Anatomical total shoulder arthroplasty (TSA) is an effective treatment for advanced osteoarthritis (OA) of the glenohumeral joint.1-4 Over the past 40 years, since the early reports appeared, the implants have evolved from the early monoblock humeral component to modular components, variable neck angled components with eccentric heads, and components that can provide variable neck angles, version angles, and dual eccentricity to match the anatomy of the proximal humerus. The goal of the new implants is to replicate the individual patient’s native anatomy using a combination of modularity, multiple neck and version angles, and dual eccentricity of the neck and head. The flexibility of the implant system is made possible by a replicator plate. There are few reports on outcomes of using these new implants for OA.
In this article, we report outcomes of using a dual eccentric, variable neck angle, variable version angle implant with a replicator plate for the treatment of OA of the shoulder at 4 centers.
Materials and Methods
The Western Institutional Review Board approved this study, and consent was prospectively obtained and retrospectively reviewed.
The data banks of a 4-center consortium were queried. Only primary TSA patients treated for OA with a fourth-generation Exactech Equinoxe implant (Exactech, Inc.) were included. For the center to be included, it had to have an 80% patient follow-up rate at a minimum of 2 years. Four centers qualified for inclusion: University of Florida, Medical College of Georgia, New York University, and Bordeaux-Merignac Clinic. Data were obtained on surgeries sequentially performed between August 1, 2006, and December 31, 2010. All data were obtained prospectively using a common data collection format.
The Equinoxe anatomical TSA allows for independent adaptation of neck angle and humeral version and provides 2 variable offset times (1 on replicator plate, 1 on humeral head) for matching the native anatomy in more than 99% of cases5 (Figure). The replicator plate is eccentric and can be angled 7.5° in any direction and rotated 360° to provide humeral head coverage. Once its optimal position is obtained, the plate is permanently fixed to the humeral stem using a breakaway screw. Some contemporary implants have similar features.
There were 218 primary shoulder arthroplasties performed on 201 patients (98 male, 103 female). Mean age at time of surgery was 67 years (range, 31-87 years), and mean follow-up was 36 months (range, 24-72 months). The collective follow-up rate at the 3-year mean follow-up and 2-year minimal follow-up was 81%. Eleven shoulders had a cemented stem, and 207 had an uncemented stem. Forty-eight shoulders used the 1.5-mm replicator plate, and 170 used the 4.5-mm offset replicator plate. The patients in this study were typically not very healthy: mean American Society of Anesthesiologists (ASA) score was 2.57 (range, 1-3).
Five outcome scores were calculated from the prospectively obtained data: Constant normalized, Shoulder Pain and Disability Index (SPADI), Simple Shoulder Test (SST), UCLA Shoulder Rating Scale (UCLA), and American Shoulder and Elbow Surgeons Shoulder Assessment (ASES). Before initiating data collection, we developed the Metric Form6 so we could calculate multiple scores while asking the minimal possible number of questions. This could be done for all 5 outcome scores, as their questions have significant overlap.
Objective outcomes included active external rotation, active scaption, active abduction, and active internal rotation. Complications, including revisions, were noted and analyzed. We focus on functional outcomes and do not present radiographic outcomes.
Results
A 2-tailed unpaired t test was used to compare preoperative values with final outcome values (P < .05). Four objective outcomes were significantly improved over preoperative levels: active external rotation (preoperative, 15°; postoperative, 42°), active scaption (pre, 92°; post, 137°), active abduction (pre, 80°; post, 121°), and active internal rotation (pre, S3; post, L2). The functional outcome scores that were significantly (P < .05) improved at final follow-up were Constant normalized (pre, 39; post, 79), SPADI (pre, 86; post, 20), SST (pre, 3.3; post, 10), UCLA (pre, 13; post, 31), and ASES (pre, 33; post, 85).
The outcome improvements at latest follow-up were active external rotation (+28), active scaption (+45), active abduction (+42), active internal rotation (+6 anatomical segments), Constant normalized (+40), SPADI (–66), SST (+6.7), UCLA (+18), and ASES (+52).
There were 32 complications in 25 shoulders. There were no bilateral complications. Seven shoulders had multiple complications, of which many were not independent events. For example, rotator cuff deficiency was associated with instability, and infection was associated with glenoid loosening. One patient had 2 procedures, the first an arthroscopic release and the second a revision shoulder arthroplasty for glenoid loosening. The most common postoperative complication was rotator cuff failure (RCF) or suspected RCF (13 shoulders, including 8 treated with revision arthroplasty). RCF occurred most commonly at the rotator cuff interval, followed by the subscapularis and the supraspinatus. RCF location was based on computed tomography scan or intraoperative observation. The few subscapularis failures occurred with both subscapularis tendon repair and osteotomy. The high RCF rate may derive from scrutinizing postoperative radiographs and was not necessarily confirmed with repeat surgery. We think this represents a more realistic estimate of true postoperative rotator cuff dysfunction, rather than including only reoperated cases. The second most common complication was infection (6 shoulders, 1 with a superficial suture abscess and 5 with deep infections). Other complications were instability (4, with 2 caused by rotator cuff insufficiency), glenoid loosening (4, with 2 caused by infection), stiffness (3), nerve issue (1), and hematoma evacuation (1).