Biomechanical comparison of a new staple technique with tension band wiring for transverse patella fractures

Biomechanical comparison of bone staple fixation methods with suture material for median sternotomy closure using 3D-printed bone models

AIM

To compare the biomechanical properties of three different sternal closure techniques in a 3D-printed bone model of a sternum from a 30-kg dog.

METHODS

Median sternotomy was performed on a total of 90 three-dimensional (3D) copies of a polycarbonate (PC) model of a sternum, generated from the CT images of the sternum of a 30-kg German Shepherd dog. Three different methods were used to repair the sternotomies: polydioxanone suture (group PDS, n = 30), stainless steel bone staples (group SS, n = 30), and nitinol bone staples (group NS, n = 30). Each repair method was tested by applying tensile force in one of three ways (longitudinally, laterally, or torsionally) resulting in a sample size of n = 10 for each repair method-loading combination. In all experiments, the loads at 1-mm and 2-mm gap formation, failure, and the displacement at the failure point were measured.

RESULTS

In lateral distraction and longitudinal shear tests, NS and SS staple repairs required application of significantly greater force than PDS across all displacement criteria (1 and 2 mm). NS exhibited significantly greater failure load than PDS. In torsion tests, NS required significantly greater application of force compared to SS or PDS at all displacement criteria (1 and 2 mm) and exhibited a greater failure load than PDS. In terms of displacement at failure point, PDS suture showed more displacement than SS or NS across all experiments (laterally, longitudinally, torsionally).

CONCLUSIONS

In this study, bone staples were mechanically superior to PDS suture in median sternotomy closure using 3D-printed bone model in terms of 1-mm, 2-mm displacement loads, and displacement at failure. NS had a higher failure load than PDS under lateral, longitudinal, and torsional distraction.

CLINICAL RELEVANCE

These study results imply that bone staples can be considered as an alternative surgical method for median sternotomy closure in dogs.

Anterior variable angle locking neutralisation plate superiority over traditional tension band wiring for treating transverse patella fractures

Purpose

This paper investigates the biomechanical benefits of using hybrid constructs that combine cannulated screws with tension band wiring (TBW) cerclage compared to cannulated screws with anterior Variable Angle locking neutralisation plates (VA LNP). These enhancements can bear heavier loads and maintain the repaired patella's integrity, in contrast to traditional methods.

Method

Eighteen fresh-frozen human cadaver patellae were carefully fractured transversely at their midpoints using a saw. They were then divided into two groups of nine for subsequent utilisation. Fixation methods included Cannulated Screw Fixation added with either TBW or VA LNP Fixation Technique. Cyclic loading simulations (500 cycles) were conducted to mimic knee motion, tracking fracture displacement with Optotrak. After that, the constructs were secured over a servo-hydraulic testing machine to determine the load-to-failure on axial mode.

Results

The average fracture displacement for the anterior neutralisation plate group was 0.09 ± 0.12 mm, compared to 0.77 ± 0.54 mm for the tension band wiring with cannulated screw group after 500 cyclic loading. This result is statistically significant (p = 0.004). The anterior neutralisation plate group exhibited a mean load-to-failure of 1359± 21.53 N, whereas the tension band wiring group showed 780.1 ± 22.62 N, resulting in a significant difference between the groups (p = 0.007).

Conclusion

This research highlights the superior biomechanical advantage of VA LNP over TBW for treating simple transverse patella fractures with two cannulated screws. It also highlights how the TBW is still a valuable option considering the load-to-failure limit.

Level of Evidence

Not Applicable.

Reconstruction of patella fractures with the tension band technique: A review on clinical results and tips and tricks

INTRODUCTION

The goals of surgical treatment of patellar fractures are a biomechanically stable joint and congruent restoration of the retro patellar joint surface. Surgical treatment strategies for patellar fractures have evolved from tension band in combination with wire cerclages to new devices.

METHODS

The modified anterior tension band (MATB) technique for fixation of patellar fractures consists of two longitudinal 1.8 mm Kirschner wires (K-wires) and an 18-gauge stainless steel wire looped in a figure-of-8 pattern over the anterior aspect of the patella. The K-wires should be inserted 5 mm from the anterior cortical surface of the patella, parallel in the coronal and sagittal planes. For mechanical reasons, the wire should be the closest to the anterior aspect of the bone. This construct converts the anterior tensile forces generated by the extensor mechanism and knee flexion into compressive forces on the anterior aspect of the fracture site. The MATB is the most widely accepted method of internal fixation for transverse and comminuted patellar fractures. Only a careful implementation of the MATB in all its phases will provide the best mechanical construct and the least aggressive construct for the soft tissues, allowing early re-education without complications.

RESULTS

Good to excellent clinical results (64-100 %) have been reported with MATB for fixation of patellar fractures. Good to excellent range of knee motion and satisfactory results have been reported despite a high percentage (up to 60 %) of secondary procedures, mainly for removal of symptomatic hardware.

CONCLUSION

This article provides an overview of the use and results of the MATB technique for patellar fractures and the means to improve results with this technique.

Transverse patella fracture fixation: A cadaveric biomechanical comparison of cannulated screws and anterior tension band versus low-profile, multiplanar mesh plating

INTRODUCTION

Multiplanar mesh plating of patella fractures has become more popular in recent years. It was the goal of this study to compare the biomechanical stability of cannulated screw with anterior tension band to multiplanar mesh plating for fixation of transverse patella fractures in cadaver specimens.

MATERIALS AND METHODS

Eight matched pairs of fresh frozen cadaveric knees were obtained and soft tissues dissected leaving the extensor mechanism, joint capsule, and retinaculum intact. Transverse fractures were created at the mid-portion of the patella. For each pair, one specimen was repaired using cannulated screws with anterior tension band, and the second was repaired using multiplanar mesh plating. Each specimen underwent cyclic extension loading with loads increasing by 1.1 kg after every 50 cycles. Interfragmentary displacement was measured at the end of each interval at both 5° and 45° of knee flexion angle, with fixation failure defined by >2 mm displacement.

RESULTS

The specimens fixed with multiplanar mesh plating survived more cycles and higher loads than the specimens fixed with cannulated screws with anterior tension band (p = 0.011 comparing survival plots). After 150 cycles of extension loading, 3 of 8 of the specimens fixed with screws/tension band had failed, whereas none of the mesh plated specimens had failed. After 400 cycles, 7 of 8 of the screws/tension band had failed, whereas half of the mesh plated specimens had failed.

CONCLUSIONS

While a more technically challenging and expensive technique, mesh plating for patella fractures appears to offer greater durability than traditional cannulated screw with tension banding.

Lateral rim variable angle locked plating versus tension band wiring of simple and complex patella fractures: a biomechanical study

INTRODUCTION

Treatment of both simple and complex patella fractures is a challenging clinical problem. Although tension band wiring has been the standard of care, it can be associated with high complication rates. The aim of this study was to investigate the biomechanical performance of recently developed lateral rim variable angle locking plates versus tension band wiring used for fixation of simple and complex patella fractures.

MATERIALS AND METHODS

Sixteen pairs of human anatomical knees were used to simulate either two-part transverse simple AO/OTA 34-C1 or five-part complex AO/OTA 34-C3 patella fractures by means of osteotomies, with each fracture model created in eight pairs. The complex fracture pattern was characterized by a medial and a lateral proximal fragment, together with an inferomedial, an inferolateral, and an inferior (central distal) fragment mimicking comminution around the distal patellar pole. The specimens with simple fractures were pairwise assigned for fixation with either tension band wiring through two parallel cannulated screws or a lateral rim variable angle locking plate. The knees with complex fractures were pairwise treated with either tension band wiring through two parallel cannulated screws plus circumferential cerclage wiring or a lateral rim variable angle locking plate. Each specimen was tested over 5000 cycles by pulling on the quadriceps tendon, simulating active knee extension and passive knee flexion within the range of 90° flexion to full extension. Interfragmentary movements were captured via motion tracking.

RESULTS

For both fracture types, the articular displacements measured between the proximal and distal fragments at the central patella aspect between 1000 and 5000 cycles, together with the relative rotations of these fragments around the mediolateral axis were all significantly smaller following the lateral rim variable angle locked plating compared with tension band wiring, p ≤ 0.01.

CONCLUSIONS

From a biomechanical perspective, lateral rim variable angle locked plating of both simple and complex patella fractures provides superior construct stability versus tension band wiring under dynamic loading.

Evolution in the Management of Patella Fractures

Patella fractures usually occur as a result of direct trauma to the anterior knee joint, indirect injury as a result of eccentric muscle contraction, or rapid knee flexion against a contracted quadriceps muscle. The patella functions as part of the extensor mechanism of the knee, where large forces are transmitted, and its subcutaneous nature has made treatment of patella fractures a challenge. In this review article, we evaluate how the management of these fractures has evolved over time and the advantages associated with the various treatment techniques. There are few comparative studies looking at the different treatment types for fractures of the patella, with the goal of achieving a functional extensor mechanism with low rates of post-traumatic arthritis and metal-work irritation.

A novel technique for treating simple transverse patellar fractures using cannulated screws: a cadaveric and clinical study

BACKGROUND

Tension band wiring (TBW) has conventionally been used for the open reduction and internal fixation of the patella. However, it suffers from distinct disadvantages such as large incision, implant irritation, and need for subsequent implant removal. Here, we propose a novel technique using closed reduction and percutaneous fixation with three cannulated screws (TCS), which may be an alternative to this established conventional technique. Although some researchers have proposed alternative methods including closed reduction and cannulated screw fixation, with or without additional wires through the screws, and arthroscopic-assisted reduction and fixation, there are few studies that focus on the biomechanical stability of percutaneous fixation using only cannulated screws. Thus, the purpose of this study was to evaluate TCS versus TBW for simple transverse patellar fractures in cadaveric and patients' level, aiming to determine whether TCS show superiority over TBW in terms of biomechanical stability in a cadaveric study with benign clinical feasibility and outcomes in patients.

METHODS

We conducted a cadaveric study with 15 knee specimens that had simple transverse patellar fractures. We used two fixation techniques: TBW (group A, n = 6) and TCS (group B, n = 9). We applied sinusoidal forces (25 N-125 N) at 1/5 Hz and 90° knee flexion to simulate knee movement. We compared the displacements at the fracture site between the two groups. We also used the same technique in a total of 23 patients and followed up them for at least 1 year.

RESULTS

TCS demonstrated favourable biomechanical stability in the cadaveric study. The technique also performed excellently in terms of postoperative pain, knee function recovery, and complication rates during the follow-up period.

CONCLUSIONS

The technique provides a surgical treatment option with small incisions, minimal soft tissue irritation, and possibly lower removal rate of bothersome material.

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.

Using shape-memory alloy staples to treat comminuted manubrium sterni fractures: A case report

BACKGROUND

Comminuted manubrium sterni fractures are rare, and internal fixation methods are limited. This report explored a practical and feasible method of internal fixation for comminuted manubrium sterni fractures.

CASE SUMMARY

A 17-year-old female was injured in a car accident for which she underwent debridement and suturing of her head and anterior chest wounds in another hospital. Eight days later, the patient was transferred to our hospital for surgical treatment. The manubrium sterni was found intraoperatively to be split into three irregular fragments with obvious overlap and separation displacement. Meanwhile, a manubriosternal joint dislocation and left first rib cartilage fracture were observed. The retraction force of the shape-memory alloy staples was used to pull the fracture fragments together. Two more titanium locking plates were then used to fix the manubrium sterni and corpus sterni longitudinally, and the left first rib cartilage fracture was repositioned and fixed with a titanium locking plate. A postoperative computed tomography scan showed reduced and rigid fixation of the comminuted manubrium sterni fractures. The patient recovered well with no significant complaints of discomfort. The patient was discharged 10 days postoperatively after the stitches had been removed.

CONCLUSION

Shape-memory alloy staples had the advantage of being safe and effective during the repositioning and internal fixation of comminuted manubrium sterni fractures. Therefore, they provided a new surgical option for comminuted manubrium sterni fractures.

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.

Anterior variable-angle locked plating versus tension band wiring of simple and complex patella fractures - a biomechanical investigation

BACKGROUND

The aim of this study was to investigate the biomechanical performance of novel anterior variable-angle locking plates versus tension band wiring used for fixation of simple and complex patella fractures.

METHODS

Sixteen pairs of human cadaveric knees were used to simulate two-part simple transverse AO/OTA 34-C1 and five-part complex AO/OTA 34-C3 patella fractures. The complex fracture pattern was characterized with a medial and a lateral proximal fragment, together with an inferomedial, an inferolateral and an inferior fragment mimicking comminution around the distal patella pole. Eight pairs with simple fractures were split for fixation via either tension band wiring (TBW) through two parallel cannulated screws or anterior variable-angle locked plating, whereas other eight pairs with complex fractures were split for either TBW through two parallel cannulated screws plus circumferential cerclage wiring, or anterior variable-angle locked plating using a cortical caudo-cranial polar screw. Each specimen was tested over 5000 cycles with a range of motion from 90° flexion to full extension by pulling on the quadriceps tendon. Interfragmentary movements were captured by motion tracking.

RESULTS

For both fracture types, the longitudinal and shear articular displacements, measured between the proximal and distal fragments at the central patella aspect between 1000 and 5000 cycles, together with the relative rotations of these fragments around the mediolateral axis were all significantly smaller following anterior variable-angle locked plating versus TBW, p ≤ 0.01.

CONCLUSIONS

From a biomechanical perspective, anterior locked plating of both simple and complex patella fractures resulted in less interfragmentary displacement under extended cyclic loading.

Transosseous suture versus suture anchor fixation for inferior pole fractures of the patella in osteoporotic bone: a biomechanical study

BACKGROUND

The surgical treatment of inferior patellar pole fractures can be a challenge, especially in geriatric patients, who are particularly frequently affected by osteoporosis. The objective of this biomechanical study was to compare the performance of suture anchor and transosseous suture fixation in fractures of the inferior patellar pole in context of bone mineral density.

METHODS

Twelve fresh-frozen human cadaveric knees received a transverse osteotomy, simulating an AO/OTA 34C1.3 inferior pole fracture of the patella. These fractures were fixated with either suture anchors (SA; Corkscrew® FT 4.5 mm) or transosseous suture (TS; #2 FiberWire®). Cyclic loading tests were performed by pulling the quadriceps tendon against gravity from 90° flexion to almost full extension (5°) for 1000 cycles. Motion and fracture gap displacement were tracked until failure occurred. Subsequently, loading to failure tests followed. Differences between groups were compared using unpaired t-tests, and correlations were calculated with Pearson's correlation coefficient.

RESULTS

The suture anchor group showed significantly fewer cycles to failure than the transosseous suture group (SA: 539.0 ± 465.6 cycles, TS: 1000 ± 0 cycles, P = 0.04). Bone mineral density correlated positively with cycles to failure in the suture anchor group (Pearson's r = 0.60, P = 0.02). No differences in fracture gap displacement could be proven after 100 cycles (SA: 4.1 ± 2.6 mm, TS: 6.5 ± 2.6 mm, P = 0.19); 500 cycles (SA: 6.4 ± 6.1 mm, TS: 9.6 ± 3.8 mm, P = 0.39); and 1000 cycles (SA: 4.0 ± 0.4 mm, TS: 11.0 ± 4.5 mm, P = 0.08). Furthermore, the mean destructive load to failure in the suture anchor group was also significantly lower than in the transosseous suture group (SA: 422.4 ± 212.2 N, TS: 825.7 ± 189.3 N, P = 0.04).

CONCLUSIONS

Suture anchors may be a viable alternative to transosseous suture in younger patients for clinical advantages, but in osteoporotic bone, the more stable osteosynthesis with transosseous suture continues to prove superior. Therefore, trauma surgeons might consider the use of transosseous suture in elderly patients, especially in those presenting with low bone mineral density values.

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.

Biomechanical comparison of a novel tensioned cable construct versus tension band wiring for transverse patella fracture fixation

PURPOSE

Tension band wiring (TBW) is the most widely accepted method for patella fracture fixation. The purpose of our study was to compare the biomechanical efficacy of a novel cable construct to TBW for the fixation of transverse patella fractures. The tensioned cable construct was hypothesized to have less fracture gapping after cyclic flexion-extension loading and greater ultimate load to failure as compared to TBW.

METHODS

Transverse patellar osteotomies (AO/OTA 34C1.1) were performed on nine pairs of fresh-frozen human cadaveric whole legs (mean age 82.2 years, range 71-101). Treatment with TBW or tensioned cable construct was randomized within each specimen pair. Fracture site displacement was measured after 5000 flexion-extension cycles from 0° to 90° at 0.5 Hz. In load to failure testing, the knee was fixed at 45° of flexion and the quadriceps tendon was pulled proximally at 0.5 mm/sec until patella fixation failure. Comparisons were made using paired t-tests with alpha values of 0.05.

RESULTS

Eight paired specimens completed the cyclic loading. The tensioned cable construct had significantly less fracture gapping than TBW (2.9 vs 10.9 mm; p = 0.020). Seven paired limbs underwent load to failure testing, which revealed no significant difference between the tensioned cable construct and TBW (1551.6 N vs 1664.0 N; p = 0.26).

CONCLUSION

In this study of transverse patella fracture fixation, a tensioned cable construct demonstrated significantly less fracture gapping compared to TBW in response to cyclic loading with no significant difference in load at failure.

A New Antirotation Strategy of K-Wire Tension Band Therapy for Patellar Fracture

Background

Patellar fracture is a common phenomenon observed in orthopedic clinics. Many methods have been shown to be effective in the fixation of patellar fracture. However, there are few studies on the antirotation effect of these methods. The purpose of this study is to present a new strategy of K-wire tension band therapy for patellar fracture and explore the antirotation effect of the modified tension band method on patellar fracture.

Methods

A retrospective clinical observation study was conducted on 75 patients with patellar fracture. Totally, 46 patients were enrolled to the traditional group, who received the traditional K-wire tension band therapy. The modified group included 29 patients on whom our new strategy was implemented. The operation time, intraoperative blood loss, and fracture healing time were collected to compare the two operations and the knee society score (KSS) scores after the operations, and complications were recorded and retrieved to indicate the effectiveness of the two treatments.

Results

The preoperative baseline data (gender, age, fracture types) of the two groups showed no significant statistical difference. Similarly, there was no significant difference in the operation time, intraoperative blood loss, and fracture healing time between the two groups. The KSS clinical scores 1 year after operation was 90 (84, 95) for the traditional group as compared with 99 (97, 100) for the modified group (p < 0.05). The KSS functional scores 1 year after operation in the two groups were 90 (65, 90) and 100 (90, 100) (p < 0.05). The incidences of complications due to the rotation of K-wires in the traditional group and the modified group were 76.1% (35 of 46) and 6.9% (2 of 29) with a significant statistical difference (p < 0.05).

Conclusion

This study shows that our modified tension band therapy is an effective strategy for antirotation in the treatment of patellar fracture and proves that it can achieve better clinical outcomes than the traditional K-wire tension band method. This new strategy may be a safe and effective clinical technique for the treatment of patellar fracture. However, more prospective randomized controlled trials with larger sample sizes are still needed to further prove its efficacy.

Cutting-Edge Progress in Stimuli-Responsive Bioadhesives: From Synthesis to Clinical Applications

With the advent of "intelligent" materials, the design of smart bioadhesives responding to chemical, physical, or biological stimuli has been widely developed in biomedical applications to minimize the risk of wounds reopening, chronic pain, and inflammation. Intelligent bioadhesives are free-flowing liquid solutions passing through a phase shift in the physiological environment due to stimuli such as light, temperature, pH, and electric field. They possess great merits, such as ease to access and the ability to sustained release as well as the spatial transfer of a biomolecule with reduced side effects. Tissue engineering, wound healing, drug delivery, regenerative biomedicine, cancer therapy, and other fields have benefited from smart bioadhesives. Recently, many disciplinary attempts have been performed to promote the functionality of smart bioadhesives and discover innovative compositions. However, according to our knowledge, the development of multifunctional bioadhesives for various biomedical applications has not been adequately explored. This review aims to summarize the most recent cutting-edge strategies (years 2015-2021) developed for stimuli-sensitive bioadhesives responding to external stimuli. We first focus on five primary categories of stimuli-responsive bioadhesive systems (pH, thermal, light, electric field, and biomolecules), their properties, and limitations. Following the introduction of principal criteria for smart bioadhesives, their performances are discussed, and certain smart polymeric materials employed in their creation in 2015 are studied. Finally, advantages, disadvantages, and future directions regarding smart bioadhesives for biomedical applications are surveyed.

A Novel Screw Drive for Allogenic Headless Position Screws for Use in Osteosynthesis-A Finite-Element Analysis

Due to their osteoconductive properties, allogenic bone screws made of human cortical bone have advantages regarding rehabilitation compared to other materials such as stainless steel or titanium. Since conventional screw drives like hexagonal or hexalobular drives are difficult to manufacture in headless allogenic screws, an easy-to-manufacture screw drive is needed. In this paper, we present a simple drive for headless allogenic bone screws that allows the screw to be fully inserted. Since the screw drive is completely internal, no threads are removed. In order to prove the mechanical strength, we performed simulations of the new drive using the Finite-Element method (FEM), validated the simulations with a prototype screw, tested the novel screw drive experimentally and compared the simulations with conventional drives. The validation with the prototype showed that our simulations provided valid results. Furthermore, the simulations of the new screw drive showed good performance in terms of mechanical strength in allogenic screws compared to conventional screw drives. The presented screw drive is simple and easy to manufacture and is therefore suitable for headless allogenic bone screws where conventional drives are difficult to manufacture.

Biomechanical Analysis of the Kirschner-Wire Depth of the Modified Tension Band Wiring Technique in Transverse Patellar Fractures: An Experimental Study Using the Finite-Element Method

Backgroud

Modified tension band wiring is one of the most preferred surgical methods for transverse patellar fractures. However, the optimal depth or sagittal position of a Kirschner wire (K-wire) in modified tension band wiring has yet to be determined. The purpose of this study was to evaluate whether the depth of a K-wire affects the biomechanical characteristics of modified tension band wiring using the finite-element method.

Methods

A patella model was designed with a cuboid shape (length, 34.3 mm; width, 44.8 mm; and thickness, 22.4 mm) and divided into the cortical and cancellous bone parts. A transverse fracture line was formed on the midline of the cuboid shape model. The cuboidal model was applied to modified tension band wiring. The depth or sagittal position of the K-wire was divided into superficial, center, and deep. With the Abaqus v2017 program (Dassault System Inc.), the distal part of the model was fixed, and a tensile load of 850 N was applied to the proximal part of the model at an angle of 45°. The maximum pressures of the cortical and cancellous bones at the fracture plane were measured. The largest von Mises values of the K-wire and stainless steel wire were also measured. The fracture gap on the distracted or anterior side was measured.

Results

In deep K-wire placement, the highest peak von Mises values of the cortical and cancellous bones were observed. The K-wire and stainless steel wire showed the highest von Mises values in deep K-wire placement. The fracture gap was also largest in deep K-wire placement.

Conclusions

The depth of the K-wire affects the biomechanical characteristics of modified tension band wiring. Deep placement of the K-wire will be more favorable for bone union than the empirically known 5-mm anterior or center placement of the K-wire.

Nitinol Staples for Olecranon Osteotomy Fixation, Juxtacortical Versus Inset, Effect on Biomechanical Stability

Purpose

Hardware prominence is a concern in the fixation of olecranon osteotomies. Staple fixation has provided low-profile secure fixation in other areas of orthopedics. Without insetting, staples still have subcutaneous prominence. This study examines whether nitinol staples, when inset into bone via cortical notching, in an olecranon osteotomy can provide fixation strength sufficient for daily activities.

Methods

Olecranon osteotomies were created in 8 cadaver arms and fixed with 2 nitinol staples. For inset and juxtacortical (noninset) staples, a micrometer measured the displacement between preplaced proximal and distal wires for 3 increasing loads: 0 N, 15 N, and 150 N. This measurement reflected the loss of osteotomy compression. We placed each arm in a pneumatic machine that flexed the elbow from 0° to 90° for 500 cycles at each load. We performed a 2-tailed t test (α value 0.05, β value 0.2) to evaluate for differences in the loss of compression between inset and noninset nitinol staples.

Results

We performed the displacement measurement procedure for both staple types at each of the 3 loads. At 0 N, the average displacement of inset was 0 mm and that of noninset was 0.02 mm. At 15 N, the average displacement of inset was 0.02 mm and that of noninset was 0.04 mm. At 150 N, the average displacement of inset was 0.05 mm and that of noninset was 0.09 mm. When comparing the displacement at the 3 force loads, there were no statistically significant differences between the staple types (P = .323).

Conclusions

This study shows that inset staples do not considerably weaken osteotomy fixation with nitinol staples. Thus, nitinol staples may provide a low-profile, operatively-efficient fixation method compared with tension-band or screw-and-plate fixation methods for olecranon osteotomies. Future research can include comparing staples with plate constructs.

Type of study/level of evidence: Therapeutic III.

Patella fracture fixation with a non-locked anterior plating technique: A biomechanical study

OBJECTIVES

The purpose of this study was to compare the biomechanical attributes of patella fracture fixation with either anterior plating utilizing two parallel, longitudinal 2.0 mm plates technique versus a cannulated screw tension band technique.

METHODS

Five matched pairs (ten specimens) of fresh frozen cadavers were utilized. A transverse patella fracture (OTA 34C1.1) was fixed using either two 4.0 mm cannulated screw anterior tension band (CATB) or with two 2.0 mm stainless steel non-locking plates along the anterior cortex secured with 2.4 mm cortical screws traversing the fracture site. Specimens underwent 1000 cycles of simulated active knee range of motion before load to failure destructive testing.

RESULTS

During cyclic loading there were no failures in the plate fixation group, and 2 out of 5 specimens catastrophically failed in the CATB group (p = 0.22). Average fracture displacement at the end of fatigue testing was 0.96 mm in the plate fixation group and 2.72 mm in the CATB group (p = 0.18). The specimens that withstood cyclic testing underwent a destructive load. Mean load to failure for the plate fixation specimens was 1286 N, which was not significantly different from the CATB group mean of 1175 N (p = 0.48). The mechanism of failure in the plate fixation cohort was uniformly via a secondary vertical patella fracture around the plates in all five specimens. In the CATB group, the mechanism of failure was via wire elongation and backing out of the screws.

CONCLUSIONS

Patella fixation with anterior plating technique statistically performed equivalent to cannulated screw anterior tension band in ultimate load to failure strength and fatigue endurance under cyclical loading. No failures were observed cyclic simulated active range of motion in the anterior plate group. There was a trend towards improved fatigue endurance in the plate fixation group, however this did not reach statistical significance. We believe plate fixation technique represents a low-profile implant option for treatment of transverse patella fractures, which may allow for early active range of motion, and these data support biomechanical equivalency to standard of care.

Comminuted patellar fractures: The role of biplanar fixed angle plate constructs

Background

Comminuted patellar fractures represent a challenging clinical problem. Treatment aims to restore the integrity of the extensor mechanism and the congruity of patellofemoral joint. Controversy exists regarding the ideal fixation method. Metallic constructs aiming to convert pulling forces on the anterior aspect of the patella into compression forces across the fracture site are the standard of care. More recently, low profile plates have been described in the management of comminuted patellar fractures. The aims of this study were to (1) develop a novel unstable patellar fracture model and (2) to compare biomechanically three different constructs for fixation comminuted patellar fractures. We hypothesized that an orthogonal biplanar disposition of the screws within an anteriorly placed locking plate provides the best biomechanical properties in the management of comminuted fractures.

Methods

Six-part complex AO 34–C3 patella fractures were simulated in 18 human cadaveric knees by means of osteotomies including comminution around the distal patellar pole. The specimens were randomly assigned to 3 fixation techniques (n ​= ​6) for either anterior plating, antero-lateral plating, or tension band wiring (TBW). Biomechanical testing was performed over 5000 cycles in active extension and passive flexion, followed by ultimate destructive quasi-static testing. Interfragmentary movements were captured by means of optical motion tracking.

Results

Displacement between the proximal and distal medial patella fragments was lower after anterior plating compared to both antero-lateral plating (P ​= ​0.084) and TBW (P ​< ​0.001). Moreover, displacement between the proximal and distal lateral fragments was significantly lower after anterior plating compared to both other techniques (P ​≤ ​0.032). In addition, it was significantly lower for antero-lateral plating versus TBW (P ​< ​0.001). Rotation around the medio-lateral axis between the proximal and distal medial fragments was significantly lower after anterior plating compared to TBW (P ​= ​0.017).

Conclusions

Anterior mesh plating with biplanar placement of locking screws provides superior stability for fixation of comminuted patellar fractures when compared to both antero-lateral mesh plating and TBW. The latter is associated with considerably inferior performance.

Surgical Treatment of Meniscal Extrusion: A Biomechanical Study on the Role of the Medial Meniscotibial Ligaments With Early Clinical Validation

Background

Meniscal extrusion refers to meniscal displacement out of the joint space and over the tibial margin, altering knee mechanics and increasing the risk of osteoarthritis. The meniscotibial ligaments have been shown to have an important role in meniscal stability. However, it remains unclear whether an isolated lesion of the medial meniscotibial ligaments will result in meniscal extrusion and whether repairing the detached ligament will reduce extrusion.

Hypothesis

A lesion of the medial meniscotibial ligament will result in meniscal extrusion, and repairing the joint capsule will eliminate the extrusion by returning the meniscus back to its original position.

Study Design

Controlled laboratory study.

Methods

Fresh-frozen human cadaveric knees (N = 6) were used for biomechanical testing. The test protocol involved 100 flexion-extension cycles. In full extension, meniscal extrusion was measured using ultrasound, in both an otherwise unloaded state and while subjected to a 10-N·m varus load. Each knee was tested in its native condition (baseline), after creating a detachment of the medial meniscotibial ligament, and finally with the joint capsule repaired using 3 knotless SutureTak anchors. We also performed a retrospective review of 15 patients who underwent meniscotibial ligament repair with a minimal follow-up of 5 weeks (mean, 14 weeks; range, 5-35 weeks).

Results

During biomechanical testing, the mean absolute meniscal extrusion at baseline was 1.5 ± 0.6 mm. After creation of the meniscotibial ligament lesion, the mean absolute meniscal extrusion was significantly increased (3.4 ± 0.7 mm) (P < .001). After repair, the extrusion was reduced to 2.1 ± 0.4 mm (P < .001). Clinically, a reduction in absolute meniscal extrusion of approximately 48% was reached (1.2 ± 0.6 vs 2.4 ± 0.5 mm preoperatively; P < .001).

Conclusion

This study indicates that the medial meniscotibial ligaments contribute to meniscal stability as lesions cause the meniscus to extrude and that repair of those ligaments can significantly reduce extrusion. Early clinical results using this meniscotibial ligament repair technique support our biomechanical findings, as a significant reduction in meniscal extrusion was achieved.

Clinical Relevance

Our biomechanical findings suggest that repair of medial meniscotibial ligaments reduces meniscal extrusion and clinically may improve meniscal function, with the possible long-term benefit of reducing the risk for osteoarthritis.

A comparison of EFECE systems with tension band wiring for patella fracture fixation in cadavers

Background

EFECE systems are newly defined internal fixation systems, which are suitable for patella fracture fixation. The aim of this study was to compare the fixation strength of EFECE Systems with tension band wiring for transverse patellar fracture simulation on fresh frozen cadaver models.

Methods

Quadriceps tendon-patella-patellar tendon (QT-P-PT) complex was prepared from human cadavers. After simulation of a transverse patella fracture, in group 1, 5 patella were fixed with a pair of 1.2 mm EFECE wires and 4 EFECE devices. In group 2, 5 patella were fixed with a pair of 1.2 mm Kirschner wires (K-wire) and a cerclage wire according to the tension band technique.

Using a testing device with custom-made jaws, increasing distraction force was applied to these QT-P-PT complexes. Extension of these complexes with the distraction forces was observed. The maximum distraction force and the elongation during maximum force were evaluated.

Results

After 5 experiments with the EFECE systems, there was no EFECE wire breakage or EFECE wire-EFECE device catching failure. The median maximum force was 740 N (720-810 N). During maximum distraction force the median extension was 2.5 mm (1.6-2.5 mm). After 5 experiments with the tension band technique, there was no K-wire breakage. The median maximum force was 330 N (240-510 N). During this maximum distraction force the median extension was 3.4 mm (2.2-3.8 mm).

Conclusions

Based on the biomechanical advantages, patella fracture treatment with EFECE systems may constitute a reasonable alternative in the treatment of patella fractures.

The Use of Nitinol Compression Staple Fixation and Bone Graft for Scaphoid Waist Fractures and Nonunion: A Surgical Technique

In the management of scaphoid fractures, nonunion is an important complication that can lead to carpal instability and early-onset arthritis. Various techniques have been described to treat scaphoid nonunions, yet a clear consensus on the superiority of one method is not yet established. The use of compression staple fixation has been described in the literature and may be a viable alternative to other fixation techniques. Volar Nitinol staple fixation avoids damage to the trapezium during retrograde fixation with a screw. It also avoids damage to the proximal dorsal cartilage, which occurs during anterograde screw fixation. Because of its shape and position on the volar aspect of the scaphoid, staple fixation provides compression, prevents graft extrusion, and avoids taking up space in the medullary canal of the scaphoid. Moreover, it may be technically easier than screw fixation. Despite these advantages, this technique has not been widely adopted. We describe the technique for utilizing Nitinol compression staples and bone grafting in the treatment of scaphoid nonunion.

Novel techniques demonstrate superior fixation of simple transverse patella fractures - A biomechanical study

INTRODUCTION

Traditional tension band wiring (TBW) remains the gold standard treatment for simple transverse patella fractures. Challenges include appropriately siting and bending Kirschner wires without damaging surrounding soft tissues. Damage to soft tissues and malposition of metalwork can lead to complications. We propose three novel techniques for fixation of simple transverse patella fractures to ease application without additional resources to traditional TBW. We tested their biomechanical integrity against traditional TBW.

METHOD

Four configurations were tested; two with longitudinal Kirschner Wires (LKW) and two with cross Kirschner Wires (CKW) fixed with either standard figure-of-eight (AO) or side TBW (STBW). An initial proof of concept human cadaveric study was conducted to ensure real world application of the constructs was feasible. The fracture fixations were tested in a biomechanical study using porcine knees. The knees were cyclically loaded in a specially designed test rig through flexion from 90 to 45 degrees. Fracture gap displacement was measured and data blindly analyzed for all tests reaching 100 cycles.

RESULTS

17/22 specimens reached 100 cycles with peak loading ranging from 75 to 80 N. CKW with STBW performed best with average fracture displacement of 0.43 mm. LKW with STBW performed worst with average fracture displacement of 1.93 mm. The incremental displacement/cycle for both CKW configurations was 0.27 mm compared to 0.41 & 0.60 mm for both LKW constructs showing that the CKW configuration conferred greater fixation stiffness under cyclic loading.

DISCUSSION

Previous studies have compared alternative methods of patella fracture fixation to TBW through biomechanical superiority often requiring new resources. The methods tested here utilize the same resources as those for standard AO TBW. Reorientating the plane of the wires and position of the cerclage TBW may reduce iatrogenic soft tissue injury; reduce operating time and the risk of complications.

CONCLUSION

This study shows biomechanical superiority for CKW with either AO or STBW compared to LKW.

Biomechanical comparison of a 3.5 mm anterior locking plate to cannulated screws with anterior tension band wiring in comminuted patellar fractures

PURPOSE

To date, surgically treated multifragmentary patellar fractures are still associated with high rates of complications, such as i.e. secondary fracture displacement. Osteosynthesis is most frequently performed with screws and cerclages. To increase primary stability, locking plates have been introduced. However, there is still a lack of biomechanical data supporting the superiority of plate fixation compared to screw fixation with cerclages in these cases. The goal of the present study was to conduct biomechanical comparison of these two techniques under dynamic loading conditions.

METHODS

A standardized 34-C3 fracture was created in eight pairs of human cadaveric knee joints. Following a randomization protocol, they were fixed with a 3.5 mm anterior locking plate (LP) or cannulated screws with anterior tension band wiring (hybrid osteosynthesis, HO).Subsequently, all constructs were tested for 100 cycles from 90° of knee-flexion to full extension by applying a pulling force to the quadriceps tendon. Outcome parameters were fracture displacement after one cycle, after 100 cycles and implant loosening. Failure was defined as fracture displacement > 2 mm.

RESULTS

Biomechanical testing showed significantly less fracture displacement following LP compared to HO both after the first (p = 0.042) and after 100 cycles (p = 0.025). The difference in loosening was significant as well (p = 0.017). Following HO, 5/8 constructs failed during cyclic loading. There was no failure in the LP group. In the HO group, loosening correlated with bone mineral density (R = - 0.857) which was not observed in the LP group (R = - 0.429).

CONCLUSION

Anterior locking plate osteosynthesis of comminuted patellar fractures biomechanically provides better primary stability compared to cannulated screws with anterior tension band wiring.

Fracture Fixation Using Shape-Memory (Ninitol) Staples

Shape-memory alloy (SMA) staples are a recent innovation in fracture fixation. These staples have inherent compressive properties that create a stable fracture environment that promotes primary bone healing. They have been used successfully for osteotomies, arthrodesis, and fracture fixation. Understanding where SMA staple compression can be optimized and using proper indications are important for obtaining consistent success and minimizing failures. SMA staples are not a substitute for lag screw fixation or traditional plate and screw constructs.

Biomechanical Comparison of Tension Band Fixation of Patella Transverse Fracture: Headless Screws Versus Headed Screws

OBJECTIVE

This study aimed to investigate the stability and strength of tension band wire fixation using headless compression screws versus headed screws for transverse patella fractures.

METHODS

Six matched pairs of fresh-frozen cadaveric knees with transverse osteotomies created at the midpoint of the patella were surgically fixed, with one knee randomly receiving fixation with headless screws (Acumed Acutrak 4/5) and the other with headed screws (Synthes 4.0 partially threaded cannulated screws). The specimens were mounted onto a servohydraulic load frame in a 45-degree flexed position and loaded through the quadriceps tendon. Interfragmentary movement was recorded with a motion analysis system. The initial fixation stiffness, range of interfragmentary motion, and strength of the headless screw construct were compared with the headed screw construct. Failure was defined as either a sudden drop in applied tendon force or 2 mm of separation on the anterior surface of the patella (ie, clinical failure), whichever occurred first.

RESULTS

Mean primary interfragmentary motion was 0.31 ± 0.28 degrees for the headed screws and 0.10 ± 0.06 degrees for headless screws under 150 N load (P = 0.03). Mean construct stiffness was 277 ± 243 N/degrees for the headed screws and 510 ± 362 N/degrees for the headless screws (P = 0.03). None of the constructs from either group displayed structural failure before reaching the clinical failure gap of 2 mm. The mean clinical failure strength was 808 ± 183 N for the headless screws construct and 520 ± 241 N for the headed screws construct (P = 0.03).

CONCLUSIONS

Headless screw tension band fixation demonstrated superior biomechanical behaviors over standard headed screw fixation with higher construct rigidity, smaller interfragmentary motion, and greater fixation strength.

A Biomechanical Study of an Alternative Internal Fixation Method for Transverse Patella Fractures

Pain and reoperation after fixation using tension band wiring and K-wires is not uncommon. A novel hook plate was designed to improve the treatment of patella fractures. The aim of this study was to compare the stability of the hook plate with that of tension band wiring and K-wires in a simulated patellar transverse fracture model (AO/OTA classification 34-C1.1). The authors tested 16 embalmed cadaver knee joints fixed with the hook plate and tension band wiring and K-wires under cyclic loading. Specimens underwent 100 cycles extending the knee joint from 90° of flexion to full extension at a velocity of 50 mm/min. The fracture gap was measured after the initial and last cycles. Data were assessed statistically using the t test, with significance set as P<.05. The fatigue test showed that the fracture gap after 100 cycles was 2.97±1.39 mm using tension band wiring and K-wires and 1.53±0.93 mm for the hook plate (P=.029). Six of 8 specimens in the tension band wiring and K-wires group met the failure criterion of fracture gap greater than 2 mm vs 1 in the hook plate group (P=.041). From a biomechanical point of view, the hook plate is a valid alternative to tension band wiring and K-wires for fixing patella transverse fractures. Compared with tension band wiring and K-wires, the hook plate may have superior ability in sustaining a reduced transverse patella fracture. [Orthopedics. 2018; 41(5):e643-e648.].

A Locked Intraosseous Nail for Transverse Patellar Fractures: A Biomechanical Comparison with Tension Band Wiring Through Cannulated Screws

BACKGROUND

Displaced transverse patellar fractures require open reduction and internal fixation. State-of-the-art stabilization techniques are tension band wiring (TBW) using Kirschner wires or cannulated screws. These techniques are associated with high rates of secondary fracture displacement, implant migration, implant prominence, wound-healing disturbances, and the need for implant removal. Recently, a locked intraosseous patellar nail prototype was developed. The aim of the present study was to investigate the biomechanical performance of this nail compared with TBW using cannulated screws.

METHODS

Seven paired fresh-frozen human cadaveric knees were stripped of all soft tissues except the extensor apparatus. A transverse osteotomy was created to simulate an OTA/AO type 34-C1 transverse patellar fracture. The specimen pairs were randomly assigned to be fixed with TBW using cannulated screws or with the new intraosseous nail. Each specimen was cyclically tested for 5,000 cycles by pulling on the quadriceps tendon and simulating active knee extension and passive knee flexion within the range from 90° of flexion to full knee extension. Anterior and articular margin displacement of the fracture as well as interfragmentary rotation around the mediolateral axis were investigated with optical motion tracking after 100, 500, 1,000, 2,500, and 5,000 test cycles.

RESULTS

Within the respective 5 testing-cycle time points evaluated, the articular margin displaced on average 68%, 60%, 72%, 76%, and 81% less after intraosseous nailing compared with TBW. Whereas the difference remained nonsignificant after 100 and 500 cycles (p ≥ 0.116), a trend toward significance was observed after 1,000 cycles (p = 0.063), which became significant after 2,500 and 5,000 cycles (p ≤ 0.043).

CONCLUSIONS

From a biomechanical point of view, the locked intraosseous patellar nail may be an alternative to TBW using cannulated screws because of the higher interfragmentary stability provided at the articular fracture site.

CLINICAL RELEVANCE

A locked patellar nail for transverse patellar fractures achieved a stable osteosynthetic construct that may reduce hardware-associated complications because of its intraosseous positioning.

Biomechanical evaluation of simulated feline patellar fracture repairs

Objective: To investigate four techniques for stabilization of feline patellar fracture.

Methods: Feline cadaveric stifles with simulated patellar fracture were stabilized with one of four techniques: Group A - circumferential wire, group B - figure-of-eight wire, group C - combined figure-of-eight and circumferential wire, group D - pin and tension band wire. All repairs were subjected to a period of cyclic loading prior to load to failure testing. Experiments were recorded by video capture to determine load at failure and failure mode. Failure was defined as an opening of the fracture gap of 3 mm.

Results: Mean fracture gap opening (±SD) during peak loading after 1000 cycles was: group A with 1.66 mm (± 0.69), group B with 1.01 mm (± 0.45), group C with 0.81 mm (± 0.58), and group D with 0.65 mm (± 0.54). Groups C and D had significantly lower mean fracture gap opening after 1000 cycles when compared to group A (p <0.05). Mean loads (± SD) at failure were: group A with 171.4 N (± 62.2), group B with 208.7 N (± 20.7), group C with 288.2 N (± 62.5), and group D with 219.5 N (± 48.0). Group C had significantly higher mean load to failure than all other groups (p <0.05). There was no difference between other groups. In groups A, B and C the principle mode of failure was wire elongation and tearing of sutures through the retinaculae and periarticular soft tissues. In group D, the principle mode of failure was the pin pulling through the bone of the distal fragment.

Conclusions: Combined figure-of-eight and circumferential wires may be useful for treatment of transverse feline patellar fracture.

Biomechanical comparison of pin and tension-band wire fixation with a prototype locking plate fixation in a transverse canine patellar fracture model

Objective: To compare a locking plate (LP) with pin and tension-band wire (pin/TBW) for fixation of mid-patellar transverse fractures.

Materials and methods: Cadaveric canine stifle joints from 10 adult mixed breed dogs (23–36 kg) were used. Mid-patellar transverse osteotomies were randomly stabilized (in pairs) with either pin/TBW or a prototype LP. Cyclic loads (1 Hz, 500 cycles) at 100% body weight (90°-135° stifle joint extension), were applied. Survival or failure of constructs was defined as <2 mm fracture gap distraction at 500 cycles, or ≥ 2 mm fracture gap distraction at the number of cycles sustained, respectively. Number of cycles at failure and distraction gap were compared with a paired Student’s t-test, and a survival analysis performed with a Mantel-Cox test. All constructs that survived cyclic testing were tested in single cycle load to failure (1.0 mm/sec; 110° stifle joint extension); yield strength was compared with a Wilcoxon rank sum test. Significance was set at p <0.05.

Results: All 10/10 LP and three out of 10 pin/ TBW fixations survived cyclic testing. Survival analysis, number of cycles at failure, and distraction gap all were significantly different between the two groups (p = 0.0011, p = 0.0013, and p <0.0001, respectively). Construct yield strength was not significantly different (p = 0.1273).

Conclusions: The failure mode with pin/TBW was consistently similar to failures observed clinically. The LP demonstrated consistent, reliable and stable fixation.

This work was performed at the Biomechanics Orthopedic Research Laboratory, Cummings School of Veterinary Medicine at Tufts University, North Grafton, MA, USA.

Curettage Using Soft-wire for Enchondroma in the Hand: A Technical Note

Introduction:

Enchondromas are benign bone cartilaginous lesions predominantly seen in the hand, possibly leading to a pathological fracture. When the lesion expands to the whole phalanx, curettage through a small fenestration is difficult. To overcome the problem, soft-wire (cerclage wire) was used as a curette. Soft-wire is commonly used for a tension band wiring method for patellar or olecranon fractures.

Technique:

Two representative cases are presented: one is a 43-year-old male with enchondroma in the middle phalanx of the left index finger, and the other is a 28-year-old female with enchondroma in the distal phalanx of the right thumb. Surgery was performed in both cases under general anesthesia. The cortex adjacent to the lesion was approached dorsally, splitting the extensor tendon (the index finger case), or laterally (the thumb case). Fenestration of the cortex was performed with a 3.2-4 mm diameter surgical air drill. A bent and looped soft-wire of 0.7 or 0.9 mm diameter was threaded through the fenestration and used as a curette. Consequently, β-tricalcium phosphate particles were implanted. Bone incorporation was observed.

Conclusion:

This easy technique of curettage is a minimally invasive procedure for enchondroma. Moreover, the length of the skin incision and the size of the cortical fenestration are the same regardless of the size of the lesion.

Biomechanical evaluation of the tension band wiring principle. A comparison between two different techniques for transverse patella fracture fixation

PURPOSE

The aim of this study was to investigate the validity of the dynamic compression principle of tension band wiring in two techniques for patella fracture treatment.

METHODS

Twelve human cadaveric knees with simulated transverse patella fractures were assigned to two groups for treatment with tension band wiring using either Kirschner (K-) wires or cannulated screws. Biomechanical testing was performed over three knee movement cycles between 90° flexion and 0° full extension. Pressure distribution in the fracture gap and fracture site displacement were evaluated at the 3^rd cycle in 15° steps, namely 90°-75°-60°-45°-30°-15°-0° extension phase and 0°-15°-30°-45°-60°-75°-90° flexion phase.

RESULTS

Mean anterior / posterior interfragmentary pressure in the groups with K-wires and cannulated screws ranged within 0.16-0.40MPa / 0.12-0.35MPa and 0.37-0.59MPa / 0.10-0.30MPa, respectively. These changes remained non-significant for both groups and loading phases (P≥0.171). Mean anterior / posterior fracture site displacement for K-wires and cannulated screws ranged within -0.01-0.53mm / 0.11-0.74mm and 0.11-0.55mm / -0.10-0.50mm, respectively. Anterior displacement remained without significant changes for both groups and loading phases (P≥0.112). However, posterior displacement underwent a significant increase in the course of knee extension for K-wires (P≤0.047), but not for cannulated screws (P≥0.202). Significantly smaller displacement at the posterior fracture site was detected in the group with cannulated screws compared to K-wires at 60° and 75° extension phase (P≤0.017), as well as at 45°, 60° and 75° flexion phase (P≤0.018). The critical value of 2mm displacement at the posterior fracture site was not reached for any specimen and fixation technique. Knee extension was accompanied by synchronous increase in quadriceps pulling force.

CONCLUSIONS

Tension band wiring fulfills from a biomechanical perspective the requirements for sufficient stability of transverse patella fracture fixation. It should, however, rather be considered as a static fixation principle than a dynamic one. Tension band wiring with cannulated screws was found advantageous over Kirschner wires in terms of interfragmentary movements at the posterior fracture site.

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.

Titanium mesh as a low-profile alternative for tension-band augmentation in patella fracture fixation: A biomechanical study

OBJECTIVES

We performed a simple biomechanical study to compare the fixation strength of titanium mesh with traditional tension-band augmentation, which is a standard treatment for transverse patella fractures. We hypothesised that titanium mesh augmentation is not inferior in fixation strength to the standard treatment.

METHODS

Twenty-four synthetic patellae were tested. Twelve were fixed with stainless steel wire and parallel cannulated screws. Twelve were fixed with parallel cannulated screws, augmented with anterior titanium mesh and four screws. A custom test fixture was developed to simulate a knee flexed to 90°. A uniaxial force was applied to the simulated extensor mechanism at this angle. A non-inferiority study design was used to evaluate ultimate force required for failure of each construct as a measure of fixation strength. Stiffness of the bone/implant construct, fracture gap immediately prior to failure, and modes of failure are also reported.

RESULTS

The mean difference in force at failure was -23.0 N (95% CI: -123.6 to 77.6N) between mesh and wire constructs, well within the pre-defined non-inferiority margin of -260 N. Mean stiffness of the mesh and wire constructs were 19.42 N/mm (95% CI: 18.57-20.27 N/mm) and 19.49 N/mm (95% CI: 18.64-20.35 N/mm), respectively. Mean gap distance for the mesh constructs immediately prior to failure was 2.11 mm (95% CI: 1.35-2.88 mm) and 3.87 mm (95% CI: 2.60-5.13 mm) for wire constructs.

CONCLUSIONS

Titanium mesh augmentation is not inferior to tension-band wire augmentation when comparing ultimate force required for failure in this simplified biomechanical model. Results also indicate that stiffness of the two constructs is similar but that the mesh maintains a smaller fracture gap prior to failure. The results of this study indicate that the use of titanium mesh plating augmentation as a low-profile alternative to tension-band wiring for fixation of transverse patella fractures warrants further investigation.

Horizontal versus vertical orientation of the loop for tension band wiring of transverse patella fractures

Conventional operative treatments of patella fractures are frequently associated with implant failure or displacement. Recent biomechanical studies showed that the orientation of the wire loop and the site of the wire twist can affect the fixation strength. The purpose of this study was to compare the clinical outcome of the tension band technique with loops in different orientations and different knot positions. For this retrospective study, 72 patella fractures (71 patients) were fixed with figure-of-eight configurations in combination with 2 K-wires. Patients were divided into 3 groups according to the orientation of tension band construct. A total of 40 patella fractures were placed with figure-of-eight configurations in a vertical orientation either with 1 wire twist (group 1; 16 patella fractures) or with 2 wire twists at the adjacent corners (group 2; 24 patella fractures). Thirty-two patella fractures were placed with figure-of-eight configurations in a horizontal orientation with 2 wire twists at the adjacent corners (group 3). Range of motion, complication rates, and knee scoring scales (Hospital for Special Surgery and Lysholm) were assessed during serial follow-up. Satisfactory reductions were achieved in all groups, but functional results in the early stage were different. Group 3 had better Hospital for Special Surgery and Lysholm scores at 3 months postoperatively; however, at 6 months and 1 year postoperatively, all groups had similar scores. At the 1-year follow-up, all groups achieved acceptable flexion and range of motion. The overall complication rate was lower in the horizontal group (12.5%). Placing the figure-of-eight tension band construct in a horizontal orientation can provide functional benefits in the early stage after patella fractures.

Fixation of multifragmentary patella fractures using a bilateral fixed-angle plate

This biomechanical study is the first to compare 3 fixation methods-bilateral fixed-angle plate, modified anterior tension wiring, and cannulated lag screws with anterior tension wiring-in multifragmentary distal patella fractures. A T-shaped 3-part fracture simulating a multifragmentary articular distal patella fracture (AO/OTA 34-C2.2) was created in 18 human cadaver knee specimens. Three groups were created using homogenous ages and bone mineral densities based on the fixation method received. Repetitive testing over 100 cycles was performed by moving the knee against gravity from 90° flexion to full extension. Failure was defined as fracture displacement greater than 2 mm. In all patellae using fixed-angle plates, an anatomical fracture reduction could be maintained throughout cyclic testing, whereas anterior tension wiring and lag screws with tension wiring showed significant fracture displacement after 100 cycles, with mean fracture gaps of 2.0±1.3 and 1.9±1.6 mm, respectively. The differences in fracture gaps between the fixed-angle plate group and the other 2 groups were statistically significant. In both groups using tension wiring, half of the constructs (3 of 6 in each group) failed due to a fracture displacement greater than 2 mm. The bilateral fixed-angle plate was the only fixation method that sustainably stabilized a multifragmentary articular distal patella fracture during cyclic loading when compared with modified anterior tension wiring and cannulated lag screws with anterior tension wiring.

Cyclic long-term loading of a bilateral fixed-angle plate in comparison with tension band wiring with K-wires or cannulated screws in transverse patella fractures

PURPOSE

A bilateral fixed-angle plate was biomechanically compared to the two currently preferred methods of osteosynthesis for transverse patella fractures. It was hypothesized that the new angle-stable implant would provide a secure and sustainable fracture fixation, superior to the established standard techniques.

METHODS

Twenty-one identical patellae made of polyurethane foam (Sawbones(®)), osteotomized to create a transverse two-part fracture, were fixed with modified anterior tension wiring, cannulated lag screws with anterior tension wiring or bilateral polyaxial 2.7-mm fixed-angle plates. The testing protocol consisted of 10,000 repetitive cycles using a non-destructive physiological load between 100 and 300 N at a simulated knee flexion of 60°.

RESULTS

All 21 Sawbone(®)-patellae sustained repetitive loading up to 10,000 cycles without failing. The anterior tension wire group displayed significant displacement of the fracture gap (0.7 ± 0.2 mm) during cyclic loading, while both lag screws with tension wiring and bilateral fixed-angle plates showed no fracture gap widening at all (p < 0.01).

CONCLUSION

The bilateral fixed-angle plate and cannulated lag screws with anterior tension wiring preserved a constantly reduced fracture gap over 10,000 tensile cycles in contrast to modified anterior tension wiring, which exhibited significant widening of the gap after initial loading. Results of in vitro testing indicate that bilateral fixed-angle plates provide sustainable fixation stability offering a promising new option in the treatment for transverse patella fractures.

Biomechanical studies on transverse olecranon and patellar fractures: a systematic review with the development of a new scoring method

INTRODUCTION

Several methods of transverse patellar and olecranon fixation have been described. This article compares biomechanical studies of various fixation methods using a newly developed scoring method.

SOURCE OF DATA

The databases PubMed, Web of Science, Science Direct, Google Scholar and Google were searched for relevant studies.

AREAS OF AGREEMENT

Fixation hardware failure remains a problem. Various materials and fixation techniques have been tested to provide an improved fixation of transverse olecranon and patellar fractures.

AREAS OF CONTROVERSY

The difference in biomechanical testing setup between the studies makes it hard to compare different fixation techniques.

GROWING POINTS

The newly developed grading method was proved to be unbiased and reliable; however, extra specifications need to be added at some criteria when adopting the scoring method.

AREAS TIMELY FOR DEVELOPING RESEARCH

Non-metallic constructs may provide an improvement to the currently used metallic tension band wiring technique; however, clinical research is required.

Biomechanical cadaver testing of a fixed-angle plate in comparison to tension wiring and screw fixation in transverse patella fractures

INTRODUCTION

Operative treatment of patella fractures is frequently associated with implant failure and secondary dislocation which can be attributed to the employed hardware. Therefore, a 2.7 mm fixed-angle plate designed for the treatment of patella fractures was tested biomechanically against the currently preferred methods of fixation. It was hypothesized that under simulated cyclic loading fixed-angle plating would be superior to modified anterior tension wiring or cannulated lag screws with anterior tension wiring.

MATERIALS AND METHODS

Eighteen human cadaver knees, matched by bone mineral density and age, were divided into three groups of six. After setting a transverse patella fracture each group received one of the osteosyntheses mentioned above. Repetitive testing over 100 cycles was performed at non-destructive loads by simulating knee motion from 90° flexion to full extension.

RESULTS

Anterior tension wiring as well as lag screws with tension wiring showed significant fracture displacement after the initial cycle already. Both constructs, lag screws plus wiring (3.7 ± 2.7 mm) as well as tension wiring alone (7.1 ± 2.2 mm) displayed fracture displacement of >2 mm which is clinically regarded as failure. Those patellae stabilized with fixed-angle plates showed no significant fracture gap widening after completion of 100 cycles (0.7 ± 0.5 mm). The differences between the fixed-angle plate group and the other two groups were statistically significant (p<0.05).

CONCLUSION

In contrast to modified anterior tension wiring and cannulated lag screws with anterior tension wiring the bilateral fixed-angle plate was the only fixation device to stabilize transverse patella fractures securely and sustainably.

Cannulated screw and cable are superior to modified tension band in the treatment of transverse patella fractures

BACKGROUND

Although the modified tension band technique (eg, tension band supplemented by longitudinal Kirschner wires) has long been the mainstay for fixation of transverse fractures of the patella, it has shortcomings, such as bad reduction, loosening of implants, and skin irritation.

QUESTIONS/PURPOSES

We conducted a retrospective comparison of the modified tension band technique and the titanium cable-cannulated screw tension band technique.

PATIENTS AND METHODS

We retrospectively reviewed 101 patients aged 22 to 85 years (mean, 56.6 years) with AO/OTA 34-C1 fractures (n = 68) and 34-C2 fractures (n = 33). Fifty-two patients were in the modified tension band group and 49 were in the titanium cable-cannulated screw tension band group. Followup was at least 1 year (range, 1-3 years). Comparison criteria were fracture reduction, fracture healing time, and the Iowa score for knee function.

RESULTS

The titanium cable-cannulated screw tension band group showed improved fracture reduction, reduced healing time, and better Iowa score, compared with the modified tension band group. In the modified tension band group, eight patients experienced wire migration, three of these requiring a second operation. There were no complications in the titanium cable-cannulated screw tension band group.

CONCLUSIONS

The titanium cable-cannulated screw tension band technique showed superior results and should be considered as an alternative method for treatment of transverse patellar fractures.

LEVEL OF EVIDENCE

Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.