Sesamoid Research Articles

Identification of Heterotopic Mineralization and Adjacent Pathology in the Equine Fetlock Region by Low-Field Magnetic Resonance Imaging, Cone-Beam and Fan-Beam Computed Tomography

Heterotopic mineralization in equine distal limbs has been considered an incidental finding and little is known about its imaging features. The study aimed to identify heterotopic mineralization and adjacent pathology in the fetlock region with cone-beam (CB) computed tomography (CT), fan-beam (FB) CT, and low-field magnetic resonance imaging (MRI). Images from 12 equine cadaver limbs were examined for heterotopic mineralization and adjacent pathology and verified by macro-examination. Retrospective review of the CBCT/MR images from 2 standing horses was also included. CBCT and FBCT identified twelve mineralization's with homogeneous hyperattenuation: oblique-sesamoidean-ligament (5) without macroscopic abnormality; deep-digital-flexor-tendon (1) and suspensory-branch (6) with macroscopic abnormalities. MRI failed to identify all mineralization's, but detected suspensory branch splitting, and T2 and STIR hyperintensity in 4 suspensory-branches and 3 oblique-sesamoidean-ligaments. Macro-examination found corresponding disruption/splitting and discoloration. All modalities identified 7 ossified fragments showing cortical/trabecular pattern: capsular (1), palmar sagittal ridge (1), proximal phalanx (2) without macroscopic abnormality, and proximal sesamoid bones (3). On MRI, fragments were most identifiable on T1 images. All abaxial avulsions had suspensory-branch splitting on T1 images with T2 and STIR hyperintensity. Macro-examination showed ligament disruption/splitting and discoloration. Suspensory-branch/intersesamoidean ligament mineralization's were identified by CBCT in standing cases; 1 had associated T2 hyperintensity. Both CT systems were generally superior in identifying heterotopic mineralization's than MRI, while MRI provided information on soft tissue pathology related to the lesions, which may be important for management.

Patella cubiti - A Continuing Etiological Mystery

A sesamoid bone in the elbow joint is a rare anatomical variation described as a Patella cubiti. Although this variation has been known for centuries its exact etiology is still unclear. Congenital, developmental, and traumatic hypotheses have been proposed. It seldom causes clinical manifestations than elbow stiffness or hypomobility. Herein, we present a case of a 31-year-old patient admitted to our department with complaints of swelling and erythema in the right elbow. An X-ray image revealed a triangular accessory bone with rounded edges, which was diagnosed as a Patella cubiti in combination with olecranon bursitis. Knowledge of this rare elbow abnormality is paramount for orthopedic surgeons and roentgenologists in their daily medical practice.

Training drives turnover rates in racehorse proximal sesamoid bones

Focal bone lesions are often found prior to clinically relevant stress-fractures. Lesions are characterized by low bone volume fraction, low mineral density, and high levels of microdamage and are hypothesized to develop when bone tissue cannot sufficiently respond to damaging loading. It is difficult to determine how exercise drives the formation of these lesions because bone responds to mechanical loading and repairs damage. In this study, we derive steady-state rate constants for a compartment model of bone turnover using morphometric data from fractured and non-fractured racehorse proximal sesamoid bones (PSBs) and relate rate constants to racing-speed exercise data. Fractured PSBs had a subchondral focus of bone turnover and microdamage typical of lesions that develop prior to fracture. We determined steady-state model rate constants at the lesion site and an internal region without microdamage using bone volume fraction, tissue mineral density, and microdamage area fraction measurements. The derived undamaged bone resorption rate, damage formation rate, and osteoid formation rate had significant robust regression relationships to exercise intensity (rate) variables, layup (time out of exercise), and exercise 2–10 months before death. However, the direction of these relationships varied between the damaged (lesion) and non-damaged regions, reflecting that the biological response to damaging-loading differs from the response to non-damaging loading.

Age estimation of puppies based on the radiographically assessed development of ossification centres in the carpal and metacarpal regions.

The need for proper age determination in puppies has increased enormously due to the growing illegal trade in puppies that are too young to be removed from the litter or too young to have been properly vaccinated against rabies. Dorsopalmar and mediolateral radiographs of the (meta)carpal region, either taken from puppy cadavers or from the Faculty's patient database, were studied in a cross-sectional study of 252 puppies of various sizes, aged 6-212 days. The appearance and development of ossification centres as a function of age in five regions of interest in the (meta)carpal region were scored using a two- to six-step scoring system based on shape and delineation. A positive correlation with age was found for all investigated regions. Intra- and interrater agreement between two observers was excellent, except for the distal epiphyses of the metacarpal bones. Postnatal ossification started after the second week of life with the carpal bones, closely followed by the radial trochlea. All ossification centres were present in all puppies from 84 days, except for the sesamoid bone in the tendon of the long abductor muscle of the first digit. Timing of appearance differed significantly between different sized breeds. There were no significant differences between the sexes. Age distribution was not balanced for all breed size classes. The radiographic timing of the appearance and development of ossification centres in the carpal region is a promising method for age estimation in puppies.

Osteology and radiology of the thoracic limb of nine-banded armadillo, dasypus novemcinctus linnaeus, 1758

In Brazil, injured nine-banded armadillos are frequently taken to wildlife rehabilitation centers due to direct or indirect anthropic interactions, however, database about osseous structures useful to radiographic interpretation are limited. This work provides bones description from thoracic limb of Dasypus novemcinctus as well as references to radiographic interpretation and the best positioning to perform the radiographies. Twelve deceased specimens seized by IBAMA (Brazilian Institute of the Environment and Renewable Natural Resources) were used to check osteology and radiographic anatomy. Radiographic images were taken in practical routine plans of small animals and were followed by limbs dissection and bones preparations. The bone structure of the thoracic limb was similar to those of other species of armadillos. The scapula presented a prominent caudal angle, as well as a thick acromion with a wide hamate process; the humerus is short, spiraled with a prominent deltoid tuberosity and a wide lateral epicondylar crest; the radius and ulna did not present any fusion between then, allowing a wide rotation movement of the forearm. In general, the bone components of the hand maintained a short and robust shape, digits with developed distal phalange followed by long claws. Several sesamoid bones were found in the metacarpal and interphalangical joints. Clear visualization of bone characteristics was possible using proposed positioning to take the radiographies.

Chondroblastoma: clinicopathological analyses of 307 cases from a single institution in China and the diagnostic value of the H3F3 K36M mutant antibody

AimsTo elucidate the clinicopathological features and the diagnostic value of mutation specific antibody H3F3 K36M of chondroblastoma (CB) in China.MethodsClinicopathological profiles were retrieved, and immunohistochemistry was performed on 185 CB...

CAN THE PERCUTANEOUS CHEVRON AND AKIN (PECA) TECHNIQUE CORRECT THE PRONATION OF THE FIRST METATARSAL IN HALLUX VALGUS?

Pronation of the first metatarsal in hallux valgus has recently been discussed among foot and ankle surgeons. This study aimed to evaluate the potential radiographic correction of moderate and severe hallux valgus using the percutaneous Chevron and Akin (PECA) technique. We evaluated 45 feet in 38 patients (mean age 65.3 years old [36 - 83]; 4 men; 34 women; 7 bilateral) who underwent surgical correction using the PECA technique. The radiographic images evaluated were anteroposterior radiographs obtained pre- and postoperatively at least 6 months after surgery, including the metatarsophalangeal angle, the intermetatarsal angle, pronation of the first metatarsal, displacement of the distal fragment, medial sesamoid position and bone union. All parameters evaluated showed significant postoperative improvement, including correction of pronation of the first metatarsal (p < .05) and position of the sesamoid (p < .05). There was a union of osteotomies in all feet. No complications were observed, such as screw loosening or necrosis of the first metatarsal head. The PECA technique can correct pronation of the first metatarsal in moderate and severe hallux valgus, and other deformity-associated parameters. Level of Evidence IV; Case Series.

The assessment and management of sesamoiditis: a focus group study of podiatrists in Aotearoa New Zealand

BackgroundSesamoiditis is a common inflammatory condition affecting the sesamoid bones at the plantar aspect of the first metatarsophalangeal joint (1MTPJ). However, there are currently no recommendations or clinical guidelines to support podiatrists in their assessment or management of sesamoiditis. The aim of this study was to explore the views of podiatrists in Aotearoa New Zealand on their approaches to the assessment and management of patients with sesamoiditis.MethodsThis qualitative study included focus group discussions with registered podiatrists. Focus groups took place online via Zoom and were guided by a detailed focus group question schedule. The questions were designed to encourage discussion around assessment approaches used in the diagnosis of sesamoiditis and the treatment tools used to manage patients with sesamoiditis. Focus groups were audio-recorded and transcribed verbatim. Reflexive thematic analysis was used to analyse the data.ResultsA total of 12 registered podiatrists participated in one of three focus groups. Four themes were constructed relating to the assessment of sesamoiditis: (1) obtaining a patient history; (2) recreating patient symptoms; (3) determining contributing biomechanical factors; and (4) ruling out differential diagnoses. Seven themes were constructed relating to the management of sesamoiditis: (1) consideration of patient factors; (2) patient education; (3) cushioning of the sesamoids to allow more comfortable weightbearing of the 1MTPJ; (4) pressure redistribution and offloading of the sesamoids; (5) immobilisation of the 1MTPJ and sesamoids; (6) facilitating efficient sagittal plane motion during gait; (7) referring to other health professionals to find different ways to treat or manage patient symptoms.ConclusionPodiatrists in Aotearoa New Zealand demonstrate an analytical approach in the assessment and management of patients with sesamoiditis based on their clinical experience and knowledge of lower limb anatomy. A range of assessment and management techniques are selected based on the practitioners personal preferences, as well as the patient’s social factors, symptomology, and lower limb biomechanics.

The Morphometric Analysis of Adult Dry Patellae: A Cross-sectional Study

Introduction: The patella is the largest sesamoid bone in the body, which develops within the tendon of the quadriceps femoris muscle. It is a flat, distally tapered, and proximally curved bone. The morphometric study of the patella is important for orthopaedic surgeries. Aim: To conduct a morphometric analysis of the adult dry patella. Materials and Methods: A cross-sectional observational study was conducted on 50 dry human patellae from both the right and left sides of unknown gender. These specimens were obtained from the “Bone Library” of the Department of Anatomy, TN Medical College, and Nair Hospital, Mumbai, Maharashtra, India, during the period from December 2022 to February 2023. Patellar length, width, thickness, as well as the width of the articular facet, were measured using an electronic digital vernier caliper. Mean, standard deviations, and p-value were calculated using the Statistical Package for Social Sciences (SPSS) version 26.0. Patellar parameters between the right and left sides were compared, and an unpaired student's t-test was applied. Results: The mean height, width, and thickness of the right patellae were 42.08±3.44 mm, 45.20±4.35 mm, and 18.85±2.16 mm, respectively, while those of the left patellae were 42.68±3.52 mm, 45.00±2.57 mm, and 19.56±1.62 mm, respectively. The mean width of the medial and lateral articular facets of the right patellae were 18.65±2.65 mm and 23.20±2.20 mm, respectively, while those of the left patellae were 19.10±2.25 mm and 22.61±1.69 mm, respectively. Conclusion: The present study evaluates different dimensions such as length, width, thickness, and the articular facet of the patella. These findings will be helpful in designing knee implants and during reconstructive surgeries related to the knee.

The Relationship Between Ossification in Metacarpophalangeal Sesamoids of the Thumb and the Period of Puberty: A Radiographic Study.

The current study aimed to determine the onset of sesamoid bones (Sbs) ossification at the thumb metacarpophalangeal (MCP) joint of the hand and its relationship with puberty. This retrospective radiographic study included patients aged 5-17 years. The presence of Sbs was investigated separately for each age group. Patients were classified based on their age, gender, and the presence of radial and ulnar sesamoids. A total of 1,020 radiographs from 939 patients were analyzed. Sbs began to ossify in girls at the age of 8 years and in boys at the age of 9 years. The ulnar-radial sesamoids were present in all individuals in the same age group at the age of 13-14 years in girls and 15 years in boys. The age at which 50% of the individuals in the same age group had a sesamoid was 10.4 years in girls and 11.9 years in boys on the radial side, 9.5 years in girls, and 11.5 years in boys on the ulnar side. In all individuals, the time between the onset of sesamoids of the MCP joint and development corresponds to the physiological period of puberty. However, the age at which puberty begins coincides with the time when Sbs begin to ossify in 50% of both sexes in the same age group.

Traumatic hallux sesamoid fracture: a case report

The authors describe an extremely rare case of traumatic fracture of both hallux sesamoid bones, which was treated non-surgically, and the indications, contraindications, and unfavorable outcomes analyzed. Level of Evidence V; Therapeutic Studies; Expert Opinion.

A Cadaveric Comparison of the Kinematic and Anatomical Axes and Arthrokinematics of the Metatarsosesamoidal and First Metatarsophalangeal Joints.

Presently, developments in weightbearing computed tomography and biplanar fluoroscopy technologies offer exciting avenues for investigating normative and pathologic foot function with increasing precision. Still, data quantifying sesamoid bone and proximal phalange motion are currently sparse. To express joint kinematics and compare various clinical cohorts, future studies of first ray motion will necessitate robust coordinate frames that respect the variations in underlying anatomy while also aligning closely with the functional, physiological axes of motion. These activity-dependent functional axes may be represented by a mean helical axis of the joint motion. Our cadaveric study quantified joint kinematics from weightbearing computed tomography scans during simulated toe lift and heel rise tasks. We compared the spatial orientations of the mean finite helical axes of the metatarsosesamoidal and metatarsophalangeal joints to the primary joint axis of two relevant methods for defining metatarsal coordinate frames: inertial axes and fitting of geometric primitives. The resultant kinematics exhibited less crosstalk when using a metatarsal coordinate system based on fitting cylindrical primitives to the bony anatomy compared to using principal component axes. Respective metatarsophalangeal and metatarsosesamoidal arthrokinematic contact paths and instantaneous centers of rotation were similar between activities and agree well with currently published data. This study outlines a methodology for quantitatively assessing the efficacy and utility of various anatomical joint coordinate system definitions. Improvements in our ability to characterize the shape and motion of foot bones in the context of functional tasks will elucidate their biomechanical roles and aid clinicians in refining treatment strategies.

The anatomical variations of the lateral sesamoid bones of the foot: a retrospective radiographic analysis.

Os peroneum and os vesalianum are sesamoid bones that could be found within fibularis longus and brevis tendons, respectively. They are rarely a cause of lateral foot pain and are often identified as incidental radiographic findings. However, in the context of trauma, these sesamoids may be radiographically misinterpreted as fractures. This study aimed to evaluate the prevalence and normal morphological variants of os peroneum and os vesalianum. Standard oblique lateral and/or anteroposterior radiographic views of 624 feet of adolescent and adult patients were retrospectively reviewed to determine the prevalence and anatomical variations of the os peroneum and os vesalianum in relation to age and gender using plain radiography. Os peroneum was found in 22% and os vesalianum was found in 1.6%. Age was found to significantly correlate with the presence of os peroneum with the highest prevalence (30%) detected in the elderly group. Among 137 feet with os peroneum, 54.0% were between 4 and 8 mm, 67.2% were close to the tubercle of cuboid, 32.8% were located at the level of calcaneocuboid joint, 81.8% were solitary, and 18.2% were bi-/multipartite. Among 10 feet with os vesalianum, type I was identified in 40% and type II in 60%. Different anatomical variants of the lateral sesamoid bones of the foot have been described in this study. A thorough knowledge of normal anatomical variants is essential for proper diagnosis and management and can enhance our diagnostic skills in detecting these sesamoids.

A MORPHOMETRIC STUDY OF PATELLA IN LUCKNOW REGION

Background: Patella is the largest sesamoid bone which develops in the tendon of Quadriceps femoris muscle and protects the front of knee joint. It has gained anatomical, clinical &amp; forensic significance due to its vital role in patellofemoral mechanics and its property of resistance to post mortem changes. Aims and Objectives: Our study aims to measure the various dimensions of left and right human patella which can be useful for the manufacture of patellar prosthesis, better suited to Indian population, in contrast to already available prosthesis which are mostly based on the western anthropometric measurements. Methods: The study involves 100 dry human patellae, 50 each from left and right sides. Total patellar height, maximum height of articular surface, maximum width, maximum thickness, shape, width of medial and lateral articular facets of patella were measured using digital Vernier calipers. Mean and standard deviation were calculated for each parameter for left and right sides and the data was analyzed using SPSS. Results: The mean of patellar width on left side came out to be 41.65± 2.78, while for right side, the mean of patellar width was observed to be 42.83± 3.02. A statistically significant difference was observed in patellar width of left and right sides (p= 0.044). Conclusion: Anthropometric study of patella in India can thus be helpful in designing femoropatellar prosthesis for our population leading to better post-operative outcome.

Numeric and morphological studies of the African lion (Panthera leo leo) pectoral limb

BackgroundThe Importance of the appendicular skeleton in the conformation, shape and physiology of wild animals especially carnivores for adaptation and survival cannot be overemphasized, as limited and obsolete information on the bones of the forelimb necessitated this study. Matured adult African lions (Male and female) that weighed 173 kg and 112 kg were obtained at different times after post mortem examinations of their carcasses. Bone preparation was achieved via cold water maceration after proper skin and muscle removal to a barest minimum.ResultsThe acromion process of the scapula consisted of a ventral hamate and caudal suprahamate processes. The Clavicle was absent in this species. The musculospiral groove of the humerus was more or less absent while its supracondyloid foramen and crest were positioned above the medial condyle and lateral condyle respectively. The radio-ulna presented a twisted appearance with the radius slightly curved thereby creating an extensive interosseous space that spanned its entire length. The seven (7) carpal bones were uniquely arranged in two rows while the 5 metacarpals anchored 5 digits with 3 phalanges except the first with 2 phalanges each. Two sesamoid bones were located on the ventral surface of each Metacarpophalangeal joint. None was seen on its dorsal surface. The 3rd phalanx had a unique appearance with a crescent plate projecting from the ventral cavity. The average total number of bones constituting the pectoral limb was 80.ConclusionNumerical information and detailed anatomical features of the pectoral limb bones of the African lion (Panthera leo leo) have added some valuable literature to science. This further serves as a baseline data for future scientific exposition on this species.

Radiomics Modeling of Catastrophic Proximal Sesamoid Bone Fractures in Thoroughbred Racehorses Using μCT.

Proximal sesamoid bone (PSB) fractures are the most common musculoskeletal injury in race-horses. X-ray CT imaging can detect expressed radiological features in horses that experienced catastrophic fractures. Our objective was to assess whether expressed radiomic features in the PSBs of 50 horses can be used to develop machine learning models for predicting PSB fractures. The μCTs of intact contralateral PSBs from 50 horses, 30 of which suffered catastrophic fractures, and 20 controls were studied. From the 129 intact μCT images of PSBs, 102 radiomic features were computed using a variety of voxel resampling dimensions. Decision Trees and Wrapper methods were used to identify the 20 top expressed features, and six machine learning algorithms were developed to model the risk of fracture. The accuracy of all machine learning models ranged from 0.643 to 0.903 with an average of 0.754. On average, Support Vector Machine, Random Forest (RUS Boost), and Log-regression models had higher performance than K-means Nearest Neighbor, Neural Network, and Random Forest (Bagged Trees) models. Model accuracy peaked at 0.5 mm and decreased substantially when the resampling resolution was greater than or equal to 1 mm. We find that, for this in vitro dataset, it is possible to differentiate between unfractured PSBs from case and control horses using μCT images. It may be possible to extend these findings to the assessment of fracture risk in standing horses.

Hit and miss: The accuracy of intra-articular injections of the first metatarsophalangeal joint

Introduction: Therapeutic injections provide a treatment option for patients with joint and periarticular pain, those who are not surgical candidates, whom conservative treatment has failed, or those that are awaiting surgery. Injectable glucocorticoids are one of the most common therapeutic interventions in musculoskeletal healthcare and are widely used in pathologies of the first metatarsophalangeal joint. The aim of this paper is to highlight current concepts around first metatarsophalangeal joint injection injection accuracy. Anatomy: The first metatarsophalangeal joint is a condyloid synovial juncture and consists of the head of the first metatarsal, the base of the proximal phalanx, six muscles, eight ligaments and two sesamoid bones, with associated ligamentous attachments. The joint capsule is shaped like a box. Methods: To achieve the research aim, a scoping review was undertaken with a search strategy that identified evidence via the following sources: Electronic databases, Google scholar, and Reference lists. Results: The search yielded 193 articles, 48 of which appeared of potential relevance. After removing duplicate articles this total was reduced to 37 articles. After scanning the content, 27 were excluded to leave 10 articles. Twenty eight further articles were found through related author research, examination of reference lists and free text searches of Google Scholar. One reference was unobtainable. The final count of papers utilised for review was 37 which produced three themes, one of which was injection accuracy. Injection accuracy: In the long history of injection therapy, infiltrations have often been performed without image guidance, i.e., using palpation guidance, anatomical landmarks and clinical judgement to direct needle entry and advancement. Needle placement may also be confirmed by use of diagnostic imaging. Typical imaging modalities are fluoroscopy or ultrasound, used alone or in combination with contrast media. Discussion: The perceived wisdom is that if an injectate misses its target it is likely to be less effective and lead to false negative reporting of poor treatment outcomes, but the literature is not equivocal. This article discusses the recent literature in the field. Conclusions: The literature suggests that steroid injections are safe and effective for the short-term relief of joint pain. When injecting small synovial joints using palpated-guided methods, clinicians must be alert to the potential for failure of technique from the needle penetrating too far into the articulation and exiting the joint on the contralateral side from the entry point. Use of shorter needles and use of imaging, +/- the use of contrast media, might reduce the number of such failures.

Gross anatomy, computed tomography, magnetic resonance imaging and bone mineral densitometry of the ovine metacarpo/metatarsophalangeal joint.

This study was aimed to provide anatomical atlas of the ovine metacarpo/metatarsophalangeal joints using computed tomography (CT) scan and magnetic resonance imaging (MRI), as well as to investigate bone mineral density (BMD) and morphometric features of this joint. The limbs of twenty adult Sanjabi sheep were examined. Imaging was performed using a 16-slice multi-detector CT scanner and a 1.5 Tesla MRI scanner. The obtained images were correlated with corresponding anatomical sections. BMD was measured by Dual Energy X-ray Absorptiometry (DEXA) method. Also morphometric features included distance between metacarpal and metatarsal heads, width of metacarpal and metatarsal head, length, width and the height of the proximal sesamoid bones were measured. In MRI images, compact bones, ligaments and tendons showed less signal intensity (hypointense). The fatty tissue and bone marrow had more signal intensity (hyperintense), but articular cartilage and synovial fluid showed moderate signal intensity. BMD in the left hind limb was significantly higher than other three limbs (p ≤0.05). The length of proximal sesamoid bones in left forelimb was higher than right forelimb (p ≤ 0.05). The thickness of proximal sesamoid bones in left limbs was higher than those in their counterparts (p ≤ 0.05). The width of the medial head in the forelimbs was significantly greater than the hind limbs (p ≤ 0.05). The present results might be useful in managing the clinical techniques on this joint. Larger volume of the proximal sesamoid bones and wider medial head in the forelimbs compared to the hindlimbs impel this speculation that the centre of gravity is closer to the forelimbs.

Radiographic and computed tomographic evaluation of supinator sesamoid bones in dogs

BackgroundThe present study evaluated the frequency of supinator sesamoid bones (SSB) on radiography and computed tomography (CT). Interobserver agreement was evaluated in the detection of the SSBs in both methods. A correlation between the existence of SSBs and elbow diseases (ED) was assessed. For these purposes, radiographs, and CT scans of 100 dogs were scored by 3 observers.ResultsThe SSB was identified as a round to oval-shaped opacity and measured 0.5–6.56 mm × 0.5–6.2 mm. SSBs were reported in an average of 8,33% of dogs on radiographs and 26% of dogs on CT; a bilateral sesamoid bone was present in 43,52% and 76,92% of these dogs, respectively. Seventy-two percent of the SSBs was identified on CT were not detected on radiographs. The Kappa test showed a substantial agreement (κ = 0.691) and a perfect agreement (κ = 1) between the observers in the detection of SSBs on radiography and on CT scans respectively. Additionally, a weak positive correlation was detected between ED and the existence of SSBs.ConclusionA supinator sesamoid bone can be detected occasionally in the evaluation of the canine elbow joints by routine radiography. CT is superior to radiography for assessing SSBs with a higher interobserver agreement. The correlation of the existence of the SSBs and ED, needs further evaluations to prove a probable pathophysiological connection.

Comparison of skeletal scintigraphy and standing 18 F-NaF positron emission tomography for imaging of the fetlock in 33 Thoroughbred racehorses.

This retrospective, methods comparison study aimed to compare skeletal scintigraphy and 18 F-NaF positron emission tomography (PET) for the detection of abnormalities in the fetlocks of Thoroughbred racehorses. Thirty-three horses (72 limbs) imaged with both scintigraphy and 18 F-NaF PET, for investigation of lameness or poor performance related to the fetlock, were included. Seven observers, including experienced racetrack practitioners, surgery and imaging residents, and a board-certified veterinary radiologist, independently reviewed all data for evidence of increased radiopharmaceutical uptake in 10 different regions of interest. The interobserver agreement was higher for PET (Kappa-weighted (K-w) 0.73 (0.51-0.84)) (median (range)) than for scintigraphy (0.61 (0.40-0.77)) (P<0.0001). When scintigraphy and PET were compared, the agreement was fair (K-w 0.29). More sites of increased uptake were identified using PET compared with scintigraphy. Agreement between the two modalities was higher for the palmar/plantar metacarpal/metatarsal condylar regions (K-w 0.59) than for the proximal sesamoid bones (K-w 0.25). Increased radiopharmaceutical uptake was detected in the medial proximal sesamoid bone in 6.9% and 22.2% of limbs with scintigraphy and PET, respectively. The high interobserver agreement for PET, despite the recent introduction of this technique, demonstrates the ease of clinical interpretation of PET scans. The higher number of lesions detected with PET compared with scintigraphy can be explained by the higher spatial resolution and cross-sectional nature of this modality. Study findings supported using PET in a clinical population of racehorses, in particular for the assessment of the proximal sesamoid bones.