Arthroscopic Resection of Fat Pad Lesions and Infrapatellar Contractures

Abstract

The infrapatellar fat pad (IFP), also known as Hoffa's fat pad, may be a common site of pain in the knee because of its susceptibility to injury and its vast innervation and vascular supply. Patients who have trauma to the IFP may undergo a process of hemorrhage, inflammation, and fibrosis that may become painful. Patients with Hoffa's disease in whom conservative treatment with medications, physical therapy, and injections has failed may receive significant pain relief and benefit from undergoing arthroscopic subtotal removal of the IFP. We describe a safe and effective way to perform this procedure allowing excellent visualization through the use of a superolateral viewing portal.

The infrapatellar fat pad (IFP), or Hoffa's fat pad, is a common site of knee pain. Patients in whom conservative treatment has failed may receive significant pain relief from subtotal removal of the IFP. Surgical treatment of Hoffa's fat pad after traumatic injury was originally described by Hoffa in 1904, in which he used an open surgical technique to remove the IFP.¹ Kumar et al.² described an arthroscopic technique using high anteromedial and anterolateral portals to resect the IFP in patients with Hoffa disease.

The purpose of this report is to describe the removal of the IFP and infrapatellar contractures with the use of a superolateral portal, which allows for easier access and better visualization of the IFP without violating the anterior capsule, patellar tendon, or anterior meniscal attachments. It is important to perform a subtotal excision removing the lobulated and bulk of the reactive fat pad. Approximately 10 mm of fat pad is left in the area of the patellar tendon region to prevent patellar tendon to tibia adhesions. Furthermore, maintaining this 10 mm of IFP on the medial and lateral borders is paramount to prevent the suction-cup effect with knee flexion that can cause dimpling of the skin. Determining the amount of fat removed can be difficult; thus we recommend using a probe before and after resection to help estimate the amount of IFP removed (Video 1).

Surgical Technique

The patient is placed in the supine position on the operating table, and after a satisfactory level of general anesthesia is achieved, the knee is prepared and draped in the normal sterile fashion (Fig 1). A well-padded proximal thigh tourniquet is applied, and the thigh is placed in a leg holder. The end of the bed is positioned to 90° to allow proper access to the knee. A “time out” is performed. The surgeon-signed operative limb is identified and confirmed. Allergies, intravenous antibiotics, and the proposed procedure are confirmed with operating room staff. The standard anteromedial and anterolateral arthroscopic portals are established. The superolateral portal is established just lateral to the vastus lateralis for an outflow. A complete diagnostic arthroscopy is then performed.

Fig 1.

(A) The patient is placed in the supine position on the operating table with a well-padded proximal thigh tourniquet. (B) Standard arthroscopic setup with anteromedial, anterolateral, and superolateral portals. (Reprinted with permission.^9,10)

Fig 2.

Arthroscopic view of IFP before partial resection.

Fig 3.

Arthroscopic view of IFP after partial resection.

Under tourniquet control, Metzenbaum scissors are placed in either the anteromedial or anterolateral portal to establish the plane between the patellar tendon and the IFP (Table 1). To establish where this plane is to be developed, the Metzenbaum scissors are placed posterior to the patellar tendon, which creates an interval between the IFP and the tendon. It is important to establish this plane before performing the arthroscopic removal of the IFP to ensure that the anterior capsule and patellar tendon will not be violated during the subtotal resection of the IFP. If a plane between the patellar tendon and the IFP cannot be established, then using an open technique for resection is recommended to avoid iatrogenic injury to the patellar tendon (Table 2).

Table 1.

Surgical Pearls and Key Points

Use Metzenbaum scissors through the anteromedial or anterolateral portal to establish a plane between the patellar tendon and IFP before beginning the arthroscopic, subtotal removal of the IFP.

The superolateral portal allows full visualization of the IFP.

Use a probe to estimate the amount of IFP that needs to be resected.

Electrocautery is used to establish and maintain hemostasis.

Emphasize motion and patellar mobilization in the postoperative period to prevent adhesions and development of an infrapatellar contracture.

Table 2.

Surgical Pitfalls

If a plane between the patellar tendon and IFP cannot be established, then open resection is recommended to avoid iatrogenic damage to the patellar tendon.

Failure to achieve hemostasis can result in postoperative hemarthrosis, which causes pain and inhibits motion. The tourniquet should be deflated before removing the arthroscope to assess for bleeding.

Over-resection of the IFP can result in infrapatellar adhesions and contractures, as well as skin dimpling.

The IFP is then visualized with the arthroscope placed in the superolateral portal (Fig 2). The outflow cannula is moved to the anteromedial portal. The tourniquet is briefly inflated for clear visualization. A Dyonics 3.5-mm full-radius shaver (Smith & Nephew, Andover, MA) is introduced through the anterolateral portal to remove the lobulated and fibrous stria of the IFP. Care is taken not to perform a total IFP because of the aforementioned reasons and to avoid damaging the patellar tendon (Fig 3). To perform an infrapatellar contracture removal, a biter is used to remove the bulk of the scar tissue and then a shaver is used to remove the remaining pathologic tissue. Partial resection of the IFP and infrapatellar contractures can cause multiple sites of bleeding; thus meticulous use of the Super Turbovac 90 IFS (ArthroCare, Austin, TX) is essential to establish hemostasis and decrease the risk of postoperative hemarthrosis after tourniquet deflation. The fluid from the knee is then drained, and the portals are closed. The knee is covered with a sterile dressing and is wrapped with a compressive Ace wrap from the foot to the thigh. The patient returns to the recovery unit in excellent condition and without complication.

Postoperatively, full weight bearing as tolerated is initiated, and the patient uses crutches until he or she is able to walk without a limp. For the first week, the patient is instructed to use ice, compression dressings, and elevation to decrease pain and swelling, as well as to decrease the chance of postoperative hemarthrosis. Full motion is allowed and patellar mobilization with patellar glides is important in the following weeks to prevent infrapatellar contractures.

Discussion

Anterior knee pain is a common problem seen in the orthopaedic setting. Hoffa disease should be suspected when the patient has pain in the medial or lateral fat pad to palpation. Patients typically have increasing pain when going from flexion to full extension. The pain is often described as a burning or aching anterior knee pain on either side of the patellar tendon around the inferior pole of the patella.³ The causes of this disease include trauma, prior arthroscopic surgery, lesions within the fat pad, synovitis, pigmented villonodular synovitis, and other inflammatory diseases.³

Radiographs should be taken to determine the presence of bony abnormalities or calcifications that may be seen in the IFP. Lateral radiographs are also used to evaluate the patellar height and check for patella infera, which can occur with an infrapatellar contracture. Magnetic resonance imaging (MRI) can be used to look for evidence of Hoffa disease, and this is best demonstrated by inflammation, fibrosis, and striations on the sagittal cuts. Von Engelhardt et al.⁴ found that in patients with Hoffa's fat pad impingement, morphologic changes such as localized edema of the superior and/or posterior part of the fat pad, a deep fluid-filled infrapatellar bursa, non-visualization of the vertical and/or horizontal clefts, fibrosis, and calcifications were noted on MRI with remarkable frequency. In the study by von Engelhardt et al., MRI findings were significant and arthroscopic surgery confirmed the diagnosis of Hoffa's fat pad impingement. Subhawong et al.⁵ found that superolateral Hoffa's fat pad edema had a significant association with patellofemoral maltracking and impingement. The MRI study is also useful in showing causes of knee pain from other sources in the fat pad, such as ganglion cysts, pigmented villonodular synovitis, calcified lesions, and other lesions within the IFP.^6,7

Direct injection of lidocaine into the IFP is another diagnostic tool that should be considered. The fat pad is a known source of substance P, which affects pain mediation by increasing sensitivity to nociceptive signals and promotes inflammation by vasodilation, extravasation of plasma proteins, and adherence of leukocytes.³ If the injection reduces the symptoms, then Hoffa's fat pad disease is confirmed. If the symptoms are not improved by the injection, then other sources such as inflammatory disease, pigmented villonodular synovitis, or other pathologies should be considered.

Historically, the IFP was removed by an open technique. Dean et al.⁸ discussed their series of 19 patients in whom they performed open excision of solitary tumors of Hoffa's fat pad. They used open resection because of the presence of a tumor and thus needed to perform excision of the entire fat pad to limit recurrence. When tumors are not present, arthroscopic techniques have been described to resect Hoffa's fat pad.^1,2,4

In patients in whom conservative management has failed, arthroscopic removal of the fat pad is a safe and less invasive way to perform this surgery (Tables 3 and 4). Arthroscopic, subtotal removal of the IFP is less invasive than open resection, and full diagnostic arthroscopy can be performed to evaluate the entire knee joint for potential pathology. We have found that when using only the standard anteromedial and anterolateral arthroscopic portals, full visualization of the fat pad can be difficult and the proper amount of fat pad resection can be difficult to perform. Using a superolateral portal allows for full visualization of the fat pad and eases the surgical resection. By using the superolateral portal to look down on the fat pad from above, one can fully assess the amount of fat pad that has been removed and take care not to violate the patellar tendon or the anterior meniscal attachments. It is difficult to assess the amount of IFP removed; thus we recommend looking from the superolateral portal both before and after resection and using the tip of a probe to estimate the amount resected and the amount remaining.

Table 3.

Indications for Arthroscopic Removal of IFP

Hoffa's fat pad that has failed conservative treatment

Infrapatellar contractures in which a plane between the patellar tendon and IFP can be established

Table 4.

Contraindications for Arthroscopic Removal of IFP

Tumors

Infrapatellar contractures in which a safe plane between the patellar tendon and IFP cannot be established—open removal is recommended in these cases

We have described an arthroscopic technique using the superolateral portal to resect the IFP (Video 1). We find that this technique allows for better visualization for complete resection of the IFP and helps to avoid unwanted damage to the anterior capsule, patellar tendon, and meniscal attachments.

Supplementary Data

Video 1

Arthroscopic technique using the superolateral portal to resect the IFP. We find that this technique allows for better visualization for complete resection of the IFP and helps to avoid unwanted damage to the anterior capsule, patellar tendon, and meniscal attachments.