First Metatarsal Headphones-Like Lesion: A Case of Unreducible Sesamoid Complex Dislocation.

CASE: A 34-year-old woman sustained a direct trauma to the left hallux during a fall. Radiographs showed a dorsal dislocation of the first metatarsophalangeal joint and a wide separation of sesamoid complex. Closed reduction was tried: postreduction radiographs displayed reduction of first metatarsophalangeal joint and a complete sesamoid complex dislocation. The patient was scheduled for surgery. Through a medial approach, open reduction together with plantar structures release and repair were performed. Functional and radiographic outcomes were satisfactory at the last follow-up. CONCLUSION: In case of a "headphones-like lesion" surgery is required, together with plantar structures repair.

Medial sesamoid position in moderate to severe hallux valgus: Correlation between three radiographic measurements.

BACKGROUND: In hallux valgus surgery, it is essential to accurately assess the position of the sesamoids both pre- and postoperatively. Weight-bearing foot anteroposterior, tangential sesamoid, and semi-weight-bearing computed tomography axial views are radiographic methods used to assess the medial sesamoid position. This study aimed to measure the medial sesamoid position and evaluate the correlation between these three radiographic methods. METHODS: This retrospective study comprised 59 feet from 49 patients who underwent hallux valgus surgery. The mean age of patients was 54.6 (range, 22-70) years. We took preoperative and postoperative measurements using the weight-bearing anteroposterior, tangential sesamoid, and semi-weight-bearing computed tomography axial views to assess the medial sesamoid position. RESULTS: The mean grades of the medial sesamoid position preoperatively and 6 months postoperatively were 2.5 and 0.8, 1.6 and 0.4, and 1.3 and 0.3 points based on the anteroposterior, tangential sesamoid, and computed tomography axial views, respectively (P < 0.001). Preoperatively, there was a strong positive correlation between the computed tomography axial and tangential sesamoid views (P < 0.001, r = 0.645) and anteroposterior and computed tomography axial views (P < 0.001, r = 0.468). In contrast, the tangential sesamoid and anteroposterior views showed a weak positive correlation (P = 0.03, r = 0.283). Six months postoperatively, there was a positive correlation between the computed tomography axial and tangential sesamoid views (P < 0.001, r = 0.473), anteroposterior and computed tomography axial views (P < 0.001, r = 0.470), and tangential sesamoid and anteroposterior views (P < 0.001, r = 0.480). CONCLUSIONS: We observed that the anteroposterior view exhibited a higher degree of medial sesamoid position displacement than the computed tomography axial and tangential sesamoid views. For the preoperative evaluation of the medial sesamoid position, the correlation between the computed tomography axial and tangential sesamoid views was stronger than that between the tangential sesamoid and anteroposterior views. However, all three views showed strong correlations postoperatively.

Deep learning model shows promise for detecting and grading sesamoiditis in horse radiographs.

OBJECTIVE: The objective of this study was to develop a robust machine-learning approach for efficient detection and grading of sesamoiditis in horses using radiographs, specifically in data-limited conditions. SAMPLE: A dataset of 255 dorsolateral-palmaromedial oblique (DLPMO) and dorsomedial-palmarolateral oblique (DMPLO) equine radiographs were retrospectively acquired from Hagyard Equine Medical Institute. These images were anonymized and classified into 3 categories of sesamoiditis severity (normal, mild, and moderate). METHODS: This study was conducted from February 1, 2023, to August 31, 2023. Two RetinaNet models were used in a cascaded manner, with a self-attention module incorporated into the second RetinaNet's classification subnetwork. The first RetinaNet localized the sesamoid bone in the radiographs, while the second RetinaNet graded the severity of sesamoiditis based on the localized region. Model performance was evaluated using the confusion matrix and average precision (AP). RESULTS: The proposed model demonstrated a promising classification performance with 92.7% accuracy, surpassing the base RetinaNet model. It achieved a mean average precision (mAP) of 81.8%, indicating superior object detection ability. Notably, performance metrics for each severity category showed significant improvement. CLINICAL RELEVANCE: The proposed deep learning-based method can accurately localize the position of sesamoid bones and grade the severity of sesamoiditis on equine radiographs, providing corresponding confidence scores. This approach has the potential to be deployed in a clinical environment, improving the diagnostic interpretation of metacarpophalangeal (fetlock) joint radiographs in horses. Furthermore, by expanding the training dataset, the model may learn to assist in the diagnosis of pathologies in other skeletal regions of the horse.

The trabecular architecture of the popliteal sesamoid bone (cyamella) from a New Zealand white rabbit (Oryctolagus cuniculus).

Sesamoid bones are ossified structures that are embedded in tendons near articulation. They consist of an inner trabecular bone architecture surrounded by a thin cortical shell. While the formation of sesamoid bones is probably mainly controlled by genetic factors, the proper development and mineralization of a sesamoid bone depends also on mechanical stimulation. While most sesamoid bones are not loaded directly by other bones during locomotion, they still experience forces directed from the tendon in which they are embedded. In cases when the sesamoid bone is experiencing forces only from a single tendon, such as the cyamella in the rabbit, this may give us a tool to study bone functional adaptation in a relatively simple loading setting. This study investigates the internal trabecular architecture of the popliteal sesamoid bone (cyamellae) in New Zealand white (NZW) rabbits (Oryctolagus cuniculus). Five hind limbs of NZW rabbits were micro-computed tomography scanned and the cortical and trabecular architectures of the cyamellae were evaluated. The results revealed that similar to the patella, the cyamella has a thin cortex and a high trabecular bone volume fraction (BV/TV), which is derived mostly from the high trabecular thickness (Tb.Th). Trabecular BV/TV and Tb.Th were not distributed homogeneously, but they were lower at the periphery and higher closer to the proximal and middle of the cyamella, near the musculotendinous junction. The results also demonstrated that trabeculae tend to align along two recognizable orientations, one with the direction of tensile stresses, in line with the popliteal tendon, and the second bridging the narrow space between the cranial and caudal cortical faces of the bone.

Fracture of the fabella with radiologic and MRI.

The fabella is an inconstant sesamoid bone. A handful of cases have been reported so far describing fabella fracture, usually involving high energy mechanism or stress fractures after total knee arthroplasty. This paper presents a fabella fracture in a man in his 40s after suffering a car crash, the clinical and radiographic presentation, treatment and complete recovery at 4-months follow-up.

The morphology of cyamella and its prevalence in Turkish society.

OBJECTIVE: The aim of this study is to determine the prevalence and morphometry of cyamella, one of the sesamoid bones around the knee joint. PATIENTS AND METHODS: In this retrospective study, a total of 9,500 plain/digital radiographs of 6,500 patients over the age of 18 who applied to Elazig Fethi Sekin City Hospital between January 2021 and January 2022 were examined. RESULTS: Examinations revealed cyamella in a total of 76 (0.8%) knees in the direct X-ray images of 49 (0.75%) patients. Eighteen (36.74%) of the patients with the presence of cyamella were males, and 31 (63.26%) were females. The mean age of the patients with cyamella was 50.9±12.9. Twenty-seven (55.1%) of the 49 cyamella were bilateral; seven (14.3%) were in the right knee, and 15 (30.6%) were in the left knee. The comparison of cyamella sizes between genders revealed a statistically significant difference in the transverse measurements only (p=0.015) in the right knee, while a statistically significant difference was found in all 3 parameters (p=0.032 for thickness; p=0.04 for transverse; p=0.026 for length) in the left knee. CONCLUSIONS: We believe that sufficient knowledge regarding the prevalence and distribution of cyamella in patients presenting with the complaint of knee pain and its differentiation from fabella, another sesamoid bone in the same region, as well as other anatomical structures, will aid an early and accurate diagnosis.

Partial Excision of a Tibial Sesamoid Fracture Nonunion in a Patient with Congenital Absence of Fibular Sesamoid: A Case Study.

BACKGROUND: Hallucal sesamoid injuries occur in approximately 5% to 10% of foot and ankle injuries. Most cases can be treated conservatively. However, when nonoperative management fails, surgical intervention is warranted. METHODS: The present case involved a 17-year-old female high school senior who presented to the clinic with right hallux pain. Radiographs were obtained and revealed congenital absence of the fibular sesamoid and evidence of a minimally displaced avulsion fracture involving the proximal medial tibial sesamoid. Treatment was complicated by the congenital absence of the fibular sesamoid and by a high activity level. RESULTS: After conservative treatment failure, the patient underwent partial excision of her tibial sesamoid. She was followed for 1.5 years after initial presentation to our clinic. The patient was able to return to daily activities; however, she was not able to return to softball competitively due to pain. CONCLUSIONS: We hypothesize she was unable to return to softball because the absence of a sesamoid can decrease push-off strength. We recommend that providers treating athletes educate their patients on the possible loss of strength and take this into account when creating a treatment plan.

Correlations of Sesamoid Bone Subluxation with the Radiologic Measures of Hallux Valgus and Its Clinical Implications.

Background and Objectives: Hallux valgus is one of the most common chronic foot complaints, with prevalences of over 23% in adults and up to 35.7% in older adults. However, the prevalence is only 3.5% in adolescents. The pathological causes and pathophysiology of hallux valgus are well-known in various studies and reports. A change in the position of the sesamoid bone under the metatarsal bone of the first toe is known to be the cause of the initial pathophysiology. Purpose: The relationships between the changes in the location of the sesamoid bone and each radiologically measured angle and joint congruency in the hallux valgus remain as yet unknown. Therefore, this study investigated the relationships of sesamoid bone subluxation with the hallux valgus angle, intermetatarsal angle, and metatarsophalangeal joint congruency in hallux valgus patients. The goal is to know the hallux valgus angle, the intermetatarsal angle, and metatarsophalangeal joint congruency's correlation with hallux valgus severity and prognosis by revealing the relationship between each measured value and sesamoid bone subluxation. Materials and Methods: We reviewed 205 hallux valgus patients who underwent radiographic evaluation and subsequent hallux valgus correction surgery in our orthopedic clinic between March 2015 and February 2020. Sesamoid subluxation was assessed using a new five-grade scale on foot radiographs, and other radiologic measurements were assessed, such as hallux valgus angle, the intermetatarsal angle, distal metatarsal articular angle, joint congruency, etc. Conclusions: Measurements of the hallux valgus angle, interphalangeal angle, and joint congruency exhibited high interobserver and intraobserver reliabilities in this study. They also showed correlations with sesamoid subluxation grade.

A modified minimally invasive osteotomy for hallux valgus enables reduction of malpositioned sesamoid bones.

BACKGROUND: The current minimally invasive distal metatarsal osteotomy for hallux valgus (HV) is V-shaped, which prevents the correction of the rotational metatarsal head deformity and reduction of the sesamoid bones. We sought to determine the optimal method for sesamoid bone reduction during HV surgery. METHODS: We reviewed the medical records of 53 patients who underwent HV surgery between 2017 and 2019 using one of three techniques: open chevron osteotomy (n = 19), minimally invasive V-shaped osteotomy (n = 18), and a modified straight minimally invasive osteotomy (n = 16). The sesamoid position was graded using the Hardy and Clapham method on weight-bearing radiographs. RESULTS: When compared to open chevron and V-shaped osteotomies, the modified osteotomy resulted in significantly lower postoperative sesamoid position scores (3.74 ± 1.48, 4.61 ± 1.09, and 1.44 ± 0.81, respectively, P < 0.001). Furthermore, the mean change in postoperative sesamoid position score was greater (P < 0.001). CONCLUSION: The modified minimally invasive osteotomy was superior to the other two techniques in correcting HV deformity in all planes, including sesamoid reduction.

New insight into the morphological characteristics of patella cubiti.

Accessory bones in the elbow region are rare anatomical variations with important clinical significance as they can be misdiagnosed as pathological lesions. Usually, they are asymptomatic and found incidentally during X-ray examination in the context of trauma. Although these bones have been previously described, their development is not fully understood. The present case provides complex macroscopic, X-ray and histological descriptions of a sesamoid bone in the posterior region of the elbow-patella cubiti and the related surrounding structures. Moreover, this report indicates the presence of a well-defined syndesmosis between patella cubiti and the proximal ulna.

An overview of the osseous palmar sesamoid in Anura, with the particular case of some Rhinella species.

Background: Sesamoids are generally regarded as structures that are not part of the tetrapod body plan. The presence of a palmar sesamoid is assumed to serve as a distribution point for the forces of the flexor digitorum communis muscle to the flexor tendons of the digits, which are embedded in the flexor plate. It has been considered that the palmar sesamoid is present in most anuran groups, and it has been suggested that it acts by inhibiting the closing of the palm, preventing grasping. Typical arboreal anuran groups lack a palmar sesamoid and flexor plate, a pattern shared with other tetrapod groups, which can retain a reduced sesamoid and flexor plate. We focus on the anatomical structure of the Rhinella group, which includes species that present an osseous palmar sesamoid and climb bushes or trees to avoid depredation or escape dangerous situations, and can exhibit scansorial and arboreal behaviors. We also add data on the bony sesamoids of 170 anuran species to study the anatomy and evolution of the osseous palmar sesamoid within this amphibian group. Our objective is to bring an overview of the osseous palmar sesamoid in anurans, unveiling the relationship between this element of the manus, its phylogeny, and the anuran habitat use. Methods: Skeletal whole-mount specimens of Rhinella were cleared and double-dyed to describe the sesamoid anatomy and related tissues. We review and describe the palmar sesamoid of 170 anuran species from CT images downloaded from Morphosource.org, representing almost all Anuran families. We performed an standard ancestral state reconstruction by optimizing two selected characters (osseous palmar sesamoid presence, distal carpal palmar surface) along with the habitat use of the sampled taxa, using parsimony with Mesquite 3.7. Results: Our primary finding is that sesamoid optimization in the anuran phylogeny revealed that its presence is associated with certain clades and not as widespread as previously anticipated. Additionally, we will also be delving into other important outcomes of our study that are relevant to those working in the field of anuran sesamoids. The osseous palmar sesamoid is present in the clade Bufonidae-Dendrobatidae-Leptodactylidae-Brachicephalidae that we named as PS clade, and also in the archeobatrachian pelobatoid Leptobranchium, all strongly terrestrial and burrowing species, though with exceptions. The osseous palmar sesamoid is always present in Bufonidae, but varies in form and size, depending on the mode that they use their manus, such as in the Rhinella margaritifera which has a cylindrical one and also grasping abilities that involve closing the manus. The scattered presence of the bony palmar sesamoid among anuran clades raises the question whether this sesamoid can be present with a different tissular composition in other groups.

Patella cubiti - a continuing etiological mystery / Patella cubiti: un misterio etiológico continuo

SUMMARY: 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.

Un hueso sesamoideo en la articulación del codo es una rara variación anatómica descrita como Patella cubiti. Aunque esta variación se conoce desde hace siglos, su etiología exacta aún no está clara. Se han propuesto hipótesis congénitas, de desarrollo y traumáticas. Rara vez causa manifestaciones clínicas que no sean rigidez o hipomovilidad del codo. Presentamos el caso de un paciente de 31 años que ingresó en nuestro servicio por presentar tumefacción y eritema en el codo derecho. Una imagen de rayos X reveló un hueso accesorio triangular con márgenes redondeados, que se diagnosticó como una Patella cubiti en combinación con bursitis del olécranon. El conocimiento de esta rara anomalía del codo es fundamental para los cirujanos ortopédicos y los médicos radiólogos en su práctica médica diaria.

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.

Radiographic and computed tomographic evaluation of supinator sesamoid bones in dogs.

BACKGROUND: The 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. RESULTS: The 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. CONCLUSION: A 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.

Locking of the Metacarpophalangeal Joint of the Thumb Caused by Entrapment of the Radial Sesamoid Bone.

Locking of metacarpophalangeal (MCP) joints of the thumb may be a consequence of dorsal subluxation from hyperextension injury. The joint is locked in mild hyperextension and cannot flex actively or passively. We report four patients with locked MCP joint of the thumb due to radial sesamoid entrapment after hyperextension or forced flexion injury. All patients had a prominent radial condyle of the metacarpal bone. Three patients had a deformity of the longitudinal groove on which the sesamoid was overlaid. The radial sesamoid was entrapped proximal to the radial condyle which could result in limited extension and hinged flexion of the joint. Excision of the radial sesamoid could release the locked joint. The radial sesamoid should be assessed if the motion of the thumb MCP joint is limited after flexion or extension injury. Level of Evidence: Level V (Therapeutic).

Exercise history predicts focal differences in bone volume fraction, mineral density and microdamage in the proximal sesamoid bones of Thoroughbred racehorses.

Medial proximal sesamoid bones (PSBs) from Thoroughbred racehorses that did (Case) or did not (Control) experience unilateral biaxial PSB fracture were evaluated for bone volume fraction (BVF), apparent mineral density (AMD), tissue mineral density (TMD), and microdamage in Case fractured, Case contralateral limb intact, and Control bones. A majority of Case bones had a subchondral lesion with high microdamage density, and low BVF, AMD, and TMD. Lesion microdamage and densitometric measures were associated with training history by robust linear regression. Exercise intensity was negatively related to BVF (0.07 ≤ R2 ≤ 0.12) and positively related to microcrack areal density (0.21 ≤ R2 ≤ 0.29) in the lesion; however, in an undamaged site, the relationships were opposite in direction. Regardless of location, TMD decreased with event frequency for both Case and Control, suggesting increased bone remodeling with exercise. Measures of how often animals were removed from active training (layups) predicted a decrease in TMD, AMD, BVF, and microdamage at regions away from the lesion site. A steady-state compartment model was used to organize the differences in the correlations between variables within the data set. The overall conclusions are that at the osteopenic lesion site, repair of microdamage by remodeling was not successful (e.g., lower bone mass, increased damage, and lower mineralization) but that in regions away from the lesion remodeling successfully controlled damage (e.g., higher bone mass, less microdamage, and lower mineralization).

The morphology of fabella and its prevalence in Turkish society.

OBJECTIVE: Fabella is a sesamoid whose prevalence is unstable and can be found as bone or cartilage, which changes over time. This study aims to reveal the prevalence, distribution, gender differences, and morphometric characteristics of cartilage and bony fabella in the Turkish population. PATIENTS AND METHODS: The study included 2.035 individuals over 18 years of age. MR images of 121 individuals, whose MR images of both knees could be obtained by anteroposterior and lateral radiographs of the participants, were evaluated retrospectively. RESULTS: The prevalence of fabella was 39.6% in females, 38.4% in males, and 38.8% in total. The prevalence of cartilage fabella was 9.1%, whereas bone fabella incidence was 29.7% regardless of gender. The fabella's mean thickness, width, length, and distance to the epicondylus lateralis femoris were 3.84 mm, 6.04 mm, 6.23, and 31.26 mm, respectively. CONCLUSIONS: The data of this study showing the occurrence and morphometric characteristics of bony and cartilaginous fabella allow early and accurate diagnosis of various pathological conditions caused by fabella.

Concentrated Bone Marrow Aspirate Injection for Hallux Sesamoid Disorders.

Concentrated bone marrow aspirate (CBMA) offers an alternative to sesamoid resection in end stage sesamoid pathology. CBMA potentiates the anti-inflammatory effect, stimulates local tissue regeneration and osteogenesis, when injected into bone. The purpose of this study is to evaluate the functional outcomes in a cohort of athletes following CBMA injection for the treatment of hallux sesamoid disorders. A retrospective case series of consecutive patients treated with CBMA injection for hallux sesamoid disorders were identified. Radiographs, Foot and Ankle Outcome Scores (FAOS), and Visual Analogue Scale (VAS) score were collected pre- and postinjections. Descriptive statistics were presented as the mean and standard deviation for continuous variables and frequency as percentages for categorical variables. Fifteen consecutive patients with were included with a mean follow-up time of 20.1 (range 12-34) months. Significant improvement in all scoring subscales of the FAOS and VAS score was noted preinjection compared to final follow-up postinjection (p < .001). Eight of 11 patients that were involved in sports prior to the CBMA injection returned to play, with 7 successfully returning to preinjury level status. Three patients required further treatment (20%). The case series suggests that CBMA injection is a safe and effective treatment option for hallux sesamoid disorders with a high rate of return to play.

Ultrasound evaluation of the first finger's sesamoid bones: diagnostic value of sesamoid and subsesamoid indices.

PURPOSE: Our analysis focuses explicitly on applying two sonographic and morphological indexes (sesamoid index and subsesamoid index) to better evaluate post-traumatic consequences to the sesamoids of the first finger. METHODS: In 2 years, we enrolled 75 patients, divided into two groups: 60 without any history of trauma and 15 reporting hyperextension trauma of the first finger. We performed clinical and instrumental examinations (sonography and X-ray) on patients with one or more symptoms compatible with sesamoiditis, while an MRI scan was performed only on patients with an acute onset and severe symptomatology. We measured both the short and long-axis diameter (in mm) for each sesamoid as well as the relation between the two parameters (sesamoid index, SI and subsesamoid index, SubI). RESULTS: All 15 patients showed sonographic alterations of the SI above the reference range, while the alterations of SubI varied according to the acuteness and gravity of trauma. In all cases, the X-ray did not show any relevant alterations. MRI scans in patients with acute symptoms confirmed the sonographic findings. CONCLUSION: Sonography enabled diagnosis of micro-injuries which were invisible to X-Ray and allowed to detect possible damages to the sesamoid complex, providing a qualitative and quantitative evaluations of the post-traumatic alteration of the metacarpophalangeal joint of the 1st finger and is therefore valid, combined with clinical examination and hand X-ray, in the evaluation of sesamoiditis without the need to perform further examinations.

The sesamoid bone in the long abductor muscle tendon of the first digit in the dog.

The sesamoid bone in the tendon of the m. abductor digiti primi longus is considered present in most dog breeds and is described to be radiologically detectable at the level of the carpus from the age of 4 months. However, an extensive investigation of this sesamoid bone has not been conducted before. The aim of this study was therefore to determine its prevalence in different dog breeds, to describe its histological development, and to determine the age at which it becomes radiologically visible. The prevalence of the sesamoid bone was assessed on radiographic images of the carpus or by dissection of the carpal region in 743 adult dogs of 115 breeds. Its development was studied by dissection and histological analysis in 45 puppies and its timing of radiological appearance was evaluated in 209 puppies. At least one sesamoid bone was present in all adult dogs, except for 14 dogs of six breeds of predominantly the small breed category. The lowest prevalence rate of 38.46% was exhibited in the French bulldog. The histological development could be divided into five stages. The first radiographic appearance corresponded to the coalescence of smaller ossification centers into one big nucleus (stage 4). The mean time of radiographic appearance was 108.4 days. This study provides extensive data on the prevalence and timing of the radiographic appearance of a sesamoid at the carpus of the dog. The data on radiographic appearance may be helpful in the age estimation of puppies.