- See:
-
Radiographic Evaluation:
-
Blood Supply to Talus
- Discussion:
- may occur following talar neck fractures or may be atraumatic (from
SLE, diabetes, MS ect);
- absence of subchondral bone atrophy in talar dome on x-ray after 6 weeks following fracture
implies AVN (see
Hawkins Sign);
- however,
there is not direct correlation between development of AVN and a poor result;
- although AVN is an important contributing factor in poor results only
rarely do patients request or require late reconstructive surgery;
- AVN of talus occursin 40% of frx of neck of talus w/ subtalar dislocation & in
90 % w/ complete dislocation of talus from ankle mortice w/ subtalar
dislocation, and 100 % w/ comminuted frx of body of talus;
-
Type I:
AVN occurs in
0% to
13%
-
Type II:
"
"
20% to
50%
-
Type III:
"
"
83% to 100%
- Frx of neck are also prone to nonunion, osteochondral frx, & DJD;
- Radiographs:
- AVN may not be present for 3 or more months following injury;
- dx of AVN is a radiographic one, w/ talar body initially showing increase density compared
to the surrounding bone (which is vascular & is undergoing disuse atrophy);
- later as revascularization occurs, there is partial or complete complete collapse of subchondral
bone, narrowing of joint space, and occasionally fragmentation of the talar body;
- the posterolateral corner of the talus will show osteonecrotic changes most often, since it
has the poorest
blood supply;
-
Hawkins Sign:
- sign provides evidence of revascularization of talar body;indicator of talar viability
- indicated by patchy subchondral osteoporosis at approx 6-8 weeks;
- resorption of subcondral bone in setting of disuse and good vascular supply
- it is important to look at
mortise x-ray & not lateral because fibula can sometimes cause increasead
density of body of talus, which can sometimes be mistaken for vascular changes;
- in many cases, the main remaining blood supply to the talus is from the medial side (deltoid
ligament brachnes), and therefore, the Hawkin's sign is often seen medially;
- MRI
-Low signal on T1-weighted images secondary to adipocyte death
-Variable signal on T2-weighted images depending on contents of avascular region
-Pathognomonic “double line” sign uncommon
- Early Management:
-
determine etiology of AVN:
- if AVN has not been caused by trauma, then it is important to investigate the cause;
- see:
pathogenesis of AVN;
- if there is an atraumatic etiology for talar AVN, then consider a
bone scan inorder to
look for early AVN in the femoral and humeral heads;
- in most cases, hip AVN will precede talar AVN, but this is not always the case;
-
quantify the extent of AVN:
- AVN can involve the entire talar body or only a small percentage;
- use of MRI to determine the percentage of AVN involvement helps with determining
potential for collapse;
-
attenpt to achieve frx union:
- first goal is always for anatomical union of frx which should occur even in face of AVN;
- talus fractures are reduced and stabilized using screw fixation;
- if secure fixation is achieved, early motion is instituted.
- a highly satisfactory result can be achieved even in face of severe injuries;
- patient should be protected from wt bearing until union is secure;
-
reconstitution of the talus:
- when union has occurred, body of the talus will still be avascular, since upto 36 months
is required for complete creeping substitution of body;
- some recommend a patellar tendon bearing brace, and is continued until reconstitution
of the talar body is complete;
- Canale has reported, however, that the best results are obtained w/ non wt bearing
until revascularization is obtained;
- Late Managment and Salvage:
-
determine amount of collapse and arthrosis:
- joint arthrosis may be present with or without adjacent talar collapse;
- MRI can be used to determine the amount of collapse and residual AVN and radiographs
can be use to evaluate joint arthrosis in the ankle, subtalar, and talonavicular joints;
- physical exam and differential lidocaine injections can help determine which joints are painful;
-
excision of the talus:
- traditionally this is not expected to yield good results, unless a tibial calcaneal arthrodesis is also performed;
- in the paper by Gunal et al 1993, the author advocates excision of the talus, displacement of the foot anteriorly
and malleolar osteotomy with lateral displacement;
- w/ this technique there is maximal tibial-calcaneal contact, minimal shortening and good preservation of motion;
- reference:
- A new technique of talectomy for severe fracture dislocation of the talus.
I. Gunal et al. JBJS. Vol 75-B. (I) 1993. p 69-71.
-
arthrodesis:
- physical exam, radiographs, and differential injections are used to determine which joints are painful;
- unlike the Blair fusion, fusion is reliable and there is no shortening;
- in most cases
ankle and
subtalar arthrodesis will be required;
- often an external fixator is helpful to stabilize the fusion (inaddition to internal fixation);
- external fixation is often removed at 12 weeks;
- bone grafting is often necessary to achieve union;
- arthrodesis options:
-
ankle arthrodesis
-
Blair fusion:
-
sub talar fusion
-
triple arthrodesis
The Talar Body Prosthesis.
T. Harnroongroj MD and V. Vanadurongwan MD.
JBJS Vol 79-A. No 9. Sep 1987. p 1313.
Aseptic necrosis of the talus following injury.
HD Morris.
Orthop Clinics of North America.
Vol 5. 1974. p 177-189.
Magnetic resonance imaging to detect avascular necrosis after open reduction and internal fixation of talar neck fractures.
Arthrodesis for the treatment of arthrosis of the ankle and osteonecrosis of the talus.
HB Kitaoka MD and GL Patzer RN.
JBJS Vol 80-A. No 3. March 1988.
Atraumatic osteonecrosis of the talus.
RE Delanois et al.
JBJS Vol 80-A. No 4. Apr. 1988. p 529.
Avascular necrosis of the talus treated by core decompression.
MA Mont et al.
JBJS. Vol 78-B (5) 1996. p 827-830.
Functional outcome after modified Blair tibiotalar arthrodesis for talar osteonecrosis.
