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

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

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?

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

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

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

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)

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

TR: unloaded vs. loaded images

PTR: unloaded vs. loaded images

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)

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

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

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