Radiographic and clinical outcomes of second generation Trabecular Metal™ glenoid components in total shoulder arthroplasty

Abstract

Background

Total shoulder arthroplasty with second generation porous tantalum glenoid implants (Trabecular Metal™) has shown good short-term outcomes, but mid-term outcomes are unknown. This study describes the clinical, radiographic, and patient-rated mid-term outcomes of total shoulder arthroplasty utilizing cemented Trabecular Metal™ glenoid components.

Methods

Patients who underwent anatomic total shoulder arthroplasty with cemented Trabecular Metal™ glenoid components for primary osteoarthritis were identified for minimum five-year follow-up. The primary outcome measure was implant survival; secondary outcome measures included patient-rated outcome scores, shoulder range of motion findings, and radiographic analysis.

Results

Twenty-seven patients were enrolled in the study. Twenty-one patients had full radiographic follow-up. Mean follow-up was 6.6 years. There was 100% implant survival. Shoulder range of motion significantly improved and the mean American Shoulder and Elbow Society score was 89.8. There was presence of metal debris radiographically in 24% of patients. Twenty-nine percent of patients had evidence of radiolucency. Fourteen percent of patients had moderate superior subluxation.

Conclusion

Total shoulder arthroplasty with second generation cemented Trabecular Metal™ glenoid components yielded good outcomes at mean 6.6-year follow-up. Metal debris incidence and clinical outcomes were similar to short-term findings. The presence of metal debris did not significantly affect clinical outcomes. Continued observation of these patients will elucidate longer-term implant survival.

Introduction

Glenoid component loosening remains a primary challenge to long-term implant survivorship in total shoulder arthroplasty (TSA).^1,2 Metal-backed glenoid components were originally explored to theoretically improve glenoid fixation through increased bony ingrowth.^2,3 However, current literature supports use of all polyethylene components over metal-backed glenoid components due to higher failure rates associated with early metal-backed designs.^1,4–6 Nonetheless, there remains interest in developing novel metal-backed glenoid components with alterations in geometry and materials in an attempt to achieve improved glenoid fixation.

In 2003, the first generation Trabecular Metal™ (TM) (Zimmer, Warsaw, IN) metal-backed polyethylene glenoid component was introduced as a potential option to improve glenoid fixation and provide long-term durability. Trabecular metal is a tantalum biomaterial with a decreased metal stiffness and a structure similar to trabecular bone, along with high porosity to allow for excellent osteointegration.^7–9 This material has been shown to have good results in total hip and knee arthroplasty as well as reverse TSA.^10–12 Unfortunately, the first generation TM-backed glenoid components showed an unacceptably high failure rate due to fracture at the component keel/tantalum disc interface and was taken off the market in 2005.⁸ After redesign, the second generation TM glenoid was introduced in 2009 and is currently in wide-spread use throughout the world. In the United States, this implant is currently only approved by the Food and Drug Administration (FDA) for use in a partially cemented fashion, with press-fit application being performed in an off-label manner. Short-term clinical studies investigating the performance of the second generation TM glenoid have yielded good to excellent patient outcomes; however, the majority of these studies only reported outcomes at a minimum two-year follow-up.^9,13–16 Furthermore, short-term reports of radiographic metal debris formation associated with these components have shed a cautionary light and raised concern for possible future implant failure.^14,16 In the current literature, five-year or greater follow-up outcomes of the second generation TM glenoid are lacking and the true rate of metal debris formation at mid- to long-term is unknown.

Therefore, the purpose of this study was to describe the radiographic, clinical, and patient-rated mid-term outcomes of TSA utilizing partially cemented TM-backed glenoid components for primary osteoarthritis at a minimum of five-year follow-up.

Materials and methods

A retrospective review was performed to identify all patients who underwent anatomic TSA with a porous tantalum glenoid component (Trabecular Metal™, Zimmer Biomet, Warsaw, IN) from January 2009 to August 2013. Patients were identified using Current Procedural Terminology (CPT) code 23472. The query was performed during September 2018 to ensure a minimum follow-up time of five years after surgery. Chart review was then performed on all patients identified by CPT code to determine which patients would qualify for the study. Patients were included in the study if their operative note stated that they underwent primary anatomic TSA utilizing a TM-backed glenoid component system for the treatment of primary glenohumeral osteoarthritis. Patients were excluded from the study if their operative note stated that they underwent reverse TSA, hemiarthroplasty, or revision shoulder arthroplasty. Included patients were then contacted by telephone and asked to return to clinic for radiographic and patient-centered outcomes studies. Patients who declined to return for clinical evaluation were given the option of answering patient-reported outcome questionnaires over the phone. Informed consent was provided to all patients who chose to participate in this study. This study and all study related documents were reviewed and approved by the author institution’s Research Subjects Review Board (RSRB), study number RSRB00071615.

The primary outcome measure was implant survival, as defined by the need for revision surgery due to glenoid component loosening or fracture. Secondary outcome measures were radiographic findings, patient-rated outcome scores, and clinical shoulder range of motion (ROM) findings. All patients who returned to clinic underwent radiographic evaluation of the operative shoulder with anteroposterior, oblique, and axillary lateral radiographs. Patient rated outcome measures (PROMs) included American Shoulder and Elbow Society (ASES) score, ASES pain score, and Patient Reported Outcome Measurement Information System (PROMIS) T-scores (physical function (PF), upper extremity (UE), pain interference (PI), and depression (D)). Shoulder ROM was also measured with a goniometer, specifically forward flexion (FF), external rotation (ER) with the arm at the patient’s side, and lateral elevation (LE). A chart review was also performed on all patients who agreed to participate in the study to capture demographic information (age, sex), preoperative imaging of the involved shoulder, immediate postoperative shoulder radiographs, and preoperative shoulder FF and ER measurements.

Radiographic analysis

All radiographs were evaluated independently by two fellowship trained shoulder and elbow surgeons. All radiographs were blinded of all patient identifying information. Preoperative imaging was reviewed and the glenoid wear pattern was graded per Walch classification. Postoperative radiographs were evaluated for four main radiographic outcome measures: evidence of metallic debris, presence of radiolucent lines, superior humeral head subluxation, and anterior/posterior humeral head subluxation.

Metal debris was graded utilizing the method described by Endrizzi et al.¹⁴ Grading is on a 0–4 scale, with Grade 0 meaning no radiographic evidence of metallic debris, Grade 1 meaning debris only at the bone–metal interface, Grade 2 meaning debris noted in the soft tissues intra-articularly, Grade 3 meaning incomplete fracture or cracking of the tantalum component, and Grade 4 meaning complete component fracture and displacement. Radiolucent lines were graded using the method described by Lazarus et al.¹⁷ The TM glenoid component was graded as a keeled implant, similar to prior studies.¹⁴ This grading scheme is on a 0–5 scale, with Grade 0 representing no radiolucency, Grade 1 showing radiolucency at the superior and/or inferior flange, Grade 2 showing radiolucency at the keel, Grade 3 with complete radiolucency ≤2 mm wide around the keel, Grade 4 with complete radiolucency >2mm wide around the keel, and Grade 5 with gross loosening. Superior humeral subluxation was measured with the technique described by Torchia et al.¹⁸ Subluxation was defined as none, mild, moderate, or severe. The classification is dependent on the position of the center of prosthetic humeral head relative to the center of the glenoid component and measured in terms of the diameter of the prosthetic head. No subluxation meant the center of the humeral head and glenoid were exactly identical, mild subluxation meant that the distance between the head and glenoid was less than one quarter the diameter of the humeral head, moderate subluxation meant translation between one quarter and one half the diameter of the head, and severe subluxation was defined as translation more than half the diameter of the humeral head. Lastly, anterior/posterior humeral subluxation was measured utilizing the same definitions as described above by Torchia et al.,¹⁸ but in the axial plane, as opposed to the coronal plane.

A grade for all four radiographic outcome measures was independently assigned for all radiographs by the two reviewers. Findings were then compared by a separate author, and differences in interpretation were noted. For discordant grades, the radiographs were re-evaluated independently and discussed until consensus was reached.

Operative technique

All patients included in this study underwent primary anatomic TSA utilizing the Zimmer Bigliani/Flatow™ Total Shoulder system with a TM-backed glenoid component (Zimmer Biomet, Warsaw, IN) for the treatment of primary glenohumeral osteoarthritis. All surgeries were performed by a single fellowship trained shoulder surgeon. All patients underwent the operative technique as outlined below. The glenoid component was partially cemented in all cases, as per the manufacturer’s guidelines. Currently in the USA, the TM-backed glenoid component is only approved by the FDA to be used in a cemented fashion.

Surgery was performed under general anesthesia with the patient in a beach-chair position with approximately 30° elevation of the torso. A deltopectoral approach was performed and the long head of the biceps tendon, if intact, was tenodesed to the pectoralis major insertion. A lesser tuberosity osteotomy (LTO) was performed and the subscapularis was circumferentially released. Humeral head osteotomy was carried out in standard fashion with 20 or 30 degrees of retroversion, depending on the glenoid wear pattern. The humeral canal was prepared with sequential reaming and a trial humeral implant was placed. The glenoid was exposed and a circumferential capsular release was performed and the glenoid labrum was removed. The glenoid bone was prepared per manufacturer’s technique guide. Correction of any glenoid wear was achieved by reaming the high side of the glenoid. The TM-backed glenoid component was then inserted with a small amount of polymethylmethacrylate cement per manufacturer’s instructions. The Bigliani/Flatow™ humeral stem implant (Zimmer Biomet, Warsaw, IN) was placed in a press-fit fashion and drill holes were placed in the bicipital groove for LTO fixation. Humeral head trialing was performed to achieve proper soft tissue balancing and the final humeral head implant was placed onto the humeral stem. The LTO was repaired by placing #5 Ethibond sutures in a reverse mattress stitch fashion at the bone–tendon junction of the subscapularis and LTO and passing the sutures through the bicipital groove bone tunnels. The sutures were then passed through a metal tissue button (Button Plate™, 7 hole, DePuy Synthes, Raynham, MA) and tied over the lateral cortex of the greater tuberosity. This provided anatomic fixation of the LTO to the humerus. The wound was copiously irrigated and closed in standard fashion and patients were placed in a shoulder immobilizer. Patients remained in a sling for four weeks after surgery. Passive ER was limited to 60° for the first six weeks postoperatively. Active range of motion (AROM) exercises in flexion were initiated at three weeks, with AROM in scaption, internal rotation, and ER added at six weeks.

Statistical analysis

All statistical analyses were performed using GraphPad Prism software (La Jolla, CA). Descriptive statistics were performed on PROMs and clinical shoulder ROM findings. Preoperative and postoperative shoulder ROM measures (FF, ER) were compared using the Wilcoxon signed rank test. Differences in PROMs and ROM findings were compared between patients with radiographic Grade 0 and Grade ≥1 metal debris using the Mann–Whitney U test. In a similar fashion, the Mann–Whitney U test was also performed to describe differences between PROMs and ROM findings in patients with Grade 0 and Grade ≥1 radiolucency. Next, correlation between the preoperative glenoid Walch classification and presence of metal debris and radiolucent lines was determined using Fisher’s exact test. Statistical significance was defined as p < 0.05 for all tests.

Furthermore, a Cohen’s kappa coefficient analysis was performed to determine the inter-rater reliability for all radiographic grading measures. Kappa results were interpreted with 0.01–0.20 meaning no to slight agreement, 0.21–0.40 as fair agreement, 0.41–0.60 as moderate agreement, 0.61–0.80 as substantial agreement, and 0.81–1.00 as near perfect agreement.¹⁹

Results

Thirty-nine patients were identified from 2009 to 2013 who underwent anatomic TSA with placement of a TM glenoid component. Of those 39 patients, six were found to be deceased. Four patients were living in nursing facilities and their families declined their participation in the study. Two other patients were unable to be contacted. The remaining 27 patients agreed to take part in the study, with 21 patients agreeing to come to the office for radiographs, physical exam measurements, and PROMs questionnaires and six patients agreeing to phone administration of PROMs surveys.

The mean follow-up time for the 27 enrolled patients was 80 months, or 6.6 years (range 5.3–9.0 years). Eighteen were male and nine were female. The average age at the time of surgery was 68.8 years (range 54–83 years). There was 100% implant survival, with no revision surgeries performed on any of the 27 patients who were enrolled in the study or any of the 12 patients who were unable to participate in the study. There were no major surgical complications noted in the 27 enrolled patients. Out of the patients unable to participate in the study, one patient sustained a humeral shaft fracture three years after the index procedure that was treated nonoperatively and another patient sustained an olecranon fracture one year after the index procedure that was treated with surgery.

Shoulder ROM and PROMs findings at a minimum follow-up time of five years are shown in Table 1. Patients demonstrated a mean active FF of 130° (standard deviation (SD) 20), a mean active ER with the shoulder at neutral of 53° (SD 22), and a mean LE of 127° (SD 29). PROMIS scores showed a mean PF T-score of 48.4 (SD 8.5), a mean UE T-score of 47.6 (SD 9.9), a mean PI T-Score of 48.0 (SD 8.2), a mean D T-score of 43.4 (SD 8.3). ASES pain scores showed a mean score of 45.6 (SD 9.2), and ASES overall score showed a mean score of 89.8 (SD 10.3). Compared to preoperative shoulder ROM data, patients exhibited a significant improvement in FF and ER (p < 0.001 for both). Preoperatively, patients had a mean FF of 89° (SD 16) and a mean ER of 17° (SD 18).

Table 1.

Clinical outcomes of TSA with TM glenoid, minimum five-year follow-up.

Outcome Measures	Data
ROM
FF	130° (20)
ER	53° (22)
LE	127° (29)
PROMs
PROMIS PF	48.4 (8.5)
PROMIS UE	47.6 (9.9)
PROMIS PI	48.0 (8.2)
PROMIS D	43.4 (8.3)
ASES pain	45.6 (9.2)
ASES score	89.8 (10.3)

ASES: American Shoulder and Elbow Society; D: depression; ER: external rotation; FF: forward flexion; LE: lateral elevation; PF: physical function; PI: pain interference; PROM: patient rated outcome measure; PROMIS: Patient Reported Outcome Measurement Information System; ROM: range of motion; TM: Trabecular Metal™; TSA: total shoulder arthroplasty; UE: upper extremity.

Radiographic analysis showed a presence of metal debris in 24% (5/21) of patients, with four rated as Grade 1 and one rated as Grade 2. All 21 patients did not have any evidence of metallic debris on six-month postoperative imaging. Twenty-nine percent (6/21) of patients had evidence of radiolucency, with four Grade 1 findings and two Grade 2. All patients showed some degree of superior subluxation, per Torchia’s definition, with 18 rated as mild and 3 as moderate.²⁰ In terms of anterior/posterior (A/P) migration, 3 patients were graded as having no A/P migration and 18 were graded as having mild A/P migration. These findings are summarized in Table 2. Kappa coefficient (k) analysis revealed excellent inter-rater reliability for grading of metal debris (k = 0.87, 95% confidence interval (CI) of 0.74–1.00), radiolucent lines (k = 0.89, 95% CI 0.78–1.00), and superior subluxation (k = 0.83, 95% CI 0.67–1.00). There was moderate inter-rater reliability for grading of A/P subluxation (k = 0.52, 95% CI 0.2–0.78). Examples of patients with characteristic radiographic findings are shown in Figures 1 and 2.

Table 2.

Radiographic grades of TSA with TM glenoid, minimum five-year follow-up.

Metal debris		Radiolucent lines		Superior migration		A/P migration
Grade	N	Grade	N	Grade	N	Grade	N
0	16	0	15	None	–	None	3
1	4	1	4	Mild	18	Mild	18
2	1	2	2	Moderate	3	Moderate	–
3	–	3	–	Severe	–	Severe	–
4	–	4	–
		5	–

A/P: anterior/posterior; TM: Trabecular Metal™; TSA: total shoulder arthroplasty.

Figure 1.

Example of study patient at 8.9-year follow-up. (a) Anteroposterior radiograph and (b) axillary lateral radiograph. Grade 0 metal debris, Grade 0 radiolucent lines, mild superior migration, no A/P subluxation. This patient had an ASES score of 95, FF to 156°, ER to 48°, and LE to 157°.

Figure 2.

Example of study patient at 5.7-year follow-up. (a) Anteroposterior radiograph and (b) axillary lateral radiograph. Grade 2 metal debris, Grade 2 radiolucent lines, moderate superior migration and mild A/P subluxation. No evidence of gross component loosening or component fracture. This patient had the worst radiographic grades in this cohort, but still demonstrated excellent clinical outcomes, with an ASES score of 95, FF to 152°, ER to 58°, and LE to 153°.

Preoperative imaging was available for 19 of the 21 patients who presented for mid-term radiographs, including all five patients who had evidence of metal debris and all six patients with evidence of radiolucent lines. Seven patients had a preoperative Walch A1 glenoid, with one patient showing mid-term evidence of metal debris (Grade 1), and three patients with radiolucent lines (two Grade 1, one Grade 2). Two patients had a Walch A2 glenoid; neither had evidence of metal debris or radiolucent lines. Two patients had a Walch B1 glenoid: one patient had evidence of metal debris (Grade 2), and one patient had radiolucent lines (Grade 2). Eight patients had a Walch B2 glenoid, with three patients showing signs of metal debris (all Grade 1) and two patients with radiolucent lines (all Grade 1). There was no significant correlation between preoperative Walch classification and development of metal debris (p = 0.507) or development of radiolucent lines (p = 0.613). There was excellent inter-rater reliability for Walch grading (k = 0.84, 95% CI 0.74–0.94).

ROM and PROMs outcome comparisons between patients with and without metal debris or radiolucent lines are shown in Table 3. When comparing patients with Grade 0 metal debris versus those with Grade ≥1 metal debris, there were generally no significant differences in shoulder ROM, PROMIS, and ASES outcomes (all p > 0.05). The only significant finding was patients with Grade ≥1 metal debris had a superior PROMIS PF T-score (mean 53.4) compared to patients with Grade 0 metal debris (mean 44.9), p = 0.041. When comparing patients with Grade 0 radiolucency versus those with Grade ≥1 radiolucency findings, there were no significant differences in any shoulder ROM, PROMIS, or ASES outcomes (all p > 0.05).

Table 3.

Comparison of outcome measures in patients with and without evidence of metal debris or radiolucent lines.

Outcome Measures	Metal debris			Radiolucent lines
	Grade 0 (n = 16)	Grade ≥1 (n = 5)	p-value	Grade 0 (n = 15)	Grade ≥1 (n = 6)	p-value
ROM
FF	126°	139°	0.362	126°	137°	0.241
ER	53°	53°	0.664	53°	54°	0.649
LE	128°	122°	0.798	127°	125°	0.903
PROMs
PROMIS PF	44.9	53.4	0.041	46.2	48.9	0.462
PROMIS UE	45.1	49.1	0.473	47.2	43.2	0.338
PROMIS PI	49.5	48.8	0.892	48.2	52.1	0.479
PROMIS D	45.1	37.4	0.071	43.5	42.8	0.612
ASES pain	46.7	45.6	0.443	46.9	45.2	0.197
ASES score	90.5	91.9	0.768	91.9	88.2	0.332

ASES: American Shoulder and Elbow Society; D: depression; ER: external rotation; FF: forward flexion; LE: lateral elevation; PF: physical function; PI: pain interference; PROM: patient rated outcome measure; PROMIS: Patient Reported Outcome Measurement Information System; ROM: range of motion; UE: upper extremity. Bold and italicized value was statistically significant.

Discussion

The purpose of this study was to report the mid-term outcomes of the second generation TM glenoid in TSA for primary osteoarthritis. At a minimum five-year follow-up (mean 6.6 years), patients demonstrated good patient-rated outcome scores with significant improvements in ROM. There were no cases of glenoid component fracture or failure and no patients required revision surgery. Radiographic analysis showed that metal debris was present in 24% of patients and radiolucent lines were present in 29%.

Porous tantalum-backed glenoid components were introduced to potentially improve upon the historically poor performance of earlier metal-backed glenoid designs.^2,8 Unfortunately, the first generation TM-backed glenoid components demonstrated unacceptably high rates of glenoid failure (21%) secondary to component fracturing at short-term follow-up.⁸ After redesign, the second generation TM glenoid has shown more promising short-term outcomes in several studies, all with a minimum two-year follow-up. At a mean follow-up of 38 months, Merolla et al.⁹ found a 0% incidence of glenoid implant failure, with no evidence of metal debris in any follow-up radiographs. Patients also improved clinically, with a mean ASES score of 93.4. Styron et al.¹⁵ also showed good clinical results at a mean 50-month follow-up, but their cohort included a combination of first and generation TM-backed glenoid components. Panti et al.¹³ found good clinical outcomes (mean ASES 88.5) with no patients requiring revision surgery at 43-month follow-up.

Other short-term studies have also demonstrated good clinical outcomes, but have raised concern about metal debris rates associated with the second generation TM glenoid. Endrizzi et al.,¹⁴ at a minimum two-year follow-up time and mean follow-up of 53 months, also demonstrated that patients had good clinical outcomes, with a mean ASES score of 89.7. However, they found a 44% incidence of metal debris that appeared to increase with longer follow-up periods and concluded that the implant should be used with caution. They did note that the presence of debris did not have an impact on clinical outcomes and only one patient required revision surgery for glenoid loosening. Watson et al.,¹⁶ at a mean follow-up of 34 months, described a 25% incidence of debris or osteolysis, with a mean ASES score of 69.2. They described a 11% revision rate, but the majority of these cases were secondary to subscapularis failure, not glenoid component failure. Nonetheless, they concluded that they were ceasing use of the TM glenoid due to their concern for metal debris and osteolysis. The authors of both of these studies implied that the presence of metal debris might foreshadow impending component failure, as was seen in the first generation TM glenoid. However, this has not been definitively proven and merits further investigation.

Given the varying rates (0–44%) of metal debris reported by the prior short-term studies as well as concern that the presence of metal debris may lead to eventual catastrophic component fracture and failure, there is a need for longer-term follow-up studies to investigate the natural course of metal debris formation and implant survivorship of the second generation TM glenoid. This study aimed to answer this question by reporting outcomes at a significantly greater follow-up time interval than all prior studies.

At a mean 6.6-year follow-up, we found a metal debris incidence of 24%, with 80% being Grade 1 and only one patient with Grade >1. This debris rate falls within the range reported by prior studies at short-term follow-up and does not appear to be significantly greater than these previous reports. Our reported metal debris rate is substantially lower than that published by Endrizzi et al.,¹⁴ whose subset of patients with ≥5 years of follow-up had a 52% incidence of metal debris. Importantly, we did not find any cases of glenoid implant fracture or catastrophic failure. This suggests that the presence of metal debris at short-term follow-up intervals may not correlate directly with eventual implant fracture at mid-term follow-up, as suggested by Endrizzi et al.¹⁴ Therefore, the isolated presence of metal debris noted on postoperative radiographs does not necessarily signify impending component failure and may be a more benign finding. Based on our findings, contrary to Watson et al.,¹⁶ we do not believe that the presence of metal debris in 24–25% of patients should cause the cessation of using this specific implant.

The other radiographic findings from this longer-term study are similar to those reported in prior studies. Radiolucent lines were found in 29% of patients. This is similar to the 36% radiolucency rate reported by Endrizzi et al.¹⁴ for this specific implant. Our reported rate is also similar to the 35% radiolucency rate for metal-backed glenoids described in a prior systematic review and is lower than the rate described for all-polyethylene glenoid components (42%).¹ Also, we found a 14% incidence of moderate superior migration. This is comparable to the 17% rate of secondary rotator cuff dysfunction found by Young et al.²¹ at long-term follow-up of anatomic TSA patients. Secondary rotator cuff dysfunction was defined as moderate or severe superior migration per Torchia’s definition. All patients in this study demonstrated either no AP subluxation or mild AP subluxation. This likely signifies that subscapularis function was intact and that the lesser tuberosity osteotomies healed appropriately. Lastly, patients had a wide range of preoperative glenoid wear patterns, with 47% Walch A subtypes and 53% Walch B. The preoperative Walch grade did not have a significant effect on formation of metal debris or radiolucent lines, similar to previous findings regarding this implant.¹⁴

PROMs and ROM findings at minimum five-year follow-up revealed good outcomes and significant improvements in function associated with the second generation TM glenoid. We demonstrated a mean ASES score of 89.8. This compares favorably to previously discussed short-term studies for this implant, with mean scores ranging from 69.2 to 93.4, and signifies a good functional outcome after TSA.^9,13–16 PROMIS scores have not been previously described for this specific implant, but have been recently validated against legacy measures for use in measuring patient-reported outcomes in TSA.²² A recent study demonstrated that patients had mean postoperative PROMIS T-scores of 44.1 for PF, 52.6 for PI, and 45.5 for D at early postoperative follow-up, which were significantly improved from preoperatively.²³ Results from our study are similar to these findings, suggesting that our PROMIS scores indicate satisfactory patient-reported outcomes after use of the TM glenoid in TSA. The improvements in shoulder ROM described in this study are also similar to that in prior studies investigating this implant.^9,16

Lastly, clinical outcomes were not significantly different between patients with or without radiographic evidence of metal debris. This was also true when comparing outcomes in patients with or without radiolucencies around the glenoid component. Prior studies have shown that the presence of radiolucent lines does not directly correlate with poor outcomes, as similarly found in this study.² Prior clinical studies of the second generation TM glenoid have also found that the presence of metal debris did not correspond to poor patient outcomes.^14,16 This consistent finding may support the hypothesis that the isolated presence of metal debris may be a more benign finding than previously anticipated, as patients continued to achieve similar outcomes to those with no radiographic debris even at greater than five-year follow-up.

The mid-term clinical outcomes of the second generation TM glenoid reported in this study also compare favorably to outcomes of other metal-backed glenoid designs at similar follow-up intervals. Utilizing a hybrid glenoid component with a central porous titanium post, Nelson et al.²⁴ found a mean ASES score of 83.7 but noted a 64% incidence of radiolucency and a 2% revision rate due to glenoid failure at minimum five-year follow-up. Castagna et al.²⁵ reported the outcomes of the SMR metal-backed glenoid (Lima Corporate, Villanova, Italy) at a mean 75.4-month follow-up and found a 23% radiolucency rate and mean constant score of 70.8.

A significant distinguishing feature between this study and the prior short-term studies investigating the second generation TM glenoid is our use of cement during glenoid component fixation. This is the only FDA approved implantation technique in the United States for this implant, whereas in Europe both press-fit and partially cemented fixation are approved. Prior studies have suggested that cementation of metal-backed glenoid components yields greater fixation strength. Budge et al.²⁰ demonstrated biomechanically that cementation of the TM glenoid yielded greater stability than press-fit implantation and suggested that cementation may enhance the osteointegration of the implant. Prior reports of other uncemented metal-backed glenoid designs have found a high clinical complication rate as well.^2,26,27 Given the potential fixation benefits of cementation, it is possible that the lower rates of metal debris formation reported in this study, when compared to Endrizzi et al.’s¹⁴ findings, are secondary to use of partially cemented implantation. Further studies comparing the long-term outcomes of press-fit TM glenoids versus our patient cohort will help elucidate the role of cementation in fixation of this component.

This study had particular strengths. First, the follow-up interval reported in this case series is the longest reported follow-up timeframe for the second generation TM glenoid implant. Prior studies investigating this specific implant were short-term outcome studies (minimum two-year follow-up). Next, all patients in this study underwent surgery for the same clinical indication by the senior author, who performed identical surgical techniques in all cases. This avoids confounding factors that can be present in multi-surgeon study cohorts. Finally, the TM glenoid components were implanted in the FDA-approved partially cemented manner for all patients in this study. The vast majority of prior studies investigating this specific implant utilized a press-fit technique for glenoid fixation. The findings from this study provide valuable insight into outcomes after cemented fixation.

This study had certain limitations. First, this study was limited by the small patient population. A substantial portion of patients who met inclusion criteria were lost to follow-up. This could in part be due to the more elderly patient population, but also due to the longer-term minimum follow-up time that was desired. Multiple patients were deceased or medically unfit to participate in the study. Next, this study was limited by factors inherent to all retrospective case series, including lack of a control group. Furthermore, patients in this study all underwent TSA for primary osteoarthritis and therefore the findings of this study may not be generalizable to patients undergoing surgery for other indications. This study also represented a single surgeon’s case series. Our findings may have been related to surgeon factors and surgical technique, such as decision to cement the glenoid component. A larger, multi-surgeon cohort may be more generalizable. Also, interval radiographs between the routine postoperative time period and the study visit were not available. These radiographs would have potentially been helpful to track the development of metallic debris over time. Nonetheless, the percentage of metallic debris found in this study was similar to the percentages found in prior short-term studies and the presence of debris did not appear to have an effect on clinical outcome. Lastly, although the follow-up length for this study was significantly greater than previous studies investigating this particular implant, even longer follow-up time periods are desirable to determine the true implant safety and survivorship.

In conclusion, the overall promising clinical, patient-centered, and radiographic findings from this study show that the second generation TM glenoid performs well at minimum five-year follow-up and is not associated with the mid-term glenoid component failures seen in the first generation implant. No patients in this case series required revision surgery and there were no glenoid component failures. Metal debris incidence (24%) was found to be similar to previously reported short-term findings. The presence of metal debris or radiolucent lines did not have significant effects on patient outcomes. We plan to continue following our cohort of patients to further elucidate the long-term durability of the second generation TM-backed glenoid component.

Ethical Approval and Patient Consent

Ethical approval to report this case/these cases was obtained from the University of Rochester Research Subjects Review Board, study number RSRB00071615. The official approval letter is attached as a separate document. Written informed consent was obtained from the patient(s) for their anonymized information to be published in this article.