This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Functionally Aligned vs Mechanical Axis Aligned Total Knee Arthroplasty (NCT04748510), a randomized na study. The primary outcome is Change in Forgotten Joint Score After 2 Years From Baseline.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT04748510 |
| Phase | NA |
| Condition | Osteoarthritis, Osteo Arthritis Knee |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Double |
| Enrollment | 100 |
| Arms in the primary outcome | 2 |
| Lead sponsor | Perth Hip and Knee |
| Results posted | Yes |
2. Clinical Question
Population
The registry describes people undergoing total knee arthroplasty for osteoarthritis. It does not report further eligibility details or a fuller description of the analyzed population in the results summarized for the primary endpoint. The trial record lists an enrollment of 100, while the outcome summaries use arm-specific counts of 48 and 44. Those counts should be understood in relation to the result being reported, rather than assumed to describe every enrolled participant.
Intervention
The intervention is total knee arthroplasty performed according to a functional alignment theory, using robotic-arm assistance as described in the study objective. The record’s brief summary calls this functionally aligned Mako robotic-assisted total knee arthroplasty. The posted result concerns alignment approach; the record does not provide enough procedural detail to characterize other aspects of the operation or postoperative care.
Comparator
The comparator is total knee arthroplasty performed according to a mechanical alignment theory, also described as robotic-arm assisted. The registry calls this mechanical-axis aligned total knee arthroplasty. Both groups are part of the randomized parallel trial, but the record does not give the details of the randomization sequence or explain how allocation was concealed.
Primary question
The primary question is whether the change in Forgotten Joint Score from before surgery to 2 years after surgery differs between the functional-alignment and mechanical-alignment groups. The scale ranges from 0 to 100, with higher scores representing a better outcome. The posted comparison is a mean difference of -3.7 for mechanical alignment relative to functional alignment, with a 95% confidence interval from -16.18 to 8.78 and an unadjusted p-value of 0.561. The interval includes no difference and also allows values in either direction. These results describe uncertainty in the reported comparison; they do not establish that either approach is superior.
3. Trial Design
The registry describes a prospective randomized controlled trial with a parallel-group design. The two groups received total knee arthroplasty using different alignment theories: functional alignment and mechanical alignment. Both procedures are described in the study objective as robotic-arm assisted. The record lists double masking, but it does not identify which people were masked or how masking was maintained. Details of sequence generation, allocation concealment, and the timing of randomization are not reported in the registry record.
The listed enrollment is 100. The registry reports that the trial is completed, with a start date of 2021-04-30 and a primary completion date of 2024-10-08. It lists Perth Hip and Knee as the sponsor. The phase is recorded as not applicable. The conditions are osteoarthritis and osteoarthritis of the knee. These descriptions locate the trial’s question in knee replacement for osteoarthritis, but they do not supply further information about participant characteristics, clinical setting, eligibility criteria, or the specific robotic system’s operative workflow beyond the wording in the summary.
The primary outcome is change in Forgotten Joint Score from baseline to 2 years after surgery. The registry also lists secondary outcomes concerning lower-limb alignment, analgesia requirements, sagittal stability, functional outcomes measured as maximal voluntary contraction of knee flexion and extension, intra-operative balance, KOOS JR, EQ-5D-5L, and operated-knee pain measured with a visual analogue scale. The record lists 12 outcome measures and 9 posted secondary outcomes. It does not provide a complete account of the timing, measurement procedures, or analysis populations for those secondary outcomes.
For the primary comparison, the reported arm summaries are based on 48 participants in the functionally aligned group and 44 in the mechanically aligned group. The registry separately reports safety at-risk counts of 50 and 49. These counts refer to different result summaries; the record does not explain the reasons for the differences. No participant flow or accounting of withdrawals and missing primary outcome data is reported in the registry record.
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
| Stage | Functionally Aligned Total Knee Arthroplasty | Mechanical Axis Aligned Total Knee Arthroplasty |
|---|---|---|
| STARTED | 50 | 50 |
| COMPLETED | 48 | 44 |
| NOT COMPLETED | 2 | 6 |
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.
Population: 100 cases were randomised. 1 MA case was then removed from cohort analysis due to protocol changes in alignment technique during surgery.
| Characteristic | Unit | Functionally Aligned Total Knee Arthroplasty | Mechanical Axis Aligned Total Knee Arthroplasty | Total |
|---|---|---|---|---|
| Participants analysed | 50 | 49 | 99 | |
| Age, Continuous | years | 65 (SD 6.2) | 65.4 (SD 7.3) | 65.2 (SD 6.8) |
| Sex: Female, Male: Female | Participants | 28 | 24 | 52 |
| Sex: Female, Male: Male | Participants | 22 | 25 | 47 |
| Race and Ethnicity Not Collected | Participants | — | — | 0 |
| BMI | kg/m^2 | 31.3 (SD 6.4) | 31.0 (SD 5.2) | 31.2 (SD 5.8) |
6. Primary Endpoint
The registry lists the primary outcome as Change in Forgotten Joint Score After 2 Years From Baseline, measured over Preoperatively and 2 years postoperatively.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | score on a scale |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is the change in Forgotten Joint Score from the preoperative assessment to 2 years postoperatively. The score ranges from 0 to 100, and a higher score represents a better outcome. It is intended to capture how much a replaced joint is forgotten in everyday life, rather than measuring only a single physical performance. The registry’s endpoint description frames the comparison as a difference in relative change between the functional-alignment and mechanical-alignment groups.
A change-from-baseline outcome focuses on how scores differ over time within each group and then compares those changes between groups. That can address the trial’s stated interest in recovery after surgery, but interpretation depends on how baseline and follow-up values were collected and how change was calculated. The registry record does not report the individual time-point summaries, the precise calculation used for relative change, or an adjusted model for this endpoint. It reports group means and standard deviations for the primary result and a mean difference with a confidence interval.
Forgotten Joint Score is used as a patient-reported measure of joint awareness after replacement. A score can complement outcomes such as pain, physical function, or radiographic alignment because it captures a patient’s experience of the joint. It is not a direct measure of every aspect of recovery, and a group mean does not show the range of individual experiences. The registry also lists other clinical, functional, alignment, and quality-of-life outcomes, but the primary result addressed is specifically the reported Forgotten Joint Score comparison at 2 years.
7. Results Posted in the Registry
- Mechanical Axis Aligned Total Knee Arthroplasty: mean 46.40 versus 50.10 on control; difference -3.70 (95% CI -16.18 to 8.78), standardized effect d = -0.12; z-test p = 0.561.
Mean difference: Mechanical Axis Aligned Total Knee Arthroplasty
95% CI: -16.18 to 8.78
Recalculated from the posted summary statistics
8. Statistical Interpretation
The reported primary mean is 50.1 in the functionally aligned group and 46.4 in the mechanically aligned group. The posted mean difference is -3.7, expressed as mechanical alignment relative to functional alignment. The negative direction means the reported average score is lower in the mechanical-alignment group for this contrast. The estimate is not precise enough to distinguish clearly between a difference favoring functional alignment, little or no difference, or a difference in the other direction.
The 95% confidence interval runs from -16.18 to 8.78. Since the interval includes zero, the results are compatible with no between-group difference under the analysis represented by the posted estimate. The interval also includes values on both sides of zero, so the data are compatible with either alignment group having the higher mean. The unadjusted p-value is 0.561. This p-value does not indicate that the groups are equivalent; it describes how unusual a result at least as incompatible with a zero-difference model would be if that model and the analysis assumptions were correct. It is not the probability that the null hypothesis is true.
The group standard deviations are 28.3 and 32.4. They describe substantial variability in scores among participants in each group relative to the observed difference between group means. A mean comparison summarizes average scores; it does not show whether every participant had a similar experience, and it cannot describe the distribution’s full shape. The record does not report a prespecified threshold for a clinically important difference, so the statistical estimate should not be translated into a claim about clinical importance.
The endpoint description refers to relative change from preoperative assessment to 2 years, while the posted summaries give one mean and standard deviation per group. The registry record does not report the baseline and follow-up components or enough detail to reconstruct the calculation. The comparison should therefore be read as the registry’s reported primary result, rather than as an independently verified change-score calculation from the displayed group summaries.
The available information supports a cautious account: the estimated difference is small relative to its uncertainty, and the confidence interval is broad enough to include potentially meaningful differences in either direction. That does not prove that the approaches have identical effects. Nor does the result show that either approach improves outcomes relative to no surgery, because both trial groups received total knee arthroplasty and the registry comparison is between alignment approaches. No adjusted analysis details or prespecified interpretation threshold are reported in the registry record.
9. Statistical Methods Explained
The primary outcome is continuous: it is a score on a scale. The registry reports a mean and standard deviation for each group, then a mean difference for the comparison. A mean represents the group’s average score. A standard deviation describes how spread out individual scores are around that average. The standard deviation is not the uncertainty around the mean difference; uncertainty in the comparison is conveyed by its confidence interval.
What does the mean difference represent?
The contrast is defined as mechanical alignment relative to functional alignment. The reported means are 46.4 for the mechanical-alignment group and 50.1 for the functional-alignment group, and the posted mean difference is -3.7. A negative estimate indicates a lower average score for the group placed first in that contrast. Because higher Forgotten Joint Scores are described as better, the sign points toward a lower average score in the mechanical-alignment group. The estimate remains uncertain, as reflected by its confidence interval.
The mean difference is an absolute contrast in score units, not a percentage difference. It is distinct from a standardized effect size, which expresses the contrast relative to a measure of score variability. The registry also reports a standardized effect estimate of -0.122. That number is useful for some planning comparisons, but it is not expressed in Forgotten Joint Score points and should not replace the original-scale mean difference when describing the clinical outcome.
Why use a confidence interval?
A confidence interval communicates a range of estimates compatible with the observed data and the statistical method. The interval for this contrast extends from -16.18 to 8.78. It includes zero and spans negative and positive values, so it reflects uncertainty both about whether there is a difference and about its direction. A confidence interval is not a range that contains every individual participant’s score. It describes uncertainty about the group-level contrast.
A p-value and a confidence interval convey related but different information. The unadjusted p-value is 0.561; it is not an effect size and does not measure the chance that the result is due to chance. The confidence interval gives a more direct view of which contrast values remain compatible with the data under the statistical method. Neither quantity, alone, establishes equivalence or clinical importance. Such conclusions need a prespecified margin or other relevant clinical interpretation, which is not reported in the registry record.
What assumptions underlie a mean comparison?
General statistical explanation: a simple comparison of means is most straightforward when the measurement is meaningful on a numeric scale and the uncertainty calculation accounts appropriately for the spread and number of observations in each group. Methods may also rely on assumptions about how participant-level observations vary and whether observations are independent. The posted summaries do not show the participant-level score distribution, so skewness, outliers, or other departures from a simple model cannot be assessed from these numbers alone.
The registry reports a standard deviation of 28.3 for the functional-alignment group and 32.4 for the mechanical-alignment group. The comparison also reports a pooled standard deviation of 30.33 for its standardized effect calculation. A pooled standard deviation combines information about variation across groups for that purpose; it is not a separate trial outcome. The record does not describe the exact inferential model or whether the primary analysis adjusted for baseline score or other covariates.
What is meant by over-dispersion?
General statistical explanation: over-dispersion occurs when observed variation is greater than a statistical model expects. It matters because a model that understates variability can produce standard errors that are too small and confidence intervals that are too narrow. The primary measure is a continuous score, and the registry reports group standard deviations, but the record does not report an over-dispersion assessment. This concept is especially relevant to count outcomes and should not be assumed to have been tested or to explain the result in this trial.
What can the posted summaries establish?
Group means and standard deviations are useful concise descriptions, but they do not reveal how many observations were missing at each time point, how missing values were handled, or whether an intention-to-treat analysis was used. They also do not show whether all randomized participants contributed to the primary analysis. The outcome counts are 48 and 44; the record does not explain their relationship to the listed enrollment or the safety counts.
The registry reports no analysis entries in its analysis listing, although it does post a primary result comparison. It does not report a detailed statistical analysis plan, model specification, covariate adjustment, or sensitivity analysis. Accordingly, the interpretation should stay close to the posted summary estimate and its uncertainty rather than assume analytic details that the record does not provide.
10. Confidence Intervals and Precision
The point estimate for the primary comparison is a mean difference of -3.7, with a 95% confidence interval from -16.18 to 8.78. The estimate is centered on a lower mean score in the mechanical-alignment group relative to the functional-alignment group, but the interval is wide enough to include zero and values in either direction. The unadjusted p-value is 0.561. Taken together, these statistics do not provide strong evidence of a difference under the reported comparison, while also leaving considerable uncertainty about the size and direction of any underlying difference.
Precision concerns how tightly the data estimate the group contrast. It is not the same as whether the estimate is clinically important, and a nonsignificant test does not establish that two approaches are equivalent. To assess equivalence, a suitable margin would need to be defined and the interval assessed against it. The registry record does not report such a margin or a threshold for a clinically important change in Forgotten Joint Score.
The outcome summaries include 48 participants in the functional-alignment group and 44 in the mechanical-alignment group. The reported standard deviations are 28.3 and 32.4, respectively. The variability in individual scores and the available outcome counts both inform the precision of a mean comparison. However, the record does not report how missing measurements were handled or provide a participant flow that would show which randomized participants contributed to the result. These gaps limit assessment of possible effects of missing data on precision or bias.
The confidence interval applies to the estimated group-level mean difference under the analysis used; it is not a prediction interval for individual outcomes. Individual scores may vary more widely than the uncertainty around the mean contrast. The posted interval is the most direct indication of precision available in the registry result, and it should be read alongside the scale direction and the absence of a reported clinical-importance threshold.
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.
| Effect to detect | Participants per arm, 80% power | Participants per arm, 90% power |
|---|---|---|
| 100% of the observed effect | 1,055 | 1,412 |
| 75% of the observed effect | 1,876 | 2,511 |
| 50% of the observed effect | 4,219 | 5,648 |
The planning figures are participants per arm, not total events. They are illustrations based on the observed effect, rather than the trial’s original design justification. The assumptions listed for these planning calculations are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set as the stated fraction of the observed effect.
For planning for 100% of the observed effect, the figures are 1,055 participants per arm for 80% power and 1,412 participants per arm for 90% power. For planning for 75% of the observed effect, they are 1,876 participants per arm for 80% power and 2,511 participants per arm for 90% power. For planning for 50% of the observed effect, they are 4,219 participants per arm for 80% power and 5,648 participants per arm for 90% power. The 80% column describes a design with an 80% chance of detecting the specified effect under the stated assumptions if that effect is real; the 90% column uses a higher target chance of detection, and therefore requires more participants under these assumptions.
Smaller effects are harder to distinguish from random variation, so planning to detect a smaller fraction of the observed effect requires more participants per arm. The plotted planning relationship should be read in that same way: as the target effect becomes smaller, the required group size increases. These calculations are not observed power. They do not show the probability that the completed trial detected an effect, and they are not evidence that the trial was designed with these assumptions. The original sample-size justification and the trial’s own design assumptions are not reported in the registry record.
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 z1−α/2 = 1.960) and the desired power (z1−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
- Observed difference Δ = -3.700; pooled standard deviation σ = 30.328.
- n = 2 × (1.96 + 0.842)2 × 30.3282 / -3.7002 = 1,054.7, rounded up to 1,055 participants per arm for 80% power.
The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).
R code
alpha <- 0.05
z_a <- qnorm(1 - alpha / 2) # two-sided
delta <- -3.7 # observed difference in means
sigma <- 30.3281149357416 # 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(4748510)
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 = 1,055 (80% power), 1,412 (90% power)
75% of observed effect: n per arm = 1,876 (80% power), 2,511 (90% power)
50% of observed effect: n per arm = 4,219 (80% power), 5,648 (90% power)
power.t.test: 1055.7
Simulated power at n = 1,055 per arm: 0.800 (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 lists a primary endpoint and a range of secondary outcomes, including alignment, analgesia requirements, sagittal stability, maximal voluntary contraction, intra-operative balance, KOOS JR, EQ-5D-5L, and pain measured by visual analogue scale. It reports 12 outcome measures and 9 posted secondary outcomes. When a trial examines multiple outcomes or multiple time points, the chance of at least one apparently unusual result can increase if each comparison is interpreted without accounting for multiplicity. The registry record does not report whether multiplicity was addressed, which outcomes were included in any adjustment, or whether a hierarchy of secondary analyses was prespecified.
The primary comparison has an unadjusted p-value of 0.561. “Unadjusted” indicates that the posted value is not described as adjusted for multiple comparisons; the record does not give a multiplicity procedure. This distinction does not change the interpretation of the confidence interval itself, but it matters when interpreting a collection of outcome tests together. The registry does not provide a complete set of analysis details that would allow the family of tests to be reconstructed.
Missing outcome data can affect both the precision and validity of a comparison, particularly if the availability of measurements differs between groups or relates to participants’ outcomes. The primary outcome summaries use 48 and 44 participants, whereas the enrollment is listed as 100. Safety summaries have separate at-risk counts. The record does not provide reasons for the different counts, the amount or pattern of missing primary outcome data, imputation methods, or sensitivity analyses. It is therefore not possible to assess from the registry record whether missing data could have changed the primary estimate.
The record also does not state whether the primary analysis followed intention-to-treat principles, whether participants were analyzed according to assigned group, or whether a per-protocol analysis was used. It does not report an adjusted primary model or the covariates, if any, included in that model. These analysis-population and modeling details are important for understanding what population the reported estimate represents. In their absence, the posted means, difference, interval, and unadjusted p-value should be treated as the registry’s reported result without inferring an analysis strategy beyond what is documented.
14. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Functionally Aligned Total Knee Arthroplasty | 1 | 50 | 2.0% |
| Mechanical Axis Aligned Total Knee Arthroplasty | 1 | 49 | 2.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Functionally Aligned Total Knee Arthroplasty | 0 of 50 |
| Mechanical Axis Aligned Total Knee Arthroplasty | 0 of 49 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Functionally Aligned Total Knee Arthroplasty | 0 of 50 |
| Mechanical Axis Aligned Total Knee Arthroplasty | 0 of 49 |
Most frequent serious adverse event terms
| Event term | Organ system | Functionally Aligned Total Knee Arthroplasty | Mechanical Axis Aligned Total Knee Arthroplasty |
|---|---|---|---|
| MUA | Injury, poisoning and procedural complications | 0 of 50 | 1 of 49 |
| Paroxsymal SVT post operative | Cardiac disorders | 1 of 50 | 0 of 49 |
Serious events with the highest arm-level rate: mua (2.0%), paroxsymal svt post operative (2.0%).
The registry reports serious adverse events for the two groups separately. In the functionally aligned group, 1 serious adverse event is reported among 50 at risk. In the mechanical-alignment group, 1 is reported among 49 at risk. The record reports 0 other adverse events in the 50 at risk in the functional-alignment group and 0 among the 49 at risk in the mechanical-alignment group. Deaths are reported as 0 in each group.
The registry also lists “MUA” and “Paroxsymal SVT post operative” as serious adverse event terms, each with a reported 2.0%. The record does not provide a group-specific breakdown for those terms in the information available for these results. The group counts and terms should not be combined or interpreted as a complete narrative of each event without further detail about event definitions, timing, severity, and attribution.
At-risk counts are the denominators reported for these safety summaries. They differ from the arm counts in the primary outcome summary, and the registry record does not explain the distinction. Counts of events are descriptive; they do not by themselves establish whether an event was caused by a procedure or whether one approach has a different safety profile. The record’s adverse-event entries are limited, so the posted figures should not be treated as a comprehensive assessment of all potential harms.
15. What the Result Does, and Does Not, Mean
The primary result estimates the difference in mean Forgotten Joint Score change between functional and mechanical alignment after total knee arthroplasty. The posted estimate is -3.7 for mechanical alignment relative to functional alignment, and its 95% confidence interval ranges from -16.18 to 8.78. The interval includes zero and allows values favoring either group. The result therefore does not clearly distinguish the two alignment approaches on the reported primary comparison.
This finding is not proof that the approaches produce identical outcomes. A failure to show a clear difference can occur when the true difference is small, when the estimate is imprecise, or for other reasons. An equivalence conclusion requires an appropriate design and a prespecified equivalence margin; the registry record does not report one. The record also does not report a threshold for a clinically important difference, so the clinical importance of values within the interval cannot be determined from the posted information alone.
The result concerns the stated endpoint and comparison. It does not compare knee arthroplasty with no operation, and it does not establish effects on every outcome patients may value. The registry lists other outcomes relating to alignment, pain, stability, function, analgesia, and quality of life, but the primary result should not be generalized to those measures. Nor does a group average describe every participant’s experience.
Interpretation is further limited by incomplete reporting of the primary analysis details. The registry does not explain the derivation of the reported change, the handling of missing measurements, the analysis population, or any adjustment for baseline measures. The outcome counts and safety at-risk counts differ, and the record does not explain why. These omissions do not invalidate the posted estimate, but they restrict how fully it can be evaluated.
In plain terms, the posted data show an uncertain average difference in Forgotten Joint Score between the two alignment groups. They do not establish a clear advantage for either group, equivalence between groups, or an effect on outcomes beyond those directly reported.
16. Why This Trial Matters Statistically
This trial asks a statistical question that is important in comparative surgery: whether changing the alignment strategy within total knee arthroplasty is associated with a difference in patient-reported joint experience. Because both groups receive the operation and the comparison varies the alignment theory, the contrast is focused on the two approaches rather than on surgery versus no surgery. A randomized parallel design is an appropriate framework for estimating such a between-group difference, though the registry record does not report the details needed to assess randomization implementation.
The primary outcome is patient-reported, which complements technical or radiological measures of alignment. A successful technical target and a patient’s experience are related questions but are not interchangeable. The trial also lists measures of alignment, pain, function, stability, analgesia, and quality of life, illustrating that surgical outcomes have multiple dimensions. The primary statistical interpretation should remain tied to the endpoint actually reported, rather than treating one score as a complete account of recovery.
The confidence interval is central to the result. The point estimate alone might appear to favor one alignment group, but the interval extends from -16.18 to 8.78 and includes both directions. That range makes precision a substantive part of the interpretation: the registry result does not resolve the direction or size of the difference. A nonsignificant p-value is not evidence that the groups are identical, and an estimated average cannot substitute for a clinical-importance threshold.
The planning illustrations also show how demanding a trial can become when the target is to detect smaller effects with conventional power targets. Those values are based on the observed effect and specified planning assumptions, not the trial’s original design. They help explain why statistical conclusions depend on both the size of a difference and the amount of information available; they do not change the interpretation of the completed trial’s estimate.
Finally, transparent reporting matters. More detail about the analysis population, missing data, endpoint calculation, and multiplicity would allow readers to evaluate the result more fully. The reported comparison remains informative, but its uncertainty and the limits of the registry record should be part of any statistical reading.
17. Limitations
- The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
- Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.
The registry record does not provide the full protocol or detailed statistical analysis plan. It does not report the rationale for the enrollment target, the original sample-size calculation, allocation concealment, the randomization method, or who was masked. Although double masking is listed, the roles of the masked participants or study personnel are not specified. These details are needed to assess how the trial was implemented and how well the reported analysis aligns with its intended design.
For the primary endpoint, the description specifies change from preoperative assessment to 2 years, but the record does not give the separate baseline and follow-up summaries or the exact calculation used. The posted result includes arm means and standard deviations and a mean difference, without a detailed model description. It is not reported whether the comparison adjusted for baseline score or other variables. No threshold for clinical importance is reported, limiting interpretation of the score-unit difference.
The primary outcome counts are 48 and 44, while safety at-risk counts are 50 and 49. The enrollment is 100. The registry record does not account for the differences among these figures, report participant flow, or describe missingness and withdrawals. It also does not state whether the primary analysis was intention-to-treat or provide sensitivity analyses for missing data. Thus, readers cannot assess whether the analysis set or missing measurements could affect the estimate.
The registry lists multiple outcome measures but does not report how multiplicity was handled or give complete analysis details for secondary outcomes. The posted safety information is limited to counts and selected serious-event terms; further information about event definitions, timing, severity, and attribution is not reported in the registry record. The record also does not provide demographic or clinical details that would permit assessment of how representative the analyzed participants are of other populations undergoing knee arthroplasty.
18. Related Tutorials
19. Related Statistical Calculators
20. Sources
- ClinicalTrials.gov: Functionally Aligned vs Mechanical Axis Aligned Total Knee Arthroplasty — NCT04748510.
- Registry record last updated 2025-08-08; status last verified 2025-07.
- Results first posted 2025-08-08.
- 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.
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21. Record Summary
The registry describes a completed prospective randomized parallel-group trial comparing functionally aligned with mechanical-axis aligned total knee arthroplasty for osteoarthritis. Both procedures are described as robotic-arm assisted, and the record lists double masking. Enrollment is 100; the start date is 2021-04-30 and the primary completion date is 2024-10-08. Perth Hip and Knee is listed as the sponsor.
The primary endpoint is change in Forgotten Joint Score from baseline to 2 years, on a 0-100 scale where higher scores are better. The reported group means are 50.1 for functional alignment and 46.4 for mechanical alignment. The mean difference for mechanical relative to functional alignment is -3.7, with a 95% confidence interval from -16.18 to 8.78 and an unadjusted p-value of 0.561. The interval includes zero and values in both directions, so the posted comparison does not clearly distinguish the groups.
The registry also lists secondary clinical, functional, alignment, and safety outcomes. Important details about the primary analysis, missing data, participant flow, multiplicity, and clinical-importance thresholds are not reported in the registry record.