Introduction

Joint kinematics following total knee replacement (TKR) is important as it affects joint loading, joint functionality, implant wear and ultimately patient comfort and satisfaction. It is believed that restoring the natural motion of the joint (such as the screw-home mechanism) with a medial pivot knee implant will improve clinical outcomes. Daily activities such as stair climbing and stair descent are among the most difficult tasks for these patients. This study analysed dynamic knee joint motion after implantation of a medial pivot knee implant using fluoroscopy during stair ascent and descent activity.

Introduction & aims

Osteonecrosis may be triggered by bone temperature above 45°C during routine orthopaedic bone cuts using power-driven saws, with potentially negative impacts on bone healing. A new oscillating-tip saw blade design (Precision; Stryker, Kalamazoo, Mich) has been recently developed but the saw blade design may influence the amount of heat generated. We have therefore sought to compare the bone temperature during a standardised cutting task with two different saw blade designs.

Existing techniques of posterior multi-point C1/2 stabilisation are technically demanding and can be hazardous. The coauthors have recently reported successful atlantoaxial fusion using a novel C1/2 stabilisation technique employing C1 multi-axial posterior arch screws (MA-PAS) in a clinical series of three patients where anatomical anomalies precluded established techniques.

The technically less demanding nature of this new technique, and possible wider application in patients with normal anatomy, led the authors to investigate its biomechanical stability compared to other established techniques.

Twenty-four human fresh-frozen cadaveric spines were harvested C0-C5. Motion was restricted to between C0 and C4. Each spine was non-destructively tested in flexion/extension, lateral bending and axial rotation, firstly in the intact state and then after Type 2 odontoid fracture destabilisation and insertion of Magerl-Gallie, Unicortical Harms, Bicortical Harms or MA-PAS instrumentation. ROM between C1 and C2 was monitored using two digital cameras. Results for each technique were compared statistically compared using ANOVA.

The C1-C2 joint of the intact spines demonstrated high flexibility in flexion/extension (16.5deg). After instrumentation all specimens showed significantly reduced ROM in flexion/extension (Magerl-Gallie FE = 4.2deg, Unicort Harms FE = 7.2deg, Bicort Harms FE = 4.4deg). Lateral bend ROM of instrumented specimens (Magerl-Gallie LB =3.8deg, Unicort Harms LB = 3.8deg, Bicort Harms LB =2.3 deg) was, however, similar or slightly greater than intact (2.7 deg) . MA-PAS showed similar ROM in flexion/extension (4.2 deg) as the Magerl-Gallie and Harms techniques but was slightly higher in lateral bend (5.3 deg).

The MA-PAS technique was shown to have similar biomechanical stability to the Magerl-Gallie and Harms techniques. Given the demonstrated biomechanical stability of the MA-PAS technique, it may be a suitable alternative to the existing technically demanding, and possibly more hazardous, multi-point fixation techniques in patients with normal, as well as anomalous, C1/2 segmental anatomy.

This study looks at the dynamic tendon-to-bone contact properties of rotator cuff (RC) repairs—comparing single row repairs (SRR) with double row transosseous- equivalent (TOE) repairs. It was postulated that relaxation during, and movement following, the repair would significantly compromise contact properties and therefore, the ability of the tendon healing.

Simulated tears were created in the supraspinatus tendon of six cadaveric human shoulders. A SRR was then performed using the OPUS System, creating two horizontal mattress sutures. An I-Scan electronic pressure-sensor (Tekscan, Boston, MA) was placed between the supraspinatus tendon and bone. The arm was then rested for 300secs (relaxation) before being passively moved twice through a range-of-motion (0-90 degrees abduction, 0-45 external and 0-45 internal rotation) and finally returned to neutral. The contact properties were recorded throughout each movement. The procedure was then repeated using two TOE techniques: parallel sutures (TOE-P) and a cross over suture pattern (TOE-C).

While peak pressures during the repair were higher in the two TOE repairs, all three methods demonstrated relaxation over 300s such that there was no significant diference in contact pressures at the end of this time. TOE parallel and cross-over repairs demonstrated no significant change in mean TTB contact pressure, force and area during abduction, external rotation and return to neutral, when compared to the 300sec relaxation state. TOE-C demonstrated a higher contact force on internal rotation (+53%). The SRR demonstrated a significant drop in contact force on abduction (−63%), and return to neutral (−43%) and a trend on external rotation (−34%). SRR exhibited no change on internal rotation.

There have been very few biomechanical studies with which observe RC repair contact properties dynamically. Relaxation of the repair can be partially reversed. Significant decrease in contact area with SRR during movement occurred, compared to the TOE repairs, which remains unaltered. This is an important consideration when determining postoperative rehabilitation.

Introduction: The complex anatomy and biomechanics of the atlantoaxial motion segment impose technical challenges in the achievement of safe and successful surgical stabilization and fusion. The coauthors have recently reported successful clinical results using a novel C1-C2 stabilization technique employing C1 multi-axial posterior arch screws (MA-PAS). This study compares biomechanical stability of MA-PAS with two established multi-point fixation techniques (Magerl-Gallie and Harms) using non-destructive and destructive testing.

Methods: 15 human fresh-frozen cadaveric occipital-C5 cervical spines (average age 77.4 [51–95], sourced from ScienceCare, USA) were randomly allocated to 3 equal groups. Screws were passed up through adjacent end vertebrae such that motion was limited to between C0 and C4. Each spinal column was non-destructively tested in flexion/extension (±1.5Nm), lateral bend (±1.5Nm) and axial rotation (±1.5Nm), firstly in their INTACT state and then after Type 2 odontoid fracture destabilization combined with MAGERL-GALLIE (n=5), HARMS (n=5) or MA-PAS (n=5) instrumentation. All 15 reconstructed spines were finally loaded to failure in forward flexion only.

Results: Non-destructive testing: The C1-C2 joint of the INTACT spines all demonstrated high flexibility in flexion/ extension (ave 16.5deg) and axial rotation (ave 52.6 deg) while lateral bending (ave 2.7deg) was less compliant (see Fig.3). After instrumentation all specimens showed significantly reduced ROM in flexion/extension (MAGERL-GALLIE=4.2deg, HARMS=4.4deg, MA-PAS=4.2deg) and axial rotation (MAGERL-GALLIE=4.05deg, HARMS=0.59deg, MA-PAS=3.7deg) while lateral bend ROM of all instrumented specimens was similar or slightly greater than INTACT (HARMS=2.3deg, MAGERL-GALLIE=3.8deg, MA-PAS=5.3deg). There was no significant difference between the instrumented groups in each loading direction.

Destructive testing: MAGERL-GALLIE was the strongest requiring an average of 13.5Nm to cause failure while HARMS was the weakest requiring 7.8Nm of torque. MA-PAS technique averaged 12.2Nm of torque to cause failure.

Conclusions: The MA-PAS technique was shown to have similar ultimate strength in flexion to the MAGERL-GALLIE and HARMS techniques and stability in flexion-extension, axial rotation and lateral bend. The MA-PAS failure load in flexion was greater than the HARMS technique, and nearly as high as the MAGERL-GALLIE. Given the biomechanical stability of the MA-PAS technique, it is proposed that this technique is an alternative to the technically demanding, and possibly more hazardous, conventional multi-point fixation techniques in patients with normal, as well as anomalous, C1/2 segmental anatomy.

Introduction: Periprosthetic bone resorption following total knee arthroplasty (TKA) is becoming a clinical concern. Decrease in bone quality jeapordises implant fixation, consequently leading to revision surgery. It has been suggested that a reduction in the local stress distribution may cause a decrease in bone mineral density (BMD). Computational bone remodelling has been used previously to predict bone adaptation in total hips. However, little has been reported on its use in TKA remodelling simulations. The aim of this study was to simulate the bone remodelling response of the femur and tibia following TKA, using an adaptive bone remodelling algorithm combined with the finite element (FE) method.

Methods: 3D femur and tibia models were constructed from human cadaveric computed tomography images. Total knee implant geometries were used to reconstruct the knee joint.(RBK, Global Orthopaedic Technology, Australia). Both the femur and the tibia models were loaded at 45% gait cycle for normal walking gait using loads based on Taylor et al. A strain-adaptive remodelling algorithm was used to predict the remodelling behaviour of the femur and tibia following TKA. Analysis was performed using ABAQUS. Virtual DEXA images were generated from the FE models at predetermined time-points, BMD gain and loss were also assessed both quantitatively and qualitatively.

Results: There was an increase and decrease in BMD for the femur and tibia models. BMD loss in the femur was predominantly experienced around the pegs and the distal femoral regions. Femoral BMD gain was displayed around the edges of the bone-implant interface, with higher activity at the anterior-medial and posterior-lateral aspects. BMD gain in the tibia was predominantly at the inferior end of the tibial tray’s keel, with the bone mass tending towards the medial aspect. Some bone gain was displayed on the medial side, surrounding the pegs and at the cortex. There was BMD loss on the lateral aspect of the tibia.

Discussion: The adaptive bone remodelling algorithm has shown a good correlation with clinical findings. Reports of clinical and FE studies have shown that for cemented knees, most bone loss occurs at the distal femoral region, especially at the anterior aspect. It has been reported that in the tibia there is generally an over-all decrease in BMD in the proximal tibia and increase below the keel. This is in accordance with our predictions. BMD gain was found to be more predominant on the medial aspect. This may be due to the more medially inclined loading ratio, which affects the stress distribution within the bone. BMD gain in the tibia is shown to follow a path, which starts at the bottom of the keel and tends medially towards the tibial cortex. This illustrates the inherent tendency of load transfer to follow along the stiffest structural path.

Introduction: High ion release along with bone resorption at the bone/implant interface is still a problem, leading to pain, poor function and the possibility of bone fracture. Treatment of a loose implant is not easy and can lead to less than satisfactory revision surgery. The reason for ion release, loosening or periprosthetic fracture of an implant is multifactorial. One factor for ion release that has been reported is inclination angle. Another can be the version angle of the implant and subjecting it to an abnormal loading environment. Few studies have been reported in the literature on hip resurfacing performance based on implant orientation. More studies are required into investigating the use of this predictive technique in orthopaedics to investigate the bearing behaviour and potential ion release due to implant surgical positioning. In this study we modeled a number of different version angles and investigated the contact area, stress and wear characteristics using the finite element method.

Methods: CT scans were used to reconstruct the part of the femur and pelvic geometry. A 3D finite element mesh was created using PATRAN (MSC Software, Santa Ana, CA). The femur loading was taken at peak load position of the gait cycle. The loading was applied to the femur and pelvis was fixed. Material properties were applied using the Hounsfield units from the CT file. Two models were generated, a preoperative and a postoperative state model. The post operative model was reconstructed using the Birmingham Hip Replacement (BHR) system (Smith & Nephew Inc, Memphis, TN). The BHR acetabular cup was oriented at different anteversion angles (5°, 30° & 45° to the saggital plane) to investigate the contact mechanics between the head and cup. Serum ion levels were taken from 12 patients and the change in ion levels over the first 12 month period were analysed statistical to investigate the correlation with anteversion angle. Radiographs from the same patients were analysed to determine the cup anteversion angle using image analysis and edge matching techniques.

Results: The contact areas increased with increasing anteversion angle, 137.3, 165.3 and 169.9mm2 respectively. As a consequence, the contact pressure decreased. The change in ion levels for the patients over the first 12 month period correlated significantly (p< .05) with the anteversion angle using Pearson’s r test.

Discussion: Statistical analysis showed a good Pearson’s correlation of anteversion angle to a change in serum ion levels, 0.867 and 0.734 with p values of 0.001and 0.012 respectively. Acetabular version angle appears to be, at the least, important in determining serum metal ion levels and in evaluating causes of metallosis, the influence of anteversion angle needs to be considered when using metal on metal bearing technology when placing the cup in the acetabulum.

Rotator cuff tendons are typically reattached to the proximal humerus using either transosseous sutures or suture anchors. Their primary mode of failure is at the tendon bone interface 1. Surgical adhesives are used to bond cartilage, tendons and bone, and to close wounds. In an attempt to increase the tendon-bone interface we investigated the addition of a novel adhesive secreted from a species of Australian frog (Notaden bennetti) 2 to different methods of rotator cuff repair.

Forty two fresh frozen sheep infraspinatus tendons were repaired using 3 different techniques: transosseous sutures; two Mitek RC Quickanchors with 1 suture per anchor and two Opus Magnum anchors with 1 suture per anchor all using a mattress stitch configuration. In each group 7 shoulders were repaired with the addition of a small amount of frog glue to the infraspinatus footprint while 7 were used as control with no adhesive. Mechanical testing was performed using a mechanical tensile testing machine.

The strongest construct in the control groups was the Mitek suture anchors (mean 86±5 N) followed by the Opus suture anchor (69±6N) and transosseous repair (50±6N). This proved significant (p< 0.05) between both metallic anchors and the transosseous repair.{BR}The addition of frog glue resulted in a significant increase in load to failure and total energy required until failure in all repair techniques (p< 0.01). There was a 2 fold increase in load to failure of both the Opus Magnum (143±8N) and Mitek RC Fastin (165N±20 N) anchors while the transosseous repair (86± 8 N) had a 1.7 fold increase in its load to failure.

This data suggests that:

suture anchor fixation is a stronger construct requiring a larger amount of total force to fail than transosseous repair using a one suture repair technique, that

The unique properties of this frog glue (strong, flexible, sets in water and biocompatibility) may ultimately lead to the production of a useful adjunct for rotator cuff repair in humans.

Rotator cuff repair failure may to some extent be attributed to tendon-bone gap formation at the repair sight caused by insufficient suture tightening. We measured the footprint contact properties over time of single row and trans-osseous equivalent repairs. We also investigated the effect of suture retightening on the repair.

Rotator cuff tears (RCT) were created in the supra-spinatus tendon of 6 cadaveric shoulders. An electronic pressure sensor (Tekscan) was placed between the tendon and bone to measure the footprint pressure. The OPUS AutoCuff System was used to consecutively repair the RCT using a single row repair (SR-R) and two trans-osseous equivalent repair (TOE-R) techniques;

two parallel sutures (TOE-P) and

Peak initial contact force, were recorded on suture tightening (peak force) and equilibrium contact properties after 300 seconds relaxation (equilibrium force). Data were analysed using pairwise ANOVA.

All techniques demonstrated a similar trend in the contact properties over the test period with an initial peak in contact force on tightening of the sutures, followed by a rapid drop in contact pressure immediately after suture tightening, and finally tending towards equilibrium contact force at 300 seconds.

The TOE-C group demonstrated the highest mean ‘peak force’ and the highest ‘equilibrium force’ after 300 seconds relaxation. The TOE-P ‘peak force’ and ‘equilibrium force’ were −15% and −3% that of TOE-C, while the SRR was −45% and −25% that of TOE-C.

Retightening the sutures a second time had little effect on the SSR contact properties, while retightening the TOE repairs increased the equilibrium contact force by 30% although this was not significant.

Significant relaxation occurs especially within the first 30s, compromising the contact properties.

TOE-R’s exhibit better contact properties than SRR. Retightening the TOE-R’s tended towards a higher final equilibrium contact force. SRR repair contact properties were unaffected by a second tightening.

TOE-R’s should be re-tightened before the suture is locked

A recurrent fracture rate after vertebroplasty and balloon kyphoplasty is as high as 20%. Biomechanically, it has not been proven that refracture rate is due to the cement stiffness alone. This finite-element study investigated effects of cement-stiffness, bone-quality, cement-volume and height-restoration in treatment of vertebral compression fractures using balloon kyphoplasty.

A finite-element model of the lumbar spine was generated from CT-scans. The model comprised of two functional spinal-units, consisting of L2-L4 vertebral bodies, intervertebral-discs, and spinal ligaments. Cement volumes modelled were in the order of 15% and 30% of total vertebral body (VB) volume. Spinal fracture was modelled as being reduced and height of VB was restored. Kyphoplasty was performed. Three different bone qualities were modelled: healthy, osteopenic, osteoporotic. A compressive load was applied to the proximal endplate of L2. An anterior shift of the centre-of-gravity of upper body was simulated by increasing the moment arm of the applied load.

All results of the analysis were compared back to an intact spinal model of the same region under the same loading regime. All parameters affected the mechanical behaviour of the spine model, although changing the bone quality from normal to osteoporotic resulted in the least change. The cement stiffness was initially modelled with an elastic modulus between 0.5GPa and 2GPa. The results showed small differences relative to intact case in the lower modulus cement. A much higher cement stiffness of 8GPa resulted in larger changes in the stresses. The most significant parameter in this study was found to be the changed load path as a result of partial height restoration. This induced a moment in the construct and increased the stresses and strains in the anterior compartments of each vertebra as well as marked in the adjacent (upper and lower) vertebrae. The factor of safety calculation showed the centre of the L3 vertebra to be the most failure prone in all cases, with the osteoporotic bone models showing higher fracture tendencies.

This study indicates that healthier bone has a better chance of survival. Cement properties with lower cement elastic moduli induce stresses/strains which are more similar to the intact model. The best way to reduce the likelihood of failure is to restore the vertebral height.

Multi-ligament knee injuries require complex surgery. Hinged external fixators propose to control the tibio-femoral relationship, protect reconstructions and allow early mobilisation. However, a uniaxial hinge may be too simplistic for such a complex joint. We investigated the influence of an external fixation device on ligament strains and joint contact forces.

Six fresh frozen cadaveric lower limbs (41–56 years old) were obtained. Displacement transducers (Microstrain, USA) were attached to mid-substance lateral (LCL) and medial collateral (MCL) ligaments, and the anterior and posterior cruciate (PCL) ligaments through minimal soft tissue incisions. Joint pressures were measured by transducers (Tekscan) introduced in the medial and lateral compartments through small sub-meniscal arthrotomies. Flouroscopic imaging was used to construct the hinged fixator centred over the epicondylar axis. Ligament tensile strains and joint contact forces were determined through a passive arc of 20 to 110 degrees of flexion and extension, with and without the external fixator (ExFix^™, EBI Biomet Australia).

The application of the external fixation device resulted in minimal change in the mean peak percentage strain of the PCL, MCL and ACL ligaments, while the LCL peak percentage strain decreased. Generally the peak percentage strain for each ligament occurred at or near the same flexion angle in both the un-instrumented and instrumented case within each limb, but the peak percentage strain flexion angles varied significantly across limbs. Peak joint contact forces increased significantly (p < 0.05) in the lateral compartment after attachment of the external fixation device. There was no difference seen in the medial compartment joint contact forces.

This study shows that a uniaxial hinged external fixator can be used in a multi-ligament reconstructed knee to maintain joint congruence and allow early postoperative rang of motion without compromising the results of reconstructions or repairs.

The morbidity associated with tendinopathy is a costly burden on our health system. Recent investigations in our laboratory have shown that alterations in mechanical stress cause significant changes in tendon expression of key matrix molecules and proteolytic enzymes including the aggrecanase molecules, (e.g. ADAMTS-5). Here, we investigate the biomechanical consequences of such altered tensile stress in tail tendons from mice with and without deletion of the ADAMTS-5 gene. Tail tendons from 12 week old C57BL6 wild type and ADAMTS-5 knock-out mice were immediately snap frozen (ex vivo), or cultured stress deprived for 120 hours in DMEM/10% FCS (eight tendons per group). Material properties including maximum stress, strain and elastic modulus were determined for each tendon in uniaxial tension to failure at a constant strain rate of 1.0 mm/second (10% strain/second) on an Instron 8874 servo-hydraulic testing apparatus. Significant differences between groups were determined with Kruskal-Wallis one-way analysis of variance, followed by Mann-Whitney U test with Benjamini-Hochberg post-hoc corrections for multiple comparisons. Stress deprivation for 120 hours led to a significant increase in maximum stress for both the wild type (~150% increase, p = 0.0008) and ADAMTS-5 deficient (~100%, p = 0.0033) mice when compared to ex vivo tendon. Stress deprivation led to a 100% increase in elastic modulus compared to ex vivo for the wild type tendons (p = 0.0033) but failed to increase this parameter in the ADAMTS-5 deficient mice. When the effect of stress deprivation of the ADAMTS-5 deficient mice was directly compared to the wild type stress deprived tendons, a 35% decrease in elastic modulus was found (p = 0.021). We have shown for the first time that deletion of an aggrecanase molecule significantly decreases the material properties of tendon. Alterations in the expression of the aggrecanase molecules may play a role in the development and progression of tendinopathy through their ability to modulate the metabolism of aggrecan [1]. Previous research in our laboratory has shown that aggrecanase expression is markedly up-regulated by stress deprivation. This finding in combination with the results of the present study suggest that the aggrecanase molecules may provide a future therapeutic target for the treatment tendinopathy.

Introduction: Osteochondral mosaic plasty is gaining popularity as a treatment for isolated chondral defects in femoral condyles. Most systems use a metal punch to impact the osteochondral grafts in pre-drilled defects. Damage to the chondrocytes during impaction grafting is of concern and new methods are being sort to minimise this deleterious effect.

This study was designed to see if using a plastic punch instead of a metal punch reduces the extent of chondrocyte damage in osteochondral mosaic plasty.

Method: Ten fresh sheep knees were used to harvest thirty osteochondral plugs using the COR system. The opposite condyles were then prepared to receive the osteochondral grafts. Ten plugs were impacted using a metal punch and ten using a plastic punch. The ten remaining plugs were used as controls. The plugs were then recovered and incubated for 24 hours prior to being stained with MTT. The stained cartilage was then photographed using a digital macroscope.

Images were interpreted using a graphics analysis programme.

Results: There was no significant difference in the extent of chondrocyte damage between the two groups. However, the extent of chondrocyte damage in the impacted groups was significantly greater than the control group.

Conclusion: Impaction grafting clearly damages chondrocytes of the osteochondral plug. In our study using a plastic punch did not reduce the extent of chondrocyte damage during mosaic plasty.

Introduction: Osteochondral mosaicplasty is gaining popularity as a treatment for isolated chondral defects in femoral condyles. Most systems use a metal punch to impact the osteochondral grafts in pre-drilled defects. Damage to the chondrocytes during impaction grafting is of concern and new methods are being sort to minimise this deleterious effect. This study was designed to see if using a plastic punch instead of a metal punch reduces the extent of chondrocyte damage in osteochondral mosaic plasty.

Method: Ten fresh sheep knees were used to harvest 30 osteochondral plugs using the COR system. The opposite condyles were then prepared to receive the osteochondral grafts. Ten plugs were impacted using a metal punch and ten using a plastic punch. The ten remaining plugs were used as controls. The plugs were then recovered and incubated for 24 hours before being stained with MTT. The stained cartilage was then photographed using a digital macroscope. The images were interpreted using a graphics analysis programme.

Results: There was no significant difference in the extent of chondrocyte damage between the two groups. However the extent of chondrocyte damage in the impacted groups was significantly greater than the control group.

Conclusions: Impaction grafting clearly damaged the chondrocytes of the osteochondral plug. In our study using a plastic punch did not reduce the extent of chondrocyte damage during mosaicplasty.