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Use of Intraoperative Computed Tomography Scanning in Determining the Magnitude of Arthroscopic Osteochondroplasty
Technical Note
Use of Intraoperative Computed Tomography Scanning in Determining the Magnitude of Arthroscopic Osteochondroplasty Ali Mofidi, M.B., B.A.O., B.Ch., M.Med., Sci., F.R.C.S.I., F.R.C.S. Orth., John S. Shields, M.D., Josh S. Tan, M.S., Gary G. Poehling, M.D., and Allston J. Stubbs, M.D.
Abstract: Femoroacetabular impingement has recently become a recognized cause of disability and hip arthritis. Hip arthroscopy and femoroacetabular reshaping have been performed to treat this condition. Quantification of the excess femoral and acetabular bone requiring resection has been challenging with the less invasive arthroscopic technique. We describe the use of intraoperative computed tomography assessing osteochondroplasty during arthroscopic surgery to treat cam- and pincer-type femoroacetabular impingement. We also describe the technical steps and present the important radiologic findings we have been able to visualize. We found intraoperative computed tomography scanning to be a reliable and reproducible method of assessing the quality of femoroacetabular impingement surgery. We believe that femoroacetabular impingement surgery can be assessed intraoperatively by use of computed tomography scanning where corrections can be made if necessary.
F
emoroacetabular impingement (FAI) is a recognized pathology associated with hip pain and the development of premature hip arthritis.1,2 FAI comprises cam-, pincer-, and combination-type impingements.1,2 Cam impingement is caused by femoral head asphericity.1,2 Cam impingement and head asphericity can be quantified with the ␣ angle.3 The ␣ angle can be measured by use of normal lateral hip radiography or axial computed tomography (CT) images (Fig 1).3 However, visualization of cam-type impingement lesions with simple radiographs may be poor, and the sensitivity and accuracy of plain radiographs have come under question.4,5 Oblique axial CT and magnetic resonance imaging have been recommended as
From the Department of Orthopaedic Surgery, Wake Forest University Baptist Medical Center, Winston-Salem, North Carolina, U.S.A. Received August 14, 2010; accepted November 9, 2010. Address correspondence to Ali Mofidi, 405 Anita Dr, WinstonSalem, NC 27104, U.S.A.; E-mail: [email protected] © 2011 by the Arthroscopy Association of North America 0749-8063/10486/$36.00 doi:10.1016/j.arthro.2010.11.009
more accurate methods of diagnosis of cam lesions.4,5 A pincer lesion typically results from increased prominence of the anterosuperior acetabular wall or acetabular retroversion.1,2 A pincer lesion is visualized as anterior wall crossover sign or anterior wall lateral– to– center edge angle. However, signs of pincer lesion are hard to quantify with plain radiographs and are affected by obliquity of anteroposterior radiographs of the pelvis or pelvic tilt.6 CT reconstruction is the best mode of imaging for visualization of the acetabular deformities causing a pincer lesion.6 Hip arthroscopy has been used extensively and successfully to treat FAI.7,8 However, success of this technique in quantification of the size of the impingement lesion intraoperatively has come under question, leading to under- or over-resection, especially of cam lesions.9,10 We have married the accuracy of intraoperative CT scan with the minimally invasive nature of hip arthroscopy to achieve reliable and accurate FAI surgery. We describe the technique of using intraoperative CT during hip arthroscopy and present 2 cases in which this technique was used.
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FIGURE 1. Oblique axial CT images of ␣ angle as measured by O-arm device: (A) The preoperative ␣ angle in the first patient measured 75°. (B) The preoperative ␣ angle in the second patient measured 70°. (C) The postoperative ␣ angle in the first patient measured 43.5°. (D) The postoperative ␣ angle in the second patient measured 41°.
TECHNIQUE The procedure is performed with the patient under general anesthesia and positioned supine on the traction table. The O-arm Surgical Imaging System (Medtronic Navigation, Louisville, CO) is then brought in for preoperative CT, specifically imaging the direction and position of cam and pincer lesions on the oblique axial CT and 3-dimensional (3D) reconstruction images (Figs 2A and 2B). Oblique images may be used to measure the ␣ angle for a quantitative measure of cam lesions (Figs 1A and 1B). Periarticular and central osteophytosis would also be visible (Fig 3A). Distraction is then applied, and mid-anterior and anterolateral portals are used to perform diagnostic arthroscopy of the central compartment. During this stage, labral pathology and the associated articular chondromalacia are identified and addressed with debridement and labral repair (Fig 4). Any pincer lesion already identified on the CT scan is treated at this stage (Figs 2A and 2B). The prominence caused by the pincer deformity is recessed and the labrum is reattached back to the newly created superior edge of
the acetabulum with 2 to 3 suture anchors (Fig 5). The cotyloid fossa can also be visualized and synovitis and osteophytosis in this region excised with an arthroscopic shaver, bur, and flexible TAC-S radiofrequency probe (Smith & Nephew Endoscopy, Andover, MA). The traction is reduced and the leg repositioned for visualization of the femoral head–neck junction and the cam lesion manifesting as a convexity, fibrillation, and discoloration across the anterior head-and-neck junction consistent with a cam lesion (Figs 6A and 6B). The cam lesion is then reshaped with an arthroscopic bur and shaver (Figs 6C and 6D), and the leg is put in the position of impingement to assess the adequacy of the impingement surgery. At this stage, all arthroscopic instrumentation is removed and a postoperative CT scan is taken with the portable O-arm device. The CT scan is used to assess the adequacy of the excision of cam and pincer lesions with 3D reconstruction images (Figs 2C and 2D), the position of anchors used in labral repair with sagittal and coronal images (Fig 7), and the adequacy of debridement of central acetabular osteophytes with axial oblique images (Fig 3B). Axial oblique images
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FIGURE 2. Three-dimensional reconstruction CT images of diseased hip by O-arm device. (A and B) Preoperative 3D reconstruction images showing cam lesion (larger arrow) and pincer lesion (small arrow). (C and D) Postoperative 3D reconstruction images showing excised cam lesion (larger arrow) and pincer lesion (small arrow).
can be used to identify the postoperative ␣ angle as a quantitative measure of the success of the cam impingement surgery (Figs 1C and 1D). PEARLS, PITFALLS, AND INDICATIONS There are caveats associated with O-arm imaging (Table 1). There is an extra expense involved with the
device, especially when the original investment is not made for the device for other reasons such as trauma and spinal surgery. Expertise is required to use the device and interpret the images produced. This results in a learning curve that needs to be mastered by the surgeon and the CT technician. Lack of clear and specific imaging goals (listed in Table 2 and illustrated in Figs 1-3, 7, and 8) results in inappropriate imaging
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FIGURE 3. Oblique axial CT images of central acetabular osteophyte using O-arm device: (A) before debridement (arrow) and (B) after debridement (arrow).
and extra radiation or time wasting. We advocate routine postoperative auditing of impingement surgery by the surgeon using 3D reconstruction images to improve the surgical technique (Fig 2). Metallic artifacts on the CT images and theater ergonomics may be problematic. This may be helped by limiting the metallic devices around the hip joint during scanning, learning the setup and operation of the O-arm Surgical Imaging System before the first case, columnating the
FIGURE 5. Arthroscopic images of treatment of labral pathology. (A) Case 1, debridement and repair of labral tear (arrows showing sutures). (B) Case 2, recession of pincer lesion and debridement and reattachment of superior labrum (arrows showing sutures).
CT scan to the femoroacetabular region, and using the fluoroscopy function of the CT scanner (to avoid needing a separate C-arm device to check for the hip joint position and distraction and to affirm the correct position of the O-arm device). This technique should only be used for bony FAI work and, in our view, is not indicated in patients who should not receive high doses of radiation, such as pregnant women. CASE REPORTS Case 1
FIGURE 4. Arthroscopic images of central compartment diagnostic arthroscopy. (A) Case 1, labral tear and perilabral chondromalacia in impingement zone (arrow). (B) Case 2, pincer lesion as depicted by superior acetabular prominence, labral tear, and perilabral chondromalacia in impingement zone (arrow).
A 21-year-old woman who had left hip pain that was refractory to conservative treatment and exacerbated by playing competitive soccer caused by FAI was treated with hip arthroscopy of the left hip. Preoperative on-table CT using O-arm imaging showed a mixed impingement pattern with a large cam lesion on a 3D CT image (Fig 2A). The preoperative ␣ angle was 75° (Fig 1A). Arthroscopy of the central compartment identified a labral tear between the 10- and 11:30-o’clock positions and grade 1 perilabral articular chondromalacia (Fig 4A). The focal chondromalacia lesion was de-
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FIGURE 6. Arthroscopic images of peripheral compartment on arthroscopy. (A) Case 1, head-neck junction convexity denoting cam lesion (large arrow). The labrum and edge of the acetabulum are denoted by small arrows. (B) Case 2, head-neck junction convexity denoting cam lesion (large arrow). The labrum and edge of the acetabulum are denoted by small arrows. (C) Case 1, head-neck junction after osteoplasty of cam lesion in femoral head–neck junction. The arrow indicates the area of osteoplasty. (D) Case 2, head-neck junction after osteoplasty of cam lesion in femoral head–neck junction. The arrow indicates the area of osteoplasty.
brided with an arthroscopic shaver, the prominent acetabulum recessed, and the labrum fixed with 2 Osteoraptor 2.3-mm suture anchors (Smith & Nephew Endoscopy) and Iberian suture technique (Fig 5A). Arthroscopy of the peripheral compartment confirmed the presence of a cam lesion between the 10- and 11:30o’clock positions (Fig 6A). This lesion was addressed by an osteoplasty of the femoral head–and–neck junction with an arthroscopic shaver and bur (Fig 6C). Adequacy of the osteoplasty was then assessed with postoperative on-table CT scan by use of the O-arm
FIGURE 7. Postoperative axial CT images of hip joint by O-arm device. (A) Case 1, position of suture anchors with respect to articular surface in axial plane (arrows). (B) Case 2, position of suture anchors with respect to articular surface in axial plane (arrows).
device (Fig 2C). We were able to measure the ␣ angle postoperatively on an oblique axial CT scan (Fig 1C). The position of the suture anchors was assessed with respect to the articular surface by use of sagittal and coronal images from the CT scan (Fig 7A). Case 2 A 15-year-old girl had bilateral hip pain refractory to conservative treatment and exacerbated by recreational karate. Her more symptomatic left hip was
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TABLE 1. Comparison of Simple Radiography or C-Arm Imaging With O-Arm Intraoperative CT Imaging Tips and pearls Use plain-film imaging to guide utility of CT scan Expect learning curve to position CT machine and use software Limit metallic artifact around hip area Columnate CT to just femoroacetabular articulation Use built-in fluoroscopy on CT scanner Pitfalls Metallic artifact around hip can limit CT data capture Avoid multiple scans on single patient (take single preoperative and postoperative scans) Save intraoperative data for further analysis to ensure full appreciation of case Indications Bony surgery about hip including FAI surgery CT-assisted hip arthroscopy where bony landmarks are crucial for operative treatment Preoperative and postoperative documentation of surgical treatment about hip joint Contraindications Surgical treatment about hip where bone modification or treatment is not performed Patients in whom radiation exposure is more of a risk than a benefit Key points Limit CT evaluation to single preoperative and postoperative scans Use in operative setting where metallic artifact about hip is minimized or eliminated Understand operative setup and software before first case
diagnosed with a labral tear resulting from FAI and was treated with hip arthroscopy. Preoperative ontable CT by use of the O-arm device showed a combination of pincer and cam lesion on 3D CT images (Fig 2B). The preoperative ␣ angle was 70° (Fig 1B). Arthroscopy of the central compartments identified a labral tear between 10 and 11:30 o’clock and grade 1 perilabral articular chondromalacia adjacent to the pincer acetabular bony prominence (Fig 4B). The acetabular prominence was recessed with an arthroscopic shaver and bur. The labral lesion was fixed with 2 Osteoraptor 2.3-mm suture anchors and Iberian su-
FIGURE 8. Herniation pits associated with impingement lesion caused by mixed impingement as seen by use of preoperative O-arm imaging (small arrow). The large arrow indicates a pincer lesion.
ture technique to the recessed edge of the acetabulum (Fig 5B). Arthroscopy of the peripheral compartment confirmed the presence of a large cam lesion between 10 and 11:30 o’clock (Fig 6B). This lesion was addressed by an osteoplasty along the femoral head– and–neck junction by use of the arthroscopic shaver and bur (Fig 6D). The adequacy of the osteoplasty was then assessed with a postoperative on-table O-arm CT scan (Fig 2D). We were able to measure the ␣ angle postoperatively on an oblique axial CT scan (Fig 1D). The position of suture anchors was assessed with respect to the articular surface by use of sagittal and coronal images from the CT scan (Fig 7B). Both patients made a successful recovery and returned to unrestricted, full activity 4 months postoperatively. DISCUSSION
TABLE 2.
Proposed Surgical Imaging Goals of O-Arm Intraoperative CT Imaging
␣ Angle (Fig 1) 3D reconstruction finding of pincer and cam lesions and decompressive surgery (Fig 2) Osteophytosis in hip joint (Fig 3) Position of suture anchors (Fig 7) Visualization of herniation pits (Fig 8)
The traditional method of treating FAI is open osteoplasty.1,11 During open osteoplasty, the hip joint may be dislocated.1,11 Dislocation of the hip allows direct vision of the femoral head and allows an adequate osteoplasty, but it may be associated with increased morbidity and a slower recovery period.11,12 Arthroscopic osteoplasty has been used successfully to treat FAI.7,8 Arthroscopic osteoplasty is a less in-
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FIGURE 9. Postoperative real-time CT scanning by O-arm device. The device is introduced without the need to change patient positioning, thus affecting theater traffic, or to end surgery. Note that this is a postoperative scan, and the surgical field is no longer sterile in this case.
vasive method of osteochondroplasty with a reduced complication rate.7,8 However, during hip arthroscopy, it may be difficult to estimate the size of the impingement lesion and the correct amount of tissue to resect.9,10 The most common mistake during arthroscopic osteoplasty is under-resection of the cam or pincer lesions.9,13,14 Anxiety about under- or overresection of cam impingement during osteoplasty has been significant enough to result in the use of computer navigation in performing osteoplasty, but with limited success.15 Recently, perioperative and intraoperative radiographic imaging with a conventional C-arm has been used successfully to assess the impingement lesion as well as the quantity of bone to be removed.16-18 Multiple techniques have been used to improve the usefulness of plain-film radiography and C-arm imag-
ing.16-18 Quantifying the deformity by use of radiologic criteria is one method.3,18 The center edge angle is used to assess the pincer lesion, whereas the ␣ angle has been used to assess the cam lesion.3,16-18 Other techniques involve dynamic C-arm imaging or marking the pincer or cam lesion on the C-arm image before femoroacetabular surgery so as to have a visual perspective of the bony prominence to be excised.16,17 However, plain 2-dimensional radiographic imaging is only successful in visualizing a deformity when the x-ray beam is perpendicular to the lesion; otherwise, the deformity may be underestimated.5 This fact has been shown for the ␣ angle and the cam lesion.4,5 Because of this, C-arm imaging may be unreliable in assessing impingement lesions.4,5 Intraoperative CT is a new technique of real-time imaging that has been used at Wake Forest University
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Baptist Medical Center to assess the quality of fixation of acetabular fracture and spinal surgery. We have used the intraoperative O-arm CT device to analyze the size of the impingement lesion and the quality of osteoplasty in selected cases. While the patient is positioned on the traction table during hip arthroscopy, the O-arm can be positioned and removed without the need for repositioning or contamination of the surgical field (Fig 9). We advocate 2 separate intraoperative CT scans, 1 before arthroscopy after positioning of the patient on the fracture table and 1 after osteoplasty to assess the quality of the osteoplasty and to appreciate the severity of the impingement lesion, as well as instant quantification of femoroacetabular reshaping (Figs 1 and 2). Intraoperative CT imaging has also been used by us to show the presence and assess the quality of the debridement of central acetabular osteophytosis (Fig 3).19 We have used intraoperative CT imaging to assess the position of arthroscopic anchors for labral repair to avoid inadvertent penetration of the hip joint or acetabular subchondral bone (Fig 7), the acetabular version, and the prominence of the pincer lesion, as well as the adequacy of the recession of the acetabular prominence (Fig 2). Preoperatively, other hip abnormalities associated with FAI, such as herniation pits on the femoral head-neck junction (Fig 8), may be seen.20 The dose of radiation imparted during intraoperative CT imaging is an area of concern, especially when osteoplasty is performed in the pelvic region of healthy young adults at their reproductive peak.21 To counter this argument, a recent study by Huppertz et al.22 has shown CT scanning to be safe and costeffective in preplanning of hip arthroplasty using computer navigation and a minimally invasive approach. The radiation dose can be halved by not imaging the patient before the osteoplasty and imaging the patient just before the end of the arthroscopy only to assess the extent and need for further osteoplasty. Finally, the alternative to intraoperative CT, which is computer navigation, also uses CT reconstruction of the hip joint and, hence, uses an equivalent dose of radiation. However, it is more invasive, is not in real time, and to date has not been shown to be as successful.15,21 This technique is only useful when hip arthroscopy involves a possible need for bony impingement surgery. We believe that, in the absence of a bony impingement lesion, intraoperative CT is of limited use because the main aim of this device is to give the surgeon a 3D ability to see bony structure that is
difficult to visualize in 2 dimensions. Like FAI surgery, intraoperative CT scanning involves a learning curve. This learning curve is because of difficulty with positioning, planning, and interpretation of data from the O-arm imaging system. This process is easily mastered by familiarity with the system, FAI, preplanning of the procedure, and reflective analysis of the saved data as well as a good CT technician. We advocate consideration of intraoperative portable CT for the assessment of osteoplasty. We have found intraoperative CT to be a useful optimization tool that can be used in combination with intraoperative dynamic assessment of osteoplasty in cases when visualization of the impingement lesion is difficult. This technology is not only an assessment tool for osteoplasty, it is also useful in documenting the findings and quality of the surgery performed. We believe that use of this device is feasible and reliable for assessing femoroacetabular hip surgery, femoral or acetabular osteoplasty, and the position of periacetabular anchors and cheilectomy of the hip joint. Acknowledgment: The authors thank Ms. Denise Buckley for her help with manuscript preparation.
REFERENCES 1. Leunig M, Beaule PE, Ganz R. The concept of femoroacetabular impingement. Current status and future perspectives. Clin Orthop Relat Res 2009;467:616-622. 2. Ganz R, Leunig M, Leunig-Ganz K, Harris WH. The etiology of osteoarthritis of the hip. An integrated mechanical concept. Clin Orthop Relat Res 2008;466:264-272. 3. Nötzli HP, Wyss TF, Stoecklin CH, Schmid MR, Treiber K, Hodler J. The contour of the femoral head-neck junction as a predictor for the risk of anterior impingement. J Bone Joint Surg Br 2002;84:556-560. 4. Rakhra KS, Sheikh AM, Allen D, Beaulé PE. Comparison of MRI alpha angle measurement planes in femoroacetabular impingement. Clin Orthop Relat Res 2009;467:660665. 5. Dudda M, Albers C, Mamisch TC, Werlen S, Beck M. Do normal radiographs exclude asphericity of the femoral headneck junction? Clin Orthop Relat Res 2009;467:651-659. 6. Köhnlein W, Ganz R, Impellizzeri FM, Leunig M. Acetabular morphology: Implications for joint-preserving surgery. Clin Orthop Relat Res 2009;467:682-691. 7. Sampson TG. Arthroscopic treatment of femoroacetabular impingement. Am J Orthop 2008;37:608-612. 8. Philippon MJ, Briggs KK, Yen YM, Kuppersmith DA. Outcomes following hip arthroscopy for femoroacetabular impingement with associated chondrolabral dysfunction: Minimum two-year follow-up. J Bone Joint Surg Br 2009;91: 16-23. 9. Ilizaliturri VM Jr. Complications of arthroscopic femoroacetabular impingement treatment: A review. Clin Orthop Relat Res 2009;467:760-768. 10. Mardones R, Lara J, Donndorff A, et al. Surgical correction of “cam-type” femoroacetabular impingement: A cadaveric com-
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12. 13. 14.
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parison of open versus arthroscopic debridement. Arthroscopy 2009;25:175-182. Ganz R, Gill TJ, Gautier E, Ganz K, Krugel N, Berlemann U. Surgical dislocation of the adult hip a technique with full access to the femoral head and acetabulum without the risk of avascular necrosis. J Bone Joint Surg Br 2001;83:1119-1124. Krueger A, Leunig M, Siebenrock KA, Beck M. Hip arthroscopy after previous surgical hip dislocation for femoroacetabular impingement. Arthroscopy 2007;23:1285-1289. Philippon MJ, Schenker ML, Briggs KK, Kuppersmith DA, Maxwell RB, Stubbs AJ. Revision hip arthroscopy. Am J Sports Med 2007;35:1918-1921. Zumstein M, Hahn F, Sukthankar A, Sussman PS, Dora C. How accurately can acetabular rim be trimmed in hip arthroscopy for pincer type femoral acetabular impingement: A cadaveric investigation. Arthroscopy 2009;25:164-168. Brunner A, Horisberger M, Herzog RF. Evaluation of a computed tomography-based navigation system prototype for hip arthroscopy in the treatment of femoroacetabular cam impingement. Arthroscopy 2009;25:382-391. Matsuda DK. Fluoroscopic templating technique for precision arthroscopic rim trimming. Arthroscopy 2009;25:1175-1182.
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17. Larson CM, Wulf CA. Intraoperative fluoroscopy for evaluation of bony resection during arthroscopic management of femoroacetabular impingement in supine position. Arthroscopy 2009;25: 1183-1192. 18. Philippon MJ, Wolff AB, Briggs KK, Zehms CT, Kuppersmith DA. Acetabular reduction for the treatment of femoroacetabular impingement correlates with pre-operative and post-operative center edge angle. Arthroscopy 2010;26:757-761. 19. Mofidi A, Shields JS, Stubbs A. Central acetabular osteophyte (sabre tooth sign), one of the earliest sign of osteoarthritis of the hip joint. Eur J Orthop Traumatol 2011;21:71-74. 20. Panzer S, Esch U, Abdulazim AN, Augat P. Herniation pits and cystic-appearing lesions at the anterior femoral neck: An anatomical study by MSCT and microCT. Eur J Radiol 2009; 39:645-654. 21. Biswas D, Bible JE, Bohan M, Simpson AK, Whang PG, Grauer JN. Radiation exposure from musculoskeletal computerized tomographic scans. J Bone Joint Surg Am 2009;91: 1882-1889. 22. Huppertz A, Radmer S, Asbach P, et al. Computed tomography for preoperative planning in minimal-invasive total hip arthroplasty: Radiation exposure and cost analysis. Eur J Radiol. 2009 Dec 18. [Epub ahead of print.]
Use of Intraoperative Computed Tomography Scanning in Determining the Magnitude of Arthroscopic Osteochondroplasty Ali Mofidi, M.B., B.A.O., B.Ch., M.Med., Sci., F.R.C.S.I., F.R.C.S. Orth., John S. Shields, M.D., Josh S. Tan, M.S., Gary G. Poehling, M.D., and Allston J. Stubbs, M.D.
Abstract: Femoroacetabular impingement has recently become a recognized cause of disability and hip arthritis. Hip arthroscopy and femoroacetabular reshaping have been performed to treat this condition. Quantification of the excess femoral and acetabular bone requiring resection has been challenging with the less invasive arthroscopic technique. We describe the use of intraoperative computed tomography assessing osteochondroplasty during arthroscopic surgery to treat cam- and pincer-type femoroacetabular impingement. We also describe the technical steps and present the important radiologic findings we have been able to visualize. We found intraoperative computed tomography scanning to be a reliable and reproducible method of assessing the quality of femoroacetabular impingement surgery. We believe that femoroacetabular impingement surgery can be assessed intraoperatively by use of computed tomography scanning where corrections can be made if necessary.
F
emoroacetabular impingement (FAI) is a recognized pathology associated with hip pain and the development of premature hip arthritis.1,2 FAI comprises cam-, pincer-, and combination-type impingements.1,2 Cam impingement is caused by femoral head asphericity.1,2 Cam impingement and head asphericity can be quantified with the ␣ angle.3 The ␣ angle can be measured by use of normal lateral hip radiography or axial computed tomography (CT) images (Fig 1).3 However, visualization of cam-type impingement lesions with simple radiographs may be poor, and the sensitivity and accuracy of plain radiographs have come under question.4,5 Oblique axial CT and magnetic resonance imaging have been recommended as
From the Department of Orthopaedic Surgery, Wake Forest University Baptist Medical Center, Winston-Salem, North Carolina, U.S.A. Received August 14, 2010; accepted November 9, 2010. Address correspondence to Ali Mofidi, 405 Anita Dr, WinstonSalem, NC 27104, U.S.A.; E-mail: [email protected] © 2011 by the Arthroscopy Association of North America 0749-8063/10486/$36.00 doi:10.1016/j.arthro.2010.11.009
more accurate methods of diagnosis of cam lesions.4,5 A pincer lesion typically results from increased prominence of the anterosuperior acetabular wall or acetabular retroversion.1,2 A pincer lesion is visualized as anterior wall crossover sign or anterior wall lateral– to– center edge angle. However, signs of pincer lesion are hard to quantify with plain radiographs and are affected by obliquity of anteroposterior radiographs of the pelvis or pelvic tilt.6 CT reconstruction is the best mode of imaging for visualization of the acetabular deformities causing a pincer lesion.6 Hip arthroscopy has been used extensively and successfully to treat FAI.7,8 However, success of this technique in quantification of the size of the impingement lesion intraoperatively has come under question, leading to under- or over-resection, especially of cam lesions.9,10 We have married the accuracy of intraoperative CT scan with the minimally invasive nature of hip arthroscopy to achieve reliable and accurate FAI surgery. We describe the technique of using intraoperative CT during hip arthroscopy and present 2 cases in which this technique was used.
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 27, No 7 (July), 2011: pp 1005-1013
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FIGURE 1. Oblique axial CT images of ␣ angle as measured by O-arm device: (A) The preoperative ␣ angle in the first patient measured 75°. (B) The preoperative ␣ angle in the second patient measured 70°. (C) The postoperative ␣ angle in the first patient measured 43.5°. (D) The postoperative ␣ angle in the second patient measured 41°.
TECHNIQUE The procedure is performed with the patient under general anesthesia and positioned supine on the traction table. The O-arm Surgical Imaging System (Medtronic Navigation, Louisville, CO) is then brought in for preoperative CT, specifically imaging the direction and position of cam and pincer lesions on the oblique axial CT and 3-dimensional (3D) reconstruction images (Figs 2A and 2B). Oblique images may be used to measure the ␣ angle for a quantitative measure of cam lesions (Figs 1A and 1B). Periarticular and central osteophytosis would also be visible (Fig 3A). Distraction is then applied, and mid-anterior and anterolateral portals are used to perform diagnostic arthroscopy of the central compartment. During this stage, labral pathology and the associated articular chondromalacia are identified and addressed with debridement and labral repair (Fig 4). Any pincer lesion already identified on the CT scan is treated at this stage (Figs 2A and 2B). The prominence caused by the pincer deformity is recessed and the labrum is reattached back to the newly created superior edge of
the acetabulum with 2 to 3 suture anchors (Fig 5). The cotyloid fossa can also be visualized and synovitis and osteophytosis in this region excised with an arthroscopic shaver, bur, and flexible TAC-S radiofrequency probe (Smith & Nephew Endoscopy, Andover, MA). The traction is reduced and the leg repositioned for visualization of the femoral head–neck junction and the cam lesion manifesting as a convexity, fibrillation, and discoloration across the anterior head-and-neck junction consistent with a cam lesion (Figs 6A and 6B). The cam lesion is then reshaped with an arthroscopic bur and shaver (Figs 6C and 6D), and the leg is put in the position of impingement to assess the adequacy of the impingement surgery. At this stage, all arthroscopic instrumentation is removed and a postoperative CT scan is taken with the portable O-arm device. The CT scan is used to assess the adequacy of the excision of cam and pincer lesions with 3D reconstruction images (Figs 2C and 2D), the position of anchors used in labral repair with sagittal and coronal images (Fig 7), and the adequacy of debridement of central acetabular osteophytes with axial oblique images (Fig 3B). Axial oblique images
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FIGURE 2. Three-dimensional reconstruction CT images of diseased hip by O-arm device. (A and B) Preoperative 3D reconstruction images showing cam lesion (larger arrow) and pincer lesion (small arrow). (C and D) Postoperative 3D reconstruction images showing excised cam lesion (larger arrow) and pincer lesion (small arrow).
can be used to identify the postoperative ␣ angle as a quantitative measure of the success of the cam impingement surgery (Figs 1C and 1D). PEARLS, PITFALLS, AND INDICATIONS There are caveats associated with O-arm imaging (Table 1). There is an extra expense involved with the
device, especially when the original investment is not made for the device for other reasons such as trauma and spinal surgery. Expertise is required to use the device and interpret the images produced. This results in a learning curve that needs to be mastered by the surgeon and the CT technician. Lack of clear and specific imaging goals (listed in Table 2 and illustrated in Figs 1-3, 7, and 8) results in inappropriate imaging
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FIGURE 3. Oblique axial CT images of central acetabular osteophyte using O-arm device: (A) before debridement (arrow) and (B) after debridement (arrow).
and extra radiation or time wasting. We advocate routine postoperative auditing of impingement surgery by the surgeon using 3D reconstruction images to improve the surgical technique (Fig 2). Metallic artifacts on the CT images and theater ergonomics may be problematic. This may be helped by limiting the metallic devices around the hip joint during scanning, learning the setup and operation of the O-arm Surgical Imaging System before the first case, columnating the
FIGURE 5. Arthroscopic images of treatment of labral pathology. (A) Case 1, debridement and repair of labral tear (arrows showing sutures). (B) Case 2, recession of pincer lesion and debridement and reattachment of superior labrum (arrows showing sutures).
CT scan to the femoroacetabular region, and using the fluoroscopy function of the CT scanner (to avoid needing a separate C-arm device to check for the hip joint position and distraction and to affirm the correct position of the O-arm device). This technique should only be used for bony FAI work and, in our view, is not indicated in patients who should not receive high doses of radiation, such as pregnant women. CASE REPORTS Case 1
FIGURE 4. Arthroscopic images of central compartment diagnostic arthroscopy. (A) Case 1, labral tear and perilabral chondromalacia in impingement zone (arrow). (B) Case 2, pincer lesion as depicted by superior acetabular prominence, labral tear, and perilabral chondromalacia in impingement zone (arrow).
A 21-year-old woman who had left hip pain that was refractory to conservative treatment and exacerbated by playing competitive soccer caused by FAI was treated with hip arthroscopy of the left hip. Preoperative on-table CT using O-arm imaging showed a mixed impingement pattern with a large cam lesion on a 3D CT image (Fig 2A). The preoperative ␣ angle was 75° (Fig 1A). Arthroscopy of the central compartment identified a labral tear between the 10- and 11:30-o’clock positions and grade 1 perilabral articular chondromalacia (Fig 4A). The focal chondromalacia lesion was de-
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FIGURE 6. Arthroscopic images of peripheral compartment on arthroscopy. (A) Case 1, head-neck junction convexity denoting cam lesion (large arrow). The labrum and edge of the acetabulum are denoted by small arrows. (B) Case 2, head-neck junction convexity denoting cam lesion (large arrow). The labrum and edge of the acetabulum are denoted by small arrows. (C) Case 1, head-neck junction after osteoplasty of cam lesion in femoral head–neck junction. The arrow indicates the area of osteoplasty. (D) Case 2, head-neck junction after osteoplasty of cam lesion in femoral head–neck junction. The arrow indicates the area of osteoplasty.
brided with an arthroscopic shaver, the prominent acetabulum recessed, and the labrum fixed with 2 Osteoraptor 2.3-mm suture anchors (Smith & Nephew Endoscopy) and Iberian suture technique (Fig 5A). Arthroscopy of the peripheral compartment confirmed the presence of a cam lesion between the 10- and 11:30o’clock positions (Fig 6A). This lesion was addressed by an osteoplasty of the femoral head–and–neck junction with an arthroscopic shaver and bur (Fig 6C). Adequacy of the osteoplasty was then assessed with postoperative on-table CT scan by use of the O-arm
FIGURE 7. Postoperative axial CT images of hip joint by O-arm device. (A) Case 1, position of suture anchors with respect to articular surface in axial plane (arrows). (B) Case 2, position of suture anchors with respect to articular surface in axial plane (arrows).
device (Fig 2C). We were able to measure the ␣ angle postoperatively on an oblique axial CT scan (Fig 1C). The position of the suture anchors was assessed with respect to the articular surface by use of sagittal and coronal images from the CT scan (Fig 7A). Case 2 A 15-year-old girl had bilateral hip pain refractory to conservative treatment and exacerbated by recreational karate. Her more symptomatic left hip was
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TABLE 1. Comparison of Simple Radiography or C-Arm Imaging With O-Arm Intraoperative CT Imaging Tips and pearls Use plain-film imaging to guide utility of CT scan Expect learning curve to position CT machine and use software Limit metallic artifact around hip area Columnate CT to just femoroacetabular articulation Use built-in fluoroscopy on CT scanner Pitfalls Metallic artifact around hip can limit CT data capture Avoid multiple scans on single patient (take single preoperative and postoperative scans) Save intraoperative data for further analysis to ensure full appreciation of case Indications Bony surgery about hip including FAI surgery CT-assisted hip arthroscopy where bony landmarks are crucial for operative treatment Preoperative and postoperative documentation of surgical treatment about hip joint Contraindications Surgical treatment about hip where bone modification or treatment is not performed Patients in whom radiation exposure is more of a risk than a benefit Key points Limit CT evaluation to single preoperative and postoperative scans Use in operative setting where metallic artifact about hip is minimized or eliminated Understand operative setup and software before first case
diagnosed with a labral tear resulting from FAI and was treated with hip arthroscopy. Preoperative ontable CT by use of the O-arm device showed a combination of pincer and cam lesion on 3D CT images (Fig 2B). The preoperative ␣ angle was 70° (Fig 1B). Arthroscopy of the central compartments identified a labral tear between 10 and 11:30 o’clock and grade 1 perilabral articular chondromalacia adjacent to the pincer acetabular bony prominence (Fig 4B). The acetabular prominence was recessed with an arthroscopic shaver and bur. The labral lesion was fixed with 2 Osteoraptor 2.3-mm suture anchors and Iberian su-
FIGURE 8. Herniation pits associated with impingement lesion caused by mixed impingement as seen by use of preoperative O-arm imaging (small arrow). The large arrow indicates a pincer lesion.
ture technique to the recessed edge of the acetabulum (Fig 5B). Arthroscopy of the peripheral compartment confirmed the presence of a large cam lesion between 10 and 11:30 o’clock (Fig 6B). This lesion was addressed by an osteoplasty along the femoral head– and–neck junction by use of the arthroscopic shaver and bur (Fig 6D). The adequacy of the osteoplasty was then assessed with a postoperative on-table O-arm CT scan (Fig 2D). We were able to measure the ␣ angle postoperatively on an oblique axial CT scan (Fig 1D). The position of suture anchors was assessed with respect to the articular surface by use of sagittal and coronal images from the CT scan (Fig 7B). Both patients made a successful recovery and returned to unrestricted, full activity 4 months postoperatively. DISCUSSION
TABLE 2.
Proposed Surgical Imaging Goals of O-Arm Intraoperative CT Imaging
␣ Angle (Fig 1) 3D reconstruction finding of pincer and cam lesions and decompressive surgery (Fig 2) Osteophytosis in hip joint (Fig 3) Position of suture anchors (Fig 7) Visualization of herniation pits (Fig 8)
The traditional method of treating FAI is open osteoplasty.1,11 During open osteoplasty, the hip joint may be dislocated.1,11 Dislocation of the hip allows direct vision of the femoral head and allows an adequate osteoplasty, but it may be associated with increased morbidity and a slower recovery period.11,12 Arthroscopic osteoplasty has been used successfully to treat FAI.7,8 Arthroscopic osteoplasty is a less in-
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FIGURE 9. Postoperative real-time CT scanning by O-arm device. The device is introduced without the need to change patient positioning, thus affecting theater traffic, or to end surgery. Note that this is a postoperative scan, and the surgical field is no longer sterile in this case.
vasive method of osteochondroplasty with a reduced complication rate.7,8 However, during hip arthroscopy, it may be difficult to estimate the size of the impingement lesion and the correct amount of tissue to resect.9,10 The most common mistake during arthroscopic osteoplasty is under-resection of the cam or pincer lesions.9,13,14 Anxiety about under- or overresection of cam impingement during osteoplasty has been significant enough to result in the use of computer navigation in performing osteoplasty, but with limited success.15 Recently, perioperative and intraoperative radiographic imaging with a conventional C-arm has been used successfully to assess the impingement lesion as well as the quantity of bone to be removed.16-18 Multiple techniques have been used to improve the usefulness of plain-film radiography and C-arm imag-
ing.16-18 Quantifying the deformity by use of radiologic criteria is one method.3,18 The center edge angle is used to assess the pincer lesion, whereas the ␣ angle has been used to assess the cam lesion.3,16-18 Other techniques involve dynamic C-arm imaging or marking the pincer or cam lesion on the C-arm image before femoroacetabular surgery so as to have a visual perspective of the bony prominence to be excised.16,17 However, plain 2-dimensional radiographic imaging is only successful in visualizing a deformity when the x-ray beam is perpendicular to the lesion; otherwise, the deformity may be underestimated.5 This fact has been shown for the ␣ angle and the cam lesion.4,5 Because of this, C-arm imaging may be unreliable in assessing impingement lesions.4,5 Intraoperative CT is a new technique of real-time imaging that has been used at Wake Forest University
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Baptist Medical Center to assess the quality of fixation of acetabular fracture and spinal surgery. We have used the intraoperative O-arm CT device to analyze the size of the impingement lesion and the quality of osteoplasty in selected cases. While the patient is positioned on the traction table during hip arthroscopy, the O-arm can be positioned and removed without the need for repositioning or contamination of the surgical field (Fig 9). We advocate 2 separate intraoperative CT scans, 1 before arthroscopy after positioning of the patient on the fracture table and 1 after osteoplasty to assess the quality of the osteoplasty and to appreciate the severity of the impingement lesion, as well as instant quantification of femoroacetabular reshaping (Figs 1 and 2). Intraoperative CT imaging has also been used by us to show the presence and assess the quality of the debridement of central acetabular osteophytosis (Fig 3).19 We have used intraoperative CT imaging to assess the position of arthroscopic anchors for labral repair to avoid inadvertent penetration of the hip joint or acetabular subchondral bone (Fig 7), the acetabular version, and the prominence of the pincer lesion, as well as the adequacy of the recession of the acetabular prominence (Fig 2). Preoperatively, other hip abnormalities associated with FAI, such as herniation pits on the femoral head-neck junction (Fig 8), may be seen.20 The dose of radiation imparted during intraoperative CT imaging is an area of concern, especially when osteoplasty is performed in the pelvic region of healthy young adults at their reproductive peak.21 To counter this argument, a recent study by Huppertz et al.22 has shown CT scanning to be safe and costeffective in preplanning of hip arthroplasty using computer navigation and a minimally invasive approach. The radiation dose can be halved by not imaging the patient before the osteoplasty and imaging the patient just before the end of the arthroscopy only to assess the extent and need for further osteoplasty. Finally, the alternative to intraoperative CT, which is computer navigation, also uses CT reconstruction of the hip joint and, hence, uses an equivalent dose of radiation. However, it is more invasive, is not in real time, and to date has not been shown to be as successful.15,21 This technique is only useful when hip arthroscopy involves a possible need for bony impingement surgery. We believe that, in the absence of a bony impingement lesion, intraoperative CT is of limited use because the main aim of this device is to give the surgeon a 3D ability to see bony structure that is
difficult to visualize in 2 dimensions. Like FAI surgery, intraoperative CT scanning involves a learning curve. This learning curve is because of difficulty with positioning, planning, and interpretation of data from the O-arm imaging system. This process is easily mastered by familiarity with the system, FAI, preplanning of the procedure, and reflective analysis of the saved data as well as a good CT technician. We advocate consideration of intraoperative portable CT for the assessment of osteoplasty. We have found intraoperative CT to be a useful optimization tool that can be used in combination with intraoperative dynamic assessment of osteoplasty in cases when visualization of the impingement lesion is difficult. This technology is not only an assessment tool for osteoplasty, it is also useful in documenting the findings and quality of the surgery performed. We believe that use of this device is feasible and reliable for assessing femoroacetabular hip surgery, femoral or acetabular osteoplasty, and the position of periacetabular anchors and cheilectomy of the hip joint. Acknowledgment: The authors thank Ms. Denise Buckley for her help with manuscript preparation.
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17. Larson CM, Wulf CA. Intraoperative fluoroscopy for evaluation of bony resection during arthroscopic management of femoroacetabular impingement in supine position. Arthroscopy 2009;25: 1183-1192. 18. Philippon MJ, Wolff AB, Briggs KK, Zehms CT, Kuppersmith DA. Acetabular reduction for the treatment of femoroacetabular impingement correlates with pre-operative and post-operative center edge angle. Arthroscopy 2010;26:757-761. 19. Mofidi A, Shields JS, Stubbs A. Central acetabular osteophyte (sabre tooth sign), one of the earliest sign of osteoarthritis of the hip joint. Eur J Orthop Traumatol 2011;21:71-74. 20. Panzer S, Esch U, Abdulazim AN, Augat P. Herniation pits and cystic-appearing lesions at the anterior femoral neck: An anatomical study by MSCT and microCT. Eur J Radiol 2009; 39:645-654. 21. Biswas D, Bible JE, Bohan M, Simpson AK, Whang PG, Grauer JN. Radiation exposure from musculoskeletal computerized tomographic scans. J Bone Joint Surg Am 2009;91: 1882-1889. 22. Huppertz A, Radmer S, Asbach P, et al. Computed tomography for preoperative planning in minimal-invasive total hip arthroplasty: Radiation exposure and cost analysis. Eur J Radiol. 2009 Dec 18. [Epub ahead of print.]