Osteochondral fractures of the dome of the talus

Transcription

1 This is an enhanced PDF from The Journal of Bone and Joint Surgery The PDF of the article you requested follows this cover page. Osteochondral fractures of the dome of the talus IF Anderson, KJ Crichton, T Grattan-Smith, RA Cooper and D Brazier J Bone Joint Surg Am. 1989;71: This information is current as of July 25, 2010 Reprints and Permissions Publisher Information Click here to order reprints or request permission to use material from this article, or locate the article citation on jbjs.org and click on the [Reprints and Permissions] link. The Journal of Bone and Joint Surgery 20 Pickering Street, Needham, MA

2 Copyright 1989 by The Journal of Bone and Joint Surgery, Incorporated Osteochondral Fractures of the Dome of the Talus* BY IAN F. ANDERSON, MB., B.S., F.R.A.C.R.t1, KEN J. CRICHTON, MB., B.S., GRAD.DIP.SPORT SC.t, CROWS NEST, TONY GRATTAN-SMITH, MB., B.S., F.R.A.C.R.1, ROBERT A. COOPER, M.B., B.S., D.D.U., F.R.A.C.P., AND DAVID BRAZIER, M.B., B.S., F.R.A.C.R4, ST. LEONARDS, NEW SOUTH WALES, AUSTRALIA From the Department of Diagnostic Radiology. Royal North Shore Hospital of Sydney. St. Leonards, and the North Sydney Orthopaedic and Sports Medicine Clinic, Crows Nest ABSTRACT: Twenty-four patients who had an osteochondral fracture of the dome of the talus were examined by plain radiography, magnetic resonance imaging, computerized tomography, and, when mdicated, scintigraphy. When plain radiographs of the ankle are relied on for the diagnosis of an osteochondral fracture of the talus, many lesions remain undiagnosed. Stage-I osteochondral fractures show no diagnostic changes on plain radiographs, and Stage-Il lesions are usually subtle and, therefore, are often overlooked by both radiologists and clinicians. The use of scintigraphy as a screening procedure and of magnetic resonance imaging for patients who have positive scintiscans showed that osteochondral fractures are more common than has previously been indicated in the literature. Scintigraphy should be used to assess patients when there is clinical suspicion of an osteochondral fracture but the plain radiographs appear to be negative. Patients who have positive scintiscans should be assessed by magnetic resonance imaging. Patients who have abnormal plain radiographs will derive no major benefits from magnetic resonance imaging; for all but one of these patients, computerized tomography was adequate for staging the fracture. Sprains of the ligaments of the ankle are the most frequent injury in sports4 #{176}.Although most such injuries are confined to the ligaments, the possibility ofan osteochondral fracture of the dome of the talus must be considered in these patients and in those who continue to complain of pain and disability despite apparently normal plain radiographs. Such fractures of the dome of the talus have been well reviewed and discussed in the 1iterature Although, in the past, they were often called osteochondritis dissecans ofthe talus, there is now general agreement that these lesions are actually osteochondral fractures and that they can be * No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject ofthis article. No funds were received in support of this study. t North Sydney Orthopaedic and Sports Medicine Clinic, 286 Pacific Highway, Crows Nest, New South Wales 2065, Australia. Please address requests for reprints to Dr. Anderson. Royal North Shore Hospital of Sydney, St. Leonards, New South Wales 2065, Australia. produced by trauma on both the medial and lateral aspects of the talus. Delay in establishing the diagnosis is common, as the initial radiographs may be negative or the evidence of fracture may be so subtle that it is overlooked. In addition, the symptoms are usually blamed entirely on the associated ligamentous injury, confusing the diagnosis and contributing to the delay. Most often the diagnosis is not made until after the fracture has progressed to a more advanced stage 316. In 1959, Berndt and Harty wrote a paper on osteochondral fractures of the talus. They noted that 191 lesions of the dome of the talus, variously called osteochondritis dissecans or osteochondral fractures, had been reported in the literature, and they added twenty-one cases. Their article reviewed and discussed the entity, rationalized the nomenclature, and proposed the name of transchondral fracture. They suggested that approximately 0.09 per cent of all fractures are transchondral fractures of the talus. Using abovethe-knee amputation specimens, they were able to reproduce fractures of both the medial and lateral aspects of the dome of the talus that were similar to those encountered clinically. Lateral fractures were produced by inversion and dorsiflexion, and medial fractures, by strong lateral rotation of the tibia on a plantar-flexed and inverted foot. Berndt and Harty proposed a four-stage classification system for these fractures, as follows: Stage I - there is a localized area of subchondral trabecular compression; Stage II - the fragment is incompletely separated; Stage III - the fragment is completely separated but undisplaced; Stage lila - the fragment is detached and rotated; and Stage IV - the fragment is displaced or inverted in its fracture bed. Since the work of Berndt and Harty, the development of new imaging techniques has made the diagnosis of osteochondral fractures easier. Computerized tomography shows bone in great detail, and now magnetic resonance imaging can show articular cartilage and subtle changes in bone marrow as well as bone detail. The purpose of this study was to assess whether the traditionally difficult diagnosis and staging of osteochondral fractures can be done more accurately with the aid of these newer imaging modalities. Materials and Methods In January 1988, as part of an over-all musculoskeletal program, the radiology department at the Royal North Shore VOL. 71-A, NO. 8, SEPTEMBER

3 F. ANDERSON ET AL. TABLE I DATA ON PATIENTS WHO HAD POST-TRAUMATIC DISABILITY OF THE ANKLE (GROUP I) AND PATIENTS WHO WERE DIAGNOSED ON THE BASIS OF RADIOGRAPHS MADE IMMEDIATELY A FTER AN INVERS ION INJURY (GR OUP 2) Review of Staging Site of Delay in First First Subsequent Computerized Magnetic Case Sex, Age Fract. Diagnosis Radiograph* Radiograph* Radiographs* Scintigraphy* Tomography Res. Imaging (Yrs.) (Mos.) Group I I M, 28 Post. med lilt I 2 M, 36 Mid. lat III and IIA III and IIA 3 F, 69 Ant. med Normal I 4 M, 39 Post. lat Ill III and ha 5 M, 27 Post. lat NP + Normal I 6 F, 31 Post. med ha ha 7 M,28 Post. med IIandIIA IlandIlA 8 F, 29 Mid. med IIA IIA 9 F, 39 Mid. med Normal I 10 F, 29 Mid. med NP + Normal I 11 F,21 Ant.med IlA IIA 12 F, 63 Post. med IIA ha 13 M, 26 Post. med III Ill 14 M, 22 Ant. med. Group 2 Post. lat M, 19 Post. med NP Ill III 16 M, 20 Post. lat NP NP III III 17 F, 12 Post. lat NP NP II II 18 M, 20 Post. lat NP + III III 19 F, 30 Post. lat NP NP IV Postop. 20 F, 27 Mid. lat NP NP II II 21 F, 44 Post. lat NP NP Normal II 22 M, 21 Post. lat NP III III M, 21 Mid. med III and ha III and IIA 24 F, 25 Ant. lat NP NP III III IIA III IIA III normal examination; + fracture present on radiographs or increased uptake on scintiscans; and NP not performed. *--. t Computerized tomography was performed three months after the initial diagnosis was made with the aid of magnetic resonance imaging. The fracture had progressed to Stage III. Hospital of Sydney embarked on a study of the ankle joint by magnetic resonance imaging. One or two ankles were examined each week, for a total of fifty-six ankles in a ninemonth period. Thirty of the fifty-six patients had been seen for posttraumatic chronic disability of the ankle, the cause of which had remained undiagnosed despite adequate plain radiographs. Most of these patients had been referred from the North Sydney Orthopaedic and Sports Medicine Clinic. The fourteen patients in Group 1 were selected from these patients. Group 2 consisted of ten patients who had been diagnosed as having an osteochondral fracture of the talus on the basis of plain radiographs and who were referred for staging of the fracture with the aid of magnetic resonance imaging. Most of these patients were referred from the hospital s casualty department. For all patients, there was an attempt to establish the mechanism of injury. Scintigraphy of the ankle was performed on all of the patients in Group 1, and the ankles of both groups were examined by computerized tomography and magnetic resonance imaging. Magnetic resonance imaging was performed with a 1.5- tesla system (Signa; General Electric Medical Systems, Milwaukee, Wisconsin), with the ankle joint placed in a cylindrical extremity coil having a 16.5-centimeter diameter. After the plane of the articular surface of the talus was determined in a coronal localizing series, a sagittal Tlweighted series was made in a plane 90 degrees to the articular surface ofthe talus. Additional Tl series were made in the coronal and axial planes. A pulse-repetition time of 600 to 800 milliseconds and an echo time of twenty milliseconds were used with two acquisitions. Images of threemillimeter-thick slices were obtained, with a one-millimeter gap between the slices, on a 256-by-256 matrix. The sagittal series was made with a sixteen-centimeter field of view, and the field was reduced to twelve centimeters for the coronal and axial series. A T2 spin-echo sequence was then made in whatever plane would contribute most to the diagnosis and staging. ThE JOURNAL OF BONE AND JOINT SURGERY

4 OSTEOCHONDRAL FRACTURES OF THE DOME OF THE TALUS Figs. 1-A through l-d: Case 14. Figs. 1-A and 1-B: Magnetic resonance images made nine months after injury. The intermediate image (pulse-repetition time, 2000 milliseconds; echo time, twenty milliseconds) and a T2-weighted image (pulse-repetition time, 2000 milliseconds; echo time, seventy milliseconds) show the presence of a subchondral cyst in the anteromedial aspect of the talar dome (arrowhead). For the computerized tomography, a 9800 system (General Electric) was used to produce most of the images. Adjacent 1.5-millimeter slices were acquired in a semicoronal plane, and a high-resolution bone algorithm with appropriate window settings for bone detail was used. Protocols for computerized tomography of the ankle were described previously by Solomon et al. Three-phase bone scintiscans were made, with flow study and early and delayed views after injection with technetium methylene diphosphonate; imaging was done in anterior and in both right and left lateral projections. The role of scintigraphy as a method of assessing the likelihood of FIG. 1-C Fig. 1-C: The cyst is well delineated on computerized tomography. Fig. 1-D: The cyst (arrowhead) is seen on this Tl-weighted axial image (pulse-repetition time, 600 milliseconds; echo time, twenty milliseconds). A large lateral fracture is also present. VOL. 71-A, NO. 8. SEPTEMBER 1989

5 1 146 I. F. ANDERSON ET AL. i;-..y 1. #{149}: #{149} FIG. 2-A Figs. 2-A, 2-B, and 2-C: Case 1. Fig. 2-A: Normal anteroposterior plain radiograph made eight weeks after injury. an osteochondral fracture in a patient who has normal radiographs has been previously recognized l.t2.23#{149} Group 1 Results (Table I) Surprisingly, of the thirty patients who had undiagnosed post-traumatic disability of the ankle, seventeen (57 per cent) had an osteochondral fracture of the ankle. Three patients had an osteochondral fracture of the tibial plafond only and were excluded from the series. The remaining fourteen patients had fifteen fractures of the dome of the talus. One patient (Case 14) had both a medial and a lateral fracture (Figs. 1-A through 1-D). We believe that this is the first reported case of a double osteochondral fracture of the talus. There were seven men and seven women, and the average age was 34.8 years (range, twenty-one to sixty-nine years). The average delay in diagnosis was 17.6 months. Although the plain radiographs of all of these patients had been initially reported as normal, in five patients (36 per cent) an osteochondral fracture of the talus was in fact visible on review. Eleven (73 per cent) of the fifteen fractures were on the medial aspect of the dome of the talus. The site of the fracture was clearly shown by magnetic resonance imaging with an axial image through the fracture. Both the medial and lateral fractures most commonly occurred posteriorly on the dome of the talus. A typical scintigraphic pattern was seen in eleven of the fifteen fractures in Group 1 (Fig. 2-B); however, three patients (Cases 3, 5, and 10) had variations in the typical pattern. One of these patients (Case 5), in addition to having uptake of the isotope in the area of the dome fracture, also had generalized uptake throughout the ankle joint that was consistent with synovitis. This patient, who owned a gymnasium, had continued to instruct aerobic classes until the diagnosis was made, nine months after the initial injury. The other two patients (Cases 3 and 10) are of particular FIG. 2-B Scintiscan made ten weeks after injury clearly demonstrates increased uptake on the medial aspect of the talus. FIG. 2-C A Ti-weighted image (pulse-repetition time, 600 milliseconds; echo time, twenty milliseconds) showing a decreased signal intensity (arrowhead) on the superomedial aspect of the talus. The appearance is that of trabecular compression and the fracture is Stage I. After the ankle was immobilized in a plaster cast, the symptoms recurred. Computerized tomography showed progression of the fracture to Stage III. interest in that they differed from the remainder of the series. Magnetic resonance imaging in these patients showed a decreased signal intensity from the subchondral marrow on THE JOURNAL OF BONE AND JOINT SURGERY

6 OSTEOCHONDRAL FRACTURES OF THE DOME OF THE TALUS 1147 Figs. 3-A and 3-B: Case 3. Fig. 3-A: Intermediate image made after injury, showing an area of decreased signal intensity (arrowhead) in the subchondral cancellous bone of the anteromedial aspect of the dome of the talus (pulse-repetition time, 2000 milliseconds; echo time, twenty milliseconds). Fig. 3-B: T2-weighted image showing an increased signal intensity(arrowhead) in the same area as in Fig. 3-A (pulse-repetition time, 2000 milliseconds; echo time, seventy milliseconds). This change in signal would indicate bone-marrow edema and cannot be detected on either plain radiographs or on computerized tomography images. the Tl-weighted images. On the T2 series, however, the affected area produced an increased signal intensity, signifying the presence of fluid (Fig. 3-B). All of the other patients had a decreased signal intensity on both the Tl and the T2-weighted images. This is thought to represent edema in the marrow, without major bone damage. One of the two patients (Case 3) had a negative bone scan, and the other (Case 10) had very weak uptake in the area of the fracture, suggesting minimum osteoblastic activity. The typical scintigraphic appearance in the remaining eight patients made it possible to predict that an osteochondral fracture would almost certainly be found on magnetic resonance imaging. However, this scintigraphic pattern can also be seen in patients who have avascular necrosis that is due to other causes, as well as in those who have a neoplasm of bone, an infection, or another injury of bone. Consequently, the finding of this pattern of uptake, although most suggestive, is not diagnostic of an osteochondral fracture. All fourteen patients were also examined by comput- FIG. 4-A FIG. 4-B Figs. 4-A and 4-B: Case 17. Fig. 4-A: Plain radiograph made twenty-four hours after injury, showing a subtle fracture of the lateral aspect of the talar dome (arrowheads). Fig. 4-B: Tl-weighted image showing an extensive area of decreased signal intensity (arrowheads) affecting more than 30 per cent of the dorsolateral aspect of the talus in this three-millimeter slice (pulse-repetition time, 600 milliseconds; echo time, twenty milliseconds). The cortex on the medial side of the fracture is intact, and the fracture is Stage II. The examination was performed with the patient s ankle in a plaster cast, two weeks after injury. VOL. 71-A, NO. 8, SEPTEMBER 1989

7 1 148 I. F. ANDERSON ET AL. FIG. 5-A FIG. 5-B Figs. 5-A through 5-E: Case 8. Fig. 5-A: No abnormality can be seen on this plain radiograph that was made immediately after injury. Fig. 5-B: Five months later, rarefaction has appeared at the superomedial aspect of the talus. The cortex appears normal. Sclerosis surrounds the area of rarefaction. erized tomography. In nine patients, the staging of the fracture corresponded to the staging assigned after magnetic resonance imaging. Of the five Stage-I patients, no abnormality could be detected by computerized tomography in four (Cases 3, 5, 9, and 10). Unfortunately, there was a delay of three months before computerized tomography could be performed on the fifth patient (Case 1), during which time the fracture had progressed from Stage I to Stage III. In one patient (Case 4), the cystic component was not demonstrated on computerized tomography. Group 2 During the nine-month period of the study, ten osteochondral fractures were diagnosed by plain radiography immediately after an inversion injury and were referred to us for staging with the aid of magnetic resonance imaging and computerized tomography. There were five men and five women, and the average age was 23.9 years (range, twelve to forty-four years). Eight of the ten fractures occurred on the lateral side of the talus, most of them posteriorly. Computerized tomography was unable to demonstrate the Stage-Il fracture in one patient (Case 2 1). In the other nine patients, the results of cornputerized tomography and magnetic resonance imaging were comparable. No definite symptoms emerged to aid in the diagnosis of an osteochondral fracture. The Group- 1 patients, however, fell into one of two patterns. The patients who had a Stage-hA fracture (to be described later) complained of a recurrent, diffuse ache in the ankle, which increased with exercise. Exercise also caused a low level of swelling. Symptom-free periods were common. The other patients in Group 1 all complained ofan unremitting ache, which dated back to the initial inversion injury. An increase in weightbearing caused an increase in pain and development of swelling. The signs and symptoms in all Group-2 patients were ligamentous injury with swelling of the ankle, pain, limitation of movement, and bruising. The presence of a fracture was further suspected if there was tenderness in the space between the talus and the tib- Comparison of the Two Groups The two groups differed, most notably with regard to the considerable delay in diagnosis in most of the Group- 1 patients. The Group- 1 patients were, on average, older than those in Group 2 (34.8 compared with 23.9 years). Lateral fractures were more common in Group 2; they were seen earlier and were more often diagnosed by plain radiographs. As has also been noted by other authors6, a thin sliver of bone was separated at the sites of the lateral fractures, whereas the medial fractures had a tendency to be cupshaped. FIG. 5-C An additional thirteen months later, sclerosis and the area of rarefaction are more definite. There is irregularity of the cortex on the medial aspect of the talus, suggesting some compression of the area. THE JOURNAL OF BONE AND JOINT SURGERY

8 OSTEOCHONDRAL FRACTURES OF THE DOME OF THE TALUS 1149 iofibular syndesmosis, as described by Davidson et al. In patients who had a medial fracture, a similar tenderness was encountered when the medial aspect of the talus was palpated in plantar flexion. In attempting to determine the mechanism of injury, a common history was obtained. All of the Group-2 patients, and all but three of the Group- 1 patients, had had a severe inversion injury and a so-called sprain. The degree of associated plantar flexion and dorsiflexion was usually difficult to determine. The mechanism, as described by two patients (Cases 3 and 9), was more of a vertical compression than an inversion, although some inversion had certainly occurred. One patient (Case 14), who had both a medial and a lateral fracture, had had forced eversion prior to inversion. Discussion The most remarkable feature in this series was how commonly an osteochondral fracture of the talus was found in patients who complained of chronic disability after a socalled sprain of the ankle. This injury was found more frequently than has been previously reported The major factors that appeared to be responsible for the increased frequency were the ease with which magnetic resonance imaging made possible earlier and more certain diagnosis of an osteochondral fracture of the talus and our increased interest in and awareness of this entity. A fracture changes the magnetic resonance-imaging signal intensity of bone marrow, and the change often involves a surprisingly large surrounding area (Fig. 4-B). The normally high-intensity signal of cancellous bone on both Tl and T2-weighted images is due to marrow fat (short Ti and short T2). After trauma, there is decreased Ti signal intensity from the cancellous bone surrounding the fracture, due to edematous reaction in the acute and subacute stages (Figs. 3-A and 3-B) and to deposition of fibrous tissue and fibrocartilage in more chronic injuries. This change is easily demonstrated, allowing detection of the most subtle fractures. Computerized tomography is ideal for assessing the progress of an osteochondral fracture and for demonstrating the formation of subchondral cysts. In our experience, however, computerized tomography was unable to detect a Stage-I lesion, but missed only one Stage-Il lesion (Case 21). The staging of osteochondral fractures that was proposed by Berndt and Harty has been generally accepted. However, there has been some difficulty and confusion, mostly surrounding the diagnosis of Stage-I lesions. Davidson et al. reported two Stage-I fractures, neither of which was illustrated or discussed. Five Stage-I fractures were reported by Berndt and Harty, but only three were illustrated and only one was discussed. Osseous changes were reported in the three illustrated cases; these lesions should have been classified as Stage II. Three fractures were classified as Stage I in the series that was reported by Blom and Strijk. In their discussion, under Classification, the staging appeared to have been arrived at by the appearance of the fracture on plain radiographs, although the visible changes on which the staging was based were not described. Flick and Gould illustrated one so-called Stage-I frac- FIG. 5-D FIG. 5-E Figs. 5-D and 5-E: Intermediate and T2-weighted magnetic resonance images made an additional three months later, twenty-two months after injury, showing localized deformity of the anteromedial aspect of the talar dome. The intermediate image (pulse-repetition time, 2000 milliseconds; echo time, twenty milliseconds) demonstrates a cavity, which is shown to contain fluid in the T2-weighted image (pulse-repetition time, 2000 milliseconds; echo time, seventy milliseconds). There is some depression of the cortex on the articular surface. The lesion is Stage IIA, and there is a subchondral cyst. VOL. 71-A, NO. 8. SEPTEMBER 1989

9 1 150 I. F. ANDERSON ET AL. I I I 1IA III FIG. 6 IV Modified staging system of Berndt and Harty. The addition of Stage IIA enables the development of subchondral cysts as a sequela of Stage I to be recognized and classified. See text for full explanation. ture, but this fracture had actually started as Stage II and progressed to Stage IV. In three of the series3, difficulties were reported in differentiating between Stages II and III, and these stages were combined. Using the advantages that are provided by magnetic resonance imaging, we re-examined the staging criteria of Berndt and Harty and made modifications (Fig. 6). Stage I - Subchondral Trabecular Compression No diagnostic changes are visible on the plain radiographs in trabecular compression. However, if an osteochondral fracture is suspected clinically and the plain radiograph is negative, scintigraphy can aid in assessing whether or not bone has been injured. If it has, the diagnosis can then be established by magnetic resonance imaging. As previously discussed, an area of abnormality in the cancellous bone marrow of the talus was present on the Tlweighted image in two patients; this area was shown to be largely fluid on the T2-weighted image. With further study of the ability of magnetic resonance imaging to show marrow edema, it may be advisable in the future to form a subgroup within Stage I, perhaps Stage IA, to separately classify this change. These lesions differ from the other Stage-I lesions in their appearance on magnetic resonance images and scintiscans, and probably also in their prognosis. and A typical Stage-I lesion is shown in Figs. 2-A, 2-B, 2-C. Stage II - Incomplete Separation of the Fragment Incomplete separation of the osteochondral fragment can be assessed well by either computerized tomography or magnetic resonance imaging (Fig. 4-B). Assignment of this stage to a fracture requires the demonstration of the attachment of the fragment. Stage I/A - Formation of a Subchondral Cyst Stage-I fractures may progress not only to an attached or unattached fragment, but to formation of a subchondral cyst, as was reported by Flick and Gould. This sequel of a Stage-I fracture, with resorption of necrotic trabeculae and formation of a cyst, was seen in eight of our patients (Table I). A Stage-hA classification allows this change to be recognized. Rhaney and Lamb suggested that subchondral cysts develop in areas of post-traumatic necrosis of bone. They found metaplastic cartilage, and osteoclastic activity with cellular and vascular granulation tissue in the wall of the cysts, which was histologically similar to that seen at fracture sites. Ondrouch, Ferguson, and Resnick et al. have supported these findings. Resnick et al. noted frequent cornmunications between the joint space and the subchondral cysts as well as dislocated pieces of articuiar cartilage within the cysts. The pathogenesis of osteonecrosis was well presented by Sweet and Madewell. They described the progressive stages of the host response that follows the initial death of hematopoietic cells, bone, and bone marrow. The response, consisting of fluid transudate, fibrin production, and inflammatory-cell infiltration, progresses to form a reactive interface around the area of osteonecrosis. This sharp line of demarcation can be appreciated by magnetic resonance imaging in more chronic lesions, the abnormal area being well separated from the surrounding normal bone marrow. As the interface between living and dead bone is delineated by THE JOURNAL OF BONE AND JOINT SURGERY

10 OSTEOCHONDRAL FRACTURES OF THE DOME OF THE TALUS 1151 INJURY PLAIN RADIOGRAPH Os ABNORMAL ( Shows teochondral fracture) V N NORMAL SCINTIGRAPH NEGATIVE C.T. POSITIVE OTHER DIAGNOSIS AND TREATMENT \/ M.R.I. TREATMENT for (C.T. progress monitoring) used FIG. 7 The diagnosis of osteochondral fracture should always be considered in a patient who has a problem of the ankle that persists for more than six weeks after an inversion injury. CT. = computerized tomography and M.R.I. = magnetic resonance imaging. by osteoblastic activity and resorption of the necrotic debris, it is not difficult to envisage the formation of a cyst. A typical appearance of a cyst on magnetic resonance imaging is shown in Figs. 1-A, 1-B, 1-C, 5-D, and 5-E. Stage III - Unattached, Undisplaced Fragment When an attachment to the talus cannot be demonstrated, but the fragment is undisplaced, the fracture is Stage II. In the T2-weighted image, the presence of synovial fluid around a large fragment can help to differentiate between Stages II and III. In practice, however, this advantage of magnetic resonance imaging does not appear to be important, and computerized tomography is the better means of identifying small, separated fragments. It is sometimes difficult to identify loose bodies on magnetic resonance images, although this problem is rapidly being overcome with the development of gradient-echo techniques. Nevertheless, magnetic resonance imaging currently appears to have no major advantage over computerized tomography in defining the staging of this group of fractures. Stage-lilA fractures, as described in Berndt and Harty s system of classification, apparently refers to a theoretical transient position of the fragment. This stage has not been accepted as important by other authors, and it was not encountered in our series. Stage IV - Displaced Fragment The only patient who had a Stage-IV lesion in this series was operated on before magnetic resonance imaging could be arranged. However, magnetic resonance imaging was performed two months postoperatively to assess the progress after treatment, and the defect was noted to be filled with fluid. An additional examination was planned to see if fibrocartilage filled the defect, as has been shown to occur in similar osteochondral defects in the knee joint. The natural history of an osteochondral fracture has been discussed in the. Irrespective of stage, healing of the fragment can occur only if the fracture is undisplaced or is reduced and immobilized until union can take place. The blood supply of the compressed or separated fragment is interrupted at the fracture line with continuing movement, and the ingrowing capillaries are sheared off. In addition, Stage-il lesions can progress to Stage The alternating application and release of pressure against the attachment of the Stage-il lesion eventually causes separation. When this occurs, healing is prevented, as the fragment becomes avascular and is encased in fibrous or fibrocartilaginous tissue. To summarize, trauma may produce a Stage-I to Stage- IV lesion at the time of injury, or a fracture may progress from an initial Stage I or II to Stage IIA, ifi, or IV, if it is inadequately immobilized. We do not know why Group-i patients predominantly had fractures of the medial side of the dome of the talus and patients in Group 2 mainly had lateral fractures; however, similar findings were reported by Blom and Strijk. The relationship between osteochondral fractures and trauma has been discussed3 6 8 All of the lateral fractures in these previous series were associated directly with a preceding inversion injury that caused a sprain of the ankle, whereas the medial lesions occasionally did not appear to follow recognized trauma. All of our patients in Group 2 had a sprain of the ankle that was severe enough for them to visit the casualty department of our hospital and to warrant immediate radiographic examination. In contrast, VOL. 71-A, NO. 8, SEPTEMBER 1989

11 1152 I. F. ANDERSON ET AL. six of the fourteen patients in Group 1, all of whom had a medial lesion, had some delay in seeking medical advice and in having an initial radiographic examination. The explanation for this apparent difference in the severity of symptoms may simply be that the severity of the associated ligamentous injury is greater with lateral lesions. Our treatment for Stage-I and Stage-Il fractures has been immobilization for six weeks. Even though healing may appear to have occurred, these patients should be followed for at least three years, as the lesion may progress to a higher stage at a later date. The experience of most authors, in the long term, has been that conservative treatment is often disappointing and that an operation is eventually necessary.2,8,14.15,22 An operation has been our treatment of choice for patients who have a Stage-hA, III, or IV fracture. In StagehA lesions, the cyst is deroofed and the base of the crater is drilled down to bleeding bone. Stage-Ill and Stage-IV fractures are managed by arthroscopic removal of the separated fragment, followed by curetting or drilling of the fracture bed down to bleeding bone. Although we have not yet established a firm regimen of treatment, it is planned to follow this group of patients as an ongoing study. We have, however, established a diagnostic protocol (Fig. 7). Whatever the final treatment regimen may be, staging, and, particularly, differentiating between Stage-I! and Stage-Ill fractures, is important. Patients who are suspected clinically of having an osteochondral fracture, but who have apparently negative plain radiographs, should be assessed by scintigraphy, and those who have positive scintiscans should have magnetic resonance imaging. Magnetic resonance imaging does not offer any major benefits to patients who have an abnormal plain radiograph; computerized tomography was shown to be adequate for staging the fractures in this group of patients in all but one instance. If plain radiography had been the only diagnostic procedure that was performed in our patients, fourteen of the fractures would not have been diagnosed. NOTE: The authors thank Hanimex Pty..the Australian agent for Fuji film. for their help in preparing the illuorations, and Sandra Huggett and Gillian Barber for their help. References 1. ALEXANDER, A. H., and LICHTMAN, D. M. : Surgical Treatment of Transchondral Talar-Dome Fractures (Osteochondritis Dissecans). Long-Term Follow-up. J. Bone and Joint Surg., 62-A: , June BERNDT, A. L., and HARTY, MICHAEL: Transchondral Fractures (Osteochondritis Dissecans) of the Talus. J. Bone and Joint Surg., 41-A: , Sept BLOM, J. M. H., and STRIJK, S. P. : Lesions of the Trochlea Tali. Osteochondral Fractures and Osteochondritis Dissecans of the Trochlea Tali. Radiol. Clin., 44: , BRAND, R. L. ; BLACK, H. M.; and Cox, J. S.: The Natural History of Inadequately Treated Ankle Sprain. Am. J. Sports Med., 5: , CAMERON, B. M. : Osteochondritis Dissecans of the Ankle Joint. Report of a Case Simulating a Fracture of the Talus. J. Bone and Joint Surg., 38-A: , 884, July CANALE, S. T., and BELDING, R. H.: Osteochondral Lesions of the Talus. J. Bone and Joint Surg., 62-A: , Jan COLTART, W. D.: Aviator s Astragalus. J. Bone and Joint Surg., 34-B(4): , DAVIDSON, A. M. ; STEELE, H. D. ; MACKENZIE, D. A. ; and PENNY, J. A. : A Review of Twenty-one Cases of Transchondral Fracture of the Talus. J. Trauma, 7: , FERGUSON, A. B., JR. : The Pathological Changes in Degenerative Arthritis of the Hip and Treatment by Rotational Osteotomy. J. Bone and Joint Surg., 46-A: , Sept FIORE, R. D., and LEARD, J. S.: A Functional Approach in the Rehabilitation of the Ankle and Rear Foot. Athlet. 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