Suture anchors and tacks for shoulder surgery, part 1: biology and biomechanics

Effect of cyclic loading on the ultimate tensile strength of small metallic suture anchors used for attaching artificial tendons in rabbits

Background –

Suture anchor failures can lead to revision surgeries which are costly and burdensome for patients. The durability of musculoskeletal reconstructions is therefore partly affected by the design of the suture anchors.

Purpose –

The purpose of the study was to quantify the strength of different suture anchors whose sizes are suitable for attaching artificial Achilles and tibialis cranialis tendons in a rabbit model, as well as determine the effect of cyclic loading on the anchoring strength.

Method –

Four anchors (two with embedded eyelet and two with raised eyelet, n=5 per group) were tested with cyclical loading (1000 cycles and 4.5 mm/sec) and without cycling, to inform the failure loads and mode of failure of the suture anchors. An eyebolt screw with smooth eyelet was used as a control for the test groups.

Results –

All samples in all groups completed 1000 cycles and failed via suture breakage in both test conditions. All anchors had failure loads exceeding the peak Achilles tendon force in rabbits during hopping gait. The data analysis showed an effect of anchor type on the maximum tensile force at failure (F max ) in all suture categories but not an effect of loading condition. Also, the Anika anchor had a significantly less adverse effect on suture strength compared to Arthrex anchor (p=0.015), IMEX anchor (p=0.004) and Jorvet anchor (p<0.001). We observed a greater percentage of failure at the mid-section for the anchors with the raised eyelets compared to the anchors with embedded eyelets, which all failed at the knot.

Conclusion –

Anchors with embedded eyelets had clinically preferred mode of failure with less adverse effects on suture and, may be more reliable than anchors with raised eyelets for attaching artificial Achilles and tibialis cranialis tendons in rabbits.

Attaching artificial Achilles and tibialis cranialis tendons to bone using suture anchors in a rabbit model: assessment of outcomes

Objective

The purpose of this study was to investigate the factors associated with outcomes of attaching artificial tendons to bone using suture anchors for replacement of biological tendons in rabbits.

Study Design

Metal suture anchors with braided composite sutures of varying sizes (USP #1, #2, or #5) were used to secure artificial tendons replacing both the Achilles and tibialis cranialis tendons in 12 New Zealand White rabbits. Artificial tendons were implanted either at the time of (immediate replacement, n=8), or four weeks after (delayed replacement, n=4) resection of the biological tendon. Hindlimb radiographs of the rabbits were obtained immediately after surgery and approximately every other week until the study endpoint (16 weeks post-surgery).

Results

All suture anchors used for the tibialis cranialis artificial tendons remained secure and did not fail during the study. The suture linkage between the Achilles artificial tendon and anchor failed in 9 of 12 rabbits. In all cases, the mode of failure was suture breakage distant from the knot. Based on radiographic analysis, the mean estimated failure timepoint was 5.3±2.3 weeks post-surgery, with a range of 2-10 weeks. Analysis of variance (ANOVA) tests revealed no significant effect of tendon implantation timing or suture size on either the timing or frequency of suture anchor failure.

Conclusion

Based on the mode of failure, suture mechanical properties, and suture anchor design, we suspect that the cause of failure was wear of the suture against the edges of the eyelet in the suture anchor post, which reduced the suture strength below in vivo loads. Suture anchor designs differed for the tibialis cranialis and did not fail during the period of study. Future studies are needed to optimize suture anchor mechanical performance under different loading conditions and suture anchor design features.

An additively manufactured titanium tilting suture anchor: a biomechanical assessment on human and ovine bone specimens

Introduction

A novel titanium tilting suture anchor was designed and fabricated using additive manufacturing. The anchor enjoyed a nonsymmetrical structure to facilitate its insertion procedure through a weight-induced tilt, a saw-teeth penetrating edge to provide a strong initial fixation into cancellous bones of various densities, and an appropriate surface texture to enhance the longterm fixation strength through bone ingrowth.

Methods

Biomechanical tests were performed on 10 ovine and 10 human cadaveric humeri to examine the insertion procedure and assess the initial fixation strength of the anchor, in comparison with a standard screw-type anchor as control.

Results

This study indicated a simple yet reliable insertion procedure for the tilting anchor. All anchors survived after 400 cycles of cyclic loadings and failed in the load-to-failure step. There were no significant differences between the displacements and fixation stiffnesses of the anchors in either group. The ultimate failure load was significantly smaller (p<0.05) for tilting anchors in ovine group (273.7 ± 129.72 N vs. 375.6 ± 106.36 N), but not different in human group (311.8 ± 82.55 N vs. 281.9 ± 88.35). Also, a larger number of tilting anchors were pulled out in ovine group (6 vs. 3) but a smaller number in human group (4 vs. 6).

Conclusion

It was concluded that the biomechanical performance of the designed tilting anchor is comparable with that of the standard screw-type anchors.

Biomechanical properties of a suture anchor system from human allogenic mineralized cortical bone matrix for rotator cuff repair

Background

Suture anchors (SAs) made of human allogenic mineralized cortical bone matrix are among the newest developments in orthopaedic and trauma surgery. Biomechanical properties of an allogenic mineralized suture anchor (AMSA) are not investigated until now. The primary objective was the biomechanical investigation of AMSA and comparing it to a metallic suture anchor (MSA) and a bioabsorbable suture anchor (BSA) placed at the greater tuberosity of the humeral head of cadaver humeri. Additionally, we assessed the biomechanical properties of the SAs with bone microarchitecture parameters.

Methods

First, bone microarchitecture of 12 fresh frozen human cadaver humeri from six donors was analyzed by high-resolution peripheral quantitative computed tomography. In total, 18 AMSAs, 9 MSAs, and 9 BSAs were implanted at a 60° angle. All three SA systems were systematically implanted alternating in three positions within the greater tuberosity (position 1: anterior, position 2: central, position 3: posterior) with a distance of 15 mm to each other. Biomechanical load to failure was measured in a uniaxial direction at 135°.

Results

Mean age of all specimens was 53.6 ± 9.1 years. For all bone microarchitecture measurements, linear regression slope estimates were negative which implies decreasing values with increasing age of specimens. Positioning of all three SA systems at the greater tuberosity was equally distributed (p = 0.827). Mean load to failure rates were higher for AMSA compared to MSA and BSA without reaching statistical significance between the groups (p = 0.427). Anchor displacement was comparable for all three SA systems, while there were significant differences regarding failure mode between all three SA systems (p < 0.001). Maximum load to failure was reached in all cases for AMSA, in 44.4% for MSA, and in 55.6% for BSA. Suture tear was observed in 55.6% for MSA and in 22.2% for BSA. Anchor breakage was solely seen for BSA (22.2%). No correlations were observed between bone microarchitecture parameters and load to failure rates of all three suture anchor systems.

Conclusions

The AMSA showed promising biomechanical properties for initial fixation strength for RCR. Since reduced BMD is an important issue for patients with chronic rotator cuff lesions, the AMSA is an interesting alternative to MSA and BSA. Also, the AMSA could improve healing of the enthesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05371-0.

Editorial Commentary: Taking a "PEEK" at Suture Anchor Composition following Arthroscopic Rotator Cuff Repair: Is Bio Really Better?

The advent of modern suture anchor technology has not only revolutionized arthroscopic treatment options for management of complex shoulder pathology, but also engendered a materials science quest to identify the ultimate composition and design. What began as an open procedure with transosseous suture fixation has evolved dramatically with the widespread adoption of an arthroscopic, anchor-based technique for rotator cuff repair. Currently, a litany of commercially available "hard" and "soft" anchors are flooding the market, with limited qualitative comparisons to suggest superiority of one type. Ideally, suture anchor design should permit preservation of native glenohumeral bone stock with gradual osseointegration, limit disruption of local tissue homeostasis, and maintain time-zero mechanical strength until soft-tissue healing has occurred. At present, a vented, open-anchor architecture may facilitate better biologic incorporation with increased bony ingrowth through access to marrow elements, although these radiographic advantages have not conferred any clinically meaningful differences for our rotator cuff repair patients. For anchor composition, the jury is still out, and we need to continue to critically evaluate for perianchor cyst formation and longer term remodeling. In fact, the true merits of increased bony ingrowth and limited osteolysis may only be realized at the time of revision rotator cuff repair, during which prior implant position or secondary cystic change may further dictate suture anchor design, size, and placement.

Biomechanical Properties and Biocompatibility of a Non-Absorbable Elastic Thread

To date, extensive studies have been conducted to assess diverse types of sutures. But there is a paucity of data regarding biomechanical properties of commonly used suture materials. In the current experiment, we compared biomechanical properties and biocompatibility, such as tensile strength and elongation, the degree of bovine serum albumin (BSA) release, in vitro cytotoxicity and ex vivo frictional properties, between a non-absorbable elastic thread (NAT; HansBiomed Co. Ltd., Seoul, Korea) (NAT-R: NAT with a rough surface, NAT-S: NAT with a smooth surface) and the Elasticum^® (Korpo SRL, Genova, Italy). The degree of tensile strength and elongation of Si threads was significantly higher in both the NAT-R and -S as compared with the Elasticum^® (p < 0.05). Moreover, the degree of tensile strength and elongation of PET threads was significantly lower in both NAT-R and -S as compared with the Elasticum^® (p < 0.05). Furthermore, the degree of tensile strength and elongation of braided Si/PET threads was significantly lower in NAT-S as compared with NAT-R and Elasticum^® (p < 0.05). The degree of BSA release was significantly higher in the NAT-R as compared with Elasticum^® and NAT-S throughout a 2-h period in the descending order (p < 0.05). The degree of cell viability was significantly higher in both NAT-R and -S as compared with Elasticum^® (p < 0.05). The degree of coefficient of friction as well as the frictional force and strength was significantly higher in NAT-R as compared with NAT-S and Elasticum^® (p < 0.05). NAT had a higher degree of biomechanical properties and biocompatibility as compared with Elasticum^®. But further experimental and clinical studies are warranted to compare the efficacy, safety, and potential role as a carrier for drug delivery between NAT and Elasticum^®.

History of surgical stabilization for posterior shoulder instability

Background

Posterior shoulder instability is common in young athletes. Although the posterior shoulder instability literature is less robust than its anterior counterpart, many surgical procedures have been developed and refined over the past several centuries to address this condition.

Materials and methods

This article represents a retrospective historical analysis of the most common procedures used to treat posterior shoulder instability after sports injuries. A systematic approach to obtain published information on posterior shoulder instability was performed using the PubMed/MEDLINE database, manual searches of high–impact factor journals, and conference proceedings and books.

Results

A wide array of both soft tissue–based and bone-based procedures have been developed for the treatment of posterior shoulder instability, ranging from procedures addressing the soft tissue alone (capsular shift, labral repair, reverse Putti-Platt) or bone-based procedures (glenoid and/or humeral osteotomy, glenoid bone block) to a combination of both bone and soft-tissue procedures (modified McLaughlin procedure).

Discussion

Over the past several centuries, a number of procedures have been developed to address posterior shoulder instability, particularly as this pathology has become better understood. Future work is required not only to continue to advance these procedures but also to assess their outcomes. An understanding of the historical perspective of posterior shoulder instability procedures is essential as surgeons continue to modify these procedures in an effort to best help their patients.

Editorial Commentary: Perianchor Cysts-We Need More Worries After Rotator Cuff Repair Like We Need Holes in the Head

Cysts or radiolucent rings are relatively common around suture anchors after rotator cuff repair. The rate of cyst occurrence is similar across anchor types and materials. Generally, perianchor cysts are benign and can be regarded as not affecting clinical outcomes.

Absorbable Mg surgical tack: Proof of concept &in situ fixation strength

A prototype magnesium (Mg) surgical tack is tested comparatively against commercially available tacks made of titanium (ProTack^tm, Medtronic) and PLGA (AbsorbaTack^tm, Medtronic). The pull-out force is measured in situ in a lap-shear pull-out test, using porcine abdominal muscle tissue as a model. The Mg tack had a pull-out force comparable to those of the commercially available tacks. The majority of the Mg tacks also had a more ductile failure mode (i.e. the tacks deformed prior to failure), compared to the commercial tacks which pulled directly from the tissue with no deformation. The Mg tacks deformed as they were removed from the tissue, causing less damage to the tissue in the process. This is the first reported use of a Mg alloy in this application, and the proof of concept indicates that this is an area that deserves further interest and study.

Mechanisms of Suture Integration in Living Tissue: Biomechanical and Histological In Vivo Analysis in Sheep

The potential of nonabsorbable suture material to augment tissue strength in the long-term is by far not exploited by most of the currently used sutures. The authors hypothesized that different sutures yield specific histological tissue reactions associated with specific mechanical shear resistance of the suture against the tissue. Four different suture types (Orthocord, Ethibond, FiberTape, and FiberWire) were implanted in 36 sheep shoulders (supraspinatus/greater tuberosity). One thread at each time point (6, 16, and 22 weeks) was used for histology, and 11 threads at each time point (0, 6, 16, and 22 weeks) were used for biomechanical longitudinal pullout testing. Histology included tissue maturity, activity of tissue reaction, and invasion of cells and tissue into the suture material. Fiber-Tape had the highest mean pullout strength at 6, 16, and 22 weeks of 4.4 N/cm (SD, 2.1 N/cm), 10.1 N/cm (SD, 5.1 N/cm), and 12.8 N/cm (SD, 6.0 N/cm), respectively. However, general pullout strength at 22 weeks was surprisingly low, particularly for Ethibond, Orthocord and FiberWire. The overall maturity of the surrounding tissue correlated (r=0.84, P=.001) with mechanical performance. Interestingly, in all 4 suture types, an intimate in- and on-growth of fibrous tissue to the filaments and into the space between suture fibers could be shown. However, for Ethibond, Orthocord, and FiberWire, the authors found an unexpected circumferential space around the sutures, often forming an inner and outer capsule, separating the sutures from the surrounding tissue with a shifting layer. [Orthopedics. 2019; 42(3):168-175.].

Cytotoxicity and biomechanics of suture anchors used in labral repairs

Background

Biodegradable suture anchors are associated with higher redislocation rates. This study examined whether the biocompatibility and/or biomechanical properties of suture anchors contribute to the increase in complications.

Methods

Human glenohumeral capsule cells were cultured with 4 types of suture anchors, Opus LabraFix (titanium alloy; ArthroCare, Austin, TX, USA), PushLock (poly-ether-ether-ketone; Arthrex, Naples, FL, USA), BioKnotless (poly-l-lactic acid; DePuy Mitek, Warsaw, IN, USA), and Suretac II (polyglycolic acid; Smith & Nephew, London, UK), to measure cell viability and pH. Four groups of 6 ovine shoulders were used to repair the labrum, which was completely detached from the glenoid rim anteroinferiorly and reattached with 2 suture anchors and subject to failure load testing.

Results

In cell culture, BioKnotless at 48 and 72 hours (85.2% ± 2.1% and 84.5% ± 3.6%) and Suretac II groups (33.9% ± 3.1% and 42.8% ± 6.4%) had fewer viable cells compared with control (P = .048). The pH of Suretac II was lower than control (7.51 to 7.65) at 24 hours (7.31 ± 0.08, P = .049), 48 hours (7.25 ± 0.02, P = .046), and 72 hours (7.29 ± 0.04, P = .04). During mechanical testing, 83% of repairs failed by the capsule tearing. Among the anchors, the BioKnotless repair group had a significantly lower failure load (37 ± 5 N) compared with the PushLock (61 ± 7 N), Opus (60 ± 6 N), and Suretac II (57 ± 7 N) groups (P = .038).

Conclusion

BioKnotless and Suretac II anchors are cytotoxic. The BioKnotless biodegradable anchor has significantly lower failure load. Absorbable suture anchors may cause higher redislocation of arthroscopic Bankart repair.

Radiolucent rings around bioabsorbable anchors after rotator cuff repair are not associated with clinical outcomes

PURPOSE

Various researchers have observed small areas of osteolysis after using bioabsorbable anchors in shoulder surgeries. The purpose of this study is to determine whether radiographic perianchor radiolucent rings after rotator cuff repair are associated with the failure of repair and also assess their clinical implications. Further, the most frequent location of the radiolucent rings in the double-row suture bridge configuration was also assessed.

METHODS

One hundred and twenty-nine consecutive patients who underwent arthroscopic rotator cuff repair by suture bridge technique were retrospectively evaluated radiographically and clinically. The number and size of the rings that appeared at each follow-up were recorded. Also, the locations of each ring were recorded as anterior, middle or posterior, and medial or lateral according to the construct of the anchors used for suture bridge technique. The size of the tear, the number of anchors used and age of the patients were compared. Re-tear rates according to ultrasound examinations were also analyzed.

RESULTS

After rotator cuff repair, the mean American Shoulder and Elbow Surgeons (ASES) score increased from 46.7 to 88.0 and the overall re-tear rate was 8.5% (11 cases). Seventy-three patients (56.6%) showed RR (total number of 99 rings) at least once during the course of their follow-up and the rings appeared at a mean period of 18.2 months after surgery. Mean size of the rings initially was 5.6 mm and the rings increased or decreased in mean size of 0.4 mm during mean follow-up of 37 months. No correlation was seen with the number of RRs and the rate of re-tears, number of anchors, size of tears, and clinical outcome as determined by the ASES score. Radiolucent ring measurement reproducibility was confirmed by independent, repeated measurements. The rings appeared mostly at anteromedial anchors (75 rings, 75.8%) and the authors suggest that mechanical factors may play a role for the cause of radiolucent rings.

CONCLUSIONS

The number and the size of RRs around bioabsorbable anchors after rotator cuff repair do not appear to adversely affect the healing and clinical outcome of ARCR. Most radiolucent rings appeared at anteromedial anchors, indicating that mechanical factors may play a role for the radiolucencies.

LEVEL OF EVIDENCE

Case series, level IV.

Dual growth factor-immobilized asymmetrically porous membrane for bone-to-tendon interface regeneration on rat patellar tendon avulsion model

Insufficient repair of the bone-to-tendon interface (BTI) with structural/compositional gradients has been a significant challenge in orthopedics. In this study, dual growth factor (platelet-derived growth factor-BB [PDGF-BB] and bone morphogenetic protein-2 [BMP-2])-immobilized polycaprolactone (PCL)/Pluronic F127 asymmetrically porous membrane was fabricated to estimate its feasibility as a potential strategy for effective regeneration of BTI injury. The growth factors immobilized (via heparin-intermediated interactions) on the membrane were continuously released for up to ∼80% of the initial loading amount after 5 weeks without a significant initial burst. From the in vivo animal study using a rat patellar tendon avulsion model, it was observed that the PDGF-BB/BMP-2-immobilized membrane accelerates the regeneration of the BTI injury, probably because of the continuous release of both growth factors (biological stimuli) and their complementary effect to create a multiphasic structure (bone, fibrocartilage, and tendon) like a native structure, as well as the role of the asymmetrically porous membrane as a physical barrier (nanopore side; prevention of fibrous tissue invasion into the defect site) and scaffold (micropore side; guidance for tissue regeneration). © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 115-125, 2018.

Viscoelastic properties of common suture material used for rotator cuff repair and arthroscopic procedures

PURPOSE

The purpose of this study was to evaluate the viscoelastic properties of 5 suture materials, commonly used in arthroscopic rotator cuff repairs, when subjected to physiological loads.

METHODS

We evaluated 5 commercially available No. 2 sutures undergoing both creep and cyclic testing in both dry air and phosphate-buffered saline solution (PBS) maintained at 37°C. The selected sutures were MagnumWire (ArthroCare, Austin, TX), Ethibond (Ethicon, Somerville, NJ), FiberWire (Arthrex, Naples, FL), Orthocord (DePuy, Warsaw, IN), and Force Fiber (Tornier, Bloomington, MN).

RESULTS

Regarding creep testing, in the PBS test environment, FiberWire showed the greatest stiffness (71.1 ± 2.1 N/mm), the smallest initial extension at the 60-N load (1.10 ± 0.04 mm), and the smallest amount of creep (0.57 ± 0.01 mm). Orthocord showed the smallest amount of relaxed elongation in PBS (0.73 ± 0.11 mm). Regarding cyclic testing, in the PBS testing environment, Ethibond exhibited the smallest dynamic creep (0.28 ± 0.02 mm), FiberWire displayed the smallest peak-to-peak displacement (0.17 ± 0.00 mm), and Orthocord showed the smallest amount of relaxed elongation after cyclic loading (0.63 ± 0.11 mm).

CONCLUSIONS

FiberWire consistently displayed more extreme viscoelastic properties--greater stiffness and less extensibility--than the other suture types studied. Orthocord showed the smallest amount of relaxed elongation in both testing environments. Differences in testing environment affect the behavior of each suture type. Testing in physiologically approximating conditions such as PBS maintained at 37°C is warranted.

CLINICAL RELEVANCE

Although many other factors affect the success of rotator cuff repairs, the viscoelastic properties of sutures may be a useful predictor of suture performance.

Biomechanical evaluation of knotless anterior and posterior Bankart repairs

PURPOSE

The value of modern tape-like suture materials and the influence of the number of anchors inserted for arthroscopic Bankart repairs compared to the intact state have yet to be investigated. It was hypothesised: (1) suture-tape repairs will show higher biomechanical strength than common suture repairs, (2) four anchors will be stronger than three, and (3) the strength of the native capsulolabral complex will be greater than repairs.

METHODS

Six matched-paired cadaveric shoulders received Bankart lesions/reconstructions and three underwent intact state testing. Anteroinferior repairs compared suture and suture-tape repairs using three anchors, while posteroinferior repairs compared three and four suture anchors using common sutures. An established testing protocol was run for biomechanical testing.

RESULTS

There was no significant difference in the maximum loads, loads at 2 mm displacement, stiffness or energy between repair groups or between repairs and the intact state (n.s.). However, failure modes were different: 16/24 (66.7%) of the repair groups showed glenoid labrum detachment compared to 2/12 (16.7%) within the intact state group (P = 0.012).

CONCLUSIONS

While biomechanical parameters of repairs and intact states showed equivalence, failure-mode analysis reaffirms previous findings that capsulolabrum complex refixation is weaker than the native attachment. Therefore, in daily clinical practice, type of suture is secondary and insertion of a fourth anchor will be unlikely to add strength but may confer additional risk and cost.

The arthroscopic treatment of shoulder instability: bioabsorbable and standard metallic anchors produce equivalent clinical results

PURPOSE

To investigate whether there are any differences in clinical outcomes and complications between absorbable and nonabsorbable suture anchors in the treatment of shoulder instability.

METHODS

We performed a comprehensive search of Medline, CINAHL (Cumulative Index to Nursing and Allied Health Literature), Embase, and the Cochrane Central Registry of Controlled Trials, from inception of the databases, using various combinations of keywords. Only studies focusing on clinical outcomes of patients who underwent arthroscopic shoulder stabilization with suture anchors were selected. Two authors (R.P. and L.D.B.) then evaluated the methodologic quality of each article using the Coleman Methodology Score.

RESULTS

Ten articles were included. Four were prospective randomized studies, 2 were prospective cohort studies, and 4 were case series. The mean modified Coleman Methodology Score was 76.2.

CONCLUSIONS

Given the overall good results reported after arthroscopic stabilization of the shoulder using different suture anchors, it is not possible to draw a definite and solid suggestion on which class of device is better advised for routine use. Thus the decision to use one of the anchor systems available may mostly depend on its cost-effectiveness, which should be the focus of future comprehensive research.

LEVEL OF EVIDENCE

Level IV, systematic review of Level I to IV studies.

The thrower's shoulder

Throwers, or athletes who engage in repetitive overhead motions, are a unique subset of athletes that experience distinct shoulder injuries. Athletes engaged in baseball comprise the majority of patients seeking orthopedic care for throwing related injuries. Injuries specific to throwers most commonly involve the labrum and the undersurface of the rotator cuff. In addition, tissue changes in both the anterior and posterior glenohumeral capsule are common with repetitive overhead motions. These capsular changes alter. This article will examine the pathomechanics of injuries to throwers, elaborate means of diagnoses of cuff and labral injury and discuss recent advances in both non-operative and operative interventions, including preventative principles.

Suture capsulorrhaphy versus capsulolabral advancement for shoulder instability

PURPOSE

The purpose of this study was to test the strength of a suture capsulorrhaphy repair versus a capsulolabral repair with knotless suture anchors in a cadaveric model with anteroinferior shoulder instability.

METHODS

Fourteen cadaveric shoulders were tested with either a suture capsulorrhaphy to the intact labrum or a capsulolabral advancement using a knotless suture anchor into the glenoid. Specimens were translated with the shoulder in an abducted, externally rotated position to failure.

RESULTS

The capsulolabral advancement showed a significantly higher load to failure than did the suture capsulorrhaphy group (P = .030).

CONCLUSIONS

Capsulolabral advancement with suture anchors may offer greater initial strength when compared with a suture capsulorrhaphy. In the setting of shoulder instability without evidence of a labral tear, the capsulolabral advancement technique may be considered biomechanically superior.

CLINICAL RELEVANCE

In the setting of shoulder instability due to capsular insufficiency, the capsulolabral advancement may be considered biomechanically superior to a traditional suture capsulorrhaphy.

Tissue anchor use in arthroscopic glenohumeral surgery

Arthroscopic surgery has become the mainstay of treatment of several common glenohumeral pathologies such as tears of the rotator cuff and labrum. Arthroscopic rotator cuff and labral repair provide outcomes comparable to those achieved with traditional open techniques, with the benefits of smaller incisions and less soft-tissue disruption. Development and improvement of tissue anchors and arthroscopic instrumentation has been integral to the increased popularity of arthroscopic glenohumeral repairs. Current anchors can be categorized by design and material composition. Awareness of the advantages and limitations of these implants may influence anchor selection.

Arthroscopic rotator cuff repair: suture anchor properties, modes of failure and technical considerations

Rotator cuff injury and tears are a common source of shoulder pain, particularly among the elderly. Arthroscopic repair has now become the mainstay in the treatment of significant injuries that have failed conservative therapy. Compared with the traditional open technique, arthroscopic repair offers patients smaller incisions and less soft-tissue trauma, which result in improved postoperative pain and rehabilitation. The advances that have made arthroscopic repairs a reality includes improvement in arthroscopic rotator cuff instrumentation, particularly suture anchors. Suture anchors are used to reattach the torn rotator cuff tissue back onto the bone. Current rotator cuff anchors vary by design, anchor composition and suture materials. A treating physician should be aware of the advantages and limitations of these implants, which may influence the choice of one anchor over another. In addition to anchor variables, other factors that may affect the success of the repair include the local environment and surgical technique. In this article, various aspects of anchor design will be discussed. In addition, a concise review of technical considerations will also be discussed.

Glenohumeral osteoarthritis after arthroscopic Bankart repair for anterior instability

BACKGROUND

Few data on shoulder arthropathy in patients undergoing arthroscopic repair for glenohumeral instability are available.

HYPOTHESIS

Arthroscopic stabilization of Bankart lesions does not prevent the development of postoperative glenohumeral osteoarthritis.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Clinical (Rowe and Constant scores) and radiographic preoperative and postoperative data from 60 patients who underwent arthroscopic Bankart repair were compared. Osteoarthritis was graded preoperatively and postoperatively with the Buscayret classification grading system. The average age at surgery was 27.6 years, and follow-up averaged 8.0 years.

RESULTS

The postoperative incidence of osteoarthritis in patients with no preoperative degenerative changes was 21.8% (12 of 55 patients). The incidence of degenerative joint disease of the glenohumeral joint showed evidence of a statistically significant association with older age at first dislocation and at surgery, increased length of time from the first episode to surgery, increased number of preoperative dislocations, increased length of time from the initial dislocation until surgery, increased number of anchors used at surgery, and more degenerated labrum at surgery. A higher number of preoperative dislocations, a greater length of follow-up, and reduced external rotation in abduction influenced Rowe and Constant scores.

CONCLUSION

The number of anchors used and the state of the labrum are the most important factors associated with a higher risk of radiographic degenerative changes. Longer follow-up investigations are needed to draw meaningful conclusions.

Intraosseous foreign body granuloma in rotator cuff repair with bioabsorbable suture anchor

Biodegradable implants lead to problems such as cyst formation, soft-tissue inflammation, loose implant fragments or local osteolysis. This report represents the first published case of an intraosseous foreign body granuloma in the humeral head after arthroscopic rotator cuff tear fixation with a poly-L: -lactide (PLLA) suture anchor. A 48-year-old female patient presented with pain in her right shoulder. A refixation of her right supraspinatus tendon with a biodegradable suture anchor was performed 11 months ago at an external hospital. Laboratory tests showed normal values for C-reactive protein, leukocytes and the erythrocyte sedimentation rate. No signs of infection or instability were noted. The visual analogue scale (VAS) was 8, the simple shoulder test (SST) was 4 and the American shoulder and elbow surgeons score (ASES) was 44. Plain radiographs showed high lucency in the area of the tuberculum majus. MRI showed an intra- and extraosseous mass surrounded by fluid in this area. Surgical care involved arthroscopic debridement and removal of the suture anchor. Histological examination revealed a foreign body granuloma. At the 18-month follow-up the patient was nearly pain-free. The VAS was 2, SST was 10 and ASES was 88. Foreign body granulomas are a well known but rarely described complication that arises after the use of biodegradable suture anchors in shoulder surgery. Every patient presenting with shoulder pain after usage of a biodegradable fixation material should be evaluated closely. Orthopaedic surgeons should be aware of the possibility of delayed foreign body reactions, especially after using PLLA anchors.

A biomechanical analysis of anterior Bankart repair using suture anchors

BACKGROUND

Arthroscopic repair of anterior Bankart lesions is typically done with single-loaded suture anchors tied with simple stitch configuration.

HYPOTHESIS

The knotless suture anchor will have similar biomechanical properties compared with two types of conventional suture anchors.

STUDY DESIGN

Controlled laboratory study.

METHODS

Fresh-frozen shoulders were dissected and an anteroinferior Bankart lesion was created. For phase 1, specimens were randomized into either simple stitch (SSA) or knotless suture anchors (KSA) and loaded to failure. For phase 2, specimens were randomized into 1 of 4 repair techniques and cyclically loaded then loaded to failure: (1) SSA, (2) suture anchor with horizontal mattress configuration, (3) double-loaded suture anchor with simple stitch configuration, or (4) KSA. Data recorded included mode of failure, ultimate load to failure, load at 2 mm of displacement, as well as displacement during cyclical loading.

RESULTS

For phase 1, the load required to 2 mm displacement of the repair construct was significantly greater in SSA (66.5 +/- 21.7 N) than KSA (35.0 +/- 12.5 N, P = .02). For phase 2, there was a statistically significant difference in ultimate load to failure among the 4groups, with both the single-loaded suture anchor with simple stitch (184.0 +/- 64.5 N), horizontal mattress stitch (189.0 +/- 65.3N), and double-loaded suture anchor with simple stitch (216.7 +/- 61.7 N) groups having significantly (P < .05) higher loads than the knotless group (103.9 +/- 52.8 N). There was no statistically significant difference (P > .05) among the 4 groups in displacement after cyclical loading or load at 2 mm of displacement.

CONCLUSION

Both knotless and simple anchor configurations demonstrated similar single loads to failure (without cycling); however, the knotless device required less single load to displace 2 mm. All repair stitches, including simple, horizontal, and double-loaded performed similarly.

CLINICAL RELEVANCE

The findings may suggest that with cyclical loading up to 25 N there is no difference in gapping greater than 2mm, but a macrotraumatic event may demonstrate a difference in fixation during the initial postoperative period. Additional in vivo studies are needed to determine whether these differences affect the integrity of the repair construct and, ultimately, the clinical outcome.

A biomechanical analysis of shoulder stabilization: posteroinferior glenohumeral capsular plication

BACKGROUND

The use of posterior capsular plication to decrease capsular volume and address capsular laxity for treatment of posterior instability, multidirectional instability, or as an additional technique in the treatment of anterior instability is common. Multiple different suturing techniques have been described.

HYPOTHESIS

The simple stitch will have inferior biomechanical properties compared with either the horizontal mattress or figure-of-8 stitches for suture plication of the posteroinferior quadrant of the glenoid.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty-one fresh-frozen shoulders with a mean age of 57.7 +/- 12.3 years were randomized into capsulolabral plication of the posteroinferior quadrant using either simple stitch configuration, horizontal mattress configuration, or figure-of-8 configuration. Each shoulder was mounted onto a materials testing machine, preloaded to 5 N for 2 minutes, cycled from 5 to 25 N for 100 cycles (1 Hz), and then loaded to failure at 15 mm/min. Capsular displacement from the glenoid was determined using digital video analysis. Data recorded included mode of failure, ultimate load to failure, load at 2 mm of displacement, as well as displacement during cyclical loading (during the entire 100 cycles and during the final cycle only).

RESULTS

There was a statistically significant difference (P < .0001) in mechanism of failure among the 3 groups with the simple stitch group failing more often in the capsular tissue than in the mattress and figure-of-8 sutures, which more commonly failed at the capsulolabral junction. There was no statistically significant difference (P > .05) among the 3 groups in gapping (displacement) after cyclical loading, load at 2 mm of displacement, or in ultimate load to failure. Conclusion/

CLINICAL RELEVANCE

Based on these results, all 3 stitches can be used effectively for capsular plication, although the simple stitch may be preferred for the capsular plication because of technical ease and decreased trauma to the capsulolabral tissue.

The effect of the trabecular microstructure on the pullout strength of suture anchors

This study investigates how the microstructural properties of trabecular bone affect suture anchor performance. Seven fresh-frozen humeri were tested for pullout strength with a 5mm Arthrex Corkscrew in the greater tuberosity, lesser tuberosity, and humeral head. Micro-computed tomography analysis was performed in the three regions of interest directly adjacent to individual pullout experiments. The morphometric properties of bone mineral density (BMD), structural model index (SMI), trabecular thickness (TbTh), trabecular spacing (TbS), trabecular number (TbN), and connectivity density were compared against suture anchor pullout strength. BMD (r=0.64), SMI (r=-0.81), and TbTh (r=0.71) showed linear correlations to the pullout strength of the suture anchor with p-values<0.0001. A predictive model was developed to explain the variances in the individual BMD, SMI, and TbTh correlations. The multi-variant model of pullout strength showed a stronger relationship (r=0.86) compared to the individual experimental results. This study helps confirm BMD is a major influence on the pullout strength of suture anchors, but also illustrates the importance of local microstructure in pullout resistance of suture anchors.

Biomechanical comparison of screw-in suture anchor-suture combinations used for Bankart repair

INTRODUCTION

Bankart repair laxity may contribute to pathologic joint instability. This biomechanical study compared two screw-in suture anchor-suture combinations under tensile loads.

METHODS

Twelve pairs of scapulae were implanted with either a 3 mm diameter, 14 mm long poly-L/D-lactide suture anchor with a suture eyelet (Group 1) or a 3.1 mm diameter, 11 mm long polylactide suture anchor with a molded eyelet (Group 2). Constructs were cyclically loaded between 25 and 50 N with a 25 N load increase every 25 cycles.

RESULTS

Group 2 displayed greater displacement at failure, had more specimens with > or =2 mm displacement by the 50 N interval (P = 0.014), and had displaced more by 100 N (P < or = 0.046). Group 1 displayed a stronger load-displacement at failure relationship than Group 2 (r (2) = 0.67 vs. r (2) = 0.37).

CONCLUSION

Construct differences may influence decisions regarding the required number of suture anchor-suture loops, the rehabilitation timetable, and the timing of return to unrestricted activities.

Pullout strength of suture anchors: effect of mechanical properties of trabecular bone

This study investigated the relationships between trabecular microstructure and elastic modulus, compressive strength, and suture anchor pullout strength. Twelve fresh-frozen humeri underwent mechanical testing followed by micro-computed tomography (microCT). Either compression testing of cylindrical bone samples or pullout testing using an Arthrex 5mm Corkscrew was performed in synthetic sawbone or at specific locations in the humerus such as the greater tuberosity, lesser tuberosity, and humeral head. Synthetic sawbone underwent identical mechanical testing and microCT analysis. Bone volume fraction (BVF), structural model index (SMI), trabecular thickness (TbTh), trabecular spacing (TbSp), trabecular number (TbN), and connectivity density were compared against modulus, compressive strength, and pullout strength in both materials. In cadaveric bone, modulus showed correlations to all of the microstructural properties, while compressive and pullout strength were only correlated to BVF, SMI, and TbSp. The microstructure of synthetic bone differed from cadaveric bone as SMI and TbTh showed little variation across the densities tested. Therefore, SMI and TbTh were the only microstructural properties that did not show correlations to the mechanical properties tested in synthetic bone. This study helps identify key microstructure-property relationships in cadaveric and synthetic bone as well as illustrate the similarities and differences between cadaveric and synthetic bone as biomechanical test materials.

Radiofrequency and its effect on suture strength

The use of radiofrequency-based electrocautery for hemostasis and ablation within the subacromial space and glenohumeral joint can cause damage to suture material. Prior studies have focused on the mechanical properties of sutures including their ability to withstand abrasion. The purpose of this study was to determine the effect of electrical energy on the mechanical properties of 5 different brands of #2 suture used for arthroscopic shoulder repair: FiberWire (Arthrex Inc, Naples, Florida); Orthocord (DePuy Mitek, Norwood, Massachusetts); Hi-Fi (formally Herculine; Linvatec Corp, Largo, Florida); MaxBraid (Teleflex Medical, Research Triangle Park, North Carolina); and Ethibond (Ethicon, Inc, Somerville, New Jersey). A matched pair of human deltoid muscle submerged in buffered saline solution (pH 7.4) was used as a test medium. The suture strengths were tested in 3 different scenarios. The 3 groups were as follows: control group without electrical current, coagulation group with direct introduction of electrical current on a coagulate setting for 2 seconds, and a cutting group with direct introduction of electrical current on a cut setting for 2 seconds. Hi-Fi suture seemed to be the least susceptible to damage by direct electrocautery application. Orthocord suffered the greatest loss of strength of all materials tested. This study demonstrates that exposure to electrocautery damages and weakens suture. Great care should be taken when electrocautery is used during arthroscopic repairs to prevent suture failure and preserve repair integrity.

A 7-year prospective, randomized, clinical, and radiographic study after arthroscopic Bankart reconstruction using 2 different types of absorbable tack

BACKGROUND

Recent studies have shown that techniques for arthroscopic Bankart reconstruction using suture anchors or tacks can equal the results after an open procedure in the treatment of posttraumatic, recurrent, unidirectional shoulder instability. Which kind of technique and which implants to be used still need further study.

PURPOSE

The aim of this study was to compare the clinical and radiographic results after arthroscopic Bankart reconstruction using 2 different types of absorbable implants.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

A randomized series of 40 patients who had recurrent shoulder instability underwent reconstruction involving either polygluconate-B polymer or self-reinforced poly-L-lactic acid polymer tack implants. The patients underwent radiographic and clinical assessments preoperatively and at 7 years. Blood levels of C-reactive protein were analyzed preoperatively and postoperatively.

RESULTS

The radiographic visibility of the drill holes was significantly (P = .0001) greater in the poly-L-lactic acid polymer group than in the polygluconate-B polymer group. The failure rate in terms of stability was 5 of 36 (14%) after 7 years and, as previously reported by Magnusson et al, 2 of 40 (5%) after 2 years. Analyses preoperatively and postoperatively of C-reactive protein revealed no significant difference between the groups. No significant differences were found between the groups in terms of strength in abduction, range of motion, and Rowe or Constant scores.

CONCLUSION

Seven years after Bankart repair using either implant, the overall clinical results were satisfactory. The visibility of the drill holes was significantly greater after using poly-L-lactic acid polymer implants.

Bearing area: a new indication for suture anchor pullout strength?

Studies performed to quantify the pullout strength of suture anchors have not adequately defined the basic device parameters that control monotonic pullout. The bearing area of a suture anchor can be used to understand and predict anchor pullout strength in a soft-bone model. First, conical-shaped test samples were varied in size and shape and tested for pullout in 5, 8, and 10 pcf sawbone models. Next, bearing area and pullout strength relationships developed from the test samples were validated against nine commercially available suture anchors, including the Mitek QuickAnchor and SpiraLok, Opus Magnum(2), ArthroCare ParaSorb, and Arthrex BioCorkscrew. The samples showed a direct correlation between bearing area and pullout strength. Increased insertion depth was a secondary condition that also increased pullout strength. The pullout strength for the suture anchors followed the predicted trends of conical devices based on their individual bearing areas. For the 5 and 8 pcf models, only two and three devices, respectively, fell outside the predicted pullout strength range by more than a standard deviation. The use of a synthetic sawbone model was validated against the pullout strength of an Arthrex Corkscrew in five fresh-frozen cadaver humeral heads. The bearing area of a suture anchor can be used to predict the pullout strength independent of design in a soft-bone model. This work helps provide a foundation to understand the principles that affect the pullout strength of suture anchors.

Suture anchor fixation strength in osteopenic versus non-osteopenic bone for rotator cuff repair

INTRODUCTION

Rotator cuff tears are increasing with age. Does osteopenic bone have an influence on the pullout strength of suture anchors?

MATERIALS AND METHODS

SPIRALOK 5.0 mm (DePuy Mitek), Super Revo 5 mm and UltraSorb (both ConMed Linvatec) suture anchors were tested in six osteopenic and six healthy human cadaveric humeri. Incremental cyclic loading was performed. The ultimate failure load, anchor displacement, and the mode of failure were recorded.

RESULTS

In the non-osteopenic bone group, the absorbable SPIRALOK 5.0 mm achieved a significantly better pullout strength (274 N +/- 29 N, mean +/- SD) than the titanium anchor Super Revo 5 mm (188 N +/- 34 N, mean +/- SD), and the tilting anchor UltraSorb (192 N +/- 34 N, mean +/- SD). In the osteopenic bone group no significant difference in the pullout strength was found. The failure mechanisms, such as anchor pullout, rupture at eyelet, suture breakage and breakage of eyelet, varied between the anchors.

CONCLUSION

The present study demonstrates that, in osteopenic bone, absorbable suture anchors do not have lower pullout strengths than metal anchors. In normal bone, the bioabsorbable anchor in this study even outperformed the non-absorbable anchor.

Pullout strength of suture anchors in comparison with transosseous sutures for rotator cuff repair

Suture anchors are increasingly gaining importance in rotator cuff surgery. This means they will be gradually replacing transosseous sutures. The purpose of this study was to compare the stability of transosseous sutures with different suture anchors with regard to their pullout strength depending on bone density. By means of bone densitometry (CT scans), two groups of human humeral head specimens were determined: a healthy and a osteopenic bone group. Following anchor systems were being tested: SPIRALOK 5.0 mm (resorbable, DePuy Mitek), Super Revo 5 mm (titanium, Linvatec), UltraSorb (resorbable, Linvatec) and the double U-sutures with Orthocord USP 2 (partly resorbable, DePuy Mitek) and Ethibond Excel 2 (non-resorbable, Ethicon). The suture anchors/double U-sutures were inserted in the greater tuberosity 12 times. An electromechanical testing machine was used for cyclic loading with power increasing in stages. We recorded the ultimate failure loads, the system displacements and the modes of failure. The suture anchors tended to bring about higher ultimate failure loads than the transosseous double U-sutures. This difference was significant in the comparison of the Ethibond suture and the SPIRALOK 5.0 mm-both in healthy and osteopenic bone. Both the suture materials and the SPIRALOK 5.0 mm showed a significant difference in pullout strength on either healthy or osteopenic bone; the titanium anchor SuperRevo 5 mm and the tilting anchor UltraSorb did not show any significant difference in healthy or osteopenic bone. There was no significant difference concerning system displacement (healthy and osteopenic bone) between the five anchor systems tested. The pullout strength of transosseous sutures is neither on healthy nor on osteopenic bone higher than that of suture anchors. Therefore, even osteopenic bone does not constitute a valid reason for the surgeon to perform open surgery by means of transosseous sutures. The choice of sutures in osteopenic bone is of little consequence anyway since it is mostly the bone itself which is the limiting factor.

Biomechanical testing of a new knotless suture anchor compared with established anchors for rotator cuff repair

Various suture anchors are available for rotator cuff repair. For arthroscopic application, a knotless anchor was developed to simplify the intra-operative handling. We compared the new knotless anchor (BIOKNOTLESStrade mark RC; DePuy Mitek, Raynham, MA) with established absorbable and titanium suture anchors (UltraSorbtrade mark and Super Revo 5mmtrade mark; ConMed Linvatec, Utica, NY). Each anchor was tested on 6 human cadaveric shoulders. The anchors were inserted into the greater tuberosity. An incremental cyclic loading was performed. Ultimate failure loads, anchor displacement, and mode of failure were recorded. The anchor displacement of the BIOKNOTLESStrade mark RC (15.3 +/- 5.3 mm) after the first cycle with 75 N was significantly higher than with the two other anchors (Super Revo 2.1 +/- 1.6 mm, UltraSorb: 2.7 +/- 1.1 mm). There was no significant difference in the ultimate failure loads of the 3 anchors. Although the Bioknotlesstrade mark RC indicated comparable maximal pullout strength, it bares the risk of losing contact between the tendon-bone-interface due to a significantly higher system displacement. Therefore, gap formation between the bone and the soft tissue fixation jeopardizes the repair. Bioknotlesstrade mark RC should be used in the lateral row only when a double row technique for rotator cuff repair is performed, and is not appropriate for rotator cuff repair if used on its own.

A biomechanical analysis of capsular plication versus anchor repair of the shoulder: can the labrum be used as a suture anchor?

PURPOSE

To determine the biomechanical strength properties of suture capsulolabral plication to an intact labrum versus glenoid bone anchor fixation.

METHODS

Fourteen paired fresh frozen shoulders with intact glenoid labrum and mean age of 43.3 +/- 11.1 were randomized to capsular plication in the anteroinferior and posteroinferior quadrants using either two suture-anchor fixation versus suture fixation to an intact labrum. The construct was then preconditioned at 10 N for 10 cycles (1 Hz), and then loaded to failure at 3 mm per minute.

RESULTS

There was no statistical difference in ultimate load to failure between the suture anchor (304.3 +/- 92.8 N) and the intact labrum (285.6 +/- 66.7 N) groups. The suture anchor group demonstrated significantly less mean displacement (2.15 +/- 1.1 mm) than suture plication (3.43 +/- 1.38 mm; P = .007) at failure. There were no statistical differences of labrum strength and stiffness between the anteroinferior and posteroinferior quadrants.

CONCLUSIONS

An intact labrum provides similar fixation strength to a glenoid anchor; however, the labrum displacement was higher with plication alone. There were no strength differences between the anteroinferior and posteroinferior labrum. However, displacement of up to 1.5 mm may be expected without the use of glenoid anchors.

CLINICAL RELEVANCE

The intact posteroinferior or anteroinferior labrum provides similar fixation strength to a glenoid anchor; however, the labrum displacement is higher versus plication alone.

The use of anchors in shoulder surgery: a shift from metallic to bioabsorbable anchors

With major advances in arthroscopy, suture anchors became the primary devices used to assist in fixing soft tissues to bone. Metallic anchors were first produced and used in soft tissue fixation around the shoulder. However, their use resulted in some reported complications, including articular surface damage from migrating implants and distortion and artifact production in postoperative magnetic resonance imaging. Bioabsorbable anchors were developed to avoid these problems. Their newer versions were proven to have pulling-out strength equal to that of metallic anchors, with a reported lower complication rate. This had led to a major shift away from metallic anchors toward bioabsorbable anchors.

The properties of damaged and undamaged suture used in metal and bioabsorbable anchors: an in vitro study

PURPOSE

The purpose of this study was to determine the mechanical properties of undamaged and damaged sutures in metal and bioabsorbable suture anchors.

METHODS

Undamaged and damaged FiberWire (Arthrex, Naples, FL), Tevdek (Deknatel, Mansfield, MA), and PDS (Ethicon, Somerville, NJ) sutures were tested by a single pull to failure while being pulled parallel to the axis of either a metal or bioabsorbable suture anchor. Sutures were damaged by use of a razor blade incorporated into a custom-designed jig. The friction of the sutures through the anchor eyelets was also tested.

RESULTS

For both anchor types, FiberWire was the strongest suture studied. Undamaged PDS had a significantly greater load to failure than Tevdek. Although all sutures lost significant strength when damaged, PDS lost the most, with damaged PDS becoming significantly weaker than damaged Tevdek. Damaged FiberWire was significantly stronger in metal anchors compared with bioabsorbable anchors, with failure of the bioabsorbable suture eyelet preventing testing of undamaged FiberWire. Neither undamaged nor damaged PDS or Tevdek had a significant difference in strength between metal and bioabsorbable anchors. However, in metal anchors the mechanical properties of undamaged Tevdek were inferior to those of the other undamaged sutures tested. For undamaged or damaged sutures through either anchor type, PDS suture had the highest coefficient of friction, significantly higher than FiberWire and Tevdek. All sutures, undamaged or damaged, had significantly less friction in bioabsorbable anchors compared with metal anchors.

CONCLUSIONS

The FiberWire-anchor construct is significantly weaker when bioabsorbable anchors are used instead of metal anchors. For Tevdek and PDS sutures, the anchor type does not affect the strength of the construct, as the suture is the limiting factor. When used with suture anchors, PDS has the most friction of the sutures tested, potentially leading to suture damage, which disproportionately weakens PDS compared with the other sutures tested. For both undamaged and damaged sutures, bioabsorbable anchors lead to less friction than do metal anchors, which may lessen suture damage in vivo.

CLINICAL RELEVANCE

The mechanical properties of damaged suture are important to all surgeons who use suture arthroscopically.

Strength of damaged suture: an in vitro study

PURPOSE

To determine the mechanical properties of damaged suture.

METHODS

Undamaged and damaged sutures were tested by a single pull to failure. Sutures were damaged with a razor blade incorporated into a custom-designed jig. Sutures were tested to failure by straight pull and by pulling at 180 degrees through a suture anchor eyelet. The friction of sutures through anchors was also tested.

RESULTS

For the straight line pull test, undamaged FiberWire (Arthrex, Naples, FL) had the highest load to failure (LTF) and ultimate tensile strength (UTS) of all sutures tested. Undamaged Orthocord (Mitek, Somerville, NJ) ranked second in both properties. Uncut polydioxanone (PDS) suture (Ethicon, Somerville, NJ) had a higher LTF and a comparable UTS with respect to Tevdek (Deknatel, Mansfield, MA) and Ethibond (Ethicon). For cut sutures, FiberWire and Orthocord had a significantly higher LTF and UTS than the other sutures tested. Suture stiffness was not significantly affected when the suture was cut. For the suture anchor test, FiberWire and Orthocord had the highest LTF, whether undamaged or damaged. When cut, PDS had the greatest loss of LTF and UTS during both tests.

CONCLUSIONS

The newer polyethylene core sutures (FiberWire and Orthocord) have superior mechanical properties compared with other sutures. Their superior properties are maintained even when cut. Although uncut PDS had equivalent or superior strength compared with Ethibond and Tevdek, once cut, PDS suture was weakened significantly more compared with all other sutures tested.

CLINICAL RELEVANCE

The mechanical properties of damaged suture are important to all surgeons who use suture arthroscopically.

New Sutures and Suture Anchors in Sports Medicine

Arthroscopic surgery requires appropriate surgical implants for effective fixation of tendons and ligaments to bone. Biodegradable suture anchors are being used with increasing frequency for various procedures in sports medicine. As companions to these biodegradable suture anchors, new sutures have been developed which possess greater strength and different material properties from the conventional braided polyester suture. Biodegradable polymers currently found in sutures and suture anchors include poly-L-lactic acid, poly-D, L lactic acid, polydioxanone, polyglycolic acid and their copolymers. Suture anchors are now available preloaded with a choice of conventional braided polyester sutures or some version of ultrahigh molecular weight polyethylene ("super") sutures. Most new suture anchors come with 2 sutures. The manner in which these sutures are attached to the anchor varies and may consist of 2 separate eyelets or 2 slots either parallel to one another or at different angles to one another. Some anchors have a very large single eyelet that allows for 2 or more sutures.

Biodegradable Materials in Arthroscopy

The use of biodegradable materials as implants has revolutionized the way medicine is practiced today. This review provides a general description of salient biodegradable polymeric materials currently used in arthroscopy. These materials include polyglycolic acid, self-reinforced polyglycolic acid, poly-L-lactic acid, self-reinforced polylactic-L-acid, poly-D-L-lactic acid, copolymer of poly-D-L-lactic acid polyglycolic acid, and polyglyconate. The mechanical strength, degradation properties, and widespread use of these materials, especially in the knee and shoulder, are discussed individually. Also discussed are the relatively few complications that are related to these materials' arthroscopic use. Future directions in biodegradable materials, including smart polymers, are also considered. In the future, novel techniques to identify the ideal polymer for a particular application will need to be developed to minimize the risk for implant complications.