In macroscopically-normal and early degenerate human articular cartilage, chondrocytes often exhibit increased volume and abnormal morphology with cytoplasmic processes. With further degeneration, chondrocyte clusters are a characteristic feature. These changes can influence matrix metabolism leading to matrix loss and predisposition to osteoarthritis (OA). Here, we report that articular chondrocytes cultured in a weak 3D agarose gel develop some of the morphological changes observed in degenerate cartilage. Cells were isolated from bovine metacarpal-phalangeal joints using collagenase. Gels were prepared with agarose (2% or 0.2% (v/v)) and cultured for 7 days (Dulbecco's modified Eagle's medium;37superscriptC;pH7.4;fetal calf serum (FCS; 1–10%)). Cells were fluorescently-labelled and volume/morphology examined by confocal microscopy. After one week of culture, chondrocytes in 2% gels (10% FCS) were mostly spheroidal; only 18.5±1% cells exhibited fine processes and 42.5±0.1% formed small clusters. However, in weak (0.2%) gels 66.9±1.3% (P=0.011) of chondrocytes had processes with lengths 7–63μm and 80.8±0.2% (P<.005) formed large clusters. In the weak gel after seven days, increasing FCS concentration markedly elevated the %age of chondrocytes in clusters from 31.1±0.2% in 1% FCS, to 87.3±0.27% in 10% FCS (P⊖.05). (Data from a minimum of three separate experiments at each condition with at least three replicates). These results suggest some similarities between the morphological changes to chondrocytes with OA development and those observed in weak agarose gels. The increased prevalence of abnormal chondrocytes with raised FCS concentration suggests that action of e.g. growth factors on chondrocytes is a more potent controller of cell shape than the strength of agarose.

Introduction

The anterior approach to primary total hip arthroplasty is an unfamiliar approach to most surgeons that is considered to be minimally invasive based on the premise that there is less soft tissue damage and quicker post-operative recovery time. We present our experience of using the anterior approach exclusively by a single surgeon at multiple surgical centers for a period of 3.5 years.

Introduction

The advantages of the direct anterior approach (DAA) for total hip arthroplasty include the preservation of external rotators and hip abductors thus leading to quicker recovery times. To our knowledge, there is no objective method in the literature to predict the level of difficulty for femoral exposure through the DAA. It would be beneficial to the surgeon learning the DAA to assess difficulty pre-operatively to avoid prolonged operative times. The purpose of this study was to develop a predictive model of femoral exposure difficulty in the DAA using a combination of demographic data and radiographic measurements.

Our aim was to determine the effects of tibial component malrotation and posterior slope on knee kinematics following Scorpio cruciate retaining total knee replacement in cadaver specimens.

The movements of the hip, thigh and lower leg were monitored in 3D using a validated infra-red Computer Navigation System via bone implanted trackers. Ten normal comparable cadaver specimens were mounted in a custom rig allowing 3D assessment of kinematics under various loading conditions. The specimens then underwent Navigated TKR as per normal operating surgical protocols however an augmented tibial component was implanted. This allowed the researchers to precisely modify the rotation of the tibial component around its predetermined central axis, as well as to alter the posterior slope of the component. A pneumatic cylinder was used to provide a simulated quadriceps extension force while the knee was tested with a variety of applied loads including anterior and posterior draw, abduction and adduction, internal and external rotation.

TKR kinematics are significantly different from those of the native knee (p< 0.05). Increasing tibial posterior slope resulted in an incremental posterior position of the femur (p< 0.05), deviation of the neutral path of motion (p< 0.05) and alteration of the normal AP envelope of laxity (p< 0.05). Tibial component malrotations over 10 degrees resulted in increasing deviations of the neutral movement path of motion (p< 0.05) without significantly affecting the envelope of laxity. Tibial component malrotations of more than 10 degrees, when combined with a posterior slope of six degrees or more, resulted in prosthetic subluxation under certain loading conditions.

This study has demonstrated significant differences in knee kinematics before and after total knee implantation. Increasing values of internal and external rotation, as well as posterior slope of the tibial tray resulted in further deviations of total knee kinematics from normal by altering the neutral path of motion and the soft tissue envelope, with combined misalignments resulting in the greatest deviations from normal with prosthetic subluxation in some cases. Deviations from normal kinematics may result in increased ligament tension and incongruence or dysfunction of the component articulations, with the generation of sheer forces in the gait cycle. These may contribute to premature wear and loosening. Surgeons should be aware of this when considering the addition of posterior slope or assessing tibial component positioning in TKR.

Aims: To determine the effects of tibial component rotation and posterior slope on kinematics following Scor-pio navigated TKR in cadaver specimens.

Methods: Knee kinematics were monitored using a validated Infra Red Navigation System. Ten normal comparable cadaver specimens were mounted in a custom rig allowing assessment of kinematics under various loading conditions. The specimens then underwent Navigated TKR. The surgery was performed as per normal operating surgical protocols by an expert knee surgeon. However an augmented tibial component was implanted allowing the researchers to precisely modify its rotation and posterior slope. A pneumatic cylinder attached to the quadriceps tendon was then used to repetitively flex and extend the knee with a variety of applied loads.

Results: Kinematics were different after TKR. Increasing posterior slope resulted in increasing posterior position of the femur, particularly at maximum flexion. Posterior slope also resulted in a deviation of the neutral path of motion and alteration of the normal envelope of laxity. Tibial component malrotations over 5 degrees resulted in deviations of the neutral path of motion without affecting the envelope of laxity. A combined malrotations over 10 degrees with posterior slopes over 6 degrees resulted in prosthetic subluxation under certain loading conditions.

Discussion: Knee kinematics are different after TKR. Increasing internal and external malrotation as well as the addition of posterior slope resulted in deviations of TKR kinematics through alteration of the neutral path of movement and or the envelope of laxity. Combined misalignments of slope and rotation resulted in the greatest deviations from normal kinematics and in some cases, prosthetic subluxation. Incompatibilities of alignment may result in increased ligament tension and component articulation dysfunction that may contribute to premature wear and loosening. Surgeons should be aware of this when considering the addition of posterior slope or assessing tibial component positioning in TKR.

AIMS: To determine the effects of tibial component rotation and posterior slope on kinematics following Scorpio CR navigated TKR in cadaver specimens.

METHODS AND RESULTS: Knee kinematics were monitored using a validated IR Navigation System. Ten normal comparable cadaver specimens were mounted in a custom rig allowing assessment of kinematics under various loading conditions. The specimens then underwent Navigated TKR. The surgery was performed as per normal operating surgical protocols by an expert knee surgeon. However an augmented tibial component was implanted allowing the researchers to precisely modify its rotation and posterior slope. A pneumatic cylinder attached to the quadriceps tendon was then used to repetitively flex and extend the knee with a variety of applied loads.

Kinematics were different after TKR. Increasing posterior slope resulted in increasing posterior position of the femur, particularly at maximum flexion. Posterior slope also resulted in a deviation of the neutral path of motion and alteration of the normal envelope of laxity. Tibial component malrotations over 5 degrees resulted in deviations of the neutral path of motion without affecting the envelope of laxity. Combined malrotations over 10 degrees with posterior slopes over 6 degrees resulting in prosthetic subluxation under certain loading conditions.

Discussion: Knee kinematics are different after TKR. Increasing internal and external tibial component malrotation as well as the addition of posterior slope resulted in deviations of TKR kinematics through alteration of the neutral path of movement and or the envelope of laxity. Combined misalignments of slope and rotation resulted in the greatest deviations from normal kinematics and in some cases, prosthetic subluxation. Incompatibilities of alignment may result in increased ligament tension and component articulation dysfunction that may contribute to premature wear and loosening. Surgeons should be aware of this when considering the addition of posterior slope or assessing tibial component positioning in TKR.

Compression staples are a popular form of fixation for osteotomy and arthrodesis. “Mechanical Compression” or “Shape Memory” designs are commercially available. We performed a biomechanical study to assess suitability for their intended functions.

Compression was measured using a load cell mounted within a simulated arthrodesis site. Two designs of mechanical compression and shape memory staples were tested and compared. The effect of altering the length of the staple limb was also assessed.

Both designs of mechanical compression staple had divergence of their fixation limbs causing inconsistent compression or even distraction. The shape memory staples all achieved a consistent compressive force at the fusion site. Staple limb length did not appear to alter the compression force generated.

The limbs of Mechanical Compression Staples splay open with a fulcrum at the intersection bridge. As a result, there is distraction of the far cortex and compression of the proximate cortex. Shape memory staples compress both the near and far cortices leading to stability and compression forces across the arthrodesis site.

Introduction: Compression staples are indicated for use in forefoot osteotomies and midfoot and forefoot fusions. The staple design can be divided into “Mechanical Compression” or “Shape Memory”. Although they are becoming increasingly popular because of their ease of use, there is little data published on the effectiveness of the true compression achieved across bony surfaces. There is no data on the optimal limb-length to staple width ratio required for compression. We aimed to compare four commercially available types of compression staple and measure the compression force achieved.

Methods and Materials: Compression in porcine tibia, cancellous bone substitute and perspex was compared using a load cell mounted within a simulated fusion site between two test blocks. The amplified output was continuously recorded using a datalogger and the data analysed. Two designs of “mechanical” compression staple and two designs of “shape memory” staple were tested. The effect of altering limb length on compression was also noted.

Results: The “mechanical” compression staples splayed open with the limbs of both designs causing either no compression or even distraction at simulated fusion site. Distractive forces of up to 23N were recorded. By contrast, the “shape memory” staples all achieved compression at the fusion site of between 5–25N. Limb length did not appear to alter the compression force achieved.

Discussion: “Mechanical” compression staples act in a similar way to basic AO principles of a 2-hole compression plate used without a lag screw technique or pre-bending. Although there is compression of the cis-cortex, the limbs of the staple splay open with a fulcrum around the bridge-limb intersection resulting in distraction of the trans-cortex. “Shape memory” staples compress both the cis- and trans-cortices along the length of the limb leading to adequate stability and compression forces across the fusion site.

Conclusion: This study demonstrates that “mechanical” compression staples cause a distractive force rather than a compressive force and manufacturers should be aware that further design modifications are required to prevent this. We recommend that “shape memory” staples, standard staples or lag screws are used instead. The limb-length to staple width ratio does not appear to be important.

Background: Several approaches to the ACL attachment and drilling methods exist, with little evidence of which method is the best.

Hypothesis: The “Retrodrill” or an “inside-out” drilling technique result in uniform intra-articular tunnel mouths compared with standard “outside-in” conventional ACL drill bits.

Study Design: Controlled laboratory study.

Methods: Sixteen cadaveric knees were divided into Anterograde (A) and retrograde “Retrodrill” (R) groups and ACL tunnels drilled. The femoral tunnel mouths were moulded using PMMA, then Nylon rods of identical diameter containing 1mm diameter K-wires were inserted into the tunnels and AP and lateral X-rays taken. Matching laboratory experiments utilised 10 pig femurs and synthetic bone.

Results: In group A, the mean difference between tunnels and their mouths was 1.6±0.5mm, compared with 0.3±0.2mm for Group R (p < 0.001). The mean femoral tunnel angulation in the sagittal plane for Group A was 45±10 degrees and 78±14 degrees for Group R (p< 0.001); and 30±12 degrees, and 71±12 degrees (p< 0.001) in the coronal plane respectively. There were similar ACL attachment hit rates from the groups. In porcine bone, tunnel mouth widening in the anterograde tibial group was 0.7±0.4mm, 0.04mm±0.1mm for the anterograde femoral group, and 0.06±0.1mm for the retrograde group (p< 0.001). In synthetic bone, the difference between the tunnels and their mouths was 0.8±0.8mm, 0.2±0.1mm and 0.1±0.1mm (p< 0.001) respectively.

Conclusions: The “Retrodrill”, or an inside out antero-grade drilling technique, produced a more uniform tunnel with no difference in ACL attachment hits.

Introduction: Open Repair of the Achilles tendon is associated with problems of wound breakdown and infection. Percutaneous methods have been associated with sural nerve injury. The Achillon system avoids these problems. However no studies have assessed the strength of this repair and whether it allows early active rehabilitation.

Materials/Methods: Simulated Achilles tendon ruptures in sheep Achilles tendons were repaired using either the Achillon method or a two strand Kessler technique with a No.2 Ticron Suture. The tendon diameter was measured in all cases, and was matched for both groups (mean 9mm, range 8–10mm). Specimens were loaded to failure using an Instron tensile testing machine.

Results: Mean load to failure for the Achillon method was 153.13N ±59.64 (range 65–270), and the mean load to failure for the Kessler Repair was 123.13N ±24.19 (range 75–150). This difference was not statistically significant p=0.209. A Pearson’s correlation coefficient was carried out for each group to see if mean load to failure was related to tendon diameter. There were statistically significant higher mean loads to failure for wider tendon repaired by the Achillon method p=0.047, however this was not the case with Kessler repairs p=0.231.

Discussion: The Achillon repair had a similar load to failure as the 2 strand Kessler repair. These results support the use of early active rehabilitation following the Achillon repair and we could not demonstrate stretching at the repair site. As this method is minimally invasive and does not grasp the tendon it may also have less effect on disruption of tendon blood supply and allow faster healing.

Conclusion: The Achillon repair has comparable tensile strength to Kessler Repair, and is a biomechanically sound method of repair of the acutely rupture Achilles tendon in suitable Patients.

Introduction: Open Repair of the Achilles tendon is associated with problems of wound breakdown and infection. Percutaneous methods have been associated with sural nerve injury. The Achillon system avoids these problems. However no studies have assessed the strength of this repair and whether it allows early active rehabilitation.

Materials/Methods: Simulated Achilles tendon ruptures in sheep Achilles tendons were repaired using either the Achillon method or a two strand Kessler technique with a No.2 Ticron Suture. The tendon diameter was measured in all cases, and was matched for both groups (mean 9mm, range 8–10mm). Specimens were loaded to failure using an Instron tensile testing machine.

Results: Mean load to failure for the Achillon method was 153.13N ± 59.64 (range 65–270), and the mean load to failure for the Kessler Repair was 123.13N ± 24.19 (range 75–150). This difference was not statistically significant p=0.209. A Pearson’s correlation coefficient was carried out for each group to see if mean load to failure was related to tendon diameter. There were statistically significant higher mean loads to failure for wider tendon repaired by the Achillon method p=0.047, however this was not the case with Kessler repairs p=0.231.

Discussion: The Achillon repair had a similar load to failure as the 2 strand Kessler repair. These results support the use of early active rehabilitation following the Achillon repair and we could not demonstrate stretching at the repair site. As this method is minimally invasive and does not grasp the tendon it may also have less effect on disruption of tendon blood supply and allow faster healing.

Conclusion: The Achillon repair has comparable tensile strength to Kessler Repair, and is a biomechanically sound method of repair of the acutely rupture Achilles tendon in suitable patients.

Introduction: Compression staples are becoming increasingly popular for osteotomies and arthrodesis. Their design can be divided into “Mechanical Compression” or “Shape Memory”. However, there are no publications investigating the actual compressive forces achieved or the ideal limb-length to staple width ratio.

Methods and Materials: Compression was compared using a load cell mounted within a previously validated simulated fusion site. Two designs each of “mechanical compression” and “shape memory” staples were tested and filmed. The effect of altering limb length on compression was noted.

Results: Both designs of “mechanical compression” staple splayed open causing either no net compression or even distraction. Distractive forces of up to 23N were recorded. The “shape memory” staples all achieved compression at the fusion site of between 5 and 25N. Limb length did not appear to alter the compression force achieved. The outcome was not affected by the material used.

Discussion: “Mechanical compression” staples act in a similar manner to the AO principle of a 2-hole compression plate used without a lag screw or pre-bending. Although there is compression of the cis-cortex, the limbs of the staple splay open with a fulcrum around the bridge-limb intersection resulting in distraction of the trans-cortex. “Shape memory” staples compress both the cis-and trans-cortices along the length of the limb leading to adequate stability and compression forces across the fusion site.

Conclusion: “Mechanical compression” staples cause a distractive force rather than a compressive force and we therefore recommend that they are not relied upon for fusion and the manufacturers need to modify the product or it’s indications for use. The “shape memory” staples do provide compression and the length-to-width ratio of the staple does not appear to be important.