Osteochondral Lesions of the Talus



Osteochondral Lesions of the Talus


Sara Lyn Miniaci-Coxhead, MD


Dr. Miniaci-Coxhead or an immediate family member serves as a board member, owner, officer, or committee member of the American Orthopaedic Foot and Ankle Society.


This chapter is adapted from Chao W, Freeland E, Dedini R: Osteochondral Lesions of the Talus in Chou LB, ed: Orthopaedic Knowledge Update: Foot and Ankle 5. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2014, pp 387-399.





Introduction

Osteochondritis dissecans was originally described in 1888 as a process of loose body formation associated with articular cartilage and subchondral bone fracture in the hip and knee.1 The first description of these lesions in the ankle was provided in 1922.2 An original anatomic study in 1959 on cadaver limbs provided insight into the etiologic mechanism advancing the concept of trauma as a primary osteochondritis dissecans factor.3 In addition, a staging system was developed based on radiographic and surgical parameters that are currently in use. Historically, a variety of terms including osteochondritis dissecans, transchondral talar fracture, and osteochondral talar fracture have been used to describe what are now universally referred to as osteochondral lesions of the talus (OLTs), a term that was introduced in 1994.4


Incidence

OLTs represent approximately 4% of all osteochondral lesions. In 1955, investigators reported a frequency of 6.5% in their series of 133 ankle sprains.5 A 2011 epidemiologic study examining active-duty US military personnel found the overall occurrence of OLTs to be 27 per 100,000 patient years over a 10-year period.6 This finding suggests that OLTs may be more common than previously considered. Several authors have reported that the incidence of bilateral lesions is approximately 10%.3,7

Medial osteochondral lesions are more common than lateral osteochondral lesions. Medial lesions have been described as deeper with extension into subchondral bone, and they often develop into cystic lesions. Lateral lesions, which are more commonly associated with a traumatic injury, are described as shallow and have the tendency to become displaced.3

In 2007, MRIs of 428 ankles with OLTs were studied.8 A grid system was used to identify the precise location of talar dome lesions. In contrast to the historically described anterolateral and posteromedial locations, the midtalar dome was involved in 80% of lesions. It was determined that the midmedial zone was the most common location (53%). The lesions in this location were the largest and deepest. The midlateral zone was the second most common zone (26%).8

In another study, the authors retrospectively reviewed the location, frequency, and size of OLTs on 77 MRI examinations based on a nine-zone grid. Their findings support the notion that the most common osteochondral lesions are not the traditionally described anterolateral and posteromedial lesions, but rather central medial and central lateral lesions. Additionally, it was determined that lesion location does not predict subject age, lesion chronicity or instability, or history of trauma. However, medial lesions were larger, and lateral lesions were seen more commonly in association with ligamentous injury.9 Using the same nine-zone grid described in 2007, investigators
in 2012 performed a retrospective examination of all preoperative MRIs obtained over a 4-year period in patients who had primary surgical management of symptomatic OLTs.10 Their results supported earlier findings, but they noted that symptomatic surgically treated OLTs were located in the lateral third of the talar dome almost twice as often as in the medial third (65% versus 35%).10


Clinical Presentation

An OLT diagnosis is rarely made immediately after an acute ankle injury. In most cases, the condition is associated with chronic ankle pain, especially after inversion injury to the lateral ligamentous complex. Patients presenting with an OLT often describe prolonged pain, recurrent ankle swelling, weakness, and continued subjective instability. Patients also may report mechanical symptoms including catching, clicking, and locking. The physical examination may reveal tenderness at the level of the ankle mortise anteriorly or posteriorly. The differential diagnosis is wide, but a high index of suspicion must be maintained for an OLT when evaluating patients with chronic ankle pain.11


Etiology/Pathoanatomy/Natural History

The etiology of an OLT may be nontraumatic or traumatic. Most authors believe that trauma has an integral role in the pathogenesis of most OLTs and that OLTs most likely represent the chronic phase of a compressed talar dome fracture. A single event of macrotrauma or repetitive microtrauma may elicit initiation of the lesion in a person who is already predisposed to talar dome ischemia. Endocrine or metabolic abnormalities, vasculopathy, and osteonecrosis are potential etiologic factors in nontraumatic OLTs.12,13

Subchondral cysts with overlying chondromalacia, osteochondral fragments, and loose bodies all represent various stages in the progression of OLTs. The development of a symptomatic OLT depends on various factors. The primary mechanism is damage and insufficient repair of the subchondral bone plate. Authors of a 2010 study theorized that water from compressed cartilage is forced into the microfractured subchondral bone during loading, which subsequently leads to localized increased fluid pressure within the subchondral bone. Local osteolysis can then predispose to the development of a subchondral cyst. The pain is believed to be a result of stimulation of the highly innervated subchondral bone under the cartilage defect.11

The precise natural history of OLTs is unclear. In a review of serial MRIs of 29 patients who had OLTs that were treated nonsurgically, 45% showed progression, 24% improved, and 31% remained unchanged.14 The authors found that bone marrow edema and subchondral cysts are not reliable indicators of lesion progression.14 Osteoarthritis of the ankle has been shown to be an uncommon final outcome.15


Imaging and Classification

In 1959, Berndt and Harty described the first staging system based on radiographic findings.3 This classification system was later modified with the addition of stage V to describe lesions with a cystic component16 (Figure 1). The overall correlation of radiographic assessment with arthroscopic findings has been found to be poor.17

Advanced imaging modalities have significantly increased the ability to accurately diagnose OLTs. CT scans are used predominantly as an adjunct for a more comprehensive evaluation of and preoperative planning for known lesions18 (Figure 2). In 1990, a four-stage system of classifying the lesions based on CT findings was described19 (Figure 3). This system corresponds to stages
described in the original classification by Berndt and Harty, but also considers subchondral cyst formation, fragmentation, and the overall extent of osteonecrosis.






FIGURE 1 Loomer and associates’ modification of the Berndt and Harty radiographic classification of osteochondral lesions of the talus. Stage I: Compression of subchondral bone. Stage II: Partially detached osteochondral fragment. Stage III: Completely detached osteochondral fragment remaining in fragment bed. Stage IV: Displaced osteochondral fragment. Stage V: Presence of a cystic component. (Adapted from Loomer R, Fischer C, Lloyd-Schmidt R, et al: Osteochondral lesions of the talus. Am J Sports Med 1993;21:13-19.)






FIGURE 2 Coronal CT demonstrates a lateral talar dome osteochondral lesion.

MRI is the preferred imaging study for detection of suspected OLTs that are not seen on initial plain radiographs20 (Figure 4) although it may find lesions that are incidental. MRI also is useful for further evaluation of known OLTs and provides improved three-dimensional localization and sizing of a lesion. It also aids in the assessment of stability and identification of a cystic component. MRI also is used to stage OLTs. In 1989, an MRI classification system based on the Berndt and Harty classification system was described.21 This classification system was later revised, primarily by subdividing stage 2 based on the presence or absence of surrounding edema.22 The same researchers reclassified lesions with subchondral cysts as stage 5.22 In 2003, an MRI grading system based on an earlier arthroscopic grading system, the Mintz classification, was described23 (Table 1). Fifty patients (52 OLTs) who had both MRI and ankle arthroscopy were studied to examine the correlation between MRI and arthroscopic staging using the Mintz classification.24 These authors concluded that MRI has an accuracy of 81% in staging of OLTs, similar to the 83% accuracy reported in the 2003 article.24 Pritsch and colleagues and the International Cartilage Repair Society17,25 have described additional arthroscopic grading systems.






FIGURE 3 Ferkel and Sgaglione’s CT classification of osteochondral lesions of the talus. Stage I: Cystic lesion within the dome of the talus, intact roof on all views. Stage IIA: Cystic lesion with communication to the talar dome surface. Stage IIB: Open articular surface lesion with overlying nondisplaced fragment. Stage III: Nondisplaced lesion with lucency. Stage IV: Displaced fragment. (Reproduced from Feinblatt J, Graves SC: Osteochondral lesions of the talus: Acute and chronic, in Pinzur MS, ed: Orthopaedic Knowledge Update Foot and Ankle 4. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2008, pp 147-158.)






FIGURE 4 Coronal (A) and sagittal (B) T2-weighted images of the left ankle demonstrate a lateral talar dome osteochondral lesion.




Feb 27, 2020 | Posted by in ORTHOPEDIC | Comments Off on Osteochondral Lesions of the Talus
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