The Impact of Nitinol Staples on the Compressive Forces, Contact Area, and Mechanical Properties in Comparison to a Claw Plate and Crossed Screws for the First Tarsometatarsal Arthrodesis

Clinical and Radiographic Outcomes of Nitinol Compression Staples for Midfoot and Chopart Arthrodesis

Nitinol staple use in orthopedic surgery has increased in recent years. Biomechanical studies provide useful data for use in foot/ankle; however, clinical data is limited. This study's purpose is to determine the efficacy of nitinol staples to achieve stable, bony arthrodesis in midfoot and Chopart joints, and examine their clinical outcomes and pain scores. A retrospective chart review was performed on 127 midfoot/Chopart joint arthrodeses (71 patients) using nitinol staples in isolation. The primary outcome variable was radiographic evidence of healing. Radiographs were blinded, randomized, and independently reviewed by 3 board certified foot and ankle surgeons. Complete/partial union was seen in 89% of all joints (113/127), increasing to 93% when including only midfoot joints (98/106). Chopart joints had significantly lower healing rates (15/21; 71%) compared to all midfoot joints (p = .01) and isolated tarsometatarsal joints (86/91; 95%) (p = .006). Neuropathy and smoking did not affect arthrodesis, but diabetes did (p = .004). Joints requiring bone grafting had worse rates of arthrodesis (38/49; 76%) (p = .002). For all joints, postoperative visual analog scale scores were significantly lower than preoperative (p < .001). Preoperative midfoot and Chopart pain scores were similar (p = .30). Midfoot joints had significantly lower pain scores postoperatively than preoperatively (p < .001). No such significance existed in Chopart joints (p = .07). Isolated nitinol staples are a viable option for midfoot arthrodesis, especially tarsometatarsal joints, and offer significant pain improvement. Chopart joints may require more rigid fixation than nitinol staples, given the lower healing rate.

Nitinol Staple Use in Primary Arthrodesis of Lisfranc Fracture-Dislocations

BACKGROUND

Primary arthrodesis of Lisfranc fracture-dislocations is a reliable treatment option, yet concerns remain about nonunion. Nitinol staple use has recently proliferated in midfoot arthrodesis. The purpose of this study is to examine the union rate of primary arthrodesis of acute Lisfranc fracture-dislocations treated with nitinol staples compared with traditional plate-and-screw fixation. The secondary objective is to assess the difference in operative times and reoperation rates.

METHODS

Midfoot fracture-dislocations treated with primary arthrodesis by 7 foot and ankle orthopaedic surgeons were reviewed. Of 160 eligible patients, 121 patients (305 joints) met the required 4-month minimum radiographic follow-up. Radiographic outcomes were analyzed at the individual joint level. Each joint was classified as either staples alone (45 patients, 154 joints), staples plus plates and screws (hybrid) (45 patients, 40 joints), or plates and screws alone (31 patients, 111 joints). The primary outcome was arthrodesis union at each joint fused.

RESULTS

Nonunion was more common (9.0%, 10/111) among joints fixed with plate and screws than with hybrid (2.5%, 1/40) or staples only (1.3%, 2/154) (P = .0085). Multivariable regression demonstrated that autograft use was independent associated with union (P = .0035) and plate-and-screw only fixation was an independent risk factor for nonunion (P = .0407). Median operating room and tourniquet times were shorter for hybrid (92 and 83 minutes) and staple only (67 and 63 minutes) constructs compared to plate-and-screw only fixation (105 and 95 minutes) (P ≤ .0001 and .0003). There was no difference in reoperation rates among patients with different fixation types.

CONCLUSION

We found that use of nitinol compression staple and bone autograft in primary arthrodesis of Lisfranc and midfoot fracture-dislocations was associated with both improved union rates and shorter tourniquet and operative times compared to traditional plate-and-screw fixation techniques.

LEVEL OF EVIDENCE

Level III, therapeutic.

Comparative Finite Element (FE) Analysis of the Mechanical Behavior in an Innovative Nitinol Staple for Arthrodesis in Distal Interphalangeal Joint

Objective

Osteoarthritis (OA) is a source of significant limitations for individuals, health systems, and economies. The most common complications of OA are often associated with risk factors related to chronic diseases, cardiovascular disease, and depression. In this article, a new kind of staple is proposed, designed to provide better strength when subjected to bending and torque loads.

Methods

This innovative staple has been numerically tested and compared to a MEMOFIX staple by Smith + Nephew, in order to evaluate its mechanical behavior. The radius and ulna were fixed at the lower extremity, while the distal interphalangeal of the little finger was loaded with a bending load of 50 N and a torque moment of 500 N/mm2.

Results

For the bending load, a maximum value of stress of 120 MPa in the traditional staple, while 90 MPa are registered in the innovative one. The torsional load produces a value of 107 MPa in the traditional staple and 85 MPa in the innovative one.

Conclusion

Computational simulations showed the biomechanical performance of a new type of nitinol staple compared with a traditional one. This staple is designed with an elliptical shape in order to support different kinds of loads. Our results confirm an optimal mechanical behavior, compared to the traditional staple, in terms of the evaluated Equivalent Von Mises stress; also the contact force exerted by the innovative staple was increased.

Cannulated screws versus nitinol staple for tarsometatarsal fusion: A cadaveric biomechanical comparison model

BACKGROUND

The objective of this study was to evaluate the biomechanical stability of a medially placed nitinol staple compared to two crossed-screws in the first TMT-1 joint fusion in a cadaveric cyclic loading model.

METHODS

Seven matched pairs (N = 7) of lower limb cadaveric specimens were utilized. TMT-1 joints from each donor were fixed with a medially placed nitinol staple or dorsally placed two 3.5 mm partially threaded cannulated crossed-screws. Specimens were tested in a 4-point bending setting with increasing cyclic forces.

RESULTS

The mean plantar gapping was not significantly different between the two groups at any loading stage below 200 N. Specimens fixed with a nitinol staple failed at a mean load of 305 ± 57 N. Conversely, those fixed with crossed-screws failed at 373 ± 86 N. (P = .09).

CONCLUSION

There was no statistical difference between a medially placed nitinol staple and dorsally placed crossed-screws in failure loads and plantar gapping under cyclic loads at the TMT-1 joint, however, the staple fixation was much more variable.

LEVEL OF EVIDENCE

Level V, basic science study, biomechanics.

Comparison of 4 Different Fixation Strategies for Midfoot Arthrodesis: A Retrospective Comparative Study

BACKGROUND

Midfoot arthrodesis is a common procedure performed both for arthritis and correction of deformity. The optimal fixation for midfoot arthrodesis has not been established, though numerous studies have been investigating the fixation techniques of midfoot arthrodesis. The purpose of this study was to compare the union rate of midfoot arthrodesis using 4 different fixation strategies and investigate risk factors of nonunion following midfoot arthrodesis.

METHODS

A retrospective chart review was performed for patients who underwent midfoot joint arthrodesis between January 2014 and May 2019. The rates of nonunion and postoperative complication were compared among 4 different fixation constructs: staple fixation, compression plate fixation, compression plate with lag screw fixation, and compression screw fixation. Predictors of nonunion following midfoot arthrodesis were investigated through a multivariable logistic regression analysis. A total of 95 patients (99 feet), including 240 midfoot joints were included in this study. The mean follow-up period was 78.4 weeks.

RESULTS

Overall, bony union was achieved in 86 out of 99 (86.9%) patients, which included 218 out of 240 (90.8%) midfoot joints. A significant difference in the nonunion rate according to the type of fixation construct was found (P = .011); the compression screw alone fixation construct was noted to have a significantly higher nonunion rate than other fixation constructs. Diabetes mellitus (odds ratio [OR] = 0.179 [95% CI: 0.059, 0.542]), the type of fixation construct (compression screw alone; OR =1.789 [95% CI: 1.071, 2.978]), lack of adjuvant bone graft (OR = 2.803 [95% CI: 1.081, 7.268], and postoperative nonanatomical alignment (OR = 3.937 [95% CI: 1.278, 12.126]) were identified as independent predictors of nonunion following midfoot arthrodesis.

CONCLUSION

The rate of nonunion following midfoot arthrodesis among 4 different commonly used fixation constructs was compared in this study. Risk factors of nonunion were investigated revealing that diabetes mellitus, compression screw fixation alone, lack of adjuvant bone graft, and postoperative nonanatomical alignment are independent predictors of nonunion following midfoot arthrodesis.

LEVELS OF EVIDENCE

Level III: Comparative cohort study.

Effect of a compression staple on correction of varus deformity during arthroscopic ankle arthrodesis

BACKGROUND

Arthroscopic ankle arthrodesis (AAA) has become popular because of its higher rate of bone union, lower invasiveness, and shorter hospital stays compared to those of open arthrodesis. However, postoperative malalignment is often observed for severe varus deformity, which can cause nonunion, pain, and adjacent joint arthrosis. A compression staple can provide a persistent, strong compressive force on the bone surface. This study aimed to clarify the difference in alignment correction in AAA by comparing a compression staple and screws fixation with screws-only fixation pre- and postoperatively.

METHODS

Seventy ankles in 67 patients undergoing AAA were retrospectively reviewed. AAA with three screws through the distal tibia was performed in 53 ankles, and 17 ankles underwent AAA with a compression staple and two screws. After the preparation of the joint surface arthroscopically, patients in the S group had three canulated cancellous screws inserted through the medial tibia. Patients in the CS group had a compression staple placed at the lateral aspect of the tibiotalar joint and two screws inserted through the medial side. Clinical scores and pre-and postoperative alignment on plain radiographs were compared between the two procedures.

RESULTS

There were no significant differences in the pre-and postoperative Japanese Society for Surgery of the Foot scale. One ankle in the S group exhibited nonunion. There were no significant differences in talar tilt and tibiotalar angles between the groups. The tibial plafond angle in the CS group was significantly lower than that in the S group (p < 0.05). Postoperatively, talar tilt and tibiotalar angles on the coronal image, and the lateral tibiotalar angle in the CS group were significantly lower than those in the S group (p < 0.05).

CONCLUSION

AAA with a compression staple and two-screw fixations could obtain more optimal alignments than AAA with screw-only fixation, even in cases with severe varus deformity.

First tarsometatarsal arthrodesis for severe hallux valgus using the tension band principle - Technical tip and case series

BACKGROUND

Hallux valgus (HV) is a common foot pathology. Severe HV in the presence of Tarsometatarsal joint (TMTJ) instability is often managed with arthrodesis of the 1st TMTJ. There are concerns regarding non-union and malunion (particularly the early loss of inter-metatarsal angle correction before complete arthrodesis). We report our medium-term results of a small series of patients that underwent an evolved surgical technique utilising orthogonal staples and a transverse suture button fixation to address biomechanical concerns with traditional Lapidus arthrodesis.

METHODS

A retrospective study of a consecutive series of patients who underwent this surgical technique between February 2017 and May 2022. Clinical outcomes were validated through Patient-reported outcomes measures (PROMS); EuroQol-5 Dimension (EQ-5D) and Manchester-Oxford Foot Questionnaires (MOXFQ). Radiographic parameters (hallux valgus (HVA), intermetatarsal (IMA), distal metatarsal articular angle (DMAA)) were assessed. Union of the arthrodesis and complications were recorded.

RESULTS

During the study period, 9 feet underwent the procedure. Radiographic data was available for all nine and PROMS data for seven (77.8%). Significant improvement occurred in all radiographic deformity parameters at mean 6-month follow-up. Mean ± standard deviation correction calculated preoperatively as HVA 40.2°, IMA 19.3° and DMAA 15.8°, corrected to HVA 15.4°, IMA 5.8° and DMAA 5.9° postoperatively. (HVA; P < 0.001, IMA; P < 0.001, DMAA; P < 0.001) Clinical PROMs at mean follow-up of 2 years were MOXFQ 34.4 ± 25.2, EQ-5D-5 L 0.819 ± 0.150 and VAS pain 13.6 ± 13.6. There were no cases of non-union, Tibialis anterior tendon irritation or hallux varus. Complications included first MTPJ stiffness in one case and CRPS and dorsiflexion malunion of the first ray in another patient.

CONCLUSION

This preliminary study of the procedure used in this series confirm this is a safe surgical technique to address severe HV with a low rate of non-union and significant radiographic improvements. A larger patient dataset is needed to evaluate this procedure robustly.

Determining the Mechanical Properties of Super-Elastic Nitinol Bone Staples Through an Integrated Experimental and Computational Calibration Approach

Super-elastic bone staples have emerged as a safe and effective alternative for internal fixation. Nevertheless, several biomechanical aspects of super-elastic staples are still unclear and require further exploration. Within this context, this study presents a combined experimental and computational approach to investigate the mechanical characteristics of super-elastic staples. Two commercially available staples with distinct geometry, characterized by two and four legs, respectively, were examined. Experimental four-point bending tests were conducted to evaluate staple performance in terms of generated forces. Subsequently, a finite element-based calibration procedure was developed to capture the unique super-elastic behavior of the staple materials. Finally, a virtual bench testing framework was implemented to separate the effect of geometry from that of the material characteristics on the mechanical properties of the devices, including generated force, strain distribution, and fatigue behavior. The experimental tests indicated differences in the force vs. displacement curves between staples. The material calibration procedure revealed marked differences in the super-elastic properties of the materials employed in staple 1 and staple 2. The results obtained from the virtual bench testing framework have showed that both geometric features and material characteristics had a substantial impact on the mechanical properties of the device, especially on the generated force, whereas their effect on strain distribution and fatigue behavior was comparatively less pronounced. To conclude, this study advances the biomechanical understanding of Nitinol super-elastic staples by separately investigating the impact of geometry and material characteristics on the mechanical properties of two commercially available devices.

A Novel Plating System for First Metatarsophalangeal Joint Arthrodesis: A Retrospective Comparison of Hybrid and Traditional Locking Plate Constructs

BACKGROUND

Dorsal plate fixation is commonly used for first metatarsophalangeal joint (1st MTPJ) arthrodesis and plate design continues to evolve. A new staple compression plate (SCP) design attempts to utilize the continuous compression of a nitinol staple across the fusion site while simultaneously providing the stability of a dorsal locked plate. Herein, we compare the radiographic, clinical, and patient-reported outcomes of 1st MTPJ joint arthrodesis using 2 dorsal locking plate constructs including a novel SCP construct.

METHODS

Forty-four patients who underwent 1st MTPJ arthrodesis between 2016 and 2020 were retrospectively evaluated. There were 2 group cohorts. Group 1 cohort included 23 patients who received a CrossRoads Extremity SCP, and Group 2 cohort included 21 patients who received a Stryker dorsal locking precontoured titanium plate (LPP). All patients were evaluated with radiographs, Patient-Reported Outcomes Measures Information System (PROMIS) outcome scores, and Foot Function Index (FFI).

RESULTS

The complication and union rates did not vary between groups with a fusion rate of 95.7% in the SCP group and 90.5 % in the LPP group. Similarly, we found no significant differences in PROMIS or FFI scores between the SCP and LPP plates.

CONCLUSION

Use of either dorsal locking plate construct for 1st MTPJ arthrodesis was associated with high union rates and comparable functional outcomes. As locked plate technology continues to evolve for 1st MTPJ arthrodesis, it is important that clinical outcomes are reported.

LEVELS OF EVIDENCE

Level IV.

The history of orthopaedic use of nitinol compression staples

INTRODUCTION

The use of nitinol continuous compression staples has shown clinical utility in the management of various orthopaedic injuries. While literature is most robust in the realm of foot/ankle and spine surgery, the use of nitinol staples has been documented in fixation of wrist, olecranon, patella, and pelvis fractures.

METHODOLOGY

A narrative review was conducted by searching three online databases - PubMed, Web of Science, and Cochrane using the terms "Nitinol" and "Staple" published between 2003 and 2023. A total of 42 articles met inclusion/exclusion criteria and were included in this review.

REVIEW

Literature outside of foot/ankle and spine surgery is largely limited to biomechanical studies, case reports, and finite element analyses. The literature is summarized within this review by anatomic location including foot/ankle, lower extremity, hand, upper extremity, spine, and pelvis.

CONCLUSION

Existing literature demonstrates a diverse array of applications for nitinol continuous compression staples in both axial and appendicular orthopaedic care. Advantages of these implants include ease of application, ability to capture small bony fragments, continuous compression across a fracture or arthrodesis, and full coaptation which maximizes the surface area for healing and/or fusion.

Canine ex vivo tarsal arthrodesis: fixation by using a new bone tissue glue

Introduction

Arthrodesis, performed as a salvage surgical procedure to treat intractable joint conditions in dogs and cats, is associated with a high incidence of complications intra and postoperative, proving the need for improved and new techniques in arthrodesis surgery. Adding a new resorbable bone glue to the arthrodesis could potentially add fixation strength and lower complications. The objectives of this experimental ex vivo biomechanical study were therefore to develop a biomechanical test model of partial tarsal arthrodesis and to determine whether the new resorbable bone glue (phosphoserine modified cement) produced measurable fixation strength in canine calcaneoquartal arthrodesis, without orthopedic implants.

Methods

Four biomechanical test models with a total of 35 canine tarsal joints were used. Soft tissues were dissected to 4 different test models with variable contributions from soft tissues. The calcaneoquartal joint was prepared as in vivo arthrodesis and the glue was applied to joint surfaces as a liquid/putty (0.4 cc). After curing for 24 h, a shear force was applied to the joint (1 mm per minute) and the failure strength was recorded.

Results

Calcaneoquartal joints, where all soft tissues had been completely resected and fixated with glue (1-1.5 cm2 joint surface), withstood 2-5 mm of displacement and an average of 100 ± 58 N/cm2 of shear force (Model 1). Similar adhesive fixation strengths were obtained in Model 2 and 3 with increasing contributions from soft tissues (80 ± 44 and 63 ± 23 N/cm2, p = 0.39, ANOVA).

Conclusion

The developed biomechanical model was sensitive enough to measure differences in fixation strengths between different glue formulations. The average fixation strength (60-100 N/cm2) should be strong enough to support short-term load bearing in medium sized canines (20 kg). The developed cadaver biomechanical test model is of potential use for other arthrodesis studies. The new resorbable glue can potentially contribute to stability at arthrodesis surgery, acting as a complement to today's standard fixation, metal implants.

Talonavicular Arthrodesis Using a Screw and Compression Staple in a Patient With Bipartite Navicular Bone: A Case Report

The bipartite navicular bone is a relatively rare pathological condition in which the navicular bone is segmented. As a high nonunion rate in talonavicular arthrodesis of the foot has been reported, an effective fixation method is required to achieve bone union. A compression staple can provide a persistent strong compressive force on the bone surface, which is advantageous for arthrodesis, especially for the joints with a high incidence of nonunion. A 13-year-old boy presenting with left foot pain was diagnosed with bipartite navicular. Imaging of the left foot showed that the navicular bone was divided into two parts and flatfoot deformity. After the failure of conservative treatment, talonavicular arthrodesis was performed. The lateral fragment was removed, and the talar and medial fragments were fixed using a cannulated cancellous screw (CCS) (Ace Medical, El Segundo, CA, USA) and compression staple (DynaNite, 15 mm × 12 mm, Arthrex, Inc., Naples, USA) to correct the flatfoot. Bone union was achieved, and flatfoot improved. Thirteen months postoperatively, his symptoms disappeared, and all categories of the Self-Administered Foot Evaluation Questionnaire scored 100 points. Although the bipartite navicular bone has no established treatment due to its rareness, talonavicular arthrodesis using a combination of CCS and compression staple yields good short-term clinical outcomes including good alignment.

First Tarsometatarsal Joint Fusion in Foot-A Biomechanical Human Anatomical Specimen Analysis with Use of Low-Profile Nitinol Staples Acting as Continuous Compression Implants

Background and Objectives: The aim of this study was to investigate under dynamic loading the potential biomechanical benefit of simulated first tarsometatarsal (TMT-1) fusion with low-profile superelastic nitinol staples used as continuous compression implants (CCIs) in two different configurations in comparison to crossed screws and locked plating in a human anatomical model. Materials and Methods: Thirty-two paired human anatomical lower legs were randomized to four groups for TMT-1 treatment via: (1) crossed-screws fixation with two 4.0 mm fully threaded lag screws; (2) plate-and-screw fixation with a 4.0 mm standard fully threaded cortex screw, inserted axially in lag fashion, and a 6-hole TMT-1 Variable-Angle (VA) Fusion Plate 2.4/2.7; (3) CCI fixation with two two-leg staples placed orthogonally to each other; (4) CCI fixation with one two-leg staple and one four-leg staple placed orthogonally to each other. Each specimen was biomechanically tested simulating forefoot weightbearing on the toes and metatarsals. The testing was performed at 35-37 °C under progressively increasing cyclic axial loading until construct failure, accompanied by motion tracking capturing movements in the joints. Results: Combined adduction and dorsiflexion movement of the TMT-1 joint in unloaded foot condition was associated with no significant differences among all pairs of groups (p ≥ 0.128). In contrast, the amplitude of this movement between unloaded and loaded foot conditions within each cycle was significantly bigger for the two CCI fixation techniques compared to both crossed-screws and plate-and-screw techniques (p ≤ 0.041). No significant differences were detected between the two CCI fixation techniques, as well as between the crossed-screws and plate-and-screw techniques (p ≥ 0.493) for this parameter of interest. Furthermore, displacements at the dorsal and plantar aspects of the TMT-1 joint in unloaded foot condition, together with their amplitudes, did not differ significantly among all pairs of groups (p ≥ 0.224). Conclusions: The low-profile superelastic nitinol staples demonstrate comparable biomechanical performance to established crossed-screws and plate-and-screw techniques applied for fusion of the first tarsometatarsal joint.

Naviculocuneiform Arthrodesis for Treatment of Adult-Acquired Flatfoot Deformity

The adult-acquired flatfoot is a complex multiplanar deformity that requires the foot and ankle surgeon to balance soft tissue, correct hindfoot valgus, and address instability of the medial column. The naviculocuneiform joint is historically underappreciated in regard to its involvement in medial column instability relative to the talonavicular and tarsometatarsal joints. Proper clinical and radiographic evaluation of the medial column, specifically evaluating for deformity at each medial column joint, will allow the surgeon to ensure correction of deformity and decrease the recurrence of instability or failure of the reconstruction.

Computational modeling of nickel-titanium orthopedic staples in the treatment of a fractured scaphoid: Effects of staple bridge configuration

Internal fixation devices made of nickel-titanium (NiTi) staples have the advantage of producing compressive stress at the fracture site due to their unique shape memory effect and superelasticity. In the present study, a comparison was made between two commercial NiTi staples of the same size but with different bridge configurations, used for scaphoid fracture fixation. The staple and scaphoid anatomical configurations were modeled using SolidWorks, while ABAQUS software was used to analyze the stress and displacement caused by staples and distributed in the scaphoid waist. In the staple with a straight bridge, the regions under the tips of the staple legs underwent the largest stress, whereas there was negligible stress in the regions closer to the staple bridge. In the staple with an S-shaped bridge, the stress concentration was highly localized in the region close to the staple bridge, with a maximum stress that was over eight times higher than in the staple with a straight bridge. Considering the amount and distribution of stress in both staples, neither of the staples was able to create the ideal healing condition on the fracture surface.

Biomechanical comparison of nitinol compression staples versus fully threaded lag screws for talonavicular arthrodesis

Background

Talonavicular arthrodesis (TNA) is indicated for treatment of disorders that require immobilization of the hindfoot. Lag screw fixation is considered the reference standard technique for TNA. Despite consistently favorable clinical results using lag screw fixation, it is still associated with higher than desired complication and failure rates. Nitinol compression staples have been used for TNA based on potential advantages over lag screw fixation. However, functional biomechanical data comparing lag screw and nitinol compression staples for TNA are lacking. Therefore, the objective of this study was to compare nitinol compression staples to fully threaded lag screws for use in TNA with respect to their biomechanical properties during functional robotic testing.

Methods

TNA was performed on cadaveric feet (n = 12; 6 matched pairs) using either two nitinol compression staples (Arthrex, Naples, FL) or two fully threaded lag screws (Arthrex, Naples, FL) in random order, alternating between paired left and right feet. After instrumentation, specimens were mounting in a robotic testing system and loaded at 89 N/sec from 30 N to 445 N for 1 min. Then, continuous compressive load of 445 N was applied while cycling from 30° plantarflexion to 15° dorsiflexion for 10 cycles. Optical tracking markers attached to the talus and navicular bone tracked displacements. Translation data were recorded along the X, Y, Z planes. Rotation data were recorded for roll, pitch, and yaw. Significant (p < 0.05) differences between fixation methods were determined using paired t-Tests for each measured variable.

Results

There were no statistically significant differences between staples and screws for translation in X, Y, or Z planes. When comparing rotation (roll, pitch, and yaw), there were no statistically significant differences with the exception of increased roll rotation for staple fixation versus lag screw fixation during static compression testing (p = 0.009).

Conclusion

Based on comparison to the reference standard lag screw fixation for clinically relevant biomechanical properties measured during functional robotic testing of the hindfoot, nitinol compression staples are a viable option for talonavicular arthrodesis.

Lisfranc Arthrodesis in Posttraumatic Chronic Injuries

Chronic injuries at the tarsometatarsal joint represent a wide array of painful malunions ranging from isolated instability to complex three-dimensional deformities with rapid development of posttraumatic arthritis. Deformity correction and arthrodesis of the symptomatic joints leads to significant pain reduction and functional improvement provided that realignment of the anatomic axes is achieved. Arthrodesis should be limited to the first to third tarsometatarsal joints, whereas interposition arthroplasty is preferred for symptomatic arthritis of the fourth to fifth tarsometatarsal joints. For complex deformities and instability, the intercuneiform and naviculocuneiform joints may need to be included into corrective fusion.

Radiographic Evaluation of Isolated Continuous Compression Staples for Akin Osteotomy Fixation

Continuous compression implants (nitinol staples) are gaining popularity secondary to their lower profile, less demanding technique, and less surgical dissection. Biomechanical support exists; however, clinical data is limited in the foot/ankle. This study's purpose is to determine the efficacy of nitinol staples to achieve stable, bony healing in Akin osteotomies and examine their clinical outcomes, complications, re-operations, and pain scores. We performed a retrospective chart review on 90 patients (93 osteotomies) who underwent an Akin osteotomy using a nitinol staple over a 2-year period. Radiographs were randomized and independently reviewed by 3 blinded foot and ankle surgeons. Osteotomies were deemed healed if greater than 50% of the osteotomy contained bridging bone, partially healed as less than 50% bridging bone, and nonunion as no healing, broken hardware, or loss of reduction. Visual analog scale pain scores were analyzed. Radiographic union was seen in 98.9% of Akin osteotomies (92/93), with no loss of reduction or broken staples (0/95). Only 3.2% (3/93) of patients returned to the operating room unplanned: 1 infection (1.1%), 1 symptomatic hardware removal (1.1%), and 1 traumatic disruption of fixation (1.1%). Postoperative pain scores were significantly lower than preoperative. Staples are lower profile and technically less demanding compared to headed screws, plates, and tension band constructs. They offer continuous compression of the osteotomy and are rigid enough to maintain reduction. Based on the findings of this paper, the use of staples provides robust and stable fixation for Akin osteotomies and has low complication and high healing rates.

Biomechanical comparison of continuous compression implants versus tension band fixation for transverse olecranon fractures

Purpose

Tension band wiring (TBW) is considered the 'gold standard' for fixation of transverse olecranon fractures (OTA/AO 2U1B1d). However, this approach requires a large exposure, can be technically demanding and operator-dependent, and is associated with hardware prominence. Continuous compression implants (CCI) may address these limitations. To the authors' knowledge, a comparison between TBW and CCI has not been performed. Therefore, this study was designed to compare biomechanical properties of CCI to TBW for 2U1B1d olecranon fractures using human cadaver elbows.

Methods

A transverse olecranon fracture was simulated in eight matched pairs of cadaveric elbows. Matched pairs were used for comparison of TBW and CCI. Cyclic loading was performed at both 10 N and 500 N, with gap formation and load to failure recorded. Results: No significant difference in gap formation at 10 N (p > 0.3) or 500 N (p = 0.6), or load-to-failure (p=.00.41), was observed between the two groups.

Discussion

CCI fixation requires a smaller incision, is easy to perform, and involves low-profile implant that may reduce morbidity. Based on biomechanical properties that match the gold standard, continuous compression nitinol implants are an appropriate option for fixation of transverse olecranon fractures with potential advantages over tension band wiring.

Two Orthogonal Nitinol Staples and Combined Nitinol Staple-Screw Constructs for a First Metatarsophalangeal Joint Arthrodesis: A Biomechanical Cadaver Study

BACKGROUND

End-stage hallux metatarsophalangeal (MTP) joint arthritis is commonly treated with arthrodesis using stainless steel or titanium implants. These implants provide static compression that is maximal at the time of implant insertion. Alternatively, nitinol staples are capable of dynamic compression. They have most frequently been used for midfoot arthrodesis procedures. However, their biomechanical performance during hallux MTP arthrodesis has not been described.

METHODS

8 matched pairs of cadaveric feet (4 female, 4 male) were prepared for hallux MTP arthrodesis using cup and cone reamers. Cadaveric pairs were then instrumented with either (1) a transarticular lag screw and dorsal nitinol staple or (2) orthogonal nitinol staples placed dorsally and medially. Walking in a short leg cast for 6 weeks was simulated by applying 90-N forces at 3 Hz to the plantar proximal phalanx for up to 250 000 cycles. Failure was defined as catastrophic implant failure or plantar gapping beyond 7 mm.

RESULTS

15 of 16 specimens failed cyclic loading. All 8 specimens fixed with orthogonal staples failed at an average of 37 ± 81 cycles. 7 of 8 specimens fixed with a dorsal staple and crossed screw failed at 14 900 ± 39 000 cycles. Collectively, 5 specimens failed because of bone fracture (1 in orthogonal staples, 4 in staple-screw group) and 10 failed because of excessive gap formation (7 in orthogonal staples, 3 in staple-screw group). The number of cycles to failure was significantly lower (P = .0469) in the orthogonal staple constructs compared with the dorsal staple and crossed screw constructs.

CONCLUSION

The tested constructs permit significant motion at the first MTP fusion surface during simulated protected weightbearing. Although multiple in vivo factors should be considered when extrapolating results from this cadaveric study, this motion may result in clinical failure with early postoperative weightbearing protocols.

CLINICAL RELEVANCE

We report the first biomechanical evaluation of hallux MTP arthrodesis using modern nitinol staples in 2 separate constructs.

Effect of Bone Quality and Leg Depth on the Biomechanical Performance of a Nitinol Staple

The use of Nitinol compression staples has increased in foot and ankle procedures due to their ease of delivery and ability to offer sustained, dynamic compression. Prior biomechanical studies have predominantly examined mechanical performance in healthy bone models without investigating the effect of unicortical versus bicortical fixation. The purpose of this study was to examine the effect of bone quality and staple leg depth on the biomechanical performance of Nitinol staples in a bicortical bone model. Two-legged Nitinol staples were implanted in bicortical sawbone of 2 densities. Two different leg depths were tested to simulate unicortical versus bicortical fixation. Interfacial compressive forces, interfacial compression area, torsional strength, and shear strength were measured for each group. The effect of leg depth was minimal compared to the effect of sawbone density on the mechanical performance of Nitinol staples. Interfacial compressive force and interfacial compression areas were greater in the low density bone model, while torsional strength and shear strength were greater in the normal density bone model. Nitinol staple's mechanical performance is highly dependent upon bone quality and less dependent on whether staple legs terminate in cancellous versus cortical bone. Low density bone allows for a higher compressive interfacial area to be imparted by the staple. Staples in normal density bone are able to resist torsion and shear deformation more readily than staples in low density bone. Bone density may have a greater effect on the Nitinol staple's stability and compressive capability in vivo as compared to unicortical versus bicortical leg fixation.

Assessing the biomechanical properties of nitinol staples in normal, osteopenic and osteoporotic bone models: A finite element analysis

OBJECTIVE

Bone staples are internal fixation devices that are frequently used in the foot, ankle, and hand to provide stabilization. Fixation stability is vital after fusion or fracture surgeries to ensure proper bone healing. Patients undergoing surgeries that require fixation to keep bones aligned and stable may present with diminishing bone mechanical properties, and this may compromise the ability of the fixation hardware to maintain a stable construct. The purpose of this study was to investigate the mechanical performance of shape memory and superelastic nitinol bone staples with different bridge geometries in normal, osteopenic, and osteoporotic bone models. Contact forces and maximum principal stress and strain in the bone were recorded.

METHODS

Finite element simulations of a bone staple fixation procedure were performed to examine the initial and post-surgery contact force, as well as the maximum principal stress and strain of 15 mm bridge and 20 mm bridge staple-bone constructs.

RESULTS

Shape memory nitinol staples exhibited higher contact forces compared to superelastic nitinol staples. Nitinol bone staples with 20 mm bridge lengths displayed higher contact forces and lower stresses in all bone types, as well as lower strains in osteoporotic bone models compared to nitinol staples with a 15 mm bridge length.

CONCLUSION

Nitinol bone staple constructs with 20 mm bridge length staples provide higher contact forces and display lower stresses in the bone than 15 mm bridge staple-bone constructs, which may be beneficial in bone with diminishing mechanical properties. Both superelastic and shape memory effect nitinol staples provide adequate compression and stress relief. However, if osteopenia is present, shape memory effect nitinol staples with a 20 mm bridge length may provide more stress relief and compression, if the bone anatomy allows.

The Importance of the Medial Column in Progressive Collapsing Foot Deformity: Osteotomies and Stabilization

Adult acquired flatfoot deformity is a complex pathologic condition that requires considerate and thoughtful surgical solutions. Medial column procedures are often supplemented by a medializing calcaneal osteotomy and/or a lateral column lengthening because of the complex nature of progressive collapsing foot deformity and its resultant peritalar instability. Other osteotomies and fusions include a Cotton osteotomy and first tarsometatarsal fusion.

Locked Dorsal Compression Plate Arthrodesis for Degenerative Arthritis of the Midfoot

Midfoot arthrodesis is the accepted surgical treatment for symptomatic midfoot arthritis. The published literature has focused on joint-spanning static fixation. Several companies have developed diamond-shaped locked dorsal compression plates, which allow for longitudinal joint compression. After dorsal plate insertion, a spreader device opens the arms of the plate mediolaterally, which allows the plate to compress longitudinally. This work describes outcomes of such locked dorsal compression plates for midfoot arthritis at a single institution. We reviewed 62 patients who underwent midfoot arthrodesis for symptomatic midfoot arthritis using locked dorsal compression plates over a 7-year period. A total of 173 joints were spanned for fusion. The primary outcome measure was radiographic union and visual analog scale pain scores. Characteristics of patients who experienced nonunion versus those who had union were evaluated. Of the 173 joints, there was a 81.5% fusion rate (141/173 joints) and 14 patients experienced nonunion. There was a statistically significant difference in the average number of joints spanned in patients with nonunion (3.6) and patients with union (2.5) (p = .02). Locked dorsal compression plate arthrodesis is a viable technique for achieving midfoot fusion. This mechanical method of compression does not, however, lend itself to improved fusion rates compared with prior reports. A greater number of arthrodesis sites is associated with a higher nonunion rate. Emerging technology using newer materials and improved biomechanical designs may show improved results.

Outcomes of Nitinol Compression Staples in Tarsometatarsal Fusion

BACKGROUND

Tarsometatarsal (TMT) arthrodesis is commonly performed in the management of midfoot arthritis, trauma, or deformity. The purpose of this study was to collect aggregate data (demographic, surgical, and perioperative outcomes) on patients who previously had a TMT fusion with BME compression staples.

METHODS

Sixty-six patients underwent TMT fusion with BME compression staples. Outcomes included demographics, surgical information, the Veterans Rand VR-12 Health Survey, Foot and Ankle Ability Measure (FAAM), visual analog scale (VAS), Revised-Foot Function Index (FFI-R), Ankle Osteoarthritis Scale (AOS), patient satisfaction survey scores, radiographic fusion rate, level of pain reduction, and complications. Sixty-six patients (68 feet) were analyzed (59 females) with an average age of 64 years (range, 18-83). The mean latest follow-up was 35.9 (range, 6-56.6 months).

RESULTS

The average surgical time was 38.1±14.3 minutes (range, 11-75). All outcomes improved significantly (P < .001) from preoperative to latest follow-up except for the VR-12 Mental and Physical score. The average time to fusion determined by radiographs was 8.4 weeks (range, 6.1-46.1 weeks). Wound complications were not seen. Indications for subsequent surgeries (26.5%, 18/68 feet) in this current study included pain (n = 14), broken staples, and nonunion (n = 3).

CONCLUSIONS

The fusion rate in this study, 89.7%, was similar to values reported in the literature. The patient satisfaction score of 81.9 at latest follow-up is consistent with patient satisfaction for other methods of fusion.

LEVEL OF EVIDENCE

Level IV, retrospective case series.

Evolution of Thinking of the Lapidus Procedure and Fixation

The evolution of Lapidus fixation has been strongly associated with the understanding of the anatomy and function of the first tarsometatarsal joint, the mechanism of hypermobility of the first tarsometatarsal joint, and cause of the hallux valgus deformity in 3 dimensions. Some methods, such as plantar plating, nitinol staples, and intramedullary fixation, have proven to be stronger biomechanically in cadaveric testing. Theoretically, stable fixation will reduce the rate of complications, in particular, that of nonunion and allow for early postoperative weight-bearing. Further clinical studies are needed to examine whether current biomechanical studies will translate to relevant clinical outcomes.

3D digital image correlation evaluation of arthrodesis implants

BACKGROUND

Hallux valgus is a pathological condition that is typically treated via the Lapidus procedure. The purpose of this study was to understand the biomechanical characteristics of bone, implant devices and the bone-implant interface.

METHODS

In-situ digital image correlation was performed on polyurethane foam, a known bone substitute in a modified three-point bend test frame. We introduced this modified rig as an enhanced methodology for characterizing bone and implant device mechanical performance. This new methodology was validated using aluminum rod specimens, in three and four-point bend setups followed by new configurations to reveal implications of load configurations on joint displacement and implant performance. Bone substitute specimens were constructed with nitinol staples or locking plate to minimize gapping at the 1^st tarsometatarsal during testing.

FINDINGS

Bone-implant interface characterization was enabled by digital image correlation, identifying maximum strain concentrations of 1.5% along the interfaces. Interfacial characteristics were analyzed in context with gap displacement allowed by the implant over cyclical loading. The locking plate implant and nitinol staples gapped an average of 2.2 mm and 3.2 mm respectively under 50 Newtons. Removing all load, the locking plate implant and nitinol staples averaged ~0.8 mm and ~0.3 mm of residual gapping respectively.

INTERPRETATION

Our results demonstrate that locking plates provide more initial stability and resistance against gapping under load but are unable to recover compression throughout repetitive loading as seen with the nitinol staple technology. This could lead to a paradigm shift in materials used for early weight bearing protocols post-operation.

Treatment of open tibial diaphyseal fractures by external fixation combined with limited internal fixation versus simple external fixation: a retrospective cohort study

Background

The treatment of open tibial shaft fractures is challenging. External fixation (EF) is comparatively safe in treating these open injuries, meanwhile it has the advantages of easy application, minimal additional disruption, and convenient subsequent soft tissue repair. Nevertheless, its application is accompanied by a series of problems in alignment and bone healing. Therefore, limited internal fixation (LIF), such as cortical screws, has been used based on the external fixator for better therapeutic effect. The aim of this study is to compare the outcomes of EF combined with LIF and simple EF in the management of open tibial shaft fractures, evaluating the efficacy and safety of using the combined technique in treating such fractures.

Methods

From January 2012 to December 2016, patients with open tibial shaft fractures treated with EF with or without LIF augmentation were identified. A total of 152 patients were included in the analysis, and there were 85 patients in the simple external fixation group and 67 patients in the EF-LIF group. General assessment indicators included the direct cost of hospitalization and the times of first surgery, full weight bearing, and complete union. Infections and complications in union or limb alignment were compared as primary outcomes. Additionally, the number of patients who changed the fixation system for various reasons were analysed.

Results

Effective follow-up of all participants for statistical analysis was obtained. The follow-up time averaged 17.15 months (range: 12.00 to 24.00 months) in the EF group and 16.20 months (range: 12.00 to 19.00 months) in the EF-LIF group. Combined fixation provided shortened time to bear full weight and achieve complete bone union, while requiring additional first surgery time. No significant difference was found in infection rates or direct cost of hospitalization. Delayed union and non-union in the EF-LIF group were significantly decreased (20.9% versus 40.0, 1.5% versus 14.1%, p < 0.05). In limb alignment, patients with combined fixation exhibited reduced malreduction, loss of reduction, and malunion. In terms of secondary fixation, the EF-LIF group showed a markedly lower incidence (5.8% versus 34.1%, p < 0.001).

Conclusion

Compared with simple EF, combined fixation is an effective and safe alternative for management of open tibial diaphyseal fractures. It provides superior initial reduction, better stability and decreases the risk of inferior alignment and delayed union without increasing the risk of infection.

Failure of Fixation With Nickel-Titanium Staples in First Metatarsophalangeal Arthrodesis With Hallux Valgus Deformity

First metatarsophalangeal (MTP) joint arthrodesis is a treatment option for patients with arthritic hallux valgus (HV). Nickel-titanium staples allow continuous compression throughout the fusion site and have been shown to achieve successful union in many procedures. However, their efficacy has not been tested in patients with underlying HV deformity. Three cases of severe HV deformity that underwent first MTP arthrodesis with 2 nickel-titanium staples placed 60° from each other and had failure are reported. The authors believe this construct does not provide adequate rotational control for first MTP arthrodesis in patients with severe HV deformity. [Orthopedics. 2019; 42(4):e402-e404.].

Nitinol Compression Staples in Foot and Ankle Surgery

Nitinol compression implants are fast and simple to insert and have a high radiographic union rate for midfoot and hindfoot arthrodeses. Applications of nitinol technology in orthopedic surgery are rapidly expanding with the improved and broadened portfolio of implants available.

Biomechanical Properties of Nitinol Staples: Effects of Troughing, Effective Leg Length, and 2-Staple Constructs

PURPOSE

Nitinol memory compression staples are a recent addition to carpal bone fixation. Compared with traditional staples, they have been shown to have superior compression at the far cortex relative to standard and traditional compression staples. The purpose of this study was to (1) determine the effective leg length of different nitinol staples, (2) confirm the effect of 1 versus 2 staples on biomechanical compression, and (3) determine the effect of troughing (countersinking the staple into bone) the bone on staple biomechanical properties.

METHODS

Three commonly used nitinol staples of various bridge and leg lengths were used in a bicortical sawbones block construct. There were 3 separate constructs tested, which included single staple, double staple, and troughed. We measured compression force, stiffness, and bending strength for each construct before and after cyclical 4-point bending. Compression mapping was used to determine the effective leg length of each staple, which included the distance that compression extended beyond the tips of the staple legs.

RESULTS

Effective leg length for each staple construct extended 2 mm distal to the tip of the shortest staple leg. Two staple constructs more than doubled compressive force and increased bending strength by greater than 90% in all staple types. There was no loss of compressive force before or after loading for single, double, or troughed constructs with any staple type.

CONCLUSIONS

This study supports that nitinol staples do not have to be placed bicortically to achieve adequate compression; placing staples 2 mm short of the far cortex has the same compression as bicortical placement; and troughing of the bone will not significantly diminish the biomechanical properties of the construct.

CLINICAL RELEVANCE

Better understanding of the effective leg length of nitinol staples provides support that bicortical placement is not necessary for adequate compression. This study supports troughing bone to minimize implant prominence.

Review of Superelastic Differential Force Archwires for Producing Ideal Orthodontic Forces: an Advanced Technology Potentially Applicable to Orthognathic Surgery and Orthopedics

PURPOSE OF REVIEW

Gentle and continuous loads are preferred for optimum orthodontic tooth movement. Nitinol, an alloy of nickel and titanium developed for the aerospace industry, found its first clinical applications in orthodontics because it has ideal load-deflection behavior. The purpose of this review is to elucidate the criteria for effective orthodontic mechanics relative to emerging Nitinol technology. The specialized materials with variable stiffness that were originally developed for orthodontics are increasingly attractive for in the temporomandibular joint, orthognathic surgery, and orthopedics.

RECENT FINDINGS

The evolution of orthodontic archwires is driven by a need to achieve low load-deflection characteristics and Nitinol is the alloy of choice. Scientific knowledge of the biological response to orthodontic forces continues to grow, but definitive guidance on optimal force levels for individual teeth is elusive. Finite element models (FEM) that take into account periodontal ligament (PDL) stresses indicate differential force archwires are needed to realize optimal treatment. However, previous wire fabrication methods, including welding of different materials and selective resistive heating, are limited by poor mechanical performance and spatial resolution. Recently, a novel laser processing technique was developed for precisely programing relative levels of stiffness in a single archwire. FEM was used to estimate the optimal force for each tooth by calculating the 3D bone-PDL surface area. There remains a general consensus that light and continuous forces are desirable for orthodontic treatment. New developments in archwire materials and technology have provided the orthodontist with a complete spectrum of load-deflection rates and differential force options to express these forces with maximized archwire economy. These technologies also appear to have application to orthopedic implant devices.

Radiographic Results of Nitinol Compression Staples for Hindfoot and Midfoot Arthrodeses

BACKGROUND

The purpose of this study was to determine the radiographic union rate after midfoot and hindfoot arthrodeses using a new generation of nitinol staples, and to compare outcomes between a nitinol staple construct and a nitinol staple and threaded compression screw construct.

METHODS

A retrospective chart review was performed to identify patients who underwent hindfoot or midfoot arthrodesis using a new generation of nitinol compression staples with or without a partially threaded cannulated screw with minimum 3-month radiographic follow-up. The primary outcome variable was radiographic evidence of arthrodesis on radiographs and, when available, computed tomographic scan in patients who underwent midfoot or hindfoot arthrodesis using nitinol staples. Ninety-six patients and 149 joints were eligible for analysis. Median radiographic follow-up was 5.7 months.

RESULTS

Radiographic union was seen in 93.8% (60/64) of patients and 95.1% (98/103) of joints using the nitinol staple construct. Radiographic union was seen in 90.6% (29/32) of patients and 95.7% (44/46) of joints using the nitinol combined staple and screw construct. There was no significant difference in radiographic union rate or revision surgery between the 2 groups. Seven patients developed nonunion, 4 in the nitinol staple construct group and 3 in the staple and screw group.

CONCLUSIONS

New-generation nitinol staples were safe and effective for hindfoot and midfoot arthrodeses, with a high radiographic union rate. The use of a partially threaded screw for additional fixation was not found to either significantly increase or decrease radiographic fusion with nitinol staple fixation.

LEVEL OF EVIDENCE

Level III, comparative cohort study.

Biomechanical comparison of pin and nitinol bone staple fixation to pin and tension band wire fixation for the stabilization of canine olecranon osteotomies

OBJECTIVE

To compare the initial biomechanical properties of olecranon osteotomies stabilized with intramedullary pins and a Nitinol bone staple to osteotomies stabilized with pin and tension band wire fixation.

STUDY DESIGN

Ex vivo mechanical evaluation on cadaveric bones.

MATERIAL AND METHODS

Ten pairs of cadaveric forelimbs from skeletally mature Greyhounds with an olecranon osteotomy stabilized with either a pin and Nitinol bone staple or a pin and tension band wire. A single load to failure was applied to each specimen through the triceps tendon. Biomechanical properties were compared based on stiffness, yield load, and maximum load to failure and load at 2 mm of axial displacement.

RESULTS

Specimens stabilized with the bone staple were biomechanically superior in all the variables tested. There was significantly greater stiffness (118.0 ± 25.9 N/mm versus 70.1 ± 40.4 N/mm; p = 0.005), yield load (319.0 ± 99.8 N versus 238.0 ± 42.5 N; p = 0.03), maximum load sustained (385.0 ± 99.2 N versus 287.0 ± 37.4 N; p = 0.009), and load at 2 mm of axial displacement (218.0 ± 51.5 N versus 138.0 ± 48.7 N; p = 0.002) in specimens stabilized with pins and a Nitinol bone staple than specimens stabilized with pin and tension band wire fixation.

CLINICAL SIGNIFICANCE

The pin and Nitinol bone staple construct provides a biomechanically superior alternative to pin and tension band wire fixation for stabilization of olecranon osteotomies, and its use warrants further clinical investigation.

Biomechanical evaluation of shape-memory alloy staples for internal fixation-an in vitro study

Background

The field of orthopaedics is a constantly evolving discipline. Despite the historical success of plates, pins and screws in fracture reduction and stabilisation, there is a continuing search for more efficient and improved methods of fracture fixation. The aim of this study was to evaluate shape-memory staples and to compare them to a currently used implant for internal fracture fixation. Multi-plane bending stability and interfragmentary compression were assessed across a simulated osteotomy using single and double-staple fixation and compared to a bridging plate.

Methods

Transverse osteotomies were made in polyurethane blocks (20 × 20 × 120 mm) and repairs were performed with one (n = 6), or two (n = 6) 20 mm nitinol staples, or an eight-hole 2.7 mm quarter-tubular plate (n = 6). A pressure film was placed between fragments to determine contact area and compressive forces before and after loading. Loading consisted of multi-planar four-point bending with an actuator displacement of 3 mm. Gapping between segments was recorded to determine loads corresponding to a 2 mm gap and residual post-load gap.

Results

Staple fixations showed statistically significant higher mean compressive loads and contact areas across the osteotomy compared to plate fixations. Double-staple constructs were superior to single-staple constructs for both parameters (p < 0.001). Double-staple constructs were significantly stiffer and endured significantly larger loads before 2 mm gap formation compared to other constructs in the dorsoventral plane (p < 0.001). However, both staple constructs were significantly less stiff and tolerated considerably lower loads before 2 mm gap formation when compared to plate constructs in the ventrodorsal and right-to-left lateral loading planes. Loading of staple constructs showed significantly reduced permanent gap formation in all planes except ventrodorsally when compared to plate constructs.

Conclusions

Although staple fixations were not as stable as plate fixations in particular loading planes, double-staple constructs demonstrated the most consistent bending stiffness in all planes. Placing two perpendicular staples is suggested instead of single-staples whenever possible, with at least one staple applied on the compression side of the anticipated loading to improve construct stability.