Easy to gain but hard to lose: the evolution of the knee sesamoid bones in Primates-a systematic review and phylogenetic meta-analysis.

Sesamoids are variably present skeletal elements found in tendons and ligaments near joints. Variability in sesamoid size, location and presence/absence is hypothesized to enable skeletal innovation, yet sesamoids are often ignored. Three knee sesamoids-the cyamella, medial fabella and lateral fabella-are present in primates, but we know little about how they evolved, if they are skeletal innovations, or why they are largely missing from Hominoidea. Our phylogenetic comparative analyses suggest that sesamoid presence/absence is highly phylogenetically structured and contains phylogenetic signal. Models suggest that it is easy to gain but difficult/impossible to lose knee sesamoids and that the fabellae may have similar developmental/evolutionary pathways that are distinct from the cyamella. Sesamoid presence/absence is uncorrelated to the mode of locomotion, suggesting that sesamoid biomechanical function may require information beyond sesamoid presence, such as size and location. Ancestral state reconstructions were largely uninformative but highlighted how reconstructions using parsimony can differ from those that are phylogenetically informed. Interestingly, there may be two ways to evolve fabellae, with humans evolving fabellae differently from most other primates. We hypothesize that the 're-emergence' of the lateral fabella in humans may be correlated with the evolution of a unique developmental pathway, potentially correlated with the evolution of straight-legged, bipedal locomotion.

The Prevalence of Fabella and Its Association With Osteoarthritic Severity of Knee in Saudi Arabia: A Multicenter Study.

INTRODUCTION: The fabella exhibits variable prevalence across populations and is associated with musculoskeletal disorders. Limited research exists on fabella-related studies, particularly in Saudi Arabia, necessitating further investigation to understand its prevalence and association with knee osteoarthritis (OA). METHODS: A retrospective multicenter study was conducted in AlAhsa, Saudi Arabia, reviewing knee X-rays of patients diagnosed with knee OA. Statistical analysis assessed potential associations between fabella presence, demographic factors, and OA severity using the Kellgren-Lawrence classification. RESULTS: Among 348 participants, 96 (27.6%) exhibited fabella presence, with 38 (39.6%) of them showing fabellar degenerative changes. No significant associations were found between fabella presence and gender, age, knee side, or OA severity, except for a marginal trend in age groups. However, there was an increasing trend in fabellar degeneration with advancing OA grades. CONCLUSION: Our study emphasizes the importance of investigating fabella prevalence and its associations with knee OA in diverse populations. While no significant correlations were found in this cohort, the findings prompt further exploration, emphasizing the need for multicenter studies to enhance understanding and clinical management of fabella-related conditions in knee OA.

X-ray Imaging Versus Anatomical Dissection for Identification of the Fabella.

INTRODUCTION: Reported prevalence rates of the fabella sesamoid bone vary widely, particularly between studies based on either X-ray imaging or anatomical dissection approaches. The purpose of this study was to directly compare these two methodologies in their detection of fabellae and investigate whether variability in the density of fabellae could explain any discrepancies. METHODS: Fifty cadaveric knee segments were examined for the presence of a fabella by both X-ray imaging and anatomical dissection. The relative density of each excised fabella specimen was then quantified using a separate set of radiographs.  Results: Fabellae were detected in 40% of the sample knees via a manual dissection approach but in just 12% of those same specimens using X-ray imaging. Relative density measurements confirmed that fabellae identifiable only via dissection were significantly less dense than fabellae visible in whole knee radiographs but denser than the surrounding tissue. CONCLUSION: Radiology cannot reliably detect cartilaginous or incompletely ossified fabellae, which were found in 28% of the study population. Clinicians should consider the potential occurrence of a fabella when diagnosing posterolateral knee pain, even if it may not be visible via X-ray.

Prevalence of the Fabella and Determination of the Fabella Index / Prevalencia de la Fabela y Determinación del Índice Fabelar

SUMMARY: The fabella is a bony anatomical variable, which in humans is located posterior to the lateral condyle of the femur, in the tendinous portion of the lateral head of the gastrocnemius muscle. Its prevalence rate has been reported in different populations, ranging from 3% to 86%. This study aimed to create an index that classifies the fabella according to its dimensions, determine the prevalence of the fabella in the Colombian population, and identify possible differences according to the fabella index (FI), sex, age, laterality, and degree of fabellar degeneration. A retrospective study used 93 lateral knee radiographs belonging to Colombian individuals. A fabella index was established to classify fabellae into longifabellar, medifabellar, and equifabellar, and radiological classification was used to identify the degree of fabellar degeneration (DFD). The prevalence of fabella was 36.30 %, and this variant was associated with the individual's sex, with male subjects having 2.66 times the probability of presenting fabella. A higher prevalence of medifabellar fabellae (57.60 %) was observed, followed by longifabellar (24.20 %) and equifabellar (18.20 %). There was a positive and moderate correlation between the DFD and age. We consider that larger fabellae can cause entrapment of the common fibular nerve, compression of the popliteal artery, and tear of the medial meniscus, so the FI becomes relevant in clinical practice, providing information on the type of fabella and its associated pathological manifestations. This study introduces a novel fabella index and investigates the frequency of fabella in the Colombian population. The findings of this study will serve as a reference for future research and contribute to the field of knee orthopedics and surgery in this population.

La fabela es una variable anatómica ósea, que en humanos se localiza posterior al cóndilo lateral del fémur, en la porción tendinosa de la cabeza lateral del músculo gastrocnemio. Su tasa de prevalencia se ha reportado en diferentes poblaciones, cuyos valores oscilan entre 3 % y 86 %. El objetivo de este estudio fue crear un índice que clasifique la fabela según sus dimensiones, determinar la prevalencia de la fabela en población colombiana, así como identificar posibles diferencias en función del índice fabelar, sexo, edad, lateralidad y grado de degeneración de la fabela. Se desarrolló un estudio retrospectivo en el que se dio uso a 93 radiografías laterales de rodilla, pertenecientes a individuos colombianos. Se estableció un índice fabelar que clasificó las fabelas en longifabelares, medifabelares y equifabelares, además utilizamos la clasificación radiológica para identificar los grados de degeneración fabelar (GDF). La prevalencia de la fabela fue del 36,30 %, se encontró asociación de esta variante al sexo del individuo, siendo los hombres quienes tuvieron 2,66 veces más probabilidades de presentar la fabela. Se observó mayor prevalencia de fabelas tipo medifabelar 57,60 %, seguido de tipo longifabelar 24,20 % y equifabelar 18,20 %. Hubo correlación positiva y moderada entre la edad y el grado de degeneración fabelar. Consideramos que las fabelas con mayores dimensiones podrían causar atrapamiento del nervio fibular común, compresión de la arteria poplítea y desgarro del menisco medial, por lo que el índice fabelar adquiere relevancia en la práctica clínica, al dar información del tipo de fabela y sus manifestaciones patológicas asociadas. El presente estudió es el primero en proponer un índice fabelar y la frecuencia de la fabela en población colombiana, por lo que servirá de referencia para futuras investigaciones, además de brindar un aporte al área traumatológica y quirúrgica de la rodilla en esta población.

Ex vivo biomechanical evaluation and comparison of lateral femoro-fabella ligament suture and lateral suture with bone anchor for cranial cruciate ligament repair in cats.

OBJECTIVE: To compare the biomechanical properties of lateral femoro-fabella ligament suture (FFLS) and lateral suture with a bone anchor suture (BAS) for management of feline cranial cruciate ligament disease. ANIMALS: 12 femurs from 6 mature cat cadavers. METHODS: The samples were collected from April to June 2023. The specimens had an FFLS and, subsequently, BAS placed and were positioned into a biomechanical testing machine, preloaded from 5 N to 15 N for 100 cycles, and subsequently, a load to suture failure was applied. The displacement at 5 N and 15 N, the total precycle displacement (millimeters), the force at 3 mm displacement and at failure (newtons), the displacement at failure (millimeters), and the stiffness to failure (Newton:millimiter) were recorded. Nonparametric Wilcoxon signed-rank tests were used to compare data between the 2 groups. RESULTS: The displacement at 5 N and 15 N and the total precycle displacement were significantly higher in the FFLS group compared to the BAS group. Additionally, the FFLS group results showed less consistent displacement and marked variability. The force (newtons) at 3 mm displacement was higher in the BAS group. There was no significant difference in force and no significant difference in displacement at failure between the 2 groups. However, the stiffness to failure (N/mm) was significantly higher in the BAS group. CONCLUSION: BAS represented a more stable and reliable femur attachment for extracapsular suture in cats. CLINICAL RELEVANCE: To demonstrate the stability and reliability between BAS and FFLS and influence implant selection in the treatment of cranial cruciate ligament rupture in cats with evaluation of biomechanical properties.

Common fibular nerve palsy due to the Fabella: A review.

One of the most common nerve palsies - common fibular nerve palsy - can be caused by the variant small sesamoid bone in the posterolateral compartment of the knee joint known as the fabella. We compared and reviewed all reported cases of common fibular nerve palsy due to fabellae in the English literature. Compression can develop spontaneously or post-surgically (total knee arthroplasty). Symptoms progress rapidly to complete foot drop. Among all the cases reviewed, 68.42% were males with a median age of 39.39 years. Fabella compression was more common in the left common fibular nerve (CFN) (63.16%). Both big (23 × 20 × 16 mm) and small (5 × 5 mm) fabellae can be responsible for compression. While diagnosis can be problematic, the treatment (either surgical fabellectomy or conservative) is relatively easy and brings quick improvement.

Entrapment neuropathy of common peroneal nerve by fabella: A case report.

BACKGROUND: Neuropathy of the common peroneal nerve caused by compression by a fabella is an extremely rare form of compression neuropathy. Involving both the superficial and deep peroneal nerves, it usually manifests as either impaired sensation from the lower lateral leg to the top of the foot or drop foot, or as a combination of both. CASE SUMMARY: We report the case of a 58-year-old Asian female who presented with inversion of the right foot during the stance phase of gait without sensory complaints related to the lower leg. Electrodiagnostic testing revealed the neuropathy of the common peroneal nerve at the level of the knee, exclusively affecting the muscular branch of the superficial peroneal nerve. A neuromuscular ultrasound disclosed swelling of the right common peroneal nerve just before it crossed over a large fabella as well as atrophy and fatty infiltration of the right peroneus longus and peroneus brevis muscles. Surgical excision of the fabella and neurolysis were performed. Subsequently, the strength of the right foot evertors improved, but the unsteady gait with occasional falls persisted for nine months after the surgery. Therefore, another procedure was performed to transfer the split posterior tibialis tendon to the peroneus brevis in order to correct the gait. CONCLUSION: This is the first case of neuropathy of the common peroneal nerve caused by compression by a fabella affecting exclusively the muscular branch of the superficial peroneal nerve. Clinicians should be aware of this unusual peripheral neuropathy while evaluating and treating patients with gait disturbance.

Prevalence and Radiological Characteristics of the Fabella in Turkish Population.

BACKGROUND: This study aimed to evaluate and analyze the prevalence and radiological characteristics of the fabella in the Turkish population, detecting differences between genders by examining magnetic resonance imaging (MRI) images of subjects. METHODS: A total number of 504 patients aged >18 years who were admitted to the orthopedics and traumatology clinic between November 2018 and October 2020 were included in this retrospective cross-sectional study. Bilateral MRI images that were taken from each patient were randomly selected. Age, sex, laterality (right or left knee), and size of the fabella were retrieved from institutional database records. P-value<0.05 is considered statistically significant. RESULTS: A total of 504 patients were included with 213 males and 291 females. The overall prevalence of fabella was 20.63%. The mean length, thickness, and width of the fabella were 6.05 mm, 4.63 mm, and 5.92 mm, respectively, in the overall population. The fabella was significantly wider, thicker, and longer in males compared to females in the Turkish population. CONCLUSION: This study revealed similar prevalence rates of the fabella in the Turkish population with Caucasian populations and similar size of the fabella in the Asian population. When different prevalence rates and sizes of the fabella among different ethnic populations are considered, it is critical to understand the prevalence or radiological features of the fabella in Turkish subjects to avoid misinterpretation of fabella diseases.

Common fibular nerve palsy due to fabella compression: An illustrative case report.

BACKGROUND: The fabella is a sesamoid bone situated in the tendon of the lateral head of the gastrocnemius muscle behind the lateral femoral condyle. Common fibular nerve injury may occur anywhere on its course and the most common etiology remains compression at the level of the head of the fibula. Compression by a fabella is a very unusual cause of common fibular nerve palsy and only few case reports are described in the literature. We present here an illustrative case. CASE DESCRIPTION: A 50-year-old female patient presented with a left drop-foot evolving for two weeks without pain or sensory deficit. Clinical examination revealed a paresis of the left foot dorsiflexors muscles (3/5). A compressive neuropathy of the common fibular nerve at the level of the fibula head was demonstrated by nerve conduction studies. Ultrasound of the left knee revealed nerve compression by a fabella. Early decompressive surgery was performed and the fabella was excised. We noticed an almost complete recovery probably due to early treatment (4+/5 two months after surgery). CONCLUSIONS: Common fibular nerve palsy related to fabella compression is very uncommon. Good clinical outcome has been described at 1-2 years with an early work-up and a prompt surgical decompression.

The prevalence and parameters of fabella and its association with medial meniscal tear in China: a retrospective study of 1011 knees.

BACKGROUND: Fabella is a sesamoid bone of knee that has potential biomechanical function. We aimed to examine the fabellar prevalence and parameters in Chinese population and test the hypothesis that fabellar presence and morphology were associated with meniscus tear or ligament injury. METHODS: A total of 1011 knee magnetic resonance imaging scans from 979 patients with knee pain were analyzed retrospectively. The exclusion criteria are postsurgical scans, difficulty in fabella discrimination, conditions not suitable for measurement, and unsatisfied image. The fabellar presence and its parameters (length, width and thickness) were documented. The association between fabellar presence and meniscus tear or ligament injury were assessed by chi-square test, in all knees and subgroups (age, gender, side, lesion part). The correlation of fabellar presence and parameters with advancing age was assessed by Spearman correlation analysis. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to investigate whether factors related with meniscus tear or ligament injury. Diagnostic performance of risk factors was assessed by receiver operating characteristic (ROC) analysis. RESULTS: The overall prevalence of fabellae was 39.8% (402/1011 knees) and increased with the increasing age (r = 0.237, P < 0.001). The size of the fabellae differed according to genders, age, and presence of articulating grooves. Fabella presented more often in knees with medial meniscus (MM) tears (66.7% vs 33.8%; P < 0.001) with a multivariate OR of 2.960 (95% CI, 1.853-3.903). The association remained in all tear parts (anterior, middle, and posterior), and in younger (age < 50 years) and older patients (age ≥ 50 years). Age, fabellar length, width, length/thickness ratio and width/thickness ratio yielded an area under the ROC curve (AUC) of 0.604-0.766 to predict an MM tear. In combination with age, fabellar width and length/thickness ratio, the AUC was improved 0.791 (95% CI, 0.744-0.837), with a sensitivity of 73.0% and a specificity of 74.6%. CONCLUSION: The presence of fabellae, increased fabellar length and width as well as flatter fabellar morphology, are significantly associated with an increased risk for MM tear. These findings might aid clinicians in identifying patients at risk for a MM tear and informing them.

Fabella syndrome in a professional football player: A case report and literature review.

INTRODUCTION AND IMPORTANCE: Fabella syndrome is a rare cause of posterolateral knee pain. The definitive diagnosis and management of this syndrome remain unclear. CASE PRESENTATION: We report a case of a 19-year-old patient who is a Vietnamese professional football player. He presented with persistent pain in the posterolateral aspect of the knee joint for 12 months that was unrelated to trauma. He was treated conservatively for 6 months without any improvement in the previous hospital. He was diagnosed with fabella syndrome and underwent open surgery to remove the bone. Evaluation after surgery 12 weeks revealed the symptoms disappeared and he was able to return to practice. CLINICAL DISCUSSION: In order to diagnose fabella syndrome, the clinicians need to be vigilant and base on the clinical signs as well as imaging to exclude other causes of posterolateral knee pain. Conservative therapy is always the first choice of treatment although the recurrence rate is high, especially in professional athletes. If the initial conservative therapies failed, the fabella surgical removal surgery should be made in athletes. CONCLUSION: Fabella syndrome is a rare cause of posterolateral knee pain in professional athletes. The definitive diagnosis and management of this syndrome remain unclear. Our case shows that surgical removal of the bone fragments can be considered if failure after the initial conservative therapies.

Relationship between Classification of Fabellae and the Severity of Knee Osteoarthritis: A Relevant Study in the Chinese Population.

OBJECTIVE: To classify the fabellae and discuss the relationship between the classification of fabellae and the severity of knee osteoarthritis (KOA) in Chinese. METHODS: From February 2019 to February 2020, 136 patients were measured and classified using three-dimensional computed tomography (CT) reconstruction. According to the CT imaging characteristics, the fabellae were divided into five types: type I, a fabella on the lateral femoral condyle; type II, a fabella on the medial femoral condyle; type III, a fabella on the lateral femoral condyle and a fabella on the medial femoral condyle; type IV, two fabellae on the medial femoral condyle; and type V, two fabellae on the lateral femoral condyle. The severity of KOA was assessed on the Recht grade by magnetic resonance imaging (MRI). The data were analyzed with SPSS 24.0. RESULTS: The classification of fabellae were correlated with KOA grades (χ2  = 35.026, P < 0.05). In terms of KOA grades, grade I and grade II were occupied most by fabellar type II (32, 72.8%); type II and other types showed significant statistical difference (P < 0.05). Grade I and grade II were also mainly fabellar type IV (four, 100%). Fabellar type V's biggest component was grade III and grade IV (six, 75%). Type IV and type V showed significant statistical difference (P < 0.05). CONCLUSION: The classification of fabellae were correlated with KOA grades. The type II may mean the lower KOA grades while type V may mean the higher KOA grades.

Treatment of Fabella syndrome with arthroscopic fabellectomy: a case series and literature review.

BACKGROUND: The fabella is a sesamoid bone in the posterolateral capsule of the human knee joint. In quadrupedal mammals, the fabella is believed to have a role similar to the patella in redirecting extension forces of the knee joint from one point to another. In bipeds, the fabella is not touching the back of the bent knee, and therefore the role in redirecting forces declines. Posterolateral knee pain can be associated with the irritation between the fabella and lateral femoral condyle, a phenomenon also known as fabella syndrome. In cases that are unresponsive to conservative management, surgical fabellectomy can be a successful treatment option. Among the surgical approaches, open resection is most commonly seen. There are also literature reporting arthroscopic-assisted open resection, but seldom mentioned the all-arthroscopic fabellectomy. CASE PRESENTATION: We present 3 patients with a long history (> 12 month) of posterolateral knee pain under suspicion of different pain origins. The diagnosis of fabella impingement was eventually made by ruling out of other causes. All the patients underwent all-arthroscopic fabellectomy for diagnosis and treatment. Investigations of the resected fabella suggested chronic impingement with apparent osteophyte formation and cartilage wearing of the articular side. All patients have been continually followed up at our outpatient department and reported to be pain free after the procedure. CONCLUSIONS: In the patients presenting posterolateral pain, fabella syndrome cannot be ignored due to its relative higher presence in Asian population. In our experience, the all-arthroscopic fabellectomy offers a smaller wound size, less post-operative pain, fewer days of hospitalization and quicker time to rehabilitation for the patients with chronic posterolateral knee pain caused by fabella syndrome.

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 21 were 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.

Relationship of the fabella with the origins of the plantaris and gastrocnemius lateral head muscles in late-term fetuses: a histological study.

Previous studies of midterm fetuses indicated that a cartilaginous fabella appeared to be embedded in the plantaris (PL), and was fused with the gastrocnemius lateral head (GL). We re-examined the topographical anatomy of the fabella or its analogue (a tight fibrous mass) originating in the GL and/or PL by evaluating histological sections of the unilateral knees of 15 late-term fetuses. Regardless of whether the cartilaginous fabella was present (6 fetuses) or absent (9 fetuses), the origins of the PL and GL muscles each had three parts. In each fetus, the fabella or its analogue was embedded in a thick common tendinous origin of the GL and PL. PL1 (whose origin is similar to that of the adult PL) originated from the femoral condyle immediately above the common tendon; PL2 originated from the posteromedial aspect of the fabella or its analogue; and PL3 originated from the inferior aspect of the fabella or its analogue. The muscle fibers of PL1, PL2, and PL3 joined to provide a thick plantaris. GL1 (which is adjacent to PL2) originated from the common tendon in the superior side of the fabella or its analogue and GL2 originated from the inferior side of the fabella or its analogue. GL1 and GL2 joined to provide a thick bundle, whereas GL3 (located far below the fabella or its analogue) originated from the posterior surface aponeurosis. Therefore, drastic reconstruction at these muscle origins was necessary during development. Due to the strong mechanical stress from the GL and the space-occupying effect of the muscle, we hypothesize that PL2 and PL3 are degraded or absorbed into the GL1 and GL2 during the postnatal period, so that the remaining PL1 was likely the remaining PL in adults.

Cyamella (a popliteal sesamoid bone) prevalence: A systematic review, meta-analysis, and proposed classification system.

The cyamella is a rare, generally asymptomatic, knee sesamoid bone located in the proximal tendon of the popliteal muscle. Only two studies have investigated cyamella presence/absence in humans, putting ossified prevalence rates at 0.57%-1.8%. We aim to (a) determine cyamella prevalence in a Korean population, (b) examine coincident development of the cyamella and fabella, and (c) perform a systematic review and meta-analysis on the cyamella in humans. Medical computed tomography scans of 106 individuals were reviewed. A systematic review and meta-analysis were performed following PRISMA guidelines. Cyamellae were found in 3/212 knees (1.4%), and presence/absence was uncorrelated to height, age, and sex. The cyamella was not found coincidentally with the fabella, although the statistical power was low. Our systematic review/meta-analysis revealed cyamellae were generally asymptomatic and ossification could occur at 14 years. Cyamellae were equally likely to be found in both sexes, knees, one or both knees, and there appeared to be no global variation in prevalence rates. Cyamellae were found in three distinct locations. There is little support for the role of intrinsic genetic and/or environmental factors in cyamella development in humans. However, the apparent phylogenetic signal in Primates suggests genetics plays a role in cyamella development. We propose a cyamella classification system based on cyamella location (Class I, popliteal sulcus; Class II, tibial condyle; Class III, fibular head) and hypothesize locations may correspond to distinct developmental pathways, and cyamella function may vary with location.

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.