Late Bone Marrow Edema Associated With Use of a Bioresorbable Polymer Suture Anchor in Foot and Ankle Surgery

Abstract

Background:

Bioresorbable orthopaedic implants have proliferated in recent years, including suture anchors, soft tissue scaffolds, and screws. At our institution, we anecdotally noticed late inflammatory-type reactions in the bone surrounding a particular bioresorbable polymer suture anchor. This bioresorbable anchor (BRA) uses ultrasonic technology to liquefy its tip, allowing interdigitation with surrounding cancellous bone. The polymer is designed to resorb around 2-3 years. In this study, we aimed to characterize complications associated with its use.

Methods:

A retrospective review was conducted of foot and ankle procedures using the BRA between 2018 and 2023, using a prospectively collected foot and ankle registry. Of the 62 patients who received at least 1 of these implants, 42 (68%) were female. Chart review was used to identify postoperative complications, particularly pain with bone marrow edema (BME) surrounding the anchor(s), as detected on magnetic resonance imaging (MRI). Patients were classified according to their primary diagnoses and level of physical activity. Patients with and without BME were compared to each other.

Results:

Twenty (32%, 95% CI 22%-45%) patients developed an inflammatory response at a mean of 27 months postoperatively. Four patients (20%) developed BME less than 1 year postoperatively, whereas the remaining 16 patients (80%) developed BME more than 2 years postoperatively. BME occurred more often in females (P = .047), and when used in the setting of trauma (P = .039). Symptoms resolved with nonoperative treatment in all but 3 cases (15%). No revision surgeries were performed.

Conclusion:

Nearly one third of the patients developed symptomatic bone marrow edema localized to the bioresorbable anchor. Female sex and ankle fracture were variables significantly associated with development of BME. Not all symptoms resolved with nonoperative treatment. These findings suggest caution should be exercised when using bioresorbable anchors.

Level of Evidence:

Level IV, retrospective review.

Keywords

suture anchor bioresorbable implant bioresorbable anchor bone marrow edema

Introduction

The use of bioresorbable implants in orthopaedic surgery has expanded substantially over recent years. Unlike traditional metallic implants, which can cause pain and require repeat surgery for removal, bioresorbable implants including suture anchors and interference screws offer temporary fixation of soft tissue to bone while gradually degrading and being replaced by native tissue.¹

One such implant is the SonicAnchor (Stryker), a bioresorbable suture anchor that uses ultrasonic technology for fixation. Composed of poly(l-lactide-co-d,l-lactide) (PLDLLA), this bioresorbable anchor (BRA) is deployed using ultrasonography-assisted insertion technology. On insertion, ultrasonic energy liquefies the polymer tip, allowing it to interdigitate with adjacent cancellous bone.² The material rapidly resolidifies, creating stable fixation in the bone’s trabecular structure.² Despite the BRA’s small bony footprint of 2.5 mm, the polymer achieves strong pull-out strength that is comparable to or even greater than conventional anchors.³

Over 24-36 months, the PLDLLA polymer of the BRA degrades via hydrolysis of its ester bonds, yielding lactic acid byproducts metabolized by the body.^4,5 Compared with similar bioresorbable anchors composed poly(l-lactide-co-d-lactide) (PLDLA), this anchor’s PLDLLA material may exhibit faster hydrolytic degradation.⁴ This mechanism of liquid osseointegration, coupled with its small footprint and high pull-out strength, contributed to its popularity in minimally invasive and open foot and ankle procedures requiring soft tissue fixation to bone.⁴

Despite increasing clinical use of bioresorbable implants, there remain limited reports detailing associated adverse complications and outcomes. Complications such as cyst formation, anchor migration, osteolysis, and inflammatory synovitis have been described for similar bioresorbable implants such as the Bio-Fastak (Arthrex) and BioKnotless anchor (DePuy Mitek), yet similar reports specific to the BRA are notably lacking.^4,6
-8

At our institution, we have anecdotally observed a subset of patients presenting with delayed pain in regions surrounding the BRA insertion site(s). These symptoms were corroborated by the identification of bone marrow edema (BME) around the BRA sites on magnetic resonance imaging (MRI), indicating inflammatory reactions in the bone adjacent to the BRA. In this study, we aimed to identify and characterize complications associated with the BRA in foot and ankle procedures.

Methods

Patients were retrospectively reviewed for inclusion from a prospectively collected, institutional review board–approved (IRB) foot and ankle registry at our institution. Prior to data acquisition, approval was obtained from the registry’s steering committee. Patients were eligible if they underwent a foot or ankle procedure using at least 1 BRA. All procedures were performed by one of 2 fellowship-trained orthopaedic foot and ankle surgeons at our institution between November 2018 and January 2023.

Age, sex, preoperative diagnosis, level of physical activity, and postoperative complications were collected from chart review. Patients’ level of physical activity was categorized as inactive, recreational, or collegiate. Inactive patients reported no regular participation in exercise or sports. Recreational activity included noncompetitive sports or casual fitness routines such as running, biking, and weightlifting. Collegiate patients were actively engaged in organized, competitive athletics at the college level.

Because this was a purely retrospective study, standardized pain scores and patient-reported outcome measure scores were not routinely collected. Magnetic resonance imaging was not obtained for all patients and was performed only in patients who presented with postoperative pain. Symptoms arising beyond the typical 6-month postoperative recovery window were self-reported and prompted further imaging. Average follow-up was defined as the time after initial surgery to acquisition of clinically indicated postoperative MRI scan.

Any postoperative MRI reports were evaluated and findings were recorded. A common observation was hyperintense bone marrow signal on fluid-sensitive sequences. This is a histologically complex process but commonly referred to as bone marrow edema (BME).^9,10 In this study, the term “inflammatory” is used descriptively to denote MRI findings consistent with BME without histologic confirmation. Patients were grouped based on the presence or absence of BME surrounding the anchor(s).

Patients who developed bone marrow edema around the anchors typically did well in their postoperative course, were discharged from care, and returned 2-3 years after surgery with new unexplained pain, at which time MRI was performed.

A 95% CI for the proportion of patients who developed BME was calculated using the Wilson method. Demographic and clinical characteristics were then compared between patients with and without BME. Two-sample t tests were used for continuous variables assuming equal variance with 95% CIs. Pearson χ² tests were used for categorical variables. Association with categorical variables was further characterized by Cramer V measure of association (V), where 0 is no association and 1 is perfect association. A significance threshold was set at P < .05. Analysis was conducted on R: A Language and Environment for Statistical Computing (R Core Team 2023).

Results

A total of 62 patients were identified, of which 42 (68%) were female. Mean follow-up time for the cohort was 20.5 ± 13.4 (range, 2-62) months. The mean age was 35.6 (range, 16-68) years in patients with BME and 44.1 (range, 13-79) years in patients without BME (P = .11, 95% CI -2.1-19.2). Mean BMI also did not differ among groups (BME: 26.1, no BME: 28.1; P = .17, 95% CI −0.86 to 4.7) (Table 1).

Table 1.

Comparison of Demographics Between Groups.

Demographics	No BME(n = 42)	BME(n = 20)	P Value(P < .05*)
Age, mean ± SD	44 ± 21	36 ± 17	.11
BMI, mean ± SD	28 ± 6	26 ± 4	.17
Female, n (%)	25 (60)	17 (85)	.047*
Male, n (%)	17 (40)	3 (15)

Abbreviations: BME, bone marrow edema; BMI, body mass index.

Among the 62 patients who underwent surgery with the BRA, 20 (32%; 95% CI 22-45%) developed an inflammatory response, evidenced by BME localized to the anchor site on postoperative MRI. The mean time to BME detection was 27 months postoperatively (range, 4-38 months). Of these 20 patients, four (20%) were diagnosed with BME within one year of surgery, while the remaining 16 (80%) were diagnosed more than two years postoperatively, indicating a predominantly delayed presentation consistent with the anticipated period of polymer anchor degradation. Anchor-associated BME was more frequently observed in female patients (P = .047). Cramer’s V measure of association indicated a small association between sex and BME (V = 0.255, 95% CI 0.127-0.519) and a medium association between diagnosis and BME (V = 0.406, 95% CI 0.254-0.657). There was negligible association between physical activity level and BME (V = 0.053, 95% CI 0.18-0.269).

Primary diagnoses identified included ankle instability (n = 22), insertional Achilles tendinitis (n = 16), flatfoot/accessory navicular (n = 9), ankle fracture (n = 8), and other conditions (n = 7). Primary diagnosis was associated with incidence of BME (P = .039), with the diagnosis of ankle fracture demonstrating the highest rate of BME development (Table 2).

Table 2.

Primary Diagnosis.

Diagnosis	No BME, n (%)(n = 42)	BME, n (%)(n = 20)	P Value
Insertional Achilles tendinitis	13 (31)	3 (15)	.039*
Ankle instability	15 (36)	7 (35)
Flatfoot/accessory navicular	8 (19)	1 (5)
Ankle fracture	2 (5)	6 (30)
Other^a	4 (10)	3 (15)

Abbreviation: BME, bone marrow edema.

“Other” diagnoses included peroneus brevis rupture, Achilles tendon avulsion, syndesmosis and deltoid ligament injury, and peroneal tendon dislocation.

P < .05.

There was no association between physical activity level and the development of BME (P = .92; Table 3). Among patients with BME, the majority (n = 17; 85%) experienced symptom resolution with nonoperative treatment, typically involving 6 weeks of limited activity in a boot. The remaining 3 patients (15%) had persistent symptoms despite conservative measures at the time of last follow-up, although none of them ended up undergoing further surgery. An example of a patient who developed late postoperative BME is shown in Figure 1. There were no wound complications, postoperative infections, or reoperations related to the bioresorbable anchor.

Figure 1.

A 16-year-old patient underwent a Kidner procedure for a painful accessory navicular in July 2021. She recovered well and had returned to gymnastics at her preoperative level by 7 months postoperatively. She eventually returned 3 years postoperatively with recurrent pain over the medial navicular. (A) MRI images at that time showed marked bone marrow edema in the medial navicular localized around the anchors. Symptoms did not fully resolve after a period of immobilization and rest. (B) Repeat MRI 6 months later shows resolution of bone marrow edema. Persistent geographic high signal at the anchor sites, which were previously foci of low signal, is of unclear significance. MRI, magnetic resonance imaging.

Table 3.

Physical Activity Level.

Physical Activity Level	No BME, n (%) (n = 42)	BME, n (%) (n = 20)	P Value
Inactive	17 (40)	7 (35)	.92
Recreational	23 (55)	12 (60)
Collegiate	2 (5)	1 (5)

Abbreviation: BME, bone marrow edema.

The number of BRAs used and the particular site of BRA placement were not associated with occurrence of BME.

Discussion

This study aimed to characterize complications associated with the use of a PLDLLA bioresorbable anchor in foot and ankle surgery, with a particular emphasis on the development of delayed BME. In this retrospective review, nearly one-third of patients who received a BRA developed BME localized to the anchor site. This reaction presented in a delayed fashion, with the majority of complications (80%) identified at more than 2 years postoperatively. Although the particular anchor used in this study has been discontinued, these adverse findings raise important clinical considerations regarding the long-term biocompatibility of similar bioresorbable suture anchors in orthopaedic surgery. It is important to note that although the pronounced bone marrow edema observed on postoperative MRI is suggestive of an inflammatory response, histologic analysis was not performed to enable a definitive diagnosis. Although the MRI findings could reflect alternative processes, prior literature on bioresorbable anchors was used to guide interpretation of the observed bone marrow edema.

In our cohort, female sex emerged as the only significant demographic predictor of anchor-associated BME. Existing literature suggests that sex-based differences in hormonal regulation and immunologic reactivity may catalyze stronger inflammatory reactions to implanted materials.^11,12 This may partially explain the higher prevalence of BME in female patients in our cohort.

Primary diagnosis was also significantly associated with the development of BME (P = .039), with patients with ankle fracture representing the highest rate of development of BME. This association may be related to differences in local cytokine expression in the setting of trauma. Intra-articular fractures of the ankle are known to trigger a release of pro-inflammatory cytokines, increased synovial inflammation, and increased macrophage infiltration—reactions that may potentiate or prolong an inflammatory response following surgery.¹³ Although the inclusion of multiple procedure types introduces procedural heterogeneity, our primary aim was to identify implant-specific complications rather than evaluate procedure-specific outcomes.

Our findings align with prior reports describing adverse reactions to bioresorbable implants composed of PLDLA, a similar biopolymer used in the BRA in the present study. Although much of the existing literature focuses on shoulder surgery, most notably in the context of rotator cuff and labral repairs, similar patterns have been observed. In a systematic review, Park et al⁵ found that PLDLA bioresorbable anchors used in patients undergoing arthroscopic superior labrum repair were associated with significantly higher failure and reoperation rates compared with nonabsorbable alternatives, with osteolysis and inflammatory reactions implicated in these outcomes. Of 348 total patients, 21 (6%) required reoperation, all of whom had undergone initial surgery with a PLDLA bioresorbable anchor. Intraoperatively at the time of reoperation, Park et al observed that the remaining absorbable anchors had lost their structural integrity, accompanied by evidence of surrounding synovitis. However, there were no signs of anchor pull-out or implant breakage.⁵

Prior work has also described expected MRI changes associated with bioresorbable anchor resorption. Pawaskar et al¹⁴ performed routine early postoperative MRI in 200 patients following rotator cuff repair with PLDLA bioresorbable anchors and observed peri-anchor signal changes that decreased over time, consistent with expected resorption-related changes. These findings suggest that tissue reactions including granulation tissue, fluid accumulation, and foreign-body signal changes may occur as part of the biologic resorption process of bioresorbable anchors.¹⁴ What is new in the present study is the finding that anchor-associated BME on MRI, occurring at the time of expected anchor resorption, also correlated with the development of new pain in patients who had previously recovered well from their surgeries and reported no new injuries.

In contrast, the existing foot and ankle literature has largely supported the safe clinical use of the BRA. Burnham et al¹⁵ described their initial experience with the BRA in which only 2 of 116 patients had adverse events. Similarly, Chen et al¹⁶ retrospectively reviewed 50 foot and ankle procedures with a minimum of 24 months’ follow-up and a mean follow-up of 33.4 months. Only 3 major complications were identified, including wound dehiscence, deep venous thrombosis, and recurrence of ankle varus.

Robbins et al³ demonstrated favorable patient-reported outcomes and satisfaction rates for patients who underwent Brostrom-Gould procedures using the BRA. Twenty-six patients who underwent Brostrom-Gould repair with the BRA were included. Minimum 3-year Patient-Reported Outcomes Measurement Information System (PROMIS) scores were collected for 20 patients. Long-term primary outcomes and PROMIS scores demonstrated a 95% success rate, 90% satisfaction rate, and high clinical success in physical health and physical function categories.

Although these reports suggest an overall low early complication rate, our findings highlight the importance of long-term surveillance of complications. Delayed inflammatory reactions may be underrecognized in the current foot and ankle literature, which is largely reliant on shorter-term follow-up of 2 years or less.

Several limitations in this study warrant discussion. First, its retrospective design limited our ability to standardize MRI and symptom monitoring beyond the typical postoperative care window. Rather, detection of complications relied primarily on voluntary patient reporting. As a result, MRI was obtained only when clinically indicated. This means that asymptomatic or subclinical cases of BME may have gone undetected. In addition, not all symptomatic cases may have been detected, as a substantial number of patients had less than 1 year of clinical follow-up. Therefore, if anything, we believe that the actual number of inflammatory reactions, symptomatic or asymptomatic, may be higher than reported here. Finally, patient-reported outcome measures were also not routinely collected, and symptom severity was assessed qualitatively according to clinical documentation.

Although the manufacturer has not publicly disclosed the specific reasons for the discontinuation of this BRA, this particular PLDLLA anchor is no longer commercially available. However, other contemporary bioresorbable anchors incorporating polylactide-based copolymers —including PLDLA, PLLA, PLGA, and biocomposite formulations—remain in clinical use across multiple orthopaedic subspecialties.

To our knowledge, this is the first study to characterize delayed-onset BME associated with bioresorbable implants in foot and ankle surgery. Our findings emphasize the importance of risk assessment and long-term surveillance monitoring. Further prospective studies with larger sample sizes and longer follow-up are needed to better understand long-term biological responses to bioresorbable polymer implants.

Conclusion

In this retrospective study, nearly one-third of the patients who underwent foot and ankle surgery with a bioresorbable polymer suture anchor developed an inflammatory response, characterized by bone marrow edema localized to the anchor site. Most reactions occurred more than 2 years after implantation. Female sex and diagnosis were the only variables significantly associated with development of BME. Although most patients’ symptoms resolved within a few months of nonoperative treatment, not all did. These results suggest that greater caution should be exercised when using bioresorbable anchors, particularly in the setting of trauma and in female patients.

Supplemental Material

sj-pdf-1-fao-10.1177_24730114261448203 – Supplemental material for Late Bone Marrow Edema Associated With Use of a Bioresorbable Polymer Suture Anchor in Foot and Ankle Surgery

Supplemental material, sj-pdf-1-fao-10.1177_24730114261448203 for Late Bone Marrow Edema Associated With Use of a Bioresorbable Polymer Suture Anchor in Foot and Ankle Surgery by Amanda I. Zeng, Philip G. Colucci, Constantine A. Demetracopoulos and Elizabeth A. Cody in Foot & Ankle Orthopaedics

Footnotes

ORCID iDs

Amanda I. Zeng, BS,

Elizabeth A. Cody, MD,

Ethical Considerations

Ethical approval for this study was obtained from Foot and Ankle Registry (IRB #2013-038)

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of Conflicting Interests

The authors declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: Constantine A. Demetracopoulos, MD, reports Responsive Arthroscopy LLC: other professional activities; Artelon: other professional activities; Exactech, Inc: other professional activities; In2Bones USA, LLC: other professional activities; Treace Medical Concepts, Inc: other professional activities; Restor3d, Inc: other professional activities; Simulate Technologies: other professional activities; American Orthopaedic Foot & Ankle Society: fiduciary officer; Arthrex: other professional activities; Enovis: other professional activities; RTI Surgical, Inc: other professional activities; HS2, LLC: stock; AOFAS Research Committee, member-at-large board of the OFAF; Foot & Ankle International, specialty content editor for total ankle replacement. Elizabeth A. Cody, MD, reports general disclosures of Sparta Biomedical: stock option; Stryker: paid consultant. Disclosure forms for all authors are available online.

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Supplementary Material

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