We used immediate post-operative in vivo three-dimensional computed tomography to compare graft bending angles and femoral tunnel lengths in 155 patients who had undergone single-bundle reconstruction of the anterior cruciate ligament using the transtibial (n = 37), anteromedial portal (n = 72) and outside-in (n = 46) techniques.

The bending angles in the sagittal and axial planes were significantly greater but the coronal-bending angle was significantly less in the transtibial group than in the anteromedial portal and outside-in groups (p < 0.001 each). The mean length of the femoral tunnel in all three planes was significantly greater in the transtibial group than the anteromedial portal and outside-in groups (p < 0.001 each), but all mean tunnel lengths in the three groups exceeded 30 mm. The only significant difference was the coronal graft- bending angle in the anteromedial portal and outside-in groups (23.5° vs 29.8°, p = 0.012).

Compared with the transtibial technique, the anteromedial portal and outside-in techniques may reduce the graft-bending stress at the opening of the femoral tunnel. Despite the femoral tunnel length being shorter in the anteromedial portal and outside-in techniques than in the transtibial technique, a femoral tunnel length of more than 30 mm in the anteromedial portal and outside-in techniques may be sufficient for the graft to heal.

Cite this article: Bone Joint J 2014;96-B:743–51.

Objectives

There remains a lack of data on the reliability of methods to estimate tibial coverage achieved during total knee replacement. In order to address this gap, the intra- and interobserver reliability of a three-dimensional (3D) digital templating method was assessed with one symmetric and one asymmetric prosthesis design.

We studied the intra- and interobserver reliability of measurements of the position of the components after total knee replacement (TKR) using a combination of radiographs and axial two-dimensional (2D) and three-dimensional (3D) reconstructed CT images to identify which method is best for this purpose. A total of 30 knees after primary TKR were assessed by two independent observers (an orthopaedic surgeon and a radiologist) using radiographs and CT scans. Plain radiographs were highly reliable at measuring the tibial slope, but showed wide variability for all other measurements; 2D-CT also showed wide variability. 3D-CT was highly reliable, even when measuring rotation of the femoral components, and significantly better than 2D-CT. Interobserver variability in the measurements on radiographs were good (intraclass correlation coefficient (ICC) 0.65 to 0.82), but rotational measurements on 2D-CT were poor (ICC 0.29). On 3D-CT they were near perfect (ICC 0.89 to 0.99), and significantly more reliable than 2D-CT (p < 0.001). 3D-reconstructed images are sufficiently reliable to enable reporting of the position and orientation of the components. Rotational measurements in particular should be performed on 3D-reconstructed CT images. When faced with a poorly functioning TKR with concerns over component positioning, we recommend 3D-CT as the investigation of choice