Poster 318: CHANGE IN POSTERIOR TIBIAL SLOPE FOLLOWING DISPLACED PEDIATRIC TIBIAL TUBERCLE FRACTURES: A POTENTIAL MODEL FOR GROWTH MODULATION IN THE ACL DEFICIENT KNEE

OBJECTIVES: Increased posterior tibial slope angle (PTSA) increases the risk for anterior cruciate ligament (ACL) tear and ACL graft failure. Proximal tibial slope changing osteotomies are employed in the adult population; growth modulation procedures may present a treatment opportunity in the skeletally immature. This procedure has not been described in the context of ACL injuries, and the rate at which posterior tibial slope could be corrected is unknown. Our purpose was to quantify the rate of change in PTSA following operatively treated displaced tibial tubercle fractures in skeletally immature patients, and to determine how this rate is affected by skeletal age. We hypothesized that there would be a progressive loss of posterior tibial slope after injury, and that rate of change in PTSA would be highest during peak growth velocity METHODS: We retrospectively reviewed skeletally immature patients with tibial tubercle fractures treated with ORIF. We measured posterior tibial slope angle (PTSA) at ˜3-, 6-, 12-months, and further postoperative time points if available. All subjects had a minimum of 6-months follow up. Bone age at the time of injury was determined. Negative PTSA was indicative of posteriorly directed slope, positive PTSA indicated anterior slope. Linear regression analysis was used to evaluate rate of change in PTSA (ΔPTSA) for individual patients and total cohort trend. Patient regression coefficients were averaged into bone age cohorts. The unit of analysis was the knee. RESULTS: Twenty-two patients with 23 knees were included. 86% of patients were male. Average chronologic and bone age was 14 years at time of injury. Average follow-up was 17 months (range 6 to 52 months). Patients had a mean PTSA of -12˚ ± 2.4˚ at the time of injury. The overall mean ΔPTSA for the cohort was 0.30˚ ± 0.31˚ per month (range -0.27˚ to 0.97˚ per month). Linear regression revealed a significant relationship between months post-fixation and PTSA, demonstrating a ΔPTSA of +0.31˚ per month (CI 95% (0.24, 0.38); p<.001) (Figure 1). The highest average ΔPTSA was seen at 14-years (0.58˚ ± 0.44˚ per month). The average overall absolute change in PTSA from injury to final follow-up was +4.1˚ (range -3.4˚ to 21˚) (Figure 2). CONCLUSIONS: Our data suggest progressively more anterior slope following ORIF. The greatest rate of change in PTSA corresponded with peak growth velocity. These findings may serve as a model for predicting the effect of anterior proximal tibia epiphysiodesis on tibial slope in ACL surgery.