Introduction: In musculoskeletal pain, injection therapy is commonly used to relieve pain. But it is not easy to insert a needle into the small joints such as finger joints exactly. And physicians do not attempt to inject finger distal interphalangeal (DIP) joints without ultrasound, because unlike other joints, it is difficult to discriminate DIP joints by touching them. The purpose of this study was to identify the exact injection point of the finger DIP joints, so we measured and evaluated the length using ultrasound by marking the distal interphalangeal crease line as a landmark.
Method: 50 subjects (male: n=23, female: n=27) were included in this study, and the average age was 54.9±17.6. Initially, we identified the distal phalangeal creases of the thumb, index, middle, ring and little fingers of each hand and marked them with clips. Then, the distance between the proximal bony border of DIP joints and distal interphalangeal creases were measured using ultrasound (figure 1) (For thumb, interphalangeal joints were used). We analyzed the radial and ulnar side of the distance in both hands. Because joint deformity such as osteophytes or deviation of joints were different from normal joints, fingers with OA were excluded in statistical analysis.
Result: The mean lengths were as follows: radial side: thumb 3.3±0.7mm, index finger 5.3±0.8mm, middle finger 4.1±0.8mm, ring finger 3.7±1.0mm, and little finger 3.6±0.9mm; ulnar side: thumb 2.6±0.9mm, index finger 4.3±0.9mm, middle finger 3.8±0.8mm, ring finger 3.9±1.1mm, and little finger 4.1±0.9mm. The longest of distance was radial side of index finger, and the shortest was ulnar side of thumb. There were no statistically significant differences between right and left hand in each side of finger (P>0.05) (figure 2). When comparing radial side and ulnar side of each finger, there were significantly different in thumb, index, middle and little fingers (P<0.05) (figure 2). The radial side of thumb, index and middle fingers were longer than the ulnar side, whereas the ulnar side of little finger was longer than the radial side. And when comparing old and young people based on age 60, there were no statistically significant differences in each side of finger (P<0.05).
Conclusion: This study evaluated the length of the distance between the finger DIP joints and distal interphalangeal creases to identify the exact location of the finger DIP joints. It may be helpful to know the average length of each fingers in the blind or ultrasound-guided injection of finger DIP joints to reduce the failure of injection therapy.
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