Clinical anatomy of the fabella
2
CLINICAL VIGNETTE Clinical Anatomy of the Fabella WILLIAM DUNCAN AND DIANE L. DAHM * Department of Orthopedic Surgery, Mayo Clinic, Rochester, Minnesota Key words: fabella; sesamoid; osteophyte; knee Objects aren’t always what they appear to be on first glance: an anatomical variant, if not recognized, may occasionally lead to a clinical quandary. The fabella (“little bean”) is one such variant that rarely acts as a source of clinical symptoms. It may, how- ever, be mistaken for a more common cause of clinical symptoms, such as an intra-articular loose body. Fabellae are sesamoid bones that are present in approximately 10 –30% of the general population and, in most cases, are found bilaterally. Formation of a sesamoid bone clearly has a biomechanical compo- nent. Mechanical stresses and loading have been shown to alter biological pathways that ultimately lead to osteocartilaginous metaplasia within tendons. Phy- logenetic studies have suggested that intrinsic genetic factors may also have a role in the development of sesamoid bones (Sarin et al., 1999). Fabellae are lo- cated in the tendon of the lateral head of the gastroc- nemius muscle and often directly articulate with the posterior surface of the lateral femoral condyle (Fig. 1). They are often mistaken for loose bodies or osteophytes and are, for the most part, asymptom- atic. Rarely, their presence may lead to a variety of clinical problems, including Fabellar Pain Syn- drome, chondromalacia fabellae, and fabella frac- ture. Additionally, enlargement of the fabella has been associated with neurologic injury of the com- mon fibular nerve, which lies in close proximity (Weiner et al., 1982; Legendre et al., 1986; Marks et al., 1998). A representative case is presented to highlight the relevant anatomy. A 91-year-old woman underwent left primary to- tal knee arthroplasty for symptoms related to her advanced osteoarthritis. Preoperative imaging re- vealed multiple loose bodies and osteophyte forma- tion within and posterior to the joint (Fig. 2). Intra- operatively, several loose bodies were, indeed, removed from the posterior joint space and the osteophytes were appropriately excised. In the pos- terolateral compartment of the knee joint, there appeared to be a rather large loose body that was held rigidly in place, encased by soft tissue. Upon further examination it was determined to represent a fabella, deemed inconsequential to the function or results of the joint arthroplasty, and left in place. Failure to recognize the structure as a fabella could have resulted in further exploration and attempted excision, significantly increasing the risk for neuro- vascular injury. Postoperative films more clearly outline the fabella and its close relationship to the popliteal artery (Fig. 3). At the time of follow-up examination, the patient was pleased with her re- sults and specifically denied any pain relative to the region of the fabella. This brief clinical vignette illustrates that even this “obscure” bone has some clinical significance. Al- though not encountered frequently, the prevalence of fabellae may be shadowed by a relatively benign ex- istence; however, the fabella’s presence is certainly deserving of attention as shown by the above exam- ple. Recognition of this variant in normal anatomy allowed for the safe removal of multiple pathologic loose bodies while leaving the fabella undisturbed. Failure to recognize the structural relationships of the fabella within the posterior knee can increase the potential for complications in surgery, such as total knee arthroplasty. *Correspondence to: Diane L. Dahm, MD, Mayo Clinic, East 14 200 First St., S.W. Rochester MN 55905. E-mail: [email protected] Received 5 March 2002; Revised 23 October 2002 Published online in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/ca.10137 Clinical Anatomy 16:448 – 449 (2003) © 2003 Wiley-Liss, Inc.
-
Upload
william-duncan -
Category
Documents
-
view
255 -
download
13
Transcript of Clinical anatomy of the fabella
CLINICAL VIGNETTE
Clinical Anatomy of the Fabella
WILLIAM DUNCAN AND DIANE L. DAHM*
Department of Orthopedic Surgery, Mayo Clinic, Rochester, Minnesota
Key words: fabella; sesamoid; osteophyte; knee
Objects aren’t always what they appear to be onfirst glance: an anatomical variant, if not recognized,may occasionally lead to a clinical quandary. Thefabella (“little bean”) is one such variant that rarelyacts as a source of clinical symptoms. It may, how-ever, be mistaken for a more common cause ofclinical symptoms, such as an intra-articular loosebody.Fabellae are sesamoid bones that are present in
approximately 10–30% of the general population and,in most cases, are found bilaterally. Formation of asesamoid bone clearly has a biomechanical compo-nent. Mechanical stresses and loading have beenshown to alter biological pathways that ultimately leadto osteocartilaginous metaplasia within tendons. Phy-logenetic studies have suggested that intrinsic geneticfactors may also have a role in the development ofsesamoid bones (Sarin et al., 1999). Fabellae are lo-cated in the tendon of the lateral head of the gastroc-nemius muscle and often directly articulate with theposterior surface of the lateral femoral condyle (Fig.1). They are often mistaken for loose bodies orosteophytes and are, for the most part, asymptom-atic. Rarely, their presence may lead to a variety ofclinical problems, including Fabellar Pain Syn-drome, chondromalacia fabellae, and fabella frac-ture. Additionally, enlargement of the fabella hasbeen associated with neurologic injury of the com-mon fibular nerve, which lies in close proximity(Weiner et al., 1982; Legendre et al., 1986; Marks etal., 1998). A representative case is presented tohighlight the relevant anatomy.A 91-year-old woman underwent left primary to-
tal knee arthroplasty for symptoms related to heradvanced osteoarthritis. Preoperative imaging re-vealed multiple loose bodies and osteophyte forma-tion within and posterior to the joint (Fig. 2). Intra-operatively, several loose bodies were, indeed,
removed from the posterior joint space and theosteophytes were appropriately excised. In the pos-terolateral compartment of the knee joint, thereappeared to be a rather large loose body that washeld rigidly in place, encased by soft tissue. Uponfurther examination it was determined to representa fabella, deemed inconsequential to the function orresults of the joint arthroplasty, and left in place.Failure to recognize the structure as a fabella couldhave resulted in further exploration and attemptedexcision, significantly increasing the risk for neuro-vascular injury. Postoperative films more clearlyoutline the fabella and its close relationship to thepopliteal artery (Fig. 3). At the time of follow-upexamination, the patient was pleased with her re-sults and specifically denied any pain relative to theregion of the fabella.This brief clinical vignette illustrates that even this
“obscure” bone has some clinical significance. Al-though not encountered frequently, the prevalence offabellae may be shadowed by a relatively benign ex-istence; however, the fabella’s presence is certainlydeserving of attention as shown by the above exam-ple. Recognition of this variant in normal anatomyallowed for the safe removal of multiple pathologicloose bodies while leaving the fabella undisturbed.Failure to recognize the structural relationships of thefabella within the posterior knee can increase thepotential for complications in surgery, such as totalknee arthroplasty.
*Correspondence to: Diane L. Dahm, MD, Mayo Clinic, East 14200 First St., S.W. Rochester MN 55905.E-mail: [email protected]
Received 5 March 2002; Revised 23 October 2002
Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ca.10137
Clinical Anatomy 16:448–449 (2003)
© 2003 Wiley-Liss, Inc.
REFERENCES
Legendre P, Fowles JV, Godin C. 1986. Chondromalacia of thefabella: a case report. Can J Surg 29:102–103.
Marks PH, Cameron M, Regan W. 1998. Fracture of the fa-bella: a case of posterolateral knee pain. Orthopedics 21:713–714.
Sarin VK, Erickson GM, Giori NJ, Bergman AG, Carter DR.1999. Coincident development of sesamoid bones and cluesto their evolution. Anat Rec 257:174–180.
Weiner DS, Macnab I. 1982. The “Fabella syndrome”: anupdate. J Pediatr Orthop 2:405–408.
Fig. 1. Normal fabella (arrow) seen within the lateral head of the gastrocnemius on MRI. A: Coronalview. B: Sagittal view.
Fig. 2. A: AP view of the left knee shows the position of the fabella preoperatively (arrowheads).B: The relationship of the fabella to the posterior aspect of the lateral femoral condyle is appreciated onlateral view.
Fig. 3. Postoperative X-ray (lateral view) shows the close prox-imity of the fabella (arrowheads) to the calcified popliteal artery(arrows) in the sagittal plane. Although not seen on X-ray, the com-mon fibular nerve often lies just superficial to the fabella.
