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Clinical and Biomechanical Research

Orthopedic Research


Journal: Journal of Orthopaedic Trauma

Publication Date: July 2024

A Novel Bone-Screw-Fastener Demonstrates Greater Maximum Compression Force Before Failure Compared with a Traditional Buttress Screw 

Thorne, Tyler MD; Featherall, Joseph MD; O'Neill, Dillon MD; Lisitano, Leonard MD; Haller, Justin MD


This study compared the maximal compression force before thread stripping of the novel bone-screw-fastener (BSF) with the traditional buttress screw (TBS) in synthetic osteoporotic and cadaveric bone models. 


The novel bone-screw-fastener generated 11%–65% greater maximal compression force than the TBS in synthetic osteoporotic and cadaveric metaphyseal bone models. A greater compression force may increase construct stability, facilitate early weight-bearing, and reduce construct failure.

Journal: Orthopedics

Publication Date: September 6, 2023


Patient-Reported Outcomes and Computed Tomography Review After Minimally Invasive Fusion of the Sacroiliac Joint With Aggressive Joint Decortication and Joint Compression 

William W. Cross III, MD; Marko N. Tomov, MD; Michelle Y. Hung, PA-C, MS; Jeffrey M. Muir, MSc, DC, MSc (Clin Epi) 


The sacroiliac joint (SIJ) is a common, underrecognized source of low back pain. This study evaluated outcomes in patients undergoing sacroiliac joint fusion (SIJF) using a novel, minimally invasive SIJF system emphasizing compressive forces across an aggressively debrided SIJ. In this study, data was reviewed from a continuous set of patients presenting to a large, tertiary care hospital from September 2017 to August 2019. 


The benefits of this approach are evident in our rates of radiographic fusion, with independent radiographic review revealing at least partial signs of radiographic fusion in 98% of joints and definitive bone bridging (grade 3 fusion) in 81% of joints at 12-month follow-up. Our study demonstrated that a SJIF system based on the principles of joint fusion - aggressive decortication, autogenous bone grafting, and joint compression - was associated with early and durable improvements in both radiographic fusion and patient-related outcomes. The results of this study support the growing body of evidence that SIJF surgery benefits patients with SIJ dysfunction. 


Journal: International Journal of Spine Surgery

Publication Date: February 8, 2023

Patient-Reported and Radiographic Outcomes After Revision Sacroiliac Joint Fusion

Jeremy C. Thompson, MD; Erick Marigi, MD; and William W. Cross, III, MD


Sacroiliac joint fusion (SIJF) has been established as an effective treatment for sacroiliac joint dysfunction. However, failure necessitating revision has been reported in up to 30% of cases. The most common indications for revision SIJF are symptomatic pseudarthrosis and implant loosening. Little is known regarding outcomes of revision SIJF. This study (the largest series of revision SIJF to date) retrospectively reviewed all revision SIJF at a single academic center between 2017 and 2020. Revision surgery was performed using the principles of joint decortication, bone grafting, compression, and rigid internal fixation. 


Utilizing a principles-based technique of joint decortication, compression, and rigid internal fixation, revision SIJF showed an improvement in patient-reported outcomes as well as high rate of fusion at 12 months. In regard to Patient-Reported Outcomes, ODI and NPRS scores demonstrated significant statistical and clinical improvements at all postoperative timepoints. Postoperative Radiographic Outcomes, utilizing CT images at 12 months, reflected no signs of radiographic lucencies, implant subsidences, or implant fractures and an 88.9% fusion rate with definitive bridging bone across the SIJ. 

Journal: Long-Term Effects of Medical Implants

Publication Date: 2022

Can Partially Threaded Cannulated Screws Be Better Designed to Maximize Purchase in the Sacrum?

Shawn Boomsma, Ishaq Ibrahim, Nishant Suneja, Arvind G. von Keudell, & Michael J. Weaver


Current partially threaded screws have standardized thread lengths involving a small portion of the screw regardless of its overall length. The purpose of this study was to perform an imaging-based anatomic evaluation of the posterior pelvic ring to determine if the distance between the lateral cortex of the ilium and medial aspect of the SI joint (lateral sacral cortex) is a consistent value that may afford an anatomic basis upon which novel sacroiliac screws may be developed. We hypothesized that this distance would be consistent within the study population and follow a normal (Gaussian) distribution.


This is the first study to define the distance from the lateral ilium to the lateral sacrum and examine its application in optimizing treatment of posterior pelvic trauma. We showed the distance from the lateral ilium to lateral sacrum is consistent and this information can be used to create improved partially threaded screws to optimize purchase within the sacrum during the surgical fixation of posterior pelvic ring injuries.

Journal: Injury

Publication Date: October 18, 2019

Biomechanical comparison of bone-screw-fasteners versus traditional locked screws in plating female geriatric bone

Malcolm R DeBaun , Steven T Swinford, Michael J Chen, Timothy Thio, Anthony A Behn, Justin F Lucas, Julius A Bishop, Michael J Gardner


To biomechanically compare plated constructs using nonlocking bone-screw-fasteners with interlocking threads verses locking screws with traditional buttress threads in geriatric female bone.


In female geriatric bone, constructs fixed with bone-screw-fasteners incorporate multiplanar interlocking thread geometry and performed similarly to traditional locked plating.

Journal: Journal of Orthopedic Trauma

Publication Date: April 2019

A New Fastener With Improved Bone-To-Implant Interface Shows Superior Torque Stripping Resistance Compared With the Standard Buttress Screw

Nicholas A Alfonso, Todd Baldini, Philip F Stahel


The conventional AO buttress screw used for fracture fixation relies on a historic buttress thread design, which is prone to stripping at the bone–implant interface. We hypothesized that a new Bone-Screw-Fastener with an innovative interlocking thread design demonstrates increased resistance to torque stripping forces compared with the buttress screw, without compromising pullout strength.


These data demonstrate the superiority of the new Bone-Screw-Fastener over the conventional AO buttress screw regarding protection from torque stripping forces. In addition, the new thread design that interlocks to the bone does not sacrifice axial pullout resistance conveyed by the buttress screw. Future controlled trials will have to validate the in vivo relevance of these findings in a clinical setting.

Journal: Injury

Publication Date: January 2019

Ideal Length of Thread Forms for Screws Used in Screw Fixation of Nondisplaced Femoral Neck Fractures

Christina Liu, Arvind Von Keudell, Michael McTaguec, Edward K. Rodrigueza, Michael J. Weaver


The purpose of this study is to determine the thread length that will maximize purchase within the femoral head while minimizing risk of crossing the fracture line. Additional analysis was conducted to identify factors associated with the maximal possible length of treads in minimally and non-displaced femoral neck fractures.


It appears that the current thread-length options available are not ideal for the fixation of minimally displaced and minimally angulated femoral neck fractures. Given the common occurrence of these injuries, fracture implants should be designed to optimize purchase within the bone while maintaining the lag screw function of the implants. The addition of a 26 mm thread length screw would substantially increase the surface area of the treads making contact within the cancellous bone of the femoral head without crossing the fracture line in the vast majority of patients.

Journal: International Journal of Spine Surgery

Publication Date: October 15, 2018

In Vitro Biomechanical Evaluation of a Novel, Minimally Invasive, Sacroiliac Joint Fixation Device

William W. Cross III, MD, Sigurd H. Bergen, MD, Nick Slater, MS, Jennifer N. Lehrman, MS, Anna G. U. S. Newcomb, MS, and Brian P. Kelly, PHD


Sacroiliac (SI) joint pathology may result in low-back pain, which causes substantial disability. Treatment failure with operative management of SI pain may be related to incomplete fusion of the joint and to fixation failure. The objective of this study was to evaluate the initial biomechanical stability of SI joint fixation with a novel implantable device in an in vitro human cadaveric model.


Instrumentation with the SI screw fixation device significantly reduced mean joint ROM compared to the destabilized condition, with similar ROM in flexion-extension and axial rotation, and it significantly reduced ROM in lateral bending compared to that for the intact joint. The ROM values observed with the instrumented condition were comparable to levels of mobility considered favorable for spinal fusion.

Journal: The Open Orthopedics Journal

Publication Date: December 29, 2017

Minimally Invasive Sacroiliac Joint Fusion: 2-Year Radiographic and Clinical Outcomes with a Principles-Based SIJ Fusion System

William W Cross, Arnold Delbridge, Donald Hales and Louis C Fielding


Sacroiliac joint (SIJ) degeneration is a common source of low back pain (LBP). Minimally invasive (MI) SIJ fusion procedures have demonstrated meaningful clinical improvement. A recently developed MI SIJ fusion system incorporates decortication, placement of bone graft and fixation with threaded implants (DC/BG/TF).


The patients in this series demonstrated significant improvement in LBP. Fusion rates at 24 months demonstrate promise for this system, which utilizes the established orthopedic principles of DC/BG/TF to achieve arthrodesis. Further study is warranted to demonstrate comparative fusion rates for different implant systems.

Journal: Patient Safety in Surgery

Publication Date: March 20, 2017

Introducing the "Bone-Screw-Fastener" for improved screw fixation in orthopedic surgery: A revolutionary paradigm shift?

Philip F Stahel, Nicholas A Alfonso, Corey Henderson, Todd Baldini


We hypothesize that the new Bone-Screw-Fastener overcomes the classic shortcomings of conventional orthopedic screws with buttress threads by ease of insertion, improved bone preservation, increased resistance to off-axis multidirectional loading forces and to stripping of the threads. These advanced biomechanical and biological properties can potentially mitigate the classic limitations of conventional buttress screws by providing better resistance to implant failure under physiological loads, preserving bone biology, and thus potentially improving patient outcomes in the future.

Implications of Hypothesis

Once validated in multicenter RCTs, the new Bone-Screw-Fastener may drive a change in paradigm with regard to its innovative biomechanical principles and biologic bone preservation for surgical applications requiring screw fixation.

International Society of Limb Salvage 21st Annual Conference

Los Angeles, CA 2022

A Mechanical Integration Rationale for Securing Implants to Bone in Orthopedic Oncology


A mechanical integration rationale can be used to design orthopedic implants for use in bone. Initial mechanical testing demonstrates several benefits over a standard thread form. There are likely to be several clinical benefits associated with this type of design, which in particular benefit the orthopedic oncology population including multi-axial stability in compromised bone, shorter implants to allow for revision, and better load sharing/distribution to complement osseointegration.

Abraham JA, Geller DS, Fauth AR, Bitter J, Paul R.

Design Elements of a Mechanically Integrated Intramedullary Stem for use in Orthopedic Oncology


A mechanically integrated intramedullary implant represents an entirely novel approach and may have significant benefits over traditional methods of fixation of implants to bone, particularly in the orthopedic oncology population. Initial Early FEA and biomechanical testing are encouraging and demonstrate more even force distribution and more intimate contact between the bone and the implant under dynamic conditions.

Abraham JA, Geller DS, Fauth AR, Bitter J, Paul R.

Musculoskeletal Tumor Society Annual Meeting

Clearwater, FL 2022

Design Elements of an Intramedullary Stem Utilizing a Mechanical Integration Rationale


Mechanical integration offers an innovative method to connect implants to bone in tumor/limb salvage scenarios. The transfer of applied stress is circumferential and independent of the direction of applied force, as shown by FEA. A mechanically integrated stem may achieve superior fixation to a traditional stem, even at a shorter length. Removal of a mechanical integrate stem may be easier or mitigate bone loss.

Abraham JA, Geller DS, Fauth AR, Bitter J, Paul R.

Veterinary Research

Journal: Frontiers in Veterinary Science

Publication Date: June 29, 2023

Ex Vivo Biomechanical Evaluation of a Bone-Screw-Fastener for Tibial Plateau Leveling Osteotomy

William S. Kettleman, Michael H. Jaffe, Robert W. Wills, Sara J. Dietz, and Steve H. Elder


The objective of this study was to investigate the effect of a novel screw type on stiffness and failure characteristics of a tibial plateau leveling osteotomy (TPLO) construct under cyclic loading conditions. The authors hypothesized that bone-screw-fasteners (BSF) would result in superior biomechanical stability compared with locking buttress screws (LBS).


The findings of this current study suggest that stabilization of the TPLO with bone-screw-fasteners provided no advantage to biomechanical stability under cyclic axial loading conditions when compared to the locking buttress screw. Bone-screw-fasteners may be an acceptable alternative to traditional locking screws for TPLO. Further research, particularly in vivo experiments, is warranted prior to clinical application.

American College of Veterinary Surgeons (ACVS) Surgery Summit 2022

Evaluation of Novel Compression Screw


Headless compression screws with UnifiMI were evaluated biomechanically in frontal plane slab fractures of the radial facet in third carpal bone fractures of racehorses. UnifiMI headless compression screws compared favorably to standard 3.5mm AO cortical screws and eliminated the need to countersink which may decrease the odds of fragmentation and soft tissue irritation.

Salinger A., Mochal-King C., Priddy L, Clinton K, Wills R, & Jaffe M.

UC Davis - Conference Presentation - American College of Veterinary Surgeons (ACVS) Surgery Summit - E-Resident’s Forum 2020

Biomechanical Comparison of an Interlocking Thread Screw and a Buttress Thread Screw for Fixation of a Simulated Slab Fracture in Cadaveric Adult Equine Third Carpal Bone

Biomechanical Comparison of a Biaxial Thread Screw and a Uniaxial Thread Screw for Fixation of a Simulated Slab Fracture in Cadaveric Adult Equine Third Carpal Bone


Screw insertion variables and shear strength were studied in simulated audult equine third carpal slab fractures.  Buttress screws and UnifiMI fasteners were compared in static shear loading. Constructs with UnifiMI fasteners showed median peak torque and max torque values three times higher than constructs with standard buttress screws. Fractures repaired with UnifiMI fastners showed a 30% increase in yield strength and showed 33% more displacement prior to failure.

Pye J, Garcia T, Kapatkin A, Stover S.

Veterinary Orthopedic Society (VOS) Conference, Sun Valley, ID 2020

In Vitro Biomechanical Comparison of Drilling, Screw Insertion and Pullout Strength Variables of Interlocking and Buttress Thread Self-Tapping 3.5 mm Cortical Bone Screws in Cadaveric Equine Third Metacarpal Condyle


Drilling, screw insertion, and pullout properties were compared between standard 3.5mm buttress screws and 3.5mm UnifiMI fasteners. Matched pair equine third metacarpal bones were used to measure drill torque, force, displacement, and bone surface temperature between standard orthopedic drill bits and Osteoguard drill bits. Screw/fastener insertion torque, and screw/fastener pullout force were compared between buttress and UnifiMI implants. Max axial force,  torque, and bone temperature changes were lower for Osteoguard drill bits. Peak torques for UnifiMI were higher than standard screws, potentially indicating better bone engagement. There were no significant differences in axial pull-out measures.

Pye J, Garcia T, Kapatkin A, Stover S.

American College of Veterinary Surgeons (ACVS) Surgery Summit - E-Resident’s Forum 2020

Interlocking Thread Screws Enhance Repair Strength in Simulated Adult Canine Humeral Condylar Fractures


UnifiMI Fasteners, Buttress Lag Screws, and Locking Buttress Screws were compared bio-mechanically in simulated canine humeral condylar fractures. Insertion torque measurements were the highest for the UnifiMI Fasteners, and mean load to failure for UnifiMI constructs were higher than Locking Buttress Screws. Mean residual condylar fragment rotation was less for the UnifiMI constructs than the Buttress constructs, indicating greater rotational stability of the fragment.

Raleigh JS, Filliquist B, Kapatkin AS, et al.

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