Clinical anatomy of the fabella

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.

Prevalence of the fabella and its general characteristics in Turkish population with magnetic resonance imaging

INTRODUCTION

The fabella is a fibrocartilaginous or ossified sesamoid bone in the knee, largely located in the lateral tendon of the head of the gastrocnemius muscle. In this study, the prevalence, gender differences, localization and size of the fabella were determined in a Turkish population to make a comparison with other population studies in the literature.

MATERIALS AND METHODS

Thousand patients (500 females, 500 males) who underwent knee magnetic resonance imaging (MRI) with fabella in all three planes, including axial, sagittal and coronal evaluated, retrospectively. All MRI examinations were performed using a 1.5 T unit. Patients with a history of trauma or operation, motion artifacts and patients who could not be evaluated due to image quality were excluded. Anteroposterior diameter in sagittal plan (sAP) of the fabella and the fabella-femur distance was measured. Measurements were evaluated with Pearson's Chi-squared and Mann-Whitney U test for non-homogeneous data in SPSS program, and ANOVA test for homogeneous data. A p value of < 0.05 was considered significant in all analyses.

RESULTS

The overall prevalence of fabella was found to be 155 cases. Unilateral fabella was detected in 72.9% of the cases, of which 56.6% were on the right side and 43.4% were on the left side. The median value of AP diameter in sagittal plan was calculated as 4.40 ± 1.31 mm. Concerning the gender-related examination the sAP diameter of the fabella was larger in men than in women (p < 0.05). The median value of FFD was calculated as 2.50 ± 0.50 mm. The distribution of FFD between genders was not statistically significant (p = 0.492).

CONCLUSION

The fabella is usually a sesamoid bone that can be detected incidentally by imaging techniques. The incidence in the Turkish population is 15.5%, and no gender difference was detected. It is clear that further studies on the basis of populations are needed, especially considering that pathological problems remain in question and there is a lack of scientific data (variations, developmental characteristics, etc.) on sesamoid bones.

Prevelance of Fabella: An MRI Study in The Eastern Anatolia Region Of Turkey

BACKGROUND

The fabella, which is generally located in the lateral head of the gastrocnemius muscle, is a sesamoid bone that articulates with the posterior face of the lateral femoral condyle. As traditional information, the prevalence of fabella is between 10-30% in the population and is usually present in both knees.

INTRODUCTION

The objective of this study was to investigate the knee MRIs in the Eastern Anatolia Region of Turkey subjects in order to assess the prevalence of the fabella and analyse the differences between gender, age and laterality and its symmetry pattern.

METHODS

This study was a retrospective study in patients older than 18 years whose knee MRIs were taken between February 2014 and February 2016. In this study, a total of 531 patients [290 females and 241 males] were included. The radiographs were examined by two orthopedic surgeons and the fabella was located. Later, an expert radiologist made the final decision and confirmed the results.

RESULTS

The number of patients included in the study was 531. We detected os fabella in 59 (11.1%) patients. Of the 59 os fabella, 33 were in the right knee and 26 were in the left knee, 38 were female and 21were male.

CONCLUSION

In this study, we investigated the age and gender differences besides the prevalence and the symmetry pattern of the fabella in the Eastern Anatolia Region of Turkey's population. Prevalence of the fabella was found to be 11.1% which is different than previously published studies.

Radiological study of fabella in Omani subjects at a tertiary care center

Ethnic diversity is associated with variability in the prevalence rates of fabella. We aimed to evaluate the prevalence and the radiological features of fabella in Omani patients. This is a retrospective analysis of hospital electronic database of patients referred for radiological investigations (radiographs and magnetic resonance imaging) of the knee, at a tertiary care referral center. Descriptive statistics were performed to determine the prevalence of fabella. Chi-square test was used to determine the association between sex or age with respect to the presence of fabella. A total of 813 knee radiographs were reviewed for the presence of fabella. Fabella was found in 24.1% of total cases. A statistically significant sex difference was observed with respect to the presence of fabella in left knees in males (P<0.01). The presence of fabella was significantly associated with age groups for the right (P<0.05) and left knees (P<0.01). In magnetic resonance imaging film reviews, all the identified fabellae (20.2%) were bony structures and were located within the lateral head of the gastrocnemius muscle. There were no cartilaginous fabellae detected. The current study revealed a prevalence of 24.1% of fabella in Omani subjects which is almost similar to the results as seen in Caucasian ethnic populations.

Common Peroneal Nerve Palsy Due to Giant Fabella After Total Knee Arthroplasty

Background

Common peroneal nerve palsy (CPNP) is a rare but serious complication following primary total knee arthroplasty (TKA). The common peroneal nerve is one of the main molecules of the sciatic nerve. CPNP is a series of symptoms caused by common peroneal nerve injury due to paralysis and atrophy of the fibula and tibia muscles. The main clinical symptoms are: ankle joint unable to extend back, toe unable to extend back, foot droop, walking in a steppage gait, and foot dorsal skin sensation having decreased or disappeared. If treatment is not timely, severe cases may result in atrophy of the anterior tibia and lateral calf muscles. The risk factors for CPNP include mechanical stretching of the nerve, disruption of the blood supply to the nerve, and compression of the nerve. The CPNP should be treated in a timely manner and according to the cause. Its function should be restored as soon as possible to avoid serious adverse consequences. It has negative effects on patients’ life and physical and mental health. To our knowledge, this is the first study to describe CPNP due to a giant fabella after TKA.

Case presentation

The present study reported on a 70‐year‐old female patient. The patient underwent a primary TKA of the right knee for osteoarthritis. Relevant examinations were conducted and the operation went smoothly. Three hours postoperation, a right partial CPNP was observed, with progressive aggravation over time. On palpation, there was a 2 × 2‐cm fixed hard mass in the posterolateral aspect of the right knee, with mild tenderness to deep palpation. Radiographs demonstrated that a giant fabella was located at the posterolateral condyle of the right femur. Fabellectomy and neurolysis of the common peroneal nerve were performed. The peroneal nerve palsy resolved gradually after the operation. At 8‐month follow up after fabellectomy and neurolysis, the function of the common peroneal nerve had fully recovered.

Conclusions

The presence of giant feballa pressing on the common peroneal nerve should be considered when common peroneal nerve palsy occurs after TKA. Surgical exploration and release compression should be performed in a timely manner.

Clinical Features and Radiological Differential Diagnoses of Symptomatic Sesamoid Bones and Accessory Ossicles: A Pictorial Essay

종자골과 부골은 정상 해부학적 변이로 그 빈도와 형태는 다양하며 일반적으로 크기가 작고 둥근 모양으로 피질로 잘 둘러싸여 있고 뼈나 관절 주위에 인접하여 관찰되고 드물게 이분 혹은 다분 형태를 보일 수 있다. 대부분의 종자골과 부골은 무증상이며 판독 업무 중에 흔히 마주치게 된다. 하지만 때때로 종자골과 부골이 증상을 일으킬 수 있는데, 종자골과 부골 자체의 골절이나 탈구, 관절염, 골괴사, 감염 등의 질환이 이환되거나, 주변에 신경압박이나 건초염, 연부조직의 포착 등에 의하여 증상을 유발할 수 있다. 이 종설에서는 다양한 해부학적 위치에서 발생한 증상이 있는 종자골과 부골의 영상을 보고, 이들의 임상적 양상과 영상의학적 감별진단을 정리해보고자 한다.

Human biological variation in sesamoid bone prevalence: the curious case of the fabella

The fabella is a sesamoid bone located in the gastrocnemius behind the lateral femoral condyle. In humans, fabellae are 3.5 times more common today than they were 100 years ago, with prevalence rates varying between and within populations. In particular, fabellae have been assumed to be more common in Asians than non‐Asians, equally common in men and women, potentially more common in older individuals, and bilateral cases (one per knee) appear to be more common than unilateral ones. The roles of genetic and environmental factors in this phenotypic variation have been hypothesized, but not rigorously investigated. Given its clinical and evolutionary significance (i.e. being associated with several knee ailments, causing medical issues on its own, interfering with medical devices, and being less common in humans than in other mammals), it is important comprehensively to understand prevalence rate variation, and the roles of genetics and environmental factors in that variation. To address these questions, we performed a meta‐analysis on data from studies published from 1875 to 2018 to investigate possible variation in sexual dimorphic (n = 22 studies, 7911 knees), ontogenetic (n = 10 studies, 4391 knees), and global (n = 65 studies, 21 626 knees) fabella prevalence rates. In addition, we investigated what proportion of cases are bilateral (n = 37 studies, 900 individuals), and among unilateral cases (n = 20 studies, 204 individuals), if fabellae are more common in the left or right knee. Our results show that, today, fabellae are 2.47–2.60% more common in men than women, and prevalence rates increase ontogenetically in old age (i.e. 70 years old), implying that fabellae can ossify early (i.e. 12 years old) or late in life. Approximately 72.94% of cases are bilateral, and among unilateral ones, fabellae are equally common in right and left knees. There is marked regional variation in fabella prevalence rates, with rates being highest in Asia, followed by Oceania, South America, Europe, Middle East, and North America, and lowest in Africa. Worldwide, an average of 36.80% of knees has ossified fabellae detectable by dissection. These results imply that, while the ability to form a fabella may be genetically controlled, the mechanisms that trigger fabella ossification may be environmentally controlled. What these environmental factors are, can only be speculated.

Sesamoids in tetrapods: the origin of new skeletal morphologies

Along with supernumerary bones, sesamoids, defined as any organized intratendinous/intraligamentous structure, including those composed of fibrocartilage, adjacent to an articulation or joint, have been frequently considered as enigmatic structures associated with the joints of the skeletal system of vertebrates. This review allows us to propose a dynamic model to account for part of skeletal phenotypic diversity: during evolution, sesamoids can become displaced, attaching to and detaching from the long bone epiphyses and diaphysis. Epiphyses, apophyses and detached sesamoids are able to transform into each other, contributing to the phenotypic variability of the tetrapod skeleton. This dynamic model is a new paradigm to delineate the contribution of sesamoids to skeletal diversity. Herein, we first present a historical approach to the study of sesamoids, discussing the genetic versus epigenetic theories of their genesis and growth. Second, we construct a dynamic model. Third, we present a summary of literature on sesamoids of the main groups of tetrapods, including veterinary and human clinical contributions, which are the best-studied aspects of sesamoids in recent decades. Finally, we discuss the identity of certain structures that have been labelled as sesamoids despite insufficient formal testing of homology. We also propose a new definition to help the identification of sesamoids in general. This review is particularly timely, given the recent increasing interest and research activity into the developmental biology and mechanics of sesamoids. With this updated and integrative discussion, we hope to pave the way to improve the understanding of sesamoid biology and evolution.

Ultrasound Evaluation and Surgical Excision of a Fabella Causing Peroneal Neuropathy in a Track Athlete

Background

There are multiple causes of posterior knee pain and radicular symptoms. A symptomatic fabella is a rare cause but should be considered in the differential diagnosis.

Purpose

Physicians should consider a symptomatic fabella as a diagnosis when common treatments for posterior knee pain have not alleviated the symptoms.

Study Design

Case report.

Methods

Review of clinical documentations of an orthopedist, physiatrist, physical therapist, 2 primary care sports medicine physicians, and the surgical report of an orthopedist.

Results

It took time and resources including several referrals and imaging modalities to make a final diagnosis.

Conclusion

Symptomatic fabellae are an uncommon finding but should be considered in the differential diagnosis with an athlete with posterior knee pain.

Clinical Relevance

Considerable time and resources were used to ultimately diagnose and treat a NCAA Division 1 athlete. Surgical excision was required of a sesamoid bone that is present in 30% of individuals.

A Comprehensive Review of the Fabella Bone

The fabella is a sesamoid bone that is embedded in the lateral head of the gastrocnemius muscle and often articulates directly with the lateral femoral condyle. It is present in 10-30% of the general population with a higher incidence in Asians. The fabella can lead to various pathologies such as fabella pain syndrome and common fibular nerve palsy. Conservative treatment involves physical therapy or injecting local anesthetics or steroids around this bone. However, if symptoms persist, then a fabellectomy can be performed. Physicians should be aware of the fabella bone and the multiple pathologies associated with it in order to provide the best treatment and management for patients.

A case report and literature review on fabella syndrome after high tibial osteotomy

RATIONALE

The fabella is a normal structure, but is occasionally reported to cause posterior knee pain. The aim of this study was to present fabella syndrome after high tibial osteotomy.

PATIENT CONCERNS

A 55-year-old female patient was admitted to the hospital due to about 1 year and 8 months of left knee pain. Sclerosis was observed in the anterior margin of the fabella in the preoperative magnetic resonance (MR) T2 image, and reactive bone marrow was found and was considered to be due to degeneration of the distal femur. Degenerative change (Kellgren and Lawrence-KL grade 2) of the left knee was observed, along with cartilage delamination corresponding to International Cartilage Repair Society (ICRS) grade 4 in the patellofemoral joint.

DIAGNOSES

We present the first reported case of fabella syndrome in Korea, after high tibial osteotomy due to degenerative arthritis and varus deformity, rather than artificial joint surgery.

INTERVENTIONS

We excised the fabella from the patient's knee.

OUTCOMES

There was no evidence of recurrence during 5 months of postoperative follow-up. Posterolateral Corner including the fabella might have sustained increased tensile force causing symptoms due to compression of the fabella by the posterior joint of the posterior femoral condyle.

LESSONS

We present the first reported case of fabella syndrome in Korea, after high tibial osteotomy due to degenerative arthritis and varus deformity, rather than artificial joint surgery. Collision syndrome caused by a fabella has previously been attributed to inconsistency of the joint surface due to excessive exercise and degenerative changes due to knee instability. We report this case since it appeared to involve collision syndrome due to mechanical change of an angular deformity.

Fabella fracture with radiological imaging: A case report

The fabella is a kind of sesamoid bone which is located in the lateral head of the gastrocnemius muscle. A slice of studies demonstrated that fabella is involved in the knee joint stabilization. Fabella fracture may cause knee pain or functional impairment as the previous reports pointed. It is extremely rare, which leads to its high rate of missed diagnosis in clinical and radiography to some extent. We report a case of a 38-year-old female who was struck by an electromobile. The fabella fracture was confirmed on X-ray plain films. After that, the degree of injury was evaluated with the magnetic resonance imaging (MRI).

How common are cranial sesamoids among squamates?

Sesamoids are elements that originate as intratendinous structures due to genetic and epigenetic factors. These elements have been reported frequently in vertebrates, although cranial sesamoids have been recorded almost exclusively in non-tetrapod Osteichthyes. The only tetrapod cranial sesamoids reported until now have been the transiliens cartilage (of crocodiles and turtles), and another one located in the quadrate-mandibular joint of birds. Here, we examined seven squamate species using histological sections, dissections of preserved specimens, dry skeletons, cleared and stained specimens, computed tomographies (CT), and report the presence of other cranial sesamoids. One is attached to the cephalic condyle of the quadrate, embedded in the bodenaponeurosis and jaw adductor muscles of Ophiodes intermedius (Anguidae). The other sesamoid is found at the base of the basicranium of several squamates, capping the sphenoccipital tubercle, on the lateral side of the basioccipital-basisphenoid suture. This bone has previously been reported as "element X." We reinterpret it as a basicranial sesamoid, as it is associated with tendons of the cranio-cervical muscles. This bone seems to have the function of resisting tension-compression forces generated by the muscle during flexion the head. This element was previously known in several squamates, and we confirmed its presence in three additional squamate families: Gymnophthalmidae, Gekkonidae, and Pygopodidae. The evidence suggests that cranial sesamoids are a widespread character in squamates, and it is possible that this feature has been present since the origin of the group.

Effect of Radial Extracorporeal Shock Wave Therapy in Patients With Fabella Syndrome

The fabella is a small sesamoid bone generally located in the tendon of the lateral head of the gastrocnemius behind the lateral condyle of the femur. Fabella syndrome is the occurrence of posterolateral knee pain associated with the fabella. It is a rare cause of knee pain that is often misdiagnosed. Fabella syndrome can be managed with conservative or surgical treatment. We applied radial extracorporeal shock wave therapy as a new treatment strategy for fabella syndrome and achieved a successful outcome.

Fabella Fractures after Total Knee Arthroplasty with Correction of Valgus Malalignment

The incidence of fabella fractures is considered to be extremely low. This report presents two patients with femorotibial osteoarthritis and considerable preoperative valgus malalignment, who developed a fracture of the fabella (as demonstrated by radiography) after total knee arthroplasty with intraoperative correction of the valgus malalignment. Special attention should be paid to the fabella for not missing a fabella fracture in these patients.

Role of Sonography in the Diagnosis and Treatment of Common Peroneal Neuropathy Secondary to Fabellae

The fabella is a sesamoid bone situated in the posterolateral knee, which may contribute to posterolateral knee pain by impinging on the adjacent common peroneal nerve (CPN). Although anatomic studies have established an relationship between the fabella and CPN, we present 4 cases of posterolateral knee pain radiating into the anterolateral leg in which sonography was able to determine the source of the pain as CPN compression by an adjacent fabella. In 2 of these cases, resolution of symptoms was achieved with ultrasound-guided CPN blocks, whereas 1 case was surgically treated, and another was managed with oral analgesics. These cases illustrate the utility of diagnostic and interventional sonography in the evaluation and treatment of posterolateral knee pain secondary to fabellar impingement of the CPN.

Fracture of the Fabella: An Uncommon Injury in Knee

The fabella is a sesamoid bone that may contribute to the stabilization of the posterolateral knee corner and it can very occasionally act as a source of atypical and rare knee pain and functional impairment. Fracture of the fabella is a rare but important clinical entity which may be overlooked clinically and radiographically. However, it causes an intermittent mechanical pain of the knee and it can mistakenly harm another knee pathology like intra-articular loose body. We report a case of a 21-year-old man who was sustaining a fracture of fabella following vehicle accident.

Incidence and radiological characteristics of fabellae in an Asian population

INTRODUCTION

The fabella, a sesamoid bone sometimes found in the lateral head of the gastrocnemius muscle, often articulates directly with the lateral femoral condyle. This study aimed to determine the incidence of fabellae in an Asian population and to characterise the radiological features of the fabella.

METHODS

Electronic radiographs and magnetic resonance imaging films of 80 consecutive patients who underwent knee arthroscopy between May 2005 and October 2009 were reviewed to determine the presence and characteristics of the fabella.

RESULTS

The incidence of fabellae was 31.25% in our study cohort. The median length, thickness, width and distance of the fabella from the lateral femoral condyle were 7.06 mm, 4.89 mm, 6.12 mm and 33.19 mm, respectively. The fabella was consistently bony and located in the lateral head of the gastrocnemius, with 52% of the fabellae having an articulating facet. Fabellae in men were found to be larger than in women, although the difference was not statistically significant. The presence of an articulating groove was associated with increased size of the fabella, but not with the distance between the fabella and its insertion onto the lateral head of the gastrocnemius.

CONCLUSION

The incidence of fabellae in our population was lower than that in regional studies. They were consistently bony and not all had articulating grooves on the lateral femoral condyle. We found that the larger the fabella, the higher the chances of it having an articulating groove. By defining the radiological characteristics of the fabella, we provide objective parameters to help differentiate the fabella from other loose bodies or calcifications in the knee.

Anatomy of the triceps surae: a pictorial essay

Gastrocnemius contracture has recently gained relevance owing to its suggested relationship with foot disorders such as metatarsalgia, plantar fasciopathy, hallux valgus, and others. Consequently this has induced a renewed interest in surgical lengthening techniques, including proximal gastrocnemius release, to resolve gastrocnemius contracture in patients with foot disorders. This article describes and discusses the general anatomy of the triceps surae and the surgical anatomy of the gastrocnemius.

Compression neuropathy of the common peroneal nerve by the fabella

The fabella is a normal anatomical variant and has been found in up to 30% of the general population. We present the case of a 67-year-old man with pain down the lateral aspect of the left lower limb of 18 months duration. A clinical examination revealed a palpable fabella and nerve conduction studies confirmed a common peroneal nerve neuropathy at its level. Dynamic ultrasound scan and MRI of the knee showed the fabella to be impinging on the common peroneal nerve. Operative excision of the fabella was performed with significant improvement at 3 months and full recovery at 1 year. A literature review has shown that the last reported case of a compression neuropathy of the common peroneal nerve was in 1976. Anatomical considerations need to be taken into account and operative treatment has been recommended due to the favourable outcome in this case.

Potentially symptomatic fabella: MR imaging review

Fabella, a small ossicle at the posterolateral aspect of the knee, is potentially a source of knee pain. Although fabella syndrome is a rare cause of knee symptoms in young adults, osteocartilaginous degeneration prominent in the fabellofemoral joint on magnetic resonance imaging may be commonly seen in elderly patients.

Influence of a fabella in the gastrocnemius muscle on the common fibular nerve in Japanese subjects

The fabella is a sesamoid bone located in the proximal tendon of the gastrocnemius muscle. In rare cases, its presence may lead to a variety of clinical problems, including fabella syndrome and common fibular (CF) nerve palsy. The purpose of this study was to analyze the morphology of the fabella and CF nerve and discuss the influence of any existing fabellae on the size of the CF nerve. The morphology of the fabella and CF nerve in the popliteal region of the lateral head of the gastrocnemius muscle was investigated in 102 knees of 51 Japanese cadavers. The maximum circumference of the thigh, knee, and calf and the frequency, position, and size of the fabella were measured. In addition, the CF nerve width and thickness were measured proximal to the fabellar region and again as the CF nerve passed posterior, lateral, or medial to the region. A fabella was observed in 70 knees (68.6%). The CF nerve adjacent to the fabella was significantly wider and thinner than in the region proximal to the fabella (P < 0.001). In cases in which a bony fabella was present, there was a significant relationship between the thickness of the CF nerve and the circumference of the thigh and knee. The following factors were observed to contribute to the presence of a fabella causing alterations in the size of the CF nerve: a bony fabella, a CF nerve path posterior or lateral to the fabella, and subjects with a thin physique and bony fabella.

Anatomic study of fabella and its surrounding structures in a Chinese population

PURPOSE

To explore the anatomic features of the fabella and its relationship with the common peroneal nerve and the fabellofibular ligament, so as to provide anatomical evidence for clinical diagnosis and treatment of fabella diseases in a Chinese population.

METHODS

Sixty-one formalin-fixed knee specimens were obtained for anatomic dissection. Structural features of the fabella were investigated by radiological and histological tests.

RESULTS

There were 53 cases (86.89%) with fabellae in the lateral head of the gastrocnemius muscle, including 34 bony ones (55.74%), whereas only 6 cases had fabellae in the medial head (9.84%). The fabellae were accompanied by common peroneal nerves on their surfaces in 11 cases (20.8%), and the presence of the fabella was not generally predictive of a fabellofibular ligament. As much as 57.9% of the cartilage fabellae were not visualized on radiograph. The structure of the ossified fabella is similar to a typical long bone.

CONCLUSIONS

Fabellae were mainly present in the lateral head of the gastrocnemius muscle in a large proportion of the Chinese population. More than half of the cartilage fabellae were not visualized on radiograph. Its clinical significance could not be ignored by physicians and anatomists.

The incidence and structure of the fabella in a South African cadaver sample

The fabella, a sesamoid bone located in the tendon of the lateral head of the gastrocnemius muscle, was dissected from 102 lower limbs of 51 cadavers of age range 40-95 years (mean, 75.5 ± 14.5 years). The incidence of this sesamoid was determined as were its dimensions and radiological and histological features. The fabella was present in 23.5% of individuals, and it was bilaterally located in 50% of cases. It had an equal likelihood of occurring in males or females (P = 0.60), and in either right or left lower limb (P = 1.0). The consistency of the fabella was mostly bony (72.2%), a variety predominantly seen in male subjects. The mean diameters were 9.98 ± 0.9 mm and 8.78 ± 1.23 mm in males and females, respectively, with a statistically significant difference of P = 0.033. Histologically, bony fabellae had a core of spongy bone surrounded by compact bone, whereas nonbony fabellae were characterized by fibrocartilage.

Anatomical study of the fabella, fabellar complex and its clinical implications

The fabella has been mainly studied using imaging methods but there are less research reports on the gross anatomical studies. We performed this anatomical study of the fabella and its surrounding structures with functional implications using 150 heads of the gastrocnemius muscles of 75 knees from 39 Japanese cadavers. This study is the direct representation of the human fabella and its functional implications. We observed 99 fabellae (66.0%) including 44 complete bony fabellae (29.3%). Of these bony fabellae, 43 (97.7%) were located in the lateral head of the gastrocnemius muscle with its surrounding structures and were positioned only on the lateral condyle of the femur. Moreover, the cartilage and bony fabellae, especially on the lateral side, contributed to the fabella complex with its surrounding muscles and ligaments and formed small articular cavity by cooperating with the femoral condyle. Although the human fabella is considered as appearing in the fabella complex with ageing and it possibly induces clinical symptoms, the fabella may play an important role as a stabilizer between the fabella complex and the femoral condyle.

Dislocation of an enlarged fabella as uncommon cause of knee pain: a case report

The fabella is a sesamoid bone that can very occasionally act as a source of atypical knee pain, often mistaken for a more common cause of clinical symptoms, such as an intra-articular loose body or an osteophyte. We report a case of symptomatic dislocation of an osteoarthritic, enlarged fabella, 4 years after total excision of the patella for a comminuted fracture, that was primarily overlooked and led to repeated diagnostic arthroscopy of the knee. A thorough history and physical examination of the joint as well as appropriate roentgenographic studies could have spared this patient an unnecessary arthroscopy and indicated the correct therapy.