Orthopedics

Feature Article 

Degradation of Cylindrical Poly-Lactic Co-Glycolide/Beta-Tricalcium Phosphate Biocomposite Anchors After Arthroscopic Bankart Repair: A Prospective Study

Keisuke Matsuki, MD; Hiroyuki Sugaya, MD; Norimasa Takahashi, MD; Takayuki Kawasaki, MD; Hideya Yoshimura, MD; Tomonori Kenmoku, MD

Abstract

The purpose of this study was to examine widening and ossification of anchor holes after arthroscopic Bankart repair with the use of cylindrical biocomposite anchors made of 70% poly-L-lactide-co-glycolide acid (PLGA) and 30% beta-tricalcium phosphate (ß-TCP). Twenty-two patients were enrolled in a clinical trial to acquire marketing approval of a PLGA/ß-TCP biocomposite suture anchor in Japan and underwent arthroscopic Bankart repairs with the anchors. Eleven of 22 patients had computed tomography scans after 2-year follow-up. Three surgeons independently evaluated width and ossification of anchor holes in 4 grades using computed tomography scans. When the evaluations disagreed, the final grade was determined based on the 3 surgeons' consensus. Seven men and 4 women were evaluated at a mean of 30 months (range, 28-32 months) after surgery, and a total of 47 anchors were implanted. Anchor holes were narrowed in 39 (83%) of 47 anchor sites and were almost or completely filled in (type 3 or 4) in 21 (45%) of 47 anchor sites. Ossification was seen in 46 (98%) of 47 anchor sites and was nearly complete or complete (type 3 or 4) in 16 (34%) of 47 anchor sites. There were no significant differences in both anchor hole width and ossification score on comparison of the anteroinferior (4- to 6-o'clock positions in the right shoulder) with other anchor sites. Cylindrical biocomposite anchors made of 70% PLGA/30% ß-TCP showed a low incidence of anchor hole widening and excellent ossification regardless of anchor site. [Orthopedics. 2018; 41(3):e348–e353.]

Abstract

The purpose of this study was to examine widening and ossification of anchor holes after arthroscopic Bankart repair with the use of cylindrical biocomposite anchors made of 70% poly-L-lactide-co-glycolide acid (PLGA) and 30% beta-tricalcium phosphate (ß-TCP). Twenty-two patients were enrolled in a clinical trial to acquire marketing approval of a PLGA/ß-TCP biocomposite suture anchor in Japan and underwent arthroscopic Bankart repairs with the anchors. Eleven of 22 patients had computed tomography scans after 2-year follow-up. Three surgeons independently evaluated width and ossification of anchor holes in 4 grades using computed tomography scans. When the evaluations disagreed, the final grade was determined based on the 3 surgeons' consensus. Seven men and 4 women were evaluated at a mean of 30 months (range, 28-32 months) after surgery, and a total of 47 anchors were implanted. Anchor holes were narrowed in 39 (83%) of 47 anchor sites and were almost or completely filled in (type 3 or 4) in 21 (45%) of 47 anchor sites. Ossification was seen in 46 (98%) of 47 anchor sites and was nearly complete or complete (type 3 or 4) in 16 (34%) of 47 anchor sites. There were no significant differences in both anchor hole width and ossification score on comparison of the anteroinferior (4- to 6-o'clock positions in the right shoulder) with other anchor sites. Cylindrical biocomposite anchors made of 70% PLGA/30% ß-TCP showed a low incidence of anchor hole widening and excellent ossification regardless of anchor site. [Orthopedics. 2018; 41(3):e348–e353.]

Suture anchors have contributed to advancements in the techniques and outcomes of arthroscopic Bankart repair. Initially, metallic suture anchors were used and provided excellent fixation; however, these anchors were associated with complications such as anchor migration or glenohumeral arthropathy.1–3 Subsequently, anchors made from biodegradable materials were developed to overcome the disadvantages of metallic anchors.4,5

Poly-L-lactic acid (PLLA) was the most popular material for the next generation of suture anchors. Excellent outcomes of arthroscopic Bankart repairs using PLLA anchors have been reported.6,7 However, it has been suggested that PLLA may take up to 7 years to degrade after insertion and may not be replaced with bone.8 Enlargement of anchor holes after insertion of PLLA anchors has also been reported.9,10 In addition, inflammatory reaction, osteolysis, and chondrolysis have been reported to be associated with the use of PLLA anchors.11,12 Polyglycolic acid (PGA) anchors have also been used clinically, but they may absorb too quickly and can cause foreign-body reactions.11,13

Recently, biocomposite anchors, which combine biodegradable polymers and osteoconductive bioceramic, have been introduced. Biocryl Rapide (BR) (DePuy Mitek, Raynham, Massachusetts) is one of the biocomposite materials made from 70% poly-L-lactide-co-glycolide acid (PLGA) and 30% beta-tricalcium phosphate (ß-TCP). The PLGA is composed of 15% PGA and 85% PLLA and is expected to degrade more rapidly than pure PLLA. The PLGA in combination with osteoconductive ß-TCP could contribute to rapid degradation and bone replacement of anchor sites. There have been a few studies about degradation of PLGA/ß-TCP anchors after labral repairs, and they have reported good anchor degradation.5,14 These studies used Lupine BR (DePuy Mitek) or Bioknotless BR (DePuy Mitek)—a toggle type of anchor. Milewski et al5 reported that 55% of anchor holes were widened and suspected that the geometry of the anchors was associated with this widening by producing micromotion around the anchors. They mentioned that changes in anchor design and geometry, such as a cylindrical anchor that completely fills the bone hole, may address this issue; however, there have been no studies assessing degradation of cylindrical biocomposite anchors after labral repair.

The purpose of this study was to examine tunnel widening and ossification of anchor holes after arthroscopic Bankart repair with the use of cylindrical biocomposite anchors. The authors hypothesized that a cylindrical anchor would result in a smaller incidence of tunnel widening and, consequently, better bony replacement.

Materials and Methods

Patients

A clinical trial to acquire marketing approval of a 70% PLGA/30% ß-TCP biocomposite suture anchor (Gryphon BR; DePuy Mitek) in Japan was conducted at one of the authors' institutes. Twenty-two patients consented to be enrolled in the trial. They underwent arthroscopic stabilization for traumatic anterior shoulder instability using the anchors between February and May 2012. The inclusion criteria of the clinical trial were (1) recurrent anterior shoulder instability due to a Bankart lesion that was confirmed with magnetic resonance arthrogram and (2) age of 16 years or older. The exclusion criteria were (1) prior surgery; (2) shoulder fractures except for bony Bankart lesions; (3) osteoarthritis or rheumatoid arthritis; (4) epilepsy; (5) allergy to PLLA, PGA, or ß-TCP; (6) bone diseases such as osteopenia or cyst in the glenoid; and (7) pregnancy. All patients provided informed consent to participate in the clinical trial. One patient withdrew from this trial after surgery for an unknown reason. The scheduled follow-up visits ended 2 years after surgery, and the patients were asked to participate in an additional computed tomography (CT) examination at the final follow-up visit. Of the 22 patients, 11 patients consented to a CT scan. The institution's research ethics committee approved the protocol of this follow-up CT study.

Surgical Technique

The patient was placed in the beachchair position while under general anesthesia. A routine diagnostic arthroscopic examination was performed through a standard posterior portal. An anterior portal was then established just superior to the subscapularis and lateral to the conjoined tendon using an outside-in technique. The procedure was performed using the posterior portal as a viewing portal and the anterior and the anterosuperior portals as working portals.

The displaced labroligamentous complex was recognized and separated from the glenoid neck using a rasp introduced through the anterior portal. Mobilization of the labroligamentous complex was performed up to the 7-o'clock position (right shoulder). In cases of a bony Bankart lesion, the bony fragments were separated from the glenoid neck together with the labroligamentous complex. In addition, a small amount of articular cartilage at the face of the glenoid from the 3- to the 7-o'clock positions was removed to promote tissue healing after repair. Next, 2 suture anchors (Gryphon BR) were inserted at the face of the anteroinferior aspect of the glenoid (at the 6-o'clock and 4:40 positions) using a drill guide through the anterior portal, and 1 limb of a suture from both anchors was placed through the labrum using the intra-articular suture relay technique.15 Knot tying was then performed, upwardly lifting the complex to retension the inferior glenohumeral ligament. Two more suture anchors were usually inserted at the 3:20 and 2-o'clock positions to fix the anterior labrum. If the lesion extended to the superior labrum, 1 or 2 additional suture anchors were used. In shoulders with a high risk of recurrence, a rotator interval closure was performed with the arm in greater than 60° of external rotation as an augmentation of the Bankart repair.16

Operated on shoulders were immobilized for 3 weeks using a sling, and then passive and assisted-active exercises were initiated. Patients were allowed to practice noncontact sports 3 months postoperatively. Full return to throwing or contact sports was permitted after 6 months, according to the functional recovery of each patient.

Computed Tomography Evaluation

Computed tomography scans were obtained at a mean of 30 months (range, 28–32 months) postoperatively. All examinations were conducted with a 16-detector CT system (Alexion; Toshiba, Tochigi, Japan). The scanning parameters were as follows: image matrix, 512×512; pixel spacing, 0.468×0.468 mm; slice pitch, 0.5 mm.

Three experienced shoulder surgeons (T. Kawasaki, H.Y., T. Kenmoku) who were blinded to the patients' data independently evaluated width and ossification of anchor holes using the CT scans. When the evaluations disagreed, the final grade was determined based on the 3 surgeons' consensus. To investigate intraobserver agreement, each surgeon evaluated the CT scans 2 times at a greater than 1-month interval.

Width of anchor holes was evaluated in 4 types: type 1, unchanged or enlarged; type 2, slightly closed (<50% of width); type 3, almost closed (≥50% of width); and type 4, completely closed (Figure 1). Ossification of tunnel was evaluated using the ossification quality score: type 1, little or no ossification; type 2, some ossification; type 3, ossification with a thin lucent rim; and type 4, good ossification (Figure 2).17 Each anchor hole was evaluated on a slice that showed the largest tunnel diameter. To determine whether the tissue replacing the anchor was bone or soft tissue, the tissue density of ossification sites in each anchor hole was measured by a single surgeon (K.M.) using Hounsfield units (HU) and OsiriX software (Pixmeo, Geneva, Switzerland) and compared with that of cancellous bones in the glenoid vault. According to a previous study,5 soft tissue density was defined as less than 120 HU.

Evaluation of anchor hole width. Type 1, the anchor hole is unchanged or enlarged (A). Type 2, the hole is slightly closed (<50%) (B). Type 3, the hole is almost closed (≥50%) (C). Type 4, the hole is completely closed (D). Arrows indicate anchor holes.

Figure 1:

Evaluation of anchor hole width. Type 1, the anchor hole is unchanged or enlarged (A). Type 2, the hole is slightly closed (<50%) (B). Type 3, the hole is almost closed (≥50%) (C). Type 4, the hole is completely closed (D). Arrows indicate anchor holes.

Ossification score. Type 1, little or no ossification (A). Type 2, some ossification; discontinuous or with a wide lucent line (B). Type 3, ossification with a thin lucent line (C). Type 4, good ossification; vague border of the tract (D). Arrows indicate anchor holes.

Figure 2:

Ossification score. Type 1, little or no ossification (A). Type 2, some ossification; discontinuous or with a wide lucent line (B). Type 3, ossification with a thin lucent line (C). Type 4, good ossification; vague border of the tract (D). Arrows indicate anchor holes.

Statistical Analysis

The Mann–Whitney test was used to examine differences in anchor hole width and ossification score by anchor sites. Spearman's correlation coefficient was also used to assess correlation between anchor hole width and ossification score. The Student's t test was used to compare HU of ossification sites and cancellous bones. To test inter- and intraobserver agreement between the 3 surgeons, a kappa coefficient was used. The level of significance was set at P<.05.

Results

Seven men and 4 women completed the imaging requirements. Mean age at surgery was 29 years (range, 20–39 years). There were 4 right and 7 left shoulders, and all patients were right-handed. There were no evident adverse events, including recurrent instability, during the follow-up period. Computed tomography scans were obtained at a mean of 30 months (range, 28–32 months) after surgery, and mean patient age at the examination was 31 years (range, 22–42 years). A total of 47 suture anchors were implanted in the 11 patients. All patients had Bankart repair with 4 anchors, and 2 patients had additional superior labrum repair using 1 and 2 anchors, respectively.

Interobserver agreement for anchor hole width and ossification score was 0.475 and 0.430, respectively, thought to be moderate agreement for both grading systems. Intraobserver agreement for the 2 grading systems was 0.494 and 0.537, respectively, also thought to be moderate agreement.

Bone holes were narrowed in 39 (83%) of 47 anchor sites and were almost or completely closed (type 3 or 4) in 21 (45%) of 47 anchor sites (Table 1). Ossification was seen in 46 (98%) of 47 anchor sites and was nearly complete or complete (type 3 or 4) in 16 (34%) of 47 anchor sites (Table 2). There were no significant differences in both tunnel width and ossification score on comparison of the anteroinferior (4- to 6-o'clock positions in the right shoulder) with other anchor sites. There was significant correlation between tunnel width and ossification score (P<.001; Table 3).

Anchor Hole Width

Table 1:

Anchor Hole Width

Ossification Scores

Table 2:

Ossification Scores

Correlation Between Anchor Hole Width and Ossification Scores

Table 3:

Correlation Between Anchor Hole Width and Ossification Scores

Ossification sites in anchor holes had a mean of 236±134 HU, and no significant difference was found when compared with cancellous bones in the glenoid vault (286±76 HU). However, 8 (17%) of 47 anchors were replaced by soft tissue density (91±25 HU).

Discussion

This study evaluated tunnel width and ossification of anchor holes at a mean of 30 months after arthroscopic Bankart repairs with the use of 70% PLGA/30% ß-TCP biocomposite anchors with a cylinder shape (Gryphon BR). The authors found that 83% of the anchor holes were narrowed and that ossification was present in 98% of the holes. In addition, 45% of the holes were almost or completely closed, and nearly complete or complete ossification was observed in 34% of the anchor sites. Mean HU were not significantly different between ossification sites and cancellous bones in the glenoid vault, although 17% of anchor holes were replaced by soft tissue density. To the authors' knowledge, this is the first study evaluating degradation of Gryphon BR anchors after arthroscopic Bankart repair.

Other implants made of the same material as the suture anchors used in this study are available, and several studies have evaluated degradation of these implants. In one study, osteoconductivity was present in 81% of interference screws (Milagro; DePuy Mitek) at 3 years after anterior cruciate reconstruction.18 In another study, osteoconductivity was present in 71% of anchors (Healix BR; DePuy Mitek) after arthroscopic rotator cuff repair.19 Although the geometry of the implants, such as diameter, length, shape, and implanted sites, was different between the studies, the osteoconductivity in the current study may be comparable with that of these studies.

There have been only a few studies of degradation of 70% PLGA/30% ß-TCP biocomposite anchors after arthroscopic Bankart repair.5,14 The incidence of ossification in the current study (98% with the ossification score and 83% with HU measurement) was much better than that (45.5% to 47%) in the previous studies using toggle-type biocomposite anchors (Lupine BR or Bioknotless BR).5,14 Because the anchors were of the same material, the biggest difference between the current study and the other 2 studies was the geometry of the suture anchors. The authors assume that the difference in the anchor geometry was the most influential factor regarding ossification of anchor sites. The toggle-type anchor has a triangle shape, and tension through its thread forces the inclination of the anchor, with which the distal tip is caught and locked in cancellous bone.10 This non-rigid fixation may cause micromotion around the anchor, which may lead to tunnel widening and less ossification.5,10 On the other hand, the cylinder-shaped anchor completely fills the hole and provides better stability in the hole than the toggle-type anchor. This may have contributed to excellent degradation and ossification of the anchors even in the anteroinferior glenoid, where less ossification was observed in a previous study.5 Considering the results of this study, cylindrical biocomposite anchors might have an advantage over toggle-type anchors in arthroscopic Bankart repair in terms of less tunnel widening and better bone replacement.

One limitation of this study was the lack of a gold standard to assess degradation and ossification of anchor sites. It would be best to histologically examine tissues from the sites; however, this would be too invasive. The authors used the established ossification score17 and the original grading for anchor hole width. Further, 3 surgeons independently evaluated CT scans and carefully determined grades based on consensus. Although the interobserver agreements were moderate, the evaluations in this study may be acceptable because of the less invasive nature of the methods. Other limitations included small sample and low follow-up rate.

Conclusion

At a mean of 30 months after arthroscopic Bankart repair using 70% PLGA/30% ß-TCP biocomposite anchors with a cylinder shape (Gryphon BR), anchor sites were narrowed in 39 (83%) of 47 anchors and were replaced to bone in 46 (98%) of 47 anchors. Osteoconductivity of the cylindrical biocomposite anchors was possibly superior to that of the toggle-type biocomposite anchors in previous studies.

References

  1. Jeong JH, Shin SJ. Arthroscopic removal of proud metallic suture anchors after Bankart repair. Arch Orthop Trauma Surg. 2009; 129(8):1109–1115. doi:10.1007/s00402-009-0847-3 [CrossRef]
  2. Rhee YG, Lee DH, Chun IH, Bae SC. Glenohumeral arthropathy after arthroscopic anterior shoulder stabilization. Arthroscopy. 2004; 20(4):402–406. doi:10.1016/j.arthro.2004.01.027 [CrossRef]
  3. Silver MD, Daigneault JP. Symptomatic interarticular migration of glenoid suture anchors. Arthroscopy. 2000; 16(1):102–105. doi:10.1016/S0749-8063(00)90136-1 [CrossRef]
  4. Kim SH, Oh JH, Lee OS, Lee HR, Hargens AR. Postoperative imaging of bioabsorbable anchors in rotator cuff repair. Am J Sports Med. 2014; 42(3):552–557. doi:10.1177/0363546513517538 [CrossRef]
  5. Milewski MD, Diduch DR, Hart JM, Tompkins M, Ma SY, Gaskin CM. Bone replacement of fast-absorbing biocomposite anchors in arthroscopic shoulder labral repairs. Am J Sports Med. 2012; 40(6):1392–1401. doi:10.1177/0363546512441589 [CrossRef]
  6. Sugaya H, Moriishi J, Kanisawa I, Tsuchiya A. Arthroscopic osseous Bankart repair for chronic recurrent traumatic anterior glenohumeral instability. J Bone Joint Surg Am. 2005; 87(8):1752–1760.
  7. Tan CK, Guisasola I, Machani B, et al. Arthroscopic stabilization of the shoulder: a prospective randomized study of absorbable versus nonabsorbable suture anchors. Arthroscopy. 2006; 22(7):716–720. doi:10.1016/j.arthro.2006.03.017 [CrossRef]
  8. Bach FD, Carlier RY, Elis JB, et al. Anterior cruciate ligament reconstruction with bioabsorbable polyglycolic acid interference screws: MR imaging follow-up. Radiology. 2002; 225(2):541–550. doi:10.1148/radiol.2252010357 [CrossRef]
  9. Take Y, Yoneda M, Hayashida K, Nakagawa S, Mizuno N. Enlargement of drill holes after use of biodegradable suture anchor: quantitative study on consecutive postoperative radiographs. Arthroscopy. 2008; 24(3):251–257. doi:10.1016/j.arthro.2008.01.007 [CrossRef]
  10. Takubo Y, Morihara T, Namura T, et al. Anchor hole enlargement after arthroscopic Bankart repair using absorbable suture anchors: a report of three cases. J Shoulder Elbow Surg. 2008; 17(6):e16–e18. doi:10.1016/j.jse.2008.02.014 [CrossRef]
  11. Athwal GS, Shridharani SM, O'Driscoll SW. Osteolysis and arthropathy of the shoulder after use of bioabsorbable knotless suture anchors: a report of four cases. J Bone Joint Surg Am. 2006; 88(8):1840–1845. doi:10.2106/JBJS.E.00721 [CrossRef]
  12. McCarty LP III, Buss DD, Datta MW, Freehill MQ, Giveans MR. Complications observed following labral or rotator cuff repair with use of poly-L-lactic acid implants. J Bone Joint Surg Am. 2013; 95(6):507–511. doi:10.2106/JBJS.L.00314 [CrossRef]
  13. Böstman OM, Pihlajamäki HK. Adverse tissue reactions to bioabsorbable fixation devices. Clin Orthop Relat Res. 2000; 371:216–227. doi:10.1097/00003086-200002000-00026 [CrossRef]
  14. Randelli P, Compagnoni R, Aliprandi A, et al. Long-term degradation of poly-lactic coglycolide/ß-tricalcium phosphate biocomposite anchors in arthroscopic Bankart repair: a prospective study. Arthroscopy. 2014; 30(2):165–171. doi:10.1016/j.arthro.2013.09.082 [CrossRef]
  15. Sugaya H, Kon Y, Tsuchiya A. Arthroscopic Bankart repair in the beachchair position: a cannulaless method using an intra-articular suture relay technique. Arthroscopy. 2004; 20(suppl 2):116–120. doi:10.1016/j.arthro.2004.04.016 [CrossRef]
  16. Matsuki K, Sugaya H. Complications after arthroscopic labral repair for shoulder instability. Curr Rev Musculoskelet Med. 2015; 8(1):53–58. doi:10.1007/s12178-014-9248-5 [CrossRef]
  17. Barber FA, Dockery WD. Long-term absorption of beta-tricalcium phosphate poly-L-lactic acid interference screws. Arthroscopy. 2008; 24(4):441–447. doi:10.1016/j.arthro.2007.10.004 [CrossRef]
  18. Barber FA, Dockery WD, Hrnack SA. Long-term degradation of a poly-lactide coglycolide/ß-tricalcium phosphate biocomposite interference screw. Arthroscopy. 2011; 27(5):637–643. doi:10.1016/j.arthro.2010.11.056 [CrossRef]
  19. Barber FA, Dockery WD, Cowden CH III, . The degradation outcome of biocomposite suture anchors made from poly L-lactideco-glycolide and ß-tricalcium phosphate. Arthroscopy. 2013; 29(11):1834–1839. doi:10.1016/j.arthro.2013.08.004 [CrossRef]

Anchor Hole Width

Anchor Hole WidthDescriptionNo. of Anchors

Total4- to 6-o'clock PositionsOther Site
Type 1Unchanged or enlarged8 (17%)35
Type 2Slightly closed (<50%)18 (38%)108
Type 3Almost closed (≥50%)17 (36%)89
Type 4Completely closed4 (9%)22

Ossification Scores

Ossification ScoreDescriptionNo. of Anchors

Total4- to 6-o'clock PositionsOther Site
Type 1Little or no ossification1 (2%)10
Type 2Some ossification; discontinuous or with a wide lucent line30 (64%)1218
Type 3Ossification with a thin lucent line11 (23%)83
Type 4Good ossification; border of tract vague5 (11%)23

Correlation Between Anchor Hole Width and Ossification Scores

Ossification ScoreAnchor Hole Width

Type 1Type 2Type 3Type 4
Type 11000
Type 271760
Type 300101
Type 40113
Authors

The authors are from Funabashi Orthopaedic Sports Medicine & Joint Center (KM, HS, NT), Funabashi, Chiba; the Department of Orthopaedic Surgery (TKawasaki), Juntendo University Faculty of Medicine, Bunkyo, Tokyo; the Department of Orthopaedic Surgery (HY), Kawaguchi Kogyo General Hospital, Kawaguchi, Saitama; and the Department of Orthopaedic Surgery (TKenmoku), Kitasato University, Sagamihara, Kanagawa, Japan.

Drs Sugaya, Takahashi, Kawasaki, Yoshimura, and Kenmoku have no relevant financial relationships to disclose. Dr Matsuki has received grants from Johnson & Johnson and Exactech.

This study was supported in part by a research grant from Johnson & Johnson.

Correspondence should be addressed to: Keisuke Matsuki, MD, Funabashi Orthopaedic Sports Medicine & Joint Center, 1-833 Hazama, Funabashi, Chiba 2740822, Japan ( kmatsuki@fff.or.jp).

Received: June 06, 2017
Accepted: December 15, 2017
Posted Online: March 02, 2018

10.3928/01477447-20180226-08

Sign up to receive

Journal E-contents