Reconstruction of the anterior cruciate ligament: dynamic strain evaluation of the graft

Which tendon graft to choose for anatomical ligament reconstruction in chronic lateral ankle instability? A biomechanical study

BACKGROUND

The need for anatomic lateral ligament reconstruction of the ankle continues to grow. This procedure usually requires a gracilis autograft or in some cases an allograft. Siegler et al. reported the mechanical characteristics of the collateral lateral ligaments of the human ankle: 231 ± 129 N for the ATFL and 307 ± 142 N for the CFL. The objective of this study was to evaluate the mechanical properties of different tendon grafts available for ATFL and CFL reconstruction. We hypothesized that the properties of the tested grafts are not inferior to the published values of those of the original ligaments on the lateral side of the ankle.

METHODS

This was a comparative biomechanical study using 6 cadaver specimens (108 grafts): The biomechanical properties of nine types of grafts were determined using validated tensile testing methods: Gracilis, SemiT, EHL, FHL, Plantaris, Peroneus longus and brevis, TA and TP. The main outcome measure was the comparison of the mechanical properties of each single-stranded tendon with each other and with the known values ​​for the ATFL and CFL, during a uniaxial static rupture test.

RESULTS

The mean load to failure for the gracilis was 257.5 ± 52.9 N. The groups had similar mean values in terms of the maximum load that they could withstand before failing except for the plantaris (137.9 ± 33.7 N) which was statistically lower than all other tested tendons (p < 0,01). The mean load to failure values of the grafts tested were equal or higher than that of the ATFL and CFL reported by Siegler et al. [14]: 231 ± 129 N for the ATFL and 307 ± 142 N for the CFL, while the grafts tested here had mean failure load between 258 ± 53 N and 464 ± 136 N.

CONCLUSION

The gracilis, peroneus longus/brevis, EHL, FHL, TA, TP and semiT are legitimate grafts for combined ATFL and CFL reconstruction in the ankle. These tendons have mechanical properties (load to failure, maximum strain at failure and stiffness) that are equal to or higher than the native ligaments on the lateral side of the ankle, except the plantaris.

CLINICAL RELEVANCE

This study validates the current use of the gracilis autograft for the anatomical reconstruction of the ATFL and CFL, and even provides proof that other tendons would be suitable for this anatomical reconstruction of the lateral ankle ligament by auto or even allograft under certain conditions.

LEVEL OF EVIDENCE

Descriptive laboratory study.

Reconstruction of a Neglected Patellar Tendon Rupture in an Adolescent: A Case Report

We present a case of a neglected patellar tendon rupture, misdiagnosed as an anterior cruciate ligament tear, in a 12-year-old child with open physis without an avulsion fracture. The patient was treated with an ipsilateral hamstring tendon autograft with preserved distal insertions, a transpatellar tunnel, and a transtibial fixation. At the final follow-up, the patient had a full range of motion and a fully functional knee. The described technique results in complete muscle strength, full range of motion, and pain-free gait. It can be used in chronic patellar tendon ruptures and is a valuable addition to the therapeutic quiver for this type of injury.

Could an Anterior Cruciate Ligament Be Tissue-Engineered from Silk?

Silk has a long history as an exclusive textile, but also as a suture thread in medicine; nowadays, diverse cell carriers are manufactured from silk. Its advantages are manifold, including high biocompatibility, biomechanical strength and processability (approved for nearly all manufacturing techniques). Silk's limitations, such as scarcity and batch to batch variations, are overcome by gene technology, which allows for the upscaled production of recombinant "designed" silk proteins. For processing thin fibroin filaments, the sericin component is generally removed (degumming). In contrast to many synthetic biomaterials, fibroin allows for superior cell adherence and growth. In addition, silk grafts demonstrate superior mechanical performance and long-term stability, making them attractive for anterior cruciate ligament (ACL) tissue engineering. Looking at these promising properties, this review focusses on the responses of cell types to silk variants, as well as their biomechanical properties, which are relevant for ACL tissue engineering. Meanwhile, sericin has also attracted increasing interest and has been proposed as a bioactive biomaterial with antimicrobial properties. But so far, fibroin was exclusively used for experimental ACL tissue engineering approaches, and fibroin from spider silk also seems not to have been applied. To improve the bone integration of ACL grafts, silk scaffolds with osteogenic functionalization, silk-based tunnel fillers and interference screws have been developed. Nevertheless, signaling pathways stimulated by silk components remain barely elucidated, but need to be considered during the development of optimized silk cell carriers for ACL tissue engineering.

An off-the-shelf decellularized and sterilized human bone-ACL-bone allograft for anterior cruciate ligament reconstruction

Approximately 1% of active individuals participating in sports rupture their anterior cruciate ligaments (ACL) every year, which is currently reconstructed using tendon autografts. Upon reconstruction, clinical issues of concern are ACL graft rupture, persistent knee instability, limited return to sports, and early onset of osteoarthritis (OA). This happens because tendon autografts do not have the same compositional, structural, and mechanical properties as a native ACL. To overcome these problems, we propose to use decellularized bone-ACL-bone allografts in ACL reconstruction (ACLR) as a mechanically robust, biocompatible, and immunologically safe alternative to autografts. Here, a decellularization protocol combined with sterilization using supercritical carbon dioxide (scCO₂) was used to thoroughly decellularize porcine and human ACLs attached to tibial and femoral bone blocks. The specimens were named ultrACLean and their compositional, structural, and mechanical properties were determined. Our results indicate that: 1) decellularization of ultrACLean allografts leads to the removal of nearly 97% of donor cells, 2) ultrACLean has mechanical properties which are not different to native ACL, 3) ultrACLean maintained similar collagen content and decreased GAG content compared to native ACL, and 4) ultrACLean is not cytotoxic to seeded tendon-derived cells in vitro. Results from an in vivo pilot experiment showed that ultrACLean is biocompatible and elicits a moderate immunological response. In summary, ultrACLean has proven to be a mechanically competent and biocompatible graft with the potential to be used in ACLR surgery.

Five-Strand Hamstring Grafts are Biomechanically Comparable to Four-Strand Grafts and Offer Greater Diameter for Anterior Cruciate Ligament Reconstruction

Purpose

The purpose of this study was to compare the biomechanics of 4-strand and 5-strand hamstring constructs for anterior cruciate ligament grafts.

Methods

Thirty-six human cadaveric hamstring grafts were tested in 3 different conditions: (1) graft femoral fixation complex, (2) graft femoral and tibial fixation (GFTF) complex using a human model, and (3) GFTF complex using a porcine model. Grafts were tested on a tensile testing machine. Four-stranded grafts served as the control group, and 5-stranded grafts served as the experimental group. Cyclic elongation, ultimate load to failure, stiffness, and diameter of the grafts were analyzed.

Results

Average 4-strand graft diameter was 7.96 mm compared to 9.32 mm for the 5-strand graft (P = .00017). Average stiffness of grafts ≥8 mm was 105.04 N/mm compared to 85.05 N/mm for grafts <8 mm (P = .04988). There was a positive correlation between graft diameter and stiffness (13.4 N/mm per every 1 mm increase in diameter, r² value of 13.1%, and F-significance of 0.02778). There were no significant differences in terms of ultimate load to failure, cyclic elongation, or stiffness between the experimental groups.

Conclusion

Five-strand hamstring grafts offer greater diameter and are biomechanically comparable to 4-strand equivalents at time 0. Grafts >8 mm offer significantly greater stiffness compared to grafts sized <8 mm. There is a weak positive correlation between graft diameter and stiffness.

Clinical Relevance

A potential drawback to hamstring grafts is their variability in size. Five-strand hamstring grafts provide increased diameter in comparison to 4-strand equivalents and might be used when quadrupled graft diameter is <8 mm.

Evaluation of anterior cruciate ligament surgical reconstruction through finite element analysis

Anterior cruciate ligament (ACL) tear is one of the most common knee injuries. The ACL reconstruction surgery aims to restore healthy knee function by replacing the injured ligament with a graft. Proper selection of the optimal surgery parameters is a complex task. To this end, we developed an automated modeling framework that accepts subject-specific geometries and produces finite element knee models incorporating different surgical techniques. Initially, we developed a reference model of the intact knee, validated with data provided by the Open Knee(s) project. This helped us evaluate the effectiveness of estimating ligament stiffness directly from MRI. Next, we performed a plethora of “what-if” simulations, comparing responses with the reference model. We found that (a) increasing graft pretension and radius reduces relative knee displacement, (b) the correlation of graft radius and tension should not be neglected, (c) graft fixation angle of 20\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{\circ }$$\end{document}∘ can reduce knee laxity, and (d) single-versus double-bundle techniques demonstrate comparable performance in restraining knee translation. In most cases, these findings confirm reported values from comparative clinical studies. The numerical models are made publicly available, allowing for experimental reuse and lowering the barriers for meta-studies. The modeling approach proposed here can complement orthopedic surgeons in their decision-making.

Biomechanical properties of common graft choices for anterior cruciate ligament reconstruction: A systematic review

BACKGROUND

This systematic review explores the differences in the intrinsic biomechanical properties of different graft sources used in anterior cruciate ligament (ACL) reconstruction as tested in a laboratory setting.

METHODS

Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, two authors conducted a systematic review exploring the biomechanical properties of ACL graft sources (querying PubMed, Cochrane, and Embase databases). Using the keywords "anterior cruciate ligament graft," "biomechanics," and "biomechanical testing," relevant articles of any level of evidence were identified as eligible and included if they reported on the biomechanical properties of skeletally immature or mature ACL grafts solely and if the grafts were studied in vitro, in isolation, and under similar testing conditions. Studies were excluded if performed on both skeletally immature and mature or non-human grafts, or if the grafts were tested after fixation in a cadaveric knee. For each graft, failure load, stiffness, Young's modulus, maximum stress, and maximum strain were recorded.

FINDINGS

Twenty-six articles were included. Most studies reported equal or increased biomechanical failure load and stiffness of their tested bone-patellar tendon-bone, hamstring, quadriceps, peroneus longus, tibialis anterior and posterior, Achilles, tensor fascia lata, and iliotibial band grafts compared to the native ACL. All recorded biomechanical properties had similar values between graft types.

INTERPRETATION

Most grafts used for ACL reconstruction are biomechanically superior to the native ACL. Utilizing a proper graft, combined with a standard surgical technique and a rigorous rehabilitation before and after surgery, will improve outcomes of ACL reconstruction.

Bench to Bedside: A Multidisciplinary Approach toward the Unknowns after ACL Injuries to Drive Individual Success

ACL injury and surgery are increasing in prevalence. Several challenges exist that can be obstacles to an individual achieving success after ACL surgery. A knowledge of these risk factors alongside a multidisciplinary collaborative team approach can result in a greater likelihood of achieving individual success after ACL surgery.

Dynamic tensile properties of porcine knee ligament

BACKGROUND

The knee plays an essential role in movement. There are four major ligaments in the knee which all have crucial functionalities for human activities. The anterior cruciate ligament (ACL) is the most commonly injured ligament in the knee, especially in athletes.

OBJECTIVE

The aim of this study was to investigate the dynamic tensile response of the porcine ACL at strain rates from 800 to 1500 s-1 for simulations of acute injury from sudden impact or collision.

METHODS

Split Hopkinson Tension Bar (SHTB) was utilized to create a dynamic tensile wave on the ACL. Stress-strain curves of strain rates between 800 s-1 to 1500 s-1 were recorded.

RESULTS

The results demonstrated that the elastic modulus of the porcine ACL at higher strain rates was six to eight times higher than that of porcine and human specimens at quasi-static strain rate. However, the failure stress was quite similar while the strain was much smaller than that at the lower strain rate.

CONCLUSIONS

ACL is highly strain rate sensitive and easier to break with lower failure strain when the strain rates increased to more than 1000 s-1. The stress-strain curves indicated that the sketching crimps at the slack region did not happen but switched to the sliding process of collagen fibers and was accompanied by some ruptures, which can develop into tears when strain and stress were large enough. On the other hand, the viscoelastic properties of the ligament, depending on the proteoglycan matrix and the cross-link, showed a limited value in the studied strain rate range.

Does Hamstring Graft Size Affect Functional Outcome and Incidence of Revision Surgery After Primary Anterior Cruciate Ligament (ACL) Reconstruction?

Purpose

The primary outcome measure of this study was to determine the effect of hamstring graft size on the functional outcome of arthroscopic anterior cruciate ligament reconstruction (ACL-R) and the secondary outcome was to ascertain the effect on revision surgery at the two-year follow-up.

Methods

This is a prospective comparative study of 144 consecutive patients undergoing primary ACL reconstruction using a hamstring autograft. All patients underwent graft harvesting and ACL reconstruction with the standard technique. The graft diameter was recorded intraoperatively using a graft sizer. All patients were followed up with the Knee Injury and Osteoarthritis Outcome Score (KOOS) recorded at preop, six weeks, six months, one year, and two years and whether they underwent revision during this period was documented.

Results

The mean KOOS for patients with a ≤ 7mm graft diameter was 80.5±13.1, which was significantly lower compared to those with graft > 7 mm of 88.3±8.5, respectively (p<0.001) at the two years follow-up. Patients with graft ≤ 7mm did poorly, especially with mean KOOS subscores of sports and recreation and quality of life (p<0.05). Twenty-three point one percent (23.1%; 3 out 13) of patients with a graft < 7mm underwent revision, whereas only 5.8% and 2.6% of patients underwent revision with a graft diameter of 7.1-8.0 and 8.1-9.0 (p=0.027).

Conclusions

The smaller Hamstring graft diameter leads to poorer functional outcomes of the patient’s ACL reconstruction. Though the number of revisions was high among those with a graft diameter of ≤ 7mm, multicentric studies with many revisions are required to confirm the relation.

The Development of a Gracilis and Quadriceps Tendons Calibration Device for Uniaxial Tensile Tests

To determine the biomechanical properties of the distal tendon of the gracilis muscle and the upper third of the quadriceps femoris muscle used for reconstruction of the medial patellofemoral ligament (MPFL), it is necessary to develop a calibration device for specimen preparation for uniaxial tensile tests. The need to develop this device also stems from the fact that there is currently no suitable regulatory or accurate protocol by which soft tissues such as tendons should be tested. In recent studies, various methods have been used to prepare test specimens, such as the use of different ratios of gauge lengths, different gripping techniques, etc., with the aim of obtaining measurable and comparable biomechanical tissue properties. Since tendons, as anisotropic materials, have viscoelastic properties, the guideline for manufacturing calibrator devices was the ISO 527-1:1993 standard, used for testing polymers, since they also have viscoelastic behaviour. The functionality of a calibrator device was investigated by preparing gracilis and quadriceps tendon samples. Fused deposition modeling (FDM) technology was used for the manufacturing of parts with complex geometry. The proposed calibrator could operate in two positions, horizontal and vertical. The maximum gauge length to be achieved was 60 mm, with the maximum tendon length of 120 mm. The average preparation time was 3 min per tendon. It was experimentally proven that it is possible to use a calibrator to prepare tendons for tensile tests. This research can help in the further development of soft tissue testing devices and also in the establishment of standards and exact protocols for their testing.

Effects of and Response to Mechanical Loading on the Knee

Mechanical loading to the knee joint results in a differential response based on the local capacity of the tissues (ligament, tendon, meniscus, cartilage, and bone) and how those tissues subsequently adapt to that load at the molecular and cellular level. Participation in cutting, pivoting, and jumping sports predisposes the knee to the risk of injury. In this narrative review, we describe different mechanisms of loading that can result in excessive loads to the knee, leading to ligamentous, musculotendinous, meniscal, and chondral injuries or maladaptations. Following injury (or surgery) to structures around the knee, the primary goal of rehabilitation is to maximize the patient's response to exercise at the current level of function, while minimizing the risk of re-injury to the healing tissue. Clinicians should have a clear understanding of the specific injured tissue(s), and rehabilitation should be driven by knowledge of tissue-healing constraints, knee complex and lower extremity biomechanics, neuromuscular physiology, task-specific activities involving weight-bearing and non-weight-bearing conditions, and training principles. We provide a practical application for prescribing loading progressions of exercises, functional activities, and mobility tasks based on their mechanical load profile to knee-specific structures during the rehabilitation process. Various loading interventions can be used by clinicians to produce physical stress to address body function, physical impairments, activity limitations, and participation restrictions. By modifying the mechanical load elements, clinicians can alter the tissue adaptations, facilitate motor learning, and resolve corresponding physical impairments. Providing different loads that create variable tensile, compressive, and shear deformation on the tissue through mechanotransduction and specificity can promote the appropriate stress adaptations to increase tissue capacity and injury tolerance. Tools for monitoring rehabilitation training loads to the knee are proposed to assess the reactivity of the knee joint to mechanical loading to monitor excessive mechanical loads and facilitate optimal rehabilitation.

Development of a 3D Printed Double-Acting Linear Pneumatic Actuator for the Tendon Gripping

The lack of standardization in tissue testing procedures results in a variety of custom-made devices. In the case of the determination of the mechanical properties of tendons, it is sometimes necessary to adapt the existing laboratory equipment for conducting experiments when specific commercial equipment is not applicable to solve issues such as proper gripping to prevent tendon slipping and rupturing, gripping control and manoeuvrability in case of tendon submerging and without contamination of the testing liquid. This paper presents the systematic development, design, and fabrication using 3D printing technology and the application of the double-acting linear pneumatic actuator to overcome such issues. It is designed to do its work submerged in the Ringers' solution while gripping the tendon along with the clamps. The pneumatic foot valve unit of the Shimadzu AGS-X tensile testing machine controls the actuator thus preventing Ringers' solution to be contaminated by the machine operator during specimen set-up. The actuator has a length of 60 mm, a bore of 50 mm, and a stroke length of 20 mm. It is designed to operate with an inlet pressure of up to 0.8 MPa. It comprises the cylinder body with the integrated thread, the piston, the piston head, and the gripper jaw. Fused deposition modeling (FDM) has been used as the 3D printing technique, along with polylactic acid (PLA) as the material for 3D printing. The 3D printed double-acting linear pneumatic actuator was developed into an operating prototype. This study could open new frontiers in the field of tissue testing and the development of similar specialized devices for medical purposes.

Biomechanical Strength of All-Inside ACL Reconstruction Grafts Using Side-to-Side and Backup Fixation

Background:

The all-inside anterior cruciate ligament reconstruction (ACLR) procedure uses a single hamstring tendon folded twice and secured to itself to form a 4-stranded graft. There are several possible configurations for preparing the graft.

Purpose:

To investigate the biomechanical properties of a new graft preparation technique in comparison with 2 commonly used configurations.

Study Design:

Controlled laboratory study.

Methods:

Five porcine flexor tendons were prepared into the test graft configuration: side-to-side fixation with a backup fixation at the button loop (graft M). The test configuration was compared with the results of a previous study that included grafts with simple interrupted sutures (graft A; n = 5) and end-to-end fixation (graft C; n = 5). All grafts were subjected to the same mechanical testing protocol to determine the mean failure load, stiffness, rate of elongation, and total elongation during both cyclic loading and pull to failure. Differences between groups were evaluated.

Results:

Graft A had a significantly lower failure load (637 ± 99 N) compared with graft M (883 ± 66 N; P = .002) and graft C (846 ± 26 N; P = .002). Graft A also had significantly lower stiffness (166 ± 12 N/mm) compared with graft M (215 ± 8 N/mm; P < .001) and graft C (212 ± 11 N/mm; P < .001). Graft C had a significantly lower elongation during cyclic loading (3.42 ± 0.24 mm) compared with graft M (4.37 ± 0.74 mm; P = .026) and graft A (4.90 ± 0.88 mm; P = .006). The unsecured fixation was the weakest graft, with the lowest failure load and stiffness. The new side-to-side configuration and end-to-end configuration were equally strong.

Conclusion:

The new side-to-side configuration was not biomechanically superior to the end-to-end configuration; however, they were both stronger than unsecured fixation.

Clinical Relevance:

As the all-inside ACLR is gaining popularity, this study provides surgeons with a new method of preparing grafts and evaluates the method with respect to currently used configurations.

Gracilis and semitendinosus moment arm decreased by fascial tissue release after hamstring harvesting surgery: a key parameter to understand the peak torque obtained to a shallow angle of the knee

PURPOSE

Semitendinosus and gracilis muscles whose tendons are used in surgical reconstruction of the anterior cruciate ligament maintain their contractile ability, but the peak torque angle of hamstring muscles shifted to a shallow angle postoperatively. The goal was to quantify the influence of the myofascial structures on instantaneous moment arms of knee muscles to attempt explaining the above-mentioned post-surgical observations.

METHODS

Hamstring harvesting procedures were performed by a senior orthopaedic surgeon on seven lower limbs from fresh-frozen specimens. Femoro-tibial kinematics and tendons excursion were simultaneously recorded at each step of the surgery.

RESULTS

No significant difference was demonstrated for instantaneous moment arm of gracilis during anterior cruciate ligament surgery (84% of the maximum intact values; P ≥ 0.05). The first significant semitendinosus moment arm decrease was observed after tendon harvesting (61% of the maximum intact values; p ≤ 0.005). After hamstring harvesting, the maximum and minimum moment arm (both gracilis and semi tendinosus) shifted to a shallow angle and 90°, respectively.

CONCLUSION

Moment arm modifications by paratenons and the loose connective tissue release are essential to understand the peak torque obtained to a shallow angle.

LEVEL OF EVIDENCE

Basic science study, biomechanics.

A study of knee anterior cruciate ligament biomechanics with respect to energy and relaxation

BACKGROUND

This research aimed to study the biomechanical properties of sheep tendon under torsion and the tendon energy absorption performance with an externally imposed initial force.

METHODS

Tendons of nine healthy knees of sheep were investigated. In both tests, we investigated energy and relaxation at rotations of 0°, 90°, 180°, and 360°. For both tensile force and tensile displacement at a sampling period of 100 milliseconds, the maximum value of 89 N was selected as the maximum tension state for 600 s of relaxation duration for testing relaxation, and analysed of the average force of the last 30 s.

FINDINGS

The difference of energy levels of the tendons are significant between twisted groups (180° and 360°) and untwisted group (0°) (P < 0.05); The relaxation force decreases significantly with twisted groups (90°,180°, and 360°) and untwists group (0°) (P < 0.05). The nine-group tendons show no significant difference at torsion 90° and 180° (P = 0.466). Peak force test shows significant differences between the twisted groups (90°,180°, and 360°) and untwisted group (0°) (P < 0.05).

INTERPRETATION

The torsion tendon has lower energy absorption and relaxation than the untwisted counterparts; thus, it may be more prone to damage. These results are useful for providing guidance on anterior cruciate ligament reconstruction.

Biomechanical comparison of tenodesis reconstruction for subtalar instability: a finite element analysis

Background

There are several types of tenodesis reconstruction designed for subtalar instability. However, no comprehensive comparison has been conducted among these procedures in terms of their correcting power so far. The objective of this study is to evaluate the biomechanical behaviors of 5 representative procedures through finite element analysis.

Methods

Finite element models were established and validated based on one of our previous studies. The Pisani interosseous talocalcaneal ligament (ITCL) reconstruction, Schon cervical ligament (CL) reconstruction and Choisne calcaneofibular ligament (CFL) reconstruction were compared on the model with the CFL, ITCL and CL sectioned. The Schon triligamentous reconstruction and Mann triligamentous reconstruction were compared on the model with the CFL, ITCL and CL, as well as the ATFL sectioned. The inversion and external/internal rotation were quantified at different ankle positions based on the rotational moment. Then, the stress in ligaments and reconstructed grafts and the contact characteristics of the subtalar joint under inversional stress test were calculated and compared accordingly.

Results

For single ligament reconstruction, the Choisne CFL reconstruction provided the greatest degree of correction for subtalar instability, followed by the Schon CL reconstruction and then the Pisani ITCL reconstruction. For triligamentous reconstruction, the Mann procedure outperformed the Schon procedure in alleviating the subtalar instability.

Conclusion

The finite element analysis showed that the Choisne CFL reconstruction and Mann triligamentous reconstruction provided the greatest degree of immediate postoperative subtalar stability. However, both procedures could not restore the biomechanical behaviors of the subtalar joint to normal. The long-term efficacy of these procedures warrants further investigation using a substantially larger sample of clinical cases.

Presoaking of Semitendinosus Graft With Vancomycin Does Not Alter Its Biomechanical Properties: A Biomechanical In Vitro-Controlled Study Using Graft From Living Donors

PURPOSE

To compare the biomechanical properties of human semitendinosus graft presoaked with or without vancomycin under a load to failure tensile test.

METHODS

Thirty semitendinosus grafts harvested during anterior cruciate ligament reconstruction were included. These were dissected equally into 2 halves and subsequently randomly allocated to a vancomycin group and to a control group. A digital caliper was used to precisely measure each samples thickness, length, and width. For the vancomycin group, samples were presoaked in a solution of 5 mg/mL vancomycin for a duration of 10 minutes and the control group samples were presoaked in a physiological serum equally for 10 minutes. Mechanical testing was performed on a universal testing machine (Instron 5566-A) after a preconditioning of 10 cycles of 1 mm extension and a progression of 10 mm/min to failure for each sample. The stress-strain curve was obtained to determine the elastic modulus (Young's modulus), the ultimate tensile stress, the ultimate tensile elongation (UTE) before failure and the elasticity limit.

RESULTS

For the control group, the average Young's modulus value was 4.8 ± 0.8, the average UTS was 25.2 ± 5.2 MPa, the average percentage of UTE was 78 ± 17%, and the average elasticity limit value was 17.3 ± 5.3 MPa. For the vancomycin group, the average Young's modulus value was 4.7 ± 0.9, the average ultimate tensile stress was 24.1 ± 6.1 MPa, the average percentage of UTE was 82 ± 14%, and the average elasticity limit value was 18.5 ± 5.9 MPa. No significant difference was observed between the 2 groups for all investigated parameters.

CONCLUSIONS

Presoaking of human semitendinosus graft with vancomycin does not alter its biomechanical properties.

CLINICAL RELEVANCE

This study demonstrates that vancomycin presoaking used to prevent post-anterior cruciate ligament reconstruction septic arthritis does not affect immediate biomechanical properties of semitendinosus tendons.

The effect of anterolateral ligament reconstruction on knee constraint: A computer model-based simulation study

BACKGROUND

To determine the influence of anterolateral ligament reconstruction (ALLR) on knee constraint through the analysis of knee abduction (valgus) moment when the knee is subjected to external translational (anterior) or rotational (internal) loads.

METHODS

A knee computer model simulated from a three-dimensional computed tomography scan of healthy male was implemented for this study. Three groups were designed: (1) intact knee, (2) combined Anterior Cruciate Ligament (ACL) and Antero-Lateral Complex (ALC) deficient knee, and (3) combined ACL and Antero- lateral Ligament (ALL) reconstructed knee. The reconstructed knee group was subdivided into four groups according to attachment of reconstructed anterolateral ligament to the femoral epicondyle. Each group of simulated knees was placed at 0°, 10°, 20°, 30°, 40° and 50° of knee flexion. For each position an external anterior (drawer) 90-N force or a five-newton meter internal rotation moment was applied to the tibia. The interaction effect between the group of knees and knee flexion angle (0-50°) on knee kinematics and knee abduction moment under external loads was tested.

RESULTS

When reconstructed knees were subjected to a 90-N anterior force or a five-newton meter internal rotation moment there was significant reduction in anterior translation and internal rotation compared with deficient knees. Only the ALLR procedure using posterior and proximal femoral attachment sites for graft fixation combined with ACL reconstruction allowed similar mechanical behavior to that observed in the intact knee.

CONCLUSIONS

Combined ACL and ALLR using a minimally invasive method in an anatomically reproducible manner prevents excessive anterior translation and internal rotation. Using postero-proximal femoral attachment tunnel for reconstruction of ALL does not produce overconstraint of the lateral tibiofemoral compartment.

ACL reconstruction using a quadruple semitendinosus graft with cortical fixations gives suitable isokinetic and clinical outcomes after 2 years

PURPOSE

The objective of this single-center randomized single-blinded trial was to assess the hypothesis that anterior cruciate ligament reconstruction (ACLR) using a four-strand semitendinosus (ST) graft with adjustable femoral and tibial cortical fixation produced good outcomes compared to an ST/gracilis (ST/G) graft with femoral pin transfixation and tibial bioscrew fixation. Follow-up was 2 years.

METHODS

Patients older than 16 years who underwent primary isolated ACLR included for 1 year until August 2017 were eligible. The primary outcome measures were the subjective International Knee Documentation Committee (IKDC) score, isokinetic muscle strength recovery, and return to work within 2 years. The study was approved by the ethics committee.

RESULTS

Of 66 eligible patients, 60 completed the study and were included, 33 in the 4ST group and 27 in the ST/G group. Mean age was 30.5 ± 8.9 years in the 4ST group and 30.3 ± 8.5 in the ST/G group (n.s.). No significant between-group differences were found for mean postoperative subjective IKDC (4ST group, 80.2 ± 12.5; ST/G group, 83.6 ± 13.6; n.s.), side-to-side percentage deficits in isokinetic hamstring strength (at 60°/s: ST group, 17% ± 16%; ST/G group, 14% ± 11%; n.s.) or quadriceps strength (at 60°/s: ST group, 14% ± 12%; ST/G group, 19% ± 17%; n.s.), return to work, pain during physical activities, side-to-side differential laxity, balance, loss of flexion/extension, or surgical complications.

CONCLUSION

This trial demonstrates that functional outcomes after 4ST for ACLR with cortical fixations could be as good, although not better, than those obtained using ST/G. The 4ST technique spares the gracilis tendon, which thus preserves the medial sided muscle and thereby could improve function and limit donor-side morbidity.

LEVEL OF EVIDENCE

Level I.

Biomechanical effects of stitches on the intra-articular mid-substance of quadruple hamstring-tendon grafts for anterior cruciate ligament reconstruction - a pilot comparative cadaveric study

Background

There is little data in the literature regarding the preparation methods of the intra-articular portion of quadruple hamstring-tendon grafts for anterior cruciate ligament (ACL) reconstruction. The aim of this study was to compare the biomechanical properties of a sutured transplant to that of a non-sutured transplant. The hypothesis was that adding stitches to the intra-articular portion of the graft increased its resistance.

Method

A comparative cadaveric study was carried out on five pairs of knees. The average age of the cadavers was 68 years. The exclusion criterion was past knee surgery. In the Sutured Group (SG) two stitches were made on the grafts. No stitches were made on the grafts of the Non-sutured Group (NSG). A tensile failure test was carried out using an Instron® loading machine. The maximal load to failure and stiffness were recorded and we observed the mode of failure for each graft. Statistical analysis was performed using the Wilcoxon rank sum test. Level of significance was set at p < 0.05.

Results

The hypothesis proposed was not confirmed; adding stitches to the intra-articular portion of the four-strand hamstring-tendon graft does not increase its biomechanical properties. The maximal load to failure was 233.5 N ± 40.6 (186.7–274.5 N) for the NSG, 19.6% higher than for the SG which was 195.2 N ± 42.9 (139.0–238.2 N). Nevertheless, the difference observed was not statistically significant (p = 0.188). The stiffness of the grafts for the NSG was 23.5 N/mm ± 5.3 (17.8–29 N/mm) and 19.7 N/mm ± 5.5 (13.2–24.7 N/mm) for the SG grafts. Overall stiffness values for the NSG were 19% higher than those of the SG; however, the results were not statistically significant (p = 0.438). The failure mode was a rupture at the fixation point except for one sample from the SG which failed at an intra-articular stitch.

Conclusion

Whilst the initial hypothesis was not verified, nevertheless, the maximal loads to failure and stiffness were approximately 20% higher when there were no intra-articular stitches compared to the situation where stitches were added to the intra-articular portion of the graft. This was a cadaveric pilot study and, therefore, whilst we are not able to extend our results to clinical practice, the outcomes would indicate the need for further development of this and related protocols deriving from the question of whether there is weakening the graft when adding stitches to its mid-substance. These results remain to be confirmed by further research.

Biomechanical Comparison of Graft Preparation Techniques for All-Inside Anterior Cruciate Ligament Reconstruction

Background:

All-inside anterior cruciate ligament reconstruction (ACLR) is an emerging technique used to treat ACL injuries. The all-inside technique uses a 4-stranded graft made from a single tendon that is looped on itself. The 4 strands of the graft must be secured to each other to become a closed-loop structure. Various suture configurations exist to secure the graft to adjustable loop devices, and there is a lack of data to support one technique over another. In addition to the primary sutures used to fasten the graft together, accessory sutures can be tied over the button as secondary fixation.

Purpose:

To evaluate biomechanical properties of 4-stranded grafts prepared in 5 different configurations.

Study Design:

Controlled laboratory study.

Methods:

Porcine flexor tendons (N = 25) were prepared in 5 different configurations (n = 5 tendons per group): simple-interrupted sutures (unsecured fixation), side-to-side fixation with and without secondary fixation, and end-to-end fixation with and without secondary fixation. The grafts were put through the same mechanical testing protocol (cyclic loading, pull to failure) to measure average load at graft failure, average displacement at failure, average stiffness, and average elongation rate. Differences between graft preparation techniques were investigated using 1-way analyses of variance (ANOVAs) with post hoc t tests (P < .05).

Results:

Significant 1-way ANOVAs for each biomechanical property were found. Unsecured fixation was the weakest graft preparation with the lowest stiffness (167 ± 12 N/mm), lowest ultimate failure load (637 ± 99 N), and highest elongation rate (0.0033 ± 0.0007 mm/s). End-to-end fixation without secondary fixation showed the highest ultimate failure load (846 ± 26 N), highest stiffness (212 ± 10 N/mm), and lowest rate of elongation (0.0025 ± 0.0001 mm/s). End-to-end fixation, both with and without secondary fixation, as well as side-to-side fixation with secondary fixation showed significantly higher ultimate failure loads than grafts with unsecured fixation. End-to-end fixation performed better than side-to-side fixation; however, for most variables, the difference was not statistically significant. Secondary fixation did not provide significant improvement.

Conclusion:

The all-inside ACL graft with simple-interrupted sutures is biomechanically inferior to a graft that has its free ends secured to the adjustable tibial loop. Adding secondary fixation to the tibial button does not significantly change the biomechanical properties. Further clinical studies are required to determine whether these findings translate into differences in clinical outcome.

Clinical Relevance:

All-inside ACLR is gaining popularity in hamstring ACL reconstructive techniques. These results provide surgeons with guidance on the best graft preparation method when using a single quadrupled hamstring tendon graft.

Every layer of quadriceps tendon's central and medial portion offers similar tensile properties than Hamstrings or Ilio-Tibial Band Grafts

PURPOSE

The aim of our cadaveric study was to compare the mechanical properties of different parts of the quadriceps' tendon in a load to failure analysis as compared to three other, and most common types of grafts that are used to perform ligament's reconstruction.

METHODS

Ten fresh-frozen cadavers (5 women, 5 men) were selected from our anatomical department. Mean age at death was 64 years (48-87 years). Tendons were harvested to prepare (1) different quadriceps tendon's specimens: lateral portion (QTlat), medial portion superficial layer (QTMsup) and deep layer (QTMdeep) and central portion superficial (QTCsup) and deep layers (QTCdeep) (2) Patellar Tendon (PT), (3) Gracilis+Semi-Tendinosus specimens (GST). Specimens were stored at - 40 °C in a freezing solution. Specimens were securely attached to a dedicated loading platform, measurements were done using a validated software. Load to failure testing was then carried out. Young's Elastic moduli, ultimate Stress (MPa) and Deformation (%) were analysed.

RESULTS

The elastic moduli of the PT was significantly higher than all other grafts, all medial and central QT layers (superficial and deep) were significantly higher than its lateral part (QTlat). In terms of Ultimate Stress, all grafts were significantly greater than QTlat, PT and GST were significantly superior to QT central portions and to ITB but there did not differ with the medial portion of QT. ITB ultimate stress values were significantly higher than QTlat. The ultimate deformations of all grafts were similar.

CONCLUSIONS

This study provides reference values in in order to characterize different parts of the QT that presents anatomically and Mechanically with complex characteristics. Every Layer of Quadriceps Tendon's Central and Medial Portion Offered Similar Mechanical Properties than Two Strand Hamstrings or Ilio-Tibial Band.

Correlation between anthropometric measurements and activity level on length and diameter of semitendinosus tendon autograft in knee ligament surgery: A prospective observational study

Introduction: Preoperative estimation of graft parameters can be useful while using hamstring grafts in knee ligament surgeries. Anthropometric parameters may be an easy way to predict the length and diameter of hamstring tendons. A prospective study was conducted to find the correlation between different anthropometric parameters and activity level of the patient on the length and diameter of the graft. Separate regression equations for males and females were also derived for easy prediction. Methods: Data were obtained from 95 patients who underwent arthroscopic anterior cruciate ligament reconstruction with autologous hamstring tendon graft. Variables studied were age, sex, height, weight, body mass index (BMI), thigh circumference, thigh length, Tegner activity level, diameter (double and quadruple) and length of semitendinosus tendon graft. Results: Height of the patient had strong correlation with graft length (r = 0.41, p < 0.001), double diameter (r = 0.29, p = 0.008) and quadruple diameter (r = 0.3, p = 0.006). Weight of the patients had strong positive correlation with graft length (r = 0.34, p = 0.002) and quadruple diameter (r = 0.34, p = 0.002). Thigh length was found to be positively correlating with graft length (r = 0.43, p < 0.001), double diameter (r = 0.29, p = 0.007) and quadruple diameter of graft (r = 0.34, p = 0.002). BMI and thigh circumference of the patients were not found to correlate with graft size. Male patients were found to have longer semitendinosus graft and larger double and quadruple diameter of the graft. There was no association between the Tegner activity scale and graft size. Regression equations between graft length and quadruple diameter and the anthropometric parameters are also derived. Conclusion: Height, weight and thigh length are useful anthropometric parameters in the prediction of hamstring tendon size. However, the patient’s Tegner activity level was not found to be associated with size of the hamstring tendon.

Current Progress in Tendon and Ligament Tissue Engineering

Background

Tendon and ligament injuries accounted for 30% of all musculoskeletal consultations with 4 million new incidences worldwide each year and thus imposed a significant burden to the society and the economy. Damaged tendon and ligament can severely affect the normal body movement and might lead to many complications if not treated promptly and adequately. Current conventional treatment through surgical repair and tissue graft are ineffective with a high rate of recurrence.

Methods

In this review, we first discussed the anatomy, physiology and pathophysiology of tendon and ligament injuries and its current treatment. Secondly, we explored the current role of tendon and ligament tissue engineering, describing its recent advances. After that, we also described stem cell and cell secreted product approaches in tendon and ligament injuries. Lastly, we examined the role of the bioreactor and mechanical loading in in vitro maturation of engineered tendon and ligament.

Results

Tissue engineering offers various alternative ways of treatment from biological tissue constructs to stem cell therapy and cell secreted products. Bioreactor with mechanical stimulation is instrumental in preparing mature engineered tendon and ligament substitutes in vitro.

Conclusions

Tissue engineering showed great promise in replacing the damaged tendon and ligament. However, more study is needed to develop ideal engineered tendon and ligament.

The effect of cyclic knee motion on the elongation of four-strand hamstring autograft in anterior cruciate ligament reconstruction: an in-situ pilot study

Background

Pretension of the viscoelastic graft by cyclic knee motion has been confirmed to decrease the graft creep and improve the outcome of anterior cruciate ligament (ACL) reconstruction. The purpose of the present study was to investigate the effect of cyclic knee motion on the elongation of the four-strand hamstring tendon autograft in situ and to explore the stable level cycle, in which the tendon length achieved a stable level.

Methods

The study was performed with 53 consecutive patients undergoing transtibial ACL reconstruction with four strand hamstring tendon from Aug 2013 to Apr 2015. 43 males and 10 females were included with mean age of 29 ± 10 years. The pretension of the tendons was operated by cyclical knee motion ranging from 0 to 110°after the femoral fixation with Endo-button. The tendon length after 10, 20, 30 and 40 cycles was measured respectively and compared by repeated measure ANOVA. Then multivariate logistic regression was used to investigate the effect of the patients’ parameters (age, gender, height, body weight, tendon length, etc.) on the elongation of the graft and the stable level cycle.

Results

The mean lengthening of the graft at 10, 20, 30 and 40 times was 3.0 ± 1.4 mm, 4.3 ± 1.5 mm, 4.8 ± 1.7 mm and 4.8 ± 1.8 mm respectively. No significant correlation was found between the elongation and the patients’ parameters. There was significant difference of the tendon length from 0 to 30 cycles (F = 264.8, df = 1.95, p<0.001). However, the tendon length achieved a stable level after 30 cycles and the median elongation from 30 cycles to 40 cycles was 0 (0–1) mm with no significant difference (F = 2.039, p = 0.159). The male and female tendon length achieved to a stable level at 20 cycles and 30 cycles respectively but with no significant difference (p = 0.074).

Conclusions

The four-strand hamstring tendon was elongated after cyclic knee motion and the elongation achieved a stable level after 30 cycles for the transtibial technique. Both of the tendon elongation and the stable level cycle were not correlated with patients’ gender, age, preoperative duration, graft diameter and length.

A bigger suture diameter for anterior cruciate ligament all-inside graft link preparation leads to better graft stability: An anatomical specimen study

BACKGROUND

In anterior cruciate ligament reconstruction, different suture types are used for graft link preparation. Thus the aim of this study was to determine whether differences in the diameter of the suture used influence biomechanical stability of the prepared graft. We hypothesized that the use of a greater suture diameter leads to a higher load to failure rate in tested graft links.

METHODS

In an anatomic specimen study, ligament preparation was enrolled in 15 cadaveric knees. The material used was the semitendinosus/gracilis tendon, which was fresh frozen (-80°) after harvesting for four weeks. The grafts were then defrosted, randomized into two groups and prepared with the same technique: 12 with a suture; FiberWire No. 2 and 12 with a FiberWire No. 0.

RESULTS

Overall, the group using FiberWire No. 2 presented with a mean load to failure rate of 730.67N, mean overall final elongation of the graft was 5.98mm. In the FiberWire No. 0 group mean load to failure was with a mean overall elongation of the graft of 6.96mm. Significant differences (P=0.006) between the two groups with regard to the load to failure rate were found, with FiberWire No. 2 withstanding forces better. There was no difference in elongation of the grafts or mode to failure between the two groups.

CONCLUSIONS

Graft preparation with a bigger suture type is recommended to gain better load to failure rates, also in smaller-diameter grafts. Regarding the elongation rate, different suture types did not influence the outcome.

LEVEL OF EVIDENCE

Anatomical specimen study, Level III.

Mechanical Analysis of Extra-Articular Knee Ligaments. Part two: Tendon grafts used for knee ligament reconstruction

OBJECTIVES

The aim of this study was to provide information about the mechanical properties of grafts used for knee ligament reconstructions and to compare those results with the mechanical properties of native knee ligaments.

METHODS

Eleven cadaveric knees were dissected for the semitendinosus, gracilis, iliotibial band (ITB), quadriceps and patellar tendon. Uniaxial testing to failure was performed using a standardized method and mechanical properties (elastic modulus, ultimate stress, ultimate strain, strain energy density) were determined.

RESULTS

The elastic modulus of the gracilis tendon (1458±476MPa) (P<0.001) and the semitendinosus tendon (1036±312MPa) (P<0.05) was significantly higher than the ITB (610±171MPa), quadriceps tendon (568±194MPa), and patellar tendon (417±107MPa). In addition, the ultimate stress of the hamstring tendons (gracilis 155.0±30.7MPa and semitendinosus 120.1±30.0MPa) was significantly higher (P<0.001, respectively P<0.05), relative to the ITB (75.0±11.8MPa), quadriceps tendon (81.0±27.6MPa), and patellar tendon (76.2±25.1MPa). A significant difference (P<0.05) could be noticed between the ultimate strain of the patellar tendon (24.6±5.9%) and the hamstrings (gracilis 14.5±3.1% and semitendinosus 17.0±4.0%). No significant difference in strain energy density between the grafts was observed.

CONCLUSIONS

Material properties of common grafts used for knee ligament reconstructions often differ significantly from the original knee ligament which the graft is supposed to emulate.

Exploring the in vitro and in vivo compatibility of PLA, PLA/GNP and PLA/CNT-COOH biodegradable nanocomposites: Prospects for tendon and ligament applications

Anterior cruciate ligament (ACL) reconstructive surgeries are the most frequent orthopedic procedures in the knee. Currently, existing strategies fail in completely restoring tissue functionality and have a high failure rate associated, presenting a compelling argument towards the development of novel materials envisioning ACL reinforcement. Tendons and ligaments, in general, have a strong demand in terms of biomechanical features of developed constructs. We have previously developed polylactic acid (PLA)-based biodegradable films reinforced either with graphene nanoplatelets (PLA/GNP) or with carboxyl-functionalized carbon nanotubes (PLA/CNT-COOH). In the present study, we comparatively assessed the biological performance of PLA, PLA/GNP, and PLA/CNT-COOH by seeding human dermal fibroblasts (HFF-1) and studying cell viability and proliferation. In vivo tests were also performed by subcutaneous implantation in 6-week-old C57Bl/6 mice. Results showed that all formulations studied herein did not elicit cytotoxic responses in seeded HFF-1, supporting cell proliferation up to 3 days in culture. Moreover, animal studies indicated no physiological signs of severe inflammatory response after 1 and 2 weeks after implantation. Taken together, our results present a preliminary assessment on the compatibility of PLA reinforced with GNP and CNT-COOH nanofillers, highlighting the potential use of these carbon-based nanofillers for the fabrication of reinforced synthetic polymer-based structures for ACL reinforcement. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2182-2190, 2017.

Primary anterior cruciate ligament reconstruction: perioperative considerations and complications

Anterior cruciate ligament (ACL) injuries are among the most commonly studied orthopaedic injuries. Despite having an excellent prognosis, complications do occur. The timely recognition and management of complications is imperative to ensure the success of reconstruction. Avoiding such complications requires thorough preoperative planning, proficient technical skills to properly manage intraoperative complications, and an extensive knowledge of possible postoperative complications.

Joint stability after canine cranial cruciate ligament graft reconstruction varies among femoral fixation sites

OBJECTIVE

To quantify stability in cranial cruciate ligament (CrCL) deficient canine stifles with hamstring grafts affixed at 3 femoral locations.

STUDY DESIGN

Canine stifle motion study using a multi-cohort, repeated measures design.

SAMPLE POPULATION

27 canine cadaver stifles.

METHODS

Hamstring grafts (HG) were affixed at the gracilis-semitendinosus insertion and on the lateral femur (1) proximal trochlear ridge (TR), (2) craniodistal to fabella (F), or (3) condyle center (CC). Total, cranial, and caudal tibial translation and total, medial, and lateral angular displacement, with and without translational load, were quantified with the CrCL intact, transected, and reconstructed. Angular displacement was quantified from points on the distal femur and proximal tibia. Graft strain was calculated from tissue displacement measured at joint angles of 30°, 60°, 90°, and 120°.

RESULTS

Tibial translation was lowest in F constructs, which also achieved the least difference in tibial translation from intact stifles. Tibial translation was lower in intact stifles than in CrCL transected or reconstructed stifles. Less angular displacement of the proximal tibia was detected in the medial than in the lateral direction, and tibial displacement was lower in the cranial than the caudal direction. Angular displacement was lowest in the F treatment group. F constructs had the lowest graft strain at joint angles greater than 30°.

CONCLUSIONS

Femoral fixation of a canine hamstring graft craniodistal to the lateral fabella conferred the best joint stability and lowest graft strain in vitro. No fixation method restored joint stability of the intact CrCL.

Change in Size of Hamstring Grafts During Preparation for ACL Reconstruction: Effect of Tension and Circumferential Compression on Graft Diameter

BACKGROUND

There is good consensus that anterior cruciate ligament (ACL) grafts should be pretensioned to remove creep prior to implantation, but the literature contains little information on the influence of graft preparation or circumferential compression on graft size. The purpose of this study was to investigate how the size of hamstring allografts changes as they are prepared for ACL reconstruction. We hypothesized that grafts decrease in diameter as they are prepared with both tension and circumferential compression. We also investigated the interrater reliability of graft diameter measurements during each step of graft preparation.

METHODS

Twenty pairs of fresh-frozen human hamstring tendons obtained from an allograft supplier were prepared in a standardized fashion for ACL reconstruction (suturing followed by longitudinal tensioning followed by circumferential compression followed by relaxation). Four blinded raters measured each graft in a sequential manner after each graft preparation step. Interrater reliability was assessed using the intraclass correlation coefficient ICC(2,1). The mean allograft diameter at each time point was calculated and compared across all time points using repeated-measures analysis of variance (ANOVA).

RESULTS

Subjecting the grafts to both tension and circumferential compression significantly decreased their mean diameter (to 7.38 mm compared with 8.28 mm at baseline; p = 0.044). Interrater reliability revealed almost perfect agreement at each measurement interval, with the ICC ranging from 0.933 to 0.961.

CONCLUSIONS

The average diameter of hamstring ACL grafts decreases by almost 1 mm after they are subjected to both tension and circumferential compression within a standard cylindrical sizing block.

CLINICAL RELEVANCE

Because ACL bone tunnels are drilled in 0.5-mm increments, preparing soft-tissue grafts with circumferential compression in addition to tension may allow creation of tunnels that are one to two incremental sizes smaller. This could permit less bone removal, which may be particularly applicable for certain reconstruction techniques such as pediatric, double-bundle, or revision ACL reconstruction, in which limited space is available for tunnel drilling.

Biomechanical study of ACL reconstruction grafts

There are no published studies describing the strength quadrupled gracilis tendon alone and quadrupled semitendinosus tendon alone in the configuration used for anterior cruciate ligament (ACL) reconstruction. The primary objective was to compare the mechanical properties of grafts used for ACL reconstruction during a tensile failure test. The secondary objective was to evaluate the effect of uniform suturing on graft strength. Fifteen pairs of knees were used. The mechanical properties of five types of ACL grafts were evaluated: patellar tendon (PT), sutured patellar tendon (sPT), both hamstring tendons (GST4), quadrupled semitendinosus (ST4), and quadrupled gracilis (G4). Validated methods were used to perform the tensile tests to failure and to record the results. Student's t-test was used to compare the various samples. The maximum load to failure was 630.8N (± 239.1) for the ST4, 473.5N (± 176.9) for the GST4, 413.3N (± 120.4) for the sPT, and 416.4N (± 187.7) for the G4 construct. Only the ST4 had a significantly higher failure load than the other grafts. The sPT had a higher failure load than the PT. The ST4 construct had the highest maximum load to failure of all the ACL graft types in the testing performed here. Uniform suturing of the grafts improved their ability to withstand tensile loading.

Pretensioning of Soft Tissue Grafts in Anterior Cruciate Ligament Reconstruction

To determine which preconditioning and pretensioning techniques should be applied to soft tissue grafts during anterior cruciate ligament (ACL) reconstruction to avoid loss of tension after surgery, fresh semitendinosus and tibialis anterior tendons underwent tensile mechanical testing with 4 pretensioning and/or preconditioning techniques. A mechanical tester was used to collect the data. Group I (n=5) was given only an initial 80 N pull for tensioning, Group II (n=4) was given pretensioning and initial tensioning, Group III (n=5) was given cyclic tensioning and initial tensioning, and Group IV (n=5) was given a combination of the 3 techniques. Group I lost 50% of the initial tension at 30 minutes. The residual tension in Groups II, III, and IV was significantly higher than that in Group I after 1, 10, and 30 minutes (P<.001). Group IV consistently showed significantly higher residual tension than Groups II and III after 10 and 30 minutes (P<.05). All groups experienced elongation during testing: Group I (10.8 mm)<Group IV (14.6 mm)<Group III (15.6 mm)<Group II (16.6 mm), with significant differences observed between groups (P<.05). All experimental groups showed significantly greater stiffness than the control group (Group I) (P<.001). This study confirmed that pretensioning or preconditioning after 30 minutes leaves a graft with higher residual tension. Moreover, pretensioning and preconditioning had an additive effect and resulted in significantly greater retained tension than either method performed individually. A simple pull up to 80 N before fixation does not impart sufficient tension to a graft to prevent it from failing. The authors recommend that clinicians performing ACL reconstructions with soft tissue grafts precondition or pretension the tendons before final tibial fixation to achieve greater retained tension in the graft after placement.

Gait knee kinematics after ACL reconstruction: 3D assessment

PURPOSE

While many studies about anterior-cruciate-ligament-deficient (ACLD) patients have demonstrated functional adaptations to protect the knee joint, an increasing number of patients undergo ACL reconstruction (ACLR) surgery in order to return to their desired level of activity. The purpose of this study was to compare 3D kinematic patterns between individuals having undergone ACLR with their healthy contralateral knee and a control group.

METHODS

Three-dimensional kinematic data were obtained from 15 patients pre- and post-ACLR, 15 contralateral knees and 15 healthy controls. Data were recorded during treadmill walking at self-selected speed. Flexion/extension, external/internal tibial rotation, adduction/abduction and anterior/posterior tibial translation were compared between groups.

RESULTS

ACLR knees showed a significantly higher knee-joint extension during the entire stance phase compared with ACLD knees. However, ACLR knees still showed a deficit of extension compared with healthy control knees. In the axial plane, there was no significant difference in pre- and postoperative kinematic data. Significant difference was achieved between ACLR knees and healthy control knees, specifically between 28 and 34 % and 44 and 54 % of the gait cycle. There was no significant difference in anterior-posterior translation or coronal plane between groups.

CONLUSION

Following ACL reconstruction, patients have better clinical and kinematic parameters. Despite improvements, knee kinematics during gait in the ACLR group differed from the control group. These kinematic changes could lead to abnormal loading in the knee joint and initiate the process for future chondral degeneration.

Can the gracilis be used to replace the anterior cruciate ligament in the knee? A cadaver study

PURPOSE

The purpose of this study was to evaluate whether a four-strand gracilis-only graft can be used in anterior cruciate ligament (ACL) reconstruction.

STUDY DESIGN

Cadaver study.

METHODS

This study involved 16 cadaver knees. The length and diameter of the native ACL were measured in each one. The same measurements were performed on a four-strand graft of the gracilis only, the semitendinosus only and both tendons. Student's t-test was used to compare the various conditions.

RESULTS

The average diameter of the G4 construct was 0.07 mm greater (1%) than the native ACL (p=0.044). The average cross-sectional area of the G4 construct was 1.2 mm(2) greater (3.9%) than the native ACL (p=0.049). The G4 was on average 38.9 mm longer than the intra-articular portion of the ACL (p<0.001).

CONCLUSION

A four-strand gracilis construct meets the anatomical specifications for use as an ACL reconstruction graft. By using the gracilis only, the morbidity associated with harvesting the gracilis and semitendinosus tendons should be reduced. Further studies must be performed to compare the biomechanical properties of this graft with other graft types and also to evaluate how this four-strand gracilis graft behaves in a clinical setting.

Transtibial versus anteromedial portal technique in single-bundle anterior cruciate ligament reconstruction: outcomes of knee joint kinematics during walking

BACKGROUND

In anterior cruciate ligament (ACL) reconstruction, the transtibial (TT) technique often creates a nonanatomically placed femoral tunnel, which is a frequent cause of surgical failure and postsurgical knee instability. Several studies reported that drilling the femoral tunnel through an anteromedial portal (AMP) yields a more anatomic tunnel position compared with the TT technique.

PURPOSE

To compare the effectiveness of these two surgical techniques in restoring the intact knee joint kinematics during a physiological loading situation.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty-four patients (TT, n = 12; AMP, n = 12; sex, weight, and height matched, and half with dominant leg involved) who underwent unilateral single-bundle ACL reconstruction by the same surgeon were recruited. Twenty healthy patients with no history of lower limb injuries were recruited as the control group. Tibiofemoral joint motion in 6 degrees of freedom (3 translations and 3 rotations) was determined during level walking by using a least mean square-based optimization algorithm. A redundant marker set was used to improve the accuracy of the motion analysis. Knee joint kinematics as well as spatiotemporal parameters were compared between these two techniques.

RESULTS

The AMP technique restored the anterior-posterior translation of the knee joint, while the TT technique resulted in significantly greater (TT, 22.2 mm vs controls, 13.2 mm; P < .01) anterior femoral translations than in the healthy controls during the swing phase. Excessive femoral external (tibial internal) rotation (3.8°; P < .05) was found at midstance in the knees that were reconstructed using the TT technique; using the AMP technique, the external rotation offset was greatly reduced during the stance phase. However, knees repaired using the AMP technique were significantly less extended (5°; P < .05) compared with the knees of the controls during the late stance phase. Neither surgical technique restored the superior-inferior femoral translation to the intact level during the swing phase.

CONCLUSION

The AMP technique better restores the anterior-posterior translation during the swing phase and femoral external rotation at midstance than the TT technique does. However, the AMP technique is also correlated with an extension loss during the late stance phase.

CLINICAL RELEVANCE

The AMP femoral tunnel drilling technique can improve overall knee joint stability, but the increased difficulty with full extension may need to be considered.

Influence of anthropometric features on graft diameter in ACL reconstruction

BACKGROUND

There is a paucity of literature regarding the influence of anthropometric features on the hamstring graft obtained in ACL reconstruction. This study was undertaken to assess the influence of anthropometric measurements on the graft diameter obtained at ACL reconstruction surgery within the European population. We hypothesise that anthropometric features do influence graft thickness in ACL reconstruction.

MATERIALS AND METHODS

Data from 121 consecutive patients who had undergone ACL reconstruction by the same surgeon using quadruple hamstring grafts were analysed. The body mass index (BMI), height and weight of these patients were correlated with the graft diameter obtained during surgery. Regression analysis was undertaken to assess the influence of individual anthropometric variables on the graft diameter.

RESULTS

There were 121 patients with mean age of 32 years (14-55). There was a statistically significant positive correlation individually between the height and graft diameter (r = 0.38, p < 0.01) as well as between the body weight and graft diameter (r = 0.29, p < 0.01). However, when the body mass index was calculated, the correlation was not statistically significant (r = 0.08, p > 0.1). Regression analysis confirmed that BMI was not statistically significant as a predictor of hamstring graft diameter whereas height was statistically the most important predictor (F = 20.1; p < 0.01).This yielded the predictive equation, graft diameter = 4.5 + 0.02 x Ht (in cm).

CONCLUSION

Although body mass index did not significantly correlate, body height may be a predictive variable in predicting the graft diameter in ACL reconstruction and provide useful pre operative information.

Anterior cruciate ligament strain and tensile forces for weight-bearing and non-weight-bearing exercises: a guide to exercise selection

There is a growing body of evidence documenting loads applied to the anterior cruciate ligament (ACL) for weight-bearing and non-weight-bearing exercises. ACL loading has been quantified by inverse dynamics techniques that measure anterior shear force at the tibiofemoral joint (net force primarily restrained by the ACL), ACL strain (defined as change in ACL length with respect to original length and expressed as a percentage) measured directly in vivo, and ACL tensile force estimated through mathematical modeling and computer optimization techniques. A review of the biomechanical literature indicates the following: ACL loading is generally greater with non-weight-bearing compared to weight-bearing exercises; with both types of exercises, the ACL is loaded to a greater extent between 10° to 50° of knee flexion (generally peaking between 10° and 30°) compared to 50° to 100° of knee flexion; and loads on the ACL change according to exercise technique (such as trunk position). Squatting with excessive forward movement of the knees beyond the toes and with the heels off the ground tends to increase ACL loading. Squatting and lunging with a forward trunk tilt tend to decrease ACL loading, likely due to increased hamstrings activity. During seated knee extension, ACL force decreases when the resistance pad is positioned more proximal on the anterior aspect of the lower leg, away from the ankle. The evidence reviewed as part of this manuscript provides objective data by which to rank exercises based on loading applied to the ACL. The biggest challenge in exercise selection post-ACL reconstruction is the limited knowledge of the optimal amount of stress that should be applied to the ACL graft as it goes through its initial incorporation and eventual maturation process. Clinicians may utilize this review as a guide to exercise selection and rehabilitation progression for patients post-ACL reconstruction.

Biomechanical evaluation of using one hamstrings tendon for ACL reconstruction: a human cadaveric study

Harvesting both the semitendinosus and gracilis tendons for anterior cruciate ligament (ACL) reconstruction has a negative impact on muscle strength as well as knee function and stability. With a new "All-inside" technique, using only one hamstrings tendon (semitendinosus or gracilis) is possible because of a reduction in length requirements. The research question of this in vitro study was whether the use of only one hamstrings tendon (semitendinosus or gracilis) could restore knee kinematics and in situ force in the ACL to the level of an intact knee.Ten human cadaveric knees were tested in the following conditions: (1) intact, (2) ACL-deficient, and (3) ACL reconstruction with the "All-inside" technique using the (a) single semitendinosus tendon graft, or (b) single gracilis tendon graft. Using a robotic testing system, external loads, i.e. (1) an anterior tibial load of 134-N and (2) combined rotatory loads of 10-Nm valgus and 5-Nm internal tibial torques, were applied. The multiple degrees of freedom knee kinematics and the in situ forces in the ACL and ACL grafts were determined. In response to a 134-N anterior tibial load, the use of either graft could restore anterior tibial translation to within 1.3 mm of the intact knee. The in situ forces in the two grafts were not significantly different from those of the intact ACL. Under the combined rotatory loads, both grafts could restore knee kinematics as well as the in situ force in the grafts to the level of the intact ACL. The "All-inside" technique using either the semitendinosus or gracilis tendon for ACL reconstruction could satisfactorily restore time-zero knee kinematics and the in situ forces in either graft to those for the intact ACL, supporting clinical findings.

Can pre-operative measures predict quadruple hamstring graft diameter?

The use of autologous grafts such as the quadrupled semitendinosus and gracilis tendon is very common in anterior cruciate ligament (ACL) reconstruction. The diameter of such grafts can be variable and thus unpredictable prior to surgery. In this study, we hypothesized that parameters such as gender, height, age, and body mass index (BMI) can be used pre-operatively to reveal the true graft diameter. All hamstring ACL reconstructions from 1994 to 2002 were reviewed. 536 cases (302 females, 234 males) met the inclusion criteria. Quadruple hamstring constructs and femoral tunnel diameters were measured using 1mm increment graft sizers. Pre-operative measures of height, weight, body mass index, gender, and age were obtained. Multiple regression analysis was used to build a predictive model of the quadruple hamstring graft diameter. The results of the study demonstrated that males had significantly larger grafts than females (8.1+/-0.8 vs. 7.5+/-0.6mm). Multiple regression analysis on the entire group showed that pre-operative height (p<0.0002) and gender (p<0.0047), but not age (p<0.06) or weight (p<0.019) were significant predictors of graft diameter. Height (p<0.0001) was a specific predictor solely in men. In females, none of the pre-operative measures were predictive of graft diameters. Patient height and gender can be used as pre-operative indicators of in vivo quadrupled hamstring graft diameter. Regardless of other variables, 42% of females will have tunnel diameters of 7mm or less. An alternative graft choice should be discussed pre-operatively if graft sizes may be of concern for the tall and large female patients.

Patellar tendon versus hamstring tendon autografts for reconstructing the anterior cruciate ligament: a meta-analysis based on individual patient data

BACKGROUND

The best means of ensuring knee stability after anterior cruciate ligament (ACL) reconstruction remains a core debate in sports medicine.

HYPOTHESIS

There is no difference between ACL reconstruction with patellar tendon or hamstring tendon autografts with regard to postoperative knee laxity and instability.

STUDY DESIGN

Meta-analysis of individual patient data.

METHODS

Pooled analysis of individual patient data from 6 published randomized clinical trials included 423 patients with symptomatic unilateral anterior cruciate ligament injury randomly assigned to reconstruction with patellar tendon or hamstring tendon autograft. Knee instability, defined as a positive pivot-shift test result, was the primary outcome, and knee laxity, defined as a positive Lachman test result, was the secondary outcome. Odds ratios were computed before and after adjustment for potential confounders and trial effect. Regression analyses were performed to look for effects of covariates on outcomes, and mixed-effects models were used to account for a trial effect. Sensitivity analyses were conducted to explore the effects of missing data and excluding each trial.

RESULTS

Anterior cruciate ligament reconstruction with patellar tendon autograft was significantly associated with a decreased risk of a positive pivot-shift test result (adjusted odds ratio, 0.46; 95% confidence interval, 0.24-0.86; P = .016). The risk of having a positive Lachman test result was not significantly different between the 2 groups. The estimated treatment effect was not substantially changed by differences in handling missing data or exclusion of any of the trials. A positive pivot-shift test result was more common in female (P = .003) and younger patients (P = .017).

CONCLUSION

Postoperative knee instability was less common after ACL reconstruction with patellar tendon autograft than with hamstring tendon autograft.

Comparative biomechanical study of the Ligament Plate and other fixation devices in ACL reconstruction

The objective of this study was to evaluate and compare the biomechanical properties of the Ligament Plate with other femoral fixation devices. The Ligament Plate and three different femoral fixation devices were used in fixation of 60 porcine femora and harvested porcine tendons. For each fixation device, a porcine graft-tendon complex was used for the simple load-to-failure test and the load-to-failure test after a cyclic loading test, and the maximal failure load was measured. The amount of graft elongation and failure pattern after the cyclic loading test and load-to-failure test were evaluated. In the BioScrew group, the mean maximal failure load in the load-to-failure test and load-to-failure test after a cyclic loading test was significantly lower and significant graft elongation was noted. There were no significant differences between the other groups. The Ligament Plate provided adequate initial fixation power suitable for early rehabilitation.

Statistics in brief: the importance of sample size in the planning and interpretation of medical research

The increasing volume of research by the medical community often leads to increasing numbers of contradictory findings and conclusions. Although the differences observed may represent true differences, the results also may differ because of sampling variability as all studies are performed on a limited number of specimens or patients. When planning a study reporting differences among groups of patients or describing some variable in a single group, sample size should be considered because it allows the researcher to control for the risk of reporting a false-negative finding (Type II error) or to estimate the precision his or her experiment will yield. Equally important, readers of medical journals should understand sample size because such understanding is essential to interpret the relevance of a finding with regard to their own patients. At the time of planning, the investigator must establish (1) a justifiable level of statistical significance, (2) the chances of detecting a difference of given magnitude between the groups compared, ie, the power, (3) this targeted difference (ie, effect size), and (4) the variability of the data (for quantitative data). We believe correct planning of experiments is an ethical issue of concern to the entire community.