Osteochondral Lesions of the Talus - Foot & Ankle

summary
- Osteochondral Lesions of the Talus are focal injuries to the talar dome with variable involvement of the subchondral bone and cartilage which may be caused by a traumatic event or repetitive microtrauma.
- Diagnosis can be made with plain ankle radiographs. MRI studies are helpful in determining the size of the lesion, the extent of bony edema, and identify unstable lesions.
- Treatment can be nonoperative or operative depending on patient age, patient activity demands, lesion size, and stability of lesion.

Epidemiology
- Incidence
  - 69% of ankle fractures
  - 70% of ankle sprains
  - 10% are bilateral
  - medial talar dome lesions more common
- Anatomic location
  - medial talar dome
    
    usually no history of trauma
    
    more posterior
    
    larger and deeper than lateral lesions
  - lateral talar dome
    
    usually have a traumatic history
    
    more superficial and smaller
    
    more central or anterior
    
    lower incidence of spontaneous healing
    
    more often displaced and symptomatic

Etiology
- Pathophysiology
  - mechanism of injury
    
    ankle inversion and dorsiflexion during axial load creates shearing of lateral talar dome and lateral OLT
    
    ankle inversion, external rotation, and plantarflexion during axial load creates shearing of medial talar dome and medial OLT
  - pathophysiology
    
    possible repeitive microtrauma creates ischemic environment and loss of integrity of subchondral bone
    
    leads to softening and disruption of overlying cartilage
- Associated conditions
  - cavus hindfoot alignment

Anatomy
- Osteology
  - talus geometrically complex structure
  - resembles a frustrum
  - anterior portion broader than posterior
  - no muscular attachments
- Cartilage
  - covers 70% of talus
  - among the thickest in the body (implications for osteochondral autografting)
  - maintains tensile strength longer than femoral head with aging process
- Blood supply
  - relies on extra-osseous blood supply
  - deltoid artery supplies majority of talar body and dome
- Biomechanics
  - ankle is a highly congruent mortise joint, oriented 15 degrees externally from midsagittal line of ankle
  - talus articulates with the medial malleolus medially, tibial plafond superiorly, posterior malleolus posteriorly, and fibula laterally

                        Classification
                    
                        Berndt and Harty Radiographic Classification
                    
                        Stage 1
                    
                        Small area of subchondral compression
                    
                        Stage 2
                    
                        Partial fragment detachment
                    
                        Stage 3
                    
                        Complete fragment detachment but not displaced
                    
                        Stage 4
                    
                        Displaced fragment
                    
                        Ferkel and Sgaglione CT Staging System
                    
                        Stage 1
                    
                        Cystic lesion within dome of talus with an intact roof on all view
                    
                        Stage 2a
                    
                        Cystic lesion communication to talar dome surface
                    
                        Stage 2b
                    
                        Open articular surface lesion with the overlying nondisplaced fragment
                    
                        Stage 3
                    
                        Nondisplaced lesion with lucency
                    
                        Stage 4
                    
                        Displaced fragment
                    
                        Hepple MRI Staging System
                    
                        Stage 1
                    
                        Articular cartilage edema
                    
                        Stage 2a
                    
                        Cartilage injury with underlying fracture and surrounding bony edema
                    
                        Stage 2b
                    
                        Stage 2a without surrounding bone edema
                    
                        Stage 3
                    
                        Detached but nondisplaced fragment
                    
                        Stage 4
                    
                        Displaced fragment
                    
                        Stage 5
                    
                        Subchondral cyst formation

Presentation
- History
  - inversion ankle sprain
- Symptoms
  - pain centered over ankle joint line
  - joint effusion
  - mechanical symptoms such as catching or locking
- Physical exam
  - inspection
    
    joint effusion
    
    palpation rarely reproduces pain
    
    cavus hindfoot alignment
  - motion
    
    often limited secondary to pain or effusion
  - provocative tests
    
    evaluate for ligamentous laxity or insufficiency

Imaging
- Radiographs
  - recommended views
    
    standard weightbearing ankle series
  - findings
    
    often normal
    
    subtle lucency or bone fragmentation
- Bone scan
  - indications
    
    suspicion for OLT in setting of equivocal radiographs
  - sensitivity and specificity
    
    94% sensitive and 96% specific for OLT
- CT
  - findings
    
    helpful in evaluating subchondral bone and cysts
    
    less reliable in purely cartilaginous lesions of nondisplaced OLTs
    
    provides fine detail of lesions for pre-operative planning
- MRI
  - indications
    
    persistent pain following injury, ankle sprains that do not heal with time
  - findings
    
    variable edema patterns, may overestimate degree of injury
    
    unstable lesions show fluid deep to subchondral bone
  - sensitivity and specificity
    
    predicts stability of lesion with 92% sensitivity

Treatment
- Nonoperative
  - immobilization and non-weight bearing
    
    indications
    
    acute injury
    
    nondisplaced fragment with incomplete fracture
- Operative
  - arthroscopy with removal of the loose fragment, debridement and marrow stimulation
    
    indications
    
    chronic lesions
    
    size < 1 cm
    
    displaced smaller fragment with minimal bone on the osteochondral fragment (poor healing potential)
  - retrograde drilling and/or bone grafting
    
    indications
    
    size > 1 cm with intact cartilage cap
  - osteochondral grafting (osteochondral autograft transplantation, autologous chondrocyte implantation, bulk allograft)
    
    indications
    
    size > 1 cm and displaced lesions, shoulder lesions
    
    salvage for failed marrow stimulation or drilling
    
    contraindications
    
    diffuse ankle arthritis
    
    bipolar kissing lesions
    
    advanced osteonecrosis of the talar done

Techniques
- Immobilization and non-weight bearing
  - period of immobilization in cast or boot for 6 weeks, followed by progressive weight bearing with physical therapy emphasizing peroneal strengthening, range of motion, and proprioceptive training
  - outcomes
    
    45% good-excellent outcomes
- Arthroscopy with marrow stimulation (microfracture or antegrade drilling)
  - approach
    
    standard arthroscopic approach to ankle
  - instrumentation
    
    debridement of unstable cartilage flaps to create stable and contained defect using curettes or shaver
    
    loose bodies and cartilage removed using shaver or grasper
  - bony work
    
    microfracture awl placed perpendicular to surface and tapped into subchondral bone 2-4 mm deep
    
    holes spaced 2-3 mm from each other
    
    inflow stopped to allow fat or blood to emanate from holes, indicating adequate penetration
    
    Kirschner wire can be passed using anterior portals, or transmalleolar for central or posterior lesions
    
    commercial targeting guides available
    
    talus dorsiflexed and plantar flex to necessitate only 1 transosseous passing of wire
  - complications
    
    articular cartilage delamination and graft failure
  - outcomes
    
    85% pain improvement
    
    65-90% improvement in patient reported outcomes
    
    fibrocartilage formation at site of lesion in 60% of patients on second-look arthroscopy, no correlation noted with patient outcomes
- Arthroscopy with retrograde drilling and bone grafting
  - approach
    
    standard arthroscopic approach to ankle
  - instrumentation
    
    evaluate cartilaginous surface for softening, dimpling with probe seen
    
    confirm integrity of cartilaginous cap
  - bony work
    
    Kirschner wire drilled from sinus tarsi into defect
    
    commercial targeting guides available
    
    fluoroscopy often helpful to confirm location
    
    if bone grafting indicated, cannulated drill placed over K wire
    
    curette out cystic material
    
    graft harvested and placed
  - complications
    
    violation of intact cartilage cap
- Osteochondral autograft and allograft transplant
  - approach
    
    dictated by location of OLT and concomitant procedures required (i.e. Brostrum)
    
    medial malleolar osteotomy for medial and posterior lesions
    
    longitudinal incision centered over medial malleolus
    
    anterior arthrotomy to expose joint line
    
    flexor retinaculum released posteriorly; PTT retracted posteriorly
    
    osteotomy guided based of 2 parallelly placed K-wires, with goal to enter plafond at lateral extent of OLT
    
    prior to osteotomy, 2 drill holes placed to aid in reduction following procedure
    
    sagittal saw and osteotome used to complete osteotomy, care taken not to cause thermal necrosis to bone or damage cartilage
    
    lateral malleolar osteotomy or ATFL/CFL release for lateral lesions
    
    longitudinal incision centered over lateral malleolus
    
    oblique osteotomy planned, with predrilling of small fragment screws holes to aid in reduction following procedure
    
    alternatively, if lateral ligament reconstruction is planned, extensor retinaculum may be released
    
    peroneal tendons retracted posteriorly and ATFL and CFL released, ankle inverted and plantarflexed to expose talar dome
    
    bone work
    
    OLT debrided and measured using sizing guide
    
    appropriately sized autograft may be harvested from knee and placed into OLT, impacted gently into defect
    
    OATs harvested from the knee have a cartilage thickness less than the native talus
    
    this will cause immediate post-operative xrays to show a prominent graft despite the cartilage surface being flush
    
    complications
    
    osteotomy site delayed- or non-union
    
    do not release deltoid ligament as may jeopardize deltoid artery blood supply
    
    ankle impingement if graft plug left proud
    
    autograft harvest site morbidity
- Autologous chondrocyte implantation
  - approach
    
    two-stage procedure consisting of
    
    arthroscopic harvest of chondrocytes (from ankle or alternatively from knee) are sent for cultured growth
    
    open approach via osteotomy for implantation
  - instrumentation
    
    debridement of lesion to create stable cartilage rim, subchondral bone exposed
    
    bone graft may be placed if underlying cyst and bone loss
    
    periosteum from tibia taken and fitted to defect
    
    this is sutured into place this small caliber suture, omitting one area to leave access to underlying defect
    
    water-tight seal confirmed, cultured chondrocytes placed under flap and suture placed, fibrin glue placed over defect
  - outcomes
    
    newer technique of matrix-based chondrocyte implantation (MACI) shown equivalent outcomes to ACI and may obviate need for osteotomy

Complications
- Graft failure
  - complication of all grafting procedures
- Persistent pain
  - small percentage of patients do not achieve pain relief regardless of treatment

Prognosis
- Lesions may progress to involve entire ankle joint

Action	Numeric Key	Letter Key	Function Key
Show Bullets		S	Enter (frontside only)
20%	1	N
40%	2	H
60%	3	F	Enter (backside only)
80%	4	E
100%	5	M
Toss	0	T

Berndt and Harty Radiographic Classification
Stage 1	Small area of subchondral compression
Stage 2	Partial fragment detachment
Stage 3	Complete fragment detachment but not displaced
Stage 4	Displaced fragment

Ferkel and Sgaglione CT Staging System
Stage 1	Cystic lesion within dome of talus with an intact roof on all view
Stage 2a	Cystic lesion communication to talar dome surface
Stage 2b	Open articular surface lesion with the overlying nondisplaced fragment
Stage 3	Nondisplaced lesion with lucency
Stage 4	Displaced fragment

Hepple MRI Staging System
Stage 1	Articular cartilage edema
Stage 2a	Cartilage injury with underlying fracture and surrounding bony edema
Stage 2b	Stage 2a without surrounding bone edema
Stage 3	Detached but nondisplaced fragment
Stage 4	Displaced fragment
Stage 5	Subchondral cyst formation