A Rehabilitation Tool to Determine Patient's Stay in Hospital After Joint Replacement: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Rehabilitation Tool to Determine Patient's Stay in Hospital After Joint Replacement (NCT03777007), a na na study. The primary outcome is Length of Stay in Hospital Through Discharge.

2. Clinical Question

3. Trial Design

The registry lists this as a completed, single-group study of the SPARTA force plate in people undergoing total joint replacement surgery. Enrollment is recorded as 55. The study is designated phase NA, and allocation is also listed as NA. Masking is recorded as none. These entries describe a study without a randomized, masked, parallel-group comparison in the registry record; the record does not identify a control arm.

The device is described as a force plate coupled with SPARTA scan software. The brief description says that it is used as a rehabilitation tool and can assess individual movement and balance within minutes. The intervention description says the rehabilitation tool is intended to provide a functional outcome score. These descriptions establish the device's stated role, but they do not establish how it was used in practice, how often assessments occurred, or what clinical decisions followed a score. Those details are not reported in the registry record.

The primary outcome is length of stay in hospital through discharge. The specified measure is the median, with inter-quartile range as the dispersion measure, and the timeframe is up to 8 days. The record also names gait aid use, Knee Society Score (KSS), and range of motion as secondary outcomes. Although the record lists 4 outcome measures, it lists 0 analyses. It therefore does not provide outcome estimates for the primary or secondary measures.

A single-group design can describe outcomes observed among participants assessed with a device, but it cannot by itself separate the device's contribution from other influences on recovery or discharge. Allocation, masking, and a comparison arm are not reported as features that would enable such a contrast. The record does not report a protocol-level statistical plan, sample-size justification, assessment schedule, or details of participant follow-up.

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: 55 participants signed informed consent; 40 were allocated to the study arm

Overall Study

Analysis population for the primary outcome, as defined in the registry: Participants with available data are included in the analysis.

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 Stay in Hospital Through Discharge, measured over Up to 8 days.

The primary endpoint is length of stay in hospital through discharge, measured in days. Its stated timeframe is up to 8 days, and the registry specifies the median as the summary measure with an inter-quartile range to describe dispersion. The outcome description says length of stay will depend on the score generated by the device.

As a general statistical explanation, the median describes the middle of an ordered set of observations and is less influenced by extreme values than the arithmetic mean. The inter-quartile range describes the spread of the central portion of the observations. These summaries can be useful when a measure is skewed, as lengths of stay may be, but the registry record does not explain why these particular summaries were selected for this study.

Length of stay is relevant to the stated aim because it records the time spent in hospital through discharge. However, an observed median alone would not show whether the device score predicts stay, whether a score was associated with earlier or later discharge, or whether using the device changes stay. Such interpretations would require reported results and an analysis suited to the question. The registry record does not report the median, the inter-quartile range, or an association between device scores and length of stay. It also does not specify additional endpoint details such as the exact timing of assessments or how any unusual discharge circumstances were handled.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies the primary outcome as a median length of stay, with inter-quartile range as its dispersion measure. It does not report an observed estimate or statistical analysis. The explanations below describe general statistical concepts; they do not imply that a particular analysis was performed in this study.

What do the median and inter-quartile range describe?

In general, the median is the central value when observations are ordered. It is often useful for outcomes with an uneven distribution or unusually long observations, because an extreme value has less influence on the median than on the mean. The inter-quartile range describes the span of the central half of observations. Together, the median and inter-quartile range give a location and a measure of spread without requiring a symmetric distribution. The registry names these summaries but does not report their values, so neither the typical observed stay nor the variation in stays can be read from the record.

A median and inter-quartile range are descriptive summaries. By themselves, they do not estimate the uncertainty around a population value, establish a predictive relationship, or show that a device caused a change. Statistical inference would require an appropriate analysis and sufficient detail about the observations and assumptions. No confidence interval or inferential result for this endpoint is reported in the registry record.

How does the design affect interpretation?

As a general principle, a single-group study can describe measurements made among the participants studied. It cannot create a concurrent comparison that controls for other influences on the outcome. Here the registry lists a single-group model, allocation NA, and masking none; it does not identify a control group. Thus, an observed relationship between a device score and length of stay, if reported, would not by itself demonstrate that the device altered length of stay. This record does not report such a relationship in any case.

Masking can reduce the influence of knowledge about an intervention on some measurements or decisions, depending on the outcome and study procedures. The record lists masking as none. It does not explain which people knew the device assessment results, how discharge decisions were made, or whether outcome measurement was standardized. Those procedural details are not reported in the registry record, so their influence cannot be evaluated.

What can a confidence interval tell a reader?

In general, a confidence interval expresses uncertainty around an estimated quantity under a specified statistical model. A narrow interval indicates greater precision than a wide interval for the same kind of estimate, while the interval's location indicates which values are compatible with the data and model. A confidence interval is not a guarantee that the true value lies within its limits, and it does not remove biases caused by study design or measurement. No confidence interval for the primary outcome is reported, so the precision of any primary finding cannot be assessed.

What do the planning assumptions mean?

The planning description refers to illustrations based on an observed effect, a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It says that the effect to detect is a stated fraction of the observed effect. These are planning assumptions, not a description of the completed study's single-group design. Such illustrations can help show how hypothetical design choices relate to sample size, but they do not establish that the original study was designed with those assumptions. The registry record does not report a sample-size justification for the study.

The planning description distinguishes between time-to-event calculations, which use total events under the Schoenfeld approach, and other calculations, which use participants per arm. It also states that sample-size illustrations are not observed power. In general, observed power calculated from an estimated effect does not provide a substitute for reporting the effect estimate and its uncertainty. The planning description does not provide an observed primary result in the registry record, and no planning values or outcome analyses are reported there.

How should time-to-event methods be read?

As a general explanation, time-to-event methods analyze the time until an event occurs and can account for observations where the event time is not fully observed, when the analysis and data support that approach. A hazard ratio is a comparative measure used in some time-to-event analyses. The registry's method description refers to time-to-event interpretation and says that only sponsor-reported hazard ratios are used. No sponsor-reported hazard ratio is included in the registry record, and the primary endpoint is described there as a median length of stay. Without a reported estimate, analysis details, and relevant data, no hazard-ratio interpretation or recalculation is available.

More generally, over-dispersion occurs when observed variation exceeds what a chosen statistical model expects. If present, it can make standard errors and inferential conclusions from a model that ignores it unreliable. The registry record does not report a model for the primary outcome or any assessment of over-dispersion, so there is no basis for saying that it occurred or affected this study.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 4 outcome measures. It identifies length of stay in hospital through discharge as the primary outcome and names gait aid use, Knee Society Score (KSS), and range of motion as secondary outcomes. The record lists 0 analyses and does not report estimates or test results for these measures.

As a general statistical issue, evaluating multiple outcomes or multiple hypotheses can increase the chance of finding an apparently notable result by chance. A prespecified hierarchy, adjustment procedure, or clear distinction between confirmatory and exploratory analyses can help readers understand how multiple questions were handled. The registry record does not report a multiplicity strategy, the statistical analysis plan, or whether any outcome analyses were designated exploratory.

The record says that participants with available data are included in the primary outcome analysis. It does not specify how many participants had available primary outcome data, how missing observations were handled, or whether the analysis population was defined in another way. The enrollment figure of 55 is not an outcome-analysis denominator and should not be taken to mean that all enrolled participants contributed data to every measure. The registry record also does not describe reasons for missing data or any sensitivity analysis assessing the influence of missingness.

These omissions limit assessment of both completeness and analytic choices. They do not establish that missing data or multiplicity problems occurred; they mean that the registry record does not report enough information to evaluate them. Without outcome estimates, analysis denominators, and a stated plan, the results for the primary and secondary questions cannot be judged for precision or robustness.

11. Safety Results

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

Deaths

Other (non-serious) adverse events

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

For the Sparta Force Plate group, the registry reports 40 at risk for serious adverse events, 0 affected, 40 at risk for other adverse events, 0 affected, and 0 deaths. No serious adverse event terms are listed. These figures describe what the registry record reports for the group; they are not a comparison with another group.

A reported count of 0 means that no events of that category are recorded in this entry. It does not establish that the risk of an event is absent, nor does it rule out events that were not collected, recognized, or entered. The record does not describe the event-collection procedures, observation period for safety, severity definitions, or how completeness was checked. The at-risk figures are specific to the safety categories and should not be assumed to describe the analysis population for the length-of-stay outcome.

As a general statistical point, safety counts are easier to interpret when the observation period, event definitions, and completeness of follow-up are clear. Those details are not reported in the registry record. With no comparison arm identified, these figures cannot estimate a relative difference in adverse events between interventions. They should be read as the recorded counts for this study group, not as proof of safety or as a comparative safety result.

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

The record describes a study using the SPARTA force plate as a rehabilitation assessment tool after total joint replacement surgery. It identifies length of stay in hospital through discharge as the primary outcome and specifies the median and inter-quartile range as the intended summary. The record also names gait aid use, Knee Society Score (KSS), and range of motion as secondary outcomes. These details describe the study questions and measures, not their answers.

No observed primary outcome estimate, secondary outcome result, or statistical analysis is reported. Accordingly, the registry information does not show the length of stay observed in the study, how much stays varied, or whether a device score was associated with discharge timing. It also does not quantify uncertainty around a result. A reader cannot use the record to conclude that the device did or did not affect recovery or hospital stay.

The single-group design is an important interpretive constraint. The record identifies no control group and lists allocation as NA. Even a reported change or association among participants in such a design would not, by itself, establish what caused it. Other aspects of care and recovery could also relate to length of stay, and the registry record does not describe a design that separates those influences.

The safety entry records 0 serious adverse events, 0 other adverse events, and 0 deaths in the Sparta Force Plate group among 40 at risk in each event category. These entries are limited to the reported counts and do not establish that risk is absent. The record does not report enough detail about safety follow-up or event ascertainment to extend the interpretation beyond those counts.

Overall, the registry provides information about the device, the study design, and intended outcomes, but not outcome findings. The absence of reported results should not be confused with evidence of no effect, a negative finding, or proof of benefit. Those conclusions require results and analyses that are not reported in the registry record.

13. Why This Trial Matters Statistically

This study is statistically informative as an example of the difference between a registered research question and an answer supported by reported results. The registry identifies a specific primary outcome, length of stay in hospital through discharge, and a summary approach using the median and inter-quartile range. It also describes the SPARTA force plate as a rehabilitation assessment tool. Yet the record lists 0 analyses and provides no observed outcome estimate. The design and questions can be described, while the outcome cannot be evaluated from the record.

The single-group model also illustrates why design matters when interpreting associations. A device score could be considered alongside length of stay, but without a comparison group the analysis would not establish how outcomes differed from an alternative approach. The record identifies no control arm. That limitation is separate from the absence of results: even complete estimates would need to be interpreted in light of the design.

Reporting the analysis population and missing-data handling is another important statistical issue. The record states that participants with available data are included in the primary analysis, but does not report how many had those data or how missing observations were handled. Enrollment alone does not tell readers the denominator for an outcome analysis.

Finally, the safety counts show why event counts need context. The registry records no adverse events in the listed categories for the stated at-risk groups, but does not detail collection methods or provide a comparator. The record therefore supports a careful description of what it reports, not broad claims about safety or effectiveness. Clear reporting of estimates, uncertainty, denominators, and methods would be needed for a fuller statistical interpretation.

14. 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 most direct limitation is the absence of reported outcome results. The registry identifies length of stay as the primary outcome and names secondary outcomes, but lists 0 analyses. It does not report the primary median or inter-quartile range, secondary outcome estimates, or uncertainty measures. The result's magnitude and precision therefore cannot be assessed.

The single-group model and absence of a listed control group limit causal interpretation. Allocation is NA and masking is none. The registry does not report a comparison that could distinguish the device's contribution from other influences on length of stay or recovery. It also does not report how device scores were related analytically to discharge timing.

There is limited information about the analyzed population. The record gives an enrollment of 55 and states that participants with available data are included in the primary analysis, but does not give the outcome-specific analysis denominator, missing-data count, reasons for missingness, or handling method. Enrollment should not be treated as the number analyzed.

The record does not report a statistical analysis plan, sample-size justification, multiplicity approach, or details of measurement and follow-up procedures. These omissions make it difficult to assess whether outcomes and analyses were prespecified, how secondary measures were treated, or whether the data were sufficiently complete for the intended questions. The safety entry reports event counts, but does not describe event ascertainment or the safety observation period. These limitations concern what can be evaluated from the registry record; they do not demonstrate that a particular bias or problem occurred.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A Rehabilitation Tool to Determine Patient's Stay in Hospital After Joint Replacement — NCT03777007.
• Registry record last updated 2023-03-24; status last verified 2023-03.
• Results first posted 2023-03-24.
• 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.

18. Record Summary

The registry record identifies NCT03777007 as a completed, single-group study of the SPARTA force plate in total joint replacement surgery. Enrollment is listed as 55. Allocation is NA, masking is none, and phase is NA. The device is described as a force plate coupled with SPARTA scan software for assessing movement and balance and generating a functional outcome score.

The primary outcome is length of stay in hospital through discharge, summarized as a median with inter-quartile range over a timeframe of up to 8 days. Secondary outcomes are gait aid use, Knee Society Score (KSS), and range of motion. The record lists 4 outcome measures and 0 analyses; it does not report outcome estimates or statistical results. It states that participants with available data are included in the primary analysis, but does not report the analysis denominator or missing-data handling.

For the Sparta Force Plate group, the safety record lists 0 serious adverse events, 0 other adverse events, and 0 deaths, with 40 at risk for each category. No control group is identified, so the record does not support a comparative estimate of effectiveness or safety.