Biomechanical Evaluation of a Novel Suture Augment in Patella Fixation
Patella fractures, although uncommon in the context of corresponding long bone fractures, carry a disproportionately high degree of morbidity, and are often challenging to treat. As such, this study sought to evaluate the efficacy of a Krackow suture augment when compared to standard tension band fixation and cerclage suture augment in patella fracture repair. Cadaveric patella extensor mechanisms were used for biomechanical testing. Specimens were divided among 3 groups, each with a different repair technique: modified anterior tension band (MATB), MATB plus cerclage suture, and MATB plus Krackow suture. Specimens were biomechanically tested in both cyclic and maximum load settings. Mean displacement and load-to-failure forces were measured for cyclic and maximum load testing, respectively. Data was then analyzed with both one-way analysis of variance and independent t-testing. Both augmentation techniques showed improved strength in both cyclic and maximum load testing, with the Krackow suture augment showing the greatest strength. In cyclic testing, cerclage augment showed a 30% decrease in mean displacement while Krackow suture augment showed a 40% decrease when compared to the MATB repair group. Likewise, in maximum load testing, cerclage repair showed a 5% increase and Krackow a 14% increase in load-to-failure force when compared to MATB. Likely due to small sample size, the increases in repair strength did not reach statistical significance. This study provides support for the use of a Krackow suture augment in patella fracture repair, and we suggest this technique may be most useful in the setting of poor bone quality where conventional repair techniques are limited. Although failing to reach statistical significance, these results are encouraging and warrant further investigation in both biomechanical and clinical settings.
Further investigation into patella repairs has mainly focused on improving the MATB technique and experimenting with different tension band materials. Rabalais and colleagues13 biomechanically tested high-strength polyethylene suture as a replacement for standard 18-gauge wire, and Bryant and colleagues14 tested a braided composite suture (FiberWire; Arthrex) as a replacement for standard 18-gauge stainless steel wire. Both found no significant difference with use of augmented tension band material, but Rabalais and colleagues13 did find more advantages with a parallel tension band construct than with a standard figure-of-8 arrangement.
In developing our novel technique, we considered that Krackow sutures are routinely used in both quadriceps tendon repair and patellar tendon repair, including partial patellectomy for distal patella fracture. With a suture placed in both tendons, the augment could be expected to resist longitudinal gapping and augment the tension band across the anterior patella. First described by Krackow and colleagues,19 the Krackow suture is widely used for tendon reconstruction. In an interlocking system of sutures, the Krackow suture provides a repair that is more stable than repair with conventional suture techniques, specifically in the context of tendon repair.20 Given the sesamoidal nature of the patella, its repair shares the goal of gap prevention with other tendon repairs. In theory, anchoring the supporting structures that are above and below the patella provides support for the intervening patella and ultimately improves fracture fixation strength.
Oh and colleagues15 reported on the clinical efficacy of a Krackow augment in distal pole patella repairs. Similarly, we found a Krackow augment to be efficacious, supporting its potential in clinical approaches to patella repairs. Our results indicate this augment can be a useful clinical adjunct in biomechanical evaluation.
Limitations of this study include its use of dissected extensor mechanisms, which may have less biofidelity than whole-knee specimens. In our model, specimens were secured at the patellar tendon and the quadriceps tendons, as opposed to the quadriceps tendon and the tibia distally. Use of this model could have led to an increase in early displacement during cyclic testing as a result of tissue slippage. Furthermore, our small sample size could have affected our ability to demonstrate a difference between these techniques.
Given its increased strength as demonstrated by mean displacement during cyclic loading and mean load to failure, as well as the early clinical data recently published, the Krackow suture augment represents a feasible technique for patella fixation. It likely will be most useful in cases in which conventional techniques are prone to failure or cannot be applied, such as severe distal comminution or poor bone density. Further biomechanical testing with a larger number of specimens may be required for statistical significance.
Conclusion
In patella fracture repair strategies, the Krackow suture augment increased strength when used with a MATB technique. Failure to reach statistical significance likely resulted from our small sample size. Further biomechanical testing and clinical studies are needed for more complete evaluation of this technique. We think it will be most useful in the setting of poor bone quality or severe comminution, which can limit fixation options. As increased repair strength allows earlier postoperative rehabilitation and maintains fracture reduction, patient outcomes should improve. This novel technique represents another strategy for managing challenging patella fractures.
