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.
Take-Home Points
- Suture augmentation improves construct strength for patella fixation.
- Krackow sutures may be placed in the quadriceps and patella tendons, then secured over the anterior patella (much like an anterior tension band).
- The Krackow technique described was superior to the suture cerclage technique based on mean load values, but did not reach statistical significance.
- The Krackow suture technique is a viable and easily applied technique for suture augmentation of patella fixation constructs.
Patella fractures are relatively uncommon, accounting for only 1% of skeletal injuries.1 Restoration of the function of the patella and the extensor mechanism is vital for knee extension and gait. However, patella fractures have an inherently high rate of complications, making these injuries challenging to treat.2-4 In patients with intact extensor function, displacement of <4 mm, and articular step-off of <3 mm, nonoperative management is extremely effective, with 99% of patients reporting favorable results.5 However, for fractures in which the extensor mechanism is disrupted, surgical intervention typically is indicated.6
Authors have reported various surgical interventions, one of the most commonly used being the anterior tension band (ATB) technique, first described by the AO (Arbeitsgemeinschaft für Osteosynthesefragen) group in the 1950s.7 By converting distractive anterior force during knee flexion to compressive force at the fracture site, the ATB technique provides a repair stronger than the previously used cerclage repair.8 Although initially considered standard of care, the ATB technique was soon found to be associated with implant failure and subcutaneous irritation prompting implant removal.9
To address these issues, Berg10 and Carpenter and colleagues11 evaluated an ATB technique that used cannulated screws instead of Kirschner wires (K-wires). This variation on the ATB technique reduced the implant-related issues while maintaining the mechanical advantage of the tension band. The more rigid design also permitted earlier postoperative rehabilitation, which significantly reduced development of arthrofibrosis.6,7,10 This modified ATB (MATB) technique has since been investigated for additional augments, mainly focusing on use of different tension band materials, including polyester suture and braided composite suture.12-14
However, there is little research on augments that incorporate the surrounding soft tissue, specifically the quadriceps and patellar tendons. In a recent retrospective clinical study, Oh and colleagues15 found positive clinical results with use of Krackow sutures, though 2 or 3 vertically oriented stainless steel wires were used instead of cannulated screws.
We conducted a study to determine the biomechanical efficacy of using a cerclage suture augment and a Krackow suture augment coupled with and compared with conventional MATB repair. If effective, this technique may represent another strategy for increasing repair strength and thereby improve postoperative outcomes.
