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Scapular notching and osteophyte formation after reverse shoulder replacement RADIOLOGICAL ANALYSIS OF IMPLANT POSITION IN MALE AND FEMALE PATIENTS C. P. Roche, Y. Marczuk, T. W. Wright, P-H. Flurin, S. Grey, R. Jones, H. D. Routman, G. Gilot, J. D. Zuckerman From NYU Hospital for Joint Diseases, New York, New York, United States  C. P. Roche, MSBE, MBA, Director of Engineering Extremities Exactech, Inc., 2320 N W 66th Court, Gainesville, Florida 32653, USA.  Y. Marczuk, MD, Orthopaedic Surgeon Chenieux Clinic, 18 Rue de General Catroux, Limoges 87000, France.  T. W. Wright, MD, Orthopaedic Surgeon, Professor University of Florida Orthopaedic & Sports Medicine Institute, 3450 Hull Road, Gainesville, Florida 32611, USA.  P-H. Flurin, M.D., Orthopaedic Surgeon Bordeaux-Merignac Clinic, 9 Rue Jean Moulin, Bordeaux-Merignac 33700, France.  S. Grey, MD, Orthopaedic Surgeon Orthopaedic Center of the Rockies, 2500 E Prospect Road, Fort Collins, Colorado 80525, USA.  R. Jones, MD, Orthopaedic Surgeon Southeastern Sports Medicine, 7 Turtle Creek Drive, Asheville, North Carolina 28803, USA.  H. D. Routman, DO, FAOAO, Orthopaedic Surgeon, Director of Palm Beach Shoulder Service Atlantis Orthopaedics, 130 JFK Drive, Suite 201, Atlantis, Florida 33462, USA.  G. Gilot, M.D., Orthopaedic Surgeon, Chairman Cleveland Clinic, 2950 Cleveland Clinic Blvd, Weston, Florida 33331, USA.  J. D. Zuckerman, M.D., Orthopaedic Surgeon, Professor, Chairman NYU Hospital for Joint Diseases, Department of Orthopaedic Surgery, 301 East 17th Street, 14th Floor, New York, New York 10003, USA. Correspondence should be sent to Dr J. D. Zuckerman; e-mail: [email protected] ©2013 The British Editorial Society of Bone and Joint Surgery doi:10.1302/0301-620X.95B4. 30442 $2.00 Bone Joint J 2013;95-B:530–5. Received 17 July 2012; Accepted after revision 28 December 2012

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This study provides recommendations on the position of the implant in reverse shoulder replacement in order to minimise scapular notching and osteophyte formation. Radiographs from 151 patients who underwent primary reverse shoulder replacement with a single prosthesis were analysed at a mean follow-up of 28.3 months (24 to 44) for notching, osteophytes, the position of the glenoid baseplate, the overhang of the glenosphere, and the prosthesis scapular neck angle (PSNA). A total of 20 patients (13.2%) had a notch (16 Grade 1 and four Grade 2) and 47 (31.1%) had an osteophyte. In patients without either notching or an osteophyte the baseplate was found to be positioned lower on the glenoid, with greater overhang of the glenosphere and a lower PSNA than those with notching and an osteophyte. Female patients had a higher rate of notching than males (13.3% vs 13.0%) but a lower rate of osteophyte formation (22.9% vs 50.0%), even though the baseplate was positioned significantly lower on the glenoid in females (p = 0.009) and each had a similar mean overhang of the glenosphere. Based on these findings we make recommendations on the placement of the implant in both male and female patients to avoid notching and osteophyte formation. Cite this article: Bone Joint J 2013;95-B:530–5.

Scapular notching is the most common complication of reverse shoulder replacement, occurring in between 44% and 96% of patients with a prosthesis that has a medialised glenoid centre of rotation.1,2 As shown in Table I,1-8 the weighted mean rate of scapular notching is about 68%, with notches classified as > Nerot-Sirveaux7 grade 2 occurring in approximately 21% of patients. Notching is caused by repetitive contact between the humeral component and the inferior scapular neck, and an osteolytic reaction to the resulting polyethylene debris. It is progressive,6,9 correlates with the presence of radiolucent lines3,6,9 and adversely affects the outcome.1,7,8 Modifications of the design10-12 and the surgical technique13-15 have been proposed, aiming to minimise impingement, improve the range of movement and improve stability by shifting the glenoid plate 2 mm to 4 mm inferior to the centre of the glenoid.10,12,15 These recommendations were obtained from computer models,10,12 sawbone surgical simulations12,15 and a cadaver study,14 and do not allow for variations in scapular morphology or the anatomical differences between males and females. The purpose of this radiological study was to quantify the rate and severity of scapular notching and the

formation of osteophytes on the scapular neck, and to determine factors that are associated with their development by assessing the position of the glenoid plate, the overhang of the glenosphere and the prosthesis scapular neck angle (PSNA),1 using a single design of reverse shoulder arthroplasty. The differences in the anatomy between males and females were also evaluated. A secondary aim was to provide recommendations on the position of the components in both males and females that would minimise notching and osteophyte formation.

Patients and Methods Anteroposterior (AP) radiographs were taken post-operatively and at the final follow-up from 151 patients (105 females and 46 males) who underwent primary reverse shoulder arthroplasty for rotator cuff tear arthropathy using a single prosthesis (Equinoxe; Exactech, Inc., Gainesville, Florida). The operations were undertaken by nine different surgeons at nine different institutions (including YM, TWW, PHF, SG, RJ, HDR, GG, JDZ and LC). The mean age of the patients at surgery was 73.3 years (SD 7.1; 55 to 93), with mean ages of 73.8 years (SD 6.8; 55 to 93) and 72.2 years (SD 7.6; 55 to 84) for female and male patients, respectively. Through a deltopectoral approach THE BONE & JOINT JOURNAL

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Table I. The reported rates of scapular notching for reverse shoulder prostheses with a medialised centre of rotation Authors

Sample size (n)

Mean follow-up (mths)

Scapular notching rate

Notches > grade 2

Boileau et al3 Karelse et al4 Kempton et al5

45 27 43 (no glenoid tilt) 28 (inferior glenoid tilt) 461 77 80 59 48

40 43 30 24 51 44 44 48 38

68% 59% 77% 61% 68% 44% 64% 87% 96%

11% 26% 23% 4% 23% 18% 17% 5% 46%

46.0

68.2%

20.9%

Levigne et al6 Simovitch et al1 Sirveaux et al7 Stechel et al8 Werner et al2 Weighted mean rate of scapular notching

Fig. 1

Fig. 2

Diagram showing the Nerot-Sirveaux system7 for grading of scapular notching.

Diagram showing the measurement of the position of the baseplate and overhang of the glenosphere.

a range of three sizes of diameter and thickness of glenosphere were implanted: 38 × 21 mm (n = 89, 74 females, 15 males), 42 × 23 mm (n = 56, 31 females, 25 males) and 46 × 25 mm (n = 6, all male). This design has a humeral neck/liner angle of 145°. The centre of rotation of each glenosphere is 2.0 mm lateral to the spherically reamed glenoid surface. Because the peg on the glenoid baseplate is shifted superiorly by 4 mm when its inferior rim is aligned with the inferior rim of the glenoid, the 38 mm, 42 mm, and 46 mm designs provide 2.25 mm, 4.25 mm and 6.25 mm of glenosphere overhang, respectively. Each surgeon reamed the glenoid at neutral so that each glenosphere was implanted perpendicular to the glenoid, without any inferior tilt. Next, the hole for the offset baseplate peg was drilled using the drill guide. The manufacturer recommends that the inferior surface of the drill guide be aligned along the inferior rim of the reamed glenoid, which positions the centre of the peg approximately 20 mm superior to the inferior rim. Radiological analysis. All nine authors assessed all radiographs for notching and osteophytes in a blinded fashion. VOL. 95-B, No. 4, APRIL 2013

Notching was assessed according to the Nerot-Sirveaux grading scale7 as described in Figure 1 and osteophytes by tracing the scapular neck from medial to lateral and noting any bony spurs. The presence of notching and osteophytes was determined by a majority consensus (e.g. agreement of five of the nine authors) and the grade of notch was determined by the mode of all scores. The distance between the peg and the inferior rim of the glenoid and the amount of overhang of the glenosphere was measured on the post-operative scapular AP radiograph using digital callipers as shown in Figure 2 and the PSNA was measured using a goniometer as shown in Figure 3.1 Statistical analysis. The radiological measurements were related to the presence of notches and osteophytes and sorted according to gender. A Student’s two-tailed, unpaired t-test was used to identify differences in the radiological measurements between patients with and without a notch and between patients with and without an osteophyte; a p value of < 0.05 denoted statistical significance.

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Table II. Radiological measurements in patients with and without a notch. Statistical analysis by Student’s two-tailed unpaired t-test Radiological measurement Mean (SD) glenoid plate position (mm) All patients Females Males Mean (SD) glenosphere overhang (mm) All patients Females Males Mean (SD) prosthesis scapular neck angle (°) All patients Females Males

Notch (n = 20)

No notch (n = 131)

p-value

20.3 (1.9) 20.8 (1.9) 19.2 (1.5)

19.1 (2.3) 18.7 (2.3) 20.2 (2.1)

0.036 0.001 0.271

3.7 (2.0) 3.2 (2.0) 4.7 (1.6)

5.1 (2.4) 5.3 (2.2) 4.7 (2.7)

0.010 0.001 0.98

102.5 (9.7) 102.1 (11.4) 103.3 (4.1)

96.3 (9.7) 96.2 (9.9) 96.5 (9.4)

0.009 0.044 0.086

glenospheres was 28.4% (n = 21) and 9.7% (n = 3), respectively. The rate of osteophyte formation in males with 38 mm, 42 mm, and 46 mm glenospheres was 73.3% (n = 11), 38.7% (n = 12) and 0%, respectively. The mean distance of the glenoid peg from the inferior glenoid rim was 19.3 mm (SD 2.3; 12.8 to 25.8) for all patients. It was significantly lower in females than in males (19.0 mm (SD 2.4) vs 20.0 mm (SD 2.1); p = 0.009). The mean overhang was 4.9 mm (SD 2.4; -1.7 to 13.8) for all patients; it was not significantly different between females and males (p = 0.47). The mean PSNA was 97.2° (SD 9.9; 80° to 130°) for all patients and was not significantly different between females and males (p = 0.86). The radiological results are shown in Tables II and III.

Fig. 3 Diagram showing the measurement of the prosthesis scapular neck angle.1

Results The mean follow-up was 28.3 months (SD 5.7; 24 to 44). A total of 20 patients (13.2%) had a scapular notch (16 Grade 1 and four Grade 2; no Grade 3 or 4 notches were observed); 14 female patients (13.3%) had scapular notching (11 Grade 1 and three Grade 2); six male patients (13.0%) had scapular notching (five Grade 1 and one Grade 2). The rate of notching in female patients with 38 mm and 42 mm glenospheres was 14.9% and 9.7%, respectively; and the rate in males with 38 mm, 42 mm and 46 mm glenospheres was 33.3%, 3.2% and 0%, respectively. Additionally, 47 patients (31.1%) had an osteophyte on the inferior scapular neck. Of the 20 patients with notching, ten (50.0%) had an osteophyte; whereas 37 of the 131 patients (28.2%) without a notch had an osteophyte. The rate of formation of an osteophyte was 22.9% (n = 24) in females and 50% (n = 23) in males. The rate of osteophyte formation in females with 38 mm and 42 mm

Discussion The rate of scapular notching of 13.2% in this study, with only 2.6% of grade 2 notches and no grade 3 or 4 notches at a mean follow-up of 28.3 months (24 to 44) compares favourably with the rates of notching for other designs of medialised glenoid centre of rotation reverse shoulder arthroplasty.1-8 Additionally, our analysis of the position of the implants helps us to understand the reduced rate of notching. Patients without notching had the baseplate positioned significantly lower on the glenoid (19.1 mm vs 20.3 mm) and had significantly more overhang of the glenosphere (5.1 mm vs 3.7 mm) than patients with notching. These results confirm the conclusions of previous work,11,12 which demonstrated that subtle changes in the design of the prosthesis such as an inferiorly shifted glenosphere, a curved back glenoid plate, a 145° humeral neck/liner, and a 2.0 mm lateralised centre of rotation, can dramatically reduce impingement. Recent changes in design and surgical technique have reduced the rate of scapular notching. These include, a reverse shoulder design with a 2.5 mm lateralised centre of rotation and a 150° humeral neck/liner,16,17 inferiorly reaming the glenoid by 10° to 15°,13,16-18 and inferiorly shifting the baseplate to reduce impingement between the humeral liner and inferior scapular neck.1,2,5,6,9,10,14,15,18,19 Simovitch et al1 shifted the baseplate of the Delta III THE BONE & JOINT JOURNAL

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Table III. Radiological measurements in patients with and without an osteophyte. Statistical analysis by Student’s two-tailed unpaired t-test Radiological measurement Mean (SD) glenoid plate position (mm) All patients Females Males Mean (SD) glenosphere overhang (mm) All patients Females Males Mean (SD) prosthesis scapular neck angle (°) All patients Females Males

Osteophyte (n = 47)

No osteophyte (n = 104)

p-value

20.3 (1.8) 20.3 (1.5) 20.3 (2.0)

18.9 (2.4) 18.6 (2.4) 19.8 (2.1)

< 0.001 0.002 0.403

3.7 (1.9) 3.5 (1.8) 3.9 (2.1)

5.4 (2.4) 5.4 (2.2) 5.5 (2.8)

< 0.001 < 0.001 0.039

99.3 (9.6) 99.5 (10.2) 99.1 (9.1)

96.2 (9.9) 96.4 (10.2) 95.7 (9.0)

0.089 0.215 0.219

Grammont reverse shoulder arthroplasty (DePuy Orthopaedics, Warsaw, Indiana) inferiorly and reported a reduced rate of scapular notching of 44%. Our findings in relation to the position of the baseplate are similar when the differences in the method of measurement are taken into account. They found that the distance between the inferior rim of the glenoid and the top of the central peg was significantly greater for notched glenoids (24.7 mm (SD 3.0) than those without notching (20.1 mm (SD 2.5)). The measurements become the same by subtracting one half of the diameter of the 8 mm Grammont glenoid baseplate peg in their study and yields similar positions of the baseplate relative to the inferior rim glenoid for both notched (20.3 mm vs 20.7 mm1) and non-notched (19.1 mm vs 16.1 mm1) patients. Our radiological analysis of the scapular morphology also helps us to understand the reduced rate of scapular notching. The mean PSNA of patients without a notch was significantly less than that of those with a notch (96.3° vs 102.5°; p = 0.009). These results are also in agreement with those of Simovitch et al1 who reported that the mean PSNA was significantly less for patients without a notch (93° (SD 15)) than that for those with a notch (124° (SD 19)) (p < 0.001). Holcomb et al13 reported that the mean PSNA was significantly greater in glenoid baseplates after revision surgery (126.3° (SD 14.8)) than in those before failure of the baseplate (111.6° (SD 12.7)) (p < 0.01). Their results reflect the fact that the glenoid was inferiorly reamed by 10° to 15° during revision surgery.13 Kempton et al16 proposed a new radiological angular measurement: the prosthesis scapular border angle (PSBA), which they considered to be preferable to the PSNA as it was not affected by either scapular notching or inferiorly tilting the glenoid.5,16,17 We reported the PSNA because the glenoids in our study were reamed at neutral, rather than inferiorly as demonstrated by the lower mean PSNA angle compared with the results reported by Holcomb et al.13 It is important to note that the PSNA also reflects scapular anatomy, the larger the PSNA the shorter the glenoid neck. Patients with shorter glenoid necks are VOL. 95-B, No. 4, APRIL 2013

more likely to develop impingement of the humeral liner on the lateral border of the scapula. In this study, 31.1% of patients had osteophytes on the inferior glenoid neck at a mean follow-up 28.3 months. This rate of formation was less than that reported by Boileau et al3 (63%), Stechel et al8 (64.4%) and Nolan et al17 (37%), and more than that reported by Simovitch et al1 (21.1%) and Kempton et al5 (28.6% and 16.2%). Kempton et al5 found no correlation between the presence of a notch and an osteophyte. Levigne et al6 reported a significant correlation between notching and the formation of an osteophyte, where 63% of notched glenoids also had an osteophyte as compared with 43% of glenoids that had an osteophyte but no notch. We observed an osteophyte in 50.0% of the patients who developed notches and 28.2% of the patients who did not; notches and osteophytes were correlated by a factor of 0.150. We also reported that in patients without an osteophyte the baseplate was positioned significantly lower on the glenoid (18.9 mm vs 20.3 mm) and had significantly more overhang of the glenosphere (5.4 mm vs 3.7 mm) than patients with an osteophyte. These results suggest that osteophyte formation is related to the position of the implant; however, the exact mechanism that causes this is unclear. While it is possible that osteophytes are a reaction to scapular notching, they may develop in reaction to the detachment of the inferior capsule from the glenoid at the time of surgery. This detachment of the inferior capsule was performed by all surgeons in this study using various techniques; however, no clear correlation was observed in the rate of formation of an osteophyte and this technique. Females had a slightly higher rate of scapular notching rate than males (13.3% vs 13.0%) but a lower rate of osteophyte formation (22.9 vs 50.0%) even though the glenoid baseplate was positioned significantly lower on the glenoid in females (p = 0.009) and each had a similar mean overhang of the glenosphere. These differences between males and females can be best explained by differences in the size of the glenoid, as reflected by the fact that more

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C. P. ROCHE, Y. MARCZUK, T. W. WRIGHT, P-H. FLURIN, S. GREY, R. JONES, H. D. ROUTMAN, G. GILOT, J. D. ZUCKERMAN

Table IV. Implant placement recommendations to avoid scapular notching Implant placement Mean (SD) glenoid plate position (mm) Females Males Mean (SD) glenosphere overhang (mm) Females Males

Patients without notch

95% confidence interval

Recommended value

18.7 (2.3) 20.2 (2.1)

0.49 0.68

18.2 19.5

5.3 (2.2) 4.7 (2.7)

0.47 0.86

5.7 5.6

Table V. Implant placement recommendations to avoid osteophyte formation Implant placement Mean (SD) glenoid plate position (mm) Females Males Mean (SD) glenosphere overhang (mm) Females Males

Patients without osteophyte

95% confidence interval

Recommended value

18.6 (2.4) 19.8 (2.1)

0.55 0.91

18.0 18.9

5.4 (2.2) 5.5 (2.8)

0.50 1.20

5.9 6.7

males (63.4%) received a 42 mm or 46 mm glenosphere than females (29.5%). Comparing these differences allows us to make recommendations for optimal placement of the baseplate and the overhang of the glenosphere necessary to avoid notching and osteophyte formation in male and female patients. Table IV and V present the 95% confidence intervals for the mean placement of the baseplate and overhang of the glenosphere for patients without notching and patients without osteophyte formation, respectively. Applying these recommendations to the distribution of the positions of the baseplate of female patients who developed notches shows that if the peg of the baseplate was placed 18.2 mm from the inferior rim of the glenoid, the rate of scapular notching would decrease from 13.3% to 0.9%. For males, if the peg was placed 19.5 mm from the inferior rim, the rate of notching would decrease from 13.0% to 6.5%. Similarly, applying these recommendations to the distribution of overhang of the glenosphere in females who notched shows that if an overhang of 5.7 mm was obtained, the rate of notching would decrease from 13.3% to 0.9%. For males, if an overhang of 5.6 mm was obtained, the rate of notching would decrease from 13.0% to 8.7%. Applying these recommendations to the distribution of positions of the baseplate of female patients who had an osteophyte shows that if the peg was placed 18.0 mm from the inferior rim of the glenoid, the rate of osteophyte formation would decrease from 22.9% to 1.9%. For males, if the peg was placed 18.9 mm from the inferior rim, the rate of osteophyte formation would decrease from 50.0% to 8.7%. Similarly, applying these recommendations to the distribution of overhang of the glenosphere in females with an osteophyte shows that if 5.9 mm of overhang was obtained, the rate of osteophyte formation would decrease from 22.9% to 1.9%. For males, if 6.7mm of overhang was obtained, the rate of formation of an osteophyte would decrease from 50.0% to 0%.

It should be noted that these recommendations are specific to the Equinoxe reverse shoulder prosthesis. Care should be taken when extrapolating these results to other reverse shoulder devices. Additionally, these recommendations describe the position of the glenoid component after reaming. However, because the baseplate has a curved back and minimal bone is removed by spherical reaming, the position after reaming can be assumed to approximate that before reaming. Kelly et al14 recommended determining the position of the baseplate before reaming to facilitate the choice of the reaming axis that will result in the Grammont glenoid baseplate lining up with the inferior rim of the glenoid. Based on CT reconstructions, they recommended that the centre peg of the baseplate be positioned 11.5 mm from the inferior rim of an unreamed glenoid or 14.5 mm from the inferior rim when the glenoid was reamed flat. At this position of the baseplate, they reported a mean overhang of the glenosphere of 0.5 mm (-1 mm to 2.5 mm). Comparing the position of the baseplate and the resulting overhang of the glenosphere that was achieved, the results of our study show that the Equinoxe glenoid baseplate was positioned a mean of 4.6 mm higher on the glenoid for patients without a notch while achieving a mean of 4.6 mm more overhang of the glenosphere. This more superior placement of the baseplate on the glenoid was achieved primarily by the 4 mm superior shift of the peg and is advantageous because it permits a comparable overhang of the glenosphere while securing the baseplate closer to the centre of the glenoid where the vault is deeper20 and because the peg can be used to fill a central cavity defect,21 which is commonly found at revision arthroplasty. This study has limitations; it is retrospective, we did not report clinical outcomes, nor did we characterise the preoperative wear pattern of the glenoid. The grading of scapular notching and osteophytes was limited by the use of AP THE BONE & JOINT JOURNAL

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scapular radiographs rather than fluoroscopy or 3D reconstructed images. Levigne et al9 reported that only 89% of the scapular notches could be observed on AP radiographs due to variations in the position of the patient. We observed that the accuracy of measurement of the PSNA was dependent upon the orientation of the radiograph; the use of fluoroscopy or 3-D reconstructed images would probably improve the accuracy of these measurements.1 Another limitation is the relatively short mean follow-up of 28.3 months, particularly given the reported progressive6,9 nature of scapular notching. However, as notching has been reported early after surgery,1,6,9 we feel that a minimum follow-up of 24 months is appropriate to assess this complication. In conclusion, scapular notching is a common complication of reverse shoulder replacement with a medialised glenoid centre of rotation. We found a rate of notching of 13.2% and a rate of osteophyte formation of 31.1% with a reverse shoulder prosthesis whose centre of rotation is slightly lateralised relative to the glenoid; grade 2 notches occurred in 2.6% of cases and no grade 3 or 4 notches were observed at a mean follow-up of 28.3 months. Most notching and osteophyte formation was related to the position of the baseplate, the amount of overhang of the glenosphere, and/or the scapular anatomy, as described by the PSNA and the size of the glenoid, which reflected the differences in gender. As a result of these observations, we were able to make recommendations on placement of the reversed shoulder prosthesis in male and female patients so as to avoid notching and osteophyte formation. The authors would like to express their appreciation to Dr. L. Crosby, D. Johnson, A. Struk and M. Christensen for their contributions to this study. The author or one or more of the authors have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article. This article was primary edited by P. Baird and first-proof edited by J. Scott.

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