1. Radiographic Prevalence of Concomitant Scaphotrapezial Arthritis with Thumb Carpometacarpal Arthritis (Abstract # 8192)
Deana Mercer, MD; Charlotte Orr, MD; Drew Newhoff, MD; Matthew Martin, MD; Christina Salas, PhD; Moheb Moneim, MD

2. Disclosure
The authors have nothing to disclose

3. Introduction
Eaton classification is commonly used to describe thumb carpometacarpal (CMC) osteoarthritis (OA)
Eaton Stage IV classification includes arthritis of the scaphotrapezial joint (ST)
Brown et al. (2003) dissected the ST joint and found ST arthritic involvement in 60% of 69 cadaveric specimens with thumb CMC OA, but only 39% of those specimens exhibited radiographic evidence of ST arthritis
Using the Eaton classification in a retrospective radiographic review, we seek to identify whether level of training affects the designation of Eaton stage by the reviewer

4. Introduction We hypothesize that
Classifications by senior reviewers will be different than classifications by junior reviewers
Classification of Eaton Stage IV arthritis will occur in less than 25% of reviewed images using standard hand radiographic views
Current radiographic views may not be adequate to clearly assess the ST joint

5. Methods
Between September 2005 and July 2012, 417 patients underwent joint arthroplasty for thumb CMC OA at our institution
Exclusion criteria were prior thumb CMC or ST joint surgery
194 patients were eligible
24 of 194 had bilateral surgery yielding 218 sets of radiographs
A hand fellowship trained attending (R1), a hand fellow (R2), a chief resident (R3), and a junior resident (R4) reviewed radiographs independently and staged them according to Eaton classification
Each reviewer read all of the images two different times
We calculated intra- and inter-observer reliability

6. Results Intra-observer reliability was rated “good”
Inter-observer reliability was rated “fair”

7. Results
Senior reviewers (R1 and R2) tended to grade lower (average 2.8 and 3, respectively) than junior reviewers (R3 and R4; average 3.1 and 3.2, respectively)
These differences were not statistically significant
47 of 218 (22%) radiographs demonstrated an average Eaton classification Stage IV from all reviewers
14 of 218 (7%) radiographs were unanimously observed as having Stage IV osteoarthritis

8. Discussion
Previous research has found that radiographic classification may be insufficient to accurately diagnose ST involvement
If the ST joint is arthritic and this is not recognized, pain level may not improve after CMC surgery
Senior surgeons graded Eaton Stage lower than junior surgeons but this was not significantly different. Unanimous Stage IV grade using standard radiographic views was under 10%

9. Summary Points
In the present study, utilizing standard plain radiographs, we show a low incidence of concomitant ST arthritis with thumb CMC arthritis (mean 21.6%; unanimous classification 6.4%)
Inter-observer reliability was “fair”, indicating the high possibility for varied assessment of the ST joint using these views
Senior reviewers assigned lower Eaton stages, but this was not significantly different than junior reviewers
The differences in Eaton grade classification may be due to lack of appropriate imaging allowing one to accurately assess the ST joint
There may be a need for an improved radiographic angle to appropriately assess the ST joint