ArticleArchives of orthopaedic and trauma surgery2026
The grand piano ratio: an adjunctive intraoperative screening tool for detecting excessive femoral component external rotation in total knee arthroplasty.
Article in Archives of orthopaedic and trauma surgery, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
backgroundAccurate femoral component rotation is essential for optimal outcomes in total knee arthroplasty (TKA), yet reliable intraoperative assessment remains challenging. The "grand piano sign" has been described as a qualitative visual cue, but its quantitative clinical value has not been clearly established. This study aimed to evaluate the diagnostic performance of the grand piano ratio as an intraoperative tool for detecting excessive femoral component external rotation using advanced postoperative imaging as a reference standard.
methodsA retrospective analysis was conducted on 170 knees undergoing primary TKA. The intraoperative grand piano ratio was measured after completion of all femoral resections and before trial component implantation using the anterior femoral resection surface. Postoperative femoral component rotation was assessed using MAVRIC-sequence magnetic resonance imaging referenced to the surgical transepicondylar axis (sTEA). Excessive femoral component external rotation was defined as postoperative external rotation greater than 3° relative to the sTEA reference. Receiver operating characteristic (ROC) analysis was performed to evaluate diagnostic performance of the grand piano ratio and determine the optimal cutoff value, while multivariable logistic regression analysis was used to identify independent predictors of excessive external rotation.
resultsExcessive femoral component external rotation (> 3°) was identified in 39 of 170 knees (22.9%). The mean grand piano ratio was significantly lower in knees with external rotation compared to those without (0.41 vs. 0.54, p < 0.001). The grand piano ratio demonstrated moderate discriminative ability for detecting femoral component external rotation greater than 3° (AUC = 0.74, 95% CI 0.65-0.83). The optimal cutoff value was 0.44, yielding a sensitivity of 71.8% and a specificity of 74.0%. In multivariable analysis, the grand piano ratio was the only independent predictor of malrotation (p < 0.001). At the identified threshold, the negative predictive value reached 89.9%, suggesting that excessive external rotation was unlikely when the grand piano ratio exceeded the proposed cutoff.
conclusionThe grand piano ratio may serve as a simple and readily available adjunctive intraoperative screening parameter for identifying excessive femoral component external rotation in TKA. A threshold value of 0.44 demonstrated a high negative predictive value and may assist surgeons in intraoperative decision-making. However, the ratio should be considered a complementary assessment tool rather than a definitive method for determining femoral component rotation. The grand piano ratio should be viewed as a complementary intraoperative assessment tool rather than an alternative to navigation or robotic-assisted techniques.
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