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

The subacromial space is important for shoulder joint function. It is confined by the acromial arch superiorly and by the humeral articular surface and greater tuberosity inferiorly. When the subacromial space is narrowed, the distance between the inferior border of the acromion and the proximal humerus, defined as the acromiohumeral distance (AHD), is shortened. The AHD has been reported to be a quantitative measurement that can be used to assess changes in the height of the subacromial space. Narrowing of the subacromial space has been linked to several shoulder pathologies, including subacromial impingement syndrome and rotator cuff disease. Abduction in the scapular plane and flexion of the shoulder joint have been reported to reduce the AHD, possibly resulting in subacromial impingement. Several anatomic variations of the acromial arch have been associated with impingement and rotator cuff disease. These include a larger lateral extension of the acromion and hooked morphology (type III) of the anterior acromion. Clinical examination of the subacromial space is important for the diagnosis of subacromial space pathologies and produces pain during forced upward elevation against the acromion. However, the structures being impinged, assuming this is causing the pain, as a function of arm elevation angle during clinical testing have not been well defined.

To better understand and treat shoulder pathology, a precise measurement of shoulder joint kinematics is required. The AHD is certainly influenced by arm position as the various structures, such as the supraspinatus tendon and footprint, rotate beneath the acromial arch. In addition to understanding how arm position affects AHD, normative values are necessary to serve as a reference when clinicians are trying to restore normal kinematics in patients with shoulder pathology, such as rotator cuff repair in patients with rotator cuff tears and subsequent superior migration of the humeral head.

Accurate and precise measurement of glenohumeral kinematics is difficult because the bones of the shoulder complex, especially the scapula, move significantly underneath the skin. Therefore, skin-based measurement techniques cannot measure shoulder joint motion with sufficient accuracy to measure AHD. A highly accurate, emerging tool to measure the in vivo 3-dimensional (3D) kinematics of a joint is biplane fluoroscopy, which eliminates this skin motion artifact by imaging the bones directly. The most accurate measurement method is roentgen stereophotogrammetry analysis, which requires the insertion of small (approximately 1.6-mm) markers inside the bone. Reported accuracies of better than 0.1 mm are possible, which make it a suitable reference method for the validation of less invasive techniques. Model- based techniques, which use bone models reconstructed from computed tomography (CT) or magnetic resonance imaging (MRI), have also been reported to have submillimeter accuracy in measurements of joint kinematics relative to marker-based techniques.

The purpose of this study was to measure the AHD in vivo during abduction in the scapular plane (scaption) and forward elevation in the sagittal plane to study how arm elevation influenced AHD by use of a biplane fluoroscopy system. Our hypothesis was that the AHD would narrow with increasing arm elevation. In addition, we hypothesized that the location of the minimum distance point on the proximal humerus from which the AHD would be measured would vary with arm position.

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

Peter Millett, MD

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39 reviews

Alexandra Thompson

Mar 23, 2024

by Alexandra Thompson on Peter Millett, MD

110%

Dr. Millett and his team did a SLAP tear repair and bicep tenodesis on my left shoulder. I use my arms as an artist, and love to swim in the ocean, surf, paddle, and telemark ski. So regaining full use of my shoulder and keeping my bicep attached was very important to me. Now, over two years later, my shoulder has the equivalent range of motion as my other arm and as before the injury, and no pain. After the first three months it felt so good and was so strong that - to my horror - I completely forgot my six-month follow-up.

Not only did Dr. Millett and his team make my arm as good as new, but having had the experience of such kindness and expertise throughout the process of surgery and recovery is like an added shoulder superpower.

Thank you Rita, Brooke, Jason, Sarah, Camille, Olivia, Dr. Millett and everyone! And see you soon when my husband comes in for his knee...

Jeff Chandler

Jan 31, 2022

by Jeff Chandler on Peter Millett, MD

Flawless procedure, Easy recovery

Dr. Millet's repaired my knee and tibia, following a botched operation by a different surgeon. That procedure was virtually pain free and I was weight bearing within a few days. That was 18 years ago and the knee is still strong. A few years after the knee incident, Dr Millet repaired my shoulder. My insurance company approved me for 3 months of disability following that surgery. I was off pain medication in 2 days and had 90% range of motion within a week. I withdrew my disability claim and returned to work within two weeks of surgery. I’m not a famous athlete—just a regular guy. Nonetheless, I was treated like an NFL at the Steadman clinic. Most notable was the time for recovery. Other surgeons perform their hour-long task in the OR and don’t involve themselves in the other functions. Peter and his team manages the entire process from diagnosis, anesthesia, nursing care, and therapy. He takes a holistic approach to patient care and doesn’t skip any steps.

Jenn West

Jul 2, 2021

by Jenn West on Peter Millett, MD

Saved My Life

I went to Dr. Millett after 7 knee surgeries (6 on my right and 1 on my left) and had seen 11 different surgeons who all refused to remove femur metal from my right leg. I am highly allergic to metal and the chronic pain was leaving me bedridden for 3.5wks out of a month. He personally wrote me back on my inquiry, listened to my concerns, scheduled my surgery within a week (due to insurance issues) and personally followed up with my recovery. The level of patient care from Dr. Millett and his ENTIRE team is above any care I have ever received in my 20 years of dealing with orthopedic surgeons. There are not enough words to describe the level of care, dedication and professionalism you receive from Dr. Millett and his staff.
My only disappointment is that I did not find him sooner!!!

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

About the Author: Peter Millett, MD