Knee Arthroplasty Performed With Conventional and Customized Instrumentation: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Knee Arthroplasty Performed With Conventional and Customized Instrumentation (NCT01124305), a randomized phase 4 study. The primary outcome is Length of Surgery.

2. Clinical Question

The primary hypothesis in the study summary predicted shorter operative time with customized instruments. The posted mean operative time was 3707 seconds in the customized-instrumentation group and 3447 seconds in the traditional-instrumentation group. The posted mean difference, expressed as customized minus traditional, was 260.0 seconds, with a confidence interval from 83.9 to 436.1 seconds. Thus, the posted point estimate is in the direction of longer, not shorter, operative time for the customized group. This is a description of the recorded comparison, not a conclusion about what would happen in other settings or a recommendation about instrumentation.

Because this was a randomized comparison, the intended contrast is between outcomes under assignment to the two instrument approaches. However, the primary outcome population is identified as per protocol, rather than all enrolled or all randomized participants. Details of exclusions, adherence, missing outcome data, and the handling of participants after randomization are not reported in the registry record. Those details matter when interpreting how closely the posted comparison represents the randomized groups.

3. Trial Design

The registry record describes a phase 4, randomized, open-label, parallel-group study comparing Customized Patient Instrumentation with Traditional Instrumentation for total knee arthroplasty. It lists knee arthritis as the condition and enrollment of 70. The sponsor is Anderson Orthopaedic Research Institute. The record gives a study start of 2010-05, primary completion of 2012-07, and a completed status.

In a parallel-group design, participants are assigned to one of the study approaches and remain in that group for the comparison. Randomization is intended to make the groups comparable at the point of assignment, on average, but the registry record does not describe the sequence-generation method, allocation concealment, or any stratification. Masking is listed as none. The record does not say whether outcome timing or other assessments were conducted by assessors unaware of the assigned instrumentation.

The customized group used instruments specifically made for each patient using pre-operative CT scans. The comparator group used traditional surgical instruments. The study summary describes video recording to time the full operation and individual surgical steps, recording the number of instrument trays, and assessing limb and component alignment on x-rays. Bone-cut thickness was also described as a comparison of interest. These are descriptions of planned or intended measurements; the posted results do not contain results for every measure named in the summary.

The registry lists a per-protocol population for the primary outcome. Posted primary outcome statistics are available for 26 participants in each group. Although the record also lists overall enrollment, it does not explain why the per-protocol outcome group is smaller than the enrollment figure or whether the figures correspond to all randomized participants. The number randomized, the number excluded from the per-protocol analysis, reasons for exclusion, and the analysis population for every secondary outcome are not reported in the registry record.

Further details needed to appraise trial conduct are not reported in the registry record, including the planned statistical analysis, how missing values were handled, whether interim analyses were considered, and the original sample-size justification. The planning illustrations associated with the posted results are based on the observed effect and are not evidence of the assumptions used to design this trial.

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.

Before assignment: Patients were excluded if their medical insurance did not cover a leg CT scan or if there was any metal in their leg.

Overall Study

Analysis population for the primary outcome, as defined in the registry: per protocol

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 Length of Surgery, measured over 1 day.

The primary endpoint is length of surgery, measured in seconds from skin incision to wound closure. The registry record gives a timeframe of one day and identifies the outcome as a mean of a continuous measure, with standard deviation as its measure of spread. The analysis population is described as per protocol.

Operative time was chosen to address the study’s stated primary question: whether customized patient instrumentation reduces the time required for primary total knee arthroplasty compared with traditional instruments. Timing the interval from incision to closure gives a defined measure of the duration of the operation. The summary says video recordings were used to time the full procedure and each surgical step, although posted results for the primary endpoint concern the full operative interval.

A mean describes the average recorded time in a group. The standard deviation describes how much individual observed times vary around that group’s mean; it is not a confidence interval for the mean. These summaries can help readers see both the group-level contrast and the variability among recorded operations. They do not, on their own, explain why a difference occurred or establish that the same pattern would be observed in another setting.

The endpoint is a procedural measure rather than a direct measure of alignment or patient experience. The registry record describes alignment and other surgical measures as additional interests, but they address different questions and should not be treated as interchangeable with operative time.

7. Results Posted in the Registry

• Customized Patient Instrumentation: mean 3,707 versus 3,447 on control; difference 260.00 (95% CI 83.90 to 436.10), standardized effect d = 0.80; z-test p = 0.004.

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.

Number of Instrument Trays Required

• 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:
  • Customized Patient Instrumentation: mean 2.50 versus 7.30 on control; difference -4.80 (95% CI -5.31 to -4.29), standardized effect d = -5.09; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Customized Patient Instrumentation than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The registry record lists secondary interests that complement, but do not duplicate, the primary operative-time question. The posted results include a comparison for instrument trays. The record also lists surgical-step timing and limb alignment as secondary outcomes, while the study summary mentions x-ray assessment and comparison of bone cuts. Results for surgical-step timing and limb alignment are not reported in the registry record. The absence of those results means the secondary record is incomplete for assessing the full set of described study questions.

Across the available results, the tray-count comparison addresses the amount of instrumentation required, whereas the primary endpoint addresses time from incision to closure. These measures may relate to different aspects of the surgical process, but a result for one cannot establish a result for the other. Nor does a result in tray count explain the observed operative-time contrast. The registry record does not report an analysis linking tray use, procedural steps, or alignment to operative duration.

Secondary outcomes are often interpreted with more caution than a prespecified primary outcome. General statistical principle: examining multiple outcomes increases the opportunity for apparently notable results to arise by chance, particularly when no adjustment or prioritization strategy is specified. The registry record does not report a multiplicity plan or adjustments for multiple comparisons. The tray comparison’s p-value is therefore an unadjusted result, not evidence that the family of secondary questions was controlled for multiplicity.

The registry record also does not report a complete secondary analysis plan, outcome-specific analysis populations, missing-data handling, or whether all planned outcomes were submitted. Consequently, the available secondary evidence can be described but should not be treated as a comprehensive account of the trial’s secondary objectives. These outcomes offer additional dimensions of the procedure, yet they cannot independently confirm or overturn the primary comparison. Their interpretation depends on the completeness of outcome reporting and on methods that are not described in the registry record.

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

• Length of Each Surgical Step (in Seconds)
• Number of Instrument Trays Required
• Limb Alignment (Mechanical Axis)

9. Statistical Interpretation

10. Statistical Methods Explained

The registry record reports group means and standard deviations for operative time, along with a mean difference, confidence interval, and unadjusted p-value. These statistics answer related but distinct questions. The means describe the observed group averages, the standard deviations describe variation among observations, the confidence interval describes precision around the estimated contrast under a statistical model, and the p-value assesses compatibility with a specified no-difference model under test assumptions.

What does a mean difference describe?

A mean difference is formed by subtracting one group mean from the other. The posted comparison is expressed as Customized Patient Instrumentation minus Traditional Instrumentation. With that direction, a positive value means the customized-group mean is higher, and a negative value would mean it is lower. The posted estimate is 260.0 seconds, so its direction is longer mean operative time in the customized group. It is important to check the direction of subtraction before interpreting any mean difference; a sign has no interpretation apart from the stated order of groups.

A mean is useful for summarizing a continuous outcome such as time. It compresses the observations into a single group-level value, which makes a comparison straightforward. It can also be affected by unusually long or short observations, and it does not show the full shape of the data. The registry record does not provide distributions or individual-level observations, so the posted summaries cannot show whether times were symmetric, clustered, or influenced by outlying values.

What does the standard deviation tell the reader?

The standard deviation describes the spread of observed values around the mean. It is a measure of variability between recorded operations within a group, not a measure of precision for the mean difference. A larger standard deviation indicates more dispersion in the observed values, while a smaller one indicates less dispersion. It does not establish that one group’s results are more predictable for every future operation, because the estimate depends on the observed sample and the setting in which it was collected.

Standard deviations can help readers judge the amount of within-group variability relative to the group means and the estimated contrast. They do not replace the confidence interval, which addresses uncertainty in the estimated comparison. The registry record gives standard deviations for both groups, but does not report individual data, distributional diagnostics, or a detailed model specification.

How should the confidence interval be read?

A confidence interval gives a range of values for the group difference that are compatible with the observed data and the method’s assumptions at its stated confidence level. In repeated use of the same procedure under its assumptions, intervals constructed in this way would have the advertised coverage. A particular interval is not a probability statement that the true difference has a specified chance of lying inside its endpoints. Nor does it describe the range of individual participant outcomes.

The reported interval for the primary mean difference runs from 83.9 to 436.1 seconds. Because the interval is stated for customized minus traditional, its positive endpoints retain the direction of longer average time in the customized group. The interval supplies information about both direction and uncertainty in magnitude. It does not identify which procedural features produced the difference, and the registry record does not report a clinically meaningful threshold against which to assess the size of the contrast.

What does the p-value add?

The unadjusted p-value of 0.004 is a measure of how compatible the observed result is with a null model of no group difference, conditional on the statistical test and assumptions. A small p-value indicates that results at least as discrepant from the null model would be relatively unusual if that model and those assumptions held. It does not give the probability that the null model is correct, the probability that chance alone caused the result, or the size of an effect.

The registry record does not identify the complete test procedure or the analysis plan, so the p-value should be read as reported rather than used to infer unreported methods. It is labeled unadjusted. The record does not report whether or how the primary and secondary comparisons were considered together when interpreting statistical evidence.

Why do analysis population and assumptions matter?

The primary outcome is identified as per protocol. Such an analysis focuses on participants meeting the protocol’s specified criteria, but the registry record does not describe those criteria or report who was omitted and why. In a randomized trial, excluding participants after assignment can affect the comparability created by randomization, depending on the reasons and patterns of exclusion. Without those details, the per-protocol result cannot be assumed to have the same properties as an analysis of everyone randomized.

General statistical principle: estimates and tests rely on assumptions about the data and the analysis. For a mean comparison, relevant considerations can include how observations are distributed, whether the analysis accounts for the design, and how missing outcomes are handled. The registry record does not report diagnostics, missing-data procedures, or a full statistical plan. This absence does not show that no such methods were used; those details are not reported in the registry record.

There is no reported indication in the registry record that a recalculated result replaces the posted sponsor comparison. The primary comparison should therefore be read as the posted result. The sample-size illustrations are separate planning calculations based on the observed effect; they do not describe the actual design justification or the analysis of this trial.

11. Confidence Intervals and Precision

The primary mean difference is reported as 260.0 seconds for Customized Patient Instrumentation minus Traditional Instrumentation. Its confidence interval extends from 83.9 to 436.1 seconds. This interval is the main summary of precision for the estimated group contrast: it shows a range of values compatible with the data and the method’s assumptions, rather than only giving a single point estimate.

The interval is entirely positive, so the values in the interval retain the same direction as the observed estimate: higher mean operative time in the customized group under the stated subtraction order. The interval does not imply that every participant in the customized group had a longer operation. Individual times vary within each group, as indicated by the reported standard deviations, and the interval concerns uncertainty in the mean difference rather than individual outcomes.

The interval also shows that the exact size of the difference is not known with precision. Its lower and upper limits are materially separated, so a range of magnitudes remains compatible with the analysis. The record does not state a threshold for an important difference in operative time, which means statistical precision alone cannot establish how important the range is from a clinical or operational perspective.

Confidence intervals depend on the statistical method and its assumptions. The registry record does not report the full model or test specification, details of missing-data handling, or a sensitivity analysis. The primary result is also based on a per-protocol population, whose formation is not described. These limitations affect how confidently the interval can be generalized beyond the posted analysis. The unadjusted p-value of 0.004 complements the interval by expressing compatibility with a no-difference model under test assumptions, but it does not provide a separate measure of the effect’s importance or resolve the uncertainties about analysis conduct.

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 figures are planning illustrations based on fractions of the observed primary effect, not a record of the trial’s original design calculation. They give the number of participants per arm for 80% power and the number of participants per arm for 90% power. They are not total event counts. The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation; the effect to detect is the stated fraction of the observed effect.

For planning at 100% of the observed effect, the illustration gives 25 participants per arm for 80% power and 33 participants per arm for 90% power. For planning at 75% of the observed effect, it gives 44 participants per arm for 80% power and 59 participants per arm for 90% power. For planning at 50% of the observed effect, it gives 98 participants per arm for 80% power and 131 participants per arm for 90% power.

In plain terms, 80% power is the chance, under the planning assumptions and if the chosen effect is the true effect, of obtaining a statistically significant result using the specified test procedure. The 90% column describes a higher chance under the same assumptions and therefore requires a larger planned sample in these illustrations. These are design calculations, not observed power. Observed power is not a useful retrospective measure of what the completed trial established.

The progression across the rows illustrates a general planning principle: smaller effects are harder to distinguish from random variation, so detecting them generally requires more participants. These calculations use the effect observed in this trial as their starting point, which may not be a reliable estimate for future planning. The trial’s original sample-size assumptions and justification are not reported in the registry record.

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 = 260.000; pooled standard deviation σ = 323.959.
2. n = 2 × (1.96 + 0.842)² × 323.959² / 260.000² = 24.4, rounded up to 25 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 <- 260                      # observed difference in means
sigma <- 323.958647052367                     # 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(1124305)
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 = 25 (80% power), 33 (90% power)
 75% of observed effect: n per arm = 44 (80% power), 59 (90% power)
 50% of observed effect: n per arm = 98 (80% power), 131 (90% power)
power.t.test: 25.4 
Simulated power at n = 25 per arm: 0.795 (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

Multiplicity arises when a study examines more than one outcome or comparison. Even if each test is considered individually, looking across several tests can increase the chance of at least one result appearing statistically notable by chance. General statistical principle: investigators may address this by specifying a hierarchy of outcomes, adjusting significance thresholds, or using another prespecified strategy. Which approach is appropriate depends on the study’s aims and analysis plan.

The registry record identifies a primary outcome and lists secondary outcomes, but a plan for handling multiplicity is not reported in the registry record. The primary comparison has an unadjusted p-value of 0.004, and the posted tray comparison has an unadjusted p-value of <0.001. These values should be understood as unadjusted results; the record does not establish whether a correction was used in the investigators’ full analysis or whether the results were interpreted within a prespecified outcome hierarchy.

Missing-data methods are also not reported in the registry record. The posted primary outcome is described as per protocol, but the record does not explain how participants entered that analysis, whether any outcome values were unavailable, why any participants might have been excluded, or how missing observations were handled. The difference between listed enrollment and the per-protocol outcome group is not explained. The randomized participant count and the flow from assignment to analysis are not reported in the registry record.

The analysis population matters because exclusions after randomization may change the balance between groups that randomization is intended to create. This does not mean the posted per-protocol comparison is invalid; it means its interpretation depends on information that is not reported. The registry record also does not report an intention-to-treat analysis or sensitivity analyses assessing alternative assumptions about missing outcomes.

The registry lists no reported analyses for the secondary outcome records, although one secondary comparison is posted. Details such as a full statistical analysis plan, interim analyses, and the original sample-size justification are not reported in the registry record. Without these details, readers cannot determine whether the outcome reporting and analysis decisions followed a prespecified approach.

15. 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 serious adverse events for both instrumentation groups. It lists 0 serious adverse events among 26 participants at risk in the Traditional Instrumentation group and 0 among 26 participants at risk in the Customized Patient Instrumentation group. The posted serious-event term list is empty. The record does not provide additional detail on the nature of serious events or their definitions.

For other, non-serious adverse events, the record lists 1 event among 26 participants at risk in the traditional group and 0 among 26 participants at risk in the customized group. These are descriptive counts in the registry record. They do not by themselves establish whether the groups differ in safety, especially without information on event type, severity, duration, ascertainment, or statistical comparison.

Death counts are not reported in the registry record. The absence of recorded serious events in these posted groups does not establish that serious events cannot occur or that the approaches have equivalent safety. These figures apply to the reported trial record and should be interpreted alongside the limited information about follow-up and adverse-event collection.

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

The posted primary result is a comparison of average operative time in the per-protocol groups. The customized-instrumentation group had a mean of 3707 seconds and the traditional-instrumentation group had a mean of 3447 seconds. The estimated difference, customized minus traditional, was 260.0 seconds, with a confidence interval from 83.9 to 436.1 seconds. In this trial’s posted analysis, the estimated mean time was longer with customized instrumentation, contrary to the direction predicted by the primary hypothesis.

This result does not establish why the groups differed. The registry record does not give enough procedural information to attribute the difference to instrument design, operating-room workflow, case characteristics, surgeon experience, or any other particular factor. Nor does the result establish the effect that would be observed in other hospitals, with other teams, or in other patient populations. A trial estimate is shaped by its participants, conduct, outcome measurement, and analysis.

The result is also not a complete evaluation of the two approaches. The study summary describes alignment, surgical-step timing, and bone-cut comparisons, and the registry lists secondary outcomes. However, results for some of these measures are not reported in the registry record. The primary endpoint answers a question about operative duration; it does not by itself answer whether alignment was equivalent or whether other procedural outcomes differed.

Statistical significance should not be equated with clinical or operational importance. The confidence interval conveys uncertainty in the estimated mean difference, but the registry record does not report a threshold for what size of time difference would matter. The p-value indicates compatibility with a no-difference model under test assumptions; it does not quantify importance, prove causation, or measure the probability that a conclusion is correct.

The per-protocol analysis population, unexplained difference between enrollment and outcome counts, and unreported details about missing data and analysis methods limit the interpretation of the randomized comparison. The record also does not report the original design assumptions or a multiplicity strategy. These gaps do not erase the posted result, but they constrain how far it can be taken. The findings are best understood as the recorded comparison for this study, not as medical advice or a general verdict on either instrumentation approach.

17. Why This Trial Matters Statistically

This trial illustrates why a randomized study’s hypothesis and its observed estimate must be kept separate. The primary hypothesis predicted reduced operative time with customized instrumentation, while the posted mean difference points toward longer time in that group. Statistical interpretation begins with the direction and scale of the estimate, not simply whether a p-value meets a conventional threshold.

The result also demonstrates the different roles of summaries. Group means provide a direct description of average operative time, standard deviations show variation among observed operations, and the confidence interval communicates uncertainty around the estimated contrast. The unadjusted p-value adds a test-based measure of compatibility with a no-difference model. These statistics are related, but none substitutes for the others, and none explains the mechanism behind the result.

For clinical researchers, the record highlights the importance of reporting the analysis population and participant flow. A randomized design is valuable, but a per-protocol outcome population can require additional information about exclusions, adherence, and missing outcomes. The record lists enrollment and outcome-group counts without explaining their relationship. That gap makes it harder to assess how the posted analysis connects to the randomized assignment.

The study also raises a broader reporting issue: a trial can describe several relevant outcomes, while registry results may cover only part of them. Operative duration, instrument use, surgical-step timing, alignment, and bone cuts address distinct questions. Clear reporting of outcome definitions, analysis plans, and results is necessary for readers to understand which questions the available evidence answers and which remain unresolved.

Finally, the planning illustrations show how sample-size requirements depend on the effect chosen for planning. Their figures are based on the observed effect and stated assumptions, not on the trial’s original justification. Keeping retrospective planning illustrations distinct from the original design process prevents an observed result from being mistaken for prospective design evidence.

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.

Several limitations specific to this record affect interpretation. First, the primary endpoint is reported for a per-protocol population, but the registry does not describe the criteria used to define that population or explain how participants moved from enrollment and randomization to the outcome analysis. The record lists enrollment of 70 and outcome groups of 26 participants each, without explaining the relationship between those figures. This limits assessment of exclusions and of how closely the analysis preserves the randomized comparison.

Second, masking is listed as none, and the record does not indicate whether video timing or any assessment was performed by assessors unaware of group assignment. Operative-time measurement has a defined start and end point, but the record does not report details about timing procedures, assessor training, or reliability. The listed use of video recording is part of the study summary, not a substitute for those methodological details.

Third, the registry record does not report the full statistical analysis plan, missing-data procedures, multiplicity handling, interim analyses, or original sample-size justification. The posted primary p-value is unadjusted. The analysis method and assumptions behind the reported estimate are not described in enough detail to assess model diagnostics or robustness.

Fourth, the posted results are incomplete relative to the range of outcomes described. A tray-count comparison is available, but results for surgical-step timing and limb alignment are not reported in the registry record. The summary also describes comparing bone cuts, but corresponding results are not available in the posted outcomes. The lack of these results prevents a full assessment of the trial’s stated procedural objectives.

Finally, the record does not report a threshold for an important operative-time difference, nor does it provide enough detail to interpret the clinical or operational significance of the estimated contrast. These limitations do not change the numbers posted for the primary outcome, but they narrow the conclusions that can be drawn from them.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Knee Arthroplasty Performed With Conventional and Customized Instrumentation — NCT01124305.
• Registry record last updated 2013-12-18; status last verified 2013-11.
• Results first posted 2013-01-21.
• 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.

22. Record Summary

NCT01124305 is a completed, phase 4, randomized, open-label, parallel-group study of Customized Patient Instrumentation and Traditional Instrumentation for total knee arthroplasty in people with knee arthritis. The registry lists Anderson Orthopaedic Research Institute as sponsor, enrollment of 70, a study start of 2010-05, and primary completion of 2012-07.

The primary outcome was mean time from skin incision to wound closure, measured in seconds, in a per-protocol population. Posted means were 3447 seconds for traditional instrumentation and 3707 seconds for customized instrumentation. The reported mean difference was 260.0 seconds, customized minus traditional, with a confidence interval from 83.9 to 436.1 seconds and an unadjusted p-value of 0.004.

The registry also posts an instrument-tray comparison and adverse-event counts. Results for some other described outcomes are not reported in the registry record. Details of the original sample-size justification, full statistical plan, missing-data handling, and the relationship between enrollment and the per-protocol outcome groups are not reported.