Patella Dislocation Recognizing the and Its Complications

Mark R. Hutchinson, MD Mary Lloyd Ireland, MD Photo: © 1995. John Laptad/F-Stock Whenever a patient has a dislocation, osteochondral frac­ tures should be considered. A case study involving a 17-year-old swim­ mer whose 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 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, 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 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 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 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 . 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 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.

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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. was performed to remove patella tilt and lateral 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 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 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, ) tated tibia, the fracture should occur during dis­ Medial or lateral _ Posterior cruciate ligament rupture location:1'·16The patella or femoral condyle frac­ Isolated popliteal 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 secondary to isolated in­ femoral condyle just above the tibiofemoral 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 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 reduction as the patella pops back in­ An extended differential diagnosis (table 1) is to place over the lateral condyle. considered if history and physical exam are not The lateral impaction lesion occurs when the classic. If there was no traumatic episode, infec­ patella is completely dislocated and the vastus tion, bleeding disorder, or tumor should be con­ medialis and quadriceps force the medial border sidered. of the patella into the lateral femoral condyle. Unlike a flake fracture of the anterior femoral Select the Best Radiographic Views condyle, the lateral impaction lesion does not If patella subluxation or dislocation is sus­ involve the weight-bearing articular surface and pected, four views of the knee (AP, lateral, notch, is more posterior and nearer to the tibiofemoral and sunrise patella view) are carefully reviewed. joint line. Radiopaque loose bodies should be searched for. The sunrise view may provide the only find­ Examine for All Damage Sites ings oflateral subluxation or loose bodies. Notch In an athlete who presents with an acute views may expose loose fragments that were knee injury accompanied by a significant hidden by overlapping shadows in routine AP hemarthrosis, the two most common diagnoses views. Lateral views may visualize fragments or are patella dislocation and ACL injury. Meniscus demonstrate patella alta, which predisposes the tears and intra-articular fractures may also de­ patient to patella subluxation. Oblique views velop an effusion; those from meniscus tears are may be added if suspicion of loose fragments is usually of less volume and those from intra-ar­ high but visualization has not been accom­ ticular fractures may contain fat droplets. plished. It is helpful to look for subtle radiolu­ A thorough physical exam often confirms the cencies in all possible sites where osteochondral diagnosis of patella dislocation. Consistent find­ fragments may be missing. ings include a voluminous hemarthrosis, focal Lateral impaction lesions may not be visual­ tenderness over the medial retinaculum and ized on plain radiographs. Diagnosis, debride-

THE PHYSICIAN AND SPORTSMEDICINE e Vol 23 • No. 10 • October 95 ment of the lesion, and loose body removal are loose osteochondral fragments. If any predis­ performed,arthroscopically. posing factors for patella dislocationare present, an.even more aggressive approach should be in­ Loose Bodies Guide Treatment Decisions stituted. For mild to moderate predisposing fac­ The treatment goal for any patient who has a tors in the proximal aspect of the extensor patella dislocation is to restore normal knee mechanism (such as a lax or tom medial quadri- function. 17 __£eps retinaculum, vastus medialis dysplasia, or In our practice, we base treatment for an retracted insertion of the vastus medialis obliqu­ acute patella dislocation without osteochondral us on the patella), arthroscopy can be accompa­ fragments on predisposing factors for recurrent nied by a lateral retinaculum release and medial dislocation. A careful physical exam is necessary retinaculum repair or reefing through a small to identify the at-risk patient. Factors increasing medial parapatellar incision. For significant pre­ the risk of recurrent dislocation include exces­ disposing factors involving bony alignment or sive genu valgum, increased Q angle, patella al ta, severe soft-tissue imbalance (such as severe generalized . a relatively low generalized ligamentous laxity. excessive Q an­ lateral femoral condylar height, a defect of the gle, low lateral femoral condyle, or severe genu vastus medialis obliquus insertion onto the valgum) an open repair with bony osteotomy patella, vastus medialis obliquus dysplasia, or and realignment may be indicated. Fortunately, 18 20 abnormal patella configuration. · If any of a large majority can be treated with arthroscopy these conditions is present, a more aggressive with the occasional addition of a small medial surgical approach may be needed. Open patellar parapatcllar repair. realignment procedures may be required if sub­ In comparison to open repair and realign­ sequent dislocations occur. ment, arthroscopic treatment with or without If no predisposing factors are present, a con­ the mini-medial repair reduces postoperative servative approach may be attempted that con­ pain, allows an accelerated rehabilitation pro­ sists of knee immobilization in extension for 3 gram, and facilitates an earlier return to sports weeks, a lateral pad or taping to maintain reduc­ participation. tion of the patella, and aggressive quadriceps re­ Postoperatively, we generally splint the knee habilitation. Patients can generally return to play in extension and place a felt pad over the lateral in 8 to 12 weeks. However, some authors2023 ad­ aspect of the patella to maintain reduction. The vocate surgical repair for most patients and for knee is immobilized for 3 weeks, after which the all athletes with an acute patella dislocation re­ patient wears a knee sleeve with a lateral pad gardless of predisposing factors. Others24 advo­ and begins active, active assisted, and passive cate diagnostic arthroscopy in all cases of acute range of motion of the knee and patellar mobi­ hemarthrosis. In one series,25 preoperative phys­ lization activities. At 4 weeks, closed-chain ical examination yielded the correct diagnosis of squats and leg press activities limiting the termi­ an osteochondral fracture in only 17% of the pa­ nal 20° of extension are begun. Motion is pro­ tients. gressed, and a range from 0° to 90° is expected by Chondral loose bodies are not seen radio­ 6to8weeks. graphically. Therefore, if the patient experiences The quadriceps strengthening program in­ recurrent swelling, locking, or can feel or show volves closed-chain through the pain­ the physician the loose fragments, arthroscopy less arc, single or double legged squats or leg is indicated. presses in an arc of 0° to 60°. Open-chain exer­ Surgery is clearly indicated if osteochondral cises such as straight-leg raising with loose bodies are seen on radiographs and the weights are best performed in near-full exten­ history and physical exam suggest patella dislo­ sion, when patellofemoral articulation forces are cation. Arthroscopy is a valuable tool for identi­ minimized. fying intra-articular pathology and removing Return to full functional activity should be

Vol 23 • No. 1 0 • October 95 • THE PHYSICIAN AND SPORTSMEDICINE based on ability to perform a single-leg leg Minimize Down Time press at a level comparable to the opposite side, Keeping in mind that multiple chondral or along with restoration of landing balance abili- osteochondral defects may be present when a ty specific to the patient's . The knee patient sustains a patella dislocation, a careful sleeve should be worn during contact or vigor- physical exam, an appropriate radiographic se­ ous stop-cut activities for at least the remainder ries, and arthroscopy when needed will guide of the season. As long as rehabilitation contin- - treatment. ues, weakness from dependence on the knee Structured rehabilitation for injuries without sleeve is not observed. The patient can usually fragments or defects and prompt arthroscopic return to sports in 3 months. The physician treatment for those with fragments or defects should urge the patient and coach to continue help accomplish the goal of restoring knee func­ the patient's quadriceps strengthening exercis- tion and returning patients to their activities. PEM es and to use a knee sleeve, .acquire .sports-spe­ Address correspondeBce to Mary Lloyd Ireland, MD, cific skills, and employ proper knee biome­ Kentucky SpOFts Medicine, 601 Perimeter Qr, L.exingtoR, chanics. KY40517.

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