The relative roles of bones and muscles in joint pathologies are often difficult to tease apart. In the March 7, 2018 issue of The Journal, Donohue et al. report findings from their attempt to identify associations between preoperative fatty infiltration in rotator cuff muscles and glenoid morphology among 190 shoulders that underwent total shoulder arthroplasty (TSA) for glenohumeral osteoarthritis.
The painstaking analysis included orthogonal CT images to determine fatty infiltration, joint-line medialization assessments, direct measurements of glenoid version, and grading of glenoid morphology (from A1 through C2) using a modified Walch classification. Here’s what Donohue et al. found:
- High-grade posterior rotator cuff fatty infiltration was present in 55% of the 38 glenoids classified as B3, compared with only 8% fatty infiltration in the 39 A1-classified glenoids.
- Increasing joint-line medialization was associated with increasing fatty infiltration of all rotator cuff muscles.
- Higher fatty infiltration of the infraspinatus, teres minor, and combined posterior rotator cuff muscles was associated with increasing glenoid retroversion.
- After the authors controlled for joint-line medialization and retroversion, B3 glenoids were more likely than B2 glenoids to have fatty infiltration of the supraspinatus and infraspinatus.
The authors say these findings “support the idea that there is a causal association between rotator cuff muscle fatty infiltration and B3 glenoid morphology,” but they are quick to add that “from this study we cannot conclude [whether] these patterns of rotator cuff muscle fatty infiltration precede the progression of bone pathology, or vice versa.” Either way, these findings may inform patient-surgeon discussions about TSA, because both glenoid morphology and rotator cuff muscle quality are factors in glenoid-component longevity.
Reporting in the September 2, 2015 issue of The Journal of Bone and Joint Surgery, European researchers Moroder et al. found that 7 of 45 patients (17.5%) without substantial glenoid bone loss who underwent open Bankart repairs had a recurrence of instability during an average 22 years of follow-up.
This high failure rate is in line with findings from previous studies, but the authors include data indicating that, compared to patients who did not experience recurrent instability, “the recurrence of instability did not appear to significantly affect the subjective and objective outcome scores or the degree of work and sports impairment.”
The study found an unsurprising association between higher shoulder-specific activity levels and an increased risk for recurrence of instability. In fact, three of the seven late failures occurred during a high-energy sports accident. Etiologically, the authors hypothesize that “a lifestyle with high demands on the shoulders leads to weakening of the Bankart repair over time because of repetitive stress of the anterior capsulolabral complex.”
The number of total shoulder arthroplasties performed in the United States has increased substantially in the past decade. In fact, since 2006, more total shoulder arthroplasties have been performed than hemiarthroplasties. Because of this surge in the number of total shoulder arthroplasties being performed, various techniques have been developed to address glenoid bone loss in patients with arthritic shoulder conditions. Indeed, primary glenoid bone loss usually occurs in association with osteoarthritis and is characterized by posterior wear patterns, whereas secondary glenoid bone loss usually occurs in association with trauma, glenoid loosening, and iatrogenic injury during revision surgery.
In the July 2015 issue of JBJS Reviews, Gowda et al. review a number of important issues related to this condition, including normal glenoid anatomy, pathological changes in glenoid substance, primary glenoid bone loss, proper imaging studies for the evaluation of the glenoid, principles of glenoid restoration, and the effects of poor implant position. Other topics, such as glenoid bone-grafting, the use of augmented components, glenoid insert design, patient-specific instrumentation, and the emergence of reverse total shoulder arthroplasty as an important component of the armamentarium of the shoulder arthroplasty surgeon, are also addressed.
The authors assert that proper preoperative imaging is critical in order to ascertain glenoid characteristics, including size, version, and depth of the vault. The treatment of glenoid bone loss is dependent on the degree of version correction that is required and consists of eccentric reaming, bone or polyethylene augmentation, and, as noted above, the potential use of reverse shoulder arthroplasty.
In the future, shoulder arthroplasty research should evaluate the long-term outcomes of biomaterial-augmented glenoid components, the use of other materials (such as ceramics), the utility of fixation within the glenoid and endosteal vault, and the use of reverse-polarity implants.
Thomas A. Einhorn, MD
Editor, JBJS Reviews