Orthopedics

Feature Article 

Subscapularis-Sparing Total Shoulder Arthroplasty: A Prospective, Double-Blinded, Randomized Clinical Trial

Young W. Kwon, MD, PhD; Joseph D. Zuckerman, MD

Abstract

Although total shoulder arthroplasty (TSA) is generally associated with good to excellent outcomes in most patients, the integrity and function of the subscapularis tendon (SSC) is of paramount importance because SSC rupture after TSA can lead to inferior outcomes. Therefore, the efficacy of a SSC-sparing TSA procedure was evaluated through a prospective, double-blinded, randomized study. Patients with end-stage osteoarthritis of the shoulder were randomized into 2 groups. Group 1 patients were treated with TSA in which the prosthesis was inserted entirely through the rotator interval without violating the SSC tendon (SPARING). Group 2 patients were treated with TSA using the SSC tenotomy approach (STANDARD). Both the patients and the evaluators remained blinded to the surgical approach throughout the study. Outcome data collected included the visual analog scale score for pain and the American Shoulder and Elbow Surgeons outcome score. Complete 2-year outcome data were collected from 32 SPARING and 38 STANDARD patients at a mean follow-up of 31.1 and 33.4 months, respectively. The American Shoulder and Elbow Surgeons and visual analog scale scores improved significantly for both groups. Differences between groups did not reach statistical significance. Complication profiles were similar for the 2 groups, with 3 patients in the SPARING group and 2 patients in the STANDARD group requiring revision surgery during the study. At short-term follow-up, the outcome of TSA using the SSC-sparing surgical approach was similar to the outcome of TSA using the standard approach. Studies with longer follow-up are required to document the potential benefits of this surgical technique. [Orthopedics. 2019; 42(1):e61–e67.]

Abstract

Although total shoulder arthroplasty (TSA) is generally associated with good to excellent outcomes in most patients, the integrity and function of the subscapularis tendon (SSC) is of paramount importance because SSC rupture after TSA can lead to inferior outcomes. Therefore, the efficacy of a SSC-sparing TSA procedure was evaluated through a prospective, double-blinded, randomized study. Patients with end-stage osteoarthritis of the shoulder were randomized into 2 groups. Group 1 patients were treated with TSA in which the prosthesis was inserted entirely through the rotator interval without violating the SSC tendon (SPARING). Group 2 patients were treated with TSA using the SSC tenotomy approach (STANDARD). Both the patients and the evaluators remained blinded to the surgical approach throughout the study. Outcome data collected included the visual analog scale score for pain and the American Shoulder and Elbow Surgeons outcome score. Complete 2-year outcome data were collected from 32 SPARING and 38 STANDARD patients at a mean follow-up of 31.1 and 33.4 months, respectively. The American Shoulder and Elbow Surgeons and visual analog scale scores improved significantly for both groups. Differences between groups did not reach statistical significance. Complication profiles were similar for the 2 groups, with 3 patients in the SPARING group and 2 patients in the STANDARD group requiring revision surgery during the study. At short-term follow-up, the outcome of TSA using the SSC-sparing surgical approach was similar to the outcome of TSA using the standard approach. Studies with longer follow-up are required to document the potential benefits of this surgical technique. [Orthopedics. 2019; 42(1):e61–e67.]

Total shoulder arthroplasty (TSA) has been used to treat patients with osteoarthritis and inflammatory arthritis of the glenohumeral joint. Several studies have shown that this procedure is associated with good to excellent outcomes in most patients.1–5 As a result, TSA has become the treatment of choice for elderly patients with end-stage glenohumeral arthritis, which has been reflected in the increased number of TSAs performed annually in the United States.6,7

Traditionally, the TSA procedure is performed through the anterior deltopectoral approach that releases the subscapularis (SSC) tendon to expose the joint. Although the SSC tendon is repaired after the prostheses are inserted, the integrity and function of this structure may be compromised in some patients, leading to inferior clinical outcomes.8–10 Therefore, some authors have supported the use of lesser tuberosity osteotomy, rather than SSC tenotomy, to enhance the potential postoperative healing.11–13 Unfortunately, even with lesser tuberosity osteotomy, postoperative function of the SSC may still be compromised.14,15

In 2009, LaFosse et al16 introduced a novel surgical technique for TSA in which the prosthesis was inserted through the rotator interval. With this technique, all rotator cuff tendons, including the SSC, remain intact during the procedure. At a minimum 2-year follow-up, they noted favorable pain relief and functional outcomes that were comparable to previously published results of TSA. Complications and other adverse event rates were also similar, while the radiographic assessment showed some residual humeral head osteophytes, which were of unclear clinical significance. Notably, these patients demonstrated superior SSC function.16

The theoretical advantages of performing TSA through the rotator interval include improved SSC function, decreased failure rate, and accelerated postoperative rehabilitation. Therefore, the authors performed a randomized clinical trial to examine the outcome of patients whose TSA was performed via this SSC-sparing approach. The authors' hypothesis was that, compared with patients who underwent TSA via the traditional SSC tenotomy technique, these patients would have comparable improvements in pain, motion, functional outcome, and failure rate.

Materials and Methods

Patient Recruitment

In 2010, approval for the randomized clinical trial was obtained from the institutional review board of the New York University School of Medicine. Appropriate patients with end-stage osteoarthritis of the shoulder who were scheduled for TSA performed by either of the investigators (Y.W.K., J.D.Z.) were identified and approached. Exclusion criteria for the trial included prior shoulder arthroplasty and full-thickness rotator cuff tears. Owing to technical issues associated with the SSC-sparing TSA procedure, additional exclusion criteria included significant me-dial erosion of the glenoid (lateral edge of the humeral head being medial to the lateral acromial rim on anteroposterior radiograph of the shoulder) and morbid obesity (body mass index >40 kg/m2). For appropriate patients, study rationale was explained, and informed consent was obtained when they agreed to participate in the clinical trial.

Randomization and Data Collection

For each enrolled patient, a number was created by a random number generator. Patients with even numbers were treated with the traditional TSA procedure (STANDARD), and patients with odd numbers were treated with the SSC-sparing procedure (SPARING). The surgeon was notified of the randomization result on the morning of the surgery. All patients remained blinded to their procedure during the entire follow-up period.

Preoperatively, all patients were evaluated with standard anteroposterior, axillary, and outlet view radiographs of the affected shoulder. Some patients were also evaluated with computed tomography of the shoulder at the surgeon's discretion. In addition, their demographic data, including age, sex, and comorbidities, were collected.

Outcome was assessed using the visual analog scale (VAS) score for pain and the American Shoulder and Elbow Surgeons (ASES) outcome score.17 Active motion of the affected shoulder, including forward elevation and external rotation, was also measured with a goniometer and documented. These data were collected preoperatively and at 3 months, 6 months, 12 months, and 24 months after the procedure. All outcome data collection was performed by a study coordinator who also remained blinded to the surgical technique. Whenever possible, the data were collected by the coordinator during a face-to-face interview. If not, clinical outcome data were collected by the coordinator by telephone, and the motion data were collected through a diagram and a questionnaire, which has been validated in shoulder arthroplasty literature.18,19

A statistical analysis comparing outcomes before and after surgery was performed using the paired, 2-tailed Student's t test. A statistical analysis comparing outcomes of the SPARING and STANDARD groups was performed using the non-paired, 2-tailed Student's t test. Statistical significance was set at P<.05.

Surgical Technique

Unlike the original description by LaFosse et al16 that used a lateral incision with a deltoid-splitting approach, this SSC-sparing TSA procedure used an anterior incision through the deltopectoral interval. Therefore, all patients in both groups were placed in a beach chair position for anterior incision. After developing the deltopectoral interval, soft tissue biceps tenodesis was performed for all patients by fixing the proximal biceps tendon to the pectoralis major tendon with No. 2 nonabsorbable sutures.

For the STANDARD TSA procedure, the SSC tendon was incised approximately 5 to 7 mm medial to its insertion at the lesser tuberosity. After release of the inferior capsule, the marginal osteophytes were excised. The implants were then inserted in a standard manner. After insertion of the implants, the SSC tendon was repaired anatomically with No. 2 nonabsorbable sutures.

For the SPARING TSA procedure, the inferior portion of the SSC, at the level of the humeral neck, was split parallel to its fibers to visualize the inferior capsule. Through this “window” in the inferior SSC, the inferior capsule and the inferior humeral neck osteophytes were excised. Subsequently, the shoulder was positioned in extension to expose the rotator interval. The rotator interval tissues were excised while protecting the SSC and the supraspinatus tendons. An extramedullary humeral head cutting guide was attached to the bicipital groove. Through the rotator interval, the humeral head was initially cut with a small microsagittal saw. This cut was then completed with an osteotome, and the humeral head was removed. Any residual osteophytes about the anterior or posterior portion of the humeral head were then removed through the rotator interval. After insertion of the prosthesis, the rotator interval was closed using No. 2 Mersilene sutures (Ethicon, Cincinnati, Ohio).

All patients received a third-generation modular total shoulder prosthesis (Equinoxe Shoulder replacement system; Exactech, Inc, Gainesville, Florida). All glenoid prostheses were placed with cement. The choice of pegged or keeled glenoid component was at the discretion of the surgeon. Similarly, the use of cement for humeral stem fixation was at the discretion of the surgeon.

After the procedure, all patients were admitted and monitored. They received inpatient counseling and instructions for passive motion exercises of the shoulder, which began on postoperative day 1. For the STANDARD group, a maximum limit on external rotation was determined during the surgery and was set for the first 4 weeks after surgery. All patients were allowed to use a sling for 2 to 4 weeks. In the SPARING group, the use of a sling was discretionary, while the STANDARD group was instructed to use a sling more regularly during ambulation and general daily activities. Active motion and resistive strengthening exercises were instituted at 6 to 8 weeks after the surgery.

Results

A total of 107 shoulders of 107 patients (57 SPARING, 50 STANDARD) were enrolled in the study. Of these, 14 TSA procedures could not be completed as initially randomized. Nine of these cases involved patients who were initially randomized to the SPARING technique, but the surgery had to be converted to standard technique. All of these patients were male, with large anterior deltoid masses that prevented adequate exposure. The remaining 5 patients were treated with reverse total shoulder replacement, as full-thickness rotator cuff tendon tears were noted during the surgery. In addition, 3 patients died (unrelated to the procedure), 7 patients withdrew from the study, and 2 moved without notification. Of the remaining 81 patients, 2-year outcome data could not be collected from 11. Thus, complete 2-year outcome data were collected from 32 SPARING and 38 STANDARD patients (Figure 1).

Consolidated Standards of Reporting Trials 2010 flow diagram for patient enrollment. Abbreviation: TSA, total shoulder arthroplasty.

Figure 1:

Consolidated Standards of Reporting Trials 2010 flow diagram for patient enrollment. Abbreviation: TSA, total shoulder arthroplasty.

Of the 32 patients in the SPARING group, 11 were male and 21 were female. Mean age was 69.6±9.5 years, and mean follow-up was 31.1±9.9 months. Nineteen of the implanted glenoids were keeled, while the remaining 13 glenoids were pegged. Only 1 of the 32 humeral implants was inserted with cement (Table 1).

Characteristics of the SPARING and STANDARD Groups of Patients

Table 1:

Characteristics of the SPARING and STANDARD Groups of Patients

Of the 38 STANDARD patients, 22 were male and 16 were female. Mean age was 69.1±8.2 years, and mean follow-up was 33.4±13.1 months. Ten of the glenoid prostheses were keeled, while 28 were pegged. Two of the 38 humeral implants were inserted with cement.

Both the SPARING and STANDARD groups of patients experienced significant improvements in pain and function after the TSA surgery. In the SPARING group, the mean VAS and ASES scores improved from 6.6±2.1 and 29.3±12.5, respectively, to 1.6±2.2 and 81.7±23.3, respectively. Mean flexion and external rotation also improved from 89.5°±28.3° and 15.8°±12.6°, respectively, to 155.8°±23.3° and 46.0°±11.5°, respectively. All of these improvements were statistically significant (P<.001). In the STANDARD group, the mean VAS and ASES scores improved from 6.3±2.4 and 32.8±16.1, respectively, to 1.0±1.7 and 87.1±14.5, respectively. Mean flexion and external rotation in this group improved from 88.0°±29.9° and 14.7°±16.9°, respectively, to 154.6°±21.7° and 52.1°±20.8°, respectively. These improvements in the STANDARD group were also statistically significant (P<.001) (Table 2).

Pre- and Postoperative Improvements in the SPARING and STANDARD Groups of Patients

Table 2:

Pre- and Postoperative Improvements in the SPARING and STANDARD Groups of Patients

In the SPARING and STANDARD groups, the improvements in the mean VAS scores from preoperative to final follow-up were 5.1±3.1 and 5.3±2.5, respectively (P=.756). Similarly, improvements in the mean ASES scores in the 2 groups were 53.9±22.3 and 54.0±18.7, respectively (P=.983). Improvements in flexion and external rotation from preoperative to final follow-up in the SPARING group were 66.9°±34.3° and 31.5°±13.5°, respectively. Similarly, improvements in flexion and external rotation in the STANDARD group were 64.4°±26.9° and 35.9°±18.1°, respectively. Again, these differences between the SPARING and STANDARD groups of patients were not statistically significant (Table 2, Figures 24).

Visual analog scale (VAS) scores for pain for the SPARING and STANDARD groups of patients.

Figure 2:

Visual analog scale (VAS) scores for pain for the SPARING and STANDARD groups of patients.

American Shoulder and Elbow Surgeons (ASES) outcome scores for the SPARING and STANDARD groups of patients.

Figure 3:

American Shoulder and Elbow Surgeons (ASES) outcome scores for the SPARING and STANDARD groups of patients.

Shoulder motion for the SPARING and STANDARD groups of patients. Abbreviation: ex, external.

Figure 4:

Shoulder motion for the SPARING and STANDARD groups of patients. Abbreviation: ex, external.

No intraoperative or immediate postoperative complications were noted in any of the patients. In the SPARING group, 3 complications were noted during the study that required revision surgery. The first patient had a fall due to complication from metastatic lung cancer 4 months after the index procedure. The fall resulted in a dislocation of the humeral head, which, in turn, dislodged the glenoid component from the bone. A retracted tear of the supraspinatus and the infraspinatus was noted during the revision surgery, and the prosthesis was converted to reverse TSA. The second patient was noted to have symptomatic glenoid loosening at 9 months after the index surgery. During the surgery, a tear in the supraspinatus was noted and the construct was also converted to reverse TSA. The third patient in the SPARING group presented with deep infection 8 weeks after the index procedure requiring surgical irrigation, debridement, and component exchange. Intraoperative cultures isolated Propionibacterium acnes.

In the STANDARD group, 2 complications were noted that required revision surgery. The first patient noted posterior subluxation of the joint approximately 6 months after surgery following minor trauma. An arthrogram showed a tear of the supraspinatus and the infraspinatus, and the patient was treated with reverse TSA. The second patient noted initial improvement, which then deteriorated approximately 4 years after the index surgery without trauma. The glenoid was noted to be loose, and the patient was treated with conversion to hemiarthroplasty.

Discussion

Total shoulder arthroplasty is generally associated with good to excellent clinical outcomes in most patients. However, inferior clinical results have been noted in patients with subsequent SSC insufficiency.8–10 This has led surgeons to consider surgical options to protect the SSC during the procedure or improve its postoperative healing. However, to date, none of these techniques have shown clinical superiority.14,15 The original description of the SSC-sparing TSA procedure by LaFosse et al16 used a lateral incision with release of the anterior deltoid from the acromion. Subsequently, the surgical technique was modified by LaFosse et al to include an anterior incision for the deltopectoral approach as described in the current study. This modification protects the integrity of the anterior deltoid and allows access to the inferior humeral head osteophytes that are prevalent in arthritic shoulders.

With this modification, the theoretical advantages of the SSC-sparing technique include reduction of SSC dysfunction and improved clinical outcome. In their early outcome analysis, La Fosse et al16 noted that their clinical outcome was comparable to previously published results after TSA. Data from this study support their conclusions, as patients treated with SPARING and STANDARD techniques had similar clinical outcomes. In fact, pre- to postoperative improvements in VAS and ASES scores were almost identical between the 2 groups of patients. Therefore, the theoretical improvement in clinical outcome was not evident during this early follow-up period. However, prosthesis survival after TSA is excellent for the first 5 to 7 years with subsequent deterioration of outcome.1,5,20 It is possible, therefore, that the patients treated with the SSC-sparing technique may show reduction in clinical failures, especially those related to SSC dysfunction, with longer follow-up.

Another potential advantage of the SSC-sparing technique is accelerated rehabilitation with early mobilization. The SPARING group of patients were able to move the shoulder without any restrictions, and their use of a sling was discretionary. Anecdotally, these patients noted a more comfortable and appealing post-operative experience compared with the patients in the STANDARD group. Unfortunately, however, their comfort during the immediate postoperative period could not be adequately quantified.

The primary disadvantage of the SSC-sparing TSA technique is the limited surgical exposure. All procedures performed in this trial used a third-generation modular TSA prosthesis. In addition, specialized instruments, such as a reduced profile humeral stem holder, were specifically designed and produced by the manufacturer for the SSC-sparing procedure. Even with these instruments, however, the surgical exposure is still limited, as the joint is approached entirely through the rotator interval.

One potential concern for the limited exposure is the inability to accurately reproduce the native anatomy of the shoulder with the prostheses. Previously, the authors found that the radiographic parameters of the shoulder prostheses in these same groups of STANDARD and SPARING patients were similar.21 However, the SPARING group contained more patients with residual osteophytes and with greater than 4-mm mismatch in the diameter of the humeral head prosthesis against the native humeral head. With the limited sample size, the overall outcomes of these patients with humeral head mismatch and residual osteophytes were not statistically inferior, and the clinical consequences of these radiographic characteristics were unclear.

Another potential concern for the limited surgical exposure is the inability to perform appropriate release of the shoulder joint capsule, thus reducing postoperative motion. In these groups of patients, however, this concern was not evident. Compared with their preoperative status, the SPARING group of patients had improvements of 67° and 32° in their shoulder flexion and external rotation, respectively. Corresponding improvements in the STANDARD group were almost identical at 64° and 36°, respectively. Thus, although the overall exposure may be limited, the SSC-sparing technique does provide the opportunity to release or excise the inferior and anterior capsules so as not to adversely affect postoperative motion.

The SSC-sparing TSA is technically challenging and cannot be performed for all patients with end-stage arthritis. Significant anterior soft tissue bulk (muscle or fat) could prevent adequate exposure through the rotator interval. Thus, patient selection is crucial, and the technique should be avoided in younger male or obese patients. In addition, in joints that are medially eroded, access through the rotator interval can be compromised by the coracoid process. To eliminate these potential variables, this trial excluded patients with body mass index greater than 40 kg/m2 or significant medial joint erosion. However, there were still 9 patients in the SPARING group whose surgery had to be converted to the traditional technique with SSC tenotomy because of insufficient exposure. All of these converted patients were male, with excessive anterior deltoid muscle mass. As a result, despite the authors' best efforts to randomize the 2 study groups, only 11 (34%) of the 32 patients in the SPARING group were male, while 22 (58%) of the 38 patients in the STANDARD group were male. In healthy patients, the ASES score is not affected by sex.22 However, it is possible that this difference in male:female ratio between the 2 groups introduced an unforeseen variable to the final analysis.

Another difference between the SPARING and STANDARD groups of patients was the percentage of keeled vs pegged glenoid components. In the SPARING group, 19 (59%) of the 32 glenoids were keeled. In contrast, only 10 (26%) of the 38 prostheses in the STANDARD group were keeled. One potential explanation for this difference was the larger percentage of female patients in the SPARING group; presumably their glenoids were smaller and could not tolerate a pegged design. Another potential explanation for this difference was the reduced glenoid exposure through the rotator interval that prevented adequate preparation and insertion of the peripheral pegs. Again, although no clinical difference between patients with keeled or pegged glenoid TSA has been shown, it is possible that this difference in the keeled:pegged glenoid ratio between the groups introduced an unforeseen variable to the analysis.23

Other limitations of the study included a fairly high rate of patient drop out after enrollment (44% for SPARING and 24% for STANDARD), limited duration of follow-up, difference in rehabilitation (duration of sling use), and lack of postoperative ultrasound to confirm the integrity of the SSC. Despite these limitations, however, the data suggest that the SSC-sparing TSA can be performed successfully to improve pain and function in patients with end-stage shoulder arthritis.

Conclusion

At short-term follow-up, the SSC-sparing technique for shoulder arthroplasty can lead to clinical outcomes that are similar to those of the standard technique. Longer follow-up is necessary to identify the potential benefit of this technique.

References

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Characteristics of the SPARING and STANDARD Groups of Patients

CharacteristicSPARING GroupSTANDARD Group
Shoulders, No.3238
Age, mean±SD, y69.6±9.569.1±8.2
Sex, male/female, No.11/2122/16
Side, right/left, No.11/2123/15
Glenoid, keeled/pegged, No.19/1310/28
Humeral cement, yes/no, No.1/312/36
Follow-up, mean±SD, mo31.1±9.933.4±13.1

Pre- and Postoperative Improvements in the SPARING and STANDARD Groups of Patients

Outcome ParameterMean±SDP

SPARING GroupSTANDARD Group
Visual analog scale score
  Preoperative6.6±2.16.3±2.4.628
  Postoperative1.6±2.21.0±1.7.188
  Difference5.1±3.15.3±2.5.756
American Shoulder and Elbow
Surgeons score
  Preoperatvie29.3±12.532.8±16.1.328
  Postoperative81.7±23.387.1±14.5.290
  Difference53.9±22.354.0±18.7.983
Flexion
  Preoperative89.5°±28.3°88.0°±29.9°.829
  Postoperative155.8°±23.3°154.6°±21.7°.848
  Difference66.9°±34.3°64.4°±26.9°.781
External rotation
  Preoperative15.8°±12.6°14.7°±16.9°.771
  Postoperative46.0°±11.5°52.1°±20.8°.219
  Difference31.5°±13.5°35.9°±18.1°.347
Authors

The authors are from the Department of Orthopaedic Surgery, Division of Shoulder & Elbow Surgery, NYU Langone Medical Center, New York, New York.

Dr Kwon has no relevant financial relationships to disclose. Dr Zuckerman is an implant design surgeon for Exactech.

Correspondence should be addressed to: Young W. Kwon, MD, PhD, Department of Orthopaedic Surgery, Division of Shoulder & Elbow Surgery, NYU Langone Medical Center, 333 E 38th St, New York, NY 10016 ( young.kwon@nyumc.org).

Received: March 16, 2018
Accepted: July 18, 2018
Posted Online: November 14, 2018

10.3928/01477447-20181109-02

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