Biomechanics and anterior cruciate ligament reconstruction

For years, bioengineers and orthopaedic surgeons have applied the principles of mechanics to gain valuable information about the complex function of the anterior cruciate ligament (ACL). The results of these investigations have provided scientific data for surgeons to improve methods of ACL reconstruction and postoperative rehabilitation. This review paper will present specific examples of how the field of biomechanics has impacted the evolution of ACL research. The anatomy and biomechanics of the ACL as well as the discovery of new tools in ACL-related biomechanical study are first introduced. Some important factors affecting the surgical outcome of ACL reconstruction, including graft selection, tunnel placement, initial graft tension, graft fixation, graft tunnel motion and healing, are then discussed. The scientific basis for the new surgical procedure, i.e., anatomic double bundle ACL reconstruction, designed to regain rotatory stability of the knee, is presented. To conclude, the future role of biomechanics in gaining valuable in-vivo data that can further advance the understanding of the ACL and ACL graft function in order to improve the patient outcome following ACL reconstruction is suggested

Can the body slope of interference screw affect initial stability of reconstructed anterior cruciate ligament?: An in-vitro investigation

© The Author(s). 2021 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. https://creativecommons.org/licenses/by/4.0/Background: Superior biomechanical performance of tapered interference screws, compared with non-tapered screws, with reference to the anterior cruciate ligament (ACL) reconstruction process, has been reported in the literature. However, the effect of tapered interference screw’s body slope on the initial stability of ACL is poorly understood. Thus, the main goal of this study was to investigate the effect of the interference screw's body slope on the initial stability of the reconstructed ACL. Methods: Based on the best screw-bone tunnel diameter ratios in non-tapered screws, two different tapered interference screws were designed and fabricated. The diameters of both screws were equal to bone tunnel diameter in one-third of their length from screw tip, then they were gradually increased by 1mm, in the lower slope (LSTIS), and 2 mm, in the higher slope (HSTIS) screws. To simulate the ACL reconstruction, sixteen soft tissue grafts were fixed, using HSTIS and LSTIS, in synthetic bone blocks. Through applying sub-failure cyclic incremental tensile load, graft-bone-screw construct's stiffness and graft laxity in each cycle, also through applying subsequent step of loading graft to the failure, maximum load to failure, and graft’s mode of failure were determined. Accordingly, the performance of the fabricated interference screws was compared with each other. Results: HSTIS provides a greater graft-bone-screw construct stiffness, and a lower graft laxity, compared to LSTIS. Moreover, transverse rupture of graft fibers for LSTIS, and necking of graft in the HSTIS group were the major types of grafts' failure. Conclusion: HSTIS better replicates the intact ACL's behavior, compared to LSTIS, by causing less damage in graft's fibers; reducing graft laxity; and increasing fixation stability. Nonetheless, finding the optimal slope remains as an unknown and can be the subject of future studies.Peer reviewedFinal Published versio

Torsional stability of interference screws derived from bovine bone - a biomechanical study

Introduction: It has been proposed that individual genetic variation contributes to the course of severe infections and sepsis. Recent studies of single nucleotide polymorphisms (SNPs) within the endotoxin receptor and its signaling system showed an association with the risk of disease development. This study aims to examine the response associated with genetic variations of TLR4, the receptor for bacterial LPS, and a central intracellular signal transducer (TIRAP/Mal) on cytokine release and for susceptibility and course of severe hospital acquired infections in distinct patient populations. Methods: Three intensive care units in tertiary care university hospitals in Greece and Germany participated. 375 and 415 postoperative patients and 159 patients with ventilator associated pneumonia (VAP) were included. TLR4 and TIRAP/Mal polymorphisms in 375 general surgical patients were associated with risk of infection, clinical course and outcome. In two prospective studies, 415 patients following cardiac surgery and 159 patients with newly diagnosed VAP predominantly caused by Gram-negative bacteria were studied for cytokine levels in-vivo and after ex-vivo monocyte stimulation and clinical course. Results: Patients simultaneously carrying polymorphisms in TIRAP/Mal and TLR4 and patients homozygous for the TIRAP/Mal SNP had a significantly higher risk of severe infections after surgery (odds ratio (OR) 5.5; confidence interval (CI): 1.34 - 22.64; P = 0.02 and OR: 7.3; CI: 1.89 - 28.50; P < 0.01 respectively). Additionally we found significantly lower circulating cytokine levels in double-mutant individuals with ventilator associated pneumonia and reduced cytokine production in an ex-vivo monocyte stimulation assay, but this difference was not apparent in TIRAP/Mal-homozygous patients. In cardiac surgery patients without infection, the cytokine release profiles were not changed when comparing different genotypes. Conclusions: Carriers of mutations in sequential components of the TLR signaling system may have an increased risk for severe infections. Patients with this genotype showed a decrease in cytokine release when infected which was not apparent in patients with sterile inflammation following cardiac surgery

Design and evaluation of a prosthetic anterior cruciate ligament replacement medical device

Rupture of the anterior cruciate ligament (ACL) is a relatively common sports-related injury for which the current treatment is reconstruction with an autograft or allograft. Drawbacks associated with each of the current options would make a prosthetic alternative advantageous, however, artificial ligaments are not widely used, having failed due to lack of biocompatibility and mechanical insufficiencies. To develop the next-generation prosthetic ACL, design control principles were applied including specification of comprehensive design inputs, risk analysis, and verification testing. A design was proposed utilizing polyvinyl alcohol and ultrahigh molecular weight polyethylene, selected for good biocompatibility and mechanical strength and stiffness suitable for ACL replacement. A biomimetic fibrous rope pattern was designed for the intra-articular ligament section of the prosthetic that produced a close match the static tensile behavior of the native ACL and which also demonstrated good resistance to fatigue and creep. A calcium phosphate coating was recommended for the sections of the device lying within the bone tunnel to increase the rate of osseointegration. The proposed design was then evaluated in a computational simulation to assess functional restoration and the effects of installation parameters such as tension and tunnel orientation on knee kinematics. The encouraging results of preclinical verification testing support further in vivo evaluation of the proposed design.PhDCommittee Chair: Ku, David; Committee Co-Chair: Cherkaoui, Mohammed; Committee Member: Cort, Laurent; Committee Member: Gleason, Rudolph; Committee Member: Guldberg, Rober

Risk factors for revision after anterior cruciate ligament reconstruction

The overall aim of this thesis was to investigate risk factors for revision anterior cruciate ligament (ACL) reconstruction with a special attention to surgical technique (graft choice and choice of graft fixation) and patients’ age and sex. Specific aims were to describe the usage of the most common grafts and fixations for ACLR in Norway and Scandinavia respectively. To answer these questions we used register data for patients with isolated ACL tear who had undergone ACL reconstruction (ACLR), with revision as the endpoint. We used data from the Norwegian National Knee Ligament Register (NNKLR) for all papers, and in addition, data from the Swedish and Danish National Knee Ligament Registries for paper III. In study I, 12,643 patients were included to evaluate the revision rate and risk factors for revision ACLR, primarily the influence of graft choice (patellar tendon [BPTB] or hamstring tendon [HT] graft). The patients’ age and sex were included in the overall analysis. The revision rate was higher for HT compared with BPTB grafts at all follow-up times, and the adjusted revision risk were twice as high for HT compared with BPTB. Young age was the strongest predictor for revision of the investigated factors. In study II, we described the usage of fixation implants for 14,034 patients with BPTB and HT in Norway and investigated the revision risk for the most common combinations of fixations for BPTB and HT. We found combinations of fixation implants with a higher risk of revision when using HT, especially when suspensory fixation in the femur was used. In study III, we described the most common fixation methods for HT grafts used in 38,666 patients in Scandinavia, and investigated the influence of fixation method on the risk of revision. We found that similar graft fixation methods influenced the risk of revision as in study II. In conclusion, we found both surgical techniques and patient-specific factors that affect the revision rate and revision-risk after ACLR. Young age was the strongest predictor for further revision surgery. Patients reconstructed with HT had twice the risk of revision compared with BPTB, and certain fixation methods for HT had an increased risk of early and overall revision

Functional Outcomes of Anterior Cruciate Ligament Reconstruction Surgery

Anterior cruciate ligament (ACL) is one of the most common sports injuries with a reported yearly incidence rate of over two million injuries worldwide. The main aim of this thesis is to investigate various aspects related to the functional outcomes of ACLR through a series of clinical studies. Ethical approval was sought and granted by the North of Scotland Research Ethics Service. A systematic review was conducted to investigate the outcome measures used in Level I and II clinical ACLR studies. The review showed wide variability in the outcome measures utilised with no consensus on the ideal outcome instrument or combination of instruments to report the outcome of ACLR. Five-year results from the UK National Ligament Registry (NLR) were analysed with review for limitations of registry data and future recommendations. The data analysed provided a comprehensive review for the demographics, surgical techniques and functional outcomes of ACLR surgery across the UK. NLR data is limited by multiple factors including high rate of incomplete data, duplication of data, poor patient compliance and lack of validation of the data. A study was conducted to examine the hypothesis that patients with ACLR do not return to their pre-injury functional status at two years postoperatively. The study showed significant improvement in patient symptoms postoperatively compare to their post-injury scores, but the majority of patients failed to achieve their pre-injury functional outcome scores at 2 years postoperatively. In a comparative study, the anteromedial portal (AM) technique in femoral tunnel drilling was compared with the trans-tibial (TT) technique with respect to radiological and functional outcomes. The hypothesis was that AM portal produces better functional outcomes compared with TT technique. We found that the AM portal achieved a more anatomical position of the graft but there was no difference between the two techniques in functional outcome at 2 years postoperatively. However, ACLR with the AM portal technique had higher graft failure rate compared with the TT technique. The medium- term outcome of all-inside meniscal repairs was investigated in a longitudinal study. Meniscal repairs with concomitant ACLR had a lower failure rate compared with isolated meniscal repairs. This indicates that surgeons should have a low threshold for repairing meniscal tear during ACLR surgery. The healing response technique was studied in a selected group of patients with complete proximal ACL tears. This technique yielded good functional outcome for most of the patients at 2 years postoperative follow up. The studies included in this thesis provides substantial information for surgeons treating patients with ACL injuries. It provides a platform for further research studies investigating the outcomes of ACLR surgery

Rehabilitation following Anterior Cruciate Ligament Reconstruction: A Comparison of Traditional and Accelerated Approaches

Rehabilitation following Anterior Cruciate Ligament (ACL) reconstruction has become an area of controversy in recent years. Most clinicians have used the traditional rehabilitation protocols which correlate mobility, weightbearing, and strength training with the bio-mechanical and surgical constraints of graft fixation and healing. However, a trend towards the use of accelerated protocols is more evident today. The accelerated approach stresses activity and weightbearing in the early periods of the rehabilitation process following the reconstructive surgery. The proponents of the accelerated protocol believe that earlier activity will enhance the healing of the graft without causing an increase in knee instability. The purpose of this independent study is to review the literature regarding the traditional and accelerated rehabilitation approaches for ACL reconstruction in an effort to explain and compare the two, and identify advantages and disadvantages of each approach. In addition, this review investigates: the minimum healing requirements which should be met before initiating rehabilitation activity, what surgical considerations are important, and if there is a preferred method of strength training following ACL reconstruction. The conclusion of this review supports the accelerated approach to rehabilitation as the best choice for patients following ACL reconstruction. This information hopefully can be of aid for physical therapists in establishing treatment programs for these patients

Novel Insights into Anterior Cruciate Ligament Injury

Anterior cruciate ligament (ACL) injury is one of the most common sports injuries of the knee. ACL reconstruction has become, standard orthopaedic practice worldwide with an estimated 175,000 reconstructions per year in the United States.6 The ACL remains the most frequently studied ligament in orthopaedic research. Hundreds of papers are published each year related to the ACL. However, the treatment options and techniques are still developing and increasing, indicating the difficulties in the treatment of this central knee ligament