, so the observed results remain compatible with differences in either direction. This broad pattern is consistent with the uncertainty in the primary comparison; it does not independently confirm a difference between the interventions or establish that the groups are equivalent.

Secondary outcomes can help describe whether an intervention comparison appears similar across related domains, and can identify questions for further study. Physical function and pain address patient-centered outcomes, while accelerometer-measured activity provides a behavioral measure related to sedentary time. Still, the secondary measures are distinct outcomes, assessed at their stated timepoints, and do not substitute for the primary endpoint.

Unadjusted secondary results carry less weight when multiple outcomes are examined because the chance of at least one apparently notable result can increase as testing expands. The registry record does not report a multiplicity strategy, a hierarchy of secondary hypotheses, or which secondary comparisons were prespecified for formal testing. Interpret individual secondary p-values cautiously, especially when considered apart from their confidence intervals and the overall study context.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Physical Function
• WOMAC Pain Subscale
• Total Physical Activity Measured by Actigraph Accelerometers
• Adherence to Calls
• Adherence to NEAT!2 App
• Response to NEAT!2 Prompts
• Physical Function Via Chair Stand Test

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is a continuous measure summarized by its mean and standard deviation in each randomized group. A mean describes the arithmetic average of the recorded measurements. A standard deviation describes how spread out individual measurements are around that average; it is not the same quantity as the uncertainty around the mean or the group difference.

What does the mean difference represent?

The reported contrast is the MyKneeGuide mean minus the NEAT!2 mean. A negative estimate therefore means that the observed average was lower in the MyKneeGuide group, while a positive estimate would mean it was higher. The estimate of -21.28 minutes per day is a difference between group averages, not a change within an individual participant. The registry record does not report a baseline-adjusted estimate for the primary endpoint.

What does the confidence interval add?

A confidence interval expresses the uncertainty around an estimated difference under the statistical method used. It gives a range of values that are compatible with the observed data and the method’s assumptions. It is not a range containing a known proportion of individual participants’ measurements, and it does not assign a probability to each possible true effect. When an interval includes zero, the data do not clearly distinguish a difference in one direction from no difference or a difference in the opposite direction.

How should the p-value be read?

The primary unadjusted p-value is 0.211. In general, a p-value measures how inconsistent the observed data are with a specified null model, assuming that model and the analysis assumptions hold. It does not quantify clinical importance, prove that the groups are equal, or account automatically for multiple outcomes. The registry record lists no reported analyses in its analysis field and does not describe the model behind the posted comparison. Consequently, details such as covariate adjustment, missing-data handling, or any prespecified testing hierarchy are not reported in the registry record.

The arm summaries and contrast are presented as means, standard deviations, and an unadjusted difference. The record does not state whether the primary comparison was prespecified in the same form as the displayed result, nor does it describe how departures from model assumptions were assessed. The p-value should therefore be interpreted alongside the estimated difference and its confidence interval, rather than in isolation.

Why do spread and sample size matter?

Greater variation among participants generally makes a group mean less precise, while more observations can improve precision. The standard deviations for the primary outcome are 75.7 in NEAT!2 and 75.56 in MyKneeGuide. The number of participants contributing to the displayed outcome is 41 and 38, respectively. These quantities help explain why an estimate can remain uncertain even when the group means differ. They do not reveal whether outcome data were missing or why the reported group counts differ from overall enrollment.

In general, over-dispersion means that observed variation is greater than a chosen statistical model expects. If present and not accommodated, it can make standard errors too small and confidence intervals too narrow. The registry record does not report a count model or an over-dispersion assessment for this continuous endpoint, so this concept is general statistical context, not a claim about the analysis used in the trial.

What can the planning illustrations tell readers?

The sample-size figures are planning illustrations based on fractions of the observed effect and the stated assumptions, not the trial’s original design calculations. They describe hypothetical participant requirements for specified power levels under those assumptions. They do not show the probability that the completed study detected an effect, and they do not replace the observed estimate and its confidence interval. The original design assumptions and sample-size justification are not reported in the registry record.

For secondary outcomes, the registry includes group means, standard deviations, and unadjusted differences for some measures. These descriptive contrasts can help readers see the direction and uncertainty of results across domains. Without reported adjustment for multiple testing or a declared analysis plan, isolated secondary p-values provide weaker evidence than a prespecified primary comparison and should be interpreted cautiously.

11. Confidence Intervals and Precision

The primary estimate is -21.28 minutes per day, with a confidence interval from -54.66 to 12.1 minutes per day. The interval crosses zero, so it includes both a negative difference and a positive difference. It therefore does not determine which group had lower average sedentary time in the underlying population. The point estimate is only one value within a substantially wider range of uncertainty.

Precision refers to how narrowly an estimate is determined by the data and method. A narrow confidence interval indicates greater precision; a wide interval indicates that a broader range of effects remains compatible with the results. The primary interval leaves room for differences in either direction, including values that could be meaningful or small. The registry record does not specify a threshold for a clinically important difference, so the interval cannot be judged against such a threshold from the posted information.

Confidence intervals are not predictions of what every participant experienced. The standard deviations describe variation among observed measurements, while the confidence interval describes uncertainty in the estimated group contrast. Keeping those concepts separate is important when interpreting an outcome with individual variability.

The secondary continuous outcomes also have intervals that cross zero. This pattern indicates uncertainty in the estimated contrasts rather than proof of equality. The registry record does not provide a formal equivalence or non-inferiority margin, and no conclusion of equivalence follows from a nonsignificant test alone. Precision is also limited by the outcome-specific numbers of observations and variability, while reasons for the reported counts and missingness are not reported in the registry record.

12. 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 illustrations report the number of participants per arm, not a total number across the study and not total events. They are based on a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect used for planning is the stated fraction of the observed effect: the full observed effect, 75% of the observed effect, or 50% of the observed effect. The trial’s original design assumptions and sample-size justification are not reported in the registry record.

The 80% power column describes the hypothetical number of participants per arm associated with an 80% chance of detecting the specified effect under the planning assumptions, if that effect and those assumptions held. The 90% power column describes the corresponding hypothetical number per arm for a 90% chance. These are planning concepts conditional on the assumed effect and analysis; they are not guarantees about a future study.

The rows illustrate that smaller effects require more participants to detect under the same assumptions. In this table, planning for 75% or 50% of the observed effect requires larger per-arm samples than planning for the full observed effect. This occurs because a smaller separation between group means is harder to distinguish from random variation.

These calculations are not observed power. They are not a retrospective measure of whether the completed trial was successful, and they do not change the interpretation of the confidence interval or the observed estimate. The displayed curve should be read in the same planning context: it reflects assumed effects and sample sizes rather than additional outcomes from participants.

13. 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 = -21.280; pooled standard deviation σ = 75.633.
2. n = 2 × (1.96 + 0.842)² × 75.633² / -21.280² = 198.3, rounded up to 199 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 <- -21.28                      # observed difference in means
sigma <- 75.6327596169327                     # 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(4482400)
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 = 199 (80% power), 266 (90% power)
 75% of observed effect: n per arm = 353 (80% power), 472 (90% power)
 50% of observed effect: n per arm = 794 (80% power), 1,062 (90% power)
power.t.test: 199.3 
Simulated power at n = 199 per arm: 0.802 (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.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome and multiple secondary outcomes, including measures of physical function, pain, physical activity, and adherence. When a study examines several outcomes, repeated testing can increase the chance of a statistically notable result arising by chance. A multiplicity plan may address this by specifying which outcomes are confirmatory, ordering tests, or adjusting the interpretation of results. Such a plan is not reported in the registry record.

The record also lists no reported analyses. It does not describe a prespecified statistical analysis plan, the model for the primary comparison, whether covariates were included, or how the analysis handled repeated measurements. Whether interim analyses were conducted is not reported in the registry record. These absences limit the ability to assess how closely the displayed comparisons follow a planned testing strategy.

Information about missing data is also not reported in the registry record. The primary outcome summaries include 41 participants in NEAT!2 and 38 in MyKneeGuide, while overall enrollment is recorded as 83. The record does not explain whether participants lacked measurements, were excluded from an analysis, or had data unavailable for another reason. It also does not describe imputation, sensitivity analyses, or assumptions about missingness.

The analysis population is not reported in the registry record. It is therefore unclear whether the estimates use all randomized participants, participants with observed measurements, or another defined group. The distinction matters because excluding participants after randomization can affect the comparability created by random assignment, depending on the reasons and patterns of exclusion. These unknowns do not invalidate the posted summaries, but they constrain how fully their analysis can be evaluated.

15. 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: gall bladder surgery (2.4%), coronary blockage (2.4%).

The registry reports serious adverse events for 1 participant at risk in NEAT!2 and 2 participants at risk in MyKneeGuide. It reports other adverse events for 16 participants at risk in NEAT!2 and 4 participants at risk in MyKneeGuide. Deaths are recorded as 0 in each group. The safety denominators are 42 for NEAT!2 and 41 for MyKneeGuide.

Gall bladder surgery and coronary blockage are each listed among the top serious adverse event terms, at 2.4%. These figures describe the posted event information; they do not establish that an event was caused by an intervention. The registry record does not provide further event-level detail, timing, severity beyond the serious-event classification, or an assessment of causal relationship in the information.

Safety counts should be read with their at-risk denominators and alongside the limited number of participants. They are descriptive, not a basis for determining comparative risk with precision. The safety counts also differ from the numbers contributing to the primary outcome, and the reason is not reported in the registry record.

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

The central result is an imprecise comparison of average sedentary time between NEAT!2 and MyKneeGuide at the primary assessment. The observed estimate is lower for MyKneeGuide, but its confidence interval includes zero and extends in both directions. The data therefore do not clearly establish a difference between the groups at that assessment.

This result does not prove that the interventions have identical effects. A failure to distinguish a difference statistically can occur when the true difference is small, when measurements vary considerably, or when the available data do not estimate the contrast precisely. The registry record does not report a predefined equivalence margin, so the result cannot be interpreted as evidence that the interventions are equivalent.

Nor does the comparison answer whether either approach is better than no technology intervention or usual care. Both randomized groups received an app-based approach and coaching calls. The contrast speaks to the relative outcomes of the two study arms as recorded, not to the effect of either intervention against an untreated comparison.

The secondary summaries offer additional context but remain uncertain and should not be elevated beyond their role in the overall evidence. The registry record does not report a complete analysis plan, missing-data methods, analysis populations, or multiplicity handling. Those omissions make the posted estimates useful for describing the recorded results, while limiting stronger claims about confirmatory evidence.

The findings are specific to the population, interventions, assessments, and follow-up described in the record. They do not establish longer-term effects, explain mechanisms, or show how every participant responded. No medical decision should be based on this statistical summary alone.

17. Why This Trial Matters Statistically

This trial is statistically informative because it makes an active comparison between two technology-supported approaches after knee replacement and uses an objective measure for its primary behavioral outcome. The comparison is aligned with a practical question about whether two different app-based programs and coaching schedules produce distinguishable average sedentary-time measurements.

The main statistical lesson is the importance of reading an effect estimate together with its confidence interval. A point estimate gives a direction and magnitude for the observed contrast, but the interval shows that the evidence remains compatible with effects in either direction. A p-value alone would not convey this range or the degree of imprecision.

The trial also illustrates why sample-size planning depends on the effect a study aims to detect. Planning illustrations based on smaller effects require more participants per arm. Those calculations are distinct from the trial’s own design justification, which is not reported in the registry record, and from retrospective claims about power.

Finally, the registry record underscores the value of complete reporting. Information on the analysis plan, missing data, analysis populations, and multiplicity would help readers understand the scope and robustness of the reported comparisons. The posted estimates still describe the outcome data, but fuller methods reporting would make their inferential interpretation more transparent.

18. 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 does not report the original sample-size justification, the planned statistical analysis strategy, or whether interim analyses were conducted. It also does not describe randomization procedures, allocation concealment, or the masking role. These gaps limit assessment of design and analysis choices beyond the broad randomized, single-masked, parallel-group description.

Outcome-specific counts are reported, but the reasons they differ from overall enrollment and from the safety denominators are not stated. The record does not report missing-data handling, participant flow, or the analysis population. As a result, it is not possible to determine from the posted information whether all randomized participants contributed to each comparison or how exclusions and unavailable measurements were addressed.

The primary timeframe is described as 2 months, while the measurement description refers to accelerometer data between baseline and 3 months. The record does not clarify the exact assessment window or how measurements within that period were summarized. It also does not report a clinically important threshold for the primary measure, making it difficult to interpret the practical importance of the estimated difference.

The study compares two active approaches, so it cannot isolate the effect of either app-and-coaching package relative to no intervention or usual care. Several secondary outcomes are listed, but their testing hierarchy and multiplicity handling are not reported. These limitations call for cautious interpretation of the posted statistical estimates rather than conclusions beyond the recorded comparison.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Technology Interventions to Improve Outcomes After Knee Replacement — NCT04482400.
• Registry record last updated 2026-03-27; status last verified 2026-03.
• Results first posted 2026-03-27.
• 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.

22. Record Summary

NCT04482400 is a completed randomized, single-masked, parallel-group study sponsored by the University of South Carolina. It enrolled 83 participants and compared NEAT!2 with MyKneeGuide after knee replacement. Both groups received an app-based intervention and a stated schedule of coaching and maintenance calls.

The primary endpoint was objectively measured sedentary behavior at 2 months, expressed as minutes per day. The posted mean difference for MyKneeGuide versus NEAT!2 was -21.28 minutes per day, with a confidence interval from -54.66 to 12.1 and an unadjusted p-value of 0.211. The interval includes zero, leaving substantial uncertainty about the direction and size of the group difference.

Numerical secondary comparisons are posted for physical function, WOMAC pain, and total physical activity. Important details about the analysis plan, missing data, and analysis populations are not reported in the registry record.