Rapid in situ chondrocyte death induced by Staphylococcus aureus toxins in a bovine cartilage explant model of septic arthritis

OBJECTIVE

To assess in situ chondrocyte viability following exposure to a laboratory strain and clinical isolates of Staphylococcus aureus.

METHODS

Bovine cartilage explants were cultured in the presence of S. aureus 8325-4 (laboratory strain), clinical S. aureus isolates or non-infected culture medium of pH values 7.4, 6.4 and 5.4. All clinical isolates were isolated from the joint aspirates of patients presenting with S. aureus-induced septic arthritis (SA). At designated time points, in situ chondrocyte viability was assessed within defined regions-of-interest in the axial and coronal plane following live- and dead-cell image acquisition using the fluorescent probes 5-chloromethylfluorescein diacetate (CMFDA) and propidium iodide (PI), respectively, and confocal laser-scanning microscopy (CLSM). Cartilage water content, following S. aureus 8325-4 exposure, was obtained by measuring cartilage wet and dry weights.

RESULTS

S. aureus 8325-4 and clinical S. aureus isolates rapidly reduced in situ chondrocyte viability (>45% chondrocyte death at 40 h). The increased acidity, observed during bacterial culture, had a minimal effect on chondrocyte viability. Chondrocyte death commenced within the superficial zone (SZ) and rapidly progressed to the deep zone (DZ). Simultaneous exposure of SZ and DZ chondrocytes to S. aureus 8325-4 toxins found SZ chondrocytes to be more susceptible to the toxins than DZ chondrocytes. Cartilage water content was not significantly altered compared to non-infected controls.

CONCLUSIONS

Toxins released by S. aureus have a rapid and fatal action on in situ chondrocytes in this experimental model of SA. These data advocate the prompt and thorough removal of bacteria and their toxins during the treatment of SA.

Lengthening the moment arm of the patella confers enhanced extensor mechanism power following total knee arthroplasty

We investigated whether a postulated biomechanical advantage conferred to the extensor mechanism by a change in knee implant design was detectable in patients by direct physical testing. 212 TKA patients were enrolled in a double blind randomized controlled trial to receive either a traditional implant or one which incorporated new design features. Extensor mechanism power output and physical performance on a battery of timed functional activities was assessed pre-operatively and then at 6, 26, and 52 weeks post-operatively. Significantly enhanced power output was observed in both groups post-arthroplasty; however, the new design implant group demonstrated a greater change in power output than the traditional implant group. Posthoc testing of between group differences highlighted greater improvement at all post-operative assessments. At 52 weeks, patients receiving the implant with the postulated biomechanical advantage achieved 116% of the power output of their contralateral limb, whereas patients with the traditional design achieved 90%. No between group difference was detected in the patient's time to complete functional tasks. Thus, patients receiving a knee implant of a modern design (theoretically able to confer a mechanical advantage to the extensor mechanism) were found to generate significantly greater extensor power than those receiving a traditional implant without the postulated mechanical advantage.

The effect of strain rate on the failure stress and toughness of bone of different mineral densities

The risk of low energy fracture of the bone increases with age and osteoporosis. This paper investigates the effect of strain rate and mineral level on the peak stress and toughness of whole ovine bones. 40 fresh ovine femurs were subjected to 3-point bending at high (17.14s(-1)) and low (8.56 × 10(-3)s(-1)) strain rates with or without a controlled amount of demineralisation. Mineral removal was achieved by ultrasonically assisted exposure in Ethylene diamine tetra-acetic acid (EDTA). The ultimate stress for whole bones of normal mineral content was 200 MPa at the high rate of strain and 149 MPa at the low rate of strain. With changes in bone mineral levels such as may occur in osteomalacia and osteoporosis, the change in toughness varied at different strain rates; a mean value of 3.7 ± 1.4 MJ/m(3) was obtained for the toughness of normal quality whole bone tested at slow loading rate and a reduction of approximately 25% was observed in the demineralised whole bone specimens at the slow loading rate (mean 2.8 ± 0.9 MJ/m(3)). When tested at the high loading rate there was a negligible difference in the toughness between the two (2.0 ± 0.6 MJ/m(3)) mineral levels. This indicated that there was a strain rate dependant effect for the mineral density, and that the removal of mineral alone did not explain all of the reduction in mechanical properties that occur with age or disease. Thus, the reduction in mechanical properties at high strain rates was likely to be due to other phenomena such as increased porosity or reduced collagen quality, rather than loss of mineral. With decreasing mineral levels, as measured by DEXA in clinical practice, the increased fracture risk is dependent on the velocity of the impact. Thus the estimates of increased fracture risk given clinically for a lower DEXA value should be different for high and low energy injuries.

Do modern total knee replacements offer better value for money? A health economic analysis

PURPOSE

Cost effectiveness is an increasingly important factor in today's healthcare environment, and selection of arthroplasty implant is not exempt from such concerns. Quality adjusted life years (QALYs) are the typical tool for this type of evaluation. Using this methodology, joint arthroplasty has been shown to be cost effective; however, studies directly comparing differing prostheses are lacking.

METHODS

Data was gathered in a single-centre prospective double-blind randomised controlled trial comparing the outcome of modern and traditional knee implants, using the Short Form 6 dimensional (SF-6D) score and quality adjusted life year (QALY) methodology.

RESULTS

There was significant improvement in the SF-6D score for both groups at one year (p < 0.0001). The calculated overall life expectancy for the study cohort was 15.1 years, resulting in an overall QALY gain of 2.144 (95% CI 1.752-2.507). The modern implant group demonstrated a small improvement in SF-6D score compared to the traditional design at one year (0.141 versus 0.143, p = 0.94). This difference resulted in the modern implant costing £298 less per QALY at one year.

CONCLUSION

This study demonstrates that modern implant technology does not influence the cost-effectiveness of TKA using the SF-6D and QALY methodology. This type of analysis however assesses health status, and is not sensitive to joint specific function. Evolutionary design changes in implant technology are thus unlikely to influence QALY analysis following joint replacement, which has important implications for implant procurement.

Chronic osteomyelitis of the pelvis

The aim of this study was to examine the aetiology and response to treatment of a series of patients with pelvic osteomyelitis. Criteria for selection were multiple positive intra-operative cultures and/or a positive radiological diagnosis. Twenty patients met these criteria (age range: 21-78 years, mean = 46). Data was recorded on host status using the Cierny-Mader classification, neurological status, causative organisms; sensitivities were recorded and the treatment and its outcome. Pelvic osteomyelitis was frequently caused by unusual organisms; a high incidence (45%) of neurologically compromised patients was noted. There were important differences in infective organisms, treatment and outcome in the paraplegic and non-paraplegic population. A high mortality and a high incidence of squamous cell carcinoma was observed. Pelvic osteomyelitis should be managed differently to long bone osteomyelitis as far as the antibiotic therapy is concerned, with a greater need for broad spectrum antibiotics in pelvic osteomyelitis. The response to surgical resection was similar to long bone osteomyelitis with a high chance of success with marginal resection in type A hosts and with wide resection in type B hosts.

Muscle 'regenerative potential' determinesphysical recovery following total knee replacement

Objectives

Lower limb muscle power is thought to influence outcome following total knee replacement (TKR). Post-operative deficits in muscle strength are commonly reported, although not explained. We hypothesised that post-operative recovery of lower limb muscle power would be influenced by the number of satellite cells in the quadriceps muscle at time of surgery.

Methods

Biopsies were obtained from 29 patients undergoing TKR. Power output was assessed pre-operatively and at six and 26 weeks post-operatively with a Leg Extensor Power Rig and data were scaled for body weight. Satellite cell content was assessed in two separate analyses, the first cohort (n = 18) using immunohistochemistry and the second (n = 11) by a new quantitative polymerase chain reaction (q-PCR) protocol for Pax-7 (generic satellite cell marker) and Neural Cell Adhesion Molecule (NCAM; marker of activated cells).

Results

A significant improvement in power output was observed post-operatively with a mean improvement of 19.7 W (95% confidence interval (CI) 14.43 to 30.07; p < 0.001) in the first cohort and 27.5 W (95% CI 13.2 to 41.9; p = 0.002) in the second. A strong correlation was noted between satellite cell number (immunohistochemistry) and improvement in patient power output (r = 0.64, p = 0.008). Strong correlation was also observed between the expression of Pax-7 and power output (r = 0.79, p = 0.004), and the expression of NCAM and power output (r = 0.84, p = 0.001). The generic marker explained 58% of the variation in power output, and the marker of activated cells 67%.

Conclusions

Muscle satellite cell content may determine improvement in lower limb power generation (and thus function) following TKR.

Does bone compaction around the helical blade of a proximal femoral nail anti-rotation (PFNA) decrease the risk of cut-out?: A subject-specific computational study

Objectives

Because of the contradictory body of evidence related to the potential benefits of helical blades in trochanteric fracture fixation, we studied the effect of bone compaction resulting from the insertion of a proximal femoral nail anti-rotation (PFNA).

Methods

We developed a subject-specific computational model of a trochanteric fracture (31-A2 in the AO classification) with lack of medial support and varied the bone density to account for variability in bone properties among hip fracture patients.

Results

We show that for a bone density corresponding to 100% of the bone density of the cadaveric femur, there does not seem to be any advantage in using a PFNA with respect to the risk of blade cut-out. On the other hand, in a more osteoporotic femoral head characterised by a density corresponding to 75% of the initial bone density, local bone compaction around the helical blade provides additional bone purchase, thereby decreasing the risk of cut-out, as quantified by the volume of bone susceptible to yielding.

Conclusions

Our findings indicate benefits of using a PFNA over an intramedullary nail with a conventional lag screw and suggest that any clinical trial reporting surgical outcomes regarding the use of helical blades should include a measure of the femoral head bone density as a covariable.

Is patient reporting of physical function accurate following total knee replacement?

The aim of this study was to determine the association between the Oxford knee score (OKS) and direct assessment of outcome, and to examine how this relationship varied at different time-points following total knee replacement (TKR). Prospective data consisting of the OKS, numerical rating scales for 'worst pain' and 'perceived mean daily pain', timed functional assessments (chair rising, stairs and walking ability), goniometry and lower limb power were recorded for 183 patients pre-operatively and at six, 26 and 52 weeks post-operatively. The OKS was influenced primarily by the patient's level of pain rather than objective functional assessments. The relationship between report of outcome and direct assessment changed over time: R2 = 35% pre-operatively, 44% at six weeks, 57% at 26 weeks and 62% at 52 weeks. The relationship between assessment of performance and report of performance improved as the patient's report of pain diminished, suggesting that patients' reporting of functional outcome after TKR is influenced more by their pain level than their ability to accomplish tasks.

The relative incidence of fracture non-union in the Scottish population (5.17 million): a 5-year epidemiological study

OBJECTIVES

In the UK there are approximately 850 000 new fractures seen each year. Rates of non-union of 5-10% of fractures have been suggested, the cost to the National Health Service of treating non-union has been reported to range between £7000 and £79 000 per person yet there are little actual data available. The objective of this epidemiological study therefore is for the first time to report the rates of fracture non-union.

DESIGN

A cross-sectional epidemiological study.

SETTING

The population of Scotland.

PARTICIPANTS

All patient admissions to hospital in Scotland are coded according to diagnosis. These data are collected by (and were obtained from) Information Services Department Scotland. Those who have been coded for a bone non-union between 2005 and 2010 were included in the study. No patients were excluded. Population data were obtained from the Registrar General for Scotland.

OUTCOME MEASURE

The number of fracture non-unions per 100 000 population of Scotland according to age, sex and anatomical distribution of non-union.

RESULTS

4895 non-unions were treated as inpatients in Scotland between 2005 and 2010, averaging 979 per year, with an overall incidence of 18.94 per 100 000 population per annum. The distribution according to gender was 57% male and 43% female. The overall peak incidence according to age was between 30 and 40 years. The mean population of Scotland between 2005 and 2010 was 5 169 140 people.

CONCLUSION

Fracture non-union in the population as a whole remains low at less than 20 per 100 000 population and peaks in the fourth decade of life. Further research is required to determine the risk of non-union per fracture according to age/sex/anatomical distribution. .

What determines patient satisfaction with surgery? A prospective cohort study of 4709 patients following total joint replacement

OBJECTIVES

To investigate the factors which influence patient satisfaction with surgical services and to explore the relationship between overall satisfaction, satisfaction with specific facets of outcome and measured clinical outcomes (patient reported outcome measures (PROMs)).

DESIGN

Prospective cohort study.

SETTING

Single National Health Service (NHS) teaching hospital.

PARTICIPANTS

4709 individuals undergoing primary lower limb joint replacement over a 4-year period (January 2006-December 2010).

MAIN OUTCOME MEASURES

Overall patient satisfaction, clinical outcomes as measured by PROMs (Oxford Hip or Knee Score, SF-12), satisfaction with five specific aspects of surgical outcome, attitudes towards further surgery, length of hospital stay.

RESULTS

Overall patient satisfaction was predicted by: (1) meeting preoperative expectations (OR 2.62 (95% CI 2.24 to 3.07)), (2) satisfaction with pain relief (2.40 (2.00 to 2.87)), (3) satisfaction with the hospital experience (1.7 (1.45 to 1.91)), (4) 12 months (1.08 (1.05 to 1.10)) and (5) preoperative (0.95 (0.93 to 0.97)) Oxford scores. These five factors contributed to a model able to correctly predict 97% of the variation in overall patient satisfaction response. The factors having greatest effect were the degree to which patient expectations were met and satisfaction with pain relief; the Oxford scores carried little weight in the algorithm. Various factors previously reported to influence clinical outcomes such as age, gender, comorbidities and length of postoperative hospital stay did not help explain variation in overall patient satisfaction.

CONCLUSIONS

Three factors broadly determine the patient's overall satisfaction following lower limb joint arthroplasty; meeting preoperative expectations, achieving satisfactory pain relief, and a satisfactory hospital experience. Pain relief and expectations are managed by clinical teams; however, a fractured access to surgical services impacts on the patient's hospital experience which may reduce overall satisfaction. In the absence of complications, how we deliver healthcare may be of key importance along with the specifics of what we deliver, which has clear implications for units providing surgical services.

The development of a novel model of direct fracture healing in the rat

Objectives

Small animal models of fracture repair primarily investigate indirect fracture healing via external callus formation. We present the first described rat model of direct fracture healing.

Methods

A rat tibial osteotomy was created and fixed with compression plating similar to that used in patients. The procedure was evaluated in 15 cadaver rats and then in vivo in ten Sprague-Dawley rats. Controls had osteotomies stabilised with a uniaxial external fixator that used the same surgical approach and relied on the same number and diameter of screw holes in bone.

Results

Fracture healing occurred without evidence of external callus on plain radiographs. At six weeks after fracture fixation, the mean stress at failure in a four-point bending test was 24.65 N/mm² (sd 6.15). Histology revealed ‘cutting-cones’ traversing the fracture site. In controls where a uniaxial external fixator was used, bone healing occurred via external callus formation.

Conclusions

A simple, reproducible model of direct fracture healing in rat tibia that mimics clinical practice has been developed for use in future studies of direct fracture healing.

Bone properties affect loosening of half-pin external fixators at the pin-bone interface

INTRODUCTION

Local bone yielding at the pin-bone interface of external fixation half-pins has been known to initiate fixator loosening. Deterioration of bone properties due to ageing and disease can lead to an increase in the risk of pin loosening. This study determines the extent, locations and mechanics of bone yielding for unilateral external fixation systems at the tibial midshaft with changes in age-related bone structure and properties. The study also evaluates the effect of the number of pins used in the fixation system and use of titanium pins (in place of steel) on bone yielding.

METHODS

We employ nonlinear finite element (FE) simulations. Strain-based plasticity is used to simulate bone yielding within FE analyses. Our analyses also incorporate contact behaviour at pin-bone interfaces, orthotropic elasticity and periosteal-endosteal variation of bone properties.

RESULTS

The results show that peri-implant yielded bone volume increases by three times from young to old-aged cases. The use of three, rather than two half-pins (on either side of the fracture), reduces the volume of yielded bone by 80% in all age groups. The use of titanium half-pins resulted in approximately 60-65% greater volumes of yielded bone.

CONCLUSIONS

We successfully simulate half-pin loosening at the bone-implant interface which has been found to occur clinically. Yielding across the full cortical thickness may explain the poor performance of these devices for old-aged cases. The models are able to identify patients particularly at risk of half-pin loosening, who may benefit from alternative fixator configurations or techniques such as those using pre-tensioned fine wires.

Slipped upper tibial epiphysis in infantile tibia vara: three cases

We describe three cases of infantile tibia vara resulting from an atraumatic slip of the proximal tibial epiphysis upon the metaphysis. There appears to be an association between this condition and severe obesity. Radiologically, the condition is characterised by a dome-shaped metaphysis, an open growth plate and disruption of the continuity between the lateral borders of the epiphysis and metaphysis, with inferomedial translation of the proximal tibial epiphysis. All patients were treated by realignment of the proximal tibia by distraction osteogenesis with an external circulator fixator, and it is suggested that this is the optimal method for correction of this complex deformity. There are differences in the radiological features and management between conventional infantile Blount's disease and this 'slipped upper tibial epiphysis' variant.

Comparative outcomes of total hip and knee arthroplasty: a prospective cohort study

PURPOSE

The comparative outcome of primary hip and knee arthroplasty is not well understood. This study aimed to investigate the outcome and satisfaction of these procedures and determine predictive models for 1 year patient outcome with a view to informing surgical management and patient expectations.

STUDY DESIGN

Prospective cohort study of all primary hip and knee arthroplasty procedures performed at the Royal Infirmary of Edinburgh between January 2006 and November 2008. General health (SF-12) and joint specific function (Oxford Score) was assessed pre-operatively and at 6 and 12 months post-operatively. Patient satisfaction was assessed at 12 months.

RESULTS

1410 total hip arthroplasty (THA) and 1244 total knee arthroplasty (TKA) procedures were assessed. Oxford Score improved by 4.9 points more in THA patients than in TKA patients. SF-12 physical scores were on average 2.7 points greater in the THA patients at one year. Satisfaction was also greater (91%) following THA compared with TKA (81%). Regression modelling was not able to predict individual patient outcome; however, mean pre-operative Oxford Scores were found to be strong predictors of mean post-operative Oxford Scores for each procedure. Age, gender and pre-operative general health scores did not influence these models.

CONCLUSIONS

Both THA and TKA confer substantial improvement in patient outcome; however, greater joint specific, general health and satisfaction scores are reported following THA. This difference is physical in nature. Regression models are presented that can be applied to predict mean hip/knee arthroplasty outcome based on preoperative values.

Age-related differences in the neck strength of adolescent rugby players: A cross-sectional cohort study of Scottish schoolchildren

Objectives

To evaluate the neck strength of school-aged rugby players, and to define the relationship with proxy physical measures with a view to predicting neck strength.

Methods

Cross-sectional cohort study involving 382 rugby playing schoolchildren at three Scottish schools (all male, aged between 12 and 18 years). Outcome measures included maximal isometric neck extension, weight, height, grip strength, cervical range of movement and neck circumference.

Results

Mean neck extension strength increased with age (p = 0.001), although a wide inter-age range variation was evident, with the result that some of the oldest children presented with the same neck strength as the mean of the youngest group. Grip strength explained the most variation in neck strength (R² = 0.53), while cervical range of movement and neck girth demonstrated no relationship. Multivariable analysis demonstrated the independent effects of age, weight and grip strength, and the resultant model explained 62.1% of the variance in neck strength. This model predicted actual neck strength well for the majority of players, although there was a tendency towards overestimation at the lowest range and underestimation at the highest.

Conclusion

A wide variation was evident in neck strength across the range of the schoolchild-playing population, with a surprisingly large number of senior players demonstrating the same mean strength as the 12-year-old mean value. This may suggest that current training regimes address limb strength but not neck strength, which may be significant for future neck injury prevention strategies. Age, weight and grip strength can predict around two thirds of the variation in neck strength, however specific assessment is required if precise data is sought.

Investigation of factors affecting loosening of Ilizarov ring-wire external fixator systems at the bone-wire interface

The potential for peri-implant bone yielding and subsequent loosening of Ilizarov ring-wire external fixation systems was investigated using non-linear finite element (FE) analyses. A strain-based plasticity model was employed to simulate bone yielding. FE models also incorporated contact behavior at the wire-bone interface, orthotropic elasticity, and periosteal-endosteal variation of bone properties. These simulations were used to determine the extent and location of yielding with change in age-related bone structure and properties for the bone-Ilizarov construct at the tibial midshaft. At critical wire-bone interfaces, the predicted volume of yielded bone with four wires (on either side of the fracture) was ∼40% of that with two wires. Old-aged cases showed considerably greater bone yielding at the wire-bone interface than young cases (1.7-2.2 times greater volumes of yielded bone). The volume of yielded bone at all wire-bone interfaces decreased with an increase in wire pre-tension. The absence of continuous through-thickness yielding offers an explanation for the clinical observation that Ilizarov ring-wire fixation can provide stable fracture fixation even in bone with high porosity.

Relating age and micro-architecture with apparent-level elastic constants: a micro-finite element study of female cortical bone from the anterior femoral midshaft

Homogenized elastic properties are often assumed for macro-finite element (FE) models used in orthopaedic biomechanics. The accuracy of material property assignments may have a strong effect on the ability of these models to make accurate predictions. For cortical bone, most macro-scale FE models assume isotropic elastic material behaviour and do not include variation of material properties due to bone micro-architecture. The first aim of the present study was to evaluate the variation of apparent-level (homogenized) orthotropic elastic constants of cortical bone with age and indices of bone micro-architecture. Considerable age-dependent differences in porosity were noted across the cortical thickness in previous research. The second aim of the study was to quantify the resulting differences in elastic constants between the periosteum and endosteum. Specimens were taken from the anterior femoral midshaft of 27 female donors (age 53.4 ± 23.6 years) and micro-FE (µFE) analysis was used to derive orthotropic elastic constants. The variation of orthotropic elastic constants (Young’s moduli, shear moduli, and Poisson’s ratios) with various cortical bone micro-architectural indices was investigated. The ratio of canal volume to tissue volume, Ca.V/TV, analogous to porosity, was found to be the strongest predictor ( r ave2 = 0.958) of the elastic constants. Age was less predictive ( r ave2 = 0.385) than Ca.V/TV. Elastic anisotropy increased with increasing Ca.V/TV, leading to lower elastic moduli in the transverse, typically less frequently loaded, directions. Increased Ca.V/TV led to a more substantial reduction in elastic constants at the endosteal aspect than at the periosteal aspect. The results are expected to be most applicable in similar midshaft locations of long bones; specific analysis of other sites would be necessary to evaluate elastic properties elsewhere. It was concluded that Ca.V/TV was the most predictive of cortical bone elastic constants and that considerable periosteal–endosteal variations in these constants can develop with bone loss.

Occurrence and treatment of bone atrophic non-unions investigated by an integrative approach

Recently developed atrophic non-union models are a good representation of the clinical situation in which many non-unions develop. Based on previous experimental studies with these atrophic non-union models, it was hypothesized that in order to obtain successful fracture healing, blood vessels, growth factors, and (proliferative) precursor cells all need to be present in the callus at the same time. This study uses a combined in vivo-in silico approach to investigate these different aspects (vasculature, growth factors, cell proliferation). The mathematical model, initially developed for the study of normal fracture healing, is able to capture essential aspects of the in vivo atrophic non-union model despite a number of deviations that are mainly due to simplifications in the in silico model. The mathematical model is subsequently used to test possible treatment strategies for atrophic non-unions (i.e. cell transplant at post-osteotomy, week 3). Preliminary in vivo experiments corroborate the numerical predictions. Finally, the mathematical model is applied to explain experimental observations and identify potentially crucial steps in the treatments and can thereby be used to optimize experimental and clinical studies in this area. This study demonstrates the potential of the combined in silico-in vivo approach and its clinical implications for the early treatment of patients with problematic fractures.

In light of the ageing population, the occurrence of bone fractures is expected to rise substantially in the near future. In 5 to 10% of these cases, the healing process does not succeed in repairing the bone, leading to the formation of delayed unions or even non-unions. In this study we used a combination of an animal model mimicking a clinical non-union situation and a mathematical model developed for normal fracture healing to investigate both the causes of non-union formation and potential therapeutic strategies that can be applied to restart the healing process. After showing that the mathematical model is able to simulate key aspects of the non-union formation, we have used it to investigate several treatment strategies. One of these strategies, the treatment of a non-union involving a transplantation of cells from the bone marrow to the fracture site, was also tested in a pilot animal experiment. Both the simulations and the experiments showed the formation of a bony union between the fractured bone ends. In addition, we used the mathematical model to explain some unexpected experimental observations. This study demonstrates the added value of using a combination of mathematical modelling and experimental research as well the potential of using cell transplantation for the treatment of non-unions.

Chondrocyte death in mechanically injured articular cartilage--the influence of extracellular calcium

Calcium is thought to be an important regulator of chondrocyte death associated with articular cartilage injury. Our objective was to determine the influence of extracellular calcium on chondrocyte death following mechanical injury. Using a surgically relevant model of sharp mechanical injury (with a scalpel) and confocal laser scanning microscopy (CLSM), in situ chondrocyte death was quantified within the full thickness of articular cartilage as a function of medium calcium concentration and time (2.5 h and 7 days). Exposure of articular cartilage to calcium-free media (approximately 0 mM) significantly reduced superficial zone chondrocyte death after mechanical injury compared with exposure to calcium-rich media (2-20 mM, ANOVA at 2.5 h, p = 0.002). In calcium-rich media, although the extent of chondrocyte death increased with increasing medium calcium concentration, cell death remained localized to the superficial zone of articular cartilage over 7 days (ANOVA, p < 0.05). However, in calcium-free media, there was an increase in chondrocyte death within deeper zones of articular cartilage over 7 days. The early (within hours) chondroprotective effect in calcium-free media suggests that the use of joint irrigation solutions without added calcium may decrease chondrocyte death from mechanical injury during articular surgery. The delayed (within days) increase in chondrocyte death in calcium-free media supports the use of calcium supplementation in media used during cartilage culture for tissue engineering or transplantation.

Osmolarity influences chondrocyte death in wounded articular cartilage

BACKGROUND

Mechanical injury results in chondrocyte death in articular cartilage. The purpose of the present study was to determine whether medium osmolarity affects chondrocyte death in injured articular cartilage.

METHODS

Osteochondral explants (n = 48) that had been harvested from the metacarpophalangeal joints of three-year-old cows were exposed to media with varying osmolarity (0 to 480 mOsm) for ninety seconds to allow in situ chondrocytes to respond to the altered osmotic environment. Explants were then wounded with a scalpel through the full thickness of articular cartilage, incubated in the same media for 2.5 hours, and transferred to 340-mOsm Dulbecco's Modified Eagle Medium (control medium) with further incubation for seven days. The spatial distribution of in situ chondrocyte death, percentage cell death, and marginal cell death at the wounded cartilage edge were compared as a function of osmolarity and time (2.5 hours compared with seven days) with use of confocal laser scanning microscopy.

RESULTS

In situ chondrocyte death was mainly localized to the superficial tangential zone of injured articular cartilage for the range of medium osmolarities (0 to 480 mOsm) at 2.5 hours and seven days. Therefore, a sample of articular cartilage from the superficial region (which included the scalpel-wounded cartilage edge) was studied with use of confocal laser scanning microscopy to compare the effects of osmolarity on percentage and marginal cell death in the superficial tangential zone. Compared with the control explants exposed to 340-mOsm Dulbecco's Modified Eagle Medium, percentage cell death in the superficial tangential zone was greatest for explants exposed to 0-mOsm (distilled water) and least for explants exposed to 480-mOsm Dulbecco's Modified Eagle Medium at 2.5 hours (13.0% at 340 mOsm [control], 35.5% at 0 mOsm, and 4.3% at 480 mOsm; p <or= 0.02 for paired comparisons) and seven days (9.9% at 340 mOsm [control], 37.7% at 0 mOsm, and 3.5% at 480 mOsm; p <or= 0.01 for paired comparisons). Marginal cell death in the superficial tangential zone decreased with increasing medium osmolarity at 2.5 hours (p = 0.001) and seven days (p = 0.002). There was no significant change in percentage cell death from 2.5 hours to seven days for explants initially exposed to any of the medium osmolarities.

CONCLUSIONS

Medium osmolarity significantly affects chondrocyte death in wounded articular cartilage. The greatest chondrocyte death occurs at 0 mOsm. Conversely, increased medium osmolarity (480 mOsm) is chondroprotective. The majority of cell death occurs within 2.5 hours, with no significant increase over seven days.

Inhibition of fracture healing

This paper reviews the current literature concerning the main clinical factors which can impair the healing of fractures and makes recommendations on avoiding or minimising these in order to optimise the outcome for patients. The clinical implications are described.

Cement restrictor function below the femoral isthmus

Cement restrictors rely on achieving an interference fit with the wall of the medullary canal. Depending on the design of the cement restrictor, the intramedullary fit may be compromised as the femur starts to widen distally. Three different designs of cement restrictor were identified; universal, press-fit, and expandable. We determined which design of cement restrictor could resist the greatest pressures in a closed column of cement. Additionally, we recorded leakage of cement past the restrictor. We reamed synthetic femora to recreate the normal distal flare of the femur below the femoral isthmus. After inserting the cement restrictor, low-viscosity cement was gradually pressurized using an electronically controlled pneumatic ram. We then simultaneously recorded cement pressure above the cement restrictor and displacement of the cement restrictor. There was variation in the performance of the cement restrictors. The expandable cement restrictors resisted the greatest pressures. The resorbable expandable (REX Cement Stop) and press-fit cement restrictors reliably prevented cement leakage. The press-fit and universal restrictors failed at low pressures when deployed below the isthmus. The choice of cement restrictor may need to be modified if preoperative templating indicates the restrictor will sit below the femoral isthmus.

The association between ulnar length and forearm movement in patients with multiple osteochondromas

PURPOSE

To determine the relationship between the length of the ulna as a proportion of height (proportional ulnar length [PUL]), forearm and wrist ranges of motion, and degree of observable deformity in people with hereditary multiple exostoses.

METHODS

One hundred forty-two people with hereditary multiple exostoses were examined; 35 were under the age of 15 years and therefore were presumed to be skeletally immature. Elbow, forearm, and wrist motion were measured, and the radius and ulna were palpated for osteochondromas. Ulnar length was estimated as a proportion of height (PUL) in skeletally immature subjects. The relationships between total active motion, number of palpable osteochondromas, and proportional length were examined for one randomly selected limb from each subject.

RESULTS

A negative correlation was found between the number of palpable osteochondromas and range of forearm rotation. The degree of forearm motion in those under the age of 15 years was directly related to PUL and indirectly related to the number of palpable osteochondromas. Children whose PUL is within the normal range have a normal range of motion.

CONCLUSIONS

In a child with hereditary multiple exostoses affecting the forearm, the PUL is associated with the range of movement and deformity, and it can be a useful adjunct in deciding the appropriate management.

The use of a nerve stimulator to allow safe placement of Ilizarov wires

OBJECTIVE

Avoidance of potential iatrogenic nerve injury during insertion of Ilizarov fine wires into areas of high anatomic risk by using a modified nerve stimulation technique.

INDICATIONS

Application of the Ilizarov ring fixator to areas of high anatomic hazard, in situations where anatomic topography may be distorted by previous surgery, trauma, or congenital anomalies.

CONTRAINDICATIONS

Use of systemic muscle relaxants. Caution in patient with cardiac pacemaker.

SURGICAL TECHNIQUE

Preliminary experiments showed that a standard nerve-stimulating device can deliver a negatively charged, monophasic square pulse of current through Ilizarov wires. During the application of an Ilizarov frame to potentially hazardous anatomic regions, providing no systemic muscle relaxants are used, a voltage field sufficient to cause nerves in close proximity to the Ilizarov wire to depolarize is produced. Identification of a distal muscle twitch provoked by the stimulation may indicate a potential for iatrogenic nerve injury.

RESULTS

Results show that with the nerve stimulator set at 2.5 mA (pulsed at a frequency of 2 Hz), peripheral nerves are stimulated if they lie within 5 mm of the wires. Should a distal muscle twitch occur, wires should be repositioned so that equivalent stimulation produces no twitch. The technique was used during Ilizarov frame application in ten patients, with only a single occurrence of distal muscle twitches in a lower-leg frame. Following repositioning of the Ilizarov wire in this case, no further twitches were observed, indicating that no Ilizarov wire was inserted close to peripheral nerves. No neurologic impairment was present postoperatively.

Finite element modelling of the pelvis: inclusion of muscular and ligamentous boundary conditions

Previous finite element studies of the pelvis, including subject-specific studies have made extensive simplifications with regards to the boundary conditions used during analysis. Fixed boundary conditions are generally utilised at the pubis and superior part of the ilium. While it can be demonstrated that these models provide a close match for certain in vitro experiments that use similar boundary conditions, the resulting stress-strain fields in the cortex in particular are unlikely to be those found in vivo. This study presents a finite element analysis in which the pelvis is supported by muscular and ligamentous boundary conditions, applied using spring elements distributed over realistic attachment sites. The analysis is compared to an analysis in which the pelvis is restrained by fixed boundary conditions applied at the sacro-iliac joints. Striking differences in the stress-strain fields observed in cortical bone in particular, are found between the two analyses. The inclusion of muscular and ligamentous boundary conditions is found to lower the occurrence of stress concentrations within the cortex.

Physiologic oxygen enhances human embryonic stem cell clonal recovery and reduces chromosomal abnormalities

Human embryonic stem cells (hESC) have great potential in regenerative medicine, provided that culture systems are established that maintain genomic integrity. Here we describe a comparison of the effects of culture in either physiologic oxygen (2%) or room oxygen (21%) on the hESC lines, H1, H9, and RH1. Physiologic oxygen enabled an average sixfold increase in clone recovery across the hESC lines tested (p < 0.001). FACS analysis showed that cells cultured in physiologic oxygen were significantly smaller and less granular. No significant changes had occurred in levels of SSEA4, SSEA1, TRA-1-60, or TRA-1-81. While karyotypic normalcy was maintained in both H1 and H9, the frequency of spontaneous chromosomal aberrations was significantly increased in room oxygen. This increase was not observed in physiologic oxygen. These results clearly demonstrate that physiologic oxygen culture conditions are indispensable for robust hES clone recovery and may enhance the isolation of novel hES lines and transgenic clones.

3D non-linear analysis of the acetabular construct following impaction grafting

The study investigates the short-term behaviour of the acetabular construct following revision hip arthroplasty, carried out using the Slooff-Ling impaction grafting technique; using 3D finite element analyses. An elasto-plastic material model is used to describe the constitutive behaviour of morsellised cortico-cancellous bone (MCB) graft, since it has been shown that MCB undergoes significant plastic deformation under normal physiological loads. Based on previous experimental studies carried out by the authors and others, MCB is modelled using non-linear elasticity and Drucker Prager Cap (DPC) plasticity. Loading associated with walking, sitting down, and standing up is applied to the acetabular cup through a femoral head using smooth sliding surfaces. The analyses yield distinctive patterns of migration and rotation due to different activities. These are found to be similar to those observed in the clinical setting.

Assessment of a self-administration protocol for extended subcutaneous thromboprophylaxis in lower limb arthroplasty

The risk of venous thromboembolism in patients following arthroplasty may be reduced by continuing chemical thromboprophylaxis for up to 35 days post-operatively. This prospective cohort study investigated the compliance of 40 consecutive consenting patients undergoing lower limb arthroplasty with self-administration of a recommended subcutaneous chemotherapeutic agent for six weeks after surgery. Compliance was assessed by examination of the patient for signs of injection, number of syringes used, and a self-report diary at the end of the six-week period. A total of 40 patients, 15 men and 25 women, were recruited. One woman was excluded because immediate post-operative complications prevented her participation. Self-administration was considered feasible in 87% of patients (95% confidence interval (CI) 76 to 98) at the time of discharge. Among this group of 34 patients, 29 (85%) were compliant (95% CI 73 to 97). Patients can learn to self-administer subcutaneous injections of thromboprophylaxis, and compliance with extended prophylaxis to six weeks is good.

Response of the tendon during limb lengthening

Little is known about the increase in length of tendons in postnatal life or of their response to limb lengthening procedures. A study was carried out in ten young and nine adult rabbits in which the tibia was lengthened by 20% at two rates 0.8 mm/day and 1.6 mm/day. The tendon of the flexor digitorum longus (FDL) muscle showed a significant increase in length in response to lengthening of the tibia. The young rabbits exhibited a significantly higher increase in length in the FDL tendon compared with the adults. There was no difference in the amount of lengthening of the FDL tendon at the different rates. Of the increase in length which occurred, 77% was in the proximal half of the tendon. This investigation demonstrated that tendons have the ability to lengthen during limb distraction. This occurred to a greater extent in the young who showed a higher proliferative response, suggesting that there may be less need for formal tendon lengthening in young children.

Recovery of function after closed femoral shortening

This prospective, longitudinal study documents the muscle strength and baseline function of 18 patients undergoing closed femoral shortening for discrepancy in limb length. Patients were studied for two years following surgery. Function was measured by a self-reported questionnaire, timed tests of performance and measurements of muscle strength and power. After two years, the self-reported function and ability to complete timed functional tests had returned to or improved on the pre-operative values. Muscle strength remained slightly below the pre-operative value and was more marked in the quadriceps than the hamstrings. This study suggests that small decreases in muscle strength and power following closed femoral shortening do not adversely affect the patients' ability to perform everyday activities.

Distraction osteogenesis in the Cbfa-1+/- mouse

Distraction osteogenesis involves division of a bone and gradually pulling the bone ends apart. This delivers mechanical stimulation to mesenchymal cells in the distraction gap, where new bone is regenerated predominantly by intramembranous ossification. The transcription factor Cbfa1 has been reported to be essential for the differentiation of mesenchymal cells to osteoblasts. In homozygous Cbfa1 knockout mice, both intramembranous and endochondral ossification mechanisms are blocked and no bone formation occurs. In heterozygous Cbfa1 knockout mice, only the cranial bones and the clavicles, which form through intramembranous ossification, fail to develop properly as in the human condition of cleidocranialdysostosis. It has been suggested, therefore, that intramembranous ossification is affected by the absence of one of the paired Cbfa1 genes. We have assessed the potential for intramembranous ossification following distraction osteogenesis in heterozygous Cbfa1 knockout mice. Fourteen skeletally mature male heterozygous mice were used, together with 10 wild-type controls. The tibia was distracted by 0.25 mm twice a day (0.5 mm/day) for 10 days using the half-ring type fixator. Nine mice were kept for a further 28 days to observe the consolidation phase. In four out of five mice of the heterozygous group and in all three wild-type mice, bony fusion within the distraction gap was observed on radiographs. Histological findings were almost the same in the two groups at various stages of the procedure and intramembranous ossification was predominant in both the groups. Despite the inhibition of intramembranous ossification during the foetal development of Cbfa1+/- mice, distraction osteogenesis was as successful as in control mice.

Severity of disease and risk of malignant change in hereditary multiple exostoses. A genotype-phenotype study

We performed a prospective genotype-phenotype study using molecular screening and clinical assessment to compare the severity of disease and the risk of sarcoma in 172 individuals (78 families) with hereditary multiple exostoses. We calculated the severity of disease including stature, number of exostoses, number of surgical procedures that were necessary, deformity and functional parameters and used molecular techniques to identify the genetic mutations in affected individuals. Each arm of the genotype-phenotype study was blind to the outcome of the other. Mutations EXT1 and EXT2 were almost equally common, and were identified in 83% of individuals. Non-parametric statistical tests were used. There was a wide variation in the severity of disease. Children under ten years of age had fewer exostoses, consistent with the known age-related penetrance of this condition. The severity of the disease did not differ significantly with gender and was very variable within any given family. The sites of mutation affected the severity of disease with patients with EXT1 mutations having a significantly worse condition than those with EXT2 mutations in three of five parameters of severity (stature, deformity and functional parameters). A single sarcoma developed in an EXT2 mutation carrier, compared with seven in EXT1 mutation carriers. There was no evidence that sarcomas arose more commonly in families in whom the disease was more severe. The sarcoma risk in EXT1 carriers is similar to the risk of breast cancer in an older population subjected to breast-screening, suggesting that a role for regular screening in patients with hereditary multiple exostoses is justifiable.

Does the type of flooring affect the risk of hip fracture?

BACKGROUND

The number of hip fractures occurring worldwide in 1990 was estimated at 1.7 million and is predicted to rise to 6.3 million by 2050. The vast majority occur as a result of simple falls and the impact of the femoral trochanter with the floor. Previous studies have addressed the problem from the patient's side of the impact. Little research has been carried out on the other surface involved in the impact, the floor. STUDY LOCATION: 34 residential care homes.

METHODS

(1) The mechanical properties of the floor were measured with force transducers. (2) The number and location of falls and fractures on the various floors were recorded prospectively for 2 years. The threshold for reporting falls in different care homes was assessed using a standardised set of scenarios.

RESULTS

A total of 6,641 falls and 222 fractures were recorded. Wooden carpeted floors were associated with the lowest number of fractures per 100 falls. The risk of fracture resulting from a fall was significantly lower compared to all other floor types (odds ratio 1.78, 95% CI 1.33-2.35). The mean impact force was significantly lower on wooden carpeted floors: 11.9 kN compared to the other floor types.

DISCUSSION

The possible implications of our findings are considerable. Residents of homes are typically frail and many have a propensity to falls. In designing safer environments for older people, the type of floor should be chosen to minimise the risk of fracture. This may result in a major reduction in fractures in the elderly.

Functional recovery in patients with nonunion treated with the Ilizarov technique

There are few reports on function after limb salvage surgery using the Ilizarov technique, and none that document the pattern of recovery or predict when maximum function returns. This prospective, longitudinal study documents the baseline functional abilities of 40 consecutive patients with nonunion of a fracture in the lower limb. Patients were studied for at least two and a half years following the completion of surgery. Function was measured by timed tests of functional performance and by the Toronto Extremity Salvage Score self-reported patient questionnaire. Recovery was slowest in the early stages after removal of the frame and greatest between six months and one year. Statistically significant improvement continued up to, but not beyond two years. This observation has important implications for the length of follow-up incorporated into the rehabilitation programmes for patients, predictions of patient status in regard to compensation and for the design of future studies to evaluate functional outcome.

Vascularity in a new model of atrophic nonunion

Our aim was to develop a clinically relevant model of atrophic nonunion in the rat to test the hypothesis that the vessel density of atrophic nonunion reaches that of normal healing bone, but at a later time-point. Atrophic nonunion is usually attributed to impaired blood supply and is poorly understood. We determined the number of blood vessels at the site of an osteotomy using immunolocalisation techniques in both normally healing bones and in atrophic nonunion. At one week after operation there were significantly fewer blood vessels in the nonunion group than in the healing group. By eight weeks, the number in the atrophic nonunion group had reached the same level as that in the healing group. Our findings suggest that the number of blood vessels in atrophic nonunion reaches the same level as that in healing bone, but at a later time-point. Diminished vascularity within the first three weeks, but not at a later time-point, may prevent fractures from uniting.

Gentamicin may have an adverse effect on osteogenesis

OBJECTIVE

To investigate the toxic effect of gentamicin at the high concentrations that can be achieved by local administration in the management of bone infection.

DESIGN

Randomized, prospective study in cultured cells, with drug exposure duration of 4 days.

SETTING

Cell culture in Dulbecco's modification of Eagle's minimal essential medium with supplements at 37 degrees C in air:CO2 (v:v, 95:5).

MATERIALS

Human osteoblastlike cells derived from cancellous bone collected from four adult patients without systemic disease during total hip replacement were cultured in antibiotic-free medium for 4 weeks.

INTERVENTION

The cultured cells were exposed to media containing various concentrations of gentamicin (0-1000 microg/mL) for 4 days.

MAIN OUTCOME MEASUREMENTS

Alkaline phosphatase activity, total DNA, and 3H-thymidine incorporation.

RESULT

Alkaline phosphatase activity was significantly decreased (p < 0.05) in all of the cultures at gentamicin concentrations of 100 microg/mL and above. 3H-thymidine incorporation was also decreased (p < 0.05) in three out of four cultures at 100 microg/mL and above. Total DNA was significantly decreased (p < 0.05) at 700 microg/mL and above.

CONCLUSION

Gentamicin, at high concentrations, as achieved following topical application, inhibits cell proliferation in vitro and, therefore, may be detrimental to the repair process in vivo.

Human atrophic fracture non-unions are not avascular

A small proportion of fractures progress to non-union. Non-unions are routinely classified into two groups either hypertrophic or atrophic according to their radiological appearance. It is a common preconception that non-unions with a hypertrophic appearance on X-ray are biologically active and vascular with potential to heal given the correct stable environment. Atrophic non-unions are considered to be avascular and inert and will not heal even under the correct stable environment. Non-unions are either infected or aseptic. In the present study, we tested the hypothesis that aseptic atrophic non-unions are less vascular than aseptic hypertrophic non-unions and healing fractures. Biopsies were taken from the fracture gap of patients with healing fractures, hypertrophic non-unions and atrophic non-unions. A dual labelling technique was used with antibodies against CD31 (JC70) and Collagen IV. Blood vessels were quantified using a Chalkley point eyepiece graticule. There was no statistically significant difference in the median vessel count between the three fracture groups. These findings do not support the hypothesis that established atrophic fracture non-union are less vascular than hypertrophic non-unions or healing fractures.

Histological assessment of the presence or absence of infection in fracture non-union

BACKGROUND

Infection is a major cause of non-unions. Infection is not always evident clinically, nor on bacteriological analysis. If it is untreated, non-union treatment may fail.

AIM

To establish whether histological analysis is of value as an adjunct to microbiology in establishing the diagnosis of infection.

METHODS

Sixty patients who had both bacteriological and histological analysis of their non-unions were studied. Infection was indicated by an acute inflammatory response. In 45 of the 60 fractures, microbiological and clinical diagnoses were in agreement; in this subset the histology results were compared to the established diagnoses.

RESULTS

The histological diagnosis for the 45 fractures in the group with a definite diagnosis gave four false negatives but no false positives. This represents a sensitivity of 87.1%, (95% CI, 70-96%) and a 100% specificity (95% CI, 77-100%). The overall accuracy was 91.1%. (95% CI, 79-98%) The predictive value of a positive test was 100% and of a negative test was 77.8%. In 25% of the series a definite diagnosis could not be made with purely clinical and microbiological information; with the additional histological information it was possible to determine the infection status of the non-union.

CONCLUSION

Histology is of particular use when the microbiology is negative or equivocal.

The vascularity of atrophic non-unions

The objective of this study was to assess the vascularity of atrophic non-unions using an experimental animal model. Twenty skeletally mature female rabbits were randomly divided into control and experimental groups that were killed 1, 8, or 16 weeks after surgery. The experimental groups underwent surgery to induce an atrophic non-union whereas the control groups underwent a similar operation but which resulted in union. Using immunocytochemical techniques blood vessels were identified in histological sections obtained from the osteotomy site. The concentration of the vessels within the osteotomy gaps was measured, as was the serum concentration of an important angiogenic factor: endothelial cell-stimulating angiogenesis factor (ESAF). The results demonstrated a significant difference between the control and the experimental groups in the concentration of vessels within the gap at 1 week but there was no significant difference between those groups at 8 weeks. There were no significant differences in the ESAF concentration between the groups at any time points. We concluded that established atrophic non-unions can be well vascularised and that measurements of serum levels of ESAF could not distinguish between those osteotomies that would unite and those that would progress to non-union.

Complications of distraction osteogenesis: a changing pattern

We reviewed Mr. Simpson's first 80 consecutive limb-lengthening procedures, using either a circular or a unilateral frame, and analyzed the complication rates. The initially high complication rate (100%) decreased significantly (P < .01) with experience. Incidence of axial deviation was reduced by changing the configuration of the fixators; delayed consolidations and fractures were reduced by prophylactic bone-grafting and by minimizing the associated complication of muscle contractures; severe pin-track infection was reduced by introducing a simple protocol; and muscle contractures and joint subluxation were reduced by adjusting the bone screw insertion sites and ensuring adequate early analgesia to allow early movement.