KEY FACTS
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The natural history of osteochondral lesions of the talus appears to be fairly benign, especially as it relates to the risk of the development of arthritis.
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Treatment is thus most appropriately based on the patient’s symptoms, a very relevant fact given that many osteochondral lesions are incidental findings.
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There are a host of classifications for osteochondral lesions, although no 1 classification is used universally, as the classifications generally do not influence treatment nor do they predict prognosis.
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Nonoperative treatment is limited in terms of options; often activity modification is a central aspect. A boot or cast may be considered, and even a period of non-weight bearing in certain settings may be warranted.
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There are a variety of surgical treatment options; the size and location of the lesion will often steer the surgeon toward one treatment vs. another. Given the relatively mild morbidity associated with marrow stimulation, it is often used as the 1st-line treatment, while more invasive treatments are often reserved for the revision setting.
Overview
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Osteochondral lesions of the talus (OLT) represent a continuum of disease that is likely not 1 single pathology but a grouping of similar pathologies.
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The historical term for this grouping of pathologies, osteochondritis dissecans (OCD), emphasized a localized vascular deficiency within the talus as the principle pathology with the symptoms being secondary to loss of adequate chondral support &/or cyst formation within the talus. Traumatic chondral defects, on the other hand, are often related to shear.
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Traditionally, lateral defects were more likely to be traumatic in nature, while medial and posteromedial defects were more likely a true OCD.
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While treatment of these lesions has advanced considerably over the years, the underlying pathogenesis of the OCD (i.e., nontraumatic) lesions remains unclear.
Natural History
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Certainly, establishing the natural history of any pathology is critical to understanding if and when intervention is warranted.
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There is surprisingly little evidence that speaks to the natural history of OLTs.
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Some surgeons theorize that asymptomatic OLTs may lead to ankle osteoarthritis if left untreated. However, there is simply very little evidence to back up this statement. What little evidence that does exist suggests that the natural history of OLTs is relatively benign.
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Given this fact, treatment for OLTs should be based chiefly on symptoms referable to the lesion. Further, it appears that the asymptomatic OLT can be summarily ignored.
Classification
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There are no fewer than 4 classification schemes depending on various imaging modalities.
Plain Radiographs
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Berndt and Harty published their original description in 1959 on what they called transchondral fractures of the talus.
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Stage I: Subchondral compression (fracture)
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Stage II: Partial detachment of osteochondral fragment
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Stage III: Completely detached fragment without displacement from fracture bed
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Stage IV: Detached and displaced fragment
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Stage V (added subsequently by Loomer et al in 1993): Radiolucent defect (i.e., subchondral cyst) present
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CT (Ferkel and Sgaglione)
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This is an extension of Berndt and Harty on CT.
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Stage I: Intact roof/cartilage with cystic lesion beneath
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Stage IIa: Cystic lesion with communication to surface
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Stage IIb: Open surface lesion with overlying fragment
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Stage III: Nondisplaced fragment with lucency underneath
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Stage IV: Displaced fragment
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MR (Hepple et al)
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This staging system was devised to allow for earlier detection of lesions.
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It is still largely based on Berndt and Harty.
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Stage 1: Articular cartilage damage only
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Stage 2a: Cartilage injury with underlying fracture and surrounding bony edema
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Stage 2b: Stage 2a without surrounding bony edema
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Stage 3: Detached but undisplaced fragment
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Stage 4: Detached and displaced fragment
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Stage 5: Subchondral cyst formation
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How To Put All This Together
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As is readily apparent, there is a lot of overlap between these classifications. None of them consistently predicts treatment or prognosis, and so, based on what is typically desired from a classification scheme, none of these schemes are ideal. Practically speaking, radiographs are often used as a screening tool, while MR is typically the study of choice for identifying an OLT. CT can be useful in characterizing cyst and lesion morphology and size.
History and Physical
History
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The history for a patient with a symptomatic osteochondral lesion can vary considerably.
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Not infrequently, patients will recall a history of trauma that they may or may not correlate with their symptoms.
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Most of the time, patients will have the insidious to relatively acute onset of pain in the ankle that is typically, at least initially, activity related.
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Patients sometimes will recall a similar episode in the past that resolved spontaneously.
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A history of an ankle fracture or repeated ankle sprains may be related to a more clear traumatic origin and therefore more chondral defects ± subchondral bone involvement.
Physical
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On inspection, an effusion of varying proportions may be the only outward sign of pathology.
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Based on the location of the lesion, patients may have some tenderness to palpation at the ankle joint line, although this finding is inconsistent at best.
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If a lesion has detached and become a loose body, then some limitation of motion may be noticeable relative to the contralateral side. For similar reasons, patients may rarely experience mechanical locking of the ankle.
Treatment
Nonoperative Treatment
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Recommendations for nonoperative treatment are largely lacking, as there is a dearth of evidence to provide much guidance.
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Generally, protection of the ankle in either a cast or a CAM walker boot is appropriate. Non-weight bearing can be considered, although the degree to which it provides benefit is questionable at best. Activity modification should be undertaken as well; it may often be the more attractive option than prolonged use of a boot or cast.
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As above, symptoms dictate treatment. Depending on symptom severity, it is often advisable to try nonoperative treatment for at least 1-3 months before moving to more aggressive treatment, as the symptoms can sometimes dissipate with time.
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Further, it is imperative to differentiate symptoms from an OLT from other symptoms. Given that OLTs can coexist with ankle instability, appropriate treatment should be instituted for the instability before aggressively treating the OLT.
Operative Treatment
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The treatment paradigms for OLTs are largely adapted from the treatment of osteochondral lesions and injury in other joints, most notably the knee.
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The different treatment options include marrow stimulation, osteochondral autograft, osteochondral allograft, and the various forms of autologous chondrocyte implantation (ACI).
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Marrow stimulation
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The basic idea behind this treatment is the removal of injured or diseased cartilage and bone with the promotion of bleeding and clot formation in the resultant defect that will eventually allow for fibrocartilage fill of the defect.
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The mechanism of marrow stimulation has varied over time. Abrasion arthroplasty was traditionally used, although microfracture is more commonly used today. Microfracture involves the perforation of the subchondral plate in several places within a lesion allowing for the egress of marrow elements.
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It is understood that the fibrocartilage that fills these defects has inferior mechanical properties to the normal hyaline cartilage. However, the fibrocartilage can often be sufficient to take away a patient’s symptoms referable to the defect.
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Results from microfracture are generally good with success rates above 80-90% in terms of pain and functional outcome at early and midterm follow-up.
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In an effort to improve the mechanical properties of repair tissue, a host of enhancements to microfracture have been proposed with varying results.
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Platelet-rich plasma and bone marrow aspiration concentrate have been used in this setting with some success in terms of improving outcomes, although there is insufficient data to comment in a definitive way at this point.
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Various forms of particulated cartilage have been used in an effort to provide allogeneic chondrocytes, which will hopefully increase the proportion of hyaline cartilage in repair tissue, although the results from these concoctions have been inconsistent.
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Osteochondral autograft
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This treatment paradigm was developed to address some of the shortcomings of marrow stimulation.
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The advantages of osteochondral autograft is principally the ability to get hyaline cartilage as opposed to fibrocartilage.
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There are potential downsides, however. Most notably, the graft must come from somewhere (most typically the lateral nonarticular trochlea) that is ostensibly normal, potentially introducing pathology into an otherwise normal joint. Also, an osteotomy is frequently necessary. Further, the graft is typically impacted into place, a trauma that can potentially cause the death of chondrocytes. Finally, if the graft fit is off, the ingress of synovial fluid can cause cyst formation underneath the graft.
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For all of these reasons, osteochondral autograft is probably best reserved for the revision setting in most cases.
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However, some authors have astutely noted that larger lesions tended to less well with microfracture, and so patients with larger lesions may be better served with a primary autograft.
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ACI
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ACI was originally developed in the knee and subsequently used in the ankle.
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It traditionally necessitated 2 surgeries. In the 1st surgery, native cartilage was harvested, which was subsequently grown in the lab. A 2nd surgery allowed for implantation of the autologous cartilage cells, which were historically placed under a periosteal sleeve.
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Matrix ACI has been developed, allowing for the implantation of a matrix implanted with with autologous chondrocytes, thereby simplifying the implantation surgery significantly.
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There is a limited amount of data on this treatment modality, although good results have been published in the revision setting.
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Given the involved nature of this procedure, it is likely most appropriate in the revision setting.
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Osteochondral allograft
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Large defects present a significant problem, especially when there is a cystic defect in the talus. Microfracture and osteochondral autograft will each have limited efficacy in this situation, as microfracture does not work well with large defects, and autograft is ultimately a limited resource.
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ACI can be used with bone grafting, although maintaining the bone graft in position can be difficult.
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In this setting, an osteochondral allograft can sometimes be the best, if not downright only, option.
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Good results have been noted in this setting.
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Particulated cartilage allograft
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Small pieces of juvenile or adult articular allograft can be implanted into the defect.
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Evidence on the efficacy of particulated graft is pending.
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Postoperative care
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When an osteotomy is necessary, postoperative care is usually dictated by the need for osteotomy healing.
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In the setting of microfracture, weight bearing was historically restricted for 6 weeks so as to limit shear stress across the filling defect.
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Recent evidence suggests 2 weeks of non-weight bearing are sufficient.
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