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Letter to the Editor |
The San Antonio Orthopaedic Group, San Antonio, Texas
Dear Editor:
I am writing this letter in reference to the case report by Drs Glueck, Wilson, and Johnson entitled "Extensive Osteolysis After Rotator Cuff Repair With a Bioabsorbable Suture Anchor" (May 2005, pages 742–744). The authors report osteolysis around 1 Bio-Corkscrew suture anchor (Arthrex, Naples, Fla) in the proximal humerus, whereas another poly(L-Lactide-co-D, L-Lactide) (PLDLA) anchor (same material as the Bio-Corkscrew) in the glenoid of the same patient did not develop osteolysis. The authors suggest a mechanical cause rather than a biologic cause for the osteolysis, possibly because of differences in bone density between the humeral head and the glenoid.
I agree with the authors that mechanical factors probably accounted for the osteolytic reaction in this case report. Rotator cuff repair involves fixation of a dynamic muscle-tendon unit, and suture anchors used for cuff repair are subjected to higher loads than are anchors used for labral repair. Furthermore, the cancellous bone in the proximal humerus is less dense than the glenoid bone, and tapping may further decrease the fixation strength, necessitating a greater number of anchors to obtain stable fixation.
As the first surgeon to use the Food and Drug Administration–approved Bio-Corkscrew suture anchors, I had access to the voluminous data generated by Arthrex in the development of this implant, and those data are very helpful in analyzing this case report, particularly in terms of recognizing how rarely osteolysis occurs.
Before the development of Arthrex biodegradable anchors (eg, Bio-Corkscrew), the literature on biodegradable implants reported occasional adverse in vivo reactions such as synovitis, osteolysis, and sinus formation. Low pH and crystalline particulates were implicated in these reactions.1,2 The factors contributing to such adverse reactions can be manipulated and controlled by suitable device designs. Arthrex expended a great deal of time, money, and effort in studying all material and production parameters of implantable polymeric devices before manufacturing any suture anchors. These parameters included molecular weight, crystallinity, potential for release of crystallites, mechanical properties of the device, and degradation characteristics (eg, rate of mass and molecular weight loss, pH in the vicinity of the device). All of these parameters were considered as a function of the intended application, the required strength and stiffness of the implant, the anatomical location for its use, and concomitant healing processes of adjacent tissues. In short, each Arthrex biodegradable suture anchor was specifically engineered for its purpose through extensive in vitro and in vivo testing. The result of this meticulous and exhaustive research was a line of biodegradable implants with outstanding strength characteristics and minimal potential for adverse tissue reactions.
In my practice, I have personally inserted more than 5000 Arthrex Bio-Corkscrew suture anchors into my patients. I have seen only 2 cases of osteolysis around Bio-Corkscrew anchors. Both cases involved anchors in relatively osteoporotic bone in which mechanical fixation was not optimal. More recently, I have been using the fully threaded Bio-Corkscrew-FT, which I insert without tapping. The internal hex drive of this anchor allows insertional torques that are 5 times those that can be developed with the standard Bio-Corkscrew so that tapping is virtually never needed after punching the bone socket. Furthermore, the cortical fixation of the fully threaded implant greatly enhances overall fixation.
Finally, it is important to recognize the very low incidence of complications, including osteolysis, with Bio-Corkscrew suture anchors. Arthrex maintains a registry for complaints and complications related to its products. For Bio-Corkscrew anchors, there have been 5 reported complaints of 405 550 Bio-Corkscrews sold, for an incidence of 0.00001%. This is an incredibly low incidence of reported complaints and complications.
In summary, adverse tissue reactions, including osteolysis, are extremely rare with Arthrex Bio-Corkscrew suture anchors. When osteolysis occurs, mechanical factors are most likely the cause. Design improvements incorporated into the fully threaded Bio-Corkscrew-FT will most likely reduce the incidence of this rare phenomenon even further.
Thank you for your attention to this letter.
FOOTNOTES
The author has declared a potential conflict of interest: royalties were received from Arthrex.
REFERENCES
Department of Orthopaedic Surgery, Division of Sports Medicine, University of Kentucky, Lexington, Kentucky
We thank Dr Burkhart for his comments and observations. Although the incidence of osteolysis around PLDLA anchors is certainly low, we agree that improvements in anchor design and surgical techniques may continue to improve their mechanical function.
Like Dr Burkhart, we continue to use Arthrex Bio-Corkscrew anchors. We are particularly mindful of the quality of the patient’s bone and use additional anchors as needed. The fully threaded Bio-Corkscrew-FT appears to be a promising improvement in anchor fixation. Future research will help determine optimum bioabsorbable anchor characteristics, which may prevent the rare occurrence of osteolysis.
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