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Original Research |
1 Department of Radiology, University of Wisconsin School of Medicine and Public
Health, 600 Highland Ave., E3/311, Madison, WI 53792-3252.
2 Department of Orthopedics and Rehabilitation Medicine, University of Wisconsin
School of Medicine and Public Health, Madison, WI.
Received June 6, 2008;
accepted after revision July 31, 2008.
Address correspondence to D. G. Blankenbaker.
Abstract
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MATERIALS AND METHODS. One hundred fifty-two hip MR arthrography examinations of patients who subsequently underwent hip arthroscopy were retrospectively reviewed. Each MR examination was reviewed for the presence of a pectinofoveal fold. If present, the fold was measured in the anteroposterior, mediolateral, and superior-inferior dimensions; evaluated for smooth or irregular contour; and evaluated for a femoral or capsular site of insertion.
RESULTS. The pectinofoveal fold was visualized on hip MR arthrograms in 144 of the 152 (95%) patients and visualized at hip arthroscopy in 150 of the 152 (99%) patients. The average thickness of the fold was 2.6 mm (range, 1-13 mm) in the mediolateral dimension and 17 mm (range, 1-32 mm) in the anteroposterior dimension. The average length of the fold in the superior-inferior dimension was 23.3 mm (range, 7-44 mm). The pectinofoveal fold had a smooth contour in 75 of the 144 (52%) patients with examinations that showed the fold and an irregular contour in 69 of 144 (48%) patients. The fold was found to insert onto the capsule in 108 of 144 (75%) patients and onto the femur in the remaining 36.
CONCLUSION. The pectinofoveal fold should almost always be visualized at MR arthrography. The fold can have various appearances and attachment sites, and these normal variations should not be mistaken for fold abnormalities. These findings should be useful in distinguishing this normal structure from normal and pathologic plicae.
Keywords: hip anatomy • hip joint • hip plicae • MR arthrography • MRI • pectinofoveal fold • sports medicine
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With the advent of hip arthroscopy, the synovial plicae of the hip have attracted increasing interest [5, 6]. Hip plicae have been described in cadavers [6], in patients undergoing diagnostic hip arthroscopy [5], and as an incidental finding at arthrography [7]. In addition, symptomatic hip plicae are now being recognized and treated at hip arthroscopy [5]. The pectinofoveal fold is an intraarticular structure of the hip that has had only limited study in the clinical and anatomic literature [8] (Figs. 1A, and 1B), but it may be confused with a plica. We wished to determine the frequency and appearance of the pectinofoveal fold on hip MR arthrography. By defining the variations in its appearance, the normal pectinofoveal fold can be distinguished from pathologic hip plicae.
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The study group consisted of 152 patients: 49 males and 103 females who ranged in age from 15 to 66 years (mean age, 39 years).
Image Analysis
All hip MR arthrography examinations were performed using the same imaging
protocol that consisted of the following sequences: coronal, oblique axial,
and sagittal fat-suppressed T1-weighted; axial T1-weighted; and coronal
fat-suppressed T2-weighted. Imaging began after intraarticular injection of
12-15 mL of a 2-mmol/L solution of gadolinium into the hip joint. A field of
view of 14-18 cm, matrix of 256-512 x 224-256, and slice thickness of
3-4 mm were achieved using a surface phased-array coil for all studies. All
hip MR arthrograms were obtained on a 1.5- or 3-T magnet.
Each MR examination was evaluated for the presence of a pectinofoveal fold. We considered a pectinofoveal fold to be present if a bandlike filling defect was noted in the medial aspect of the joint extending in a superoinferior direction from the proximal aspect of the joint capsule to the femur because this location has been noted on cadaveric dissections. If present, the fold was measured in the anteroposterior, mediolateral, and superior-inferior dimensions. The morphology of the pectinofoveal fold also was evaluated to determine if the contour was smooth or irregular. The final assessment of the pectinofoveal fold was whether the site of insertion was the femur or joint capsule.
Arthroscopic Technique
All of the hip arthroscopies were performed with the patient in the supine
position as described by Byrd and Jones
[9,
10]. With this technique, both
the central and peripheral hip joint compartments are examined. The
pectinofoveal fold is located and is readily observed in the peripheral
compartment (Fig. 2). In all
152 hips, the presence or absence of the fold was determined and recorded on
each patient's operative "hip sheet" and in the operative notes.
In addition, intraoperative photographs of the pectinofoveal fold were
available for review in 75 patients.
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Pathologic synovial hip plicae are readily detected during diagnostic hip arthroscopy [5]. A case of a symptomatic hip plica in a competitive runner has been reported [5]. In that individual, the onset of pain was insidious and aggravated by repetitive loading that was refractory to conservative management. A small click and minor restriction of motion were documented on clinical examination. Resection of the plica was curative for the click and relieved the pain. As hip arthroscopy becomes a more commonly performed procedure, it should be expected that the diagnosis of plica syndrome will become more common.
Fu et al. [6] described two forms of hip plicae: flat and villous. In addition, they characterized three types of plicae by location: labral (adjacent to the inferomedial region of the acetabular labrum), ligamental (at the acetabular base of the ligament of the head of the femur), and neck (in the synovial reflection at the superior portion of the femoral neck) [6]. They concluded that some of the plicae may be vulnerable to impingement and may cause associated symptoms [6]. In their anatomic study, Fu et al. surmised that the plica adjacent to the femoral neck (our pectinofoveal fold) is situated farthest from the joint surfaces and as a result does not seem to be injured during joint movements. Although those authors described the normal pectinofoveal fold as a plica, it should be described as a fold that is a normal variant.
Symptomatic plicae of the hip currently are thought to represent a rare condition, with only six cases reported in the literature to date [5, 7, 11]. This rarity may be due to the fact that symptomatic hip plicae cannot be recognized clinically [5]. Because the use of hip MR arthrography and arthroscopy is increasing, symptomatic hip plicae may be found to be more common than originally thought [5]. Therefore, it is important to define and understand the normal internal structures of the hip joint to distinguish them from abnormal plicae in the hip.
The results of our study have shown that the pectinofoveal fold is visualized in 95% of patients who undergo hip MR arthrography and that the normal fold has various appearances on MR arthrography. Specifically, the mediolateral dimension can range from 1 to 13 mm, the anteroposterior dimension can range from 1 to 32 mm, and the superior-inferior dimension can range from 7 to 44 mm. The contour can be either smooth, as was seen in 52% of the patients in our study, or irregular. The irregular appearance should not make one think that the pectinofoveal fold is pathologically abnormal. The pectinofoveal fold more commonly inserts onto the hip capsule (75%) rather than onto the femur. The main distinction for correctly diagnosing the normal pectinofoveal fold is by its location: If this structure were found elsewhere in the joint, it would be considered a plica that may or may not be a cause of hip symptoms.
Limitations of our study include the retrospective design. The arthroscopic notes by the orthopedic hip arthroscopist documented the presence of pectinofoveal folds but did not document thickening or abnormalities related to the pectinofoveal fold. In addition, the clinical notes did not indicate whether any of the patients were thought to have symptomatic folds as a cause of their hip pain. All of our patients underwent hip arthroscopy for other intraarticular abnormalities including labral tears and cartilage defects. Finally, we did not evaluate the MR arthrograms for the presence of hip plicae. A prospective study to evaluate the imaging appearance of hip plicae and to correlate the imaging appearance with symptoms would provide further understanding to the significance of plicae.
Finally, we did not evaluate any patients thought to have clinical symptoms of a pathologic pectinofoveal fold. A future prospective study is needed to determine whether the pectinofoveal fold can be a cause of impingement that results in hip pain. In addition, it would be of interest to evaluate the MR arthrographic appearance of the plicae around the hip joint that are thought to cause impingement and to determine their true incidence.
In summary, the pectinofoveal fold should nearly always be visualized at MR arthrography. The fold can have various appearances and attachment sites, but it should not be considered an abnormal or pathologic structure. These findings should be useful in distinguishing this normal structure from pathologic symptomatic plicae.
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