O

C

Pp

L

G

I

Iwpmrdcmtoea

1d

rthopaedics & Traumatology: Surgery & Research (2011) 97, 776—778

ASE REPORT

osttraumatic dislodgement of the infrapatellar fatad: An unusual type of superolateral impingement

. Mathieu ∗, M. Chetouani, D. Janku, E. Vandenbussche, B. Augereau

eorges-Pompidou European Hospital, Department of Orthopaedic Surgery, 20/40, rue Leblanc, 75908 Paris cedex 15, France

Accepted: 23 May 2011

KEYWORDS Summary The authors report a rare case of dislodgement of the infrapatellar fat pad induced

Infrapatellar fat pad;Impingementsyndromes;Hoffa’s disease;Anterior knee pain

by traumatic hyperflexion. Because of the unusual clinical presentation, open excision wasperformed to exclude a possible tumoral etiology. This entity seems to be an acute form ofsuperolateral fat pad impingement.© 2011 Elsevier Masson SAS. All rights reserved.

C

Asfpwtwridmf

ntroduction

mpingement of the infrapatellar fat pad is a rare entityhich is often diagnosed by elimination in the presence ofersistent anterior knee pain [1]. These are traumatic oricrotraumatic syndromes, with two main entities: poste-

ior impingement in the femorotibial joint space in Hoffa’sisease and superior impingement with the lateral femoralondyle which is less well known but which seems to beore frequent [2]. The authors describe an atypical presen-

ation of superolateral impingement whose diagnosis couldnly be made postoperatively. The clinical, therapeutic andtiopathogenic signs of this unusual form are discussed with

review of the literature.

∗ Corresponding author.E-mail address: laurent tom2@yahoo.fr (L. Mathieu).

oEatossl

877-0568/$ – see front matter © 2011 Elsevier Masson SAS. All rights reoi:10.1016/j.otsr.2011.05.009

ase report

50-year-old patient who was an amateur weight-lifter, con-ulted for left knee pain which had persisted for 15 daysollowing traumatic hyperflexion from a fall. There was norior history of trauma or pain in this knee. He presentedith mechanical anterolateral pain which had begun after

he fall, had continued since when walking and which wasorse when going up or down stairs. The patient did not

eport any fluid accumulation, locking or instability. On clin-cal examination, knee alignment was normal, the knee wasry and range of motion was normal. There was no liga-ent laxity. There was palpable swelling above the lateral

emorotibial joint space which corresponded to the sourcef pain. This was a solid mass that was painful when touched.xtension of the knee did not increase pain, but there wascute pain at 20◦ of flexion and the mass disappeared underhe lateral condyle. There was no patellar instability. X-rays

f the knee were normal, with no patella alta or patellarubluxation. Proton density MRI with fat suppression (PD fatat) revealed an abnormal image of the superior infrapatel-ar fat pad with a heterogeneous oval mass near the lateral

served.

Traumatic dislodgement of the infrapatellar fat pad 777

owin

annq

D

Twtodeifnt

Figure 1 Axial (a) and coronal (b) PD fat sat MRI sh

joint capsule. On axial and coronal slices with the knee inextension, the mass came in contact with the iliotibial bandwith a peripheral high intensity signal (Fig. 1).

The results suggested a traumatic infrapatellar fat padinjury, but the unusual features of the mass posed aproblem of differential diagnosis with a tumoral or pseu-dotumoral lesion. Open surgical excision was decided torelease impingement and for histology. Surgery was per-formed by lateral parapatellar approach. The swelling rosefrom under the joint capsule in front of the iliotibial band.Arthrotomy revealed dislocation of the superior infrapatel-lar fat pad in the anterolateral joint space with an area ofcompression across from the lateral condyle and an edemain the area corresponding to the oval lesion seen on MRI(Fig. 2). The dislocated part of the fat pad was excisedand an aspiration drain was placed in the joint before clos-ing. The histolopathological analysis of the resected tissue(measuring 1 × 3 cm) confirmed the absence of tumoral pro-

liferation and showed inflammation and contusion of theadipose tissue. The postoperative course was uneventful.The patient went back to work 2 months after surgery andbegan biking and swimming after 3 months. Seven months

Figure 2 Anterolateral arthrotomy revealing the dislocatedpart of the infrapatellar fat pad.

ffiteafaliet

fiFtfktwu

bnc

g a heterogeneous mass of the infrapatellar fat pad.

fter surgery, he reported occasional infrapatellar pain, witho patellofemoral pain syndrome. The knee was dry withormal range of motion and there was no amyotrophy of theuadriceps.

iscussion

raumatic infrapatellar fat pad lesions are a rare entityhich may occur following an anterior cruciate ligament

ear, patellar instability or arthroscopy; or they may be partf a fat pad impingement syndrome [2]. Hoffa’s diseaseescribed in 1904 [3] is the most well-known form of thisntity and includes posterior impingement in the femorotib-al joint space due to infrapatellar fat pad hypertrophyollowing acute trauma or microtraumas [4]. The mecha-ism is repeated hyperextension or rotational strains [5]. Inhe acute stage, hypertrophy is associated with an edemarom hemmorhage and inflammation. In the chronic stage,broblast proliferation transforms the inflammatory adiposeissue into fibrous scar tissue [3,4]. Features of superolat-ral impingement were recently been described on MRI [6]s a result of damage to the superior infrapatellar fat padrom chronic impingement between the patellar ligamentnd the lateral femoral condyle. Patella alta and/or patel-ar tracking anomalies are predisposing factors. Although its not well known and has rarely been reported in the lit-rature, superolateral impingement may be more frequenthan Hoffa’s disease [2].

In the present case, an acute form of Hoffa’s disease wasrst suspected, but several elements did not support this.irst, the Hoffa test was negative. This is performed withhe knee in flexion by applying pressure to the infrapatellarat pad on the border of the patellar ligament, then thenee is extended. The test is positive if pain is worse whenhe knee is extended [3]. Also, the palpable mass extendedell beyond the patellar ligament and was accompanied bynusual acute pain.

MRI confirmed the damage to the infrapatellar fat pad,ut did not provide a definite diagnosis. The increased sig-al intensity of the superior infrapatellar fat pad did notorrespond to features of Hoffa’s disease, but was more

7

sipamHittaocitonwt

uaneFgtidccfotfcd

C

Tlsdth

D

Tc

R

[

[

[

[

[

[

78

uggestive of chronic superolateral impingement character-zed by disappearance of the superior fat pad between theatellar ligament and the lateral femoral condyle [2]. Thenterolateral oval mass was also characteristic of the for-ation of nodules found in superolateral impingement [6].owever, the clinical history did not correspond to chronic

mpingement and the patient did not have predisposing fac-ors. Moreover, the volume and heterogeneous feature ofhe mass could also suggest a tumoral lesion of the infrap-tellar fat pad which was revealed by trauma. A chondromar lipoma was improbable because there were no visible cal-ifications which are characteristic of the former, or lowntensity signal on fat saturation sequences for the latter. Onhe other hand, it might have been a synovial hemangiomar a sarcomatous malignant tumor whose characteristics areon specific on MRI [7]. Histological evaluation of the massas therefore necessary to avoid missing the diagnosis of a

umor.Surgery is only indicated in Hoffa’s disease after

nsuccessful medical treatment and normally includesrthroscopic resection of the diseased area [1,4]. There iso generally accepted protocol for treatment of superolat-ral impingement and there are no series in the literature.unctional measures are effective and the outcome is oftenood [6]. In this patient, surgical treatment was indicatedo exclude a suspected tumor and because of the functionalmpairment from acute pain. Open surgery was thereforeecided upon for direct access to the lesion and to performomplete resection without dissemination. The pathologi-al examination excluded the diagnosis of a tumor and theat pad dislocation corresponded to a posttraumatic formf superolateral impingement. It may have developed from

earing of the superior attachments of the infrapatellarat pad on the patella and the anterior rim of the lateralondyle, as well as from a lesion of the infrapatellar plicauring hyperflexion.

[

L. Mathieu et al.

onclusion

he presentation of traumatic dislocation of the infrapatel-ar fat pad in this patient seems to be an acute form ofuperolateral fat pad impingement which has not yet beenescribed. Because of the atypical clinical signs and MRI fea-ures, the diagnosis could only be made after surgery andistological evaluation of the excised tissue.

isclosure of interest

he authors declare that they have no conflicts of interestoncerning this article.

eferences

1] Kumar D, Alvand A, Beacon JP. Impingement of infrapatellar fatpad (Hoffa’s disease): results of high-portal arthroscopic resec-tion. Arthroscopy 2007;23:1180—6.

2] Saddik D, McNally EG, Richardson M. MRI of Hoffa’s fat pad.Skeletal Radiol 2004;33:433—4.

3] Hoffa A. Influence of adipose tissue with regard to the pathologyof the knee joint. JAMA 1904;43:795—6.

4] Hager JP, Moyen B, Brunet-Guedj E. La maladie de Hoffa :revue de la littérature à propos de 11 cas. J Traumatol Sport1999;16:93—100.

5] Duri ZA, Aichroth PM, Dowd G. The fat pad. Clinical observa-tions. Am J Knee Surg 1996;9:55—66.

6] Chung CB, Skaf A, Roger B, Campos J, Stump X, Resnick D.Patellar tendon-lateral femoral condyle friction syndrome: MRimaging in 42 patients. Skeletal Radiol 2001;30:694—7.

7] Helpert C, Davies AM, Evans N, Grimer RJ. Differential diagnosisof tumors and tumors-like lesions of the infrapatellar (Hoffa’s)fat pad: pictorial review with an emphasis on MR imaging. EurRadiol 2004;14:2337—46.