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Year |
2005 |
|---|---|
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Question Number |
95. |
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Category |
Musculoskeletal Trauma |
Question
In a type III Hawkins talar neck fracture, the only remaining blood supply to the talar body may be provided by the
1- dorsalis pedis artery.
2- deltoid branch of the posterior tibial artery.
3- perforating peroneal artery.
4- artery of the tarsal sinus.
5- artery of the tarsal canal.
Figures
Answer (click for answer)
PREFERRED RESPONSE: 2
For this question you need to know the Hawkins classification (pretty easy to remember) and the blood supply to the talus (not so easy to remember.) Hawkins classification:
I-nondisplaced
II-displaced with subluxation or dislocation of the subtalar joint
III- subluxation or dislocation of the subtalar AND ankle joints (the talar body may be "spit out" of the joint)
IV-subluxation or dislocation of the subtalar AND ankle AND talonavicular joints (all pieces of the talus may be disarticulated) (note type IV was not originally described by Hawkins but was an addendum by Canale and Kelly)
TTalar Blood Supply
The talus is 60% covered by cartilage, leaving only 40% of the surface accessible to vascular supply. 3 Main sources of inflow (Posterior tibial artery, Dorsalis Pedis artery, and perforating peroneal artery) and their branches form an anastamosing network of vessels that feed the talus.
1. Posterior tibial artery: Comes in from posteromedial ankle. At the most medial aspect of the talus, it forms 2 terminal branches: The deltoid branch, which passes superomedially through the deltoid ligament and supplies the medial 1/3rd of the talar body, and the artery of the tarsal canal which passes inferomedially, forms and anastamotic sling with the artery of the tarsal sinus, and supplies most of the talar body.
2. DP artery: Continuation of anterior tibial artery at the ankle. Passes anteriorly and feeds the head and neck of the talus
3. Perforation peroneal artery: Comes in from anteromedially and one of its terminal branches- the artery of the sinus tarsi, passes posteriorly and forms an anastamotic sling under the talar neck with the artery of the tarsal canal. The artery of the sinus tarsi feeds the head and neck along with the DP artery.
With Type III talar neck fractures, branches from dorsalis pedis artery, artery to tarsal canal, and artery to tarsal sinus are ruptured. The only remaining blood supply to the talar body is the deltoid artery, thus care must be taken with medial dissection in surgical treatment.
Although this may seem like a random fact that you either know or more likely didn’t know, one can arrive at the correct answer if you know the anatomy. The question asks the remaining blood supply to the talar body. This eliminates the DP artery, perforation peroneal artery, and artery of the tarsal sinus, none of which are major sources for the body. Of the remaining 2 that supply the body. It would make sense that small perforating branches of the artery of the tarsal canal would be less likely to survive a Subtalar + Tibiotalar subluxation/dislocation than the deltoid artery. It would also make anatomic sense that if a talonavicular dislocation is thrown in (Hawkins IV), the deltoid artery small perforating branches would also become disrupted, leading to a 100% rate of talus AVN.
Reference: RECOMMENDED READINGS: Richardson EG (ed): Orthopaedic Knowledge Update: Foot and Ankle 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2004, pp 35-46.
Sarrafian SK: Anatomy of the Foot and Ankle: Descriptive, Topographic, Functional. Philadelphia, PA, JB Lippincott, 1983.
Fortin PT, Balazsy JE: Talus fractures: Evaluation and treatment. J Am Acad Orthop Surg 2001;9:114-127.