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Volume 83-B, Issue 2 March 2001

D. Hannouche H. Petite L. Sedel
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D. I. Rowley D. W. McGurty
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Y. Yasunaga T. Hisatome Y. Ikuta S. Nakamura
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We studied nine patients who had had a transtrochanteric anterior rotational osteotomy, as developed by Sugioka, for osteonecrosis of the femoral head. At a mean of 2.5 years after the initial operation we carried out a histological study of the previously necrotic femoral head which had not shown collapse of the new primary weight-bearing site. In seven joints, there was proliferation of fibrous tissue in the dead trabeculae with vascular ingrowth. New bone covering dead trabeculae created the characteristic appearance of ‘creeping substitution’. However, these changes were limited and did not extend over the entire necrotic area. Dead bone remained in all the cases. In the other two heads we did not observe proliferation of fibrous tissue or vascular ingrowth, only dead trabeculae and dead bone marrow.


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K. Ito M.-A. Minka-II M. Leunig S. Werlen R. Ganz
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We have observed damage to the labrum as a result of repetitive acetabular impingement in non-dysplastic hips, in which the femoral neck appears to abut against the acetabular labrum and a non-spherical femoral head to press against the labrum and adjacent cartilage. In both mechanisms anatomical variations of the proximal femur may be a factor. We have measured the orientation of the femoral neck and the offset of the head at various circumferential positions, using MRI data from volunteers with no osteoarthritic changes on standard radiographs. Compared with the control subjects, paired for gender and age, patients showed a significant reduction in mean femoral anteversion and mean head-neck offset on the anterior aspect of the neck. This was consistent with the site of symptomatic impingement in flexion and internal rotation, and with lesions of the adjacent rim. Furthermore, when stratified for gender and age, and compared with the control group, the mean femoral head-neck offset was significantly reduced in the lateral-to-anterior aspect of the neck for young men, and in the anterolateral-to-anterior aspect of the neck for older women. For patients suspected of having impingement of the rim, anatomical variations in the proximal femur should be considered as a possible cause.


A. H. Taylor M. Shannon S. L. Whitehouse M. B. Lee I. D. Learmonth
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We describe the results of 76 total arthroplasties of the hip for stage-III or stage-IV avascular necrosis of the femoral head. Harris Galante Porous cups were used in 63 patients between 1986 and 1994 and followed prospectively. We reviewed 70 hips with a follow-up of more than five years (mean 7.6).

At the latest review the mean Harris Hip Score had improved from a preoperative value of 29 ± 14.7 to 94 ± 6.8. Radiologically, there was no evidence of acetabular migration. The rate of revision for the femoral component was 8.6%, three being undertaken for loosening and three to allow downsizing of the femoral head. The rate of revision for the acetabular component was 7.1% (five cups). At the time of revision none of the cups was clinically loose, and only required the liner to be changed.

The rate of complications was low with no case of deep infection or dislocation, but nine of the 76 hips (11.8%) showed grade-III heterotopic ossification. Previous studies of patients undergoing cemented total hip arthroplasty for the treatment of advanced avascular necrosis have indicated a high incidence of loosening of the acetabular component. Our findings show good medium-term results using the Harris Galante Porous cup for acetabular reconstruction, together with a variety of cemented femoral components, for the treatment of this difficult problem.


A. S. W. Bruce R. M. Kerry P. Norman I. Stockley
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We report two cases of fungal infection of prosthetic joints which were successfully treated by the incorporation of fluconazole into polymethylmethacrylate beads inserted at the time of debridement.


D. I. Rowley D. W. McGurty
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We describe a method of audit of a type of total knee replacement, including some details of the organisational difficulties of administering multicentre studies, and draw attention to how this can be done using industrial funding without prejudicing the study. This is a prospective record of 1439 patients who had an Insall-Burstein II (IBII) prosthesis implanted between 1990 and 1994. The data were collected using the American Knee Society scoring system. A method of storing radiographs digitally at low cost is also described.

The results emphasise the need for the long-term collection of data on commonly used devices implanted by a cross-section of surgeons. We conclude that for most patients the IBII cemented, posteriorly stabilised, cruciate-substituting prosthesis will relieve pain and give excellent functional results throughout the patients’ remaining years with a very small incidence of revision, except in cases of infection.


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U. C. G. Svärd A. J. Price
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We describe the outcome of a series of 124 Oxford meniscal-bearing unicompartmental arthroplasties carried out for osteoarthritis of the medial compartment. They had been undertaken more than ten years ago in a non-teaching hospital in Sweden by three surgeons. All the knees had an intact anterior cruciate ligament, a correctable varus deformity and full-thickness cartilage in the lateral compartment. Thirty-seven patients had died; the mean time since operation for the remainder was 12.5 years (10.1 to 15.6).

Using the endpoint of revision for any cause, the outcome for every knee was established. Six had been revised (4.8%). At ten years there were 94 knees still at risk and the cumulative survival rate was 95.0% (95% confidence interval 90.8 to 99.3). This figure is similar to that reported by the designers of the prosthesis and to the best published results for independent series of total knee replacement. If patients are selected appropriately, this implant is a reliable treatment for anteromedial osteoarthritis of the knee.


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C. R. C. Walker C. Myles R. Nutton P. Rowe
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We used electrogoniometers to measure the range of movement (ROM) of the knee during various activities, comparing 50 patients with osteoarthritis of the knee (OA) with 20 healthy age- and sex-matched subjects.

The minimum and maximum joint angles and the ranges of excursion of the patient and control groups were tested for significant differences, using an unrelated Student’s t-test with pooled variance. Knee flexion in patients with OA was significantly reduced during all activities (p < 0.05), but differences in knee extension were not significant except when patients negotiated stairs. We believe that this reduction in ROM is caused by inhibition due to pain when load-bearing. Static non-load-bearing measurements of the ROM poorly reflected the functional ROM, with a coefficient of determination (r2) of 0.59 in the patient group and 0.60 in the control group. Electrogoniometry of the ROM of the knee provides a reliable, accurate and objective measurement of knee function.


Trauma
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M. G. Dennison R. D. Pool R. B. Simonis B. S. Singh
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Between 1994 and 1999, we treated six patients with avascular necrosis of the talus by excision of the necrotic body of the talus and tibiocalcaneal fusion using an Ilizarov frame. This was combined with corticotomy and a lengthening procedure. Shortening was corrected in all patients except two, who were over 60 years of age.

All patients had previous operations which had failed. All achieved solid bony fusion, with five out of six having either a good or an excellent result.

We conclude that this is an effective reconstructive technique which gives a good functional result.


R. H. Thomas M. D. Holt S. H. James P. G. White
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The imaging techniques available to aid the diagnosis of ruptures of tendo Achillis, the rotator cuff and the tendon of tibialis posterior in rheumatoid patients are well described. However, ruptures of tendon or muscle at other sites are uncommon and may be overlooked. Diagnosis is often made by localised tenderness, swelling and a lack of active movement associated with a palpable defect. Clinical examination may be inconclusive and can be aided by imaging studies. We report two cases in which ruptures of a tendon were suspected, and ultrasound imaging demonstrated the palpable defect to be a cleavage plane in the subcutaneous fat – a ‘fat fracture’.


J. N. S. Davison S. J. Calder G. H. Anderson G. Ward C. Jagger W. M. Harper P. J. Gregg
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We performed a prospective, randomised trial comparing three treatments for displaced intracapsular fractures of the hip in 280 patients aged 65 to 79 years.

The mean patient survival was significantly higher in the group undergoing reduction and internal fixation (79 months) compared with that with a cemented Thompson hemiarthroplasty or a cemented Monk bipolar hemiarthroplasty (61 months and 68 months, respectively). After three years, 32 of 93 patients (34.4%) who had undergone fixation had local complications, necessitating further intervention in 28 (30%). There were no significant differences in the functional outcome in survivors, who were reviewed annually to five years.

Either reduction and internal fixation or cemented hemiarthroplasty may be offered as alternative treatments for a displaced intracapsular fracture in a mobile and mentally competent patient under the age of 80 years. The choice of procedure by the patient and the surgeon should be determined by the realisation that the use of internal fixation is associated with a 30% risk of failure requiring further surgery. If this is accepted, however, hemiarthroplasty is avoided, which, in our study has a significantly shorter mean survival time. The use of a bipolar prosthesis has no significant advantage.


Shoulder
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O. Levy S. A. Copeland
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Cementless surface replacement arthroplasty of the shoulder is designed to replace the damaged joint surfaces and restore normal anatomy with minimal resection of bone. We have used the Copeland shoulder arthroplasty for 14 years. Between 1986 and 2000, 285 surface replacement arthroplasties were implanted in our unit. The prosthesis has evolved during this time, but the principle of minimal bone resection has remained the same. Between 1990 and 1994, 103 Mark-2 prostheses were inserted into 94 patients (9 bilateral). The operations were carried out for the treatment of osteoarthritis, rheumatoid arthritis, avascular necrosis, instability arthropathy, post-traumatic arthropathy and cuff arthropathy. The mean follow-up was for 6.8 years (5 to 10).

The best results were achieved in primary osteoarthritis, with Constant scores of 93.7% for total shoulder replacement and 73.5% for hemiarthroplasty. The poorest results were seen in patients with cuff arthropathy and post-traumatic arthropathy with adjusted Constant scores of 61.3% and 62.7%, respectively. Most patients (93.9%) considered their shoulder to be much better or better than before the operation. Of the 88 humeral implants available for radiological review, 61 (69.3%) showed no evidence of radiolucency, nor did 21 (35.6%) of the 59 glenoid prostheses. Three were definitely loose, and eight shoulders required revision (7.7%), two (1.9%) for primary loosening. The results of this series are comparable with those for stemmed prostheses with a similar follow-up and case mix. The cementless surface replacement arthroplasty diminishes the risk of complications involving the humeral shaft and periprosthetic fractures. Revision or arthrodesis can be undertaken easily since the bone stock has been maintained with no loss of length.


Spine
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S. Y. Bhojraj N. Shetty P. J. Shah
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Tuberculosis of the craniocervical junction is rare even where the condition is endemic. It poses problems in both diagnosis and management. We describe 25 cases followed over a period of 12 years, and relate the presentation, diagnosis and management. Of our 25 patients 16 were managed conservatively and nine by surgery. In order to diagnose this condition a high index of suspicion and advanced imaging techniques are necessary. Early diagnosis and adequate treatment led to good results without fatal complications.


M. Ide J. Ide M. Yamaga K. Takagi
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We investigated the incidence of evidence of irritation of the brachial plexus in 119 patients with whiplash injuries sustained in road-traffic accidents. We compared the symptoms, physical signs, autonomic status, psychological status and findings from radiographs of the cervical spine using examination charts and a modified Cornell Medical Index Health questionnaire, in patients in two distinct groups: those with irritation of the brachial plexus and those without.

There were 45 patients (37.8%) in the first group. The ratio of women to men was significantly higher in patients with irritation of the plexus as was the incidence of symptoms other than neck pain. There was no significant difference between the two groups with regard to psychological status or findings in radiographs of the cervical spine. Symptoms and signs attributable to stretching of the brachial plexus do occur in a significant proportion of patients after a whiplash injury. Their presence and persistence are associated with a poor outcome.


Upper Limb
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B. Saedén H. Törnkvist S. Ponzer M. Höglund
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We compared the long-term outcome in 61 patients (62 fractures) treated operatively or conservatively for an acute fracture of the carpal scaphoid. A total of 30 fractures was randomised to conservative treatment using a cast and 32 to operative treatment using a Herbert bone screw.

The duration of sick leave was shorter for patients treated by operation, but this was only significant in patients with blue-collar occupations. There were no differences between the groups in respect of function, radiological healing of the fracture, or carpal arthritis after follow-up at 12 years. Those managed by operation showed radiological signs of arthritis of the scaphotrapezial joint more often, but this finding did not correlate with subjective symptoms.

Operative treatment of an acute fracture of the scaphoid allows early return of function and should be regarded as an alternative to conservative treatment in patients in whom immobilisation in a cast for three months is not acceptable for reasons related to sports, social life or work.


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J. J. Dias B. Bhowal C. J. Wildin J. R. Thompson
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The different attributes of the Patient Evaluation Measure (PEM) questionnaire were investigated in 80 patients with a fracture of the scaphoid. Assessments were made at 2, 8, 12, 26 and 52 weeks. Reliability was assessed by measurement of the internal consistency of the different questions in 275 completed PEM forms.

Cronbach’s alpha, which needs to lie between 0.7 and 0.9, was 0.9 for the PEM. Pain, tenderness, swelling, wrist movement and grip strength correlated with the PEM score confirming the validity of the assessment. Changes in the different variables between visits correlated significantly with changes in the PEM score; its effect size and standardised response mean were comparable to those of grip strength and movement, confirming the responsiveness of this questionnaire. Gender, dominance and the side injured did not influence the scores. Older patients had a poorer outcome as assessed by the score which appeared to be a true effect and not age bias. Our study confirmed that the PEM is a reliable, valid and responsive instrument in assessing outcomes of disorders of the hand.


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G. P. Guyton C. M. Shearman C. L. Saltzman
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The results of a cadaver dye-infusion experiment suggested that the hand has ten muscle compartments and that the volar interossei occupy a separate anatomical compartment from the adjacent dorsal interossei. This is not supported by clinical findings. With various minor modifications, we repeated the experiment, infusing Omnipaque into the second dorsal interosseus muscle of four cadaver hands. We used real-time CT imaging to monitor the spread of contrast medium and side-ported needles to measure compartmental pressures. In all four hands, the tissue barrier between dorsal and volar interossei became incompetent at pressures of less than 15 mmHg.

Our data indicate that, although cadaver infusion studies can delineate potentially significant musculoskeletal barriers, their physiological relevance must be confirmed clinically.


Lower Limb
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G. P. Guyton C. M. Shearman C. L. Saltzman
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Previous dye-infusion experiments on cadavers have suggested that the hindfoot should be divided into four muscle compartments including a newly described ‘calcaneal’ element containing quadratus plantae. Since there are no clinical data to support this proposed division, we re-examined the validity of the infusion experiment. We made infusions of dilute Omnipaque at a constant rate into flexor digitorum brevis of four cadaver feet. We monitored the spread of the infusate by real-time CT imaging and measured the pressures at the infusion site by side-ported needles.

In all feet, the barrier between flexor digitorum brevis and quadratus plantae became incompetent at pressures of less than 10 mmHg. Pressure gradients in this range cannot be expected to affect tissue perfusion significantly and independently generate compartment syndromes. These results do not confirm those of previous studies carried out by uncontrolled and unmonitored injections made by hand.

Injection studies in cadaver limbs can give dramatically different results depending upon the assumptions made when designing the experiment. The technique cannot adequately act as a model of the physiology of the compartment syndrome. As the existence of a physiologically significant compartmental boundary between flexor digitorum brevis and quadratus plantae is based solely on a cadaver infusion experiment the presence of a ‘calcaneal’ compartment has not been confirmed.


M. C. Solan M. Lemon S. P. Bendall
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Most techniques described for the correction of hallux valgus require exposure of the distal aspect of the first metatarsal. A dorsomedial incision is often recommended. Texts counsel against damaging the dorsal digital nerve, as a painful neuroma is an unwelcome surgical complication.

Our study on cadavers aimed to investigate the anatomy of the dorsomedial cutaneous nerve in the metatarsophalangeal region, with special reference to surgical incisions. A constant, previously unrecognised branch of the nerve was identified. This branch is likely to be damaged if a dorsomedial approach is used. It is recommended that a mid-medial incision be used instead, i.e. at the junction of the plantar and dorsal skin.


Children's Orthopaedics
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A. R. Bhaskar J. A. Roberts
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Unstable fractures of the forearm in children present problems in management and in the indications for operative treatment. In children, unlike adults, the fractures nearly always unite, and up to 10° of angulation is usually considered to be acceptable. If surgical intervention is required the usual practice in the UK is to plate both bones as in an adult. We studied, retrospectively, 32 unstable fractures of the forearm in children treated by compression plating. Group A (20 children) had conventional plating of both forearm bones and group B (12 children) had plating of the ulna only. The mean age was 11 years in both groups and 23 (71%) of the fractures were in the midshaft. In group B an acceptable position of the radius was regarded as less than 10° of angulation in both anteroposterior (AP) and lateral planes, and with the bone ends hitched. This was achieved by closed means in all except two cases, which were therefore included in group A.

Union was achieved in all patients, the mean time being 9.8 weeks in group A and 11.5 weeks in B. After a mean interval of at least 12 months, 14 children in group A and nine in group B had their fixation devices removed.

We analysed the results after the initial operation in all 32 children. The 23 who had the plate removed were assessed at final review. The results were graded on the ability to undertake physical activities and an objective assessment of loss of rotation of the forearm.

In group A, complications were noted in eight patients (40%) after fixation and in six (42%) in relation to removal of the radial plate. No complications occurred in group B.

The final range of movement and radiological appearance were compared in the two groups. There was a greater loss of pronation than supination in both. There was, however, no limitation of function in any patient and no difference in the degree of rotational loss between the two groups. The mean radiological angulation in both was less than 10° in both AP and lateral views, which was consistent with satisfactory function.

The final outcome for 23 patients was excellent or good in 12 of 14 (90%) in group A, despite the complications, and in eight of nine in group B (90%).

If reduction and fixation of the fracture of the ulna alone restores acceptable alignment of the radius in unstable fractures of the forearm, operation on the radius can be avoided.


N. S. El-Said
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Transfer of flexor carpi ulnaris combined with selective release of the flexor pronator origin was undertaken in 35 patients with hemiplegic cerebral palsy for a pronation flexion deformity of the forearm, hand and wrist. The patients were divided into four groups depending on the severity of the deformity, the surgical procedure recommended, potential hand function and prognosis.

The procedure reduces the power of wrist and finger flexion by release of the flexor pronator origin, and reinforces the strength of extension and supination of the wrist by transfer of flexor carpi ulnaris. After a mean follow-up of four years the appearance of the hand and forearm improved in all patients. None lost movement and all gained improved mobility of the forearm, wrist and hand. There was no overcorrection.


S. R. Burrow B. Alman J. G. Wright
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Slipped capital femoral epiphysis may be associated with hypothyroidism and other endocrinopathies. Routine screening for such abnormalities is unlikely to be cost-effective since the overall incidence of these disorders, in association with slipped capital femoral epiphysis, is low. The identification of a presenting characteristic which would predict the chance of an associated endocrinopathy would allow only selected children to be screened.

Our aim was to determine if certain characteristics were useful as a screen for patients with an underlying endocrinopathy who presented with slipped capital femoral epiphysis. Between January 1988 and December 1996 we recorded gender, age, height, unilateral or bilateral involvement and an associated diagnosis of endocrinopathy for all patients who were treated for slipped capital femoral epiphysis. Of 166 such patients 13 (7.8%) had an endocrinopathy. Height was the only useful screening characteristic, although bilateral involvement was more likely in those with an endocrinopathy. Most (90.9%) of this latter group were below the tenth percentile for height compared with only 5.4% in those who did not have an endocrinopathy (p < 0.005). The sensitivity and negative predictive value of detecting an underlying endocrinopathy in a patient presenting with a slipped capital femoral epiphysis and short stature (tenth percentile or less) were 90.2% and 98.6%, respectively.

Patients who are on or below the tenth percentile for height at the time of presentation should be screened for a possible endocrine abnormality using measurement of thyroid-stimulating hormone and free thyroxine as a preliminary screening test. These hormones are most likely to be abnormal in the presence of endocrine dysfunction.


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T. M. P. O’Donnell A. T. Devitt S. Kutty E. E. Fogarty
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A five-day-old boy was referred with a soft-tissue mass in his right upper arm. Plain radiographs and ultrasound demonstrated a lesion extending from the axilla to the elbow on the posterolateral aspect of the humerus. Open biopsy confirmed the diagnosis of congenital haemangiopericytoma. After MRI and selective angiography, excision biopsy was carried out, but no adjuvant therapy was administered. At further examination, four years and ten months later, he was noted to have three small nodules at the site of the original tumour. Excision biopsy confirmed this to be a local recurrence, although the lesion was less cellular with no appreciable mitotic activity. Congenital haemangiopericytoma is a rare cause of a soft-tissue mass in children. Most tumours are benign, and recurrence is uncommon. The treatment is controversial, but most centres recommend the use of adjuvant chemotherapy, combined with complete excision. We recommend treatment with doxorubicin. Orthopaedic surgeons should be familiar with this tumour since 30% to 50% of cases occur in the limbs.


W. Drescher T. Schneider C. Becker J. Hobolth W. Rüther E. S. Hansen C. Bünger
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Treatment with corticosteroids is a risk factor for non-traumatic avascular necrosis of the femoral head, but the pathological mechanism is poorly understood. Short-term treatment with high doses of methylprednisolone is used in severe neurotrauma and after kidney and heart transplantation. We investigated the effect of such treatment on the pattern of perfusion of the femoral head and of bone in general in the pig.

We allocated 15 immature pigs to treatment with high-dose methylprednisolone (20 mg/kg per day intramuscularly for three days, followed by 10 mg/kg intramuscularly for a further 11 days) and 15 to a control group. Perfusion of the systematically subdivided femoral head, proximal femur, acetabulum, humerus, and soft tissues was determined by the microsphere technique. Blood flow in bone was severely reduced in the steroid-treated group. The reduction of flow affected all the segments and the entire epiphysis of the femoral head. No changes in flow were found in non-osseous tissue. Short-term treatment with high-dose methylprednisolone causes reduction of osseous blood flow which may be the pathogenetic factor in the early stage of steroid-induced osteonecrosis.


J. A. Wimhurst R. A. Brooks N. Rushton
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We have investigated whether the particle-stimulated release of inflammatory cytokines from human primary macrophages in vitro was dependent upon the type of bone cement used. Particles of clinically relevant size were produced from Palacos R without radio-opacifier, Palacos R with BaSO4, Palacos R with ZrO2 and from CMW3 which contains BaSO4. All four preparations produced significantly greater release of tumour necrosis factor alpha, interleukin-6 and interleukin-1 beta than a negative control but there were no significant differences between them. The differences in the ability to stimulate bone resorption and in clinical performance between proprietary bone cements previously recorded are not explained by the release of the cytokines most commonly implicated in osteolysis.


J. M. Wilkinson N. F. A. Peel R. A. Elson I. Stockley R. Eastell
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We aimed to evaluate the precision and longitudinal sensitivity of measurement of bone mineral density (BMD) in the pelvis and to determine the effect of bone cement on the measurement of BMD in femoral regions of interest (ROI) after total hip arthroplasty (THA).

A series of 29 patients had duplicate dual-energy x-ray absorptiometry (DXA) scans of the hip within 13 months of THA. Pelvic analyses using 3- and 4-ROI models gave a coefficient of variation (CV) of 2.5% to 3.6% and of 2.5% to 4.8%, respectively. Repeat scans in 17 subjects one year later showed a significant change in BMD in three regions using the 4-ROI model, compared with change in only one region with the 3-ROI model (p < 0.05).

Manual exclusion of cement from femoral ROIs increased the net CV from 1.6% to 3.6% (p = 0.001), and decreased the measured BMD by 20% (t = 12.1, p < 0.001). Studies of two cement phantoms in vitro showed a small downward drift in bone cement BMD giving a measurement error of less than 0.03 g/cm2/year associated with inclusion of cement in femoral ROIs.

Changes in pelvic periprosthetic BMD are best detected using a 4-ROI model. Analysis of femoral ROI is more precise without exclusion of cement although an awareness of its effect on the measurement of the BMD is needed.


G-I. Im D-Y. Kim J-H. Shin C-W. Hyun W-H. Cho
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In 16 mature New Zealand white rabbits mesenchymal stem cells were aspirated from the bone marrow, cultured in monolayer and implanted on to a full-thickness osteochondral defect artificially made on the patellar groove of the same rabbit. A further 13 rabbits served as a control group. The rabbits were killed after 14 weeks. Healing of the defect was investigated histologically using haematoxylin and eosin and Safranin-O staining and with immunohistochemical staining for type-II collagen. We also used a reverse transcription-polymerase chain reaction (RT-PCR) to detect mRNA of type-I and type-II collagen.

The semiquantitative histological scores were significantly higher in the experimental group than in the control group (p < 0.05). In the experimental group immunohistochemical staining on newly formed cartilage was more intense for type-II collagen in the matrix and RT-PCR from regenerated cartilage detected mRNA for type-II collagen in mature chondrocytes. These findings suggest that repair of cartilage defects can be enhanced by the implantation of cultured mesenchymal stem cells.


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Y.-H. Kim J.-S. Kim S.-H. Cho
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Six pairs of human cadaver femora were divided equally into two groups one of which received a non-cemented reference implant and the other a very short non-dependent experimental implant. Thirteen strain-gauge rosettes were attached to the external surface of each specimen and, during application of combined axial and torsional loads to the femoral head, the strains in both groups were measured.

After the insertion of a non-cemented femoral component, the normal pattern of a progressive proximal-to-distal increase in strains was similar to that in the intact femur and the strain was maximum near the tip of the prosthesis. On the medial and lateral aspects of the proximal femur, the strains were greatly reduced after implantation of both types of implant. The pattern and magnitude of the strains, however, were closer to those in the intact femur after insertion of the experimental stem than in the reference stem. On the anterior and posterior aspects of the femur, implantation of both types of stem led to increased principal strains E1, E2 and E3. This was most pronounced for the experimental stem.

Our findings suggest that the experimental stem, which has a more anatomical proximal fit without having a distal stem and cortex contact, can provide immediate postoperative stability. Pure proximal loading by the experimental stem in the metaphysis, reduction of excessive bending stiffness of the stem by tapering and the absence of contact between the stem and the distal cortex may reduce stress shielding, bone resorption and thigh pain.


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J. D. Witt
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Authors’ reply Pages 307 - 309
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D. A. SHERLOCK R. A. DUNSMUIR
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E. SHERRY
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N. EMMS S. SCOTT
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Author’s reply Pages 308 - 309
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R. M. SMITH
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K. B. MUKHERJEE
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J. PFÖRTNER
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A. J. STARR
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Authors’ reply Pages 309 - 309
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M. G. UGLOW N. M. P. CLARKE
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Authors’ reply Pages 309 - 309
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R. M. SMITH
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Richard N. Villar
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Michael Laurence
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A. Catterall
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Paul Staker
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Michael Laurence
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Leslie Klenerman
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