To determine the biomechanical effect of increasing scaphoid malunion and scaphoid non-union on carpal kinematics during dynamic wrist motion using an active wrist motion simulator.

Seven cadaveric upper extremities underwent active wrist flexion and extension in a custom motion wrist simulator with scaphoid kinematics being captured with respect to the distal radius. A three-stage protocol of progressive simulated malunion severity was performed (intact, 10° malunion, 20° malunion) with data analyzed from 45° wrist flexion to 45° wrist extension. Scaphoid malunions were modelled by creating successive volar wedge osteotomies and fixating the resultant scaphoid fragments with 0.062 Kirshner wires. At the completion of malunion motion trials, a scaphoid non-union trial was carried out by removing surgical fixation to observe motion differences from the malunion trials. Motion of the scaphoid, lunate, capitate, and trapezium-trapezoid was recorded and analyzed using active optical trackers.

Increasing scaphoid malunion severity did not significantly affect scaphoid or trapezium-trapezoid motion (p>0.05); however, it did significantly alter lunate motion (p<0.001). Increasing malunion severity resulted in progressive lunate extension across wrist motion (Intact – Mal 10: mean dif. = 7.1° ± 1.6, p<0.05; Intact – Mal 20: mean dif. = 10.2° ± 2.0, p<0.05;) although this change was not as great as the difference seen during non-union trials (native – non-union: mean dif. = 13.8° ± 3.7, p<0.05).

In this in-vitro model, increasing scaphoid malunion severity was associated with progressive extension of the lunate in all wrist positions. The clinical significance of this motion change is yet to be elucidated, but this model serves as a basis for understanding the kinematic consequences of scaphoid malunion deformities.

This study examined the regional variations of cortical and cancellous bone density present in superiorly eroded glenoids. It is hypothesized that eroded regions will contain denser bone in response to localized stress. The shift in natural joint articulation may also cause bone resorption in areas opposite the erosion site.

Clinical CT scans were obtained for 32 shoulders (10m/22f, mean age 72.9yrs, 56–88yrs) classified as having E2-type glenoid erosion. The glenoid was divided into four measurement regions - anterior, inferior, posterior, and superior - as well as five depth regions. Depth regions were segmented in two-millimeter increments from zero to 10 millimeters, beginning at the center of the glenoid surface. A repeated-measures multiple analysis of variance (RM-MANOVA) was performed using SPSS statistical software to look for differences and interactions between mean densities in each depth, quadrant, and between genders. A second RM-MANOVA was performed to examine effects of gender and quadrant on cortical to cancellous bone volume ratios. Significance was set at p < 0 .05.

Quadrant and depth variables showed significant multivariate main effects (p 0.147 respectively). Quadrant, depth, and their interaction showed significant univariate main effects for cortical bone (p≤0.001) and cancellous bone (p < 0 .001). The lowest bone density was found to be in the inferior quadrant for cancellous bone (307±50 HU, p < 0 .001). The superior quadrant contained the highest mean density for cortical bone (895±97 HU), however it was only significantly different than in the posterior quadrant (865±97 HU, p=0.022). As for depth, it was found that cortical bone is most dense at the glenoid surface (zero to two millimeters, 892±91 HU) when compared to bone at two to eight millimeters in depth (p < 0 .02). Cancellous bone was also most dense at the surface (352±51 HU), but only compared to the eight to 10 millimeters depth (p=0.005). Cancellous bone density was found to decrease with increasing depth. For cortical-to-cancellous bone volume ratios, the inferior quadrant (0.37±0.28) had a significantly lower ratio than all other quadrants (p < 0 .001)

The superoposterior region of the glenoid was found to have denser cancellous bone and a high ratio of cortical to cancellous bone, likely due to decreased formation of cancellous bone and increased formation of cortical bone, in response to localized stresses. The inferior quadrant was found to have the least dense cortical and cancellous bone, and the lowest volume of cortical bone relative to cancellous bone. Once again, this is likely due to reduction in microstrain responsible for bone adaptation via Wolff's law. The density values found in this study generally agree with the range of values found in previous studies of normal and arthritic glenoids. An important limitation of this study is the sizing of measurement regions. For a patient with a smaller glenoid, a depth measurement of two millimeters may represent a larger portion of the overall glenoid vault. Segments could be scaled for each patient based on a percentage of each individual's glenoid size.

The role of anconeus in elbow stability has been a long-standing debate. Anatomical and electromyographic studies have suggested a potential role as a stabilizer. However, to our knowledge, no clinical or biomechanical studies have investigated its role in improving the stability of a lateral collateral ligament (LCL) deficient elbow.

Seven cadaveric upper extremities were mounted in an elbow motion simulator in the varus position. An LCL injured model was created by sectioning of the common extensor origin, and the LCL. The anconeus tendon and its aponeurosis were sutured in a Krackow fashion and tensioned to 10N and 20N through a transosseous tunnel at its origin. Varus-valgus angles and ulnohumeral rotations were recorded using an electromagnetic tracking system during simulated active elbow flexion with the forearm pronated and supinated. During active motion, the injured model resulted in a significant increase in varus angulation (5.3°±2.9°, P=.0001 pronation, 3.5°±3.4°, P=.001 supination) and external rotation (ER) (8.6°±5.8°, P=.001 pronation, 7.1°±6.1°, P=.003 supination) of the ulnohumeral articulation compared to the control state (varus angle −2.8°±3.4° pronation, −3.3°±3.2° supination, ER angle 2.1°±5.6° pronation, 1.6°±5.8° supination).

Tensioning of the anconeus significantly decreased the varus angulation (−1.2°±4.5°, P=.006 for 10N in pronation, −3.9°±4°, P=.0001 for 20N in pronation, −4.3°±4°, P=.0001 for 10N in supination, −5.3°±4.2°, P=.0001 for 20N in supination) and ER angle (2.6°±4.5°, P=.008 for 10N in pronation, 0.3°±5°, P=.0001 for 20N in pronation, 0.1°±5.3°, P=.0001 for 10N in supination, −0.8°±5.3°, P=.0001 for 20N in supination) of the injured elbow. Comparing anconeus tensioning to the control state, there was no significant difference in varus-valgus angulation except with anconeus tensioning to 20N with the forearm in supination which resulted in less varus angulation (P=1 for 10N in pronation, P=.267 for 20N in pronation, P=.604 for 10N in supination, P=.030 for 20N in supination). Although there were statistically significant differences in ulnohumeral rotation between anconeus tensioning and the control state (except with anconeus tensioning to 10N with the forearm in pronation which was not significantly different), anconeus tensioning resulted in decreased external rotation angle compared to the control state (P=1 for 10N in pronation, P=.020 for 20N in pronation, P=.033 for 10N in supination, P=.001 for 20N in supination).

In the highly unstable varus elbow orientation, anconeus tensioning restores the in vitro stability of an LCL deficient elbow during simulated active motion with the forearm in both pronation and supination. Interestingly, there was a significant difference in varus-valgus angulation between 20N anconeus tensioning with the forearm supinated and the control state, with less varus angulation for the anconeus tensioning which suggests that loads less than 20N is sufficient to restore varus stability during active motion with the forearm supinated. Similarly, the significant difference observed in ulnohumeral rotation between anconeus tensioning and the control state suggests that lesser degrees of anconeus tensioning would be sufficient to restore the posterolateral instability of an LCL deficient elbow. These results may have several clinical implications such as a potential role for anconeus strengthening in managing symptomatic lateral elbow instability.

Previous biomechanical studies of lateral collateral ligament (LCL) injuries and their surgical repair, reconstruction and rehabilitation have primarily relied on gravity effects with the arm in the varus position. The application of torsional moments to the forearm manually in the laboratory is not reproducible, hence studies to date likely do not represent forces encountered clinically.

The aim of this investigation was to develop a new biomechanical testing model to quantify posterolateral stability of the elbow using an in vitro elbow motion simulator.

Six cadaveric upper extremities were mounted in an elbow motion simulator in the varus position. A threaded screw was then inserted on the dorsal aspect of the proximal ulna and a weight hanger was used to suspend 400g, 600g, and 800g of weight from the screw head to allow torsional moments to be applied to the ulna. An LCL injured (LCLI) model was created by sectioning of the common extensor origin, and the LCL. Ulnohumeral rotation was recorded using an electromagnetic tracking system during simulated active and passive elbow flexion with the forearm pronated and supinated. A repeated measures analysis of variance was performed to compare elbow states (intact, LCLI, and LCLI with 400g, 600g, and 800g of weight).

During active motion, there was a significant difference between different elbow states (P=.001 pronation, P=.0001 supination). Post hoc analysis showed that the addition of weights did not significantly increase the external rotation (ER) of the ulnohumeral articulation (10°±7°, P=.268 400g, 10.5°±7.1°, P=.156 600g, 11°±7.2°, P=.111 800g) compared to the LCLI state (8.4°±6.4°) with the forearm pronated. However, with the forearm supinated, the addition of 800g of weight significantly increased the ER (9.2°±5.9°, P=.038) compared to the LCLI state (5.9°±5.5°) and the addition of 400g and 600g of weights approached significance (8.2°±5.7°, P=.083 400g, 8.7°±5.9°, P=.054 600g).

During passive motion, there was a significant difference between different elbow states (P=.0001 pronation, P=.0001 supination). Post hoc analysis showed that the addition of 600g and 800g but not 400g resulted in a significant increase in ER of the ulnohumeral articulation (9.3°±7.8°, P=.103 400g, 11.2°±6.2°, P=.004 600g, 12.7°±6.8°, P=.006 800g) compared to the LCLI state (3.7°±5.4°) with the forearm pronated. With the forearm supinated, the addition of 400g, 600g, and 800g significantly increased the ER (11.7°±6.7°, P=.031 400g, 13.5°±6.8°, P=.019 600g, 14.9°±6.9°, P=.024 800g) compared to the LCLI state (4.3°±6.6°).

This investigation confirms a novel biomechanical testing model for studying PLRI. Moreover, it demonstrates that the application of even small amounts of torsional moment on the forearm with the arm in the varus position exacerbates the rotational instability seen with the LCL deficient elbow. The effect of torsional loading was significantly worse with the forearm supinated and during passive elbow motion. This new model allows for a more provocative testing of elbow stability after LCL repair or reconstruction. Furthermore, this model will allow for smaller sample sizes to be used while still demonstrating clinically significant differences. Future biomechanical studies evaluating LCL injuries and their repair and rehabilitation should consider using this testing protocol.

Joint hemiarthroplasty replaces one side of a synovial joint and is a viable alternative to total joint arthroplasty when one side of the joint remains healthy. Most hemiarthroplasty implants used in current clinical practice are made from stiff materials such as cobalt chrome or ceramic. The substitution of one side of a soft cartilage-on-cartilage articulation with a rigid implant often leads to damage of the opposing articular cartilage due to the resulting reductions in contact area and increases in cartilage stress. The improvement of post-operative hemiarthroplasty articular contact mechanics is of importance in advancing the performance and longevity of hemiarthroplasty. The purpose of the present study was to investigate the effect of hemiarthroplasty surface compliance on early in-vitro cartilage wear and joint contact mechanics.

Cartilage wear tests were conducted using a six-station pin-on-plate apparatus. Pins were manufactured to have a hemispherical radius of curvature of 4.7 mm using either Bionate (DSM Biomedical) having varying compliances (80A [E=20MPa], 55D [E=35MPa], 75D [E=222MPa], n=6 for each), or ceramic (E=310GPa, n=5). Cartilage plugs were cored from fresh unfrozen bovine knee joints using a 20 mm hole saw and mounted in lubricant-containing chambers, with alpha calf serum diluted with phosphate buffer solution to a protein concentration of 17 g/L. The pins were loaded to 30N and given a stroke length of 10 mm for a total of 50,000 cycles at 1.2 Hz. Volumetric cartilage wear was assessed by comparing three-dimensional cartilage scans before and during wear testing. A two-way ANOVA was used for statistical analysis. To assess hemiarthroplasty joint contact mechanics, 3D finite element modelling (ABAQUS v6.12) was used to replicate the wear testing conditions. Cartilage was modeled using neo-Hookean hyper-elastic material properties. Contact area and peak contact stress were estimated.

The more compliant Bionate 80A and 55D pins produced significantly less volumetric cartilage wear compared with the less compliant Bionate 75D and ceramic pins (p 0.05). In terms of joint contact mechanics, the more compliant materials (Bionate 80A and 55D) had significantly lower maximum contact stress levels compared to the less compliant Bionate 75D and ceramic pins (p < 0 .05).

The results of this study show a relationship between hemiarthroplasty implant surface compliance and early in vitro cartilage wear, where the more compliant surfaces produced significantly lower amounts of cartilage wear. The results of the joint contact mechanics analysis showed that the more compliant hemiarthroplasty materials produced lower maximum cartilage contact stresses than the less compliant materials, likely related to the differences in wear observed. More compliant hemiarthroplasty surfaces may have the potential to improve post-operative cartilage contact mechanics by increasing the implant-cartilage contact area while reducing peak contact stress at the implant-cartilage interface, however, such materials must be resistant to surface fatigue and longer-term cartilage wear/damage must be assessed.

Superiorly eroded glenoids in cuff tear arthropathy represent a surgical challenge for reconstruction. The bone loss orientation and severity may influence glenoid component fixation. This computed-tomography study quantifies both the degree of erosion and orientation in superiorly eroded Favard E2 glenoids. We hypothesized that the erosion in E2 glenoids does not occur purely superiorly, rather, it is oriented in a predictable posterosuperior orientation with a largely semicircular line of erosion.

Three-dimensional reconstructions of 40 shoulders with E2 glenoids (28 female, 12 male patients) at a mean age of 74 years (range, 56–88 years) were created from computed-tomography images. Point coordinates were extracted from each construct to analyze the morphologic structure. The anatomical location of the supra- and infraglenoid tubercle guided the creation of a superoinferior axis, against which the orientation angle of the erosion was measured. The direction and, thus, orientation of erosion was calculated as a vector. By placing ten point coordinates along the line of erosion and creating a circle of best fit, the radius of the circle was placed orthogonally against a chord that resulted by connecting the two outermost points along the line of erosion. To quantify the extent of curvature of the line of erosion between the paleo- and neoglenoid, the length of the radius of the circle of best fit was calculated. Individual values were compared against the mean of circle radii. The area of bony erosion (neoglenoid), was calculated as a percentage of the total glenoid area (neoglenoid + paleoglenoid). The severity of the erosion was categorized as mild (0% to 33%), moderate (34% to 66%), and severe erosion (>66%).

The mean orientation angle between the vector of bony erosion and the superoinferior axis of the glenoid was 47° ± 17° (range, 14° – 74°) located in the posterosuperior quadrant of the glenoid, resulting in the average erosion being directed between the 10 and 11 o'clock position (right shoulder).

In 63% of E2 cases, the line of erosion separating the paleo- and neoglenoids was more curved than the average of all bony erosions in the cohort. The mean surface area of the neoglenoid was 636 ± 247 mm2(range, 233 – 1,333 mm2) and of the paleoglenoid 311 ± 165 mm2(range, 123 – 820 mm2), revealing that, on average, the neoglenoids consume 67% of the total glenoid surface. The extent of erosion of the total cohort was subdivided into one mild (2%), 14 moderate (35%) and 25 severe (62%) cases.

Using a clock-face for orientation, the average orientation of type E2 glenoid defects was directed between the 10 and 11 o'clock position in a right shoulder, corresponding to the posterosuperior glenoid quadrant. Surgeons managing patients with E2 type glenoids should be aware that a superiorly described glenoid erosion is oriented in the posterosuperior quadrant on the glenoid clock-face when viewed intra-operatively. Additionally, the line of erosion in 63% of E2 glenoids is substantially curved, having a significant effect on bone removal techniques when using commercially available augments for defect reconstruction.

Hinged elbow orthoses (HEO) are often used to allow protected motion of the unstable elbow. However, biomechanical studies have not shown HEO to improve the stability of a lateral collateral ligament (LCL) deficient elbow. This lack of effectiveness may be due to the straight hinge of current HEO designs which do not account for the native carrying angle of the elbow. The aim of this study was to determine the effectiveness of a custom-designed HEO with adjustable valgus angulation on stabilizing the LCL deficient elbow.

Eight cadaveric upper extremities were mounted in an elbow motion simulator in the varus position. An LCL injured (LCLI) model was created by sectioning of the common extensor origin, and the LCL. The adjustable HEO was secured to the arm and its effect with 0°, 10°, and 20° (BR00, BR10, BR20) of valgus angulation was investigated. Varus-valgus angles and ulnohumeral rotations were recorded using an electromagnetic tracking system during simulated active elbow flexion with the forearm pronated and supinated. We examined 5 elbow states, intact, LCLI, BR00, BR10, BR20.

There were significant differences in varus and ER angulation between different elbow states with the forearm both pronated and supinated (P=0 for all). The LCLI state with or without the brace resulted in significant increases in varus angulation and ER of the ulnohumeral articulation compared to the intact state (P 0.05). The difference between each of the brace angles and the LCLI state ranged from 1.1° to 2.4° for varus angulation and 0.5° to 1.6° for ER.

Although there was a trend toward decreasing varus and external rotation angulation of the ulnohumeral articulation with the application of this adjustable HEO, none of the brace angles examined in this biomechanical investigation was able to fully restore the stability of the LCL deficient elbow. This lack of stabilizing effect may be due to the weight of the brace exerting unintentional varus and torsional forces on the unstable elbow. Previous investigations have shown that the varus arm position is highly unstable in the LCL deficient elbow. Our results demonstrate that application of an HEO with an adjustable carrying angle does not sufficiently stabilize the LCL deficient elbow in this highly unstable position and varus arm position should continue to be avoided in the rehabilitation programs of an LCL deficient elbow.

Introduction

At present, orthopaedic surgeons utilize either CT, MRI or X-ray for imaging a joint. Unfortunately, CT and MRI are quite expensive, non weight-bearing and the orthopaedic surgeon does not receive revenue for these procedures. Although x-rays are cheaper, similar to CT scans, patients incur radiation. Also, all three of these imaging modalities are static. More recently, a new ultrasound technology has been developed that will allow a surgeon to image their patients in 3D. The objective of this study is to highlight the new opportunity for orthopaedic surgeons to use 3D ultrasound as alternative to CT, MRI and X-rays.

Altered distal radioulnar joint contact (DRUJ) mechanics are thought to cause degenerative changes in the joint following injury. Much of the current research examining DRUJ arthrokinematics focuses on the effect of joint malalignment and resultant degenerative changes. Little is known regarding native cartilage contact mechanics in the distal radioulnar joint. Moreover, current techniques used to measure joint contact rely on invasive procedures and are limited to statically loaded positions. The purpose of this study was to examine native distal radioulnar joint contact mechanics during simulated active and passive forearm rotation using a non-invasive imaging approach.

Testing was performed using 8 fresh frozen cadaveric specimens (6 men: 2 women, mean age 62 years) with no CT evidence of osteoarthritis. The specimens were thawed and surgically prepared for biomechanical testing by isolating the tendons of relevant muscles involved in forearm rotation. The humerus was then rigidly secured to a wrist simulator allowing for simulated active and passive forearm rotation. Three-dimensional (3D) cartilage surface reconstructions of the distal radius and ulna were created using volumetric data acquired from computed tomography after joint disarticulation. Using optically tracked motion data and 3D surface reconstructions, the relative position of the cartilage models was rendered and used to measure DRUJ cartilage contact mechanics.

The results of this study indicate that contact area was maximal in the DRUJ at 10 degrees of supination (p=0.002). There was more contact area in supination than pronation for both active (p=0.005) and passive (p=0.027) forearm rotation. There was no statistically significant difference in the size of the DRUJ contact patch when comparing analogous rotation angles for simulated active and passive forearm motion (p=0.55). The contact centroid moved 10.5±2.6 mm volar along the volar-dorsal axis during simulated active supination. Along the proximal-distal axis, the contact centroid moved 5.7±2.4 mm proximal during simulated active supination.

Using the technique employed in this study, it was possible to non-invasively examine joint cartilage contact mechanics of the distal radioulnar joint while undergoing simulated, continuous active and passive forearm rotation. Overall, there were higher contact area values in supination compared with pronation, with a peak at 10 degrees of supination. The contact centroid moved volarly and proximally with supination. There was no difference in the measured cartilage contact area when comparing active and passive forearm rotation. This study gives new insight into the changes in contact patterns at the native distal radioulnar joint during simulated forearm rotation, and has implications for increasing our understanding of altered joint contact mechanics in the setting of deformity.

Distal radius fractures are the most common fracture of the upper extremity. Malunion of the distal radius is a common clinical problem after these injuries and frequently leads to pain, stiffness loss of strength and functional impairments. Currently, there is no consensus as to whether not the mal-aligned distal radius has an effect on carpal kinematics of the wrist. The purpose of this study was to examine the effect of dorsal angulation (DA) of the distal radius on midcarpal and radiocarpal joint kinematics, and their contributions to total wrist motion.

A passive wrist motion simulator was used to test six fresh-frozen cadaveric upper extremities (age: 67 ± 17yrs). The specimens were amputated at mid humerus, leaving all wrist flexor and extensor tendons and ligamentous structures intact. Tone loads were applied to the wrist flexor and extensor tendons by pneumatic actuators via stainless steel cables. A previously developed distal radius implant was used to simulate native alignment and three DA deformity scenarios (DA 10 deg, 20 deg, and 30 deg). Specimens were rigidly mounted into the simulator with the elbow at 90 degrees of flexion, and guided through a full range of flexion and extension passive motion trials (∼5deg/sec). Carpal motion was captured using optical tracking; radiolunate and capitolunate joint motion was measured and evaluated.

For the normally aligned radius, radiolunate joint motion predominated in flexion, contributing on average 65.4% (±3.4). While the capitolunate joint motion predominated in extension, contributing on 63.8% (±14.0). Increasing DA resulted in significant alterations in radiolunate and capitolunate joint kinematics (p<0.001). There was a reduction of contribution from the capitolunate joint to total wrist motion throughout flexion-extension, significant from 5 degrees of wrist extension to full extension (p = 0.024). Conversely, the radiolunate joint increased its contribution to motion with increasing DA; significant from 5 degrees of wrist extension to full extension as the radiolunate and capitolunate joint kinematics mirrored each other. A DA of 30 degrees resulted in an average radiolunate contribution of 72.6% ± 7.7, across the range of motion of 40 degrees of flexion to 25 degrees of extension.

The results of our study for the radius in a normal anatomic alignment are consistent with prior investigators, showing the radiocarpal joint dominated flexion, and the midcarpal joint dominated extension; with an average 60/40 division in contributions for the radiocarpal in flexion and the midcarpal in extension, respectfully. As DA increased, the radiocarpal joint provided a larger contribution of motion throughout flexion and extension. This alteration in carpal kinematics with increased distal radius dorsal angulation may increase localised stresses and perhaps lead to accelerated joint wear and wrist pain in patients with malunited distal radial fractures.

Despite reverse total shoulder arthroplasty (RTSA) being primarily indicated for massive rotator cuff tears, it is often possible to repair portions of the infraspinatus and subscapularis of patients undergoing this procedure. However, there is disagreement regarding whether these tissues should be repaired, as their effects remain unclear. Therefore, we investigated the effects of rotator cuff repair and changes in humeral and glenosphere lateralisation (HLat & GLat) on deltoid and joint loading.

Six shoulders were tested on an in-vitro muscle driven active motion simulator. Cuff tear arthropathy was simulated in each specimen, which was then implanted with a custom adjustable RTSA fitted with a six axis load sensor. We assessed the effects of 4 RTSA configurations (i.e. all combinations of 0&10mm of HLat & GLat) on deltoid force, joint load, and joint load angle during abduction with/out rotator cuff repair. Deltoid and joint loads recorded by the load cell are reported as a % of Body Weight (%BW). Repeated measures ANOVAs and pairwise comparisons were performed with p<0.05 indicating significance.

Cuff repair interacted with HLat & GLat (p=0.005, Fig. 1) such that with no HLat, GLat increased deltoid force without cuff repair (8.1±2.1%BW, p=0.012) and this effect was significantly increased with cuff repair (12.8±3.2%BW, p=0.010). However, adding HLat mitigated this such that differences were not significant. HLat and GLat affected deltoid force regardless of cuff status (−2.5±0.7%BW, p=0.016 & +7.7±2.3%BW, p=0.016, respectively). Rotator cuff repair did significantly increase joint load (+11.9±2.1%BW, p=0.002), as did GLat (+13.3±1.5%BW, p<0.001).

The increases in deltoid and joint load caused by rotator cuff repair confirm that it acts as an adductor following RTSA and increases deltoid work. Additionally, cuff repair's negative effects are exacerbated by GLat, which strengthens its adduction affect, while Hlat increases the deltoid's abduction effect thus mitigating the cuff's antagonistic effects. Cuff repair increases concavity compression within the joint; however, Hlat produces a similar effect by wrapping the deltoid around the greater tuberosity – which redirects its force – and does so without increasing the magnitude of muscle and joint loading. The long-term effects of increased joint loading due to rotator cuff repair are unknown, however, it can be postulated that it may increase implant wear, and the risk of deltoid fatigue. Therefore, RTSA implant designs which improve joint compression without increasing muscle and joint loading may be preferable to rotator cuff repair.

Wrist motion is achieved primarily via rotation at the radiocarpal and midcarpal joints. The contribution of each carpal bone to total range of motion has been previously investigated, although there is no consensus regarding the influence of each structure to global wrist motion. The objective of this comprehensive in-vitro biomechanical study was to determine the kinematics of the capitate, scaphoid and lunate during unconstrained simulated wrist flexion-extension. In addition, this study examined the effect of motion direction (i.e. flexion or extension) on the kinematics and contribution of the carpal bones.

Seven fresh frozen cadaveric upper limb specimens (age: 67±18 yrs) were amputated mid-humerus, and the wrist flexors/extensors were exposed and sutured at their musculotendinous junctions. Each specimen was mounted on a wrist motion simulator in neutral forearm rotation with the elbow at 90° flexion. Passive flexion and extension motion of the wrist was simulated by moving a K-wire, inserted into the third metacarpal, through the flexion/extension motion arc at a speed of ∼5 mm/sec under muscle tone loads of 10N. Carpal kinematics were captured using optical tracking of bone fixated markers. Kinematic data was analysed from ±35° flexion/extension.

Scaphoid and lunate motion differed between wrist flexion and extension, but correlated linearly (R‸2=0.99,0.97) with capitate motion. In wrist extension, the scaphoid (p=0.03) and lunate (p=0.01) extended 83±19% & 37±18% respectively relative to the capitate. In wrist flexion, the scaphoid (p=1.0) and lunate (p=0.01) flexed 95±20% and 70±12% respectively relative to the capitate. The ratio of carpal rotation to global wrist rotation decreased as the wrist moved from flexion to extension. The lunate rotates on average 46±25% less than the capitate and 35±31% less than the scaphoid during global wrist motion (p=0.01). The scaphoid rotates on average 11±19% less than the capitate during wrist flexion and extension (p=0.07). There was no difference in the contribution of carpal bone motion to global wrist motion during flexion (p=0.26) or extension (p=0.78).

The capitate, lunate and scaphoid move synergistically throughout planar motions of the wrist. Our study found that both the scaphoid and lunate contributed at a greater degree during wrist flexion compared to extension, suggesting that the radiocarpal joint plays a more critical role in wrist flexion. Our results agree with previous studies demonstrating that the scaphoid and lunate do not contribute equally to wrist motion and do not function as a single unit during planar wrist motion. The large magnitude of differential rotation observed between the scaphoid and lunate may be responsible for the high incidence of scapholunate ligament injuries relative to other intercarpal ligaments. An understanding of normal carpal kinematics may assist in developing more durable wrist arthroplasty designs.

Wrist motion is achieved primarily via rotation at the radiocarpal and midcarpal joints. The contribution of each carpal bone to total range of motion has been previously investigated, although there is no consensus regarding the influence of each structure to global wrist motion. The objective of this comprehensive in-vitro biomechanical study was to determine the kinematics of the capitate, scaphoid and lunate during unconstrained simulated wrist flexion-extension. In addition, this study examined the effect of motion direction (i.e. flexion or extension) on the kinematics and contribution of the carpal bones.

Seven fresh frozen cadaveric upper limb specimens (age: 67±18 yrs) were amputated mid-humerus, and the wrist flexors/extensors were exposed and sutured at their musculotendinous junctions. Each specimen was mounted on a wrist motion simulator in neutral forearm rotation with the elbow at 90° flexion. Passive flexion and extension motion of the wrist was simulated by moving a K-wire, inserted into the third metacarpal, through the flexion/extension motion arc at a speed of ∼5 mm/sec under muscle tone loads of 10N. Carpal kinematics were captured using optical tracking of bone fixated markers. Kinematic data was analysed from ±35° flexion/extension.

Scaphoid and lunate motion differed between wrist flexion and extension, but correlated linearly (R^2=0.99,0.97) with capitate motion. In wrist extension, the scaphoid (p=0.03) and lunate (p=0.01) extended 83±19% & 37±18% respectively relative to the capitate. In wrist flexion, the scaphoid (p=1.0) and lunate (p=0.01) flexed 95±20% and 70±12% respectively relative to the capitate. The ratio of carpal rotation to global wrist rotation decreased as the wrist moved from flexion to extension. The lunate rotates on average 46±25% less than the capitate and 35±31% less than the scaphoid during global wrist motion (p=0.01). The scaphoid rotates on average 11±19% less than the capitate during wrist flexion and extension (p=0.07). There was no difference in the contribution of carpal bone motion to global wrist motion during flexion (p=0.26) or extension (p=0.78).

The capitate, lunate and scaphoid move synergistically throughout planar motions of the wrist. Our study found that both the scaphoid and lunate contributed at a greater degree during wrist flexion compared to extension, suggesting that the radiocarpal joint plays a more critical role in wrist flexion. Our results agree with previous studies demonstrating that the scaphoid and lunate do not contribute equally to wrist motion and do not function as a single unit during planar wrist motion. The large magnitude of differential rotation observed between the scaphoid and lunate may be responsible for the high incidence of scapholunate ligament injuries relative to other intercarpal ligaments. An understanding of normal carpal kinematics may assist in developing more durable wrist arthroplasty designs.

There are a variety of sizes currently available for reverse total shoulder arthroplasty (RTSA) implant systems. Common sizing options include a smaller 36 to 38 mm or a larger 40 to 42 mm glenosphere, and are typically selected based on surgeon preference or patient size. Previous studies have only evaluated the abduction and adduction range of motion within a single plane of elevation, providing a limited view of the joint's possible range of motion. The purpose of this study was to use computer modeling to evaluate the abduction and adduction range of motion across multiple planes of elevation for a range of glenosphere sizes.

Computed tomography images of four cadaveric specimens (age: 54 ± 24 years) were used to obtain the osseous anatomy to be utilised in the model. Solid-body motion studies of the RTSA models were constructed with varying glenosphere diameters of 33, 36, 39, 42, and 45 mm in Solidworks (Dassault Systems, US). The implant components were scaled, while maintaining a consistent centre of rotation. Simulations encompassing the full range of abduction and adduction were conducted for the planes of elevation between −15˚ and 135˚ at 15˚ intervals, with the motion of the humerus being constrained in neutral internal-external rotation throughout all planes. Angles of elevation were obtained utilising the humeral long axis and the RTSA centre of rotation. Statistical analysis was performed using repeated measures ANOVA.

Glenosphere diameter was found to significantly affect the adduction range of motion (p=0.043), in which the largest size provided approximately 17˚ more adduction range of motion than the smallest. However, abduction range of motion was not found to be significantly affected through the alteration of glenosphere size (p=0.449). The plane of elevation was not found to significantly affect abduction or abduction (p=0.585 & p=0.225, respectively).

Increasing glenosphere diameter resulted in an increased adduction range of motion when averaged across the tested planes of elevation; however the observed influence on abduction was not significant. These are similar to the trends observed in the previous single plane of elevation studies. These findings illustrate the importance of implant sizing related to range of motion. Further studies are required to determine the influence of glenosphere size on internal and external range of motion.

Shoulder arthroplasty, both primary (TSA) and reverse (RTSA), are common interventions for arthritis and cuff tear arthropathy. The effect of shoulder arthroplasty on shoulder motion is of particular interest in assessing the effectiveness of the procedure and the development and biomechanical testing of implants. A comparison of the arthroplasty shoulder to that of the non-operated contralateral shoulder provides insight into how well the reconstruction has restored natural shoulder motion. The purpose of this study was to ascertain the shoulder motion of patients who have undergone shoulder arthroplasty and to compare the motion of the reconstructed and contralateral natural sides.

Eleven human subjects (70±9yrs) who had undergone total shoulder arthroplasty wore a custom instrumented shirt for the waking hours of one day. The 3D orientation of each humeral sensor was transformed with respect to the torso to allow for the calculation of humeral elevation and plane of elevation angles. Joint angles for each subject were then discretised, and the operative and contralateral normal (control) shoulders were then compared.

The majority of both the arthroplasty and control shoulder elevation motions took place below 80° of elevation, totaling on average 1910±373 and 1887±312 motions per hour, respectively. Conversely, elevations greater than 80° were significantly less with occurrences totaling only 55±31 and 78±41 motions per hour for the arthroplasty and control shoulders, respectively (p<0.01). Both the arthroplasty and control shoulder were at elevations below 80° for 88±7% and 87±7% of the day, respectively. When the total motion of the arthroplasty and non-operative control shoulders were compared, no statistically significant difference was detected (p=0.8), although the non-operated side exhibited marginally more motion than the operated side, an effect which was larger at higher elevation angles (p=0.3).

This study provides insight into the effects of shoulder arthroplasty on thoraco-humeral motion and compares it to the non-operative side. Interestingly, there were no significant differences measured between the arthroplasty and the control side, which may demonstrate the effectiveness of reconstruction on restoring natural shoulder motion. It is interesting to note that on average, each shoulder arthroplasty elevated above 80° approximately 55 times per hour, corresponding to just under 330,000 motions per year. Similarly, when elevations greater than 60° are extrapolated, the resulting yearly motions total approximately 1.5 million cycles (Mc), which suggests that the ‘duty cycle’ of the shoulder is similar to the hip, approximated to be between 1–2 Mc per year. Arthroplasty wear simulators should be calibrated to simulate these patterns of motion, and component design may be improved by understanding the kinematics of actual shoulder motion.

Fracture or resection of the radial head can cause unbalance and long-term functional complications in the elbow. Studies have shown that a radial head excision can change elbow kinematics and decrease elbow stability. The radial head is also important in both valgus and varus laxity and displacement. However, the effect of radial head on ulnohumeral joint load is not known. The objective of this experimental study was to compare the axial loading produced at the ulnohumeral joint during active flexion with and without a radial head resection.

Ten cadaveric arms were used. Each specimen was prepared and secured in an elbow motion simulator. To simulate active flexion, the tendons of the biceps, brachialis, brachioradialis, and triceps were attached to servo motors. The elbow was moved through a full range of flexion. To quantify loads at the ulnohumeral joint, a load cell was implanted in the proximal ulna. Testing was conducted in the intact then radial head resected case, in supination in the horizontal, vertical, varus and valgus positions.

When comparing the average loads during flexion, the axial ulnar load in the horizontal position was 89±29N in an intact state compared to 122±46N during radial head resection. In the vertical position, the intact state produced a 67±16N load while the resected state was 78±23N. In the varus and valgus positions, intact state resulted in loads of 57±26N and 18±3N, respectively. Conversely, with a radial head resection, varus and valus positions measured 56±23N and 54±23N loads, respectively. For both joint configurations, statistical differences were observed for all flexion angles in all arm positions during active flexion (p=0.0001). When comparing arm positions and flexion angle, statistical differences were measured between valgus, horizontal and vertical (p<0.005) except for varus position (p=0.64).

Active flexion caused a variation in loads throughout flexion when comparing intact versus radial head resection. The most significant variation in ulnar loading occurred during valgus and horizontal flexion. The vertical and varus position showed little variation because the position of the arm is not affected by the loss of the radial head. However, in valgus position, the resected radial head creates a void in the joint space and, with gravity, causes greater compensatory ulnar loading. In the horizontal position, the forearm is not directly affected by gravitational pull and cannot adjust to counterbalance the resected radial head, therefore loads are localised in the ulnohumeral joint. These findings prove the importance of the radial head and that a radial head resection can overload the ulnohumeral side.

To evaluate the efficacy of using a novel button-suture construct in place of traditional screws to provide bone block fixation for the Latarjet procedure.

Four paired cadaveric shoulders (n=8) were denuded, with the exception of the conjoint tendon on the coracoid, and were potted. A 15% anterior glenoid bone defect was simulated. Right and left specimens were randomised into two groups: double-screw versus quadruple-button Latarjet reconstruction techniques. A uniaxial mechanical actuator loaded the Latarjet reconstructed glenoid articular surface via a 47mm diameter metallic hemisphere. Cyclic loading between 50–200N was applied to the glenoid at a rate of 1Hz for 1000 cycles. Testing was repeated three times for conjoint tendon loads of 0N, 10N and 20N. The relative positions of three points on the inferior, central and superior edges of the coracoid bone fragment were optically tracked with respect to a glenoid coordinate system throughout testing. Screw and button constructs were compared on the basis of maximum relative displacement at these points (RINF, RCENT, RSUP). Statistical significance was assessed using a paired-samples t-test in SPSS.

When conjoint tendon loading was not present the double screw and quadruple button constructs were not significantly (P>0.779) different (0N: RINF: 0.11 (0.05)mm vs. 0.12 (0.03)mm, RCENT: 0.12 (0.04)mm vs. 0.12 (0.03)mm, RSUP: 0.13 (0.04)mm vs. 0.12 (0.03)mm). Additionally, the double screw construct was not found to differ (P>0.062) from the quadruple button in terms of resultant coracoid displacement for all central and superior points, regardless of conjoint loading (10N: RCENT: 0.11 (0.03)mm vs. 0.19 (0.05)mm, RSUP: 0.11 (0.01)mm vs. 0.18 (0.04)mm; 20N: RCENT: 0.13 (0.01)mm vs. 0.30 (0.13)mm, RSUP: 0.13 (0.03)mm vs. 0.26 (0.14)mm). It was only for the inferior point with conjoint loading of 10N and 20N that the double screw construct began to produce significantly lower displacements than the quadruple button (10N: RINF: 0.11 (0.03)mm vs. 0.23 (0.05)mm, P=0.047; 20N: RINF: 0.12 (0.02)mm vs. 0.39 (0.15)mm, P=0.026).

The results of the screw and button constructs when conjoint tendon loading was absent suggest that the button may be a suitable substitute to the screw when the coracoid is used as a bone block. Due to the small resultant displacements (max: screw = 0.19mm, button = 0.52mm), it is suggested that buttons may also act as a substitute to screws for Latarjet procedures, provided conjoint tendon overloading is minimised during the post-operative graft healing period. These in-vitro results support the in-vivo results of Boileau et al (2015) that demonstrated the suture-button technique to be an excellent alternative to screw fixation Latarjet, with graft healing in 91% of their subjects.

Purpose: Glenoid component loosening is a common reason for failed total shoulder arthroplasty. Multiple factors have been suggested as causes for component loosening including asymmetric loading of the glenoid prosthesis by the humeral head (rocking horse phenomenon). A novel technique was employed to measure in-vitro strain in the subchondral bone adjacent to a cemented all polyethylene pegged glenoid prosthesis. The purpose of the study was to develop and validate a testing protocol to investigate load transfer in the polyethylene glenoid implant and bone construct.

Method: Eight polyethylene components were implanted using standard cementing techniques in eight cadaveric specimens. Loading was performed with a pneumatic actuator capable of applying loads at various angles. A dynamic 10 N/s force was applied for a total of 15 seconds producing a maximum force of 150N at angles of 0, 10, 20, 30, 40 and 50o. Strain gauges were placed around the implant 1mm proximal to the bone-cement interface at the four quadrants. The humeral head was simulated with a custom steel ball with a non-conforming diameter in relation to the prosthesis that is typical in total shoulder arthroplasty.

Results: During pure compressive loading, tension was observed in the superior and inferior quadrants of the glenoid. Superior and inferior loading caused increasing same side (ipsilateral) tension, occurring from 0 to 30o and 0 to 20o, respectively. Compression was recorded superiorly when loading was applied at 40o and 50o in the superior direction while contralateral tension was recorded in the inferior gauges. Strain measurements were less consistent in the anterior and posterior glenoid quadrants and varied between tension and compression.

Conclusion: Tension measurements in the ipsilateral direction at lower angles were unexpected. This observation differs from the previous assumption that applied loads at relatively perpendicular angles to the implant should dissipate as compression. Tension at the bone cement interface is unfavorable. The identification of tension in some quadrants of the implant in this study, therefore, may have revealed a mechanism of implant loosening. Our data support the previously described rocking horse phenomena and also illustrate a new umbrella type effect of polyethylene flexure, which causes the periphery of the glenoid implant to flex upwards superiorly and inferiorly. These findings have the potential to influence future designs of total shoulder arthroplasty perhaps leading to increased implant survival.

Purpose: Blocking screws placed adjacent to intramedullary nails supplement fixation in long bone fractures with a short proximal or distal segment. Clinically, blocking screws are placed using fluoroscopy, resulting in variability in screw placement. The clinical significance of the accuracy of screw placement is unknown. Recently, a targeted blocking screw device was developed, enabling precise placement of screws adjacent to the nail. The purpose of this study was to evaluate the mechanical effects of locking screws (LS) and targeted (TBS) and non-targeted blocking screws (NBS) in distal femur fractures.

Method: Sawbone^® femurs were used to create a fracture model. Femoral sawbone specimens were osteotomized eight cm proximal to the knee joint and a two cm gap was created. Intramedullary nails were used for stabilization, including one proximal locking screw and varying the distal screw configuration for study purposes. Targeted blocking screws were inserted directly adjacent to the intramedullary device using the commercially-available targeting device. Non-targeted screws were inserted one screw diameter medial or lateral to the “ideal” position. Four study groups were created; group one consisted of TBS and two distal LS. Group two had TBS and one LS. Group three had NBS and two LS, and group four consisted of NBS and one LS. Specimens were subjected to a cyclic compression protocol along the mechanical axis of the femur. Applied load varied from 100 to 700 N in 100 N incremental staircase loading protocol. Load-displacement curves recorded construct stiffness. Fracture gap motion was measured with electronic calipers.

Results: Targeted constructs were stiffer at all load levels, and 10% stiffer overall. Differences were statistically significant at moderate load levels (Group one vs three, 400N and 500N, p< 0.05).

Conclusion: Targeted constructs were stiffer at all load levels despite Sawbones^® undergoing significant deformation at the proximal femur, masking the relatively smaller differences in motion at the fracture site. A difference in sagittal motion was found between groups with one and two LS, independent of the position of blocking screws. In conclusion, targeted blocking screw constructs were stiffer at all load levels compared to non-targeted constructs. The number of LS was a factor in sagittal plane stability. This study suggests that using targeted blocking screws in distal femur fractures may reduce fracture motion and decrease post operative malalignment.

Purpose: Current techniques for the investigation of elbow stability following injury or surgical interventions rely on kinematic descriptors. Typically, the motion pathways of the bones are employed to describe the effect of various clinical variables on alignment joint stability. This study describes a new approach to better visualize joint motion pathways that relates the anatomical geometry of the joint, obtained using medical imaging, with the recorded motion of the joint. The clinical aim of our study was to use this approach to investigate the effect of radial head resection and subsequent radial head arthroplasty on joint kinematics and elbow stability.

Method: Five fresh-frozen cadaveric specimens were employed. Computed tomography (CT) scans of each upper extremity were obtained to create a three-dimensional model of the joint. Simulated active elbow flexion with the arm in the valgus gravity loaded position was achieved using an upper arm simulator previously developed in our laboratory. Receivers from an electromagnetic tracking device were attached to the humerus and ulna in order to record their relative motion. Sutures were secured to the tendons of relevant muscles, which were connected to servomotors and pneumatic actuators, used to simulate motion. Kinematic data was collected with the radial head intact, radial head resected and following placement of metallic radial head implant. A repeated-measures analysis of variance was used to detect statistical differences. After testing, each specimen was denuded of all soft tissue and disarticulated. Fiducial markers were attached to the humerus and the ulna. The joint was then re-imaged in the CT scanner to obtain a volumetric image of each fiducial. Using the kinematic data recorded during simulated motion, and the knowledge of the position of each fiducial, a direct visualization of the recorded motion, using the 3D models was obtained. The bony position was then compared to the traditional graphical kinematic analysis examining changes in valgus angulations throughout the arc of motion.

Results: We observed a close agreement between the kinematic output and the registered bony 3D models showing the joint position. Following resection of the radial head, in the valgus dependent position, there was an increase in the valgus angulation of the ulna with respect to the humerus (p< 0.05).

Conclusion: Using this visualization approach, these changes in bony alignment were readily observed and understood visually in the 3D model of the ulna. Unlike the traditional graphical approach used to investigate elbow stability, this technique allows for the representation of coupled motion (rotation) of the bones. This technique also permits direct visualization the relative position of the bones within the joint, hence improving the overall understanding of joint motion.