Sit to stand assessment and prognosis after total knee arthroplasty

Main conclusions

Sit-to-stand assessment after total knee arthroplasty (TKA) should distinguish whether a person can transfer, how quickly or repeatedly they can do it, and how the two limbs and the trunk contribute. Five-rise time and thirty-second repetition count provide useful performance information, but neither demonstrates restoration of operated-knee loading. A patient may achieve a faster time by shifting demand to the contralateral leg, using the arms, changing foot position or increasing trunk and hip contribution.

The most defensible routine approach is a standardized chair-rise test accompanied by observation of assistance and strategy. Record chair height, hand support, foot position, pain, completeness and the exact timing endpoint. Use a separately labelled assisted version when independent performance is unsafe or impossible. For selected patients, force plates or a validated bilateral force system can show loading asymmetry that total time misses. Kinematic and force measures must remain distinct: a camera can document movement without directly measuring knee moment or muscle power.

Direct TKA reliability evidence is useful but narrow. A 24-person unilateral-TKA study found excellent observer agreement, yet repeated task performance showed systematic bias and heteroscedasticity. A 33-person late bilateral-TKA paper has conflicting smallest-real-difference values in its prose and original table. A 41-person seventh-month simultaneous bilateral-TKA study reported five-rise MDC95 of 3.49 seconds, but excludes aid-dependent patients and does not establish an acute unilateral threshold. Preoperative OA estimates do not become postoperative estimates because those patients later underwent replacement. [1–4]

Prospective prognosis is less developed than concurrent association. Preoperative chair performance can relate to later performance, but this is not the same as a validated prediction of independence, falls or community activity. A large serial study titled “predictive validity” analysed same-visit weight-bearing symmetry and gait speed across recovery, without a lagged forecast. Conversely, a recent trial-based analysis truly assessed later daily activity and found no association with the earlier thirty-second chair stand. These distinctions should be visible in both the report and any clinical software. [5–7]

Scope and evidence approach

The main population is adults undergoing primary elective unilateral TKA for knee osteoarthritis. Simultaneous bilateral TKA, mixed hip/knee arthroplasty, revision procedures, unicompartmental replacement and other indications are separate populations. The nonoperated limb may have OA, pain or weakness and cannot be assumed a healthy reference. Bilateral replacement particularly changes the meaning of interlimb comparison because neither limb is a nonsurgical control.

The report separates preoperative prognosis, inpatient or immediate recovery, early outpatient rehabilitation, three-to-six-month recovery and twelve months or longer. These labels organize the evidence; the actual elapsed days or weeks should remain in the patient record. A surgical recovery trajectory is not an isolated rehabilitation treatment effect, and a study collected longitudinally is not necessarily prognostic if it only models variables measured concurrently.

This is a critical narrative synthesis rather than a registered systematic review. The dated sit-to-stand PubMed query yielded 243 records. All five connector pages were retained, but overlapped and represented only 154 distinct identifiers. Official ESearch and EFetch recovered and reconciled all 243. A more title-focused Scopus search produced 101 unique records across five pages. These are retrieval totals rather than eligible-study counts, and the two sources overlap. Primary studies were prioritized, with reviews used to identify patterns and original sources. Exact queries, coverage and citation-search limits are provided in the search appendix.

What a chair rise measures

Transfer ability and repeated performance

A single chair rise asks whether a person can move the body from sitting to stable standing under specified conditions. The result may be independent, supported with the arms, assisted by a person, unsafe, incomplete or unattempted. Those categories are meaningful outcomes. Reducing all of them to a long time can obscure improvement from physical assistance to independent transfer.

Five-times sit-to-stand (5STS) asks the person to complete repeated rises rapidly. It reflects the combined capacity of both lower limbs, balance, movement coordination, confidence, pain and endurance over a short sequence. Thirty-second chair stand (30CST or 30STS) measures the number of completed repetitions during a fixed interval. It additionally depends on pacing and the ability to sustain repeated effort. Neither is an isolated test of quadriceps maximal strength. Describing five-rise performance as “power” may be clinically intuitive, but seconds are not watts and the test does not directly quantify knee-extensor power.

The timing endpoint is a substantive difference between protocols. Sarac stopped at the fifth return to sitting. Huber's protocol ended at the fifth stand. Both can be called five-times sit-to-stand in the literature, but one contains an additional descent. A database that omits this detail can compare different tasks while appearing to compare the same test. [3, 8]

The thirty-second test also needs a precise rule for what counts as a completed stand, the position at the start and finish, whether an incomplete final attempt counts, and whether pauses are permitted. A score of zero after a valid attempt is not equivalent to a missing observation, inability to perform one independent rise, or a test stopped for symptoms. These states should be represented separately.

Limb loading and movement strategy

Ground-reaction force under each foot describes the external load borne by each limb. Peak force, mean force and force impulse provide different summaries. A mean force ratio over five complete sit–stand cycles is not the same construct as the ratio of peak forces during one rise. The denominator also matters: operated/nonoperated, weaker/stronger and an absolute symmetry index cannot be substituted for one another.

Christiansen's longitudinal study used average vertical force during a five-rise test. Pua's much larger clinical study used a ratio of peak vertical forces measured with modified digital scales. A patient could therefore meet a reference for one measure and still have abnormal timing or joint moments. A group average near symmetry can conceal people who overload opposite sides. Reporting the direction of asymmetry, absolute bilateral forces and the task phase prevents some of these errors. [5, 9]

Joint moments estimated through motion capture and force plates add information about demand at the knee and hip. They are net moments, not a direct measure of the force of one muscle. Co-contraction, segment modelling and soft-tissue artefact influence interpretation. A near-equal vertical force can coexist with reduced operated-knee extensor moment and greater hip contribution. This is why faster, more symmetrical or stronger cannot be treated as three interchangeable definitions of recovery. [10–13]

Pain and compensation

Pain can influence performance, but the relationship depends on the stage and task. In some early postoperative studies, quadriceps strength symmetry was more consistently related to loading asymmetry than pain. In other later studies, pain and strength both related to particular kinetic outcomes. An absent correlation in a selected cohort does not show that pain is irrelevant for the individual in front of the clinician. [9, 12, 14]

A strategy that appears compensatory may be temporarily useful. Arm support or an elevated chair can enable safe independence while strength and motion recover. The assessment question is whether the patient can perform a specified task, not whether every adaptation is undesirable. Clinical interpretation should consider symptoms, capacity, goals and postoperative instructions before pursuing symmetry as an end in itself.

Selecting the assessment

Table 1 Selecting the assessment

The 2020 TKA physical-therapy guideline recommends collecting thirty-second sit-to-stand with TUG and KOOS JR at the first visit and discharge in each setting. Its outcomes statement is a best-practice consensus recommendation based on insufficient evidence. It supports routine collection and communication; it is not proof that a specific repetition cutoff is valid for every TKA patient. The guideline also recognizes gait and movement-symmetry training, but does not establish that one chair-rise symmetry target will improve every downstream outcome. [15]

Reliability and measurement error

Excellent scoring agreement is not excellent repeat performance

Medina-Mirapeix and colleagues studied 24 outpatients four to 52 weeks after unilateral knee replacement, with a mean postoperative interval of twenty weeks. Participants had to stand and walk five metres without assistance. A physiotherapist and a trauma physician timed the same task simultaneously, and the physiotherapist repeated measurement 45–60 minutes later. The chair was armless and 43 cm high. [1]

The interobserver ICC was 0.998, with SEM 0.24 seconds and smallest real difference 0.66 seconds. These exceptionally small values describe two observers scoring the same patient performance, not two independent patient performances. The task-retest ICC was 0.982, with SEM 0.76 seconds and smallest real difference 2.10 seconds. The reported confidence interval for that latter error estimate was wide, 1.40–3.18 seconds. [1]

More importantly, retest performance had a mean difference of 1.20 seconds and heteroscedasticity, and the authors described higher retest times. Their text printed the agreement limits as 1.76 to 4.16 seconds, which cannot surround a mean of 1.20. The original figure shows the lower limit below zero, consistent with approximately −1.76 to +4.16 seconds. This figure–text issue must be disclosed. A high ICC did not remove systematic bias or guarantee equal absolute error at fast and slow performance levels. [1]

The study's small sample and broad stage range increase heterogeneity, which can elevate an ICC while leaving important within-person uncertainty. Its strong correlations with TUG and usual four-metre walking support overlapping mobility constructs, not prediction of falls or proof that 5STS measures isolated quadriceps strength. The useful lesson is that timing can be scored consistently, but changing patient performance requires a different and more cautious interpretation.

The bilateral thirty second study and its inconsistent threshold

Unver and colleagues recruited 33 bilateral-TKA recipients at least six months after surgery, excluding revision surgery, marked resting pain and disorders affecting gait. The original text's future-tense wording is awkward, but the eligibility and results identify patients already operated on. Participants used a 17-inch chair, crossed their arms and completed as many chair stands as possible in thirty seconds. They performed two test sessions on the same day separated by an hour, with five minutes between the walk and chair tests. [2]

The chair-count ICC(2,1) was 0.92, with 95% CI 0.82–0.96. Mean count rose from 11.06 to 11.57. Original Table 2 reports SEM 0.35 repetitions and SRD95 0.81 repetitions, whereas the abstract and results prose state SRD95 0.96 repetitions. The printed formula uses SEM × 1.95 × √2. The PDF table was visually inspected: the discrepancy is present in the source, not just text extraction. The corresponding walking SRD also disagrees between prose and table. [2]

It would be tempting to round any of these values to one repetition and declare that a one-rise gain is real. That would compound several problems: unresolved numerical reporting, same-day rather than between-day design, a high-functioning late bilateral sample, and no patient-importance anchor. The paper supports relative reproducibility of this task in that sample; it does not supply a defensible universal one-repetition response rule.

Next day reliability after simultaneous bilateral surgery

Sarac and colleagues tested 41 people in the seventh month after simultaneous primary bilateral TKA for severe OA. Eligibility required walking and standing without auxiliary equipment. Tests were repeated the next day by the same assessor, after familiarization and in randomized order. The five-rise test used a firm, flat-backed, armless 45-cm chair; arms crossed; timing from lifting the hips to the final return to sitting. [3]

Table 4 gives 5STS ICC 0.96 (95% CI 0.92–0.98), SEM 1.26 seconds and MDC95 3.49 seconds. Mean performance was 13.66 seconds initially and 13.14 on retest. This is a useful direct TKA estimate with a clinically relevant separate-day design. Its transfer boundary remains substantial: bilateral surgery, no aid dependence and a late, selected cohort. It does not define error in a patient two weeks after unilateral TKA using the arms to rise. [3]

Concurrent correlations with the Berg Balance Scale and Falls Efficacy Scale were strong enough to support shared mobility/balance constructs. However, the Berg score is not an independent gold standard for all elements of balance, and the study did not record future falls. Calling the chair test a valid balance measure should therefore not be extended to a falls prediction claim. The study's own limitation explicitly recognizes the absence of predictive validity for falls.

Preoperative reliability must remain preoperative

Tolk's OA-TKA cohort included 85 surgical candidates and a 30-person preoperative retest subgroup assessed after thirty minutes. Thirty-second chair-stand ICC was 0.90, SEM 0.85 repetitions and the table SDC95 2.4 repetitions; the discussion rounds to 2.5. Mean count increased from 9.0 to 9.8 on retest. These estimates concern end-stage OA before surgery, not postoperative TKA. [4]

They are often relevant to preoperative assessment and illustrate familiarization, but should not be used to interpret a postoperative visit without justification. The later twelve-month recovery observations in the same paper answer responsiveness questions, not postoperative test–retest reliability. Mixing those two study components can create a seemingly TKA-specific error estimate that was never measured after TKA.

Interpreting change for one patient

An ICC describes relative ranking in the studied sample and depends partly on between-person variation. An SEM describes uncertainty in the original units. An individual MDC combines repeated-score error at a stated confidence level. Neither tells us whether the patient values the change, and a group-level detectable difference is not an individual threshold.

The same basic logic applies to force asymmetry. Pua's small reliability subset comprised thirteen people tested approximately 2.5 weeks apart at around three months after surgery. ICC(3,1) was 0.80 for standard and 0.72 for constrained weight-bearing symmetry. That interval allows genuine recovery, the sample is small, and there is no established patient-important difference for the ratio. A device's bench agreement with laboratory force plates also does not fully establish patient-level repeatability. [5]

For clinical communication, show the raw repeated measurements and conditions. If a matching error estimate is defensible, identify its confidence level, interval and population. If it is not, say that a threshold is unavailable rather than importing one from healthy older adults, stroke, hip replacement or conservatively managed OA. A one-repetition improvement accompanied by less arm support may be clinically valuable even when the repetition change alone cannot be classified confidently.

Measurement interpretation at a glance

Table 2 Measurement interpretation at a glance

Construct validity and responsiveness

Improvement in pain and improvement in performance can diverge

Pain relief after surgery may improve a questionnaire more quickly than repeated-rise performance. Conversely, a person can improve a timed test while reporting persistent difficulty with a low sofa or a toilet at home. Patient-reported function and standardized capacity are related but different. Low correlations do not automatically make either measure invalid; the adequacy of the comparator and prespecified hypotheses matters.

Tolk's thirty-second chair stand met only 42% of baseline construct-validity hypotheses and 50% of responsiveness hypotheses over surgery to twelve months, despite reproducibility and mean improvement. The title's strong negative wording should not be paraphrased as proof that chair-rise testing has no clinical value. The narrower conclusion is that this test did not behave consistently enough against those comparators and hypotheses to support all intended interpretations. [4]

Huber's 44-person secondary analysis examined a five-rise test before surgery and at three months. It timed from the command to the fifth stand. Change correlated more strongly with TUG change than with KOOS ADL or summed knee-extensor force. Mean test performance did not improve as expected. The accessible thesis chapter supports stage- and construct-specific interpretation; it does not establish that chair-rise change is a direct measure of strength recovery. [8]

A statistically significant mean improvement across surgery does not itself establish valid individual responsiveness. The clinical question is whether the score changes in the expected direction and magnitude when the intended construct changes, whether stable people remain stable, and whether a patient-important anchor supports the interpretation. Postoperative trajectories also depend on rehabilitation exposure, selection, baseline function and the time interval studied.

Important change remains a gap

The retrieved direct postoperative chair-rise literature does not support one broadly validated anchor-based MIC for either 5STS or 30CST across all recovery phases. Reliability papers often discuss sensitivity to change without measuring patient importance. Trials reporting improved chair counts show a treatment or recovery response in their sample; they do not automatically identify the smallest meaningful change.

A postoperative application should therefore avoid a simple “responded/not responded” label based solely on a transferred repetition or second cutoff. Separate real-change evidence, patient-rated benefit, transfer independence and strategy. If the purpose is a trial endpoint, group responsiveness may be sufficient; if it is a decision about an individual patient's progress, measurement error and the consequences of misclassification matter more.

Recovery of loading and movement quality

Early asymmetry and the influence of prior strategy

Christiansen's study followed 36 unilateral OA-TKA recipients before surgery and at one, three and six months, with seventeen healthy comparators. Force was recorded under each foot during five chair rises. Weight-bearing asymmetry increased at one month, returned toward the preoperative level by three months and improved by six months. The absolute asymmetry index at six months was not statistically different from controls. [9]

That group comparison does not prove that all participants became symmetric. Two-thirds still had lower average force on the operated side at six months. The absolute index and the operated/nonoperated ratio answer somewhat different questions, and the study did not quantify joint angles or joint moments during the task. Thus apparent normalization of mean vertical-force distribution cannot establish normalized knee mechanics. Modest correlations with function persisted even as the group improved. [9]

Christiansen and colleagues' related analysis included 59 people drawn from control arms of three rehabilitation trials. At one month, the mean operated/nonoperated force ratio was 0.69, compared with 0.87 preoperatively. The model selected preoperative weight-bearing asymmetry plus contemporaneous quadriceps and hamstrings strength ratios; adjusted R² was 0.30. [14]

There is a genuine temporal component in the preoperative asymmetry term. However, the strength measurements entered from the postoperative assessment, so the complete model is not a purely preoperative predictor. Pre-screening and selection among candidate models in a small, selected sample increase uncertainty. The findings support considering both established movement habits and bilateral muscle capacity; they do not prove that changing either variable by a specified amount causes a corresponding reduction in asymmetry.

The Colorado cohorts share investigators, rehabilitation programmes and potentially overlapping source participants. Their papers should be read as complementary analyses rather than simply counted as independent replications. More broadly, exclusion of marked contralateral symptoms, severe obesity or major comorbidity can make laboratory samples easier to test than routine rehabilitation populations.

Persistent deficits at later follow up

Farquhar's one-year work documented altered movement patterns after unilateral TKA despite improvements in strength and clinical performance. Its author-posted original has now been recovered and its qualitative movement findings checked; detailed figure coordinates and the final version after correction were not independently re-extracted, so detailed numerical kinematic claims are not reproduced. A linked correction was located and checked: it adds the omitted dynamometer manufacturer, rather than revising the study's findings. [10, 16]

Alnahdi and colleagues assessed 142 people at six or twelve months after unilateral TKA. The original abstract reports weaker operated quadriceps, lower operated-limb vertical force and lower hip/knee extension moments. Strength symmetry, and at some time points pain, related to loading symmetry. The measurements were concurrent within those postoperative groups; the title's “predicts” should not be read as a forecast from an earlier visit. [12]

The 2023 systematic review of later unilateral-TKA chair-rise kinetics found small pooled deficits beyond one year, with peak-force symmetry closer to one than knee-moment symmetry. Its seven contributing studies should not be added to their primary studies as further independent cohorts. Moreover, a pooled ratio is a group estimate rather than an individual pathological boundary. The review's suggestion that contralateral loading might contribute to OA progression is biologically plausible but is not direct evidence that a specified chair-rise ratio predicts future contralateral disease. [17]

These studies do not contradict the earlier average-force recovery study simply because one reports persistent asymmetry and another no significant control difference. They use different force summaries, joint outcomes, sampling and stages. The clinically relevant synthesis is that total performance and some loading metrics can recover while other mechanical deficits remain.

Foot position is an intervention as well as a protocol choice

Farquhar's 26-person experiment compared self-selected foot position with both knees positioned at ninety degrees at three months after primary unilateral OA-TKA. The chair height matched the standing knee-joint line, the arms were crossed, speed was self-selected and eight trials per condition were averaged. The constrained condition increased hip demand and did not produce the intended increase in operated quadriceps contribution; side-to-side kinetic compensation could become more marked. The conditions were not randomized in order, and the sample excluded people unable to rise without their arms. [11]

Pua's constrained task is different. The operated foot was placed farther back, with its first metatarsophalangeal joint aligned with the opposite heel, and the patient was asked to load the operated limb more. In 706 unilateral primary-TKA recipients assessed at four, eight, twelve and sixteen weeks, this condition produced greater peak-force symmetry than standard foot placement. The mean difference across time was approximately 6.4 percentage points. [5]

The two results should not be presented as a single inconsistent verdict on “constrained STS.” One constrained both knees to a symmetrical starting posture; the other deliberately staggered the feet to encourage operated-limb contribution. Their outcomes also differed: joint kinetics and muscle activity versus peak vertical-force ratio. The task instruction is part of the measurement and changes the strategy being observed.

A clinician may choose either condition to answer a particular question, but should not switch conditions mid-series without marking the change. A higher symmetry score immediately after cueing is evidence of a task response, not proof that a learned movement pattern will persist, transfer to stairs or reduce future OA risk.

Large clinical recovery curves and their limits

Pua's 706-person study is valuable because it moves force measurement beyond a small laboratory cohort. Participants attended one Singapore centre; the investigators used a 46-cm chair and modified bilateral bathroom scales acquiring continuous force at 80 Hz. The symmetry score was 100 × operated-limb peak force / nonoperated-limb peak force. Arm support was allowed when necessary and recorded. This is a custom instrumented system, not two ordinary scales whose displayed values are read at rest. [5]

The standard and staggered-foot curves improved nonlinearly over the first four months. The paper describes ninety-per-cent symmetry at approximately sixteen and eight weeks respectively. These curves include between-patient variation; they are not deadlines or recovery targets for every individual. Ninety per cent was not demonstrated to be a patient-important or safety boundary. Patients with conditions preventing completion were excluded, and the reference population and task instructions must accompany any comparison.

The strongest correlates of standard symmetry included both quadriceps, whereas constrained symmetry was most strongly related to the operated quadriceps. Contralateral pain was associated with greater apparent symmetry. That is a particularly important interpretive warning: a ratio can look better because the comparison limb is painful, not because the operated limb is fully restored. The absolute force values and both knees' symptoms remain necessary. [5]

Prognosis and causal interpretation

Serial association labelled predictive validity

The Pua study analysed the relation between standard or constrained symmetry and fast gait speed across all postoperative visits, adjusting for demographic and knee-impairment variables. Its method used same-visit time-varying measurements in generalized least-squares models. It did not test whether a four-week symmetry value predicted twelve- or sixteen-week gait speed. [5]

Consequently, the reported nonlinear association is repeated concurrent evidence. It is useful for construct interpretation and hypothesis generation, but does not validate a future walking-speed calculator. The inverted-U relationship also argues against a simple “more symmetry is always better” rule. A constrained task adding explanatory value beyond a standard task is not the same as showing incremental prognostic benefit, calibration or clinical utility.

Christiansen and colleagues' analysis similarly combines a preoperative component with concurrent postoperative strength. Alnahdi's “predictor” terminology describes regression among measurements at six or twelve months. These studies should be kept distinct from designs in which every predictor is available before the outcome. Clear temporal classification prevents a rehabilitation tool from promising a forecast that the original paper never tested. [12, 14]

Preoperative performance and later performance

A 2025 retrospective study followed 43 TKA patients before surgery and at ninety and 180 days. Its 43-cm thirty-second chair test used arms crossed; TUG used normal speed. Higher preoperative chair counts were associated with higher later counts, with correlations around 0.68 and 0.71. Mean counts improved substantially across the six months. [6]

This is genuine longitudinal association, but the analysis did not provide a calibrated, externally validated individual prognosis. Selection required complete follow-up and ASA class 2–3, and adjustment for demographics and comorbidity was limited. Reported functional categories were drawn from external age/sex references, rather than validated TKA decision thresholds. The study supports collecting a baseline and following the trajectory, not assigning a future independence probability or a treatment plan from one preoperative count.

The same-day-discharge paper on five-rise testing is a separate prognostic question. It concerns an outpatient total-joint-arthroplasty pathway rather than later transfer recovery in a TKA-only cohort. Its original full text was not retrieved here. Even a well-performing local discharge cutoff would depend on selection, anaesthesia, pain control, home support and discharge policy. It should not be imported as a generic postoperative mobility threshold. [18]

Later real world activity and negative evidence

The Veterans study assessed chair stands and TUG at fourteen weeks after TKA, then measured daily steps and peak cadence using thigh accelerometry at 38 weeks. Of 92 randomized participants, 87 had the required follow-up, with further missingness in fitted models. The group was predominantly male and participated in a trial of an added activity-behaviour intervention. [7]

Thirty-second chair-stand performance was not associated with later step count or peak cadence in the preliminary analyses. TUG and a physical-health questionnaire contributed to some continuous-outcome models, but none of the tested predictors significantly classified the selected 7,500-step threshold. This does not make the chair test useless. It shows that transfer capacity and later daily walking behaviour are not the same construct, and that prognosis is outcome specific.

No sufficiently appraised original in this report established a chair-rise cutoff for prospectively recorded falls across the primary unilateral-TKA recovery pathway. A correlation with balance confidence, a slow score in people reporting falls, or a cutoff from older adults without TKA should not be substituted for that evidence. Prospective falls models require clear fall definitions, follow-up ascertainment, events, adjustment and validation.

Training effects do not validate measurement or prediction

An intervention can improve time, loading or confidence without establishing how much of a small individual change exceeds error. Conversely, a measure may be reliable and responsive even when a particular intervention has no effect. Trials of cueing, feedback, strengthening or task practice can inform treatment, but causal treatment evidence must not be inferred from cross-sectional strength–symmetry correlations.

A symmetry target also requires a defensible clinical purpose. It may be used to encourage operated-limb participation under supervision, but current evidence does not establish that reaching an arbitrary ratio prevents contralateral OA, falls or revision. The relation among capacity, strategy and long-term health outcomes remains a research question.

Prognostic evidence at a glance

Table 3 Prognostic evidence at a glance

Instrumented assessment and emerging technology

Force systems and interpretable asymmetry

For bilateral force measurement, first define the task phase and output. Peak force ratio can depend on whether each limb's separate peak or a simultaneous time point is used. Average force across the entire test includes sitting, rising and lowering in a way that may obscure brief unloading. An impulse incorporates duration. All need clear side labelling and a documented formula.

Force-plate or scale calibration, zeroing, drift and sampling affect small differences. The chair must not transmit its load to the plates in a way that contaminates foot forces. Foot placement and hand support need recording. A ratio based on a very small denominator can be unstable, while an absolute asymmetry index loses direction. For a patient with bilateral surgery or symptomatic contralateral OA, a unilateral reference curve may be inappropriate even if the ratio can be calculated.

The modified-scale study shows a feasible clinical pathway, but not the equivalence of every inexpensive scale. Its small patient retest subset and absence of an established important-change threshold should accompany any implementation. A tool should present bilateral forces, the ratio and the conditions together, rather than generating an unexplained red/green symmetry indicator. [5]

Video and markerless assessment

Video can help document arm use, foot staggering, trunk lean, incomplete extension and controlled descent. It can also support event timing or repetition review. This observational use is different from claiming precise joint angles or estimating forces. Camera position, occlusion, clothing, chair height, field of view and the operated side can affect visibility and algorithm performance.

Validation in nonoperative OA, healthy adults or an unrelated neurological population is not direct TKA validation. After surgery, aids, pain-limited ranges, slower movement and occlusion from assistance may change performance. A model trained to identify complete independent rises may fail exactly in the early patients who most need monitoring. Non-detection should be retained as a quality flag, not converted silently to zero repetitions or discarded.

A useful validation study compares the actual intended output with an appropriate synchronized reference, reports individual agreement and error across the range, and includes the target postoperative stage. Rescoring the same video tests scorer reliability; repeating the chair task on another day tests patient measurement reliability. Their errors should not be combined or substituted without an explicit model.

Muscle simulation is mechanistic evidence

Blessinger and colleagues' 2025 study analysed seven individuals with predominantly medial-compartment OA before and six months after primary posterior-stabilizing TKA. Participants rose from a 55.2-cm chair with arms crossed. Motion capture, force plates and EMG informed dynamic musculoskeletal simulations. One representative rise was selected at each visit according to data quality. The study found little postoperative change in several sagittal-plane strategies and modelled muscle-function patterns. [19]

Its 2026 extension used the same seven surgical participants with seven age-matched healthy controls. Differences in kinematics and estimated mechanical advantage helped explain how available strength might not translate into the same task contribution. The paper's correction adds previously missing electronic supplementary material; it does not announce changed numerical findings. The two papers are companion analyses of the same surgical sample, not independent replication. [20, 21]

These studies deepen understanding of compensation, but the estimated muscle forces are model outputs constrained by assumptions and experimental signals. They are not direct in vivo muscle-force measurements or validated individual prognosis. A high chair reduces demand relative to many everyday seats, and selection of a high-quality representative trial differs from averaging all attempts or observing natural home transfers. The studies should guide questions about strategy, not supply universal clinical angle or muscle-force cutoffs.

Power needs a defined mechanical quantity

A faster rise is not automatically more operated-knee power. Mechanical power is work per unit time or, at a joint, moment multiplied by angular velocity under an explicit convention. A chair-rise estimate based on body mass, estimated vertical displacement and time represents a model of whole-body external performance. It does not separately quantify knee, hip and ankle contributions, nor capture all effects of hand support.

No chair-time-to-watts formula should be presented as direct postoperative quadriceps power without validation against the intended reference in TKA. Likewise, force-rise or torque-rise slopes require adequate sampling, defined onset and analysis windows. Those dynamometry constructs belong in a complementary strength/rapid-force assessment; they cannot be inferred reliably from a repetition count alone.

Stage specific use

Before surgery, record both knees' symptoms and the strategy the patient already uses. This provides context for postoperative compensation and a performance baseline. Because the baseline may already be impaired, return to it is not synonymous with healthy function. Assess prognosis with measures whose predictor timing and validation match the intended counselling question.

During inpatient recovery, prioritize safe transfer ability, assistance and the environment. A raised chair or arm support may be necessary and clinically appropriate. Do not require an unassisted standardized five-rise test simply to populate a score. If the standard test cannot be completed, record the reason, the level of assistance and a reproducible alternative task. Surgical precautions and medical stability take precedence over comparability.

During early outpatient recovery, serial chair performance becomes more feasible, but swelling, analgesia, fatigue and practice can change results. Keep a stable chair and instruction. Record whether the patient uses one or both arms and whether the operated foot is placed forward to avoid loading. If progression involves removing hand support or lowering the chair, identify it as a changed testing condition rather than interpreting the new number against the old condition's error band.

At three to six months, examine the relation between capacity and strategy. An acceptable five-rise time does not guarantee operated-limb participation. Where the observed pattern or patient goal warrants it, add force or movement analysis. Consider contralateral pain, which can make a symmetry ratio look reassuring while both limbs remain limited. A plateau in one test need not mean that all aspects of recovery have stopped.

At twelve months or later, ask whether the task matches real-world goals. Toilet, sofa, low-chair, loaded or repeated transfers may remain difficult despite adequate performance on a standard clinic chair. Those activities can be assessed separately, but their scores are not interchangeable with the published standard test. Persistent deficits merit a broader assessment of bilateral strength, joint motion, pain, confidence and activity context rather than automatic attribution to the implant.

Protocol checklist for clinical tools

The minimum dataset includes operation date, indication and laterality; contralateral disease or replacement; exact test variant; chair seat height, firmness, back and arms; initial sitting position; feet and footwear; hand support and person assistance; instruction and speed; practice, number of scored trials and aggregation; start and end events; count rule; rest; symptoms and test completion. It should also distinguish a repeat score under the same conditions from a score under a deliberately progressed task.

For instrumented testing, add device, placement, acquisition rate, filtering, calibration, event detection, chosen trial/phase, force or moment normalization and the full symmetry formula. Preserve absolute bilateral values. Record whether arm force was measured or merely allowed, because unmeasured upper-limb support changes how lower-limb loading should be interpreted.

The interpretation layer should identify the source population and the type of claim. “Reliable timing of the same trial, ” “repeat-task error, ” “recovery reference, ” “concurrent association, ” “later-outcome association” and “validated prognosis” should not be blended into one evidence badge. A source with a unresolved discrepancy should be displayed with a qualification rather than silently corrected.

A worked interpretation illustrates the difference. If a patient performs one more rise but changes from pushing on both arms to arms crossed, report the count and the reduced support; do not use the old assisted score as though it were a standardized no-arm baseline. If the count improves while a force ratio falls, neither measure automatically invalidates the other: total task performance improved while limb contribution changed. The clinician must decide whether the strategy is appropriate for that stage and goal.

Evidence limits and research priorities

The core limitations are small reliability samples, frequent same-day testing, heterogeneous chair protocols, inconsistent endpoint definitions, selection of successful independent performers, and sparse direct MIC evidence. A high ICC and a narrow study-specific confidence interval do not overcome a mismatch in stage, laterality or assistance. Contradictory source numbers further argue against automatic threshold deployment.

The next useful studies would estimate between-day error at clearly defined postoperative stages; include patients using arms and aids without erasing their modified status; establish patient-important change using a relevant anchor; compare video and inexpensive force systems with appropriate references; and prospectively test whether early chair performance or mechanics adds to models of independence, activity or falls. Such models need external validation, calibration and demonstration that their use improves a decision.

The most important unresolved mechanistic question is not simply whether asymmetry exists. It is which type of asymmetry, at which phase, under which task and in which patient, is related to a meaningful later outcome. Until that is clearer, individualized interpretation is more defensible than a universal symmetry target.

Conclusion

Chair-rise testing is a useful part of TKA rehabilitation assessment when the task is defined and assistance is preserved. Time or count should be interpreted alongside limb loading and movement strategy when clinically relevant. Direct postoperative reliability evidence supports several protocols, but important-change thresholds and prognosis are less secure. The safest tool records the task faithfully, distinguishes capacity from mechanics, and communicates the limits of the evidence rather than converting every improvement into an unsupported success label.

Primary study evidence matrix

A denotes measurement properties; B concurrent association; C longitudinal recovery or association; D prediction development. Values retain original units and confidence levels. An ICC or a paper's “predictor” label does not override the actual design.

Table 4 Primary study evidence matrix

[15] is a guideline with a consensus outcome statement. [17] is secondary synthesis of seven later-TKA kinetic studies and is not an additional cohort. [21] and [16] are corrections linked to their parent articles. No numerical quality score or pooled estimate is generated from these heterogeneous records.

Search appendix

Exact executed PubMed query

("Arthroplasty, Replacement, Knee"[MeSH Terms] OR "total knee arthroplasty"[Title/Abstract] OR "total knee replacement"[Title/Abstract]) AND ("sit to stand"[Title/Abstract] OR "sit-to-stand"[Title/Abstract] OR "chair stand"[Title/Abstract] OR "chair rise"[Title/Abstract] OR transfer*[Title/Abstract]) AND (reliab*[Title/Abstract] OR valid*[Title/Abstract] OR responsiv*[Title/Abstract] OR asymmetr*[Title/Abstract] OR biomechan*[Title/Abstract] OR "measurement error"[Title/Abstract] OR "minimal detectable"[Title/Abstract] OR "minimal important"[Title/Abstract] OR prognos*[Title/Abstract] OR predict*[Title/Abstract] OR longitudinal[Title/Abstract]) AND ("1800/01/01"[Date - Publication] : "2026/10/02"[Date - Publication])

Exact executed Scopus query

TITLE-ABS-KEY("total knee arthroplasty" OR "total knee replacement") AND TITLE("sit-to-stand" OR "sit to stand" OR "chair stand" OR "chair rise" OR "chair-rise" OR transfer*) AND PUBYEAR < 2027

Coverage and reconciliation

Scopus reported 101 records. The returned pages contained 101 distinct Scopus identifiers. This query is title-focused and narrower than PubMed, not a second identical search. PUBYEAR < 2027 is a yearly restriction; electronically published papers were checked against the actual cutoff where relevant.

Counts are retrieval records, not included studies. Sources and domains overlap and cannot be summed. Deduplication used DOI, PMID/provider ID and title/author/year. Treatment-only, technical implant wear, off-indication, revision and mixed-population records were screened for report relevance rather than removed by aggressive query exclusions.

Targeted follow on work

Reference and citation discovery was used for Kennedy 2005, Christiansen 2011 and Pua 2016; these provider-limited calls are discovery, not exhaustive citation coverage. Original retrieval targeted each cited DOI through bibliographic databases, official PMC and publisher pages, and author or institutional repositories. A targeted search located the Huber thesis chapter, Farquhar correction and recent Blessinger companion papers/correction. Failed or restricted retrieval stayed explicitly marked. No access was inferred from a metadata open-access flag.

Main limitations

The measurement/prognosis terminology and title-focused Scopus strategy can miss biomechanical or technology studies not using these labels. Targeted chasing reduces but does not eliminate this problem. The manuscripts therefore characterize the evidence appraised and its limits rather than claim exhaustive absence of studies. Later publications are not included.

References

References are numbered in first citation order. Source descriptions identify the material examined and do not constitute a study quality rating. Links identify the original publication or the named primary source version.

1. Medina-Mirapeix F, Vivo-Fernández I, López-Cañizares J, García-Vidal JA, Benítez-Martínez JC, Del Baño-Aledo ME. Five times sit-to-stand test in subjects with total knee replacement: Reliability and relationship with functional mobility tests. Gait & posture. 2018;59:258-260. DOI 10.1016/j.gaitpost.2017.10.028 Source examined: Original PDF and Figure 1 available; text/figure lower agreement-limit discrepancy.

Source note: SRC-ad0cc42cdafe Medina-Mirapeix F 2018

2. Unver B, Kalkan S, Yuksel E, Kahraman T, Karatosun V. Reliability of the 50-foot walk test and 30-sec chair stand test in total knee arthroplasty. Acta ortopedica brasileira. 2015;23(4):184-7. DOI 10.1590/1413-78522015230401018 Source examined: Original PDF; Table 2 visually checked, unresolved SRD discrepancy.

Source note: SRC-5add70458765 Unver B 2015

3. Sarac DC, Unver B, Karatosun V. Validity and reliability of performance tests as balance measures in patients with total knee arthroplasty. Knee surgery & related research. 2022;34(1):11. DOI 10.1186/s43019-022-00136-4 Source examined: Complete original article and tables.

Source note: SRC-7757dfb24f28 Sarac DC 2022

4. Tolk JJ, Janssen RPA, Prinsen CAC, Latijnhouwers DAJM, van der Steen MC, Bierma-Zeinstra SMA, et al. The OARSI core set of performance-based measures for knee osteoarthritis is reliable but not valid and responsive. Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA. 2019;27(9):2898-2909. DOI 10.1007/s00167-017-4789-y Source examined: Original article; preoperative reliability distinguished.

Source note: SRC-a6727b5507a5 Tolk JJ 2019

5. Pua YH, Tan JW, Poon CL, Chew ES, Seah FJ, Thumboo J, et al. Sit-to-Stand Weight-Bearing Symmetry Performance in Total Knee Arthroplasty: Recovery Curves, Correlates, and Predictive Validity With Gait Speed. American journal of physical medicine & rehabilitation. 2022;101(7):666-673. DOI 10.1097/phm.0000000000001882 Source examined: Complete accepted manuscript.

Source note: SRC-5796e3c1b5da Pua YH 2022

6. Yücel MO, Sağlam S, Dalaslan RE, Arıcan M, Karaduman ZO, Akar B, et al. Significance of Preoperative Multidisciplinary Assessment with 30-Second Sit-to-Stand and Timed Up-and-Go Tests in Predicting Postoperative Outcomes. Journal of clinical medicine. 2025;14(4). DOI 10.3390/jcm14041085 Source examined: Complete original article; selected retrospective cohort.

Source note: SRC-d797499566cf Yucel MO 2025

7. Kline PW, Hanlon SL, Richardson VL, Hoffman RM, Melanson EL, Juarez-Colunga E, et al. Functional Capacity at Rehabilitation Discharge Predicts Physical Activity Characteristics 24 Weeks Later for People With Total Knee Arthroplasty: A Secondary Analysis of a Randomized Controlled Trial. Archives of physical medicine and rehabilitation. 2025;106(6):845-852. DOI 10.1016/j.apmr.2025.01.416 Source examined: Complete original article; later activity outcome.

Source note: SRC-c0b74bd10b4b Kline PW 2025

8. Huber EO, Meichtry A, de Bie RA, Bastiaenen CH. Construct validity of change scores of the Chair Stand Test versus Timed Up and Go Test, KOOS questionnaire and the isometric muscle strength test in patients with severe knee osteoarthritis undergoing total knee replacement. Manual therapy. 2016;21:262-7. DOI 10.1016/j.math.2015.09.012 Source examined: Publisher abstract and author thesis chapter 7 (pp 134–139).

Source note: SRC-02d380eed3db Huber EO 2016

9. Christiansen CL, Bade MJ, Judd DL, Stevens-Lapsley JE. Weight-bearing asymmetry during sit-stand transitions related to impairment and functional mobility after total knee arthroplasty. Archives of physical medicine and rehabilitation. 2011;92(10):1624-9. DOI 10.1016/j.apmr.2011.05.010 Source examined: Complete original article and tables.

Source note: SRC-764ccd67a90d Christiansen CL 2011

10. Farquhar SJ, Reisman DS, Snyder-Mackler L. Persistence of altered movement patterns during a sit-to-stand task 1 year following unilateral total knee arthroplasty. Physical therapy. 2008;88(5):567-79. DOI 10.2522/ptj.20070045 Source examined: Author-posted original body now recovered; qualitative findings checked. Detailed figure coordinates and the final version after correction were not independently re-extracted; separate correction inspected.

Source note: SRC-d5509b300307 Farquhar SJ 2008

11. Farquhar SJ, Kaufman KR, Snyder-Mackler L. Sit-to-stand 3 months after unilateral total knee arthroplasty: comparison of self-selected and constrained conditions. Gait & posture. 2009;30(2):187-91. DOI 10.1016/j.gaitpost.2009.04.007 Source examined: Complete accepted manuscript and table.

Source note: SRC-138da958b404 Farquhar SJ 2009

12. Alnahdi AH, Zeni JA, Snyder-Mackler L. Quadriceps strength asymmetry predicts loading asymmetry during sit-to-stand task in patients with unilateral total knee arthroplasty. Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA. 2016;24(8):2587-94. DOI 10.1007/s00167-015-3827-x Source examined: Abstract verified; full article unavailable.

Source note: SRC-d8e2ac5b8e7d Alnahdi AH 2016

13. Mizner RL, Snyder-Mackler L. Altered loading during walking and sit-to-stand is affected by quadriceps weakness after total knee arthroplasty. Journal of orthopaedic research : official publication of the Orthopaedic Research Society. 2005;23(5):1083-90. DOI 10.1016/j.orthres.2005.01.021 Source examined: Abstract verified; full article unavailable.

Source note: SRC-98f4579514d6 Mizner RL 2005

14. Christiansen CL, Bade MJ, Weitzenkamp DA, Stevens-Lapsley JE. Factors predicting weight-bearing asymmetry 1 month after unilateral total knee arthroplasty: a cross-sectional study. Gait & posture. 2013;37(3):363-7. DOI 10.1016/j.gaitpost.2012.08.006 Source examined: Complete original article and tables.

Source note: SRC-38155fd24384 Christiansen CL 2013

15. Jette, Diane U, Hunter, Stephen J, Burkett, Lynn, Langham, Bud, Logerstedt, David S, Piuzzi, Nicolas S, et al. Physical Therapist Management of Total Knee Arthroplasty. Physical therapy. 2020. DOI 10.1093/ptj/pzaa099 Source examined: Complete guideline.

Source note: SRC-27ba0555a48c Jette 2020

16. “Persistence of altered movement patterns…” Farquhar SJ, Reisman DS, Snyder-Mackler L. Phys Ther. 2008; 88:567–579. Physical Therapy. 2008. DOI 10.2522/ptj.20070045.cx Source examined: Official publisher correction inspected; omitted equipment manufacturer, no revised findings.

Source note: SRC-9168fd3deae6 Persistence of altered movement 2008

17. Almonroeder TG, Friedrich JO, Hyoda H, Grabowski P, Jagim A, Dobbs W, et al. Inter-limb kinetic asymmetries during sit-to-stand performance persist following unilateral total knee arthroplasty: A systematic review and meta-analysis. Clinical biomechanics (Bristol, Avon). 2023;110:106103. DOI 10.1016/j.clinbiomech.2023.106103 Source examined: Review abstract verified; original retrieval incomplete; secondary context only.

Source note: SRC-b71eae79e1c5 Almonroeder TG 2023

18. Camillieri S. The five times sit-to-stand test predicts same-day discharge for outpatients undergoing total joint arthroplasty. International orthopaedics. 2024;48(2):351-356. DOI 10.1007/s00264-023-05994-5 Source examined: Abstract verified; mixed total-joint pathway, full article unavailable.

Source note: SRC-99b7996e5453 Camillieri S 2024

19. Blessinger, Kathryn S, Roelker, Sarah A, Lloyd, Reese A, Schmitt, Laura C, Chaudhari, Ajit M W, Siston, Robert A. Do Kinematics or Muscle Function During Sit-to-Stand Change Following a Primary Total Knee Arthroplasty? Annals of biomedical engineering. 2025. DOI 10.1007/s10439-025-03782-3 Source examined: Complete original article.

Source note: SRC-d2ce195ba51d Blessinger 2025

20. Blessinger, Kathryn S, Lloyd, Reese A, Schmitt, Laura C, Chaudhari, Ajit M W, Siston, Robert A. Kinematics Limit the Potential to Capitalize on Available Muscle Strength During Sit-to-Stand for Patients Before and After Total Knee Arthroplasty. Annals of biomedical engineering. 2026. DOI 10.1007/s10439-026-04338-9 Source examined: Original article; companion analysis of the 2025 study cohort.

Source note: SRC-489dee1778d2 Blessinger 2026

21. Blessinger, Kathryn S, Lloyd, Reese A, Schmitt, Laura C, Chaudhari, Ajit M W, Siston, Robert A. Correction: Kinematics Limit the Potential to Capitalize on Available Muscle Strength During Sit-to-Stand for Patients Before and After Total Knee Arthroplasty. Annals of biomedical engineering. 2026. DOI 10.1007/s10439-026-04361-w Source examined: Original correction PDF; adds missing electronic supplement.

Source note: SRC-5bfb84a01347 Blessinger 2026