Introduction
Although lipomas constitute nearly half of all the soft tissue tumors [1, 3], intra-articular lipomas have rarely been reported [1,5,7,8,13]. Two types of lipomas have been described for the knee joint: real intra-articular lipomas and lipoma arborescens. Intra-articular lipomas are typically located on the infrapatellar fat pad; they are solitary lesions with slow growth, create insignificant symptoms and contain only fat tissue. Lipoma arbo-rescens generally develops secondary to a degenerative joint disease and is not regarded as a real neoplasm [1,3,
6,8]. In this article, we present a case of painful stran-gulated lipoma localized within the infrapatellar fat pad and discuss the similar reports.
Case presentation
A 42-year-old female patient presented herself with the complaints of increasing pain, swelling and limitation
of motion of her right knee that had initiated 2 weeks before. She did not have any history of trauma but reported increased physical activity within the last 3 months owing to the new aerobics classes. She had intermittent pain on her right knee, which was not so bothering. On physical examination parapatellar sulci was found to have disappeared and there was signifi-cant tenderness of the patellar tendon. There was no erythema or increase in the local temperature. There was severe pain during the last 20 of extension. The examination of the lower extremities for alignment, ligaments and menisci were normal. There was no patellar crepitation or effusion. Patellar mobility tests were normal. Direct X-rays of the knee and routine laboratory tests did not reveal any pathology. These findings were consistent with Hoffa disease (retropa-tellar bursitis) and 3 weeks of rest, cold compresses and nonsteroidal anti-inflammatory drugs (NSAIDs) were prescribed. As there was no improvement in her con-dition on the control visit, magnetic resonance (MR)
imaging was performed, which showed a
Selc¸uk Keser Ahmet Bayar Gamze Numanog˘lu
An unusual cause for anterior knee pain:
strangulated intra-articular lipoma
Received: 10 February 2004 Accepted: 21 September 2004 Published online: 27 January 2005 Springer-Verlag 2005
Abstract Lipoma is the most fre-quently encountered benign soft tis-sue tumor. However, intra-articular lipomas are rarely seen. Anterior knee pain is a frequent complaint of adults and is of diverse etiology. This 42-year-old female patient had severe anterior knee pain, unre-sponsive to medical treatment. Magnetic resonance imaging
revealed an intra-articular tumor of the knee joint. Arthroscopic inter-vention and subsequent histological examination resulted in the diagno-sis of strangulated lipoma originat-ing from infrapatellar fat pad. We present clinical, radiological and operative features of this rare case of intra-articular lipoma.
Keywords Intra-articular lipoma Æ Knee joint Æ Arthroscopy Æ MRI Æ Hoffa disease Æ Lipoma arborescens
DOI 10.1007/s00167-004-0595-4
G. Numanog˘lu
Department of Pathology,
Karaelmas University Medical School, Zonguldak, Turkey
Knee Surg Sports Traumatol Arthrosc
(2005) 13: 585–588 K N E E
S. Keser (&) Æ A. Bayar Department of Orthopaedics and Traumatology, Karaelmas University Medical School, 67600 Kozlu/ Zonguldak, Turkey
E-mail: selkeser@hotmail.com Tel.: +90-372-2610170 Fax: +90-372-2610155
20·10·0.8 mm mass with lobulated contours on the posterior aspect of Hoffa’s fat pad (Fig.1a). The mass had low signal intensity on T1A sequences (Fig. 1b). While the central portion had slightly high signal intensity on T2IFEE, the peripheral portion had low signal intensity (Fig.1c). The mass also had regular contrast enhancement at its periphery (Fig. 1d). Knee arthroscopy was performed for definitive diagnosis and treatment. When viewed from the anterolateral portal, anterior to the tibial end of the anterior cruciate liga-ment (ACL), there was a round, mobile, yellow mass with well-defined borders that was connected to the infrapatellar fat pad with a thin pedicle. The arthro-scopic examination of other structures were normal. Since the mass was considered to be too large for
arthroscopic en-bloc resection, a lateral parapatellar arthrotomy was performed (Fig.2). After the pedicule had been identified and released, the mass was totally excised. On macroscopic examination the mass was measured as 2·1.5·1 cm. It was yellow in color with moderate consistency and had regular borders while being covered with a fibrous capsule (Fig.3). Presence of necrotic fat cells and fibrous capsule on histopath-ological examination revealed the diagnosis of infarcted lipoma (Fig.4). Most of the tumor had undergone fat necrosis due to torsion of the stalk. The patient was relieved of her complaints during the control visit on the first postoperative month. Knee examination was normal on 1-year control. Control MR did not reveal any recurrence or further pathology.
Fig. 1 a Magnetic resonance (MR) imaging of right knee demon-strated a 20·10·0.8 mm mass with lobulated contours on the posterior aspect of Hoffa’s fat pad. b The mass posterior to infrapatellar fat pad had low signal intensity on T1-weighted sagittal sequences. c While the central portion had slightly high
signal intensity on T2-weighted sagittal sequences, the peripheral portion had low signal intensity. d The mass also had regular contrast enhancement at its periphery. The mass was protruding into the joint cavity
Discussion
Anterior knee pain is a frequent complaint among the patients of orthopedics departments, yet underlying etiology could not easily be identified in some cases [4,
10,11]. In the absence of a history of trauma in an adult patient, the complaint is due to the diseases of the
patello-femoral joint, generally resulting from the alignment disturbances of the extensor mechanism or repetitive activity of the knee [4,12].
The clinical features of our patient had been initially considered to be consistent with Hoffa disease. Hoffa disease is the hypertrophy and inflammation of the inf-rapatellar fat pad resulting from its impingement be-tween femoral condyles and tibial plateau during extension of the knee [4, 7]. The enlarged fat pad can mimic a mass by protruding into the joint space from the synovial membrane [7]. Repetitive trauma and strenuous exercise can be causative factors [4,12].
Lipoma arborescens and lipoma are among the fre-quent masses originating from infrapatellar fat pad; however MR findings were not typical for these tumors [7, 8]. Lipoma arborescens is encountered more frequently in the knee joint compared to a lipoma [8]. Non-neoplastic villous or polypoid synovial prolifera-tions or subsynovial fat hyperplasia resulting from chronic irritations of the synovial membrane are com-monly observed in the suprapatellar pouch. The patients with such a lesion typically complains of increasing but painless swelling of the knee [2, 6, 8]. Lipoma of the infrapatellar fat pad has rarely been reported. Yeomans et al. [13] performed arthroscopy in a patient who was admitted with the complaints of sudden onset of pain with increasing severity and locking of the knee. They identified a 0.8·0.6·0.5 cm, tan color and hemorrhagic mass originating from the infrapatellar fat pad and excision was performed. Histological examination revealed necrotic hemorrhagic fat tissue partially cov-ered with synovium and the diagnosis was established as infarcted intra-articular polypoid lipoma resulting from strangulation of the pedicle [13]. In the case of Marui et al. [7] the complaint was knee pain and physical examination revealed a mass on the anterolateral part of the knee. Following the arthroscopic examination of the
Fig. 2 Appearance of the mass with lateral parapatellar arthro-tomy
Fig. 3 Gross histologic specimen was yellow in color with moderate consistency and had regular borders while being covered with a fibrous capsule. Appearance of released pedicule (black arrow)
Fig. 4 Microscopic appearance of infracted lipoma; presence of necrotic fat cells and fibrous capsule. (HEx10)
mass, macroscopic examination had shown a soft and yellow mass of 4·3·3 cm with regular borders. As fat cells demonstrating significant mixoid changes were identified during the pathological examination, the diagnosis was established as lipoma [7]. Mine et al. [9] have described yellow colored intra-articular masses with regular borders and pedicles that were originating from infrapatellar fat pad in two separate cases. Both cases complained of mechanical symptoms of the knee joint. Following arthrotomic excision, although defini-tive diagnosis could not be established, tissue necrosis was observed in both specimens [9]. In cases of lipoma that were originating from fat pads in other areas of the knee, pain was of lesser degree and surgery was per-formed because of significant mass lesions [1,5,8]. There was not severe pain or mechanical symptoms as observed in the cases of lipomas with infrapatellar localization. Macroscopical and histological diagnoses could easily be established. In our case, the pain of sudden onset with increasing intensity was related to the
development of necrosis due to strangulation of the li-poma. We think that the possibility of necrosis increased due to the fact that the region of infrapatellar fat pad was narrow in the knee joint and that the mobile mass was frequently entering the joint space as seen in the histological examination of the other lipoma cases in this region.
In conclusion, in cases with sudden onset of anterior knee pain, limitation of movement and tenderness surrounding the patellar tendon are identified, stran-gulated lipoma should be considered in the differential diagnosis, albeit a rare possibility. Although MR examination demonstrates the presence of a mass, arthroscopy could be beneficial in establishing the diagnosis and planning the type of treatment. Though lipoma cases are reported to be excised arthroscopically [1,13], because of the size of the mass en-bloc resection might not be possible in all of the cases. Arthroscopic or arthrotomic excision results in the cure of the intra-articular lipoma.
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