Low inter-observer agreement among experienced shoulder surgeons assessing overstuffing of glenohumeral resurfacing hemiarthroplasty based on plain radiographs

Extra-short humeral heads reduce glenohumeral joint overstuffing compared with short heads in anatomic total shoulder arthroplasty

Background

Rotator cuff tears and glenoid loosening remain the two most common causes for revision after anatomic total shoulder arthroplasty. Oversizing of the humeral head leads to increased contact force across the glenohumeral joint and is hypothesized to contribute to clinical and radiographic failure. The purpose of this study is to compare the rate of radiographic overstuffing between standard short humeral heads and newer extra-short heads with decreased lateral offset.

Methods

Fifty-five consecutive anatomic total shoulder arthroplasties performed using extra-short humeral heads were retrospectively reviewed and compared with age- and sex-matched controls receiving standard short heads. A total of 110 postoperative radiographs were analyzed using the Iannotti's perfect circle method to compare the prosthesis' center of rotation (COR) with the native humeral head COR. A difference in the COR of >3.0 mm was considered malpositioned. Malpositioning medially was considered overstuffed, and malpositioning laterally was considered understuffed. The direction of displacement of malpositioned prostheses was categorized using a quadrant system. Furthermore, we used a novel method to evaluate medial and superior overstuffing by measuring the displacement between the anatomic and prosthetic head positions along perpendicular axes.

Results

Using the Iannotti's perfect circle method, 56% of heads were malpositioned. Overstuffing occurred more frequently with short heads compared with extra-short heads (47% vs. 4%, P < .001). Conversely, understuffing occurred more frequently with extra-short heads (47% vs. 15%, P = .001). Malpositioned extra-short heads were most frequently placed in the inferomedial quadrant (93% vs. 24%, P < .001), whereas malpositioned short heads were most commonly placed in the superomedial quadrant (56% vs. 7%, P < .001). Our novel measurement method demonstrated that extra-short heads reduced medial overstuffing (2.8 ± 2.8 mm vs. 0.3 ± 2.0 mm, P < .001). Both extra-short and short heads had similar rates of superior malpositioning (1.6 ± 2.2 mm vs. 1.4 ± 1.5 mm, P = .683).

Conclusion

Routine use of extra-short humeral head sizes reduces the rate of medial glenohumeral joint overstuffing but not superior malpositioning. This is hypothesized to improve clinical outcomes, but future studies are needed to assess the relationship between improved humeral head fit and clinical outcomes.

Promising results after hemi-shoulder arthroplasty using pyrolytic carbon heads in young and middle-aged patients

INTRODUCTION

The objective of this prospective cohort study was the assessment of short-term outcome results of shoulder hemiarthroplasty (HA) using pyrolytic carbon (PC) heads. PC has been introduced as a new material to avoid surgical revision due to glenoid erosion after HA. Glenoid erosion due to the use of metallic heads is known to reduce durability.

HYPOTHESIS

HA using PC heads shows comparable or better radiographic and clinical outcome compared to the conventional HA using metallic heads in the short-term.

PATIENTS AND METHODS

This study was conducted as a single center prospective cohort follow-up study including a total number of 16 consecutive HA with PC heads. Inclusion criteria were indication for HA, an intact rotator cuff, no proximal humeral fractures in patient's history and age>18years. Mean age at the time of arthroplasty was 52.8±10.8years. The mean follow-up was 24.3±8.1months. Baseline and follow-up Numeric Rating Scale (NRS), Constant Scores (CS), Range of Motion (ROM) and radiographs were assessed.

RESULTS

At a mean follow-up of 24.3months the mean CS (p<0.001), mean NRS (p<0.001) and mean ROM (p<0.05) improved statistically significant. Subgroup analysis revealed no differences between subgroups (sex, age, diagnosis, and handedness). Survival rate was high (94.1%). One periprosthetic fracture occurred as the only complication during follow-up. Radiographs showed glenoid erosion in one case and subacromial space reduction in two cases.

DISCUSSION

PC heads in HA show satisfying short-term results at a mean follow-up of two years, which are comparable to those of conventional HA. The clinical improvements were highly significant with good implant survival. However, long-term follow-up results are necessary, especially compared to conventional HA.

LEVEL OF EVIDENCE

IV; observational therapeutic cohort study.