Analysis of Trapeziometacarpal Joint Mechanics During Spanning and Nonspanning Fixation for Thumb Metacarpal Distraction Lengthening

Abstract

Background: Thumb trapeziometacarpal joint (TMj) contact area, pressures, and stability were quantified during metacarpal osteotomy and distraction lengthening with and without TMj-spanning fixation in a cadaver model. Spanning fixation was hypothesized to decrease TMj contact pressure, contact area, joint space narrowing, and subluxation compared with metacarpal fixation alone.

Methods: Twenty matched-paired cadaver specimens underwent ligament-sparing thumb TMj dissection. A metacarpal external fixator was applied with and without a TMj-spanning component in 2 groups: spanning and nonspanning. A diaphyseal osteotomy was performed. The TMj contact pressure and area were recorded with an intraarticular sensor at baseline and at distraction intervals of 10, 20, 30, and 35 mm. The number of overloaded sensor cells (sensels), (>2000 psi) were recorded. The TMj subluxation and joint space width were assessed at all intervals with lateral thumb radiographs. Statistical analysis used paired 2-tailed t tests to account for inherent specimen characteristics.

Results: Group 1 (TMj-spanning) exhibited a nonstatistically significant reduction in contact area and demonstrated fewer overloaded sensels. There was significantly less joint space narrowing and joint subluxation from 10 to 30 mm of distraction compared with group 2 (nonspanning).

Conclusions: The TMj spanning fixation during metacarpal distraction decreased joint space narrowing and TMj subluxation. Despite finding reduced contact area and fewer overloaded sensels in group 1, these parameters did not reach statistical significance. Spanning TMj fixation may mitigate TMj instability during metacarpal distraction osteogenesis.

Keywords: carpometacarpal; distraction lengthening; osteotomy; pressure sensors; thumb amputation; thumb metacarpal.

Figure 1.

Cadaver specimens: (a) trapeziometacarpal joint spanning external fixation—group 1; (b) nonspanning external fixation—group 2 with metacarpal osteotomy and a sensor (S) placed in the joint. Note. Sets of pins #1 and #2 are in the metacarpal, whereas set of pins #3 are in the trapezium.

Figure 2.

Pressure mapping reading sample of a trapeziometacarpal joint during distraction. On the right, the scale bar represents the gradient pressure from the lowest (eg, blue) to the highest (eg, red). Pink represents overloaded sensels.

Figure 3.

Radiographic lateral profile views. (a and b) A sample specimen from the spanning group without and with distraction, respectively. (c and d) A sample specimen from the nonspanning group without and with distraction, respectively. Note. Measurements outlined in boxes were used for joint subluxation calculations.

Figure 4.

Flowchart showing methodology and testing mechanical results of both groups. Note. TMj = trapeziometacarpal joint; AOL = anterior oblique ligament.