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Osteochondritis Dissecans of the Tibial Plafond

Imaging Characteristics and a Review of the Literature

¹ All authors: Department of Radiology, Wake Forest University School of Medicine, Medical Center Blvd., Winston-Salem, NC 27157-1088.

Received March 6, 2000; accepted after revision May 2, 2000.

 
The opinions and assertions contained herein are those of the authors and should not be construed as official or as representing the opinions of the Department of the Army or the Department of Defense.

Address correspondence to L. T. Bui-Mansfield.

Abstract

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OBJECTIVE. Osteochondritis dissecans of the talar articular surface of the ankle joint has been well described. We report the imaging characteristics of osteochondritis dissecans of the tibial articular surface (tibial plafond).

CONCLUSION. Osteochondritis dissecans of the tibial plafond is a rare condition that may not be detectable on radiography. Its radiologic findings are similar to those of osteochondritis dissecans located elsewhere in the body.

Introduction

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Osteochondritis dissecans in the ankle accounts for approximately 4% of all osteochondritis dissecans [1]. Most osteochondritis dissecans in the ankle is found in the talar dome. Osteochondritis dissecans of the tibial plafond is rarely described. In the radiology literature, we are aware of only one textbook describing this entity, without a specific reference [2]. Recently, we encountered three patients with osteochondral injury of the tibial plafond. We report the imaging appearance of osteochondral injury of the tibial plafond on conventional radiography, CT, and MR imaging and review the literature describing osteochondritis dissecans of the tibial plafond.

Materials and Methods

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We retrospectively reviewed the medical records of three patients with osteochondral injury in the tibial plafond. The patients were referred to our department of radiology, and their conditions were diagnosed with various imaging techniques within a 2-week period. All patients underwent radiography, one patient underwent CT, and one patient underwent MR imaging. All three patients were men. The average age was 39 years (age range, 33-49 years). All patients complained of ankle pain. One patient had a twisting injury, but the other two patients did not recall an incidence of trauma. Two patients underwent arthroscopy.

A literature search was conducted on the MEDLINE database using the PubMed search engine of the National Library of Medicine [3]. The search was limited to English literature and human subjects.

Results

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Apart from the location, osteochondral injury of the tibial plafond has radiographic findings similar to those of osteochondritis dissecans of the talar dome. In our series, two of three osteochondral lesions of the tibial plafond were detected on radiography. On conventional radiographs, the lesions appear lucent, seen best on anteroposterior images (Fig. 1A). On lateral images, osteochondritis dissecans is less apparent. Osteochondritis dissecans is suggested by a loss of the sharp cortical line (Fig. 1B). In the ankle joint, helical CT has the advantage of multiplanar capability. On axial scans, osteochondral lesions of the tibial plafond may be initially mistaken for osteochondritis dissecans of the talar dome (Fig. 1C). However, coronal and sagittal images clearly show that the lesion originates from the tibial plafond. Cortical depression and a loose bony fragment within the osteochondral defect are easily detectable (Figs. 1D, 1E, and 2A,2B).

View larger version (112K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A. —33-year-old man with ankle pain and limp. Mortise view of radiograph of ankle shows lucent lesion (arrow) in central portion of tibial plafond.

View larger version (91K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B. —33-year-old man with ankle pain and limp. Lateral radiograph of ankle shows subtle loss of cortical line posteriorly (arrow). Note os trigonum.

View larger version (137K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1C. —33-year-old man with ankle pain and limp. Axial CT scan of ankle obtained at level of ankle joint shows how, initially, osteochondritis dissecans (arrow) was thought to be in talus.

View larger version (138K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1D. —33-year-old man with ankle pain and limp. Sagittal reconstruction of CT scan shows cortical depression (arrow) in posterior half of distal tibia. Note os trigonum.

View larger version (134K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1E. —33-year-old man with ankle pain and limp. Coronal CT scan shows osteochondral lesion with loose body (arrow) in medial aspect of tibial plafond.

View larger version (113K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A. —39-year-old man with ankle pain. Anteroposterior radiograph of ankle shows lucent lesion (arrow) in lateral aspect of distal tibia, with two calcified bodies located in lucency.

View larger version (110K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B. —39-year-old man with ankle pain. Lateral radiograph of ankle shows subtle loss of cortical line anteriorly (arrow).

On MR imaging, osteochondral defect of the tibial plafond has low signal intensity on T1-weighted images and high signal intensity on T2-weighted images, with adjacent bone marrow edema (Figs. 3A and 3B). Cortical depression is clearly seen (Fig. 3C).

View larger version (166K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A. —46-year-old man with ankle pain and swelling. Sagittal T1-weighted MR image shows abnormally low signal intensity in posterior aspect of tibial plafond (arrow).

View larger version (153K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B. —46-year-old man with ankle pain and swelling. Sagittal short tau inversion-recovery MR image shows abnormally high signal intensity in posterior aspect of tibial plafond (arrow).

View larger version (149K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3C. —46-year-old man with ankle pain and swelling. Coronal T2-weighted MR image shows cortical depression (arrow) in posterolateral aspect of distal tibia and adjacent bone marrow edema.

Table 1 summarizes the findings in our three patients and the cases in the literature. In our series, the average size of the osteochondral lesions was 1.4 x 1.3 cm. All lesions were centrally located, superior to the talus, without a predominant site.

One patient was treated conservatively; currently, this patient is asymptomatic. Two patients underwent ankle arthroscopy. In one patient, markedly hyperemic proliferative synovial tissue involved the entire ankle. The tibial plafond cartilage was intact without any visible defect or flap. However, the talar dome was irregular, with areas of ruffled tissue. Five months after arthroscopy and débridement, the patient continued to have medial ankle pain, but the severity of the pain decreased. In the other patient, ankle arthroscopy revealed a depressed area in the posterolateral aspect of the tibial plafond filled with fibrocartilage. We noted a large amount of scar tissue infolding onto the lateral shoulder of the talus, which was débrided. Two months after ankle arthroscopy, the patient was asymptomatic.

Discussion

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Our literature search yielded three articles on osteochondritis dissecans of the ankle, which included cases of osteochondral lesions of the tibial plafond [4,5,6]. Five patients were diagnosed with osteochondral injury of the tibial plafond. The sex and age were known in only two patients; both patients were women, 46 and 51 years old. We noted no predominant location of the osteochondritis dissecans. Three patients had a history of trauma, and all patients were symptomatic, requiring orthopedic evaluation and surgery. One patient had osteochondritis dissecans in both the tibia and talus [4].

In a series of 15 patients undergoing operative arthroscopy of the ankle, Parisien and Vangsness [5] described two patients (13%) with osteochondral lesions of the tibial plafond and nine with osteochondritis dissecans of the talar dome, giving a ratio of the talar dome to the tibial plafond of 9:2. Bauer et al. [6] reported on a series of 30 patients who had osteochondritis dissecans of the ankle. Two patients (7%) had osteochondritis dissecans of the tibial plafond; the remaining had osteochondritis dissecans of the talar dome, giving a ratio of talar dome to tibial plafond of 28:2 or 14:1. Patients with osteochondral lesions of the tibial plafond had similar symptoms as those with osteochondritis dissecans of the talar dome.

The prevalence of osteochondritis dissecans in the tibial plafond detected on radiography is unknown. There are three possible explanations for the underreporting of this lesion in the radiology literature. The lesion may not be visible on conventional radiographs, as was the case in one of our patients. Radiologists may not be aware of this entity and may not recognize the lesion on conventional radiographs. A less likely explanation is that some patients may undergo surgery without radiologic examination or that the radiographs were obtained in the orthopedist's office and were not available to the radiologists for review.

The imaging characteristics of an osteochondral injury in the tibial plafond are similar to those of osteochondritis dissecans found elsewhere in the body. On conventional radiographs, osteochondritis dissecans of the tibial plafond appears lucent and may contain a loose bony fragment. CT and MR imaging are able to show the exact location and extent of the lesion. Bachmann et al. [7] reported that radiographic findings corresponded with arthroscopic staging in only 56% of the patients because fibrosis may provide stability in instances of osseous separation; this may explain the discrepancy between the arthroscopic findings and the imaging findings in one of our patients.

The cause of osteochondral injury in the tibial plafond is unknown. However, a case of mirror image osteochondral defects of the talus and distal tibia suggests trauma as a potential cause of this lesion [4]. Also, in one of the patients who had ankle arthroscopy, the talar dome was irregular, suggesting traumatic contact between the talus and the tibial plafond.

Clinical and experimental evidence has confirmed the traumatic nature of osteochondritis dissecans of the talus [8, 9]. Under experimental conditions, Berndt and Harty [8] produced osteochondritis dissecans in the middle or anterior half of the talar dome with strong inversion of the dorsiflexed ankle. As the dorsiflexed foot was inverted, the lateral border of the talar dome was compressed against the articular surface of the distal fibula. Inversion and rotation of a plantar flexed foot causes compression of the posterior half of the talar dome by the posterior malleolus, resulting in osteochondritis dissecans [8].

A 1995 study [9] of the biomechanic topography of human ankle cartilage supports the experimental study of Berndt and Harty [8]. Athanasiou et al. [9] measured the thickness and mechanical properties of the articular surface of the distal tibia and talus. In general, tibial cartilage was stiffer than talar cartilage. The softest cartilage was found in the posterior half of the talus. The cartilage in the anterolateral aspect of the distal tibia was stiffer and thicker than that in the anterolateral aspect of the talus. Also, the posteromedial aspect of the tibial plafond was stiffer than that of the posteromedial aspect of the talus. Although the biomechanic topography of human ankle cartilage explained the occurrence of osteochondritis dissecans in the talus, it did not explain the cause for an osteochondral lesion in the distal tibia. However, this study was small, consisting of only seven cadavers, and anatomic variation may be present. Perhaps in some individuals, the tibial plafond is less stiff than the talar dome, placing them at risk for osteochondritis dissecans of the tibial plafond.

Vascular insult is an unlikely cause of osteochondral injury in the tibial plafond. The ankle joint has a rich arterial supply.

The appropriate treatment for osteochondral injury of the tibial plafond is unclear. Three of the patients described in the literature underwent surgery, curettage of subchondral cyst with bone graft [4] or débridement of the damaged articular surface followed by a period of non—weight-bearing on crutches for 6 weeks [5]. The indications for arthroscopic exploration were disabling symptoms and a previous history of ankle injury [5]. Two of the patients were treated conservatively. No complication was reported at a 20-year follow-up examination [5].

In conclusion, we presented the imaging findings of osteochondritis dissecans of the tibial plafond, with three different imaging techniques and a review of the world literature. Osteochondral injury of the tibial plafond is not as rare as previously reported in the radiologic literature. The lesion can be subtle on conventional radiographs. Consequently, radiologists must be aware of this entity and its imaging characteristics on different imaging techniques.

Acknowledgments
 
We thank Ellen Henson and Debbie Parker for their assistance with the photographs.

References

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1. Lindholm TS, Osterman K, Vankka E. Osteochondritis dissecans of elbow, ankle, and hip: a comparison survey. Clin Orthop 1980;148:245 -253
2. Resnick D. Diagnosis of bone and joint disorders, 3rd ed. Philadelphia: Saunders, 1995: 2624-2626
3. National Institutes of Health. National Library of Medicine PubMed Web site. Available at: www.ncbi.nlm.nih.gov/PubMed. Accessed November 11, 1999
4. Canosa J. Mirror image osteochondral defects of the talus and distal tibia. Int Orthop 1994;18:395 -396[Medline]
5. Parisien JS, Vangsness T. Operative arthroscopy of the ankle: three years' experience. Clin Orthop 1985;199:46 -53
6. Bauer M, Jonsson K, Linden B. Osteochondritis dissecans of the ankle: a 20-year follow-up study. J Bone Joint Surg Br 1987;69-B:93 -96
7. Bachmann G, Jurgensen I, Siaplaouras J. The staging of osteochondritis dissecans in the knee and ankle joints with MR tomography: a comparison with conventional radiology and arthroscopy. Rofo Fortschr Geb Rontgenstr Neuen Bildgeb Verfahr 1995;163:38 -44[Medline]
8. Berndt AL, Harty M. Transchondral fracture (osteochondritis dissecans) of the talus. J Bone Joint Surg Am 1959;41-A:988 -1020[Abstract/Free Full Text]
9. Athanasiou KA, Niederauer GG, Schenck RC Jr. Biomechanical topography of human ankle cartilage. Ann Biomed Eng 1995;23:697 -704[Medline]

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