Overtightening of the syndesmosis revisited and the effect of syndesmotic malreduction on ankle dorsiflexion

BACKGROUND

Ankle syndesmotic injuries are a significant source of morbidity and require anatomic reduction to optimize outcomes. Although a previous study concluded that maximal dorsiflexion during syndesmotic fixation was not required, methodologic weaknesses existed and several studies have demonstrated improved ankle dorsiflexion after removal of syndesmotic screws. The purposes of the current investigation are: (1) To assess the effect of compressive syndesmotic screw fixation on ankle dorsiflexion utilizing a controlled load and instrumentation allowing for precise measurement of motion. (2) To assess the effect of anterior & posterior syndesmotic malreduction after compressive syndesmotic screw fixation on ankle dorsiflexion.

MATERIAL AND METHODS

Fifteen lower limb cadaveric leg specimens were utilized for the study. Ankle dorsiflexion was measured utilizing a precise micro-sensor system after application of a consistent load in the (1) intact state, (2) after compression fixation with a syndesmotic screw and (3) after anterior & (4) posterior malreduction of the syndesmosis.

RESULTS

Following screw compression of the nondisplaced syndesmosis, dorsiflexion ROM was 99.7±0.87% (mean±standard error) of baseline ankle ROM. Anterior and posterior malreduction of the syndesmosis resulted in dorsiflexion ROM that was 99.1±1.75% and 98.6±1.56% of baseline ankle ROM, respectively. One-way ANOVA was performed showing no statistical significance between groups (p-value=0.88). Two-way ANOVA comparing the groups with respect to both the reduction condition (intact, anatomic reduction, anterior displacement, posterior displacement) and the displacement order (anterior first, posterior first) did not demonstrate a statistically significant effect (p-value=0.99).

CONCLUSION

Maximal dorsiflexion of the ankle is not required prior to syndesmotic fixation as no loss of motion was seen with compressive fixation in our cadaver model. Anterior or posterior syndesmotic malreduction following syndesmotic screw fixation had no effect on ankle dorsiflexion. Poor patient outcomes after syndesmotic malreduction may be due to other factors and not loss of dorsiflexion motion.

LEVEL OF EVIDENCE

IV.

Achieving fixation in glenoids with superior wear using reverse shoulder arthroplasty

BACKGROUND

Superior glenoid wear is a common challenge with reverse shoulder arthroplasty and, if left uncorrected, can result in superior glenoid tilt, which increases the risk of aseptic glenoid loosening. This study evaluates the impact of an E2 superior defect on reverse shoulder glenoid fixation in composite scapulae after correction of glenoid tilt by use of 2 different glenoid reaming techniques: eccentric reaming and off-axis reaming.

MATERIALS AND METHODS

A superior glenoid defect was created in 14 composite scapulae. The superior defect was corrected by 2 different glenoid reaming techniques: (1) eccentric reaming with implantation of a standard glenoid baseplate and (2) off-axis reaming with implantation of a superior-augment glenoid baseplate. Each corrected superior-defect scapula was then cyclically loaded (along with a control group consisting of 7 non-worn scapulae) for 10,000 cycles at 750 N; glenoid baseplate displacement was measured for each group to quantify fixation before and after cyclic loading.

RESULTS

Regardless of the glenoid reaming technique or the glenoid baseplate type, each standard and superior-augment glenoid baseplate remained well fixed in this superior-defect model scenario after cyclic loading. No differences in baseplate displacement were observed either before or after cyclic loading between groups.

DISCUSSION

Our results suggest that either glenoid reaming technique may be used to achieve fixation in the clinically challenging situation of superior wear with reverse shoulder arthroplasty.

LEVEL OF EVIDENCE

Basic science, biomechanical study.

The effect of stem surface treatment and material on pistoning of ulnar components in linked cemented elbow prostheses

BACKGROUND

The ulnar component of a total elbow replacement can fail by "pistoning." Stem surface treatments have improved stability at the stem-cement interface but with varied success. This study investigated the role of surface treatment and stem substrate material on implant stability under axial loading.

MATERIALS AND METHODS

Sixty circular stems (diameter, 8 mm) made of cobalt chrome (n = 30) or titanium (n = 30) had different surfaces: smooth, sintered beads, and plasma spray. The surface treatment length was either 10 mm or 20 mm. Stems were potted in bone cement, allowed to cure for 24 hours, and tested in a materials testing machine under a compressive staircase loading protocol. Failure was defined as 2 mm of push-out or completion of the protocol. Two-way analyses of variance compared the effects of surface treatment and substrate material on interface strength and motion.

RESULTS

Significant interactions were found between surface treatment and substrate material for both interface strength and motion (P < .05). For titanium, the 20-mm beaded stems had greater interface strength than all other stems (P < .05) and had less motion than the 10-mm plasma-spray and smooth stems (P < .05). For cobalt chrome, the 20-mm beaded stems showed greater interface strength (P < .05) and similar motion (P > .05) to the 20-mm plasma-spray stems (P < .05), which outperformed all other stems (P < .05). Mechanisms of catastrophic failure varied: smooth stems debonded at the stem-cement interface, beaded stems experienced debonding of the beads from the stem, and plasma-spray stems showed loss of frictional force between the surface treatment and cement.

DISCUSSION AND CONCLUSION

Stem surface treatment can enhance ulnar component stability but is dependent on substrate material.