Patellar Fracture Forces Are Not Affected by Proximal Versus Distal Bone Block Anterior Cruciate Ligament Reconstruction Harvest Sites in a Cadaveric Model

Abstract

Purpose: To quantify the maximum load to fracture in patellae from which bone–patellar tendon–bone (BPTB) and bone–quadriceps tendon (BQT) autografts have been harvested for anterior cruciate ligament reconstruction in a cadaveric model. Methods: Forty-six fresh-frozen patellae were isolated and divided into the BPTB harvest and BQT harvest groups with matching based on donor age and sex. Computed tomography scans were obtained to calculate bone mineral density (BMD) and patellar height, width, and thickness. BPTB and BQT grafts were harvested from the inferior patella and superior patella, respectively, and then ramped to failure in a 3-point bend test configuration to simulate a postoperative fracture produced by a direct impact after a fall. The presence of fracture, fracture pattern, and maximum load to fracture were recorded. Donor demographic characteristics; patellar height, width, and thickness; and maximum load were compared by the Student t test. Pearson correlations were used to determine whether maximum load was affected by BMD or patellar morphology. The level of significance was set at P < .05. Results: Maximum load to fracture was not significantly different (P = .91) between the BPTB (5.0 ± 2.3 kN) and BQT (5.1 ± 2.6 kN) groups. Maximum load to fracture in the BPTB group did not correlate with BMD (P = .57) or patellar measurements (P = .57 for thickness, P = .43 for width, and P = .45 for height). Maximum load to fracture in the BQT group positively correlated with BMD and negatively correlated with patellar height. Maximum load to fracture in the BQT group did not correlate with patellar thickness or width. Fracture through the harvest site was observed in 87% of BPTB specimens and 78% of BQT specimens. Conclusions: The location of the BPTB or BQT autograft harvest site did not significantly affect patellar load to fracture in a cadaveric model. Clinical Relevance: It is important to understand patellar morphology and the effect of BPTB and BQT graft harvest-site locations on the biomechanical strength of the patella after anterior cruciate ligament reconstruction.