It is still unclear whether it is best, when revision surgery is required for replacement of an acetabular component, to treat femoral focal osteolysis with bone-grafting or instead to leave it untreated because the defect is too small and uncontained; the concern is to prevent bone graft from escaping into the hip joint. We hypothesized that progression of osteolysis can halted if the cause of particulate generation is removed and the femoral component is well osseointegrated. We prospectively followed 21 patients (24 hips) who underwent acetabular revision and curetting of proximal femoral osteolysis. These patients were followed for the minimum 3 years (mean, 4.3 years; range, 3–7.4 years).

At the time of the latest follow-up examination, all hips were judged to be stable and to have well-fixed acetabular cups and femoral stems. No hips had significant progression of the osteolytic defect through the follow-up period and none demonstrated any new osteolytic lesion.

Provided that a femoral component is bone ingrown with osseointegration sufficient to provide long-term stability, that the osteolytic defect is in the proximal aspect of the femur, and that the defect is uncontained, simple curettage is an effective alternative to additional bone-grafting.

Ultra-high molecular weight polyethylene (UHMWPE) has been used for the bearing liner or inlay components in total joint replacements such as total hip, knee, and artificial disk since 1960’s. UHMWPE components generate wear debris during articulation, which play a key role in osteolysis, subsequent aseptic loosening, and eventually revision surgery. Efforts to solve the wear problem in UHMWPE and to quantify the amount of wear have driven many studies. But in vivo radiographic penetration depth measurement is the result of both wear and viscoelastic creep. Previous study reported that over 70% of the dimensional changes in UHMWPE acetabular cups were due to creep. Creep deformation was quantified under the static and dynamic compressive pressures (2, 4, 8Mpa) that are clinically relevant for the hip joint loads in normal motions. However, according to the finite element stress analyses in UHMWPE components under the active motions in hip, knee, and artificial disk replacements, very high level of contact pressures locally ranged from under 10MPa up to over 60Mpa. In this study, we quantified the creep of UHMWPE under the several high levels of dynamic compressive pressures and compared the results from the previous results.

For creep tests, UHMWPE rectangular blocks (10mm long, 10mm wide, 8mm thick) were manufactured from molded unirradiated Chirulen^® 1020 sheet (MediTECH, Deutchland). MTS 858 hydraulic test machine was used for conducting the dynamic compressive creep tests under the four different sinusoidal (1Hz) maximum pressures of 10, 20, 40, and 60MPa and minimum pressures of 1, 2, 4, and 6MPa, respectively. All tests were conducted for a total duration of 4×103 minutes at ambient conditions. During the test the displacements of crosshead were stored and the changes in thickness of block specimen devided by the initial thickness were calculated to get the creep strain.

The mean dynamic compressive creep strain increased as the loading time increased and had a linear relationship (R2=0.96) with the logarithmic scale of time for all maximun pressures. Over 90% of total creep strain occurred within the first 103 minutes. The rates of creep strain (slopes of curve fitting in logarithmic scale of time) for each maximum pressure were listed in Table 1 with the rates of creep strain for low maximum pressures from the previous study [3]. The rates of creep strain increased linearly as the maximum pressure increased for both current study (R2=0.96) and previous study (R2=0.99). The slope of linearity for the current study with high levels of contact pressures was a little larger than that for the previous study with low levels of contact pressures. This difference in the slope of linearity between current and previous studies lies in the creep recovery during measurement of specimen thickness by micrometer in the previous study. Neglecting this difference, the results of current study can be extrapolated to anticipate the creep strain of UHMWPE under the dynamic compression for the low levels of contact pressures.

Background: A common clinical scenario encountered by an orthopaedic surgeon is a patient with a secure cementless acetabular shell and a failed polyethylene liner. One treatment option is to cement a new liner into the fixed shell. The purpose of this study was to evaluate the radiographic outcome of this technique.

Materials and Methods: From November 2001 to April 2006, 11 liner were cemented into well-fixed cementless acetabular shell of 10 patients. There were 6 males and 5 women of average age 54.3 (range 41~73) years at the time of the revision surgery. The indication for the revision procedure were aseptic loosening and wear in 9 cases, and periprosthetic fracture in 2 cases. The pre-existing screws in the shell were removed, and screw holes were filled with allogenic bone graft or cementaion. The patients were evaluated the radiographic evidence of progressive loosening and osteolysis. The average follow up period was 35.2 (range 24~76) months.

Results: There were no changes in cup and liner position or progression of osteolytic lesion around the femoral or acetabular components in the last follow-up radiographs. No compications such as a deep or superficial infection or deep vein thrombosis occurred. There were no hip dislocations.

Conclusion: A liner cemented into a secure, well-positioned cementless acetabular shell provide stability and durability at short and long term follow up. This technique also has advantages of preventing bone loss associated with removal of a well fixed component, and lower surgical morbidity and more liner options. Careful attention to the preparation of the liner, the sizing of the component, and the cementing technique are likely to reduce the failure of this construct.

Audible squeaking following ceramic-on-ceramic total hip arthroplasty (THA) is a rare but troublesome problem. We retrospectively reviewed records of 1002 patients where a ceramic-on-ceramic THA had been done during the study period. Fifteen patients complained of squeaking, at any time following their arthroplasty. Fourteen of these 15 patients were evaluated clinically and radiologically. The demographics of these patients were compared to that of all the other patients who did not have squeaking following ceramic-on-ceramic THA. The radiographic data was compared to a control group matched for age, sex, body mass index (BMI), primary diagnosis, type of implant, date of surgery and length of follow-up.

There were 12 males and 2 females of a mean age of 44.5 years (range, 25–65 years). These 14 patients were found to have significantly higher BMI of 25.98 kg/m2 (range, 21.6–32.3 kg/m2) as compared to the other patients who had ceramic-on-ceramic THA (mean, 23.61 kg/m2; range, 15.8 –30.3 kg/m2) (p=0.005). The lateral opening angle was found to be significantly lower (mean, 34°; range 29°–40°) in these patients than the matched control group (mean, 38°; range 30°–41°) (p=0.016). Mean acetabular anteversion was 22° (range 9°–37°), which was not significantly different to that of the matched controls (mean 23°; range 2°–33°) (p=.957). Limb length shortening of more than 5mm was observed in 12 of the 14 (85.7%) patients as compared to only 4 of 14 (28.6%) patients in the matched control group. Two patients had intermittent squeaking while the other 12 had continuous squeaking. Flexion and sitting cross legged were identified as the movements which most commonly (11 of 12) resulted in squeaking. Mean Harris hip score (HHS) improved from 44 (range, 19–66) to 94 (range, 88–100) and most patients (13 of 14) were satisfied with the outcome of the surgery.

Thus the incidence of squeaking was found to be low (1.5%, 15 of 1002) in our series. We identified high BMI, decreased lateral opening angle and limb length shortening as factors associated with occurrence of squeaking. Proper patient selection, implant placement, and avoidance of limb length discrepancy are likely to further reduce the incidence of this complication of ceramic-on-ceramic THA.

Background: The purpose of the present study was to report the perioperative complications that occurred among the initial 50 consecutive cases of HINTEGRA total ankle replacement.

Methods: This was a retrospective study of 50 cases composed of 30 men and 18 women of average age 57 years. Perioperative complications were used to compare the first 25 cases (Group A) with the subsequent 25 (Group B).

Results: Perioperative complications occurred in 15 cases (60%) in Group A but in only five (20%) in Group B. No major wound complications requiring a soft-tissue coverage procedure were encountered. Minor wound complications occurred in three cases in each group, and resolved with skin grafting or topical dressing changes. One deep infection occurred in Group A, which required implant removal and antibiotic impregnated spacer prior to revision TAR. Four patients sustained intraoperative malleolus fractures in Group A, but only one in Group B. Coronal malposition of the tibial component occurred in three cases in Group A and in two in Group B. Sagittally increased slope of the tibial component occurred in two cases in only Group B and sagittal malposition of the talar component occurred in two cases in only Group A. There were 7 instances of anterior translation of the talar component with respect to the tibial component; four in Group A and three in Group B.

Conclusions: The results of the present study suggest that TAR has a steep learning curve. Moreover, knowledge of the perioperative complications of TAR may reduce the incidence of potential complications.

Recently with the introduction of operations using various instrument of total ankle arthroplasty, we are showing quite satisfactory short term results on the treatment of resolved pain of ankle joint. However, there have been reports of high probability of complication from total ankle arthroplasty to other arthroplasty applied to other joints. Therefore in order to make the results of ankle arthroplasty superior, it is necessary to reduce these complications. We try to analyze complications that occur often and come up with the best results.

There were 45 cases of 42 patients of HINTEGRA^® (Newdeal SA, Lyon, France) model from November 2004 to August 2006. Follow up averaged 33.5 months, the average age of patients was 61.1 years, with 14 males and 28 females. We evaluated the complications and analyzed the causes of failures. There was a total 15 cases of complications; 5 cases of medical impingement syndrome, 3 cases of varus malposition, 2 cases of delayed healing of wound, 1 case of peroneal nerve problem, medial malleolar fracture, postoperative deep infection and gouty arthritis pain and Achilles tendinitis.

Our conclusion is that total ankle arthroplasty had more complication rate than other joint arthroplasty, so we need a more meticulous preoperative and perioperative care.

Beta–tricalciumphosphate(β-TCP)coatinglayerisknown to be resorbed much faster than hydroxyapatite(HA), however, there has been few reports explaining the exact mechanism until now. Therefore, we investigated whether the resorption mechanisms of these two compounds are same, if not, what is the difference.

Eighty titanium discs with 12mm in diameter and 2mm in thickness were coated with HA(n=40) or β-TCP(n=40) by dip and spin coating method. In each group, the specimens were divided into 2 subgroups respectively; Dissolution (D, n=20) group and Osteoclast culture (C, n=20) group. The coated discs in D group were immersed in the cell culture media for 5 days, whereas, in C group, osteoclast-like cells (5×103 cells/500μ), which were isolated form human giant cell tumor, were seeded on the specimens and cultured for 5 days. Cultured cells were defined as osteoclast by the determination of osteoclast marker (tartrate-resistant acid phosphatase, TRAP). After immersion or osteoclast culture, the dissolution characteristics of coating surface were observed using light microscope (LM) and scanning electron microscope (SEM). And the area fraction of resorption lacunae formed by osteoclast was analyzed by image analysis to evaluate the activity of osteoclastic degradation.

After 5 days of dissolution, there were much more cracks and denuded areas in β-TCP coating compared to HA coating. In C group, the osteoclasts covering the coating layer were identified on LM and SEM images. Mean area fraction of resorption lacunae in HA-C group was 11.62%, which was significantly higher than that of 0.73% of β-TCP-C group (p=0.001).

We conclude that the resorption mechanism of HA and β-TCP coating layers was different each other in vitro study. The coated β-TCP was degraded mainly by dissolution and also tended to be separated from implant, on the other hand, the HA coating layer was resorbed by osteoclastic activity

Observation of sub-clinical neurological abnormalities has led to the proposal of a neuro-developmental etiologic model for AIS. Our research group have demonstrated longer latency in somatosensory–evoked potential (SSEP) and impaired balance control in AIS subjects. A previous pilot study compared the regional brain volume between right thoracic AIS subjects and normal controls. Significant regional brain differences were found relating to corpus callosum, premotor cortex, proprioceptive and visual centers. Most of these regions involved the brain unilaterally, indicating there might be abnormal asymmetrical development in the brain in right thoracic AIS. In this pilot study, we investigated whether similar changes are present in left thoracic AIS patients who differ from matched control subjects. Nine AIS female patients with atypical left thoracic AIS (mean age 14.8, mean Cobb angle 19°) and 11 matched controls as well as 20 right thoracic AIS (mean Cobb angle 33.8°) and 17 matched controls, underwent three-dimensional isotropic magnetization prepared rapid acquisition gradient echo (3D_MPRAGE) magnetic resonance (MR) imaging of the brain. Fully automatic morphometric analysis was used to analyse the MR images; it included brain-tissue classification into grey matter (GM), white matter (WM) and cerebrospinal fluid (CSF). and non-linear registration to a template brain. Tissue densities were compared between AIS subjects and controls. There was no significant difference between AIS subjects and normal controls when comparing absolute and relative (i.e. brain-size adjusted) volumes of grey and white matter. Using voxel-based morphometry, significant group differences (controls > left AIS) were found in the density of WM in the genu of the corpus callosum, the left internal capsule (anterior arm) and WM underlying the orbitofrontal cortex of the left hemisphere. The above differences were not observed in the right AIS group. This first controlled study of regional tissue density showed that corpus callosum, which is the major commissural fiber tract, was different in the atypical left thoracic scoliosis while significant regional brain changes have not yet been found in those with typical right thoracic scoliosis. Further investigation is warranted to see whether the above discrepancy is related to laterality of the scoliotic curves and infratentorial neuroanatomical abnormalities. A larger sample and a longitudinal study is required to establish whether the brain abnormalities are predictive of curve progression.

Introduction: Observation of sub-clinical neurological abnormalities has led to the proposal of a neuro-developmental etiologic model for adolescent idiopathic scoliosis (AIS). We have previously demonstrated prolonged latency in somatosensory evoked potentials (SSEP) and impaired balance control in subjects with AIS. Furthermore we have compared regional brain volumes in right thoracic AIS subjects and normal controls. Significant neuro-anatomic regional differences were observed in the corpus callosum, premotor cortex, proprioceptive and visual centers of the AIS subjects compared to control subjects. Most of these regional differences involved the brain unilaterally, indicating there may be abnormal asymmetrical development in the brain of subjects with right thoracic AIS.

Methods: Following ethical committee approval a total of 29 subjects with AIS were recruited. Patients with congenital, neuromuscular or syndromic scoliosis were excluded from the study. Twenty-eight age- and sex-matched controls were recruited from local schools. All recruits underwent three-dimensional isotropic magnetization prepared rapid acquisition gradient echo (3D_MPRAGE) magnetic resonance (MR) imaging of the brain. Modern morphometric analyses of the MR images were carried out including classification of tissue into grey matter (GM), white matter (WM) and cerebrospinal fluid (CSF). Tissue densities were compared between AIS subjects and controls. Comparisons were made between those subjects with left thoracic AIS (n=9) and age and sex-matched controls (n=11) and those subjects with right thoracic AIS (n=20) and age and sex-matched controls (n=17).

Results: For subjects with left thoracic curves the mean Cobb angle was 19 degrees. For subjects with right thoracic curves the mean Cobb angle was 33.8 degrees There was no significant differences observed between AIS subjects and normal controls when comparing both absolute and relative (i.e. adjusted for brain size) volumes of GM and WM. However voxel-based morphometric analysis identified significant differences in the density of WM in the genu of the corpus callosum, the left internal capsule and WM underlying the left orbitofrontal cortex when comparing those subjects with left thoracic scoliosis to controls. The above differences were not not observed when those subjects with right thoracic scoliosis were compared to controls..

Discussion: This controlled study of regional brain tissue density has demonstrated important differences in the corpus callosum, the left internal capsule and the left orbitofrontal cortex when the brain of those subjects with left thoracic scoliosis is compared to age and sex matched controls. In this study significant regional brain differences have not been identified in those subjects with right thoracic scoliosis. Further studies are warranted to ascertain whether these morphologial differences in the brain are linked with the etiopathogenisis of left sided thoracic scoliosis. A larger sample and a longitudinal study are required to establish whether brain abnormalities are predictive of curve progression.

We describe the surgical technique and results of arthroscopic subtalar release in 17 patients (17 feet) with painful subtalar stiffness following an intra-articular calcaneal fracture of Sanders’ type II or III. The mean duration from injury to arthroscopic release was 11.3 months (6.4 to 36) and the mean follow-up after release was 16.8 months (12 to 25). The patient was positioned laterally and three arthroscopic portals were placed anterolaterally, centrally and posterolaterally. The sinus tarsi and lateral gutter were debrided of fibrous tissue and the posterior talocalcaneal facet was released. In all, six patients were very satisfied, eight were satisfied and three were dissatisfied with their results. The mean American Orthopaedic Foot and Ankle Society ankle-hindfoot score improved from a mean of 49.4 points (35 to 66) pre-operatively to a mean of 79.6 points (51 to 95). All patients reported improvement in movement of the subtalar joint. No complications occurred following operation, but two patients subsequently required subtalar arthrodesis for continuing pain.

In the majority of patients a functional improvement in hindfoot function was obtained following arthroscopic release of the subtalar joint for stiffness and pain secondary to Sanders type II and III fractures of the calcaneum.

Introduction: The purpose of this study was to evaluate the effectiveness of free vascularized fibular grafting (VFG) for the treatment of osteonecrosis of the femoral head.

Materials and Methods: We reviewed the results in a consecutive series of 115 hips (88 patients) who had undergone free VFG between July 1991 and February 1999. Among them, 46 hips (32 patients, 28 males and 4 females) were available with periodic follow-up of at least 5 years. The mean follow up period was 7.1 years (range, 5 to 13 years). An average age of patients was 37.6 years at the time of VFG. We performed survival analysis by the Kaplan-Meier method according to the stage, etiology, age of patients, size of involvement, and degree of collapse of the femoral head. We used the Harris hip score for clinical evaluation, and used plain radiographs and MRIs for radiological evaluation.

Results: The survival rates were 85% in Ficat stage 2a, 34.7% in stage 2b, and 76.2% in stage 3. Eleven hips were evaluated as failures of VFG of which 7 hips were converted to a prosthetic joint. Harris Hip Scores were 67.8 points preoperatively, and increased to 80.4 points postoperatively. Good or excellent results were found in 69.5% of hips clinically and 56.5% of the hips radiologically. Age and size of necrosis affected the postoperative Harris Hip Score significantly, but other factors did not.

Discussion: Free VFG for the early osteonecrosis of femoral head revealed satisfactory results with good survival of the joint and improvements in Harris Hip Scores.

The purpose of this study was to determine the annual incidence of Perthes’ disease in Korea and compare this with other populations. A survey identified all newly diagnosed children with Perthes’ disease aged 14 years or younger in South Honam, Korea, between January 1999 and December 2001. A total of 84 children were included: 29 in 1999, 28 in 2000 and 27 in 2001. The mean annual incidence was 3.8 per 100 000. This is similar to that reported in other Asian countries, but higher than in black populations and lower than in Caucasians.

Free, vascularised fibular grafting is well described in limb salvage surgery. The mechanical properties of the fibula make it ideal for replacement of bony defects after tumour resection and it can be sacrificed with minimal morbidity. We review the outcome of a consecutive series of 24 patients.

Between 1993 and 2002 we performed free vascularised fibular grafts in 24 patients as part of a limb salvage procedure following tumour excision. Pre-operatively patients were staged using the Musculoskeletal Tumour Society (MSTS) system. Post-operatively patients were followed up with radiographs and clinical examination. From the radiographs graft hypertrophy and time to bony union was documented. Functional outcome was assessed using the MSTS scoring system. Complications were recorded.

There were 15 women and 9 men with a mean age of 26 years (6–52). Mean follow up was 51 months (12–106). There were 19 malignant tumours, all stage 2b, and 5 giant cell tumours. The mean length of graft was 12.5 cm. (4.5–25). 16 grafts were used in the upper limb and 8 in the lower limb. Arthrodesis was performed in 8 cases and intercalary reconstruction in 16 cases. Fixation of grafts was achieved with a plate and screws in 21, a blade plate in 2 and an IM nail in 1. In 6 cases the resected tumour bone was reinserted as autograft after extracorporeal irradiation. In all but one patient the tumour margins were clear. Primary bony union was achieved in 22 patients (92%) at a mean of 35 weeks (12–78). Graft hypertrophy was seen in 7/29 cases (24%). Complications included 2 wound breakdowns, 3 stress fractures, 1 muscle contracture, 1 malunion and 1 painful plate. Overall 8 patients (33%) required second operation. 2 patients died of recurrent disease and one has metastases. The mean MSTS functional score was 87% (80–93).

Free vascularised fibula grafts offer a reliable method of reconstruction after excision of bone tumours. The complication rate appears high and some patients require a revision procedure. However, the problems are relatively easy to correct, bony union is achieved in the majority and functional outcome is good.

Introduction: It is very important to evaluate the healing process in the femoral head after free vascularized fibular graft (VFG) in osteonecrosis of the femoral head (ONFH). Bone scintigraphy combined with a pinhole collimator, which is simple and not expensive, is used for very high resolution images of small organs, such as thyroid and certain skeletal regions. The purpose of this study was to assess the changes using pinhole bone scintigraphy in ONFH after VFG.

Materials and Methods: Changes of Tc-99m-HDP pinhole bone scintigraphy were analyzed in 22 cases of ONFH which were treated with VFG and had satisfactory results in patient evaluations at least 2 years after surgery. Harris Hip Scores were 90 points or more; and femoral head collapse was less than 2 mm.

Results: The results were: (1) At 1 week, the pinhole image showed no significant change in cold area but two linear RI uptakes corresponding to the fibular graft were noted. (2) At 3 months, localized hot uptakes just above the tip of the graft were observed in 17 cases (77.2%), and diffuse increased uptake surrounding the cold area were observed. (3) At 6 months, localized hot uptake were increased in size and replaced cold areas and delineated the shape of the superolateral aspect of the femoral head. (4) At 1 year, increased RI uptake of the superolateral aspect of the femoral head expanded medially in all cases. (5) After 2 years, cold areas faded away in 18 cases (81.8%).

Discussion: In conclusion, the authors believe that the Tc-99m-HDP pinhole bone scintigraphy is an excellent method to delineate the healing process in ONFH after VFG.

Introduction: Osteonecrosis of the femoral head remains a challenging problem especially in young patients. The purpose of this study was to evaluate the clinical results of a viable iliac bone graft for treating osteonecrosis of the femoral head.

Materials and Methods: Seventy-one hips in 52 patients underwent a viable iliac bone graft (9 hips-vessel pedicle iliac bone graft and 62 hips-muscle pedicle iliac bone graft). The clinical and radiographic results were evaluated after an average of 3 years and 4 months (range, 2 to 5 years). Patient age ranged from 20 to 40 years with an average of 31 years. Twenty-three hips were classified as Ficat stage 2 disease and 48 as stage 3 disease. The causes of osteonecrosis were excessive alcohol consumption in 30, steroid use in 13, posttraumatic in 4, decompression sickness in 1, and unknown in 23 hips. The clinical results were evaluated based on the patients’ satisfaction and pain score. The radiographical results were evaluated by serial follow-up roentgenography and pinhole bone scintigraphy.

Results: The clinical and radiological results were satisfactory. Overall, the survival rate was 96 percent. Excellent results were obtained in 15 hips, good in 39, fair in 6 and poor in 8. Three hips underwent total hip replacement, including one infected case. Excellent or good results were obtained in 82 percent of stage 2 cases and in 65 percent of stage 3 cases. The serial roentgenographic examination revealed a gradual incorporation of the grafted bone, and the scintigraphic examination revealed a gradual increase in the uptake which suggested an increased blood supply to the femoral head.

Discussion: The overall results of viable iliac crest bone grafting were very satisfactory. This technique is recommended particularly for young patients with stage 2 or 3 osteonecrosis of the femoral head. Pinhole bone scintigraphy was quite useful for evaluating the healing process after the revascularization procedure.

In 1980, Morrison and O’Brien reported their experiences with the reconstruction of an amputated thumb using a wrap-around neurovascular free flap from the great toe, but its indication has been limited distal to the metacarpophalangeal joint.

We have performed 37 wrap-around free flaps from the great toe for the reconstruction of thumbs amputated at distal or proximal to the MP joint. The amputation was distal and proximal to the MP joint in 25 and 12 cases respectively.

The opposition of reconstructed thumb to the other fingers was completely possible in all cases amputated distal to the MP joint. In the 12 cases amputated proximal to the MP joint of the thumb, opposition was completely possible in 6 cases in which the lilac bone block was fixated in the position of 30° flexion and 45° internal rotation. However, in the other six cases in the fixation of 30° flexion and 30° internal rotation, the opposition of the reconstructed thumb to the ring and little fingers was impossible in five cases and only to the little finger in one case.

We concluded that amputation proximal to the MP joint is not an absolute contraindication to the wraparound free flap procedure for thumb reconstruction. However, for a better functional outcome we recommend iliac bone block fixation in the position of 30° flexion and 45° internal rotation.

Fifty-four cobalt-chrome alloy femoral heads were retrieved at revision surgery or at post-mortem; 23 came from uncemented, eight from hybrid and 23 from cemented hip arthroplasties. The uncemented and hybrid implants had porous coating, metal backing and modular femoral heads; with one exception none of the cemented implants had any of these. Twenty-five of the 31 heads from uncemented and hybrid arthroplasties, and 11 of the 23 heads from cemented arthroplasties showed surface damage involving more than 25% of the surface. Scanning electron microscopy revealed multidirectional fine scratches 1 micron to 10 microns in depth and width which appeared to have been made by fine, hard particles. There was a higher rate of such damage in the uncemented and hybrid arthroplasties than in the cemented implants, suggesting that the abrasive particles were mainly released from the metal, rather than from the cement or polyethylene components of the implants.

The total plasma alkaline phosphatase level has long been recognised as an indicator of osteoblastic activity, but lack of specificity makes it an insensitive index of the progress of disease and the response to treatment. Selective precipitation by wheatgerm lectin allows measurement of the plasma bone-specific alkaline phosphatase. We measured the plasma levels of this isoenzyme in 170 normal Chinese adolescents and adults, in 49 adults with fractures of a long bone, in 15 patients with osteosarcoma and in 38 patients with osteolytic metastases. The enzyme activity was also determined in 39 patients with liver disease. Of the patients with fractures, 94% had increased plasma activity during the healing process. The level was also increased in those with osteosarcoma but not in those with osteolytic bone metastases. There was no significant increase in activity in the patients with liver disease. We conclude that the plasma bone-specific alkaline phosphatase activity is a sensitive and reliable measure of osteoblastic activity.