ObjectiveTo study the experimental biomechanics of acetabular posterior wall fractures so as to provide theoretical basis for its clinical treatment. MethodsSix formalin-preserved cadaveric pelvises were divided into groups A and B (n=3). The fracture models of superior-posterior wall and inferior-posterior wall of the acetabulum were created on both hips in group A;fractures were fixed with two interfragmentary screws and a locking reconstruction plate. The fracture models of superior-posterior wall of acetabulum were created on both hips in group B;fractures were fixed with two interfragmentary screws and a locking reconstruction plate at one side, and with acetabular tridimensional memory fixation system (ATMFS) at the other side. The biomechanical testing machine was used to load to 1 500 N at 10 mm/min speed for 30 seconds. The displacement of superior and inferior fracture sites was analyzed with the digital image correlation technology. ResultsNo fracture or internal fixation breakage occurred during loading and measuring;the displacement valuess of the upper and lower fracture lines were below 2 mm (the clinically tolerable maximum value) in 2 groups. In group A, the displacement values of the upper and lower fracture lines at superior-posterior wall fracture site were significantly higher than those at inferior-posterior wall fracture site (P<0.01), and the displacement values of the upper fracture line were significantly higher than those of lower fracture line (P<0.01) in two fracture types. In group B, the displacement values of the upper and lower fracture lines at the side fixed with screws and a locking reconstruction plate were similar to the values at the side fixed with ATMFS, all being close to 2 mm;the displacement values of the upper fracture line were significantly higher than those of lower fracture line (P<0.05) in two fixation types. ConclusionThe actual biomechanical effect of the superior-posterior wall of acetabulum is much greater than that of the inferior-posterior wall of acetabulum and they should be discriminated, which might be the reasons of reduction loss, femoral head subluxation, and traumatic arthritis during follow-up.
ObjectiveTo compare difference in the establishment of animal model of cartilage defect by resection of medial collateral ligament and meniscus and by cartilage excavation so as to provide a proper way for the choose of animal model preparation of catilage defect. MethodsTen healthy beagles, male or female, weighing 5.0-10.0 kg, were randomly divided into 3 groups. Resection of knee collateral ligament and meniscus was performed on 4 beagles of group A, cartilage excavation of knee-joints in 4 beagles of group B, and no treatment on 2 beagles of group C as controls. At 16 weeks after modeling, MRI, gross observation, HE staining, Safranin O staining, and toluidine blue staining were performed, and Osteoarthritis Research Society International (OARSI) score was recorded. ResultsMRI and histology observation showed no obvious cartilage defect in group A; obvious cartilage defects were observed in group B and gross observation showed dramatic dark red cartilage defects. OARSI score was significantly lower in group A (0.940±0.574) than group B (4.500±0.516) (t=18.461, P=0.000). ConclusionThe cartilage excavation is better than resection of both meniscus and medial collateral ligament, which provides a good method of establishing an animal model of cartilage defect at 16 weeks after operation.