European Journal of Cardiovascular Medicine

Total knee arthroplasty (TKA) is a definitive option for end-stage knee arthritis, aiming to relieve pain and restore mobility when conservative measures fail. Radiographic grading systems such as Kellgren–Lawrence support standardized assessment of osteoarthritis severity and assist in selecting candidates for surgery [1]. Even with reliable implant longevity, a substantial minority report persistent symptoms or dissatisfaction after surgery, highlighting that technical success does not always translate into perceived recovery [7]. Modern reporting therefore integrates radiology, clinician-based scores, and validated patient-reported outcome measures (PROMs).

Coronal limb alignment is central to the biomechanics of the replaced knee. Long-leg radiographs allow measurement of the mechanical axis and the hip–knee–ankle (HKA) angle, which reflects the load distribution line across the knee. Classic work demonstrated that malalignment increases abnormal forces and is associated with a higher incidence of loosening, particularly when deviation exceeds a narrow tolerance around neutral [4]. These observations shaped conventional mechanical alignment strategies that seek near-neutral HKA after TKA.

PROMs provide a direct measure of pain and disability and are essential for patient-centred evaluation. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) is a validated tool that captures pain, stiffness, and functional limitation relevant to knee osteoarthritis and recovery after arthroplasty [2]. The Knee Society clinical rating system complements PROMs by separating a knee score (joint-specific status) from a function score (walking and stair climbing), enabling clearer interpretation of rehabilitation and global mobility [3]. A simple satisfaction rating further captures the patient’s overall appraisal of the procedure.

Evidence on the alignment–outcome relationship remains heterogeneous. Several studies report that better coronal alignment is linked to improved early function and faster rehabilitation, suggesting short-term benefits of accurate alignment [5,6]. However, long-term analyses of modern cemented TKAs show small survivorship differences within commonly used alignment thresholds, and strict mechanical alignment does not consistently deliver superior function at extended follow-up [8,9,13]. In addition, constitutional varus challenges the assumption that neutral mechanical alignment is a universal native phenotype [10], and contemporary reviews discuss a transition toward more personalised alignment within defined safety limits [11,14].

In this context, we performed an observational correlation study in a tertiary care setting to relate radiological alignment parameters with PROMs after primary TKA. The objectives of this study were: (i) to quantify the change in coronal limb alignment and component coronal alignment following TKA, and (ii) to assess the correlation between postoperative HKA alignment and functional outcomes measured using Knee Society scores, WOMAC, and patient satisfaction.

Study design and setting: An observational correlation study was conducted in the Department of Orthopaedics, Government Medical College (GMC), Ananthapuramu, Andhra Pradesh, India, from May 2023 to December 2023.

Sample size and sampling: The study aimed to enroll 100 consecutive eligible patients undergoing primary unilateral TKA during the study period. For correlation analyses, complete paired radiographs and complete PROM datasets were required. Participants with missing paired imaging or incomplete questionnaires were excluded from the corresponding analyses, resulting in a complete-case analytical cohort.

Eligibility criteria: Adults aged ≥45 years planned for primary unilateral TKA for end-stage knee arthritis were included. Osteoarthritis severity was graded radiographically using the Kellgren–Lawrence framework [1], and inflammatory arthritis was diagnosed using standard clinical criteria. Exclusion criteria were revision arthroplasty, prior corrective osteotomy around the knee, severe extra-articular deformity requiring staged correction, neuromuscular disorders affecting gait, active infection, and inability to complete questionnaires.

Surgical technique and perioperative protocol: All surgeries followed a standardized institutional pathway. A medial parapatellar approach was used. Femoral cuts were guided by intramedullary alignment, and tibial cuts by extramedullary alignment jigs, aiming to restore coronal alignment and achieve balanced flexion–extension gaps. Cemented femoral and tibial components were implanted. Thromboprophylaxis, antibiotic prophylaxis, and multimodal analgesia were administered as per hospital protocol. Early mobilization and structured physiotherapy were initiated postoperatively.

Radiological evaluation: Standardized standing long-leg radiographs were obtained preoperatively and postoperatively with the patella positioned forward. The HKA angle was measured as the coronal mechanical axis (positive values denoting varus). Postoperative femoral and tibial component coronal alignment angles were recorded relative to the respective mechanical axes. Neutral alignment was defined as postoperative HKA within ±3° of neutral. Measurements were performed using a consistent method and recorded in degrees.

Outcome assessment: PROMs were recorded preoperatively and at postoperative assessment. Knee Society Score (KSS) knee and function components were documented using the Knee Society clinical rating system [3]. The WOMAC total score was recorded using the validated WOMAC questionnaire [2]. Patient satisfaction was captured using a 5-point Likert-type scale (1 = very dissatisfied to 5 = very satisfied).

Statistical analysis: Data were entered and checked for consistency. Continuous variables are presented as mean ± SD and categorical variables as n (%). Pre- and postoperative differences in radiological and PROM variables were tested using paired t-tests (two-sided), with p < 0.05 considered statistically significant. Correlations between postoperative HKA angle and outcomes (KSS-knee, KSS-function, WOMAC) were assessed using Pearson correlation coefficients (r). The association between alignment category (neutral vs outlier) and satisfaction was assessed using correlation analysis with p-values.

Ethics and consent: The study adhered to institutional ethical standards. Written informed consent was obtained from all participants, and confidentiality was ensured by de-identifying data prior to analysis.

During the study period, 100 patients underwent primary unilateral TKA. Complete paired radiographs and complete PROMs suitable for correlation analysis were available for 80 participants and constitute the analytical cohort.

Baseline demographic and clinical characteristics are presented in Table 1. The mean age was 64.1 ± 7.8 years, with 52.5% females. Osteoarthritis was the predominant indication (90.0%), and the mean BMI was 27.3 ± 3.6 kg/m². Right-sided procedures were slightly more common than left-sided procedures.

Table 1. Baseline Demographic and Clinical Characteristics (n = 80)

Radiological parameters before and after surgery are summarized in Table 2. Mean preoperative HKA (9.6° varus) corrected to 1.8° postoperatively, indicating near-neutral mechanical alignment. Neutral alignment within ±3° was achieved in 62 knees (77.5%). Mean femoral and tibial component coronal alignment angles were 89.4° and 90.8°, respectively.

Table 2. Radiological Alignment Parameters Pre- and Post-TKA

Patient-reported outcomes improved significantly after TKA (Table 3). KSS-function increased from 42.6 ± 9.4 to 78.9 ± 10.6, and KSS-knee increased from 46.2 ± 10.1 to 82.4 ± 9.8. WOMAC total scores decreased from 64.8 ± 12.3 to 22.7 ± 9.6. Patient satisfaction rose from 2.1 ± 0.8 to 4.3 ± 0.6. All changes were statistically significant (p < 0.001).

Table 3. Patient-Reported Outcome Measures Before and After Surgery

Figure 1: Patient-Reported Outcome Measures Before and After Surgery

Correlation results between alignment and outcomes are shown in Table 4. Postoperative HKA angle demonstrated a moderate positive correlation with KSS-function (r = 0.48) and KSS-knee (r = 0.44), and a moderate negative correlation with WOMAC total score (r = −0.41). Alignment category (neutral vs outlier) showed a positive association with satisfaction (r = 0.52).

Table 4. Correlation Between Radiological Alignment and Functional Outcomes

Figure 2: Correlation Between Radiological Alignment and Functional Outcomes

In this observational correlation study, primary TKA produced substantial correction of varus mechanical alignment and large improvements in PROMs. The analytical cohort achieved a mean postoperative HKA close to neutral, and most knees fell within the conventional ±3° range. Parallel gains were observed in KSS knee and function scores and in WOMAC, indicating that radiographic correction occurred alongside clinically meaningful symptom relief and functional recovery.

The moderate correlations between postoperative HKA and PROMs fit the mechanical rationale that coronal malalignment alters load transfer and can compromise joint mechanics. Early work linked coronal malalignment to increased loosening risk, supporting routine long-leg assessment of alignment [4]. Our findings are also consistent with reports that good alignment supports earlier functional improvement and a smoother rehabilitation trajectory [5,6].

Component positioning and the proportion of alignment outliers are relevant because they represent modifiable surgical factors. In our cohort, component coronal angles clustered close to orthogonal, and a high percentage achieved neutral mechanical alignment. This technical consistency likely contributed to the substantial PROM gains. At the same time, the observed correlations were moderate rather than strong, which suggests that alignment explains only part of outcome variation.

Alignment is not a solitary predictor of long-term success. Long-term survival analyses of modern cemented TKAs have reported minimal differences in survivorship across common alignment categories, and strict neutral mechanical alignment does not consistently deliver superior function at extended follow-up [8,9,13]. Studies also report that immediate postoperative mechanical axis is not always a dominant driver of revision risk when other determinants are favourable [12]. These findings underscore the influence of soft-tissue balance, rotational positioning, implant design, pain sensitization, and adherence to rehabilitation.

The evolving concept of constitutional alignment adds further nuance. Neutral mechanical alignment is not a universal native phenotype, and constitutional varus has been described as a normal variant for many individuals [10]. Contemporary perspectives therefore argue for thoughtful individualization while maintaining safety thresholds, especially when transitioning from systematic alignment targets to more personalised approaches [11,14]. In our cohort, the association between closer-to-neutral alignment and better outcomes supports continued emphasis on accurate coronal restoration in routine practice.

Patient satisfaction remains a complex endpoint. Even when radiographs appear acceptable, dissatisfaction can persist due to expectations, residual pain, contralateral joint disease, and comorbidity burden [7]. In this study, alignment category correlated with satisfaction, suggesting that coronal restoration contributes to perceived success in this population. Larger regional studies with longer follow-up, broader radiographic parameters, and multivariable modelling can clarify independent predictors of PROMs and guide future alignment strategies.

Limitations

This was a single-centre study with a modest complete-case analytical cohort, limiting generalizability. Follow-up duration was short, so implant survivorship and late complications were not evaluated. Correlation analyses were unadjusted for confounders such as baseline deformity severity, implant design, and rehabilitation adherence. Satisfaction was captured using a single-item scale, and radiographic measurements were based on standard long-leg radiographs rather than 3D assessment

Primary unilateral TKA at a tertiary centre corrected varus mechanical alignment toward near-neutral HKA and improved patient-reported outcomes. Knee Society knee and function scores rose markedly, WOMAC symptom burden fell, and satisfaction increased. Postoperative coronal alignment showed moderate associations with outcomes: closer-to-neutral HKA correlated with higher Knee Society scores, lower WOMAC, and better satisfaction. Routine long-leg radiography with defined thresholds can complement PROM monitoring and flag alignment outliers for targeted rehabilitation. Nonetheless, patient benefit also depends on soft-tissue balance, expectation setting, comorbidity control, and consistent physiotherapy follow-up. These findings support alignment audit together with structured patient-reported outcome review. Studies with longer follow-up should evaluate personalised alignment approaches in this region

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