A novel classification system for anterior femoral notching in total knee arthroplasty

Femoral notching in Total Knee Arthroplasty (TKA) is traditionally associated with an increased risk of periprosthetic fracture in cases of excessive anterior resection. Beyond fracture risk, notching can influence implant fit, patellofemoral and tibiofemoral balance, joint stability, and overall biomechanics. Despite its clinical importance, a standardized system for describing femoral notching is lacking. We propose a novel Femoral Notch Classification, based on resection depths and trochlear geometry, intended as a common language applicable both intraoperatively and on lateral radiographs, independent of alignment philosophy.

The classification was developed through clinical observation and biomechanical rationale, focusing on preserving anterior cortical integrity while permitting a controlled notch when required. Definitions relate resection depths to implant thickness, distal femoral anatomy, and trochlear geometry, with attention to balancing anterior and posterior gaps. Perpendicularity of the anterior cut relative to the cortex can be evaluated and adapted according to implant design and alignment technique. Four descriptive categories were established, providing a structured framework for assessment.

(1) Type 0-No Notch: Complete preservation of the anterior cortex with no visible step-off or indentation. Anterior resection may match implant thickness precisely; if not, anterior overstuffing or posterior over-resection should be controlled. (2) Type 1-On the Line: Anterior resection is flush with the femoral cortex, creating a subtle notch that remains biomechanically stable without compromising the cortex. (3) Type 2-Controlled Notch: A deeper anterior resection (ideally, < 3 mm) beyond the cortical line in the presence of specific trochlear geometry or distal femoral anatomy. This configuration is acceptable when the radiographic pattern is consistent with trochlear accommodation. Posterior gaps must still be carefully controlled to avoid overstuffing. (4) Type 3-Critical Notch: Excessive anterior resection (> 3 mm) characterized by significant cortical interruption and the absence of a radiographically identifiable anatomical correlate. This configuration may compromise distal femoral strength and is associated with increased risk of periprosthetic fracture when not justified by trochlear geometry. Surgeons should exercise caution and verify proper implant alignment. Inter-observer reliability was substantial (Fleiss' κ = 0.80; quadratic weighted κ = 0.87) and intra-observer reliability was almost perfect (mean Cohen's κ = 0.91). The majority of cases were classified as Type 0 and Type 1.

The Femoral Notch Classification provides a practical, reproducible framework for assessing femoral notching in TKA, suitable for intraoperative guidance and radiographic analysis. It may help surgeons avoid over- or under-resection while allowing a controlled notch when required. Further clinical validation is needed to assess its impact on long-term patient outcomes.