INTRODUCTION
Intra-articular synovial lipoma is rare, but if found, it can be found either in knee joints, hips, or in lumbar spinal cords [1,2]. In the case of knee joints, lipoma can occur in either the patellar fat pad, the retinaculum, or the suprapatellar pouch. Depending on the size or the location of the tumor, different symptoms such as mass effect of the tumor itself or catching or locking of the knee can be seen [3]. Further, synovial lipoma can be differentiated from other similar lipomatoid conditions, such as villous lipomatous proliferation of the synovial membrane (lipoma arborescens) or Hoffa disease. At present, there is only one documented case of Intra- articular synovial lipoma in the Korean literature [4], and there are no reported cases so far of an arthroscopic removal of the tumor. The authors present a case of intra- articular lipoma that was arthroscopically shown to be around the posterior horn of the medial meniscus in the posteromedial compartment of the knee and exhibited
symptoms of intermittent locking of the knee like a loose body. The authors are first to report of a total excision and treatment of an intra-articular synovial lipoma under arthroscopic guidance.
CASE REPORT
A 37-year-old female patient first complained of a dull pain at the posterior part of the right knee around a year ago, and recently reported of an intermittent catching and locking of the knee. It was noted that the catching of the knee was painless and no clicking accompanied the symptom. The locking of the knee occurred 2-3 times over a period of 2 months, and no particular position triggered this symptom and was resolved by the voluntary flexion and extension of the knee. The patient’s medical history was clean and no concomitant systemic disease was present. No visible mass was detected around the knee joint upon physical examination, and neither was there edema of the knee nor effusion within the joints.
Intra-articular synovial lipoma of the knee joint is exceedingly rare. Although there has been one documented case of an open excision in Korean literature, our report presents a first description treated entirely by arthroscopic methods.
A 37-year-old female patient suffered from a catching or intermittent locking of the knee, like a loose body. The arthroscopy revealed a globular, yellowish tumor extending from the posteromedial capsule into the joint space. The mass was around the posterior horn of the medial meniscus and showed signal intensity similar to subcutaneous fat on T1- and T2-weighted magnetic resonance images. The tumor was totally excised under arthroscopic guidance and histological examination of the specimen revealed a tumor composed of mature adipose cells covered with a thin fibrous tissue. Thus, intra-articular synovial lipoma should be considered in the differential diagnoses when examining a patient with catching or locking of the knee.
Keywords: Arthroscopic excision; Intra-articular synovial lipoma; Knee
Intra-articular synovial lipoma in the posteromedial compartment of the knee
Jung Hoei Ku, Hyung Lae Cho, Jong Tae Park, Tae Hyun Wang, Hui Sun Yang
Department of Orthopaedic Surgery, Good Samsun Hospital, Busan, Korea
Copyright © 2014 Korean Arthroscopy Society and Korean Orthopedic Society for Sports Medicine. All rights reserved.
CC This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/
by-nc/3.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
AOSM
Received July 30, 2013; Revised August 9, 2013; Accepted August 9, 2013
Correspondence to: Hyung Lae Cho, Department of Orthopaedic Surgery, Good Samsun Hospital, 193-5 Jurye-dong, Sasang-gu, Busan 617-718, Korea. Tel: +82-52-310-9289, Fax: +82-52-310-9348, E-mail: [email protected]
The range of motion of her right knee was normal and slight posteromedial joint line tenderness was noted by palpation, but no pain or click were elicited by McMurray or Apley tests. Laboratory results for peripheral blood examinations such as the erythrocyte sedimentation rate, white blood cells counts, C-reactive protein, and rheumatoid factor were all within the normal range. Plain radiographs likewise gave no particular abnormalities.
However, a high signal intensity mass was found around the posterior horn of the medial meniscus on T1-weighted magnetic resonance imaging (MRI) (Fig. 1). The mass was situated on the upper part of the posterior horn of the medial meniscus and seemed to be interposed between the medial femoral condyle and the intercondylar eminence. On coronal T2-weighted images, the mass had a low signal intensity capsule and its content showed similar signal intensity to bone marrow or subcutaneous fat (Fig. 2A). The tumor on the posterior horn of the medial meniscus seemed to protrude into the intra-articular space from the posteromedial compartment when viewed
from the sagittal T2-weighted image (Fig. 2B).
As conservative methods employed during a previous hospital visit did not alleviate symptoms, biopsy and arthroscopic excision to completely remove the mass were carried out. Under general anesthesia, a tourniquet was applied and, standard anterolateral and anteromedial arthroscopic portals were created. Initial arthroscopic examination from the anterolateral portal showed no visible mass in the posteromedial side. However, when lowering the intra-articular pressure by suctioning of the irrigating fluid with a shaver, we could identify a soft yellowish mass protruding above the upper portion of the posterior horn of the medial meniscus (Fig. 3A). The tumor was capsulated, about 1.8 × 1.6 mm in dimension and seemed to have originated from the synovium of the posteromedial compartment, and jutted out into the intra-articular space. Interestingly, increasing the pressure of the irrigating fluid caused the tumor to be pushed back towards the posteromedial compartment. However, flexion or extension of the knee during the arthroscopic
Fig. 2. (A) Coronal T2-weighted magnetic resonance imaging (MRI) showed high signal intensity from a small, round, mass-like loose body with a low signal intensity wall (arrow head) and (B) sagittal T2-weighted MRI showed mass with intensity similar to fat above the posterior horn of medial meniscus (arrows).
Fig. 1. Coronal (A) and sagittal (B) T1- weighted magnetic resonance imaging revealed a mass around the posterior horn of the medial meniscus (arrows) with similar signal intensity to subcutaneous fat tissue.
examination did not induce movement of the tumor.
Nevertheless, movement of the tumor induced upon changes in pressure made en bloc resection difficult.
Thus, an arthroscopic punch and shaver were utilized to carefully cut out the tumor and the surrounding synovium simultaneously (Fig. 3B). Stability of the posterior horn of the medial meniscus was confirmed by giving it a firm
pull with a probe (Fig. 3C), so additional meniscal repair was not performed. After excision, negative pressure was applied to the knee joint to test for any protruding residual tumor. Residual fat and the surrounding fibrous septal tissue were removed through the posteromedial portal (Fig. 3D).
Macroscopically, the tumor tissues collected during
Fig. 3. The arthroscopic excision of the lipoma from the anterolateral portal. (A) Smooth, soft, yellowish mass above the posterior horn of the medial meniscus. (B) Excision of the intraarticular lipoma using an arthroscopic punch and (C) the stability of the posterior horn was checked after complete excision. (D) Residual fibro-fatty capsular wall was identified using a needle from the posteromedial portal during excision. MFC, medial femoral condyle;
MMPH, medial meniscus posterior horn,
*lipoma.
Fig. 4. The histologic appearance of the lesion reveals (A) mature adipose tissue within the subsynovial layer with fibrous septae (H&E, ×100). (B) No lipoblasts or atypical cells were found, and the resulting histopathologic diagnosis was lipoma (H&E, ×200).
the surgery were similar in appearance as that of lipoma of other regions. Likewise, histopathological observation detected mature adipose cells surrounded by thin fibrous septae within a synovium, which is a typical finding for a lipoma (Fig. 4). The mature cells found were largely mature adipose cells, with no apparent presence of lipoblasts or malignant proliferative cells. Further, scanty chronic inflammatory cells and small blood vessels were present amongst adipocytes. Therefore, a histopathological dia- gnosis of an intra-articular lipoma was made. Immo bili- zation of the knee joint was not employed postsurgically, and active motion of the knee and weight-bearing were allowed the day after operation. The patient returned to day-to-day routine exercise within 2 weeks after surgery.
At 6-months follow-up, the patient was clear of locking or pain of the knee, and showed no suspicious signs of recurrence.
DISCUSSION
More than half the soft-tissue tumors prevalent are tumors of the adipose cells, also called a lipoma. Lipoma commonly occurs in subcutaneous fat, muscle cells, the nervous system, or in thoracic, abdominal, or oral cavities.
However, intra-articular synovial lipoma is exceedingly rare and seldom reported even in international literature [3,5-7]. In the Korean literature, Kim et al. [4] reported a case of a synovial lipoma of the knee, located in the medial gutter and suprapatellar pouch, which was successfully excised through an open incision. Yet, there have been no reports of an arthroscopic approach to excise the tumor. A synovial lipoma can occur as a painless tumor, or if large in size, can cause a sense of dull pain due to pressurization. However, in general, these tumors come in small sizes and become interposed between patella- femoral joints, and abrasion against tendons may induce locking of the knee. In some cases, acute pain is caused by the torsion of the capsular stalk [7]. In this report, we presented the development of a synovial lipoma within the posteromedial compartment of the knee. Intriguingly, the tumor led to symptoms such as catching and locking of the knee that is similar to symptoms found in the bucket handle tear of the meniscus or loose bodies. It is thought that the intermittent locking of the knee was due to the repetitive movement of the tumor to and fro the intra-articular space as a result of the changes in the pressure level within.
Diagnosis of the disease is difficult solely by physical
examination or observing the medical history, and although palpation of the mass does help to an extent, the basis of diagnosis is made principally through MRI.
Typically, lipomas usually give out signal intensity similar to that of subcutaneous fat on both T1- and T2-weighted MRI, and on fat suppression imaging there is clear decrease in the overall signal intensity [3]. Low intensity signals within or around lipomas can sometimes be seen on T2-weighted images, but this is believed to be because of the presence of fibrotic septum or capsule inside or outside the tumor mass, respectively. The lipoma concerned also showed low intensity signal, presumably from the fibrous capsule surrounding the mass, on T2- weighted imaging, and before our surgery this was mistaken for loose bodies within the posteromedial compartment.
It is important to be able to differentiate between synovial lipoma of the knee and other similar lipomas such as lipoma arborescens and Hoffa disease, which are both fat cell proliferative diseases. Lipoma arborescens is a pseudotumor of the synovium of the knee and is characteristic for marked villous proliferation of the synovium and hyperplasia of the subsynovial fat. Macro- scopically, villous or lobular appearance of lipoma arborescens distinguishes itself from the small, round or oval contours of synovial lipomas [8]. Lipoma arborescens can further be ruled out if there is an absence of numerous underlying diseases such as, degenerative arthritis, rheumatoid arthritis, diabetes, gout, or psoriasis, that tend to accompany this type of lipoma. As a true intra- articular tumor, synovial lipoma is not associated with any underlying diseases.
Hoffa disease on the other hand, is typically a syndrome of recurrent impingement of a hypertrophic infrapatellar fat pad [9]. The repeated irritation of the intra-articular fat pad leads to inflammation and edema, and before the condition is able to resolve, swollen and inflamed fat pad receives further repetitive impingement from the patella- femoral and femoral-tibia joints, thereby aggravating the condition. Hypertrophy is believed to be caused by posttraumatic hemorrhage and subsequent fibrosis, leading to clinical signs that are similar to synovial lipoma.
However, unlike synovial lipomas, Hoffa disease usually exhibits an isolated or repeated trauma history. Further, in contrast to synovial lipomas, Hoffa disease shows low intensity signals on both T1- and T2-weighted MRI, due to the accumulation of hemosiderin and fibrin from repeated hemorrhage [10]. On histological examination,
proliferation of the synovium and chronic inflammatory cells, and progressive fibroblast infiltration can be seen. Thus, comparing the location of tumor, MRI and histological findings together enable us to differentiate these three diseases. In terms of treatment, intra-articular synovial lipoma or Hoffa disease usually require excision of the affected region either by open or arthroscopic approaches, whereas, as a villous lipomatous proliferation of the synovium, lipoma arborescens is normally treated by open or arthroscopic synovectomy [7,8,10].
In summary, synovial lipoma of the knee is a rare disease of usually inconspicuous origin, and unlike other similar lipoproliferative conditions such as lipoma arborescens and Hoffa disease that come with comorbidities, it is a
true tumor that comes irrespective of the trauma or other underlying diseases. Further, as in this report, if the tumor grows to a relatively small size or around the meniscus, similar clinical symptoms may occur to when a patient has loose bodies inside the knee joint or a meniscal tear.
Therefore, discerning whether a patient has catching or locking of the knee could be a useful tool for orthopaedic surgeons to consider synovial lipoma as a differential diagnosis.
CONFLICT OF INTEREST
No potential conflict of interest relevant to this article was reported.
1. Margheritini F, Villar RN, Rees D. Intra-articular lipoma of the hip:
a case report. Int Orthop 1998;22:328-9.
2. Husson JL, Chales G, Lancien G, Pawlotsky Y, Masse A. True intra-articular lipoma of the lumbar spine. Spine (Phila Pa 1976) 1987;12:820-2.
3. Hirano K, Deguchi M, Kanamono T. Intra-articular synovial lipoma of the knee joint (located in the lateral recess): a case report and review of the literature. Knee 2007;14:63-7.
4. Kim KY, Hwang YS, Lee JH, Yoon SH. Intra-articular synovial lipoma of the knee joint: a case report. J Korean Arthrosc Soc 2012;16:47-51.
5. Matsumoto K, Okabe H, Ishizawa M, Hiraoka S. Intra-articular lipoma of the knee joint: a case report. J Bone Joint Surg Am 2001;83:101-5.
6. Motsis E, Vasiliadis HS, Xenakis TA. Intraarticular synovial lipoma
of the knee located in the intercondylar notch, between ACL and PCL: a case report and review of the literature. Knee Surg Sports Traumatol Arthrosc 2005;13:683-8.
7. Yamaguchi S, Yamamoto T, Matsushima S, Yoshiya S, Matsubara N, Matsumoto T. Solitary intraarticular lipoma causing sudden locking of the knee: a case report and review of the literature.
Am J Sports Med 2003;31:297-9.
8. Hallel T, Lew S, Bansal M. Villous lipomatous proliferation of the synovial membrane (lipoma arborescens). J Bone Joint Surg Am 1988;70:264-70.
9. Hoffa A. The Influence of the adipose tissue with regard to the pathology of the knee joint. J Am Med Assoc 1904;43:795-6.
10. Ogilvie-Harris DJ, Giddens J. Hoffa’s disease: arthroscopic resection of the infrapatellar fat pad. Arthroscopy 1994;10:184- 7.
