Summary

Coating of titanium implants with BMP-2-loaded polyelectrolyte multilayer films conferred the implant surface with osteoinductive properties which are fully preserved upon both air-dried storage and γ-sterilization.

Although BMP-2 is recognised as an important molecule for bone regeneration, its supraphysiological doses currently used in clinical practice has raised serious concerns about cost-effectiveness and safety issues. Thus, there is a strong motivation to engineer new delivery systems or to provide already approved materials with new functionalities. Immobilizing the growth factor onto the surface of implants would reduce protein diffusion and increase residence time at the implantation site. To date, modifying the surfaces of metal materials, such as titanium or titanium alloys, at the nanometer scale for achieving dependable, consistent and long-term osseointegration remains a challenging approach.

In this context, we have developed an osteoinductive coating of a porous titanium implant using biomimetic polyelectrolyte multilayer (PEM) films used as carriers of BMP-2. The PEM films were prepared by alternate deposition of 24 layer pairs of poly(L-lysine) (PLL) and hyaluronic acid (HA) layers (∼3.5 µm in thickness); such films were then cross-linked by means of a water-soluble carbodiimide (EDC) at different degrees. The amount of BMP-2 loaded in these films was tuned (ranging from 1.4 to 14.3 µg/cm²) depending on the cross-linking extent of the film and of the BMP-2 initial concentration. Because packaging, and storage of the devices are important issues that may limit a wide application of biologically functionalised materials, we assessed in the present study the osteoinductive performance of the BMP-2 loaded PEM coatings onto custom-made 3D porous scaffolds made of Ti-6Al-4V in vitro and in vivo pertinent to long-term storage in a dry state and to sterilization by gamma irradiation.

Analysis of PEM films by infrared spectroscopy evidenced that the air-dried films were stable for at least one year of storage at 4°C and they resisted exposure to γ-irradiation at clinically approved doses. The preservation of the growth factor bioactivity was evaluated both in vitro (using C2C12 cell model) and in vivo (in a rat ectopic model). In vitro, BMP-2 loaded in dried PEM films exhibited shelf-life stability at 4°C over a one-year period. However, its bioactivity decreased from 50 to 80% after γ-irradiation at 25 and 50 kGy, respectively. Remarkably, the in vivo studies showed that the amount of new bone tissue formation induced by BMP-2 contained in PEM-coated Ti implants was not affected after air-drying of the implants and sterilization at 25 kGy indicating the full preservation of the growth factor bioactivity.

Altogether, our results provided evidence of the remarkable property of PEM film coatings that both sequester BMP-2 and preserve its full in vivo osteoinductive potential upon both storage and γ-sterilization. The protective effects of PEM films on the growth factor bioactivity may be attributed to both the high water content in (PLL/HA) films (∼90%) and to their porosity, which may provide a “protein-friendly” environment similar to the natural extracellular matrix. This novel “off-the-shelf” technology of functionalised implants opens promising applications in prosthetic and tissue engineering fields.

Purpose of the study: Secondary chondrosarcoma is rare (1% of malignant bone tumours). Most cases develop from solitary exostosis or concern an exostosis disease. Localisations predominate in the girdles. Management is difficult and no consensus has been reached. The purpose of this study was to present a series of 25 secondary chondrosarcomas in order to improve diagnostic and therapeutic management.

Material and methods: This was a retrospective analysis of 25 cases of secondary chondrosarcoma (10 on solitary exostosis and 15 on exostosis disease) treated by one surgical team from 1970 to 2008. The epidemiological features, clinical signs, radiographic findings, type of treatment and outcome at last follow-up were analysed for the two groups.

Results: Patients with secondary chondrosarcoma were 10 to 20 years young than those with primary chondrosarcoma. There were an equivalent number of men and women and the predominant sites involved flat bones in both groups. The radiographic signs of sarcomatous degeneration most widely observed included heterogeneous calcifications, irregular contours, and soft tissue invasion. Tumours were generally well differentiated. The rate of local recurrence after surgery was 15% at five years and 20% at ten years. Mortality was 2% at five years and 5% at ten years. Most of the deaths occurred after local recurrence. Metastases were identified in four patients after the initial resection. The rate of local recurrence was lower after wide surgical resection.

Discussion: The real objective with secondary chondrosarcoma is to ensure a regular effective follow-up of these patients with a known risk of recurrence (exostosis disease) in order to recognise early signs of sarcomatous degeneration. One of the most reliable signs is recent development of unusual pain on a known exostosis. Education of at-risk patients is crucial and should enable early screening and detection.

Conclusion: Secondary chondrosarcoma occurs 10 to 20 years earlier than primary sarcoma and generally involves the girdles. Outcome and management practices are similar to primary chondrosarcoma. The most important issue is to ensure good patient follow-up in order to enable early diagnosis in patients at risk.

Purpose of the study: The process of bone lengthening involves three phases: a latence period, distraction, then healing. The healing phase required stability maintained by an external fixator (EF) for 1.16 months/cm lengthening. This time exposes the patient to serious complications. The objective is to accelerate the healing phase in order to shorten the time the patient has to wear the EF. The effect of BMP on osteogenesis in distraction remains a controversial issue. This work was conducted to evaluate the benefit provided by rhBMP-2 for healing the regenerate bone after distraction.

Material and methods: Thirty-nine subadult male rabbits were selected at random. On day 0, a tibial osteotomy was performed followed by installation of a M101 EF. After the latency period of seven days, the distraction began at the rate of 0.5mm/12 h for 21 days. At day 28, at the end of distraction, a new operation was performed and three groups of 13 individuals were created at random. The first group received no material, the second a collagen type 1 sponge, and the third group a collagen type 1 sponge soaked in 100 μg/kg rhBMP-2. The animals were monitored with x-rays, absorptiometry and ultrasound for the qualitative and quantitative analysis. Histological and biomechanical analyses were performed at two months.

Results: Our complication rate was 41%. Qualitative analysis of the x-rays showed, in group 3, the development of more or less voluminous and dense, sometimes hypertrophic calluses. The progression curves of the bone mineral content showed higher values in group 3. The bone mineral content curves remained nevertheless parallel for the three groups. The calluses were thus denser in group 3 but with an early peak density. Groups 1 and 2 had equivalent radiographic and absorptiometric results. The statistical analysis of the imaging findings is ongoing. The histology and biomechanical exams are being performed.

Discussion: The preliminary results show that rhBMP-2 used early in the healing phase enables formation of more dense and hypertrophic calluses. rhBMP-2 does not acceleration the rate of callus formation but stimulates its mineralization. Use of a collagen sponge alone had no effect on healing. Analysis of the histological and mechanic properties observed in the three groups will provide a more precise description of the hypertrophic and strongly mineralized calluses.

Conclusion: Our early results show superior bone mineralization in the treated group.

Purpose of the study: We present our cases of hemangiopericytomas treated surgically in our department of orthopaedic oncology. The purpose of this work was to study this vascular tumour rarely reported in the orthopaedic surgery in order to establish epidemiological, management, and prognostic elements.

Material and methods: This was a retrospective descriptive study of patients seen since 1995 with benign (n=4) or malignant (n=16) hemangiopericytoma. The large majority were FNCLCC grade 2. Mean follow-up was ten years. Course before diagnosis was longer for benign tumours (14 years) than malignant tumours (0.9 years). Tumour localization was the lower limb (55%), the upper limb (3%) (constantly involving the scapular girdle) and isolated tumours (sternum, dorsal tumours). Two patients presented metastasis at diagnosis. A biopsy was obtained in all cases.

Results: The sample contained soft haemorrhagic tissue in all cases. The typical histology was a proliferating vascular architecture with either a fibrous or muscular component. Immunohistochemistry studies revealed positive labelling for vimentin and CD99. The diagnosis of malignancy was particularly difficult, often because of the poor knowledge of pericyte differentiation. For the benign tumour, treatment consisted in resection followed by clinical and radiographic surveillance every six months. No recurrence was observed at more than five years follow-up. For the malignant tumours, all patients were given neoadjuvant chemotherapy followed by wide resection. Adjuvant chemotherapy, determined according to the resection margins and presence of not of metastasis, was instituted for 60% of patients and associated with radiotherapy for two. The total-remission survival for malignant tumours was 60% at five years. Local recurrence was noted in 18% of patients and development of metastasis in 10%. Mortality was 20%.

Discussion: The histology diagnosis was not straightforward, particularly for confirming the benign nature of the tumour; search for specific markers is needed for routine diagnosis.

Conclusion: The results obtained in this series provide valuable information for the diagnosis of sarcoma, particularly concerning the controversial issue of the aggressiveness of malignant tumours.

Purpose of the study: Little work has been reported on the effects of BMP on bone healing after distraction and the data available in the literature are contradictory. The type of BMP as well as the optimal dose remain to be defined. We present the results and complications linked with the use of different doses of rhBMP-2 in a model of osteogenesis in distraction.

Material and methods: Fifteen subadult New Zealand rabbits were selected at random and divided into three groups. On day 0, a mediodiaphyseal tibial osteotomy was cut and an M103 fixation implanted. In group I (5 rabbits), 750μg of rhBMP-2 with a type I collagen sponge (Inductos, Medtronic) were deposited on the osteotomy site. In group II (5 rabbits), 350 μg were deposited on the collagen sponge and in group III (controls, 5 rabbits), nothing was deposited. After the 7-day latency period, distraction was conducted for 21 days (0.5 mm(12hr). At the second week of distraction, the callus was analysed on the x-rays and ultrasounds and a weekly absorptiometry was obtained. The animals were sacrificed three weeks after healing was confirmed.

Results: Quantitative radiographic assay showed significantly superior grading (Kirker-Head) in groups I and II (p< 0.05) compared with group III. The qualitative analysis showed premature healing of the regenerate preventing completion of the distraction (pin distortion) for 3/5 rabbits in group I and 1/5 in group II. Bone mineral content was superior in groups I and II in all times studied than in group III (p< 0.05). The difference was also significant between groups I and II (p=0.0087) demonstrating an expected dose effect.

Discussion: Premature healing was achieved for the majority of animals in group I, underlining the importance of the dose of BMP used to stimulate bone healing after callotasis. The undesirable effect thus obtained should be taken into account in the clinical context. A dose of 100 μg/kg (350 μg, group III) appears to suffice in this model and defines the upper dose limit. Differed application of the compound (after distraction) should be useful and should be studied.

Conclusion: The dose of rhBMP-2 used to stimulate bone healing is an essential parameter that should be defined for each experimental model. The dose effect of rhBMP-2 is demonstrated in this particular model.

Purpose of the study: We conducted an experimental study of the effects of rh-BMP-7 on healing rate in the tibia of the immature rabbit exposed to bone distraction. As seen in previous models using bone stock loss or lumbar fusion, we hypothesized that rh-BMP-7 accelerates osteogenesis of the distracted segment.

Material and methods: Twenty-eight immature male New Zealand rabbits weighing 2 to 3 kg were randomly selected from a homogeneous population. Two groups of 14 rabbits were constituted by random selection: the control group (group I) and the BMP group (group II). An Orthofix M-103 external fixator was installed on the left tibia in all rabbits before performing a mid-shaft osteotomy. 70 g rh-BMP-7 was applied to the osteotomy surfaces in group II animals. After a postoperative latency period of 7 days, bone distraction was instituted at the rate of 0.5 mm/12 hr for 21 days in all animals. Radiographic qualitative grading, ultrasonography, and bone mineral density measurements on the callus were performed each week on each animal from the second week to sacrifice. After sacrifice, the distracted callus was removed and embedded in resin for histomorpho-metric analysis without decalcification.

Results: Two animals from each group were excluded from the analysis because of a fracture on the pin line of the operated tibia. There were no wound or pin track infections. The radiographic grade noted in group I was constantly greater than in group II. Bone mineral content was significantly higher in group I animals compared with group II. The ultrasound examination of the callus revealed more rapid distraction gap filling in group I than group II. An liquid-filled cyst was noted early in 92% of the rabbits in group II, which retarded osteogenesis. This type of cyst was not observed in any of the group I animals. At the time of sacrifice, the ultrasound and bone density measurements tended toward similar values in the two groups, the results for group II catching up with those for group I. This trend was concomitant with resolution of the cysts within the callus in group II animals. The histological examination demonstrated earlier osteogenesis and remodeling in group I animals.

Discussion: Early formation of cysts would be the only factor causing late maturation of the callus in group II. The fact that the results tended toward similar values for the ultrasound and bone density studies late in the study (when the cysts were being resorbed) favors this hypothesis. Interposing rh-BMP-7 in solid form between the osteotomy surfaces may have inhibited the formation of the primary callus and caused an inflammatory reaction with cyst formation. The rh-BMP-7 may have been applied to early or may in itself had a negative effect, which might explain the absence of the expected acceleration of healing.

Conclusion: Early local application of 70 g rh-BMP-7 on osteotomy section surfaces in a rabbit model of tibial distraction did not lead to expected accelerated healing rate. The application of this compound after formation of a primary callus or in another formulation (liquid) might avoid the development of cysts within the callus and allow the active substance to play is potential role as an accelerator of bone healing.

Purpose of the study: Chondroblastoma is a rare benign cartilage tumor usually observed in secondary ossification centers of long bone in subjects aged 10 to 20 years. We report a multicentric series of 63 cases of chondro-blastoma in children and attempt to identify particular pediatric epidemiological features and identify factors of risk of recurrence.

Material and methods: Clinical data an pre and postoperative imaging were analyzed as well as the histological findings reported by one observer. Files were collected from ten pediatric orthopedic units in France (two in Lyon, three in Paris, Rennes, Strasbourg, Toulouse, Saint-Etienne, Nice). Data were stored in a single database. The series included 35 boys, and 29 girls (sex ratio 1.25=. Mean age at diagnosis was 12 years (18 months to 17 years), 13 years for boys and 11 years for girls. Tumors were located in the epiphysis of the proximal tibia (n=17), the proximal femur (n=16), proximal the humerus (n=16), the distal femur (n=4), tarsal bones (n=4), the distal tibia (n=2), the fibula (n=2), the pelvis (n=1) and the distal radius (n=1). Preoperatively, the Springfield classification was: latent (n=14), active (n=36), aggressive (n=8); five tumors could not be classified. Treatment consisted in curettage-graft (n=40), curettage alone (n=17), curettage and cement filling (n=3), en bloc resection with reconstruction (n=3). Adjuvant alcoholization was used in one case. The histological study searched for an aneurysmal component within the tumor. Four patients were lost to follow-up and 59 patients were analyzed with a mean follow-up of 53 months (range 1–162 months). Statistical tests were applied to the data set to search for factors of risk of recurrence.

Results and discussion: The inaugural syndrome was pain (n=52) or a palpable mass (n=3); the tumor was a fortuitous discovery in one case. Comparison with series including both children and adults revealed certain specific features of this pediatric series. The sex ratio was lower in our series; the distal femur localization, frequent in adults, was rare in children. AT one year, the rate of recurrence was 34% in our series (18/53). Fifteen of the 18 recurrences concerned radiologically active (n=12) or aggressive (n=3) tumors. Recurrence predominated in the tarsal bones (3/3), the proximal humerus (6/14), the proximal femur (5/13) and the proximal tibia (3/14). An aneurysmal component was found in 22% of the recurrent tumors and in 16% of those without recurrence. Statistical tests failed to distinguish any significant correlation with recurrence for age, gender, type of treatment, Springfield grade or localization.

Conclusion: The epidemiological data in this series of pediatric chondroblastoma showed features different from adults. The rate of recurrence was particularly high in this multicentric series (but not statistically significant) for localizations in the tarsal bones or a deep joint (with difficult access such as the shoulder and the hip) or with an aneurysmal component.

Purpose: Partial epiphysiodesis of the growth plate due to physeal aggression is a common problem in paediatric patients. Surgical management requires precise imaging. We recall other imaging techniques currently employed and describe a novel method for studying the characteristic features of epiphysiodesis bridges of the growth plate: 3D-magnetic resonance imaging (3D-MRI).

Material and methods: We analysed retrospectively MRI series of 27 epiphysiodesis bridges in 23 children (ten boys and thirteen girls) aged 11.3 years (range 2.5 – 15). We recorded information concerning the cause of the physeal aggression, the joint involved, the type of bony bridge (Ogden classification), the clinical deformation, and the proposed treatment. The 27 bridges were studied on coronal MRI acquired with echo-gradient and fat suppression sequences. Data were processed with a manual 3D reconstruction program in 15 minutes to precisely define the localisation, the volume, and the morphology of the bony bridge and the active physis.

Results: The epiphysiodeses were caused by trauma (65%), iatrogenic aggression (17%), ischemia-infection (purpura fulminans) (9%), juxta-physeal essential cyst (4.5%), and unknown causes (4.5%). Eighty-seven percent involved a lower limb joint, 75% of which involved the tibia. The surface of the epiphysiodesis bridge covered 20% of the physis. The bridges were peripheral (46.5%), central (46.5%), and linear (7%).

Discussion: It is difficult to determine the position and the 3D relations of an epiphysiodesis bridge in a healthy active physis with imaging techniques such as plain x-rays, scintigraphy, tomography and computed tomography. The 3D-MRI method described here provides a sure way to distinguish the active growth plate which gives a high intensity signal and the epiphyseal bridge which gives a low intensity signal. Morphological (size, form) and topographic characteristics of the bony bridge and the physis can be described with precision facilitating therapeutic decision making and guiding surgery. The lack of radiation risk is also an advantage of MRI.

Conclusion: The quality of the images obtained, the safety of MRI and the easy interpretation of 3D reconstructions makes this imaging technique an excellent method for pre-therapeutic analysis of epiphysiodesis bridges.

Purpose: Treatment of femoral epiphysiolysis with major displacement remains a controversial subject. Open repositioning of the epiphysis via a lateral approach as proposed by Dunn allows nearly anatomic restitution but with a high rate of complications. We report our experience with open repositions via an anterior approach which has been more reliable in our hands.

Material and methods: During the last decade, we operated nine hips for epiphysiolysis with major displacement, using the anterior approach to spare the medial circumflex artery. External reduction was not attempted. Preoperative and residual displacement were evaluated using the Southwick technique and according to the position of the femoral head in relation to the Klein line. Early after surgery, a bone scintigram was obtained for all hips. We followed these patients to bone maturity, with a mean follow-up of four years.

Results: The early postoperative scintigrams did not reveal any case of insufficient uptake in the femoral head. Mean correction was 43° on the lateral view, with a mean preoperative displacement of 72°. Mean residual displacement after surgery was 23°. After repositioning, position of the epiphysis in relation to the Klein line was not significantly different from the position observed on the healthy side. Postoperatively, leg length discrepancy was 1 cm. At last follow-up, there have been no signs of osteonecrosis, chondrolysis or osteoarthritic degeneration. At mean 44 months follow-up, all of the patients have unlimited activities, including sports. Only one patient complained of mild climate-related pain.

Discussion: Compared with the lateral approach with trochanterotomy as proposed by Dunn, we have found the anterior approach technically easier and more reliable in terms of protecting the epiphyseal blood supply. The correction obtained, voluntarily preserving a certain degree of under-correction, associated with resection of a portion of the neck enables repositioning without risking vessel stress. Use of a stable internal fixation which allows early mobilisation would be an explanation of the absence of postoperative chondrolysis.

Conclusion: These results appear to be sufficiently encouraging to advocate this technique previously described by PH Martin in 1948.