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Construct failure is a rare complication of tibial cranial closing wedge ostectomy for the management of cranial cruciate ligament disease. Construct failure can present significant challenges for reconstruction. This case report describes three dogs with construct failure which were successfully revised by the repurposing of an inverted femoral supracondylar femoral plate as part of the revision. Data were obtained from the medical records and telephone update. The use of an inverted supracondylar plate in the proximal tibia generally had good outcomes for the management of bone implant failure following cranial closing wedge ostectomy and offers a hitherto undescribed technique using a low-cost and accessible implant for repair., (© 2024 The Author(s). Journal of Small Animal Practice published by John Wiley & Sons Ltd on behalf of British Small Animal Veterinary Association.)

Objective: To establish reference intervals for radial joint orientation angles in the frontal and sagittal planes in small-breed dogs and to compare them to those previously reported for medium- and large-breed dogs., Animals: Antebrachii of 30 skeletally mature, nonchondrodystrophic small-breed dogs were evaluated radiographically., Procedures: Orthogonal radiographs were retrospectively assessed to determine the anatomic medial proximal radial angle, anatomic lateral distal radial angle, anatomic cranial proximal radial angle (aCrPRA), and anatomic caudal distal radial angle (aCdDRA). The frontal plane angle, θ angle, and procurvatum were also calculated. The radial joint orientation angles determined were compared to those previously reported for medium- and large-breed dogs via a 1-sample t test., Results: Mean and SD values for anatomic medial proximal radial angle, anatomic lateral distal radial angle, aCrPRA, and aCdDRA were 80.86 ± 2.86°, 85.60 ± 1.74°, 87.99 ± 2.79°, and 83.08 ± 3.14°, respectively. The mean and SDs for frontal plane angle, θ angle, and procurvatum were 4.75 ± 2.46°, 11.88 ± 1.76°, and 16.79 ± 4.13°, respectively. aCrPRA and aCdDRA were significantly different when compared to previously reported radial joint angles for medium- and large-breed dogs., Clinical Relevance: Reference intervals for small-breed dog radial joint orientation angles were reported. Significant differences were identified for some joint orientation angles when compared to medium- and large-breed dogs. This small-breed reference interval reported can be utilized in planning of radial angular limb deformity corrective surgery, particularly when dogs are bilaterally affected.

Backfround: Treatment options for metacarpal/metatarsal fractures include conservative and surgical management. The aim of this study is to determine whether there is any significant difference in healing and complication rates, between open and closed treatment. Medical records of dogs and cats with metacarpal/metatarsal fractures with complete follow-up were retrospectively reviewed. Patients were allocated in two groups: open or closed stabilization. Minor and major complications were recorded and compared. Fracture healing was classified as good, delayed and non-union, and it was statistically compared., Results: Sixty-three patients (35 dogs and 28 cats) were included. Thirty-one were treated with an open approach and 32 by a closed stabilization. Regarding fracture healing a significantly higher proportion of delayed healing/non-union was found in the closed group (12/32 vs 2/31). Regarding postoperative complications, a significantly higher number of animals in the open group did not develop any complications (12/31 vs 3/32). A significantly higher proportion of minor complications were reported in the closed group (27/32 vs 12/31). However, a higher number of major complications was reported in the open group (7/31 vs 2/32) although this was not statistically significant. Fracture malalignment was significantly more prevalent in patients undergoing closed stabilization (11/32 vs 2/31)., Conclusion: According to the results, better healing, fracture alignment and a lower complication rate are found when fractures are stabilised with an open technique. However, other factors such as configuration of the fracture, soft tissue involvement, patient´s character and client´s situation would also need to be taken into account in the decision of stabilization technique., (© 2022. The Author(s).)

Objective:  The aim of this study was to establish breed-standard mechanical tibial joint reference angles in the frontal plane in Dachshunds., Study Design:  Craniocaudal ( n  = 38) and mediolateral ( n  = 32) radiographs of normal tibiae from Dachshunds were retrospectively reviewed. The mechanical medial proximal, mechanical medial distal, mechanical caudal proximal and mechanical cranial distal tibial angles were measured on three occasions by two separate observers using previously established methodology. Interclass correlation coefficient was used to assess the reliability of radiographic measurements., Results:  The mean and standard deviation for mechanical medial proximal, mechanical medial distal, mechanical caudal proximal and mechanical cranial distal were 93.1 degrees ± 4.2, 97.5 degrees ± 3.9, 75.3 degrees ± 3.7 and 85.0 degrees ± 5.3 respectively. Intra-observer reliability was good to excellent for all measures, while inter-observer reliability was moderate to excellent in the frontal plane and poor to good in the sagittal plane. Dachshund-specific joint reference angles were similar to a range of previously reported non-chondrodystrophic breeds in the frontal plane but differed to most in the sagittal plane., Conclusion:  Dachshund tibial joint reference angles are reported which can be used in surgical planning for correction of bilateral pes varus., Competing Interests: None declared., (Thieme. All rights reserved.)

Objective: To identify whether a theoretical predictable safe corridor is available in cats for placement of trans-iliac pins without the use of fluoroscopy., Methods: Twenty-one cats with straight orthogonal normal pelvic radiographs were included. Two start points were evaluated: a midpoint and a dorsal point. The midpoint was defined as midway between the dorsal lamina of the sacral vertebral canal and the cranial dorsal iliac spine. The dorsal start point was 2 mm ventral to the cranial dorsal iliac spine. The pin was assumed to be driven at 90 degrees to the lateral face of the ilium, and considered surgeon accuracy was ±4 degrees from the perpendicular. The angular range and the distance between the iliac wings from the ventrodorsal radiograph were used to calculate the possible cross-sectional area and pin exit location if driven from one iliac wing to the other. The corridor was then evaluated for repeatability in six randomly selected cats., Results: Vertebral foramina penetration risk was identified in some cats when using a 1.6 and 2 mm-diameter pin using the mid-iliac wing start point. The dorsal start point decreased the available pin placement area but reduced the risk of entering the hazardous zone for all pin sizes up to 2 mm., Conclusion and Relevance: A theoretical defined safe corridor is available for trans-iliac pin placement in cats between 2.0 and 5.5 kg. A 1.2-mm pin is the safest if using the mid-iliac wing start point. A more dorsal start point can accommodate up to a 2.0-mm pin if correctly aligned to the sacrum., (© 2021 The Authors. Australian Veterinary Journal published by John Wiley & Sons Australia, Ltd on behalf of Australian Veterinary Association.)

The objective of this study was to determine whether a novel reverse-transverse cross pin insertion technique could increase the stability of type II external skeletal fixators (ESF) in dogs compared with an alternate, same side cross pin ESF. Reverse-transverse cross pin technique and type II ESFs same side cross pin technique were applied and compared among subjects. Two of 42 ESFs (4.8%) applied with the reverse-transverse cross pin technique and 39 of 47 ESFs (83%) applied with the same side cross pin technique were subjectively unstable at the time of fixator removal (P < 0.001). The same side cross pin ESFs had significantly more pin tract new bone formation than the reverse-transverse ESFs (P = 0.038). In summary, this approach may provide a method of treating a variety of musculoskeletal conditions and soft tissue cases, which reverse-transverse cross pin ESFs are tolerated in dogs for a variety of conditions.

Objective: Chronological age is a powerful epidemiologic risk factor for osteoarthritis (OA), a multifactorial disease that is characterized by articular cartilage (AC) degradation. It is unclear from a molecular perspective how aging interacts with OA to produce this risk to AC integrity. To address this key question, we used in vivo time-course analysis of OA development and murine interstrain variability in natural susceptibility to OA to examine changes in non-OA-prone CBA mice versus OA-prone STR/Ort mice, which develop disease that bears significant histologic resemblance to human OA. Through global transcriptome profiling, we attempted to discover the molecular signature linked with both OA vulnerability and progression., Methods: Affymetrix Mouse Gene 1.0 ST Array profiles were generated from AC samples derived from CBA and STR/Ort mice at 3 different ages, corresponding to the stages prior to, at, and late after the natural onset of OA in the STR/Ort mice., Results: We found that the OA in STR/Ort mice exhibited a molecular phenotype resembling human OA, and we pinpointed a central role of NF-κB signaling and the emergence of an immune-related signature in OA cartilage over time. We discovered that, strikingly, young healthy AC has a highly expressed skeletal muscle gene expression program, which is switched off during maturation, but is intriguingly retained in AC during OA development in STR/Ort mice., Conclusion: This study is the first to show that AC chondrocytes share a high-abundance gene-expression program with skeletal muscle. We show that failure to switch this program off, as well as the restoration of this program, is associated with inappropriate expression of NF-κB signaling pathways, skeletal muscle-related genes, and induction and/or progression of OA., (Copyright © 2012 by the American College of Rheumatology.)

Workplace learning (WPL) is seen as an essential component of clinical veterinary education by the veterinary profession. This study sought to understand this type of learning experience more deeply. This was done utilising observations of students on intramural rotations (IMR) and interviews with students and clinical staff. WPL was seen as an opportunity for students to apply knowledge and develop clinical and professional skills in what is generally regarded as a safe, authentic environment. Clinical staff had clear ideas of what they expected from students in terms of interest, engagement, professionalism, and active participation, where this was appropriate. In contrast, students often did not know what to expect and sometimes felt under-prepared when entering the workplace, particularly in a new species area. With the support of staff acting as mentors, students learned to identify gaps in their knowledge and skills, which could then be addressed during specific IMR work placements. Findings such as these illustrate both the complexities of WPL and the diversity of different workplace settings encountered by the students.

Veterinary schools in the UK are required by the Royal College of Veterinary Surgeons to ensure that their students have attained essential 'Day one' skills (DOS) by graduation. To aid students' understanding of how they could satisfy this requirement, the Royal Veterinary College produced a DOS guide, which was distributed in the 2007 to 2008 academic year to students in the third and fourth years of the professional veterinary course. The same students were surveyed towards the end of the 2008 to 2009 session about the guide, when they were in the fourth and final years, to rate its usefulness and to indicate their perceived levels of competence, both currently and expected at graduation. Focus group discussions were subsequently conducted to explore the findings of the survey. Responses from 88 fourth-year (39 per cent) and 174 (87 per cent) final-year students revealed that while almost all respondents were aware of the DOS guide, their use of it was low. Final-year students rated themselves as being more competent than fourth-year students, but were less optimistic about their expected level of competence regarding several invasive procedures, which some students considered to be 'unattainable' by graduation, despite the apparent value of extramural studies and intramural rotations in providing opportunities for learning.

Canine osteoarthritis (OA) commonly occurs in association with articular diseases, such as hip dysplasia (HD), elbow dysplasia (ED), or cranial cruciate ligament rupture (CCLR). We hypothesized that a common genomic risk for the development of canine joint disease and canine OA would be identified by evaluating the allele frequencies of candidate gene single nucleotide polymorphisms (SNPs) in dogs with OA associated with different articular diseases when compared with a general population of breed-matched dogs. DNA was extracted from blood samples obtained from Labrador Retrievers and Golden Retrievers surgically treated for ED, HD, and CCLR and confirmed to have radiographic evidence of OA. One hundred and thirteen SNPs in 20 candidate genes were genotyped. No significant associations were identified for SNPs or haplotypes in the candidate genes for the diseases evaluated. The candidate gene approach for the study of genetic association is unlikely to be successful for complex canine diseases such as OA without prior trait mapping evaluation.

Pandemic 2009 influenza A H1N1 has spread rapidly since its first report in Mexico in March 2009. This is the first influenza pandemic in over 40 years and it atypically affects previously healthy young adults, with higher rates of morbidity and mortality. The medical literature has been inundated with reports of H1N1 infection, the majority found in critical care and internal medicine journals with a relative paucity in the surgical literature. Despite this, it remains an important entity that can impact greatly on acute surgical emergencies. We present a case of previously healthy 31-year-old male who underwent open appendectomy. His post-operative recovery was complicated by acute respiratory distress syndrome secondary to H1N1 infection. This case report highlights the impact that H1N1 virus can have on acute surgical emergencies and how it can complicate the post-operative course.

Competency at graduation, in a variety of physical and attitudinal skills, is an essential outcome measure for courses training veterinary surgeons. The approach adopted by the Royal Veterinary College, London, to identify and define the expected skill competencies required of our veterinary undergraduates by the time of graduation is described. In addition, we demonstrate how this skill set was built into a framework that was aligned with other student learning objectives. This two-year project resulted in the publication of a day-one skills handbook, which was introduced to the college staff and students in 2007.

The medical records of 155 dogs with patellar luxation (PL) from three different centres were analysed. Each case was classified according to the nature of its luxation and any concurrent orthopaedic conditions plus the age at diagnosis were also noted. Measurements relating to angle of inclination (AOI) of the femoral neck and medio-lateral bowing of the femur and tibia at the stifle were also recorded. The femoral and tibial data were compared to dogs with another orthopaedic condition in a case-control assessment. Labradors were most commonly affected (21%). Most luxations were medial (92%) and 54% of affected dogs were female. The mean AOI of the hip was 148.95 degrees . There was a statistically significant difference between the stifles of dogs with PL compared to a control population. This study concluded that PL in large breeds is increasing. Lateral luxation was uncommon and was not associated exclusively with large breeds. Females were more likely to have PL than males and being female was a risk factor associated with coxa valga. There are significant differences in medio-lateral stifle conformation between dogs with PL and control dogs.

The purpose of this paper is to introduce a new educational development and research program; to describe the vision which created the LIVE Centre for Excellence in Teaching and Learning (CETL) at the Royal Veterinary College, University of London, UK; and to give details of the educational developments and research that have been pursued in LIVE since 2005. LIVE's purpose, to act as an "incubator" to help support all those interested in veterinary teaching and learning, and associated research, is discussed. The paper describes how the aims of the initial funding bid are being realized through the development of a multi-layered strategy. The discussion concludes by suggesting that new faculty models such as the US Academy Network for Medical Educators or veterinary hubs such as LIVE could act as catalysts for the development of a new breed of clinical teachers and educational researchers, empowered by innovative teaching and learning methods relevant to both medical and veterinary education.

The objective of this retrospective study was to report the clinical use, advantages, disadvantages, complications and outcome of an epoxy putty external skeletal fixator (EPESF) used for the repair of fractures of all four main metatarsal or metacarpal bones in a single limb in 11 dogs and 11 cats. The aim of this technique was to achieve satisfactory alignment of the proximal and distal joints and the digits, rather than anatomical reconstruction of the metacarpal/metatarsal bones themselves. All of the cases achieved fracture union and they all recovered fully without any residual lameness.

Background and Objective: We surveyed delegates at the Group of Anaesthetists in Training (UK) meeting to investigate evidence of a training-gap (number of fibreoptic intubations believed to bestow competence vs. number actually performed)., Methods: Questionnaires were distributed to and collected from delegates in person. Questions covered six areas, including experience of fibreoptic intubation and cricothyrotomy, fibreoptic intubation as a specialist skill and ethical issues., Results: We received 221 replies (76%). All trainees believed competence to be achievable with 10 intubations (interquartile range (IQR) 10-20); the median number performed was 2 (IQR 0-4). This was statistically significant for the groups' senior house officers, 1st and 2nd year registrars and 3rd and 4th year registrars; P < 0.0001. Many final year trainees (12/20, 60%) also failed to achieve their competency target. Few trainees had seen or performed any cricothyrotomies (medians 0, IQRs 0-1 and 0-0). Most (195/208, 94%) believed that fibreoptic intubation was a core skill and 199/212 (94%) believed that all should be competent by completion of training. Ten percent (n = 208) felt it unethical to perform an awake training intubation with full consent and 10% believed it acceptable without explanation. Most (82.7%) would fibreoptically intubate an asleep patient (requiring intubation) without consent., Conclusion: Trainees reported a gap between their perception of competence and achievement in awake fibreoptic intubation. Simple and complex simulations and structured training programmes may help. Anaesthetists must address the ethics of clinical training in advanced airway management.

Ten labrador retrievers and their owners undertook a programme to determine the effect of passive stretching on the dogs' osteoarthritic joints, which had a restricted range of motion. The range of motion of the joints was measured before and after the 21-day study, during which the owners performed 10 passive stretches for a hold of 10 seconds twice daily. Goniometric measurements showed that the passive stretching had significantly increased the range of motion of the joints.

Objectives: To compare ulnar trochlear notch bone radiopacity in Labrador retrievers with and without fragmented medial coronoid process using quantitative analysis of film density on digitised radiographs., Methods: Mediolateral view elbow radiographs from Labrador retrievers (n=34) aged between six and 18 months were obtained and digitised. Images from dogs with an arthroscopic diagnosis of fragmentation of the medial coronoid process (n=17) were compared with that of a control population (n=17), and this data subject to statistical analysis., Results: A statistically significant relationship between the presence of increased trochlear notch radiopacity and a fragmented medial coronoid process was identified. Fractional analysis of this area shows the region of greatest difference in radiopacity between normal and fragmented medial coronoid process cohorts to be in the trochlear region of the medial coronoid process of the ulna. A decrease in radiopacity values in the dysplastic group versus the normal cohort was observed for the region of the proximo-caudal ulnar trochlear notch., Clinical Significance: An increase in ulnar trochlear notch radiopacity is a finding associated with fragmentation of the medial coronoid process in Labrador retrievers.

This study was conducted to compare the anatomical tibial plateau angle (TPA) with that measured by observers from a lateral radiograph of the limb, the hypothesis being that there would not be any statistically significant differences between the observer measured TPA and the true anatomical TPA. Twelve pelvic limbs from skeletally mature greyhound cadavers, without any clinical or radiographic evidence of stifle pathology, were used in this study. The radiographs were taken of each limb in a lateral position with the primary beam centered over the tibial eminences and collimated to include the stifle and tarso-crural joints. For subsequent radiographs, Kirschner wires were inserted to enable identification of the tibial plateau. The TPA was then measured, by three observers, from the plain radiographs and by one observer from the marked radiographs. The mean observer TPA was 24.4 degrees (range 17-30 degrees) and the mean anatomical TPA was 23.8 degrees (range 15-31 degrees). The mean and median discrepancy between the anatomical TPA and the observer TPA was negative and very small (- 0.64 degrees and 0 degrees). The magnitude of the discrepancy between individual measurements made by the observers tended to overestimate small angles and underestimate the large ones, and this trend is statistically significant. These results suggest that the measurements made by observers accurately represent the anatomical slope of the tibial plateau. Therefore, observer TPA is suitable for the planning and assessment of TPLO procedures. However, as the anatomical TPA moves away from a median angle (23.25 degrees) the magnitude of error in the measurement increases.

Children requiring long-term mechanical ventilation or with abnormalities of the upper airway may need a tracheostomy for prolonged periods of time. For these children, insertion of a larger tracheostomy tube may be required to match somatic growth. We describe a new method of enlarging the tracheal stoma in children, based on the existing technique of percutaneous dilational tracheostomy.

Six medium to large breed dogs with osteoarthritis were treated with 2 mg/kg of racemic carprofen, mixed with their morning feed, daily for 28 days. The treatment significantly (P < 0.01) reduced their mean lameness score, measured on a visual analogue scale, and there was a trend (P = 0.11) for the peak vertical forces exerted on a forceplate to be increased in the most severely affected limb. The plasma concentration-time relationships of the S(+) and R(-) enantiomers were studied for 24 hours after the first dose and after seven days and 28 days. There were no significant differences between the mean pharmacokinetic parameters measured on the three occasions, suggesting that carprofen was not accumulated and that tolerance to the drug did not develop. Although the pharmacokinetic parameters of the S(+) and R(-) enantiomers were generally very similar, there were wide variations both between and within dogs.

In a retrospective study, 11 radial carpal bone (RCB) fractures in nine dogs were studied. Chronic lameness was reported in all dogs. Reduced range of motion and soft-tissue swelling of the carpal joints were clinical signs seen most frequently. Three common fracture patterns were identified: oblique fracture with a large medial fragment, sagittal fracture with a small medial fragment, and comminuted fracture. Radial carpal bone sclerosis and carpal osteoarthritis were identified in all dogs. Pancarpal arthrodesis was used to manage 55% of the RCB fractures in this report. Although RCB fracture is not associated with obvious trauma, the fracture mechanism is unknown.

Three cases of haemanglosarcoma in the scapula of the dog are reported. Two cases were euthanased soon after diagnosis, due to the presence of metastases, while the third was treated surgically and recovered well. However, seven months after surgery, this dog was re-presented with a cervical spinal problem which was presumed to be a metastatic lesion.

The bisphosphonate drug alendronate was used to suppress bone remodelling and tumour osteolysis as a palliative treatment for two dogs with osteosarcoma, one of the tibia and one of the maxilla. A spiral fracture associated with the tibial tumour healed after it was stabilised with an external skeletal fixator. Both dogs remained comfortable and survived for 12 and 10 months respectively after diagnosis, despite the fact that neither primary tumour was resected.

A seven-year-old male weimaraner developed an acute-onset non-weightbearing pelvic limb lameness without a history of significant trauma. Radiographs demonstrated an oblique fracture of the femur associated with a lytic bone lesion, while cytology and histopathology of the lesion were consistent with osteomyelitis. A pure growth of Streptococcus intermedius was obtained from culture of affected tissue samples. The fracture healed without complication after rigid internal fixation and antibiotic therapy.

Methicillin-resistant Staphylococcus aureus infection was identified in 11 dogs. The infection was associated with surgical treatment especially orthopaedic surgery. Infection after traumatic wounding, and recurrent pyoderma was also seen. Oral antibiotic treatment improved or resolved the infection in nine of the 11 dogs, although the methicillin-resistant isolates were susceptible to relatively few antibiotics.

A study was undertaken to compare the efficacy of two surgical techniques for the treatment of caudal cervical spondylomyelopathy (CCSM): ventral decompression (slot) and vertebral distraction and stabilisation with a screw and washer (screw/washer). Twenty-eight dobermanns managed surgically for disc-associated CCSM during a four-year period were studied retrospectively. The maximum postoperative period was 40 months. Cases were excluded if a minimum follow-up of 24 months after surgery could not be made. A 'slot' took a longer time to perform and had a higher rate of immediate postoperative deterioration. Duration of hospital stay was similar for both procedures. At six months after surgery the two techniques were comparable; 12/14 (screw/washer) and 13/14 (slot) patients were deemed to have a satisfactory outcome. Recurrence of cervical spinal cord disease was higher in the screw/washer dogs. At one year after surgery the recurrence rate was zero (slot) and 5/14 (screw/washer), respectively. At two years after surgery 4/14 of the slot dogs had deteriorated compared to 7/14 of the screw/washer dogs. Where investigated, the cause of deterioration was either a domino disc lesion or vertebral endplate collapse and dorsal displacement of the screw and washer.

This paper describes an investigation to evaluate the properties and uses of the different casting materials available for small animals. After a consideration of the properties that make an 'ideal cast', clinically relevant tests were performed on tubular casts of the various products. No single product demonstrated consistent superiority by all the criteria. All the products tested can be useful in a variety of situations, and suggestions for their uses are set out.

A nine-week-old labrador was presented with a deformed left forelimb causing obvious lameness. Radiographs suggested that the dog had suffered a fracture involving the radius and ulna which had healed resulting in a synostosis. There was a concurrent radial physeal injury. The dog was treated initially by osteotomy of the radius and ulna stabilised using a static external skeletal fixator. At a subsequent surgery lengthening of the limb was achieved by using an Ilizarov apparatus. Worsening carpal hyperflexion was managed by bandaging in forced extension. A successful outcome was achieved with a final result of a 24 per cent discrepancy in length between the two radii at 17 months of age. An increase in length of the ipsilateral humerus was seen in association with the shortened forelimb.

The tibiae and fibulae of 14-week-old rats were subjected to a single 5 minutes period of cyclic longitudinal loading at 1 Hz. The activity of the enzymes glucose 6-phosphate dehydrogenase (G6PD) and alkaline phosphatase (ALP) in osteocytes and periosteal osteoblasts was measured immediately and 24 h after loading. In osteocytes G6PD activity was increased immediately after loading but returned to control values 24 h later. There was no detectable ALP activity in these cells regardless of loading history. In periosteal osteoblasts G6PD activity was raised immediately after loading and remained higher than controls 24 h later. ALP activity in periosteal cells was unaffected immediately after loading but 24 h later was substantially increased. These findings are consistent with osteocytes and periosteal cells both being immediately responsive to periods of intermittent loading in their adjacent matrices. In both cell types an early feature of this response is an increase in G6PD activity. In osteocytes this response is short-lived, suggesting that it is an early biochemical change associated with strain perception that does not progress to matrix synthesis. The increase in G6PD activity with unaffected ALP levels in periosteal cells immediately after loading is consistent with a similar response. In these cells the increase in G6PD accompanied by increased ALP levels 24 h after loading suggests that the loading-related response progresses to new bone formation.

A model was developed for the application of cyclic mechanical loads to 17 day embryonic chick tibiotarsi in culture. A single 20 minute period of intermittent loading at 0.4 Hz, producing physiologic peak strains and strain rates, resulted in two peak strain magnitude-related responses that were previously reported in vivo: (1) a rapid increase in glucose 6-phosphate dehydrogenase activity in osteoblasts and osteocytes and (2) increased RNA synthesis, as shown by increased incorporation of [3H]uridine into extracted RNA. The RNA response was detectable 8 h following loading but was more pronounced by 24 h. Both responses were blocked by indomethacin (10(-6) M). These results demonstrate that embryonic chick bones in organ culture exhibit cellular responses to loading similar to those previously identified in adult canine cancellous bone cultures in vitro and adult avian cortical bone in vivo. These findings are consistent with a sequence of events between loading and new bone formation that includes an immediate strain magnitude-related, prostanoid-dependent increase in activity of the pentose monophosphate shunt in osteoblasts and osteocytes, followed by a similarly strain magnitude-related increase in RNA synthesis over the subsequent 24 h.

The effect of pulsed electromagnetic fields (PEMFs) on bone loss associated with disuse was investigated by applying 1.5 Hz repetitions of 30 ms bursts of asymmetric pulses, varying from +2.5 to -135 mV, to bones deprived of their normal functional loading. The proximal portion of one fibula in each of a group of ovariectomised adult female beagle dogs was isolated from functional loading in vivo by proximal and distal osteotomies. Comparison of these prepared bones with their intact contralateral controls after 12 weeks, showed a 23% reduction in cross-sectional area. In similarly prepared bones exposed to PEMFs for 1 h per day, 5 days per week, this bone loss was substantially and significantly reduced to 9% (p = 0.029). There was no evidence of any new bone formation on the periosteal surface of prepared fibulae in treated or untreated situations. PEMF treatment was not associated with any significant change in number of osteons per mm2 formed within the cortex of the bones, their radial closure rate, or their degree of closure. The modulation in loss of bone area associated with exposure to PEMFs can, therefore, be inferred to be due to a reduction in resorption on the bone surface.

The capacity of bone to organize and reorganize its structure in response to changing mechanical demands is well recognized. However, the mechanism by which the changing mechanical environment is detected, and the means by which this information is translated into a stimulus for structural modification, are not understood. A group of substances suggested to be involved in the initial transduction of strain information are the prostaglandins. In this experiment we used a single period of dynamic loading to stimulate an adaptive osteogenic response in vivo. Loading was performed in the presence and absence of indomethacin. Measurements of the periosteum 5 days after loading showed that the presence of indomethacin at the time of loading reduced the osteogenic response. Though consistent with the hypothesis that prostaglandins are involved in the initial transduction of tissue strain into a biochemical response, this result is not sufficient to demonstrate this conclusively because reduced prostaglandin levels during the 24 hours immediately after the period of loading may affect many other points in the cascade of events between strain transduction and adaptive new bone formation. Furthermore, indomethacin at the relatively high levels we used (40 mg/kg) may have effects other than those on prostaglandin synthesis.

Both ulnas of skeletally mature roosters (Gallus domesticus) were deprived of functional load bearing by proximal and distal submetaphyseal osteotomies. Twenty-four hours later the animals were injected with 1.5 mCi of 3H-uridine and the ulna on one side was subjected to a single period of a cyclical load engendering physiological strain levels at 1 Hz for 6 min. Twenty-four hours after loading the animals were killed. Autoradiographic examination of comparable regions of cortex in sections from the bone's midshafts showed that in the loaded bones, 72 +/- 2.7% of osteocytes were labeled compared with 12 +/- 3.5% in the corresponding areas of their contralateral nonloaded pair (P less than 0.001). The number of grains per labeled osteocyte was also higher in the loaded side (6 +/- 0.5 compared with 4 +/- 0.5, P less than 0.01). There was no obvious correlation between the longitudinal strain distribution during artificial loading and the distribution of labeled osteocytes throughout the bone cross-section. However, previous long-term experiments using a similar loading preparation had consistently shown the site of most periosteal new bone formation to also not be directly related to the local strain magnitude. Perhaps it is significant that the greatest percentage of labeled cells were found in the cortex where the long-term experiments had shown most new bone formation to subsequently occur.

The concept of resorption preceding formation in a coupled response is well established as the normal sequence of remodeling in adult bone. So prevalent is this concept, however, that the idea of the direct activation of osteogenic modeling in normal adult bone is often ignored. This experiment documents the direct transformation of the normal, quiescent, adult periosteum to active bone formation. The osteogenic stimulus was provided by a single short period of dynamic loading. Periosteal activation and the production of new bone within 5 days of loading was unaccompanied by resorption or the presence of osteoclasts. We therefore conclude that an adult resting periosteum can become directly converted to formation as a physiologic response to an appropriate osteogenic stimulus without the need for resorption. To distinguish this process from remodeling we suggest it be called renewed modeling. It is notable that a single short exposure to an "osteogenic" loading regime can influence the full cascade of cellular events between quiescence and active bone formation.