1. Partial Trapeziectomy with Local Capsular Interposition vs
Partial Trapeziectomy with Local Capsular Interposition vs. Total Trapeziectomy: A Cadaveric Biomechanical Study
Deana Mercer, Christina Salas, Moheb Moneim
Proceedings of the 1st ITOW
Newport, RI

2. Disclosure
None

3. Thumb carpometacarpal (CMC) joint osteoarthritis (OA)
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 complete trapeziectomy

4. Complications of complete trapeziectomy
Metacarpal collapse
abutment against trapezoid, scaphoid
Thumb shortening
loss of function
loss of strength
Recurrence of pain
MCP Joint hyperextension
Is it possible to achieve pain relief with IMPROVED function by maintaining thumb length?

5. Purpose
To biomechanically evaluate a proposed treatment of thumb basal joint arthritis with three components
Partial trapezium resection
Partial metacarpal base resection
Local capsular interposition
Maintains more length?
We took our questions to the lab

6. Methods
In a cadaveric hand model utilizing 9 matched pairs, we compared thumb metacarpal to scaphoid distance on x-ray after
partial resection of the trapezium and base of the first metacarpal with capsular interposition (PTCI)
and after complete resection of the trapezium with capsular interposition (TTCI)

7. Methods
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

8. Methods
Opponens pollicus, Flexor pollicus brevis and Adductor pollicus (3kg)
Abductor pollicus longus (2.5 kg)
Tendons tagged per Cooney/Chao theoretical analysis JHS
Flexor pollicus longus (2.5 kg)
Abductor pollicus brevis (1.5 kg)

9. Methods Native joint data collected for all hands
provides a baseline measure of thumb length
thumb in a loaded and unloaded position
Surgical procedure
PTCI vs. TTCI
3 readers
independently measured
distances from x-ray images
(3 readings/load-unload
cycle)
TTCI PTCI

10. TTCI: unloaded vs. loaded images

11. PTCI: unloaded vs. loaded images

12. Highly Accurate Measurement Tool Developed
Hough Transform Mathematical Model
Uses an object of known dimensions in images to covert pixels to mm (0.1mm accuracy)

13. Results: Mean metacarpal to scaphoid distance under applied load
PTCI
N=9
TTCI
Native Joint /- SD (mm)
25.6 ± 3.3
23.1 ± 3.4
After Procedure /- SD (mm)
21.3 ± 2.7
15.4 ± 2.5
Difference/SD
4.3 ± 3.3
7.8 ± 3.1
% Reduction
17%
34%
P-value
0.05
Nice catch that I switched the “difference” numbers

14. Results: Inter-rater reliability
We found no main effect or interaction between reviewers (p=0.98) or between trials (p=0.90).
Bland-Altman charts plot the difference between each reader for every data point measured. For instance, in the Reader 1 vs 2 chart above the far left point shows that the measurement taken by reader 1 was only different than the measurement taken by reader 2 by less than 0.2mm. Any data points lying on zero mean that there is no difference. If it lies below zero then reader 2 had a measurement greater than reader 1. It seems that no measurement differences were greater than 1mm attesting to the accuracy of the measurement tool.

15. Conclusion
We showed that the thumb shortens less after the PTCI(~4mm) procedure when compared to the TTCI (~8mm) procedure.
Thumb shortening after surgery for thumb CMC OA has been correlated with decreased ability to pinch and grip.
PTCI is a viable alternative to TTCI as treatment for thumb CMC OA

16. Limitations
Cadaveric study
Simulated loading of the thumb CMC joint

17. Thank You