(aspects of sports medicine • an original study) Characterization of a Consistent Radiographic Finding in Chronic Anterior Cruciate Ligament Deficiency: The Posteromedial Osteophyte Brian H. Mullis, MD, Spero G. Karas, MD, and Scott S. Kelley, MD ABSTRACT tudies have shown that After the ACL is débrided dur- Often found in patients undergoing the posterior horn of the ing total knee arthroplasty (TKA) for total knee arthroplasty (TKA) is an medial meniscus resists osteoarthritis, there is often a block to osteophyte, at the posterior lateral anterior translation of the anterior tibial translation. When this corner of the medial tibial plateau, Stibia after anterior cruciate ligament block is present, there is consistently a that prevents anterior translation. (ACL) transection.1-3 This block to stabilizing osteophyte at the posterior This osteophyte does not occur in the presence of an entirely nor- anterior tibial translation is lost when lateral corner of the medial tibia pla- mal anterior cruciate ligament (ACL) the medial meniscus is removed. teau (Figure 1). After this osteophyte with normal vascularity. Although Animal studies have demonstrated is removed, the tibia easily translates similar findings have been reported adaptive responses to improve sta- anteriorly. This osteophyte can also be in animal studies, to our knowledge bility after ACL transection.4-7 The seen on standard preoperative x-rays this has never been documented medial meniscus, especially the pos- (Figures 2A, 2B). It is best viewed in humans. To determine the inci- terior horn, thickens several months on the lateral x-ray as an extension dence of this finding in our patient after the ACL is surgically transected. off the posterior medial tibial plateau population, anteroposterior and lat- Others studies have shown radio- extending posteriorly and superiorly eral x-rays of the affected knee of 90 patients undergoing TKA were graphic evidence of osteophyte for- (Figure 2B). Intraoperatively, the ACL reviewed. Forty-two percent (43/102 mation in this area several months is often present, but it is consistently knees) had radiographic signs of this after the ACL is sacrificed or rup- lax and has fibrosis and poor vascular stabilizing osteophyte. This finding tured.4-6,8-10 markings. confirms previous animal research and may lead to a better under- standing of how the knee adapts to improve stability in a chronic ACL- deficient state. Dr. Mullis is Chief of Orthopaedic Trauma, Indiana University School of Medicine, Indianapolis, Indiana. Dr. Karas is Assistant Professor of Orthopaedic Surgery, Emory University, Atlanta, Georgia. Dr. Kelley is Clinical Professor of Orthopaedic Surgery, Duke University, Durham, North Carolina. Requests for reprints: Scott S. Kelley, MD, North Carolina Orthopaedic Clinic, Duke University Medical Center, 4309 Medical Park Dr, Suite 100B, Durham, NC 27704 (tel, 919-471-9622; fax, 919-471- 1929; e-mail, [email protected]). Am J Orthop. 2007;36(9):494-497. Copyright Quadrant HealthCom Inc. 2007. Figure 1. A typical osteophyte at the posterior lateral border of the medial tibial All rights reserved. plateau. 494 The American Journal of Orthopedics® B. H. Mullis et al Dr. Kelley performed all the sur- geries, and all operative notes were available for review. All patients were asked to complete a questionnaire regarding previous injury to the knee, with a separate form for each knee when both knees were operated on. These forms were mailed to patients, and a phone call was made within 1 week to answer questions regard- ing the form. The x2 test was used for statistical analysis. The study was approved by the Committee on the Protection of the Rights of Human Subjects, and all patients were informed and agreed to participate. A B RESULTS Figure 2. Anteroposterior (A) and lateral (B) x-rays show a typical osteophyte Of 102 knees (90 patients), 43 at the posterior lateral border of the medial tibial plateau. (42%) were positive for the stabiliz- ing osteophyte. In patients with this Biomechanical studies of human osteophyte extending off the poste- osteophyte, ACL status was assessed knees have shown very little AP rior lateral corner of the medial tibial at time of surgery, and in all cases the motion in the medial compartment plateau (Figure 2B). The osteophyte ACL either was completely absent relative to the lateral compartment was considered a typical lesion when or showed evidence of attenuation, (Figure 3).11-14 This suggests there it was at least 5 mm in diameter and scarring, or decreased vascularity. may be a mechanical advantage to extended posteriorly and superiorly Of these 43 knees, 22 (51%) were a stable medial compartment, which directly off the lateral edge of the positive on the left, and 21 (49%) may explain why animals have devel- medial plateau. were positive on the right. There was oped a means to adapt to an unstable medial compartment after injury. In a comparison of Figures 1 and 3, the location of this osteophyte is well positioned to impede anterior transla- tion without compromising rotation. The consistent location of this osteo- phyte is shown in Figure 3. MATERIALS AND METHODS The study was performed at the University of North Carolina-Chapel Hill, where a database was kept of all patients undergoing TKA. From this database, we selected the last 132 patients who underwent primary TKA for osteoarthritis. Lateral x-rays for 40 patients were inadequate. Twelve of the remaining patients had bilateral TKA, Figure 3. Lines have been drawn connecting the flexion facet (FF) centers of so we had adequate x-rays for 102 the medial and lateral femoral condyles as the knee is taken through –5° to knees (57 left, 45 right) in 90 patients 120° of flexion. Movement in the anteroposterior (AP) plane on the medial side (37 men, 53 women). These knees is within the observer error (±1.5 mm); however, AP translation on the lateral were the basis of our review. Mean age side is 18 mm. Typical osteophyte location is represented by filled circle. EF was 66 years at time of surgery. represents extension facet. Reprinted and modified from Insall JN, Scott WN, Drs. Mullis and Kelley reviewed eds., Surgery of the Knee, 3rd ed., Pinskerova V, Iwaki H, Freeman MA. The knee x-rays and at that time desig- shapes and relative movements of the femur and tibia in the unloaded cadav- nated them either positive or nega- eric knee: a study using MRI as an anatomic tool, page 275, copyright 2001, tive based on presence of a typical with permission from Elsevier.26 September 2007 495 Chronic Anterior Cruciate Ligament Deficiency: Posteromedial Osteophyte no statistically significant difference between the 2 sides. Questionnaires Table. History of Knee Injury Compared With Radiographic were received from 58 (64%) of Presence of a Stabilizing Osteophyte the 90 patients for 67 (66%) of the 102 knees. There was no difference Osteophyte Present? Yes No between the presence or absence Questionnaire returned 29 38 of the stabilizing osteophyte with Prior injury 13 (45%) 14 (37%) respect to recall of prior injury, prior Prior treatment for injury 12 (41%) 10 (26%) medical treatment for the injury, or Prior surgery for injury 8 (28%) 8 (21%) prior surgery for the injury (Table). DISCUSSION mation of osteophytes similar to the the medial meniscus reduces ante- Traditionally, the femur has been posterior osteophyte described in this rior translation of the tibia after the thought to “roll back” on the tibia report. Studies of dogs, cats, and goats ACL is sacrificed.1-3 Shoemaker and during flexion. Recent findings dem- have shown that the knee gains stabil- Markolf3 found that the most impor- onstrate almost 2 cm of AP transla- ity as this osteophyte matures.4-7 As tant part of the medial meniscus tion in the lateral compartment of the early as 1971, Marshall and Olsson6 was the posterior horn. Allen and knee but relatively little movement demonstrated osteophyte formation colleagues1 confirmed these results (≤2 mm) on the medial side.11-14 This as a response to ACL deficiency in a and showed that the lateral meniscus suggests there might be a mechanical dog model: “Large osteophytes were played no role in AP stability after advantage to translational stability of found on the posterior aspect of the ACL transection. the medial compartment. medial tibial condyle.” Mechanical The only previously identified pat- As many knees are found to be testing of the knees of the animals tern unique to ACL deficiency is ACL-deficient at the time of TKA,11 showed that they became stabler osteophyte formation in the femoral we suggest some stability might be with time. Pournaras and colleagues4 notch and tibial spine.18 In retrospec- “...we suggest some stability might be gained by an osteophyte consistently found on the posterior lateral border of the medial tibial plateau.” gained by an osteophyte consistently described osteophyte formation at tive clinical studies, osteophyte for- found on the posterior lateral border the posterior edge of the medial tib- mation associated with early degen- of the medial tibial plateau. ial plateau in an ACL-deficient dog erative changes have been report- Osteophytes are considered a model. Suter and colleagues5 sacri- ed in ACL-deficient knees. Feagin “classic” finding in osteoarthritic ficed the ACL of cats in a study simi- and colleagues10 noted “buttressing knees.15 It is still unclear why osteo- lar to that conducted by Marshall and osteophytosis.” Fetto and Marshall9 phytes form. Some authors have sug- Olsson.6 Suter and colleagues noted, likewise noted osteophyte formation gested that they arise in response to “Over time, osteophytes appeared “at the intercondylar and peripheral joint instability and help alleviate on … the medio-dorsal border of the joint margins.” Jacobsen8 focused on pain.16 Pottenger and colleagues17 tibia.” They found that, “16 weeks the timing of osteophyte appearance, reported finding, in osteoarthritic [after ACL transection], anterior tib- noting formation within 2 years of human knees, marginal osteophytes ial translation relative to the femur is ACL rupture, followed years later by that provided varus and valgus stabil- reduced by about 50%.” Jackson and osteoarthrosis.