Name: Histologic and Biomechanical Analysis of Two Small Glenoid Anchors for use in Labral Repair
Uploaded: 2014-03-05T00:00:00Z
Channel: Arthrex
Description: James Cook, DVM, PhD, director of the Comparative Orthopaedic Laboratory at the University of Missouri, presents his research on the biomechanical and biological comparisons of a traditional bioabsorbable anchor versus the “all suture” style anchors currently available for clinical use.

<p>James Cook, DVM, PhD, director of the Comparative Orthopaedic Laboratory at the University of Missouri, presents his research on the biomechanical and biological comparisons of a traditional bioabsorbable anchor versus the “all suture” style anchors currently available for clinical use.</p>

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VPT1-00216-EN | A | Histologic and Biomechanical Analysis of Two Small Glenoid Anchors for use in Labral Repair

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Histologic and Biomechanical Analysis of Two Small Glenoid Anchors for use in Labral Repair

I'm Jimmy Cook and I'm the director of orthopedic research at the University of Missouri. Today, I'm pleased to present the results of a study we performed examining histologic and biomechanical analysis of two small glenoid anchors for use in labor repair. I want to acknowledge and thank my co-investigators for this work. Doctors Pfeifer, Smith, and Kuroki. This study was funded by Arthrex and will be available via E-pub in the Journal of Shoulder and Elbow Surgery within the next few days. As you all well know. Shoulder dislocation is extremely common and importantly, recurrence can be expected in up to 90% of young patients. The glenoid labrum is torn in essentially all of these cases, and repair of the labral tear is considered to be critical to long term success for these patients. We also see other causes for labral tears requiring surgery. With current technology, arthroscopic label repair is very feasible and is typically successful when done well. However, we do see a significant number of failures in labor repair. Labor repairs primarily fail because of loss of reduction or apposition of torn labral tissue to glenoid bone as little as 2 to 3mm of displacement can result in clinical failure. So the goal for label payers is to maintain very solid fixation with less than three millimeters of displacement during the critical healing period, which we would consider to be the first eight weeks following repair. One key to success is to increase the number of fixation points for the repair. The more points of fixation, the better. So there is a clinical need for small suture anchors that can safely be placed in the glenoid and still allow for secure fixation. Two major types of small anchors are currently available soft all suture anchors and the traditional solid anchors. So the purpose of our study was to perform a direct head to head comparison of these two types of small glenoid anchors for the traditional solid anchor. We chose the 2.4mm Biocomposite SutureTak. These absorbable anchors accomplish fixation by interdigitation with the glenoid bone for the soft all suture anchor. We chose the juggernaut. This anchor is dependent on change in configuration or its geometry. After insertion, so that it lodges in the bony socket, the Socket. The geometry change must be maintained throughout healing, as this is a non absorbable suture material that does not integrate. So when we test anchors in most of the orthopedic literature, most commonly suture anchors are evaluated by performing in vitro pull out testing to determine ultimate pull out strength. While this provides important information, we would submit that it is not the most critical or clinically relevant data because alone it cannot predict success or failure. We really don't care how strong the implant is, unless the strength of fixation prevents displacement for long enough for healing to occur. In addition, this assessment does not give us any information regarding biocompatibility or tissue responses to the material, which of course are critical to both safety and efficacy of the device. So for our head to head comparison, we perform two parallel study arms to test biology using an in vivo canine model and clinically relevant biomechanics using human cadaveric glenoid tissues for the in vivo canine model. After AKC approval, we used adult research dogs and we placed anchors through a mini approach into the glenoid, into either the anterior or posterior area of the glenoid rim, and we alternated those sites. We put a simple stitch from the anchor around the adjacent labrum and the capsule, and the dogs were allowed full ambulation in their runs for the duration of the study. At the eight week sacrifice, we did histological assessments for the biomechanical portion. We did an ex vivo human study with IRB approval. We used four matched pairs of fresh human cadaveric glenoid. The anchors were implanted into the anterior inferior quadrant of each glenoid, again alternated between sites. And then we used biomechanical testing. Importantly for the biomechanical testing in the human glenoid, the anchor constructs were preloaded to five Newtons, cycled from five newtons to 25 newtons for 100 cycles, and then pulled to failure at 15mm per minute. Displacement, yield load, ultimate load displacement, and ultimate load. Cyclic displacement and loads at one millimeter and two millimeter displacement were determined. So let's cut right to the chase. In terms of results for the in vivo study we saw very consistent results. All of the juggernaut anchors were associated with cyst like cavities in the glenoid bone, as seen in the two images. On the upper right, you can see the large cysts containing remaining suture material walled off by a rim of dense lamellar bone. In contrast, all of the SutureTak anchors seen on the lower right were intact and showed very close approximation of trabeculae lamellar bone that interdigitated well with the anchors. No overt foreign body reaction or other pathological findings were noted for the SutureTak anchors. In order to quantify the amount of socket expansion in the glenoid bone for each anchor type, we directly measured socket width at the eight week time point using histo Morphometry mean socket diameter noted for juggernaut anchors was 6.3mm, expanded from the original drillbit diameter of 1.4mm, while mean socket diameter for SutureTak anchors was 2.7mm, expanded from the original drillbit diameter of 2.4mm. These concentric circle diagrams on the right illustrate the significantly greater amount of socket expansion seen during the first eight weeks after implantation for the juggernaut anchors. Compared to the SutureTak anchors, with SutureTak anchors maintaining appropriate interdigitation with host bone for the eight week duration of the study. For the biomechanical testing in cadaveric glenoid bone, we saw very consistent and very contrasting results for each anchor type. For the juggernaut, all suture anchors graphed here in blue, we noted multiple peaks over a large degree of displacement on the force displacement curves. This was noted to be caused by slipping of the implant in the socket, with associated change in the geometry of the construct. Essentially, the all suture not sequentially unraveled, allowing for large displacement with relatively little applied load. Seven of the juggernauts failed by pullout, while one failed by suture breakage. In contrast, the SutureTak anchors graphed here in red consistently showed steep and linear forced displacement curves, indicating solid fixation with little displacement in reaching ultimate load. Mode of failure for SutureTak was pull out in five and breakage in three. These results illustrate the importance of the method of biomechanical testing and data reporting. Note that while ultimate loads were similar between the anchors, amount of displacement was remarkably different. If we put the zone of acceptable displacement on this graph in the pink highlighted area, we see that the SutureTak anchors did not displace past the three millimeters limit at ultimate load, while the juggernaut anchors displaced more than the three millimeters limit at significantly lower loads and displaced a total of 25mm at its ultimate load. These displacement characteristics of the juggernaut would be expected to result in rapid loss of acquisition and failure to heal. When we look at the biomechanical characteristics, statistically, SutureTak was superior to juggernaut in all of the clinically important categories displacement and ultimate load. Cyclic displacement and loads at one and two millimeters of displacement were all significantly better for SutureTak when compared to juggernaut. Most importantly, the values for SutureTak are considered to considered to be clinically significant with respect to the ability of the SutureTak to maintain fixation at physiologic loads in order for healing to occur, while those for the juggernaut were well below the levels associated with healing. So when we put the two studies together, the data suggests that the soft all suture anchor evaluated in this study, the juggernaut showed large displacements at sub failure loads and was significantly inferior to SutureTak in all biomechanical outcome measures. Biologically, juggernaut resulted in the formation of large diameter cystic cavities in the glenoid bone. In all cases, based on histologic assessments and biomechanical testing, the formation of the cystic cavities was likely the result of the amount and type of formed material within the bone that this all suture anchor entails. The combination of poor biology and poor biomechanics suggests that the juggernaut does not have the characteristics desired for optimal labral repair. The limitations of this study should be considered when interpreting and applying the data. For the in vivo portion, we used a short term canine model. There are certainly differences in dogs with respect to respect to anatomy and host responses. However, translational canine models for shoulder pathology are widely accepted, and as a veterinary orthopedic surgeon, I perform rotator cuff and label repairs on the shoulders of clinical patients routinely. And while eight weeks is a relatively short time frame, we contend that it is the most critical time period for study based on the fact that effective healing needs to be accomplished within this time frame in order for long term success to be realized. In other words, if it's not working within eight weeks, it is not going to work for the ex-vivo testing in human cadaveric glenoid. We only included two anchor types and were not able to compare to a gold standard fixation method that has been validated to consistently result in healing. Those data just are not available in the literature. However, the two anchors tested are the two most common commercially available anchors used for labor repair, and our results in biomechanical testing match those of mazurkas very well. So the clinically relevant findings we took away from this study were that juggernaut soft. All suture anchors were associated with extensive Displacement under physiologic or actually even sub physiologic loads such that the healing threshold was rapidly breached. This appeared to be the result of the less rigid, deformable nature of this anchor type that resulted in micro-motion and loss of apposition. This rapid displacement and loss of secure fixation would likely result in a failure to heal. These concerns are heightened by the in vivo findings of cyst formation in all cases with marked expansion of the glenoid socket. In contrast, the SutureTak anchors all maintained interdigitation with the glenoid bone and had biomechanical characteristics that are consistent with adequate maintenance of apposition under real life loading, such that labral healing could be expected. Therefore, the soft all suture anchor evaluated in this study, the juggernaut appears to carry a high risk for clinical failure. While the traditional solid anchor, the SutureTak, possesses the characteristics desired for safe and effective labral repairs.

Histologic and Biomechanical Analysis of Two Small Glenoid Anchors for use in Labral Repair

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