Observational Examination of Thermoregulation in Total Joint Arthroplasty: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Observational Examination of Thermoregulation in Total Joint Arthroplasty (NCT02225743), a registered phase not stated study. The primary outcome is Incidence of Hypothermia.

2. Clinical Question

The study addresses the timing and course of temperature change during total joint arthroplasty. Its stated motivation is that hypothermia has been associated with increased infection risk and blood loss, while prior studies had not examined when during the operation temperatures change or how quickly they drop. The examination was intended to describe those temperature patterns and identify when changes occur, with the possibility that such information could inform prevention strategies. That motivation is not itself a study finding: the posted record does not provide temperature trajectories, the number of participants who met the hypothermia definition, or an estimate of the timing or rate of temperature change.

This is a descriptive clinical question rather than a randomized treatment-effect question. Temperature was observed during the perioperative period; the registry does not identify a randomized allocation or a comparison group suitable for estimating a causal effect. Accordingly, the key statistical quantity would be the proportion of observed participants who met the stated definition, alongside information about the completeness and timing of their measurements. Those outcome data and details about how missing measurements were handled are not reported in the registry record.

3. Trial Design

NCT02225743 is titled Observational Examination of Thermoregulation in Total Joint Arthroplasty. The registry lists the study as completed, with a start date of 2014-08, a primary completion date of 2015-06, and enrollment of 120. The sponsor is Medical University of South Carolina. The listed condition is hypothermia.

The intervention is classified as Observation Of Temperature and its type is OTHER. The listed group, Joint Arthroplasty, consists of participants undergoing joint replacement. The registry record does not describe an assigned temperature-management treatment or a randomized intervention. It explicitly notes that the study was not a randomized comparison, that allocation was not stated, and that the arms are not a like-for-like control comparison. The study should therefore be read as an observational examination, not as a trial comparing the effects of two assigned treatments.

The primary outcome is Incidence of Hypothermia, measured as a count of participants. The outcome timeframe starts with temperature measurement before leaving preoperative holding for the operating room and ends after temperature is taken on arrival in the recovery room. The definition is ever having a temperature < 36.0 °C at one or more measurements. Temperature was assessed with an Exergen temporal thermometer described as precise to 0.1 °C. Each temporal measurement was taken and recorded three times, and the mean was used for analysis at each time point.

The record specifies temperature measurement on leaving the holding area, on arrival in the operating room, after anesthetic induction, after initiation of the upper-body forced-air warmer used for all patients, at incision, every 30 minutes after incision, on leaving the operating room, and on arrival in PACU. Operating-room temperature and humidity were recorded throughout. The registry record does not report the actual primary outcome count, a statistical analysis, the analysis population, or a justification for the enrollment target. The study's completion status does not supply those missing results.

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: Ever hypothermic (temperature \<36.0 degrees C) during the perioperative period

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 Incidence of Hypothermia, measured over Starting with temperature measurement prior to leaving preoperative holding for OR and ending after temperature taken on arrival in recovery room.

The primary endpoint is the incidence of ever being hypothermic during the specified perioperative observation window. A participant meets the endpoint definition if at least one measured temperature is < 36.0 °C. The registry describes the endpoint as a count of participants and identifies the relevant population as those who were ever hypothermic during the perioperative period.

This endpoint is used to turn repeated temperature observations into a participant-level binary outcome: each participant either met the threshold at one or more measurements or did not. In general, a threshold-based incidence measure can communicate how often a prespecified condition occurred within an observation period. It does not, by itself, describe how low temperatures went, how long a participant remained below the threshold, or the exact point at which a change began. Those questions would require additional summaries of the repeated measurements.

The measurement approach is described in some detail. Temperatures were taken with an Exergen temporal thermometer, stated to be precise to 0.1 °C. Each measurement was taken and recorded three times; the mean value was used for analysis at that time point. The registry lists measurements beginning before departure from preoperative holding and ending on arrival in the recovery room, with operating-room temperature and humidity also recorded throughout. These details define the intended observation window and measurement process, but do not establish how many participants had complete observations.

The registry record does not report the number or proportion of participants who met the endpoint, uncertainty around that incidence, or any analysis of temperature patterns over time. It also does not report how missing or unusable temperature readings were handled. Without the outcome data, the endpoint's observed frequency and precision cannot be assessed.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The study's primary outcome is binary at the participant level. The endpoint asks whether a participant ever had a temperature < 36.0 °C at one or more measurements within the stated perioperative window. In general, a binary endpoint reduces a sequence of observations to an event status for each participant. It can answer whether the threshold was crossed, but it does not retain the full pattern of the measurements once they are reduced to that status.

What does an incidence measure describe?

For this outcome, incidence refers to the count of participants meeting the event definition over the specified observation period. Interpreting an incidence estimate requires knowing both the event count and the number of participants whose endpoint status could be assessed. A confidence interval, when reported, describes uncertainty around an estimate; it does not correct for incomplete measurements or make an observational comparison causal. The registry record gives the endpoint definition but does not report an event count, an analyzed denominator, or a confidence interval.

How were temperatures measured?

The registry describes use of an Exergen temporal thermometer, stated to be precise to 0.1 °C. Each temporal measurement was taken and recorded three times, and the mean was used at each time point. In general, repeated readings can reduce the influence of variation between individual readings, but the record does not report reliability analyses or how often readings were unavailable. The averaging procedure does not reveal whether the recorded temperature values were complete across participants or measurement times.

The planned sequence begins when participants leave the holding area, continues through operating-room arrival, anesthetic induction, initiation of the upper-body forced-air warmer, incision, measurements every 30 minutes after incision, and departure from the operating room, and ends on arrival in PACU. Operating-room temperature and humidity were recorded throughout. These repeated observations potentially describe the course of temperature over time, but the registry record does not report an analysis of those trajectories or of the relationship between room conditions and participant temperatures.

Why does the observational design matter?

In general, an observational study records exposures or outcomes without randomly assigning participants to comparison conditions. Such a design can describe what was observed in the study group, but comparisons may be affected by differences between groups or other factors. The registry states that this was not a randomized comparison, allocation was not stated, and the arms are not a like-for-like control comparison. There is no reported randomized contrast from which to estimate a treatment effect. The intervention entry is Observation Of Temperature, classified as OTHER, and the listed group is Joint Arthroplasty.

What can be learned from the planning illustrations?

In general, a sample-size calculation describes the sample size that would be needed under specified assumptions; it is not a result from participants and is not observed power. The planning assumptions associated with this record describe a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and effects defined as stated fractions of the observed effect. For time-to-event tables, the stated convention is total events; for other tables, it is participants per arm. These are planning illustrations based on an observed effect, not the study's own design. The registry does not report the trial's sample-size justification, and its study description does not establish a randomized two-arm comparison. The illustrations should therefore not be read as evidence that the observational study had those design features or as an estimate of its achieved power.

The registry lists one outcome measure and zero analyses. It does not report a statistical plan, adjustment methods, the handling of repeated measures, the treatment of missing data, or a primary endpoint analysis. In general, those choices matter because they determine which observations contribute to an estimate and how uncertainty is calculated. Without them, readers cannot reproduce or fully evaluate an analysis. No recalculated outcome estimate is available to compare with a sponsor analysis, and the registry record does not report an inferential result.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Hypothermia")
n      <- c(102)
events <- c(74)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Hypothermia  102  74  72.5  62.8  80.9  63.2  80.3  63.2  80.3

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure and zero analyses. It identifies Incidence of Hypothermia as the primary outcome, but does not report an analysis of that outcome. The registry record does not describe a multiplicity plan, such as how statistical testing would be handled if multiple outcomes, time points, or comparisons were analyzed. This omission does not establish that multiple testing occurred; it means the record does not provide enough information to evaluate it.

Repeated temperature measurements were scheduled at several points during the perioperative period, with additional measurements every 30 minutes after incision. In general, analyzing many time points can raise questions about whether each point is being tested separately or whether a single prespecified summary is used. The primary outcome definition combines readings into an ever-hypothermic participant-level event, but the record does not state whether or how other analyses of the repeated temperatures were planned. The number of analyses is listed as zero.

Missing-data handling is not reported in the registry record. The record does not state how many temperature readings were missing, whether participants with incomplete measurement sequences were included in the primary analysis, or what rules were used to classify endpoint status when readings were unavailable. These details matter because a participant can be classified as never having crossed the threshold only when the relevant observation period is sufficiently assessed. The registry information does not permit an assessment of that issue.

The analysis population is also not reported. Enrollment is listed as 120, while the adverse-event group separately lists 102 participants at risk. The registry does not explain the relationship between those counts, and the adverse-event denominator should not be assumed to be the primary endpoint denominator. It does not report how many participants contributed to the primary analysis or whether exclusions occurred. The registry record also does not report a statistical analysis plan or the handling of protocol deviations.

12. 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 0% reporting threshold.

The serious and other adverse-event figures list the Joint Arthroplasty group with 102 participants at risk. The reported counts of participants affected are 0 for serious events and 0 for other events. No serious-event terms are listed. These figures describe the safety information recorded for that group and denominator.

In general, a zero count means that no event was reported in the stated group during the reporting period; it does not establish that an event is impossible or that there is no risk. The registry record does not provide a detailed adverse-event collection period, event definitions, or further safety analysis. It also does not explain why the safety denominator is 102 when enrollment is listed as 120. The difference should not be attributed to any particular reason based on this record.

These safety counts are distinct from the primary endpoint. The primary outcome concerns participants with a temperature < 36.0 °C at one or more perioperative measurements, while the adverse-event figures concern serious and other adverse events. The registry record does not report the primary hypothermia count, so the zero adverse-event figures cannot be used to infer the incidence of hypothermia or the completeness of temperature data.

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

The study is designed to observe perioperative temperature in participants undergoing joint replacement. Its primary endpoint is defined as ever having a temperature < 36.0 °C during the specified period, and its measurement description identifies the timing and method of temperature collection. The registry record does not report the endpoint result, so it cannot establish the observed incidence of hypothermia or the precision of that estimate.

The record also does not report temperature trajectories or estimates of when temperatures changed or how quickly they dropped. Although repeated measurements and operating-room temperature and humidity were recorded, the presence of a measurement schedule is not a substitute for the resulting data and analysis. The stated motivation about infection prevention and blood loss provides context for the study question; it is not evidence that this study measured those outcomes or found a relationship with temperature.

Because the study is observational and does not describe a randomized comparison, it cannot be interpreted as a randomized evaluation of a temperature-management strategy. The registry specifically notes that allocation was not stated and that the arms are not a like-for-like control comparison. No causal effect of an intervention can be inferred from the design information reported.

The record's COMPLETED status and enrollment of 120 do not resolve these limitations. Enrollment is not necessarily the number analyzed, and the primary analysis denominator is not reported. The adverse-event figures refer to 102 participants at risk and should be read separately from the missing primary outcome result. The registry does not report missing-data procedures, a statistical analysis plan, or an analysis population.

In general, a result is most useful when its definition, estimate, uncertainty, and analysis population are all clear. Here, the outcome definition and measurement process are described, but the endpoint estimate and its uncertainty are not reported. The record therefore supports an understanding of what investigators intended to observe, but not a quantitative conclusion about the frequency or timing of perioperative hypothermia in this study.

14. Why This Trial Matters Statistically

This study raises a statistical challenge common to perioperative research: the underlying clinical process unfolds over time, while a simple endpoint may reduce that process to a yes-or-no status. The primary definition asks whether temperature ever crossed a specified threshold. That is a useful way to define an event for each participant, but it does not describe duration, depth, or timing of a temperature change. The registry's repeated measurement schedule recognizes the time-dependent nature of the question, even though no trajectory analysis is reported.

Measurement details also matter. The record specifies a temporal thermometer, three readings at each measurement occasion, and use of their mean. It lists the perioperative time points and notes that operating-room temperature and humidity were recorded throughout. Clear measurement procedures help readers understand how an endpoint was intended to be assessed. To evaluate the resulting evidence, readers would also need the observed values, the endpoint denominator, and information on missing readings, none of which is reported for the primary outcome.

The design is statistically important as well. The registry describes an observational study and says it was not a randomized comparison. It also notes that allocation was not stated and that the arms are not a like-for-like control comparison. This directs interpretation toward description, rather than causal comparison. The design information should not be replaced by assumptions based on planning illustrations that describe equal allocation between two arms; those are planning assumptions, not evidence about how this study was conducted.

Finally, the record distinguishes between an outcome definition and an outcome result. It identifies one primary outcome and describes the study as completed, but lists zero analyses and does not report the primary estimate. That gap matters: a well-specified question and measurement plan are not enough to assess frequency or precision without the analyzed data. The statistical value of this record is therefore chiefly in its description of the question and measurement process, while the main quantitative finding remains unreported.

15. 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 main limitation for interpretation is that the primary endpoint result is not reported in the registry record. The number of participants who met the definition of ever having a temperature < 36.0 °C, the analyzed denominator, and any uncertainty estimate are absent. Without these quantities, the incidence and its precision cannot be assessed.

The registry lists enrollment of 120 but does not state how many participants contributed to the primary endpoint analysis. The adverse-event information uses a separate at-risk group of 102, and the record does not explain the relationship between that denominator and enrollment. It would be inappropriate to assume that either figure is the primary analysis population. Missing temperature readings and the rules for classifying participants with incomplete observations are not reported.

The design is observational. The registry says the study was not a randomized comparison, allocation was not stated, and the arms are not a like-for-like control comparison. The listed group is participants undergoing joint replacement, and the intervention is observation of temperature. These details limit the record's ability to support causal claims about a treatment or temperature-management strategy.

Although the registry describes the temperature measurement procedure and schedule, it does not provide the measured temperatures or an analysis of changes over time. It also does not report whether the planned measurement occasions were completed consistently, how operating-room temperature and humidity were incorporated into analysis, or whether other relevant factors were considered. A statistical analysis plan, multiplicity approach, and sample-size justification are not reported in the registry record. The study's completed status does not fill these reporting gaps.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Observational Examination of Thermoregulation in Total Joint Arthroplasty — NCT02225743.
• Registry record last updated 2019-01-24; status last verified 2019-01.
• Results first posted 2019-01-24.
• 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.

19. Record Summary

NCT02225743 is a completed observational examination of thermoregulation in total joint arthroplasty, sponsored by Medical University of South Carolina. The registry lists enrollment of 120, a start date of 2014-08, and a primary completion date of 2015-06. The listed group is Joint Arthroplasty, and the intervention is Observation Of Temperature.

The primary outcome is the incidence of ever having a temperature < 36.0 °C during the period from before leaving preoperative holding through arrival in the recovery room. The registry describes repeated temporal temperature readings, use of the mean of three readings at each time point, and recording of operating-room temperature and humidity.

The primary outcome result, analysis population, missing-data handling, statistical analysis plan, and sample-size justification are not reported in the registry record. The record states that this was not a randomized comparison and that the arms are not a like-for-like control comparison. Safety figures list 102 participants at risk, with 0 serious and 0 other adverse events reported.