Tibial Eminence Avulsion Fracture Reduction With a Novel Adjustable-Loop Suture Repair Device: A Biomechanical Analysis

Abstract

Background:

The use of adjustable-loop devices (ALDs) has become increasingly common due to the ability to intraoperatively precondition a repair and retension the construct to provide additional stabilization. While ALDs have been supported for anterior cruciate ligament (ACL) repair and reconstruction, a biomechanical rationale for the addition of ALDs for the reduction of tibial eminence avulsion fracture is limited.

Purpose:

To biomechanically compare standard suture fixation to suture fixation with an ALD for the reduction of tibial eminence avulsion fractures.

Study Design:

Controlled laboratory study.

Methods:

Twenty porcine stifles were dissected of soft tissue, sparing the ACL. Type 3 tibial eminence avulsion fractures were created and reduced with suspensory suture fixation through 1 tunnel using either a standard suture technique (n = 10) or suture fixation with the addition of an ALD (n = 10). Repaired specimens underwent 10 preconditioning cycles to simulate intraoperative knee cycling, manual retensioning (ALD repairs only), cyclic loading between 10 and 50 N, 10 and 100 N, and 10 and 150 N for 100 cycles each, and then pull to failure. Cyclic elongation, cyclic stiffness, and ultimate load outcomes were statistically compared (P < .05).

Results:

Total displacement after the cyclic loading protocol showed significantly less total elongation (P < .001) for the ALD group (mean, 0.76 mm; 95% CI, 0.60-0.94 mm) compared with the control group (mean, 5.50 mm; 95% CI, 4.59-6.41 mm). All constructs survived cyclic loading. Significantly higher ultimate loads (P = .023) were achieved by the ALD repairs (mean, 532 N; 95% CI, 461-604 N) compared with the standard repair (mean, 410 N; 95% CI, 327-495 N). There were no statistical differences in cyclic stiffness between repair groups for each load block.

Conclusion:

The addition of an ALD to suture fixation for tibial eminence avulsion fractures significantly reduced the total cyclic elongation by 86% and increased the ultimate load by 30% when compared with a standard suture fixation. The results suggest better time-zero biomechanics as compared with standard suture fixation.

Clinical Relevance:

Incorporation of ALD fixation into a standard suture repair may help stabilize fragment reduction, minimizing loss of reduction and potentially improving the bone healing response in tibial eminence fracture repair by minimizing micromotion. Future clinical studies are warranted to complement these biomechanical findings.

Keywords

anterior cruciate ligament adjustable-loop device tibial eminence fracture biomechanics

With an incidence of 3 in every 100,000 children within the pediatric population, tibial eminence avulsion fractures primarily occur in skeletally immature individuals due to a relatively weaker epiphysis compared with the anterior cruciate ligament (ACL).¹¹ Tibial eminence avulsion fractures present similar insufficiencies and origin to ACL tears. Long-term consequences such as pain, residual laxity from nonunion of the bone, instability induced by dysfunction of the ACL, and limited knee extension due to impingement of the bone fracture can occur if left untreated.¹⁷

Tibial eminence avulsion fractures can be classified by the fracture pattern. Based on the Meyers and McKeever classification, a type 1 fracture is described as a nondisplaced fracture, a type 2 fracture as a partially displaced fracture, a type 3 fracture as a completely displaced fracture, and a type 4 fracture as a comminuted fracture.²⁵ There is some debate about whether type 1 or 2 fractures require surgical intervention and may be determined by the identification of concomitant injuries.^29,33 However, surgical intervention is typically indicated for all type 3 and 4 fractures.^14,18

Currently, there is no gold standard for the fixation of tibial eminence avulsion fractures. Both screw and suture constructs can provide adequate reduction of the avulsed fragment.^16,22 Specifically in the pediatric population, sutures have been found to be biomechanically comparable to screw fixation.¹⁹ However, suture fixation has become increasingly common due to higher revision rates and hardware removal associated with screws.¹⁶ Other disadvantages of screw fixation include further fracture comminution during insertion and the possibility of crossing the physis with hardware.^15,30 A recent meta-analysis comparing clinical outcomes of screw versus suture fixation found that screw fixation resulted in a significantly greater rate of hardware removal (44%), whether it was planned or unplanned, compared with suture fixation (3%). However, no differences in functional outcomes or knee stability were found between the 2 techniques.⁶ Because of these concerns with screw fixation, suture fixation is commonly utilized and is especially favorable in more comminuted fracture cases in which screw fixation is not feasible.

Adjustable-loop devices (ALDs) are commonly used for the repair and reconstruction of the ACL due to the option of intraoperatively preconditioning the repair and retensioning the construct, which can provide additional stabilization.² Although there is abundant research supporting the use of ALDs for ACL repair and reconstruction,^2,21,28 ALDs can likely be expanded into other applications, including the fixation of tibial eminence avulsion fractures. The addition of ALDs for the fixation of tibial eminence avulsion fractures is a novel technique variation that may create higher initial compressive forces and alleviate initial creep via retensioning, as shown in previous biomechanical studies.^2,13,27

To date, several clinical studies and technical reports have described the success of ALD fixation of tibial eminence fractures; however, a biomechanical validation is not available.^20,34,36 The purpose of this study was to biomechanically compare standard suture fixation to suture fixation with an ALD for the fixation of tibial eminence avulsion fractures. It was hypothesized that the ALD fixation would have less cyclic elongation and a higher ultimate load than the standard suture fixation and therefore maintain better reduction of the avulsed fragment.

Methods

Twenty fresh-frozen porcine knees, 4 months of age (J&J Packing Company), were dissected of all soft tissue, with the exception of the ACL. Porcine specimens were used due to the incidence of these fractures occurring most prominently in the pediatric population (and the extremely limited availability of pediatric tissue) and the highly variable properties of human cadaveric specimens.⁷ The proximal femur and the distal tibia were transversely cut 4 inches from the joint line and potted in fiberglass resin (Bondo; 3M) to be mounted into a custom testing fixture. Specimens were then refrozen at −20°C until the time of testing and were stored at 4°C during the testing period. Specimens were randomly chosen to receive 1 of 2 repair techniques to reduce the avulsed fragment: a standard suture repair or a suture repair with the addition of an ALD. For both repair groups, a 2.4-mm tunnel was prepared through the anterior third of the tibial ACL footprint and exited along the medial tibial metaphysis.

A type 3 tibial eminence avulsion fracture was replicated by angling a small osteotome along the tibial ACL footprint, creating a triangular prism with dimensions 3 × 2 × 1 mm. A type 3 fracture was chosen for greater reproducibility and due to controversy about whether type 1 or 2 fractures need to be treated surgically.^14,18 If necessary, any microavulsed fragments were removed from the fracture cavity to ensure proper reduction of the avulsed fragment.

Specimens were loaded with the femur secured to a 10-kN load cell of an Instron testing machine (ElectroPuls E10000; Instron) using a custom fixture that allows for aligning the specimen in the transverse, sagittal, and coronal planes. The tibia was secured to the base of the machine and angled so that the repair tunnel was parallel to the load axis. The femur was adjusted so that the ACL fibers were parallel to the direction of the load (Figure 1).^3,14 Once orientations were established, all fixtures were locked in position for the duration of testing.

Figure 1.

Biomechanical test setup where F indicates the force vector. (A) Anteromedial view of custom multidegree freedom fixture and angled vise with repair tunnel parallel to the load direction. (B) Posterior view showing the anterior cruciate ligament fibers parallel to the load direction.

Fixation Techniques

The standard suture fixation, used as the control group, consisted of 2 No. 2 sutures with a closed loop on one end (FiberLink; Arthrex Inc), with one suture passed medially and the other passed laterally through the distal ACL. The sutures were passed approximately 10 mm proximal to the fracture surface, in a luggage tag fashion.³⁶ The avulsion fracture was reduced, and the sutures were then shuttled through the tibial tunnel (Figure 2). Sutures were manually tensioned to the maximum achievable load and tied over an 11-mm metal cortical button (TightRope ABS Button; Arthrex) using 5 alternating half-hitches.

Figure 2.

Luggage tag suture fixation for type 3 tibial eminence avulsion fractures.

ALD fixation was accomplished by passing two 25-mm No. 2 suture loops (FiberRing; Arthrex) through the ACL, in the same manner as the standard suture fixation. The fracture was reduced, and sutures were converted through the ALD (TightRope II ABS; Arthrex). The ALD was shuttled through the previously drilled tunnel and manually tensioned to 50 N. The ALD was retensioned after position-controlled cycling and secured over an 11-mm metal cortical button (Arthrex) using 5 alternating half-hitches. Five alternating half-hitches were included in the repair, although not required, to eliminate the variable of knot-tying between the 2 fixation groups.

Biomechanical Testing

To evaluate the native biomechanical properties and remove initial creep in the ligament, the native ACL was manually preloaded to 5 N and then was cyclically loaded between 10 and 50 N, 10 and 100 N, and 10 and 150 N for 100 cycles each at 1 Hz. After native testing, a type 3 tibial eminence avulsion fracture was created and reduced while the specimen remained on the testing machine. Specimens then underwent position-controlled cycling from 0 to 3 mm at 0.5 Hz for 10 cycles to simulate intraoperative preconditioning. ALD repairs were retensioned to the maximum achievable load after position-controlled cycling; this was completed within a 1-minute window. Repair states underwent the same load-controlled protocol as the native state, followed by a pull-to-failure rate of 200 mm/min (Figure 3).

Figure 3.

The loading protocol included simulated intraoperative preconditioning via position-controlled cycling and rehabilitation forces via load-controlled cycling. ALD, adjustable-loop device.

All data were recorded with a data acquisition rate of 100 Hz (WaveMatrix 2; Instron). Load-displacement data were used to calculate cyclic elongation (mm), cyclic stiffness (N/mm), and ultimate load (N). After preconditioning, displacement was initially zeroed (point A) and was used to calculate cyclic elongation for each of the load blocks (points A-D, A-G, and A-J in Figure 3). Cyclic stiffness was calculated from the slope of the last cycle for each load block (points B-C, E-F, and H-I in Figure 3). The ultimate load was defined as the maximum load during the pull-to-failure step.The mode of failure was recorded for all samples.

Statistical Analysis

Statistical analysis was performed using Sigma Plot Version 14.0 (Systat Software Inc). A 1-way repeated-measures analysis of variance with a post hoc Bonferroni multiple comparisons procedure was used to determine significant differences in cyclic elongation and cyclic stiffness between the repair groups. A Shapiro-Wilk test was used to confirm normality of the data, and post hoc power analysis was performed to confirm a power level ≥0.8. A Student t test was used to evaluate significant differences in ultimate load between the repair groups. Significance was determined by a P value <.05 for all statistical analyses.

Results

Cyclic elongation was measured on the completion of testing and was calculated after each load block. Cyclic elongation after the first load block was found to have a mean of 0.004 mm (95% CI, –0.06 to 0.06 mm) for the ALD group and 1.61 mm (95% CI, 1.15 to 2.06 mm) for the standard fixation group.The mean cyclic elongation after the second load block was found to be 0.318 mm (95% CI, 0.2 to 0.43 mm) for the ALD group and 3.54 mm (95% CI, 2.81 to 4.26 mm) for the standard suture fixation group.Total cyclic elongation after 300 cycles of load-controlled cycling showed less total elongation for the ALD group (mean, 0.76 mm; 95% CI, 0.60 to 0.94 mm) compared with the control group (mean, 5.50 mm; 95% CI, 4.59 to 6.41 mm). Significant differences were found between the ALD group and the standard fixation group after each load block (P < .001) (Figure 4).

Figure 4.

Total cyclic elongation after each cyclic load block. Shaded regions are indicative of the probability distribution. Adjustable-loop device (ALD) fixation had significantly less cyclic elongation than the control fixation group at each load level.

Cyclic stiffness was calculated for each of the fixation groups during the last cycle of each load block. For the first load block, the mean stiffness was determined to be 64.5 N/mm (95% CI, 54.4-74.6 N/mm) for ALD fixation and 64.4 N/mm (95% CI, 56.1-72.7 N/mm) for standard fixation. The mean cyclic stiffness for the second load block was 74.7 N/mm (95% CI, 65.9-83.5 N/mm) for ALD fixation and 74.5 N/mm (95% CI, 65.6-83.4 N/mm) for standard fixation. The third load block had mean cyclic stiffness values of 86.38 N/mm (95% CI, 75.9-96.8 N/mm) and 84.3 N/mm (95% CI, 74.7-94.0 N/mm) for ALD and standard fixation, respectively. There were no statistical differences in cyclic stiffness between fixation groups (Figure 5).

Figure 5.

Cyclic stiffness of adjustable-loop device (ALD) group versus control group.There were no significant differences found between fixation groups. Shaded regions indicate the probability distribution.

All constructs survived cyclic loading and were subsequently pulled to failure. Significantly higher mean ultimate loads (P = .023) were achieved by the ALD fixation (532 N; 95% CI, 461-604 N) as compared with the standard fixation (410 N; 95% CI, 327-495 N) (Figure 6). Failure modes for the standard fixation included suture tear through the ACL (7/10), suture tear at the button interface (2/10), and button migration through the bone (1/10). Failure modes for the ALD fixation included suture tear through the ACL (4/10), button migration through the bone (3/10), and suture tear at the ALD interface (3/10).

Figure 6.

Ultimate load of fixation groups. Adjustable-loop device (ALD) fixation had significantly higher ultimate loads compared with the control group.Shaded regions indicate the probability distribution.

Discussion

In this biomechanical study, the most important finding was that the addition of ALDs significantly reduces cyclic elongation and contributes to withstanding higher ultimate loads, thus supporting the initial hypothesis. Additionally, ALDs were shown to have a more concentrated distribution of results compared with the standard fixation, which may indicate that ALDs may offer a higher degree of consistency. The addition of an ALD did not alter cyclic stiffness compared with the standard suture fixation. Failure modes suggest, in both fixation states, that the fixation was stronger than the surrounding tissue, represented by 70% of failures being a suture tear through the ACL or button migration through the bone.

ALDs have been increasingly utilized for ACL reconstruction and repair due to the removal of creep via retensioning and additional compressive stability.² The addition of ALDs to standard suture fixation for the reduction of tibial eminence avulsion fractures, while technically more complex than standard suture fixation, would provide not only similar advantages but also greater reduction and compression of the avulsed fragment due to the retensioning system that allows for the removal of creep.³⁶ Increased compressive forces can aid in fracture healing as compression is important for primary bone healing by stimulating osteoclast and osteoblast activities.¹² While the addition of ALDs for tibial eminence fractures is a rather novel concept, a few techniques have been described. Williams etal³⁶ described their technique using 2 No. 2 FiberRing sutures as luggage tags through the ACL. These devices are loaded into an adjustable ACL Repair TightRope, which is then intraoperatively cycled and retensioned. Kelly etal²⁰ similarly described a retensionable method using 2 SutureTapes tied over a button, but with a Tuckahoe sliding knot that is retensioned after cycling. This technique, however, relies on the quality of hand-tied knots to maintain reduction. One additional study by Faivre etal¹⁰ described a similarly retensionable technique utilizing an ALD, with clinical results reported in 8 patients. In their technique, a TightRope is deployed such that the button sits intra-articularly, with an additional ABS Button over the tibial cortex. All fractures healed, with no significant difference in anterior knee laxity as compared with the contralateral knee (P = .73) and a mean International Knee Documentation Committee score of 70.71 ± 17.56 at a mean follow-up of 10 months. ALDs were incorporated into the current study design due to limited biomechanical data on the addition of ALDs for the reduction of tibial eminence avulsion fractures.

Cyclic loading is intended to represent physiological loading, such as ambulation, which has been estimated to produce peak forces of around 150 to 300 N.^26,32 However, a tibial eminence repair is likely to be subjected to even lower forces during early rehabilitation, as most patients are braced postoperatively and full weightbearing is delayed in many.³⁷ Previous biomechanical studies have included loading forces between 75 N and 250 N to replicate forces seen during early rehabilitation.^{1,8,14,19,23,24,30,35} The cyclic loading peaks of the current study were chosen based on the estimated peak forces that could be seen during early rehabilitation and previous biomechanical studies. Many of the previous biomechanical studies, such as a study presented by Sawyer etal,³⁰ used cyclic loading protocols to compare variations of suture techniques with screw techniques for reducing tibial eminence avulsion fractures.^{1,8,9,14,23,30} For the suture fixation, the authors found a mean elongation of 6.31 ± 3.7 mm after 200 cycles and peak loads of 150 N. Another study by Li etal²³ looked at 2 suture fixation variations with peak loads of 100 N and found a mean elongation of 4.08 ± 0.28 mm for the suture fixation shuttled through the fracture fragment and 3.86 ± 0.19 mm for the other suture fixation with neckwear knots. While direct comparisons across studies are still limited by differences in biomechanical models, fixation techniques, and loading protocols, mean elongation ranges between 1.3 ± 0.8 mm and 8.5 ± 4.0 mm across various fixed suture repair techniques^{1,2,8,14,19,23,24,30,35} and is consistent with the suture fixation of the current study. These studies did not analyze ALDs, which the current study shows to produce elongation values among the lowest in the literature.

Load-to-failure protocols simulate traumatic events that may occur before bone healing. In the current study, the ALD fixation sustained a mean force of 532 ± 100 N before succumbing to failure. This was statistically significantly more than that sustained by the standard fixed suture repair (mean, 410 ± 118 N; P = .023). The majority of fixed suture repairs in the literature failed below 500 N of force,^{1,4,5,14,19,23,24,30,31} with the exceptions being a single No. 5 FiberWire construct failing at a mean of 582 ± 67 N in juvenile porcine knees in a study by Eggers etal⁸ and a construct of 2 No. 2 FiberWires failing at a mean of 1319 N (95% CI, 1032-1686 N) in mature porcine knees in a study by Thome etal.³⁵ A study by Ezechieli etal⁹ compared both a suture and another variation of an ALD construct.⁹ The mean ultimate failure load was found to be 367 ± 116 N for the suture construct and 402 ± 118 N for the ALD group.

Limitations

There are several limitations present in this study. One limitation of this study is that fixation techniques were tested in a porcine model, which may not account for morphological differences between porcine and human ACLs; however, porcine specimens have been shown to be a viable alternative to human cadaveric specimens in biomechanical studies.^7,38 Also, because of the overall size of the porcine stifles, fixation with double tunnels could not effectively be performed, and therefore only single-tunnel fixation was evaluated. While only single tunnels were evaluated, studies have shown that double-tunnel fixation is also a viable option to reduce tibial eminence avulsion fractures.^20,23 Additionally, this was a time-zero analysis, which did not permit in vivo healing and, as a result, simulated a worst-case scenario. Additional clinical studies with ALDs can provide further functional and stability outcomes after allowing for in vivo healing.

Conclusion

Footnotes

Acknowledgements

The authors acknowledge Justin Boyle and Tim McIntyre for assisting in the creation and support of the work and Anthony Khoury for assistance with manuscript preparation.

Final revision submitted January 30, 2025; accepted March 17, 2025.

One or more of the authors has declared the following potential conflict of interest or source of funding: This work was supported by Arthrex (grant No. AIRR-0171). B.J.G., C.A.W., and O.L.H. are paid employees of Arthrex. E.C.B. had received grants from Arthrex and Smith & Nephew. J.C.R. has received consulting fees from Arthrex and Smith & Nephew. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

Ethical approval was not sought for the present study.

ORCID iD

Elise C. Bixby

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