Outcomes Measure in Joint Arthroplasty

Archival Presentation Notice: This article modernizes the multimedia presentation “Outcomes Measures after TKA” originally presented by Jess H. Lonner, MD (Director, Knee Replacement Surgery, Pennsylvania Hospital). The historical Flash lecture has been reconstructed into the synchronized video slide presentation above, with the original file preserved in the digital archives (Outcomes_Measure_in_Joint_Arthroplasty_Lonner.swf).

1. High-Yield Summary

Total knee arthroplasty (TKA) and total hip arthroplasty (THA) represent two of the most cost-effective, life-enhancing reconstructive interventions in modern surgical medicine. Historically, orthopaedic success was quantified primarily through surgeon-derived surrogate parameters: implant survivorship on Kaplan-Meier life tables, radiographic component alignment, and gross physical examination findings such as range of motion and joint stability. However, a profound paradigm shift has decoupled objective surgical success from patient perception: despite implant survivorship rates routinely exceeding 95% at 15 to 20 years, approximately 15% to 20% of primary total knee arthroplasty patients report dissatisfaction or functional impairment in daily life.

• The Satisfaction Disconnect: While primary total hip arthroplasty yields patient satisfaction rates of 90% to 95%, primary total knee arthroplasty achieves satisfaction rates of only 80% to 85%. This satisfaction gap is driven primarily by unmet preoperative expectations, residual anterior knee pain, difficulty with deep flexion (stair descent, squatting, kneeling), and stiffness.
• Evolution of Arthroplasty Rating Systems: Early scoring instruments, such as the 1989 Knee Society Clinical Rating System, conflated joint-specific clinical examination with general functional capacity. Because functional walking and stair scores were severely confounded by systemic comorbidities (cardiac, pulmonary, spinal, and contralateral joint disease), modern evaluation mandates independent, psychometrically validated subscales.
• Modern Multi-Domain Architecture: The 2011 Knee Society Knee Scoring System (KSS), co-developed by Scuderi, Bourne, Noble, and Lonner, overhauled outcomes tracking by parsing outcomes into four discrete domains: an Objective Knee Score (physician-derived), Patient Satisfaction Score, Patient Expectation Score, and Functional Activity Score (capturing walking, standard daily tasks, advanced athletics, and discretionary activities).
• Patient-Reported Outcome Measures (PROMs): Standardized validated instruments—including the Oxford Knee Score (OKS), Knee Injury and Osteoarthritis Outcome Score (KOOS / KOOS JR), and Forgotten Joint Score (FJS-12)—eliminate observer bias and provide direct quantification of the patient’s lived experience.
• The “Forgotten Joint” Horizon: In high-functioning, active arthroplasty recipients, traditional instruments (such as the WOMAC and 1989 KSS) demonstrate substantial ceiling effects (> 40%). The Forgotten Joint Score-12 (FJS-12) measures joint awareness during daily life, offering low ceiling effects (10% to 20%) and superior discriminative capacity between high-performing reconstructive modalities, including unicompartmental knee arthroplasty (UKA) versus TKA.
• Clinically Meaningful Metrics: Raw statistical significance does not equate to clinical importance. Validated outcome interpretation relies on three critical psychometric benchmarks: the Minimal Clinically Important Difference (MCID), Patient Acceptable Symptom State (PASS), and Substantial Clinical Benefit (SCB).

2. Evolution of Arthroplasty Outcome Measurement

The science of outcomes measurement in joint arthroplasty has undergone three distinct evolutionary epochs over the past six decades:

The Mechanical and Implant Era (1960s–1980s)

In the foundational decades of Charnley low-friction arthroplasty and early total condylar knee prostheses, surgical outcomes were defined almost exclusively by mechanical and radiographic longevity. Success was judged by the absence of revision surgery, lack of progressive radiolucent lines at bone-cement interfaces, and maintenance of coronal mechanical alignment within ± 3° of neutral. Physician-derived composite scores—such as the original 1970s Hospital for Special Surgery (HSS) Knee Score—dominated the literature. However, these systems suffered from profound inter-observer variability, observer bias, and paternalistic assessment: surgeons routinely graded outcomes as “excellent” based on radiographic component stability and passive flexion on an examination table, even when the patient experienced disabling pain during functional weight-bearing.

The Dual Scoring and Transitional Era (1989–2000s)

Recognizing the conflation of knee-specific pathology with systemic functional decline, Insall, Dorr, Scott, and Scott introduced the 1989 Knee Society Clinical Rating System. This pivotal system split scoring into two separate 100-point scales: an objective Knee Score (evaluating pain, stability, and range of motion, with deductions for flexion contracture, extension lag, and malalignment) and a Function Score (evaluating walking distance and stair climbing, with deductions for walking aids). While this represented a monumental advance, the 1989 KSS had major vulnerabilities: the function score remained vulnerable to non-knee medical comorbidities (e.g., severe lumbar stenosis, congestive heart failure), and active, younger patients rapidly hit the 100-point ceiling, obscuring differences between surgical techniques and prosthetic designs.

The Modern Patient-Reported and Value-Based Era (2010s–Present)

Over the past fifteen years, outcomes measurement has shifted to rigorous patient-reported outcome measures (PROMs), health-related quality of life (HRQoL) metrics, and health economics. Regulatory agencies, national arthroplasty registries (e.g., American Joint Replacement Registry [AJRR], UK National Joint Registry [NJR], Swedish Knee Arthroplasty Register [SKAR]), and third-party payers (such as the Centers for Medicare & Medicaid Services [CMS] Comprehensive Care for Joint Replacement [CJR] model) have instituted mandatory collection of pre- and postoperative PROMs. Contemporary research prioritizes patient-centered goals: expectation fulfillment, satisfaction, joint awareness, and return to recreational activities.

3. Objective Clinician-Administered Rating Systems

Clinician-administered rating systems continue to provide essential objective data regarding mechanical joint integrity, soft-tissue balance, and physical examination findings that cannot be captured by patient questionnaires alone.

The 1989 Knee Society Clinical Rating System (Original KSS)

The 1989 KSS remains widely cited in historical registries and longitudinal cohort studies. It is bifurcated into two distinct domains:

• Objective Knee Score (100 Points Maximum): Evaluates pain (50 points: none = 50, mild/occasional = 45, mild stairs only = 40, moderate occasional = 30, moderate continuous = 20, severe = 0), range of motion (25 points: 1 point per 5° of flexion, maximum 25 for 125°), and joint stability (25 points: anteroposterior stability < 5 mm = 10 points; mediolateral stability 5°, extension lags > 5°, and coronal malalignment outside 5° to 10° anatomic valgus.
• Function Score (100 Points Maximum): Evaluates walking distance (50 points: unlimited = 50, > 10 blocks = 40, 5–10 blocks = 30, < 5 blocks = 20, housebound = 0) and stair climbing (50 points: normal up/down = 50, normal with rail = 40, step-by-step with rail = 30, unable down = 15), with deductions for assistive devices (cane -10 points, crutches/walker -20 points).

Limitations: The 1989 system cannot differentiate between high-functioning patients who participate in low-impact athletics versus those who can merely walk 10 blocks. Furthermore, aging patients frequently experience declining functional scores due to spinal stenosis, cardiovascular disease, or cognitive impairment despite maintaining a pain-free, flawlessly functioning knee implant.

4. Modern Multi-Domain Architecture: The 2011 Knee Society Scoring System

To overcome the critical psychometric deficiencies of the 1989 system, the Knee Society commissioned an international steering committee (led by Scuderi, Bourne, Noble, Benjamin, Lonner, and Scott) to develop a validated, four-component scoring system that explicitly measures patient expectations, satisfaction, and advanced functional activities.

Component Architecture of the 2011 KSS

• 1. Objective Knee Score (100 Points Max, Surgeon-Completed): Evaluates alignment (anatomic angle), mechanical instability (coronal laxity at 0° and 30°, sagittal drawer), joint motion (flexion and extension lag), and intra-articular symptoms (effusion, patellofemoral crepitus).
• 2. Patient Satisfaction Score (40 Points Max, Patient-Completed): Five questions graded on a 7-point Likert scale assessing satisfaction with the knee during sitting, lying in bed, walking on flat ground, performing light activities, and overall satisfaction.
• 3. Patient Expectation Score (15 Points Max, Patient-Completed): Evaluates three specific questions regarding the patient’s preoperative expectations versus postoperative reality regarding pain relief, performance of daily activities, and ability to participate in recreational or sports activities.
• 4. Functional Activity Score (100 Points Max, Patient-Completed): Subdivided into four distinct categories: walking and standing tolerance (30 points), standard daily activities such as stairs and chair rising (30 points), advanced activities such as squatting, kneeling, and heavy lifting (25 points), and discretionary recreational activities such as golf, cycling, or swimming (15 points).

By capturing advanced and discretionary activities, the 2011 KSS successfully eliminates the ceiling effect that crippled previous systems, providing sensitive discrimination between contemporary implant designs, alignment strategies, and surgical techniques.

5. Patient-Reported Outcome Measures (PROMs) in Arthroplasty

Modern clinical practice relies on a battery of joint-specific and general health status instruments administered preoperatively and at standardized postoperative intervals (6 weeks, 3 months, 1 year, 2 years, and 5 years).

Oxford Knee Score (OKS)

Developed by Dawson, Fitzpatrick, Murray, and Carr in 1998, the OKS is a 12-item joint-specific questionnaire designed specifically for patients undergoing total knee replacement. Each question is scored from 0 to 4 (in the modern scoring system), yielding an overall range of 0 to 48 points (where 48 represents the best possible outcome). The OKS exhibits outstanding internal consistency (Cronbach’s alpha > 0.85), low respondent burden (taking < 5 minutes to complete), and high sensitivity to postoperative recovery.

Knee Injury and Osteoarthritis Outcome Score (KOOS & KOOS JR)

Originally formulated by Roos et al. in 1998, the full KOOS comprises 42 items evaluating five separate dimensions: Pain, other Symptoms, Function in Daily Living (ADL), Function in Sport and Recreation (Sport/Rec), and Knee-Related Quality of Life (QOL). Each subscale is transformed to a normalized score of 0 to 100 (where 0 indicates extreme knee problems and 100 indicates no knee problems). Because the 42-item questionnaire imposes significant administrative burden in busy surgical clinics, the American Academy of Orthopaedic Surgeons (AAOS) developed the shortened KOOS JR (Joint Replacement). KOOS JR consists of 7 items selected through item-response theory (IRT) to represent pain and physical function, scored on an interval scale from 0 to 100, which has been widely adopted by CMS and institutional registries.

Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)

Introduced by Bellamy et al. in 1988, the WOMAC consists of 24 items divided into three subscales: Pain (5 items), Stiffness (2 items), and Physical Function (17 items). While historically the international benchmark for clinical trials of osteoarthritis therapeutics and arthroplasty, WOMAC is plagued by high ceiling effects in active postoperative cohorts: up to 40% to 50% of patients achieve the maximum score despite ongoing limitations in advanced recreational sports.

NIH PROMIS (Patient-Reported Outcomes Measurement Information System)

NIH PROMIS leverages computerized adaptive testing (CAT) and modern item response theory to measure patient-reported outcomes dynamically. Rather than presenting fixed questions, PROMIS algorithms tailor subsequent questions based on the respondent’s previous answers. The PROMIS Physical Function (PF) CAT and Pain Interference (PI) CAT achieve high psychometric precision with an average of only 4 to 6 questions per domain, drastically minimizing respondent fatigue while correlating strongly with legacy instruments like the KOOS and OKS.

6. Joint Awareness and The “Forgotten Joint” Concept

As surgical techniques have advanced and implant survivorship has stabilized at exceptional levels, the ultimate aspiration of total joint arthroplasty has evolved beyond mere pain relief to the restoration of a natural, unconscious joint sensation during daily activities—the concept of the “Forgotten Joint.”

Forgotten Joint Score-12 (FJS-12)

Developed and validated by Behrend, Giesinger, Giesinger, and Kuster in 2012 (and validated in British populations by Hamilton et al. in 2017), the FJS-12 comprises 12 items assessing joint awareness across various daily activities, ranging from resting in bed and walking for more than 15 minutes to climbing stairs and participating in favorite sports. Each item is rated on a 5-point Likert scale (never, almost never, seldom, sometimes, mostly), and the sum is transformed linearly to a 0 to 100 scale, where 100 indicates complete unawareness of the prosthetic joint during everyday life.

The primary psychometric advantage of the FJS-12 is its remarkably low ceiling effect. In postoperative arthroplasty populations at 1 to 2 years, the ceiling effect of the FJS-12 is typically between 10% and 20%, compared to 40% to 50% for the WOMAC and KOOS ADL subscales. This renders the FJS-12 uniquely sensitive to subtle differences in kinematic balance, soft-tissue tensioning, and bearing designs. Multiple comparative trials have demonstrated that patients undergoing unicompartmental knee arthroplasty (UKA) achieve significantly higher FJS-12 scores than those undergoing total knee arthroplasty (TKA), reflecting the retention of the cruciate ligaments, normal patellofemoral mechanics, and native joint proprioception.

7. Psychometric Standards: Validity, Reliability, and Responsiveness

To be clinically credible and scientifically sound, any outcome instrument used in joint arthroplasty must satisfy rigorous psychometric criteria established by the COSMIN (COnsensus-based Standards for the selection of health Measurement INstruments) initiative:

• 1. Validity (Construct & Content): The degree to which an instrument truly measures the construct it purports to measure. Content validity ensures that the instrument covers all relevant aspects of the disease process from the patient’s perspective, while construct validity confirms expected convergent and divergent correlations with established external metrics.
• 2. Reliability (Internal Consistency & Test-Retest): The extent to which an instrument yields reproducible, consistent scores free from measurement error. Internal consistency is quantified by Cronbach’s alpha (acceptable threshold: 0.70 to 0.90; values > 0.95 indicate redundant questioning), while test-retest reliability across clinically stable intervals is quantified by the Intraclass Correlation Coefficient (acceptable threshold: ICC > 0.75).
• 3. Responsiveness (Sensitivity to Change): The ability of a measure to detect meaningful clinical improvement or deterioration following a surgical intervention. Quantified using the Standardized Response Mean (SRM) or Effect Size (ES), where values > 0.80 indicate strong responsiveness.
• 4. Floor and Ceiling Effects: A floor or ceiling effect is present when more than 15% of respondents achieve the lowest (worst) or highest (best) possible score, respectively. Marked ceiling effects prevent detection of further improvement, impairing comparative surgical research.

8. Clinically Meaningful Thresholds: MCID, PASS, and SCB

In modern evidence-based orthopaedics, statistical significance (p < 0.05) is often clinically misleading in large cohort studies, where even a 1-point change on a 100-point scale may reach statistical significance without conferring any discernible benefit to the patient. To interpret clinical trials and registry data accurately, three clinical thresholds must be evaluated:

• Minimal Clinically Important Difference (MCID): The smallest change in score that patients perceive as beneficial and which would mandate a change in clinical management. Representative MCID thresholds after primary TKA include 5.0 to 6.5 points for the Oxford Knee Score, 7.0 to 9.0 points for KOOS JR, 10.5 to 14.0 points for the Forgotten Joint Score (FJS-12), and 4.0 to 5.0 points for PROMIS Physical Function.
• Patient Acceptable Symptom State (PASS): An absolute cutoff score beyond which patients consider their current symptom state acceptable (“satisfactory”). Unlike MCID (which measures change), PASS measures the absolute postoperative status (e.g., an absolute OKS threshold of approximately 30 to 33 points out of 48 at 1 year).
• Substantial Clinical Benefit (SCB): The degree of improvement that a patient perceives as a substantial, meaningful breakthrough rather than just minimal improvement. It represents a more rigorous benchmark for defining operative success in comparative implant studies.

9. The Satisfaction Dilemma: Evaluating the Unsatisfied TKA

A central focus of Dr. Lonner’s presentation and contemporary arthroplasty literature is the phenomenon of the unsatisfied knee: why do 15% to 20% of patients remain dissatisfied after primary TKA despite anatomically aligned, solidly fixed, and uninfected implants?

Key Determinants of Dissatisfaction

Landmark prospective multi-center registry studies (Bourne et al., 2010; Dunbar et al., 2013) have identified the primary drivers of postoperative dissatisfaction, which can be categorized into patient-specific, surgical, and biomechanical factors:

• 1. Unmet Preoperative Expectations: The single strongest independent predictor of dissatisfaction. Patients frequently expect complete restoration of a normal teenage knee, including effortless kneeling, squatting, and return to high-impact sports. When these expectations are not calibrated preoperatively, disappointment ensues regardless of surgical perfection.
• 2. Residual Pain and Sensory Dysesthesia: Persistent anterior knee pain during stair descent, patellofemoral crepitus, and numbness or neuroma formation over the infrapatellar branch of the saphenous nerve contribute heavily to functional limitation and negative score reporting.
• 3. Psychosocial Factors and Central Sensitization: Patients with elevated preoperative depression, anxiety, catastrophizing, or fibromyalgia have statistically worse PROM trajectories. Central pain amplification impairs peripheral joint adaptation, leading to persistent hyperalgesia despite a mechanically stable reconstruction.
• 4. Biomechanical and Gap Balancing Imperfections: Subtle mid-flexion instability (laxity between 30° and 60° of flexion), joint line elevation (> 4 mm), overstuffing of the patellofemoral compartment, and excessive internal rotation of either the femoral or tibial components cause abnormal kinematics, extensor mechanism strain, and joint awareness.

10. Comparative Matrix of Major Joint Arthroplasty Scoring Systems

The selection of an appropriate outcomes instrument requires balancing clinical granularity against administrative burden, respondent fatigue, and measurement properties.

11. Implementation in Digital Health, Registries, and Value-Based Care

The institutionalization of outcomes measurement has moved from paper forms in clinic waiting rooms to integrated electronic health record (EHR) pipelines, remote patient monitoring platforms, and national quality databases:

• Electronic PROMs (ePROMs) and Automated Capture: Modern clinical workflows capture preoperative PROMs via secure patient portal links sent automatically 2 to 4 weeks prior to surgery. Postoperative assessments are triggered autonomously at 6 weeks, 90 days, 1 year, and annually thereafter, achieving survey response rates exceeding 80% to 85% compared to < 50% with traditional mailed paper surveys.
• Value-Based Payment Models (CMS CJR and MIPS): Under the CMS Comprehensive Care for Joint Replacement model, hospitals and surgical practices are financially incentivized to collect matched pre- and postoperative PROMs (specifically KOOS JR, VR-12 / PROMIS-10) for a minimum of 70% to 80% of primary joint replacement cases. Risk-adjusted PROM improvement serves as a quality metric linked directly to reimbursement.
• National Arthroplasty Registries: Registries such as the American Joint Replacement Registry (AJRR), the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), and the UK National Joint Registry (NJR) have linked PROM data directly with implant survivorship and revision epidemiology. This allows early detection of implant designs or bearing surfaces that produce poor functional outcomes or early loosening before catastrophic failures become widespread.

12. Diagnostic Algorithm for Discrepant Poor Outcome Scores

When an arthroplasty patient demonstrates persistently low PROM scores or an unexpected decline in satisfaction at the 6-month or 1-year mark despite seemingly “normal” radiographs, the clinician must execute a rigorous, standardized diagnostic triage:

• Step 1: Rule Out Periprosthetic Joint Infection (PJI): Always the primary imperative. Obtain serum ESR and CRP. If either is elevated (or if high clinical suspicion exists), perform diagnostic knee arthrocentesis for synovial fluid cell count, differential, alpha-defensin, and aerobic/anaerobic cultures. Low-grade, indolent infections (e.g., Cutibacterium acnes, coagulase-negative Staphylococci) frequently present as unexplained pain and stiffness without overt erythema or systemic signs.
• Step 2: Scrutinize Radiographic and Rotational Alignment: Obtain weight-bearing full-length mechanical axis alignment films, true AP, lateral, and Merchant/skyline views. Scrutinize for subtle joint line elevation (> 4 mm), posterior condylar offset reduction, patellar tilt/subluxation, or component overhang. If anterior knee pain or mid-flexion tightness persists, obtain a high-resolution CT arthroplasty protocol to measure rotational alignment of the femoral component (relative to the surgical epicondylar axis) and tibial component (relative to the medial third of the tibial tubercle); internal rotation > 3° is a potent cause of persistent pain and patellofemoral tracking failure.
• Step 3: Physical Examination of Dynamic Instability: Examine the knee at 0°, 30°, 60°, and 90° of flexion. Mid-flexion instability (laxity during active flexion from 30° to 60°) cannot be detected on static radiographs but causes disabling joint apprehension, recurrent effusions, and poor FJS-12 scores.
• Step 4: Rule Out Extrinsic Pain Generators: Perform a thorough hip and lumbar spine evaluation. Ipsilateral hip osteoarthritis, severe lumbar spinal stenosis, L3/L4 radiculopathy, or vascular claudication frequently mimic or exacerbate persistent knee symptoms.
• Step 5: Psychosocial and Neuropathic Evaluation: Differentiate nociceptive mechanical joint pain from neuropathic pain (e.g., infrapatellar branch saphenous neuroma, complex regional pain syndrome [CRPS]) or centralized pain syndromes. Referral to multimodal pain management and cognitive behavioral therapy is significantly more effective than revision surgery in the absence of an identifiable mechanical or infectious etiology.

11. Evidence-Based Synthesis

Modern clinical decision-making is grounded in high-quality randomized controlled trials and prospective registry analyses, corroborated by seminal biomechanical and anatomical descriptions.

12. References

• Scuderi GR, Bourne RB, Noble PC, Benjamin JB, Lonner JH, Scott WN. The new Knee Society Knee Scoring System. Clin Orthop Relat Res. 2012. doi:10.1007/s11999-011-2135-0 [Level II: Prospective Multi-Center Validation Study]
• Noble PC, Scuderi GR, Brekke AC, et al. Development of a new Knee Society scoring system. Clin Orthop Relat Res. 2012. doi:10.1007/s11999-011-2152-z [Level II: Prospective Multi-Center Cohort Study]
• Insall JN, Dorr LD, Scott RD, Scott WN. Rationale of The Knee Society Clinical Rating System. Clin Orthop Relat Res. 1989. doi:10.1097/00003086-198911000-00004 [Level V: Expert Consensus & Clinical Validation]
• Dawson J, Fitzpatrick R, Murray D, Carr A. Questionnaire on the perceptions of patients about total knee replacement. J Bone Joint Surg Br. 1998. doi:10.1302/0301-620x.80b1.7859 [Level II: Prospective Cohort Validation Study]
• Behrend H, Giesinger K, Giesinger JM, Kuster MS. The “Forgotten Joint” as the Ultimate Goal in Joint Arthroplasty. J Arthroplasty. 2012. doi:10.1016/j.arth.2011.06.035 [Level II: Prospective Cross-Sectional Validation Study]
• Hamilton DF, Loth FL, Giesinger JM, et al. Validation of the English language Forgotten Joint Score-12 as an outcome measure for total hip and knee arthroplasty in a British population. Bone Joint J. 2017. doi:10.1302/0301-620X.99B2.BJJ-2016-0606.R1 [Level II: Prospective Cohort Validation Study]
• Bourne RB, Chesworth BM, Davis AM, Mahomed NN, Charron KDJ. Patient Satisfaction after Total Knee Arthroplasty: Who is Satisfied and Who is Not?. Clin Orthop Relat Res. 2010. doi:10.1007/s11999-009-1119-9 [Level II: Prospective Multi-Center Registry Cohort Study]
• Dunbar MJ, Richardson G, Robertsson O. I can’t get no satisfaction after my total knee replacement. Bone Joint J. 2013. doi:10.1302/0301-620X.95B11.32767 [Level II: National Registry Observational Cohort Study]
• Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD. Knee Injury and Osteoarthritis Outcome Score (KOOS)—Development of a Self-Administered Outcome Measure. J Orthop Sports Phys Ther. 1998. doi:10.2519/jospt.1998.28.2.88 [Level II: Prospective Instrument Development & Psychometric Validation]

15. Master Class Pro-Tip

Preoperative Expectation Calibration and The Dissatisfaction Phenotype: The single most effective strategy to optimize arthroplasty outcome measures begins before the surgical incision is made. Prospective registry data confirm that unmet expectations regarding kneeling, squatting, and sports participation drive over 60% of persistent patient dissatisfaction despite flawless mechanical axis restoration. During preoperative evaluation, actively calibrate patient expectations: explicitly delineate the difference between predictable pain relief during walking and residual joint awareness during deep flexion. In patients with minimal radiographic osteoarthritis who present with disproportionately severe disability scores, screen aggressively for centralized pain amplification, catastrophizing, and mental health distress (e.g., VR-12 MCS < 40); operating on these patients without preoperative psychological conditioning carries a high risk of poor PROM trajectories. Intraoperatively, precise soft-tissue balancing that avoids mid-flexion tightness and patellofemoral overstuffing is paramount to achieving a “forgotten joint.” Ligamentous tension asymmetry is perceived by patients as joint awareness rather than frank instability, directly depressing Forgotten Joint Scores (FJS-12) even when static radiographs appear immaculate.

Master Class Surgical Pearl: Joint Arthroplasty Reconstruction