The haematoma and its role in bone healing

Fracture treatment is an old endeavour intended to promote bone healing and to also enable early loading and regain of function in the injured limb. However, in today's clinical routine the healing potential of the initial fracture haematoma is still not fully recognized. The Arbeitsgemeinschaft für Osteosynthesefragen (AO) formed in Switzerland in 1956 formulated four AO principles of fracture treatment which are still valid today. Fracture treatment strategies have continued to evolve further, as for example the relatively new concept of minimally invasive plate osteosynthesis (MIPO). This MIPO treatment strategy harbours the benefit of an undisturbed original fracture haematoma that supports the healing process. The extent of the supportive effect of this haematoma for the bone healing process has not been considered in clinical practice so far. The rising importance of osteoimmunological aspects in bone healing supports the essential role of the initial haematoma as a source for inflammatory cells that release the cytokine pattern that directs cell recruitment towards the injured tissue. In reviewing the potential benefits of the fracture haematoma, the early development of angiogenic and osteogenic potentials within the haematoma are striking. Removing the haematoma during surgery could negatively influence the fracture healing process. In an ovine open tibial fracture model the haematoma was removed 4 or 7 days after injury and the bone that formed during the first two weeks of healing was significantly reduced in comparison with an undisturbed control. These findings indicate that whenever possible the original haematoma formed upon injury should be conserved during clinical fracture treatment to benefit from the inherent healing potential.

BMP delivery complements the guiding effect of scaffold architecture without altering bone microstructure in critical-sized long bone defects: A multiscale analysis

Scaffold architecture guides bone formation. However, in critical-sized long bone defects additional BMP-mediated osteogenic stimulation is needed to form clinically relevant volumes of new bone. The hierarchical structure of bone determines its mechanical properties. Yet, the micro- and nanostructure of BMP-mediated fast-forming bone has not been compared with slower regenerating bone without BMP. We investigated the combined effects of scaffold architecture (physical cue) and BMP stimulation (biological cue) on bone regeneration. It was hypothesized that a structured scaffold directs tissue organization through structural guidance and load transfer, while BMP stimulation accelerates bone formation without altering the microstructure at different length scales. BMP-loaded medical grade polycaprolactone-tricalcium phosphate scaffolds were implanted in 30mm tibial defects in sheep. BMP-mediated bone formation after 3 and 12 months was compared with slower bone formation with a scaffold alone after 12 months. A multiscale analysis based on microcomputed tomography, histology, polarized light microscopy, backscattered electron microscopy, small angle X-ray scattering and nanoindentation was used to characterize bone volume, collagen fiber orientation, mineral particle thickness and orientation, and local mechanical properties. Despite different observed kinetics in bone formation, similar structural properties on a microscopic and sub-micron level seem to emerge in both BMP-treated and scaffold only groups. The guiding effect of the scaffold architecture is illustrated through structural differences in bone across different regions. In the vicinity of the scaffold increased tissue organization is observed at 3 months. Loading along the long bone axis transferred through the scaffold defines bone micro- and nanostructure after 12 months.

Electrochemical degradation of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in groundwater

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) represent hazardous pollutants and are frequently detected in the environment, e.g. in contaminated groundwater. PFASs are persistent to biodegradation and conventional oxidation processes such as ozonation. In this study electrochemical degradation of PFASs on boron-doped diamond (BDD) electrodes is demonstrated. Experiments were performed with model solutions and contaminated groundwater with a dissolved organic carbon (DOC) content of 13 mg/L. The perfluorinated carboxylic acids (PFCAs) perfluorobutanoate, perfluoropentanoate, perfluorohexanoate, perfluoroheptanoate and perfluorooctanoate, and the perfluorinated sulfonic acids (PFSAs) perfluorobutane sulfonate, perfluorohexane sulfonate, perfluorooctane sulfonate and 6:2 fluorotelomer sulfonate were detected in the groundwater samples. At PFAS concentrations ranging from 0.26 to 34 mg/L (0.7 to 79 μM), the degradation of PFASs was achieved despite of the high DOC background. Pseudo first-order kinetic constants of PFSA degradation increased with the increase of carbon chain length. Fluoride formation as well as the generation of PFCAs with shortened chain lengths was observed. Inorganic byproducts such as perchlorate were also formed and have to be considered in further process optimization.

Deterioration of fracture healing in the mouse model of NF1 long bone dysplasia

Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disease resulting from inactivating mutations in the gene encoding the protein neurofibromin. NF1 manifests as a heritable susceptibility to tumours of neural tissue mainly located in the skin (neurofibromas) and pigmented skin lesions. Besides these more common clinical manifestations, many NF1 patients (50%) have abnormalities of the skeleton. Long bones are often affected (usually the tibia) and the clinical signs range from bowing to spontaneous fractures and non-unions. Here we present the analysis of bone fracture healing in the Nf1(Prx1)-knock-out mouse, a model of NF1 long bone dysplasia. In line with previously reported cortical bone injury results, fracture healing was impaired in Nf1(Prx1) mice. We showed that the defective fracture healing in Nf1(Prx1) mice is characterized by diminished cartilaginous callus formation and a thickening of the periosteal bone. These changes are paralleled by fibrous tissue accumulation within the fracture site. We identify a population of fibrous tissue cells within the Nf1 deficient fracture as alpha-smooth muscle actin positive myofibroblasts. Additionally, histological and in-situ hybridization analysis reveal a direct contact of the fracture site with muscle fascia, suggesting a possible involvement of muscle derived cells in the fracture deterioration.

An experimental setup to evaluate innovative therapy options for the enhancement of bone healing using BMP as a benchmark--a pilot study

Critical or delayed bone healing in rat osteotomy (OT) models is mostly achieved through large defects or instability. We aimed to design a rat OT model for impaired bone healing based on age, gender and parity. The outcome should be controllable through variations of the haematoma in the OT including a bone morphogenetic protein (BMP) 2 guided positive control. Using external fixation to stabilise femoral a 2 mm double OT in 12 month old, female Sprague Dawley rats after a minimum of 3 litters healing was characterised following in situ haematoma formation (ISH-group)), transplantation of a BMP charged autologous blood clot (BMP-group) and the artificial blood clot only (ABC-group) into the OT-gap. In vivo micro-computer tomography (µCT) scans were performed after 2, 4 and 6 weeks. After 6 weeks specimens underwent histological analyses. In µCT examinations and histological analyses no bony bridging was observed in all but one animal in the ISH-group. In the BMP group complete bridging was achieved in all animals. The ABC-group showed less mineralised tissue formation and smaller bridging scores during the course of healing than the ISH-group. In this pilot study we introduce a model for impaired bone healing taking the major biological risk factors into account. We could show that the in situ fracture haematoma is essential for bone regeneration. Using BMP as a positive control the presented experimental setup can serve to evaluate innovative therapeutical concepts in long bone application.

Time kinetics of bone defect healing in response to BMP-2 and GDF-5 characterised by in vivo biomechanics

This study reports that treatment of osseous defects with different growth factors initiates distinct rates of repair. We developed a new method for monitoring the progression of repair, based upon measuring the in vivo mechanical properties of healing bone. Two different members of the bone morphogenetic protein (BMP) family were chosen to initiate defect healing: BMP-2 to induce osteogenesis, and growth-and-differentiation factor (GDF)-5 to induce chondrogenesis. To evaluate bone healing, BMPs were implanted into stabilised 5 mm bone defects in rat femurs and compared to controls. During the first two weeks, in vivo biomechanical measurements showed similar values regardless of the treatment used. However, 2 weeks after surgery, the rhBMP-2 group had a substantial increase in stiffness, which was supported by the imaging modalities. Although the rhGDF-5 group showed comparable mechanical properties at 6 weeks as the rhBMP-2 group, the temporal development of regenerating tissues appeared different with rhGDF-5, resulting in a smaller callus and delayed tissue mineralisation. Moreover, histology showed the presence of cartilage in the rhGDF-5 group whereas the rhBMP-2 group had no cartilaginous tissue. Therefore, this study shows that rhBMP-2 and rhGDF-5 treated defects, under the same conditions, use distinct rates of bone healing as shown by the tissue mechanical properties. Furthermore, results showed that in vivo biomechanical method is capable of detecting differences in healing rate by means of change in callus stiffness due to tissue mineralisation.

Osteochondral defect repair after implantation of biodegradable scaffolds: indirect magnetic resonance arthrography and histopathologic correlation

BACKGROUND

Biodegradable scaffolds have become an important option in the treatment of osteochondral defects. Therefore, accurate and reproducible monitoring of scaffold repair tissue is crucial.

PURPOSE

To assess the feasibility of indirect magnetic resonance (MR) arthrography in determining the quality of osteochondral repair after scaffold implantation using an MR imaging (MRI) scoring and grading system with histology as reference.

MATERIAL AND METHODS

Osteochondral defects created at ovine condylar facets were treated with either a commercial poly (DL-lactide-co-glycolide) (PLG) scaffold or a modified softer one (n=6/group; 87% and 55% of the elastic modulus of ovine subchondral bone, respectively). Empty defects at the contralateral condyle served as control group. A 1.5T MRI scan was performed after 6 months with proton density (PD)-weighted (w) fat-saturated (fs) fast spin-echo (FSE), T1-w two-dimensional (2D), and 3D fs gradient echo (GE) sequences 30 min after intravenous Gd-DTPA administration and passive joint movement. Two independent radiologists evaluated the repair tissue. The MR findings were correlated with histological findings.

RESULTS

MRI and histological grading correlated well (10/12 cases). The stiff-scaffold group showed significantly superior repair in comparison to the control group (P<0.05). The 3D fs GE sequence proved to be most valuable in evaluating morphologic status. Complete defect filling and integration, intact surface and isointense signal to the adjacent native cartilage, subchondral incorporation with bone marrow edema, and graft plug enhancement were associated with a good histological outcome. Histologically, we found a smooth fibrocartilaginous layer and osseous replacement of the scaffold. Incomplete cartilage repair and irregular subchondral structures on the MRI correlated histologically with fibrocartilage-like repair and subchondral sclerosis, due to substantial degradation of the scaffold.

CONCLUSION

Indirect MR arthrography is an accurate, noninvasive monitoring tool in the follow-up of scaffold implants. The MRI scoring and grading system allows reliable assessment of normal and pathological repair, with high correlation to histological findings.

Spatial and temporal variations of mechanical properties and mineral content of the external callus during bone healing

After bone fracture, various cellular activities lead to the formation of different tissue types, which form the basis for the process of secondary bone healing. Although these tissues have been quantified by histology, their material properties are not well understood. Thus, the aim of this study is to correlate the spatial and temporal variations in the mineral content and the nanoindentation modulus of the callus formed via intramembranous ossification over the course of bone healing. Midshaft tibial samples from a sheep osteotomy model at time points of 2, 3, 6 and 9 weeks were employed. PMMA embedded blocks were used for quantitative back scattered electron imaging and nanoindentation of the newly formed periosteal callus near the cortex. The resulting indentation modulus maps show the heterogeneity in the modulus in the selected regions of the callus. The indentation modulus of the embedded callus is about 6 GPa at the early stage. At later stages of mineralization, the average indentation modulus reaches 14 GPa. There is a slight decrease in average indentation modulus in regions distant to the cortex, probably due to remodelling of the peripheral callus. The spatial and temporal distribution of mineral content in the callus tissue also illustrates the ongoing remodelling process observed from histological analysis. Most interestingly the average indentation modulus, even at 9 weeks, remains as low as 13 GPa, which is roughly 60% of that for cortical sheep bone. The decreased indentation modulus in the callus compared to cortex is due to the lower average mineral content and may be perhaps also due to the properties of the organic matrix which might be different from normal bone.

Nuclear and neuritic distribution of serine-129 phosphorylated alpha-synuclein in transgenic mice

Parkinson's disease and dementia with Lewy bodies are very frequent neurological disorders of the elderly. Mutations in the alpha-synuclein (alphaSYN) gene cause Parkinson's disease, often associated with dementia. Neuropathologically these diseases are characterized by the presence of Lewy bodies and Lewy neurites, intraneuronal inclusions mostly composed of alphaSYN protein fibrils. Moreover, alphaSYN is phosphorylated at S129 (phospho-serine-129 [PSer129]) in neuropathological lesions. Using our (Thy1)-[A30P]alphaSYN transgenic mouse model that develops age-dependent impairment in fear conditioning behavior, we investigated PSer129 immunostaining in the brain. We found distinct staining patterns using new, sensitive monoclonal antibodies. Somal and nuclear PSer129 immunoreactivity increased with age in hippocampal and cortical areas as well as the lateral/basolateral amygdalar nuclei and was present also in young, pre-symptomatic mice, but not wild-type controls. The tendency of PSer129 immunostaining to accumulate in the nucleus was confirmed in cell culture. (Thy1)-[A30P]alphaSYN transgenic mice further developed age-dependent, specific neuritic/terminal alphaSYN pathology in the medial parts of the central amygdalar nucleus and one of its projection areas, the lateral hypothalamus. Interestingly, this type of PSer129 neuropathology was thioflavine S negative, unlike the Lewy-like neuropathology present in the brain stem of (Thy1)-[A30P]alphaSYN mice. Thus, alphaSYN becomes phosphorylated in distinct parts of the brain in this alpha-synucleinopathy mouse model, showing age-dependent increases of nuclear PSer129 in cortical brain areas and the formation of neuritic/terminal PSer129 neuropathology with variable amyloid quality within the fear conditioning circuitry and the brain stem.

[Marked improvement in scleromyxedema with high-dose intravenous immunoglobulin]

Scleromyxedema is a rare chronic skin disorder of unknown etiology, often accompanied by monoclonal gammopathies. Clinically the disease is characterized by generalized thickening and stiffening of the skin due to dermal mucin deposition. We report on a 56-year-old women with scleromyxedema, whose skin findings markedly improved following high-dose intravenous immunoglobulin therapy (Sandoglobulin((R)), 2 g/KG). The pronounced clinical benefit was documented by increased flexibility of the fingers, reduction of skin induration, and a decrease in number and size of mucinous papules. All previous therapeutic approaches were ineffective. High-dose intravenous immunoglobulin appears to be a promising treatment option for patients with scleromyxedema. Clinical studies are desirable, but difficult to perform in such a rare disease. Long-term follow-up on individual patients so treated is desirable.

Digital image correlation: A technique for determining local mechanical conditions within early bone callus

Local mechanical conditions are known to play a role during the regeneration of musculoskeletal tissues, and histomorphometrical investigations of the time course of healing have enabled specific conclusions regarding the mechanosensitivity of tissue differentiation. However, the mechanism for this influence is not clearly understood. In order to extend this analysis, it is essential to link local histological understanding with direct characterisation of the local mechanical environment. Digital image correlation (DIC) is a computer-based image analysis technique that enables the non-contact measurement of strains on material surfaces and is finding application in many areas of biomechanics. Here we report a DIC technique to investigate the local distribution of mechanical strain within regenerating soft tissue sections. We provide exemplary data from analysis of a section of sheep bone callus. An assessment of displacement measurement accuracy gave an RMS error of 4.2 microm, corresponding to an estimated strain error of 1.4%. The sections showed concentrations of up to four times the applied strain and comparison of the strain patterns with histological analysis confirmed that these concentrations reflected boundaries between hard and soft callus.

Do serological tissue turnover markers represent callus formation during fracture healing?

Serological parameters of bone and fibrous tissue turnover were demonstrated to monitor the course of fracture healing. The aim of this study was to evaluate the correlation between the serological parameter levels during fracture healing and callus development in a standardised ovine model of fracture healing. Two years old female sheep received a standardised 3 mm tibial bone defect stabilised by an external fixator. The serological levels of the C-terminal propeptide of procollagen type I (PICP), bone specific alkaline phosphatase (bALP), total alkaline phosphatase (tALP), osteocalcin, tartrate-resistant acid phosphatase (TRAP), calcium, phosphate and the N-terminal peptide of procollagen type III (PIIINP) were observed over a 9-week healing period. The course of fracture healing was monitored radiographically, and the callus composition was evaluated histologically at 2, 3, 6 and 9 weeks post-surgery. The serological results were compared with an untreated control group. Additionally, the maximum values during healing were compared with juvenile values to gauge the level of the serological response. The histological and radiographical results demonstrated callus formation without complications. All serological parameters showed broad inter-individual variations, and the response to the standardised fracture scenario was strongly individual. Maximum values during fracture healing did not reach the juvenile levels. The fractured as well as the control animals showed significant changes in the parameter levels. No correlations were observed between the histological course of healing and the course of bone formation markers whilst the TRAP level was reduced during bony callus formation. The PIIINP level increased when the amount of soft callus tissue decreased during healing. The observed bone formation markers were not suitable as general markers to detect the course of fracture healing, whilst PIIINP was able to reflect soft callus degradation.

Gait evaluation: a tool to monitor bone healing?

BACKGROUND

Current clinical methods for monitoring fracture healing are often invasive and inaccurate. This paper evaluates the use of a pressure sensitive platform to improve monitoring.

METHODS

Standardised 3 mm diaphyseal bone defects were created in the right tibia of 64 female sheep and stabilised with either a rigid monolateral external fixator or a more flexible variant. Over a nine week healing period gait parameters were measured using a pressure sensitive platform and interfragmentary movements at the fracture site were monitored. Frequency spectra were calculated for the ground reaction forces. The tibiae were tested biomechanically after sacrifice and callus sections were analysed histomorphometrically.

FINDINGS

All animals unloaded the operated and overloaded the contralateral hindlimb. Callus mineralisation and stiffness, as well as limb loading increased during healing whilst interfragmentary movements were reduced. Larger interfragmentary movements resulted in a slower fracture healing rate as documented histologically and biomechanically. Frequency analysis showed upto 14 dB loss of power at frequencies associated with bone mechanotransduction at four weeks postoperatively, reducing to a 3 dB loss at nine weeks.

INTERPRETATION

Gait analysis is a valuable tool for monitoring the course of fracture healing. Different fixation stiffnesses caused different initial interfragmentary movements leading to different healing rates. Ground reaction forces were strongly related to the course of callus mineralisation and thus directly reflected the recovery of stiffness at the fracture site. Reduced levels of loading frequencies that may affect bone healing persist to nine weeks postoperatively.

Poly(D,L-lactide) coating is capable of enhancing osseous integration of Schanz screws in the absence of infection

Pin loosening is a major complication in external fixation. Biological and mechanical conditions play an important role in the maintenance and enhancement of the implant-bone interface in fracture fixation. It is thought that biodegradable coatings may be capable of preventing pin track infection and pin loosening. The goal of this study was therefore to analyze the influence of a biodegradeable coating on the osseous integration of Schanz' screws during fracture treatment. Standardized osteotomies (3-mm fracture gap) of the right tibiae were performed on 16 sheep and stabilized by an AO mono-lateral external fixator. Additional, mechanically less loaded Schanz' screws were also mounted. All screws were randomly coated with biodegradable poly(D,L-lactide). The sheep were sacrificed after 9 weeks. All screws were removed and rolled on blood agar plates for microbiological analysis. Histological sections of the pin tracks were histochemically and morphometrically analyzed. Clinically, no signs of severe infection were visible. Microbiological analysis revealed 14.8% colonization by Staphylococcus aureus in the coated and 29% in the uncoated screws. Histomorphometry of the bone surrounding the Schanz' screws revealed that significantly more osseous integration had occurred on poly(D,L-lactide)-coated screws in the absence of bacterial colonization. Significantly more bone remodeling and a higher osteoclastic activity was seen near the screw-bone interface in the uncoated screw group. Up to a threefold increase in new bone formation and more severe remodeling was observed around the screw entry compared to the pin exit in all groups. Loaded screws showed significantly more callus formation around the exit sites than their less loaded counterparts. In the present study, poly(D,L-lactide) coating of Schanz' screws was found to enhance osseous integration in the absence of bacterial colonization in sheep by causing less cortical remodeling and less osteoclastic activity in the cortices compared to uncoated screws. Additionally, the coating appeared to reduce the instances of pin track infections. Mechanical loading showed an adverse effect on bone formation and remodeling. It has been shown that both biological and mechanical factors play an important role in the maintenance of osseous integrity of the pin-bone interface. Poly(D,L-lactide) coating of Schanz' screws does not prevent osseous destruction and severe bacterial colonization along the pin tracts, but can improve osseous integration of Schanz' screws in the absence of infection.

Angle stable locking reduces interfragmentary movements and promotes healing after unreamed nailing. Study of a displaced osteotomy model in sheep tibiae

BACKGROUND

Large interfragmentary movements may delay bone-healing. The hypothesis of the present study was that a reduction of interfragmentary movements, especially of torsional rotation and bending angles, would support the healing process and lead to improved healing following unreamed tibial nailing. The objective of this study was to investigate healing of an unstable tibial osteotomy site following stabilization with unreamed nailing with a modified tibial device that had angle stable holes for the locking bolts. We compared those findings with healing after stabilization of such sites with standard unreamed tibial nailing. The duration of the study period was nine weeks.

METHODS

The site of a standardized displaced osteotomy (3-mm gap) in twelve ovine tibiae was stabilized with unreamed tibial nailing: six animals were treated with a modified nail that had angle stable holes for the locking bolts, and six were treated with standard unreamed tibial nailing. In vivo gait analysis with optical measurements of interfragmentary movements and simultaneous measurements of ground reaction parameters were performed three days after the operation and once weekly afterward. After the animals were killed at nine weeks, the treated and contralateral tibiae were explanted, the implants were removed, and radiographs were made and evaluated for bridged cortices. Each pair of tibiae was also mechanically tested until torsional failure, after which the whole callus region was subjected to histological and histomorphometric analysis.

RESULTS

Throughout the examination period, the interfragmentary movements in all directions were significantly smaller in the group treated with the angle stable tibial nail than they were in the group treated with standard unreamed tibial nailing. The limbs treated with the angle stable tibial nails returned to almost full weight-bearing during the period of the investigation, whereas those treated with standard nailing did not. Histomorphometric analysis, radiographic data, and mechanical testing showed superior bone-healing following treatment with the angle stable tibial nail.

CONCLUSIONS

Use of an angle stable tibial nail may help to reduce interfragmentary movements in vivo and thus lead to superior bone-healing compared with that following standard unreamed tibial nailing.

The course of bone healing is influenced by the initial shear fixation stability

Fracture healing is influenced by fixation stability and experimental evidence suggests that the initial mechanical conditions may determine the healing outcome. We hypothesised that mechanical conditions influence not only the healing outcome, but also the early phase of fracture healing. Additionally, it was hypothesised that decreased fixation stability characterised by an increased shear interfragmentary movement results in a delay in healing. Sixty-four sheep underwent a mid-shaft tibial osteotomy which was treated with either a rigid or a semi-rigid external fixator. Animals were sacrificed at 2, 3, 6 and 9 weeks postoperatively and the fracture callus was analysed using radiological, biomechanical and histological techniques. The tibia treated with semi-rigid fixation showed inferior callus stiffness and quality after 6 weeks. At 9 weeks, the calluses were no longer distinguishable in their mechanical competence. The calluses at 9 weeks produced under rigid fixation were smaller and consisted of a reduced fibrous tissue component. These results demonstrate that the callus formation over the course of healing differed both morphologically and in the rate of development. In this study, we provide evidence that the course of healing is influenced by the initial fixation stability. The semi-rigid fixator did not result in delayed healing, but a less optimal healing path was taken. An upper limit of stability required for successful healing remains unknown, however a limit by which healing is less optimal has been determined.

Comparison of unreamed nailing and external fixation of tibial diastases--mechanical conditions during healing and biological outcome

Locked intramedullary nailing and external fixation are alternatives for the stabilization of tibial shaft fractures. The goal of this study was to determine to what extent the mechanical conditions at the fracture site influence the healing process after unreamed tibial nailing compared to external fixation. A standardized tibial diastasis was stabilized with either a locked unreamed tibial nail or a monolateral fixator in a sheep model. Interfragmentary movements and ground reaction parameters were monitored in vivo throughout the healing period. After sacrifice, the tibiae were examined mechanically and histologically. Bending angles and axial torsion at the fracture site were larger in the nail group within the first five weeks post-operatively. Unlike the fixator group, the operated limb in the nail group did not return to full weight bearing during the treatment period. Mechanical and histomorphometrical observations showed significantly inferior bone healing in the nail group compared to the fixator group. In this study, unreamed nailing of a tibial diastasis did not provide rotational stability of the osteosynthesis and resulted in a significant delay in bone healing.

Are bone turnover markers capable of predicting callus consolidation during bone healing?

The aim of this study was to determine the ability of the following bone turnover markers to monitor the course of callus consolidation during bone healing: Carboxy-terminal propeptide of procollagen type I (PICP), skeletal alkaline phosphatase (sALP), and amino-terminal propeptide of type III procollagen (PIlINP). Since interfragmentary movements have been proven to possess the ability to document the progression of bone healing in experimental studies, correlations between bone turnover markers and interfragmentary movements in vivo were investigated. Therefore, two different types of osteosyntheses representing different mechanical situations at the fracture site were compared in an ovine osteotomy model. Blood samples were taken preoperatively and postoperatively in weekly intervals over a nine-week healing period. At the same intervals, interfragmentary movements were measured in all sheep. After nine weeks, animals were sacrificed and the tibiae were evaluated both mechanically and histologically. Wide interindividual ranges were observed for all bone turnover markers. The systemic PICP level did not increase with callus consolidation. The bone-healing model seemed to influence the systemic level of PIIINP and sALP but no general correlation between bone turnover markers and interfragmentary movements could be detected. No differences between the different types of osteosyntheses and thus the different mechanical situations were observed. All analyzed markers failed as general predictors for the course of callus consolidation during bone healing.

[Locally recurrent and metastatic malignant melanoma. Long-term results and prognostic factors after percutaneous radiotherapy]

PURPOSE

Radiotherapy (RT) is used as last resort for patients with advanced cutaneous malignant melanoma (MM). Herein our 20-year clinical experience is presented analyzing different endpoints and prognostic factors in patients with locally advanced, recurrent or metastatic MM.

PATIENTS AND METHODS

From 1977 to 1995, 2,917 consecutive patients were entered in the MM registry of our university hospital. RT was indicated in 121 patients (56 females, 65 males) for palliation in locally advanced recurrent and metastatic MM stages UICC IIB to IV. At the time of RT initiation, 11 patients had primary or recurrent lesions which were either not eligible for surgery or had residual disease (R2) after resection of a primary or recurrent MM lesion (UICC IIB); 57 patients had lymph node (n = 33) or in-transit metastases (n = 24) (UICC III), and 53 had distant organ metastases (7 M1a, 46 M1b) (UICC IV). The time from first diagnosis to on-study RT averaged overall 19 months (median: 18; range: 3 to 186 months). In 77 patients conventional RT and in 44 patients hypofractionted RT was applied with 2 to 6 Gy fractions up to a mean total RT dose of 45 (median: 48; range: 20 to 66) Gy.

RESULTS

At 3 months follow-up, complete response (CR) was achieved in 7 (64%), overall response (CR + PR) in all (100%) UICC IIB patients, in 25 (44%) and 44 (77%) of 57 UICC III patients, and in 9 (17%) and 26 (49%) of 53 UICC IV patients. Tumor progression during RT occurred in 25 (21%) patients. Patients with CR survived longer (median: 40 months) than those without CR (median 10 months) (p < 0.01). At the time of evaluation and last FU (December 31, 1996), 26 patients were still alive: 6 (55%) stage UICC IIB, 17 (30%) stage UICC III, and 3 (6%) stage UICC IV patients (p < 0.01). Univariate analysis revealed following prognostic factors for CR and long-term survival: UICC stage (p < 0.001), primary location in the head and neck, total RT dose > 40 Gy (all p < 0.05), while age, gender and primary histological subtype had no impact. In multivariate analysis, UICC stage was the only independent favorable prognostic factor for achievement of CR and long-term survival (p < 0.001).

CONCLUSION

External RT provides effective palliation in advanced UICC stages. The UICC staging system is a good predictor of initial and long-term tumor response in metastatic MM. Prospective randomized trials using RT with or without adjuvant therapy for advanced MM are justified.

[Ulcerative stomatitis as clinical clue to inadvertent methotrexate overdose]

Gastrointestinal side effects and the development of toxic liver fibrosis are well-known side effects of low dose methotrexate therapy. A female patient receiving a long term low dose methotrexate therapy for a seronegative chronic polyarthritis developed an ulcerative stomatitis, as clinical clue to an inadvertently given methotrexate overdose. A summary of other side effects of methotrexate and of oral side effects of other cytostatic agents and immunosuppressive drugs is given.

[Long term results following radiation therapy of locally recurrent and metastatic malignant melanoma]

The 20-year radiotherapy (RT) experience in patients with locally advanced, recurrent or metastatic malignant melanoma (MM) is analyzed with respect to different endpoints and prognostic factors. From 1977 to 1995, 2917 consecutive patients were entered in our MM registry. RT was indicated in 121 patients (56 females, 65 males) for palliation in advanced MM stages. The histology of the primary lesion was nodular in 51, superficial spreading in 35, acral-lentiginous in 8 and lentigo maligna in 4 patients); 22 were missing or could not be reclassified. Eleven patients had primary or recurrent lesions which were ineligible for surgery or had residual disease (R2) after resection of a primary or recurrent lesion (UICC IIB); 57 patients had lymph node (33) or in-transit metastases (24) (UICC III), 53 had distant organ metastases (7 M1a; 46 M1b) (UICC IV). Time from first diagnosis to on-study RT averaged 19 (median: 18; range: 3-186) months. In most cases conventional RT was applied (2-6 Gy single fractions) up to a mean total RT dose of 45 (median: 48; range: 20-66) Gy. At 3 months follow-up (FU), complete response (CR) was achieved in 7 (64%) and overall response (CR+PR) in all (100%) UICC IIB patients, in 25 (44%)/44 (77%) of 57 UICC III patients, and in 9 (17%)/26 (49%) of 53 UICC IV patients. Progression during RT occurred in 25 (21%) patients. Patients with CR survived longer (median: 40 months) than those without CR (median: 10 months) (p<0. 01). At last FU, 26 patients were alive: 6 (55%) UICC IIB, 17 (30%) UICC III, and 3 (6%) UICC IV patients (p<0.01). In univariate analysis following favorable prognostic factors for CR and long-term survival were identified: low UICC stage (p<0.001), primary site head and neck and total dose >40 Gy (all p<0).

Papillary cystadenoma: a rare tumor of the minor salivary glands

Papillary cystadenoma of the minor salivary glands is a rare benign neoplasm that clinically resembles mucous cysts. Characteristic histological features are diagnostic. However, salivary gland histology is particularly difficult to interpret. Primarily, as further clinical and histological differential diagnoses have to take into account the well-differentiated cystic mucoepidermoid carcinoma and the papillary cystic type of acinic cell carcinoma, both malignant neoplasms of the salivary glands. We report on a 39 year old female with a bluish cystic lesion at the buccal mucosa, which occurred 14 years after the excision of a similar appearing, histologically proven mucous retention cyst at the same location. The histology of this tumor, however, revealed a papillary cystadenoma. Although rare, benign and malignant salivary gland neoplasms occur in minor salivary glands, and are clinically indistinguishable from mucous retention cysts. The dermatologist should be familiar with these differential diagnoses, since different therapeutic consequences result from an early diagnosis obtained by excision and histological examination of oral cystic tumors.

Palliative radiotherapy for recurrent and metastatic malignant melanoma: prognostic factors for tumor response and long-term outcome: a 20-year experience

PURPOSE

Radiotherapy is used as a "last resort" for patients with advanced cutaneous malignant melanoma. We have analyzed our 20-year clinical experience with respect to different endpoints and prognostic factors in patients with locally advanced, recurrent, or metastatic malignant melanoma.

METHODS

From 1977 to 1995, 2,917 consecutive patients were entered in the melanoma registry of our hospital. Radiotherapy was indicated in 121 patients (56 females, 65 males) for palliative reasons in advanced malignant melanoma stages UICC IIB/III/IV. The histology of the primary lesion was nodular in 51 patients, superficial spreading in 35, acral-lentiginous in 8, and lentigo maligna melanoma in 4 patients. Eleven patients had primary or recurrent lesions which were either not eligible for surgery or had residual disease (R2) after resection of a primary or recurrent lesion (UICC IIB); 57 patients had lymph node (n = 33) or in-transit metastases (n = 24) (UICC III), and 53 had distant organ metastases (7 M1a; 46 M1b) (UICC IV). Time from first diagnosis to on-study radiotherapy averaged 19 (median: 18; range: 3-186) months. In most cases, conventional RT was applied with 2-6 Gy single fractions up to a median total radiation dose of 48 (mean: 45; range: 20-66) Gy.

RESULTS

At 3 months follow-up, complete response (CR) was achieved in 7 (64%) and overall response [complete (CR) and partial response (PR)] in all (100%) UICC IIB patients, in 25 (44%) and 44 (77%) of 57 UICC III patients, and in 9 (17%) and 26 (49%) of 53 UICC IV patients. Tumor progression during radiotherapy occurred in 25 (21%) patients. Patients with CR survived longer (median: 40 months) than those without CR (median 10 months) (p < 0.01). At last follow-up (Dec 31, 1996), 26 patients were still alive: 6 (55%) UICC IIB, 17 (30%) UICC III, and 3 (6%) UICC IV patients (p < 0.01). Univariate analysis revealed the following prognostic factors for complete response and long-term survival: UICC stage (p < 0.001), primary location in the head and neck region, total radiation dose above 40 Gy (all p < 0.05), while age, gender, and histology had no impact. In multivariate analysis, UICC stage was the only independent prognostic factor (p < 0.001).

CONCLUSION

External beam radiotherapy can provide long-term local control and effective palliation in malignant melanoma UICC stages IIB-IV. The current UICC staging system is an excellent prognostic factor for initial and long-term tumor response in metastatic melanoma. Therefore, prospective randomized trials using external radiotherapy with or without adjuvant therapy for advanced malignant melanoma are justified.

Differentiation between Spitz nevi and malignant melanomas by interphase fluorescence in situ hybridization

Spitz nevi are benign melanocytic neoplasias which have distinct pathological features that make the pathological differential diagnosis from malignant melanomas extremely difficult. The Spitz nevi may be misdiagnosed as malignant melanoma and vice versa. Therefore, interphase fluorescence in situ hybridization (I-FISH) was used for a possible discrimination between Spitz nevi and malignant melanomas on the basis of numerical aberrations of the chromosome complement in interphase nuclei of thin sections. Previous studies had shown changes in malignant melanomas which were not found at the same level in normal tissue or benign tumors. Thin sections of archival paraffin material from 42 Spitz nevi with different histological type and grade of anomaly were subjected to FISH-analyses using commercially available biotinylated and/or digoxigenated alphoid DNA probes of chromosomes 1, 6, 7, 9, 17 and 18, which were applied in combinations in a two- or three-color-FISH. Unaffected epithelial areas from the same sections served as. The obtained data were compared with those collected previously from thin sections of malignant melanomas prepared in the same way. Due to the sometimes limited nevus area investigated, the number of evaluable nuclei was lower than expected from previous experiences with malignant melanomas. Therefore, only 20 nevi could be reliably evaluated. The comparison of the group of Spitz nevi with the group of controls did not show any significant difference regarding chromosomes 1, 6, 7, 9 and 17 (Wilcoxon test). The method used to detect chromosomal loss or gain in the individual Spitz nevi demonstrated only two nevi (one of the spindle cell type with a low to middle grade of anomaly, the other of the epitheloid cell type with a middle grade of anomaly) with a gain of chromosome 7 and chromosome 17, respectively. So, with respect to the histological type and grade of anomaly, no numerical aberrations could be detected in Spitz nevi. The comparison of the group of Spitz nevi with subgroups of malignant melanomas (metastatic, non-metastatic, melanomas with a thickness <1.5 mm and melanomas with a thickness >2. 0 mm) and with the whole group of malignant melanomas showed significant differences concerning chromosome 9 (Mann-Whitney U test), signal indices, which were higher in the melanomas than in the Spitz nevi. Regarding chromosomes 6, 7 and 17 no significant differences could be shown, although a trend of gain in melanomas and of loss in Spitz nevi was observed of these chromosomes.

Deletion monitoring in skin tumors by interphase-FISH using band-specific DNA probes

Thin sections from archival paraffin blocks of various skin tumors (26 melanomas, 15 squamous cell carcinomas, 5 keratoacanthomas, 5 basal cell carcinomas) were subjected to interphase-FISH (I-FISH) with DNA probes which are specific for chromosomal regions often involved in deletions in human cancer. These were probes for chromosome 3p21, the p53 gene on chromosome 17p13, and, in a few selected cases, a probe for chromosome 9p21. It was demonstrated that deletions of these regions could be reliably detected and related to tumor type and histology, i.e. grading. The most common deletion was that of 3p21 which was found in all studied squamous cell carcinomas (SCC) of low differentiation, in 60% of the Bowen carcinomas, in 70% of the metastatic melanomas less than 1.5 mm thick, and in over 55% of those which thickness over 2 mm. In contrast, FISH-detected p53 deletion was a rare finding in the investigated tumors. However, this gene was even found in an increased copy number in 60% of the poorly differentiated SCCs (grade 4) and in 50% of the non-metastatic melanomas less than 1.5 mm thick. Deletion of 9p21 was detected in 13 of the 14 tumors on which pertinent examinations could be performed. I-FISH was shown to be a reliable technique for the rapid detection of chromosome band specific deletions in archival material of human skin tumors.

[Papillary cystadenoma of the minor salivary glands]

Papillary cystadenoma of the minor salivary glands is a rare benign tumor that clinically resembles a mucous cyst. We demonstrate its histologic features and differential diagnosis by a case report. Benign and malignant neoplasms of the minor salivary glands are not well acknowledged in the dermatologic literature, but should be considered in the differential diagnosis for mucous cysts.

[Dose-dependent pellagroid skin reaction caused by carbamazepine]

A 11-year-old girl suffering from grand mal epilepsy underwent antiepileptic therapy with carbamazepine (600 mg/daily). Two weeks after increasing the dose (900 mg/day) she suddenly developed relatively sharply limited, sunburn-like brown reddish macular lesions with central scaling and partly hyperkeratotic areas on the hands, feet, face, knees, gluteal and axillar regions. Otherwise no health disorders were found; in particular no neurological or gastrointestinal symptoms occurred. After reduction of the doses (450 mg/day) these skin lesions faded away. With exception of elevated serum levels of carbamazepine, nicotinamide and vitamin B6, all blood tests were in normal range. Interactions of carbamazepine with the vitamin B6- nicotinamide metabolism are the reason for these previously undescribed cutaneous side effects in connection with carbamazepine therapy. The present case demonstrates a toxic, non-allergic reaction during carbamazepine treatment with pellagroid skin symptoms.

Interphase-FISH examinations in paraffin sections from benign, precancerous, and cancerous lesions of the skin and oral mucosa

In a preliminary pilot study centromeric probes for chromosomes #7, #8, #11, and #17 and two-colour-FISH were applied on interphase nuclei of 10 coded histologic thin sections obtained from archival paraffin material from precancerous lesions and malignant tumors of the mouth epithelium. Brilliant signals could be obtained in this material without any computerized processing. Among the ten coded probes, localized malignant areas within grade 2 leukoplakias could be detected by their increased number of aneusomic cells, as could the samples from carcinomas. In extension of this study archival paraffin material from 30 epithelial tumors of the skin were examined. The studied squamous cell and Bowen carcinomas were characterized by a large number of chromosomally aberrant subclones and gains of chromosomes were the prevailing finding. In contrast, keratoacanthomas showed distinctly less clonal variation, their majority exhibiting small, but significant clones with chromosome loss, particularly of chromosome #7, less distinctly of chromosome #17.

Chromosome gain and loss in paraffin sections from malignant melanomas of the skin

Alphoid DNA probes specific for the chromosomes #6, #7, #9, and #17 were used to screen interphase nuclei for numerical chromosome aberrations in histologic thin sections obtained from archival paraffin material of 25 human melanomas of different type, thickness and stage of progression. An alphoid probe for chromosome #3 was applied in four of these tumors. Besides a general large variation of the number of subpopulations of cells characterized by gains and losses of the studied chromosomes, there was a trend to higher variability in metastatic melanomas as compared to small (<1.5 mm thickness) non-metastatic ones and, particularly, to normal skin tissue. Chromosomes #6 and #9 were those often affected by loss in thick melanomas (>2 mm), while subpopulations showing a gain of these chromosomes, and, in addition, of chromosome #7 seemed more frequently to be associated with thin and non-metastatic ones. The frequency of cases showing gain of chromosome #17 clearly exceeded those with loss of this chromosome in the studied melanomas, but was most pronounced in thicker metastatic tumors.

Clinical relevance of sonometry-derived tumour thickness in malignant melanoma--a statistical analysis

High-frequency sonography has been shown to be a useful tool in planning operative strategy in the surgery of malignant melanoma (MM). The purpose of the present study was to compare sonometric and histometric data of tumour thickness in primary cutaneous MM, applying statistical methods in order to evaluate the pre-operative relevance of sonometry. The thickness of 259 melanomas was measured preoperatively by a 20-MHz B scan, and postoperatively by histometry. Statistical analysis was performed using Pearson's correlation coefficient and absolute and relative differences. Although the correlation between sonometry and histometry was good (r = 0.88), there was a mean difference of 0.39 mm (relative difference 28%). Overall, sonometry was in agreement with the corresponding histological classes in 75% of cases. However, tumours assessed by ultrasound as between 0.55 and 0.95 mm thick were incorrectly classified according to histology in 34%, and those between 1.30 and 1.70 mm were incorrectly classified in 50% of cases. Our data reveal greater differences between sonometry and histometry using appropriate statistical methods. A concept to assess differences between sonometry and histometry is recommended.

[Hair growth promoters in androgenetic alopecia. Expectations and reality]

Androgenetic hair loss is the most frequent reason for the topical application of hair-growth-promoting agents. Such preparations should arrest or even reverse androgen-induced hair follicle regression as well as prolonging the hair cycles, especially of the shortened anagen phase, and thus protect from increased hair loss. True evidence of drug effects on hair growth is problematic, since trichograms, the method chiefly applied by the manufacturers, fail to reveal every factor involved in the follicular activity, especially the duration of anagen stage. For example, an increase in the anagen rate does not always reflect a lengthening of the anagen stage, but may also be due to shortened hair cycles. Accordingly, drug effects on hair growth should be investigated by methods that analyse the cell cycle kinetics. For this approach DNA-flowcytometry of the outer root sheath in plucked anagen hairs and of complete anagen hair bulbs taken by micropreparative techniques from scalp biopsies offers a reproducible method for quick and reliable evaluation of hair growth.

Cell kinetics of anagen scalp hairs under physiological and pathological conditions

The cell kinetics of anagen scalp hair bulbs taken by punch biopsies from healthy male volunteers (n = 50) were determined at defined bulbar hair segments using microdissection and DNA flow cytometry. The highest proliferative activity (S phase) was measured within the lower most bulbar segment (14.0%) but decreased to the Auber's segment (7.6%) and to the isthmus segment (5.9%). The results support histoautoradiographic data demonstrating most of the proliferative activity in the hair bulb below the Auber's level [1]. Furthermore, cell kinetic data of dissected anagen hair bulbs segmented at Auber's level from an androgen-sensitive scalp area were studied in male pattern baldness (n = 15, Hamilton IV) and hirsutism (n = 13). The results revealed a significant increase of S phase cells in male pattern baldness (8.9%) compared to healthy males (n = 10, 7.9%) as well as in hirsutism (10.2%) compared to healthy females (n = 10, 7.5%). In hirsutism the percentages of S phase cells ran parallel to the plasma levels of dehydroepiandrosterone sulfate whereas no correlation to testosterone could be proved. Similar, 6 hypothyroid and 6 hyperthyroid patients were studied. In hyperthyroidism an increase of S phase values (10.3%) was found, while it decreased in hypothyroidism (6.1%). A correlation between the height of S phase and plasma triiodothyronine level was noted. Our studies demonstrate that DNA flow cytometry is a suitable method for the evaluation of physiological or hormonal influences on cell cycle kinetics of human anagen hair bulbs in vivo.

Sex hormones and antiandrogens influence in vitro growth of dermal papilla cells and outer root sheath keratinocytes of human hair follicles

Anagen hair bulb papillae, interfollicular dermal fibroblasts, and interfollicular keratinocytes isolated from fronto-parietal scalp biopsies as well as outer root sheath keratinocytes from plucked anagen hairs were separately grown in subculture for 14 d. The effect of different concentrations (2.4 nM-17.3 microM) of testosterone, dihydrotestosterone, and the antiandrogens cyproterone acetate or 17 alpha-propylmesterolone on growth behavior of the mesenchymal and epithelial cell types of the hair follicle were comparatively studied by means of growth curves, cell doubling times, and 3H-thymidine incorporation. For control, all cell lines were subcultured in hormone-free medium. Testosterone and dihydrotestosterone (345 nM) significantly reduced proliferation of papilla cells compared with dermal fibroblasts (p < 0.01) and outer root sheath keratinocytes compared with interfollicular keratinocytes (p < 0.01), as well as compared with cells cultured in control medium. Low concentrations of 17 beta-estradiol were ineffective, whereas doses of 180 nM 17 beta-estradiol increased the growth velocities of all cell types, especially of papilla cells, compared with dermal fibroblasts. Low doses of either cyproterone acetate (24 nM) or 17 alpha-propylmesterolone (29 nM) induced a growth enhancement, especially of papilla cells and outer root sheath keratinocytes, whereas high doses of cyproterone (1.20 microM) and 17 alpha-propylmesterolone (1.45 microM) had opposite effects. These changes were significant between papilla cells and dermal fibroblasts as well as between outer root sheath keratinocytes and interfollicular keratinocytes. Applying increasing doses of androgens to cyproterone acetate (24 nM)- or 17 alpha-propylmesterolone (29 nM)-containing media neutralized the growth-stimulating effect of antiandrogens, particularly in papilla cells and outer root sheath keratinocytes. However, minor differences between testosterone and dihydrotestosterone effects on cell growth were found. The data clearly demonstrate that the changes of in vitro growth of hair follicle cells depend on the concentrations of androgens and antiandrogens, as higher doses of both antiandrogens tested retarded the cell proliferation similar to testosterone or dihydrotestosterone. The papilla cells and outer root sheath keratinocytes reacted more sensitively to the hormones tested, thereby confirming the concept of a distinct androgen sensitivity of these specialized hair follicle cells.

[Incidence of ocular pigment changes in patients with cutaneous melanoma]

Between October 1990 und April 1992, 116 patients with primary cutaneous melanoma and 6 with primary ocular malignant melanoma underwent both dermatological and ophthalmological examination, standardized personal and clinical criteria being applied. In addition to the record of the DDG melanoma file, the skin type, eye and skin colour, number of naevi, occurrence of any other cutaneous alterations, and the family history with respect to additional malignant neoplasms were documented. It was found that 18/116 patients with cutaneous melanoma also had naevi of the iris, but none had concomitant ocular melanoma. Notably, 32% of first degree relatives (n = 37) had a malignant neoplasm, as against 12% of the dermatological patients with no oncological conditions who acted as controls. Although the occurrence of additional changes in ocular pigmentation alterations in patients with malignant cutaneous melanoma cannot be regarded as significant on the basis of our prospective study, the eye, as a potential location of metastases or the original site in primary malignant melanoma, should be examined during staging and follow-up examinations, especially as isolated cases of oculo-cutaneous correlation have already been reported.

Distribution of adhesion molecules, IgE, and CD23 in a case of angiolymphoid hyperplasia with eosinophilia

Angiolymphoid hyperplasia with eosinophilia developed in a 13-year-old boy. The immune phenotype of infiltrating cells and the distribution of adhesion molecules of the integrin, immunoglobulin, and selectin families were analyzed with monoclonal antibodies. The infiltrate consisted mainly of helper lymphocytes, monocytes, eosinophils, CD1+ dendritic cells, and mast cells. A CD23/Fc epsilon receptor was present on 40% of these cells, and surface bound IgE was present on 30% of these cells. The latter was found on all cell types. A cellular adhesion molecule analysis revealed that the proliferating endothelial cells were expressing constitutive ICAM-1, LFA-3, VLA-1, VLA-3, VLA-5, alpha 6, and beta 3-integrin chain as well as activation-dependent VLA-2, VCAM-1, and human lymphocyte antigen-DR. The infiltrating cells expressed LFA-1 and CD2, the correlating ligands for ICAM-1 and LFA-3. Our studies support previous observations of an unusual IgE-mediated immune reaction, and suggest an additional pathogenic role for adhesion events in the development of the pathognomonic cellular composition in angiolymphoid hyperplasia with eosinophilia.

In situ [3H]thymidine labelling of human hair papilla: an in vitro autoradiographic study

The labelling index (LI) and the location of labelled cells in the papilla of human anagen scalp hair have been studied after in vitro [3H]thymidine (3H-TdR) pulse labelling. Forty-three anagen stage VI papillae from 2 individuals (both females, 25 and 55 years) obtained by micropreparation from deep scalp biopsies were analysed. Labelled cells were found only paraaxially in the basal third of the papilla, i.e. below Auber's line. The 3H-TdR-LI of the papilla cells (0.13 and 0.16%) is about 200-times lower than that of the hair matrix cells below the line of Auber (25.5 and 29.5%). The biological significance of this low proliferation rate in the anagen stage VI hair papilla of healthy human should be defined.