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Soft Tissue-To-Bone Ratio Outperforms Body Mass Index in Predicting Periprosthetic Joint Infection in Total Knee
Alexander Price1, Max White2, Austin Shaji2
1Department of Trauma & Orthopaedics, University Hospital Galway, Galway, Ireland; Royal College of Surgeons Ireland, Dublin, Ireland.
Background:
Periprosthetic joint infection (PJI) remains one of the most devastating complications following total knee arthroplasty (TKA), often leading to prolonged treatment and poor patient outcomes. Traditionally, body mass index (BMI) has been used as a key risk factor in predicting PJI, but BMI fails to reflect local anatomical variations influencing surgical outcomes. This study explored whether the soft tissue-to-bone (STiB) ratio, a novel radiographic measurement, could serve as a more accurate predictor of PJI compared to BMI.
Methods:
We conducted a retrospective case-control study involving 25 culture-confirmed PJI cases and 75 matched total knee arthroplasty controls, with no evidence of infection at least 24 months after total knee arthroplasty. Participants were matched for BMI to reduce its confounding influence, allowing a focused comparison of STiB ratios between those who developed PJI and those who did not. Preoperative radiographs were analyzed to measure the STiB ratio at three different anatomical locations: antero-posterior (AP), Lateral 1, and Lateral 2. The ratios were calculated as the total soft tissue structures divided by the osseous structures at each location. Multivariate logistic regressions and receiver operating characteristic (ROC) analyses were performed to assess predictive validity.
Results:
The STiB ratio at Lateral 1 was significantly higher in the PJI group compared to the control group, with a mean of 1.92 versus 1.80 (P = 0.037). Logistic regressions showed that this site was an independent predictor of infection (odds ratio (OR) 2.2; 95% confidence interval (CI): 1.10 to 4.40; P = 0.025). The BMI was not statistically significant (P = 0.845). The receiver operating characteristic curves showed modest discriminative performance for Lateral 1 (area under the curve (AUC) = 0.52).
Conclusions:
The STiB ratio, particularly at Lateral 1, may be a more accurate and clinically useful predictor of PJI risk than BMI. Its accessibility and objective nature make it a compelling addition to preoperative risk stratification protocols.
Insights
The soft tissue-to-bone (STiB) ratio, especially at Lateral 1, shows promise as a superior predictor of periprosthetic joint infection (PJI) after total knee arthroplasty (TKA) compared to body mass index (BMI). This radiographic measure offers a more accurate risk assessment for PJI.
Area of Science:
- Orthopedic Surgery
- Radiology
- Infectious Disease
Background:
- Periprosthetic joint infection (PJI) is a severe complication of total knee arthroplasty (TKA).
- Body mass index (BMI) is a traditional but limited predictor of PJI.
- Novel radiographic measures are needed for improved PJI risk assessment.
Purpose of the Study:
- To evaluate the soft tissue-to-bone (STiB) ratio as a predictor of PJI after TKA.
- To compare the predictive accuracy of STiB ratio against BMI for PJI risk.
Main Methods:
- Retrospective case-control study of 25 PJI cases and 75 TKA controls.
- Matched for BMI to isolate the effect of STiB ratio.
- Preoperative radiographs analyzed for STiB ratio at AP, Lateral 1, and Lateral 2 locations.
- Multivariate logistic regression and ROC analyses performed.
Main Results:
- The STiB ratio at Lateral 1 was significantly higher in the PJI group (1.92 vs. 1.80, P=0.037).
- Lateral 1 STiB ratio independently predicted PJI (OR 2.2, P=0.025).
- BMI was not a significant predictor (P=0.845); ROC analysis showed modest discrimination for Lateral 1 (AUC=0.52).
Conclusions:
- The STiB ratio at Lateral 1 shows potential as a more accurate PJI predictor than BMI.
- This objective radiographic measure can enhance preoperative risk stratification for TKA patients.
- The STiB ratio offers a clinically useful tool for assessing PJI risk.
