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. Author manuscript; available in PMC: 2026 Mar 10.
Published in final edited form as: J Biomech Eng. 2026 Mar 1;148(3):031003. doi: 10.1115/1.4070647

Age-Related Increases in Graft Tendon Size and Stiffness During Skeletal Growth Enhance ACL Graft Function and Joint Stability in an Early Adolescent Porcine Model

Yukun Zhang 1,2,Ψ, Kaan Gurbuz 3,4,Ψ, Joshua Chavez-Arellano 5, Logan Opperman 6, Jeffrey T Spang 7, Matthew B Fisher 8,9,10,11,*
PMCID: PMC12849221  NIHMSID: NIHMS2148998  PMID: 41385220

Abstract

Anterior cruciate ligament (ACL) reconstruction in pediatric patients has a higher graft failure rate compared to adults. Restoring joint stability and reducing graft failure is essential. However, how graft biomechanical properties change with age and affect reconstruction outcomes remains unclear. This study investigated the biomechanical development of porcine flexor tendons across skeletal growth and evaluated how graft size and stiffness influence knee biomechanics in a pediatric porcine model. Flexor tendons (n = 57) were harvested from pigs at 0.5, 1.5, 5, and 9 months of age to measure cross-sectional area (CSA), stiffness, and failure load. ACLs in nine early adolescent porcine knees were reconstructed using both 1.5- and 5-month-old (1.5mo and 5mo) grafts and tested under anterior-posterior, compressive, and varus-valgus loading at 40° flexion using a robotic system. ACL and graft forces were calculated using the principle of superposition, and in situ properties were derived from force-displacement curves. Tendon CSA, stiffness, and failure load increased with age, and stiffness associated with CSA. The CSA of 5mo tendons was 57% greater than that of 1.5mo tendons, but stiffness increased only 20%. ACL reconstruction with 5mo grafts resulted in 29% less anterior-posterior tibial translation and 44% higher graft force compared to 1.5mo grafts. In situ stiffness of 5mo grafts was 51% higher than 1.5mo grafts. These findings highlight the differences between tendon size and biomechanical development, which together contribute to the improvements in joint function following ACL reconstruction.

1. INTRODUCTION

The incidence of pediatric anterior cruciate ligament (ACL) injuries has been increasing rapidly due in part to greater participation in youth sports [1,2]. Surgical reconstruction is the preferred treatment for ACL injuries, as it restores knee function and stability while also preventing further injuries such as meniscus tears and chondral injury [3,4]. However, data indicate that pediatric patients have a higher rate of ACL graft failure compared to adults, likely due to their return to higher levels of activity and challenges in adhering to activity restrictions [5,6]. As such, there is a need to improve the understanding of variables associated with the high ACLR failure rate in this patient population [1,7]. One of the variables is graft selection, including the biomechanical properties of the graft used for reconstruction.

Previous studies have examined various factors that could impact the biomechanical properties of adult graft tissues for ACL reconstruction (ACLR), given that the graft must be capable of withstanding the forces taken by the native ACL [8]. Graft age is an essential factor that affects the tensile properties in adults. An age-related decrease in stiffness (reduced by 26%) and failure load (reduced by 70%) of the cadaveric ACL was observed from the younger group (22–35 years old) to the older group (60–97 years old) [9]. Similarly, patellar tendon grafts from donors aged 29–50 years old showed significantly greater ultimate tensile strength than those from donors aged 64–93 years old [10]. Age-related effects of graft tensile properties during skeletal growth are not known.

Graft size is another factor that affects the failure rate [3]. Previous clinical data in adults showed that hamstring grafts with a diameter smaller than 8 mm had higher failure rates (2.71%) compared to grafts larger than 8 mm (1.87%) [11,12]. Pediatric data also demonstrated a lower failure rate with larger grafts [13], and the best practice is to match the graft size to the native ACL for pediatric patients. However, excessively large grafts are typically avoided to prevent the need for large-diameter tunnels in growing bones and to reduce the risk of postoperative complications such as cyclops lesions [14,15]. Additionally, placing a large graft on a small native footprint may further increase the risk of impingement [16,17]. Despite its importance, there is limited data on how graft size affects joint biomechanics within pediatric models due to the limited availability of human pediatric specimens.

Stiffness of the ACL graft can also affect joint biomechanics of the reconstructed knee [18–20]. Previous adult data demonstrated that most ACL grafts were biomechanically superior to the native ACL, which would protect against graft failure. However, a graft more stiff than the ACL may overconstrain knee motion [21]. To better assess ACL graft for skeletally immature patients, it is essential to match the biomechanical properties of the graft to the native ACL to maintain the initial joint stability following ACLR. However, the optimal graft stiffness for pediatric patients is still unknown, which could be either the current properties of the native ACL or the anticipated properties after skeletal maturity. In clinical practice, surgeons may need to choose between grafts of varying size or stiffness depending on the patient’s age, anatomy, and tissue availability, especially in pediatric cases where some autograft options may be underdeveloped [3,22]. It is therefore important to consider how supra-physiological graft stiffness may impact initial joint stability within the pediatric joint.

The porcine model has been extensively utilized in ACL studies due to its anatomical and biomechanical similarities to the human knee and the availability of skeletally immature specimens [23,24]. Previous studies have shown that deep digital flexor tendon from 6 months old pigs exhibited comparable stiffness (211 N/mm) and failure load (1795 N) to human semitendinosus tendons (range 61–83 years, 208 N/mm, 1406 N) [25], making it an appropriate option for in vitro studies on ligament and tendon reconstruction techniques. The porcine flexor tendon has been used as graft to evaluate variables in ACLR procedures, including interface screw fixation [26], stitch configurations [27], and pretensions of graft [28]. However, the age of the specimens used in these studies is unknown. Given that the biomechanics of the porcine knee joint and the in situ stiffness of the porcine ACL change throughout skeletal growth [24], the effect of age requires careful examination.

Therefore, the objective of this work was to investigate the biomechanical properties of the porcine flexor tendon at different ages throughout skeletal growth and evaluate the impact of flexor tendon graft size and stiffness on knee biomechanics following ACLR in an age-specific pediatric porcine model. To accomplish this, we performed 3D scanning and tensile testing on porcine flexor tendons from different age groups to assess their size and tensile properties. We then used the flexor tendon from different ages as a graft to reconstruct the ACL and utilized a 6-degree-of-freedom (DOF) robotic testing system to measure joint kinematics and the forces taken by the native ACL and the reconstructed ACL under various applied loads. We hypothesized that older flexor tendons, with larger size and higher stiffness, would provide greater joint stability when used as an ACL graft.

2. METHODS

2.1. Tensile Testing of Tendons from Different Aged Animals

A total of 57 paired deep digital flexor tendons were collected from both left and right hindlimbs of female Yorkshire cross-breed pigs at 0.5 months (n=16, early juvenile), 1.5 months (n=16, juvenile), 5 months (n=16, early adolescent), and 9 months (n=9, adolescent) of age. The animals were bred at the North Carolina State University Swine Educational Unit, and the animal use was approved by North Carolina State University Institutional Animal Use and Care Committee. The flexor tendons from 0.5-month-old, 1.5-month-old, and 5-month-old groups were saved as a whole-tendon graft, while those from the 9-month-old group were utilized as half-tendon grafts due to their larger size and load cell testing limitation. The 9-month-old tendons were longitudinally split in the middle using a curved scissor and then trimmed until one half-tendon graft can pass through a 7 mm sizer. Subsequently, the specimens were wrapped in phosphate-buffered saline (PBS)-soaked gauze and stored at −20°C. Prior to testing, specimens were thawed at room temperature (70°F).

A 3D model of each tendon was obtained by using a 3D scanner (EinScan-SP, Shining 3D, Hangzhou, China) to measure the cross-sectional area (CSA) (Figure 1A). The CSA values were calculated as the average CSA of the middle 50% of each 3D tendon model using a custom MATLAB script (MathWorks, Natick, MA, USA) [24]. Following 3D scanning, biomechanical testing was performed for all specimens on a universal testing system with a 2 kN load cell (Instron 5944, Instron, Norwood, MA, USA) and pneumatic clamps (6 bar). The specimens were loaded from 5 N to 3% strain for 10 cycles as preconditioning, followed by a tensile load to failure test at a constant rate of 0.1mm/s (Figure 1A) [29,30]. The force and displacement were recorded. The stiffness of each sample was calculated as the slope of the linear regression within the linear region of the force-displacement curve using a custom MATLAB code (MathWorks, Natick, MA, USA), with the linear region manually identified between the transition point following the toe region and the yield point. Load at failure was defined as the peak load just before tendon rupture, which was indicated by an 80% drop in load.

Figure 1.

Figure 1

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Experimental protocol overview. (A) Paired deep digital flexor tendons were collected from pigs at 0.5, 1.5, 5, and 9 months of age. 3D scanning and tensile testing were performed to assess the size and tensile properties of the flexor tendons. (B) A 6-degree-of-freedom robotic testing system was utilized to perform biomechanical testing. The 4.5-month-old porcine knee was tested in the intact and ACL-transected states, followed by ACL reconstruction (ACLR) using 1.5-month-old and 5-month-old tendon grafts. Joint stability and ACL/graft forces were calculated and compared across different joint states. Created in BioRender. Fisher, M. (2025) https://BioRender.com/f7bu8fe

2.2. Biomechanical Testing of ACL-Reconstructed Joints Using Tendon Grafts

Hindlimbs were collected from 4.5-month-old (early adolescent) pigs (n=9), and deep digital flexor tendons were harvested from both 1.5-month-old and 5-month-old pigs (n=9 for each age group) (Figure 1B). Use of these ages allows tendons to be used as grafts without trimming. A 6-degree-of-freedom robotic testing system (KR300 R2500, KRC4, Kuka) along with a universal force-moment sensor (Omega160 IP65, ATI Industrial Automation) was used for biomechanical testing (Figure 1B) [24,31,32]. The joints were prepared as previously described [24,32]. The flexor tendons and joints were then thawed at room temperature prior to robotic testing.

The intact joint was first subjected to an 80 N anterior-posterior (AP) load, a 120 N compression, and a 4 N·m varus-valgus (VV) torque at 40° of flexion (full-extension position of porcine knee model). Kinematics were recorded, then repeated while recording forces for the intact joint and after capsule removal. The same loading conditions were then applied after ACL transection (ACLT) while recording the kinematics. ACL reconstruction (ACLR) with the smaller graft (1.5-month-old) was then performed (procedure described below). The same AP, compression, and VV loads were applied following ACLR. The recorded kinematics were repeated after removing the 1.5-month-old graft. Following that, ACLR with the larger graft (5-month-old) was performed by enlarging the original tunnels. The robotic testing protocol was identical to the previous reconstruction.

Anterior-posterior tibial translation (APTT) under applied AP load, anterior tibial translation (ATT) under compression, and VV rotation under applied VV torques were calculated. Delta APTT, delta ATT under compression, and delta VV rotation relative to intact state were then calculated for the ACLR states with both 1.5- and 5-month-old grafts. Force-displacement curves were recorded. The anterior force taken by ACL/graft under maximum anterior translation, compression, varus rotation, and valgus rotation were calculated by the principle of superposition [33]. In situ properties of the joint and ACL were calculated based on previous methods [32]. In situ stiffness was defined as the slope of the linear region of the anterior force–displacement curve, while in situ slack was defined as the displacement range between the onset of the linear region in the anterior and posterior directions [32].

All reconstructions were performed by a single surgeon via an arthrotomy. ACLR was first performed with the smaller flexor tendon graft (1.5-month-old). A complete transphyseal technique was performed with 6 mm diameter tunnels. The tibial tunnel was placed at the midpoint between the anteromedial (AM) and posterolateral (PL) bundle footprints using an ACL tip aimer set at 55° (Smith & Nephew, Watford, England), while the femoral tunnel was centered between the AM and PL bundle footprints using anteromedial drilling. Femoral fixation was performed by a #2 FiberWire (Arthrex) with an ABS button (Arthrex), followed by 5 cycles of passive flexion-extension with 22 N pretension. Tibial fixation was then accomplished by a staple (Arthrex) with 100 N pretension applied to the graft at maximum posterior translation at 40° of flexion. Following that, ACLR with the larger graft (5-month-old) was performed by enlarging the original tunnels to 8 mm. The surgical procedure was identical to the previous reconstruction.

2.3. Statistical Analysis

Statistical analysis was conducted using Prism (GraphPad). For tensile testing, one-way ANOVA followed by Tukey’s Honestly Significant Difference (HSD) post hoc test was performed to assess the CSA, stiffness, and load at failure of flexor tendons between age groups. To investigate the impact of CSA on stiffness, linear regression analyses were performed for flexor tendon stiffness versus CSA for specimens across ages as well as with each age group to account for age as a potential covariate. For joint biomechanical testing, one-way repeated measures ANOVA with Tukey’s HSD post hoc test was utilized to compare joint biomechanics across different states and to assess tissue function between the native ACL and reconstructed grafts. Significance was set at 0.05.

3. RESULTS

3.1. Tendon size and tensile properties

Both size and tensile properties of the porcine flexor tendon increased with age (Figure 2). The average CSA of the flexor tendon at 5 months (33.2 ± 2.8 mm2) was significantly bigger than that from 0.5-month-old group (7.6 ± 1.3 mm2, 95% CI [−29.8, −21.4], P < .001) and 1.5-month-old group (21.2 ± 6.3 mm2, 95% CI [−16.2, −7.8], P < .001) groups (Figure 2A). After trimming to 7 mm in diameter, the 9-month-old tendon CSA (36.9 ± 6.3 mm2) was comparable to the 5-month-old group. The average stiffness of 5-month-old whole tendons (176.5 ± 17.3 N/mm) and 9-month-old trimmed tendons (142.9 ± 25.4 N/mm) were significantly greater than 0.5-month-old (87.0 ± 8.5 N/mm) and 1.5-month-old (146.3 ± 20.8 N/mm) tendons (P < .001 for all) (Figure 2B). Additionally, 5-month-old tendons showed significantly higher load at failure (1113.0 ± 134.7 N) compared to 0.5-month-old (260.2 ± 40.7 N), 1.5-month-old (705.4 ± 83.6 N), and trimmed 9-month-old (962.2 ± 206.3 N) tendons (Figure 2C). A significant difference in load at failure was similarly observed across each of the age groups.

Figure 2.

Figure 2

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Size and tensile properties of flexor tendon increase during skeletal growth. (A) Cross-sectional area (CSA) and (B) stiffness of the 5-month-old tendon and trimmed 9-month-old tendon were greater. (C) 5-month-old tendon showed significantly higher load at failure compared to other age groups. Data points presented with mean and 95% CI. Statistical significance (P < .05) between states indicated (*).

A linear regression between whole tendon stiffness and CSA was significant across throughout skeletal growth from 0.5 months to 5 months (R2 = 0.75, P < 0.001) (Figure 3A). However, within each age group, tendon stiffness and CSA were not associated (R2: 0.00 – 0.05, P > 0.05) (Figure 3B).

Figure 3.

Figure 3

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Flexor tendon stiffness correlated with cross-sectional area (CSA) throughout skeletal growth but not within individual age groups. (A) Linear regression for flexor tendon stiffness vs. CSA, independent of age. (B) Linear regressions for flexor tendon stiffness vs. CSA within 0.5-month-old, 1.5-month-old, and 5-month-old groups. Statistical results are shown in the graph.

3.2. Joint and ACL function

Based on flexor tendon size and tensile properties, 1.5-month-old and 5-month-old tendon grafts were chosen to quantitively assess joint stability after ACLR. Under anterior-posterior drawer, ACL transection resulted in an average increase in APTT of 15.6 mm compared to the intact state (95% CI [12.8, 18.3], P < .001), where ACLR with 1.5-month-old and 5-month-old graft both showed lower APTT compared to ACLT state but still greater than intact state (P < .001 for all) (Figure 4A). The average increase in APTT following ACLR with the 5-month-old graft was 29% smaller than that with the 1.5-month-old graft (−3.1 mm, 95% CI [−5.8, −0.4], P = .02) (Figure 4B). Under compression, ATT increased by 7.4 mm after ACLT (vs. intact, 95% CI [2.7, 12.1], P = .001), with no differences between the intact joint and both ACLR joints (Figure 4C). The average increase in ATT under compression following ACL with 5-month-old graft was 1.4 mm, which was 81% smaller than that of the ACLT joint (−6.0 mm, 95% CI [−10.4, −1.7], P = .01) (Figure 4D). Under VV torque, the ACLT and ACLR joints showed similarly greater instability compared to the intact joint (Figure 4E), but the average increase in VV rotation was similar between the two grafts (P > .05) (Figure 4F).

Figure 4.

Figure 4

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ACL reconstruction (ACLR) with 5-month-old (5mo) graft showed better joint stability in early adolescent porcine joints compared to using 1.5-month-old (1.5mo) graft. Joint stability was measured under different loading conditions. (A) Anterior-posterior tibial translation (APTT) under anterior load. (B) Delta APTT relative to intact joint. (C) Anterior tibial translation (ATT) under compressive load. (D) ATT relative to intact joint. (E) Varus-valgus rotation (VV) under VV torque. (F) Delta VV rotation relative to intact joint. Data points presented with mean and 95% CI. Statistical significance (P < .05) between states indicated (*).

Under each applied loading condition, the tissue function of the ACL, 1.5-month-old graft, and 5-month-old graft was evaluated. Under 80 N anterior tibial force, the intact ACL carried 72.5 N of anterior forces (Figure 5A). Following ACLR, the 5-month-old graft carried 44% higher anterior forces compared to the 1.5-month-old graft (14.8 N, 95% CI [4.1, 25.6], P = .01) (Figure 5A), while both were smaller than the ACL (P < .001 for both). Under compression, the average anterior force taken by the smaller grafts was 63% smaller than the native ACL (−5.6 N, 95% CI [−11.0, −0.3], P = .04), but 5-month-old graft showed comparable anterior force to the ACL (Figure 5B). Similarly, under varus rotation, both 1.5- and 5-month-old graft took smaller anterior forces than the ACL (P < .05 for both), with no differences between the grafts (P > .05) (Figure 5C). Most AP forces were smaller than 5 N under valgus rotation, with no differences between the ACL, 1.5-month-old graft, and 5-month-old graft (P > .05) (Figure 5D).

Figure 5.

Figure 5

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The 5-month-old graft carried greater anterior force compared to the 1.5-month-old graft. (A) Under anterior loading, the 5-month-old graft carried significantly more anterior force than the 1.5-month-old graft, though neither matched the native ACL. (B) Under compression, the 1.5-month-old graft carried less anterior force compared to the native ACL. Under varus (C) and valgus (D) rotational loading, anterior force carried by the 1.5- and 5-month-old grafts was similar. ⨂ represents the ACL anterior force direction pointing into boards. Data points presented with mean and 95% CI. Statistical significance (P < .05) between states indicated (*).

Force-displacement curves during the AP load were recorded to assess submaximal properties of the joint and the ACL (Figure 6A). The posterior curves were similar between different states while the anterior tibial translation showed differences (Figure 6A). In situ joint slack following ACLR was similar between 1.5- and 5-month-old graft (P > .05), but both were significantly greater than the intact state (P < .001) (Figure 6B). Similarly, the in situ joint stiffness of the intact joint was greater than the ACLR joint with both grafts (P < .05) (Figure 6C). The in situ stiffness of the 5-month-old graft was 51% greater than the 1.5-month-old graft (2.4 N/mm, 95% CI [0.2, 4.6], P = .01), but both were smaller than 10 N/mm and not comparable to the native ACL (P <.001 for both) (Figure 6D).

Figure 6.

Figure 6

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5-month-old graft showed greater in situ stiffness compared to the 1.5-month-old raft. (A) Anterior-posterior (A-P) force-displacement curve was recorded to calculate submaximal properties. In situ joint slack (B) and stiffness (C) following ACL reconstruction (ACLR) with either graft were similar but did not return to intact joint levels. (D) The 5-month-old graft exhibited significantly greater in situ stiffness than the 1.5-month-old graft. Data points presented with mean and 95% CI. Statistical significance (P < .05) between states indicated (*).

4. DISCUSSION

This study firstly showed changes in both the size and tensile properties of porcine deep digital flexor tendons during skeletal growth. The CSA, stiffness, and load at failure increased with age. Both stiffness and load at failure increased with CSA with increasing skeletal maturity but not within a single age group. Further, 1.5-month-old and 5-month-old tendons were selected to be used as ACL grafts for an early-adolescent (4.5-month-old) porcine knee model. ACL reconstruction using a larger graft (5-month-old, 8 mm tunnel) resulted in improved initial joint stability and graft function relative to the smaller graft (1.5-month-old, 6 mm tunnel). The submaximal properties showed higher in situ stiffness of the larger graft compared to the smaller one, but the overall in situ joint stiffness and joint slack were similar between the two groups.

Previous biomechanical work compared tensile properties of ACL and grafts between young and old age groups but not within the skeletal immature populations [34,35]. At different stages of skeletal growth, the size and biomechanical function of the native ACL change [36–38]. Therefore, it is necessary to evaluate the tendon grafts at different pediatric ages to better match the size and tensile properties to the native ACL. The average CSA and stiffness were 21.2 mm2 and 146.3 N/mm for 1.5-month-old grafts, and 33.2 mm2 and 176.5 N/mm for 5-month-old grafts, resulting in a 57% increase in CSA but only a 20% increase in stiffness. The correlation between CSA and stiffness indicates that CSA alone cannot serve as a reliable predictor of stiffness within a skeletally immature age group, though it does reflect general age-related trends—where older tendons tend to be larger and stiffer. These mismatches in the rate of change between size and mechanical function highlight the importance of considering both morphological and biomechanical properties in graft selection. When comparing in-situ force of the graft, the 5-month-old graft had a 44% higher load relative to the 1.5-month-old graft, suggesting differences in size and stiffness lead to differences in initial graft force following reconstruction. These findings may enable more age-specific surgical strategies aimed at better matching the native ACL function in pediatric patients.

In the current study, ACL reconstruction was performed using 1.5-month-old and 5-month-old whole-tendon grafts within the shared joints and tunnel configuration, where the tunnel was enlarged to accommodate the larger graft. This approach minimized potential variability in joint morphology, joint function, and tunnel orientation across specimens. In this early adolescent model, the use of larger grafts led to improved joint stability and graft function. These findings align with clinical data reporting lower graft failure rates in both adult and pediatric patients receiving grafts with larger diameters [11–13]. However, reconstruction with either graft type did not fully restore joint stability or graft function to the intact state, consistent with outcomes from previous porcine ACL reconstruction studies [39,40]. While selecting a larger graft may enhance joint stability and reduce failure risk, graft size selection must also consider the likely post-operative changes in graft size. Previous pediatric data showed a significant increase of 2.2 mm (23%) in ACL graft diameter at an average of 1.7 years of follow-up (age range: 12–16) [36]. Therefore, understanding the variation in graft size and function among younger pediatric age groups can help guide the selection of appropriately sized grafts for skeletally immature patients.

In situ submaximal properties were evaluated to assess joint and graft function following ACL reconstruction. While significant differences in graft stiffness were observed between the two grafts, no significant differences were found in joint stiffness or joint slack, suggesting that variations in joint stability after ACLR were primarily driven by differences in graft stiffness. Notably, in situ graft stiffness was substantially lower than values obtained from isolated tensile testing. For instance, the 5-month-old flexor tendon exhibited an average stiffness of 176.5 N/mm in uniaxial tensile testing, compared to only 7.1 N/mm in situ after reconstruction. This discrepancy likely results from differences in loading conditions and fixation methods. In tensile testing, the graft was loaded along its longitudinal axis in a controlled clamp-to-clamp configuration, whereas in situ loading occurred through anatomical joint motion, with graft fixation achieved via sutures at the bones. These biomechanical differences highlight the importance of evaluating graft performance in anatomically relevant conditions.

This study has several limitations. First, the load at failure for the 9-month-old flexor tendons would have exceeded the capacity of the testing machine if the entire tendon had been used. As a result, these tendons had to be trimmed, and their CSA and stiffness data were excluded from the correlation analysis across skeletal growth. Second, this a time zero analysis on joint function, which does not account for biological processes such as graft remodeling, healing, or the influence of muscle forces. Future in vivo studies will be essential to further characterize the long-term biomechanical behavior of grafts and their impact to joint stability. Third, during tensile testing, most flexor tendons failed near the clamp site rather than through a mid-substance rupture. Consequently, typical mid-substance tensile properties such as ultimate strength were not reported. Additionally, no markers were placed on the tendons to track regional deformations. Therefore, the reported biomechanical properties are based solely on clamp-to-clamp measurements. Lastly, compositional and microstructural assessments were not included in this study. Since tendon growth and maturation involves both size and microstructural changes, future work characterizing all of these factors will be necessary to fully explain different graft biomechanical properties across ages.

5. CONCLUSION

In conclusion, this study investigated the changes in size and tensile properties of the porcine deep digital flexor tendon across skeletal growth and assessed the impact of graft size on joint stability and ACL function following reconstruction in an early-adolescent (4.5-month-old) porcine model. Both size and tensile properties increased throughout the skeletal growth from 0.5 to 9 months of age, with a positive correlation between CSA and stiffness across age. ACLR with the larger (5-month-old) graft resulted in better joint stability and ACL function compared to the smaller (1.5-month-old) graft. This study highlights the importance of considering tendon growth and biomechanical development when selecting grafts for pediatric ACL reconstruction, offering valuable insight for optimizing graft selection based on age-specific anatomical and functional needs.

ACKNOWLEDGEMENTS

We would like to thank the NC State College of Veterinary Medicine and Laboratory Animal Resources for their contribution to this work. Funding for this study was provided by NIH (R01 AR071985). One of the co-first authors, KG, was supported by The Scientific and Technological Research Council of Türkiye (BAYG-2219; Grant # 1059B192200) as a visiting post doctorate researcher.

Contributor Information

Yukun Zhang, Lampe Joint Department of Biomedical Engineering, North Carolina State University & University of North Carolina at Chapel Hill, Raleigh, NC, USA;; Comparative Medicine Institute, North Carolina State University, Raleigh, NC, USA

Kaan Gurbuz, Department of Orthopedics and Traumatology, Kayseri Medical Faculty, University of Health Sciences, Kayseri, Türkiye;; Lampe Joint Department of Biomedical Engineering, North Carolina State University & University of North Carolina at Chapel Hill, Raleigh, NC, USA

Joshua Chavez-Arellano, Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC, USA.

Logan Opperman, Department of Statistics, North Carolina State University, Raleigh, NC, USA.

Jeffrey T. Spang, Department of Orthopaedics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA

Matthew B. Fisher, Lampe Joint Department of Biomedical Engineering, North Carolina State University & University of North Carolina at Chapel Hill, Raleigh, NC, USA;; Comparative Medicine Institute, North Carolina State University, Raleigh, NC, USA; Department of Orthopaedics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA 4130 Engineering Building III, CB7115, Raleigh, NC 27695.

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