Bioabsorbable suture anchor (co-polymer 85/15 D,L lactide/glycolide) implanted in bone: correlation of physical/mechanical properties, magnetic resonance imaging, and histological response

Materials and Devices for Biodegradable and Soft Biomedical Electronics

Biodegradable and soft biomedical electronics that eliminate secondary surgery and ensure intimate contact with soft biological tissues of the human body are of growing interest, due to their emerging applications in high-quality healthcare monitoring and effective disease treatments. Recent systematic studies have significantly expanded the biodegradable electronic materials database, and various novel transient systems have been proposed. Biodegradable materials with soft properties and integration schemes of flexible or/and stretchable platforms will further advance electronic systems that match the properties of biological systems, providing an important step along the path towards clinical trials. This review focuses on recent progress and achievements in biodegradable and soft electronics for biomedical applications. The available biodegradable materials in their soft formats, the associated novel fabrication schemes, the device layouts, and the functionality of a variety of fully bioresorbable and soft devices, are reviewed. Finally, the key challenges and possible future directions of biodegradable and soft electronics are provided.

Suture slippage in knotless suture anchors resulting in subacromial-subdeltoid bursitis

Rotator cuff repair using a suture bridge and knotless suture anchors is a relatively new, but increasingly used technique. The suture bridge technique creates an anatomically similar and more secure rotator cuff repair compared with conventional arthroscopic techniques and the use of knotless anchors eliminates the challenges associated with knot tying during arthroscopic surgery. However, previous in vitro biomechanical tests have shown that the hold of the suture in a knotless suture anchor is far lower than the pullout strength of the anchor from bone. Up until now slippage has been a theoretical concern. We present a prospectively diagnosed case of in vivo suture loosening after rotator cuff repair using a knotless bridge technique resulting in subacromial-subdeltoid bursitis.

Postoperative imaging of bioabsorbable anchors in rotator cuff repair

BACKGROUND

Bioabsorbable anchors may lead to osteolysis and cyst formation. However, the prevalence of these outcomes is not known for rotator cuff repairs.

PURPOSE

To evaluate cyst formation after placement of bioabsorbable anchors for rotator cuff repairs and to verify whether bioabsorbable anchors degraded as intended and preserved bone stock for possible revision compared with metal anchors. The null hypothesis was that the rate and severity of cyst formation around the anchor are negligible.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Between April 2008 and November 2011, a total of 209 patients (85 men, 124 women) underwent rotator cuff repair with bioabsorbable suture anchors (113 with polylactic acid enantiomers [PLLA] and 96 with poly-D,L-lactide from L-lactide and D-lactide [PLDLA]); the patients underwent magnetic resonance imaging (MRI) evaluation more than 10 months after surgery. The fluid signal around the anchor on T2-weighted MRI scans was graded as follows: grade 0, no fluid around anchor; grade 1, minimal fluid around anchor; grade 2, local fluid around anchor; grade 3, fluid collection around entire length of anchor with cyst diameter less than twice the anchor diameter; and grade 4, cyst diameter larger than grade 3. The integrity of repairs was also evaluated.

RESULTS

Cysts were observed in 97 instances (46.4%). There were 41 grade 1 cases (19.6%), 16 grade 2 (7.7%), 22 grade 3 (10.5%), and 18 grade 4 (8.6%). Healing of repaired tendon was observed in 131 patients (62.7%). There was no statistical difference in healing rate between patients with and without cyst formation (66.1% vs 58.8%; P = .276). Altered anchor shape and absorption were not observed in most of the patients. However, in 12 patients (6 with PLLA and 6 with PLDLA anchors), T2-weighted scans showed that the signal intensity of anchors had changed since surgery, which could indicate that absorption had taken place; nonetheless, even in these 12 patients, anchors were clearly visible on T1-weighted scans.

CONCLUSION

Osteolysis and cyst formation are common complications following the use of bioabsorbable anchors in rotator cuff repairs. Considering that adequate absorption of anchors and preservation of bone stock are the reasons for using bioabsorbable anchors, use of these anchors should be reconsidered because of possible interference with revision surgery.

Morphological effects of HA on the cell compatibility of electrospun HA/PLGA composite nanofiber scaffolds

Tissue engineering is faced with an uphill challenge to design a platform with appropriate topography and suitable surface chemistry, which could encourage desired cellular activities and guide bone tissue regeneration. To develop such scaffolds, composite nanofiber scaffolds of nHA and sHA with PLGA were fabricated using electrospinning technique. nHA was synthesized using precipitation method, whereas sHA was purchased. The nHA and sHA were suspended in PLGA solution separately and electrospun at optimized electrospinning parameters. The composite nanofiber scaffolds were characterized by FE-SEM, EDX analysis, TEM, XRD analysis, FTIR, and X-ray photoelectron. The potential of the HA/PLGA composite nanofiber as bone scaffolds in terms of their bioactivity and biocompatibility was assessed by culturing the osteoblastic cells onto the composite nanofiber scaffolds. The results from in vitro studies revealed that the nHA/PLGA composite nanofiber scaffolds showed higher cellular adhesion, proliferation, and enhanced osteogenesis performance, along with increased Ca⁺² ions release compared to the sHA/PLGA composite nanofiber scaffolds and pristine PLGA nanofiber scaffold. The results show that the structural dependent property of HA might affect its potential as bone scaffold and implantable materials in regenerative medicine and clinical tissue engineering.

Does bone density of the greater tuberosity change in patients over 70?

INTRODUCTION

There are no published studies on bone density of the greater tuberosity of the humerus, which could influence the stability of reinsertion by suture anchors. The goal of our study was to determine the influence of age, gender and the type of tear on the quality of bone in the greater tuberosity.

METHODOLOGY

Ninety-eight patients over the age of 60 were included, 41 without a rotator cuff tear and 57 with an isolated stage 1 or 2 supraspinatus tear and fatty infiltration (FI) ≤ 2. The areas of measurement included cancellous bone located under the cortex of the greater tuberosity. Measurements were obtained either across from the tear or from the middle facet with greater tuberosity if the cuff was not torn. We measured average, maximum and minimum bone density and the standard deviation (SD) in each region with Osirix software.

RESULTS

The two groups were similar for age (73), investigated side and mean densities (0.282 g/cm(2) vs 0.210 g/cm(2)). Age over 70 was a predictive factor for osteoporosis of the greater tuberosity whether or not a rotator cuff tear was present (P<0.0001). There was less trabecular bone in women with cuff tears (P=0.009). Stage 2 cuff retraction was predictive of osteoporosis of the greater tuberosity (P=0.0001).

CONCLUSION

This is the first study in the literature to evaluate bone density of the greater tuberosity in relation to the presence or not of a rotator cuff tear in an elderly population. Female gender, age over 70 and stage 2 cuff retraction are factors responsible for osteoporosis of the greater tuberosity of the humeral head. The osteoporosis is not severe, and normally the quality of bone of the greater tuberosity should not limit stability of suture anchors.

LEVEL OF EVIDENCE

3.

Bone replacement of fast-absorbing biocomposite anchors in arthroscopic shoulder labral repairs

BACKGROUND

Newer generation biocomposite anchors are hypothesized to resorb more reliably and faster, while allowing for bone ingrowth and replacement.

PURPOSE

The purposes of this study were to (1) assess anchor resorption and bone ingrowth over time, (2) identify tunnel widening or potential reactions to the implants, (3) compare imaging findings for different sites of labral repair, and (4) determine patient subjective outcomes with the use of biocomposite anchors in glenoid labral repair.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

We enrolled 22 patients to participate in a 24-month outcomes study that included subjective and objective outcome assessments after glenoid labrum repair surgery. Magnetic resonance imaging (MRI) was performed at 6 and 12 months to identify any potential reactions to implants. Computed tomography (CT) scans were performed at 12 and 24 months to determine anchor resorption and bone ingrowth. Sixteen patients and 47 anchors were available for follow-up at 24 months. An independent, fellowship-trained musculoskeletal radiologist read the scans. Subjective outcome scores measured at 24 months postoperatively included Simple Shoulder Test, Tegner activity scale, American Shoulder and Elbow Surgeons (ASES), and University of California, Los Angeles (UCLA) shoulder scores.

RESULTS

No adverse events were reported with the use of biocomposite anchors at the end of the study period. At 12 and 24 months, respectively, CT scans demonstrated that an estimated 68% and 98% of combined anchor material had been absorbed, 56% and 78% of the anchor material had been replaced by soft tissue of variable density, and 9% and 20% of total anchor volume was replaced by bone. No obvious mechanical failure of the labral repairs was detected on nonarthrogram MRI. Three of the 47 anchors showed bone cyst formation. Tunnel widening (expansion beyond tunnel diameter of 3 mm; 2.9-mm drill hole utilized) was seen in 55% of the anchors but decreased between 12 and 24 months, consistent with bone replacement. Tunnel widening was seen more in anteroinferior and posterior glenoid anchor locations (84% and 57%, respectively) than in superior labral anchors (13%). Subjective outcome scores at 24 months for ASES and UCLA shoulder scores averaged 88 and 30, respectively. All but one patient were satisfied with their outcome at 24 months.

CONCLUSION

Our imaging evaluation indicates resorption of newer generation biocomposite anchors with progressive bone replacement at 12 and 24 months while maintaining acceptable subjective outcomes.

EXTENSIVE OSTEOLYSIS AFTER THE USE OF A BIOABSORBABLE SUTURE ANCHOR: CASE REPORT AND LITERATURE REVIEW

Bioabsorbable implants are very frequently used to treat rotator cuff and shoulder labrum injuries. Many researchers have observed small areas of osteolysis after treating pathological conditions of the shoulder using bioabsorbable anchors. Biological and mechanical theories have been put forward to account for the osteolysis caused by these materials. The case of a patient who was simultaneously treated for a rotator cuff lesion using the double-row technique and a Bankart lesion using bioabsorbable PLLA anchors and Fiber Wire®, and developed extensive osteolysis of the anatomical neck of the humerus, is described. Given that an anchor was used in the glenoid, and this did not present osteolysis, the hypothesis that mechanical factors are important in the etiology of this complication is raised.

The evaluation of the possibilities of using PLGA co-polymer and its composites with carbon fibers or hydroxyapatite in the bone tissue regeneration process - in vitro and in vivo examinations

Synthetic polymers belonging to the aliphatic polyester group have become highly promising biomaterials for reconstructive medicine. The purpose of the present work is a biological evaluation of lactide-glycolide co-polymer (PLGA) and its composites with carbon fibers (PLGA+CF) or hydroxyapatite (PLGA+HA). The cytotoxicity of the evaluated materials towards hFOB 1.19 human osteoblast-like cells was assessed. Moreover, during the one-year contact of the assessed materials with living osseous tissue, the progress of bone formation was analyzed and the accompanying process of the materials’ degradation was evaluated. The materials under evaluation proved to be biocompatible.

Comparison of poly-L-lactide and polylactide carbonate interference screws in an ovine anterior cruciate ligament reconstruction model

PURPOSE

The purpose of this study was to compare polylactide carbonate (PLC) interference screws with poly-L-lactide (PLLA) screws in an ovine anterior cruciate ligament reconstruction model.

METHODS

A PLC screw or PLLA screw was placed in the center of a 4-strand soft-tissue autograft fixating the graft within the tibial tunnel. Assessments were made at 6 and 12 weeks for fixation strength and at time points of 6, 12, 26, and 52 weeks via computed tomography and histology.

RESULTS

No adverse or inflammatory reactions were noted for either material at any time point. Mechanical fixation strength increased from 6 to 12 weeks for both the PLC and PLLA screws, with no significant differences in fixation strength being found between the 2 groups. By 26 weeks, the PLC screw was partially replaced by new bone, a process that was completed by 52 weeks. The PLLA screws were intact and surrounded by a fibrous layer at 52 weeks with no obvious resorption. New bone formation within the tendon construct located in the bone tunnel proximal to the interference screw was also noted in the PLC screw group but was not observed in the PLLA group.

CONCLUSIONS

This study has supported the hypothesis that this bioabsorbable composite has sufficient mechanical properties and strength retention to function successfully as an interference screw but also stimulates a biologic healing response, enabling replacement by bone and tunnel healing.

CLINICAL RELEVANCE

This study shows both the satisfactory mechanical characteristics and osteoconductive nature of PLC used in an interference screw in an ovine anterior cruciate ligament reconstruction model.

Long-term in vivo Degradation of Poly-L-lactide (PLLA) in Bone

The use of absorbable orthopedic implants has increased substantially during the last decade. Currently, most of them are fabricated from poly-L-lactide (PLLA), its co-polymers, or mixtures with other constituents. In vivo, PLLA persists for years after its surgical role has ended, which is confirmed by a long-term histological study of PLLA implanted in sheep either as functional interference screws or nonfunctional rods. The first tissue reaction is the sequestration of the implant within new bone during the initial 3 months. After a nonreactive period, a second tissue reaction is associated with the early signs of structural disintegration of the PLLA at 1 year. Subsequently, as the polymer mass reduces, it is replaced by a relatively avascular fibrous tissue containing macrophages and having an occasional multinucleated giant cell on the implant surface. After 3 years much of the polymer is still present, although as isolated fragments. The tissue reactions can be explained in terms of the physical chemistry of PLLA degradation. Though biocompatible, the excessive longevity of PLLA and the absence of its replacement by bone, indicates that despite being satisfactory clinically, it is not an ideal implant material, and that improved absorbable materials need to be developed.

Influence of test temperature and test speed on the mechanical strength of absorbable suture anchors

PURPOSE

Absorbable implant materials offer various advantages but are mechanically far weaker than metals. Despite known temperature dependence of the biomechanical properties of these materials, mechanical testing has almost exclusively been performed at room temperature in the literature. In this study, the difference in mechanical performance at room and body temperature was assessed in vitro at different test speeds.

TYPE OF STUDY

Biomechanical bench study.

METHODS

Five absorbable suture anchor models were held in a metallic holder and loaded under tension using 0.5-mm steel wires until failure. Testing temperature was 20 degrees C +/- 1 degrees C or 37 degrees C +/- 1 degrees C, test speed was 50 mm/min or 5 mm/min. Tensile load at failure and failure mode were recorded. To test creep behavior, a constant load of 100 N was applied, and time to failure was recorded at both temperatures.

RESULTS

Both raising the temperature and decreasing test speed significantly (P <.0001) impaired the mechanical performance of the tested implants. Increase of temperature (20 degrees C to 37 degrees C) resulted in a decrease of the maximal failure strength by up to 40% and decreased time to failure by up to 98% under static load. At 37 degrees, decreasing the test speed from 50 to 5 mm/min lowered the load to failure by up to 18%. Failure of the anchors always occurred by eyelet cutout of the wire.

CONCLUSIONS

The lower the test speed, the higher is the influence of the testing temperature. Testing of implants at room temperature instead of body temperature may falsely improve test results by a factor of up to 50 under static load. Therefore, testing absorbable implants at body temperature seems mandatory, preferably at slow test speeds.

Single-step ultrasound localization of breast lesions and lumpectomy procedure

BACKGROUND

This review was made to evaluate whether the efficiencies of intraoperative ultrasound-guided localization could be extended to stereotactic biopsy cases by using a marker visible by sonography and mammography.

METHODS

A retrospective review identified 170 stereotactic directional vacuum-assisted biopsy (DVAB) procedures marked with an ultrasound-visible marker. Localization device, imaging method, lesion retrieval, and margin status were assessed for patients having subsequent lumpectomy or wider excision.

RESULTS

Nineteen of 170 patients underwent lumpectomies (12) or wider excision (7) localized by a radiofrequency device or 18G needle up to 7 weeks after stereotactic biopsy. In 15 of 19 procedures, an ultrasound-guided localization was performed intraoperatively, targeting the marker. All targeted lesions were successfully excised. In the 13 malignant lesions (of 19 surgeries), only 1 had a positive margin (8%).

CONCLUSIONS

Marking stereotactic biopsies with a sonographically visible marker allows ultrasound-guided intraoperative localization, improving efficiencies for the patient, surgeon, and operating room schedule.

Mechanical testing of absorbable suture anchors

PURPOSE

Absorbable suture anchors offer great advantages but are made of mechanically weak material. The weakest link in the fixation of soft tissue to bone may therefore be the anchor itself. In this study, several commercially available anchors were mechanically tested in vitro.

TYPE OF STUDY

Biomechanical bench study.

METHODS

Twelve absorbable suture anchor models were implanted into an artificial test bone according to the recommended technique. Testing temperature was 37 degrees C +/- 1 degrees C. The anchors were loaded with an Instron testing machine with the suture material (USP No. 2, Ethibond, Ethicon, Somerville, NJ) in line with the anchor axis, with and without previous abrasion of the suture at the eyelet. Tensile load at failure and failure mode were recorded. To test creep behavior, a permanent load of 100 N was applied to the anchors, and time to failure was recorded. Suture anchor weight and crystallinity were analyzed.

RESULTS

Mean failure load on tensile testing using a cross-head speed of 60 mm/min ranged from 124 to 244 N. Failure modes were eyelet failure in 5 cases, suture failure in 6 cases, and anchor pullout in 1 case. In creep testing, eyelet failure occurred in 8 anchor models after a mean duration of 0.5 to 99 hours; 3 anchor models remained intact after 300 hours, and 1 anchor model failed by pullout of the test sample. Crystallinity ranged from 0% (amorphous) to 57.2%; anchor weight ranged from 0.036 to 0.161 g. Mechanical properties did not correlate with crystallinity but with anchor weight. Abrasion of the suture material at the eyelet had little effect on failure load.

CONCLUSIONS

At 37 degrees C, structural failure (breaking) of absorbable suture anchors may occur if loaded to the mechanical limit. Absorbable anchors are particularly sensitive to static, long-term loading.

Bone tunnel remodeling at the site of biodegradable interference screws used for anterior cruciate ligament reconstruction: 5-year follow-up

PURPOSE

The purpose of this prospective study was to review, using expanded clinical-assessment tools, the long-term results of the local effects of a bioabsorbable interference screw (copolymer 85/15 D,L lactide/glycolide) in anterior cruciate ligament (ACL) reconstruction.

TYPE OF STUDY

This prospective study was initiated in May 1993. The inclusion criteria for patient selection included rupture of the ACL in athletic patients without involvement of the collateral ligaments, arthroscopic ACL reconstruction using middle third of the ligamentum patella, and magnetic resonance imaging (MRI) and plain radiographic examinations of the knee joint during follow-up.

MATERIALS

Between May 1993 and October 1994, 32 patients were enlisted in the study; 48 patients did not fit the inclusion criteria. There were 25 men 7 women. The average age was 29.1 years (range, 19 to 50 years). There were 21 right knees and 11 left knees. The follow-up examinations were performed by an independent examiner. There were 28 patients available for follow-up at a medium of 5.2 years (range, 4.1 to 6.4 years). The evaluation included various testing systems (i.e., OAK, IKDC, Lysholm) as well as MRI and plain radiographic studies to investigate the longevity of the implant and potential adverse effects of this new bioabsorbable material.

RESULTS

The clinical results were good. The OAK score (Orthopädische Arbeitsgruppe Knie) showed 93% excellent and good results, and 7% fair results. The IKDC and Lysholm scores were 92% and 96% good and excellent results, respectively. MRI showed bone remodeling and new bone formations at the site of the implant in the femoral as well as in the tibial bone tunnel at follow-up. No cystic or osteolytic changes where seen on MRI or plain radiographs.

CONCLUSIONS

This study showed the correlation between histology and MRI: there was minimal surgical-site edema, minimal reaction to this material, and complete replacement by new bone formation of the previous site of this implant. At 5 years, this bioabsorbable interference screw appeared clinically safe and effective for fixation of bone blocks during ACL reconstruction and MRI showed complete absorption and replacement with new bone.

Serial magnetic resonance imaging evaluation of operative site after fixation of patellar tendon graft with bioabsorbable interference screws in anterior cruciate ligament reconstruction

Magnetic resonance imaging (MRI) is accepted as the imaging procedure of choice for showing internal derangement of the knee. In contrast to metal implants, bioabsorbable interference screws do not produce an artifact and provide an opportunity to expand the evaluation of the postoperative anterior cruciate ligament (ACL) ligament repair. There is the potential to evaluate the implant, the graft, the adjacent tissue, and the surgically created bone tunnels. The purpose of this study was to evaluate with MRI the postoperative site of ACL patellar tendon autografts in which bioabsorbable screws were used for fixation. It was hypothesized that a time line of bone tissue changes resulting from this type of surgery could be developed based on the expanded evaluation of MRI. From January 1993 through October 1997, 270 patients underwent surgical repair of a disrupted native ACL. There were 173 men 97 women; the average age was 25.1 years, (range, 17 to 50 years). There were 155 right knees and 115 left knees. In addition to the conventional postoperative clinical assessment and plain film radiographs, opportunistic MRIs were obtained with the patient's permission. The examinations were performed at different postoperative intervals from the third postoperative day to 4 years postoperatively. A total 206 MRIs from various time intervals were available for study. The study protocol was designed to look for loss of integrity of the screws, adjacent fluid collection, tunnel widening, and tunnel healing or narrowing. The hypothesis was substantiated in this study. The use of MRI provided observations not available by other imaging methods. The absence of metal implants for fixation provided an opportunity to examine the adjacent tissue in detail and to form a time line of the tissue response in this type of surgery.