D. G. Norman

Cortical bony thickening of the lateral intercondylar wall : the functional attachment of the anterior cruciate ligament

Background: The anatomy of the anterior cruciate ligament (ACL) has become the subject of much debate. There has been extensive study into attachment points of the native ligament, especially regarding the femoral attachment. Some of these studies have suggested that fibers in the ACL are of differing functional importance. Fibers with higher functional importance would be expected to exert larger mechanical stress on the bone. According to Wolff’s law, cortical thickening would be expected in these areas. Purpose: To examine cortical thickening in the region of the ACL footprint (ie, the functional footprint of the ACL). Study Design: Descriptive laboratory study. Methods: Using micro–computed tomography with resolutions ranging from 71 to 91 μm, the cortical thickness of the lateral wall of the intercondylar notch in 17 cadaveric knees was examined, along with surface topography. After image processing, the relationship between the cortical thickening and surface topology was visually compared. Results: A pattern of cortical thickening consistent with the functional footprint of the ACL was found. On average, this area was 3 times thicker than the surrounding bone and significantly thicker than the remaining lateral wall (P < .0001). This thickening was roughly elliptical in shape (with a mean centroid at 23.5 h:31 t on a Bernard and Hertel grid) and had areas higher on the wall where greater thickness was present. The relationship to previously reported osseous landmarks was variable, although the patterns were broadly consistent with those reported in previous studies describing direct and indirect fibers of the ACL. Conclusion: The findings of this study are consistent with those of recent studies describing fibers in the ACL of differing functional importance. The area in which the thickening was found has been defined and is likely to represent the functional footprint of the ACL. Clinical Relevance: This information is of value to surgeons when determining the optimal place to position the femoral attachment site of the reconstructed ACL.

The cutting edge — Micro-CT for quantitative toolmark analysis of sharp force trauma to bone

Toolmark analysis involves examining marks created on an object to identify the likely tool responsible for creating those marks (e.g., a knife). Although a potentially powerful forensic tool, knife mark analysis is still in its infancy and the validation of imaging techniques as well as quantitative approaches is ongoing. This study builds on previous work by simulating real-world stabbings experimentally and statistically exploring quantitative toolmark properties, such as cut mark angle captured by micro-CT imaging, to predict the knife responsible. In Experiment 1 a mechanical stab rig and two knives were used to create 14 knife cut marks on dry pig ribs. The toolmarks were laser and micro-CT scanned to allow for quantitative measurements of numerous toolmark properties. The findings from Experiment 1 demonstrated that both knives produced statistically different cut mark widths, wall angle and shapes. Experiment 2 examined knife marks created on fleshed pig torsos with conditions designed to better simulate real-world stabbings. Eight knives were used to generate 64 incision cut marks that were also micro-CT scanned. Statistical exploration of these cut marks suggested that knife type, serrated or plain, can be predicted from cut mark width and wall angle. Preliminary results suggest that knives type can be predicted from cut mark width, and that knife edge thickness correlates with cut mark width. An additional 16 cut marks walls were imaged for striation marks using scanning electron microscopy with results suggesting that this approach might not be useful for knife mark analysis. Results also indicated that observer judgements of cut mark shape were more consistent when rated from micro-CT images than light microscopy images. The potential to combine micro-CT data, medical grade CT data and photographs to develop highly realistic virtual models for visualisation and 3D printing is also demonstrated. This is the first study to statistically explore simulated real-world knife marks imaged by micro-CT to demonstrate the potential of quantitative approaches in knife mark analysis. Findings and methods presented in this study are relevant to both forensic toolmark researchers as well as practitioners. Limitations of the experimental methodologies and imaging techniques are discussed, and further work is recommended.

Correction to: Quantitative topographic anatomy of the femoral ACL footprint: a micro-CT analysis

An author has corrected their first name and updated their email address - see the affiliation section below. Daniel G. Norman should now be Danielle G. Norman as shown in the authorgroup section above.

Quantitative topographic anatomy of the anterior cruciate ligament femoral footprint - do the ridges exist

Objectives: Anatomic ACL reconstruction has become an accepted technique to restore functional stability to the knee. Bony landmarks have been described which aid placement of the graft in mid bundle or specific anteromedial/posterolateral bundle positions. The objective of this study was to produce objective quantitative validation of the lateral intercondylar ridge and bifurcate ridge using micro CT technology, so a to better understand these important anatomical landmarks. nMethods: Cadaveric human knees were imaged using a XT 320 H LC subjects (mean length 9.3 mm; mean height 1.5 mm) with the bifurcate ridge present in 14% (mean length 4.3 mm, height 0.9 mm). A relief map of the ACL footprint was produced which showed the individual variability of the anatomical ridges. nConclusions: This study demonstrates that the bony anatomical landmarks of the ACL footprint are a variable entity in individuals. When present, they can be used as a guide for femoral tunnel placement in ACL reconstruction. However, if absent, other techniques need to be adopted such as the ‘ruler technique’ or intraoperative fluoroscopy, so as to be able to reproducibly replicate anatomic tunnel positioning.