Biomechanical Evaluation of Posterior Shoulder Instability with a Clinically Relevant Posterior Bone Loss Model

Authors:

Waltz RA, Brady AW, Brown J, Bartolomei C, Dornan GJ, Miles JW, Arner JW, Millett PJ, Provencher MT

Abstract:

Background:

Existing biomechanical studies of posterior glenoid bone loss and labral pathology are limited by their use of anterior instability models, which differ in both orientation and morphology and have been performed in only a single, neutral arm position.

Purpose:

To evaluate the biomechanical effectiveness of a posterior labral repair in the setting of a clinically relevant posterior bone loss model in various at-risk arm positions.

Study design:

Controlled laboratory study.

Methods:

Ten fresh-frozen cadaveric shoulders were tested in 7 consecutive states using a 6 degrees of freedom robotic arm: (1) native, (2) posterior labral tear (6-9 o’clock), (3) posterior labral repair, (4) mean posterior glenoid bone loss (7%) with labral tear, (5) mean posterior glenoid bone loss with labral repair, (6) large posterior glenoid bone loss (28%) with labral tear, and (7) large posterior glenoid bone loss with labral repair. Bone loss was created using 3-dimensional printed computed tomography model templates. Biomechanical testing consisted of 75 N of posterior-inferior force and 75 N of compression at 60° and 90° of flexion and scaption. Posterior-inferior translation, lateral translation, and peak dislocation force were measured for each condition.

Results:

Labral repair significantly increased dislocation force independent of bone loss state between 10.1 and 14.8 N depending on arm position. Dislocation force significantly decreased between no bone loss and small bone loss (11.9-13.5 N), small bone loss and large bone loss (9.4-14.3 N), and no bone loss and large bone loss (21.2-26.5 N). Labral repair significantly decreased posterior-inferior translation compared with labral tear states by a range of 1.0 to 2.3 mm. In the native state, the shoulder was most unstable in 60° of scaption, with 29.9 ± 6.1-mm posterior-inferior translation.

Conclusion:

Posterior labral repair improved stability of the glenohumeral joint, and even in smaller to medium amounts of posterior glenoid bone loss the glenohumeral stability was maintained with labral repair in this cadaveric model. However, a labral repair with large bone loss could not improve stability to the native state.

Clinical relevance:

This study shows that larger amounts of posterior glenoid bone loss (>25%) may require bony augmentation for adequate stability.

You may request the complete study: Biomechanical Evaluation of Posterior Shoulder Instability with a Clinically Relevant Posterior Bone Loss Model

Peter Millett, MD

Average rating:

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!!!