Patella Dislocation Recognizing the Injury and Its Complications Mark R. Hutchinson, MD Mary Lloyd Ireland, MD Photo: © 1995. John Laptad/F-Stock Whenever a patient has a patella dislocation, osteochondral frac­ tures should be considered. A case study involving a 17-year-old swim­ mer whose knee was injured playing baseball details a patella dislocation that was accompanied by a defect of the me­ dial patellar facet and a lateral impaction lesion of the lateral femoral gutter-both producing loose bodies. Careful physical examination and a radiographic series that includes anteroposterior, lateral, notch, and sunrise patella views assist in making an accurate diagnosis and guide the clinician to the appropriate treatment. Treatment involves a knee stabilizer fol­ lowed by aggressive quadriceps strength­ ening. Loose bodies require arthroscopic surgery. leg twists on a planted foot and the patient feels and hears a "pop." Such a scenario is common in the history A of a knee injury. If a significant hemarthrosis quickly develops, three diagnoses are immediately considered: rupture of the an- Dr Hutchinson is assistant professor of orthopedics in the Department of Orthopaedics, Sports Medicine Service, at the University of Illinois in Chicago. He is also team physician for the University of Illinois hockey team, The Chicago Chee­ tahs professional roller hockey team, and the US Olympic rhythmic gymnastics team. Dr Ireland is assistant professor in the Department of Surgery (Orthopaedics) and assistant professor in the Department of Family Medicine at the Uni­ versity of Kentucky in Lexington. She is an orthopedic con­ sultant for the University of Kentucky and Eastern Kentucky University sports teams and director of the Kentucky Sports Medicine Clinic in Lexington. Copyright © The McGraw-Hill _Companies, Inc. Reprinted with permission. THE PHYSICIAN AND SPORTSMEDICINE e Vol 23 • No. 10 • October 95 Figure 1: Rich Pennell Figure 1. A diagram of the left knee indicates possible origins of osteochondral fractures caused by patella dislocation. Contact between the patella and the femur can damage the patella (la, lb, and le} and/or femur (Ila, llb, and lie). The lateral impaction fracture {lie) involves the non-weight­ bearing femoral gutter. Adapted with permission from Muller W: The Knee: Form, Function, and Medial Lateral Ligament Reconstruction. New York City, Springer-Verlag New York Inc, 1983, p 83 terior cruciate ligament (ACL), intra-articular Case Report fracture, and patella dislocation. A peripheral A 17-year-old competitive swimmer injured meniscus tear usually causes a smaller effu­ his left knee while playing baseball. He was at­ sion. tempting to catch a fly ball and was struck by an­ In 1905, Kroner 3 was the first to report the other player from the lateral side. He said his association between patella dislocation and foot was planted and "got stuck;" his knee twist­ osteochondral loose bodies. Prior to arthrosco­ ed, then popped. Significant swelling developed py, multiple authors presented what was within 30 minutes of the injury. He denied any thought to be an uncommon association be­ previous knee injuries. tween patella dislocations and osteochondral On physical examination, the left knee was fractures. 2·rn More recent reports state that os­ significantly swollen and the patella was ballot­ teochondral fractures occur in approximately table. The knee was exquisitely tender over the 12 16 5% to 30% of acute patella dislocations. - The medial patella and focally tender over the lateral site of origin is most commonly the medial aspect of the lateral femoral condyle. Lateral patellar facet, and more rarely the lateral translation of the patella produced apprehen­ 13 16 femoral condyle. • The loose fragment may sion and pain. Knee range of motion was 10° to also originate by impaction of the medial bor­ 70°. Ligament examination was normal and der of the patella on the lateral nonarticulating symmetrical. There were no meniscal signs. Dis­ condyle of the femur (the lateral impact lesion) tal neurovascular status was normal. as seen in figure l.' Fractures may be isolated Radiographic examination included antero­ or associated with other osteochondral frac­ posterior (AP), lateral, notch, and sunrise patella tures. views (figure 2). Two osteocartilaginous loose The following case study provides a frame­ bodies could be seen radiographically: one in work for reviewing osteochondral fractures and the lateral gutter and a second one above the loose bodies that are often associated with patel­ tibial eminence. The osteochondral fragments la dislocations. were best seen on the notch and sunrise views. Vol 23 • No. 10 • October 95 e THE PHYSICIAN AND SPORTSMEDICINE c Figure 2. A radiographic series of a 17-year-old boy's left knee includes anteroposterior (AP) (a), lateral (b), notch (c), and sunrise patella (d) views. Patella dislocation during a baseball game led to osteochondral loose bodies that are best seen in the AP (a) and sunrise patella (d) views (arrows). A radiolucent medial lesion of the patella seen on the sunrise patella view (d} (arrowhead) suggests the origin of the fragment. The sunrise patella view also showed increased figure 3a. Arthroscopy was performed to remove patella tilt and lateral subluxation on the affect­ two loose bodies and to locate and saucerize ed side compared to the normal side. There was (debride) the origin of the osteochondral frac­ no genu valgum or patella alta. ture fragment on the medial patellar facet (figure The diagnosis of patella dislocation with os­ 3b). One osteochondral fragment was seen in teochondral loose bodies was made. Arthro­ front of the ACL (figure 3c). scopic findings are diagrammatically shown in The second fragment, from an impaction le- THE PHYSICIAN AND SPORTSMEDICINE e Vol 23 • No. 10 • October 95 Figure 3a:Rich Pennell; Figures 3b-3d: Courtesy of Mary Lloyd Ireland, MD a Lateral \ ' \ I / . --'"'\ c d Figure 3. A diagram of injuries a 17-year-old boy sustained when his patella dislocated during a baseball game (a} demonstrates the location of osteochondral fractures involving the patella and lateral femoral gutter. On arthroscopy, the source of the loose body (b}, a 3 x 3-cm defect in the medial patellar facet (arrow}, was located and debrided. Note the thickness of the cartilage on the patella. On an arthroscopic view of the anterior cruciate ligament (ACL} (c}, a large osteochondral fragment (arrow} was found in the intercondylar notch in front of the ACL. On a view of a 2 x 2-cm lateral impaction lesion {d) on the lateral aspect of the lateral nonarticulating part of the femoral condyle in the lateral gutter, shallow impaction of the bone and shearing of the periosteal covering are noted along with associated smaller loose bodies. sion of the femoral condyle, was seen in the lization were then initiated. Closed kinetic chain nonarticulating femoral gutter (figure 3d). All squats and leg lifts limiting the terminal 20° of other intra-articular structures were normal. flexion were begun 4 weeks postoperatively. The Arthroscopically, the patella tracked centrally in patient attained 90° range of motion 2 months the femoral groove. after surgery and regained full range of motion The knee was splinted in extension with a felt at 3 months. He was urged to wear a lateral pad placed over the lateral patella. The knee was padded knee sleeve during all lifting activities immobilized for 3 weeks. Active, active assisted, and running. The patient resumed swimming and passive range of motion and patellar mobi- competitively 3 months after surgery. Vol 23 • No. 10 • October 95 e THE PHYSICIAN AND SPORTSMEDICINE How Do Fractures Occur? The patella fracture may occur from the dis­ Table 1. Differential Diagnosis of Acute Knee Hemarthrosis location or the reduction. Most feel the chondral injury occurs as the patella dislocates. If the in­ Anterior cruciate ligament rupture jury occurs with the knee flexed in forced inward Patella dislocation/subluxation rotation of the femur with a fixed externally ro­ Osteochondral fracture (patella, femur, tibia) tated tibia, the fracture should occur during dis­ Medial or lateral meniscus tear _ Posterior cruciate ligament rupture location:1'·16The patella or femoral condyle frac­ Isolated popliteal tendon rupture tures as the patella dislocates over the promi­ Bleeding dyscrasias nence of the lateral condyle. Muller, 1 however, argues that reduction cre­ ates the osteochondral fragment. He notes that if rotation was part of the disloq1tion mechanism, vastus medialis insertion, .and.apprehension on a meniscus tear:wouldbe present--yet none has lateral subluxation.of the;patella....Tendemess to ever been reported. Muller presented two cases palpation on the middle to posterior lateral of patellar dislocation secondary to isolated in­ femoral condyle just above the tibiofemoral joint ternal rotation of the tibia. He argued that the line but away from the patellofemoral articula­ dislocation occurred in extension with contrac­ tion should raise suspicion. Pain on palpation of tion of the vastus lateralis. In this portion, the the lateral femoral gutter just above the joint line path of least resistance is above the lateral suggests a lateral impaction lesion. On examina­ condyle, which would have no bony obstruction tion, the ligaments are usually stable. Meniscus to cause an osteochondral fracture. The osteo­ tears are rarely associated with patella disloca - chondral fracture, he argued, would therefore tions.1" occur with