To develop a novel double-flap plate internal fixation system for arthroscopic treatment of tibial spine avulsion fractures (TSAFs), and to demonstrate its feasibility and practicability.

CT data of 50 TSAFs patients (those with knee fractures and abnormal bone metabolism diseases, etc. were exluded) in Songshan Lake Hospital were gathered to explore the size and anatomical distribution of fracture blocks. The bone space around the intercondylar fossa and anterior fork ligament insertion in eight fresh adult knee specimens was measured to determine the size and characteristics of the anterior insertion space. Sixty knee specimens of swines were selected and made into TSAFs model. Simple random sampling method was used to divide the samples into four groups, 15 samples in each group. The samples were treated with different internal fixation methods: single-strand wire loop fixation (the wire loop fixation group), hollow nail fixation (the hollow nail group), and finger steel plate fixation with non-absorbent Fiber Wire( the finger steel plate wire group). The experimental group were fixed with double plate (the double plate group). The biomechanical experiment of tensile force was conducted and comparative analysis was conducted by variance test among the groups, and SNK-q test was utilized for paired comparison. Arthroscopic surgery was conducted using double-flap plate internal fixation system on eight TSAFs patients aged from 17 to 45 years; osteogenic diseases were excluded. Lysholm knee function score and International Knee Documentation Committee (IKDC) 2000 subjective knee function score were used to evaluate effects before and after surgery, and t test was conducted for data comparisons.

The distribution area of TSAFs fracture fragments was characterized as O point (the " O" point was the intersection point between the free margin of the lateral meniscus anterior angle and the mid line of the anterior cruciate ligament insertion). The size of the anterior part of the bone fragments was about (10±5) mm× (15±4) mm, and the inner and lateral parts were six millimeters apart, which could accommodate a thin slice of internal fixation with a thickness of less than two millimeters, which would not impact the articular cartilaginous surface under multiple angle movements. Considering the biomechanical determination of swine knee joints, the differences in the first-order tensile force and maximum tensile force among the groups were statistically significant (F=38.091, 15.885, both P<0.001); the first-order tensile force and maximum tensile force of the double-flap steel plate group were (105±6) N and (346±21) N respectively, which were superior to those of the other three groups (all P<0.05), providing biomechanical evidence for clinical application. The fracture healing time of eight TSAFs patients was (3.5±0.8) months, and Lysholm knee functional score was increased from (43±7) before surgery to (89±6) three months after surgery, with statistically significant differences (t=-14.87, P<0.05). IKDC 2000 subjective score increased from preoperative (55±6) to (92±5) three months after surgery, and the difference was statistically significant (t=-13.54, P<0.05). The internal fixations were removed in five cases of bone union by arthroscope, and no articular cartilage abrasion was observed.

The double-flap plate internal fixation system utilizes the characteristics of the osseous space of the tibial intercondylar fossa, and can directly fix the TSAFs fracture block with intraventricular plate under arthroscope. It simplifies the intramuscular operation steps, and provides the advantages of simple operation, reliable fixation and exact efficacy. It does not increase the damage to articular cartilage, and is worthy of further study and promotion.