Physeal Disruption During ACL Reconstruction in Skeletally Immature Patients: Does Independent Femoral Tunnel Drilling Place the Physis at Greater Risk?

OBJECTIVES: The purpose of this study was to radiographically assess differences in distal femoral physeal disruption between transtibial and independent femoral tunnel drilling techniques following ACL reconstruction in skeletally immature patients. METHODS: A retrospective, matched comparative cohort study was performed of skeletally immature patients who underwent transphyseal ACL reconstruction between January 1, 2008 and March 31, 2011. All skeletally immature patients between ten and fifteen years old who underwent independent femoral tunnel drilling and had adequate baseline and post-operative radiographs were analyzed. These patients were matched with a transtibial technique cohort based on age and sex. Demographic characteristics and peri-operative metrics were collected. Radiographic measurements were recorded from pre-operative MRI and post-operative plain radiographs. RESULTS: Twenty patients were analyzed. Between groups, there were significant differences between independent tunnel drilling and transtibial tunnel drilling in the estimated area of physeal disruption (1.64 cm2 vs. 0.74 cm2, P<0.001), femoral (32.1º vs. 72.8º, P<0.001) and tibial (50.1º vs. 60.5º, P=0.003) tunnel angles, medial/lateral location of the femoral tunnel (24.2 mm vs. 36.1 mm from lateral cortex, P=0.001), and distance from the lateral aspect of the distal femoral physis and the femoral tunnel exit (4.7 mm vs. 26.7 mm from the perichondrial ring, P<0.001), respectively. All patients who underwent femoral tunnel drilling at an angle of less than 25º from the transverse axis experienced a greater than 6% disruption of physeal area. There was a significant inverse correlation between femoral tunnel angle and estimated area of femoral physeal involvement (r=-0.8255, P=0.003). CONCLUSION: With femoral tunnel drilling techniques that create more oblique tunnels, the area of distal femoral physeal damage is larger, more eccentric and closer to the perichondrial ring. Since most studies noting the safety of transphyseal ACL reconstruction have utilized a vertical femoral tunnel, surgeons should be aware that if an independent femoral tunnel drilling technique is utilized during transphyseal ACL reconstruction, the physis is at greater risk when drilling at more horizontal angles. Angles greater than 25º from the transverse axis may safely create <6% physeal area damage.