Basic Science
The effects of arm elevation on the 3-dimensional acromiohumeral distance: a biplane fluoroscopy study with normative data

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Hypothesis and background

Narrowing of the subacromial space has been implicated in several shoulder pathologies. However, the location of the minimum distance points during clinical testing has not been defined. We sought to measure the in vivo minimum distance and location of the minimum distance points on the acromion and proximal humerus during arm elevation.

Methods

Eight healthy male subjects (mean age, 30 years) underwent a dynamic in vivo biplane fluoroscopy assessment of scaption and forward elevation. For each frame, the 3-dimensional position and orientation of the humerus and scapula were determined, and the acromiohumeral distance (AHD) was measured as the shortest distance between the acromion and proximal humerus.

Results

The minimum AHD was 2.6 ± 0.8 mm during scaption and 1.8 ± 1.2 mm during forward flexion at elevation angles of 83° ± 13° and 97° ± 23°, respectively. The minimum distance point was located on the articular surface of the humeral head from the neutral arm position until 34° ± 8° for scaption and 36° ± 6° for forward flexion. Upon further elevation, the minimum distance point was located within the footprint of the supraspinatus muscle until 72° ± 12° for scaption and 65° ± 8° for forward flexion. At greater elevation angles, the minimum distance points were between the acromion and the proximal humeral shaft, distal from the greater tuberosity.

Conclusions

The shortest AHD was at approximately 90° of arm elevation. The AHD was no longer measured intra-articularly or within the supraspinatus footprint above approximately 70° of arm elevation.

Section snippets

Subjects

For this descriptive laboratory study, 8 healthy male subjects (mean age, 30 ± 7 years; mean height, 1.84 ± 0.05 m; mean weight, 90 ± 9 kg) were recruited. Before participation, all participants signed an informed consent form. Four right shoulders (all dominant side) and four left shoulders (one dominant and three nondominant) were used for analysis. To rule out shoulder pathology, a medical history was taken and full clinical examination of the shoulders was performed. The data collection

Results

The mean AHD as a function of arm elevation angle for the 2 exercises is shown in Figure 2. The AHD was significantly affected by the plane of elevation (P = .009) and by the elevation angle and decreased with arm elevation until a minimum occurred, after which the AHD increased (P < .0001). This pattern was consistent among the subjects and exercises. The AHD was significantly higher for scaption compared with forward flexion for arm elevation angles of 120° and 130°. The minimum AHD measured

Discussion

We found that the minimum AHD occurred at approximately 90° of arm elevation with minimum distance points at the undersurface of the acromion and the proximal humeral shaft. The minimum distance point was located within the footprint of the supraspinatus on the greater tuberosity between 34° and 72° of scaption and between 36° and 65° of forward elevation. We confirmed our hypothesis that the AHD narrowed during elevation exercises and that the location of the AHD measurement between the

Conclusion

In vivo normative AHDs were measured in 8 healthy male subjects by biplane fluoroscopy during 2 arm elevation exercises to understand how arm position influenced AHD and to provide reference measures for future studies of shoulder pathology. The minimum AHD measured was 2.6 ± 0.8 mm during scaption and 1.8 ± 1.2 mm during forward flexion at elevation angles of 83° ± 13° and 97° ± 23°, respectively. In addition, the minimum distance points between the acromion and the proximal humerus were

Acknowledgment

The authors thank Robert F. LaPrade, MD, PhD, for his invaluable input to the manuscript. In addition, they thank Michael R. Torry and Kevin B. Shelburne for their assistance during the conduct of this study. Also, they thank J.D. Pault, J.P. Brunkhorst, Tyler Anstett, and Nils H. Horn for their support in the processing of the biplane fluoroscopy data. Finally, they thank Arthrex for funding the Research Fellow position at the Steadman Philippon Research Institute held by Olivier A.J. van der

Disclaimer

This research was supported in part by the Gumbo Foundation and by the Steadman Philippon Research Institute, which is a 501(c)(3) nonprofit institution supported financially by private donations and corporate support from the following entities: Smith & Nephew Endoscopy, Arthrex, Siemens Medical Solutions, OrthoRehab, ConMed Linvatec, Ossur Americas, SBi, Opedix, and Alignmed.

Peter J. Millett is a consultant for Arthrex and has stock options in Game Ready.

Olivier A.J. van der Meijden’s

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