Fabella Syndrome as an Uncommon Cause of Posterolateral Knee Pain after Total Knee Arthroplasty: A Case Report and Review of the Literature

The fabella is a sesamoid bone located behind the lateral femoral condyle. It is common in non‐human mammals, but the prevalence rates in humans vary from 3 to 87%. Here, we calculate the prevalence of the fabella in a Korean population and investigate possible temporal shifts in prevalence rate. A total of 52.83% of our individuals and 44.34% of our knees had fabellae detectable by computed tomography scanning. Men and women were equally likely to have a fabella, and bilateral cases (67.86%) were more common than unilateral ones (32.14%). Fabella presence was not correlated with height or age, although our sample did not include skeletally immature individuals. Our systematic review yielded 58 studies on fabella prevalence rate from 1875–2018 which met our inclusion criteria, one of which was an outlier. Intriguingly, a Bayesian mixed effects generalized linear model revealed a temporal shift in prevalence rates, with the median prevalence rate in 2000 (31.00%) being ~ 3.5 times higher than that in 1900 (7.64%). In all four countries with studies before and after 1960, higher rates were always found after 1960. Using data from two other systematic reviews, we found no increase in prevalence rates of 10 other sesamoid bones in the human body, indicating that the increase in fabella prevalence rate is unique. Fabella presence/absence is due to a combination of genetic and environmental factors: as the prevalence rates of other sesamoid bones have not changed in the last 100 years, we postulate the increase in fabella prevalence rate is due to an environmental factor. Namely, the global increase in human height and weight (due to improved nutrition) may have increased human tibial length and muscle mass. Increases in tibial length could lead to a larger moment arm acting on the knee and on the tendons crossing it. Coupled with the increased force from a larger gastrocnemius, this could produce the mechanical stimuli necessary to initiate fabella formation and/or ossification.

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“…; Okano et al. ). This implies there may be no significant mechanical, evolutionary advantage to having a fabella (Sarin et al.…”

Section: Resultsmentioning

confidence: 96%

“…; Okano et al. ). The absence of an articulating groove in the back of the lateral femoral condyle, which serves to stabilize the fabella and is present in some anatomical variants (e.g.…”

Section: Introductionmentioning

confidence: 96%

Fabella prevalence rate increases over 150 years, and rates of other sesamoid bones remain constant: a systematic review

2019

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“…Other described features include posterolateral knee swelling, pain on direct pressure of the fabella, pain on extension of the knee, clicking sensations, and common peroneal nerve dysfunction. Fabella syndrome has been described secondary to total knee arthroplasty [16, 21-25], however, we describe the only known documented case of fabella syndrome occurring secondary to femoral de-rotation surgery.…”

Section: Discussionmentioning

confidence: 89%

Fabella Syndrome Following De-Rotation Surgery to Correct a Femoral Malunion

Rankin¹,

Rehman²,

Ashcroft³

2018

TOORTHJ

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Background:The fabella is a sesamoid bone situated within the lateral head of the gastrocnemius tendon, close to the lateral femoral condyle, and adjoined to the fabellofibular ligament. It is a normal variant, found in up to 87% of patients. Fabella Syndrome describes traditionally posterolateral knee pain, occurring due to biomechanical pressure of the fabella against the lateral femoral condyle. Given its rarity, its diagnosis is often overlooked. We present a case of Fabella Syndrome with a modified surgical excision technique and review of the literature.Methods and Results:A thirty-four-year-old man presented with posterolateral knee pain following de-rotation surgery to correct a femoral malunion, from a previous femoral shaft fracture. Due to the patient’s complex orthopaedic history, Fabella Syndrome was not initially diagnosed. Fabellectomy eliminated all symptoms of knee pain, with no limitations in knee function.Conclusion:Review of the literature identified ten publications (evidence level IV) describing Fabella Syndrome. This is the first reported case of Fabella Syndrome secondary to femoral de-rotation surgery. The authors recommend fabellectomy as a definitive treatment for Fabella Syndrome, in keeping with published literature.

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“…As fabella could cause KOA and it may be an atavistic pattern. Some people insisted, fabellae could be excised and found the posterolateral pain would disappear or greatly improve when removing the fabella [40] .…”

Section: Discussionmentioning

confidence: 99%

Relationship Between Classification of Fabellae and the Severity of Keen Osteoarthritis: A Relevant Study in Chinese Population

Zhang¹,

Wen²,

He³

et al. 2020

Preprint

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Background: The fabella is a sesamoid bone having anatomical variations and it is more common in patients with primary keen osteoarthritis (KOA). The purpose of this study was to classify the fabellae and discuss the relationship between the classification of fabellae and the severity of KOA in Chinese. Material and methods: 136 patients were measured and classified using CT three-dimensional reconstruction. According to the CT imaging characteristics, the fabellae were divided into 5 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 MRI. The data were analyzed with SPSS 24.0. Results: The classification of fabellae were correlated with KOA grades (c 2 =35.026, P<0.05). In terms of KOA grades, grade Ⅰ and grade Ⅱ were occupied most of fabellar type Ⅱ (32, 72.8%); type Ⅱ and other types were significant statistical difference (P<0.05). Grade Ⅰ and grade Ⅱ were also the most of fabellar type Ⅳ (4, 100%). Fabellar type Ⅴ’s biggest component were grade Ⅲ and grade Ⅳ (6, 75%). Type Ⅳ and type Ⅴ were 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. Trial registration: the Ethics Inspection Committee at Southwest Medical University, V1.0/20180801. Registered 20 August 2018.

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Fabella Syndrome as an Uncommon Cause of Posterolateral Knee Pain after Total Knee Arthroplasty: A Case Report and Review of the Literature

Cited by 15 publications

References 12 publications

Fabella prevalence rate increases over 150 years, and rates of other sesamoid bones remain constant: a systematic review

Fabella prevalence rate increases over 150 years, and rates of other sesamoid bones remain constant: a systematic review

Fabella Syndrome Following De-Rotation Surgery to Correct a Femoral Malunion

Relationship Between Classification of Fabellae and the Severity of Keen Osteoarthritis: A Relevant Study in Chinese Population

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