Implant characteristics affect in vivo shoulder kinematics during multiplanar functional motions after reverse shoulder arthroplasty

Abstract

The purpose of this study was to determine how implant characteristics affect in vivo shoulder kinematics after reverse shoulder arthroplasty (RSA). Kinematics of the affected upper limb were measured in 32 participants during five motions (scapular plane abduction, hand-to-head, hand-to-back, internal/external rotation at 90° abduction, and circumduction) using optical motion capture. Shoulder abduction, plane of elevation, and internal/external rotation range of motion (ROM), peak angles, and continuous kinematics waveforms were calculated for each motion. Multiple regression was used to identify associations between kinematics and implant characteristics of lateralization, humeral retroversion, glenosphere size, glenosphere tilt, glenoid eccentricity, and implant neck-shaft angle (135° or 145°). Less humeral retroversion was associated with greater shoulder rotation ROM (p = 0.036) and greater plane of elevation ROM (p = 0.024) during circumduction, while less eccentricity was associated with more posterior plane of elevation during hand-to-back (p = 0.021). The 145° implant was associated with greater internal/external shoulder rotation ROM (p < 0.001), greater internal shoulder rotation (p = 0.002), and greater plane of elevation ROM (p = 001) during the hand-to-back. The 145° implant was also associated with more internal/external rotation ROM (p = 0.043) during shoulder rotation and more abduction ROM during circumduction (p = 0.043). During the hand-to-back motion, individuals having 135° neck-shaft angle implants were more abducted from 21 to 51% of the motion and were less internally rotated from 70 to 100% of the motion, while more lateralization was associated with less internal rotation from 90 to 100% of the motion. Retroversion and implant neck-shaft angle are the primary implant characteristics associated with in vivo shoulder kinematics during complex motions after RSA.

Keywords: RSA; Reverse shoulder arthroplasty; Shoulder; Shoulder kinematics.

Figure 1.

Marker location for right RSA subjects. Markers 5 and 7–12 on left arm for left RSA subjects. (B) Schematic for dynamic motions of abduction/adduction, hand-to-head, hand-to-back, shoulder internal/external rotation, and circumduction. (C) Schematic for calculated shoulder components of rotation for abduction/adduction, plane of elevation, and internal/external shoulder rotation.

Figure 2.

Continuous kinematics during scapular plane abduction. Motion cycle of 50% indicates maximum point of elevation above the participant’s head. Dark solid line is the group mean, the shaded region is ±1 standard deviation. Thin lines represent kinematics curves for each individual.

Figure 3.

Continuous kinematics plots for hand-to-head. Motion cycle of 100% indicates point where participant’s hand is behind their head. Dark solid line is the group mean, the shaded region is ±1 standard deviation. Thin lines represent kinematics curves for each individual.

Figure 4.

Continuous kinematics for hand-to-back. Motion cycle of 100% indicates point where participant’s hand is rested behind their back. Dark solid line is the group mean, the shaded region is ±1 standard deviation. Thin lines represent kinematics curves for each individual.

Figure 5.

Continuous kinematics for internal/external shoulder rotation. Motion cycle of 50% indicates maximal external rotation and motion cycle of 100% indicates end point of motion. Dark solid line is the group mean, the shaded region is ±1 standard deviation. Thin lines represent kinematics curves for each individual.

Figure 6.

Continuous kinematics for circumduction. Motion cycle of 25% represents cross-body, 50% indicates hand above the head, 75% represents arm out on ipsilateral side of body and 100% indicates the arm returning to starting point. Dark solid line is the group mean, the shaded region is ±1 standard deviation. Thin lines represent kinematics curves for each individual.

Figure 7.

Differences in the continuous kinematic curves during (A) circumduction and (B-D) hand-to-back between neck-shaft angle (A, C-D), and lateralization (B). Solid blue and red lines indicate group means and shaded areas represent standard deviations. Portions of the movement that are significantly different are represented by the solid black line.