Teaching simulated arthroscopic Bankart repair: residents' assessment at the Annual Shoulder Course

Background: This study's aim was to evaluate the performance of senior orthopedic residents during simulated arthroscopic anterior stabilization (Bankart repair) before and after a national shoulder review course. Methods: Participants were assessed before and after the Annual Shoulder Review Course over a 3-day period, using a multiple-choice examination and surgery performance assessment. The surgical evaluation was completed by fellowship-trained surgeons using a standardized procedure checklist and a global rating scale. All Canadian senior orthopedic residents were invited to participate in the course. Results: The 57 participants showed improvement following the course. The written knowledge evaluation mean score increased, and all 3 surgical performance measurements improved: surgical task time improved from 4:40 min to 2:53 min (p < 0.001), surgical technique evaluation increased from 56% to 67% after the procedure checklist (p < 0.001), and anchor placement improved for all 3 aspects. Anchor entry point was the sole measure not to improve enough to reach statistical significance (p = 0.37). Conclusion: Our data support the inclusion of dry model surgical simulation as part of a surgical skills course for both training and assessment of orthopedic surgery residents.

Contexte: Le but de cette étude était d'évaluer le rendement des résidents seniors en orthopédie durant une simulation de stabilisation arthroscopique antérieure (intervention de Bankart) avant et après un cours de révision national sur l'articulation de l'épaule. Méthodes: Les participants ont été évalués avant et après l'Annual Shoulder Review Course sur une période de 3 jours, à l'aide d'un examen à choix multiples et d'une épreuve chirurgicale pratique. L'évaluation chirurgicale était effectuée par des chirurgiens spécialisés, à l'aide d'une liste de vérification normalisée des procédures et d'une échelle d'évaluation globale. Tous les résidents séniors canadiens en orthopédie étaient invités à participer au cours. Résultats: Les 57 participants ont montré une amélioration après le cours. Lesrésultats à l'examen écrit ont augmenté, tout comme ceux des 3 évaluations chirurgicales : le temps chirurgical a diminué, passant de 4:40 min à 2:53 min (p < 0,001), l'évaluation de la technique chirurgicale a augmenté de 56 % à 67 % selon la liste de vérification (p < 0,001) et le positionnement des ancres s'est aussi amélioré pour les 3 positionnements. Le point d'entrée des ancres a été la seule mesure à ne pas s'améliorer suffisamment pour atteindre une portée statistique (p = 0,37). Conclusion: Nos données appuient l'inclusion d'un modèle de simulation sec pour la formation et l'évaluation des résidents en chirurgie orthopédique.

Biomechanical study comparing 3 fixation methods for rotator cuff massive tear: Transosseous No. 2 suture, transosseous braided tape, and double-row.

BACKGROUND: Important rotator cuff repair failure rates have prompted this study of the techniques and materials used in order to optimize clinical results. QUESTIONS/PURPOSES: Is the reconstruction of the rotator cuff biomechanically stronger when using: 1) transosseous with 2 mm braided tape suture (TOT), 2) transosseous with multi-strand No. 2 sutures (TOS), or 3) double row suture bridge with suture anchors loaded with No. 2 braided sutures (DRSB)? METHODS: Twenty-four cadaveric pig shoulders were randomized in the three repair constructs. The infraspinatus muscle was detached to mimic a complete laceration, repaired with one of the three repair groups and tested with a traction machine. Cameras recorded tendon displacement during trials. The ultimate strength (US), failure mode, and tendon displacement, qualified by the bare footprint area (BFA), during cycling phases were compared. RESULTS: The US for DRSB was 175 ± 82 Newton (N), 91 ± 51 N for TOS, and 147 ± 63 N for TOT. The BFA after 200 cycles was 81 ± 34% for TOS, 57 ± 41% for TOT, and 26 ± 27% for DRSB repairs. No significant difference was observed between the DRSB and TOT results for US or BFA percentage of loss during all the cycling phases. TOS proved to be weaker than TOT and DRSB. CONCLUSION: All the ruptures occurred in the tendon, which seems to be the weakness of rotator cuff repairs. The use of braided tape suture with a transosseous technique seems to be a cost effective, equivalent alternative implant compared to anchor fixation.

Does radiographic beam angle affect the radiocapitellar ratio measurement of subluxation in the elbow?

BACKGROUND: Radial head alignment is the key to determine elbow reduction after treatment of subluxations or Monteggia fractures. The radiocapitellar ratio (RCR) quantifies the degree of subluxation, by evaluating radial head alignment with the capitellum of the humerus; this ratio is reproducible when measured on true lateral radiographs of nonsubluxated elbows. However, the impact of beam angulation on RCR measurement is unknown. QUESTIONS/PURPOSES: Our hypotheses were that the RCR of the nonsubluxated elbow would remain in the normal range as the beam angle changed and that the RCR variability would increase for the subluxated elbow with small deviations in the beam angle. METHODS: Radiographs were taken of six healthy cadaveric extremities using beam angles ranging from -20° to 20° along the inferosuperior axis and from -20° to 20° along the dorsoventral axis. The same views then were taken of the six arms with anterior radiocapitellum subluxation followed by posterior radiocapitellum subluxation. RCRs were measured by one observer. As a reference value, the RCR was measured in the 0° to 0° position and the difference between each RCR in a nonreference position was subtracted from each RCR reference to obtain the delta-RCR. An ANOVA was performed to assess the main and interactive effects on the RCR measured in each C-arm position compared with the RCR measured on a true lateral radiograph. RESULTS: The RCR remained in the normal range even as the beam angle of the C-arm varied between -20° and 20°. The position of the beam did not affect the RCR in anteriorly subluxated elbows (p = 0.777), whereas RCR variation increased especially in the presence of posterior radial head subluxation when the C-arm position was 10° or more out of plane (p = 0.006). The inferosuperior malposition of the C-arm had a greater impact on quantification of radial head alignment measurement. Despite that, the RCR measurement is reliable in reduced and subluxated elbows on lateral radiographs with a C-arm position deviation of as much as 20°. CONCLUSIONS: Identification of a subluxated elbow could be made on any lateral radiograph with a beam angulation deviation of as much as 20°. This suggests that the RCR is a useful diagnostic tool for clinical and research purposes, although for subluxated elbows, it is important to pay careful attention to the inferosuperior position of the C-arm.

Demographic and anthropometric factors affecting elbow range of motion in healthy adults.

BACKGROUND: To use elbow range of motion routinely as a diagnostic index, it is important to explain the normal variability among the population. Consequently, this study assessed the possible associations between age, sex, laterality, body mass index, joint laxity, level of physical activities, upper limb dimensions, and the elbow range of motion in flexion/extension. MATERIALS AND METHODS: Maximal flexion and extension were measured on the lateral radiographs of 102 elbows of 51 volunteers. The difference of range of motion regarding sex and laterality was assessed with Student t tests. The Pearson correlation coefficient was used to evaluate the relationship between elbow mobility and the other factors, and a stepwise multiple regression analysis was performed. RESULTS: Among the 51 volunteers, a correlation was found between flexion and body mass index, age, and midbrachial and forearm circumferences (r = -0.234 to -0.594). Age (r = 0.268) and hyperlaxity (r = -0.323) were the only factors associated with a change in elbow extension. No correlation was found between the level of physical activity or with the laterality and changes in elbow mobility. Finally, women presented with more flexion and total elbow range of motion than men. CONCLUSIONS: This study confirms the association between various demographic and anthropometric factors and elbow range of motion in healthy adults. Among these, the body mass index and forearm circumference are the most likely responsible for mobility variations among the population.

Initial tension loss in cerclage cables.

Cerclage cables, frequently used in the management of fractures and osteotomies, are associated with a high failure rate and significant loosening during surgery. This study compared the capacity to maintain tension of different types of orthopaedic cable systems. Multifilament Cobalt-Chrome (CoCr) cables with four different crimp/clamp devices (DePuy, Stryker, Zimmer and Smith&Nephew) and one non-metallic Nylon (Ny) cable from Kinamed were instrumented with a load cell to measure tension during insertion. Significant tension loss was observed with crimping for all cables (P<0.05). Removing the tensioner led to an additional unexpected tension loss (CoCr-DePuy: 18%, CoCr-Stryker: 29%, CoCr-Smith&Nephew: 33%, Ny: 46%, and CoCr-Zimmer: 52%). The simple CoCr (DePuy) cable system outperformed the more sophisticated locking devices due to its significantly better ability to prevent tension loss.

Impact of prone surgical positioning on the scoliotic spine.

OBJECTIVE: To study the impact of patient-specific prone positioning on the sagittal and coronal curves of scoliotic spines, including the impact of various patient and surgical frame factors. SUMMARY OF BACKGROUND DATA: Prone operative positioning has been shown to impact the geometry of various individual spinal segments. Its impact on global spinal geometry and influential factors remains unknown. METHODS: Lateral and coronal radiographs were acquired of 6 scoliotic patients while standing, prone on a dynamically adjustable surgical frame and intraoperatively on the Relton-Hall frame. Standing lateral bending radiographs were also acquired. Lordosis, kyphosis, and Cobb angles were measured in each position. Personalized finite element models (FEMs), including the spine, ribcage, pelvis, and lower limbs were generated for each patient based on their standing radiographs. The FEM's ability to reproduce prone spinal geometry was evaluated by using different values of intervertebral disc elastic moduli: published, optimized based on lateral bending radiographs and optimized based on prone radiographs. The 6 FEMs were then exploited to study the impact of surgical frame cushion configuration, standing curve magnitudes, and patient weight on spinal geometry changes due to prone positioning. RESULTS: All coronal and sagittal curves decreased in the prone position; averaging 12% in lordosis, 19% in kyphosis, 7%, 14%, and 26%, respectively, for proximal thoracic, main thoracic, and thoracolumbar/lumbar Cobb angles. FEM prone simulations yielded best results when optimized by using the prone position radiographs (Δ<5 degrees for all segmental curves). Lateral bending optimization yielded similar results by using published properties. Surgical frame cushion configuration, standing curve magnitudes, and patient weight all had an important impact on spinal geometries with the exception of thoracic cushion longitudinal position. A strong correlation (R=0.86) was found between standing kyphosis and its reduction in the prone position. CONCLUSIONS: Prone positioning results in a reduction of all spinal segmental curves which is dependent on a number of patient and surgical frame factors.

Biomechanical study of patient positioning: influence of lower limb positioning on spinal geometry.

OBJECTIVE: The objective of this study was to use finite element model (FEM) simulations and experimental testing to study the relationship between lower limb positioning for surgeries of the spine and changes in sagittal curves. METHODS: Four volunteers underwent lower limb flexibility and range of motion testing before being placed prone on a new surgical frame where lateral radiographs of their spines were taken in positions of hip flexion (average 48 degrees) and extension (average 13 degrees). Personalized FEMs were created representing each volunteer's spine, rib cage, pelvis, and lower limbs. Optimization of model behavior was performed by adjustment of lower limb muscle initial strains. The FEMs were exploited to examine the impact of more extreme and intermediate lower limb positions; 30 degrees of hip extension to 90 degrees of flexion at intervals of 20 degrees. RESULTS: With increased hip flexion, lordosis and kyphosis decreased to an average of 52% (35 degrees) and 16% (6 degrees), respectively. Personalization of the 4 FEMs allowed reproduction of the experimental results within 5 degrees and their subsequent exploitation showed the linear changes in lordosis and kyphosis between extreme positions decreasing an average of 84% (59 degrees) and 34% (13 degrees) with increased hip flexion. A strong correlation was found between experimental change in lordosis and individual hamstring flexibilities (R=-0.93) which allowed for the development of a predictive equation for lordosis in terms of hip flexion which factors straight leg raise test results. CONCLUSIONS: Knowledge gained through this study can be used to improve intraoperative control of sagittal curves through lower limb positioning.

Radial head translation measurement in healthy individuals: the radiocapitellar ratio.

HYPOTHESIS: We hypothesized that the radiocapitellar ratio (RCR) is a valid and reproducible method to assess radial head translation in healthy individuals and that the normal RCR of healthy individuals is 0%. MATERIALS AND METHODS: Lateral radiographs of the elbow were examined in 40 healthy patients. The measurement method of the RCR was the displacement of the radial head (minimal distance between the right bisector of the radial head and the center of the capitellum) divided by the diameter of the capitellum. Intraobserver and interobserver reliability was evaluated using intraclass correlation (ICC). RESULTS: The RCR was 4% ± 4% (range, -7% to 19%). The mean RCR of 4% measured in this cohort represents an anterior displacement of 1 mm in a capitellum of 25 mm. Intraobserver reliability was good (ICC, 0.72) and interobserver reliability was fair (ICC, 0.52). A significant side-to-side correlation was observed (r = 0.4, P = .009). No difference was identified between men and women, and no correlation was identified between age and the RCR. The standard deviation of the centered RCR measurements was 3%, which represented the variability of RCR measurements. CONCLUSIONS: The results of this study confirm the traditional belief that in the normal elbow, the radial head is generally aligned towards the capitellum on lateral radiographs. Accordingly, a RCR observed outside the ranges of 1 mm posterior (-5%) to 3 mm anterior (13%) in a 25 mm capitellum suggests a misalignment at the RC joint of the elbow. The RCR method to assess RC joint translations has demonstrated a normal distribution in healthy individuals and good reliability.

The influence of proximal ulnar morphology on elbow range of motion.

BACKGROUND: Physiologic dorsal apex angulation of the proximal ulna is present in 96% of the population. We hypothesize that a correlation exists between the physiologic dorsal ulnar angulation and elbow range of motion (ROM). METHODS: Fifty healthy adults underwent bilateral lateral elbow radiographs in neutral forearm rotation in the following positions: terminal flexion (TF), 90° of flexion, and terminal extension (TE). The proximal ulna dorsal angulation (PUDA), TF, and TE were measured on the digital lateral radiographs by 2 independent observers. ROM was calculated as the difference between TF and TE measurements. Subjects were divided into 2 groups: those with PUDA measurements less than the median and those with PUDA measurements equal to or greater than the median. The relationship between the PUDA and TE, TF, and ROM was evaluated by use of Pearson correlation coefficients. RESULTS: The mean age of the cohort was 31 ± 9 years, and there were 30 women among the 50 volunteers. The sample of 100 elbow radiographs had a mean TF of 150.8° ± 4.5°, a mean TE (ie, flexion contracture) of 11.5° ± 7.3°, and a mean ROM of 139.3° ± 8.4°. The mean PUDA was 5.2° ± 2.8°. Elbows with a greater PUDA had significantly less TE (r = 0.381, P ≤ .001) and ROM (r = -0.351, P ≤ .001). The group of elbows with a lesser PUDA had better TE (9.4° vs 13.6°, P = .004) and ROM (142.0° vs 136.7°, P = .001) than elbows with a greater PUDA. CONCLUSION: The increasing magnitude of the PUDA is associated with decreased maximal elbow extension and global elbow ROM.

Validity of goniometric elbow measurements: comparative study with a radiographic method.

BACKGROUND: A universal goniometer is commonly used to measure the elbow's ROM and carrying angle; however, some authors question its poor intertester reliability. QUESTIONS/PURPOSES: We (1) assessed the validity of goniometric measurements as compared with radiographic measurements in the evaluation of ROM of the elbow and (2) determined the reliability of both. METHODS: The ROM and carrying angle of 51 healthy subjects (102 elbows) were measured using two methods: with a universal goniometer by one observer three times and on radiographs by two independent examiners. Paired t-test and Pearson's correlation were used to compare and detect the relationship between mean ROM. The maximal error was calculated according to the Bland and Altman method. RESULTS: The intraclass correlation coefficients (ICC) ranged from 0.945 to 0.973 for the goniometric measurements and from 0.980 to 0.991 for the radiographic measurements. The two methods correlated when measuring the total ROM in flexion and extension. The maximal errors of the goniometric measurement were 10.3° for extension, 7.0° for flexion, and 6.5° for carrying angle 95% of the time. We observed differences for maximum flexion, maximal extension, and carrying angle between the methods. CONCLUSION: Both measurement methods differ but they correlate. When measured with a goniometer, the elbow ROM shows a maximal error of approximately 10°. CLINICAL RELEVANCE: The goniometer is a reasonable and simple clinical tool, but for research protocols, we suggest using the radiographic method because of the higher level of precision required.

Progressive osteolysis of the radius after distal biceps tendon repair with the bioabsorbable screw.

BACKGROUND: Several complications have been reported with the use of the PLLA (poly-L-Lactide) bioabsorbable screw in orthopedic surgery. The hypothesis was that the use of a bioabsorbable screw in distal biceps tenodesis results in significant osteolysis of the radial bone. The correlation between osteolysis and functional and clinical outcomes was also studied. METHODS: All consecutive patients who underwent anatomic repair of the distal biceps tendon with a bioabsorbable screw were included. From the x-ray taken immediately after the surgery, the ratio between the volume of the bone tunnel and the volume of the radius bone section was measured. This relation was calculated at different follow-up periods to obtain the percentage of tunnel enlargement over time. Complications, as well as functional and clinical outcomes, were also assessed. Mayo Elbow Performance Score (MEPS), the quick-Disability Arm Shoulder Hand (DASH), and the Short-Form 12 (SF-12) were used. RESULTS: Nineteen consecutive patients were available for follow-up. The average initial relative volume occupied by the screw tunnel was 49% of the bone section and increased to 61% at the last follow-up at an average of 22 months (range, 3-62 months). Eight of the 19 patients presented postoperative complications. There was only 1 case of complete bone filling of the tunnel, which was observed at a 5-year and 2-months follow-up. There was no significant correlation between the volume of bone resorption and functional and clinical outcomes. DISCUSSION: No correlation was found between the volume of bone tunnel and the functional outcome. However, the results indicate that the use of a bioabsorbable screw in distal biceps tendon repair results in significant bone osteolysis.

The impact of intra-operative sternum vertical displacement on the sagittal curves of the spine.

Patient positioning is an important step in spinal surgeries. Many surgical frames allow for lumbar lordosis modulation due to lower limb displacement, however, they do not include a feature which can modulate thoracic kyphosis. A sternum vertical displacer (SVD) prototype has been developed which can increase a subject's thoracic kyphosis relative to the neutral prone position on a surgical frame. The kyphosis increase is obtained by lifting the subject's torso off the thoracic cushions with a dedicated sternum cushion that can be displaced vertically. The objective of this study was to evaluate the impact of SVD utilization on the sagittal curves of the spine. Experimental testing was performed on six healthy volunteers. Lateral radiographs were taken in the neutral and sternum raised positions and then analyzed in order to compare the values of sagittal curves. The displacement of volunteers and surgical frame components between positions was recorded using an optoelectronic device. Finally, interface pressures between the volunteers and surgical frame cushions were recorded using a force sensing array. Average results show that passing from the neutral to sternum raised positions caused an increase of 53% in thoracic kyphosis and 24% in lumbar lordosis; both statistically significant. Sensors showed that the sternum was raised a total of 8 cm and that interface pressures were considerably higher in the raised position. The SVD provides a novel way of increasing a patient's thoracic kyphosis intra-operatively which can be used to improve access to posterior vertebral elements and improve sagittal balance. It is recommended that its use should be limited in time due to the increase in interface pressures observed.

Measurement of combined glenoid and Hill-Sachs lesions in anterior shoulder instability.

BACKGROUND: Recurrent glenohumeral anterior instability (RGAI) frequently induces combined glenoid and Hill-Sachs bone lesions and is a risk factor for soft tissue repair failure. This cohort study describes a simple preoperative quantification method for bone loss, the Clock method, the first that combines glenoid and humeral lesions. METHODS: Computed tomography scans of 34 shoulders with RGAI were twice reviewed by three independent observers, who measured bone lesions using the new Clock method and existing validated methods. Intra- and inter-observer reliability of the Clock method was evaluated (intraclass correlation coefficient). Pearson correlation was used to correlate Clock method with existing methods, and with function (Western Ontario Shoulder Instability, Quick-Disabilities of the Arm, Shoulder and Hand). RESULTS: Thirty-two patients met the inclusion criteria: three females and 29 males, mean age 28 years. The intra- and inter-observer reliability was excellent, with intraclass correlation coefficient ranging from 0.817 to 0.938 for the novel Clock method. Humeral Clock and Glenoid Clock strongly correlated with Humeral Ratio (r = 0.882, p < 0.001) and Glenoid Surface Area and Glenoid Ratio (r = 0.793 and 0.717, p < 0.001), respectively. The classic threshold of 25% of the glenoid diameter with the Glenoid Ratio method corresponds to 4 hours with the Glenoid Clock method. CONCLUSIONS: The Clock method is quick and reliable, with more studies being needed to investigate whether it is correlated with surgical outcomes.

Effect of elbow position on radiographic measurements of radio-capitellar alignment.

AIM: To evaluate the effect of different elbow and forearm positions on radiocapitellar alignment. METHODS: Fifty-one healthy volunteers were recruited and bilateral elbow radiographs were taken to form a radiologic database. Lateral elbow radiographs were taken with the elbow in five different positions: Maximal extension and forearm in neutral, maximal flexion and forearm in neutral, elbow at 90° and forearm in neutral, elbow at 90° and forearm in supination and elbow at 90° and forearm in pronation. A goniometer was used to verify the accuracy of the elbow's position for the radiographs at a 90° angle. The radiocapitellar ratio (RCR) measurements were then taken on the collected radiographs using the SliceOmatic software. An orthopedic resident performed the radiographic measurements on the 102 elbows, for a total of 510 lateral elbow radiographic measures. ANOVA paired t-tests and Pearson coefficients were used to assess the differences and correlations between the RCR in each position. RESULTS: Mean RCR values were -2% ± 7% (maximal extension), -5% ± 9% (maximal flexion), and for elbow at 90° and forearm in neutral -2% ± 5%, supination 1% ± 6% and pronation 1% ± 5%. ANOVA analyses demonstrated significant differences between the RCR in different elbow and forearm positions. Paired t-tests confirmed significant differences between the RCR at maximal flexion and flexion at 90°, and maximal extension and flexion. The Pearson coefficient showed significant correlations between the RCR with the elbow at 90° - maximal flexion; the forearm in neutral-supination; the forearm in neutral-pronation. CONCLUSION: Overall, 95% of the RCR values are included in the normal range (obtained at 90° of flexion) and a value outside this range, in any position, should raise suspicion for instability.

Does malpositioning of the arm influence radiographic range of motion measurement?

PURPOSE: Radiographic range of motion measurement of the elbow has been shown to be both precise and reliable. For this method to be used routinely in research studies, it is important to describe its limits regarding: (1) rotation of the arm from the perfect lateral position and (2) the length of humerus and ulna visible on the radiograph. MATERIAL AND METHODS: A 3D bone reconstruction was performed from an upper limb CT scan. Planar radiographs were simulated for rotations of the elbow within a range of ±30o from the perfect lateral position. The field of view was modified, ranging from five visible centimeters of diaphysis on the radiograph to full visibility of the upper limb. RESULTS: The disparity was less than 2.5° (mean=0.68°, SD=0.43°) when the flexed arm was rotated between -30.0° (external rotation, ER) and + 18.0° (internal rotation, IR). When considering the extended arm, measured angles differed by less than 2.5° (mean=0.79°, SD=0.57°) within a range of -15.0° (ER) to +30.0° (IR). When a minimum of 12 cm of humerus and ulna, from the capitellum, were visible on the radiograph measured angles varied very slightly (mean disparity of 0.71°, SD= 0.71°). Finally a qualitative description of the appearance of the radiographs was included to help surgeons estimate acceptable degrees of rotation. CONCLUSION: Range of motion (ROM) measurement shows consistent results, despite 15 to 30 degrees of internal or external rotation. The middle third of the humeral and ulnar diaphyses should be visible on the radiographs to ensure the validity of measurement. Radiographic ROM measurement is still recommended over the goniometer for research purposes because of its high reliability and precision. Moreover, malpositioning of the elbow should not jeopardize results since it will most likely be an angle measurement variation of less than 2.5°.

Radial Head Subluxation After Malalignment of the Proximal Ulna: A Biomechanical Study.

OBJECTIVES: Understanding the anatomy of proximal ulna is important when treating complex injuries, since nonanatomic reconstruction may lead to malunion, arthrosis, and instability. The proximal ulna has a sagittal bow, termed the proximal ulna dorsal angulation (PUDA). The purpose of this study was to evaluate the magnitude of angular malalignment at the PUDA that would lead to radial head subluxation. METHODS: This biomechanical study was conducted on 6 fresh frozen upper extremities with an elbow movement simulator. An osteotomy was performed at the PUDA and stabilized with internal fixation at 5 angles. Lateral elbow fluoroscopic images were taken in 4 elbow and 3 forearm positions, with the annular ligament intact and then released. The displacement of the radial head was quantified with the radiocapitellar ratio measurement. RESULTS: A significant interaction exists between elbow positions, angles of malalignment, and annular ligament integrity (P < 0.001). The greatest magnitudes of radial head subluxation were with annular ligament tear, ranging from -4% to 88% (P < 0.001). Significant differences were found between the different internal fixation angles (P = 0.002) and elbow positions (P < 0.001). Anterior subluxation increased as malalignment was fixed into extension and with progressive elbow flexion. Posterior subluxation increased as malalignment advanced into flexion and decreased with elbow flexion. CONCLUSIONS: Proximal ulna malalignment combined with an annular ligament tear affect the biomechanics of the elbow and can lead to radial head subluxation. This study demonstrates the importance of an anatomic reconstruction, specifically recreation of each individual's unique PUDA. Thus, in the setting of a comminuted proximal ulna fracture with associated annular ligament insufficiency, radiographs of the contralateral elbow may assist with the restoration of the normal anatomy to limit radial head instability.

Repositioning of the humeral tuberosities can be guided by pectoralis major insertion.

In complex proximal humerus fractures, positioning of the tuberosities can be a challenge. This study demonstrates the constant angle between the pectoralis major (PM) and the medial lip of the bicipital groove (BG) on the horizontal axial plane. This angle can be used to determine the rotation, as well as the positioning of the tuberosities, when planning a hemiarthroplasty or a reconstruction. Thirty-one shoulder MRIs were reviewed by three independent observers. The measurements were taken by superposing the axial cut of the proximal humerus, at the level of the distal bicipital groove, and the cut at the top of the PM insertion. By aligning the centers of rotation, we could determine the arcs of rotation between the insertion of the PM and the lips of the medial and lateral bicipital groove (MBG and LBG). Both angles were compared in terms of reliability, reproducibility, and precision. The mean PM-MBG angle was 3.7° [standard deviation (SD) 14.7°] and 27.4° (SD 14.4°) for the PM-LBG angle. We obtained good and very good intra-class correlation coefficient (ICC) results for inter- (0.675) and intra-observer (0.793) reliabilities on the medial angle, plus excellent results for the lateral angle (inter-observers 0.962 and intra-observer 0.895). This study demonstrates that the repositioning of humeral tuberosities can be guided by pectoralis major insertion. This will help achieve proper positioning of the metaphysis in relation to the diaphysis during surgery for complex proximal humerus fractures.

A biomechanical study comparing polyaxial locking screw mechanisms.

OBJECTIVE: Locking plates have become ubiquitous in modern fracture surgery. Recently, manufacturers have developed locking plates with polyaxial screw capabilities in order to optimise screw placement. It has already been demonstrated that inserting uniaxial locking screws off axis results in weaker loads to failure. Our hypothesis was that even implants specifically designed for polyaxial insertion would experience a drop-off in resistance when using non-perpendicular screws. METHODS: Four different types (one monoaxial and three polyaxial locking plates) of readily available small fragment plates were tested. A biomechanical model was developed to test the screws until failure (defined as breakage and rapid loss of >50% force). Screws were inserted at 0, 10 and 15°. RESULTS: The standard monoaxial locking mechanism sustained saw a 60% reduction in force (332N vs. 134N) when screws were inserted cross-threaded at 10°. Two polyaxial systems saw similar significant reductions in force of 45% and 34%, respectively at 15°. A third system utilizing an end cap locking mechanism showed highly variable results with large standard deviations. Polyaxial screws showed on average only limited reduction at 10 degrees of insertion angle. CONCLUSION: Newer designs of locking plates have attractive properties to allow more surgical options during fixation. However this freedom comes at the price of reduced force. Our results show that the safe zone for inserting these screws is closer to 20°, rather than the 30° indicated by the manufacturers. Also, the various polyaxial locking mechanisms seem to influence the overall resistance of the screws.

Effect of force tightening on cable tension and displacement in greater trochanter reattachment.

The purpose of this study was to evaluate cable tension during installation, and during loading similar to walking in a cable grip type greater trochanter (GT), reattachment system. A 4th generation Sawbones composite femur with osteotomised GT was reattached with four Cable-Ready® systems (Zimmer, Warsaw, IN). Cables were tightened at 3 different target installation forces (178, 356 and 534 N) and retightened once as recommended by the manufacturer. Cables tension was continuously monitored using in-situ load cells. To simulate walking, a custom frame was used to apply quasi static load on the head of a femoral stem implant (2340 N) and abductor pull (667 N) on the GT. GT displacement (gap and sliding) relative to the femur was measured using a 3D camera system. During installation, a drop in cable tension was observed when tightening subsequent cables: an average 40+12.2% and 11 ± 5.9% tension loss was measured in the first and second cable. Therefore, retightening the cables, as recommended by the manufacturer, is important. During simulated walking, the second cable additionally lost up to 12.2+3.6% of tension. No difference was observed between the GT-femur gaps measured with cables tightened at different installation forces (p=0.32). The GT sliding however was significantly greater (0.9 ± 0.3 mm) when target installation force was set to only 178 N compared to 356 N (0.2 ± 0.1 mm); p<0.001. There were no significant changes when initial tightening force was increased to 534 N (0.3 ± 0.1 mm); p=0.11. In conclusion, the cable tightening force should be as close as possible to that recommended by the manufacturer, because reducing it compromises the stability of the GT fragment, whereas increasing it does not improve this stability, but could lead to cable breakage.

Force relaxation and sprinback of novel elastic orthopedic cables.

UNLABELLED: Cerclage cables have proven to be very useful in the orthopedic field for bones stabilization and plate fixation but the initial enthusiasm for metallic cables has declined with their high complication rates. Metal materials provide limited elastic deformation compromising their ability to maintain compression. This study compares the mechanical properties of new elastic cables with cobalt-chrome and stainless-steel cables. METHODS: Stainless-steel, cobalt-chrome, nylon and nickel-titanium cables were first loaded up to 356 N, then elongation was maintained for 12 hours, next unloaded and finally reloaded to failure. Initial elongation (%), Relative force relaxation (% loss of initial load after a 12h), elastic springback (%) and force to failure (N) were extracted from force-elongation curves. FINDINGS: Initial elongation was the highest for nylon cables (9%), followed by the nickel-titanium (4%) and both metallic cables (0.3%). During 12 hours, no relaxation was observed for the nickel-titanium and the cobalt-chrome cables, whereas 28 and 45% of the tension was lost respectively for the stainless-steel and the nylon cables. The elastic springback of the nickel-titanium and nylon cables (4.4 and 4.7% respectively) was 20 times higher than that of the stainless-steel and cobalt-chrome cables (0.12 and 0.16% respectively). The force to failure of the stainless steel and cobalt-chrome cables was twice that of the nickel-titanium cables. INTERPRETATION: Multi-braided stainless-steel and cobalt-chrome cables have a high-stiffness with limited ability to tolerate displacement, leading to early cable loosening. Novel low-stiffness cables made of nylon or nickel-titanium offer significant elastic springback improving binding stability.