Dorsal cortex line more reliable than transepicondylar axis for rotation in revision TKA with severe bone loss: study

Dorsal cortex line is more reliable than transepicondylar axis for rotation in revision total knee arthroplasty with severe bone loss: study

The transepicondylar axis is a well-established reference for the determination of femoral component rotation in total knee arthroplasty (TKA). However, when severe bone loss is present in the femoral condyles, rotational alignment can be more complicated. There is a lack of validated landmarks in the supracondylar region of the distal femur. Therefore, Salzmann et al conducted a study to analyze the correlation between the surgical transepicondylar axis (sTEA) and the suggested dorsal cortex line (DCL) in the coronal plane and the inter- and intraobserver reliability of its CT scan measurement.

A total of 75 randomly selected CT scans were measured by three experienced surgeons independently. The DCL was defined in the coronal plane as a tangent to the dorsal femoral cortex located 75 mm above the joint line in the frontal plane. The difference between sTEA and DCL was calculated. Descriptive statistics and angulation correlations were generated for the sTEA and DCL, as well as for the distribution of measurement error for intra- and inter-rater reliability.

The key findings of the study were:

• This study introduces a novel landmark for femoral component rotation in revision total knee arthroplasty with severe bone loss.

• The validity and reliability are shown in comparison to the transepicondylar axis.

• This landmark can be helpful, when the condyles are destroyed or total femur replacement is planned.

• The external rotation of the DCL to the sTEA was a mean of 9.47° (SD 3.06°), and a median of 9.2° (IQR 7.45° to 11.60°), with a minimum value of 1.7° and maximum of 16.3°.

• The measurements of the DCL demonstrated very good to excellent test-retest and inter-rater reliability coefficients (intraclass correlation coefficient 0.80 to 0.99).

The author opined - ‘In conclusion, the DCL at 75 mm above the joint line can be measured reproducibly and is approximately 10°externally rotated to the sTEA. This may serve as a valuable landmark for determining femoral component rotation in revision TKA with significant bone loss, when the epicondyles are difficult to assess radiologically, or when the epicondyles are absent. Surgeons should be aware that there are outliers in this study in up to 17% and the trochlea design of the of the implant does not match the natural knee.’

Further reading:

Dorsal cortex line more reliable than trans epicondylar axis for rotation in revision TKA with severe bone loss M. Salzmann, E. Kropp, R. Prill, N. Ramadanov, M. Adriani, R. Becker Bone Jt Open 2024;5(12): 1067–1071. DOI: 10.1302/2633-1462.512.BJO-2024-0140.R1