20° Anchor Insertion Technique Toward the Subchondral Bone in Rotator Cuff Repairs for Patients With Osteoporosis Compared With the Traditional 45° Deadman Angle

Abstract

Background:

Rotator cuff repair in patients with osteoporosis is challenging due to compromised bone anchor stability. While the traditional 45°Deadman angle is biomechanically favored in normal bone, its efficacy in osteoporosis remains uncertain, potentially contributing to complications such as anchor-related cysts and retears. This study compared the clinical outcomes and complication rates between a traditional 45° angle and a shallower 20° angle directed toward the denser subchondral bone in patients with osteoporosis undergoing double-row rotator cuff repair.

Purpose:

To compare the clinical outcomes of rotator cuff repair in patients with osteoporosis using the traditional 45° Deadman angle versus the insertion angle of approximately 20° directed toward the subchondral bone.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

A retrospective analysis was conducted on patients diagnosed with rotator cuff tears and osteoporosis who underwent double-row suture anchor repair from January 2018 to January 2022. Patients were divided into 2 groups based on the angle of the medial row anchors, measured coronally, during intraoperative implantation and on postoperative magnetic resonance imaging (MRI). Group 1 (n = 62) had the medial row anchors inserted at an angle of approximately 45° (the Deadman angle) in the coronal direction, while group 2 (n = 65) had the inner row anchors inserted at an angle of approximately 20° in the coronal direction. A comparison of the general data between the 2 groups is presented. After a minimum follow-up of 2 years, postoperative clinical outcomes were compared with the American Shoulder and Elbow Surgeons (ASES), University of California, Los Angeles (UCLA), Constant Score (CS), and visual analog scale (VAS) scores, as well as the shoulder range of motion (ROM). Perianchor cyst and retear were evaluated through MRI.

Results:

Significant improvements were observed in all clinical outcomes for both groups, from baseline preoperative evaluations to the final follow-up assessments (P = .001 for ASES score, UCLA score, CS, VAS score, and ROM), with no significant differences between the 2 groups (P > .05). However, at the final follow-up, group 2 demonstrated significantly lower perianchor cyst grading and a significantly lower retear rate (13.84% vs 37.09%) compared with group 1 (P < .05).

Conclusion:

Both anchor insertion techniques resulted in acceptable shoulder clinical outcomes for patients with osteoporosis undergoing rotator cuff repair. However, the 20° insertion angle toward the subchondral bone was associated with a significantly lower incidence of perianchor cysts and retears than the traditional 45° Deadman angle.

With the aging population and the increasing activity levels among older adults, the number of rotator cuff repairs is rising.^15,18 Consequently, it is common to encounter elderly patients with osteoporosis presenting with rotator cuff tears. Double-row suture anchors have become the standard for securing a torn tendon stump to its footprint in the surgical repair of rotator cuff tears. ²¹ While they offer a viable alternative to traditional transosseous suture repair, several factors can influence the initial fixation strength. These include the anchor design, suture material properties, tendon stump tissue quality, bone quality at the footprint, and the anchor insertion angle.^4,11,16 The insertion angle of suture anchors in rotator cuff repairs significantly affects fixation strength and stress distribution. ²⁹ However, most clinicians still adhere to Burkhart's Deadman angle theory, opting for a 45° insertion angle for medial row anchors to achieve maximum fixation strength. ¹⁷ In patients with osteoporosis, the significantly decreased bone mineral density (BMD) and cortical thinning at the footprint of the greater tuberosity weaken the fixation strength of anchors inserted at the traditional Deadman angle. ¹⁰ This weakened fixation strength increases the risk of early anchor pullout and compromises the anchors' long-term stability. Research indicates that decreased bone density increases micromotion between the anchor and surrounding bone tissue, leading to cyst formation around the anchor, which is significantly associated with higher retear rates and poor shoulder function postoperatively. ⁸ Therefore, given the unique circumstances of patients with osteoporosis, reassessing and optimizing the insertion angle of anchors is crucial for improving surgical outcomes and reducing complications.

Some studies suggested that inserting inner row anchors at a 45° angle increased insertion depth and contact area with bone tissue, thereby achieving greater fixation strength.^13,24 However, this is not the case for patients with osteoporosis. Two computed tomography (CT) studies on cadaveric humeral head specimens found that cancellous bone exhibited progressively deteriorating bone quality, as indicated by parameters such as bone volume to total volume ratio, trabecular number, trabecular thickness, and trabecular separation.^10,34 This deterioration begins at the outer cortical surface and extends into the deeper regions of the greater and lesser tuberosities.^10,32 In patients with osteoporosis, there is a significant decrease in cancellous bone density, whereas the decline in subchondral bone density is relatively less pronounced. ³² Therefore, directing inner row anchors toward the subchondral bone (approximately 20° angle anchor insertion) may enhance the fixation strength of the anchors due to the relatively increased bone density. This approach could improve the biomechanical performance of the anchor-bone interface and lead to better clinical outcomes. However, few studies have focused on this aspect to date. This study aimed to compare the clinical outcomes of rotator cuff repair in patients with osteoporosis between the traditional 45° Deadman angle and the insertion angle of approximately 20° toward the subchondral bone. We hypothesized that the 20° insertion angle toward the subchondral bone would yield a lower incidence of retears compared with the traditional 45° Deadman angle insertion.

Methods

Patient Enrollment

The study protocol was approved by our institution's institutional review board. As this was a retrospective study, the ethics committee waived the requirement for written informed consent specific to this analysis. All patients had previously provided general written informed consent for their surgical procedure and for the use of their anonymized data for research purposes. A retrospective analysis was conducted on cases diagnosed with rotator cuff tears and osteoporosis who underwent double-row suture anchor repair from January 2018 to January 2022. The assignment to the 2 groups was chronological, reflecting an evolution in our standard surgical technique. From January 2018 to March 2020 (the early phase), all patients underwent surgery using the traditional 45° Deadman angle for medial row anchor insertion (group 1, n = 62). From April 2020 to January 2022 (the latter phase), the surgical protocol was updated, and all subsequent patients received the medial row anchors at an angle of approximately 20° directed toward the subchondral bone (group 2, n = 65). The insertion angles for all patients were confirmed by coronal measurements on both intraoperative implantation and postoperative magnetic resonance imaging (MRI).

The study inclusion criteria were (1) osteoporosis (T score <–2.5 SD^30,31); (2) patients undergoing double-row rotator cuff (supraspinatus tendon) repair;(3) comprehensive preoperative and final follow-up MRI scans, CT scans, and functional assessments of the shoulder; and (4) a minimum follow-up duration of 24 months. The exclusion criteria were (1) severe tendon retraction that resulted in the inability to reposition the tendon during surgical intervention ¹⁴ ; (2) grade of fatty infiltration >2 according to the Goutallier fatty infiltration grade ⁶ ; (3) a history of surgery on the affected shoulder; (4) the follow-up period for the patients was <24 months; and (5) subscapularis tear.

Surgical Techniques

All surgical procedures were performed by the same team of experienced arthroscopic specialists (F.B.). Each patient received general anesthesia along with a brachial plexus block and was positioned in the beach-chair posture. A standard posterior portal was used to evaluate the biceps long head tendon, humeral head cartilage, and joint-side rotator cuff tears. Superficial and deep adhesions in the rotator cuff were meticulously released. In the subacromial space, the proliferative bursa was cleared, and acromioplasty was performed for patients with acromion impingement. Next, the torn rotator cuff tendon was exposed and grasped to assess tension and tear size. Repair was initiated using the double-row anchor suture technique. ³⁵ Two 5.5-mm inner row anchors (China Ruijian Medical or Johnson & Johnson), each preloaded with two No. 2 sutures, were placed at the posteromedial and anteromedial margins of the footprint adjacent to the cartilage-bone interface. In group 1, the anchors were inserted at an approximate angle of 45° to the tangent of the greater tuberosity in the coronal plane, specifically along the lateral edge of the humeral head cartilage at the footprint of the greater tuberosity (Figures 1A and 2A), whereas in group 2, they were inserted at an approximate angle of 20° to the tangent of the greater tuberosity in the coronal plane (Figures 1B and 2B). Subsequently, sutures were passed through the full thickness of the torn tendon from the articular side to the bursal side using lasso loop stitches (Smith & Nephew). The tendon was first anatomically reattached using a medial row mattress stitch. Subsequently, the free suture limbs were bridged over the tendon and secured laterally with 1 or 2 knotless anchors (China Ruijian Medical or Johnson & Johnson) placed 10 mm distal to the greater tuberosity, the number of which was determined by the tear size, thereby finalizing the suture-bridge technique. The rotator cuff was successfully reattached with appropriate tension (Figure 3). A schematic diagram illustrating the utilized surgical methodologies is presented in Figure 1

Figure 1.

Schematic diagram of the surgical techniques. (A) The inner row anchor insertion angle is set at approximately 45° (Deadman angle). (B) The inner row anchor insertion angle is set at approximately 20°.

Figure 2.

Intraoperative images of 2 surgical techniques. (A) The intra-row anchors were inserted at approximately 45°. (B) The intra-row anchors were inserted at approximately 20°.

Figure 3.

Intraoperative view of the completed construct. The bridging sutures (red arrowheads) from the medial row are tensioned and secured to the tendon using lateral knotless anchors, thereby compressing the rotator cuff footprint.

Postoperative Rehabilitation

Postoperative rehabilitation was standardized for both groups. Immediately after surgery, patients wore a shoulder abduction brace for 4 to 6 weeks to immobilize the shoulder. Passive shoulder movements were introduced during this period. The brace was removed after 4 to 6 weeks, and active-assisted shoulder exercises with a progressive range of motion (ROM) began. Strengthening exercises started 3 months after surgery, with a return to sports activities allowed at 6 months.

Clinical and Radiological Assessment

Shoulder function was assessed preoperatively and at the final follow-up using the Constant Score (CS), ³³ the American Shoulder and Elbow Surgeons (ASES) score, ¹⁹ and the University of California, Los Angeles (UCLA) score. ²⁶ Pain levels were measured using the visual analog scale (VAS) at the same intervals. Postoperative MRI examinations were performed uniformly at 6 months for all patients to assess tendon integrity, anchor placement, and the formation of perianchor cysts. A standardized MRI protocol, established by the institutional musculoskeletal radiology team, was used for all postoperative assessments to ensure uniform measurement. Examinations were performed on Siemens 1.5-T or 3-T scanners (Avanto; MAGNETOM Skyra; TrioTim) using a dedicated shoulder coil with the patient in the supine position. The oblique coronal sequences, acquired parallel to the supraspinatus tendon, were utilized for the angle measurements. The key parameters for these sequences were consistent for all patients: slice thickness of 3 mm, slice gap of 0.3 mm, repetition time of 1500 msec, echo time of 40 msec, and a field of view of 16 × 16 cm. The insertion angles on postoperative MRI were measured independently by 2 authors of this study (Y.Z. and C.L.), who are both experienced orthopaedic sports medicine surgeons. The angle of suture anchor insertion was measured on postoperative coronal MRI images: a horizontal line parallel to the tangent at the apex of the greater tuberosity was drawn, and another line was made along the long axis of the inner row suture anchor. The angle formed by the intersection of these 2 lines represents the angle of anchor insertion (Figure 4). The grading of perianchor cysts was based on the criteria provided by Kim et al, ⁹ with modifications to include all anchor types. The modified grading criteria were as follows: grade 0, no fluid accumulation around the anchor; grade 1, minimal fluid accumulation around the anchor; grade 2, localized fluid accumulation at the anchor insertion site; grade 3, perianchor fluid accumulation less than twice the diameter of the original anchor; grade 4, perianchor fluid accumulation more than twice the diameter of the original anchor. At 6 months postoperatively, fluid signals were assessed on T2-weighted fat-suppressed images and graded. If there is fluid collection around both medial row anchors, then the anchor with the more severe fluid collection is evaluated. Tendon integrity was assessed using the Sugaya classification system (grades 1-5; 1-3 indicating intact tendons and 4-5 denoting retears). ²⁵ Muscle fat infiltration was assessed based on the MRI grading criteria established by Fuchs et al ⁵ (ranging from 0 to 4, with 0 signifying no infiltration and 4 indicating predominant fat presence over muscle). Muscle atrophy was assessed using the Thomazeau et al ²⁷ grading system (grades 1-3, where 1 and 3 represent minimal and severe atrophy, respectively). BMD at the femoral neck and spine was measured using CE Lunar DXA devices—including the GE Lunar Prodigy and DPX Bravo DXA scanners (GE Healthcare) for dual-energy X-ray absorptiometry.

Figure 4.

The angle of intra-row anchor insertion was measured on postoperative coronal T1-weighted MRI images. A horizontal line parallel to the tangent at the apex of the greater tuberosity was drawn and labeled as a. Another line was drawn along the long axis of the suture anchor and labeled as b. The angle formed by the intersection of lines a and b represents the angle of anchor insertion. (A) The intra-row anchors were inserted at approximately 45°. (B) The intra-row anchors were inserted at approximately 20°. MRI, magnetic resonance imaging.

Statistical Analysis

Intraclass correlation coefficients (ICCs) were used to assess the consistency of imaging indicator evaluations. Depending on data normality, functional scores and shoulder ROM were analyzed preoperatively and at final follow-up using paired t tests or Wilcoxon signed-rank tests. Continuous variables between groups were compared using Student t tests or Mann-Whitney U tests, whereas categorical variables were assessed with Pearson chi-square tests, whereas categorical variables were assessed using Pearson chi-square or Fisher exact tests. P < .05 was considered statistically significant. Data were analyzed using SPSS Version 23.0 (IBM Corp).

Results

Descriptive Data

A retrospective review of the medical records encompassed 658 consecutive patients diagnosed with rotator cuff tears from January 2018 to January 2022. Among these, 127 patients were diagnosed with rotator cuff tears accompanied by osteoporosis (T-score ≤–2.5 SD). All patients underwent double-row suture anchor repair for rotator cuff tears, with the inner row anchor insertion angle set at approximately 45° (Deadman angle) in group 1 (n = 62) and at approximately 20° in group 2 (n = 65). The flow diagram of this study is presented in Figure 5. The general characteristics of both study groups are presented in Table 1, revealing no significant differences in patient or surgical characteristics across the groups.

Figure 5.

Flow diagram of this study.

Table 1.

Characteristics of the Study Patients (N = 127) ^a

Characteristic	Group 1, n = 62	Group 2, n = 65	P
Age, years	51.7 ± 9.5	53.8 ± 11.3	.215
Sex, male/female, n	13/49	10/55	.492
BMI, kg/m2	27.2 ± 3.9	27.1 ± 4.5	.534
Smoking history, yes/no, n	10/52	7/58	.440
Arm involvement, dominant/nondominant, n	38/24	42/23	.717
Level of sports activity, low/medium/high, n	33/12/17	43/8/14	.319
Tear size of anteroposterior dimension, cm	3.45 ± 1.22	3.83 ± 1.87	.146
Amount of tendon retraction, cm	3.12 ± 1.47	3.41 ± 1.32	.261
Fatty degeneration, 5 grades 0/1/2/3/4, n	23/39/0/0/0	27/38/0/0/0	.609
Amount of lateral row anchors, 1/2, n	32/30	34/31	.938
Acromion type (1/2/3), n	6/25/31	7/32/26	.539
Bone mineral density, T score	–3.39 ± 0.67	–3.52 ± 0.58	.103
Bone mineral density, g/cm3	0.47 ± 0.15	0.42 ± 0.13	.112
Labrum repair, yes/no, n	3/59	5/60	.718
Duration of surgery, min	70.5 ± 18.3	74.3 ± 15.2	.188
Follow-up time, months	35.2 ± 5.2	34.1 ± 6.21	.282

^aData are presented as mean ± SD unless otherwise indicated. P < .05 indicates a statistically significant difference between groups. Inner row anchor insertion angle set at approximately 45° (Deadman angle) in group 1 and at approximately 20° in group 2. BMI, body mass index.

Clinical Outcomes

Both groups of patients showed substantial improvements in all clinical outcomes from preoperative evaluations through final follow-up. This is indicated by P of .001 across various metrics—including UCLA, ASES, CS, and VAS scores, as well as forward flexion, abduction, and external rotation measurements. No statistical differences were observed between the 2 groups (Table 2). Furthermore, there were no reported shoulder infections, stiffness, or dislocations in either group.

Table 2.

Functional Score Outcomes ^a

Score	Group 1, n = 62	Group 2, n = 65	P
UCLA score
Preop	14.93 ± 5.33	16.58 ± 3.87	.237
Final follow-up	30.71 ± 4.52	32.13 ± 4.11	.399
P	.001	.001
ASES score
Preop	44.73 ± 6.80	48.17 ± 7.43	.139
Final follow-up	81.51 ± 9.02	83.14 ± 11.52	.113
P	.001	.001
CS
Preop	49.71 ± 9.51	51.41 ± 8.49	.143
Final follow-up	82.33 ± 12.38	85.32 ± 13.31	.291
P	.001	.001
VAS score
Preop	5.23 ± 1.31	4.86 ± 1.67	.753
Final follow-up	1.87 ± 0.63	1.72 ± 0.79	.453
P	.001	.001
Forward flexion, deg
Preop	122.23 ± 14.16	125.12 ± 16.37	.295
Final follow-up	147.29 ± 26.54	150.38 ± 27.15	.109
P	.001	.001
Abduction, deg
Preop	63.21 ± 9.32	66.14 ± 11.21	.189
Final follow-up	145.23 ± 21.05	151.34 ± 29.20	.176
P	.001	.001
External rotation, deg
Preop	47.24 ± 8.35	46.38 ± 9.25	.138
Final follow-up	67.39 ± 11.23	70.13 ± 10.23	.482
P	.001	.001

^aData are presented as the mean ± SD. Bold P values indicate a statistically significant difference (P < .05). See footnote at Table 1 for group definition. ASES, American Shoulder and Elbow Surgeons; CS, Constant Score; Preop, preoperative; UCLA, University of California, Los Angeles; VAS, visual analog scale.

Radiological Outcomes

The ICC values for tendon integrity, fatty degeneration, muscle hypotrophy, and perianchor cyst were 0.85, 0.88, 0.93, and 0.82, respectively, indicating excellent reliability in assessing these radiological indicators. Table 3 and Figure 6 display the radiological outcomes. The postoperative MRI measurements of the angle of anchor insertion were consistent with the intraoperative angles for both groups. Group 1 had an angle of 45.02 ± 2.46, whereas group 2 had an angle of 20.43 ± 2.59. At the final follow-up, both groups exhibited significant improvements in tendon integrity as measured by Sugaya MRI grades compared with preoperative levels (P = .001). There were notable differences in tendon integrity between groups 1 and 2 at the final assessment (P = .002). Additionally, the grading of perianchor cysts was significantly lower in group 2 compared with group 1 at the 6-month postoperative assessment (P = .001). Moreover, the tendon retear rates at final follow-up differed significantly, with 37.09% in group 1 compared with 13.84% in group 2 (P = .002). There were no substantial changes in the grades of fatty degeneration or muscle hypotrophy from the initial evaluation to the final follow-up in either group.

Table 3.

Radiological Outcomes ^a

	Group 1, n = 62	Group 2, n = 65	P
The angle of anchor insertion, deg	45.02 ± 2.46	20.43 ± 2.59	.001
Tendon integrity, 25 grades 1/2/3/4/5, n
Preop	0/0/0/3/59	0/0/0/4/61	.745
Final follow-up	13/9/17/7/16	20/25/11/3/6	.002
P	.001	.001
Fatty degeneration, 5 grades 0/1/2/3/4, n
Preop	23/39/0/0/0	27/38/0/0/0	.609
Final follow-up	19/38/4/1/0	24/35/4/2/0	.809
P	.145	.098
Muscle hypotrophy, 27 grades 1/2/3, n
Preop	29/30/3	34/26/5	.573
Final follow-up	27/29/6	32/27/6	.794
P	0.580	0.918
Perianchor cyst, 8 grades 0/1/2/3/4, n	17/13/16/9/7	49/15/1/0/0	.001
Retear, n (%)	23 (37.09)	9 (13.84)	.002

^aBold P values indicate statistically significant differences (P < .05). See footnote at Table 1 for group definition. Preop, preoperative.

Figure 6.

Coronal T2-weighted MRI images showing perianchor cysts. (A) Grade 0, no fluid accumulation is observed around the anchor (yellow arrow); (B) Grade 1, minimal fluid accumulation is observed around the anchor (yellow arrow); (C) Grade 3, the perianchor fluid accumulation is less than twice the diameter of the original anchor (yellow arrow); (D) Grade 4, the perianchor fluid accumulation is more than twice the diameter of the original anchor. MRI, magnetic resonance imaging.

Discussion

The main findings of the present study were that (1) both the 20° and 45° anchor insertion surgical techniques resulted in acceptable shoulder function outcomes for patients with osteoporosis, and (2) the 20° anchor insertion angle toward the subchondral bone significantly improved the retear rate (13.84% vs 37.09%; P = .002) and reduced the incidence of perianchor cysts (P = .001) compared with the 45° insertion angle.

The rise in physical demands and athletic activity among the elderly has made surgical repair of rotator cuff injuries increasingly crucial. ³ Unfortunately, compromised bone quality and osteoporotic alterations can lead to postoperative issues such as loosening suture anchors, impaired tendon healing, and eventual failure of the rotator cuff repair. ²⁰ According to Jiang et al, ⁷ rotator cuff tears are linked to decreased trabecular bone volume and greater tuberosity connectivity. This deterioration can result in diminished bone quality, characterized by reduced biomechanical strength. Therefore, inserting anchors into the weakened footprint area of the humeral greater tuberosity will inevitably result in decreased fixation strength. ² An anatomic study has shown that in patients with osteoporosis, the density and volume of cancellous bone in the humerus decrease more significantly than those of cortical bone and subchondral bone. ²⁸ Therefore, we opted to reduce the insertion angle of the anchors in the footprint area of the humeral greater tuberosity and directed the anchors toward the subchondral bone. This technique increased the contact area between the anchors and the higher-density subchondral bone in osteoporotic patients while reducing the contact area with the cancellous bone compared with the traditional Deadman insertion technique—this modification aimed to enhance anchor fixation strength.

Postoperative retear remains a focal point of interest in rotator cuff repair surgery. Despite the challenge of differentiating retears from postoperative changes such as edema and artifacts, MRI remains the primary investigative tool for this purpose.^1,12 In the present study, the 20° anchor insertion angle surgical technique significantly improved the retear rate and reduced the incidence of perianchor cysts compared with the 45° anchor insertion angle. Kim et al ⁸ found that postoperative perianchor cysts were significantly associated with retears after surgery.

Ro et al ²² observed that larger perianchor cysts were associated with a threefold increase in the retear rate. These were consistent with the findings of our study. For patients with osteoporosis, the traditional 45° anchor placement, which is more vertical than the 20° insertion, results in greater contact with the less dense cancellous bone, which may increase micromovement between the anchor and the osteoporotic bone. This increased micromovement led to the early formation of cysts postoperatively, thereby reducing the anchor's fixation strength. In the complex stress transmission of the rotator cuff, a decrease in anchor fixation strength may lead to excessive stress concentration at the tendon end, thereby increasing the rate of postoperative retear. ²³ In contrast, the optimized 20° insertion angle directed the anchor toward the denser subchondral bone, leading to tighter integration between the anchor and the subchondral bone, thereby reducing micromovement between the anchor and the bone. This also prevented subsequent complications such as reduced fixation strength, the formation of perianchor cysts, and an increased rate of retears, all caused by micromovement.

This study found that both anchor insertion techniques significantly improved short-term shoulder function scores, pain levels, and ROM in patients with osteoporosis. However, this does not imply that long-term clinical outcomes are identical. During follow-up periods of >24 months, we observed an increased rate of postoperative retears with the traditional 45° Deadman-angle insertion. Tendon integrity was evaluated using the Sugaya classification system on MRI during follow-up assessments. Group 1 had a higher retear rate than group 2, and some patients had minimal symptoms. Therefore, there was no statistically significant difference in shoulder function scores between the 2 groups, and further follow-up observation is still required. During intraoperative procedures, we frequently encountered issues in patients with osteoporosis in which the standard 45° anchor placement led to loosening or disengagement during initial insertion. In such cases, the 20° insertion angle, directed toward the subchondral bone, significantly increased the success rate of initial anchor placement and minimized damage to the footprint area caused by repeated anchor insertions. This study aimed to provide arthroscopic surgeons with a novel anchor insertion strategy for treating rotator cuff tears in patients with osteoporosis as a valuable reference.

Limitations

This study has several limitations. First, although we indicated that the anchor insertion angle toward the subchondral bone was approximately 20°, we did not utilize the most precise intraoperative measurement methods. Instead, the angle was estimated based on surgical experience and later verified using postoperative MRI scans. Second, retear rate assessment was limited by a short follow-up period and a relatively small sample size. Third, the study's retrospective, nonrandomized design also represents a limitation. This study did not perform a post hoc power analysis. While the sample size was sufficient to detect statistically significant differences in primary outcomes such as the retear rate, it may have been underpowered to identify smaller yet clinically relevant differences in some secondary endpoints or subgroup analyses. Future prospective studies with an a priori sample size calculation are warranted to confirm and extend our findings.

Conclusion

In this retrospective comparative study, both anchor insertion techniques were associated with acceptable shoulder function outcomes at a minimum 2-year follow-up in patients with osteoporosis undergoing rotator cuff repair. The findings suggest that an insertion angle of approximately 20° toward the subchondral bone may be correlated with a lower incidence of perianchor cysts and a reduced retear rate compared with the traditional 45° Deadman angle. These observations warrant further validation through prospective, randomized controlled studies.