Comparison of fluorescent single-strand conformation polymorphism analysis and denaturing high-performance liquid chromatography for detection of EXT1 and EXT2 mutations in hereditary multiple exostoses

EXT1 and EXT2 are two genes responsible for the majority of cases of hereditary multiple exostoses (HME), a dominantly inherited bone disorder. In order to develop an efficient screening strategy for mutations in these genes, we performed two independent blind screens of EXT1 and EXT2 in 34 unrelated patients with HME, using denaturing high-performance liquid chromatography (DHPLC) and fluorescent single-strand conformation polymorphism analysis (F-SSCP). The mutation likely to cause HME was found in 29 (85%) of the 34 probands: in 22 of these (76%), the mutation was in EXT1; seven patients (24%) had EXT2 mutations. Nineteen of these disease mutations have not been previously reported. Of the 42 different amplicon variants identified in total in the cohort, 40 were detected by DHPLC and 39 by F-SSCP. This corresponds to mutation detection efficiencies of 95% and 93% respectively. We have also found that we can confidently distinguish between different sequence variants in the same fragment using F-SSCP but not DHPLC. In light of this, and the similarly high sensitivities of the two techniques, we propose to continue screening with F-SSCP.

Leg lengthening over an intramedullary nail

Distraction osteogenesis is widely used for leg lengthening, but often requires a long period of external fixation which carries risks of pin-track sepsis, malalignment, stiffness of the joint and late fracture of the regenerate. We present the results of 20 cases in which, in an attempt to reduce the rate of complications, a combination of external fixation and intramedullary nailing was used. The mean gain in length was 4.7 cm (2 to 8.6). The mean time of external fixation was 20 days per centimetre gain in length. All distracted segments healed spontaneously without refracture or malalignment. There were three cases of deep infection, two of which occurred in patients who had had previous open fractures of the bone which was being lengthened. All resolved with appropriate treatment. This method allows early rehabilitation, with a rapid return of knee movement. There is a lower rate of complications than occurs when external fixation is used on its own. The time of external fixation is shorter than in other methods of leg lengthening. The high risk of infection calls for caution.

Contamination of the medullary canal following pin-tract infection

We developed an ovine model of an external-fixator pin-tract infection. With use of a novel method of tissue sampling, infection of the medullary canal was confirmed in all (10 of 10) external-fixator pins that were contaminated with Staphylococcus aureus after they were inserted. In addition, all (five of five) adjacent, uncontaminated pins became infected. We demonstrated that pin-tract infection can be difficult to diagnose clinically, despite gross infection of the tract, and that bacteria can spread within the medulla. Three of the infected pins (20%) did not appear clinically infected, were not loose, and were normal on radiographs after 1 week. Staphylococcus aureus was isolated from the medulla around all 15 pin tracts, and nine other organisms were isolated from the tracts. Despite the presence of infection, the majority of the pins remained well fixed in the bone after 2 weeks.

Pyoderma gangrenosum. A diagnosis not to be missed

We describe a case of pyoderma gangrenosum which presented with severe wound breakdown after elective hip replacement. The patient was treated successfully with minimal wound debridement and steroids. This diagnosis should always be considered when confronted with an enlarging painful skin lesion which does not grow organisms when cultured and fails to respond to antibiotic therapy, especially if there are similar lesions in other sites. In patients who have a past history of pyoderma gangrenosum, prophylactic steroids may be indicated at the time of surgery or may be required early in the postoperative period.

The neoplastic pathogenesis of solitary and multiple osteochondromas

Many theories of osteochondroma pathogenesis have been advanced. Genetic research into the inherited multiple form, hereditary multiple exostoses, has revealed a new family of tumour suppressor genes denoted EXT. Patterns of EXT gene mutation in hereditary multiple exostoses, in solitary and multiple osteochondromas, and in chondrosarcoma are analogous to those found in other tumour suppressor genes responsible for family cancer traits and associated malignancies. With one exception, most features of osteochondroma behaviour are comparable to those of benign neoplasms. The neoplastic pathogenesis of osteochondromas provides an alternative to the traditional 'skeletal dysplasia' theory to explain the growth disturbance associated with hereditary multiple exostoses. Recent studies on the physiological function of EXT genes are reviewed and implications for osteochondroma 'cell-of-origin' theories are discussed.

Effect of lengthening rate on angiogenesis during distraction osteogenesis

This study investigated the angiogenic response to four varying rates (0.3, 0.7, 1.3, and 2.7 mm/day) of distraction in a rabbit model of leg-lengthening. Immunostaining was performed with use of specific antibodies to type-IV collagen and endothelial cell antigen to examine semiquantitatively the presence of blood vessels in the developing tissues. With use of the Chalkley counting method, the greatest number of positive-staining blood vessel cells was found in the central fibrous zone of the groups that underwent lengthening at 0.7 and 1.3 mm/day compared with any other zone in any group (p < 0.05, t test). There were no statistical differences in the positive labeling indices in the mineralization front and the new bone zone adjacent to the mineralization front in any of the groups. However, the decrease in the number of positive-staining blood vessel cells in the new bone zone distant to the mineralization front compared with any other zone in any group was statistically significant. The results suggest that during distraction osteogenesis, the precursor cells of new capillaries were present in abundance within the fibrous interzone. These cells connected into the capillary network at the junction of the mineralization front and the fibrous zone. The angiogenic response was weaker in the more mature regions within the new bone zones. A slow rate of distraction (0.3 mm/day) did not maximally stimulate angiogenesis in the central fibrous zone, whereas high rates (2.7 mm/day) appeared to impair this response. In this model of distraction osteogenesis, the vascularization process in the central fibrous zone was maximally stimulated at distraction rates of 0.7 and 1.3 mm/day.

Repeatability of goniometer measurements of the knee in patients wearing an Ilizarov external fixator: a clinic-based study

OBJECTIVE

To examine the intra-tester and inter-tester reliability of three different methods of measurement of knee range of motion in patients undergoing limb reconstruction with the Ilizarov external fixator.

DESIGN

Twenty-five patients had the passive range of motion of their knee measured by 13 physiotherapists who were experienced in the use of goniometry. The testers were assigned into random pairs, each tester measured three or four patients who were allocated to them using the three different methods. These were: (1) a universal goniometer aligned against anatomical landmarks, (2) a universal goniometer aligned against the Ilizarov frame and (3) a modified universal goniometer.

SETTING

Orthopaedic limb reconstruction outpatient clinics.

SUBJECTS

Twenty-five patients undergoing limb reconstruction using an Ilizarov external fixator on both the femur and tibia.

RESULTS

Comparison of the three different goniometry methods showed that using a modified goniometer there was enhanced reliability compared with other methods. This method demonstrated good repeatability for both intra-tester and inter-tester measurements.

CONCLUSIONS

When serial measurements of knee range of motion are taken in patients wearing an Ilizarov external fixator the modified model of goniometer should be used.

The role of chondrocytes in intramembranous and endochondral ossification during distraction osteogenesis in the rabbit

We have used a rabbit leg-lengthening model for detailed studies of the histology of distraction osteogenesis. Some unusual features of the endochondral ossification that occurs during the rapid transition of cartilage to bone in the regenerate were observed. Histological staining techniques together with immunohistochemistry and nonradioactive in situ mRNA hybridization for cartilage and bone-related molecules have been used to document the presence of an overlapping cartilage-bone phenotype in cells of the cartilage-bone transitional region. In those particular areas, some chondrocytes appeared to be directly transformed into newly formed bone trabeculae which are surrounded by bone matrix. Acid phosphatases were found within the cartilage matrix in some of the cartilage/bone transitional regions and type I collagen mRNA and type II collagen protein were found together in some of the marginal hypertrophic chondrocytes. This study indicates an unusual role of chondrocytes in the process of ossification at a distraction rate of 1.3 mm/day in the rabbit. Further direct evidence is required to prove the hypothesis that the hypertrophic chondrocytes may transdifferentiate into bone cells in this model.

Biologic model of bone transport distraction osteogenesis and vascular response

We developed an experimental model in the rabbit of distraction osteogenesis through bone transport that closely corresponds to the clinical use of bone transport in humans. We also applied injection angiography to study the arterial response of a limb undergoing bone transport. This model includes a proximal osteotomy and bone transport to fill in a segmental tibial diaphyseal defect. Regenerate bone formed well in the gap that was created that trailed the transport segment, and slow healing at the docking site was observed, as seen in humans. The angiographic techniques clearly revealed, by radiography and anatomic dissection, the arterial response to bone transport. The results showed that the transport segment had an arterial supply after osteotomy and after transport. They also demonstrated an extensive increase in vessels in limbs that had undergone distraction osteogenesis, an observation made clinically in humans but not well demonstrated experimentally. Furthermore, angiography showed proximal stretching and distal kinking of the major artery of the leg. This model closely resembles distraction osteogenesis through bone transport in humans and definitively demonstrates that the transport segment can maintain blood supply and remain viable during the transport process. The results of this study provide a basis for further work on factors that enhance and interfere with successful bone transport in humans.

Measurement of impact force, simulation of fall and hip fracture

It has been shown that the incidence of hip fracture in the elderly may be influenced by the type of floor covering commonly used in homes for the elderly. This study describes the development of a method for modelling a fall during a hip fracture event, to examine the influence of different floors on impact force. An impact transducer is dropped in free fall through a smooth plastic tube. The impactor nose of the transducer models the curvature of the greater trochanter, and a steel spring is used to simulate the compliance of the skeletal structure. A weight, which corresponds to one-sixteenth of average body mass, compresses the spring and applies force to the impactor nose on striking the floor. The temporal variation in the force of impact with the floor is measured by the transducer to within 0.41 percent (SD = 0.63%, n = 10). Five common floor coverings were tested over a concrete floor slab (vinyl, loop carpet and pile carpet--both with and without underpad). ANOVA analysis showed that the differences between mean forces for each floor covering were highly significant (p > 0.001), with the thicker coverings producing 7 percent lower forces. The transducer may be used to examine the correlation between impact force and fracture incidence for a variety of different floors in homes for the elderly.

Biomaterial particle phagocytosis by bone-resorbing osteoclasts

Abundant implant-derived biomaterial wear particles are generated in aseptic loosening and are deposited in periprosthetic tissues in which they are phagocytosed by mononuclear and multinucleated macrophage-like cells. It has been stated that the multinucleated cells which contain wear particles are not bone-resorbing osteoclasts. To investigate the validity of this claim we isolated human osteoclasts from giant-cell tumours of bone and rat osteoclasts from long bones. These were cultured on glass coverslips and on cortical bone slices in the presence of particles of latex, PMMA and titanium. Osteoclast phagocytosis of these particle types was shown by light microscopy, energy-dispersive X-ray analysis and SEM. Giant cells containing phagocytosed particles were seen to be associated with the formation of resorption lacunae. Osteoclasts containing particles were also calcitonin-receptor-positive and showed an inhibitory response to calcitonin. Our findings demonstrate that osteoclasts are capable of phagocytosing particles of a wide range of size, including particles of polymeric and metallic biomaterials found in periprosthetic tissues, and that after particle phagocytosis, they remain fully functional, hormone-responsive, bone-resorbing cells.

Mutation screening of the EXT1 and EXT2 genes in patients with hereditary multiple exostoses

Hereditary multiple exostoses (HME), the most frequent of all skeletal dysplasias, is an autosomal dominant disorder characterized by the presence of multiple exostoses localized mainly at the end of long bones. HME is genetically heterogeneous, with at least three loci, on 8q24.1 (EXT1), 11p11-p13 (EXT2), and 19p (EXT3). Both the EXT1 and EXT2 genes have been cloned recently and define a new family of potential tumor suppressor genes. This is the first study in which mutation screening has been performed for both the EXT1 and EXT2 genes prior to any linkage analysis. We have screened 17 probands with the HME phenotype, for alterations in all translated exons and flanking intronic sequences, in the EXT1 and EXT2 genes, by conformation-sensitive gel electrophoresis. We found the disease-causing mutation in 12 families (70%), 7 (41%) of which have EXT1 mutations and 5 (29%) EXT2 mutations. Together with the previously described 1-bp deletion in exon 6, which is present in 2 of our families, we report five new mutations in EXT1. Two are missense mutations in exon 2 (G339D and R340C), and the other three alterations (a nonsense mutation, a frameshift, and a splicing mutation) are likely to result in truncated nonfunctional proteins. Four new mutations are described in EXT2. A missense mutation (D227N) was found in 2 different families; the other three alterations (two nonsense mutations and one frameshift mutation) lead directly or indirectly to premature stop codons. The missense mutations in EXT1 and EXT2 may pinpoint crucial domains in both proteins and therefore give clues for the understanding of the pathophysiology of this skeletal disorder.

Assessment of cell proliferation in regenerating bone during distraction osteogenesis at different distraction rates

An experimental model of lengthening of the lower limb was used to study the morphology and cellular proliferation of regenerating bone tissue after 20% lengthening at four rates of distraction. Groups of rabbits were killed at different times 1-8 weeks after surgery. The regenerated area was divided into three zones: fibrous, primary mineralization front, and new bone. As the rate of distraction increased, the size of the fibrous zone increased and that of the new bone zone decreased. Necrosis, formation of cysts, and cartilage were found in the regenerated area at the higher distraction rates. Cell proliferation was assessed by in vivo labelling with bromodeoxyuridine, and the positive staining index for anti-bromodeoxyuridine antibody was calculated in the zones of the regenerated tissue. The index values for the fibrous zones and the new bone zones did not differ significantly in any of the groups. The value increased significantly (p < 0.05) in the primary mineralization front as the rate of distraction increased from 0.3 to 0.7 mm/day, but there was no further significant increase at higher distraction rates. In conclusion, cell proliferation was increased at all of the higher rates (more than 0.3 mm/day) of distraction studied. Higher rates of distraction caused tissue damage. A distraction rate of 0.7 mm/day appeared optimal for cell proliferation and histological characteristics.

Prevention of deformity during limb lengthening

Deformity occurs frequently at the site of distraction during leg lengthening and can add to disability. The elastic and nonelastic displacements have been measured in a model that simulates leg lengthening in the laboratory. Measurements have been made for different fixator systems. The angulation in the vertical plane that occurs during leg lengthening is minimized if the distance between the bone and the fixator bar is kept as small as possible, if three screws are inserted in the proximal and distal bone fragments, and if the peak loads on the fixator are reduced by adjusting the rhythm of distraction. However, even if these precautions are taken, the results show that some fixators designed for leg lengthening will fail and lead to deformity at the osteotomy site. This may occur under the repeated cycles of high loads associated with the rises in soft tissue tension that are known to occur in certain groups of patients. This study suggests that deformity can be prevented by the proper selection of a suitable frame and the adjustment of its configuration to meet the loading requirements.

A method of examining the magnitude and origin of "soft" and "hard" tissue forces resisting limb lengthening

Complications arising from limb-lengthening procedures such as muscle contracture, axial malalignment of the bone and traction injuries to the nerves and vessels, are often severe. Often complications arise from the build-up of forces in the biological tissues which are resisting lengthening. Little is known about the origin and magnitude of these forces, although three studies have identified the regenerate (new bone tissue) as the dominant resisting tissue. This study describes the development of a method to examine these forces. It employs load measurement devices in the structural columns of Ilizarov fixators which measure the compressive load on the frame exerted by the biological tissues. The distribution of this load between the columns of the frame, in conjunction with a transverse radiograph of the limb at the regenerate site, is used to examine the origin of the resisting force. Accuracy was determined by a laboratory simulation which found the predicted position of the force to be within 5 mm of the actual position in all four cases tested. Mean error in the total measured force was 2 N (SD, 1 N). A pilot study on a patient undergoing a 60 mm femoral lengthening revealed a peak force of 717 N originating in the Vastus Lateralis or the illiotibial tract. Negligible contribution to resistance was provided by the regenerate, contrary to that found with other studies.

Osteoclasts are capable of particle phagocytosis and bone resorption

Osteoclasts are multinucleated cells specialized for the function of lacunar bone resorption. Although they are known to be capable of phagocytosis of inert particles, it is not known whether this abolishes their ability to respond to hormones or to form resorption lacunae. Human and rat osteoclasts were isolated from giant cell tumours of bone and rat long bones, respectively, and cultured on coverslips and cortical bone slices, both in the presence and in the absence of particles of latex (1 micron diameter) and polymethylmethacrylate (PMMA) (< 50 microns). By light microscopy, it was evident that osteoclasts which had phagocytosed both latex and PMMA particles remained responsive to calcitonin. Osteoclast phagocytosis of particles was also evident on scanning electron microscopy, where it could also be seen that these cells were associated with the formation of resorption lacunae. These findings underline the fact that the osteoclast is a true member of the mononuclear phagocyte system and that phagocytosis does not abrogate either its hormonal response to calcitonin or its highly specialized function of bone resorption. That osteoclasts which have phagocytosed biomaterial particles such as PMMA are still able to carry out lacunar bone resorption is of interest in clinical conditions such as aseptic loosening, where a heavy foreign body particle load is often associated with extensive bone resorption.

The forces which develop in the tissues during leg lengthening. A clinical study

Axial forces were measured during limb lengthening in a series of ten patients with varying pathologies in order to assess the mechanical characteristics of the distracted tissues and the levels of axial force to which soft tissues are subjected during leg lengthening. The pattern of force was found to vary according to the underlying pathology. For post-traumatic shortening in adults both the peak and the resting forces rose steadily during lengthening reaching maximum forces of the order of 300 N. Patients with congenitally short limbs developed very high peak forces (in some cases over 1000 N) and also showed large amounts of force relaxation (typically 400 to 500 N). When very high levels of force were recorded, there was a higher complication rate. In particular, there was a high instance of angular deformity. This occurred because the loads encountered resulted in failure of some of the external fixation frames.

Manual assessment of fracture stiffness

A fracture stiffness of 15 Nm/degree measured biomechanically has been proposed as a reliable indicator of early fracture union. This study used a fracture model to examine the ability of orthopaedic surgeons to assess the stiffness of a fracture manually. Twenty orthopaedic surgeons were tested along with 20 controls. They each estimated the stiffness of seven rods representing mid-shaft diaphyseal fractures at different stages of healing, and were asked whether the stiffness suggested that union had progressed to the stage where the stabilizing device could be removed. Surgeons were unable to estimate the fracture stiffness accurately, and greatly overestimated rod stiffness particularly for the lower values. This meant that on 83 per cent of occasions when the stiffness was less than 15 Nm/degree, the surgeons considered the fracture models united to a sufficient degree to prescribe removal of the fixator. The results suggest that clinical assessment of fracture stiffness alone may put 83 per cent of patients at risk of refracture or malunion. Manual testing of the mechanical stability of a fracture appears not to be reliable.

Accidents with horses: what has changed in 20 years?

Horse riding is a dangerous pastime with more accidents occurring per hour than during motor-cycling. Since a prospective survey of horse-related injuries conducted at a major centre in 1971-1972, equestrian groups and the medical profession have encouraged improvements in training and protective riding wear. By conducting a similar study at the same centre 20 years later we hoped to assess the effects of these measures on the pattern of injuries resulting from contact with horses. Patient and injury details were recorded prospectively for all those presenting to the Accident Service at Oxford during the whole of 1991. Total admissions fell by 46 per cent on average. Most of the decrease was due to a near fivefold fall in those admitted with head injuries (P < 0.001). A reduction in the severity of such injuries was associated with an increased use of riding helmets. However, the most commonly injured group remained amateur young female riders suggesting the need for increasing awareness and training of this group. In seven cases, severe digital injuries were caused by the habit of entwining reins around the fingers. This practice should be discouraged. Up to 12 per cent of all injuries might have been prevented if adequate footwear had been worn.

How to minimize failures of fixation of unstable intertrochanteric fractures

Sliding hip screws have improved the treatment of unstable intertrochanteric hip fractures and their success, compared with fixed devices, is in large part due to the sharing of load between the implant and the fracture fragments. In a prospective study of 100 patients with such fractures, five factors concerned with the fracture and its fixation were studied and odds ratios calculated of their relative importance in prediction of failure. The most important factor affecting the load borne by the fracture fragments was the amount of slide available within the device, and that affecting the load carried by the device was the position of the screw in the femoral head. For fractures fixed with a device allowing less than 10 mm of slide, and those with superior screw position, the risk of failure was increased by factors of 3.2 and 5.9, respectively. Anatomical reduction alone, rather than osteotomy, together with sliding hip screw fixation, has been recommended for these fractures in three prospective randomized trials. It is calculated here that to allow sufficient slide when employing this technique, it is essential to use a short barrel device when using dynamic screws of 85 mm or less. This has not been demonstrated before.

Use of the Russell-Taylor reconstruction nail in femoral shaft fractures

Of 242 patients with injuries treated by locked intramedullary nailing of the femur, 52 (22 percent) were considered suitable for insertion of the reconstruction nail. The Russell-Taylor reconstruction nail was found to be useful in a greater variety of fractures than those for which it was originally designed. In addition to ipsilateral neck and shaft fractures, the Russell-Taylor reconstruction nail proved successful in high-energy comminuted subtrochanteric fractures, elderly subtrochanteric fractures and pathological lesions. In two cases, problems were encountered due to the relative straightness of the nail, but in the remaining patients there were no technical problems. In the 43 elderly patients and those with pathological lesions, seven complications occurred: a number which compares favourably with published reports for extramedullary devices. There were no cases of implant failure and in all patients the device supported the fracture to union or death.

The response of muscle to leg lengthening

We used an experimental rabbit model of leg lengthening to study the morphology and function of muscle after different distraction rates. Lengthening was in twice-daily increments from 0.4 to 4 mm per day. New contractile tissue formed during lengthening, but some damage to the muscle fibres was seen even at rates of less than 1 mm per day; abnormalities increased with larger rates of lengthening. There was proliferation of fibrous tissue between the muscle fibres at distraction rates of over 1 mm per day. Active muscle function showed adaptation when the rate was 1.0 mm per day or less, but muscle compliance was normal only after rates of 0.4 mm per day. Muscle responded more favourably at rates of distraction slower than those shown to lead to the most prolific bone formation. At present the rate of distraction in clinical practice is determined mainly by factors which enhance osteogenesis. Our study suggests that it may be advisable to use a slower rate of elongation in patients with poor muscle compliance associated with the underlying pathology; this will allow better accommodation by the contractile and connective tissues of the muscles.