Introduction

Kager's fat pad (KFP) is located in Kager's triangle between the Achilles tendon (AT), the superior cortex of the calcaneus and Flexor Hallucis Longus (FHL) muscle & tendon. Although the biomechanical functions of KFP are not yet fully understood, a number of studies suggested that KFP performs important biomechanical roles including assisting in the dynamic lubrication of the AT subtendinous area, protection of AT vascular supply, and load and stress distribution within the retrocalcaneal bursa space. Similar to the knee meniscus, KFP has become under increasing investigations since strong indications were found that it serves more than just a space filler. Both KFP and the knee meniscus are anchored to their surrounding tissues via fibrous attachments, they can be found in encapsulated (or ‘air tight’) regions, lined by synovial membranes, and they both slide within their motion ranges. The protruding wedge (PW) of KFP was observed to slide in and out of the retrocalcaneal bursal space during ankle plantarflexion and dorsiflexion, respectively. In-vitro studies of KFP suggest that it reduces the load by 39%, which is similar to that of the knee meniscus (30%-70% of the load applied on the knee joint). This study investigated the in-vivo load bearing functionality of KFP.

Paratenonitis describes inflammation of the paratenon and commonly presents as an overuse injury. The paratenon is the connective tissue sheath that surrounds tendons - including tendo Achilles, and serves to minimise friction with the outer layer of the tendon, the epitenon. Whilst this conjunction allows the tendon to glide smoothly on muscular contraction, the presentation of paratenonitis typically follows periods of frequent, repetitive musculoskeletal movements; hence, paratenonitis commonly afflicts the elite and, albeit to a lesser extent, amateur athlete. The extent to which friction at the epitenon-paratenon juncture contributes to this tendinopathy remains unclear, and this study is therefore concerned with the coefficient of friction and the lubrication regime.

By using a specially designed and validated apparatus, the in vivo paratenon-epitenon conjunction was approximated using bovine flexor tendon paratenon and a glass disc; this is being an equivalent experimental set-up to that used in other studies exploring soft tissue contacts. Bovine synovial fluid was used to lubricate the conjunction at 37 deg C, and the frictional characteristics were analysed over a range of sliding speeds and loads.

The coefficient of friction was found to generally lie between 0.1 – 0.01. This range suggests that a system of mixed lubrication applies - where the synovial fluid is causing partial separation of the two surfaces. However, when the data is plotted in the form of a Stribeck curve, the trend suggests that boundary lubrication prevails - where lubrication is determined by surface-bound proteins.

The coefficient of friction at the epitenon-paratenon interface appears to be approximately one order of magnitude greater than that typically reported within the healthy synovial joint. Additionally, the synovial joint is thought to exhibit some fluid film lubrication (i.e. total surface separation), whereas the epitenon-paratenon lubrication regime appears to vary only between the inferior mixed and boundary systems - depending on the specific biomechanical conditions. This data would suggest that the coefficient of friction at the epitenon-paratenon interface is relatively high and thus is potentially significant in the incidence of paratenonitis. Such a hypothesis could be of particular interest to sports-medicine and orthopaedic specialists.

Introduction: There has been an increasing use of orthotic knee braces in the management of knee injuries. To ensure the biomechanics of the knee are not adversely affected, it is important that orthotic knee braces accurately provide the desired angle of immobilisation. The objective of our study was to measure the actual knee flexion angles for a lockable orthotic knee brace, and measure the resulting knee flexion moment.

Materials and methods: Eight healthy male volunteers participated in the study looking at six different types of knee immobilisation: locked in 0, 10, 20, 30 degrees of knee flexion, with the brace unlocked, and without a brace. Force and 3-dimensional motion data were collected using a single Kistler force plate and an eight-camera Qualisys ProReflex motion analysis system.

Results: The kinematic knee flexion angles were significantly different when compared with the angles set at the orthotic knee brace for 0 degrees (p=0.001) and 10 degrees (p=0.011). The kinematic knee flexion angle when no brace was used was significantly different from the angle for the unlocked orthotic knee brace (p= 0.003). The knee flexion moment was directly proportional to the knee flexion angle. There was a statistically significant difference between the knee flexion moment for the six types of immobilisation (p< 0.001).

Discussion: The knee flexion angles measured using the kinematic data did not always correspond with the angle set at the orthotic knee brace. These findings highlight inadequacies in the design of lockable orthotic knee braces, especially at low flexion angles of 0 and 10 degrees. The resulting higher actual knee flexion angles were associated with greater knee flexion moments and joint reaction forces at the tibiofemoral and patellofemoral joints. This can, at best result in increased energy expenditure and decreased agility, and at worse potentially augment injuries to the knee.

Background: Sacro-iliac (SI) joint is vertically oriented and subject to a large shear force on weight bearing. Gluteus maximus is strongly active when we experience an abrupt limb loading and need a stable SI joint. Suboptimal gluteus activity could disrupt weight transference and lead to low back pain as the body attempts compensation by recruiting biceps femoris, which could exert its influence through attachment to sacrotuberous ligament. A biomechanical model of SI joint dysfunction was proposed. The model was tested on a pilot study.

Methods: Two male volunteers participated in the study. One was a normal subject. The other had pain suggestive of SI origin. Electromyogram was recorded using pairs of disposable bipolar surface Ag/AgCl electrodes on the symptomatic side for the lumbar multifidus, gluteus maximus and biceps femoris muscles. Subjects were asked to walk in a straight line. Each test was taken three times for two full gait cycles. Two dimensional high speed video was used to capture data of walking motion. Raw electromyogram data was processed according to published protocols.

Results and discussion: Gluteus activation was poor in the symptomatic individual and failed to reach a peak in loading response. Biceps remained activated on terminal swing event with another peak activation in ipsilateral pre-swing event. Unlike normal volunteer, gluteus failed to show increased activity in terminal stance to pre swing events. The study showed a difference in gluteus maximus and biceps femoris activity in between the two volunteers. A larger study is planned to validate the model.

Introduction: In this study the optimal angle of fixation or splintage for partially weight bearing fractures of the patella was determined by a gait analysis measurement system.

Subjects and Methods: A knee brace was applied to eight subjects and locked at 0, 10, 20 and 30 degrees. Measurements were also taken for an unlocked brace and in the absence of a brace. The subjects were instructed on partial weight bearing mobilisation. Three dimensional motion analyses were performed using an infrared 8-camera system. The ground reaction force was recorded by two 3-dimensional force plates embedded in the walkway. Kinematic and kinetic data was collected and the data was transferred to a computer programme for further analysis and the forces acting on the patella were calculated.

Results: The results showed that the forces acting on the patella were directly proportional to the knee flexion angle. The results also showed that the knee flexion angle does not always correspond with the angle set at the knee brace; however they did exhibit a direct relationship.

Conclusion: Our findings show that, for partially weight bearing patella fractures, the optimum form of splintage corresponds with a low knee flexion angle.

Patella and extensor mechanism injuries are common injuries and are generally managed with some degree of immobilisation and partial weight bearing to facilitate healing. The aim of this project was to determine the type of immobilisation or splintage during partial weight bearing that results in minimal forces acting through the extensor mechanism.

Gait analysis studies were performed on eight healthy male subjects mobilising partially weight bearing. Measurements were taken for six types of immobilisation: locked at 0, 10, 20, 30 degrees and unlocked in an orthotic knee brace, and without a brace. The ground reaction force, knee joint angle and the knee flexion moment were measured using Qualisys Track Manager and Visual 3D Software. The extensor mechanism moment and the extensor mechanism force were calculated using static equilibrium equations and documented data. A one-way analysis of variance statistical test was performed to determine the statistical significance of the differences between the six types of immobilisation.

There was a direct relationship between the knee flex-ion angle and the extensor mechanism force. The extensor mechanism force at 0 degrees of immobilisation was significantly lower than that for 20 and 30 degrees (p< 0.05). The increase in the extensor mechanism moment arm with increasing knee flexion was not suf-ficient to offset the increase in the extensor mechanism force caused by the increase in the knee flexion moment. The results also showed that the knee flexion angle does not always correspond with the angle set at the knee brace; however they did exhibit a direct relationship.

These results have important implications for the management of patients with patella and extensor mechanism injuries. The results suggest that improvements in knee brace design to allow 0 degrees of knee flexion, rather than the 10 degrees as seen in this study, are likely to result in significantly reduced extensor mechanism tensile forces.

We describe the influence of the angle of immobilisation during partial weight-bearing on the forces across the extensor mechanism of the knee. Gait analysis was performed on eight healthy male subjects with the right knee in an orthotic brace locked at 0°, 10°, 20° and 30°, with the brace unlocked and also without a brace. The ground reaction force, the angle of the knee and the net external flexion movement about the knee were measured and the extensor mechanism force was calculated.

The results showed a direct non-linear relationship between the angle of knee flexion and the extensor mechanism force. When a brace was applied, the lowest forces occurred when the brace was locked at 0°. At 30° the forces approached the failure strength of some fixation devices. We recommend that for potentially unstable injuries of the extensor mechanism, when mobilising with partial weight-bearing, the knee should be flexed at no more than 10°.

This study aimed to explore the relationship between the geometry of the tuberosity located superior to the Achilles tendon enthesis and the thickness of its fibro-cartilaginous periosteum. The tuberosity acts as a pulley for the tendon during dorsiflexion of the foot and is thus compressed by the overlying tendon. This can result in pressure-related injuries which account for a significant number of Achilles-related problems among sportsmen or women. We postulated that variations in the contact area between the tendon and the tuberosity (and consequently the pressure exerted by the tendon) affects the periosteum thickness. Here, we report four methods of portraying the two dimensional geometry of the superior tuberosity. Material was obtained from 10 elderly dissecting room cadavers donated to the Cardiff University for anatomical examination and prepared for routine histology. Serial sagittal sections were collected at 1 mm intervals, and stained with Masson’s trichrome, toluidine blue and haematoxylin & eosin. In the first method, the area of the bursal cavity was measured between the deep surface of the tendon and the tuberosity within a 9mm radius of the proximal part of the attachment site. The second technique was similar, though used the long axis of the tendon as a reference, rather than its deep surface. The third technique measured the area of the tuberosity within 20 degrees of the tendon long axis. The final technique measured the cumulative gradient of the first 5 mm of the tuberosity, with reference to the tendon long axis. The periosteum thickness was measured at 500 μm intervals from the proximal part of the enthesis and mean values calculated. A good correlation was seen between all techniques, with the tuberosities having the most localised area of contact with the tendon, showing the thickest periosteum.

Aim: To determine the ultimate strength at failure of three different methods of repairing meniscal tears Method: Artiþcial tears were created in 21 fresh bovine menisci. These were then divided into three groups. Group one were repaired using a single 2–0 Ticron vertical suture. Group 2 were repaired using a single Clear-þx meniscal screw. Group 3 were repaired using a single Mitek fastener from the Mitek meniscal repair system. The repaired constructs were then loaded onto a tensiometer and distracted at a rate of 16mm/min. The extension during loading, maximum tensile strength and mode of failure were all recorded.

Results: The single vertical suture failed by breaking at the knot at a mean load of 64.38N and mean extension of 19.91mm. The Clearþx screw failed by pulling out of the peripheral portion of the meniscus. The mean load at failure of the Clearþx screw was 38.06N and mean extension was 17.10mm. The Mitek fastener failed by pulling out of the peripheral meniscus at a mean load of 15.50N and mean extension of 13.87mm.

Conclusion: The single vertical suture failed at higher loads than both the Mitek fastener and the Clearþx screw in the bovine meniscus.

The purpose of this study was to analyse the effects of two different biomechanical configurations on the tensile properties of equine patellar tendons. The study looked at a comparison of straight untwisted patellar tendons and double stranded, twisted specimens. The aim was to attempt a more anatomical Anterior Cruciate Ligament configuration when performing reconstruction using the patellar tendon.

Thirty four specimens were harvested and each sample group consisted of a pair of equine ligaments taken from the same animal. The first of the pair served as an ‘untwisted, straight ligament’ control group and the second as the ‘twisted, double stranded test group’. The ligament dimensions were measured for each specimen and the specimen was mounted on an Instron Series 4411© tensile testing machine and tensile load was applied until failure.

Results showed a clearly statistically significant reduction in the tensile properties (p< 0.005) of the twisted double stranded specimens which was against our original hypothesis. The results indicated that the twisted double stranded ligaments had only 65% of the tensile strength of their untwisted counterparts. Similar reductions were demonstrated when calculating energy to yield point and load at zero point yield stress. The results also demonstrated a significant reduction in the stiffness (Young’s Modulus) between the two test configurations.

The application of a double stranded twist to the patellar tendon confers no advantage in terms of tensile property of the ligament. In fact the application of such a model may cause significant reduction in strength and stiffness of the construct which may lead to early failure of the ACL patellar tendon autograft.