Microstructural and Mechanical Properties of Grafts Commonly Used for Cruciate Ligament Reconstruction

Increased risk for early revision with quadriceps graft compared with patellar tendon graft in primary ACL reconstructions

PURPOSE

Bone patella-tendon bone (BPTB) and hamstring tendon (HT) autografts are the most used grafts in primary anterior cruciate ligament (ACL) reconstructions (ACLR) in Norway. Quadriceps tendon (QT) autograft has gained more popularity during the past years. The purpose of this study is to compare revision rates and patient-reported outcomes of primary QT with BPTB and HT autograft ACL reconstructions in Norway at 2-year follow-up. It was hypothesized that there would be no difference in 2-year revision rates between all three autografts.

METHODS

Data included primary ACLR without concomitant ligament surgeries, registered in the Norwegian Knee Ligament Register from 2004 through 2021. Revision rates at 2 years were calculated using Kaplan-Meier analysis. Hazard ratios (HR) for revision were estimated using multivariable Cox regression analysis with revision within 2 years as endpoint. Mean change in patient-reported outcome was recorded preoperatively and at 2 years through the Knee Injury and Osteoarthritis Outcome Score (KOOS) subcategories 'Sport' and 'Quality of Life' was measured for patients that were not revised and analysed with multiple linear regression.

RESULTS

A total of 24,790 primary ACLRs were identified, 10,924 with BPTB, 13,263 with HT and 603 with a QT graft. Patients in the QT group were younger (23.5 years), more of them were women (58.2%) and over 50% had surgery <3 months after injury. The QT group had the highest prevalence of meniscal injuries (61.9%). Revision estimates at 2-years were 3.6%, 2.5% and 1.2% for QT, HT and BPTB, respectively (p < 0.001). In a Cox regression analysis with QT as reference, BPTB had a lower risk of revision (HR 0.4, 95% Cl 0.2-0.7, p < 0.001). No significant difference was observed in the revision risk between QT and HT (HR 1.1, 95% Cl 0.7-1.8, n.s.). The two most common reported reasons for revision were: traumatic graft rupture and nontraumatic graft failure. There were no differences between the groups in change of KOOS in subcategories 'Sport' and 'Quality of Life' at 2-years follow-up.

CONCLUSION

The 2-year risk of revision after ACLR with QT was higher than BPTB and similar to HT. No difference was found between the groups in patient-reported outcomes. This study provides valuable insights for both surgeons and patients when making decisions about the choice of autografts in primary ACL reconstructions.

LEVEL OF EVIDENCE

Level II.

Tape-Reinforced Graft Suturing and Retensioning of Adjustable-Loop Cortical Buttons Improve Quadriceps Tendon Autograft Biomechanics in Anterior Cruciate Ligament Reconstruction: A Cadaveric Study

PURPOSE

To investigate the biomechanical effects of tape-reinforced graft suturing and graft retensioning for all-soft tissue quadriceps tendon (ASTQT) anterior cruciate ligament reconstruction (ACLR) in a full-construct human cadaveric model.

METHODS

Harvested cadaveric ASTQT grafts were assigned to either (1) double-suspensory adjustable-loop cortical button device (ALD) fixation in which both graft ends were fixed with a suspensory fixation device with (n = 5) or without (n = 5) tape-reinforced suturing or (2) single-suspensory distal tendon fixation in which only the patellar end was fixed with an ALD (n = 5) or fixed-loop cortical button device (FLD) (n = 5). All specimens were prepared using a No. 2 whipstitch technique, and tape-reinforced specimens had an integrated braided tape implant. Graft preparation time was recorded for double-suspensory constructs. Samples were tested on an electromechanical testing machine using a previously published protocol simulating rehabilitative kinematics and loading.

RESULTS

Tape-reinforced graft suturing resulted in greater graft load retention after cycling (11.9% difference, P = .021), less total elongation (mean [95% confidence interval (CI)], 5.57 mm [3.50-7.65 mm] vs 32.14 mm [25.38-38.90 mm]; P < .001), greater ultimate failure stiffness (mean [95% CI], 171.9 N/mm [158.8-185.0 N/mm] vs 119.4 N/mm [108.7-130.0 N/mm]; P < .001), and less graft preparation time (36.4% difference, P < .001) when compared with unreinforced specimens. Retensioned ALD constructs had less cyclic elongation compared with FLD constructs (mean total elongation [95% CI], 7.04 mm [5.47-8.61 mm] vs 12.96 mm [8.67-17.26 mm]; P = .004).

CONCLUSIONS

Tape-reinforced graft suturing improves time-zero ASTQT ACLR construct biomechanics in a cadaveric model with 83% less total elongation, 44% greater stiffness, and reduced preparation time compared with a whipstitched graft without tape reinforcement. ALD fixation improves construct mechanics when compared with FLD fixation as evidenced by 46% less total elongation.

CLINICAL RELEVANCE

Tape-reinforced implants and graft retensioning using ALDs improve time-zero ACLR graft construct biomechanics in a time-zero biomechanical model. Clinical studies will be necessary to determine whether these implants improve clinical outcomes including knee laxity and the incidence of graft rupture.

Differences in the microstructural and mechanical qualities of semitendinosus tendon grafts between skeletally immature and mature patients in anterior cruciate ligament reconstruction

BACKGROUND

This study aimed to investigate the microstructural and mechanical properties of semitendinosus tendon graft tissues during anterior cruciate ligament reconstruction and the clinical outcomes in skeletally immature and mature patients.

METHODS

Twenty-two patients who underwent primary anterior cruciate ligament reconstruction using a hamstring tendon graft were analyzed and divided into skeletally immature (n = 7) and mature groups (n = 15) based on magnetic resonance imaging findings of the epiphyseal plate of the distal femur. Tissue samples were collected from the mid-portion of the semitendinosus tendon. The collagen fibril diameter, maximum stress, and strain at maximum stress point in the semitendinosus tendon tissues were calculated for comparison of the microstructural and mechanical properties between the two groups. Postoperative outcomes were also assessed between the two groups.

RESULTS

The mean and 60th and 80th percentiles of fibril diameters in the skeletally immature group were significantly smaller than those in the mature group (65.9 ± 13.0, 73.5 ± 19.3, and 91.3 ± 27.4 nm in the skeletally immature group; and 90.3 ± 14.7, 94.0 ± 18.4, and 125.3 ± 19.9 nm in the skeletally immature group; p = 0.001, 0.024, and 0.004, respectively). Additionally, the strain at maximum stress was higher in the skeletally immature group (237.2 ± 102.4% vs. 121.5 ± 51.9%, p = 0.024). However, there was no difference in maximum stress between the skeletally immature and mature groups (19.9 ± 14.3 MPa vs. 24.5 ± 23.4 MPa, p = 0.578). Strain was negatively correlated with the mean fibril diameter and the 60th and 80th percentiles of fibril diameters, whereas stress was positively correlated with the mean fibril diameter. The skeletally immature group had a higher pivot shift test-positive rate than the mature group at the last follow-up (p = 0.023).

CONCLUSION

Semitendinosus tendon graft tissues differed microstructurally and mechanically between skeletally immature and mature patients.

LEVEL OF EVIDENCE

Level Ⅳ.

Speed whip ripstop technique during anterior cruciate ligament reconstruction using quadriceps tendon results in higher fixation strength

PURPOSE

To compare the biomechanical strength of different fixation configurations using a suspensory button in a soft-tissue quadriceps tendon graft for Anterior Cruciate Ligament (ACL) reconstruction.

METHODS

Thirty fresh-frozen bovine Achilles tendons (10 mm wide, 50 mm long, and 4 mm thick) were used in this study. Tendons were assigned to three groups (n = 10 per group) with different suture configurations using adjustable loops with a suspensory button: group A, with the threads of an adjustable loop fixed by crossing at the tip of the loop and the entire loop; group B, continuous loops with hanging buttons were directly sutured to the tendon with eight simple sutures; group C, fixation was performed using the speed whip ripstop technique. Tensile tests with five cycles of preloading were performed at 50 N, held at 50 N for 1 min, and load-to-failure testing was conducted until rupture at 5 mm/min. The difference in the elongation and the maximum load-to-failure force were measured.

RESULTS

The average elongation was significantly larger in group B (16.6 ± 2.2 mm) than in groups A (10.3 ± 2.4 mm) and C (10.0 ± 1.0 mm), (p < 0.001). The average load-to-failure force varied significantly between the three groups, 157.5 ± 33.4 N in group A, 253.4 ± 45.5 N in group B, and 337.7 ± 21.0 N in group C, (p < 0.001).

CONCLUSION

Fixation using the speed whip ripstop technique to fix the suspensory button and soft-tissue transplant tendon resulted in minimal elongation and higher fixation strength. Simple devices that use this method have already been developed. Since it can be fixed using a relatively simple method, speed whip ripstop technique was shown to be advantageous for femoral fixation in ACL reconstruction using soft-tissue quadriceps tendon. The findings of this study could help surgeons reduce graft re-tear rates in ACL reconstruction using quadriceps tendons.

LEVEL OF EVIDENCE

N/A, laboratory control study.

Current trends in graft choice for anterior cruciate ligament reconstruction - part I: anatomy, biomechanics, graft incorporation and fixation

Graft selection in anterior cruciate ligament (ACL) reconstruction is critical, as it remains one of the most easily adjustable factors affecting graft rupture and reoperation rates. Commonly used autografts, including hamstring tendon, quadriceps tendon and bone-patellar-tendon-bone, are reported to be biomechanically equivalent or superior compared to the native ACL. Despite this, such grafts are unable to perfectly replicate the complex anatomical and histological characteristics of the native ACL. While there remains inconclusive evidence as to the superiority of one autograft in terms of graft incorporation and maturity, allografts appear to demonstrate slower incorporation and maturity compared to autografts. Graft fixation also affects graft properties and subsequent outcomes, with each technique having unique advantages and disadvantages that should be carefully considered during graft selection.

Characterizing the viscoelastic properties of the anterolateral ligament and grafts commonly used in its reconstruction

BACKGROUND

Current anatomic anterolateral ligament reconstruction is typically performed using either a gracilis tendon or an iliotibial band graft based on their quasi-static behavior. However, there is limited knowledge about their viscoelastic behaviors. This study aimed to characterize the viscoelastic properties of the anterolateral ligament, distal iliotibial band, distal gracilis tendon and proximal gracilis tendon for graft material choice in anterolateral ligament reconstruction.

METHODS

All the tissues were harvested from thirteen fresh-frozen cadaveric knees and subjected to preconditioning (3-6 MPa), sinusoidal cycle (1.2-12 MPa), dwell at constant load (12 MPa), and load to failure (3%/s). The quasi-static and viscoelastic properties of the soft tissues were computed and compared using a linear mixed model (p < 0.05).

FINDINGS

The hysteresis of anterolateral ligament (mean:0.4 Nm) was comparable with gracilis halves (p > 0.85) but iliotibial band (6 Nm) was significantly higher (p < 0.001,ES = 6.5). In contrast, the dynamic creep of anterolateral ligament (0.5 mm) was similar to iliotibial band (0.7 mm, p > 0.82) whereas both gracilis halves were significantly lower (p < 0.007,ES > 1.4). The elastic modulus of anterolateral ligament (181.4 MPa, p < 0.001,ES > 2.1) was the lowest compared to the grafts materials (distal gracilis tendon:835 MPa, distal gracilis tendon:726 MPa, iliotibial band:910 MPa). Additionally, the failure load of the anterolateral ligament (124.5 N, p < 0.001,ES > 2.9) was also the lowest.

INTERPRETATION

The mechanical properties of the gracilis halves and iliotibial band were significantly different from anterolateral ligament, except for hysteresis and dynamic creep, respectively. Our findings showed that the gracilis halves may be a more appropriate graft choice for anterolateral ligament reconstruction due to its low energy dissipation and permanent deformation under dynamic loads.

Quadriceps tendon autograft for anterior cruciate ligament reconstruction: state of the art

The ideal graft for anterior cruciate ligament reconstruction (ACLR) continues to be debated. Although first described in 1984, use of the quadriceps tendon (QT) autograft has only recently gained popularity. The biomechanical properties of the QT autograft are favourable compared to bone-patellar tendon-bone (BPTB) and doubled hamstring (HS) grafts with a higher load to failure and a modulus of elasticity that more closely approximates the native anterior cruciate ligament (ACL). The QT graft can be harvested with or without a bone plug, as either a full thickness or a partial thickness graft, and even through minimally invasive techniques. The surgeon must be aware of potential harvest risks including patellar fracture or a graft that is of insufficient length. Numerous short-term studies have shown comparable results when compared to BPTB or hamstring HS autografts with similar graft failure rates, patient-reported outcomes. A major advantage of QT ACLR is reduced donor site morbidity compared to BPTB. However, some persistent quadriceps weakness after QT ACLR has also been reported. The current literature shows that use of the QT autograft for ACLR provides equivalent clinical results compared to other autografts with less donor site morbidity. However, future studies with longer follow-up and higher level of evidence are needed to identify specific populations where the QT may have additional advantage.

Anterior cruciate ligament reconstruction with all-soft tissue quadriceps tendon versus quadriceps tendon with bone block

PURPOSE

The purpose of this study was to evaluate whether there was a difference in clinical outcomes between patients who underwent primary ACL reconstruction (ACLR) with all-soft tissue quadriceps tendon (sQT) autograft versus QT with bone block (bQT).

METHODS

A retrospective cohort study of 708 patients who underwent QT ACLR was conducted. Primary ACLR patients with at least 1 year of follow-up were identified and those who received sQT were compared to those who received bQT. Data collection entailed patient demographics, surgical variables, patient reported outcomes (PROs), knee stability testing, and complications. The primary outcome of interest was International Knee Documentation Committee (IKDC) score, reported as mean score, pre- and postoperative difference, and number who met minimum clinically important difference (MCID). Secondary outcomes included Lachman and pivot shift grade, other patient reported outcomes (PROs), complication rates, and return to sport (RTS).

RESULTS

A total of 195 patients (147 sQT, 48 bQT) who underwent primary QT ACLR met criteria for analysis, with mean follow-up of 17.0 ± 7.9 months. No difference was detected between cohorts with respect to postoperative IKDC score (sQT: n = 120, 81.0 ± 18.9, bQT: n = 10, 80.9 ± 20.4, n.s.), proportion of patients who met MCID (sQT: 68/78 [87%], bQT: 6/7 [86%], n.s.), or results of stability testing. In the sQT cohort, 86% (106/123) of athletes achieved full RTS, compared to 85% (34/40) in the bQT cohort (n.s.). Time to RTS was less than a year in both cohorts (sQT: 10.5 ± 3.8 months [n = 106], bQT: 11.1 ± 3.9 months [n = 31], n.s.). Graft rupture occurred in 7 (5%) sQT patients and 3 (6%) bQT patients (n.s.), and all clinical failures were due to graft rupture (n.s.). No differences were detected for rates of postoperative complications.

CONCLUSION

No differences in clinical outcomes were detected between patients who underwent primary ACLR with sQT autograft versus bQT autograft. Currently, the decision to employ sQT or bQT is largely determined by surgeon preference. This study demonstrates excellent outcomes with both preparations and supports the use of either graft type at the discretion of the treating surgeon.

LEVEL OF EVIDENCE

III.

Donor age and sex have limited effects on the mechanical and microstructural properties of human connective tissues

Connective tissues, such as tendons, ligaments, and capsules, play a large role in locomotion and joint stability and are often subjected to traumatic injuries and degeneration. The purpose of this study was to evaluate if the mechanical and microstructural properties of connective tissues correlate with the age and sex of the human donor. Dissected samples were prepared for mechanical testing, consisting of 10 cycles of preconditioning, a stress-relaxation ramp and hold, and a quasi-static ramp to failure. During the testing protocol, the microstructural organization of tissues was analyzed using quantitative polarized light imaging. A linear mixed model was used to assess whether tissue type, donor age, or donor sex were significantly associated with mechanical and microstructural tissue properties. Tissue type had a significant effect on all parameters, while donor age and sex did not. Groupings by tissue type (i.e., tendon vs. ligament vs. capsule) were evident for microstructural data, with tendons having a tighter grouping and ligaments having a larger spread of values. The interaction of tissue type and age yielded a significant effect for linear modulus only (p = 0.007), with the palmaris tendon appearing to have the largest contribution to this effect. There were no significant interaction effects between sex and tissue type or donor age. Donor age appears to affect linear modulus in some, but not all, tissue types. Otherwise, age and sex do not have significant effects on the mechanical and microstructural properties of the range of connective tissues that were analyzed in this study.

Direct suturing quadriceps tendon to a continuous loop with a suspensory button provides biomechanically superior fixation in ACL reconstruction

PURPOSE

To compare the biomechanical strength of different fixation configurations using suspensory buttons in a soft-tissue quadriceps tendon (QT) grafts in anterior cruciate ligament (ACL) reconstruction.

METHODS

Forty bovine QTs, 6-cm long and 10-mm wide, were allocated into four groups with different suture configurations using suspensory buttons (n = 10 in each group): Group A, a baseball suture with a knot tied to the continuous loop with a suspensory button; Group B, same configuration as in Group A but with the knot tied at the opposite end of the baseball suture; Group C, a continuous loop with a suspensory button stitched directly to the QT with simple sutures, and Group D, a baseball suture tied directly to a suspensory button. Biomechanical testing was performed by preloading followed by cyclic loading for 500 cycles between 10 and 100 N. The length of elongation (mm) and maximum load to failure (N) were recorded, and compared among the four groups.

RESULTS

Group C showed significantly smaller elongation (4.1 mm [95% CI 3.1-5.2]) than Group A (8.2 mm [95% CI 7.0-9.4]), Group B (10.5 mm [95% CI 7.7-13.3]), and Group D (8.5 mm [95% CI 7.0-9.9]) (A-C; P = 0.004, B-C; P = 0.0001, C-D; P = 0.0018). The maximum load to failure in Group C (386 N [95%CI 306-466]) was significantly higher than that in Group A (196 N [95% CI 141-251]), Group B (226 N [95% CI 164-289]), and Group D (212 N [95%CI 171-253]) (A-C; P = 0.0001, B-C; P = 0.0009, C-D; P = 0.0002). No significant differences were observed between Group A, B, and D in terms of elongation and maximum load to failure.

CONCLUSION

The soft-tissue QT graft fixation configuration stitched directly to a continuous loop with suspensory button using simple sutures exhibits small elongation and high maximum load to failure among the four configurations. Regarding clinical relevance, direct suturing of the soft-tissue QT to a continuous loop with a suspensory button may be advantageous for femoral fixation in ACL reconstruction from a biomechanical perspective, and warrant future development of a novel fixation device using this principle.

Low to moderate risk of nerve damage during peroneus longus tendon autograft harvest

PURPOSE

This study aims to evaluate the proximity of the tendon stripper to both the peroneal and sural nerves during peroneus longus tendon (PLT) autograft harvesting.

METHODS

Ten fresh-frozen human cadaveric lower extremities were used to harvest a full-thickness PLT autograft using a standard closed blunt-ended tendon stripper. The distance to the sural nerve from the PLT (at 0, 1, 2 and 3 cm proximal to lateral malleolus (LM), and the distance to the peroneal nerve and its branches from the end of the tendon stripper were measured by two separate observers using ImageJ software.

RESULTS

The average distance from the PLT to the sural nerve increased significantly from 0 to 2 cm proximal to LM. The average distance to the sural nerve at the LM was 4.9 ± 1.5 mm and increased to 10.8 ± 2.4 mm (2 cm proximal to LM). The average distance from the tendon stripper to the deep peroneal nerve was 52.9 ± 11.4 mm. The average distance to the PLT branch of peroneal nerve was 29.3 ± 4.2 mm. The superficial peroneal nerve, which coursed parallel and deep to the tendon stripper, was on average 5.2 ± 0.7 mm from the end of the stripper. No transection injuries of the nerves were observed in any of the ten legs after harvesting.

CONCLUSION

This cadaver study found during a full-thickness PLT harvest, the distances between the tendon stripper and the nerves were greater than 5 mm with an initial incision at 2 cm proximal to LM which is recommended.

Quadricep ACL Reconstruction Techniques and Outcomes: an Updated Scoping Review of the Quadricep Tendon

PURPOSE OF REVIEW

The purpose of this review is to provide an up-to-date summary on the most recent literature examining techniques and outcomes in anterior cruciate ligament (ACL) reconstruction using quadriceps tendon (QT) which will enable surgeons to make well informed evidence-based decisions when choosing a particular graft option and technique in ACL reconstruction.

RECENT FINDINGS

Several RCTs and systematic reviews have been published recently on this topic, and overall, there were no differences found between the QT, HT, and BPTB groups in patient-reported outcomes, stability testing, or graft re-rupture rates. In terms of strength testing, the QT group did have inferior knee extensor strength on isokinetic testing when compared to the HT group, whereas the HT group had inferior knee flexor strength compared to the QT group. No differences were found on strength testing between the QT and BPTB groups. Currently, two large RCTs, the Stability2 and SQuASH trials, are ongoing examining the effectiveness of the QT vs BPTB with or without LET and QT vs HT in the pediatric population which will help shed further light on the effectiveness of the QT as a graft choice in ACL reconstruction. The findings of this scoping review demonstrate that the QT is an excellent graft option in ACL reconstruction both in the primary and revision settings, among adult and pediatric populations. This review provides surgeons with further assurance when selecting QT autograft in ACL reconstruction.