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.

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.

Long term outcomes of distal radius fractures have rarely been studied prospectively and do not traditionally extend past 1–2 years following treatment. The purpose of this study was to describe the long term patient-rated pain and disability of patients after a distal radius fracture and to also determine the differences in patient reported pain and disability after one year following injury and at the long term follow-up.

Patients who had previously participated in a prospective study, where baseline and standardised one year follow-up were performed following a distal radius fracture were contact to participate in this long term follow-up (LTFU) study. Eligible cases that consented agreed to evaluation which included being sent a package in the mail contain a letter of information and questionnaire. Baseline demographic data including age and sex, as well as date of fracture, mechanism of fall and attending physician information was obtained for all participating subjects. Patient rated pain and disability was measured at baseline, one year and at long-term follow-up using the Patient Rated Wrist Evaluation (PRWE). Patients were categorised as having had a worse outcome (compared to one year follow-up PRWE scores) if their LTFU PRWE score increased by 5 points, having no change in status (if their score changed by four or less points) or improved if their LTFU PRWE score decreased by 5 or more points.

Sixty-five patients (17 male, 48 female) with an average age of 57 years at the time of injury and 67 years at follow-up were included in the study. The mean length of follow-up was 10.7 (± 5.8) years (range: 3–19 years). Overall, 85% of patients reported having no change or had less patient-reported pain and disability (PRWE) at their long-term follow-up compared to their one year PRWE scores. As well, one year PRWE scores were found to be predictive (20.2%) of the variability in long term PRWE score (p=0.001).

This study provided data on a cohort of prospectively followed patients with a distal radius fracture, approximately 10 years after injury. This data may be useful to clinicians and therapists who are interested in determining the long term effects of this frequently occurring upper extremity fracture. The results of this study indicate that after 10 years following a distal radius fracture, 85% of patients will have good outcomes. The results of this study also indicate that majority of cases, if patients have a low amount of pain and disability at one year, then these outcomes will also be true approximately 10 years later.

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.

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.

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.

This study examined the effect of wrist fracture deformities on the work and kinematics of forearm rotation in vitro.

An osteotomy was performed on eight fresh frozen upper extremities just proximal to the distal radioulnar joint and a three-degree of freedom modular implant designed to simulate distal radius fracture deformities was secured in place. This allowed for accurate adjustment of dorsal angulation, dorsal displacement, and radial shortening. The study was divided into two parts, the first phase examining the effects of distal radius deformity and the second sectioned the TFCC and repeated the testing, reviewing the effects of a progressive soft tissue injury in conjunction with distal radius deformity.

The magnitude of muscle activity required to achieve the motion, namely the work of rotation, was affected by the degree of simulated malunion and whether the TFCC was intact or sectioned. Increasing dorsal angulation caused a significant reduction in forearm pronation and supination. Once the TFCC ligaments were sectioned, the range of motion was restored to the pre-injured state for both pronation and supination. Dorsal displacement decreased the forearm range of motion significant at 10mm from native (p=0.02) and 5mm (p=0.03) for intact pronation. Radial shortening of 5mm or less had no effect on forearm rotation. However, 7.5mm of radial shortening could not be achieved in any of the specimens until the TFCC was divided.

Our results reveal that a significant loss of forearm rotation can be expected if a radius fracture exceeds thirty degrees dorsal angulation or 10mm of dorsal displacement. Radial shortening greater than 7.5mm could only be achieved concomitant with a TFCC rupture. This and further study in this area, should assist clinicians in developing treatment strategies for their patients with fractures and deformities of the distal radius.

We compared the initial strength of two techniques for repair of rotator cuff tears. Eight paired cadaveric shoulders with a standardized supraspinatus defect were studied. A transosseous suture and anchor repair was conducted on each side. Specimens were tested under cyclic loading, while fixation was monitored with an optical tracking technique. Mode of failure, number of cycles and load to failure were measured for 50% (5 mm) and 100% (10 mm) loss of repair. Anchors provide improved repair strength at 50% repair loss, in comparison to sutures (p< 0.05). Strength was unaffected by bone mineral density, age and gender.

The purpose of this study was to compare the initial strength of two rotator cuff repair techniques.

Repair strength with anchors was superior to sutures. Strength was unaffected by bone quality.

Anchors, enabling a quicker, less invasive arthroscopic repair, offer improved fixation over sutures, which are more time consuming and invasive.

Eight paired shoulders with a standardized supra-spinatus defect were randomized to anchor or suture repair, and subjected to cyclic loading. Repair migration was measured using a digital camera. Failure mode, cycles and load were measured for 50% and 100% loss of repair. Results were correlated with bone mineral density, age and gender.

The anchors failed at the anchor-tendon interface, whereas the sutures failed through the sutures. Mean values for 50% loss of repair were 205.6 ± 87.5 cycles and 43.8 ± 14.8 N for the sutures, and 1192.5 ± 251.7 cycles and 156.3 ± 19.9 N for the anchors (p< 0.05). The corresponding values for 100% loss of repair were 2457.5 ± 378.6 cycles and 293.8 ± 27.4 N for the sutures, and 2291.9 ± 332.9 cycles and 262.5 ± 28.0 N for the anchors (p> 0.05). These results did not correlate with bone quality.

This study has demonstrated that anchors provide improved repair strength, in comparison to sutures. This may be due to the relative less deformability of the anchors. Repair strength did not correlate with bone quality. This may be attributed to each repair failing primarily through the repair construct or at the anchor-tendon interface, and not through bone.

Purpose: Radial head replacement with a prosthesis that is too thick has been reported to be associated with stiffness, pain and capitellar wear. Radiographic widening of the lateral ulnohumeral joint following radial head replacement has been used as a criterion to diagnose overstuffing of the radiocapitellar joint. The purpose of this study was to show that widening of the lateral ulnohumeral joint is a normal anatomic variant and therefore cannot be used conclusively to diagnose radiocapitellar joint overstuffing.

Methods: Fifty normal standardized anteroposterior elbow radiographs from 50 patients with a mean age of 48 years were reviewed to evaluate variations in the joint space between the medial and lateral facets of the ulnohumeral joint. Using computer software at 4x magnification (GE, Fairfield, CT), two lines were drawn perpendicular to the lateral ulnohumeral joint and two lines perpendicular to the medial ulnohumeral joint. The difference in length of these two lines was used to assess how parallel the lateral and medial joint spaces are. The lengths of the two lines were averaged to compare lateral joint space thickness to medial joint space thickness.

Results: The width of the lateral ulnohumeral joint space (3.6mm & #61617; 0.8mm) was greater than the medial ulnohumeral joint space (2.8mm & #61617; 0.5mm) (p< 0.001). The lengths of the two medial joint space perpendicular lines were similar (p> 0.05), indicating the medial joint space is normally parallel. The lengths of the lateral joint space perpendicular lines were greater laterally (p= 0.02), indicating the lateral joint is not normally parallel.

Conclusions: The lateral ulnohumeral joint space is often wider than the medial ulnohumeral joint space on an anteroposteror radiograph of the normal elbow. While the medial ulnohumeral joint space is usually parallel, the lateral ulnohumeral joint space may be non-parallel and wider laterally, therefore, lateral joint space widening is not a reliable indicator of radiocapitellar joint overstuffing. A non-parallel medial ulnohumeral joint space may be suggestive of possible overstuffing of a radial head arthroplasty, however, comparison radiographs of the uninjured elbow is likely the best investigation to consider when overstuffing is suspected.

This cohort study reports outcomes of patients with comminuted radial head fractures treated with a modular radial head arthroplasty. Twenty-six patients (mean age = fifty-four) were prospectively followed at three, six, twelve, and twenty-four months following surgery. Patient satisfaction with this procedure was high. This data indicates favorable results using a modular radial head arthroplasty with rapid improvement in disability and physical impairment occurring in all measures in the first six months and further improvement in most patients up to two years. The Mayo Elbow Performance Index was at one year and eighty-four at two years.

To investigate the objective and subjective outcomes of unreconstructable radial head fractures treated with a modular radial head arthroplasty.

This data indicates favorable results using a modular radial head arthroplasty with improvement in satisfaction, disability and physical impairment occurring in all measures in the first six-months and continued improvement for up to two-years.

Comminuted radial head fractures are challenging to treat with ORIF. Radial head arthroplasty is an alternative treatment that compares favorably to reported results for ORIF of similar fractures.

Significant improvements were noted over time in self-reported and measured impairments as follows: ASES pain: baseline = 30/50, two years = 15/50; ASES function: baseline = 5/36, two years 27/36; MEPI one year = eighty-two, two years = eight-four. At two years, little impairment was observed compared to the unaffected side in grip 22/26 kg, flexion 141°/145°, or pronation 74°/79°. Moderate differences were noted in extension 28°/2°, supination 57°/72° and strength measures: extension = 29/38, flexion = 31/40, supination = 43/65, pronation = 37/53 (Nm). Patient satisfaction was high at three months (9/10) and remained high at two years (9.1/10).

A cohort of twenty-six patients (seventeen female, mean age fifty-four) with non-reconstructable radial head fractures was treated using a modular metallic radial head arthroplasty (Evolve TM, Wright Medical Technology, Arlington, TN). All patients were prospectively followed at three, six, twelve and twenty-four months. Self-report of limb function, general health, measured ROM and isometric strength were assessed by an independent observer.

Funding Institution research foundation support was provided by Wright Medical Technology. None of the authors received direct compensation for commercial products related to the content of this study.

Purpose: To develop an experimental testing method to measure bone strains as a function of multiple implant stem designs in a single specimen, and to show the efficacy of this method with an application in the distal ulna.

Methods: Twenty-four strain gauges were applied to the surface of an isolated cadaveric ulna to measure anterior-posterior (AP) and medial-lateral (ML) bending loads at six locations along its length. The bone was potted in a custom-designed jig and positioned in a materials testing machine. Loads (5-25N) were applied to the ulnar head while strains were recorded. The ulnar head was removed and an 8cm threaded rod (diameter=5.8mm) was cemented into the canal, and subsequently removed after cement curing. This established a threaded cement mantle that would accept various threaded stem designs. To show the efficacy of this technique, testing was repeated with 5 and 7cm stems. The entire canal was then filled with cement and testing repeated to determine the effect of the residual cement void.

Results: All 24 strain gauges provided quality signals throughout the testing period. Strain varied linearly with load (R-squared=0.94–0.99). The initial threaded rod was easily removed, and there was no difficulty in placing subsequent stems within the mantle. Comparing the 5 and 7cm stems, little difference in strains was observed for the most proximal gauges (2%), with higher variations in the stem exit regions (17%). The cement-filled canal exhibited distal strains similar to the intact baselines (average 2% difference at 25N).

Conclusions: A reliable method has been developed that allows multiple stems to be tested in a single bone. Observed strain differences are therefore a function of implant parameters only (such as stem length), and are not influenced by differences in bone properties as occurs when testing multiple specimens. The layer of threaded bone cement did not impact the native bone strains. This experimental method will be useful to compare stem designs in a variety of bones, avoiding the need for large numbers of specimens due to the repeated measure experimental protocol.

A load cell, capable of measuring medial and lateral loads independently, was used to evaluate current methods of ligamentous balancing in total knee arthroplasty. Ten cadaveric knees were randomized with the surgeons blinded or unblinded to the load cell’s output. Before ligament resection, there were differences between medial and lateral forces (p< 0.05). Balance improved in both groups following ligamentous releases. There was a trend for superior balance (medial-lateral compressive force) with load cell feedback provided: 30°(11.1 vs. 44.4N), 60°(7.1 vs. 36.9N), and 90°(3.0 vs. 8.7N). Further in-vivo studies with this device may improve load transfer and the longevity of TKA.

The purpose of this study was to employ a tibial load cell to assess current methods of ligamentous balance during total knee arthroplasty, and to determine whether the load cell can improve load distribution between the medial and lateral compartments.

Current methods achieve imperfect load balance, however this may be improved with the assistance of an intra-operative load cell.

Intra-operative assessment and quantification of load balance with a load cell may improve the longevity of TKA.

TKA was performed on five pairs of cadaveric knees which were randomly assigned into one of two groups based upon whether the surgeons were blinded or unblinded to the load cell’s output. A validated tibial load cell, capable of measuring medial and lateral loads independently, was inserted. Compartment forces were recorded at discrete flexion angles prior to ligamentous balancing and again after soft tissue balancing with final components cemented into position.

Initially, there were significant differences between the loads in the medial and lateral compartments (p< 0.05). With soft tissue release, there was improved balance. There was a trend for superior balance (medial minus lateral compressive force) in the unblinded group at 30°: 11.1N unblinded vs. 44.4N blinded, 60°: 7.1 vs. 36.9N, and 90°: 3.0 vs. 8.7N.

Failure to achieve ligamentous balance results in instability and unequal load distribution. Current balancing techniques are not perfect, but appear to be improved with the use of the load cell. Further in-vitro and in-vivo studies are needed to improve the load distribution following TKA.

Quantitative measurements of load transfer through the distal radioulnar joint (DRUJ) are limited. An instrumented ulnar head prosthesis was developed to measure bending and torsion moments about the three anatomic axes of the ulna. This device has shown repeatable loading data following insertion in a cadaveric specimen during active forearm rotation trials conducted in an in-vitro upper extremity joint simulator. The data acquired from this device will have important implications for upper extremity modeling, implant fixation and design, and optimizing surgical procedures related to DRUJ arthroplasty.

To develop a system to quantify in-vitro load transfer through the distal radioulnar joint (DRUJ) following ulnar head arthroplasty during simulated active forearm rotation. Also, the effect of an eccentric ulnar head implant design was investigated.

A load-measuring system was developed that was easily surgically inserted, and produced repeatable loading data.

The instrumented implant developed in this study will contribute to the optimization of surgical procedures and implant design parameters related to distal ulnar arthroplasty.

Four pairs of strain gauges were applied to the stem of an ulnar head prosthesis to measure bending and torsion moments about the three anatomic axes of the ulna. Three ulnar heads were machined with varying eccentricities (axisymmetric, 1.5 mm offset and 3.0 mm offset). The implant was inserted in one unpreserved cadaveric upper extremity and active forearm rotation induced using a computer controlled joint simulator. Repeatability (assessed using the maximum standard deviation over 5 trials of pronation and supination) was less than 9% of the output range for all loads. Bending and torsion moments between −0.4 and 0.5 Nm, correlating to joint loads between 0 and 50 N, were measured. The measured loads followed a consistent pattern with forearm position. Higher loads were noted for the eccentric implant heads compared to the axisymmetric head, especially at the extreme ranges of rotation. Clinical interpretation of these findings is difficult since the optimal loading scenario for distal ulnar implant longevity remains unknown.

Please contact author for diagrams and graphs.

The functional outcomes of twenty-eight patients with capitellum and trochlea fractures treated with open reduction and internal fixation were evaluated at a mean follow-up of fifty-five ± thirty-three months. Patients were independently evaluated by a series of questionnaires, radiographs, physical examination and strength testing. Patients with simple fractures did better than those with complicated fractures. The average DASH score was 19/100 and the average ROM was 20 – 130°. Two fractures did not unite and required conversion to total elbow arthroplasty.

A classification system is proposed based on fracture patterns, surgical technique and clinical outcomes.

Capitellum and trochlea fractures are uncommon fractures of the distal humerus. There is limited information about the functional outcome of patients managed with open reduction and internal fixation.

The functional outcome of twenty-eight patients (average age: forty-three ± thirteen years [range, twenty – seventy-one]) who were treated with open reduction and internal fixation for capitellum and trochlea fractures was evaluated at a mean follow-up of fifty-five ± thirty-three months (range, fourteen – one hundred and twenty-one). Patient outcomes were assessed by physical examination, radiographs, range of motion measurements, strength testing and self reported questionnaires (DASH, SF-36 ASES and PREE elbow scales).

There were eleven fractures involving the capitellum, four involving the capitellum and trochlea as one piece and thirteen in which the capitellum and trochlea were separate fragments. These fractures were further defined by the presence or absence of posterior comminution. Fourteen had isolated fractures and fourteen were associated with other elbow, forearm or wrist injuries. Patients with complicated fractures required more extensive surgery, had more complications resulting in secondary procedures and had poorer outcomes compared to those with simple fractures. The average DASH score (19/100), quality of life scores (SF-36: Physical=46, Mental=49) and the average ROM (20 – 130°) suggest favorable patient outcomes overall.

Patients with simple fractures had better results than those with more complicated fractures. A fracture classification system based on fracture patterns, surgical technique and clinical outcomes is proposed.

Purpose: This in-vitro study was conducted to assess the effect of a computer-assisted method of performing shoulder hemiarthroplasty, in comparison to traditional techniques, on passive glenohumeral joint kinematics during abduction.

Methods: Seven pairs of fresh-frozen cadaveric shoulders were tested. One specimen from each pair was randomized to the computer-assisted technique, while the contralateral shoulder underwent a traditional hemiar-throplasty using standard surgical guides by an experienced shoulder surgeon. A simulated four-part proximal humerus fracture was created in each shoulder and was reconstructed using a modular shoulder hemiarthroplasty system (Anatomical Shoulder Hemiarthroplasty System, Centrepulse Orthopaedics Inc, Austin, TX). CT data and computerized simulations of anatomical characteristics were used in the computer-assisted technique. An electromagnetic tracking device (Flock of Birds, Ascension Technologies, Burlington, VT) in conjunction with custom-written software (LabVIEW, National Instruments, Austin, TX) enabled real-time intra-operative feedback.||Passive abduction of the glenohumeral joint was conducted and the resulting motion was quantified using the aforementioned tracking device. Coordinate systems, created on both the humerus and scapula from digitized anatomical landmarks, were used to transform the kinematic data into clinically relevant parameters. Statistical analyses were performed using one-way Analyses of Variance (ANOVAs) followed by post-hoc Student-Newman-Keuls multiple comparisons (p< 0.05).

Results: In the superior-inferior direction, a significant difference in joint kinematics (p=0.011) was found between the computer-assisted and the traditional technique, with the traditional technique resulting in a more inferiorly positioned humeral head at all angles of elevation. There was no difference in translation between the native shoulders and the computer-assisted hemiarthroplasty (p> 0.05). In the anterior-posterior direction there was no difference measured in the position of the humeral head between the two surgical techniques, which were both similar to the native shoulder (p> 0.05).

Conclusions: This is the first known study to examine the effects of a computer-assisted method for performing shoulder hemiarthroplasty. Our results show that the computer-assisted approach should allow improved restoration of glenohumeral joint kinematics relative to conventional techniques, potentially resulting in improved patient outcomes and implant durability.

This study quantified the joint reaction forces in the distal radioulnar joint using an instrumented ulnar head replacement implant. Muscle activity was simulated in-vitro to determine the effects on joint reaction force. Forces were found to linearly increase with simulated muscle load in all forearm positions for the biceps and pronator teres muscles. However, this did not occur for simulations of the supinator and pronator quadratus muscles, likely due to their broader insertion, smaller size and non-linear lines-of-action. This work has important implications in forearm biomechanical modelling, implant design, fixation and rehabilitation protocols following arthroplasty.

To determine the relationship between forearm muscle activity and joint reaction force (JRF) in the distal radioulnar joint (DRUJ).

The DRUJ reaction force is linearly related to the muscle activity of the PT and biceps, but not necessarily to the activity of the supinator and PQ.

This work has implications for biomechanical modelling, implant design, fixation and rehabilitation protocols following DRUJ arthroplasty.

JRFs were found to increase linearly with muscle load for all muscles simulated (biceps, pronator teres (PT), pronator quadratus (PQ), supinator) in all forearm positions tested (supination, neutral and pronation) (correlation coefficient r> 0.85, p< 0.01) with two exceptions; simulation of the PQ in the neutral position (r=−0.65, p=0.2), and the supinator in the pronated position (r=0.72, p=0.2). Biceps simulation generated larger JRF magnitudes in all positions compared to other muscles (p< 0.001), and the PQ generated larger JRF magnitudes compared to the supinator (p=0.05).

Ulnar head arthroplasty was performed with a replacement ulnar head implant instrumented with strain gauges to allow measurement of the DRUJ reaction force. An upper extremity joint simulator applied muscle loads in seven fresh frozen cadaveric upper extremities through computer-controlled pneumatic actuators. Load was varied in 10N increments from 10-80N (biceps and PT) and from 10-50N (PQ and supinator). A hand clamp was used to restrain the forearm in varying positions. The results illustrate that broad insertion and non-linear muscles may not be linearly correlated to joint reaction force in the DRUJ.

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Purpose: Accurate determination of the flexion-extension axis of the elbow is critical to the successful placement of elbow arthroplasties, articulated external fixators and ligament reconstructions. We expect axis alignment using computer-assisted techniques to improve the outcome of these procedures. For image-based procedures, registration (i.e. the transformation needed to align two sets of points) during surgery is critical for accurate alignment. A surface-based registration technique, employing a hand-held laser scanner, was evaluated against a stand-alone paired-point registration method to determine whether it led to improved alignment of the elbow’s flexion-extension axis.

Methods: Twelve cadaveric distal-humeri were selected for registration. To perform paired-point (TP-PP) registration, key anatomical landmarks (capitellum, trochlear sulcus and distal humeral shaft) were digitized using a tracked-probe (TP) and an electromagnetic tracking device (Flock of Birds, Ascension Tech). Using the geometric centers of these landmarks, TP-PP registration to CT data was performed. Surface registration was achieved using the iterative closest point (ICP) least-squares algorithm and the results were evaluated for two devices; registration employing the tracked-probe (TP-ICP) and registration employing a hand-held laser scanner, HHS-ICP (FastSCAN, Polhemus). For surface registration, to be consistent with the amount of the joint exposed during a typical surgical procedure, only the articular surface was used for alignment.

Results: Registration error (Figure 1) was lowest for the HHS-ICP method with a mean of 0.8±0.3-mm (maximum error, 1.4-mm) in translation, compared with a mean error of 1.5±0.5-mm (maximum error, 2.4-mm) for the TP-ICP method and 1.9±1.0-mm (maximum error, 4.4-mm) for the TP-PP method (p< 0.001). Errors in TP-PP registration were greatest in the coronal plane while TP-ICP registration often resulted in an error along the transverse plane (Figure 2).

Conclusions: Overall, the reliability of surface-based registration combined with the implementation of the hand-held laser scanner demonstrated greater registration accuracy. A reliable surface-based registration technique may lead to a more accurate determination of the elbow’s flexion-extension axis during surgical procedures, leading to improved joint motion and implant longevity. The implications of these results can also be extended to other joints that employ comparable computer-assisted surgical techniques.

Purpose: Anterior flanges have been added to the humeral components of some total elbow arthroplasty systems. Surgeons have the option of placing a wedge of bone or bone cement between the anterior surface of the humerus and the flange in an effort to improve implant stability and load transfer. The purpose of this study was to quantify the cortical strains in the humerus after arthroplasty for different materials placed behind the flange.

Methods: Five fresh-frozen cadaveric distal humeri were thawed and cleaned of all soft tissues. Strain gauges were applied to the anterior and posterior surfaces to record bending and axial strains. The bending gauges were positioned just proximal to the location of the flange tip. Cantilever bending and axial compression were applied using a materials testing machine. Following intact testing, the humeral component of a total elbow was implanted by an experienced surgeon and fixed using bone cement. Testing was repeated three times, each with a different material behind the flange: no graft (simulating a humeral component without an anterior flange), cancellous bone graft, and cement graft. Strains were normalized to the intact state and for the applied moments. Data were analyzed using repeated-measure ANOVAs (p< 0.05).

Results: For bending, the strain values were approximately 80% of the intact values with no graft material, 80% with the bone graft, and 87% with the cement graft. These differences among the graft materials were not significant (p=0.5). Similar results were found for the axial strains (p=0.3).

Conclusions: The intention of the anterior flange is to transfer a portion of the load carried by the implant stem to the distal humerus, thereby reducing stress-shielding and improving strength of the construct. In this investigation that employed bending and axial loads, the presence of an anterior flange had no significant effect on load transfer through the distal humerus regardless of graft material used. This would suggest that for the humeral component employed in this study, the flange might not be fulfilling its intended purpose.

The strength of the intact and four reconstruction techniques (figure-eight, docking, single strand utilizing interference screws, and a single strand) of the medial collateral ligament (MCL) of the elbow were compared. Twenty cadaveric specimens were tested with a cyclic valgus loading protocol. The peak loads to failure of the MCL reconstructions were inferior compared to the intact ligament (p< 0.05). The docking and single strand reconstruction utilizing an endobutton for ulnar fixation were equivalent and had greater initial strength than the interference screws or figure-eight technique. It is suggested that improved interference screws are required for this repair.

The purpose of this study was to compare the initial strength of the intact medial collateral ligament (MCL) of the elbow and four reconstruction techniques.

The docking and endobutton reconstructions showed equivalent peak load to failure.

Improved interference screws are required before they are employed clinically.

The average peak load to failure or 5mm of joint gapping was 142.5±39.4N for the intact, 53.0±9.5N for the docking, 52.5±10.4N for the endobutton, 41.0±16.0N for the interference screw, and 33.3±7.1N for the figure-eight reconstructions. The peak load to failure was higher for the intact specimens compared to any of the reconstructions (p< 0.001). The docking reconstruction showed higher peak loads than the figure-eight or interference screw reconstruction, and the endobutton reconstruction showed higher peak loads than the figure-eight reconstruction (p< 0.004). There was no difference in peak loads between the docking and endobutton reconstructions (p> 0.05).

Twenty (ten pairs) unpreserved cadaveric upper extremities were mounted in a custom jig with the elbow at 90°, and a valgus force was applied 12cm from the elbow joint. The specimens were loaded starting at 20N with the load increased in increments of 10N (200 cycles at each load), until either complete ligament failure or a 5mm increase in the distance between the attachment sites of the MCL. The results support that a single strand or multistrand ligament reconstruction can be equivalent with respect to maximal peak loads and cyclic loading. There are concerns with regard to the use of interference screw fixation in the clinical situation.

Passive and active elbow flexion was performed in eight cadaveric arms to determine the effect of Type 1 coronoid fractures and suture repair on kinematics. Testing was performed in ligamentously intact and MCL deficient elbows; with radial head arthroplasty (RHA); with an intact coronoid, following a Type 1 fracture, and with suture repair of the coronoid. There was an alteration in elbow kinematics and stability following Type 1 coronoid fractures that was not corrected with coronoid repair. Suture fixation of the coronoid is probably unnecessary if the lateral ligaments are repaired and the radial head is repaired or replaced.

To determine the effect of fixation of Type 1 coronoid fractures on elbow stability and kinematics in ligamentously intact and medial collateral ligament (MCL) deficient elbows with radial head arthroplasty (RHA).

Type 1 coronoid fractures cause changes in elbow kinematics and stability that are not corrected with suture repair.

Suture fixation of Type 1 coronoid fractures is probably unnecessary if the lateral ligaments are repaired and the radial head is repaired or replaced.

With intact ligaments, there was an increase in valgus angulation following a Type 1 coronoid fracture (p< 0.05) that was not corrected with fixation. With MCL deficiency, there was no change in valgus angulation for all coronoid states. For both ligament states, there was an increase maximum varus-valgus laxity after a Type 1 coronoid fracture with forearm pronation (p=0.03) that was not corrected with fixation (p=0.4). Kinematic data was collected from eight cadaveric arms during passive and simulated active elbow motion. The protocol was performed in stable and MCL deficient elbows with RHA. Testing occurred with the coronoid intact, following Type 1 coronoid fracture, and with suture repair of the fracture. Valgus angulation and maximum varus-valgus laxity were measured.

With intact ligaments, Type 1 coronoid fractures cause an alteration in elbow kinematics and laxity that is not corrected with suture fixation. With MCL disruption, Type 1 coronoid fractures have no effect on elbow kinematics and a small effect on laxity that is not corrected with coronoid repair.

Funding: Research and Institutional Support received from Wright Medical Technologies.

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Purpose: Glenoid replacement remains challenging due to the difficult visualization of anatomical reference landmarks and highly variable version angles. Improper positioning of the glenoid component leads to loosening, early wear, and instability. The objective of this study was to develop and evaluate a tracking system for glenoid implantation. We hypothesized that Computer Assisted Glenoid Implantation (CAGI) would achieve a more accurate and reliable placement of the glenoid component compared to traditional methods.

Methods: 3D CT models of sixteen paired cadaveric shoulder specimens were reconstructed and angles were measured using 3D modeling softwares. Jigs were developed to track instruments and to correct for scapular motion. A standardized protocol for determining in real-time via electromagnetic tracking the glenoid centre, version, inclination and ultimate component placement was previously developed and validated in our laboratory. Specimens were randomized to either traditional or CAGI performed by one of two blinded fellowship trained shoulder surgeons. The mean age was 67 years (range 61–88). Native version and inclination were similar in both groups. All phases of glenoid implantation were navigated.

Results: CAGI was more accurate in achieving the correct version during all phases of glenoid implantation (p < 0.05; paired t-test). CAGI CONTROL Initial pin * 6.3 ± 2.9° Reaming *7.0 ± 3.9° Post drilling * 0.6 ± 0.4° 8.3 ± 4.6°|Post cement * 2.3 ± 2.0° 7.9 ± 3.6°|Post implant CT * 1.8 ± 0.9° 7.7 ± 4.0°. Table 1. Absolute values of the mean error ± SD of version angles obtained with either CAGI or the traditional method (goal = 0° version; * p < 0.05). The largest errors with traditional were observed during drilling and reaming where visualization was especially obscured by the reamer heads. The trend was to retrovert the glenoid. There was no difference with respect to inclination angles (p > 0.05).

Conclusions: Preoperative planning using CT imaging with 3D modeling and intra-operative tracking were combined to produce improved accuracy and reliability of glenoid implantation.

Funding : Other Education Grant

Funding Parties : National Sciences & Engineering Research Council research grant

This study investigated the effect of the articulation position on joint load transfer in total elbow arthroplasty. To quantify loading, an adjustable humeral component, instrumented with a load cell, was developed to measure ulnohumeral loads in-vitro. Computer guidance was implemented to accurately place the linked articulation into eight cadaveric elbows. Axial compression and bending about the flexion axis produced the greatest loads during simulated active elbow flexion. An anteriorly malpositioned flexion-extension axis resulted in increased joint loads during flexion. Translational positional errors were more influential than rotational position on articular loading.

To quantify the relationship between total elbow arthroplasty position and elbow joint loading.

Eight cadaveric upper extremities were tested using a motion-controlled testing device, which simulated muscle activity. Computer guidance was employed to accurately position a linked implant consisting of a custom-designed adjustable humeral component and commercial ulnar component. The testing apparatus was instrumented with a six-degree-of-freedom load cell to measure axial and bending loads. Seven implant positions were tested including anterior-posterior translation (−5.0, −2.5, 0.0, 2.5, 5.0 mm) and internal-external rotation (−5, 0, 5°) during supinated and pronated flexion.

The resultant joint force decreased for all prosthetic hinge positions as elbow flexion increased (p< 0.001). Anterior hinge positions produced greater ulnohumeral loads (p< 0.001) and moments (p< 0.001) than posterior hinge positions during simulated elbow flexion. The greatest bending moment occurred about the flexion axis which reached maximum magnitudes during mid-flexion. Implant hinge malrotation did not have a significant effect on axial (p=0.07) or bending (p=0.6) forces experienced at the joint. The distance between the flexion (hinge) axis and the muscular line-of-action of flexors is reduced with anterior hinge placement, likely increasing the force necessary to produce flexion.

An anteriorly malpositioned flexion-extension axis resulted in an increase in joint loading during flexion and should be avoided during elbow arthroplasty.

This is the first reported study to measure the effect of elbow prosthesis positioning on joint loading. The knowledge gained about joint loads should improve future prosthetic designs and treatment options.

Funding: Canadian Institute for Health Research.

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Purpose: Metal radial head arthroplasty is a proven technique for the treatment of complex radial head fractures. Little previous research is available on the utility and longevity of metal radial head arthroplasty for elbow reconstruction. The purpose of this study was to evaluate the functional outcome of patients with metal radial head arthroplasty (RHA) for elbow reconstruction.

Methods: This was a retrospective review from one institution with three senior orthopaedic surgeons. 23 consecutive patients with 23 RHA were included in the study, 4 patients were lost to follow up. RHA was performed for conditions of rheumatoid arthritis, post traumatic radial head nonunion, post traumatic radial head malunion, elbow instability following previous radial head excision and failed silicone radial head implants. Patients were excluded from the study if they were treated for an acute injury with RHA (under 2 months from injury). There were 8 males and 15 females with a minimum of 2 year follow up. Analysis included chart review, personal interview, physical examination, radiographs and strength testing. Region specific questionnaires were used including: DASH, ASES, MEPI, PRWE, WOS and SF-36. Mean follow up was 9 yrs.

Results: Mayo elbow performance scores were excellent in 11 patients, good in 4 patients, fair in 4 patients and poor in 4 patients. Subjective patient satisfaction was averaged at 8.4 out of 10. Patients demonstrated significantly less isometric strength and grip strength in the affected versed unaffected elbow. There was no statistically significant difference seen in ulnar variance or ulnohumeral joint space between the affected and unaffected limbs.

Conclusions: In conclusion, RHA for elbow reconstruction is a safe procedure that provides patients with long term functional ROM and pain relief.

The purpose of this study was to determine if arthroscopic release is safe and effective in the management of elbow contracture. Twenty patients (mean age of forty-two), undergoing arthroscopic contracture release were retrospectively reviewed at a minimum follow-up of one year (mean twenty-five months). Most patients had combined extrinsic & intrinsic causes for contractures. Mean flexion improved from 122 to 137°. Mean extension improved from 38° to 18°. The mean arc improvement was 35° (p < 0.001). None of the patients had instability and there were no major neuro-vascular complications. All patients had decreased pain and improved elbow function.

To determine if arthroscopic release is safe and effective in the management of elbow contracture.

Twenty patients (mean age of forty-two), undergoing arthroscopic contracture release were retrospectively reviewed at a minimum follow-up of one year (mean twenty-five months). Most patients had combined extrinsic & intrinsic causes for contractures. Motion and strength were measured with standard goniometry and the LIDO isokinetic system by independent evaluators.

Mean flexion improved from 122 ± 16° to 137 ± 12°. Mean extension improved from 38 ± 18° to 18 ± 14°. The mean arc improvement was 35 ± 21° (p < 0.001). Arthroscopic release did not affect forearm rotation or strength. One patient developed a permanent medial antebrachial cutaneous neuroma. One patient required a repeat surgery to remove a loose body. There were no instability and no major neurovascular complications. All patients had improved elbow function with a mean ASES score of thirty-one out of thirty-six. Most patients were satisfied with their surgery, had minimal pain, considered themselves in good physical health on the SF-36, and had minimal impairment on the DASH.

Arthroscopic release is safe and effective in experienced hands.

Results are comparable to traditional open techniques. The theoretical advantages of arthroscopy include improved joint visualization, decreased morbidity and earlier rehabilitation.

Disadvantages include the potential for serious neurovascular complications, and the inability to deal with ulnar nerve pathology or heterotopic ossification. Indications for conversion to open release include excessive swelling, and failure to maintain adequate view.

This study was conducted to determine the effect of passive and active muscle loading on humeral head translation during glenohumeral abduction. A shoulder simulator produced unconstrained active glenohumeral abduction using several sets of loading ratios. Significantly greater translations occurred in passive motion as compared to active motion between 30 and 70 degrees of elevation in three dimensions and in the anterosuperior plane. No difference was found between the active motions. Also, translations of the humeral head decreased with active simulation of abduction emphasizing the importance of the rotator cuff muscles in creating and maintaining the ball-and-socket kinematics of the shoulder.

This in-vitro study was conducted to determine the effect of passive and active loading on humeral head translation during glenohumeral abduction.

Five cadaveric shoulders were tested using a shoulder simulator designed to produce unconstrained abduction of the humerus. Forces were applied to simulate loading of the supraspinatus, subscapularis, infraspinatus/teres minor, anterior, middle, and posterior deltoid muscles using four different sets of loading ratios. These were based on:

equal loads to all cables (Constant-Constant);

In three dimensions, significantly greater translations occurred in passive motion as compared to active motion between 30 and 70 degrees of elevation (p< 0.001). No difference was found between the active motions. Similar results were observed in the two-dimensional resultant translations in the anterosuperior plane of the scapula, with more translation occurring during passive motion (3.6 ± 1.1mm) than active (2.1 ± 1.0mm) (p=0.002), and no significant differences between the active loading methods (Figure 1). The majority of translation tended to occur in the superior-inferior direction for all loading ratios employed.

It was clearly shown that the translations of the humeral head decreased with active simulation of abduction. These findings are in agreement with other in-vivo and in-vitro investigations.

This emphasizes the importance of the rotator cuff muscles in creating and maintaining the ball-and-socket kinematics of the shoulder.

The influence of the supinator and pronator quadratus (PQ) muscles on distal radioulnar joint stability were evaluated using a joint simulator capable of producing forearm rotation, before and after ulnar head excision. Multiple pronation trials were conducted with incremental loading of the PQ relative to the pronator teres; supination trials were similarly conducted with the supinator and biceps. Incremental supinator muscle loading did not alter forearm kinematics. Increased PQ loading did not affect intact kinematics, but did alter joint motion following ulnar head excision. PQ activation will likely aggravate forearm instability following ulnar head excision; suggesting rehabilitation should incorporate immobilization in supination.

The purpose of this study was to study the effect of pronator quadratus (PQ) and supinator loads on forearm kinematics in both an intact distal radioulnar joint (DRUJ) and following ulnar head excision.

The PQ muscle appears to aggravate instability of the DRUJ following ulnar head excision, while incremental loading of the supinator muscle had no effect.

Patients with DRUJ instability and/or who have undergone surgical removal of the ulnar head should be rehabilitated in supination to limit the influence of the PQ muscle.

Eight cadaveric upper extremities were tested in a custom joint simulator employing motion and load-controlled tendon loading to produce forearm rotation. Pronation was achieved via loading of the pronator teres and PQ muscles. Repeated trials were conducted in which the ratio of the PQ load was increased incrementally relative to the pronator teres load. Supination trials were similarly conducted using the biceps and supinator muscles. Testing was conducted in the intact forearm and following ulnar head excision. An electromagnetic tracking device was used to record motion of the radius and ulna. Kinematic data was analyzed with a planar analysis that measured dorsal palmar displacements and diastasis of the DRUJ.

Greater diastasis and dorsal translation of the radius relative to the ulna were noted under increased PQ loading following ulnar head excision (p< 0.05). Increased supinator load had no effect on kinematics before or after ulnar head excision. This effect is likely due to the location of the two muscles. The effect of PQ muscle loading was only noted in neutral to full pronation. These results suggest that rehabilitation of the forearm following ulnar head excision should be conducted with the forearm in supination to minimize joint instability.

Funding: Natural Sciences and Engineering Research Council of Canada, The Arthritis Society (Canada)

Single-strand medial collateral elbow ligament (MCL) reconstruction strength was evaluated using double docking (DD) and interference screw (IS) methods with either palmaris longus (PL) or Graft Jacket_ (GJ) as the reconstruction material. Thirteen upper-extremities were mounted in 90° valgus orientations, and subjected to increasing cyclic valgus loading until failure. DD reconstructions outperformed IS reconstructions (P< 0.05), while PL and GJ performed comparably (P> 0.05). The initial Graft Jacket strength makes it a potential alternative to palmaris longus tendons; Laboratory evaluation of graft strength during healing is required. For its simplicity and strength, the DD technique should be considered, clinically.

Single-strand medial collateral elbow ligament (MCL) reconstruction strength was evaluated using double docking (DD) and interference screw (IS) methods with either palmaris longus (PL) or Graft Jacket_ (GJ) as the reconstruction material.

Thirteen, fresh-frozen upper-extremities (66 ±5 years) were cleaned of all soft tissues except the medial and lateral collateral ligaments, flexed to 90° and mounted in a rigid, valgus testing system. DD or IS reconstructions were performed using either PL or GJ. A cyclic (0.5Hz) load was applied 12cm distal to the medial epicondyle. After 500 cycles, the load was increased by 10N until catastrophic failure or a length increase of 10mm.

The mean maximum load for the DD with GJ was 65 ±12N; for the IS with GJ: 45 ±5N; for the DD with PL: 59 ±11N; and for the IS with PL: 56 ±14N. The mean maximum number of cycles endured by the DD with GJ was 1292 ±562; for the IS with GJ: 356 ±292; for the DD with PL: 1104 ±479; and for the IS with PL: 924 ±690. For both the maximum load and number of cycles, the DD outperformed the IS (P< 0.05) and the GJ and PL performed comparably (P> 0.05).

Single-strand reconstructions using the double dock method outperform the interference screw technique. For its simplicity and strength, the DD technique should be considered, clinically. The initial Graft Jacket strength makes it a potential alternative to palmaris longus tendons; laboratory evaluation of graft strength during healing is required.

Funding: This study was partially funded by Wright Medical Technology (Arlington, TN) and the Canadian Institute for Health Research.

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The reliability and accuracy of plain radiographs, MRI and CT Arthrography to detect the presence of loose bodies was evaluated in twenty-six patients with mechanical elbow symptoms. The location of loose bodies found by the imaging studies was compared to arthroscopic findings. Overall sensitivity for the detection of loose bodies was 88 – 100% and specificity was 20 – 70%. Plain radiographs had a similar sensitivity and specificity of 84% and 71% respectively. MRI and CT Arthrography were similar to plain radiography, suggesting that routine use of these modalities is not indicated.

The purpose of this study was to determine the clinical utility of MRI and CT Arthrography (CTA) to reliably and accurately predict the presence of loose bodies in the elbow.

Twenty-six patients with mechanical elbow symptoms underwent plain radiography, MRI and CTA, followed by standard elbow arthroscopy. Three musculoskeletal radiologists reviewed the ‘blinded’ plain radiographs with both the MRI and CTA at separate sittings. The location and number of loose bodies on the MRI and CTA were recorded. The preoperative plain radiographs, MRI and CTA were compared to the arthroscopic findings.

Agreement between radiologists was higher for the number of loose bodies identified in the posterior compartment (ICC=0.72 for both MRI and CTA) than in the anterior compartment (ICC=0.41 and 0.52 for MRI and CTA respectively). The correlation between the number of lose bodies observed on MRI and CTA compared to those found arthroscopically was also higher in the posterior compartment (r=0.54–0.85) than in the anterior compartment (r=0.01–0.45). Both MRI and CTA had excellent sensitivity (92–100%) but moderate to low specificity (15–77%) in identifying posteriorly located loose bodies. Neither MRI nor CTA were consistently sensitive (46–91%) or specific (13–73%) in predicting anterior loose bodies. Overall sensitivity for the detection of loose bodies in either compartment was 88–100% and specificity was 20–70%. The preoperative radiographs had a similar sensitivity and specificity of 84% and 71% respectively.

MRI and CTA were similar to plain radiography in the prediction of elbow loose bodies.

Introduction and Aims: Computer-assisted bone and soft tissue balancing in total knee arthroplasty (TKA) may aid in achieving perfect knee alignment leading to better function and prosthesis survival. The ‘Measured Resection’ technique was compared to a ‘Computer Assisted Gap Equalisation’ (CAGE) technique of knee balancing in TKA.

Method: TKAs were performed on eight pairs of cadaver knees. One side of each pair was randomly selected to the control group in which measured resection was used for balancing. The experimental technique (CAGE) using a computer-assisted ligament-tensioning device to equalise gap symmetry and load was used on the contralateral side. Post-operatively, a simulator applied forces to the quadriceps and hamstring tendons and a tibial load transducer measured compartmental force at five flexion angles (0, 30, 45, 60, 90 degrees). Outcome assessment consisted of measuring gap loads and symmetry under ligament tension pre-component insertion and compartmental force post-component insertion.

Results: Although there was no significant difference between the two groups in the symmetry of the extension (p = 0.27) and flexion (p=0.07) gaps pre-component insertion, there was a trend towards improved gap symmetry in the CAGE group. As well, pre-component insertion there was a significant (p< 0.05) equalisation of flexion and extension gap loads in the CAGE group. However, post-component insertion there was no significant difference (p> 0.05 using 2-way repeated measures ANOVA) in medial to lateral compartment load balance between the two groups. As well, the measured loads with the knee in full extension (zero degrees of flexion) were significantly higher (p< 0.001) in both groups compared to other flexion angles.

Conclusion: CAGE improves knee balance pre-component insertion by improving surgical accuracy with computer-assistance. However, component design, posterior capsular tension and tibial rotation preclude sustaining the improved balance post-component insertion leaving final knee balance unchanged. Further work is needed to translate the improved surgical accuracy into improved balance following component insertion.

Introduction and Aims: Suture anchors allow consistent reattachment of tendons and ligaments to bone. Many options are available. The purpose of this study was to compare the initial strength of two rotator cuff repair techniques. The hypothesis was that rotator cuff repair strength with anchors would be inferior to transosseous sutures.

Method: Eight paired shoulders with a standardised supraspinatus defect were randomised to bioabsorbable nonsuture-based anchor or transosseous suture repair. Each specimen was then subjected to a stepwise cyclic loading protocol, utilising a custom-designed loading apparatus. Repair site migration was measured using an optical measurement system, consisting of a digital camera and custom software. Mode of failure, number of cycles and load to failure were measured for 50% (5 mm) and 100% (10 mm) loss of repair. These results were correlated with bone mineral density, age and gender. Statistical analysis utilised paired t-tests and Pearson correlations.

Results: The anchors failed at the anchor-tendon interface, whereas the sutures failed through the sutures. Mean values for 50 percent loss of repair were 206 ± 88 cycles and 44 ± 15 N for the sutures, and 1193 ± 252 cycles and 156 ± 20 N for the anchors (p< 0.05). The corresponding values for 100 percent loss of repair were 2458 ± 379 cycles and 294 ± 27 N for the sutures, and 2292 ± 333 cycles and 263 ± 28 N for the anchors (p> 0.05). These results may be due to the relative less deformability of the anchors. This may be relevant clinically, as in the early post-operative period, while tendon healing to bone is occurring, anchors may offer improved strength, allowing improved initial healing. Strength was unaffected by bone quality. This may be attributed to each repair failing primarily through the repair construct or at the anchor-tendon interface, and not through bone. Strengths of this study include the use of paired specimens, the stepwise cyclic loading protocol, as well as increased accuracy of our measurement system. Limitations include the use of an in vitro model, as well as a simulated, standardised rotator cuff tear.

Conclusion: Repair strength with anchors was superior to sutures. Strength was unaffected by bone quality. Anchors facilitate an arthroscopic procedure, decrease operative time, and may allow a faster post-operative recovery. This study has described a new high-resolution method of measuring tendon repair failure and may be useful in future studies.

The formation of a painful neuroma after operations on the medial or lateral sides of the elbow is a common problem. Our aim was to determine the relationship of the cutaneous nerves to the three usual skin incisions around the elbow. In 18 freshly frozen cadaver arms we made three standard 16 cm incisions in the skin medially, laterally, and posteriorly and explored them using loupe magnification. The number of nerves crossing each incision was determined by gross observation and their diameter measured by electronic microcallipers. In ten arms, biopsies of the nerves in each incision were sent for histological examination. We found significantly more cutaneous nerves crossing the medial and lateral incisions than the posterior. The diameter of the nerves crossing the posterior incision was significantly smaller than those crossing the lateral incision. Cutaneous nerves are at considerable risk of injury when medial or lateral incisions are used to approach the elbow, but the posterior approach carries less hazard. The routine use of the posterior incision may reduce the incidence of symptomatic paraesthesia and the formation of a painful neuroma after operation.