Dominik C Meyer

University of Zurich, Zürich, Zurich, Switzerland

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Publications (61)134.7 Total impact

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    ABSTRACT: If revision of a failed anatomic hemiarthroplasty or total shoulder arthroplasty is uncertain to preserve or restore satisfactory rotator cuff function, conversion to a reverse total shoulder arthroplasty has become the preferred treatment, at least for elderly patients. However, revision of a well-fixed humeral stem has the potential risk of loss of humeral bone stock, nerve injury, periprosthetic fracture, and malunion or nonunion of a humeral osteotomy with later humeral component loosening.
    Clinical Orthopaedics and Related Research 10/2014; · 2.79 Impact Factor
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    ABSTRACT: It was the purpose of this paper to analyze structural, functional, and electrophysiologic variables that may determine preserved overhead function for patients with massive rotator cuff tears.
    Journal of shoulder and elbow surgery / American Shoulder and Elbow Surgeons ... [et al.] 08/2014; · 1.93 Impact Factor
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    ABSTRACT: No. 5 FiberWire (Arthrex, Naples, FL, USA) cerclage (FWC) and 1.25-mm stainless steel wire cerclage (SSWC) are biomechanically similar in resistance to prosthetic subsidence in shoulder arthroplasty. In this laboratory bench study, 3 different surgical knot configurations (4-throw knot, cow hitch, and simple hitch) using a No. 5 FWC were evaluated and compared with a 1.25-mm SSWC. First, distraction tests were performed using bovine femoral cortical half shells mounted on a testing jig. Cerclage tightening, load to a 3-mm gap opening, and load to total failure were measured. Second, uncemented humeral prosthetic stems were inserted into an experimentally split humeral medullary canal, secured by the cerclage. After 100 N of preloading, the prosthesis was advanced into the humerus at a speed of 0.2 mm/s, and resistance during subsidence up to a penetration depth of 10 mm, as well as gap opening, was measured. Tightening force showed higher values for SSWC (618 N) than FWC (131-137 N) (P < .001). Load to total failure was comparable among the 3 different FWC knots (2,642-2,804 N), which were significantly stronger than SSWC (1,775 N, P < .001). At 3 mm of distraction, SSWC (1,820 N), cow hitch (1,803 N), and single-throw hitch (1,709 N) performed significantly better than a 4-throw knot (1,289 N) (P < .01). Subsidence testing showed no difference in force restraint or gap opening between the best FWC and SSWC. FWCs appear, in vitro, equally suitable to steel wires to stabilize nondisplaced periprosthetic humeral fractures. To actively reduce a displaced fracture, steel wires may still be the first choice.
    Journal of shoulder and elbow surgery / American Shoulder and Elbow Surgeons ... [et al.] 05/2014; · 1.93 Impact Factor
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    ABSTRACT: Chronic tearing of tendons is associated with molecular and structural alterations causing biomechanical changes, which compromise musculotendinous function and become limiting factors for tendon repair. This study investigated the histological response of chronically retracted sheep rotator cuff tendons to mechanical and pharmacological stimulation in view of tendon repair. Sixteen weeks after experimental release of the infraspinatus tendon in 20 sheep, the retracted musculotendinous unit was subjected to continuous traction either with [anabolic steroids (nandrolone) group/insulin-like growth factor (IGF) group] or without (control group) additional pharmacological treatment during 6 weeks. A new degeneration score for tendinous tissues (DSTT), based on established knowledge on histological changes associated with tendon degeneration, was used for histological analysis at the time of tendon release, at the beginning of continuous re-lengthening and at repair in all animals. The DSTT score (inter-observer correlation: r = 0.83), quantifiably representing tendon degeneration, improved from 15.5 (SD 1.3) points before to 9.8 (SD 3.8) points after re-lengthening. It improved in a qualitatively and quantitatively similar fashion if pharmacological stimulation was added. The nandrolone group improved from 13.7 (SD 1.6) to 9.8 (SD 1.9) and the IGF group from 13.3 (SD 3.6) to 8.8 (SD 1.8) points. Mechanical stimulation significantly reduced tissue degeneration. However, the addition of a pharmacological stimulation with anabolic steroids or IGF had neither a measurable positive nor negative effect on the degenerative process. Therefore, this investigation does neither support the additional pharmacological use of the anabolic steroid nandrolone or of IGF decanoate for restoration of tendon degeneration, nor otherwise provide evidence for additional tendon damage, if those substances are used to alter the muscular metabolism.
    Knee Surgery Sports Traumatology Arthroscopy 05/2014; · 2.68 Impact Factor
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    ABSTRACT: Introduction Early clinical and radiographic diagnosis of failed or loosened anterior cruciate ligament (ACL) reconstructions can be challenging. The aim of the present study is to retrospectively evaluate the use of radiologically visible markers in the ACL graft, serving as a potential diagnostic tool in ACL graft rupture and insufficiency. Methods Twenty patients were included in the study. ACL reconstruction was performed with use of a hamstring autograft in hybrid fixation technique. The graft was marked with two radiodense suture knots, one at tibial and femoral tunnel opening. X-rays were performed postoperatively, after 6 weeks and 12 months. Four distances between markers and landmarks were measured in anteroposterior and three in lateral x-ray views and the positional change between the timepoints of measurement was calculated. Results Measurements of the marker distances on x-rays showed an excellent interobserver reliability (κ = 0.97). In two measured distal anteroposterior distances statistically significant changes could be detected between 6 weeks and 12 months postoperatively in one patient with MRI-documented ACL rerupture and in five patients with ACL elongation defined as anteroposterior-translation with side-to-side difference of ≥ 3 mm measured with a Rolimeter device. In lateral x-rays, marker distances were highly variable and did not correlate with clinical ACL elongation. Conclusion The application of radiodense ACL graft markers is a straight-forward, non-expensive and potentially useful diagnostic tool to identify the position of the transplant and for diagnosis of graft elongation or failure. However, the method is sensitive to the radiological projection, which should be further studied and optimized.
    The Knee 01/2014; · 2.01 Impact Factor
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    ABSTRACT: Hypothesis No. 5 FiberWire (Arthrex, Naples, FL, USA) cerclage (FWC) and 1.25-mm stainless steel wire cerclage (SSWC) are biomechanically similar in resistance to prosthetic subsidence in shoulder arthroplasty. Methods In this laboratory bench study, 3 different surgical knot configurations (4-throw knot, cow hitch, and simple hitch) using a No. 5 FWC were evaluated and compared with a 1.25-mm SSWC. First, distraction tests were performed using bovine femoral cortical half shells mounted on a testing jig. Cerclage tightening, load to a 3-mm gap opening, and load to total failure were measured. Second, uncemented humeral prosthetic stems were inserted into an experimentally split humeral medullary canal, secured by the cerclage. After 100 N of preloading, the prosthesis was advanced into the humerus at a speed of 0.2 mm/s, and resistance during subsidence up to a penetration depth of 10 mm, as well as gap opening, was measured. Results Tightening force showed higher values for SSWC (618 N) than FWC (131-137 N) (P < .001). Load to total failure was comparable among the 3 different FWC knots (2,642-2,804 N), which were significantly stronger than SSWC (1,775 N, P < .001). At 3 mm of distraction, SSWC (1,820 N), cow hitch (1,803 N), and single-throw hitch (1,709 N) performed significantly better than a 4-throw knot (1,289 N) (P < .01). Subsidence testing showed no difference in force restraint or gap opening between the best FWC and SSWC. Conclusions FWCs appear, in vitro, equally suitable to steel wires to stabilize nondisplaced periprosthetic humeral fractures. To actively reduce a displaced fracture, steel wires may still be the first choice.
    Journal of Shoulder and Elbow Surgery. 01/2014;
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    ABSTRACT: It seems appropriate to assume, that for a full and strong global shoulder function a normally innervated and active deltoid muscle is indispensable. We set out to analyse the size and shape of the deltoid muscle on MR-arthrographies, and analyse its influence on shoulder function and its adaption (i.e. atrophy) for reduced shoulder function. The fatty infiltration (Goutallier stages), atrophy (tangent sign) and selective myotendinous retraction of the rotator cuff, as well as the thickness and the area of seven anatomically defined segments of the deltoid muscle were measured on MR-arthrographies and correlated with shoulder function (i.e. active abduction). Included were 116 patients, suffering of a rotator cuff tear with shoulder mobility ranging from pseudoparalysis to free mobility. Kolmogorov-Smirnov test was used to determine the distribution of the data before either Spearman or Pearson correlation and a multiple regression was applied to reveal the correlations. Our developed method for measuring deltoid area and thickness showed to be reproducible with excellent interobserver correlations (r = 0.814--0.982).The analysis of influencing factors on active abduction revealed a weak influence of the amount of SSP tendon (r = -0.25; p < 0.01) and muscle retraction (r = -0.27; p < 0.01) as well as the stage of fatty muscle infiltration (GFDI: r = -0.36; p < 0.01). Unexpectedly however, we were unable to detect a relation of the deltoid muscle shape with the degree of active glenohumeral abduction. Furthermore, long-standing rotator cuff tears did not appear to influence the deltoid shape, i.e. did not lead to muscle atrophy. Our data support that in chronic rotator cuff tears, there seems to be no disadvantage to exhausting conservative treatment and to delay implantation of reverse total shoulder arthroplasty, as the shape of deltoid muscle seems only to be influenced by natural aging, but to be independent of reduced shoulder motion.
    BMC Musculoskeletal Disorders 08/2013; 14(1):247. · 1.88 Impact Factor
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    ABSTRACT: PURPOSE: High-strength sutures allow tightening of a suture knot beyond the strength of the surgeon, possibly inflicting skin damage through the gloves. This study was undertaken to evaluate whether such effort is useful and how much tensioning on a surgical knot is necessary. METHODS: Three different suture materials were tested: No. 2 Vicryl™, FibreWire™, and PDS™. First, the force spontaneously applied on sutures during experimental knot tightening ("tying load") was measured in fifteen experienced surgeons. Second, with each suture material, surgical square knots were tied with increasing, standardized loads (range 0.5-50 N) using a custom-made apparatus. Thereby, knot seating after tying was evaluated, and by loading the knots to failure, evaluation for failure mode and failure load was performed. RESULTS: FibreWire™ 5-throw square knots always failed by complete slipping of all knots (resolving), independent on the tying load. A nonlinear decrease of knot slippage and increased failure load were seen with increasing tying loads for all sutures. Major differences were seen between 0.5 and 10 N for FibreWire™ (slippage: 25 mm) and PDS™ (99.6 mm), whereas Vicryl™ showed major differences (22.7 mm) between 0.5 and 2 N. Increasing the tying load from 10 to 50 N decreased the mean knot slippage from 12 (FibreWire™, ±2.6 SD), 9 (PDS™, ±1.8 SD) and 8 (Vicryl™, ±1.3 SD) mm to 6 (±2.9 SD), 3 (±1.5 SD) and 4 mm (±0.9 SD), respectively. CONCLUSION: Slippage and self-seating of the knots under load is unavoidable even with highest tying loads. Relatively minor but possibly important differences can be seen for tying loads exceeding 2 N (Vicryl™) and 10 N (PDS™ and FibreWire™) for failure load and knot slippage. But also with a tying load of 50 N, a minimal slippage of approximately 3 mm seems unavoidable for all suture types. However, it is important to state that intense tightening does not prevent knot resolution and is only necessary in clinical situations that demand very tight sutures. Numbers and proper appliance of throws are more relevant than tying strength to reach the maximum failure load.
    Knee Surgery Sports Traumatology Arthroscopy 03/2013; · 2.68 Impact Factor
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    ABSTRACT: OBJECTIVES:: On standard axillary radiographs of normal shoulders, the clavicle may appear subluxated posteriorly. This subluxation might be viewed as an indication for surgical stabilization in acromioclavicular (AC) injury. The purpose of this study was to assess the reliability of identification of anteroposterior displacements of the AC joint on standard axillary radiographs of the human shoulder. METHODS:: We performed 170 radiographs of the AC joint in ten cadaveric shoulders using various projection angles. The distance from the anterior margin of the acromion to the distal clavicle was measured to identify an "optimal" view to image the true anteroposterior alignment of normal AC joints. RESULTS:: On the standard axillary view of intact shoulders we found an average posterior translation of 1.7mm (range, -3 to 7; SD 2.8) and of 0.9mm (range, -5 to 5; SD 2.8) in an "optimal view", tilted 15° dorsal and 15° lateral. CONCLUSION:: The standard axillary radiograph has a very high sensitivity, but poor accuracy in identifying a posterior clavicular translation in the AC joint. We could not identify a reliable modification of the axillary radiographic projection to improve the accuracy. Therefore, an apparent posterior subluxation of the clavicle identified on an axillary radiograph is more likely a false positive finding than an identification of a true pathology.
    Journal of orthopaedic trauma 03/2013; · 1.78 Impact Factor
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    ABSTRACT: BACKGROUND: The Latarjet procedure has widely become the preferred treatment option for recurrent anterior glenohumeral instability in the presence of glenoid bone loss. The success of this procedure is largely dependent on accurate placement of the coracoid bone graft relative to the glenoid margin. With malpositioning of the coracoid graft, complications can arise, such as recurrent instability if placed too medially or impingement and subsequent early degenerative changes if positioned too laterally. To increase the accuracy and reproducibility of coracoid graft placement, we developed a simple and efficient drill guide that assists in accurate and safe positioning of the graft against the anterior glenoid to provide a congruent articular surface. MATERIALS AND METHODS: A new drill guide was used in 12 consecutive open Latarjet procedures. Accuracy of placement of the graft with respect to the anterior glenoid rim was assessed using postoperative computed tomography imaging. RESULTS: Accurate graft placement with a distance between the glenoid and the graft surface of less than 1 mm was obtained in all 12 interventions. The mean angulation of the screws relative to the glenoid face was 4.3° (range, 1°-7°). All screw heads were positioned medial to the articular edge of the graft, and the distance was always greater than 3 mm. CONCLUSIONS: The use of a simple drill guide allows safe and accurate graft placement during an open Latarjet procedure.
    Journal of Shoulder and Elbow Surgery 12/2012; 2013(22):701-708. · 2.32 Impact Factor
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    ABSTRACT: BACKGROUND:Long-standing rotator cuff tendon tearing is associated with retraction, loss of work capacity, irreversible fatty infiltration, and atrophy of the rotator cuff muscles. Although continuous musculotendinous relengthening can experimentally restore muscular architecture, restoration of atrophy and fatty infiltration is hitherto impossible. HYPOTHESIS:Continuous relengthening with pharmacological stimulation of muscle growth using an anabolic steroid or insulin-like growth factor (IGF) can reverse atrophy and fatty infiltration as well as improve the work capacity of chronically retracted rotator cuff muscles in sheep. STUDY DESIGN:Controlled laboratory study. METHODS:Sixteen weeks after tenotomy of the infraspinatus (ISP) tendon, atrophy and fatty infiltration had developed in the retracted ISP muscle. The musculotendinous unit was continuously relengthened in 14 sheep during 6 weeks: Four sheep were treated without pharmacological stimulation, 4 with intramuscular administration of an anabolic steroid, and 6 with IGF before final repair and rehabilitation (12 weeks). Changes were documented by intraoperative measurements of muscle work capacity, histology, and computed tomography/magnetic resonance imaging. RESULTS:Musculotendinous relengthening by continuous traction resulted in gains of length ranging from 0.7 cm in the IGF group to 1.3 cm in the control group. Fatty infiltration progressed in all groups, and the muscle's cross-sectional area ranged from 71% to 74% of the contralateral side at sacrifice and did not show any differences between groups in weight, volume, histological composition, or work capability of the muscle. The contralateral muscles in the anabolic steroid group, however, showed significantly higher (mean ± standard deviation) muscle work capacity of 10 ± 0.9 N·m than the contralateral muscles of the control group (6.8 ± 2.4 N·m) (P < .05). This was accompanied by an increased mean muscle fiber area as well as by an unusual gain in the animals' weight after injection of the anabolic steroid. CONCLUSION:Subcutaneous continuous relengthening of a chronically retracted musculotendinous unit is feasible and advances the retracted musculotendinous junction toward its original position. This does not change the muscle work capacity. Whereas anabolic steroids have been shown to be effective in preventing classic degenerative muscle changes after tendon tears, neither an anabolic steroid nor IGF contributes to regeneration of the muscle once degenerative changes are established. CLINICAL RELEVANCE:The findings demonstrate that muscle cells lose reactiveness to an anabolic steroid and IGF once retraction has led to fatty infiltration and atrophy of the muscle. Retraction of the muscle after tendon tears must be avoided by early repair, particularly in an athlete, as no regeneration can be achieved by mechanical or pharmacological means at this time.
    The American journal of sports medicine 09/2012; · 3.61 Impact Factor
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    ABSTRACT: PURPOSE: To quantify the strength of suture fixation of knotless suture anchors in relation to the anchors' pullout strength and to compare these results with the static friction between different sutures and anchor materials. METHODS: Suture slippage within the anchor and pullout strength of 4 different knotless suture anchor models were assessed in a bovine bone model. Furthermore, the peak force before onset of slippage of different sutures trapped between increasingly loaded 4-mm rods made of commonly used anchor material (polyetheretherketone, poly-L-lactide acid, metal) was assessed. RESULTS: In all but 1 of the tested anchors, there was a relevantly lower load needed for slippage of the sutures than to pull out the anchor from bone. The mean load to anchor pullout ranged between 156 and 269 N. The load to suture slippage ranged between 66 and 109 N. All sutures were better held between the metal rods (mean, 21; 95% confidence interval [CI], 19.2 to 23.3) than with polyetheretherketone rods (mean, 17; 95% CI, 15.7 to 18.1) or poly-L-lactide acid rods (mean, 18; 95% CI, 17.6 to 18.4). CONCLUSIONS: In the case of suture anchors that hold the sutures by clamping, the hold of the suture in the anchor may be far lower than the pullout strength of the anchor from bone, because the sutures just slip out from the anchor through the clamping mechanism. This is well explained by the low static friction achieved between the tested sutures and the test rods made of anchor materials. CLINICAL RELEVANCE: The use of knotless suture anchors appears quick and easy to perform; however, most of the anchor systems could not even reach half of the anchor pullout strength from bone before suture slippage occurred.
    Arthroscopy The Journal of Arthroscopic and Related Surgery 09/2012; · 3.10 Impact Factor
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    ABSTRACT: Efficient and successful arthroscopic surgery relies on methodical and well-organized suture management. However, it is relatively common, especially in complex arthroscopic procedures, that sutures invariability become entangled or twisted as a result of repeated suture shuttling from portal to portal and between individual suture limbs. When this occurs, this can make antegrade suture passage or arthroscopic knot tying challenging. We describe a simple and efficient technique that allows simultaneous retrieval of 2 suture limbs while ensuring that the sutures are disentangled.
    Arthroscopy techniques. 09/2012; 1(1):e87-9.
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    ABSTRACT: The structural failure rate of rotator cuff repair can exceed 50%. Important predictors for repair failure are preoperative fatty muscle infiltration and myotendinous retraction. To quantitatively assess the prognostic value of preoperative retraction of both the supraspinatus muscle and tendon for the outcome of supraspinatus repair. Cohort study; Level of evidence, 3. In 33 shoulders with complete supraspinatus tendon ruptures subjected to arthroscopic repair, magnetic resonance imaging (MRI) scans taken preoperatively and after a mean follow-up of 24 months were studied. The exact position of the lateral extension of the supraspinatus muscle and of the tendon end was evaluated and correlated with the preoperative stage of fatty infiltration (Goutallier) and the failure rate of tendon repair. The mean lengthening of the muscle and tendon end was -3 mm and 4 mm in the failed repairs (n = 19) and 14 mm and 8 mm in the successful repairs (n = 14). If the supraspinatus had preoperative Goutallier stages 2 to 3 and a tendon length of less than 15 mm, the failure rate was 92%, but if the tendon length was greater than 15 mm, the failure rate was only 33%. With Goutallier stages 0 to 1, the corresponding failure rates were 57% and 25%, respectively. Rotator cuff repair lengthens the tendon, even if the repair fails. The possibility to lengthen the myotendinous unit is related to the preoperative length of the tendon. The combination of Goutallier grading and preoperative tendon length appears to be a more powerful predictor for the reparability of a tendon tear than Goutallier grading alone.
    The American journal of sports medicine 08/2012; 40(10):2242-7. · 3.61 Impact Factor
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    ABSTRACT: PURPOSE: This study was designed to compare the pull-out strength of simple suture stitches in human supraspinatus tendons with respect to the position of the rotator cable. METHODS: Fifty-four tests were performed on 6 intact, human supraspinatus tendons, to assess the cutout strength of a simple suture configuration in different positions; medial to, lateral to, or within the rotator cable. Tendon thickness was measured and correlated for each positioned suture. RESULTS: Suture positioning lateral to or in the rotator cable showed significantly lower suture retention properties compared with positioning the suture medial to the cable (p = 0.002). In all tested specimens, the central stitch in the row medial to the rotator cable provided the optimum retention properties (mean: 191 N; SD: ± 44; p < 0.01), even after correcting for tendon thickness. CONCLUSION: This study shows that it is desirable to identify the rotator cable and to pass sutures just medial to it, close to the middle of the tendon, which provided highest possible suture retention properties.
    Knee Surgery Sports Traumatology Arthroscopy 06/2012; · 2.68 Impact Factor
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    ABSTRACT: The purposes of this study were (1) to establish a reproducible, standardized testing protocol to evaluate the performance of different shaver systems and blades in a controlled, laboratory setting, and (2) to determine the optimal use of different blades with respect to the influence of contact pressure and speed of blade rotation. A holding device was developed for reproducible testing of soft-tissue (tendon and meniscal) resection performance in a submerged environment, after loading of the shaver with interchangeable weights. The Karl Storz Powershaver S2 (Karl Storz, Tuttlingen, Germany), the Stryker Power Shaver System (Stryker, Kalamazoo, MI), and the Dyonics Power Shaver System (Smith & Nephew, Andover, MA) were tested, with different 5.5-mm shaver blades and varied contact pressure and rotation speed. For quality testing, serrated shaver blades were evaluated at 40× image magnification. Overall, more than 150 test cycles were performed. No significant differences could be detected between comparable blade types from different manufacturers. Shavers with a serrated inner blade and smooth outer blade performed significantly better than the standard smooth resectors (P < .001). Teeth on the outer layer of the blade did not lead to any further improvement of resection (P = .482). Optimal contact pressure ranged between 6 and 8 N, and optimal speed was found to be 2,000 to 2,500 rpm. Minimal blunting of the shaver blades occurred after soft-tissue resection; however, with bone resection, progressive blunting of the shaver blades was observed. Arthroscopic shavers can be tested in a controlled setting. The performance of the tested shaver types appears to be fairly independent of the manufacturer. For tendon resection, a smooth outer blade and serrated inner blade were optimal. This is one of the first established independent and quantitative assessments of arthroscopic shaver systems and blades. We believe that this study will assist the surgeon in choosing the optimal tool for the desired effect.
    Arthroscopy The Journal of Arthroscopic and Related Surgery 06/2012; 28(10):1497-503. · 3.10 Impact Factor
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    ABSTRACT: The tensile viscoelastic behaviour of tendon tissue is of central biomechanical importance and well examined. However, the viscoelastic tendon adaptation to external compression, such as when a tendon graft is fixated with an interference screw, has not been investigated before. Here, we quantify this adaptive behaviour in order to develop a new method to mechanically precondition tendon grafts and to better understand volumetric changes of tendinous tissue. The hypothesis of this study was that under compressive loads, tendon grafts will undergo a temporary volumetric (and therefore diametric) reduction, due to the extrusion of water from the tendon. Compressive testing was performed on a material testing machine and load applied through the use of a custom-made mould, with a semi-circular cross section to accommodate the tendon graft. The effects of different compressive forces on the length, diameter and weight of tendon grafts were measured by calipers and a weighing scale, respectively. Further, different strain rates (1 vs. 10 mm/min) (n = 6, per rate), compression method (steady compression vs. creep) (n = 15 for each method) and different compression durations (1, 5, 10 min) (n = 5 for each duration) were tested to identify the most effective combination to reduce graft size by preserving its macroscopic structure. The effect of compression on volume reduction (75 % of initial volume and weight) reached a plateau at 6,000 N on an 8-mm tendon bundle. Length thereby increased by approximately 10 %. Both steady compression and creeping were able to reduce dimensions of the graft; however, creeping was more effective. There was no difference in effect with different durations for compression (p > 0.05) in both methods. The viscoelastic behaviour of hamstring tendon grafts under pressure allows preconditioning of the grafts for reduction of volume and diameter and therefore to drill a smaller bone tunnel, retaining more of the original bone. At the same time, the collagen content of the transplant is preserved and a tight fit of the transplant in the bone tunnel achieved.
    Archives of Orthopaedic and Trauma Surgery 06/2012; 132(9):1315-20. · 1.36 Impact Factor
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    ABSTRACT: Retraction, atrophy and fatty infiltration are signs subsequent to chronic rotator cuff tendon tears. They are associated with an increased pennation angle and a shortening of the muscle fibers in series. These deleterious changes of the muscular architecture are not reversible with current repair techniques and are the main factors for failed rotator cuff tendon repair. Whereas fast stretching of the retracted musculotendinous unit results in proliferation of non-contractile fibrous tissue, slow stretching may lead to muscle regeneration in terms of sarcomerogenesis. To slowly stretch the retracted musculotendinous unit in a sheep model, two here described tensioning devices have been developed and mounted on the scapular spine of the sheep using an expandable threaded rod, which has been interposed between the retracted tendon end and the original insertion site at the humeral head. Traction is transmitted in line with the musculotendinous unit by sutures knotted on the expandable threaded rod. The threaded rod of the tensioner is driven within the body through a rotating axis, which enters the body on the opposite side. The tendon end, which was previously released (16 weeks prior) from its insertion site with a bone chip, was elongated with a velocity of 1 mm/day. After several steps of technical improvements, the tensioner proved to be capable of actively stretching the retracted and degenerated muscle back to the original length and to withstand the external forces acting on it. This technical report describes the experimental technique for continuous elongation of the musculotendinous unit and reversion of the length of chronically shortened muscle.
    BMC Veterinary Research 05/2012; 8:50. · 1.86 Impact Factor
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    ABSTRACT: Background A well-defined, reproducible small animal model that allows quantitative assessment of musculotendinous changes would be desirable for investigations concerning rotator cuff pathology.Methods The supraspinatus tendon was released by osteotomy of the greater tuberosity in seven New Zealand rabbits. The musculotendinous unit was then allowed to retract during 6 weeks. Retraction was monitored with computed tomography (CT). At sacrifice, CT measurements of retraction were validated by measurement of the total length of the musculotendinous unit after sacrifice and by correlation with functional and structural properties of the musculotendinous unit at tendon release and at sacrifice.Results Mean (SD) retraction of the musculotendinous unit was 1.8 (0.2) cm on CT, precisely, and negatively correlated with the total length of the retracted musculotendinous unit at sacrifice (r = −0.87, p = 0.011) but not significantly correlated with CT measurements of atrophy (r = 0.20, p = 0.699) or fatty infiltration (r = 0.13, p = 0.78). Mean (SD) muscle work decreased from 1.6 (0.23) Nm to 1.2 (1) Nm (p = 0.056). Mean (SD) muscle fibre diameter decreased from 65 (10) µm to 48 (16) µm (p = 0.063). This decrease was significantly correlated with the amount of fatty infiltration (r = 0.79, p = 0.033).Discussion Tendon release using osteotomy of the rabbit greater tuberosity allows precise measurement of musculotendinous retraction and offers the possibility for functional muscular testing. Changes in the rabbit supraspinatus muscle caused by myotendinous retraction correspond to those observed in established sheep models.
    Shoulder & Elbow 04/2012; 4(2).
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    ABSTRACT: PURPOSE: Interference screw fixation of hamstring tendon grafts in bone has to overcome the challenges that tendons have a slippery surface and viscoelastically adapt under pressure. As the typical failure mode of the graft is to slip past the interference screw, it was hypothesized that the position and configuration of the graft end may be of influence on the fixation strength. METHODS: Different configurations of the graft ending and its effect to primary fixation with interference screws after viscoelastic adaptation were tested in six groups: I: graft and the screw inserted at the same depth, II/III: the graft overlaps the tip of the screw (interference screw of 28 and 19 mm in length, respectively), IV: strengthening of the graft ending with additional suture knots, V: Endopearl, respectively, and VI: effect of partial retraction of the screw after excessive insertion. In vitro tests were performed with fresh calf tendon grafts and interference screws in bone tunnels (fresh porcine distal femur) all of 8 mm in diameter. RESULTS: The relative position of the graft ending to the tip of the interference screw thereby was recognized as a significant factor on pullout forces. Further strengthening at the graft endings with additional suture knots or an Endopearl device could improve primary hold as well. CONCLUSIONS: Better fixation strength is achieved if the tip of interference screw does not extend past the end of a tendon graft. Enforcement of the tendon end with sutures or an implant can further improve fixation.
    Knee Surgery Sports Traumatology Arthroscopy 03/2012; · 2.68 Impact Factor