Elias Bachmann

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Bachmann

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Elias

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0000-0002-1422-3104

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Publications 1 - 10 of 16

Evaluation of Tibial Fixation Devices for Quadrupled Hamstring ACL Reconstruction
Ammann, Elias; Hecker, Andreas; Bachmann, Elias; et al. (2022)
Orthopaedic Journal of Sports Medicine
Background: Shortcomings to tibial-side fixation have been reported as causes of failure after anterior cruciate ligament reconstruction. Adjustable-loop suspensory devices have become popular; however, no comparison with hybrid fixation (ie, interference screw and cortical button) exists to our knowledge. Purpose: The purpose of this study was to compare the biomechanical properties of adjustable loop devices (ALDs) in full-tunnel and closed-socket configurations in relation to hybrid fixation. We hypothesized that primary stability of fixation by a tibial ALD will not be inferior to hybrid fixation. Study Design: Controlled laboratory study. Methods: Tibial fixation of a quadrupled tendon graft was biomechanically investigated in a porcine tibia–bovine tendon model using 5 techniques (n = 6 specimens each). The tested constructs included hybrid fixation with a cortical fixation button and interference screw (group 1), single cortical fixation with the full-tunnel technique using an open-suture strand button (group 2) or an ALD (group 3), or closed-socket fixation using 2 different types of ALDs (groups 4 and 5). Each specimen was evaluated using a materials testing machine (1000 cycles from 50-250 N and pull to failure). Force at failure, cyclic displacement, stiffness, and ability to pretension the graft during insertion were compared among the groups. Results: No differences in ultimate load to failure were found between the ALD constructs (groups 3, 4, and 5) and hybrid fixation (group 1). Cyclic displacement was significantly higher in group 2 vs all other groups (P < .001); however, no difference was observed in groups 3, 4, and 5 as compared with group 1. The remaining tension on the construct after fixation was significantly higher in groups 3 and 4 vs groups 1, 2, and 5 (P < .02 for all comparisons), irrespective of whether a full-tunnel or closed-socket approach was used. Conclusion: Tibial anterior cruciate ligament graft fixation with knotless ALDs achieved comparable results with hybrid fixation in the full-tunnel and closed-socket techniques. The retention of graft tension appears to be biomechanically more relevant than tunnel type. Clinical Relevance: The study findings emphasize the importance of the tension at which fixation is performed.
Biomechanical Analysis of Posterior Open-Wedge Osteotomy and Glenoid Concavity Reconstruction Using an Implant-Free, J-Shaped Iliac Crest Bone Graft
Ernstbrunner, Lukas; Borbas, Paul; Ker, Andrew M.; et al. (2022)
The American Journal of Sports Medicine
Background: Posterior open-wedge osteotomy and glenoid reconstruction using a J-shaped iliac crest bone graft showed promising clinical results for the treatment of posterior instability with excessive glenoid retroversion and posteroinferior glenoid deficiency. Purpose: To evaluate the biomechanical performance of the posterior J-shaped graft to restore glenoid retroversion and posteroinferior deficiency in a cadaveric shoulder instability model. Study Design: Controlled laboratory study. Methods: A posterior glenoid open-wedge osteotomy was performed in 6 fresh-frozen shoulders, allowing the glenoid retroversion to be set at 0 degrees, 10 degrees, and 20 degrees. At each of these 3 preset angles of glenoid retroversion, the following conditions were simulated: (1) intact joint, (2) posterior Bankart lesion, (3) 20% posteroinferior glenoid deficiency, and (4) posterior J-shaped graft (at 0 degrees of retroversion). With the humerus in the Jerk position (60 degrees of glenohumeral anteflexion, 60 degrees of internal rotation), stability was evaluated by measuring posterior humeral head (HH) translation (in mm) and peak translational force (in N) to translate the HH over 25% of the glenoid width. Glenohumeral contact patterns were measured using pressure-sensitive sensors. Fixation of the posterior J-graft was analyzed by recording graft micromovements during 3000 cycles of 5-mm anteroposterior HH translations. Results: Reconstructing the glenoid with a posterior J-graft to 0 degrees of retroversion significantly increased stability compared with a posterior Bankart lesion and posteroinferior glenoid deficiency in all 3 preset degrees of retroversion (P < .05). There was no significant difference in joint stability comparing the posterior J-graft with an intact joint at 0 degrees of retroversion. The posterior J-graft restored mean contact area and contact pressure comparable with that of the intact condition with 0 degrees of retroversion (222 vs 223 mm(2), P = .980; and 0.450 vs 0.550 MPa, P = .203). The mean total graft displacement after 3000 cycles of loading was 43 +/- 84 mu m, and the mean maximal mediolateral graft bending was 508 +/- 488 mu m. Conclusion: Biomechanical analysis of the posterior J-graft demonstrated reliable restoration of initial glenohumeral joint stability, normalization of contact patterns comparable with that of an intact shoulder joint with neutral retroversion, and secure initial graft fixation in the cadaveric model.
Rabbit Achilles tendon full transection model – wound healing, adhesion formation and biomechanics at 3, 6 and 12 weeks post-surgery
Meier Bürgisser, Gabriella; Calcagni, Maurizio; Bachmann, Elias; et al. (2016)
Biology Open
After tendon rupture repair, two main problems may occur: re-rupture and adhesion formation. Suitable non-murine animal models are needed to study the healing tendon in terms of biomechanical properties and extent of adhesion formation. In this study 24 New Zealand White rabbits received a full transection of the Achilles tendon 2 cm above the calcaneus, sutured with a 4-strand Becker suture. Post-surgical analysis was performed at 3, 6 and 12 weeks. In the 6-week group, animals received a cast either in a 180 deg stretched position during 6 weeks (adhesion provoking immobilization), or were re-casted with a 150 deg position after 3 weeks (adhesion inhibiting immobilization), while in the other groups (3 and 12 weeks) a 180 deg position cast was applied for 3 weeks. Adhesion extent was analyzed by histology and ultrasound. Histopathological scoring was performed according to a method by Stoll et al. (2011), and the main biomechanical properties were assessed. Histopathological scores increased as a function of time, but did not reach values of healthy tendons after 12 weeks (only around 15 out of 20 points). Adhesion provoking immobilization led to an adhesion extent of 82.7±9.7%, while adhesion inhibiting immobilization led to 31.9±9.8% after 6 weeks. Biomechanical properties increased over time, however, they did not reach full strength nor elastic modulus at 12 weeks post-operation. Furthermore, the rabbit Achilles tendon model can be modulated in terms of adhesion formation to the surrounding tissue. It clearly shows the different healing stages in terms of histopathology and offers a suitable model regarding biomechanics because it exhibits similar biomechanics as the human flexor tendons of the hand.
Deepening trochleoplasty may dramatically increase retropatellar contact pressures- a pilot study establishing a finite element model
Kaiser, Dominik; Götschi, Tobias; Bachmann, Elias; et al. (2022)
Journal of Experimental Orthopaedics
Rotator Cuff Repair and Overlay Augmentation by Direct Interlocking of a Nonwoven Polyethylene Terephthalate Patch Into the Tendon: Evaluation in an Ovine Model
Meyer, Dominik C.; Bachmann, Elias; Darwiche, Salim; et al. (2023)
The American Journal of Sports Medicine
Background: Arthroscopic repair of large rotator cuff tendon tears is associated with high rates of retear. Construct failure often occurs at the suture-tendon interface. Patch augmentation can improve mechanical strength and healing at this interface. Purpose: To introduce a novel technique for suture-free attachment of an overlaid patch and evaluate its biomechanical strength and biological performance. Study Design: Descriptive and controlled laboratory studies. Methods: An established ovine model of partial infraspinatus tendon resection and immediate repair was used. After a nonwoven polyethylene terephthalate patch was overlaid to the resected tendon, a barbed microblade was used to draw fibers of the patch directly into the underlying tissue. In vivo histological assessment of healing was performed at 6 and 13 weeks after implantation. Ex vivo models were used to characterize primary repair strength of the suture-free patch fixation to tendon. Additional ex vivo testing assessed the potential of the technique for patch overlay augmentation of suture-based repair. Results: The in vivo study revealed no macroscopic evidence of adverse tissue reactions to the interlocked patch fibers. Histological testing indicated a normal host healing response with minimal fibrosis. Uniform and aligned tissue ingrowth to the core of the patch was observed from both the tendon and the bone interfaces to the patch. There was no evident retraction of the infraspinatus muscle, lengthening of the tendon, or tendon gap formation over 13 weeks. Ex vivo testing revealed that direct patch interlocking yielded tendon purchase equivalent to a Mason-Allen suture (150 ± 58 vs 154 ± 49 N, respectively; P =.25). In an overlay configuration, fiber interlocked patch augmentation increased Mason-Allen suture retention strength by 88% (from 221 ± 43 N to 417 ± 86 N; P <.01) with no detectable difference in repair stiffness. Conclusion: Testing in an ovine model of rotator cuff tendon repair suggested that surgical interlocking of a nonwoven medical textile can provide effective biomechanical performance, support functional tissue ingrowth, and help avoid musculotendinous retraction after surgical tendon repair. Clinical Relevance: The novel technique may facilitate patch augmentation of rotator cuff repairs.
Reinforced lengthening Achilles tendon Z-plasty - ex vivo assessment of biomechanical augmentation with surgical-fiberlock technology
Dreher, Thomas; Moehl, Andrea; Bachmann, Elias; et al. (2025)
International Orthopaedics
Purpose Tendon lengthening is a common lower limb surgical procedure in paediatric orthopaedics and deformity correction. Healing of a lengthened tendon is typically supported by casting and unloading of the operated limb. Although tendon rupture or overcorrection may adversely affect surgical outcomes, few studies have examined surgical means of improving post-operative stability of the tendon. We aim to evaluate a novel method for augmenting Z-Plasty tendon lengthening as a first step to clinical translation. Methods In this experimental ex vivo study, we employed a bovine flexor tendon model (n = 18) to examine a novel mechanical augmentation method after tendon lengthening by Z-plasty. Conventional surgical suturing of the imposed Z-plasty (n = 6) and an experimental group (n = 6), in which additional augmentation was performed by interlocking fibres of a biomaterial scaffold to the underlying tendon using a novel micro-needling technique, were compared to native tendons (n = 6). Results The needle interlocked scaffold successfully augmented the suture repair, showing more than doubled ultimate failure force compared to controls (482 +/- 107 N vs. 206 +/- 37 N, p < 0.01), and more than 1.5-fold repair stiffness (41 +/- 7 N/mm vs. 26 +/- 9 N/mm, p < 0.01). Conclusion We conclude that the use of an interpenetrating biomaterial scaffold represents a promising new approach for improving biomechanical tendon properties, which may have an implication on the stability of tendon suture, lengthening and tendon transfer procedures as well as on post-operative management and earlier mobilization.
Biomechanical comparison of sagittal-parallel versus non-parallel pedicle screw placement
Farshad, Mazda; Farshad-Amacker, Nadja A.; Bachmann, Elias; et al. (2014)
Acta Neurochirurgica
Background While convergent placement of pedicle screws in the axial plane is known to be more advantageous biomechanically, surgeons intuitively aim toward a parallel placement of screws in the sagittal plane. It is however not clear whether parallel placement of screws in the sagittal plane is biomechanically superior to a non-parallel construct. The hypothesis of this study is that sagittal non-parallel pedicle screws do not have an inferior initial pull-out strength compared to parallel placed screws. Methods The established lumbar calf spine model was used for determination of pull-out strength in parallel and non-parallel intersegmental pedicle screw constructs. Each of six lumbar calf spines (L1-L6) was divided into three levels: L1/L2, L3/L4 and L5/L6. Each segment was randomly instrumented with pedicle screws (6/45 mm) with either the standard technique of sagittal parallel or non-parallel screw placement, respectively, under fluoroscopic control. CT was used to verify the intrapedicular positioning of all screws. The maximum pull-out forces and type of failure were registered and compared between the groups. Results The pull-out forces were 5,394 N (range 4,221 N to 8,342 N) for the sagittal non-parallel screws and 5,263 N (range 3,589 N to 7,554 N) for the sagittal-parallel screws (p = 0.838). Interlevel comparisons also showed no statistically significant differences between the groups with no relevant difference in failure mode. Conclusion Non-parallel pedicle screws in the sagittal plane have at least equal initial fixation strength compared to parallel pedicle screws in the setting of the here performed cadaveric calf spine experiments.
Mechanical properties of Triclosan sutures
Jungwirth-Weinberger, Anna; Grubhofer, Florian; Imam, Mohamed A.; et al. (2018)
Journal of Orthopaedic Research
T1- and T2*-Mapping for Assessment of Tendon Tissue Biophysical Properties: a Phantom MRI Study
Bachmann, Elias; Rosskopf, Andrea B.; Götschi, Tobias; et al. (2018)
Investigative Radiology
Osteoconductive Scaffold Placed at the Femoral Tunnel Aperture in Hamstring Tendon ACL Reconstruction: A Randomized Controlled Trial
Götschi, Tobias; Hodel, Sandro; Kühne, Nathalie; et al. (2023)
Orthopaedic Journal of Sports Medicine
Background: Bone tunnel enlargement after single-bundle anterior cruciate ligament reconstruction remains an unsolved problem that complicates revision surgery. Hypothesis: Positioning of an osteoconductive scaffold at the femoral tunnel aperture improves graft-to-bone incorporation and thereby decreases bone tunnel widening. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: In a 1:1 ratio, 56 patients undergoing primary anterior cruciate ligament reconstruction were randomized to receive femoral fixation with cortical suspension fixation and secondary press-fit fixation at the tunnel aperture of the tendon graft only (control) or with augmentation by an osteoconductive scaffold (intervention). Adverse events, patient-reported outcomes, and passive knee stability were recorded over 2 years after the index surgery. Three-dimensional bone tunnel widening was assessed using computed tomography at the time of surgery and 4.5 months and 1 year postoperatively. Results: The intervention group exhibited a similar number of adverse events as the control group (8 vs 10; P =.775) including 2 partial reruptures in both groups. The approach was feasible, although 1 case was encountered where the osteoconductive scaffold was malpositioned without adversely affecting the patient’s recovery. There was no difference between the intervention and control groups in femoral bone tunnel enlargement, as expressed by the relative change in tunnel volume from surgery to 4.5 months (mean ± SD, 36% ± 25% vs 40% ± 25%; P =.644) and 1 year (19% ± 20% vs 17% ± 25%; P =.698). Conclusion: Press-fit graft fixation with an osteoconductive scaffold positioned at the femoral tunnel aperture is safe but does not decrease femoral bone tunnel enlargement at postoperative 1 year. Registration: NCT03462823 (ClinicalTrials.gov identifier).

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