Proper femoral tunnel placement for medial patellofemoral ligament reconstruction requires optimal radiographic technique.

Femoral tunnel malposition has been shown to be a risk factor for medial patellofemoral ligament reconstruction failure. Palpation of the “saddle point” between the adductor tubercle and medial epicondyle can be an effective strategy; however, compared to using fluoroscopy, tunnel placement using palpation alone may result in significantly more frequent malposition. Accordingly, use of radiographic landmarks has gained in popularity. However, the technique is not without its pitfalls. The first issue lies with obtaining an adequate x-ray. Deviation from a true lateral x-ray by as little as 5° can result in significant tunnel malposition. Including sufficient visible femoral shaft is also required; a minimum requirement is 4 cm. The literature widely varies as to the anatomic, fluoroscopic position. Schottle’s point (1.3 mm anterior to the PCEL) is the most well-studied. Femoral tunnel malposition has been shown to be a risk factor for medial patellofemoral ligament reconstruction failure. Palpation of the “saddle point” between the adductor tubercle and medial epicondyle can be an effective strategy; however, compared to using fluoroscopy, tunnel placement using palpation alone may result in significantly more frequent malposition. Accordingly, use of radiographic landmarks has gained in popularity. However, the technique is not without its pitfalls. The first issue lies with obtaining an adequate x-ray. Deviation from a true lateral x-ray by as little as 5° can result in significant tunnel malposition. Including sufficient visible femoral shaft is also required; a minimum requirement is 4 cm. The literature widely varies as to the anatomic, fluoroscopic position. Schottle’s point (1.3 mm anterior to the PCEL) is the most well-studied. Femoral tunnel malposition is recognized as a common cause for medial patellofemoral ligament reconstruction (MPFLR) failure.1Walker M. Maini L. Kay J. Siddiqui A. Almasri M. de Sa D. Femoral tunnel malposition is the most common indication for revision medial patellofemoral ligament reconstruction with promising early outcomes following revision reconstruction: a systematic review.Knee Surg Sports Traumatol Arthrosc. Apr. 2022; 30: 1352-1361https://doi.org/10.1007/s00167-021-06603-xCrossref PubMed Scopus (16) Google Scholar,2Tscholl P.M. Ernstbrunner L. Pedrazzoli L. Fucentese S.F. The Relationship of Femoral Tunnel Positioning in Medial Patellofemoral Ligament Reconstruction on Clinical Outcome and Postoperative Complications.Arthroscopy. Aug. 2018; 34: 2410-2416https://doi.org/10.1016/j.arthro.2018.02.046Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar This in turn, has led to the development of techniques to identify the anatomic femoral origin intraoperatively over the last 20 years. Palpation of the “saddle point” between the adductor tubercle and medial epicondyle can be an effective strategy;3Kruckeberg B.M. Chahla J. Moatshe G. et al.Quantitative and Qualitative Analysis of the Medial Patellar Ligaments: An Anatomic and Radiographic Study.Am J Sports Med. Jan. 2018; 46: 153-162https://doi.org/10.1177/0363546517729818Crossref PubMed Scopus (73) Google Scholar however, compared to using fluoroscopy, tunnel placement using palpation alone may result in significantly more frequent malposition.4Koenen P. Shafizadeh S. Pfeiffer T.R. et al.Intraoperative fluoroscopy during MPFL reconstruction improves the accuracy of the femoral tunnel position.Knee Surg Sports Traumatol Arthrosc. Dec. 2018; 26: 3547-3552https://doi.org/10.1007/s00167-018-4983-6Crossref PubMed Scopus (19) Google Scholar Accordingly, use of radiographic landmarks, such as Schottle’s point, has gained in popularity.5Schottle P.B. Schmeling A. Rosenstiel N. Weiler A. Radiographic landmarks for femoral tunnel placement in medial patellofemoral ligament reconstruction.Am J Sports Med. May. 2007; 35: 801-804https://doi.org/10.1177/0363546506296415Crossref PubMed Scopus (483) Google Scholar However, the technique is not without its pitfalls. The first issue lies with obtaining an adequate x-ray. Ziegler et al demonstrated, deviation from a true lateral x-ray by as little as 5° can result in significant tunnel malposition, due in part to apparent changes in the posterior cortical extension line (PCEL).6Ziegler C.G. Fulkerson J.P. Edgar C. Radiographic Reference Points Are Inaccurate With and Without a True Lateral Radiograph: The Importance of Anatomy in Medial Patellofemoral Ligament Reconstruction.Am J Sports Med. Jan. 2016; 44: 133-142https://doi.org/10.1177/0363546515611652Crossref PubMed Scopus (57) Google Scholar In their recent cadaver study, “Radiographic landmark measurements for the femoral footprint of the medial patellofemoral complex may be affected by the visible femoral shaft length on lateral knee radiographs”, Bhimani, Ashkani-Esfahani, Mirochnik, Lubberts, Waryasz, and Tanaka identify visible femoral shaft length as another radiographic confounder.7Bhimani R, Ashkani-Esfahani S, Mirochnik K, Lubberts B, Waryasz G, Tanaka MJ. Radiographic landmark measurements for the femoral footprint of the medial patellofemoral complex may be affected by the visible femoral shaft length on lateral knee radiographs. Arthroscopy in press, available online 3 December, 2023. doi:10.1016/j.arthro.2023.11.025.Google Scholar After dissecting out the medial patellofemoral complex (MPFC), they labeled its femoral origin with a radiographic marker, then took a series of fluoroscopic images, each including progressively less visible femoral shaft. As the amount of visible femoral shaft decreased, the apparent PCEL shifted anteriorly (particularly when less than 4 cm was visible). Even if a perfect intraoperative x-ray can be obtained, there is debate as to where the goal femoral tunnel placement should be relative to radiographic landmarks. A review of the literature finds the reported anterior-posterior position to vary extensively between investigations. Studies by Wijdicks8Wijdicks CA, Griffith CJ, LaPrade RF, et al. Radiographic identification of the primary medial knee structures. J Bone Joint Surg Am. Mar 1 2009;91(3):521-529. doi:10.2106/JBJS.H.00909Google Scholar and Kruckeberg3Kruckeberg B.M. Chahla J. Moatshe G. et al.Quantitative and Qualitative Analysis of the Medial Patellar Ligaments: An Anatomic and Radiographic Study.Am J Sports Med. Jan. 2018; 46: 153-162https://doi.org/10.1177/0363546517729818Crossref PubMed Scopus (73) Google Scholar found the origin to be 8.8 mm and 8.3 mm anterior to the PCEL. Barnett et al9Barnett A.J. Howells N.R. Burston B.J. Ansari A. Clark D. Eldridge J.D. Radiographic landmarks for tunnel placement in reconstruction of the medial patellofemoral ligament.Knee Surg Sports Traumatol Arthrosc. Dec. 2012; 20: 2380-2384https://doi.org/10.1007/s00167-011-1871-8Crossref PubMed Scopus (52) Google Scholar and Schottle et al5Schottle P.B. Schmeling A. Rosenstiel N. Weiler A. Radiographic landmarks for femoral tunnel placement in medial patellofemoral ligament reconstruction.Am J Sports Med. May. 2007; 35: 801-804https://doi.org/10.1177/0363546506296415Crossref PubMed Scopus (483) Google Scholar also found the MPFL origin to be anterior to the PCEL, but only by 3.8 mm and 1.3 mm, respectively. Conversely, Stephen et al10Stephen J.M. Lumpaopong P. Deehan D.J. Kader D. Amis A.A. The medial patellofemoral ligament: location of femoral attachment and length change patterns resulting from anatomic and nonanatomic attachments.Am J Sports Med. Aug. 2012; 40: 1871-1879https://doi.org/10.1177/0363546512449998Crossref PubMed Scopus (151) Google Scholar, Redfern et al11Redfern J. Kamath G. Burks R. Anatomical confirmation of the use of radiographic landmarks in medial patellofemoral ligament reconstruction.Am J Sports Med. Feb. 2010; 38: 293-297https://doi.org/10.1177/0363546509347602Crossref PubMed Scopus (81) Google Scholar and Ishikawa et al12Ishikawa M. Hoo C. Ishifuro M. et al.Application of a true lateral virtual radiograph from 3D-CT to identify the femoral reference point of the medial patellofemoral ligament.Knee Surg Sports Traumatol Arthrosc. Nov. 2021; 29: 3809-3817https://doi.org/10.1007/s00167-020-06403-9Crossref PubMed Scopus (6) Google Scholar, and Bhimani et al13Bhimani R. Ashkani-Esfahani S. Mirochnik K. Lubberts B. DiGiovanni C.W. Tanaka M.J. Radiographic Landmarks for the Femoral Attachment of the Medial Patellofemoral Complex: A Cadaveric Study.Arthroscopy. Aug 2022; 38: 2504-2510https://doi.org/10.1016/j.arthro.2022.01.046Abstract Full Text Full Text PDF PubMed Scopus (4) Google Scholar, found the MPFL midpoint to be 1.3 mm, 2.5 mm, and 4 mm, posterior to the PCEL, respectively. Some of this discrepancy may be due to the long MPFC footprint, as previously described by the senior author of the current study.14Tanaka M.J. Femoral Origin Anatomy of the Medial Patellofemoral Complex: Implications for Reconstruction.Arthroscopy. Dec. 2020; 36: 3010-3015https://doi.org/10.1016/j.arthro.2020.06.015Abstract Full Text Full Text PDF PubMed Scopus (15) Google Scholar,15Dhawan A. Editorial Commentary: Back to the Future With the Medial Patellofemoral Complex.Arthroscopy. Dec 2020; 36: 3016-3018https://doi.org/10.1016/j.arthro.2020.09.023Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar While it is currently unknown which point is optimal, for what it’s worth—as a young attending, I will be using Schottle’s point (1.3 mm anterior to the PCEL), as it is the most well-studied, and I find it to be the most reproducible (immediately in front of the PCEL). Additionally, it has been shown that a tunnel position 5 mm or less from the origin,16Smirk C. Morris H. The anatomy and reconstruction of the medial patellofemoral ligament.Knee. Sep. 2003; 10: 221-227https://doi.org/10.1016/s0968-0160(03)00038-3Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar and possibly 10 mm,17Cregar W.M. Huddleston H.P. Wong S.E. Farr J. Yanke A.B. Inconsistencies in Reporting Risk Factors for Medial Patellofemoral Ligament Reconstruction Failure: A Systematic Review.Am J Sports Med. Mar. 2022; 50: 867-877https://doi.org/10.1177/03635465211003342Crossref PubMed Scopus (20) Google Scholar does not change MPFL isometry. Accordingly, I prefer the more central position of Schottle’s point, as it is more likely to be within the “safe zone”, as opposed to the more posterior or anterior positions, which could fall to an extreme. Fortunately, there is much less variation in the literature in the suggested proximal-distal tunnel position , which has been shown to have a much larger effect on graft biomechanics.10Stephen J.M. Lumpaopong P. Deehan D.J. Kader D. Amis A.A. The medial patellofemoral ligament: location of femoral attachment and length change patterns resulting from anatomic and nonanatomic attachments.Am J Sports Med. Aug. 2012; 40: 1871-1879https://doi.org/10.1177/0363546512449998Crossref PubMed Scopus (151) Google Scholar,18Stephen J.M. Kaider D. Lumpaopong P. Deehan D.J. Amis A.A. The effect of femoral tunnel position and graft tension on patellar contact mechanics and kinematics after medial patellofemoral ligament reconstruction.Am J Sports Med. Feb. 2014; 42: 364-372https://doi.org/10.1177/0363546513509230Crossref PubMed Scopus (137) Google Scholar My main takeaway from this study is the need to incorporate visible femoral shaft in my assessment of intraoperative x-ray adequacy. The same way I would not start trying to place my femoral tunnel until I obtained a true lateral, I will now also make sure I have sufficient femoral shaft length (at least 4 cm) before proceeding. Regardless of where you think your tunnel should be relative to the PCEL, if you use the PCEL as a landmark, it is clear from this study you need sufficient visible femoral shaft length for it to be reliable. Obtaining an image that is both a true lateral and has sufficient visible shaft length can be challenging, particularly with a mini C-arm. For this reason, I prefer a large C-arm, which can provide a larger field of view. I also find it easier to obtain a true lateral with the large C-arm, as there is more space to move/rotate the knee as needed. That being said, I have seen mentors use both mini and large C-arms very effectively. There are also negatives of using the large C-arm, including need for an additional operator and increased radiation exposure. Whichever your modality of choice, if you plan on using radiographic landmarks to help with femoral tunnel placement, make sure you have enough femoral shaft in view to give yourself a reliable target! Download .docx (.01 MB) Help with docx files Radiographic Landmark Measurements for the Femoral Footprint of the Medial Patellofemoral Complex May Be Affected by Visible Femoral Shaft Length on Lateral Knee RadiographsArthroscopyPreviewTo assess the effect of visible femoral shaft length on the accuracy of radiographic landmarks of the medial patellofemoral complex (MPFC). Full-Text PDF