A Biomechanical Study of Two Distinct Methods of Anterior Cruciate Ligament Rupture, and a Novel Surgical Reconstruction Technique, in a Small Animal Model of Posttraumatic Osteoarthritis.

Small animal models are critical for studies of sports-related knee injury and disease such as posttraumatic osteoarthritis (PTOA) following anterior cruciate ligament (ACL) rupture. In such models, ACL damage can be achieved by surgical transection or, using a more recent innovation, by noninvasive biomechanical means. Whether these approaches differentially alter normal mechanics is unknown. Furthermore, while surgical reconstruction of ruptured ACL can greatly improve joint stability, its effect on PTOA development is also unclear. Our primary purpose was to characterize rodent knee joint mechanics in two models of ACL rupture using a novel quantitative laxity mechanical test. Our secondary aim was to characterize a new reconstruction technique using autograft tail tendon, and to assess its effect on joint mechanics. Our hypothesis was that surgical ACL transection would have a greater effect on joint mechanics. A total of 24 rat knee specimens underwent surgical or biomechanical ACL rupture and were stabilized using a new reconstruction technique using autograft tail tendon. Joint mechanics were assessed three times; preinjury, postinjury, and again after reconstruction, using quantitative joint laxity testing. Primary test readouts were maximum anteroposterior (AP) laxity, loading curve slope, and energy absorption. Student's t-tests were performed to identify intragroup differences. All surgical transections were completed successfully; maximum load in the biomechanical model was 67 ± 7.7 N, with a coefficient of variation of 11.43%. Surgical transection caused increased AP laxity, while biomechanical injury nonsignificantly increased this parameter. In both cases, these changes recovered to baseline by reconstruction. Loading curve slope was reduced in both models and was also returned to baseline by repair. Energy absorption followed the same pattern except it remained significantly different from baseline postreconstruction in the surgical group. This study supports our hypothesis knee joint mechanics is differentially affected by injury mechanism in a small animal model. We also report a novel reconstruction technique in this model, using autograft tail tendon.

Automated Bone Segmentation and Surface Evaluation of a Small Animal Model of Post-Traumatic Osteoarthritis.

MicroCT imaging allows for noninvasive microstructural evaluation of mineralized bone tissue, and is essential in studies of small animal models of bone and joint diseases. Automatic segmentation and evaluation of articular surfaces is challenging. Here, we present a novel method to create knee joint surface models, for the evaluation of PTOA-related joint changes in the rat using an atlas-based diffeomorphic registration to automatically isolate bone from surrounding tissues. As validation, two independent raters manually segment datasets and the resulting segmentations were compared to our novel automatic segmentation process. Data were evaluated using label map volumes, overlap metrics, Euclidean distance mapping, and a time trial. Intraclass correlation coefficients were calculated to compare methods, and were greater than 0.90. Total overlap, union overlap, and mean overlap were calculated to compare the automatic and manual methods and ranged from 0.85 to 0.99. A Euclidean distance comparison was also performed and showed no measurable difference between manual and automatic segmentations. Furthermore, our new method was 18 times faster than manual segmentation. Overall, this study describes a reliable, accurate, and automatic segmentation method for mineralized knee structures from microCT images, and will allow for efficient assessment of bony changes in small animal models of PTOA.