Introduction. The accuracy of hexapod circular external fixator deformity correction is contingent on the precision of radiographic analysis during the planning stage. The aim of this study was to compare the SMART TSF (Smith and Nephew, Memphis, Tennessee) in-suite radiographic analysis methods with the traditional manual deformity analysis methods in terms of accuracy of correction. Materials and Methods. Sawbones models were used to simulate two commonly encountered clinical scenarios. Traditional manual radiographic analysis and digital SMART TSF analysis methods were used to correct the simulated deformities. Results. The final outcomes of all six analysis methods across both simulated scenarios were satisfactory. Any differences in residual deformity between the analysis methods are unlikely to be clinically relevant. All three SMART TSF digital analyses were faster to complete than manual radiographic analyses. Conclusions. With experience and a good understanding of the software, manual radiographic analysis can be extremely accurate and remains the gold standard for deformity analysis. In-suite SMART TSF radiographic analysis is fast and accurate to within clinically relevant parameters. Surgeons can with confidence trust the SMART TSF software to provide analysis and corrections that are clinically acceptable

Imageless computer navigation systems have the potential to improve acetabular cup position in total hip arthroplasty (THA), thereby reducing the risk of revision surgery. This study aimed to evaluate the accuracy of three alternate registration planes in the supine surgical position generated using imageless navigation for patients undergoing THA via the direct anterior approach (DAA).

Fifty-one participants who underwent a primary THA for osteoarthritis were assessed in the supine position using both optical and inertial sensor imageless navigation systems. Three registration planes were recorded: the anterior pelvic plane (APP) method, the anterior superior iliac spines (ASIS) functional method, and the Table Tilt (TT) functional method. Post-operative acetabular cup position was assessed using CT scans and converted to radiographic inclination and anteversion. Two repeated measures analysis of variance (ANOVA) and Bland-Altman plots were used to assess errors and agreement of the final cup position.

For inclination, the mean absolute error was lower using the TT functional method (2.4°±1.7°) than the ASIS functional method (2.8°±1.7°, ρ = .17), and the ASIS anatomic method (3.7°±2.1, ρ < .001). For anteversion, the mean absolute error was significantly lower for the TT functional method (2.4°±1.8°) than the ASIS functional method (3.9°±3.2°, ρ = .005), and the ASIS anatomic method (9.1°±6.2°, ρ < .001). All measurements were within ± 10° for the TT method, but not the ASIS functional or APP methods.

A functional registration plane is preferable to an anatomic reference plane to measure intra-operative acetabular cup inclination and anteversion accurately. Accuracy may be further improved by registering patient location using their position on the operating table rather than anatomic landmarks, particularly if a tighter target window of ± 5° is desired.

Aim

Culture-based conventional methods are still the gold standard to identify microorganisms in hip and knee PJIs diagnosis. However, such approach presents some limitations due to prior antimicrobial treatment or the presence of unusual and fastidious organisms. Molecular techniques, in particular specific real-time and broad-range polymerase chain reaction (PCR), are available for diagnostic use in a suspected PJI. However, limited data is available on their sensitivity and specificity.

This study aimed to evaluate the performance of a rapid and simple Investigational Use Only (IUO) version of the BioFire® JI multiplex PCR panel when compared to traditional microbiological procedures.

Background

Currently, the gold standard for the microbiological diagnosis remains the culturing of preoperative aspirated joint fluid and intraoperative periprosthetic tissue samples, which give false negative results in about 7 % of cases. Lytic bacteriophages are viruses that specifically infect and lyse bacteria within their replication cycle.

Background

Cementless Total Knee Arthroplasty has been developed to reduce the incidence of failure secondary to aseptic loosening, osteolysis and stress-induced osteopenia, especially in younger and more active patients. However, failures are still more common compared to cemented components, especially those involving the tibia. It is hypothesized that this is caused by incomplete contact between the tibial tray and the underlying bony surface due to: (i) inadequate flatness of the tibial osteotomy, or (ii) failure of implantation to spread the area of contact over the exposed cancellous surface. In the present study we compare the contact area developed during implantation of a cementless tray as a function of the initial flatness of the tibial osteotomy.

Objective. The efficacy and safety of tranexamic acid (TXA) on reducing blood loss and transfusion has been confirmed in primary total hip arthroplasty (THA). The main methods of administration includes intravenous, topical alone or combined use, and the most appropriated methods remains undecided. This study was aimed to compare the efficacy and safety of different methods of TXA following primary THA. Methods. We prospectively collected patients' data through National Health Database from January 2013 to December 2016. The patients were divided into control group, intravenous group, topical group and combined group according to the different methods of TXA. The primary outcome was the incidence of transfusion and venous thromboembolism. Secondary outcomes were total blood loss, hemoglobin level on postoperative day 3 and decrease in hemoglobin, incidence of wound complications and other adverse events. Results. A total of 7537 primary THA procedures were collected, 4102 with TXA, 3435 without TXA. 2847 (37.8%) patients received intravenous TXA alone, 235 (3.1%) patients received topical TXA alone and 1020 (13.5%) patients received combined use. The transfusion rate decreased from 33.07% to 12.7% with the use of TXA (p< 0.001). The transfusion rate was 30.21% in topical group, 10.68% in intravenous group, and 14.31% in combined group, with a significant difference between treatment groups (p< 0.01 for all). The hemoglobin on postoperative day 3 in control group was 91.24±17.09 g/L, which was significantly lower than that in topical group (101.38±16.71 g/L), intravenous group (102.79±32.37 g/L) and combined group (104.34±16.67 g/L, p<0.05 for all). The hemoglobin drop on POD 3 in control group was 38.07±18.10 g/L, which was significantly higher than that in topical group (30.02±17.11 g/L), intravenous group (29.35±16.05 g/L) and combined group (29.22±16.37 g/L, p<0.05 for all). The total blood loss in control group was (1377.74 ± 851.97 ml), which was significantly higher than that in topical group (1123.15±628.59 ml), intravenous group (971.08±671.39 ml) and combined group (946.4±724.82 ml, p<0.05 for all). A total of 14 DVT (0.41%) in control group, 4 patients (0.1%) in TXA group occurred DVT, and the difference was significant (0.10%, p= 0.006). Cardiac infarction occurred in 3 patients (0.04%), stroke occurred in 2 patients (0.03%), and 3 patients (0.04%) developed wound infection. No episode of PE or death occurred. Conclusion. TXA was effective and safe to decrease blood loss and transfusion following primary THA no matter of intravenous, topical use alone or combined use. In order to achieve better hemostatic effect, intravenous or combined application was recommended if no contradictions were found

Background. Shoulder impingement syndrome (SIS) is a common debilitating condition, treated across multiple health disciplines including Orthopaedics, Physiotherapy, and Rheumatology. There is little consistency in diagnostic criteria with ‘Shoulder impingement syndrome’ being used for a broad spectrum of complex pathologies. We assessed patterns in diagnostic procedures for SIS across multiple disciplines. Methods. This is a systematic review of electronic databases MEDLINE, PubMed, The Cochrane Library, Embase, Scopus and CINAHL five years of publications, January 2009 - January 2014. Search terms for SIS included subacromial impingement syndrome, subacromial bursitis. Searches were delimited to articles written in English. The PRISMA guidelines were followed. Two reviewers independently screened all articles, data was then extracted by one reviewer and twenty percent of the extraction was independently assessed by the co-reviewer. Studies included were intervention studies examining individuals diagnosed with SIS and we were interested in the process and method used for the diagnosis. Results. The search strategy yielded 3339 articles of which 1931 were duplicates. A further 1260 were excluded based on relevance obtained from title/abstract. A total of 148 articles were identified investigating SIS across thirty different journals internationally. Fourteen different health disciplines have investigated twenty-five different surgical and conservative treatments. Studies document their diagnostic approach, reporting on duration of symptoms, medical history, physical examination tests and radiological investigations. Duration of symptoms for inclusion ranged from a minimum of 2 weeks to 18 months where the median duration of symptoms is 3 months observed in 46 percent of the studies. Commonly used physical tests were Neer's test, Hawkins-Kennedy test, Jobe and Yocum, and a further eight tests identified. Neer's test or Hawkins-Kennedy tests were individually used in 72 percent of studies. Thirty of the studies used more than one and up to six physical tests per study to determine the presence of impingement. Radiological investigations were reported in twenty-eight studies, sixteen of these required more than one radiological investigation to confirm the diagnosis of SIS. Comparisons between disciplines identify important differences in diagnostic criteria used by different health professionals. Conclusions. This study highlights the variety of diagnostic methods which are currently used between health disciplines and will be a useful comparative tool for clinicians. Diagnostic transparency is pertinent for shoulder impingement syndrome to ensure all disciplines are treating the same pathology and importantly to contribute to our understanding of the common pathology

Background. The optimal surgical treatment for osteonecrosis of the femoral head has yet to be elucidated. To evaluate the role of femoral fixation techniques in hip resurfacing, we present a comparison of the results for two consecutive groups: Group 1 (75 hips) received hybrid hip resurfacing implants with a cemented femoral component; Group 2 (103 hips) received uncemented femoral components. Both groups received uncemented acetabular components. Methods. We retrospectively analyzed our clinical database to compare failures, reoperations, complications, clinical results, metal ion test results, and x-ray measurements. Using consecutive groups caused time interval bias, so we required all Group 2 patients be at least two years out from surgery; we compared results from two years and final follow-up. Results. Patient groups matched similarly in age, BMI, and percent female. Despite similar demographics, the uncemented, Group 2 cases showed a lower raw failure rate (0% vs. 16% p<0.0001), a lower 2-year failure rate (0% vs. 7%, p=0.04), and a superior 8-year implant survivorship (100% vs. 91%, log-rank p=0.0028, Wilcoxon p=0.0026). In cases that did not fail, patient clinical (p=0.05), activity (p=0.02), and pain scores (p=0.03), as well as acetabular component position (p<0.0001), all improved in Group 2, suggesting advancements in surgical management. There were no cases of adverse wear related failure in either group. Conclusions. This study demonstrates a superior outcome for cases of osteonecrosis with uncemented hip resurfacings compared to cases employing hybrid devices

Introduction. A recent meta-analysis published in the British Medical Journal suggested an increased risk of infection, but none of the studies were large enough to reach statistical significance. A prospective, randomised trial was designed at our institution to investigate the wound healing and complications related to surgery following fracture neck of femur in the elderly. Objectives. The primary aim was to compare the wound problems and infection following two different methods of skin closure: Subcuticular monocryl suture to metal clips for closure of skin. The secondary aim was to look at the duration of surgery after both types of closure. We received ethical approval for this study. We screened and recruited all eligible patients admitted with acute hip fracture undergoing hemi-arthroplasty or dynamic hip screw. We recruited 541 patients in the study over the period of 3.5 years at our institution. Methods. The study was approved by ethics committee. Inclusion Criteria: Age 18 years and above undergoing DHS/ Hemiarthroplasty and with full mental capacity. Exclusion criteria: Patients with no capacity or undergoing Total Hip Replacement or Nailing of femur. The randomisation was done by using the sealed envelopes. The wound review was done on post op days 2, 5, 7, 10 & 14. Results. 516 patients were included in the study. They were divided in to two groups, 252 Hemiarthroplasty and 264 DHS. Average age was 79.48 yrs. (range 31–100 yrs.), 357 Females and 159 males. Total 196 patients were followed up till day 14 and rest of the patients were discharged by the 10. th. post op day. Out of 516 patients, 278 patients had clips and 238 patients had sub cut monocryl suture for the wound closure. The average score was 1.20 (range 1–3) for the wounds (the group of 278 patients) closed with clips mainly due to bruising and oozing. The average score was 0.71(range 0–1) for the wounds (the 238 group of patients) closed with sub cut monocryl mainly due to bruising. We did not find any significant wound infection in either of these groups. Conclusion. The final review of our study showed that the wounds closed with sub cut monocryl had less wound healing issues (average score 0.71) as compared to the wounds closed with clips (average score 1.20)

Introduction. Pre-clinical testing of orthopaedic devices could be improved by comparing performance with established implants with known clinical histories. Corail and Summit (DePuy Synthes, Warsaw) are femoral stems with proven survivorship of 95.1% and 98.1% at 10 years [1], which makes them good candidates as benchmarks when evaluating new stem designs. Hence, the aim of this study was to establish benchmark data relating to the primary stability of Corail and Summit stems. Methods. Finite Element (FE) simulations were run for 34 femurs (from the Melbourne femur collection) for a diverse patient cohort of joint replacement age (50 – 80 yrs). To account for the diversity in shape, the cohort included femurs with the maxima, minima and medians for 26 geometric parameters. Subject-specific FE models were generated from CT scans. An in-house developed algorithm positioned idealized versions of Corail and Summit (Figure 1) into each of the femur models so that the stem and femur shaft axes were aligned, and the vertical offset between the trunnion centre and the femoral head centre was minimised. For such a position, the algorithm selected the size that achieved maximum fill of the medullary canal without breaching the cortical bone boundaries. Joint contact and muscle forces were calculated for level gait and stair climbing[2] and scaled to the body mass of each subject. Femurs were rigidly constrained at the condyles. Risk of failure was assessed based on (i) stem micromotion, (ii) equivalent strains (iii) percentage of the bone-prosthesis contact area experiencing micromotions < 50 μm, micromotions > 150 μm and strains > 7000 μstrains [3]. Results. Stair climb loads resulted in higher micromotion and interface strains, compared to level gait loads. For level gait, on average, Corail had 89% and Summit had 91% of the contact area experiencing less than 50 μm and less than 1% of the contact area with micromotion greater than 150 μm. For stair climbing, the average area experiencing <50 μm was about 75% for both stems. On average, Corail and Summit had less than 1% of the contact area with micromotion greater than 150 μm during stair climbing. The average percentage of the contact are with strains greater than 7000 μstrains was about 2% for both stems during level gait, and 8% (Corail), 10% (Summit) during stair climbing (Figure 2). Discussion and Conclusion. It is desirable for the micromotion at the entire contact area to be below 50 μm. Despite the reported good survivorship of Corail and Summit [1], results of the FE simulations do not show such a distribution. Instead, results suggest that primary stability may be achieved with up to 25% of the contact area with micromotion greater than 50 μm. Hence, the 75th percentile may be a suitable metric for benchmarking femoral stems

Aim

To compare the performance of sonication and chemical methods (EDTA and DTT) for biofilm removal from artificial surface.

Background. Humeral retroversion is variable among individuals, and there are several measurement methods. This study was conducted to compare the concordance and reliability between the standard method and 5 other measurement methods on Twodimensional (2D) computed tomography (CT) scans. Methods. CT scans from 21 patients who underwent shoulder arthroplasty (19 women and 2 men; mean age, 70.1 years [range, 42 to 81 years]) were analyzed. The elbow transepicondylar axis was used as a distal reference. Proximal reference points included the central humeral head axis (standard method), the axis of the humeral center to 9 mm posterior to the posterior margin of the bicipital groove (method 1), the central axis of the bicipital groove –30° (method 2), the base axis of the triangular shaped metaphysis +2.5° (method 3), the distal humeral head central axis +2.4° (method 4), and contralateral humeral head retroversion (method 5). Measurements were conducted independently by two orthopedic surgeons. Results. The mean humeral retroversion was 31.42° ± 12.10° using the standard method, and 29.70° ± 11.66° (method 1), 30.64°± 11.24° (method 2), 30.41° ± 11.17° (method 3), 32.14° ± 11.70° (method 4), and 34.15° ± 11.47° (method 5) for the other methods. Interobserver reliability and intraobserver reliability exceeded 0.75 for all methods. On the test to evaluate the equality of the standard method to the other methods, the intraclass correlation coefficients (ICCs) of method 2 and method 4 were different from the ICC of the standard method in surgeon A (p < 0.05), and the ICCs of method 2 and method 3 were different form the ICC of the standard method in surgeon B (p < 0.05). Conclusions. Humeral version measurement using the posterior margin of the bicipital groove (method 1) would be most concordant with the standard method even though all 5 methods showed excellent agreements

Introduction. 11%–19% of patients are unsatisfied with outcomes from Total Knee Arthroplasty (TKA). This may be due to problems of alignment or soft-tissue balancing. In TKA, often a neutral mechanical axis is established followed by soft tissue releases to balance and match the flexion/extension gaps with the distal femoral and proximal tibial resections at right angles to the mechanical axis. Potential issues with establishment of soft tissue balance are due to associated structures such as bone tissue of the knee, the static (or passive) stabilizers of the joint (medial and lateral collateral ligaments, capsule, and anterior and posterior cruciate ligaments), and the dynamic (or active) stabilizers around the knee. An optimized balance among these systems is crucial to the successful outcome of a TKA. Additionally, the importance of correct femoral rotation has been well documented due to its effect on patella alignment and flexion instability, range of motion, and polyethylene wear. There are several methods used in TKA procedures to establish femoral component rotation. The more prominent ones are a conventional method of referencing to the posterior condylar axis with a standard external rotation of 3° (PCR), anterior-posterior line or “Whiteside's line” (AP axis), transepicondylar axis (TEA) (Figure 1), and the gap balancing technique, however, it is not yet clear, which method is superior for femoral rotational component alignment. In the current study, we sought to investigate an alternative method based on soft-tissue, dynamic knee balancing (DKB) while using an alternative analysis approach. DKB dictates femoral component rotation on the basis of ligament balance and force measures. DKB has become more prominent in TKA surgeries. While retaining ligament balance in TKA, it is possible that this technique also leads to higher precision of rotational alignment to the anatomical axis. The primary objective of this study was to compare efficiency of DKB versus other methods for rotational implant alignment based on post-surgery computed tomography (CT). Methods. 31 patients underwent computer-navigated total knee arthroplasty for osteoarthritis with femoral rotation established via a flexion gap balance device (Synvasive eLibra). Alternative, hypothetical alignments were assessed based on anatomical landmarks during the surgery. Postoperative computed tomography (CT) scans were analyzed to investigate post-surgery rotational alignment. Repeated measures ANOVA and Cochran's Q test were utilized to test differences between the DKB method and the other techniques. Results. Significant differences were observed between the DKB method and TEA method (p=0.02), between DKB and AP method (p=0.04), and DKB and PCR method (p=0.02): The DKB method showed the lowest rotational deviation from CT-determined true anatomical TEA (aTEA)(Figure 2). The DKB method established femoral rotation within ±3 more often than the other techniques (Figure 3), further analysis revealed a significant proportional difference between DKB and PCR method (p=0.01), between DKB and TEA (p=0.02) and DKB and AP (p=0.04). Conclusions. DKB showed promising results in our study regarding femoral rotation accuracy in comparison to other methods. DKB may be a valuable tool due to its ability to establish soft-tissue balance in addition to high accuracy of femoral rotation

Traditional use of tourniquets and reinfusion drains in total knee replacement (TKR) has recently been challenged. Many studies have challenged the benefits of their use. Our aim was to compare the outcomes of three different blood management techniques in primary TKR.

We conducted a prospective randomised study of 87 patients with a mean age of 71 years. All patients were randomised into three groups: Group A (29 patients without tourniquet and drain), Group B (27 patients without tourniquet or drain but cell salvage system) and Group C (31 patients with the use of tourniquet and drain).

The results showed no difference between the postoperative haemoglobin drop and blood transfusion rate between the groups. At day two, range of knee movements (Group A: 80.2 degree; Group B: 79.6 degree; Group C: 77.9 degree) showed no significant difference. Two Group C patients (6.4%) had postoperative thromboembolic events (one DVT, one TIA). Knee stiffness leading to readmission (Group A: 6.8%; Group B: 7.4%; Group C: 3.2%) and superficial wound problems did not reveal any significant difference. The average operative time and hospital stay were the same in all groups and there was no wound haematoma or deep infection in any groups.

There was no statistical difference between the groups for any outcome measure assessed thus the use of tourniquets and drains in total knee arthroplasty are controversial and questionable. We can conclude that all techniques are safe and it is the surgeon's choice as to which they apply routinely in their clinical practice.

Background. There are limited previous findings detailed biomechanical properties following implantation with mechanical and kinematic alignment method in robotic total knee arthroplasty (TKA) during walking. The purpose of this study was to compare clinical and radiological outcomes between two groups and gait analysis of kinematic, and kinetic parameters during walking to identify difference between two alignment method in robotic total knee arthroplasty. Methods. Sixty patients were randomly assigned to undergo robotic-assisted TKA using either the mechanical (30 patients) or the kinematic (30 patients) alignment method. Clinical outcomes including varus and valgus laxities, ROM, HSS, KSS and WOMAC scores and radiological outcomes were evaluated. And ten age and gender matched patients of each group underwent gait analysis (Optic gait analysis system composed with 12 camera system and four force plate integrated) at minimum 5 years post-surgery. We evaluated parameters including knee varus moment and knee varus force, and find out the difference between two groups. Results. The mean follow up duration of both group was 8.1 years (mechanical method) and 8.0 years (kinematic method). Clinical outcome between two groups showed no significant difference in ROM, HSS, WOMAC, KSS pain score at last follow up. Varus and valgus laxity assessments showed no significant inter-group difference. We could not find any significant difference in mechanical alignment of the lower limb and perioperative complicatoin. In gait analysis, no significant spatiotemporal, kinematic or kinetic parameter differences including knee varus moment (mechanical=0.33, kinematic=0.16 P0.5) and knee varus force (mechanical=0.34, kinematic=0.37 P0.5) were observed between mechanical and kinematic groups. Conclusions. The results of this study show that mechanical and kinematic alignment method provide comparable clinical and radiological outcomes after robotic total knee arthroplasty in average 8 years follow-up. And no functional difference were found between two knee alignment methods during walking

Introduction. The elbow is the second most common site of non prosthetic joint dislocation. Simple elbow dislocation alone contributes to 11-28% of all elbow injuries. Post-reduction treatment methods include traditional plaster of Paris (POP) immobilisation followed by physiotherapy, sling application followed by early mobilisation and rapid motion. The aim of the study was to evaluate the final outcome and cost-effectiveness of the pop and the sling groups. Study Design. Retrospective cohort study. Methods. We reviewed 42 simple elbow dislocations treated between 1998-2003. 20 patients in POP group and 22 patients in the sling group were assessed at a minimum follow-up of two years. The data collected consisted of age, gender, duration of immobilisation, length of physiotherapy, and return to work. All were assessed using MEPI (Mayo Elbow Performance Index) score and Quick DASH questionnaire. The final outcome was graded as excellent, good, fair and poor. Results. The final functional outcome in the POP group was 10 excellent, 3 good, 4 fair and 3 poor. In the sling group, we had 19 excellent, 1 good and 2 fair results. The mean MEPI scores in the POP and sling group were 89.2 and 98.2 respectively (p<0.05). The mean quick DASH scores in the POP and sling group were 12.8 and 2.7 respectively (p<0.05). The final functional outcome is directly dependent on the length of immobilisation (R=0.91). The mean time to return to work in POP group and sling groups was 6.6 and 3.2 weeks respectively (p<.001). Conclusion. Sling and early mobilisation is a safe and cost-effective method of treatment for simple elbow dislocation. The length of physiotherapy and time taken to return to work were significantly shorter in the sling group. Early mobilisation did not result in redislocation or late instability. The final outcome of the sling and early mobilisation group was significantly better than POP immobilisation group

Background. There are limited previous findings detailed biomechanical properties following implantation with mechanical and kinematic alignment method in robotic total knee arthroplasty (TKA) during walking. The purpose of this study was to compare clinical and radiological outcomes between two groups and gait analysis of kinematic, and kinetic parameters during walking to identify difference between two alignment method in robotic total knee arthroplasty. Methods. Sixty patients were randomly assigned to undergo robotic-assisted TKA using either the mechanical (30 patients) or the kinematic (30 patients) alignment method. Clinical outcomes including varus and valgus laxities, ROM, HSS, KSS and WOMAC scores and radiological outcomes were evaluated. And ten age and gender matched patients of each group underwent gait analysis (Optic gait analysis system composed with 12 camera system and four force plate integrated) at minimum 5 years post-surgery. We evaluated parameters including knee varus moment and knee varus force, and find out the difference between two groups. Results. The mean follow up duration of both groups was 8.1 years (mechanical method) and 8.0 years (kinematic method). Clinical outcome between two groups showed no significant difference in ROM, HSS, WOMAC, KSS pain score at last follow up. Varus and valgus laxity assessments showed no significant inter-group difference. We could not find any significant difference in mechanical alignment of the lower limb and perioperative complicatoin. In gait analysis, no significant spatiotemporal, kinematic or kinetic parameter differences including knee varus moment (mechanical=0.33, kinematic=0.16 P0.5) and knee varus force (mechanical=0.34, kinematic=0.37 P0.5) were observed between mechanical and kinematic groups. Conclusions. The results of this study show that mechanical and kinematic alignment method provide comparable clinical and radiological outcomes after robotic total knee arthroplasty in average 8 years follow-up. And no functional differences were found between two knee alignment methods during walking

Stable, anatomical fixation of acetabular fractures gives the best chance of a good outcome. We performed a biomechanical study to compare fracture stability and construct stiffness of three methods of fixation of posterior wall acetabular fractures.

Two-dimensional motion analysis was used to measure fracture fragment displacement and the construct stiffness for each fixation method was calculated from the force / displacement data.

Following 2 cyclic loading protocols of 6000 cycles, to a maximum 1.5kN, the mean fracture displacement was 0.154mm for the rim plate model, 0.326mm for the buttress plate and 0.254mm for the spring plate model. Mean maximum displacement was significantly less for the rim plate fixation than the buttress plate (p=0.015) and spring plate fixation (p=0.02).

The rim plate was the stiffest construct 10962N/mm (SD 3351.8), followed by the spring plate model 5637N/mm (SD 832.6) and the buttress plate model 4882N/mm (SD 387.3).

Where possible a rim plate with inter-fragmentary lag screws should be used for isolated posterior wall fracture fixation as this is the most stable and stiffest construct. However, when this method is not possible, spring plate fixation is a safe and superior alternative to a posterior buttress plate method.

Introduction:

Open bone graft harvesting continues to be recognized as the gold standard of obtaining autograft in patients needing bone graft. Conventional bone graft harvesting using the iliac crest is often cited as having significant donor site morbidity and complications. Intramedullary harvesting, using a reamer irrigation aspiration system (RIA) has recently become available.

Modern hip implants feature a modular design, whereby the individual components of the implant are assembled during the surgery. Increased reported failure rates associated with the utilization of modular junctions have raised many clinical concerns about the increased release of metal ions/debris leading to adverse local tissue reactions. Implant materials are subject to a myriad of mechanical motion and forces, and varying electrochemical conditions and pH changes from the surrounding environment. To date, no studies have attempted to model the collected data in order to predict the performance of the materials so that precautions can be taken before the problem reaches the critical stage. This study reports the effects of pH variation, displacement variation, and load variation on the mechanical and corrosion behavior of the hip implant modular junction system, tested with a custom-built fretting-corrosion apparatus. The main objective of this study is to combine the complete data set of the in-vitro experiments to create fretting-corrosion wear maps that can predict the dangerous domains of the hip implant modular system.

For each test, the flat portions of two CoCrMo pins were loaded perpendicularly against a Ti6Al4V Rod (Ti alloy) in a Flat-on-flat configuration in a simulated synovial fluid in order to simulate the modular hip implant system. A schematic diagram of contact conditions is presented in Figure 1. A sinusoidal displacement was applied onto the rod, which articulated against the CoCrMo alloy pins, at a frequency of 1Hz. The experiential data from the fretting-corrosion tests has been used to create fretting-corrosion maps. The variables incorporated into the maps include: total mass loss, electrochemical destabilization, pH variation, load variation, displacement variation, and visual examination of the wear features of the contact zone. Total mass loss has been estimated via measurement of the simulator fluid by ICP-MS technique. Electrochemical destabilization was evaluated by a single parameter (V_Drop). The electrochemical destabilization of the tribosystem was evaluated by measuring the drop in potential, V_Drop (V vs. SCE), resultant from the initiation of the fretting phase. The V_Drop refers to the initial cathodic drop in potential in response to the initial onset of fretting motion.

The data from the in vitro fretting-corrosion experiments has been combined to create four fretting-corrosion maps (Figures 2A–3D). Partial slip wear features and mechanical behavior was observed at 25µm displacement. 25–150µm displacement amplitudes showed gross slip behavior. Anything larger than 150µm displayed wear features that were indistinguishable from sliding wear. In general, total mass loss and V_Drop increased with increasing displacement. Samples that were tested at pH 6.0 or higher showed signs of material transfer and higher V_Drop. Finally, there was a general decrease in V_Dropwith increased applied load and pH.

In general, the wears maps were able to offer some predictive validity, however, there were some discrepancies between visual observations and the observed damage parameters. It is possible that other parameters could offer better correlation. Future studies will be conducted to measure other parameters.

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