521 COPYRIGHT Ó 2009 BY THE JOURNAL OF BONE AND JOINT SURGERY,INCORPORATED Radiographic Identification of the Primary Medial Knee Structures By Coen A. Wijdicks, MSc, Chad J. Griffith, BS, Robert F. LaPrade, MD, PhD, Steinar Johansen, MD, Adam Sunderland, MSc, Elizabeth A. Arendt, MD, and Lars Engebretsen, MD, PhD Investigation performed at the Orthopaedic Biomechanics Laboratory, Department of Orthopaedic Surgery, University of Minnesota, Minneapolis, Minnesota, and the Orthopaedic Center, Ulleval University Hospital and Faculty of Medicine, University of Oslo, Oslo, Norway Background: Radiographic landmarks for medial knee attachment sites during anatomic repairs or reconstructions are unknown. If identified, they could assist in the preoperative evaluation of structure location and allow for postoperative assessment of reconstruction tunnel placement. Methods: Radiopaque markers were implanted into the femoral and tibial attachments of the superficial medial collateral ligament and the femoral attachments of the posterior oblique and medial patellofemoral ligaments of eleven fresh-frozen, nonpaired cadaveric knee specimens. Both anteroposterior and lateral radiographs were made. Structures were assessed within quadrants formed by the intersection of reference lines projected on the lateral radiographs. Quantitative mea- surements were performed by three independent examiners. Intraobserver reproducibility and interobserver reliability were determined with use of intraclass correlation coefficients. Results: The overall intraclass correlation coefficients for intraobserver reproducibility and interobserver reliability were 0.996 and 0.994, respectively. On the anteroposterior radiographs, the attachment sites of the superficial medial collateral ligament, posterior oblique ligament, and medial patellofemoral ligament were 30.5 ± 2.4 mm, 34.8 ± 2.7 mm, and 42.3 ± 2.1 mm from the femoral joint line, respectively. On the lateral femoral radiographs, the attachment of the superficial medial collateral ligament was 6.0 ± 0.8 mm from the medial epicondyle and was located in the anterodistal quadrant. The attachment of the posterior oblique ligament was 7.7 ± 1.9 mm from the gastrocnemius tubercle and was located in the posterodistal quadrant. The attachment of the medial patellofemoral ligament was 8.9 ± 2.0 mm from the adductor tubercle and was located in the anteroproximal quadrant. On the lateral tibial radiographs, the proximal and distal tibial attachments of the superficial medial collateral ligament were 15.9 ± 5.2 and 66.1 ± 3.6 mm distal to the tibial inclination, respectively. Conclusions: The attachment locations of the main medial knee structures can be qualitatively and quantitatively correlated to osseous landmarks and projected radiographic lines, with close agreement among examiners. Clinical Relevance: The present study identifies medial knee structure attachment sites with use of radiographic landmarks and thus allows for reliable preoperative and postoperative assessments of surgical repairs and reconstructions of the main medial knee structures. njuries to the medial (tibiofemoral) knee structures, col- medial patellofemoral ligament is the main medial stabilizer of lectively called the medial collateral ligament, are the most the patellofemoral joint16, and its femoral attachment is located common knee ligament injuries1-6. Previous studies have in close proximity to the femoral attachments of the medial I 15 demonstrated that the superficial medial collateral ligament knee stabilizers . and the posterior oblique ligament are the main stabilizing Areviewoftheliteratureprovidesnumerousqualita- structures of the medial tibiofemoral joint7-15. In addition, the tive4,8,11,17-21 and quantitative15 gross anatomic descriptions of Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from the Research Council of Norway, grant #175047/D15, and Health East Norway, grant #10703604. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated. J Bone Joint Surg Am. 2009;91:521-9 d doi:10.2106/JBJS.H.00909 522 THE J OURNAL OF B ONE &JOINT S URGERY d JBJS. ORG RADIOGRAPHIC I DENTIFICATION OF THE PRIMARY VOLUME 91-A d NUMBER 3 d M ARCH 2009 MEDIAL KNEE S TRUCTURES Fig. 1 A and B: Illustrations demonstrating the placement of radiopaque markers for the medial knee structure attachment sites (spheres at attachment sites and cut T-pins at osseous landmarks). MPFL = medial patellofemoral ligament, POL = posterior oblique ligament, and sMCL = superficial medial collateral ligament. these medial knee structures; however, there is a lack of es- very difficult, and radiographic guidelines could assist with the tablished and validated radiographic descriptions of the medial interpretation of medial structure location on these radiographs. knee anatomy. Understanding both the gross and radiographic In addition, quantitative assessment of the radiographic location anatomy is important for the surgical treatment of medial knee of structures would assist in the evaluation of postoperative injuries. In revision surgery cases, the frequent presence of het- placement of these structures. Thus, radiographic orientation erotopic ossification after injury 22 or obliteration of the normal should be an important adjunct to utilize for the preoperative osseous anatomy by previous surgical hardware or tunnels can planning and postoperative assessment of repairs or recon- make identification of the normal medial knee attachment sites structions of medial knee structures. Fig. 2 Illustration (left) and anteroposterior knee radiograph (right) demonstrating the placement of the reference line intersecting the distalmost points of the lateral and medial femoral condyles. A = adductor tubercle, B = medial patellofemoral ligament (MPFL) attachment, C = gastrocnemius tubercle, D = posterior oblique ligament (POL) attachment, E = superficial medial collateral ligament (sMCL) attachment, and F = medial epicondyle. 523 THE J OURNAL OF B ONE &JOINT S URGERY d JBJS. ORG RADIOGRAPHIC I DENTIFICATION OF THE PRIMARY VOLUME 91-A d NUMBER 3 d M ARCH 2009 MEDIAL KNEE S TRUCTURES Fig. 3 Illustration (left) and anteroposterior knee radiograph (right) demonstrating the placement of a reference line crossing the most proximal aspects of the lateral and medial tibial plateaus. A = direct arm of semimembranosus muscle (DASM) attachment, B = proximal tibial superficial medial collateral ligament (sMCL) attachment, and C = distal tibial superficial medial collateral ligament attachment. The purpose of the present study was to qualitatively and collateral ligament and the femoral attachment sites of the quantitatively define radiographic landmarks for the locations medial patellofemoral ligament and posterior oblique ligament. of the femoral and tibial attachments of the superficial medial Our hypothesis was that a standardized radiographic mea- Fig. 4 Illustration (left) and lateral knee radiograph (right) demonstrating the placement of the femoral reference lines. Line 1 was drawn as an extension of the posterior femoral cortex, and line 2 was drawn perpendicular to line 1 and passed through the posterior portion of the Blumensaat line. The numbers 1 through 4 in the radiograph indicate quadrants of the lateral aspect of the distal part of the femur. A = adductor tubercle, B = medial patellofemoral ligament (MPFL) attachment, C = gastrocnemius tubercle, D = posterior oblique ligament (POL) attachment, E = superficial medial collateral ligament (sMCL) attachment, F = medial epicondyle, quadrant 1 = anteroproximal, quadrant 2 = posteroproximal, quadrant 3 = anterodistal, and quadrant 4 = posterodistal. 524 THE J OURNAL OF B ONE &JOINT S URGERY d JBJS. ORG RADIOGRAPHIC I DENTIFICATION OF THE PRIMARY VOLUME 91-A d NUMBER 3 d M ARCH 2009 MEDIAL KNEE S TRUCTURES Fig. 5 Illustration (left) and lateral knee radiograph (right) demonstrating the technique used to identify the center of the tibial di- aphyseal axis (line 1) and the line parallel to the medial tibial plateau (line 2). A = direct arm of semimembranosus muscle (DASM) attachment, B = proximal tibial superficial medial collateral ligament (sMCL) attachment, and C = distal tibial superficial medial collateral ligament attachment. surement method would reproducibly describe the locations Parts, Miami Lakes, Florida) was embedded into the center of of these important medial knee attachment sites in reference each attachment site by placing the sphere within the center of an to each other, to projected radiographic reference lines, and to osteochondral transfer device (OATS system; Arthrex, Naples, other osseous and soft-tissue medial knee landmarks. Florida) that corresponded to the diameter of the attachment site of the respective structure and by using a small mallet to drive the Materials and Methods sphere into the subchondral bone. The sharp ends of 1-mm- Specimen Preparation diameter T-pins (Advantus, Jacksonville, Florida), cut to ap- leven fresh-frozen, nonpaired cadaveric knees from donors proximately 5 mm in length, were embedded