Original Article
Biomechanical analysis of bioabsorbable suture anchors for rotator cuff repair using osteoporotic and normal bone models

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Abstract

Background

This study aimed to compare the failure load of suture anchors used in rotator cuff repair between normal and osteoporotic bone models.

Methods

A total of 16 anchors made from metal (TwinFix Ti 5.0 or 6.5 mm, Corkscrew FT 4.5, 5.5, or 6.5 mm), polyether ether ketone (HEALICOIL PK [HC-PK] 4.5 or 5.5 mm, SwiveLock PK 4.75 or 5.5 mm), or bioabsorbable material (HEALICOIL RG [HC-RG] 4.75 or 5.5 mm, Corkscrew Bio 4.75, 5.5, or 6.5 mm, SwiveLock BC 4.75 or 5.5 mm) were included. Moreover, 10- and 5-pounds per cubic foot (pcf) Sawbone® models were set as normal and osteoporotic cancellous bone models, respectively. Pullout testing was performed in parallel to the insertion axis at a displacement rate of 12.5 mm/s using a universal testing machine. To evaluate the change in failure load between the two Sawbone® models with different densities, the remaining failure load ratio (RFLR) was defined as the ratio of the failure load in 10 pcf to that in 5 pcf.

Results

In the 10-pcf Sawbone®, TwinFix Ti 6.5 mm showed the highest mean failure load (304.0 ± 15.2 N). In the 5-pcf Sawbone® model, HC-PK 5.5 mm showed the highest failure load (146.3 ± 5.8 N). Among anchors with the same diameter, HC-PK and HC-RG showed a significantly higher failure load than other anchors in the 10- and 5-pcf Sawbone® models. HC-PK 5.5 mm (62.1%) and HC-PK 4.5 mm (51.1%) have the highest RFLR among anchors with the same diameter.

Conclusions

HC-PK and HC-RG showed higher failure load than the other anchors in both normal and osteoporotic bone models, except for TwinFix Ti 6.5 mm in the 10-pcf Sawbone® model. Based on our results, bioabsorbable anchors had sufficient failure load for rotator cuff repair in addition to bioabsorbability.

Introduction

Rotator cuff (RC) tears are one of the common shoulder injuries in older populations. RC tears cause nocturnal shoulder pain and difficulty in performing overhead activities. The prevalence of RC tear in each decade of age was 15.2% in the 60s, 26.5% in the 70s, and 36.6% in the 80s [1]. Symptomatic patients accounted for 65.3% of all RC tear patients [1]. On the contrary, without operative treatment, the risks of persisting and recurring symptoms, lack of healing, tear extension, fatty infiltration, muscle atrophy, tendon retraction, and RC arthropathy increase [2]. Finally, repairable RC tears progress to irreparable RC tears and patients need reverse total shoulder arthroplasty [3]. Although the appropriate timing for the treatment of RC tears differs depending on the case, symptomatic tears sometimes require repair before they progress to irreparable tears.

Previously, RC repair was performed by open surgery. Nowadays, arthroscopic surgeries are commonly performed with some advantages: less postoperative pain, quick recovery time, good cosmetic results, and avoidance of deltoid detachment [4,5]. In arthroscopic RC repair, suture anchors are frequently used to reattach the torn RC tissue to the bone. New anchors have been developed to improve the initial repair strength and healing rates. Over the past 20 years, metal has been the material most frequently used for the manufacture of anchors; however, new materials have been used more recently (over the last decade): polyglycolic acid, polylactic acid, polyether ether ketone (PEEK), tricalcium phosphate, and hydroxyapatite [6].

To date, several studies have investigated anchor failure load [7]. Biomechanical testing has revealed that the anchor failure load was correlated to bone density and quality [8]. In the past, commonly used titanium suture anchors caused metal artifacts in postoperative magnetic resonance imaging (MRI), and the persistent anchors limited the positioning of subsequent suture anchors for revision surgery [9]. In recent years, some new absorbable suture anchors are attracting attention because of their material and design. The HEALICOIL REGENESORB (HC-RG: Smith and Nephew ASD, Inc., Andover, MA, USA) has been used as one of the bioabsorbable anchors. This anchor material is completely resorbed within 2 years after arthroscopic RC repair and replaced by new bone formation [10]. This anchor avoids the postoperative MRI artifacts and contributes to easier revision surgery. Although some studies have reported on the effect of structural design on the pullout strength of suture anchors [11,12], few studies have compared the failure load between these new bioabsorbable anchors and anchors with other diameters, designs, and material compositions using osteoporotic bone models.

Thus, this study aimed to compare the failure load of anchors of different diameters, designs, and material compositions using both normal and osteoporotic bone models. For this study, we hypothesized that the new bioabsorbable anchors have a comparable failure load to metal or PEEK anchors even in osteoporotic bone models.

Section snippets

Materials

Synthetic bone models (Sawbone®, Pacific Research Laboratories, Vashon, WA) were used for anchor pullout testing. A 10-pound per cubic foot (pcf) model (part #1522-01) was used as a normal cancellous bone model, and a 5-pcf model (part #1522-23) was used as an osteoporotic cancellous bone model [13]. The anchors that were tested in this study varied in diameter, design, and material composition (Fig. 1). Metal anchors were TwinFix Ti 5.0 mm and 6.5 mm (Smith and Nephew ASD, Inc., Andover, MA,

Failure mode

The most frequent failure mode was anchor pullout in the 10- and 5-pcf Sawbone® models (Table 2). Eyelet break was found in HC-PK 5.5 mm, HC-RG 5.5 mm, Corkscrew Bio 4.75 mm, and Corkscrew Bio 5.5 mm. Suture break was found only in Corkscrew Bio 6.5 mm in the 10-pcf Sawbone® model. HC-PK 4.5 mm was deformed after the pullout testing in the 10-pcf Sawbone® model (Fig. 2).

Failure load

In the 10-pcf Sawbone® model, TwinFix Ti 6.5 mm showed the maximum failure load (304.0 ± 15.2 N) (Fig. 3). In the 5-pcf

Discussion

In this study, the failure load and RFLR of 16 anchors were compared using two Sawbone® models with different densities. When comparing anchors of the same design, failure load increased concomitantly with increased anchor diameter. Subsequently, when comparing anchors of the same diameter, the HC-PK and HC-RG showed higher failure loads than the other anchors. Especially, in the 5-pcf Sawbone® models which simulated osteoporotic bone, HEALICOIL anchors showed significantly higher failure load

Conclusions

HC-PK and HC-RG showed higher failure load than the other anchors in both normal and osteoporotic bone models except for TwinFix Ti 6.5 mm in the 10-pcf Sawbone® model. Based on our results, bioabsorbable anchors had sufficient failure load for RC repair in addition to its bioabsorbability.

Data statement

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declaration of competing interest

The authors have no competing interests to declare.

Acknowledgment

We would like to thank Editage (www.editage.com) for English language editing.

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