Suspension button constructs restore posterior knee laxity in solid tibial avulsion of the posterior cruciate ligament

Abstract

Purpose: Dislocated tibial avulsions of the posterior cruciate ligament (PCL) require surgical intervention. Several arthroscopic strategies are options to fix the fragment and restore posterior laxity, including two types of suspension button devices: adjustable (self-locking) and rigid knotted systems. Our hypothesis was that a rigid knotted button construct has superior biomechanical properties regarding laxity restoration compared with an adjustable system. Both techniques were compared with standard screw fixation and the native PCL.

Methods: Sixty porcine knees were dissected. The constructs were tested for elongation, stiffness, yield force, load to failure force, and failure mode in a material testing machine. Group N (native, intact PCL) was used as a control group. In group DB (Dogbone™), TR (Tightrope™), and S (screw), a standardized block osteotomy with the osteotomized fragment attached to the PCL was set. The DB and TR groups simulated using a suspension button system with either a rigid knotted (DB) or adjustable system (TR). These groups were compared to a screw technique (S) simulating antegrade screw fixation from posterior.

Results: Comparing the different techniques (DB, TR, S), no significant elongation was detected; all techniques achieved a sufficient posterior laxity restoration. Significant elongation in the DB and TR group was detected compared with the native PCL (N). In contrast, screw fixation did not lead to significant elongation. The stiffness, yield load, and load to failure force did not differ significantly between the techniques. None of the techniques reached the same level of yield load and load to failure force as the intact state.

Conclusion: Arthroscopic suspension button techniques sufficiently restore the posterior laxity and gain a comparable construct strength as an open antegrade screw fixation.

Keywords: PCL; Posterior knee laxity; Suspension button; Tibial avulsion.

Fig. 1

a Preparing the PCL attachment model in the porcine knee; (b) Standardized osteotomy of the tibial PCL attachment; (c) The osteotomized solid fragment is attached to the PCL fibers. PCL posterior cruciate ligament

Fig. 2

Illustration of the posterior cruciate ligament guiding device used intraoperatively to position the 2.4-mm bone tunnel. Then, either the Fiber tape™ or the Tightrope™ system can be inserted via the 2.4-mm drill hole

Fig. 3

Illustration of the three fixation techniques used in this study. a The dogbone technique uses two Dogbone™ devices. The Fiber Tape™ is knotted against the anterior button. b The tightrope technique uses two Tightrope™ devices. The self-locking Tightrope™ mechanism acts like a Chinese finger trap by pulling the free sutures. c The screw technique uses a solid 4-mm partially-threaded screw from a posterior approach

Fig. 4

Boxplot Diagram: Elongation (mm). The TR, DB and S groups did not differ significantly. The elongation behavior of the Screw fixation was not significantly increased compared with the intact state. Compared with the native posterior cruciate ligament, the TR and DB groups showed an elongation. TR Tightrope^™; DB Dogbone^™ ;S screw

Fig. 5

Boxplot Diagram: Final stiffness (N/mm²). Compared with the native group, the DB group showed no significant reduction of stiffness; the screw and TR groups showed a decrease. DB Dogbone™

Fig. 6

Boxplot Diagram: Yield force (N). The yield force was obviously lower in all groups compared with the native posterior cruciate ligament. The yield force was significantly lower only in the DB group. DB Dogbone™

Fig. 7

Boxplot Diagram: Maximum Force (N). None of the groups (S, TR, DB) reached the maximum force of the native PCL. No significant difference between the reconstruction groups was detected. S screw; TR Tightrope™; DB Dogbone™