It has been proposed that the amount of energy transferred to the bone during a high velocity projectile injury determines the extent of bony injury. We studied the validity of this theory Fresh rear skeletally mature deer femurs were subjected to progressively increasing velocity projectile injuries within a pneumatic ballistic chamber with non-deforming steel spheres capturing the energy transferred. Analysis of fracture severity was performed including micro computer tomography analysis of micro-fractures. The effect of projectile caliber size was then analyzed.

Characteristic fractures patterns were observed with fracture lines extending radially from the impact site, often propagating longitudinally along the sample. It was found that a greater energy transfer resulted in more severe fracture for a given projectile. However, fractures of differing severity were produced by different projectiles for similar energy transfer. Neither specific energy transfer nor energy density could explain this phenomenon.

Although energy transfer plays a role in ballistic fracture, it is not the sole determinant. Other factors such as contact surface area, projectile mass and angle of impact may need to be considered.

The Nerve Root Sedimentation Sign in transverse magnetic resonance imaging has been shown to discriminate well between selected patients with and without lumbar spinal stenosis (LSS), but the performance of this new test, when used in a broad patient population, is not yet known (Barz et al. 2010).

We conducted a retrospective study of consecutive patients with suspected LSS from 2004–2006, before the sign had been described, to assess its association with health outcomes. Based on clinical and radiological diagnostics, patients had been treated with decompression surgery or conservative treatment (physical therapy, oral pain medication). Changes in the Oswestry Disability Index (ODI) from baseline to 24 month follow-up were compared between Sedimentation Sign positives and negatives in both treatment arms.

Of the 146 included patients (52% female, mean age 59 yrs), 71 underwent surgery. Baseline ODI in this treatment arm was 52%, the sign was positive in 44 patients (mean ODI improvement 25 points) and negative in 27 (ODI improvement 24), with no significant difference between groups. In the 75 patients of the conservative treatment arm, baseline ODI was 44%, the sign was negative in 45 (ODI improvement 17), and positive in 30 (ODI improvement 5). Here a positive sign was associated with a smaller ODI improvement compared with sign negatives (t-test, p=0.003).

This study allowed an unbiased clinical validation of the Sedimentation Sign by avoiding it influencing treatment selection. In the conservative treatment arm a positive sign identifies a group of patients who are less likely to benefit. In these cases, surgery might be effective; however, this needs confirmation in prospective studies.

Most people experience low back pain (LBP) at least once in their lifetime. A minority goes on to develop persistent LBP causing significant socioeconomic costs. Aim of this study was to identify factors that influence the progression of acute to persistent LBP at an early stage (Hilfiker et al. 2007).

Prospective inception cohort study of patients attending a health practitioner for their first episode of acute LBP or recurrent LBP after a pain free period of at least six months. Patients were assessed at baseline addressing occupational and psychological factors as well as pain, disability, quality of life and physical activity, and followed up over six months. Baseline and follow-up questionnaires were based on the recommendations of the Multinational Musculoskeletal Inception Cohort Study (MMICS) Statement (Pincus et al. 2008). Variables were combined to the three indices ‘working condition’, ‘depression and maladaptive cognitions’ and ‘pain and quality of life’.

The index ‘depression and maladaptive cognitions’ comprising of depression, somatisation, a resigned attitude towards the job, fear-avoidance, catastrophizing and negative expectations on return to work was found to be a significant baseline predictor for persistent LBP up to six months (OR 5.1; 95%CI 1.04–25.1). The diagnostic accuracy of the predictor model had a sensitivity of 0.54 and a specificity of 0.90. Positive likelihood ratio was moderate with 5.3, negative likelihood ratio 0.5. Overall predictive accuracy of the model was 81%. The area under the curve in receiver operating characteristic (ROC) analysis of the index was 0.78 (CI95% 0.65–0.92), demonstrating a satisfactory quality of discrimination.

Psychological factors in patients with acute LBP in a primary care setting correlated with a progression to persistent LBP up to six months. The benefit of including factors such as ‘depression and maladaptive cognition’ in screening tools is that these factors can be addressed in primary and secondary prevention.

We compared revision and mortality rates of 4668 patients undergoing primary total hip and knee replacement between 1989 and 2007 at a University Hospital in New Zealand. The mean age at the time of surgery was 69 years (16 to 100). A total of 1175 patients (25%) had died at follow-up at a mean of ten years post-operatively. The mean age of those who died within ten years of surgery was 74.4 years (29 to 97) at time of surgery. No change in comorbidity score or age of the patients receiving joint replacement was noted during the study period. No association of revision or death could be proven with higher comorbidity scoring, grade of surgeon, or patient gender.

We found that patients younger than 50 years at the time of surgery have a greater chance of requiring a revision than of dying, those around 58 years of age have a 50:50 chance of needing a revision, and in those older than 62 years the prosthesis will normally outlast the patient. Patients over 77 years old have a greater than 90% chance of dying than requiring a revision whereas those around 47 years are on average twice as likely to require a revision than die. This information can be used to rationalise the need for long-term surveillance and during the informed consent process.

Posterior lumbar fusion is a frequently performed procedure in spinal surgery. High percentages of good and excellent results are indicated by physicians. On the other hand patient-based outcomes are reported. Little is known about the correlations of these two assessment types. We aimed at their comparison.

The analysis included 1013 patients with degenerative spinal disease or spondylolisthesis from an international spine registry, treated with posterior lumbar fusion. All patients were pre/postop assessed by physician-based McNab criteria (‘excellent’, ‘good’, ‘fair’, ‘poor’). Of these patients, 210 (mean age 61 years; 57% females) were in addition assessed by patient-based Oswestry Disability Index (ODI). The remaining 803 patients (mean age 59 years; 56% females) were assessed by patient-based Core Outcome Measure Index (COMI), including

Visual Analogue Scale (VAS) for back and leg pain as well as verbal self-rating (‘helped a lot’, ‘helped’, ‘helped only little’, ‘didn’t help’, ‘made things worse’). McNab criteria were compared to the Minimal Clinically Important Difference (MCID) in ODI (12.8), in VAS back (1.2) and leg pain (1.6). We investigated the correlations between McNab criteria and these patient-based outcomes.

In the ‘excellent’ group as rated by physicians, the proposed MCID was reached in 83% of patients for ODI, in 69% for VAS back and in 83% for VAS leg pain. All patients said the treatment had ‘helped’ or ‘helped a lot’. In the ‘good’ group 56% (ODI), 66% (back pain) and 86% (leg pain) reached the MCID. 96% of patients perceived the treatment as positive. In the ‘fair’ group 37% (ODI), 55% (back pain) and 63% (leg pain) reached the MCID. 49% had positive treatment considerations. The ‘poor’ group revealed 30% (ODI), 35% (back pain) and 44% (leg pain) of patients with reached MCID. Only 15% rated the treatment as positive.

The Spearman correlation coefficients between McNab criteria on the one hand and ODI, back and leg pain as well as patients’ verbal self-rating on the other hand were 0.57, 0.37, 0.36 and 0.46 respectively.

The comparison of physician and patient-based outcomes showed the highest correlations between McNab criteria and ODI, somewhat weaker correlations with patients’ self-rating and the weakest correlations with back and leg pain. Based on these findings, physicians’ evaluation of patient outcomes can be considered a valuable part of patient assessment, corresponding very well with patients’ perceptions of success or failure of spinal surgery.

Statistics New Zealand states “Over the next five decades the 65+ dependency ratio is projected to more than double, from 18 (people aged 65+ years) per 100 (people aged 15 – 64 years) in 2006 to 45 per 100 in 2061. This means that for every person aged 65+ years, there will be 2.2 people in the working-age group in 2061, compared with 5.4 people in 2006 “. This will have a profound impact on health care, specifically in those fractures sustained by the elderly e.g. fractured neck of femur (#NOF).

Also at present little is proven regarding outcome following #NOF in the New Zealand population. These two factors (population change and patient outcome) led to disagreement and healthy debate at the 2008 NZOA ASM. After a pilot study in Dunedin we have examined national electronic records of 52,456 patients presenting with a first admission due to #NOF over the last 20 years.

The mean age at which a patient sustained their first #NOF was around 80 and 71% of these patients have since died. Approximately 10% of patients had a subsequent readmission for #NOF. There was a trend for increasing age over the last twenty years proportional to the increased average age of the general population. One year survival was 75% and mean survival was 3½ years with a third of patients living longer than six years. We found differences in outcome for gender and fracture type (intracapsular vs. extracapsular). Our patients also showed a trend to higher survival risk ratios (i.e. they are clinically “sicker” than they used to be). The incidence of #NOF has increased over the last 20 years with a projected doubling in the number of cases (to 5600 per year) at around 25yrs from now based on the most conservative estimates.

Introduction: Lumbar spinal stenosis (LSS) is diagnosed by a history of claudication, clinical investigation, treadmill test, and cross sectional area (CSA) in MRI or CT. Because commonly used radiological findings not always correlate with clinical symptoms, additional parameters with high specificity and sensitivity are needed.

Methods: Prospective study of dorsal lumbar nerve root sedimentation in MRI scans in supine position of 2 groups of 100 consecutive patients each between 01/2007 – 12/2007. Patients in group 1 had non-specific low back pain (LBP), no claudication, and a CSA above 120 mm2 (LBP group); patients in group 2 showed claudication with or without LBP and a CSA below 80 mm2 (LSS group). We excluded patients with a previous spine surgery. In addition to the sedimentation sign, in both groups VAS, ODI, and walking distance in the treadmill test were measured.

Results: The sedimentation sign was positive in 94 patients in the LSS group but in no patient in the LBP group, showing a specificity of 100%, a sensitivity of 94%, and an accuracy of 97%. There was no difference between segmental levels L1 – L5. Walking distance in the LSS group was shorter than in the LBP group (67 m vs. > 1000 m; p< 0.001). There were no significant differences between both groups regarding VAS and ODI.

Conclusion: In patients without LSS during MRI in supine position lumbar nerve roots sediment due to gravity to the dorsal part of the dural sac leading to a positive sedimentation sign. This sedimentation is not observed in patients with LSS. Therefore, a negative sedimentation sign is a predictor of LSS in patients without prior spine surgery with a high specificity and sensitivity. Level S1 and below were excluded in our study because nerve roots S1 and S2 leave the dural sac in a ventral position inhibiting sedimentation to the dorsal part of the dural sac. The sedimentation sign is a reliable additional diagnostic parameter in patients with LSS.

Background: context: Length of hospital stay (LOS) varies widely within patients with posterior spinal fusion. So far there is little evidence on its co-variates.

Purpose: This study examined which co-variates influence LOS in posterior spinal fusion. Study design: Prospective consecutive documentation of hospital based interventions in the international spine registry Spine Tango. Patient sample: Between 05/2005 and 11/2006 data of 3437 patients were documented in the registry. 790 patients with degenerative spinal disease (614) or spondylolisthesis (176), who had been treated with posterior decompression and spinal fusion, were included in this study. Median age was 62.8 yrs (min 13.2 yrs, max 89.8 yrs) with a female to male ratio of 2:1. Median LOS was 11 days (IQR 8–14 d). Outcome measures: LOS was chosen as dependent outcome variable.

Methods: Multiple linear regression was performed on following independent variables: age, gender, main pathology, number of spinal segments of posterior fusion, level of fusion, number of previous spinal surgeries, operation time, clinic (number of fusions, academic status), surgeon credentials, type of fusion (sole fusion, fusion + instrumentation, fusion + instrumentation + cage).

Results: Clinic (p< 0.0001) was found to be a highly significant co-variate for LOS (min 7 d, max 14 d). Number of fusions per clinic (min 25, max 434) and academic status of clinic had no influence on LOS. Further significant covariates were surgeon credentials (surgeons in training: 8.5 d, specialised spine surgeons: 11 d, orthopaedic or neurosurgeons: 12 d; p=0.001), number of spinal segments of posterior fusion (1 segment: 10 d, 2–3 segments: 12 d, 4–5 segments: 12.5 d, > 5 segments: 15 d; p=0.002), and age group (< 50 yrs: 9 d, 50–59 yrs: 11 d, 60–69 yrs: 12 d, ≥70 yrs: 13 d; p=0.01). Borderline significance was found for gender (women: 12 d, men: 10 d; p=0.05). All other variables showed no influence on LOS.

Conclusion: Co-variates of LOS of patients with posterior spinal fusion are clinic, independent of number of spinal surgeries per clinic and academic status of clinic, surgeon credentials, number of segments of fusion, age group, and gender. A short LOS in surgeries performed by surgeons in training is explained by a smaller number of segments of fusions in these procedures. A subgroup analysis on the co-variate clinic should be performed assessing further explanatory variables. However, this goes beyond the possibilities of documentation in a spine registry.

As an example of benchmarking in spinal surgery using Spine Tango, we extracted data on dural tears, one of the most frequent types of complications in posterior spinal fusion. Little is known about their predictors. This study examined which factors predict the occurrence of dural tears in posterior spinal fusion.

Prospective consecutive documentation of hospital based interventions with an evidence level 2++. Between May 2005 and November 2006 data of 3437 patients were documented in the registry. Nine hundred and twenty nine patients, who had been treated with posterior spinal fusion after opening of the spinal canal, were included in this study. Dural tears being the most frequent type of complications in the registry were chosen as dependent outcome variable. Multiple linear regression with stepwise elimination was performed on potential predictor-variables of the occurrence of dural tears. Benchmarking compared the performance of single hospitals with international peers. Median age was 62.7 years (min 12.5, max 90.5 yrs) with a female to male ratio of 2:1. In 18 of 929 cases a dural tear occurred. Hospital (p=0.02) and number of segments of fusion (p=0.018) were found to be predictors of the occurrence of dural tears in posterior spinal fusion. Number of fusions per hospital (min 25, max 526) and academic status of hospital had no influence on the rate of dural tears. Fusions of four and more segments showed an increase of the rate of dural tears by a factor of three compared to fusions of less than four segments. There was no significant difference between fusions of one segment and fusions of two or three segments (1.3 vs. 1.9%) as well as between fusions of four or five segments and fusions of more than five segments (4.6 vs. 4.2%). Differences between hospitals remained when benchmarking dural tears with case mix.

Predictors of dural tears in posterior spinal fusion are

hospital and

In fusions of four and more segments a threefold higher risk of dural tears in comparison to fusions of less than four segments should be taken into consideration.

We determined the survival of primary total hip and knee replacements and patients who had undergone surgery between 1989 and 2007 in Dunedin with the aim to using these figures to provide information on

whether our arthroplasty population is changing,

The initial search using records held by the audit department at Dunedin Hospital returned 6,328 patient records with total hip and knee arthroplasty between 1988 and 2007. These reports however, included many procedures which were neither hip/knee nor primary/revision total joint arthroplasty. The data was filtered, resulting in 4,773 hip and knee arthroplasties. The final data included 3194 primary total hip replacements and 1579 primary total knee replacements. Comorbidity scoring of these patients was also undertaken.

The mean age of patients who underwent primary hip replacement was 67.6 yrs (SD 12.4) and the mean age of patients who underwent a primary knee replacement was 70.8 yrs (SD 9.8). Around 25% of patients who have had a primary joint replacement died after a mean of 10 yrs after the operation. In the group of patients who died after 10 years, the mean age at surgery was around 74 years. The mean age at the time of death was around 80 years. No difference was found in the death rate, revision rate, and the combined outcomes with death or revision as the end point with respect to the following-THRs. TKR, the grade of the surgeon, the comorbidity score or in men vs. women as compared to the general population.

Patients over 59 years of age at time of primary arthroplasty have a > 90% chance of dying before the need for revision surgery. Patients of less than 51 years of age have a > 90% chance of requiring revision surgery. Patients of 55 years of age have a 50% chance of requiring revision surgery. In a setting of ongoing scarce resources symptomatic/questionnaire targeted follow-up with radiology may be the only long term viable solution.

Posterior lumbar fusion is one of the most frequent procedures in spinal surgery. This study examined which factors predict physician-based outcomes in posterior lumbar fusion within the international spine registry Spine Tango.

This study used prospective consecutive hospital based documentation. Between May 2005 and October 2007 720 patients had been treated with posterior lumbar fusion for degenerative disease or spondylolisthesis. McNab criteria as commonly used physician-based outcomes were chosen as dependent outcome variable. We dichotomised the original McNab criteria combining “excellent” with “good” to “good”, and “fair” with “poor” to “poor”. Multivariate logistic regression was performed on following potential predictor-variables: age, gender, main pathology, number of previous spinal surgeries, number of spinal segments of posterior fusion, operation time, surgeon credentials, follow-up interval.

Median age was 63 years (range 13–90 yrs) with a female to male ratio of 6.3:3.7. Number of previous spinal surgeries (p< 0.001) and follow-up interval (p< 0.001) were found to be predictors of the dichotomised McNab criteria. Patients without previous spinal surgery showed the highest ratio of “good” to “poor” outcome (80.5%:19.5%). This ratio was almost consistently decreasing with the number of previous spinal surgeries to 40%:60% in patients with more than five previous surgeries. At six and twelve-weeks follow-up outcomes were significantly better than after one year, without significant differences between other follow-up intervals. Other examined co-variables showed no influence on the outcomes.

Predictors of physician-based outcomes in posterior lumbar fusion are “number of previous spinal surgeries” and “follow-up interval”. In patients with more than five previous spinal surgeries a higher likelihood of “poor” outcomes should be taken into consideration. A too positive outcome may occur at six or twelve-week’s follow-up.

Introduction: With a life of over five years, Spine Tango can be considered the first truly International Spine Registry. The Swedish Spine Registry has already shown the feasibility of a registry on a national level. But, there is a need for an international spine registry allowing a benchmarking on an international level. Here we demonstrate the genesis of questionnaire development, the constantly increasing activity, and limitations of the International Spine Registry Spine Tango.

Methods: From 2002 until 2007 about 9000 datasets were submitted by 28 hospitals in nine countries worldwide. Three different generations of Spine Tango questionnaires were used for documentation.

Results: To cope with varying international administrative issues and legal requirements of data anonymisation, national Spine Tango modules are necessary. Four national Spine Tango modules are in operation to date, another three modules are in the process of roll-out. Considering all these participants, Spine Tango will soon expand to include data from 52 hospitals in 18 countries. One-fourth of these hospitals are University Hospitals, which are destined to take the lead in the Spine Tango registry as opinion leading hospitals. Although the number of participants is steadily growing, no country is yet represented with a sufficient number of hospitals. Indisputably, a marketing concept is needed. An acquisition of new centres via national spine societies seems an obvious strategic approach. Further limitations of Spine Tango include the low number and short duration of follow-ups and the lack of sufficiently detailed patient based data on subgroup level.

Discussion: Spine Tango has achieved a firm position as international spine registry and with its increasing acceptance it is also gaining importance. The strengths of Spine Tango include a potentially very large network, the participation of a specialized international society and an academic partner with expertise and extensive experience in registry implementation. Data analysis from Spine Tango is possible but complicated by the incompatibility of generations one and two with the more recent generation three. Consequently findings cannot yet be generalized to any specific country or patient population. Nevertheless, the potential benefits of the project for the whole spine community become increasingly visible. In the near future, the established Spine Tango version three with standardised patient based data will make outcome evaluations possible. In parallel to the International Spine Registry Spine Tango, a National Spine Registry in Australia could be set up – comparable to AOA’s National Joint Replacement Registry.

Introduction: As an example of possibilities of Spine Tango we extracted data on dural tears, one of the most frequent types of complications in posterior spinal fusion. Little is known about their predictors. This study examined which factors predict the occurrence of dural tears in posterior spinal fusion.

Methods: Prospective consecutive documentation of hospital based interventions with an evidence level 2++. Between 05/2005 and 11/2006 data of 3437 patients were documented in the registry. 929 patients, who had been treated with posterior spinal fusion after opening of the spinal canal, were included in this study. Median age was 62.7 yrs (min 12.5, max 90.5 yrs) with a female to male ratio of 2:1. In 18 of 929 cases a dural tear occurred. Dural tears being the most frequent type of complications in the registry were chosen as dependent outcome variable (3–6). Multiple linear regression with stepwise elimination was performed on potential predictor-variables of the occurrence of dural tears. Benchmarking compared the performance of single hospitals with international peers.

Results: Hospital (p=0.02) and number of segments of fusion (p=0.018) were found to be predictors of the occurrence of dural tears in posterior spinal fusion. Number of fusions per hospital (min 25, max 526) and academic status of hospital had no influence on the rate of dural tears. Fusions of four and more segments showed an increase of the rate of dural tears by a factor of three compared to fusions of less than four segments. There was no significant difference between fusions of one segment and fusions of two or three segments (1.3 vs. 1.9%) as well as between fusions of four or five segments and fusions of more than five segments (4.6 vs. 4.2%). Differences between hospitals remained when benchmarking dural lesions with case mix.

Discussion: The feasibility of data analysis and benchmarking from the International Spine Registry Spine Tango could be demonstrated. Predictors of dural tears in posterior spinal fusion are

hospital and

In fusions of four and more segments a threefold higher risk of dural tears in comparison to fusions of less than four segments should be taken into consideration. A subgroup analysis on the predictor-variable hospital should be performed assessing further covariates. However, this goes beyond the possibilities of documentation in this international spine registry.

Introduction: Lumbar spinal stenosis is a frequent indication for spinal surgery. The predictive quality of treadmill testing and MRI for diagnostic verification is not yet clearly defined. The aim of our study was to assess correlations between treadmill testing and MRI findings in the lumbar spine.

Methods: Patients with lumbar spinal stenosis who had been admitted for surgical treatment by means of decompression with or without stabilisation were prospectively examined. We included patients with lumbar spinal stenosis as defined by clinical symptoms like low back and/or leg pain, which increased when walking, and by the area of the dural sac examined by MRI. We excluded patients with clinically manifest peripheral arterial disease, polyneuropathy or musculoskeletal impairments compromising the ability to walk. Treadmill tests were performed using the standardized testing protocoll by Deen at a speed of 0.5 m/sec without inclination. After the onset of symptoms (pain, weakness or dysaesthesia), each patient decided when to end the test.

The area of the dural sac and neuroforamina was examined with MRI for the narrowest spinal segment. ODI and VAS were used for clinical assessment.

Results: 25 patients were included with a median age of 67 years (Interquartile range IQR 60–72 yrs). In the narrowest spinal segment the median area of the dural sac was 91mm2 (IQR 67–135 mm2). The median ODI was 66 percent (IQR 64–72 percent). The median walking distance in the treadmill test was 70 m (IQR 30–130 m). The distance reached in the treadmill test correlated with the area of the dural sac (Spearman’s rho=0.53) and ODI (rho=0.51), but not with the area of the neuroforamina and VAS.

Discussion: The treadmill test helps objectifying pre- and postsurgical clinical complaints and verifying a lumbar spinal stenosis by creating a situation of dynamic strain. Moreover, the treadmill test lets the patient experience his own physical limits and enables the examiner to attain a replicable postoperative assessment. The distance reached in the treadmill test predicts the grade of stenosis in MRI but has a limited diagnostic importance for the level of clinical symptoms in lumbar spinal stenosis.

SPINE TANGO is the first International Spine Register. While it has now been fully operational for five years, no results of its collected data have been presented yet. The Swedish Spine Register has already shown that a National Spine Register can generate valid and meaningful data. Here we present data from the first three versions of SPINE TANGO.

From 2002 until 2006 about 6000 datasets were submitted by 25 hospitals worldwide. Descriptive analysis was performed for demographic, surgery, and follow-up data comparing all three versions of SPINE TANGO.

Over the course of its existence the SPINE TANGO data base showed a rise in median patient age from 52.3 years to 58.6 years and an increasing percentage of degenerative disease as main pathology from 60.1% to 71.4 %. Posterior decompression was the most frequent surgical measure. About one third of all patients had follow-ups. Rehabilitation was arranged more frequently, especially home-based and outpatient rehabilitation. The complication rate was decreasing below 10%.

The feasibility of data analysis from the International Spine Register SPINE TANGO could be demonstrated performing descriptive analysis with an evidence level III. In the near future, the meanwhile established SPINE TANGO version 3 with patient based data will make outcome

evaluation possible. This will enable us to present more comprehensive analyses of SPINE TANGO and to make the data base even more beneficial for the whole spine community. In parallel to the International Spine Register SPINE TANGO, a National Spine Register in New Zealand could be set up – comparable to NZOA’s National Joint Register.

Hip and knee replacements are common and successful surgeries in orthopaedics. One of the known complications is fat embolism. Cemented implants used in arthroplasty allow good implant fixation and excellent long term results. However this has been associated with an increased incidence of fat embolism.

This experimental animal study compared the amount of fat embolism following three different surgeries in 30 Sprague Dawley rats. These surgeries simulated hip replacement procedures and included a control surgery, an un-cemented implant and a cemented implant. These animals were then sacrificed at 24 hours. All the lungs were fixed in formalin and then stained using Osmium Tetroxide. The amount of fat was then counted using a light microscope at 40x power.

Both the uncemented implant group (p < 0.001) and the cemented implant groups (p < 0.003) had significantly higher fat emboli from the surgical control group. There were also a significantly higher number of emboli (p < 0.05) in the cemented implant group compared to the uncemented implant group.

We conclude that fat embolism occurs in both the un-cemented and cemented hip replacement. The amount of emboli created by un-cemented hip replacement is less than the cemented hip replacement. The cement itself does not cause the complication of fat embolism. It is the high intramedullary pressure associated with the insertion of the implant, and the cementing process, that contributes to fat embolism. Devices or surgery that minimise this rise in pressure could reduce the amount of fat embolism.

Introduction Vertebroplasty (VP), where vertebral bodies are injected with polymethylmethacrylate (PMMA) cement, is used to treat various spinal lesions. More recently VP has been used for augmenting osteoporotic vertebral bodies that have fractured or are at risk of fracture. Although the complication rate for VP is low, thermal damage caused by the exothermic curing of PMMA has been implicated.

The aim of this series of experiments was to measure the temperatures reached during VP using a sheep model. The cement volume effect and inter cement differences were assessed. Spinal cord monitoring was undertaken to monitor spinal cord function during this procedure to validate this for clinical use.

Methods In the in vivo experiment each of the lumbar vertebral bodies of 10 sheep were injected with one of two cements (Simplex & Vertebroplastic) and one of two volumes (3.0ml or 6.0ml). This was undertaken through an open approach in the lumbar vertebrae. While performing the in vivo experimental studies 6 of the sheep were concurrently monitored using epidural Motor Evoked Potentials (MEP’s).

Results There was a significant increase in the temperature at the bone cement interface. The mean peak temperature at the bone-cement interface was 49.5 C (3.0ml Simplex); 61.47 C (6.0ml Simplex); 42.1 C (DePuy 3ml) and 47.2 (DePuy 6ml).

Spinal cord monitoring showed that when PMMA was injected into the correct location within the vertebral body there was no change in amplitude of the evoked potentials. When significant leakage of PMMA occurred, there was a decrease in amplitude of MEP’s.

Discussion In this sheep model, using cement volumes similar to those used in human clinical practice, we were able to monitor temperature changes within the vertebral body at the bone cement interface. The temperature of the bone cement interface reached temperatures that are known to cause tissue necrosis.

Using epidural monitoring we were able to show that when PMMA is injected into the correct location within the vertebral body there is no change in amplitude of MEP’s.

Percutaneous vertebroplasty (PVP), where vertebral bodies are injected with polymethylmethacrylate (PMMA) cement, is used to treat various spinal lesions. Although the complication rate for PVP is low, thermal damage caused by the exothermic curing of PMMA has been implicated.

This study was to measure the temperatures reached during PVP as PMMA cures as well as assessing the cement volume effect and inter cement differences. Validating spinal cord monitoring during PVP was also undertaken.

In the in vivo experiment each of the lumbar vertebral bodies of 10 sheep were injected with one of two cements and one of two volumes. Thermocouple monitoring was undertaken at the bone cement interface. While undertaking the in vivo experimental studies 6 sheep underwent epidural monitoring using Motor Evoked Potentials (MEPs).

The mean peak temperature at the bone-cement interface was 49.5 C (3.0ml Simplex); 61.47 C (6.0ml Simplex); 42.1 C (DePuy 3ml) and 47.2 (DePuy 6ml). Spinal cord monitoring showed that when cement was injected into the correct location within the trabeculae of the vertebral body no change in amplitude monitoring was noted. When leakage occurred, deliberate or unintended, amplitude changes were noted.

Using cement volumes similar to those used in human clinical practice in a sheep model we were able to monitor temperature changes. The temperature of the bone cement interface reached temperatures that are known to cause tissue necrosis. Using epidural monitoring we were able to detect leakage of cement during injection.

Locking compression plate is part of a new plate generation requiring an adapted surgical technique and new thinking about commonly used concepts of internal fixation using plates.

They offer a number of advantages in fracture fixation combining angular stability through the use of locking screws with traditional fixation techniques. This makes the implant suitable for poor bone stock and for fractures in metaphyseal areas.

However the system is complex and cases of plate loosening and plate breakage reported by many authors recently, many of these authors believe it is attributed to the choice of inappropriate plate and/or fixation technique rather than to the features of locking compression plate system.

We are reporting 2 cases of plate breakage after using it to fix diaphyseal femoral shaft fractures; in each case we discuss the pitfalls in the fixation method.

The locking plate manual did not highlight the important pitfalls, which was published later on in the literature as guidelines for their clinical application. Careful and detailed attention to the biomechanical principles of locking compression is crucial to the success of implant in fixing fractures in diaphyseal areas.

Cementless implants have gained popularity in modern orthopaedic practice. The type implants and surface characteristics on fixation has been extensively investigated, however there is insufficient data on the effect of the host bone bed status on implant fixation. This study aims to determine if there is a correlation between the fixation strength of cementless press-fit implants and bone mineral density (BMD) of the host bone bed.

Implants coated with pure titanium, Hydroxyapatite (HA) with or without Hyaluronic Acid (HY) and implants coated with bone growth factors – Bone Morphogenetic Protein 2 (BMP-2) were inserted into tibiae and femora of 32 skeletally mature ewes (109 implants) for a period of 1, 2 and 4 weeks. Mechanical pull-out testing was performed after each time interval to evaluate the ultimate load of failure (Nmm⁻²). The BMD (gcm⁻³) surrounding the implant site was measured using a CT scanner.

The mean BMD (S.D.) was 1.515gcm⁻³ (0.147gcm⁻³). The mean (S.D.) mechanical pull-out strength at 1, 2 and 4 weeks was 0.37 (0.31), 3.14 (0.17) and 9.74 (2.31) Nmm⁻² respectively. The overall correlation co-efficient between BMD and pull out strength is 0.31.

Early fixation strength of implants is independent of BMD, however, the strength of fixation increases with time in a ‘normal’ sheep population. This suggests that the fixation of implants is dependent on the type of implant and surface coating used rather than the density of the host bone bed.

The aim of this study was to evaluate a new joint arthroplasty clinical priority scoring tool.

A new arthroplasty scoring tool based on pain, function, social limitation, potential of benefit from surgery and consequence of more than 6 months delay was developed and evaluated using 16 patient scenarios (vignettes) related to hip and knee osteoarthritis. Sixteen orthopaedic surgeons were asked to score the vignettes using clinical ranking, ISS tool and the new tool.

Significant variation in ranks allocated by surgeons was recorded for all three tools. Vignettes at either end of the scale ie. those who are severely or minimally disabled had less variability compared to a large group in the middle range. Comparing the three tools there did not appear to by any advantage of one over the other. Most of the variations occurred in the interpretation of benefit from the operation and consequence of delay.

Scoring tools rely heavily on judgement based decisions. More work is required to understand judgement processes used by surgeons and audit/feedback mechanisms may help in reducing the variations in priority assignment.

We analysed the clinical outcome of infected hip and knee replacements treated in Dunedin over a 10 year period.

Using the departmental audit data base all infected arthroplasties treated between 1990 and 2000 and the clinical notes reviewed.

Fifty-three hips and 20 knees were identified. 69% of patients had debridement and antibiotics as the primary treatment. In terms of prosthesis retention 41% of patients had retained the original prosthesis, 30% had implants in place following revision and 29% had a resection arthroplasty or arthrodesis. Retention of the original prosthesis was significantly higher in early as compared to late infections and knees did better than hips. The most common organisms identified were staphylococci (47%) and streptococci (29%). We did not see any difference in outcome of streptococcal infections.

The treatment of infected arthroplasties remains controversial. We propose management guidelines based on outcomes of a series of 73 cases.

Purpose: There are numerous papers from specialist arthroplasty centres outlining results of total knee arthroplasties but little information from outside these major centres. We carried out a review of a fixed bearing total condylar knee replacement used in Dunedin by a variety of surgeons for over 10 years.

Method: All patients who received a Duracon/PCA fixed bearing total knee replacement between 1992 and 1996 were assessed clinically, fluoroscopically and completed an SF12, WOMAC and IKSS questionnaire.

Results: At a mean 9.7 (8–12) years follow up, 126 (69.6%) patients were available for review and 46 (25%) were deceased. The average age was 72 years (52–88) and the primary diagnosis was osteoarthritis in 95% of the cases. There were 34% Charnley Grade A, 37% Grade B and 29% Grade C respectively.

The average IKS Knee score was 72 (23–97) and the functional score was 68 (0–100) with 74% experiencing none or only mild pain. The SF12 assessment revealed a mean physical score of 55 (14–99). Ninety per cent of patients were satisfied with their knee and 89% would have the operation again if required.

There was one operative death (PE), one deep infection, 3 PE’s, 3 DVT’s and 5 superficial infections. An MUA was required in 9 cases.

Eight knees were revised. Using ‘all revisions’ as an end point. The survival rate was 95.3% at 10 years.

Conclusion: These results suggest that knee replacements carried out outside specialist arthroplasty centres perform very well with a survival rate of the implant of 95% at 10 years.

Purpose: To investigate the effect of pressurizing vertebral bodies during vertebroplasty using different materials in the development of fat embolism (FE) and any associated cardiovascular changes.

Polymethylmethacrylate (PMMA) is the material of choice for vertebroplasty (VP). However, PMMA has several disadvantages such as exothermic curing, uncertain long-term biomechanical effects and biocompatibility. As a result alternative materials are being developed to overcome these problems.

In order to determine the role of PMMA in the generation of cardiovascular changes following vertebroplasty we compared injection of cement with wax in an animal model.

Method: In twenty sheep, four vertebral bodies were augmented either with PMMA or bone wax. Heart rate, arterial, central venous and pulmonary artery pressure, cardiac output and blood gas values were recorded. At postmortem the lungs were subjected to histological evaluation.

Results: The consecutive augmentation of four vertebral bodies with PMMA induced cumulative fat embolism causing significant deterioration of baseline mean arterial blood pressure (MABP) and blood gas values. Injection of bone wax resulted in similar cardiovascular changes and amount of intravascular fat in the lungs.

Conclusion: In this animal model cardiovascular complications during multiple VP happen regardless of the augmentation material used. The deteriorating baseline MABP during VP is associated with the pressurization and displacement of bone marrow/fat into the circulation rather than caused by polymethylmethacrylate.

Current research efforts aim at enhancing osseointegration of cementless implants to improve early bone fixation.

Purpose: The aim of the present study was to investigate whether bone morphogenic protein (BMP) 2 had a positive effect on the osseointegration of hydroxyapatite coated implants.

Method: Hydroxyapatite (HA) implants were coated with BMP-2 and hyaluronic acid (HY) as the carrier or with HY alone. Uncoated HA-implants served as controls. The osseointegration of the implants was evaluated either by light microscopy or by pullout tests after 1, 2 and 4 weeks of unloaded implantation in the cancellous bone of 18 sheep.

Results: The BMP-2 coating significantly increased bone growth into the perforations of HA-implants. The proportion of bone-ingrowth at 4 weeks was 32% for the BMP-implants compared to 12% for HA implants. However, BMP-2 did not enhance the percentage of bone implant contact and interface shear strength values.

Conclusion: This study indicates that BMP-2 may help to increase bone growth across gaps of cementless implants in the early stages of bone healing improving fixation and decreasing the risk of loosening.

Introduction Polymethylmethacrylate (PMMA) has been widely used in orthopaedic procedures for fixation of joint replacements or enhancing the fixation of implants. However, the use of PMMA has been associated with cardiovascular deterioration and even death. More recently, PMMA has also been used for augmenting osteoporotic vertebral bodies which have fractured or are at risk of fracture. The main complication is PMMA leakage into adjacent structures. Transient hypotension and fatal fat embolism (FE) have also been reported.

The pathomechanism of cardiovascular deterioration after the injection of PMMA (i.e. FE) remains a highly controversial subject. The exact role of PMMA in the development of FE remains unclear. The aim of the present study was to elucidate the acute effects of injecting PMMA compared with bone wax into vertebral bodies on the cardiovascular system using an established animal model for vertebroplasty (VP) (Aebli, N, et al. Spine. 2002).

Methods In 8 skeletally mature mixed-bred ewes (2–4 years) 6.0ml PMMA (CMW3-Depuy) or bone wax (Bone Wax, Ethicon) were injected unilaterally, through an open approach into the L1 & L2 pedicles. Blood pressure, heart rate, and cardiac output were measured.

Results The major difference between the cardiovascular response of the PMMA and that of the bone wax group was the recovery in Pulmonary Artery Pressure (PAP) and Pulmonary Vascular Resistance (PVR). Three minutes post-injection, PAP had fully recovered to baseline values in the wax group. However in the PMMA group, PAP had only recovered by 52% after 3 min and fully recovered after 10 min.

Discussion The augmentation of vertebral bodies resulted in transient cardiovascular changes regardless of the material used. However, the recovery of PAP and PVR values took significantly longer with the PMMA group. The peak response was a result of pulmonary vasoconstriction triggered by a reflex reaction to the embolisation of bone marrow particles or by vasoactive cytokines. The peak response was therefore mainly associated with the increase in intraosseous pressure during the augmentation causing release of bone marrow contents into the and not the cement monomer. The cement monomer however plays a role in the cardiovascular complications during FE. The delayed recovery of PAP and PVR in the PMMA group may be due to a vasoconstriction effect of the cement monomer on the pulmonary vascular system.

Potentially serious cardiovascular complications may occur during VP regardless of the material used. The injection of PMMA may cause prolonged pulmonary hypertension during vertebro- and also arthroplasty. Continuous invasive cardiovascular monitoring may be required in patients with impaired cardiovascular and pulmonary function

Introduction and Aims: Current research efforts aim at enhancing osseointegration of cementless implants to improve early bone fixation. The aim of the present study was to investigate whether bone morphogenic protein (BMP) 2 had a positive effect on the osseointegration of hydroxyapatite-coated implants in an animal model.

Method: Hydroxyapatite (HA) implants were coated with BMP-2 and hyaluronic acid (HY) as the carrier or with HY alone. Uncoated HA-implants served as controls. The osseointegration of the implants was evaluated by light microscopy and pullout tests after one, two and four weeks of unloaded implantation in the cancellous bone of 18 sheep.

Results: The BMP-2 coating significantly increased bone growth into the perforations of HA-implants. The proportion of bone-ingrowth at four weeks was 32% for the BMP-implants compared to 12% for HA implants. However, BMP-2 did not enhance the percentage of bone implant contact and interface shear strength values.

Conclusion: This study indicates that BMP-2 may help to increase bone growth across gaps of cementless implants in the early stages of bone healing improving fixation and decreasing the risk of loosening.

Introduction and Aims: To determine whether sagittal laxity has an effect on functional outcome following posterior cruciate retaining total knee replacement using two differing tibial insert designs.

Method: Ninety-seven knees in 83 patients were reviewed clinically, radiologically and underwent KT1000 testing at minimum five-year follow-up post-TKA. Knee society, WOMAC and SF12 scores were calculated. The same femoral component (Duracon, Stryker) was used in all patients. Two differing tibial inserts were used (51 Condylar and 46 AP lipped).

Results: The two groups were comparable for age, sex, Charnley category and Body mass index. There was no significant difference in knee society score, WOMAC scores, SF12 scores, knee flexion, posterior tibial slope or KT1000 laxity measurements between the two groups. Total laxity measured by KT1000 was 5mm in the AP lipped group and 4mm in the condylar group. There was no correlation between anterior, posterior or total laxity and functional outcome as measured by WOMAC, KSS, SF12 or knee flexion.

Conclusion: Increased sagittal laxity does not have a strong influence on functional outcome following TKA. The differing tibial insert designs had no significant influence on laxity or function.

Introduction and Aims: Polymethylmethacrylate (PMMA) has been widely used in orthopaedic surgery including more recently vertebroplasty. The reported rate of complications following vertebroplasty is low and mainly related to PMMA leakage.

The aim of this study was to elucidate the acute cardiovascular effects of PMMA or bone wax in a vertebroplasty animal model.

Method: Eight skeletally mature sheep were used and PMMA or bone wax were injected unilaterally into L1 and L2 at 10-minute intervals. Arterial, central venous, pulmonary artery and left ventricular pressures were recorded using Statham pressure transducers and Swan Ganz catheters were used for monitoring cardiac output.

Results: Augmentation resulted in a two-phase response regardless of which material was used. First the mean arterial blood pressures started to drop after approximately two seconds. Secondly the pulmonary artery pressure and central venous pressure increased after approximately 11 seconds, whereas cardiac output and left ventricular pressure decreased. There was no significant change in heart rate for both groups. There was a significant difference (p< 0.05) in the pulmonary artery pressure values in the PMMA group compared to the basal values at one, three and five minutes, whereas in the wax group the pulmonary artery pressure recovered within three minutes.

Conclusion: Augmentation resulted in a two-phase cardiovascular response regardless of which material was used. Peak responses were similar for both groups, but pulmonary artery pressure and cardiac output recovered quicker in the wax group. The late recovery of pulmonary artery pressure and cardiac output in the PMMA group may be due to a vasoconstriction effect of the cement monomer.

To investigate the effect of pressurizing vertebral bodies during vertebroplasty using different materials in the development of fat embolism (FE) and any associated cardiovascular changes.

Polymethylmethacrylate (PMMA) is the material of choice for vertebroplasty (VP). However, PMMA has several disadvantages such as exothermic curing, uncertain long-term biomechanical effects and biocompatibility. As a result alternative materials are being developed to overcome these problems.

In order to determine the role of PMMA in the generation of cardiovascular changes following vertebroplasty we compared injection of cement with wax in an animal model.

In twenty sheep, four vertebral bodies were augmented either with PMMA or bone wax. Heart rate, arterial, central venous and pulmonary artery pressure, cardiac output and blood gas values were recorded. At postmortem the lungs were subjected to histological evaluation.

The consecutive augmentation of four vertebral bodies with PMMA induced cumulative fat embolism causing significant deterioration of baseline mean arterial blood pressure (MABP) and blood gas values. Injection of bone wax resulted in similar cardiovascular changes and amount of intravascular fat in the lungs.

Conclusion: In this animal model cardiovascular complications during multiple VP happen regardless of the augmentation material used. The deteriorating baseline MABP during VP is associated with the pressurization and displacement of bone marrow/fat into the circulation rather than caused by polymethylmethacrylate.

We report early major complications encountered following TEN fixation of femoral fractures in children.

A case series of four children aged 8– 16 years who had primary TEN fixation of isolated femoral diaphyseal fractures.

Three of the four patients had major complications. These were: significant knee stiffness requiring manipulation, haemarthrosis requiring washout and nail removal, loss of position and refracture. Two required revision to locked intramedullary nails without early complication.

In the skeletally immature child TEN fixation of femoral fractures has a significant major complication rate. This needs to be recognised when comparing TEN fixation with other treatment options.

The ability to assess the blood flow to a bone (IBF) is important for orthopaedic surgeons when deciding the fate of an injured or diseased bone. Currently there is no easy and effective method for quickly assessing the blood flow status of a bone. There is accumulating evidence that suggests that IBF may be correlated to intraosseous pressure (IOP).

Therefore, we aimed to investigate whether the two variables are correlated so that the orthopaedic surgeon could confidently use IOP as an indicator of IBF.

Using 8 mature female ewes (B.W. ~56 kg) we measured cardiovascular (eg. arterial blood pressure – ABP), and intraosseous (ie. IOP and IBF) responses to nor-adrenaline (0–1.5 μg/kg/min. i.v.) and nitroglycerine (0–80 μg/kg. i.v.) IBF was measured using semi-quantitative technique of laser Doppler flowmetry (LDF).

Our results revealed that changes in ABP were directly correlated to changes in IOP (p < 0.001). Due to technical difficulties that were encountered when using LDF, the collected IBF data were limited. However, there was compelling evidence that there is a positive and direct correlation between IBF and IOP.

This opens an exciting possibility of using IOP for quickly and accurately assessing IBF as well as providing insight into the pathological mechanisms responsible for bone and joint disorders.

Current research efforts aim at enhancing osseointegration of cementless implants to improve early bone fixation.

The aim of the present study was to investigate whether bone morphogenic protein (BMP) 2 had a positive effect on the osseointegration of hydroxyapatite coated implants.

Hydroxyapatite (HA) implants were coated with BMP-2 and hyaluronic acid (HY) as the carrier or with HY alone. Uncoated HA-implants served as controls. The osseointegration of the implants was evaluated either by light microscopy and pullout tests after 1, 2 and 4 weeks of unloaded implantation in the cancellous bone of 18 sheep.

The BMP-2 coating significantly increased bone growth into the perforations of HA-implants. The proportion of bone-ingrowth at 4 weeks was 32% for the BMP-implants compared to 12% for HA implants. However, BMP-2 did not enhance the percentage of bone implant contact and interface shear strength values.

Conclusion: This study indicates that BMP-2 may help to increase bone growth across gaps of cementless implants in the early stages of bone healing improving fixation and decreasing the risk of loosening.

This study explores the outcomes of a pilot project involving five Orthopaedic services in developing approaches to improve the consistency and equity of clinical decision-making for access to treatment.

The pilot was conducted in two phases; the first involved development of retrospective and prospective data collection and analysis tools including use of:

The Orthopaedic Integrated CPAC tool:

Large variations in internal equity were found within most services. Additionally a significant, systemic equity issue is apparent between patients prioritised for major joints versus other conditions. The pilot has made useful progress in developing improvement tools and processes targeting electives service management, improvements in prioritisation and clinical decision making, and funding and planning decisions. The pilot has also raised issues for further CPAC development and national service policy.

Surgical waiting lists have led to development of clinical priority access criteria (CPAC) for prioritisation of patients selected for surgery. Although introduced widely into clinical practice in New Zealand CPAC tools have not been validated. Reliability studies were therefore undertaken by the CPAC Evaluation Consortium.

Methodology Thirty eight orthopaedic surgeons practising in public hospitals were randomly selected to participate in a prioritisation exercise using computer administered clinical vignettes. Fifty vignettes were developed from the clinical histories of patients selected for total knee arthroplasty (15), carpal tunnel decompression (15) and miscellaneous orthopaedic procedures (20). These were prioritised using each of 3 priority tools producing scores between 0 and 100: visual analogue scale reflecting global clinical opinion (VAS), a generic point scoring system based on points assigned to 5 clinical domains (GOPC), and diagnosis-specific 5 point Likert scale of priority combined with a predetermined table of a range of scores for each diagnosis (ISS).

The extent of inter-surgeon variability was striking but significantly less for ISS than GOPC or VAS. This was entirely explained by the complication of a predetermined table. The other two tools were similar except that the inter centile gap was larger for the clinical opinion based tool (VAS).

As access to elective surgery is determined by a fixed financial threshold a reliable scoring system will ensure equity of access. This seems to be best achieved by using the Integrated Scoring System.

To determine whether increased sagittal laxity has an effect on functional outcome following posterior cruciate retaining total knee replacement using two differing tibial insert designs.

Ninety-seven patients were reviewed clinically, radiologically and underwent KT1000 testing of their TKR at a minimum follow up of 5 years (mean 6.5 yrs). The femoral component design was the same in all patients (Duracon/PCA). Fifty two patients had a relatively flat tibial insert design (group 1), while 45 patients had an AP lipped insert (group 2) following a change in design in 1995.

The 2 groups were comparable for age, sex, Charnley category, BMI, tibial slope and follow up. There was no significant difference in laxity measurements, IKS or WOMAC scores between the groups. There was no significant correlation between laxity and outcome score or flexion range.

Increased sagittal laxity in a knee replacement does not have a strong influence on functional outcome. The differing tibial insert designs had no significant effect on either laxity or function.

Introduction: Vertebroplasty (VP) is a new prophylactic treatment for preventing osteoporotic compression fractures of vertebral bodies. During this procedure polymethylmethacrylate (PMMA) is injected into several vertebral bodies. It has been shown that fat embolism (FE) with acute cardiopulmonary deterioration occurs during VP as in a variety of other orthopaedic procedures (e.g. knee and hip replacements). The aim of the study is to investigate cardiovascular changes during FE caused by multiple VP using an animal model.

Method: In six sheep, PMMA was injected unilaterally, into L1 – L6, with ten minutes in-between injections. Arterial, venous and pulmonary artery pressure, cardiac output and blood gas values were recorded pre injection and 1, 3, 5 and 10 minutes post injection. Post mortem lungs were harvested and the histopathologic score (percentage of lung fields occupied by intravascular fat globules as seen in the microscope) was calculated.

Results: The sequential injection of bone cement into six vertebral bodies from values pre injection of L1 to 10 minutes post injection of L6 resulted in: significant falls in arterial blood pressure (P< 0.0001), cardiac output (P< 0.0001) (P=0.0049), pO₂ and pH (P< 0.0001) and significant rises in pulmonary arterial pressure (P=0.0005) and pCO₂ (P< 0.0001),but no significant change in central venous pressure. The histopathological score was 19.1±1.94%.

Conclusion: This study clearly shows that multiple VP in sheep leads to FE with major cardiovascular reactions. Arterial blood pressure showed a stepwise, cumulative fall and was clearly the best parameter to demonstrate these reactions. This suggests, in human patients, particular attention should be paid to falls in arterial blood pressure during multiple VP.

We carried out a histological study of a proximally hydroxyapatite (HA)-coated femoral component, retrieved after 9.5 years of good function. The HA coating had completely degraded. Bone was in direct contact with the titanium surface in all the areas which had been coated, with no interposing fibrous tissue. There were no signs of particles, third-body wear, adverse tissue reactions or osteolysis. Bone remodelling was evident by the presence of resorption lacunae; tetracycline labelling showed bone laid down six years after implantation.

The loss of the HA-coating had no negative effect on the osseo-integration of the stem. We conclude that the HA coating contributes to the fixation of the implant and that its degradation does not adversely affect the long-term fixation.

Magnetic Resonance Imaging is increasingly utilised for the assessment of knee pathology. The aim of this study was to review our entire knee MRI scans and to assess the accuracy of diagnosis when compared with operative diagnosis. Using data from the radiology department and medical records (public and private) all patients having knee MRI scans in a 6-year period were identified.

There were 956 scans performed on 930 patients. Scan diagnosis, operative diagnosis and diagnostic accuracy were assessed. Of the scanned patients 181 (19.5%) had normal scans and of these 168 (92.8%) were accurately diagnosed as normal. The remaining 749 (80.5%) had an abnormality noted on scan and of these 298 (39.8%) proceeded on to surgery. Of those patients having surgery, diagnosis at surgery was found to exactly match the results of the scan in 163 (57.0%) patients. Furthermore 51.5% of patients with a diagnosis of meniscal degeneration by scan actually had a meniscal tear at operation. However the sensitivity for diagnosis of ACL tears was 89.0% and that of medial meniscal tears was 90.6%.

MRI diagnosis is far from infallible and clinicians should be conscious of its limitations. However it is particularly reliable in confirming the lack of pathology within a knee with an accuracy of 93%. It also has high sensitivity for diagnosis of ACL and meniscal tears.

There are numerous papers from specialist arthroplasty centres outlining results of total knee replacement. This review was performed as there is little information on results in general orthopaedic centres. All patients received a Duracon/PCA replacement between 1992 and 1996. Patients were assessed clinically, fluoroscopically and completed SF12, WOMAC and IKSS questionnaires. At a mean of 6.7 (5–9) years follow up 93 (78%) were available for review. The average age was 70 years (52–88) with 58% being male. The primary diagnosis was osteoarthritis in 94.3%, with 41 %, 38% and 21 % being Charnley grades A, B and C respectively.

The average IKS knee score was 71.4 (23–96) and functional score 70 (0–100), with 72.7% experiencing none or only mild pain. The SF12 assessment revealed a mean physical score of 38 (14–63) and mental score of 53 (25–67). There were 88.6% of patients satisfied with their knee and 92% would have the operation again if required. There were no deep infections or PE’s but there were 7 superficial infections and 2 DVT’s. A MUA was required in 8 patients. One patient retains a radiologically loose prosthesis at 8 years but had mild pain with stairs only, a WOMAC functional score of 85 and was happy. There was a best-case survival of 94.4% at 5 years. There were 5 knees revised in 5 patients and no revisions of the deceased patients, all surviving greater than 5 years from surgery. These results suggest that those in general orthopaedic centres are a little less reliable than those in specialist centres. However they are acceptable and patient satisfaction remains high.

INTRODUCTION: Vertebroplasty (VP) is a new prophylactic treatment for preventing osteoporotic compression fractures of vertebral bodies. During this procedure polymethylmethacrylate (PMMA) is injected into several vertebral bodies. It has been shown that fat embolism (FE) with acute cardiopulmonary deterioration occurs during VP as in a variety of other orthopaedic procedures (eg knee and hip replacements). The aim of the study is to investigate cardiovascular changes during FE caused by multiple VP using an animal model.

METHOD: In six sheep, PMMA was injected unilaterally, into L1 – L6, with ten minutes in between injections. Arterial, venous and pulmonary artery pressure, cardiac output and blood gas values were recorded pre injection and one, three, five and 10 minutes post injection. Post mortem lungs were harvested and the histopathologic score (percentage of lung fields occupied by intravascular fat globules as seen in the microscope) was calculated.

RESULTS: The sequential injection of bone cement into six vertebral bodies from values pre injection of L1 to 10 minutes post injection of L6 resulted in: significant falls in arterial blood pressure (P< 0.0001), cardiac output (P=0.0049), pO2 (P< 0.0001) and pH (P< 0.0001) and significant rises in pulmonary arterial pressure (P=0.0005) and pCO2 (P< 0.0001), but no significant change in central venous pressure. The histopathological score was 19.1±1.94%.

CONCLUSION: This study clearly shows that multiple VP in sheep leads to FE with major cardiovascular reactions. Arterial blood pressure showed a stepwise, cumulative fall and was clearly the best parameter to demonstrate these reactions. This suggests, in human patients, particular attention should be paid to falls in arterial blood pressure during multiple VP.

The purpose of this study was to audit screening and treatment programmes for Developmental Dysplasia of the Hip (DDH) over a 12-year period from 1989 to 2000 with respect to late presentation and treatment rate and duration.

All babies born in Queen Mary Hospital are clinically screened for DDH by a consultant orthopaedic surgeon. Unstable hips are treated by Pavlik Harness and attend an ultrasound clinic run by an orthopaedic surgeon within 2 weeks. High-risk babies or those with suspected instability can also be referred for ultrasound. Serial ultrasound exams assisted with determining the duration of splintage. Radiographs are taken at 4 to 6 months. Late presenters were identified and analysed.

Over the 12-year period 13 cases of late presenting DDH were identified (0.6 per 1000). Half of these had not been screened. None had ultrasound screening. Our treatment rate was approximately 4 per 1000 live births.

Our screening programme can be improved by increased capture of patients for clinical screening. Ultrasound is a useful tool in managing neonatal hip instability allowing duration of splintage to be tailored to the individual and allows early detection of treatment failure.

Introduction: Vertebroplasty (VP) is a relatively new procedure to treat osteoporotic compression fractures of vertebral bodies. During this procedure polymethyl-methacrylate (PMMA) is injected into vertebral bodies. However there is the concern, that fat embolism (FE) and acute hypotension could occur as in a variety of other orthopaedic procedures.

Aim: To investigate whether FE and acute hypotension are potential complications of VP using an animal model.

Methods: In six sheep, 6.0 ml PMMA were injected unilaterally into the L1 vertebral body. Transœsophageal echocardiography was used to monitor the pulmonary artery for bone marrow and fat particles until 30 minutes post-operatively. Pulse, arterial and venous pressures were also recorded. The lumbar spine and the lungs were harvested post mortem. The histopathologic score, (percentage of lung fields occupied by intravascular fat globules as seen through the microscope), was calculated.

Results: The first showers of echogenic material were visible approximately seven seconds after the beginning of the cement injection and lasted for about 2.5 minutes. The injection of bone cement caused a very rapid decrease in the heart rate after two seconds followed by a fall in the mean arterial pressure after 6.0 seconds. A maximum fall in heart rate was accompanied by a delayed fall in mean arterial pressure of 33.0 mmHg (P=0.0003) at 36seconds. The heat rate had returned to the baseline by 89 seconds and had increased by 10 beats/min (P=0.02) at 25 minutes. Mean arterial pressure had recovered by 209 seconds and was not different from the baseline at 25 minutes. Post mortem examination showed that no leakage of cement into the spinal cord had occurred. The histology revealed fat globules and bone marrow cells in the smaller and larger vessels throughout the lungs. The histopathologic score was 5.2 ± 0.9%.

Conclusions: This study clearly showed that VP resulted in FE with a two-phase decrease in heart rate and arterial blood pressure. The first phase was probably due to an autonomic reflex and the second phase was due to the passage of fat emboli through the right heart and obstructing the lungs.

Introduction: After more than 10 years of clinical experience, hydroxyapatite (HA) coated orthopaedic implants are now an established, viable alternative to porous coatings for achieving good implant fixation. However, developments are continuing to improve the nature and adhesion of the HA coating.

Aim: To investigate the biological attachment characteristics of titanium and highly crystalline HA implant coatings in the metaphysis of an animal model.

Method: Titanium alloy implants with a coating of commercially pure titanium (Ti) or highly crystalline HA were evaluated by light microscopy and pullout tests after one, two and four weeks of unloaded implantation in the tibial and femoral metaphyses of 18 sheep.

Results: The interface shear strength pullout increased from approximately 29N/cm2 at one week to approximately 326N/cm² at two weeks. At four weeks the pull-out strength for Ti and HA coated implants was 1,004.87 ± 189.82N/cm2 and 1,043.26 ± 260.61N/cm2 respectively. The pullout strength increased significantly over time up to four weeks, but the difference between the coatings was not statistically significant at any time interval.

Histomorphometric analysis showed an increase of bone-implant contact between one and two weeks from 0 to 15% for Ti and 0 to 20% for HA coated implants. At four weeks Ti and HA implants showed 44% and 60% bone-implant contact respectively. There was a significant increase in bone-implant contact over time for both coatings. HA implants had significantly higher bone-implant contact at two and four weeks. Light microscopy revealed that bone grew into HA coated surfaces in the form of feet, spreading over the surface. Whereas for Ti the newly formed bone looked like a bridge linking the original bone with the implant surface.

Conclusion: The different growth patterns of bone into Ti and HA surfaces resulted in different bone-implant contact areas. Highly crystalline hydroxyapatite coatings enhanced the osseointegration in the early stages of bone healing. However there was a discrepancy between the mechanical and histological results. This may suggest that the mechanical failure does not occur at the implant-bone interface.

Purpose: The ABG Total Hip Joint Replacement is a cementless, hydroxyapatite coated prosthesis designed to be metaphyseal loading. The aim of our study was to analyze the changes in proximal femoral bone mineral density (BMD) following implantation of this prosthesis.

Method: Dual energy x-ray absorptiometry (DEXA) scanning has been shown to be an accurate and reliable method of assessing BMD following total hip arthroplasty. 14 patients undergoing primary ABG Total Hip Joint Replacement were recruited into the study following informed consent. BMD was determined for each of the seven periprosthetic zones of Gruen from DEXA scans, which were performed serially at preoperative,, 3 months, 6 months, 1 year and 2 years.

Results: 8 patients have now completed their scans. The most dramatic change in BMD was found in zone 7 which is the femoral calcar. In this region there was a progressive decrease in average BMD to 75% of the preoperative value at 2 years. In zones 2 and 3 representing the femoral cortex lateral to the prosthesis there was an increase in BMD to approximately 114.5% at 3 months and this was maintained at 2 years. In the remaining zones BMD was reasonably stable between 97.5 and 101%.

Conclusion: We have found that in the 2 years following ABG hip arthroplasty there is a dramatic decrease in BMD to 75% within the region of the femoral calcar. Further scans are required to determine if this is progressive. In the remaining regions BMD is either increased or relatively well preserved.

Introduction: Vertebroplasty (VP) is a new prophylactic treatment for preventing osteoporotic compression fractures of vertebral bodies. During this procedure polymethylmethacrylate (PMMA) is injected into several vertebral bodies. It has been shown that fat embolism (FE) with acute cardiopulmonary deterioration occurs during VP as it does in a variety of other orthopaedic procedures (e.g. knee and hip replacements).

Aim: To investigate the cardiovascular changes during FE caused by multiple VP using an animal model.

Method: PMMA was injected unilaterally, into L1 – L6 in six sheep, with 10 minutes between injections. Arterial, venous and pulmonary arterial pressure, cardiac output and blood gas values were recorded before injection and again after the injection at one, three, five and 10 minutes. The lungs were harvested post mortem and the histopathologic score (percentage of lung fields occupied by intravascular fat globules as the field of the microscope) was calculated.

Results: The sequential injection of bone cement into six vertebral bodies from values before injection of L1 to 10 minutes after injection of L6 resulted in significant falls in arterial blood pressure (P< 0.0001), cardiac output (P=0.0049), pO² (P< 0.0001) and pH (P< 0.0001). There were also significant rises in pulmonary arterial pressure (P=0.0005) and pCO2 (P< 0.0001), but no significant change in central venous pressure. The histopathological score was 19.1±1.94%,

Conclusions: This study clearly showed that multiple VP in sheep leads to FE with major cardiovascular reactions. Arterial blood pressure showed a stepwise, cumulative fall and was clearly the best parameter to demonstrate these reactions. This suggests that in human patients, particular attention should be paid to falls in arterial blood pressure during multiple VP.

Aim: To demonstrate the pattern and mechanism of injury of alpine skiing and snowboarding, and to evaluate the potential risk factors.

Methods: We analysed prospectively all cases of orthopaedic injuries requiring hospital admission that were the result of snowboarding or skiing accidents in the winter of 2000. This included four popular skiing facilities in the South Island of New Zealand.

Results: Seventy-six patients were reviewed. Of those, 30 cases were the results of accidents from snowboarding and 44 cases were from skiing. In addition to appropriate medical evaluations and medical care, a detailed examination was performed on every patient to determine various factors, including demographics, their level of experience and the cause and mechanism of the accident. There were 47 males and 29 females, with an average age of 28 (range: seven to 62)years. Snowboarders tended to be younger men with an average age of 23 years compared with 31 years in skiers. Males constituted 77% of snowboarders and 54% of skiers.

There were 14 patients in the beginners’ group, 32 intermediate, 20 advanced and nine at an extreme-skill level. Thirty-eight patients sustained injuries of the lower extremities, 24 of the upper extremities, 13 of the spine, and one of the pelvis. Lower extremity injuries were more common in skiers (59% of lower limbs, versus 25% of upper limbs), while in snow boarding upper extremity injuries were more common (43% upper limbs versus 36% lower limbs). Ulnar collateral ligament injuries of the metacarpophalangeal joint of the thumb, were far more common in skiers (six in skiers versus one on snowboard). Sixteen patients (nine skiers and six snow-boarders) sustained diaphyseal fractures of their tibiae. In all nine patients in the skiing group, the mechanism of injury was failure of the binding to release resulting in a twisting force to the leg, while in the snowboarding group, three patients (50%) fractured their tibiae on landing badly from a jump and in the other three on colliding with another person or a fixed object.

Conclusions: Lower extremity, equipment-related injuries are common in alpine skiing. The data suggested that currently used bindings are insufficient. Research, technical developments and optimal adjustment of binding are required.

Vertebroplasty (VP) is a new prophylactic treatment for preventing osteoporotic compression fractures of vertebral bodies. During this procedure polymethylmethacrylate (PMMA) is injected into several vertebral bodies. However, there is the concern, that fat embolism (FE) and acute hypotension could occur as in a variety of other orthopaedic procedures.

This study was undertaken to investigate whether FE and acute hypotension are potential complications of VP using an animal model.

In six sheep 6.0 ml PMMA were injected unilaterally into L1. Transesophageal echocardiography was used to monitor the pulmonary artery for bone marrow and fat particles until 30 minutes postoperatively. Pulse, arterial and venous pressure were also recorded. Post mortem the lumbar spine and the lungs were harvested. The lungs were subjected to histological evaluation.

The first showers of echogenic material were visible approximately 7.0 seconds after the beginning of the cement injection and lasted for about 2.5 minutes.

Injection of bone cement elicited a very rapid decrease in heart rate after 2.0 seconds followed by a fall in mean arterial pressure after 6.0 seconds. A maximum fall in heart rate was accompanied by a delayed fall in mean arterial pressure of 33.0 mmHg (P=0.0003) at 36.0 seconds. Heat rate had returned to baseline by 89.0 seconds and had increased by 10.0 beats/min (P=0.02) at 25 minutes. Mean arterial pressure had recovered by 209.0 seconds and was not different to the baseline at 25 minutes.

The post mortem inspection revealed disseminated haemorrhages on the lung surface and throughout the parenchyma mainly in the caudal lobes of all six animals. No leakage of cement into the spinal cord was detected. In histology fat globules and bone marrow cells were observed in both the smaller and larger vessels throughout the lung.

This study clearly shows that VP resulted in a two-phase decrease in heart rate and arterial blood pressure. The first phase was probably due to an autonomic reflex and the second phase was due to the passage of fat emboli through the right heart and obstructing the lungs.

Aim: To analyse the Dunedin residual orthopaedic waiting list based on a simple patient questionnaire and a quality of life assessment using EuroQol and SF12.

Method: All patients on the residual waiting list were sent a postal questionnaire enquiring about their need for surgery and their quality of life. Based on their answers, patients were entered into three action groups: 1. back to GP care 2. clinical review 3. booked for surgery. Those patients requiring a clinical review were seen in a special clinic and reassessed in relation to their need for surgery.

Results: Two hundred and sixty-one patients were surveyed. One hundred and fifty-eight had complete data available for analysis and of the remaining 103 patients, 88 were taken off the waiting list for various reasons. Fifteen did not reply. The average time on the waiting list was 19 months (range: < six months to eight years). Sixty percent of the patients felt that their condition had changed and 99% felt that they still required the surgery. The results of the EuroQol and DF12 questionnaire revealed three groups of patients. 1. normal (9 patients). 2. slight impairment (115 patients) 3. moderate impairment (34 patients). Most of these patients had stable conditions except the sub group with deteriorating osteoarthritis of the hip/knee. Group 1 patients were all referred back to their GP. Thirty percent of group 2 patients were referred back to their GP, 60% were booked for a review and 10% were booked for surgery. None of Group 3 patients were referred back to their GP. Seventy percent required a clinical review and 30% were booked for surgery. Our clinical review is continuing but it is anticipated that those who still require surgery and score above the financial threshold will probably be less than one third of the cases.

Conclusion: This paper describes a decision making rationale in relation to assessment of continuing need for surgery in patients on the residual orthopaedic waiting list. Eighty percent of patients had stable conditions, which were not interfering significantly with their activities of daily living and could be managed safely by the GP. Further work is required to identify those patients who are at risk of deteriorating and to work out a practical and cost effective monitoring programme.

Previous clinical studies have studied tibiofibular torsion by measuring the angular difference between a proximal (often bicondylar) plane and a distal bimalleolar plane. We measured the angular difference between the proximal and distal posterior tibial planes as defined by ultrasound scans. We found no significant torsional difference between the right and left tibiae of 87 normal children, nor between their different age groups. The mean external torsion of 58 legs with congenital talipes equinovarus was 18 degrees; significantly less than the mean 40 degrees in the normal children and 27 degrees in the clinically normal legs of the 22 patients with unilateral congenital talipes equinovarus. We did not confirm the previously reported increase in external torsion with increasing age. The relative internal tibial torsion we have demonstrated in patients with congenital talipes equinovarus must be differentiated from the posterior displacement of the distal fibula observed by others and which may result from manipulative treatment. The relative internal tibial torsion we found in the clinically normal legs of children with congenital talipes equinovarus is further evidence that in this condition the pathology is not confined to the clinically affected foot.