Biomechanical comparison of anatomical plating systems for comminuted distal humeral fractures

Biomechanical Design Optimization of Distal Humerus Fracture Plates: A Review

The goal of this article was to review studies on distal humerus fracture plates (DHFPs) to understand the biomechanical influence of systematically changing the plate or screw variables. The problem is that DHFPs are commonly used surgically, although complications can still occur, and it is unclear if implant configurations are always optimized using biomechanical criteria. A systematic search of the PubMed database was conducted to identify English-language biomechanical optimization studies of DHFPs that parametrically altered plate and/or screw variables to analyze their influence on engineering performance. Intraarticular and extraarticular fracture (EAF) data were separated and organized under commonly used biomechanical outcome metrics. The results identified 52 eligible DHFP studies, which evaluated various plate and screw variables. The most common plate variables evaluated were geometry, hole type, number, and position. Fewer studies assessed screw variables, with number and angle being the most common. However, no studies examined nonmetallic materials for plates or screws, which may be of interest in future research. Also, articles used various combinations of biomechanical outcome metrics, such as interfragmentary fracture motion, bone, plate, or screw stress, number of loading cycles to failure, and overall stiffness (Os) or failure strength (Fs). However, no study evaluated the bone stress under the plate to examine bone "stress shielding," which may impact bone health clinically. Surgeons treating intraarticular and extraarticular distal humerus fractures should seriously consider two precontoured, long, thick, locked, and parallel plates that are secured by long, thick, and plate-to-plate screws that are located at staggered levels along the proximal parts of the plates, as well as an extra transfracture plate screw. Also, research engineers could improve new studies by perusing recommendations in future work (e.g., studying alternative nonmetallic materials or "stress shielding"), clinical ramifications (e.g., benefits of locked plates), and study quality (e.g., experimental validation of computational studies).

The feasibility, acceptability, safety, and effects of early weight bearing in humeral fractures - a scoping review

PURPOSE

Non-weight bearing is often recommended after humeral fractures. This review aims to summarise the extent and nature of the evidence for the feasibility, acceptability, safety, and effects of early weight bearing (EWB) in people with humeral fractures, treated operatively or non-operatively. .

METHODS

Data sources identified published (PUBMED, EMBASE, CINAHL) and unpublished (ClinicalTrials.gov, CENTRAL, NIHR Open Research, OpenGrey) literature. Independent data extraction was conducted by two reviewers.

RESULTS

13 901 records were retrieved. Ten studies, involving 515 post-operative patients and 351 healthcare professionals, were included. EWB was found to be feasible in nine studies. There was limited evidence regarding adherence to EWB. Trauma and orthopaedic surgeons reported that EWB was acceptable. This depended on surgery type and whether it was a post-operative polytrauma case. No acceptability data was reported from patients' perspectives. Only one study reported two patients who developed unsatisfactory outcomes from excessive post-operative EWB. Positive effects of EWB were reported on disability level, pain, shoulder and elbow motion, and union.

CONCLUSION

There is some evidence for the feasibility, safety, and effectiveness of post-operative EWB after humeral fractures. There was limited data on the acceptability of EWB. Heterogeneous study designs, and variations in EWB protocols limit conclusions.

Weak Points of Double-Plate Stabilization Used in the Treatment of Distal Humerus Fracture through Finite Element Analysis

BACKGROUND

Multi-comminuted, intra-articular fractures of the distal humerus still pose a challenge to modern orthopedics due to unsatisfactory treatment results and a high percentage (over 50%) of postoperative complications. When surgical treatment is chosen, such fractures are fixed using two plates with locking screws, which can be used in three spatial configurations: either parallel or one of two perpendicular variants (posterolateral and posteromedial). The evaluation of the fracture healing conditions for these plate configurations is unambiguous. The contradictions between the conclusions of biomechanical studies and clinical observations were the motivation to undertake a more in-depth biomechanical analysis aiming to indicate the weak points of two-plate fracture stabilization.

METHODS

Research was conducted using the finite element method based on an experimentally validated model. Three variants of distal humerus fracture (Y, λ, and H) were fixed using three different plate configurations (parallel, posterolateral, and posteromedial), and they were analyzed under six loading conditions, covering the whole range of flexion in the elbow joint (0-145°). A joint reaction force equal to 150 N was assumed, which corresponds with holding a weight of 1 kg in the hand. The biomechanical conditions of bone union were assessed based on the interfragmentary movement (IFM) and using criteria formulated by Steiner et al. Results: The IFMs were established for particular regions of all of the analyzed types of fracture, with distinction to the normal and tangential components. In general, the tangential component of IFM was greater than normal. A strong influence of the elbow joint's angular position on the IFM was observed, with excessive values occurring for flexion angles greater than 90°. In most cases, the smallest IFM values were obtained for the parallel plaiting, while the greatest values were obtained for the posteromedial plating. Based on IFM values, fracture healing conditions in particular cases (fracture type, plate configuration, loading condition, and fracture gap localization) were classified into one of four groups: optimal bone union (OPT), probable union (PU), probable non-union (PNU), and non-union (NU).

CONCLUSIONS

No plating configuration is able to ensure distal humerus fracture union when the full elbow flexion is allowed while holding a weight of 1 kg in the hand. However, flexion in the range of 0-90° with such loadings is acceptable when using parallel plating, which is a positive finding in the context of the early rehabilitation process. In general, parallel plating ensures better conditions for fracture healing than perpendicular plate configurations, especially the posteromedial version.

Cadaveric biomechanical assessment of different configurations for a novel pin and plate fixation method in distal humerus fractures

Use of dual pre-contoured plates has been accepted as the treatment of choice in distal humerus fractures despite challenges especially in very distal or highly fragmented fractures. Aiming to improve results in such instances, our newly proposed method uses several K-wires fixated by a small reconstruction plate. Drawing on the results of previous finite element studies, the current study aims to compare the stiffness of three clinically common variations of this method using biomechanical testing in cadaveric humeri. 24 samples were divided into three groups and fractures were simulated. Groups I and II used 1.5 mm K-wires in differing configurations while 2 mm wires were used in group III. All samples underwent compression, anterior and posterior bending, and torsional testing as well as failure testing. Our results indicated that Group III had significantly higher stiffness in flexion, extension, and torsion (p < 0.05). In failure, group III had the highest mean stiffness in anterior bending and torsion (861.2 N, 30.9 Nm). Based on previous and current results, this new Persian fixation method, especially when implemented using 2 mm K-wires, shows promise in achieving suitable stability and may be useful as an alternative approach in complex distal humerus fractures.

Biomechanical analysis of a novel Y-plate designed for the treatment of extraarticular distal humerus fractures

Adult distal humerus fractures are infrequent, yet they account for one-third of all humerus fractures. For the treatment of comminuted and osteoporotic fractures, locking plates are claimed to be biomechanically superior to alternative internal fixing techniques. Treatment remains difficult despite recent advancements and the use of locking plates due to frequent comminution, low bone quality, and limited healing ability in osteoporotic bone. An optimal design of the newly constructed plate and the control model were selected. The biomechanical characteristics of non-osteoporotic and osteoporotic synthetic bone were compared on six models. The biomechanical properties of the new plate were tested and compared on 54 osteoporotic synthetic humerus models. The control models were reconstructive and parallel LCPs. The tests were carried out under static and dynamic axial, lateral and bending loads. Fracture displacements were measured by optical measuring system Aramis. The test model is significantly stiffer for lateral load (p = 0.0007) and for bending load at the moment of model failure (p = 0.0002), while for axial load the LCP model showed greater stiffness (p = 0.0017). During lateral dynamic loading, all three LCP models broke and there was a significant difference compared to the test model (p = 0.0125). The LCP model is dynamically significantly more durable under axial load, while the largest displacements were recorded with the test model (p = 0.029). The displacements induced by all three loads are within the limits that fulfil the parameters of appropriate biomechanical stability. A novel locking plate for extra-articular distal humerus fractures may provide an alternative to the traditional two-plate.

Biomechanical comparison of three internal fixation configurations for low transcondylar fractures of the distal humerus

BACKGROUND

We aimed to evaluate the biomechanical stiffness and strength of different internal fixation configurations and find suitable treatment strategies for low transcondylar fractures of the distal humerus.

METHODS AND MATERIALS

Thirty 4^th generation composite humeri were used to create low transcondylar fracture models that were fixed by orthogonal and parallel double plates as well as posterolateral plate and medial screw (PPMS) configurations (n=10 in each group) using an anatomical locking compression plate-screw system and fully threaded medial cortical screws. Posterior bending (maximum 50 N), axial loading (maximum 200 N) and internal rotation (maximum 10 N·m) were tested, in that order, for each specimen. Stiffness under different biomechanical settings among different configurations were compared. Another 18 sets of fracture models were created using these three configurations (n=6 in each group) and the load to failure under axial loading among different configurations was compared.

RESULTS

Under posterior bending, the stiffness of parallel group was higher than orthogonal group (P<0.001), and orthogonal group was higher than PPMS group (P<0.001). Under axial loading, the stiffness of parallel group was higher than orthogonal group (P=0.001) and PPMS group (P<0.001); however, the difference between orthogonal and PPMS group was not statistically significant (P>0.05). Under internal rotation, the stiffness of parallel group was higher than orthogonal group (P=0.044), and orthogonal group was higher than PPMS group (P=0.029). In failure test under axial loading, the load to failure in the orthogonal group was lower than parallel group (P=0.009) and PPMS group (P=0.021), but the difference between parallel group and PPMS group was not statistically significant (P>0.05). All specimens in orthogonal group demonstrated "distal medial failure"; most specimens had "distal medial and trochlear failure" in the parallel group; most specimens exhibited "contact failure" in the PPMS group.

CONCLUSION

For treating low transcondylar fractures, the overall stiffness and strength of the parallel configuration were superior to those of the orthogonal and PPMS configurations. Nevertheless, the PPMS configuration can provide adequate stability and stiffness comparable to double-plate configurations under axial loading. Therefore, the PPMS construct may have certain clinical value.

Hemiarthroplasty for the treatment of distal humerus fractures: long-term clinical results

BACKGROUND

Total elbow arthroplasty is a treatment for unreconstructable distal humerus fractures; implant longevity remains a concern, especially in younger patients. However, distal humeral hemiarthroplasty (DHH) offers an alternative with potential long-term advantages.

METHODS

This is a retrospective study of 10 patients who underwent DHH for distal humerus fractures over a 4-year period (2008-2012) by a single surgeon. Patients underwent testing of range of motion, Mayo Elbow Performance Scores (MEPS), Disabilities of the Arm, Shoulder, and Hand questionnaire (DASH), visual analog scale (VAS), Single Assessment Numeric Evaluation (SANE), Simple Shoulder Test, Charlson Comorbidity Index (CCI), and American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES) scores. Average patient age at surgery was 71.9 years (range 56-81 years); average follow-up was 115.2 months (range 96-144 months).

RESULTS

Patients maintained improvements in MEPS (mean 88, range 75-100) and DASH scores (mean 37.1, range 11.21-55.09), along with no statistically significant decrease in range of motion or scores in comparison to either short- or midterm results. Mean VAS score was 2.2 (range 0-7), SANE 69 (range 55-85), ASES 76.66 (range 51.67-100), and CCI 4.3 (range 1-7). Participants had an average flexion of 126° (range: 90°-140°), extension of 36° (range: 30°-45°), supination of 66° (range: 60°-70°), and pronation of 64° (range: 45°-80°). No elbow dislocations, subluxations, or heterotopic ossification were observed. Complications included 1 fracture and 1 complaint of prominent hardware. Four patients were deceased, and 1 patient was lost to follow-up.

CONCLUSION

This long-term review suggests that DHH may be an effective treatment for certain distal humerus fractures. The data suggest that elbow range of motion and functional use are maintained from comparison with short- and midterm studies, with no appreciable change in radiographic cartilage wear along the radius or ulna.

Modified pin and plate fixation for low intercondylar fractures of the humerus: biomechanical study corroborated with a case series

BACKGROUND

Establishing fracture union of low and comminuted intercondylar fractures of the humerus is inherently challenging. The purposes of the present study were to investigate the biomechanical effectiveness of pin & plate (PP) fixation compared to other dual-plating techniques by finite element analysis, and to present a technical description as well as retrospectively review the outcomes of PP fixation in such difficult fractures.

METHODS

Low-level intercondylar fracture 3D models of the humerus were virtually stabilized with three fixations on lateral side including PP, lateral pre-contoured locking compression plate (L-LCP), and variable angle lateral pre-contoured locking plate (VA-L-LCP) whereas medial pre-contoured locking compression plate (M-LCP) on medial side. Loading conditions under consideration were axial compression, internal rotation, posterior bending, and valgus rotation. Regarding the clinical series, eight patients with intra-articular and comminuted fractures of the distal humerus (6 intercondylar fractures, 1 fracture-subluxation, and 1 isolated lateral condylar fracture) were operated by isolated PP fixation or combinations of PP and the other standard implants. Data were collected on fracture union, perioperative complications, and objective clinical outcomes.

RESULTS

Biomechanical results revealed the most instability of the fracture occurring under posterior bending. PP fixation presented comparable fracture stability and fragment displacement compared to other dual-plating fixations, except stress on the Kirschner wire under internal rotation which was higher than other fixations. Regarding the clinical series, fracture union was achieved in all cases with an average union time of 17 weeks (range 12-20). All except one patient had good-to-excellent MEPS results with an average Disabilities of the Arm, Shoulder, and Hand (DASH) score of 14.6 (range 0-45) and an average arc of elbow motion of 107.5 degrees (range 60-140).

CONCLUSION

By the biomechanical performance, PP fixation is a reliable technique for fixation of low intercondylar fractures of the humerus. Supported by the clinical outcomes, the present technique could be an alternative for this particular fracture especially when severe comminution prevents the use of the standard dual plating technique.

Does posterior configuration have similar strength as parallel configuration for treating comminuted distal humerus fractures? A cadaveric biomechanical study

BACKGROUND

The posterior plating technique could be used as a clinical alternative to parallel plating for treating comminuted distal humerus fractures (DHFs) successfully with good clinical results. However, the biomechanical characteristics for posterior fixation are still unclear. The purpose of this study is to evaluate the biomechanical properties of the posterior fixation and to make comparisons between the parallel and the posterior fixation systems.

MATERIALS AND METHODS

We performed a cadaveric biomechanical testing with two posterior plating systems (a posterior two plating and a single posterior pre-contoured Y plating system) and one parallel two plating system to treat AO/OTA type-C2.3 DHFs. Among three groups, we compared construct stiffness, failure strength, and intercondylar width changes after 5000-cycle fatigue loading and failure loads and failure modes after destructive tests in both the axial compression and (sagittal) posterior bending directions. The correlations between construct failure loads and bone marrow density (BMD) were also compared.

RESULTS

In axial direction, there were no significant differences in the stiffness and failure load between the posterior and the parallel constructs. However, in sagittal direction, the two-plate groups (posterior two plating and parallel plating group) had significant higher stiffness and failure loads than the one-plate group (single posterior Y plating). There was no fixation failure after 5000-cyclic loading in both directions for all groups. Positive correlation was noted between BMD and failure loads on parallel fixation.

CONCLUSIONS

We found that when using two plates for treating comminuted DHFs, there were no significant differences in terms of most biomechanical measurements between posterior and parallel fixation. However, the single pre-contoured posterior Y plate construct was biomechanically weaker in the sagittal plane than the parallel and the posterior two-plate constructs, although there was no fixation failure after the fatigue test for all groups regardless of the fixation methods.

LEVEL OF EVIDENCE

Biomechanical study.

Chronic type C3 distal humeral fracture associated with massive bone defects treated by open reduction and internal fixation with iliac crest autografts: a case report

Background

Chronic intercondylar fractures of the distal humerus with massive bone defects and severe comminution in the metaphysis are rare and complex injuries that are challenging for surgeons to treat, as reconstructing the triangular structure of the distal humerus is difficult and may have a severe impact on functional outcomes, especially in young patients, for whom total elbow arthroplasty is usually not a suitable option due to significant impairment in upper limb strength. Here, we report a patient in such scenario who was young and active and was treated by structural iliac bone autografting and internal fixation.

Case presentation

A 26-year-old male patient experienced a major car accident and was diagnosed with an open fracture (Gustilo-Anderson type IIIB) of the right distal humerus with massive bone defects and severe intra-articular involvement, without neurovascular injuries or other associated injuries. Surgical debridement, negative pressure vacuum sealing drainage, and immobilization by braces were initially performed, and the wound was closed after 15 days. When the wound had finally healed and the soft tissue was in good condition without infection or effusion 45 days later, this young and active patient was diagnosed with a chronic type C3 distal humeral fracture associated with massive bone defects at the supracondylar level in both columns and severe comminution at the trochlear groove. We performed surgical debridement and arthrolysis around the fracture site, and then, we successfully reconstructed the triangular structure of the distal humerus using structural iliac crest autografts in both columns as well as in the defective trochlear groove. Finally, internal fixation via a parallel double-plate configuration was performed. Over a follow-up period of 3 years, the patient achieved almost full recovery of range of motion and an excellent functional score, without minor or major postoperative complications.

Conclusion

In this study, we proposed a surgical reconstruction strategy for complex chronic distal humeral fractures associated with massive bone defects and severe articular involvement in young and active patients using metaphyseal shortening and structural iliac crest bone autografting together with open reduction and internal fixation via a parallel configuration.

A custom-made distal humerus plate fabricated by selective laser melting

This study aims to evaluate the mechanical performance of custom 3D-printed titanium plates in the treatment of distal humerus fractures. Rigidity of four plating configurations were investigated by finite element analysis. The results reveal that implementation of custom designs with minimal screw holes, lateral-medial linking screw and lateral brim could significantly improve stiffness and consequently leads to better biomechanical stability as compared to standard osteosynthesis design. Biomechanical testing was also performed to validate practical usability. The results confirm that newly designed custom plates fabricated by selective laser melting is a possible alternative for the treatment of distal humerus fracture.

Fatigue Crack Growth and Fracture of Internal Fixation Materials in In Vivo Environments-A Review

The development of crack patterns is a serious problem affecting the durability of orthopedic implants and the prognosis of patients. This issue has gained considerable attention in the medical community in recent years. This literature focuses on the five primary aspects relevant to the evaluation of the surface cracking patterns, i.e., inappropriate use, design flaws, inconsistent elastic modulus, allergic reaction, poor compatibility, and anti-corrosiveness. The hope is that increased understanding will open doors to optimize fabrication for biomedical applications. The latest technological issues and potential capabilities of implants that combine absorbable materials and shape memory alloys are also discussed. This article will act as a roadmap to be employed in the realm of orthopedic. Fatigue crack growth and the challenges associated with materials must be recognized to help make new implant technologies viable for wider clinical adoption. This review presents a summary of recent findings on the fatigue mechanisms and fracture of implant in the initial period after surgery. We propose solutions to common problems. The recognition of essential complications and technical problems related to various approaches and material choices while satisfying clinical requirements is crucial. Additional investigation will be needed to surmount these challenges and reduce the likelihood of fatigue crack growth after implantation.

A pilot biomechanical study comparing a novel, intramedullary Nail/Plate construct to standard Dual-Plate fixation of intra-articular C2.3 distal humerus fractures

BACKGROUND

The gold-standard treatment for intra-articular distal humerus fractures (DHFs) is dual-plate/dual-column fixation, though optimal orientation is not yet established. With a superior method not yet identified, we propose a load-sharing construct, combining absolute stability (extramedullary plate fixation) for distal articular fragments and relative stability (load-sharing intramedullary nail) for the metaphyseal segment. The purpose of this pilot study was to evaluate the biomechanical performance of a novel implant compared to orthogonal dual-plating.

MATERIALS AND METHODS

Ten fresh-frozen matched-pairs of human cadaveric upper extremities with no prior elbow pathology/surgery were used. Pairs were randomized into two groups: Dual-Plate (medial and posterolateral) or novel Nail/Plate (cross-locked medial nail and posterolateral plate). AO/ASIF type 13-C2.3 multifragmentary fractures with simulated metaphyseal comminution. Biomechanical testing included stiffness (MPa) and load to failure (Newtons) in axial (100 cycles at 3 Hz at 20 N increments from 20 to 100 N) and coronal (varus/valgus; 4,000 cycles from 50N-100 N at 3 Hz) planes. Failed specimens were not analyzed and mechanisms were identified. For all failures, mechanisms were identified and reviewed by three consultant surgeons for revision vs. immobilization, to attempt to recreate a real-world scenario. All outcomes were compared between groups.

RESULTS

During stiffness testing, zero Nail/Plate specimens failed, but two (20%) Dual-Plate specimens failed (mechanisms: fracture diastasis; bone collapse and intussusception into osteotomy, yielding articular congruency loss). For remaining samples, Nail/Plate (n = 10) coronal (varus/valgus) stiffness was comparable to Dual-Plate (n = 8) constructs (41.5 vs. 39.0 MPa, p = 0.440). Remaining Dual-Plate constructs had greater axial overall stiffness than Nail/Plate (118.3 ± 48.3 vs. 95.6 ± 34.7 MPa, p = 0.020). Failure loads were comparable between Nail/Plate and Dual-Plate constructs (1,327.8 vs. 1,032.4 N, p = 0.170). Individual nail yield strength ranged from 1,101.1-1,124.4 N (n = 2). In review of all failures, the most common overall mechanism was fracture/osteotomy site posterolateral plate bending. Revision recommendation rate was comparable between constructs (Nail/Plate, 22.2% vs. Dual-Plate, 44.4%, p>0.05).

CONCLUSIONS

The novel Nail/Plate construct demonstrated non-inferior coronal (varus/valgus) stiffness, despite producing lower axial stiffness than orthogonal dual-plating, potentially due to the load-sharing cross-locked design. Considering comparable biomechanical performance, with no failures and comparable recommendations for revision, this novel construct warrants further evaluation as an alternative to the gold-standard, dual-plate fixation method for intra-articular distal humerus fractures.

LEVEL OF EVIDENCE

N/A.

Elbow hemiarthroplasty versus open reduction and internal fixation for AO/OTA type 13 C2 and C3 fractures of distal humerus in patients aged 50 years or above: a randomized controlled trial

Background

Intraarticular distal humeral fractures of AO/OTA type 13 C2 and C3 pose a surgical challenge despite the evolution of surgical implants and techniques. Open reduction and internal fixation (ORIF) is often preferred as the first choice of treatment, but the results vary and are sometimes disappointing. Total elbow arthroplasty (TEA) has been widely used for fractures that are not amenable to ORIF in elderly patients, but the mechanical complications remain a challenge, especially in active patients. Elbow hemiarthroplasty (EHA) provides a modern alternative that might avoid the mechanical complications and weight bearing restrictions related to the linked articulation in semi-constrained TEA. No studies have compared the results of EHA to that of ORIF, but case series have reported promising results.

Methods/design

This is a study protocol describing an investigator-initiated, non-blinded randomized controlled trial comparing the outcome of EHA with ORIF for AO/OTA type 13 C2 and C3 fractures of the distal humerus in patients who are 50 years or older. Forty-four patients with AO/OTA type 13 C2 and C3 fractures of distal humerus will be randomized to either EHA or ORIF. The Oxford Elbow Score (OES) will be used as primary outcome. Mayo Elbow Performance Score (MEPS), pain severity score (VAS), range of motion, and patient satisfaction will be used as secondary outcomes. Reoperations, complications, and the length of sick leave will be recorded. The patients will be examined after the operation and at 3 months and 1, 2, 5, and 10 years.

Discussion

The main objective of this study is to investigate the best treatment option for AO/OTA type 13 C2 and C3 fractures of distal humerus in patients aged 50 years or above. We hypothesize that EHA results in fewer complications and superior functional outcome compared with ORIF and that the mechanical complications related to the linked articulation of TEA can be avoided.

Trial registration

ClinicalTrials.gov, PRS, NCT04163172. Registered November 13, 2019. https://clinicaltrials.gov/ct2/results?cond=&term=evori&cntry=&state=&city=&dist= (Table 2).

The protocol has been approved by The Scientific Ethics Committee of the Capital Region of Denmark (Jr. no.: H^{− 19,035,590}).

The processing of personal data has been approved by the Danish Data Protection Agency (Jr. no. P-2019-246). Inclusion started on February 1, 2020.

The column procedure preserves elbow stability on biomechanical testing

PURPOSE

The effect of open release of a post-traumatic elbow contracture on the stability of the joint has not been so far studied in vivo. Resection of elbow joint capsule, the key element of surgery, was reported to have no effect on the stability of cadaveric elbows. The joint capsule is yet known to participate in maintaining elbow stability as one of secondary stabilizers.

METHODS

We assessed elbow joint laxity in 39 patients who underwent an open contracture release via the 'column procedure' described by B. Morrey and P. Mansat within the preceeding three to nine months. The measurements were taken with an apparatus designed particularly for this experiment according to the predetermined protocol. A preliminary part of the experiment showed that there was no significant difference between laxity of two elbow joints in healthy volunteers. Laxity of the operated elbows could be then compared with the contralateral joints.

RESULTS

Mean absolute difference of laxity between healthy and operated elbows was 1.55° (0.1°-4.1°, SD = 1.1) being significantly lower than 2°, p = 0.0056. The difference of the joint laxity between the operated and healthy elbows did not differ statistically significantly by more than 0.6° from the difference of the laxity of two healthy elbows and, therefore, is not clinically noticeable.

CONCLUSIONS

Our experiment confirmed that the 'column procedure' is a safe procedure which does not compromise the stability of the elbow joint.

Locking design affects the jamming of screws in locking plates

The seizing of locking screws is a frequently encountered clinical problem during implant removal of locking compression plates (LCP) after completion of fracture healing. The aim of this study was to investigate the effect of two different locking mechanisms on the seizing of locking screws. Specifically, the removal torques before and after cyclic dynamic loading were assessed for screws inserted at the manufacturer-recommended torque or at an increased insertion torque. The seizing of 3.5-mm angular stable screws was assessed as a function of insertion torque for two different locking mechanisms (Thread & Conus and Thread Only). Locking screws (n=10 for each configuration) were inserted either according to the manufacturer-recommended torque or at an increased torque of 150% to simulate an over-insertion of the screw. Half of the screws were removed directly after insertion and the remaining half was removed after a dynamic load protocol of 100,000 cycles. The removal torques of locking screws exceeded the insertion torques for all tested conditions confirming the adequacy of the test setup in mimicking screw seizing in locked plating. Screw seizing was more pronounced for Thread Only design (+37%) compared to Thread & Conus design (+14%; P<0.0001). Cyclic loading of the locking construct consistently resulted in an increased seizing of the locking screws (P<0.0001). Clinical observations from patients treated with the Thread & Conus locking design confirm the biomechanical findings of reduction in seizing effect by using a Thread & Conus design. In conclusion, both over-tightening and cyclic loading are potential causes for screw seizing in locking plate implants. Both effects were found to be less pronounced in the Thread & Conus design as compared to the traditional Thread Only design.

Parallel versus orthogonal plate osteosynthesis of adult distal humerus fractures: a meta-analysis of biomechanical studies

PURPOSE

There are two widely used distal humerus fracture (DHF) fixation methods with either orthogonal or parallel double-plate osteosynthesis. However, biomechanical studies have shown inconsistent results on which technique is more effective. We performed a meta-analysis to compare these two fixation methods for adult DHF fixation.

METHODS

We searched the literature for entries discussing the biomechanical testing of orthogonal and parallel fixation techniques for DHFs. We then performed a meta-analysis of the following biomechanical outcome measures: axial/sagittal/coronal/torsional stiffness, load to failure, and torque to failure.

RESULTS

Seventeen studies comparing both constructs were included. The parallel configuration exhibited greater mechanical strength with respect to axial stiffness/load to failure, torsional stiffness, and posterior bending load to failure than the orthogonal constructs. Subgroup analysis revealed that parallel constructs also had higher torsional stiffness in supracondylar fractures.

CONCLUSIONS

This meta-analysis shows that parallel constructs provide greater axial stiffness, axial strength, and torsional stiffness than orthogonal plate for DHF fixation. A subgroup analysis revealed that parallel constructs had better torsional stiffness in supracondylar fracture fixation.

LEVEL OF EVIDENCE

IA.