Osteochondral Lesions of the Talus


Background

The earliest report of osteochondritis dissecans (OCD) was published in 1888 by Konig, who characterized a loose-body formation associated with articular cartilage and subchondral bone fracture. [1In 1922, Kappis described this process in the ankle joint. [2]

On the basis of a review of all literature describing transchondral fractures of the talus, Berndt and Harty developed a classification system for radiographic staging of osteochondral lesions of the talus (OLTs). [3Their classification system has been the foundation for other systems, yet it remains the most widely used system today (see Staging).

Conservative treatment should be attempted first, whenever possible. Surgical treatment depends on a variety of factors, including patient characteristics and lesions (see Treatment). Surgery is contraindicated when the risks outweigh the perceived benefits.

For patient education resources, see Ankle ArthroscopyUnderstanding X-rays, and Magnetic Resonance Imaging (MRI).

Anatomy

The dome of the talus is covered by the trochlear articular surface, which supports the weight of the body. The talar dome is trapezoidal in shape, and its anterior surface is, on average, 2.5 mm wider than the posterior surface. The medial and lateral articular facets of the talus articulate with the medial and lateral malleoli. The articular surface of these facets is contiguous with the superior articular surface of the talar dome. (See the image below.)

Osteochondral lesions of the talus. Modified stagiOsteochondral lesions of the talus. Modified staging system by Loomer et al.

Approximately 60% of the talar surface is covered by articular cartilage. [4The talus has no muscular or tendinous attachments. Most of its blood supply enters through the neck via the sinus tarsi. The dorsalis pedis artery supplies the head and neck of the talus. The artery of the sinus tarsi is formed from branches of the peroneal and dorsalis pedis arteries. The artery of the tarsal canal branches from the posterior tibial artery. The sinus tarsi artery and the tarsal canal artery join to form an anastomotic sling inferior to the talus, from which branches enter the talar neck.

Pathophysiology

Anterolateral lesions on the talar dome result from inversion and dorsiflexion forces, which cause the anterolateral aspect of the talar dome to impact the fibula. These lesions are usually shallower and more wafer-shaped than medial lesions, possibly because of a more tangential force vector that results in shearing-type forces. [5]

Posttraumatic medial lesions are deeper and cup-shaped. They result from a combination of inversion, plantarflexion, and external rotation forces that cause the posteromedial talar dome to impact the tibial articular surface with a relatively more perpendicular force vector.

A study of the contact pressures on the talus with varying degrees of lateral ligament transections and ankle positions showed that the medial rim of the talus was subjected to high pressures, even without ligamentous transection. [5Results of another study implicated the difference in cartilage stiffness; the tibial cartilage is 18-37% stiffer than the corresponding sites on the talus. [6]

The results of other studies indicated that the mean cartilage thickness is inversely related to the mean compressive modulus. [78These findings may lend credence to the clinically observed etiology of OLTs (ie, repetitive overuse syndrome in medial lesions and an acute traumatic event in lateral lesions).

Observations from biomechanical studies suggest that the size of the lesion may alter the contact stresses in the ankle. Statistically significant changes in contact characteristics occur with lesions larger than 7.5 mm × 15 mm; this finding indicates that lesion size may play a role in predicting long-term outcome. [9]

Etiology

Both Konig [1and Kappis [2believed that lesions due to OCD were the result of ischemic necrosis of the underlying subchondral bone that eventually led to separation of the fragment and its overlying articular cartilage.

Inflammation has not been shown to be a significant factor in the etiology of OCD. Therefore, the term OCD may be misleading. In addition, OCD may be mistakenly understood to refer to the common term osteochondral defect. Assenmacher proposed the term osteochondral lesions of the talus (OLTs). [10]

A history of trauma is documented in more than 85% of patients. [1112131415Pritsch et al reported that a traumatic event preceded 75% of both medial and lateral lesions in 24 patients. [16Trauma is implicated less often in posteromedial lesions. [171819]

Although the etiology of nontraumatic OLTs is unknown, a primary ischemic event may cause this form of the disease. Nontraumatic OLTs can also be familial. Multiple lesions can occur in the same patient, and identical medial talar lesions have occurred in identical twins. [20]

Epidemiology

Osteochondral lesions are rare joint disorders. Most often, they affect the knee, followed by the elbow and the talus. Lesions of the talus account for 4% of all osteochondral lesions in the body. [17 However, they have been found in more than 40% of patients after operative treatment of ankle fractures. [21]

Prognosis

Nonoperative treatments of OLTs are associated with published success rates of 45-50%. [2223Operative interventions have repeatedly been reported with significantly better success rates.

In a meta-analysis by Tol et al, the combination of excision, curettage, and drilling had an 85% success rate and better outcomes than did excision and curettage without drilling or excision alone. [22In a systematic review by Donnenwerth et al, 80.2% good-to-excellent results were identified with arthroscopic debridement and microfracture, regardless of lesion location or lesion size. [24]

Choi et al demonstrated an independent prognostic effect with lesion containment, for which poorer outcomes were identified with uncontained lesions. [25In this same study, lesion location did not result in an independent prognostic effect. Choi et al identified that a critical defect size related to poor outcomes following arthroscopic marrow stimulation techniques at 150 mm2, correlating to increased risk for a poor outcome. [26]

Autologous osteochondral grafting has likewise had favorable outcomes. Reports on both mosaicplasty and the osteochondral autograft transfer system (OATS) procedure for OLTs cited success rates around 90% at follow-up of 4 years and 16 months. [2728]

The autologous chondrocyte transplantation (ACT) procedure in the knee has been associated with good-to-excellent results at 2-year follow-up. [29In the ankle, good results have been reported, with arthroscopically confirmed cartilage coverage of the graft site, but whether this newly generated cartilage will hold up to the stresses on the ankle remains to be determined. [3031A meta-analysis of the available reports concluded that the evidence for ACT remained elusive despite a reported 89.9% clinical success rate. [32]

A concept review article revealed grade B (fair evidence from level II or III studies with consistent findings) for bone-marrow stimulation techniques and autologous osteochondral transplantation (OATS or mosaicplasty). Grade C recommendations (conflicting or poor-quality [level IV or V] evidence) were made for osteochondral allograft transplantation and autologous chondrocyte implantation. Biologic adjuncts lacked sufficient evidence to allow a recommendation. 



History

In most cases, the mechanism of injury is an inversion injury with simultaneous or preexisting disruption of the lateral ligamentous complex. Patients typically present with chronic ankle pain along with intermittent swelling and, possibly, weakness, stiffness, instability, and giving way.

Physical Examination

Upon physical examination, assess joint laxity with the anterior drawer test, and assess strength by comparison with the contralateral ankle. Physical examination findings of joint laxity are uncommon. Palpation may reveal tenderness behind the medial malleolus when the ankle is dorsiflexed, indicating a posteromedial lesion. Anterolateral lesions may be tender when the anterolateral ankle joint is palpated with the joint in maximal plantarflexion.



Radiography

Patients with an acute ankle injury with hemarthrosis or substantial tenderness first undergo weightbearing plain radiography (anteroposterior [AP], lateral, and mortise views). Radiographs in varying degrees of plantarflexion and dorsiflexion may help in diagnosing posteromedial and anterolateral lesions, respectively. [34 Plain radiographs of the opposite ankle should be considered, especially if symptoms are apparent, because of the 10-25% incidence of a contralateral lesion. [35]

Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) can be used to identify occult injuries of the subchondral bone and cartilage that may not be detected with routine radiographs. [3637 Postoperative MRI evaluation may also be considered to assess healing after surgical management. [38]

Classic MRI findings include areas of low signal intensity on T1-weighted images, which suggest sclerosis of the bed of the talus and indicate a chronic lesion. [3940 T2-weighted images reveal a rim that represents instability of the osteochondral fragment. [3941 Posttreatment MRI depicts a reduction or disappearance of the low signal intensity on T1-weighted images and the rim on T2-weighted images.

Arthroscopy

Arthroscopy may be used as the basis for staging osteochondral lesions of the talus (OLTs). In 1995, Cheng et al developed a comprehensive arthroscopic classification system (see Staging). [42 Typically, arthroscopy is performed to confirm the diagnosis and in conjunction with treatment. Isolated diagnostic arthroscopy is rarely performed.

Staging

OLTs should be staged. MRI is used to evaluate the quality of the overlying cartilage and to assess the stability of the lesion. [43 Several staging systems have been developed on the basis of the first system that Berndt and Harty proposed in 1959 (see the image below). [3 

Berndt and Harty staging system for osteochondral Berndt and Harty staging system for osteochondral lesions of the talus, with grades 1-4.

In 1996, Ferkel modified this classic system and developed another system, based on computed tomography (CT) findings. [44 (See the images below.) Ferkel's system corresponds to the stages in the Berndt and Harty classification but also considers fragment separation, the presence of subchondral cysts, and the extent of osteonecrosis.

Osteochondral lesions of the talus. ClassificationOsteochondral lesions of the talus. Classification system based on CT.
Osteochondral lesions of the talus. Modified stagiOsteochondral lesions of the talus. Modified staging system by Loomer et al.

MRI is sensitive in detecting bone signal changes. In 1999, Hepple et al devised the following staging system [45:

  • Stage 1 - Articular cartilage damage only
  • Stage 2 - Cartilage injury with underlying fracture
  • Stage 2a - Cartilage injury with underlying fracture and edema
  • Stage 2b - Cartilage injury with underlying fracture but no edema
  • Stage 3 - Detached (rim signal) but not displaced fragment
  • Stage 4 - Displaced fragment
  • Stage 5 - Subchondral cyst formation

Cheng et al developed the following arthroscopic staging system [42:

  • Stage A - Smooth, intact, but soft or ballotable; stable
  • Stage B - Rough surface; stable
  • Stage C - Fibrillation/fissuring; stable
  • Stage D - Flap present or bone exposed; unstable
  • Stage E - Loose, undisplaced fragment; unstable
  • Stage F - Displaced fragment; unstable.

Approach Considerations

Conservative treatment of osteochondral lesions of the talus (OLTs) should be attempted first, whenever possible. After a period of immobilization followed by physical therapy, patients with continued symptoms should be evaluated with magnetic resonance imaging (MRI) and other imaging studies to assess the condition of the articular cartilage and stability, as well as to detect any intra-articular bodies. [36]

Symptoms of intra-articular derangement are indications for operative intervention. Such symptoms include effusion, catching or locking of the ankle, instability preceded by pain, and ankle pain relieved with diagnostic local anesthetic injection.

Surgery to treat OLTs is contraindicated when the risks outweigh the perceived benefits. Risks include active infection in the operative area, patient noncompliance, and medical instability in patients. Relative contraindications include degenerative changes of the ankle involving more than an isolated OLT.

Future controversies will likely revolve around minimizing operative morbidity and costs. Early reports with allografts showed some subsidence and resorption, necessitating ankle arthrodesis. If this trend continues, the use of allografts will likely fall from favor.

Thus far, autologous osteochondral grafting seems to be the most reproducible and stable grafting technique. As this procedure gains favor, more reported complications at the knee donor site may evolve. A study suggested that when failure of grafting occurs, using a metal resurfacing inlay implant for revision surgery of moderate-sized lesions may be considered; however, this technique has not been validated by additional studies, and the long-term results are unknown. [46]

The autologous chondrocyte transplantation (ACT) procedure is based on actual repair of deficits of articular cartilage. Additional histologic and long-term clinical data are needed to determine the success or failure rate of this therapy. Currently, this technology is fairly cost-prohibitive, with the expense of cell culture and two surgical procedures. Future possibilities may include the use of adhesive patches instead of the periosteal flap, as well as the addition of growth factors. [30]

In conjunction with marrow-stimulation techniques, [47 restorative tissue (juvenile particulated allograft cartilage, allograft extracellular matrix) biologic adjuncts (ie, mesenchymal stem cells, platelet-rich plasma [PRP], bone marrow aspirate concentrate) may play a role in the management of OLTs. Limited research is available in this area, and the practicality and long-term efficacy of this technique remain to be established. [48495051]

In July 2018, a supplemental issue of Foot and Ankle International was published that dealt extensively with current concepts related to management of OLTs, as well as a review of existing literature and recommendations for future research. [52 Surgeons desiring to follow future research efforts would be well advised to familiarize themselves with this material.

Medical Therapy

Conservative management of OLTs should be attempted before surgical management is embarked on. (See the images below.) 

Osteochondral lesions of the talus. Illustration oOsteochondral lesions of the talus. Illustration of percutaneous transmalleolar drilling.
Osteochondral lesions of the talus. Cannulated driOsteochondral lesions of the talus. Cannulated drill placed over a guidewire.

Symptomatic patients with negative findings on plain radiographs should undergo an initial period of immobilization, followed by physical therapy. Studies have shown that a trial of conservative therapy does not adversely affect surgery performed after conservative therapy has failed. [1719 One study demonstrated that nonoperative conservative treatment can sometimes result in healing of higher-stage lesions. [14 Patients whose plain images indicate OLTs and those who remain symptomatic after 6 weeks should undergo additional evaluation with MRI.

Surgical Therapy

Surgical treatment depends on a variety of factors, including patient characteristics (eg, activity level, age, degenerative changes) and lesions (eg, location, size, chronicity). Generaly, however, surgical treatment adheres to one of the following three principles:

  • Loose-body removal with or without stimulation of fibrocartilage growth (microfracture, curettage, abrasion, or transarticular drilling) [53]
  • Securing OLTs to the talar dome through retrograde drilling, bone grafting, or internal fixation
  • Stimulating the development of hyaline cartilage through osteochondral autografts (osteochondral autograft transfer system [OATS], mosaicplasty), allografts (particulated juvenile cartilage), or cell culture (Carticel; Genzyme Biosurgery, Cambridge, MA)

Preparation for surgery

Radiographic imaging is essential to assess alignment and grade the OLT. A marked distortion of normal mechanical alignment must be corrected at the same operative setting as the surgery to address the OLT. Grading the OLT allows for proper prognostication and influences whether the lesion can be approached with an antegrade or a retrograde technique.

Operative details

Surgical exposure

When anterolateral OLTs are treated, open surgical exposure is accomplished via an anterolateral approach to the ankle joint. Plantarflexion aids in exposing the lesion; however, this approach requires caution to avoid damaging the branches of the superficial peroneal nerve.

The open approach is also challenging when posteromedial OLTs are treated. An osteotomy cut that enters the joint too far laterally can endanger the weightbearing plafond, and a cut that enters the joint too far distally on the medial malleolus limits exposure. Screw holes must be predrilled before osteotomy. In addition, care must be taken to avoid injury to the allograft nerve and vein, anterior tibial tendon, posterior tibial tendon, flexor digitorum longus (FDL), posterior tibial artery, and tibial nerve.

An apex proximal chevron bone cut provides excellent visualization, and Cohen et al had no nonunions or malunions when using a chevron medial malleolar osteotomy in 19 patients. [1154]

Posteromedial OLTs have also been treated by using a combined anterior and posterior arthrotomy exposure. This approach allows access to 80% of the talar dome while it avoids the medial malleolar osteotomy in most cases. [55]

Arthroscopic treatment of OLTs can be accomplished by using wide-angle 2.7-mm arthroscopes, which provide more maneuverability than the older 4- and 5-mm arthroscopes. Noninvasive joint distraction techniques enable easier visualization of the entire talar dome. [56575859]

Treatment of completely detached lesions

For a completely detached lesion believed to be inappropriate for internal fixation, removal of the loose body and debridement of the bony bed are indicated. The base of the bed should be debrided back to bleeding bone, and the edges should be trimmed back to viable cartilage. Instruments available for use in this procedure include blunt-tipped probes, pituitary graspers, gouges, Kirschner wires (K-wires), awls, full-radius shavers, ring curettes, and high-speed burrs.

Studies have shown that excision and nonoperative treatment yield poor results and that excision, curettage, and drilling provide the best outcomes. [22 Although high-level evidence is lacking, long term follow-up of microfracture has been associated with good results. [60]

Treatment of intact lesions

Drilling of the subchondral bone creates channels to enable revascularization of the fragment. Drilling can be accomplished by using existing arthroscopic portals, a curved meniscus-repair needle guide, and transmalleolar drill holes. [3561]

Sinus tarsi approaches to posteromedial lesions, also known as retrograde drilling or transtalar drilling, do not disrupt the articular surface. Retrograde drilling can facilitate bone grafting, which is ideal for large subchondral cystic lesions with intact articular cartilage. The COLT (Interpore Cross, Irvine, CA) provides for accurate positioning of the drill hole and a cannula for bone graft delivery. Studies have shown good clinical and radiographic results with transarticular/transmalleolar drilling and retrograde/transtalar drilling. [6263]

Internal fixation

The use of traditional bone screws passed in an antegrade fashion is discouraged because irreparable damage to the intact articular cartilage results. Screw fixation typically is used for anterolateral lesions only because of the difficulty in gaining good exposure for posteromedial lesions. K-wires can be inserted in a retrograde manner through a nonarticular portion of the talus. Bioabsorbable pins can be advanced immediately below the articular surface, then cut off at the skin.

Bone grafting

The authors have reported successful fixation after autogenous osteochondral grafting of an osteochondritis dissecans (OCD) of the knee. [64Another report described treating 27 large (8 mm × 8 mm and larger) ankle lesions with a cortical bone peg technique. [65The pegs, which were 2-3 mm wide and 15-20 mm long, were harvested from the distal tibia and passed through the articular surface. Good clinical results were reported in 89% of patients at an average of 7 years of follow-up.

The contemporary consensus is that lesions with a depth of more than 5 mm should be bone-grafted.

Another study, with an 11-year mean follow-up, reported nine cases of fresh osteochondral allografting. [66Of nine grafts, six remained in situ, and three patients required ankle arthrodesis because of resorption and fragmentation of the graft. These authors discouraged the use of allografting in OLTs. A high rate of complications has been reported in patients who underwent tibiotalar osteochondral allografting. [67]

Autologous osteochondral grafting

Autologous osteochondral grafting techniques, including the OATS procedure and mosaicplasty, involve grafting a plug from the femoral trochlea or condyle into the OLT on the talar dome. [68]

The OATS procedure transplants a single plug into the OLT, and mosaicplasty is used to harvest and transplant multiple plugs. [69Single-plug grafts result in reduced ingrowth of the fibrocartilage, though donor-site morbidity may be greater because of the need to harvest a single larger plug. [70The mosaicplasty procedure is said to provide a better match to the talar dome contour and surface area of the defect, though 20-40% of the defect is filled with fibrocartilage. [27]

Several groups have reported good results with both procedures. In one study, 11 patients who underwent mosaicplasty had good-to-excellent results at 24 months. [71The lesions averaged 18 mm × 10 mm, and there were no adverse effects on the knee. Another study reported that 94% of 36 patients undergoing mosaicplasty had good-to-excellent results, with follow-up ranging from 2 to 7 years. [28Previous surgical procedures had failed in 29 of the patients.

In another study, plugs were harvested from the ipsilateral medial or lateral articular facet of the talus in 12 patients. Significant improvement in American Orthopaedic Foot and Ankle Society (AOFAS) scores was reported, and no structural failures occurred in the graft or donor site. [72]

A modified mosaicplasty technique has also been proposed for management of severe OLTs. Leumann et al discussed using autologous bony periosteum–covered plugs harvested from the iliac crest for management of lesions larger than 1.5 cm2. [73]

Autologous chondrocyte transplantation

Two reports described good early results with ACT. [74Koulalis et al reported the results of ACT in eight patients (average follow-up, 17.6 months). [75Patients first underwent diagnostic arthroscopy, cartilage biopsy, chondrocyte extraction, and culture; an average of 2.5 weeks later, they underwent arthrotomy, malleolar osteotomy, bone debridement, and chondrocyte transplantation. They were kept on nonweightbearing status for 6-7 weeks. Routine arthroscopic examination performed 6 months after the transplant showed cartilagelike tissue completely covering the OLTs. (Histologic examination of one biopsy sample did not show hyaline cartilage.)

Giannini et al reported similar results 24 months post transplant, showing that hyaline cartilage can be transplanted in the ankle joint and that good function can be expected. [76]

ACT has been performed more often in the knee. Results of the first 100 patients undergoing this procedure in a multicenter 5-year study found that 79% showed improvement at 5 years. Compared with a control group undergoing different procedures, such as drilling or abrasionplasty, patients undergoing the transplant procedure had better functional outcomes. [77]

Particulated juvenile cartilage allograft

This technique uses particulated juvenile cartilage allograft from donors younger than age 13 years. It is proposed that immature chondrocytes have an increased propensity to regenerate hyalinelike cartilage and have greater metabolic activity. [78Limited studies are available using this technique, with only relatively short-term follow-up. [798081]

Early results for small to moderate-sized lesions demonstrated good outcomes at short-term follow-up. [7980Coetzee et al reported that for lesions with a diameter of 15 mm or greater, only 56% of patients reported good-to-excellent results on the AOFAS Ankle-Hindfoot Scale at 16-month follow-up. [79]

Treatment of coexisting OLT and ligamentous instability

Acute ankle ligament injuries with a large, unstable fragment typically first undergo surgical repair of the talar lesion. The ligament is allowed to heal postoperatively.

Treatment decisions for treating chronic OLTs with chronic ankle instability are less clear. Postoperatively, OLTs require early motion, which is not appropriate for reconstructed ligaments. Options include first repairing the OLT and then repairing the ligamentous injury at another time, or else repairing the two injuries simultaneously and postponing early ankle motion until the ligament has healed. Thermal capsular shrinkage may also be a possible treatment solution. [64]

Postoperative Care

A postoperative rehabilitation program should be tailored to each patient's individual circumstances and goals by a licensed physical therapist. With the goal of attaining full ankle range of motion (ROM), physical rehabilitation includes active and passive ROM exercises and a home program, edema control, and strength and proprioceptive training.

Rehabilitation can generally begin after healing is demonstrated, which may occur after 6-7 weeks of nonweightbearing status if drilling or internal fixation was performed. Lee et al compared early (2 weeks) weightbearing with delayed (6 weeks) weightbearing following arthroscopic debridement and microfracture of small to medium-sized OLTs and found no difference in outcome between the two groups. [82]

Complications

Operative treatment of OLTs has inherent risks. Open exposure entails use of a medial malleolar osteotomy or anterior plafond bone block to gain exposure of the tibiotalar joint. The medial malleolar osteotomy typically heals well with low incidence of nonunion, but care must be taken to place the osteotomy correctly and protect the adjacent tendons and neurovascular structures. [54]

With second-look arthroscopy, Kim et al found that postoperative pain (Visual Analog Scale [VAS]) and function (AOFAS Ankle-Hindfoot Scale) scores were significantly worse when the tibial plafond at the malleolar osteotomy site was uneven. [83An anterior tibial bone-block access window is associated with a lower risk of malunion but may limit access to posterior lesions. [72]

Arthroscopic intervention is associated with less surgical morbidity and joint stiffness, decreased rehabilitation time, and an increased functional outcome. [84]

Schuman reviewed 22 patients who underwent arthroscopy with curettage and drilling at an average follow-up of 4.8 years, with 86% good-to-excellent results. [85Complications associated with arthroscopy include hyperesthesia around the portal incision and, occasionally, neuralgia of the superficial peroneal nerves, but these were minor and transient.

Some have advocated the use of allograft implants, but these grafts may become resorbed over time and fragment, necessitating ankle arthrodesis. [66So far, no reports have been made of allograft rejection by the host.

The osteochondral transplantation procedures carry the additional risk of a second surgical site, which adds to the risk of possible complications. A 4-year follow-up of 36 mosaicplasty patients reported six patients with donor-site complaints during strenuous exercise, but this resolved after the first year. [28Woelfle et al, in a study of 32 patients who underwent the OATS procedure, determined that advanced age (>40 years) is associated with higher donor site morbidity. [86The OATS procedure is thought to have greater donor-site morbidity, in that larger plugs are taken than are taken with mosaicplasty.

Gautier et al evaluated 11 patients at a 24-month follow-up and found that 10 of 11 had graft incorporation and were without major complications. [71Subjectively, patients may report mild pain or stiffness in the knee or ankle, but this is without objective deficits. Similarly, other authors have found good graft incorporation without serious complications. [1028Restoration of articular surface congruity may be very difficult, particularly in talar shoulder lesions.

Published reports of ACT are relatively few but include good results. [75The procedure does necessitate two operations and is difficult technically, but no complications have been reported.

Long-Term Monitoring

Pain after operative treatment of OLTs is common for up to 1 year. MRI changes, including edema, are slow to resolve and often match the patient's report of an achy feeling in the joint. After 6 months, a persistent effusion, a catching sensation, or severe pain signifies that healing is not progressing as intended, and further investigation with computed tomography (CT) or MRI is appropriate.

In a study by Cuttica et al, follow-up MRI at a minimum of 9 months' follow-up revealed an odds ratio of 7.8 for a poor outcome when moderate or severe edema intensity was present as compared with mild or no edema intensity following microfracture.