Tunnel enlargement and changes in synovial fluid cytokine profile following anterior cruciate ligament reconstruction with patellar tendon and hamstring tendon autografts

There is growing evidence that cytokines such as tumor necrosis factor (TNF) α, interleukin (IL) 1β, IL-6, bone morphogenetic proteins (BMP), and nitric oxide (NO) play an important role in the pathogenesis of bone tunnel enlargement following anterior cruciate ligament (ACL) reconstruction. Furthermore, the release of these mediators has been considered a possible reason for the higher incidence of bone tunnel enlargement following hamstring tendon (HST) than following patellar tendon (PT) ACL reconstruction observed in several studies. In this investigation synovial fluid samples from 13 patients were collected immediately before (24±7 days after ACL rupture) and 7 days after ACL surgery and values of TNF-α, IL-1β, IL-6, NO, and BMP-2 were analyzed. Furthermore, the incidence of bone tunnel enlargement was assessed using radiographs 38±7 weeks after surgery. Six patients underwent autologous HST ACL reconstruction, and in seven patients an PT autograft was used. In the overall patient population there were significantly higher synovial fluid concentrations of IL-6 and BMP-2 postoperatively than preoperatively; TNF-α showed a trend towards lower postoperative levels while IL-1β and NO remained unchanged. The concentrations of NO, TNF-α, and IL-6 found in the present study were clearly higher than normal values given in the literature. Assessment of bone tunnel enlargement revealed an average increase in tibial tunnel width of 28.4±3.1% with comparable values for HST and PT ACL reconstructions. There was no significant correlation between bone tunnel enlargement and postoperative synovial fluid concentrations of TNF-α, IL-1β, IL-6, NO, and BMP-2. However, all patients with bone tunnel enlargement had higher postoperative concentrations of TNF-α, IL-6, and NO in the synovial fluid. There were no significant differences in concentrations between HST and PT groups. In conclusion, we observed an association between tibial bone tunnel enlargement and elevated synovial fluid concentrations of IL-6, TNF-α, and NO 7 days after ACL surgery indicating the potential involvement of these biological mediators in the pathogenesis of bone tunnel enlargement. However, there was no difference between HST and PT ACL reconstructions regarding synovial fluid contents of IL-6, TNF-α, IL-1β, NO, and BMP-2, suggesting a comparable biological response between these autografts following their use in ACL reconstruction.