Hoffa's fat pad tumours like: results of the arthroscopic resection

We performed a retrospective cohort study to increase awareness in orthopaedic community of this rare but interesting disease which is often misdiagnosed as meniscal pathology and to analyze present results of arthroscopic resection in seven patients. we retrospectively reviewed records from 2008-2012 and identified 7 patients with symptomatic Hoffa's fat pad impingement. The diagnosis was made by clinical exam, MRI imaging and verified arthroscopically. Of the 7 patients 2 were excluded due to receiving open resection. The remaining five underwent arthroscopic resection. Lysholm and American knee society scores were obtained pre and post operative and at final follow up. There was a significant improvement in their symptoms and function after the surgery at an average follow-up of 14 months. The one poor result was because of paresthesia over the distribution of the infrapatellar branch of the saphenous nerve after open resection. tumours like of the fat pad should be treated by arthroscopic resection because of less residual pain and less complication was found using arthroscopy. In case of high volume of tumours only open excision can provide complete excision.


Introduction
Many tumours or tumours like can affect the Hoffa's fat pad. They usually occur in young active patients participating in activities involving repetitive microtrauma to the knee joint. Hoffa's disease was first described by Albert Hoffa in 1904 [1][2][3]. It's characterized by an impingement between the patellofemoral or femorotibial joints due to large volume tumours in the infrapatellar fat pad, causing chronic anterior knee pain [2]. The diagnosis was established by clinical signs, MR imaging and histological findings.
The objective of this study is to increase awareness in orthopaedic community of this rare but interesting disease which is often misdiagnosed as meniscal pathology and to analyze present results of arthroscopic resection in seven patients. Hypothesis: arthroscopic resection of symptomatic Hoffa's fat pad tumours results in significant clinical improvement at final follow up.

Details
We performed a retrospective analysis of a consecutive series of seven patients with the diagnosis of isolated Hoffa's tumour treated with arthroscopic resection of the infrapatellar fat pad between January 2008 and December 2012. The gender and age of the patients at presentation, the clinical features (Figure 1), investigations, preoperative diagnosis, operative findings, the anatomical site of origin of the tumour, the treatment and complications, including recurrence, were recorded. The Lysholm knee and American knee society were used for assessment preoperatively and at 3 months and at 1 year postoperatively, as well as at the conclusion of this study [4,5]. The clinical features of the syndrome are well described and consist of pain and tenderness around the patellar tendon. Hoffa´s sign consists of applying pressure to the medial side of the fat pad, with a knee flexed. On extension the patient will experience pain as the fat pad is pinched intraarticularly [6]. Imaging All our patients had radiographic examinations of the knee radiographic examinations (anteriorposterior, lateral, and skyline views) and MR imaging 3 T to identify or exclude other knee pathology (Figure 2).

Surgical technique
The arthroscopy surgery was performed by using the standard anteromedial and anterolateral portals. Each knee compartment was inspected thoroughly and palpated using a blunt hook. The infrapatellar area is difficult to see in arthroscopic examination using the conventional anteromedial and anterolateral portals. We, therefore, made two accessory portals on the far medial and lateral sides of the conventional portals. Arthroscopic examination through these two accessory portals revealed a mass at the posterior border of the patellar tendon (Figure 3). There was requirement for a large arthrotomy (Figure 4) in two cases. The surrounding soft tissues were excised along with the tumors (Figure 5).
Postoperatively the patients were placed on a vigorous physiotherapy program to strengthen the quadriceps power and regain range of movement. They were allowed full weight-bearing on the knee. Anti-inflammatory drugs were prescribed for the first 10 days postoperatively. The patients were reviewed using the Lyshlom knee and American knee society scores. This was compared with the preoperative score.

Clinical features
In this study seven patients were diagnosed and treated for isolated tumours of Hoffa's fat pad. There were 5 females and 2 males. The average age at operation was 35 years with a range of 23-44 ( Table 1). The average duration of symptoms was 16 months with a range of 7 to 36 months. Five cases occurred in the right knee and two were in the left knee. Six patients had sustained minor injuries in the past but were unsure whether that precipitated their current symptoms, and just one denied any history of injury whatsoever.

Outcomes after excision
The average time to follow-up was 14 months [7]. The mean preoperative Lysholm knee score was 37.44, and it improved postoperatively to 82.20, 93.02, and 90.76 at 3 months, at 1 year, and at the latest follow-up, respectively. The average score for symptoms preoperatively was 32 and postoperatively was 46 (p < 0.001) ( Table 2). The mean paired difference was 14 with a standard deviation of 6.3 and a 95% confidence interval of 9 to 18.

Discussion
The classically pain is present on the anteromedial aspect of knee joint like in Hoffa´s disease. [8] Knee joint has many fat pads which are extrasynovial but intracapsular. First one of the anterior fat pads is anterior suprapatellar (quadriceps), the second one is posterior suprapatellar (prefemoral), and the third one is infrapatellar (Hoffa, IFP) [1,3,9]. As per Ushiyama et al., HFP modulates chondrocyte function through production of cytokines like tumor necrosis factor (TNF), interleukin (IL)-1, basic fibroblast growth factor (bFGF), and vascular endothelial growth factor (VEGF) in the joint fluid [10].
Hoffa´s disease occurs in normal knees and Hoffa's syndrome is associated with hypertrophy of fat pad due to meniscal, capsular, or ligamentous lesions [1,11]. Hoffas fat pad tumours like can be defined by their origin intrinsec or extrinsec to Hoffas fat pad. The intrinsec are characterized by pain, swelling, bruising, and flexion deformity of knee. The extrinsec are characterized by knee discomfort, recurrent hydroarthrosis, and joint weakening [1,11,12]. But in Hoffa's disease the Movements are usually less affected. Hoffa´s test is specific but difficult to elicit. Examiner presses on either side of the patellar tendon in flexed knee and the patient gradually extends the knee. Positive sign is pain, apprehension, or antalgic block during terminal extension [1,12].
Clinical diagnosis poses difficulty as there are no definitive clinical symptoms and signs, but a palpable mass may suggest the diagnosis.
The main differential diagnosis involves meniscal lesions Metheny and Mayor [6]described the anatomy of the infrapatellar fat pad based on their cadaveric study and were the first investigators to report its arthroscopic resection, in 4 patients. Jacobson et al. [3] and Saddik et al.

Competing interests
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Authors declare no conflict of interest.

Authors' contributions
All authors have read and agreed to the final version of this manuscript and have equally contributed to its content and to the management of the case.

Acknowledgments
We would like to thank Doctors Hammou Nassreddine and Bensaad Soufiane, and acknowledge their work in the preparation of this article.