Abstract

Lower back pain (LBP) is a global problem. Countless in vitro studies have attempted to understand LBP and inform treatment protocols such as disc replacement devices (DRDs). A common method of reporting results is applying a linear fit to load-displacement behaviour, reporting the gradient as the specimen stiffness in that axis. This is favoured for speed, simplicity and repeatability but neglects key aspects including stiffening and hysteresis. Other fits such as polynomials and double sigmoids better address these characteristics, but solution parameters lack physical representation. The aim of this study was to implement an automated method to fit spinal load-displacement behaviour using viscoelastic models.

Six porcine lumbar spinal motion segments were dissected to produce isolated disc specimens. These were potted in Wood's metal, ensuring the disc midplane remained horizontal, sprayed with 0.9% saline and wrapped in saline-soaked tissue and plastic wrap to prevent dehydration. Specimens were tested using the University of Bath spine simulator operating under position control with a 400N axial preload.

Specimens were approximated using representative viscoelastic elements. These models were constructed in MATLAB Simulink R2020b using the SimScape library. Solution coefficients were determined by minimizing the sum of squared errors cost function using a non-linear least squares optimization method.

The models matched experimental data well with a mean % difference in model and specimen enclosed area below 6% across all axes. This indicates the ability of the model to accurately represent energy dissipated. The final models demonstrated reduced RMSEs factors of 3.6, 1.1 and 9.5 smaller than the linear fits for anterior-posterior shear, mediolateral shear and axial rotation respectively.

These nonlinear viscoelastic models exhibit significantly increased qualities of fit to spinal load-displacement behaviour when compared to linear approximations. Furthermore, they have the advantage of solution parameters which are directly linked to physical elements: springs and dampers. The results from this study could be instrumental in improving the design of DRDs as a mechanism for treating LBP.

Lower back pain (LBP) is a worldwide clinical problem and a prominent area for research. Numerous in vitro biomechanical studies on spine specimens have been undertaken, attempting to understand spinal response to loading and possible factors contributing to LBP. However, despite employing similar testing protocols, there are challenges in replicating in vivo conditions and significant variations in published results. The aim of this study was to use the University of Bath (UoB) spine simulator to perform tests to highlight the major limitations associated with six degree of freedom (DOF) dynamic spine testing.

A steel helical spring was used as a validation model and was potted in Wood's metal. Six porcine lumbar spinal motion segments were harvested and dissected to produce isolated spinal disc specimens. These were potted in Wood's metal, ensuring the midplane of the disc remained horizontal and then sprayed with 0.9% saline and wrapped in saline-soaked tissue and plastic wrap to prevent dehydration. A 400N axial preload was used for spinal specimens. Specimens were tested under the stiffness and flexibility protocols.

Tests were performed using the UoB custom 6-axis spine simulator with coordinate axes. Tests comprised five cycles with data acquired at 100Hz. Stiffness and flexibility matrices were evaluated from the last three motion cycles using the linear least squares method.

According to theory, inverted flexibility matrices should equal stiffness matrices. In the case of the spring, the matrices matched analytical solutions and inverted flexibility matrices were equivalent to stiffness matrices. Matrices from the spinal tests demonstrated some symmetry, with similarities between inverted flexibility- and stiffness matrices, though these were unequal overall. Matrix element values were significantly affected by displacements assumed to occur at disc centre.

Spring tests proved that for linear, elastic specimens, the spine simulator functioned as expected. However, multiple factors limit the confidence in spine test results. Centre of rotation, displacement assumptions and rigid body transformations are known to impact the results from spinal testing, and these should be addressed going forward to improve the replication of in vivo conditions.

Injury of the intervertebral disc (IVD) can occur for many reasons including structural weakness due to disc degeneration. A common disc injury is herniation. A herniated nucleus can compress spinal nerves, causing pain, and nucleus depressurisation changes mechanical behaviour. Many studies have investigated in vitro IVD injuries including endplate fracture, incisions, and nucleotomy. There is, however, a lack of consensus on how the biomechanical behaviour of spinal motion segments is affected. The aim of this study was to induce defined changes to IVDs of spine specimens in vitro and apply 6 degree of freedom testing to evaluate the effect of these changes.

Six porcine lumbar spinal motion segments were harvested from organically farmed pigs. Posterior structures were removed to produce isolated spinal disc specimens. Specimens were potted in Wood's metal, ensuring the midplane of the IVD remained horizontal. After potting, specimens were sprayed with 0.9% saline, wrapped in saline-soaked tissue and plastic wrap to prevent dehydration. A 400N axial preload was equilibrated for 30 minutes before testing. Specimens were tested intact and after a partial nucleotomy removing ~0.34g of nuclear material with a curette through an annular incision.

Stiffness tests were performed using the University of Bath's custom 6-axis spine simulator with coordinate axes and displacement amplitudes. Tests comprised five cycles with data acquired at 100Hz. Stiffness matrices were evaluated from the last three motion cycles using the linear least squares method.

Stiffness matrices for intact and nucleotomy tests were compared. No significant differences in shear, axial or torsional stiffnesses were noted. Nucleotomy caused significantly higher stiffness in lateral bending and flexion-extension with increased linearity and the load-displacement behaviour in these axes displayed no neutral zone (NZ).

Induced changes were designed to replicate posterolaterally herniated discs. Unaffected shear, axial and torsional stiffnesses suggest the annulus is crucial in these axes. However, reduced ROM and NZ after nucleotomy suggests bending is most affected by herniation. Increased linearity and lack of defined NZ in these axes demonstrates herniation causes major changes to the viscoelastic behaviour of spine specimens in response to loading.

Abstract

Back pain is a significant socio-economic problem affecting around 80% of the population at some point during their lives. Chronic back pain leads to millions of days of work absence per year, posing a burden to health services around the world. In order to assess surgical interventions, such as disc replacements and spinal instrumentations, to treat chronic back pain it is important to understand the biomechanics of the spine and the intervertebral disc (IVD). A wide range of testing protocols, machines and parameters are employed to characterise the IVD, making it difficult to compare data across laboratories.

The aim of this study was to compare the two most commonly used testing protocols in the literature: the stiffness and the flexibility protocols, and determine if they produce the same data when testing porcine specimens in six degrees of freedom under the same testing conditions. In theory, the stiffness and the flexibility protocols should produce equivalent data, however, no detailed comparison study is available in the literature for the IVD, which is a very complex composite structure.

Tests were performed using the unique six axis simulator at the University of Bath on twelve porcine lumbar functional spinal unit (FSU) specimens at 0.1 Hz under 400 N preload. The specimens were divided in two groups of six and each group was tested using one of the two testing protocols. To ensure the same conditions were used, tests were firstly carried out using the stiffness protocol, and the equivalent loading amplitudes were then applied using the flexibility protocol.

The results from the two protocols were analysed to produce load-displacement graphs and stiffness matrices. The load-displacement graphs of the translational axes show that the stiffness protocol produces less spread between specimens than the flexibility protocol. However, for the rotational axes there is a large variability between specimens in both protocols. Additionally, a comparison was made between the six main diagonal terms of the stiffness matrices using the Mann-Whitney test, since the data was not normally distributed. No statistically significant difference was found between the stiffness terms produced by each protocol. However, overall the stiffness protocol generally produced larger stiffnesses and less variation between specimens.

This study has shown that when testing porcine FSU specimens at 0.1 Hz and 400 N preload, there is no statistically significant difference between the main diagonal stiffness terms produced by the stiffness and the flexibility protocols. This is an important result, because it means that at this specific testing condition, using the same testing parameters and environment, both the stiffness and flexibility methods can be used to characterise the behaviour of the spine, and the results can be compared across the two protocols. Future work should investigate if the same findings occur at other testing conditions.

Chronic back pain is the leading cause of disability worldwide, affecting millions of people. The source of pain is usually the intervertebral disc (IVD), thus there has been a growing interest in developing new improved implants such as disc replacements to treat the condition. However, to ensure the artificial devices being designed replicate the intact disc, the biomechanical behaviour of the IVD must be well understood (Adams and Dolan, 2005). The two most widely used testing procedures in the spinal industry to characterise the behaviour of the disc are the flexibility and the stiffness protocols (Stokes et al, 2002 and Panjabi et al, 1976).

For elastic specimens, the results produced by the flexibility and the stiffness protocols should in theory be identical. However, this does not hold true for inelastic specimens, such as the IVD. For this reason, the custom developed Spine Simulator (Holsgrove et al, 2014) at the University of Bath has been used to compare, in six degrees of freedom, the extent of the difference produced by these two testing protocols.

A biomechanical model of the IVD was tested, which consisted of two cylindrical nylon blocks attached together with a layer of nitrile rubber, representing respectively the vertebral bodies (VB) and the IVD. Two steel pins were inserted into the VB, spanning the thickness of the disc, to ensure the stiffness raise either side of the neutral zone was replicated by the model. Tests were performed at a frequency of 0.1 Hz using triangular wave cycles. The specimen was firstly subjected to the stiffness protocol, characterised by displacements of ±0.5 mm in anterior-posterior and lateral shear, ±0.35 mm in axial compression and ±1.5 deg in all rotational axes. The resulting loads were applied to the specimen when subjected to the flexibility protocol. In addition, the effect of a preload was studied by testing specimens with an axial compressive load of 250 N.

The stiffness matrix was calculated for each test and the main diagonal terms produced for the two protocols were compared using the Mann-Whitney test. Overall, results showed that there was a significant difference in the stiffness terms produced by the two protocols when tests were performed with (p ≤ 0.016) and without (p = 0.004) a preload. The only exception was found in the flexion-extension axis when the test was performed with a preload (p = 0.337). Additionally, differences were also recorded when comparing the shape and linearity of the load-displacement hysteresis curve (Figure 1) and the area enclosed by the curve.

This preliminary study has provided important information regarding the differences in the data produced by the flexibility and the stiffness protocols, it is therefore impractical to compare results produced using these two methods. To ensure that in the future results can be compared across laboratories, there is a need for a standardised testing procedure in the spinal industry.

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Introduction

The emergence of a new variant of subtrochanteric stress fractures of the femur affecting patients on oral bisphosphonate therapy has only recently been described. This fracture is often preceded by pain and distinctive radiographic changes, and associated with a characteristic fracture pattern. We undertook a review of this cohort of patients in our service.

Introduction

A comprehensive met-analysis of anterior knee pain post intramedullary nailing of the tibia was performed by Katsoulis et al in 2006. The principle findings were that 47.4% of patients had anterior knee pain at 2 years post tibial nailing. Worse results were found following a patella tendon splitting approach when compared with a medial para-patellar tendon approach. These conclusions were drawn from 20 studies including 1460 patients.

Currently both approaches to the proximal tibia for nailing are used at JCMH Blanchardstown. A retrospective study was performed to compare the results of tendon splitting and tendon sparing approaches to tibial nails and to compare the results of JCMH with those stated in literature.

Conservative management remains the gold standard for many fractures of the humeral diaphysis with union rates of over 90% often quoted. Success with closed management however is not universal.

Introduction

The incidence of osteochondral lesions following ankle fractures varies in the literature between 17-70%. They are commonly associated with chronic pain and swelling in patients diagnosed with such pathology. There is less evidence about the relationship between OCL and the development of post-traumatic osteoarthritis, the most common type of ankle arthritis.

Introduction: K wiring is a popular technique to help maintain anatomic reduction of distal radial fractures. It has the advantage of being a semi-closed procedure, which is simple to perform. Complications related to K wires include infection, migration and damage to tendons and nerves.

We aimed to perform a randomized prospective study to determine the outcome of Buried versus Exposed K wire placement.

Methods: We prospectively recruited 60 consecutive patients with displaced distal radius fractures requiring K wiring to our study. They were randomized to Buried versus Exposed K wire groups.

Patient details were collected and follow up was performed at 2 and 6 weeks post op.

Infection at pin sites was measured on a 0 to 6 point scale. Superficial radial nerve was assessed with light touch and 2 point discrimination. EPL tendon was also assessed for damage.

Results: 60 consecutive patients were recruited to the study and randomized to buried or exposed k wires. There were 30 patients in each group.

No damage to EPL tendon was recorded in either group at 6/52 follow up.

There was a slight increased rate of superficial infection at exposed pin sites noted at 2/52 follow up however this was not seen at the 6/52 follow up. Superficial radial nerve damage was noted in one case only. This was in the buried k wire group and occurred following removal of the radial wire.

Conclusion: There appears to be slight increased risk of superficial pin site infection in the exposed k wire group at 2/52 but this is not seen at 6/52 follow up. Buried k wires require a second procedure to remove the wires and this runs the risk of superficial radial nerve damage.

Introduction: K wiring is a popular technique to help maintain anatomic reduction of distal radial fractures. It has the advantage of being a semi-closed procedure, which is simple to perform. Complications related to K wires include infection, migration and damage to tendons and nerves.

We aimed to perform a randomized prospective study to determine the outcome of Buried versus Exposed K wire placement.

Methods: We prospectively recruited 60 consecutive patients with displaced distal radius fractures requiring K wiring to our study. They were randomized to Buried versus Exposed K wire groups.

Patient details were collected and follow up was performed at 2 and 6 weeks post op.

Infection at pin sites was measured on a 0 to 6 point scale. Superficial radial nerve was assessed with light touch and 2 point discrimination. EPL tendon was also assessed for damage.

Results: 60 consecutive patients were recruited to the study and randomized to buried or exposed k wires. There were 30 patients in each group.

No damage to EPL tendon was recorded in either group at 6/52 follow up.

There was a slight increased rate of superficial infection at exposed pin sites noted at 2/52 follow up however this was not seen at the 6/52 follow up. Superficial radial nerve damage was noted in one case only. This was in the buried k wire group and occurred following removal of the radial wire.

Conclusion: There appears to be slight increased risk of superficial pin site infection in the exposed k wire group at 2/52 but this is not seen at 6/52 follow up. Buried k wires require a second procedure to remove the wires and this runs the risk of superficial radial nerve damage.

Thus it would appear that leaving k wires exposed is the safer and more convenient method of K wiring the displaced distal radius fracture.

In a prospective randomized trial, we divided a group of patients with a clinically suspicious, although radiographically normal, acute fracture of the scaphoid into 2 groups, 1 treated with a cast (group I), the other with a splint (group II). There were 14 patients in group I, and 18 in group II. Patients were reviewed at 2,6, and 12 weeks for range of movement, grip strength, pain and satisfaction rating. Work disability costs were also calculated for both groups. Patients in group II had better range of movement and grip strength at 2 weeks, although complained of more pain. There was no difference in range of movement, grip strength, or pain at 6 or 12 weeks. Group II was more satisfied at 2 weeks, although not at 6 or 12 weeks. Group I required more time off work, and disability costs were significantly higher [€15,209 per person compared to €3,317 per person]. We recommend that all patients, with only a clinical suspicion of a fractured scaphoid, should have a short period of splint immobilization until symptoms resolve, or until further investigations reveal a fracture which can be appropriately treated. This policy is cost efficient and improves the short term outcome.

Introduction: Fasting overnight NPO (Nulla per os) has been routine before surgery for the past century. The practice was previously designed to reduce the risk of pulmonary aspiration on induction. However this practice has been challenged over the recent years and is changing anaesthetic practices are now more liberal. There are many new concepts aimed at improving patient outcome by regulating metabolic, endocrine, inflammatory and immune responses. This combined with better patient satisfaction and lower anxiety has led to research in this area.

Overnight fasting can induce post operative insulin resistance. Insulin resistance is related to infectious morbidity and increased hospital length of stay (HLOS). Previously this concept was only important in diabetic patients. Surgery places the body under metabolic stress and even a short period of fasting will change the metabolic state of the patient. Indeed physical trauma can cause a triad known as the “diabetes of injury”: insulin resistance, hyperglycaemia and glucose intolerance. Preparation for surgery by maintaining a fasted state and catabolic metabolism may have deleterious consequences for the patient.

Previous studies on elective patients has shown that pre operative carbohydrate loading can reduce insulin resistance and mitigate the inflammatory response by immunomodulation. It has not previously been shown to have an effect in the hip fracture population. This particular group of patients are often elderly and require medical and anaesthetic work up. This delay can mean that the patient is kept fasting for prolonged periods and often overnight.

Methods: With full ethical approval at Connolly Hospital we prospectively randomised all femoral and hip fractures for surgery. We excluded diabetics and pregnant women from the study. A high carbohydrate drink called Nutritia Pre Op was selected. Random serum glucose was taken on admission. Patients were randomised and selected for the trial by hidden ballot. Anaesthetic approval was sought for each case. We compared our standard treatment for hip and femoral fractures of strict NPO prior to surgery versus giving patients the Pre Op drink. Each carton was 200ml and up to 4 were given the night before surgery. In the morning the patients were given another 2 drinks. There was a strict minimum 2 hour NPO period before leaving the ward. Glucose levels were then taken at 1 and 12 hours post operatively to assess whether hyperglycaemia was present. As per laboratory values a normoglycaemia was considered as 4–6mmol/l. Gender, age, type of operation, HLOS, complications and re-admissions were noted.

Results: In total 17 patients were enrolled in the study. Group A had 9 patients and were kept NPO as the control group. Group B had 8 patients enlisted in the Pre Op Drink group. In group A, 6 of 9 (67%) patients had a post operative hyperglycaemia. Average age in group A was 79.6 years with an average HLOS of 15.8 days. 4 patients between them required 8 readmissions over a 3 month post operative period. Group B showed 2 out of 8 (25%) patients had a hyperglycaemia. They had an average age of 69 years with an average HLOS of 11.75 days. 4 patients required 4 readmissions.

Conclusions: Pre Op high carbohydrate drinks significantly decrease post operative hyperglycaemia as per the laboratory ranges. This in turn supports that it decrease insulin resistance by preparing the body for surgery in a fed state. In the same way that one would not prepare for a marathon by fasting 24 hours before hand so the body recognizes that the surgical stress is not best dealt with when in a fasted state. The control group had twice as many readmissions and a longer HLOS. Previous studies show that there is decreased anxiety, thirst and hunger both pre and post operatively. We have shown that this is a safe drink to give and that post operative hyperglycaemia was better controlled.

Introduction: It is standard procedure in our unit to use compartment pressure monitoring in all patients presenting with tibial fractures. A sustained difference of less than 30mmhg between the diastolic blood pressure and the compartment pressure (known as the delta pressure) is taken as an indication for fasciotomy.

Aim: To review the impact continuous compartment pressure monitoring has on the management of patients with tibial fractures.

Methods and materials: Between January 2004 and June 2006, 28 patients admitted to our unit following tibial fracture had a compartment pressure monitor inserted. The outer sheath from a 16G cannula connected to an arterial manometer was used in each case.

The records of these 28 patients were reviewed. Twenty three were male. Ages ranged from 19 to 83 years old. Eight patients had open fractures and 20 had closed fractures. Seven patients (25%) had difficulties with communication which could have impeded or delayed the diagnosis of a compartment syndrome.

Results: Average delta pressure ranged from nine to 69mmHg in our patient population. High energy injuries resulted in a significantly lower delta pressure (p=0.05). Open fractures were more likely to result from high energy, although this was not statistically significant (p=0.068). Two patients had fasciotomy performed based on clinical picture and a sustained decrease in delta pressure. No patient had a missed compartment syndrome.

Conclusion: Continuous compartment pressure monitoring is especially useful in patients who are most at risk for compartment syndrome i.e. those having sustained high energy injury or open fractures. It can also aid decision making when the clinical picture of compartment syndrome is equivocal, or when a patient’s ability to communicate pain is impaired.

However, due to the ease of use and the low cost involved, we recommend that all patients with tibial fracture should have continuous compartment pressure monitoring performed.

With the increasing availability of magnetic resonance imaging, there is potentially less emphasis being placed on making a definitive clinical diagnosis. Changes in the undergraduate curriculum have also reduced the emphasis on orthopaedic clinical evaluation. This aim of this study was to evaluate the predictability of clinical examination alone in comparison with arthroscopic findings in 50 consecutive patients presenting for arthroscopy to our service. Four trainees examined each patient; each examiner was blinded to the clinical diagnosis made by their colleagues. All patients were examined in the ward and subsequently underwent examination under anaesthesia and arthroscopy.

Of the tests for meniscal injuries joint line tenderness was the most sensitive (77%) and specific (68%). Apley’s and McMurray’s test while specific (92%, 98%) lacked sensitivity (9%, 30%). Overall the tests for anterior cruciate ligament (ACL) disruption were more reliable than the tests for meniscal injuries. The anterior drawer and Lachmann tests had high specificity (90%, 75%) and sensitivity. The pivot shift test also had very high specificity (75%) and sensitivity (98%) for detecting ACL injuries. These data demonstrate that joint line tenderness is the most reliable sign of menis-cal injury. In the absence of joint line tenderness Apley & McMurray’s tests have little role in routine clinical examination. Clinical tests and signs of ACL deficiency are consistently reliable in diagnosing ACL rupture.

Antegrade intramedullary nailing of fractures of the shaft of the humerus is reported to cause impairment of the shoulder joint. We have reviewed 33 patients with such fractures to assess how many had injuries to the ipsilateral shoulder. All had an MR scan of the shoulder within 11 days of injury. The unaffected shoulder was also scanned as a control. There was evidence of abnormality in 21 of the shoulders (63.6%) on the injured side; ten had bursitis of the subacromial space, five evidence of a partial tear of the rotator cuff, one a complete rupture of the supraspinatus tendon, four inflammatory changes in the acromioclavicular joint and one a fracture of the coracoid process. These injuries may contribute to pain and dysfunction of the shoulder following treatment, and their presence indicates that antegrade nailing is only partly, if at all, responsible for these symptoms.

Total hip arthroplasty has improved the quality of life for many patients with osteoarthritis. Infection is a serious complication, difficult to treat and often requires removal of the prosthesis to eradicate the infection.

An analysis of the surgical management, risk factors, complications and outcome of infected total hip replacements. Thirty one consecutive patients underwent revision hip arthroplasty for infection between 1997 and 2003. Risk factors, co-morbidity, clinical presentation, biochemical profiles, microbiology, management and radiology were recorded. Outcome and complications following surgery are reviewed. Classification of infection after total hip arthroplasty was based on their clinical presentation—early postoperative, late chronic, or acute hematogenous infection, and positive intraoperative cultures.

All patients underwent resection arthroplasty, 26 had a two-stage revision, 1 had a three stage, 4 did not have a re-implantation. Staph Aureus was the most common organism identified. 16 patients were classified as late chronic insidious, 8 early post operative infection, 6 acute haematogenous and 1 occult intraoperative. Average total blood loss was 5 litres, average replacement was 7 units. 1 patient had a persistent infection. 3 underwent further surgery for dislocation, stem perforation or fracture. 5 patients had a persistent limp.

In infected revisions the bone stock is usually adequate, the soft tissues are very poor. Bivalving the femur allows for optimal cement removal. Blood loss can be significant with average replacement of 7 units. Meticulous removal of infected components, cement and tissue is essential for good long-term results.

Introduction: An arthroplasty database, such as the Swedish Hip Registry, provides a crude means of quality control over the sizable number of prosthetic implants available on the market today. It provides relatively rapid feedback on the performance of orthopaedic devices and surgical techniques, allowing inferior devices and methods to be discontinued. The maintenance of an arthroplasty register is inexpensive and of enormous benefit to the patient. At present, there is no nationwide arthroplasty register in operation in the Republic of Ireland.

Aim: To develop an arthroplasty register which prospectively captures all clinical, radiographic and medical outcome data on patients undergoing surgery in our unit

Materials and methods We are using an existing computer software programme (Bluespier Patient Manager) to capture our information, although our database is stored independently of this.

Data recorded includes medical outcome scores (WOMAC and MOS SF-36), patient data, operative details (including type of prostheses used and operative technique employed), inpatient course, and any postoperative events. For revision procedures, additional data such as location of bony defects (Gruen zones) and acetabular bone loss (Paprosky classification) are also recorded. Follow up in a special Joint Register Clinic is at six months, two years and every five years thereafter for primary procedures. This is reduced to every two years in the case of revision procedures.

To date, a pilot study involving four surgeons has prospectively captured data on 82 patients undergoing both primary and revision procedures in our unit. We aim to enrol all our patients in the register from July 2005, increasing the amount of data collected, which we hope will subsequently benefit patients undergoing hip and knee arthroplasty in the future.