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Address correspondence and reprint requests to Dean K. Matsuda, M.D., Department of Orthopedic Surgery, Southern California Permanente Medical Group, Kaiser West Los Angeles Medical Center, 6041 Cadillac Ave, Los Angeles, CA 90034, U.S.A.
Department of Orthopedic Surgery, Southern California Permanente Medical Group, Kaiser West Los Angeles Medical Center, Los Angeles, California, U.S.A.
Arthroscopic rim trimming for femoroacetabular impingement can be technically challenging to perform with precision. Intraoperative assessment of the extent of acetabular rim resection is very important. Over-resection can lead to hip instability and even iatrogenic dislocation. Under-resection may leave residual impingement. A novel imaging technique is presented that is simple, practical, and readily available. The technique involves matching the fluoroscopic C-arm image intensifier to the operative pelvis while under the desired amount of hip distraction so that a horizontal anteroposterior hip image appears on the viewing monitor. An erasable marking pen is used to draw the desired area of planned acetabular rim resection directly on the viewing monitor screen. Intermittent fluoroscopic images with the raised stationary C-arm device allow assessment of superior (lateral) and anterior rim resection. The surgeon “wipes away” the drawn template with the radiopaque metallic bur until the all-important medial template border is reached, indicating that the actual rim resection matches that intended in a controlled and precise manner.
Femoroacetabular impingement (FAI) is gaining acceptance as a significant clinical entity with symptomatic and likely degenerative consequences. Recognition and treatment of the pincer or acetabular component of this condition comprise an important step in the eradication of ongoing hip impingement and associated acetabular chondral damage. Patients with pincer and cam-pincer FAI often undergo an open or arthroscopic rim-trimming procedure to reduce or eliminate acetabular overcoverage. The arthroscopic management of FAI presents an attractive option over open surgical dislocation for this generally young and athletic group of patients.
However, the arthroscopic equivalent is technically demanding, and the intraoperative assessment of the amount of rim reduction is particularly challenging. Over-resection may contribute to iatrogenic hip instability
; under-resection may leave residual symptomatic impingement and/or residual areas of pathologic cartilage. A simple and practical fluoroscopic templating technique is introduced that may add precision and consistency to arthroscopic rim trimming (Table 1, Table 2).
Table 1Potential Benefits of Fluoroscopic Templating Technique
Increased precision of arthroscopic rim trimming
Improved consistency of arthroscopic rim trimming
Fluoroscopic “timeout” before commencement of each surgery
Increased surgeon confidence for challenging procedure
Increased efficiency of arthroscopic rim trimming with decrease in operative and traction times
Improved utilization of fluoroscopy technician (once setup has been completed, the technician may depart)
Table 2Steps Involved in Setup and Application of Fluoroscopic Templating Technique
1. Obtain AP pelvis view without hip distraction.
2. Obtain horizontal AP pelvis view under hip distraction.
3. Translate C-arm over operative hip.
4. Raise C-arm to maximum allowable height.
5. Arrange arthroscopic monitor and fluoroscopic monitor to preference.
6. Draw template (with erasable marking pen) over planned area of rim reduction on viewing monitor.
7. Mark hip distraction device so that traction amount may be replicated.
8. Release distraction while sterile preparation and draping are performed.
9. Reset operative hip distraction and confirm that template lies over desired area of planned rim resection.
10. Establish beginning margins of anterolateral acetabular rim by placing metallic device (e.g., bur) adjacent to rim at direct superior and direct anterior positions.
11. Wipe away templated area (anterolateral overhang) with bur until medial border of template is reached.
NOTE. For further information, please see Video 1 (online only, available at www.arthroscopyjournal.org) and the American Academy of Orthopaedic Surgeons Orthopaedic Surgical Video Library DVDs entitled “Supine Hip Arthroscopy Setup and Fluoroscopic Templating for Acetabular Rim Trimming” and “Comprehensive Dual Portal Arthroscopic Surgery for Femoroacetabular Impingement,” available at www.aaos.org.
Beginning with the goal in mind (i.e., accurate acetabular rim reduction to eliminate ongoing hip impingement as well as reduce or eliminate the area of pathologic articular cartilage), the key steps are as follows:
1
Obtain a horizontal anteroposterior (AP) view of the distracted operative hip on the fluoroscopic viewing monitor.
2
Delineate the “template” of the planned area of superior (lateral) and anterior acetabular rim resection directly on the fluoroscopic viewing monitor (with an erasable marker).
3
Erase or “wipe away” the templated area with the arthroscopic bur until the medial template border is reached, indicating the completion of both superior (lateral) and anterior rim resection.
Obtain Horizontal AP View of Distracted Operative Hip on Fluoroscopic Viewing Monitor
We perform the fluoroscopic templating technique with the patient in the supine position. The patient's pelvis must “match” the image intensifier device so that a horizontal AP image of the central pelvis is obtained. This requires a radiolucent central pelvic support. The patient's pelvis may be matched to the image intensifier by adjusting table tilts (our preference) (Fig 1), or the image intensifier may be adjusted to match the patient's pelvis. At a minimum, we want the fluoroscopic field of view to encompass the pubic symphysis, the obturator foramina, and the coccyx. The latter is sometimes poorly visualized, and we have used a coin taped to the palpable coccyx on occasion. The pubic symphysis should have a vertical orientation and align with the coccyx (correcting lateral pelvic tilt) (Fig 2). The obturator foramina should be symmetric and match the preoperative AP pelvis radiograph. A good AP pelvis view should have neutral sagittal tilt, and the distance between the sacrococcygeal joint should be 2 to 3 cm above the superior margin of the symphysis in male patients and between 2 and 6 cm in female patients.
Figure 1Typical supine setup for fluoroscopic templating viewed from foot of fracture table. The C-arm device is positioned over the central pelvis (red arrow), and the image intensifier x-ray detection monitor is parallel to the floor (large black arrow) and elevated well above the operative field. The table is adjusted so that the pelvis matches the image intensifier with the fluoroscopic monitor showing an AP view of the central pelvis (arrowhead) and the operative right lower extremity positioned in moderate internal rotation (small black arrow).
Figure 2Fluoroscopic monitor shown in Fig 1. The central pelvis has a horizontal AP pelvis position as confirmed by the vertical alignment of the symphysis pubis (large arrow), the symmetry of the obturator foramina (large arrowheads), and the coccyx (small arrowhead) in vertical alignment with the pubic symphysis and approximately 3 cm (in this patient) from its superior border. The apex of the padded central post shadow (small arrow) towards the operative right hip and away from the midline should be noted.
Next, the surgeon's standard technique for application of hip distraction is used. We routinely apply countertraction to the nonoperative extremity (to prevent excessive lateral pelvic tilt) followed by traction to the operative extremity to obtain our desired amount of hip distraction. Inevitably, there will be lateral pelvic tilt toward the side of operative hip distraction (Fig 3), which—if not corrected—may exaggerate any acetabular overcoverage and may result in excessive rim resection. Hence the fluoroscopic image is adjusted so that the horizontal AP image is restored with the operative hip distracted. We use an imaginary horizontal line connecting the inferior-most margins of the ischial rami parallel to the floor and a vertical pubic symphyseal orientation on the fluoroscopic viewing monitor. Once the horizontal AP image has been restored, the image intensifier is translated over the distracted operative hip (Fig 4). Then it is raised to minimize intrusion in the operative field (Fig 5).
Figure 3Fluoroscopic image after sufficient traction is applied to the operative right lower extremity to distract that hip. (This occurs despite some initial countertraction applied to the contralateral lower extremity.) One should note the obvious lateral tilt toward the side of operative hip distraction and the alignment aid immediately before adjustment to a horizontal alignment.
Figure 4View from foot of fracture table with hip distraction applied to operative right hip. The image intensifier is translated over the operative hip (large arrow), and the fluoroscopic monitor displays a horizontal AP view of the distracted hip (small arrow).
Figure 5Operative side view of patient shown in Fig 4. The image intensifier x-ray detection head is positioned over the operative right hip and elevated well above the operative field (long arrow). The arthroscopic and fluoroscopic monitors are arranged adjacent to each other and ergonomically positioned for surgeon comfort with the fluoroscopic monitor confirming a horizontal AP image of the distracted hip (short arrow).
Delineate Template of Planned Area of Superior (Lateral) and Anterior Acetabular Rim Resection Directly on Fluoroscopic Viewing Monitor (With Erasable Marker)
We then use an erasable marking pen to draw a template on the operative fluoroscopic viewing monitor screen (Fig 6). The template delineates the area of planned rim trimming. The medial border indicates the desired amount of anterosuperior rim remaining after arthroscopic rim trimming is completed.
Figure 6Fluoroscopic detail of distracted right hip. The template has been drawn around the area of desired rim resection with an erasable marking pen. The medial border is marked as a red line (done in Photoshop; Adobe Systems, San Jose, CA) to emphasize the desired endpoint of rim trimming in this patient. The image is a horizontal AP image of the distracted hip.
We position our arthroscopic and fluoroscopic monitor screens in adjacent and ergonomically friendly configurations. The ability to see adjacent arthroscopic and fluoroscopic screens, though not mandatory, permits nearly seamless assessment of the rim-trimming procedure in real time. We rarely use “live” fluoroscopic capture because intermittent “spot” images achieve our goal while minimizing irradiation.
We also mark the distraction device (Fig 7) so that the distraction may be released, thereby minimizing traction time during the sterile preparation and draping phase. We then reapply operative extremity traction and confirm superimposition of the template over the desired area of planned rim resection.
Figure 7The traction device being marked with an erasable marking pen so that traction may subsequently be released during the sterile preparation and draping phase (minimizing traction time) followed by accurate reapplication of operative hip distraction. The arrow shows the horizontal AP of the distracted hip on another viewing monitor screen in the background.
Erase or Wipe Away Templated Area With Arthroscopic Bur Until Medial Template Border Is Reached, Indicating Completion of Both Superior (Lateral) and Anterior Rim Resection
We begin our arthroscopic rim trimming with an arthroscopic and fluoroscopic image of our arthroscopic bur at the direct superior (lateral) 12-o'clock position (Fig 8) and then at the direct anterior (generic 3-o'clock) position. We then perform arthroscopic rim trimming typically from the 12-o'clock superior position down to the lowest extent of our drawn template (usually around the 2- to 3-o'clock anterior position) (Fig 9). We will often adjust the arc of resection to “match” the arc of visualized chondral damage. Once the arthroscopic bur tip reaches the medial template border, the rim resection is complete for that level of acetabulum (e.g., direct superior 12-o'clock position) (Fig 10). The arthroscopic rim resection is complete once the bur tip reaches the entire medial template border (e.g., superior and anterior acetabulum) (Fig 11).
Figure 8Operative side view as the surgeon performs arthroscopic rim trimming of this supine patient using the fluoroscopic templating technique. The C-arm x-ray detection head is on the right, and the adjacent arthroscopic and fluoroscopic monitors are on the left. The arrow shows the fluoroscopic image of the bur at the direct superior, or 12-o'clock, position just before commencement of arthroscopic rim resection.
Figure 9Fluoroscopic image prior to rim trimming with bur on the lateral margin of the region of anterolateral overcoverage near the direct superior position. The red arrow demarcates the 12-o'clock (direct superior) position while the red arrowhead demarcates the 2-o'clock (anterior) position at the level of this patient's radiographic crossover sign. The blue arrow shows a positive ischial spine sign. Both radiographic signs are indicative of acetabular retroversion.
Figure 10Fluoroscopic image after superior rim trimming is completed. The bur is at the medial template border (red arrow). The blue line indicates the amount of resected superior acetabular rim at this level.
Figure 11Fluoroscopic image after anterior rim trimming is completed. The bur is at the medial border (red arrow). The blue line indicates the amount of resected anterior rim at this level. The planned amount of anterolateral acetabular rim reduction has been accomplished and the crossover sign is now absent.
To summarize, one should obtain an AP view of the distracted hip, followed by demarcation on the fluoroscopic monitor screen of the template to be resected during arthroscopic rim trimming. The all-important medial template border is emphasized, as is the ability to assess both the lateral (by means of center-edge [CE] angle change) and the anterior rim reduction while leaving the C-arm device motionless and as minimally intrusive (in the raised position) as possible.
Discussion
Arthroscopic rim trimming is becoming an integral and important procedure in the surgical management of patients with pincer and cam-pincer FAI. A discussion of the merits of rim trimming versus reverse periacetabular osteotomy is beyond the scope of this article. However, experts who perform both procedures state that the latter open procedure may be indicated in the relative minority of patients who exhibit retroversion combined with frontal-plane dysplasia.
Rim resection may help eliminate ongoing hip impingement by removing relative anterior bony overgrowth and also reduce or eliminate the adjacent area of damaged articular cartilage. Previous methods of assessing the amount of rim reduction have included estimating the resection width compared with bur width or estimating the remaining distance from the nearest edge of the acetabular notch. Intermittent fluoroscopic imaging is commonly used, but the observed setup has been somewhat haphazard and a horizontal AP pelvic inclination while the hip is under distraction may not be obtained, leading to potential errors in rim reduction. The fluoroscopic templating technique encourages a thoughtful presurgical consideration of the planned rim resection and, by drawing a template on the actual viewed monitor screen with the operative hip distracted, encourages the surgeon to wipe away the template with a radiopaque bur until the all-important medial border is reached, hence allowing both lateral and anterior rim reduction in a controlled and precise manner.
The fluoroscopic templating technique was originally developed in response to an iatrogenic anterior hip dislocation after arthroscopic hip impingement surgery.
Though originally designed to minimize inadvertent over-resection of the acetabular rim, perhaps just as importantly, the technique may instill surgeon confidence to trim a sufficient amount of the acetabular rim, thereby minimizing under-resection and possible residual pincer impingement. Moreover, by enhancing surgeon confidence, we have consistently reduced our arthroscopic rim trimming and traction times. Despite a somewhat longer (5 to 10 minutes) setup time, our rim trimming usually progresses rapidly as we watch the adjacent arthroscopic and fluoroscopic monitors in a fairly seamless manner until the anterosuperior rim within the fluoroscopic template has been removed and the rim reduction completed. An arthroscopic labral preservation procedure typically follows, as does an arthroscopic femoral head-neck resection osteoplasty if indicated.
The described fluoroscopic templating technique provides 2-dimensional imaging of a 3-dimensional reality (in this instance, the operative acetabulum). Although 3-dimensional imaging such as intraoperative computed tomography and 3-dimensional isocentric fluoroscopy with and without navigation
could conceivably be used in this surgical setting, we believe our simple, practical, readily available, and relatively economical fluoroscopic templating technique permits a reasonable approximation of surgically induced volumetric reduction by permitting the assessment of both superior (lateral) and anterior rim reduction. Moreover, we have successfully used this technique in less common instances of posterior rim reduction in cases of global acetabular overcoverage (e.g., coxa profunda). A recent cadaveric investigation (without fluoroscopic assistance) has shown relative accuracy in determining arthroscopic acetabular resection arcs (not widths) for the anterosuperior region but more variance and an underestimation of similar resection arcs when performed for posterosuperior rim trimming.
We believe that the fluoroscopic absence of the acetabular subchondral rim that appears at the 12-o'clock position (without bur superimposition) may actually reflect an actual arc of resection extending slightly posterior toward the 11-o'clock position, considered by some surgeons to be desirable in most instances of pincer FAI.
The CE angle of Wiberg is a fairly standard measure of acetabular geometry; its decrement with lateral rim trimming can be a gauge of superior (lateral) acetabular rim reduction. However, although a CE angle of 20° to 25° has been suggested as the limit to rim reduction,
have recently shown increased hip microinstability with increasing severity of acetabular dysplasia. It is conceivable that over-resection of the anterosuperior rim may induce iatrogenic microinstability, a possible pathway toward coxarthrosis.
The CE angle is popular because it is easily visualized, but it has limited utility because it measures only the superior (lateral) acetabular rim. To assess the anterior rim, one could take intermittent false profile views with the image intensifier, but this is more cumbersome, time-consuming, and difficult to reproduce during surgery. The fluoroscopic templating technique permits intraoperative assessment of anterior rim resection while leaving the image intensifier motionless.
We realize that in the purest sense, a “true” AP view of the operative acetabulum is not easily achieved. We base our radiographic assessment of acetabular morphology and spatial positioning on the AP pelvis radiograph. Our setup obtains a horizontal AP pelvis view under hip distraction, visualizing the aforementioned central pelvic anatomic landmarks. However, because of the limited field of view of most image intensifier devices, one must translate or angle the C-arm to visualize the operative hip. We prefer the former for greater consistency. At least with regard to the acetabulum, we now have a true AP hip (under distraction), not AP pelvis, orientation. Tannast et al.
have shown that the radiographic relationship of the anterior to posterior acetabular landmarks is altered to some degree with this maneuver. However, from a practical perspective, we believe that the fluoroscopic AP hip view approximates reality (as defined by the AP pelvis view) and improves upon our previous intraoperative imaging techniques. We have noticed a significant improvement in the precision and consistency of our rim resections based on the postoperative AP pelvis radiographs that we have obtained since developing and implementing this technique.
We use the fluoroscopic templating technique routinely. Besides allowing improved intraoperative assessment, we have found that this technique encourages thoughtful preoperative planning and demarcation of the desired amount of rim reduction. Although one may assume that this should always be the case, the realities of a high-volume hip arthroscopy practice may occasionally introduce confusion or error. The fluoroscopic templating technique helps us verify our preoperative game plan without confusion between patients, essentially serving as a fluoroscopic “timeout.”
We routinely perform comprehensive dual-portal arthroscopic surgery for FAI (as seen in the American Academy of Orthopaedic Surgeons Orthopaedic Surgical Video Library DVD entitled “Comprehensive Dual Portal Arthroscopic Surgery for Femoroacetabular Impingement,” available at www.aaos.org); both portals (anterolateral viewing portal and modified mid anterior working portal) are more laterally positioned than the standard anterior portal and permit relatively unimpeded instrument navigation when done in the supine position with the raised image intensifier x-ray detection head positioned well above the operative hip. We occasionally use an anterior portal and have verified the utility of the fluoroscopic templating technique when using this portal.
The image intensifier remains stationary and motionless throughout surgery until such time when we remove it to perform unobstructed hip range of motion during arthroscopic dynamic testing at the termination of each case (to confirm eradication of hip impingement). Although it may prove applicable (and would not require a radiolucent table), we have no experience using this technique with lateral hip arthroscopy.
Fluoroscopic templating is an example of learning from our surgical complications. It is a simple yet practical and readily available technique that has significantly improved the precision of our arthroscopic rim reductions.
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