Background:Reoperation rates in clavicular fractures and acromioclavicular (AC) joint dislocations are high, often indicated for plate removal due to plate prominence and poor cosmesis. The recently designed 2.7 mm variable angle locking compression plate (VA-LCP®) Clavicle Plate and 2.7 mm VA-LCP® Clavicle Hook Plate (J&J MedTech) are intended to have an improved plate-to-bone fit, are precontoured, and have a low profile. Additionally, the Clavicle Hook Plate has a more anatomically adapted hook design to reduce the risk of painful osteolysis leading to earlier plate removals. All screw holes in these plates accept 2.7 mm screws. Primary objectives of this observational, post-marketing, prospective, multicenter case series are to gather early and mid- to long-term evidence on the clinical performance, safety, and usability of the 2.7 mm VA-LCP Clavicle Plates and 2.7 mm VA-LCP Clavicle Hook Plates, specifically to describe (1) safety, (2) clinical performance, (3) functional outcomes, (4) patient-reported outcomes (PROs) and (5) usability and surgeons' experience with the devices. Methods:Approximately 76 patients with clavicle fractures and primary surgical treatment with the 2.7 mm VA-LCP Clavicle Plate or 2.7 mm VA-LCP Clavicle Hook Plate will be enrolled prospectively over 15 months. Outcome measures include adverse events related/potentially related to the investigational device, clinical performance, functional outcomes (QuickDASH), PROs (PROMIS® upper extremity score, local pain, discomfort, and plate prominence), and radiographic outcomes. Data will be collected at baseline, 2w, 6w, 3m, 6m, 1y and 2y after surgery. The surgeons' experience with and perceived utility of the devices will be surveyed. Interim analysis will be performed when 30 patients per group have reached 6 months after surgery. Long-term outcomes will be evaluated using 2-year follow-up results. A Statistical Analysis Plan will be prepared before final analysis summarizing the descriptive statistics to be used. Discussion:The study described in this protocol on patients with clavicular fracture or AC joint dislocations undergoing surgical fracture fixation aims to gather first evidence on the clinical performance, safety, and usability of the 2.7 mm VA-LCP Clavicle Plates and 2.7 mm VA-LCP Clavicle Hook Plate Systems. This study will provide valuable data from a standard-of-care setting and may help design future comparative studies for relevant performance parameters. Clinical Trial Registration:https://clinicaltrials.gov/study/NCT04921865?term=NCT04921865%20&rank=1, identifier NCT04921865.

PURPOSE:Optimizing fracture reduction quality is key to achieve successful osteosynthesis, especially for epimetaphyseal regions such as the proximal humerus (PH), but can be challenging, partly due to the lack of a clear endpoint. We aimed to develop the prototype for a novel intraoperative C-arm-based aid to facilitate true anatomical reduction of fractures of the PH. METHODS:The proposed method designates the reduced endpoint position of fragments by superimposing the outer boundary of the premorbid bone shape on intraoperative C-arm images, taking the mirrored intact contralateral PH from the preoperative CT scan as a surrogate. The accuracy of the algorithm was tested on 60 synthetic C-arm images created from the preoperative CT images of 20 complex PH fracture cases (Dataset A) and on 12 real C-arm images of a prefractured human anatomical specimen (Dataset B). The predicted outer boundary shape was compared with the known exact solution by (1) a calculated matching error and (2) two experienced shoulder trauma surgeons. RESULTS:A prediction accuracy of 88% (with 73% 'good') was achieved according to the calculation method and an 87% accuracy (68% 'good') by surgeon assessment in Dataset A. Accuracy was 100% by both assessments for Dataset B. CONCLUSION:By seamlessly integrating into the standard perioperative workflow and imaging, the intuitive shape-matching-based aid, once developed as a medical device, has the potential to optimize the accuracy of the reduction of PH fractures while reducing the number of X-rays and surgery time. Further studies are required to demonstrate the applicability and efficacy of this method in optimizing fracture reduction quality.

Background and purpose: It is unclear whether total shoulder arthroplasty (TSA) results in better outcomes in patients with degenerative shoulder diseases compared with hemiarthroplasty (HA). This randomized controlled trial (NCT01288066) is an international, multicenter study with the primary aim to assess pain and shoulder joint function at 5-year follow-up in adults surgically treated with TSA or HA. Methods: The inclusion criteria were patients aged 18 and older with primary or secondary osteoarthritis, with a functionally intact rotator cuff and glenoid morphology of Walch type A1, A2, or B1. Randomization to either TSA or HA occurred intraoperatively after full surgical preparation for glenoid prosthetic implantation in all patients. The primary outcome measure was the Constant–Murley scores (CMS) at 5-year follow-up. Secondary outcomes were patient-reported outcomes (Shoulder Pain and Disability Index [SPADI], EQ-5D, and EQ VAS), adverse events, and implant survivorship at 5-year follow-up. Results: There were 79 patients eligible, of whom 40 and 39 patients were randomized to receive TSA or HA, respectively. The dropout rate at 5 years was 34% due to 27 of 79 patients withdrawing consent or being lost to follow-up. The mean CMS improved from preoperative to 5 years’ follow-up for both TSA and HA treatment groups. At 5 years, the TSA group had a significantly better mean CMS (77, 95% confidence interval [CI] 72–82) than the HA group (65, CI 57–73). The mean treatment difference was 12 (Cl 2.8–22; P = 0.01). The adverse event rate and relative risk of revision were not significantly different between the groups. Conclusion: In patients with glenohumeral osteoarthritis randomized to either TSA or HA, TSA was the favorable approach based on less pain and better joint function 5 years after surgery.

The survival rate of total elbow arthroplasty (TEA) is negatively impacted by the lack of available data on elbow biomechanics. This study developed a modified humeral component for TEA that is purposed to be instrumented to generate real-time 6 degrees of freedom (d.o.f) force and moment data during activities of daily living (ADL). The objectives are twofold: (1) to assess the safety of the modified humeral component under peak anticipated loads in fatigue, and (2) verify the strains measured under physiological loads with strains modelled using finite element analysis (FEA). Four modified titanium alloy humeral components were welded, and fatigue tested at 5 Hz for 5 million cycles under a compressive load of 700 N corresponding to moderate ADL. The strains were measured using triaxial 350 Omega rectangular rosette (45 degrees) strain gauges bonded to three specific locations on the humeral component confirmed through an FE study. The four welded humeral components successfully withstood fatigue conditions and did not deform. The measured and modelled principal strains were confirmed to be highest at the external wall of the lateral cavity, with a percentage difference of <10 %.

The Osteosynthesis App (OSapp, https://osapp.aofoundation.org/) is a freely available biomechanics knowledge hub conceived to address an apparent knowledge gap in the comprehension and application of principles of biomechanics to fracture fixation and healing. These principles, founded in Perren strain theory of fracture healing, are presented in a virtual learning environment familiar to surgeons in training and demonstrated through interactive, self-directed, 4-dimensional (4D) simulations. With >260 content pages (currently), the app has been viewed >1.5M times by >61,000 users from 185 different countries between September 2023 and August 2024. A real-time feedback poll, embedded in the OSapp website, showed that >90% of >1600 responders reported the content to be "very useful" or "useful". OSapp animations have been directly integrated into the "Basic techniques of fracture management" module of AO Surgery Reference. OSapp models have supplemented faculty presentations in AO Courses; subsequently, content is being integrated into Faculty Support material in collaboration with the AO Trauma Residents Educational Task Force. Six of the AO Skills Lab stations have been digitally replicated in OSapp to facilitate engagement in learning this important clinically relevant material, and encourage postevent reflective practice and permit distance learning. Using "gamification" as an educational concept in a virtual environment familiar to current generations of residents in training, it is anticipated that OSapp will become a valuable component of musculoskeletal education. In summary, the multiple applications of the virtual learning experience provided by OSapp are anticipated to enhance eventual clinical performance of the management of fractures.

OBJECTIVES This study aimed at evaluating the effectiveness of an online interactive biomechanical teaching tool called OSapp. Our main hypothesis was that through the presentation of appropriate science-based content in an interactive, self-directed learning environment familiar to residents the OSapp could significantly improve the knowledge, comprehension, and retention of clinically relevant biomechanical principles of osteosynthesis. DESIGN Thirty-one orthopaedic residents from the same institution were enrolled. Their knowledge of basic biomechanical principles of osteosynthesis was assessed using 24 multiple-choice questions, in 3 assessment rounds: at baseline; directly after a 1-week self-directed OSapp-based learning period; and 2 months later to measure retention. Results of the junior (1-3 years) and senior (4-5 years) resident groups were compared. SETTING Orthopaedics and Traumatology Department, Italian Hospital of Buenos Aires, Argentina. PARTICIPANTS Orthopaedic residents of the same Department at the time of investigation, including residency years 1 to 5. RESULTS Twenty-eight participants completed all 3 assessment rounds. Assessment scores significantly improved after the intervention compared to baseline (p < 0.05) and did not decline after 2 months (p > 0.99). Both juniors and seniors showed significant knowledge gain (p < 0.05) that was retained (p > 0.99). Although seniors were better than juniors at baseline (p ≤ 0.01) and postintervention (p < 0.05), after the intervention, juniors reached the level of baseline seniors (p > 0.21). No difference was observed between the 2 groups after 2 months (p > 0.21). CONCLUSIONS Self-directed learning with the interactive 3D models available in the freely available online tool OSapp led to a significant and sustained improvement of residents’ knowledge and understanding of the biomechanical principles of osteosynthesis. Utilizing OSapp in surgical education could help to improve the efficiency and effectiveness of training and may thus lead to decreased fracture treatment complications including failure of osteosyntheses.

BACKGROUND:Fatigue failure of osteosynthesis plates in load bearing constructs remains a significant clinical challenge, with plate working length (PWL) influencing stress distribution and implant life span. Despite conflicting evidence on PWL's impact, finite element (FE) models offer potential for predicting fatigue life, yet their application to PWL-specific fatigue in bone-plate constructs is limited. METHODS:This study investigated the effect of PWL on fatigue life in load bearing constructs using experimental cyclic testing and FE modeling. Synthetic bone models with a 10 mm osteotomy gap were stabilized with 3.5 mm stainless steel locking compression plates, testing short (1 empty hole), medium (3 empty holes), and long (5 empty holes) PWL configurations (N = 6 per group) under sinusoidal loading (260 N peak, 3 Hz). A second sub-study assessed the medium PWL across nine load levels (220-380 N). FE models, validated against experimental force-displacement curves, predicted cycles to failure using Basquin's stress-based criteria. Statistical analyses compared experimental and FE-predicted cycles. RESULTS:Shorter PWL significantly increased fatigue life (short: 1.19 × 106 ± 0.28 × 106 cycles; medium: 0.35 × 106 ± 0.07 × 106; long: 0.20 × 106 ± 0.04 × 106; p < 0.003). FE predictions closely matched experimental cycles for medium and long PWL (p > 0.05) but underpredicted for short PWL (p = 0.03), likely due to tied interface assumptions. Most short PWL constructs survived beyond 106 cycles, reaching up to 1.5 million cycles in the very high-cycle fatigue regime without failing, where Basquin's accuracy may decrease. Sub-study 2 showed a strong load-life correlation (R2 = 0.96), with FE predictions achieving high accuracy (CCC = 0.972, REE = 6.3 %). CONCLUSION:Shorter PWL enhances fatigue life in load bearing constructs by reducing plate stress, challenging traditional beliefs favoring longer PWL. FE models effectively predict fatigue life for medium and long PWL, supporting preoperative optimization, but require refinement for short PWL, including frictional contact modeling and alternative fatigue models for very high-cycle fatigue. Validation in physiological conditions is needed to enhance clinical applicability.

Objective Functional posterior shoulder instability (FPSI) (type B1) is a severe type of instability, mainly in teenagers and young adults, that leads to loss of function, pain, and stigmatization among peers. An experimental nonsurgical treatment protocol based on neuromuscular electrical stimulation (NMES) showed very promising early results in the treatment of FPSI. The hypothesis of this study was that NMES-enhanced physical therapy leads to better outcomes than physical therapy alone as the current gold standard of treatment in patients with FPSI. Methods In this multicenter randomized controlled trial, patients with FPSI were randomly allocated in a 1:1 ratio to either 6 weeks of physical therapy or 6 weeks of physical therapy with simultaneous motion-triggered NMES. Baseline scores as well as outcome scores at 6 weeks, 3 months, 6 months, and 12 months after the intervention were obtained. The predefined primary outcome of this trial was the Western Ontario Shoulder Instability Index (WOSI) at the 3-month time point. Results Forty-nine patients were randomized and eligible for the trial. The group that received physical therapy with simultaneous motion-triggered NMES showed a significantly better main outcome measurement in terms of the 3-month WOSI score (64% [SD = 16%] vs 51% [SD = 24%]). Two-thirds of the patients from the physical therapist group crossed over to the group that received physical therapy with simultaneous motion-triggered NMES due to dissatisfaction after the 3-month follow-up and showed a significant increase in their WOSI score from 49% [SD = 8%] to 67% [SD = 24%]. The frequency of instability episodes showed a significant improvement in the group that received physical therapy with simultaneous motion-triggered NMES at the 3-month follow-up and beyond, while in the physical therapist group, no significant difference was observed. Conclusion The current study shows that NMES-enhanced physical therapy led to statistically significant and clinically relevant improvement in outcomes in the treatment of FPSI compared to conventional physical therapy alone—from which even patients with prior unsatisfactory results after conventional physical therapy can benefit. Impact Based on the results of this study, NMES-enhanced physical therapy is an effective new treatment option for FPSI, a severe type of shoulder instability. NMES-enhanced physical therapy should be preferred over conventional physical therapy for the treatment of patients with FPSI.

Instability arthropathy of the sternoclavicular joint is most commonly managed by rehabilitation, injection, and either arthroscopic or open debridement with or without interposition arthroplasty. When these options fail to achieve symptom relief, excision arthroplasty is an option. This is associated with a risk of persistent instability and incomplete pain relief. We describe two cases in which custom sternoclavicular joint replacement was performed for painful insufficiency of scapular suspension. Although the prostheses remained secure in both cases, the first case was complicated by persistent instability due to insufficient reconstruction of the intrinsic sternoclavicular capsular ligaments. This was recognised and corrected for in the second case, in which stability of the sternoclavicular joint replacement has been noted on more than a 5-year review. We conclude that sternoclavicular joint replacement is an option for patients in whom instability arthropathy remains an intrusive problem in daily life after other conventional treatments have not controlled symptoms. Stability of the joint remains a concern. We offer one method of achieving stability through an iterative design process including the ability to reconstruct the intrinsic capsular ligaments around the articulation.

Good clinical practice guidelines are based on randomized controlled trials or clinical series; however, technical performance bias among surgical trials is under-assessed. The heterogeneity of technical performance within different treatment groups diminishes the level of evidence. Surgeon variability with different levels of experience-technical performance levels even after certification-influences surgical outcomes, especially in complex procedures. Technical performance quality correlates with the outcomes and costs and should be measured by image or video-photographic documentation of the surgeon's view field during the procedures. Such consecutive, completely documented, unedited observational data-in the form of intra-operative images and a complete set of eventual radiological images-improve the surgical series' homogeneity. Thereby, they might reflect reality and contribute towards making necessary changes for evidence-based surgery.

To evaluate the principal strain and von Mises stress on a humeral component of an elbow arthroplasty system.

Hardware prominence remains a clinical challenge in focus for implant design in subcutaneous plate applications. Existing evaluation of hardware prominence relies on plate-to-bone distance at a single point or on average. A reproducible measure for plate prominence remains undefined. This study mathematically defines the plate prominence linked to the cross-sectional area change due to the plate presence on the bone. Two anatomical plate designs were fitted to 100 clavicles, and afterwards plate prominence parameters were evaluated and compared. This methodology enables the quantification of hardware prominence for different plate designs to inform the development of implants targeting low prominence.

The periclavicular space is a conduit for the brachial plexus and subclavian-axillary vascular system. Changes in its shape/form generated by alteration in the anatomy of its bounding structures, e.g. clavicle malunion, cause distortion of the containing structures, particularly during arm motion, leading to syndromes of thoracic outlet stenosis etc., or alterations of scapular posture with potential reduction in shoulder function. Aim of this study was developing an in vitro methodology for systematic and repeatable measurements of the clinically poorly characterized periclavicular space during arm motion using CT-imaging and computer-aided 3D-methodologies. A radiolucent frame, mountable to the CT-table, was constructed to fix an upper torso in an upright position with the shoulder joint lying in the isocentre. The centrally osteotomized humerus is fixed to a semi-circular bracket mounted centrally at the end of the frame. All arm movements (ante-/retroversion, abduction/elevation, in-/external rotation) can be set and scanned in a defined and reproducible manner. Clavicle fractures healed in malposition can be simulated by osteotomy and fixation using a titanium/carbon external fixator. During image processing the first rib served as fixed reference in space. Clavicle, scapula and humerus were registered, segmented, and triangulated. The different positions were displayed as superimposed surface meshes and measurements performed automatically. Initial results of an intact shoulder girdle demonstrated that different arm positions including ante-/retroversion and abduction/elevation resulted solely in a transverse movement of the clavicle along/parallel to the first rib maintaining the periclavicular space. A radiolucent frame enabling systematic and reproducible CT scanning of upper torsos in various arm movements was developed and utilized to characterize the effect on the 3D volume of the periclavicular space. Initial results demonstrated exclusively transverse movement of the clavicle along/parallel to the first rib maintaining the periclavicular space during arm positions within a physiological range of motion.

To evaluate the principal strains and strain energy densities developed around a screwed glenoid prosthesis with a lateralised centre of rotation (COR) when subjected to functional loads.

Background and Objectives: Proximal humerus fractures (PHFs) are common in the elderly, but the treatment results are often poor. A clear understanding of fracture morphology and distribution of cortical bone loss is important for improved surgical decision making, operative considerations, and new implant designs. The aim of this study was to develop a 3D segmentation fracture mapping technique to create a statistical description of the spatial pattern and cortical bone loss of complex PHFs. Materials and Methods: Fifty clinical computed tomography (CT) scans of complex PHFs and their contralateral intact shoulders were collected. In-house software was developed for semi-automated segmentation and fracture line detection and was combined with manual fracture reduction to the contralateral template in a commercial software. A statistical mean model of these cases was built and used to describe probability maps of the fracture lines and cortical fragments. Results: The fracture lines predominantly passed through the surgical neck and between the tuberosities and tendon insertions. The superior aspects of the tuberosities were constant fragments where comminution was less likely. Some fracture lines passed through the bicipital sulcus, but predominantly at its edges and curving around the tuberosities proximally and distally. Conclusions: A comprehensive and systematic approach was developed for processing clinical CT images of complex fractures into fracture morphology and fragment probability maps and applied on PHFs. This information creates an important basis for better understanding of fracture morphology that could be utilized in future studies for surgical training and implant design.

BACKGROUND:Proximal humerus fractures (PHF) should be subject to standardized monitoring during treatment, whether non-operative or operative, to document and adequately assess bone healing. The purpose of this study was to develop a standardized protocol for an image-based monitoring of PHF for joint-preserving treatment options, including a minimum set of descriptors or definitions of features of radiographic images, to be applied in clinical routine practice and studies.METHODS:A Delphi exercise was implemented with an international panel of experienced shoulder trauma surgeons self-selected after invitation of all AO Trauma members. Using open questions participants recommended the type and timing of desired diagnostic images, and formulated definitions for the imaging parameters they considered most important. Formulated recommendations for the type and timing of radiological fracture monitoring and clarification of the definitions of the proposed radiological parameter set were subjected to further survey. Consensus for each factor was considered to have been reached when there was at least a two-thirds agreement in the survey participants.RESULTS:Response rates of 231 interested surgeons were 66% and 44% for the first and second survey respectively. Sixty percent of participants to the first survey responded to the second (131/219). 93% of respondents considered radiographic monitoring to be an important part of fracture care. 92% of respondents to the first survey considered that 'malreduction' should be assessed, and 165 of 189 respondents provided a suggestion for a definition for this parameter. 88% of respondents to the second survey agreed on a redefinition of the term 'malreduction' as 'non-anatomical fracture reduction'. There was substantial agreement about the radiographic views and orientation of radiographs to be recorded (80%) and the timing of radiological reviews (67- 78% for time points during follow up). Just over half of respondents recommended cessation of radiological review when fracture healing was considered to have occurred by radiological evaluation.CONCLUSION:Our work confirmed the need for clear definitions of radiological features that should be considered in the follow-up of proximal humeral fractures. It has resulted in the development of an international consensus monitoring protocol for PHF treatment with a structured core set of radiological parameters. Clinical application and validation of the monitoring process are needed.

Abstract Introduction The clinical and economic burden of clavicle fractures in England is not well documented. This study evaluated rates of surgical treatment, post-surgical complications, reoperations and costs in patients with clavicle fractures using the Clinical Practice Research Datalink (CPRD) database. Methods CPRD data were linked to National Health Service Hospital Episode Statistics data. Patients with a diagnosis of clavicle fracture between 2010–2018 were selected in CPRD (date of fracture = index date). Of those, patients with surgical intervention within 180 days from index fracture were identified. Rates of post-surgical complications (i.e., infection, non-union, and mal-union), reoperations (for device removal or for postoperative complications), post-operative costs and median time to reoperations were evaluated up to 2 years after surgery. Results 21,340 patients with clavicle fractures were identified (mean age 35.0 years(standard deviation (SD): 26.5), 66.7% male). Surgery was performed on 672 patients (3.2% of total cohort) at an average 17.1 (SD: 25.2) days post-fracture. Complications (i.e., infection, non-union, or malunion) affected 8.1% of surgically treated clavicle fracture patients; the rate of infection was 3.5% (95% CI, 1.7%- 5.2%), non-union 4.4% (95% CI, 2.4%-6.5%), and mal-union 0.3% (95% CI, 0%-0.7%). Adjusting for age, gender, comorbidities and time to surgery, the all-cause reoperation rate was 20.2% (13.2%-30.0%) and the adjusted rate of reoperation for implant removal was 17.0% (10.7%-25.9%)—84% of all-cause reoperations were thus performed for implant removal. Median time to implant removal was 254 days. The mean cost of reoperations for all causes was £5,000. The most expensive reoperations were for cases that involved infection (mean £6,156). Conclusions Complication rates following surgical clavicle fracture care averaged 8.1%. However, reoperation rates exceed 20%, the vast majority of reoperations being performed for device removal. Technologies to alleviate secondary device removal surgeries would address a significant clinical unmet need.

The functions of the subclavius muscle (SM) are described as stabilization of the sternoclavicular joint (SCJ) and resisting elevation of the lateral end of the clavicle. During systematic cadaveric dissections, we observed additional fibrous structures, previously described as variants of the anatomy, extending from the SM and inserting into the coracoid process (CP). Due to the high incidence of these structures in our dissections, we hypothesized that the attachment at the CP is more common than appreciated and that, as a corollary, the function of the SM was (or has been) more complex than simply depressing the clavicle and generating stability at the SCJ. For our investigation, fifty-two upper extremities of 26 human cadavers were dissected. The SM was demonstrated from costal to clavicular attachment. We documented additional fibrous structures apparently derived from the SM inserting into the CP. Measurements of the length of the SM, the length of its attachment, and the length of the clavicle were taken in situ, with the specimens supine and the upper extremity in the anatomical position. Variations in the anatomy of the SM and its coracoidal attachment were recorded, and potential correlations were investigated. For documentation purposes photographs and video sequences of passive motion of the shoulder girdle of the specimens were taken. In 49 of the 52 specimens we found additional fibrous structures passing from the SM to the CP. We differentiated three types: (1) a strong cord-like structure; (2) a small or thin cord-like structure or structures; and (3) a planar twisted sheet-like structure. The SM and its extension to the CP appears to contribute to a 'functional scapular suspension system' together with the other muscles enveloped by the clavipectoral fascia (pectoralis minor, coracobrachialis and the short head of the biceps brachii). This system assists in the control of the position of the scapula in relation to the thorax, particularly in elevated positions of the upper extremity. We speculate that the differentiation of the fibrous structure depends on the functional demands of the individual.

BACKGROUND:Minimally invasive plate osteosynthesis (MIPO) is one of the generally accepted surgical techniques for the treatment of humeral shaft fractures. However, despite the high bone union rate, a variety of complications are still prevailing. Moreover, the current literature lacks data comparing the anterolateral MIPO approach using dynamic compression plates accommodating different numbers of screws. The aim of this study was to analyze the biomechanical performance of comminuted humeral shaft fractures fixed with dynamic compression plates using either two or three screws per fragment.METHODS:Six pairs of fresh-frozen human cadaveric humeri from donors aged 66.8 ± 5.2 years were randomized to two paired study groups for simulation of bridge-plated comminuted shaft fracture type AO/OTA 12-C1/2/3 without interfragmentary bony support, using a dynamic compression plate positioned on the anterolateral surface and fixed with two (group 1) or three (group 2) screws per fragment. All specimens underwent nondestructive quasistatic biomechanical testing under lateral bending, anterior bending, axial bending, and torsion in internal rotation, followed by progressively increasing cyclic torsional loading in internal rotation until failure.RESULTS:Initial stiffness of the plated specimens in lateral bending, anterior bending, axial bending, and torsion was not significantly different between the groups (P ≥ 0.22). However, cycles to 10°, 15°, and 20° torsional deformation and cycles to construct failure were significantly higher in group 2 compared with group 1 (P ≤ 0.03).CONCLUSIONS:From a biomechanical perspective, no significant superiority is identified in terms of primary stability when using two or three screws per fragment for bridge compression plating of comminuted humeral shaft fractures. However, three-screw configurations provide better secondary stability and maintain it with a higher resistance towards loss of reduction under dynamic loading. Therefore, the use of a third screw may be justified when such better secondary stability is required.