Correction to: Qualitative and quantitative analysis of glenoid bone stock and glenoid version: inter-reader analysis and correlation with rotator cuff tendinopathy and atrophy in patients with shoulder osteoarthritis

Validation of a novel 3-dimensional classification for degenerative arthritis of the shoulder

INTRODUCTION

A novel three-dimensional classification to comprehensively describe degenerative arthritis of the shoulder (DAS) was recently published by our group. The purpose of the present work was to investigate intra- and interobserver agreement as well as validity for the three-dimensional classification.

MATERIALS AND METHODS

Preoperative computed tomography (CT) scans of 100 patients who had undergone shoulder arthroplasty for DAS were randomly selected. Four observers independently classified the CT scans twice, with an interval of 4 weeks, after prior three-dimensional reconstruction of the scapula plane using a clinical image viewing software. Shoulders were classified according to biplanar humeroscapular alignment as posterior, centered or anterior (> 20% posterior, centered, > 5% anterior subluxation of humeral head radius) and superior, centered or inferior (> 5% inferior, centered, > 20% superior subluxation of humeral head radius). Glenoid erosion was graded 1-3. Gold-standard values based on precise measurements from the primary study were used for validity calculations. Observers timed themselves during classification. Cohen's weighted κ was employed for agreement analysis.

RESULTS

Intraobserver agreement was substantial (κ = 0.71). Interobserver agreement was moderate with a mean κ of 0.46. When the additional descriptors extra-posterior and extra-superior were included, agreement did not change substantially (κ = 0.44). When agreement for biplanar alignment alone was analyzed, κ was 0.55. The validity analysis reached moderate agreement (κ = 0.48). Observers took on average 2 min and 47 s (range 45 s to 4 min and 1 s) per CT for classification.

CONCLUSIONS

The three-dimensional classification for DAS is valid. Despite being more comprehensive, the classification shows intra- and interobserver agreement comparable to previously established classifications for DAS. Being quantifiable, this has potential for improvement with automated algorithm-based software analysis in the future. The classification can be applied in under 5 min and thus can be used in clinical practice.

A 3-Dimensional Classification for Degenerative Glenohumeral Arthritis Based on Humeroscapular Alignment

Background

Seminal classifications of degenerative arthritis of the shoulder (DAS) describe either cuff tear arthropathy in the coronal plane or primary osteoarthritis in the cross-sectional plane. None consider a biplanar eccentricity.

Purpose/Hypothesis

The purpose of this study was to investigate humeroscapular alignment (HSA) of patients with DAS in both the anteroposterior (A-P) and superoinferior (S-I) planes on computed tomography (CT) after 3-dimensional (3D) reconstruction and develop a classification based on biplanar HSA in 9 quadrants. It was hypothesized that biplanar eccentricity would occur frequently.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

The authors analyzed 130 CT scans of patients who had undergone shoulder arthroplasty. The glenoid center, trigonum, and inferior angle of the scapula were aligned in a single plane using 3D reconstruction software. Subluxation of the HSA was measured as the distance from the center of rotation of the humeral head to the scapular axis (line from trigonum through glenoid center) and was expressed as a percentage of the radius of the humeral head in both the A-P and the S-I directions. HSA was described in terms of A-P alignment first (posterior/central/anterior), then S-I alignment (superior/central/inferior), for a total of 9 different alignment combinations. Additionally, glenoid erosion was graded 1-3.

Results

Subluxation of the HSA was 74.1% posterior to 23.5% anterior in the A-P direction and 17.2% inferior to 68.6% superior in the S-I direction. A central HSA was calculated as between 20% posterior to 5% anterior (A-P) and 5% inferior to 20% superior (S-I), after a graphical analysis. Posterior subluxation >60% of the radius was labeled as extraposterior, and static acetabularization was labeled as extrasuperior. Overall, 21 patients had central-central, 40 centrosuperior, and 1 centroinferior alignment. Of 60 shoulders with posterior subluxation, alignment was posterocentral in 31, posterosuperior in 25, and posteroinferior in 5. There were 3 patients with anterocentral and 4 anterosuperior subluxation; in addition, 4 cases with extraposterior and 17 with extrasuperior subluxation were identified.

Conclusion

There was a high prevalence of biplanar eccentricity in DAS. The 3D classification system using combined HSA and glenoid erosion can be applied to describe DAS comprehensively.