Parsons' knob, the bony landmark of the tibial insertion of the anterior cruciate ligament, evaluated by three-dimensional computed tomography

BackgroundIn recent years, highly detailed evaluations have been performed using three-dimensional computed tomography (3D CT). Very small bony ridges, such as Resident's ridge and the lateral bifurcate ridge can be visualised by 3D CT. The purpose of this study was to ascertain whether Parsons' knob, which was recognised as the bony landmark of the anterior cruciate ligament insertion on the tibia, can be visualised by 3D CT, and, if this is possible, to clarify its location and morphology.MethodsOne hundred knees were scanned by CT in this study and 3D models were created using the volume-rendering technique. Parsons' knob was detected on the axial 3D CT view of the tibial plateau. The location of the knob was presented on a grid aligned with the medial-to-lateral and anterior-to-posterior anatomical tibial axes. All measurements were expressed as a percentage of the corresponding maximum dimension. The width and height of Parsons' knob were also measured.ResultsParsons' knob was detected in all 100 knees and was ordinarily found as a ridge that ran obliquely forward from the anterior edge of the medial spine. The knob was located at an average of 22 ± 3.1% of the anterior-to-posterior tibial plateau depth from the anterior edge of the tibia and extended from a mean ± s.d. of 46.9 ± 2.1% to 54 ± 3.6% of the medial-to-lateral tibial plateau width from the medial edge of the tibia. The average width of the knob was 11.5 ± 3.1 mm, and the average height was 1.2 ± 0.3 mm at the most medial portion, 0.2 ± 0.3 mm at the most lateral portion, and 1.2 ± 0.3 mm at the intermediate portion between them. The medial and intermediate portions of the knob were significantly higher than the lateral portion (p < 0.05).ConclusionThe location and morphology of Parsons' knob can be well-visualised using 3D CT.