Objectives:
Tibial spine fractures are common in the pediatric population because their subchondral bone is significantly weaker. Two techniques predominate the tibial spine fracture repair: screw fixation and high-tensile-strength suture fixation. Most studies in porcine or adult human bone suggest suture fixation is superior to screw fixation, but porcine and adult human bone may be poor approximates for pediatric bone. No prior study has evaluated fixation methods in human pediatric knees. This study aims to quantify the biomechanical properties of two-screw and two-suture tibial spine fracture repair in pediatric knees.
Methods
Pediatric knee specimens were randomized to either two-screw or two-suture fixation. A standardized Meyers-Mckeever Type III tibial spine fracture was induced. Screw fixation was accomplished with two 4.0 mm cannulated screws and washers placed in convergent trajectories.?For knees assigned to suture fixation, two No. 2 FiberWire suture were passed through the fracture fragment and the base of the ACL, one through the anterior 1/3, the other through the posterior 1/3. The fracture was reduced, and the sutures were secured over a 1cm bony bridge. Specimens were then mounted for biomechanical testing at approximately thirty degrees of flexion to simulate typical ACL loading conditions. A cyclic loading protocol consisting of 500 cycles between 5 and 75N at a crosshead speed of 100mm per minute, sampled at 20Hz, was applied to each specimen. Then, a load to failure protocol was conducted at a rate of 0.5mm per second. A priori power analyses determined that eight total samples would need to be tested to achieve a power of 0.8. The primary outcome was ultimate failure load in newtons (N). An independent t-test compared biomechanical properties between two-screw and two-suture fixation in this study. One-sample t-tests were used to assess differences between ultimate failure loads recorded in this study and those described by previous studies in cadaveric and porcine bone.
Results
A total of twelve age (Range: 5 years – 10 years) and laterality-matched pediatric cadaveric knees were tested (Expected Power: 0.94). The repair groups had identical mean (8.3 years) and median (8.5 years) ages and an identical number of samples of each laterality. Ultimate failure load did not significantly differ between screw (Mean: 143.52N, SD: 41.97N) and suture (Mean: 135.35N, SD: 47.94N) fixations (p = 0.7597). One screw construct and one suture fixation construct did not survive the cyclic loading protocol. Suture and screw fixations in pediatric bone displayed failure loads that were statistically lower than those reported in nearly every previous porcine and cadaveric study at the p <0.001 and p <0.05 levels, respectively.
Conclusions
Screw and suture fixation of tibial spine fractures in pediatric bone are biomechanically comparable, in stark contrast with previous literature. This study is the first to evaluate different fixation methods in pediatric bone and demonstrates that failure loads are statistically and practically lower than adult cadaveric and porcine bone, such that inferences drawn from previous studies may be misleading. Further investigation should be conducted into repair constructs that are more biomechanically sound in pediatric bone.