1. Orthopaedic Research Society 2013 Annual Meeting
Biomechanical Study Investigating Partial Trapeziectomy with Local Soft Tissue Interposition as Potential Treatment for Trapeziometacarpal Osteoarthritis
Deana Mercer, MD
Christina Salas, MS
Mahmoud Reda Taha, PhD
Moheb Moneim, MD
Orthopaedic Research Society 2013 Annual Meeting
San Antonio, TX

2. Thumb carpometacarpal (CMC) joint osteoarthritis (OA)
Base of the first metacarpal and the distal aspect of the trapezium
Affects 25% of people over 45 y/o; 6:1 F predominance
Leads to pain and functional loss of the hand
Most common procedure worldwide is trapeziectomy

3. Complications of complete trapeziectomy
Carpal collapse
abutment against trapezoid, scaphoid
Limb shortening
loss of function
loss of strength
Recurrence of pain
Joint hyperextension
Is it possible to achieve pain relief
with IMPROVED function?

4. Partial trapeziectomy with local soft tissue interposition
A new surgical procedure with the goals of:
↓morbidity from the surgical procedure
↓ pain
↑ thumb function
Characterized by:
partial removal (2mm) of the trapezium
partial removal (2mm) of base of first metacarpal
local capsular interposition

5. Biomechanical study Specific Aim:
In a cadaveric hand model utilizing 9 matched pairs, we compared thumb metacarpal to scaphoid distance after
partial resection of the trapezium and base of the first metacarpal (PTR)
and after complete resection of the trapezium (TR)
Hypothesis:
We hypothesized that thumb shortening after PTR is less than the amount of thumb shortening after TR

6. Measurement references
K-wires were placed in the first metacarpal and scaphoid as points of measurement reference
A calibration marker of known size was placed in the x-ray field

7. Lateral pinch loading
Abductor pollicis brevis (1.5 kg)
Opponens pollicus, Flexor pollicus brevis and Adductor pollicus (3kg)
Abductor pollicus longus (2.5 kg)
Flexor pollicus longus (2.5 kg)

8. Native joint data collected for all hands
provides a baseline measure of thumb length
thumb in a loaded and unloaded position
Surgical
procedure
partial vs. total
TR PTR

9. TR: unloaded vs. loaded images

10. PTR: unloaded vs. loaded images

11. In-house measurement tool developed
Hough Transform Mathematical Model
Object of known dimensions used to covert pixels to mm (0.1mm accuracy)
3 readers independently measured across 3 trials for each hand (648 total)

12. Partial trapezium resection Total Trapezium Resection
Inter-rater Reliability of Metacarpal to Scaphoid Distance (Three-way ANOVA)
Reviewer 1
Reviewer 2
Reviewer 3
p-value
Partial trapezium resection
Native +/- SD(mm)
0.9±0.9
0.7±0.8
0.9±0.8
0.92
PTR+/- SD(mm)
2.3±1.8
2.4±1.8
2.6±1.8
0.96
Total Trapezium Resection
Native+/- SD(mm)
0.6±0.9
0.6±0.8
0.98
TR+/- SD(mm)
4.5±1.6
4.5±1.7
4.4±1.7
0.88

13. TR vs. PTR Metacarpal to Scaphoid Distance (Paired t-test)
Partial Resection;
N=9
Total Resection;
p-value
t-test
Native Joint /- SD (mm)
0.8±0.8
0.6±0.8
0.65
After Procedure /- SD (mm)
2.4±1.8
4.4 ±1.7
0.03

14. Conclusion
Thumb shortening after surgery for thumb CMC arthritis has been correlated with decreased ability to pinch and grip.
We showed that the thumb shortens less after the PTR(~2mm) procedure when compared to the TR (~4mm) procedure.
These findings support further clinical work with PTR; specifically to measure pain relief, function and shortening in RCT of 40 patients at 1 yr f/u