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Osteochondritis Dissecans of the Knee Dennis C. Crawford, MD, PhD Marc R. Safran, MD Dr. Crawford is Assistant Professor, Sports Orthopaedic and Arthroscopic Surgery, Department of Orthopaedics and Rehabilitation, Oregon Health & Abstract Osteochondritis dissecans is a condition of the joints that appears to affect subchondral bone primarily, with secondary effects on articular cartilage. With progression, this pathology may present clinically with symptoms related to the integrity of the articular cartilage. Early signs, associated with intact cartilage, may be related to a softening phenomenon and alteration in the mechanical properties of cartilage. Later stages, because of the lack of underlying support of the cartilage, can present with signs of articular cartilage separation, cartilage flaps, loose bodies, inflammatory synovitis, persistent or intermittent joint effusion, and, in severe cases, secondary joint degeneration. Selecting and recommending a surgical intervention require balancing application of nonsurgical interventions with assessment of the degree of articular cartilage stability and the potential for spontaneous recovery. Science University, Portland, OR. Dr. Safran is Associate Professor and Director, Sports Medicine, Department of Orthopaedic Surgery, University of California, San Francisco, San Francisco, CA. None of the following authors or the departments with which they are affiliated has received anything of value from or owns stock in a commercial company or institution related directly or indirectly to the subject of this article: Dr. Crawford and Dr. Safran. Reprint requests: Dr. Safran, Department of Orthopaedic Surgery, University of California, 500 Parnassus Avenue, MU 320W, San Francisco, CA 94143-0728. J Am Acad Orthop Surg 2006;14:90-100 Copyright 2006 by the American Academy of Orthopaedic Surgeons. he etiology of osteochondritis dissecans (OCD), in contrast to its etymology, remains unclear. Al-though also described by Pare and Paget, the disease was named by Konig1 in 1888, who by his nomen-clature indicated an inflammatory basis to explain a phenomenon of loose bodies in the joint.1,2 No theory regarding the cause of OCD is uni-versally accepted, even though, as Konig later recognized, an inflamma-tory origin is unlikely. Repetitive mi-crotrauma, secondary effects associ-ated with vascular insufficiency, and potentially inherited factors remain important areas for investigation and clarification. Classification of OCD in the knee involves identification of a specific location, potential frag-mentation and/or displacement, and the status of the growth plate (Table 1). Skeletal age at onset of symptoms appears to be the most important de- terminant of prognosis and remains an essential factor, directing the tim-ing and nature of treatment deci-sions. Confusion regarding the etiol-ogy, treatment, and natural history of these lesions is compounded by the common practice of referring to both osteochondritis dissecans and osteo-chondral defects (which can be sec-ondary to osteochondritis dissecans or to traumatic osteochondral frac-ture) as OCD. Incidence of OCD has been esti-mated at between 0.02% and 0.03%, based on a survey of knee radio-graphs, and at 1.2%, based on knee arthroscopy.3,4 The highest rates ap-pear among patients aged between 10 and 15 years. Male-to-female ra-tio historically is approximately 2:1. Bilateral lesions, typically in differ-ent phases of development, are re-ported in 15% to 30% of cases, man-dating assessment of both knees in 90 Journal of the American Academy of Orthopaedic Surgeons Dennis C. Crawford, MD, PhD, and Marc R. Safran, MD all patients presenting with this di-agnosis.5 Etiology Lesions described as OCD can be caused by several factors, the signif-icance of which may vary depending on the area of the knee affected.1,6 The essential mechanisms responsi-ble are divided into constitutional or hereditary, vascular, and traumatic. Constitutional Factors Table 1 Imaging and Arthroscopic Criteria for Classifying Osteochondritis Dissecans Lesions in the Knee Magnetic Resonance Radiographic Imaging* Arthroscopic Open vs closed Low signal between the Stable: Cartilage physis osseous fragments softening, cartilage Location of lesion Low signal breaching breach Size of lesion the cartilage Unstable: Cartilage flag Presence of loose Focal defect ³5 mm tears, osteochondral bodies loose body Osteochondral defects * T2-weighted (fluid-weighted) sequence Ribbing7 suggested that OCD may represent a variation or sub- group of epiphyseal dysplasia and might separate from these epiphys- ated with “classic” lesions of thus may display a similar inheri-tance pattern. One report of familial predisposition to OCD-type lesions supports this idea;8 however, Petrie,9 in a study showing minimal trans- eal areas and subsequently act as the precursors for OCD lesions.9,11 More recent data from equine OCD stud-ies suggest a role for elevated matrix-metalloproteinase activity in sub- OCD.15,16 Similarly, Linden and Tel-hag17 demonstrated limited uptake of tetracycline and radionucleotide in 14 adults with OCD lesions and so concluded that the reparative pro- mittance to first-degree relatives, chondral bone.12,13 Whether a cess of subchondral bone was arrest- found limited evidence for a genetic pattern and suggested that the usual presentation is not familial. Despite this determination, an association of OCD has been found with a variety of inherited conditions, including dwarfism (described only as “short predisposition to this condition is manifest in genetic inheritance is likely to prove to be multifactorial. Vascular Factors Analogous pathophysiology be-tween osteonecrosis and OCD con- ed at a fibrocartilage stage, possibly the result of poor blood supply. Traumatic Factors A history of injury is reported in as many as 40% of patients with OCD,althoughsomestudiessuggest stature”), tibia vara, Legg-Calvé- stituted a popular theory for etiolo- a far more limited role for direct in-Perthes disease, and Stickler’s syn- gy among many early investigators jury.18 Cahill and colleagues19,20 drome.5 (eg, Paget, Ficat, Enneking).2 En- found no specific history of direct The relationship between the na- neking specifically championed a trauma among 204 patients in ture of developing OCD lesions, pos-sible hereditary factors, and the po-tential for abnormal ossification of the growth plate remains uncertain. Abnormalities of epiphyseal matura-tion are common and typically re-solve without long-term sequelae. Distinguishing normal ossification centers of the distal femur is critical theory centered on poor end-arterial cascades in the distal femur and a predisposition for this bone to devel-op and behave in a manner analo-gous to a sequestrum. Often cited as evidence against this hypothesis is an anatomic study of 200 adult, 16 newborn, and 4 “juvenile” femurs that indicated extensive vascular whom they attributed the pathology to a stress fracture. This theory is based on the unproven hypothesis that a series of pathologic reactions within articular cartilage and sub-chondral bone occur secondary to re-petitive microtrauma and yield a chronic osteochondral injury that manifests as an OCD lesion. in evaluating the young patient with anastomosis.14 Further proof is Shear forces particular to the lat- knee pain. Caffey et al10 describe the presence of irregularities of ossifica-tion in the distal femoral growth plates as the rule and explain them as an imbalance between rapid carti-lage proliferation and ossification. These areas are typically benign, re-solve without sequelae, and should found in another study that exam-ined six detached lesions from pa-tients with diagnosed osteochondri-tis with no histopathologic evidence of osteonecrosis.11 Despite these in-vestigations, several recent reports have suggested that the cause is a paucity of vascular supply to the me- eral aspect of the medial femoral condyle may be a contributing fac-tor. Fairbank21 described repetitive impingement from the tibial spine as causal for OCD of the lateral as-pect of the medial femoral condyle. In this hypothesis, supported by bio-mechanical studies later performed not be confused with OCD lesions. dialfemoralcondylesubjacenttothe by Nambu et al,22 shear forces Some investigators, however, have posterior cruciate ligament inser- caused by impingement are generat-proposed that accessory nuclei tion, an area most commonly associ- ed as the knee rotates medially with Volume 14, Number 2, February 2006 91 Osteochondritis Dissecans of the Knee loading in flexion. Smillie23 also fa-vored this hypothesis, citing factors that could increase contact forces, including meniscectomy, instability, genu recurvatum, and condylar flat-tening. Several investigators subse-quently have shown an association between discoid lateral meniscus and the less common lateral femoral takenduringchildhooddidnotreveal OCD. Later, during adulthood, the patientsdidhaveradiographicallyap-parent OCD. However, the patients presented by Cahill likely had child-hood OCD that may not have been apparent on the plain radiographs, possibly because of the position of the lesion relative to the angle of the is that, in internal rotation and ex-tension, the tibial eminence imping-es on the OCD lesion, causing pain, and that external rotation moves the eminence away from the lesion, re-lieving the pain. A recent case series has shown a poor predictive value of this maneuver with radiographically proven OCD.28 However, the same condylar lesion.24-26 Specifically, the knee during radiography. It has authors suggest use of this maneu- amount of direct microtrauma or macrotrauma necessary to produce an osteochondritis cannot be ascer-tained from the literature. What is clear is that distinguishing osteo-chondral fractures that fail to unite from lesions of OCD based on static radiographic and histologic evidence has proved to be difficult and re-mains controversial. Smillie23 distinguished two essen-tial forms of OCD, juvenile and adult, and suggested unique etiolo-gies. In the variety manifested in the skeletallyimmatureindividual,there clearly been shown that OCD (in the “classic” location, the lateral aspect of the medial femoral condyle) may be missed on posteroanterior radio-graphs with the knee in full exten-sion, yet may be visualized on flexed-knee views.26 Adult-onset OCD may simply be a delayed onset of previ-ously asymptomatic juvenile OCD that failed to heal and presents later with loosening and joint degenera-tion. Early presentation often encom-passes poorly defined complaints. Pain is generalized to the anterior ver, when it is initially positive, as a tool for following disease resolution. Standard techniques for testing sta-bility and joint palpation are neces-sary to identify concurrent patholo-gy,includingloosebodies,associated meniscal tears, malalignment, and ligamentous injury. Imaging Studies Characterizing the lesion type and assessing growth plate status typically begins by making standard weight-bearing anteroposterior and lateral radiographs of both knees. may be a fundamental disturbance of knee, with variable amounts of Lateral radiographs allow recogni- the epiphyseal development, with re-sultant formation of small accessory areas of subchondral bone that sepa-rate from the principal ossification center of the epiphyseal plate. Min-imal trauma, whether repetitive mi-crotrauma or direct macrotrauma, then may cause osteonecrosis within this region, as separation of the frag-ments disturbs the balance of oxygen tension necessary for ossification. In contrast to this type of developmen-tal etiology, Smillie postulated a more direct traumatic causation for the adult form. Clinical Presentation Cahill19 and Mubarak and Carroll8 emphasized a distinction between the juvenile and adult types of OCD, based on the osseous age of the pa-tient at the time of symptom onset. Those with open physes are consid-ered to have juvenile-onset OCD, whereasthosewithskeletalmaturity are considered to have the adult form.Cahill19 reportedcasesofadult-onset OCD in which radiographs swelling that is typically intermit-tent. Anecdotal but consistent re-ports suggest an association between periods of increased activity and ep-isodes of swelling and effusion. An effusion may be found in association with joint synovitis and does not necessarily reflect a loose osteocarti-laginous fragment. The true source of this synovitis and/or effusion is elusive. In patients with more ad-vanced OCD, persistent swelling or effusion may be accompanied by catching, locking, or giving way. In late-stage disease, the sensation of a loose body is often described. Physical findings may be correlat-ed with the area of the lesion. Wil-son27 describes an external rotation of the tibia during gait as signifying compensation for impingement of the tibial eminence on an OCD le-sion of the medial femoral condyle. Wilson’s test involves reproduction of pain on examination by internal-ly rotating the tibia during extension of the knee between 90° and 30°, then relieving the pain with tibial external rotation. The presumption tion of a relatively anteroposterior lesion location and identification of normal, benign accessory ossifica-tion centers in the skeletally imma-ture knee, as described by Caffey et al.10 An axial view can be added when lesions of the patella or troch-lea are suspected. In addition, the ra-diographic “notch view,” taken with the knees bent 30° to 50°, may help identify the lesions in the posterior condyles. Plain radiographs provide initial data to determine lesion size, pres-ence or absence of sclerosis, poten-tial dissection, and assignment to one of several classification systems. Cahill and Berg29 describe a method of localizing lesions by dividing the knee into 15 distinct alphanumeric zones (Figure 1). From medial to lat-eral, five zones numbered 1 through 5 are divided centrally by the notch; each compartment is then divided in half. The lateral radiograph uses Blu-mensaat’s line anteriorly and the posterior cortical line to divide zone A (anterior) from B (central) and C (posterior). This alphanumeric sys- 92 Journal of the American Academy of Orthopaedic Surgeons Dennis C. Crawford, MD, PhD, and Marc R. Safran, MD tem provides standardization for re-search purposes, although it has Figure 1 found limited application to date.6,26 Cahill and Berg29 also describe a classification system for juvenile OCD based on technetium Tc 99m phosphate scintigraphy findings. Grading is based on the relative de-gree of scintigraphic activity in rela-tion to plain radiographs. Stage 0 is normal in both. Stage 1 demon-strates a defect on plain radiographs butnoincreasedactivityonthebone scan.Stage2showsincreaseduptake in the lesion but not in the adjacent femoral condyle. Stage 3 indicates isotopeuptakeinboththelesionand the adjacent condyle. Finally, stage 4 demonstrates increased isotope up-take in both the lesion and adjacent tibial surface. Patients with stage 3 or 4 disease were described as having symptomatic OCD. Cahill et al20 lat-er reported limited correlation be-tween this staging system and pre-diction of lesion stability or the need for subsequent surgery. However, Paletta et al30 suggested a role for this imaging technique that distin-guishes between results in juveniles and those in adults. They reported that four of four patients with open Anteroposterior (A) and lateral (B) views of the knee, demonstrating the 15 alphanumeric radiographic regions described by Cahill and Berg.29 The five numbered zones on the anteroposterior view are divided centrally by the notch (zone 3). The lettered zones on the lateral view are divided by Blumensaat’s line anteriorly and the posterior cortical line. The half-moon–shaped shaded area in each view of the distal femur represents an old lesion. (Adapted with permission from Cahill BR, Berg BC: 99m-Technetium phosphate compound joint scintigraphy in the management of juvenile osteochondritis dissecans of the femoral condyles. Am J Sports Med 1988;11:329-335.) physeal plates and increased activity evidenced by high signal intensity nology (eg, cartilage-specific se-on bone scan healed with nonsurgi- on T2-weighted images when a quences) may eliminate the necessi- cal treatment, whereas the two pa-tients without increased activity did not heal. In contrast, among patients with closed growth plates, only 33% (2/6) healed despite having similar increased activity within the le-sion. breach of the cartilage surface was detected. They distinguished carti-lage breach with an attached frag-ment by interpreting interposed low signal intensity on the rim as fibrous tissue (Figure 2). Others have added criteria for ty of intra-articular injections and allow distinction between areas of interposed synovial fluid, fibrocarti-lage, and degenerated or lytic sub-chondral bone. Classification and Magnetic resonance imaging fragment instability to include the Characterization (MRI) has proved to be particularly valuable in assessing osteochondral lesions. Several investigators have attempted to characterize the stabil-ity of the OCD lesion with findings on MRI. Dipaola et al31 classified le- following: an area of increased ho-mogenous signal ³5 mm in diameter beneath the lesion; a focal defect ³5 mm in the articular surface; and a high signal line traversing the sub-chondral plate into the lesion.32 In Distribution of OCD lesions in the knee are most commonly associ-ated with the lateral aspect of the medial femoral condyle. Aichroth26 described this as the classic location and confirmed it in 69% (72) of 105 sions according to appearance on cases of limited joint effusion, knees (Figure 3). The patella was in- MRI and associated specific findings with the potential for fragment de-tachment. They described lesions containing fluid behind the joint as partially or completely detached, as Volume 14, Number 2, February 2006 Kramer et al33 expressed a high level of confidence for predicting lesion stability using intra-articular gado-linium Gd 153 contrast material. More recent advances in MRI tech- volved in five patients (5%); the re-mainder of the lesions involved the lateral femoral condyle (15% [16]) and the medial femoral condyle (69% [72]). In a large multicenter ret- 93 Osteochondritis Dissecans of the Knee Figure 2 lesions are more commonly associ-ated with discoid meniscus or with occurrence after meniscal sur-gery.26,34 Sagittal MRI scans of unstable osteochondritis lesions of the distal femur. T2-weighted (fluid-weighted) images of osteochondral separation are indicated by high signal line between the osseous components (A) and extending from the intraosseous portion to the joint surface, “breaching” the cartilage (B). Figure 3 Knee radiographs provide not only the initial basis for distinction of growth plate maturation but also as-sessment of lesion location and sta-bility (ie, free or loose bodies). Berndt and Harty35 described four stages of chondral lesions based on plain ra-diographs of the talus; this system has been widely applied to lesions about the knee: stage I, involvement of a small area of compression of the subchondral bone; stage II, partially detached osteochondral fragment; stage III, completely detached frag-ment that remains in the underlying crater; and stage IV, complete detachment/loose body. Other crite-ria, such as lesion size, have been used to assess the potential for heal-ing with nonsurgical intervention. Several authors20,32,36 have thought that patients could be successfully treated nonsurgically when the mean area was smaller than between 194 and 424 mm2. In contrast, le-sions larger than between 436 to 815 mm2 were associated with poor out-comes. Others have suggested the presence of “marked sclerosis” as a poor predictor of successful nonsur-gical management.37-39 Understanding and characterizing the spectrum of OCD lesions as sta-ble or unstable is often considered central to the treatment plan. How-ever, this characterization has Anteroposterior radiographs demonstrating an OCD lesion on the lateral aspect of the medial femoral condyle before (A) and after (B) displacement. proved to be difficult to determine prior to surgical intervention and of-ten remains a clinical judgment. MRI criteria have proved to be rea-sonably accurate compared with the gold standard of arthroscopic find-ings in predicting lesion integrity. Strict adherence to the MRI criteria of Dipaola was shown in one rospective study of 713 patients and 798 knees, Hefti et al5 described a slightly different distribution. The medial femoral condyle was typical-ly affected, with the majority of le-sions involving the lateral aspect (51%), 19% the central, and 7% the medial aspect. Involvement of the lateral condyle in all areas encom-passed 17% of lesions; those of the patella, 7%; and 0.2% (one lesion), the tibial plateau. Lateral condylar study40 to have an 85% correlation with arthroscopic findings when ap-plying Guhl’s arthroscopic staging system. Guhl’s intraoperative classi-fication is defined by cartilage integ-rity and fragment stability.37 Type I 94 Journal of the American Academy of Orthopaedic Surgeons ... - tailieumienphi.vn