Surgical site infection (SSI) is a significant postoperative complication following orthopaedic implant surgery, contributing to increased morbidity, prolonged hospitalisation, additional antimicrobial therapy, repeated surgical interventions, and increased healthcare costs. Despite advances in surgical techniques, aseptic precautions, and perioperative antibiotic prophylaxis, SSI remains an important concern in orthopaedic practice. Early identification and appropriate management are essential to prevent infection progression, implant-related complications, and adverse functional outcomes. Evidence-based recommendations emphasise preventive strategies and continuous postoperative surveillance to minimise infection-related complications.[1] Therefore, identifying reliable inflammatory markers that facilitate early recognition of SSI may improve postoperative monitoring and clinical decision-making. The diagnosis of SSI following orthopaedic implant surgery can be challenging because clinical manifestations of infection may overlap with the normal inflammatory response associated with surgical trauma. Superficial incisional infections and deep infections involving fixation devices or prosthetic joints differ in their clinical presentation, severity, and management. International recommendations for fracture-related infections emphasise the importance of distinguishing suggestive clinical findings from confirmatory diagnostic evidence, including microbiological and histopathological investigations. [2,3] Although inflammatory biomarkers may indicate an increased likelihood of infection, they should be interpreted alongside clinical examination and other relevant diagnostic findings. C-reactive protein (CRP) is a commonly used inflammatory biomarker for monitoring postoperative recovery and identifying possible infectious complications. CRP concentrations typically increase following surgical trauma and subsequently decline during uncomplicated recovery. Persistent elevation or an unexpected secondary increase may raise suspicion of postoperative infection. Scherer et al. investigated postoperative CRP patterns following fracture surgery and demonstrated their potential usefulness in detecting deep wound infections.[4] Similarly, Neumaier et al. reported that postoperative CRP concentrations are influenced by surgical technique and the extent of tissue injury.[5] Further investigations highlighted the importance of evaluating CRP according to the postoperative period rather than relying exclusively on a single threshold.[6] These findings support the assessment of CRP at defined postoperative intervals for identifying patients at increased risk of SSI. The neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) have emerged as accessible and cost-effective inflammatory markers derived from routine complete blood count parameters. NLR reflects the balance between neutrophil-mediated inflammatory activity and lymphocyte-associated immune responses, whereas PLR provides additional information regarding platelet activation and systemic inflammation. These indices have gained attention because of their availability, simplicity, and potential diagnostic relevance. Yu et al. evaluated the usefulness of NLR in identifying early periprosthetic joint infection, while Tirumala et al. investigated platelet-related inflammatory indices in patients undergoing revision knee arthroplasty. [7,8] Furthermore, systematic reviews have demonstrated the potential diagnostic value of these markers in orthopaedic infections, although their performance varies across patient populations, surgical procedures, and infection definitions. [9,10]. Although CRP, NLR, and PLR have individually been evaluated in orthopaedic infections, evidence directly comparing their diagnostic performance during the early postoperative period remains limited, particularly among patients undergoing different types of orthopaedic implant procedures. Normal postoperative inflammatory changes may influence these markers, making the timing of measurement particularly important. Evaluation on postoperative day 3 may provide useful information for identifying patients who require closer monitoring for subsequent infectious complications. However, the relative diagnostic accuracy and clinically applicable cutoff values of these inflammatory markers require further investigation. Therefore, the present prospective observational study was conducted at RVM Institute of Medical Sciences and Research Center, Telangana, India, from April 2025 to March 2026, involving 50 patients undergoing orthopaedic implant surgery. The primary objective was to compare the diagnostic performance of postoperative day 3 NLR, PLR, and CRP in identifying patients who developed SSI within 30 days following surgery. The secondary objectives were to compare inflammatory marker levels between patients with and without SSI, determine optimal cutoff values using receiver operating characteristic (ROC) curve analysis, and evaluate the sensitivity, specificity, and predictive values of these markers. The study aimed to assess their potential usefulness as adjunctive tools for early postoperative infection surveillance and clinical decision-making.

Study Design and Setting This prospective observational study was conducted at RVM Institute of Medical Sciences and Research Center, Laxmakkapally, Mulugu, Siddipet, Telangana, India, from April 2025 to March 2026. The study aimed to evaluate and compare the diagnostic performance of postoperative day 3 neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and C-reactive protein (CRP) in predicting early surgical site infection (SSI) following orthopaedic implant surgery. Patients were followed for 30 days postoperatively to assess the occurrence of SSI. The study was reported in accordance with relevant STROBE and STARD recommendations. [11,12]. Study Participants and Sample Size A total of 50 patients undergoing orthopaedic implant surgery, including plate-and-screw fixation, intramedullary nailing, and arthroplasty, were included in the study. The sample size comprised patients recruited during the study period who fulfilled the eligibility criteria. Demographic characteristics, clinical history, comorbidities, operative details, and postoperative inflammatory markers were recorded. Patients were monitored for the development of SSI during the 30-day postoperative follow-up period. The sample size was based on the number of eligible patients included during the study period, rather than a formal statistical sample-size calculation. Eligibility Criteria Inclusion Criteria: Patients undergoing orthopaedic implant surgery, including plate-and-screw fixation, intramedullary nailing, or arthroplasty, who provided informed consent and were available for postoperative assessment and follow-up were eligible for inclusion. Exclusion Criteria: Patients with pre-existing surgical site infection, active systemic infection, concurrent inflammatory conditions, or medical conditions likely to significantly influence inflammatory biomarkers were considered for exclusion. Patients receiving immunosuppressive treatment or those with incomplete essential laboratory or follow-up data were also considered for exclusion. Clinical and Laboratory Assessment Demographic and clinical information, including age, sex, diabetes mellitus, hypertension, smoking status, type of orthopaedic implant procedure, and operative duration, was recorded. Blood samples were obtained on postoperative day 3 for assessment of complete blood count parameters and CRP concentrations. NLR was calculated by dividing the absolute neutrophil count by the absolute lymphocyte count, whereas PLR was calculated by dividing the platelet count by the absolute lymphocyte count. CRP concentrations were expressed in mg/L. These inflammatory markers were evaluated to determine their association with subsequent SSI development. Outcome Measures and Follow-up The primary outcome was the development of SSI within 30 days following orthopaedic implant surgery. SSI was classified as superficial or deep incisional infection based on clinical findings and applicable diagnostic criteria. Postoperative follow-up included assessment for wound-related complications and clinical features suggestive of infection. The diagnostic performance of postoperative day 3 NLR, PLR, and CRP was evaluated in relation to subsequent SSI occurrence. Inflammatory marker results were considered adjunctive indicators rather than independent confirmation of infection, consistent with recommendations for fracture-related infection assessment. [2,3]. Statistical Analysis Data were analysed using appropriate statistical methods. Continuous variables were expressed as mean ± standard deviation, while categorical variables were presented as frequencies and percentages. Differences in inflammatory marker levels between patients with and without SSI were assessed using two-sided Welch's independent-samples t-test. Receiver operating characteristic (ROC) curve analysis was performed to evaluate the diagnostic performance of NLR, PLR, and CRP. The area under the ROC curve (AUC) was calculated for each marker, and optimal cutoff values were identified using the Youden index. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were determined to assess diagnostic accuracy. A p-value of less than 0.05 was considered statistically significant. Ethical Considerations The study was conducted after obtaining the necessary permissions from RVM Institute of Medical Sciences and Research Center, Laxmakkapally, Mulugu, Siddipet, Telangana, India. Ethical principles were followed throughout the study in accordance with the Declaration of Helsinki. Written informed consent was obtained from participants before enrolment, and confidentiality of personal and clinical information was maintained. Patient data were used exclusively for research purposes, with appropriate measures taken to protect participant privacy.

A total of 50 patients undergoing orthopaedic implant surgery were included in the analysis. The mean age was 46.8 ± 14.2 years. Of the participants, 32 (64.0%) were male and 18 (36.0%) were female. Hypertension was present in 15 (30.0%) patients, diabetes mellitus in 12 (24.0%), and current smoking in 11 (22.0%) (Table 1). Table 1 Demographic and Clinical Characteristics of the Study Participants (N = 50) Characteristic Value Age (years), mean ± SD 46.8 ± 14.2 Male, n (%) 32 (64.0) Female, n (%) 18 (36.0) Diabetes mellitus, n (%) 12 (24.0) Hypertension, n (%) 15 (30.0) Current smoking, n (%) 11 (22.0) Note. SD = standard deviation. Percentages are based on N = 50. Surgical Characteristics and Surgical Site Infection Outcomes Plate-and-screw fixation was performed in 24 (48.0%) patients, intramedullary nailing in 18 (36.0%), and arthroplasty in 8 (16.0%). The mean operative duration was 102.6 ± 28.4 minutes. SSI occurred in 8 (16.0%) patients within 30 days, comprising 6 superficial and 2 deep incisional infections. Median time to SSI identification was 8 days (range, 5–12 days) (Table 2). Table 2 Surgical Characteristics and Early Infection Outcomes (N = 50) Characteristic Value Plate-and-screw fixation, n (%) 24 (48.0) Intramedullary nailing, n (%) 18 (36.0) Arthroplasty, n (%) 8 (16.0) Operative duration (minutes), mean ± SD 102.6 ± 28.4 Any SSI, n (%) 8 (16.0) No SSI, n (%) 42 (84.0) Superficial incisional SSI, n (%) 6 (12.0) Deep incisional SSI, n (%) 2 (4.0) Time to SSI identification (days), median (range) 8 (5–12) Note. Percentages use the full cohort (N = 50). Time to SSI identification applies only to eight SSI cases. SSI = surgical site infection. Comparison of Postoperative Inflammatory Markers Postoperative day 3 marker levels were higher in patients who subsequently developed SSI. Mean NLR was 7.00 ± 2.28 versus 4.63 ± 1.59 (p = .022); PLR was 197.05 ± 52.76 versus 150.92 ± 50.67 (p = .047); and CRP was 100.34 ± 20.22 versus 70.03 ± 23.32 mg/L (p = .003) (Table 3). Table 3 Postoperative Day 3 Inflammatory Markers by Subsequent SSI Status Marker SSI (n = 8) Mean ± SD No SSI (n = 42) Mean ± SD p NLR 7.00 ± 2.28 4.63 ± 1.59 .022 PLR 197.05 ± 52.76 150.92 ± 50.67 .047 CRP (mg/L) 100.34 ± 20.22 70.03 ± 23.32 .003 Note. Two-sided Welch independent-samples t tests; unadjusted p values. NLR = neutrophil-to-lymphocyte ratio; PLR = platelet-to-lymphocyte ratio; CRP = C-reactive protein. Diagnostic Performance of NLR, PLR, and CRP ROC analysis showed the highest numerical AUC for CRP (0.842), followed by NLR (0.777) and PLR (0.738). CRP had 87.5% sensitivity at the selected threshold, whereas NLR had the highest specificity (90.5%). Thresholds and diagnostic measures are presented in Table 4. Differences between AUCs were not formally tested. Table 4 Discrimination and Cutoff Performance of Postoperative Day 3 Markers Marker AUC Cutoff ≥ Sensitivity (%) Specificity (%) PPV (%) NPV (%) NLR 0.777 7.30 75.0 90.5 60.0 95.0 PLR 0.738 194.12 62.5 83.3 41.7 92.1 CRP 0.842 86.53 mg/L 87.5 76.2 41.2 97.0 Note. Cutoffs were selected by maximising the Youden index in the supplied dataset. Classification used unrounded values. AUC = area under the receiver operating characteristic curve; PPV = positive predictive value; NPV = negative predictive value. Classification Performance at Selected Cutoffs CRP identified 7 of 8 SSI cases but yielded 10 false positives. NLR identified 6 SSI cases and correctly classified 38 of 42 patients without SSI. PLR identified 5 SSI cases and yielded 7 false positives (Table 5). No combined-marker or adjusted model was reported. Table 5 Classification Counts at the Selected Cutoff Values Marker True positive False positive True negative False negative NLR 6 4 38 2 PLR 5 7 35 3 CRP 7 10 32 1 Note. Each row represents 8 patients with SSI and 42 without SSI. Positive denotes a marker value at or above the selected cutoff.

The present study evaluated the diagnostic performance of postoperative day 3 neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and C-reactive protein (CRP) in identifying early surgical site infection (SSI) following orthopaedic implant surgery. The reported findings showed significantly higher levels of all three inflammatory markers among patients who subsequently developed SSI. CRP demonstrated the highest numerical area under the receiver operating characteristic curve (AUC = 0.842) and sensitivity (87.5%), whereas NLR showed the highest specificity (90.5%). PLR demonstrated comparatively lower discriminatory performance. These findings suggest that routine inflammatory markers may have potential value as adjuncts to postoperative infection surveillance, although differences in diagnostic performance require cautious interpretation. In the present dataset, SSI was identified in 8 of 50 patients (16.0%), including six superficial and two deep incisional infections. The observed infection proportion should be interpreted in relation to the study population, surgical procedures, and follow-up duration rather than as an estimate of institutional SSI incidence. Postoperative inflammatory responses may complicate early recognition of infection, particularly after major orthopaedic procedures. Scherer et al. reported that CRP concentrations increase following uncomplicated fracture surgery, whereas abnormal postoperative CRP patterns may indicate infectious complications.[4] Similarly, Neumaier et al. demonstrated that the magnitude of CRP elevation is influenced by surgical trauma and operative technique.[5] These observations highlight the importance of interpreting inflammatory markers according to postoperative timing and clinical findings. CRP demonstrated the highest numerical diagnostic discrimination among the three investigated markers, with an AUC of 0.842. At a cutoff value of ≥86.53 mg/L, CRP showed a sensitivity of 87.5% and specificity of 76.2%. Neumaier et al. reported that a CRP threshold of 96 mg/L after postoperative day 4 identified deep wound infection following fracture surgery with a sensitivity of 92% and specificity of 93%.[6] Although both findings indicate the potential usefulness of CRP in postoperative infection detection, differences in sampling time, surgical procedures, and infection definitions may explain variations in optimal thresholds and diagnostic accuracy. Consequently, the cutoff identified in the present analysis requires further validation before routine clinical application. NLR was also elevated among patients who subsequently developed SSI, with mean values of 7.00 ± 2.28 in the SSI group and 4.63 ± 1.59 in the non-SSI group (p = 0.022). ROC analysis demonstrated an AUC of 0.777, with sensitivity and specificity of 75.0% and 90.5%, respectively, at a cutoff of ≥7.30. Yu et al. reported an AUC of 0.802 for NLR in the assessment of early periprosthetic joint infection.[7] Similarly, Salimi et al., in a systematic review and meta-analysis, reported pooled sensitivity and specificity of approximately 73% and 75%, respectively, for NLR in periprosthetic joint infection.[10] These findings support the potential diagnostic relevance of NLR in orthopaedic infections. However, differences in study populations, infection characteristics, and timing of laboratory investigations should be considered when comparing results across studies. PLR demonstrated a significant difference between patients with and without SSI (197.05 ± 52.76 vs. 150.92 ± 50.67; p = 0.047). Its diagnostic performance was comparatively lower, with an AUC of 0.738, sensitivity of 62.5%, and specificity of 83.3% at a cutoff value of ≥194.12. Tirumala et al. investigated platelet-derived inflammatory ratios in revision total knee arthroplasty and highlighted their potential contribution when interpreted alongside established serum and synovial diagnostic parameters.[8] Festa et al. reported pooled PLR sensitivity of 77% and specificity of 75% in a systematic review, although substantial heterogeneity was observed among studies.[9] These findings suggest that PLR may provide supplementary inflammatory information, but its independent diagnostic utility remains uncertain. Further investigations are required to determine whether combining PLR with CRP or NLR improves diagnostic accuracy. The relative differences in sensitivity and specificity have important clinical implications. CRP correctly identified seven of the eight patients who developed SSI but produced ten false-positive results, indicating that postoperative inflammation may reduce specificity. Conversely, NLR demonstrated greater specificity, correctly identifying 38 of 42 patients without infection, although two infections were not detected at the selected cutoff. CRP also demonstrated a negative predictive value of 97.0%, compared with 95.0% for NLR and 92.1% for PLR. However, predictive values are influenced by infection prevalence and may differ in other surgical populations. Furthermore, the small number of SSI cases and absence of a formal statistical comparison between AUCs prevent conclusions regarding the diagnostic superiority of any single marker. The diagnosis of infection following orthopaedic implant surgery requires integration of clinical findings, laboratory investigations, imaging, and microbiological evidence when indicated. International diagnostic frameworks for periprosthetic joint infection emphasise the importance of combining multiple diagnostic parameters rather than relying on isolated inflammatory markers.[13,14] Therefore, postoperative NLR, PLR, and CRP should be considered supportive investigations rather than definitive diagnostic tests. Their clinical utility may be improved through serial measurement, integration with wound assessment, and evaluation of changes in inflammatory marker concentrations over time. Overall, the reported findings indicate that CRP and NLR may have potential usefulness in identifying patients at increased risk of early SSI following orthopaedic implant surgery. CRP demonstrated greater numerical sensitivity and overall discrimination, whereas NLR showed higher specificity. Nevertheless, the relatively small study population, limited number of infection events, and internally derived cutoff values indicate the need for cautious interpretation. Larger prospective studies involving clearly defined orthopaedic procedures, standardised infection criteria, and external validation are necessary to establish the clinical applicability of these inflammatory markers. LIMITATIONS The study had several limitations. The relatively small sample size of 50 patients and the occurrence of only eight SSI events limited statistical precision and the reliability of diagnostic estimates. Inclusion of different orthopaedic implant procedures may have introduced variability in postoperative inflammatory responses. Inflammatory markers were evaluated at a single postoperative time point, without serial measurements or preoperative baseline comparisons. The 30-day follow-up period may not have captured late-onset implant-associated infections. Furthermore, the cutoff values were derived from the same dataset and were not independently validated. The absence of multivariable adjustment and detailed microbiological findings also limits interpretation of the reported associations.

The reported findings indicate that postoperative day 3 CRP, NLR, and PLR levels were significantly higher among patients who developed early surgical site infection following orthopaedic implant surgery. CRP demonstrated the highest numerical diagnostic discrimination and sensitivity, whereas NLR showed greater specificity. PLR exhibited comparatively lower diagnostic performance. These inflammatory markers may serve as useful adjuncts to clinical assessment and postoperative infection surveillance. However, their interpretation should consider postoperative inflammatory changes, surgical characteristics, and clinical findings. Larger prospective studies with standardised diagnostic criteria, serial biomarker measurements, and external validation are recommended to establish reliable cutoff values and determine their clinical applicability.

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