Effects of graft pretensioning in anterior cruciate ligament reconstruction

Application of the 3D-MRI on post-operative graft assessment in adolescent patients with ACL reconstruction: A minimal 2-year follow-up

Background

The purpose of the present study was to assess the prognostic morphological changes of the reconstructed hamstring auto-grafts by using reconstructed three-dimensional MRI (3D-MRI) in adolescent patients with ACLR.

Methods

22 adolescent patients (less than 17 years old) were retrospective included between January 1, 2018, and October 31, 2020, in our department. The patients were divided into 2 subgroups: subgroup A (<14 years old) and subgroup B (≥14 years old). 3D-MRI was used to detect the total cross-sectional area (TCA) and long-to-short axis (LSA) ratio of the reconstructed ACL graft at the proximal, mid-point, and distal regions. The minimal follow-up was 2 years.

Results

The averaged follow-up of subgroup A and B was 37.8 ± 5.6 and 37.6 ± 6.5 months, respectively. Comparing to the initial graft (ACLR operation), the TCA of reconstructed ACL was increased by 30.6% on average, and the TCAs at proximal, mid-point, and distal regions were increased by 56.4%, 50.0%, and 17.7%, respectively, inner-group comparisons showed that the TCAs of the 3 region in subgroup A were all increased at the follow-up (P = 0.002) (P < 0.001) (P < 0.001), however, only increased mid-point (P = 0.024) and distal TCAs (P < 0.001) were found in subgroup B. Comparing to the native ACL, the proximal LSA ratio in subgroup A was comparable, while it was lower in subgroup B than the native ACL (P = 0.004), the distal LSA ratios in the 2 subgroups were both lower than the native ACL (P = 0.004) (P = 0.006).

Conclusions

3D-MRI assessment can exactly identify the morphological changes of the graft in adolescent patients with ACLR, the TCA of the constructed ACL was increased compared to the initial graft, however, the LSA ratio was still lower than the native ACL. Younger adolescent patients may have a better potential on the ligamentization after ACLR than the older adolescent patients.

Age-related changes in mechanical properties of semitendinosus tendon used for anterior cruciate ligament reconstruction

Background

Hamstring tendons are a popular choice for autografts in anterior cruciate ligament (ACL) reconstruction. However, there is increasing evidence that hamstring tendon autografts carry a high risk of revision and residual instability in young patients. To elucidate the reasons for the inferior outcome of the reconstructed ACL with hamstring tendon autografts in young patients, we investigated the Young’s modulus and the extent of cyclic loading-induced slackening of the semitendinosus tendon used for ACL reconstruction across a broad range of ages.

Methods

Twenty-six male patients (aged 17–53 years), who were scheduled for ACL reconstruction surgery using the semitendinosus tendon autograft, participated in this study. The distal portion of the harvested semitendinosus tendon, which was not used to construct the autograft, was used for cyclic tensile testing to calculate the Young’s modulus and the extent of slackening (i.e., increase in slack length).

Results

Spearman correlation analysis revealed that the Young’s modulus of the semitendinosus tendon was positively correlated with the patient’s age (ρ = 0.559, P = 0.003). In contrast, the extent of tendon slackening did not correlate with the patient’s age.

Conclusions

We demonstrated that the Young’s modulus of the semitendinosus tendon increases with age, indicating that the semitendinosus tendon used for ACL reconstruction is compliant in young patients.

How preconditioning and pretensioning of grafts used in ACLigaments surgical reconstruction are influenced by their mechanical time-dependent characteristics: Can we optimize their initial loading state?

PURPOSE

Consensus about a pre-implant preparation protocol adaptable to any graft used in Anterior Cruciate Ligament reconstruction is still lacking. In fact, there is not agreement on reliable metrics that consider both specific graft dimensional characteristics, such as its diameter, and the inherent properties of its constitutive material, i.e. ligaments or tendons. Aim of the present study was to investigate and propose the applied engineering stress as a possible metrics.

METHODS

Preconditioning and pretensioning protocol involved groups of grafts with different section (10 or 32 mm²) and materials (i.e. human patellar and hamstring tendons, and synthetic grafts). A 140 N load was applied to the grafts and maintained for 100 s. Initial stress and following stress-relaxation (a mechanical characteristic that can be related to knee laxity) were specifically analysed.

FINDINGS

Initial stress, ranging between 4 and 12 MPa, was affected primarily by the graft cross-section area and secondarily by the choice of the graft material. In terms of loss of the initial stress, stress-relaxation behaviour varied instead on a narrower range, namely 13-17%.

INTERPRETATION

Engineering stress can be identified as the correct metrics to optimize the initial state of each graft to avoid excessive stiffness, laxity or fatigue rupture phenomena.

Optical Microscopy and Electron Microscopy for the Morphological Evaluation of Tendons: A Mini Review

The morphological characteristics of tendons have been thoroughly evaluated via microscopy. Optical microscopy and electron microscopy are the most commonly used techniques for tendon tissue observation. According to the principles of both microscopy types, preparation and evaluation methods vary. Simple optical microscopy is commonly used in the observation of cells and extracellular matrix, and many stains, including hematoxylin–eosin, Van Gieson, Prussian blue, Alcian blue, and toluidine blue, are used for evaluating cells, collagen fiber arrangement, and noncollagenous proteins. Histological scoring systems have been used in many studies for semi‐quantification. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are the most commonly used electron microscopy types, and special consideration is needed for the fixation and embedding protocols. Glutaraldehyde followed by osmium is most commonly used in the chemical fixation of tendon tissue, followed by epoxy resin embedment. Longitudinal sections captured in SEM images show the arrangement of collagen fibrils and the cells and lipid drops among them, while cross sections captured in TEM images show the diameter and distribution of collagen fibrils. SEM and TEM are used together for comprehensive evaluations. This mini review is focused on the preparation methodology and related evaluation indexes for the morphological evaluation of tendons.

Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs

BACKGROUND

Anterior cruciate ligament (ACL) graft conditioning protocols to decrease postoperative increases in anterior tibial translation and pivot-shift instability have not been established.

PURPOSE

To determine what ACL graft conditioning protocols should be performed at surgery to decrease postoperative graft elongation after ACL reconstruction.

STUDY DESIGN

Controlled laboratory study.

METHODS

A 6 degrees of freedom robotic simulator evaluated 3 ACL graft constructs in 7 cadaver knees for a total of 19 graft specimens. Knees were tested before and after ACL sectioning and after ACL graft conditioning protocols before reconstruction. The ACL grafts consisted of a 6-strand semitendinosus-gracilis TightRope, bone-patellar tendon-bone TightRope, and bone-patellar tendon-bone with interference screws. Two graft conditioning protocols were used: (1) graft board tensioning (20 minutes, 80 N) and (2) cyclic conditioning (5°-120° of flexion, 90-N anterior tibial load) after graft reconstruction to determine the number of cycles needed to obtain a steady state with no graft elongation. After conditioning, the grafts were cycled a second time under anterior-posterior loading (100 N, 25° of flexion) and under pivot-shift loading (100 N anterior, 5-N·m internal rotation, 7 N·m valgus) to verify that the ACL flexion-extension conditioning protocol was effective.

RESULTS

Graft board tensioning did not produce a steady-state graft. Major increases in anterior tibial translation occurred in the flexion-extension graft-loading protocol at 25° of flexion (mean ± SD: semitendinosus-gracilis TightRope, 3.4 ± 1.1 mm; bone-patellar tendon-bone TightRope, 3.2 ± 1.0 mm; bone-patellar tendon-bone with interference screws, 2.4 ± 1.5 mm). The second method of graft conditioning (40 cycles, 5°-120° of flexion, 90-N anterior load) produced a stable conditioned state for all grafts, as the anterior translations of the anterior-posterior and pivot-shift cycles were statistically equivalent ( P < .05, 1-20 cycles).

CONCLUSION

ACL graft board conditioning protocols are not effective, leading to deleterious ACL graft elongations after reconstruction. A secondary ACL graft conditioning protocol of 40 flexion-extension cycles under 90-N graft loading was required for a well-conditioned graft, preventing further elongation and restoring normal anterior-posterior and pivot-shift translations.

CLINICAL RELEVANCE

There is a combined need for graft board tensioning and robust cyclic ACL graft loading before final graft fixation to restore knee stability.

Effects of graft preconditioning on γ-irradiated deep frozen tendon allografts used in anterior cruciate ligament reconstruction

Preconditioning of the grafts prior to implantation into the knee is considered to reduce the loss of tension caused by graft viscoelasticity after anterior cruciate ligament reconstruction. The present study analyzed the impacts of different preconditioning forces on the biomechanical properties of the γ-irradiated deep frozen tendon allografts. A total of 36 tendon grafts were randomly divided into three groups and were preconditioned at 80 N (group 1), 160 N (group 2) and 320 N (group 3) for 10 min. Subsequently, the grafts were gradually completely relaxed for 1 min and subsequently received 25 cyclic loads of 0–80 N. Afterwards, the grafts were loaded to 80 N, which was maintained for 30 min. Finally, load was gradually increased until ultimate failure at maximum load (UFML) was obtained. There were significant differences in the stiffness and UFML values between the 3 groups (all P<0.05). The graft stiffness in group 3 significantly increased compared with the other 2 groups, and the stiffness of group 2 grafts increased compared with group 1. The UFML in group 3 was significantly lower compared with groups 1 and 2, while there was no significant difference between groups 1 and 2. In the present study, the results suggested that increasing the initial tension could effectively reduce the loss of stiffness due to viscoelasticity for the γ-irradiated deep frozen allogeneic tendon grafts. However, overloaded initial tension decreased the tensile strength.

High-load preconditioning of human soft tissue hamstring grafts: An in vitro biomechanical analysis

PURPOSE

In order to minimize viscoelastic elongation of ACL reconstruction grafts, preconditioning protocols have been employed in clinical practice prior to final graft fixation. The purpose of this study was to evaluate two separate high-load static preconditioning protocols of double-looped semitendinosus-gracilis grafts and compare these results to both a current clinical protocol and a control group with no preconditioning protocol applied. It was hypothesized that a high-load, static preconditioning protocol would minimize graft elongation during a simulated progressive early rehabilitation compared to both the "89 N" clinical protocol and control groups.

METHODS

Grafts were randomly allocated into four preconditioning study groups: (1) control (no preconditioning), (2) clinical protocol (89 N for 15 min), (3) high-load, short duration (600 N for 20 s), and (4) high-load, long duration (600 N for 15 min). After preconditioning, grafts were cyclically loaded between 10 and 400 N at 0.5 Hz for 450 cycles to simulate early postoperative rehabilitation. Graft displacement (elongation) was recorded during both preconditioning and cyclic loading.

RESULTS

Increased preconditioning load magnitude and duration significantly reduced graft elongation during cyclic loading (p < 0.05) which corresponded to an inverse relationship with increased elongation during preconditioning. The "600 N for 15 min" protocol resulted in significantly less elongation during simulated early rehabilitation than both the control group and the "89 N for 15 min" protocol (p < 0.001, p < 0.05).

CONCLUSIONS

Graft elongation during simulated early rehabilitation was significantly reduced by a high-load preconditioning protocol applied for an extended period of time compared to a current common clinical protocol and grafts that were not preconditioned. In addition, the amount of elongation during simulated early rehabilitation was similar between grafts preconditioned using the current clinical practice protocol and the high-load/short-duration protocol, implying that the latter could potentially induce the same viscoelastic changes in soft tissue grafts as the current clinical practice. The "600 N for 20 s" preconditioning protocol may provide similar postoperative results as the clinical protocol, "89 N for 15 min", and also reduce or maintain operative time. A high-load preconditioning protocol that reduces graft elongation may benefit patients undergoing ACL reconstruction, especially for cases of failed primary reconstruction, genu recurvatum, and increased tibial slope, where maintaining graft length is imperative to restore knee stability.

Lack of consensus regarding pretensioning and preconditioning protocols for soft tissue graft reconstruction of the anterior cruciate ligament

PURPOSE

Pretensioning and preconditioning of soft tissue grafts are often performed to obviate graft stress relaxation and elongation due to viscoelastic graft properties following anterior cruciate ligament (ACL) reconstruction. It was hypothesized that a consensus could be identified in the current literature regarding the biomechanical effects and clinical benefits of an optimal protocol.

METHODS

A systematic electronic literature search was performed by two independent reviewers to identify relevant publications. Only studies describing and/or comparing pretensioning or preconditioning protocols of soft tissue grafts or equivalent animal research models were eligible for inclusion. Study design, graft type, and protocol, including method, magnitude, mode (cyclic and/or static loading), and duration of load application, were compared. Research results and clinical conclusions were also evaluated for each study.

RESULTS

Five studies, including four in vitro biomechanical investigations and one histological analysis of patient tissue, met the predefined criteria for inclusion. Studies described numerous pretensioning and/or preconditioning protocols with varying force, time, and application modalities for multiple soft tissue graft types and animal models. The majority of studies (80 %) utilized at least one pretensioning or preconditioning protocol between 80 and 89 N, while only one study investigated substantially higher loads (500 N).

CONCLUSIONS

Despite common trends demonstrating the effects of pretensioning and preconditioning, no clear consensus regarding an optimal protocol, magnitude, or modality could be identified within the currently available relevant literature. Further multidisciplinary research is required before an optimal or consensus protocol can be established for soft tissue ACL reconstruction. Regardless, the current biomechanical literature demonstrates the potential clinically beneficial effects of pretensioning and preconditioning, including reduced graft elongation and greater preservation of graft tension and stiffness following fixation.

LEVEL OF EVIDENCE

Systematic review, Level II.

Do graft diameter or patient age influence the results of ACL reconstruction?

PURPOSE

Hamstring tendons are commonly used as a graft source for ACL reconstruction. This study seeks to determine whether either the diameter of the tendon graft or the age of the patient influences the outcome of the ACL reconstruction when measured using a standard, previously validated laxity measurement device.

METHODS

This is a retrospective study of 88 patients who underwent ACL reconstruction with a short, quadrupled tendon technique, using the semitendinosus ± gracilis tendons. Patients included in this study were sequential, unilateral, complete ACL ruptures. The patients were followed for a minimum of 1 year postoperatively, with a mean follow-up of 26 months. Patients were divided into three groups according to the diameter (Ø) of the graft: group 1 (32 patients): 8 mm ≤ Ø ≤ 9 mm; group 2 (28 patients): 9 mm < Ø ≤ 10 mm; and group 3 (28 patients): Ø > 10 mm. Three groups with differential laxity at 134 N (Δ134 = healthy side vs. operated side) measured with the laximeter GNRB(®) were compared. The risk of residual laxity (OR) between the three groups taking age, gender, BMI and meniscus status into account was calculated. A side-to-side laxity >3 mm was considered as a residual laxity.

RESULTS

The mean patient age at the time of reconstruction was 29.4 years. The three groups were comparable. Postoperative Δ134 was 1.50 ± 1.3, 1.59 ± 1.5 and 2 ± 1.7 mm for groups 1 through 3, respectively. Δ134 > 3 mm was observed in three patients in group 1, four patients in group 2 and nine patients in group 3. As compared to group 1, OR was 1.46 (95 % CI 0.35-6.05) and 3.31 (95 % CI 0.89-12.34) in groups 2 and 3, respectively. Adjustment for age, gender, BMI and meniscus did not change the estimates [OR 1.44 (95 % CI 0.34-6.16) and 3.92 (95 % CI 1-15.37)] in groups 2 and 3, respectively. Patients younger than 20 had a significantly higher average postoperative laximetry (2.4 ± 1.5 mm) compared to those aged 20 years and over (1.5 ± 1.5 mm) (p = 0.03), regardless of the diameter of the graft.

CONCLUSION

The diameter of the graft between 8 and 10 mm does not affect the laximetric results of an ACL reconstruction. Therefore, there does not appear to be a benefit to harvesting and adding further tissue to increase the diameter of the graft above 10 mm. Patients younger than 20 represent a population at risk of graft elongation. In these patients at risk, postoperative management needs to be modified (delayed weight bearing, articulated splinting, slower rehabilitation) in the first months.

LEVEL OF EVIDENCE

Retrospective case series, Level IV.

High-load preconditioning of soft tissue grafts: an in vitro biomechanical bovine tendon model

PURPOSE

No consensus exists regarding the optimal preconditioning protocol that will minimize postoperative elongation while creating a graft that is biomechanically equivalent to the native anterior cruciate ligament (ACL). It was hypothesized that a preconditioning protocol of specific mode and magnitude would create a graft with equivalent stiffness to the native ACL.

METHODS

Thirty-six bovine extensor tendon grafts were randomly allocated among six preconditioning groups (n = 6 per group) including three cyclic (10 cycles at 0.5 Hz between 10-80, 100-300, and 300-600 N) and three static loading protocols (20 s at 80, 300, and 600 N). Grafts were then cyclically loaded between 50 and 250 N at 0.5 Hz for 500 cycles to simulate an early rehabilitation protocol.

RESULTS

Cyclic 300-600 N and static 600 N loading protocols both demonstrated significantly less elongation during simulated rehabilitation when compared to lower, current clinical standard preconditioning levels of 10-80 N (-62% Δ) and 80 N (-69% Δ). The same high-load preconditioning protocols demonstrated statistical equivalence in stiffness when compared to the previously reported stiffness of the native ACL.

CONCLUSIONS

In this experimental model, increased force applied to soft tissue grafts during preconditioning significantly decreased the subsequent elongation experienced during simulated early rehabilitation. A static load of 600 N removed the most graft elongation during preconditioning, had the least amount of cyclic displacement during simulated early rehabilitation, and was statistically equivalent to the native ACL stiffness. Implementation of high-load preconditioning of soft tissue grafts may help improve outcomes following ACL reconstruction by reducing residual knee laxity resulting from postoperative graft elongation and the intrinsic viscoelastic properties of the graft tissue while imparting biomechanical characteristics (e.g. stiffness) equivalent to the native ACL.

Anatomical Reconstruction of Lateral Ankle Ligaments Using Free Tendon Allografts and Biotenodesis Screws

BACKGROUND

Lateral ankle instability is one of the most common musculoskeletal disorders and can result in ankle damage. This study reports on the results of the anatomical reconstruction of ligaments using semitendinosus tendon allograft and bioabsorbable tenodesis screws for chronic lateral ankle instability, as well as the functional and radiological results of this procedure.

METHODS

From February 2007 to January 2013, 70 patients (72 ankles) underwent this procedure. Six patients were lost to follow-up, and ultimately 64 patients (66 ankles) were evaluated. Visual Analog Scale (VAS) pain scores, American Orthopaedic Foot & Ankle Society (AOFAS) scores, Karlsson-Peterson ankle scores, and patient satisfaction were evaluated at a mean of 22.1 months (range, 12-68 months) postoperatively. The talar tilt angle and anterior translation were assessed radiographically in pre- and postoperative ankle stress views. The mean patient age at surgery was 30.1 years (range, 16-59 years).

RESULTS

The mean VAS pain score decreased from 5.5 to 1.3 (P < .05), and the mean AOFAS improved from 71.0 to 90.9 (P < .05). The mean Karlsson-Peterson score improved from 55.1 to 90.3, whereas talar tilt decreased from 14.8 degrees to 3.9 degrees. There was no significant difference in clinical outcomes between the pretensioned and nonpretensioned groups.

CONCLUSION

This procedure yielded successful results, including satisfactory ankle stability and clinical outcomes, in ankles with poor lateral ligament tissues.

LEVEL OF EVIDENCE

Level IV, case series.

Effect of cyclic tension on the biomechanical properties of flexor tendon grafts. Results of an ex-vivo porcine study

BACKGROUND

Autologous flexor tendons are widely used for anterior cruciate ligament (ACL) reconstruction. Pretension of the graft before fixation has been described as part of the surgical technique, nevertheless there is no consensus on the type and amount to tension needed to increase the stiffness without affecting its biomechanical properties.Our hypothesis is cyclic tension increases flexor tendon stiffness without affecting its ultimate failure at maximum loads (UFML).

METHODS

Forty-five flexor digitorum profundus tendons harvested from domestic pigs (Sus scrofa domestica) were randomly divided into three groups: E1 (n=15), E2 (n=15) and C (n=15). Groups E1 and E2 were subjected to 50 cyclic loads at a 1 Hz frequency, at 70N and 100N respectively, group C was not intervened. The three groups were then tested for UFML. Cyclic loads and measurements were performed using a Stress-Strain machine (SST 1.0 Kinetecnic). Results were analyzed using GrapgPad statistical software. Groups were compared using Mann-Whitney test with a 95% confidence interval.

RESULTS

Significant increased stiffness for group E1 (p=0.02) and group E2 ( p<0.01) when compared to group C. The stiffness of group E2 was also significantly higher than E1 (p=0.03). There was a significant reduction on the UFML between group E2 and C (p<0.01), which was not observed when comparing groups E1 and C.

CONCLUSION

Cyclic loads at 70N result in an increased stiffness of flexor tendons without affecting its ultimate failure at maximum loads. Cyclic loads at higher tensions might cause a deleterious effect on the biomechanical properties of flexor tendon grafts.