Central Defect Type Partıal ACL Injury Model on Goat Knees: The Effect of Infrapatellar Fat-Pad Excision

OBJECTIVES: The aim of this study is to investigate the primary healing capacity of the anterior cruciate ligament (ACL) and the possible effect of fat pad excision on it. For this purpose, a central defect type ACL injury model was performed. Histopathological and biomechanical studies were performed on this model. METHODS: Total of ten female adolescent Anatolian Black Goats were included in the study. A midsubstance central defect was created successfully with a four mm. arthroscopic punch in the ACLs of right knees of all the subjects through a medial mini-arthrotomy and goats were assigned to groups whether the fat pad was preserved (group I, n=5) or excised completely (group II, n=5). The left knees served as control. The histopathological evaluations of the defect area were performed utilizing Hematoxylene-Eosine, Masson Trichrome, Van Gieson, and elastic Van Gieson staining as well as measurement of type I collagen immunohistochemically in one sample from each group at 10th week postoperatively. The remaining knees were evaluated biomechanically at the 12th week, measuring anterior tibial translation (ATT) of the knee joints at 90 degrees of flexion and tensile properties (Maximum Tensile Load (MTL), Maximum Elongation (ME), Stiffness (S), failure mode (FM)) of the femur-ACL-tibia complex. Statistical analysis was performed utilizing SPSS v18 package program. Mann – Whitney U and Wilcoxon’s signed rank test were used for inter and intragroup analysis, respectively. Statistical significance was set at 0.05. RESULTS: Histopathological analysis revealed that the central defect area was fully filled macroscopically and microscopically. However, mucoid degeneration was observed in group II. Relative collagen type I content increased in group II. There was no significant difference both within and between groups in terms of ATT values (p=0.715 and p=0.149 respectively). There was no statistical significance between and within groups in terms of MTL and ME; however group II demonstrated greater stiffness than group I (p=0,043) Overall (n=16 knees), tibial avulsion was the commonest mode of failure (n=9) in both control and operated knees. CONCLUSION: These findings revealed that the central defect type partial ACL injury model acted stable on A-P direction and had full healing capacity. The excision of the fat-pad had no additional effect except increased stiffness. Tibial insertion site seemed to be the weakest portion of the femur-ACL-tibia complex in adolescent goat knees.