Initial Fixation Stability Research Articles

Morphometric and Biomechanical Comparison of the Scapular Spine and Coracoid Graft in Anterior Shoulder Instability

Background: The scapular spine has been described as a relatively new bone graft alternative used in glenoid augmentation. The classic Latarjet procedure, which transfers the coracoid as a graft, is regarded as the gold standard. The comparison of these 2 techniques has not been fully reported. Purpose: To compare the anatomic and biomechanical properties of glenoid augmentation using scapular spine graft or coracoid graft. Study Design: Controlled laboratory study. Methods: The study used 20 fresh-frozen human cadaveric shoulders. A 25% anterior glenoid defect was created, and the specimens were divided randomly to receive glenoid augmentation by scapular spine or coracoid grafts. For both procedures, the grafts were secured to the glenoid defect with 2 screws. Morphometric data, including the glenoid articular area, amount of restoration, and graft dimensions, were obtained. A biomechanical test was conducted in a direct-loading scenario. The construct stiffness, cyclic displacement, and ultimate failure of each specimen were collected. Results: No significant difference was found in glenoid articular restoration between the scapular spine group and the coracoid group (31% vs 33%, respectively; P = .311). Morphometric analysis indicated that coracoid grafts exhibited significantly greater thickness and height than scapular spine grafts. In biomechanical results, the scapular spine group exhibited significantly greater construct stiffness than the coracoid group (206.3 ± 58.8 vs 148.3 ± 76.0 N/mm, respectively; P = .023). The average failure load in the scapular spine group was not significantly higher than that in the coracoid group. No significant differences in cyclic displacement were found between the 2 techniques. Conclusion: In a simulated 25% anterior glenoid bony defect, a scapular spine graft was comparable with the classic Latarjet procedure in restoring the glenoid articular dimension and exhibited superior construct stiffness in a cadaveric model. Clinical Relevance: The scapular spine may serve as an alternative graft choice in glenoid augmentation surgery considering the amount of articular restoration and initial fixation stability.

Tensioning device increases biomechanical stability of tuberosity fixation technique with cerclage sutures in reverse shoulder arthroplasty for fracture

Complex proximal humeral fractures in elderly patients are increasingly treated with primary reverse total shoulder arthroplasty. Many surgeons use cerclage sutures for tuberosity fixation in reverse total shoulder arthroplasty for proximal humeral fractures. In this study, we hypothesized that sutures fixated with a tensioning device would achieve higher initial fixation stability of the tuberosities compared with manually knotted cerclage sutures in a biomechanical model. A 4-part fracture was created in 7-paired human cadaver proximal humeri. The tuberosities were reduced anatomically and fixed with 3 cerclage sutures in a standardized technique. Tightening was performed either manually (n = 7) or with a cerclage tensioning device with 50 Newton meter (N m) (n = 7). The humeri were placed in a custom-made test setup enabling internal and external rotation. Cyclic loading with gradually increasing load was applied with a material testing machine starting with 20 N m and increasing by 5 N m after each 100th cycle until failure (>15° rotation of the tuberosities). Motion of the tuberosities was measured with a 3-dimensional camera system. Overall, the knot group reached 1040 ± 152 cycles, and the device group reached 1820 ± 719 cycles (P = .035). Major fragment motion was detected in the humeral shaft axis and in the distal divergence of the tuberosities. After 900 cycles, the knot group showed increased rotation of both lesser and greater tuberosities in all 3 axes around the humeral shaft compared with the device group. Biomechanical stability of the reattached tuberosities is significantly increased, and rotational movement of the tuberosities is decreased after tightening of the applied cerclage sutures with a tensioning device compared with manual knotting. However, transferability of these promising biomechanical results and their clinical relevance have to be verified with clinical studies.

Tapered stem geometry provides superior initial fixation stability to cylindrical stem geometry in the setting of severe bone loss: A finite element analysis

AbstractInitial stability of cementless stems used in total hip arthroplasty (THA) is critical for subsequent osseointegration at the bone/implant interface. In the setting of revision THA, there is frequently less intact femoral bone available for fixation of the new stem. This study aims to compare the initial fixation stability between a cylindrical and tapered stem, designed for diaphyseal fixation in a revision THA setting, with increasing bone defect severity. Using finite element analysis, severe Paprosky Type III femoral bone defects were simulated. The cylindrical stem had a 13.3% higher construct stiffness as compared to the tapered stem for the least severe bone defect modeled. In contrast, for the most severe bone defect, the tapered stem showed a 12.3% higher construct stiffness than the cylindrical stem. At the bone/implant interface, the tapered design resulted in less than 20 μm of maximum tangential micromotion for all the bone defect models, whereas the cylindrical stem exceeded 20 μm for all and was as high as 70 μm in the most severe case. Given the limitations of the models presented, the results suggest the tapered stem obtained superior initial fixation as compared to cylindrical stem with increasing bone defect severity.

Long-term study on the osteogenetic capability and mechanical behavior of a new resorbable biocomposite anchor in a canine model

BackgroundBiodegradable suture anchors are commonly used for repairing torn rotator cuffs, but these biodegradable materials still suffer from low mechanical strength, poor osteointegration, and the generation of acidic degradation byproducts. MethodThe purpose of this study was to evaluate the long-term mechanical behavior and osteogenetic capabilities of a biocomposite anchor injection molded with 30% β-tricalcium phosphate microparticles blended with 70% poly (L-lactide-co-glycolide) (85/15). This study investigated in vitro degradation and in vivo bone formation in a canine model. The initial mechanical behavior, mechanical strength retention with degradation time, and degradation features were investigated. ResultsThe results showed that the biocomposite anchor had sufficient initial mechanical stability confirmed by comparing the initial shear load on the anchor with the minimum shear load borne by an ankle fracture fixation screw, which is considered a worst-case implantation site for mechanical loading. The maximum shear load retention of the biocomposite anchor was 83% at 12 weeks, which is desirable, as it aligns with the rate of bone healing. The β-tricalcium phosphate fillers were evenly dispersed in the polymeric matrix and acted to slow the degradation rate and improve the mechanical strength of the anchor. The interface characteristics between the β-tricalcium phosphate particles and the polymeric matrix changed the degradation behavior of the biocomposite. Phosphate buffer saline was shown to diffuse through the interface into the biocomposite to inhibit the core accelerated degradation rate. In vivo, the addition of β-tricalcium phosphate induced new bone formation. The biocomposite material developed in this study demonstrated improved osteogenesis in comparison to a plain poly (L-lactide-co-glycolide) material. Neither anchor produced adverse tissue reactions, indicating that the biocomposite had favorable biocompatibility following long-term implantation. ConclusionIn summary, the new biocomposite anchor presented in this study had favorable osteogenetic capability, mechanical property, and controlled degradation rate for bone fixation. Translational potential of this articleThe new biocomposite anchor had sufficient initial and long-term fixation stability and bone formation capability in the canine model. It is indicated that the new biocomposite anchor has a ​potential for orthopedic application.

Clinical outcomes of 119 miniature- and toy-breed dogs with 140 distal radial and ulnar fractures repaired with free-form multiplanar type II external skeletal fixation.

To report the clinical outcomes of miniature- and toy-breed dogs with primary and previously treated distal radial and ulnar fractures (RUF) treated with a free-form multiplanar type II external skeletal fixation (ESF). Retrospective study. One hundred nineteen dogs with 140 distal RUF. Medical records (2003-2017) were reviewed for dogs weighing up to 7 kg that had been treated for distal RUF with a free-form multiplanar type II ESF. Data collected included signalment, fracture location and configuration, fracture reduction, intraoperative realignment, time to bone union and implant removal, duration of destabilization and postoperative splint, complications, and outcomes. Follow-up consisted of clinical and radiographic evaluation or telephone interview. All fractures healed, with a median time of 60 days, and entire ESF was removed, with a median time of 89 days. Major complications occurred in four fractures: premature pin loosening, elbow subluxation, osteomyelitis, and delayed union. Minor complications occurred in 52 fractures (61 events). All dogs had a successful return to normal limb function at final follow-up (median, seven months; range, 2-97). All primary and previously treated distal RUF in miniature- and toy-breed dogs healed and allowed return to normal function after fixation with a free-form multiplanar type II ESF. The free-form multiplanar type II ESF provides an alternative for minimally invasive fixation of distal RUF in miniature- and toy-breed dogs that facilitates fracture reduction, intraoperative realignment, adequate initial fixation stability, destabilization, and implant removal.

Reverse total shoulder glenoid baseplate stability with superior glenoid bone loss

Superior wear of the glenoid bone is common in patients with rotator cuff arthropathy. This can become a treatment challenge for patients who require shoulder arthroplasty. In reverse shoulder arthroplasty (RSA), glenoid bone loss may affect the stability of baseplate fixation. The primary purpose of this biomechanical laboratory study was to assess the initial fixation stability of RSA glenosphere baseplates in the presence of variable amounts of superior glenoid bone loss. High-density solid rigid polyurethane foam (30 pounds/cubic foot) was machined to model the glenoid with variable superior defects that provided different levels of support (100%, 90%, 75%, and 50%) for the glenosphere baseplate. The samples were cyclically loaded (0-750 N at 1 Hz for 5000 cycles) at a 60° glenohumeral angle. The micromotion and migration of the baseplate were calculated from displacement data captured during the loading tests with an array of 3 linear variable differential transformers mounted around the baseplate. Micromotion was significantly greater in samples with 50% defects compared with those with smaller defects. Migration was significantly greater after testing for all defect sizes. Initial fixation of RSA glenosphere baseplates was significantly reduced in models with 50% bone loss on the superior edge compared with models with less bone loss in this high-density bone foam model.

Biomechanical Analysis of Latarjet Screw Fixation: Comparison of Screw Types and Fixation Methods

To compare the initial fixation stability, failure strength, and mode of failure of 5 different screw types and fixation methods commonly used for the classic Latarjet procedure. Thirty-five fresh-frozen cadaveric shoulder specimens were allocated into 5 groups. A 25% anteroinferior glenoid defect was created, and a classic Latarjet coracoid transfer procedure was performed. All grafts were fixed with 2 screws, differing by screw type and/or fixation method. The groups included partially threaded solid 4.0-mm cancellous screws with bicortical fixation, partially threaded solid 4.0-mm cancellous screws with unicortical fixation, fully threaded solid 3.5-mm cortical screws with bicortical fixation, partially threaded cannulated 4.0-mm cancellous screws with bicortical fixation, and partially threaded cannulated 4.0-mm captured screws with bicortical fixation. All screws were stainless steel. Outcomes included cyclic creep and secant stiffness during cyclic loading, as well as load and work to failure during the failure test. Intergroup comparisons were made by a 1-way analysis of variance. There were no significant differences among different screw types or fixation methods in cyclic creep or secant stiffness after cyclic loading or in load to failure or work to failure during the failure test. Post-failure radiographs showed evidence of screw bending in only 1 specimen that underwent the Latarjet procedure with partially threaded solid cancellous screws with bicortical fixation. The mode of failure for all specimens analyzed was screw cutout. In this biomechanical study, screw type and fixation method did not significantly influence biomechanical performance in a classic Latarjet procedure. When performing this procedure, surgeons may continue to select the screw type and method of fixation (unicortical or bicortical) based on preference; however, further studies are required to determine the optimal method of treatment. Surgeons may choose the screw type and fixation method based on preference when performing the Latarjet procedure.

Stem geometry changes initial femoral fixation stability of a revised press-fit hip prosthesis: A finite element study.

Stable femoral fixation during uncemented total hip arthroplasty is critical to allow for subsequent osseointegration of the prosthesis. Varying stem designs provide surgeons with multiple options to gain femoral fixation. The purpose of this study was to compare the initial fixation stability of cylindrical and tapered stem implants using two different underreaming techniques (press-fit conditions) for revision total hip arthroplasty (THA). A finite element femur model was created from three-dimensional computed tomography images simulating a trabecular bone defect commonly observed in revision THA. Two 18-mm generic femoral hip implants were modeled using the same geometry, differing only in that one had a cylindrical stem and the other had a 2 degree tapered stem. Surgery was simulated using a 0.05-mm and 0.01-mm press-fit and tested with a physiologically relevant loading protocol. Mean contact pressure was influenced more by the surgical technique than by the stem geometry. The 0.05-mm press-fit condition resulted in the highest contact pressures for both the cylindrical (27.35 MPa) and tapered (20.99 MPa) stems. Changing the press-fit to 0.01-mm greatly decreased the contact pressure by 79.8% and 78.5% for the cylindrical (5.53 MPa) and tapered (4.52 MPa) models, respectively. The cylindrical stem geometry consistently showed less relative micromotion at all the cross-sections sampled as compared to the tapered stem regardless of press-fit condition. This finite element analysis study demonstrates that tapered stem results in lower average contact pressure and greater micromotion at the implant-bone interface than a cylindrical stem geometry. More studies are needed to establish how these different stem geometries perform in such non-ideal conditions encountered in revision THA cases where less bone stock is available.

A novel suture anchor constructed of cortical bone for rotator cuff repair: a biomechanical study on sheep humerus specimens.

The aim of this study was to evaluate biomechanical properties of a new type of suture anchors constructed of human cortical allograft bone and compare it with the similar standard titanium screw anchor for rotator cuff tears in sheep humerus model. Twenty-four paired sheep humeri were harvested from 12 male sheep aged 18months. Specimens were divided into cortical bone anchor group and titanium screw anchor group. The anchors loaded with two sutures were placed at the footprint of infraspinatus tendon. Cyclic loading test was performed from 10 to 60N at 1Hz for 500cycles and followed by a load-to-failure test at 33mm/sec. A paired t-test was used to compare the biomechanical properties of the anchors of each type. No anchors failed during the cyclic phase, and the cortical bone anchors were all pulled out intact. The cyclic displacement of the cortical bone anchor was not significantly greater than that of the titanium screw anchor (P > 0.05). Student's t test showed no statistically significant difference between anchors in terms of failure load (cortical bone anchor: 304.74 ± 64.46N versus titanium screw anchor: 328.45 ± 89.58N; P = 0.213), ultimate load (cortical bone anchor: 325.82 ± 76.45N versus titanium screw anchor: 345.61 ± 83.56N; P = 0.183), yield load (cortical bone anchor: 273.78 ± 44.75N versus titanium screw anchor: 284.72 ± 56.37N; P = 0.326) or stiffness (cortical bone anchor: 52.97 ± 14.28N/mm versus titanium screw anchor: 62.38 ± 18.35N/mm; P = 0.112). In vitro, this experimental study suggested no statistically significant difference in initial fixation stability between the new type anchor and titanium screw anchor at a chosen level of significance (P < 0.05). The new type of suture anchor constructed of cortical bone provides comparable initial fixation strength to a similar metallic anchor for rotator cuff repair.

Tapered vs Cylindrical Stem Fixation in a Model of Femoral Bone Deficiency in Revision Total Hip Arthroplasty

BackgroundDistal fixation achieved with a tapered stem design has demonstrated favorable clinical results in revision total hip arthroplasty in the setting of severe bone defects. However, stem subsidence is common with this stem design. PurposeThe purpose of this study is to compare the initial fixation stability of a tapered stem design to a fully porous-coated cylindrical stem design in a model of severe femoral bone deficiency. MethodsTapered and cylindrical stems (n = 8) were implanted into a model femur with progressively shorter segments for fixation (9, 6, or 3 cm). The stems were axially loaded, and the force to produce subsidence was recorded. ResultsAverage loads to produce 150 μm of displacement with a 3-cm segment were higher for the tapered stem (393 N vs 221 N, P < .01). No difference was observed in the 6- or 9-cm models. Average loads to produce failure (>4-mm subsidence) were also higher for tapered stems with a 3-cm segment (1574 N vs 500 N, P < .0001). A regression analysis determined the minimum segment length of 1.5-2.5 cm to obtain stable fixation with a tapered stem design (R2 = 0.78, P < .001). ConclusionsTapered stems required higher loads to produce subsidence than cylindrical stems in a revision THA model. Revision tapered stems require a minimum intact segment of 1.5-2.5 cm to obtain adequate initial fixation stability. Revision tapered stems have superior initial fixation stability to cylindrical stems in the setting of severe bone loss.

Perceptual learning in patients with macular degeneration.

Patients with age-related macular degeneration (AMD) or hereditary macular dystrophies (JMD) rely on an efficient use of their peripheral visual field. We trained eight AMD and five JMD patients to perform a texture-discrimination task (TDT) at their preferred retinal locus (PRL) used for fixation. Six training sessions of approximately one hour duration were conducted over a period of approximately 3 weeks. Before, during and after training twelve patients and twelve age-matched controls (the data from two controls had to be discarded later) took part in three functional magnetic resonance imaging (fMRI) sessions to assess training-related changes in the BOLD response in early visual cortex. Patients benefited from the training measurements as indexed by significant decrease (p = 0.001) in the stimulus onset asynchrony (SOA) between the presentation of the texture target on background and the visual mask, and in a significant location specific effect of the PRL with respect to hit rate (p = 0.014). The following trends were observed: (i) improvement in Vernier acuity for an eccentric line-bisection task; (ii) positive correlation between the development of BOLD signals in early visual cortex and initial fixation stability (r = 0.531); (iii) positive correlation between the increase in task performance and initial fixation stability (r = 0.730). The first two trends were non-significant, whereas the third trend was significant at p = 0.014, Bonferroni corrected. Consequently, our exploratory study suggests that training on the TDT can enhance eccentric vision in patients with central vision loss. This enhancement is accompanied by a modest alteration in the BOLD response in early visual cortex.

Do the Traditional and Modified Latarjet Techniques Produce Equivalent Reconstruction Stability and Strength?

Background: The Latarjet procedure has been described as a reconstructive option for instability associated with substantial glenoid bone defects. A modification, termed the Congruent-Arc, is thought to improve glenoid reconstruction through better articular congruency and greater bone reconstitution. The strengths of these techniques, however, have not been reported. Purpose/Hypothesis: To compare the fixation stability, strength, glenoid vault load transfer, and joint contact between the Classic and Congruent-Arc techniques. The authors hypothesized that the Classic Latarjet would exhibit inferior joint contact characteristics while having greater stability and strength and more normal glenoid vault strain. Study Design: Controlled laboratory study. Methods: Sixteen shoulder specimens (8 pairs) were tested by loading the glenohumeral joint with the glenoid intact, following creation of a 25% anterior bone defect, and after random assignment to the Classic or Congruent-Arc Latarjet techniques. Specimens were mounted to a testing apparatus that allowed concentric, centralized loading and loading 30° anterior on the glenoid rim. Cyclic loading (100 cycles at 1 Hz) was applied with a staircase protocol (50, 100, 150, and 200 N). Graft interface displacement and glenoid load transfer, quantified in terms of strain, were recorded during loading. Contact was quantified during 50-N loading using a thin pressure sensor. After cyclic loading, specimens were loaded to failure, defined as 5 mm of graft interface displacement. Results: The 30° loading ≥100 N resulted in significantly greater graft displacement (P < .004) in the Congruent-Arc group as compared with the Classic (mean displacement range, 0.9-2.6 vs 0.1-0.5 mm, respectively). Failure testing yielded a significantly (P = .010) greater ultimate strength for the Classic (557 N) as compared with the Congruent-Arc (392 N). Load-transfer measurements demonstrated that neither technique’s glenoid vault strain values significantly differed from intact (P ≥ .076). Both techniques resulted in contact areas significantly less than intact (P < .035); however, the Congruent-Arc trended toward better contact characteristics (P = .074). Conclusion: The Congruent-Arc results in significantly poorer fixation stability as compared with the Classic technique but did more closely reproduce intact joint contact, which may yield more favorable long-term outcomes. Clinical Relevance: Care must be taken in balancing the consideration of initial fixation stability and joint contact for the Congruent-Arc and Classic Latarjet, as these factors have opposing implications for each of the 2 reconstructions’ outcomes.

The Effects of Interfacial Conditions and Stem Length on Potential Failure Mechanisms in the Uncemented Resurfaced Femur

It is hypothesized that changes in stem length and implant-bone interfacial conditions would affect the mechanical environment within the uncemented resurfaced femur, thereby influencing potential short- and long-term failure mechanisms. This study is aimed at investigating the influence of changes in implant-bone interfacial conditions and stem length on eventual failure, using 3D FE models integrated with bone remodeling simulations. Musculoskeletal forces corresponding to normal walking and stair climbing were used as applied loading conditions. Sliding micromotions of 26-72 microm at the implant-bone interfaces for both the stem designs suggest bone ingrowth on the coated surface of the implant was likely. The initial risk of femoral neck fracture was less for the uncemented designs as compared to the cemented designs, irrespective of interfacial conditions and variation in stem length. For the uncemented variety, shortening the stem length provided only slight advantages (5%) with regard to strain shielding and bone remodeling. However, bone resorption was considerably higher when fully bonded interfaces were simulated. It may, therefore, be concluded that cementless fixation seems to be a viable alternative to cemented fixation, provided sufficient initial fixation and secondary stability through bone ingrowth into the coated surface of the implant can be achieved.

The influence on the contact condition and initial fixation stability of the main design parameters of a self-expansion type anterior cruciate ligament fixation device

This paper proposes a self-expansion type anterior cruciate ligament fixation device. The proposed fixation device provides graft fixation force by maintaining contact with the bone tunnel. Since the device maintains contact with the bone tunnel by the force that expands by the self-driven elastic force of the device, the main design parameters that determine the performance of this device are the ring thickness and expansion angle. This paper develops the three-dimensional finite element models of the fixation device and bone. By simulation with the developed finite element model, this paper studies the influence of the main design parameters of the device on the maximum stress around the ring when grasping the fixation device. Through the analysis of the stress on the bone tunnel wall when the fixation device comes in contact with the bone tunnel, this paper shows the influence of the main design parameters of the fixation device on the contact condition. In addition, through the analysis of the migration that occur upon application of the pull-out force, this paper studies the influence of the main design parameters on the initial fixation stability of the fixation device.

Biomechanical in vitro evaluation of the effect of cyclic loading on the postoperative fixation stability and degradation of a biodegradable ankle plate

The effect of cyclic loading on the postoperative fixation stability of a biodegradable ankle plate was tested biomechanically during 12 weeks of hydrolytic degradation. Fracture of the lateral malleolus was simulated, and the parameters of cyclic loading were chosen to represent the physiological conditions during the healing period. Additionally, the effect of cyclic loading on degradation was investigated by measuring the inherent viscosities. In Group I, the cyclic loading was conducted in four phases with gradual increases in estimated walking distance and speed during the healing period. In Group II, cyclic loading was conducted after 12 weeks. Group III was used as a control for inherent viscosity measurements. None of the specimens failed under cyclic loading. No significant differences were found between the loaded groups in any of the parameters measured. Additionally, no significant difference was found in inherent viscosities at 12 weeks. The initial fixation stability provided by the biodegradable ankle plate remains biomechanically unchanged over 12 weeks. Cyclic loading, applied either during or after 12 weeks of hydrolytic degradation, does not seem to have any clinically relevant effect on the fixation stability or the degradation properties.

Addition of a short central extension to surface cemented tibial trays in primary TKA: An in vitro study of the effect on initial fixation stability and its relationship to supporting bone density

Background Short central extensions which do not enter the tibial medullary canal are incorporated to cemented tibial components to increase initial stability in primary total knee arthroplasty. Their role in tibiae of differing preoperative mechanical quality has been little studied. Methods Twelve embalmed cadaveric tibiae were paired and divided into two groups, receiving a similar cemented tibial component with or without a non-cemented short central extension (10 mm diameter, 35 mm length). The specimens were subjected to 6000 cycles of a medially applied 1350 N load. Relative bone–tray displacements were measured and the evolution of inducible and permanent micromotions were computed. The apparent density of the cancellous bone under the tibial tray and at the area to support the extension was computed from computed tomography images of each specimen. Findings No significant differences between groups were detected for any parameters. For the group with extension, a significant negative linear correlation ( P = 0.009, r 2 = 0.849) was found between the inducible tilt of the tray and the bone density at the zone of the extension. Also a trend towards a negative linear relation ( P = 0.07, r 2 = 0.59) was observed for the same group between maximum subsidence and apparent density at the zone of the extension. Interpretation The study did not find that the addition of a non-cemented short central extension provides any overall improvement of the initial fixation stability. However, it was found that short extensions may enhance tilting stiffness of the bone–implant construct if bone of sufficient mechanical quality is located around its supporting area.

Initial fixation and cyclic loading stability of knotless suture anchors for rotator cuff repair

This study evaluated the resistance to gapping and the mode of failure for 2 knotless suture anchor systems used for rotator cuff repair compared with the performance of a conventional titanium anchor system. Eight matched pairs of fresh-frozen humeri were dissected free of all soft tissues and scanned to measure bone mineral density (BMD). The suture anchor systems tested were the TwinFix 5.0 Titanium (Smith & Nephew, Andover, MA), Bioknotless RC (DePuy Mitek, Norwood, MA), and Magnum (Opus Medical, San Juan Capistrano, CA), and each was inserted into each humerus. Cyclic, tensile loading was applied through the suture loop for 5000 cycles, or until failure, by using a servohydraulic testing machine. Gapping distances, defined as increasing elongation of the bone/anchor/suture system, were continuously measured. Total cycles to failure and mechanism of failure were documented. Mean initial (first cycle) and final (last cycle) gapping distances were 3.81 mm and 5.36 mm for the TwinFix 5.0, 4.02 mm and 5.34 mm for the Bioknotless RC, and 3.56 mm and 4.98 mm for the Magnum anchors. No significant difference was detected among mean gap openings (P > .05). However, the Bioknotless RC had more early failures (5) than the other 2 implants (1 each), approaching significance (P = .07). Trials of the Bioknotless RC that did not fail early were found to have significantly less gap opening than the other 2 systems for both initial (1.89 mm vs 3.82 mm for the TwinFix 5.0 and 3.56 mm for the Magnum) and final (2.00 mm vs 4.68 mm for the TwinFix 5.0 and 4.24 mm for the Magnum) gap opening. BMD was a significant predictor of initial (P = .029) and final (P = .008) gap opening, whereas the site of anchor insertion was a significant predictor of final displacement. The Opus Magnum was comparable with a conventional suture anchor, but the Mitek Bioknotless RC showed a trend toward early failure. Biomechanical analysis of knotless suture anchor systems can demonstrate trends among implants in an experimental setting. Knowledge of these trends could influence implant selection.

Anterior Cruciate Ligament Reconstruction with Use of Autologous Quadriceps Tendon Graft

Anterior cruciate ligament rupture is the most common knee ligament injury. Of the grafts that are used for anterior cruciate ligament reconstruction, bone-patellar tendon-bone is still the most common because of its initial fixation stability and its ultimate tensile strength and elastic modulus, which are superior to those of other graft sources. Hamstring tendon grafts recently have demonstrated functional results equivalent to those of bone-patellar tendon-bone grafts. While most recent studies have failed to demonstrate significant differences between the two types of grafts, many authors have reported on their strengths and weaknesses1-12. While there has been a trend toward better stability in association with bone-patellar tendon-bone grafts, postoperative complications, including anterior knee pain and patellofemoral problems, have been reported frequently13-20. Knee-extension deficits have been reported to occur more frequently in association with bone-patellar tendon-bone grafts as compared with hamstring tendon grafts1,7. Graft laxity and tunnel enlargement have been reported in association with hamstring tendon grafts, and some authors have found persistent muscular deficits in knee flexion and internal rotation strength after treatment with hamstring tendon grafts5,21. In 2004, we reported the early results for a series of patients undergoing anterior cruciate ligament reconstruction with use of a quadriceps tendon autograft22. The central quadriceps tendon-patellar bone autograft has been proposed as a reasonable source of anterior cruciate ligament graft by some authors as it offers adequate mechanical strength and easier rehabilitation, while some postoperative complications can be avoided23-28. The anatomy and mechanical properties of the quadriceps tendon were well described in a series of studies by Staubli et al.27,29-31. The cross-sectional area of the quadriceps tendon was almost twice that of the patellar …

The course of bone healing is influenced by the initial shear fixation stability

Fracture healing is influenced by fixation stability and experimental evidence suggests that the initial mechanical conditions may determine the healing outcome. We hypothesised that mechanical conditions influence not only the healing outcome, but also the early phase of fracture healing. Additionally, it was hypothesised that decreased fixation stability characterised by an increased shear interfragmentary movement results in a delay in healing. Sixty-four sheep underwent a mid-shaft tibial osteotomy which was treated with either a rigid or a semi-rigid external fixator. Animals were sacrificed at 2, 3, 6 and 9 weeks postoperatively and the fracture callus was analysed using radiological, biomechanical and histological techniques. The tibia treated with semi-rigid fixation showed inferior callus stiffness and quality after 6 weeks. At 9 weeks, the calluses were no longer distinguishable in their mechanical competence. The calluses at 9 weeks produced under rigid fixation were smaller and consisted of a reduced fibrous tissue component. These results demonstrate that the callus formation over the course of healing differed both morphologically and in the rate of development. In this study, we provide evidence that the course of healing is influenced by the initial fixation stability. The semi-rigid fixator did not result in delayed healing, but a less optimal healing path was taken. An upper limit of stability required for successful healing remains unknown, however a limit by which healing is less optimal has been determined.

Stability, bone healing and loss of correction after valgus realignment of the tibial head. A roentgen stereometry analysis

In high tibial closing-wedge osteotomies (HTO), closure of an osteotomy gap after resection of a bony wedge can be associated with a fissure of the medial cortex of the tibial head (MCT). The effect of a broken MCT on the recurrence of varus deformity is disputed. In this study, serial roentgen stereometric analysis (RSA) was used to determine the fixation stability of a rigid internal "L" plate after HTO. Full weight lower limb radiographs were used to determine the sagittal alignment in patients with varying degrees of varus malalignment and correction over time. Forty-two patients with varus gonarthrosis stage I-III (Ahlback) were treated with HTO and internal fixation with an L-shaped rigid plate. Patients were followed by serial RSA, conventional radiographs, and clinical evaluation (Hospital of Special Surgery score) over a 12-month period. In 19 of 42 successive patients, an average wedge size of 6.9 degrees was resected leaving the MCT intact (group 1). In 23 of 42 of patients, the MCT was unintentionally fissured during surgery when an average 10.3 degrees -wedge was resected (group 2). In group 2, RSA revealed a fivefold increase in lateral displacement of the distal tibial segment within 3 weeks after HTO. Twelve weeks after HTO, translations between tibial segments were below the accuracy of the RSA setup in the majority of patients. Group 1 patients demonstrated a higher initial fixation stability, less occurrence of varus deformity, and a higher HSS score compared to patients with larger wedge sizes and frequent fracture of the MCT (group 2). Before bone healing is achieved, the integrity of the MCT plays a crucial role for the clinical and radiological outcome after HTO.