Objective      To invent a specialized distractor for subtalar arthroscopy and observe its effectiveness and safety in vitro and in clinical practice.       Methods      Our distractor for subtalar arthroscopy was in a rectangular configuration of parallelism between the tibia-talus bones and the calcaneus. Therefore

the generated distraction force was fully perpendicular to the subtalar articular surface so as to achieve maximal distraction effect. Sixteen fresh human ankle specimens were randomly divided into 2 groups (n=8 for each group)

group A receiving traditional non-invasive distraction and group B with our designed distractor. The distraction distance at any identical distraction force was observed in the 2 groups of specimens. The safe distances of the K-wires in the distractor from the surrounding neurovascular and tendinous tissues were measured in all 16 specimens. From June 2006 to May 2008

the specialized distractor was used to treat 12 cases of subtalar diseases

including 8 cases of traumatic arthritis

2 of talar cartilage injuries and 2 of sinus tarsal syndrome. American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot scores were used to evaluate the outcome during follow-up.       Results      No difference was found between the 2 groups of ankle specimens when the distraction force was 5.2 or 10.3 N

but when the force was increased to 17.6

24.4 and 33.8 N

the distance was significantly greater in group B than group A (P0.05). The maximal distraction distance was achieved in both groups when the distraction force was increased to 41.8 N

but it was still larger in group B than group A (3.3 vs 2.2 mm

P0.01). Anatomical measurement indicated that all specimens had enough safe distances between the K wires in the distractor and the surrounding vital tissues. All the 12 patients were followed up for 15 to 35 months (mean

26.1 months). No complication was observed. At the last follow-up

there were 4 patients achieving excellent

6 good and 2 fair outcomes

with an excellent and good rate of 83.3%.       Conclusion      Our self-designed distractor specialized for subtalar arthroscopy can effectively open the subtalar joint

and thus facilitate arthroscopic manoeuvrability with higher safety and easy manipulation.