Preoperative fatty infiltration predicts functional outcomes after arthroscopic rotator cuff repair: does trauma or degeneration matter?

Abstract

Background

The impact of tear etiology (traumatic vs. degenerative) compared to tissue quality on outcomes after arthroscopic rotator cuff repair (ARCR) remains debated. This study aimed to evaluate the influence of preoperative fatty infiltration (FI) and injury mechanism on postoperative functional recovery.

Methods

We retrospectively reviewed 386 patients undergoing primary ARCR for isolated full-thickness supraspinatus tears. Patients were stratified by etiology into traumatic (n = 132) and degenerative (n = 254) groups. FI was graded using the Goutallier classification. Functional outcomes were assessed using Visual Analog Scale (VAS), American Shoulder and Elbow Surgeons (ASES) score, and University of California, Los Angeles (UCLA) score. Multivariate regression analysis was performed to identify independent predictors of poor functional recovery.

Results

Advanced FI was significantly more prevalent in the degenerative group (p = 0.013). Regardless of tear etiology, patients with advanced FI exhibited significantly inferior postoperative functional scores (VAS, ASES, and UCLA; all p < 0.05) and higher rates of joint stiffness compared to those with early FI. Multivariate analysis identified advanced FI (OR = 3.32; p < 0.001) as a significant independent risk factor for poor recovery, whereas injury etiology did not independently predict outcomes.

Conclusions

Preoperative fatty infiltration is a more critical determinant of functional recovery than injury etiology. The perceived clinical superiority of traumatic tears likely reflects the better baseline muscle quality in this patient population. Consequently, surgeons should prioritize the comprehensive assessment of individualized muscle quality when establishing surgical expectations and counseling patients.

Level of evidence

Level III, Retrospective cohort study.

Background

Rotator cuff tears (RCTs) are prevalent, affecting a broad demographic ranging from young laborers to the elderly population [1]. A fundamental distinction in clinical management relies on the etiology of the tear: traumatic versus degenerative [2]. As a prevalent cause of shoulder pain and disability, RCTs often necessitate surgical intervention when conservative management fails. While arthroscopic rotator cuff repair (ARCR) generally yields satisfactory outcomes, prognosis varies significantly among patients [2–4]. Traumatic tears, typically occurring in younger patients following acute events, are often hypothesized to have superior healing potential due to better baseline tendon quality and acute presentation [5–8]. Conversely, degenerative tears are viewed as the culmination of chronic tendinopathy, often associated with poorer tissue quality and compromised biology [9–11].

However, this etiological distinction may be confounded by preoperative muscle quality, specifically fatty infiltration (FI). FI is a well-established, irreversible predictor of poor structural and functional outcomes [12–14]. Degenerative tears frequently present with advanced FI, whereas traumatic tears are more likely to exhibit early-stage muscle changes [15, 16]. Consequently, it remains unclear whether the reportedly inferior outcomes in degenerative cases are due to the etiology itself or simply reflect a higher prevalence of poor muscle quality. Previous studies comparing these etiologies have often failed to strictly control for FI severity, leaving the independent prognostic value of “trauma” versus “muscle quality” undefined.

The purpose of this study was to evaluate the influence of tear etiology versus tissue quality (FI) on postoperative functional outcomes. We aimed to determine whether the perceived prognostic advantage of traumatic tears is independently associated with the injury mechanism or confounded by baseline muscle quality.

Methods

Participants

We retrospectively reviewed patients who were diagnosed with isolated full-thickness tear of the supraspinatus tendon and underwent primary ARCR at the Zhongda Hospital, Southeast University between January 1, 2019, and June 30, 2024 (Fig. 1). The study was approved by our institutional review board, which waived the requirement for informed consent due to the retrospective nature of the analysis.

Fig. 1.

Flowchart of patient selection and grouping

Inclusion criteria were: (1) age ≥ 18 years with a minimum follow-up of 6 months; (2) complete preoperative magnetic resonance imaging (MRI) data of the affected shoulder available for RCI diagnosis and FI grading; and (3) undergoing primary ARCR.

Exclusion criteria were: (1) massive rotator cuff tears; (2) concomitant glenohumeral osteoarthritis, shoulder instability, shoulder dislocation or fractures, or any other rotator cuff tendon tears; (3) a history of previous surgery on the ipsilateral shoulder.

From an initial cohort of 441 patients, 55 patients were excluded based on the criteria above, resulting in a final study population of 386 patients (Fig. 1).

Cohort stratification

Etiological Grouping: Patients were stratified into two groups based on clinical history and MRI findings. The Traumatic Group (n = 132) included patients with a clear history of a specific acute injury event, onset of symptoms immediately following the event, and surgery performed within 3 months of injury. The Degenerative Group (n = 254) included patients with insidious onset of pain, no specific history of trauma, or symptoms persisting > 3 months prior to presentation.

Fatty Infiltration (FI) Grading: Preoperative FI of the supraspinatus muscle was assessed on T1-weighted sagittal oblique MRI views using the Goutallier classification [17](Fig. 2). Grading was performed by two independent radiologists blinded to the clinical history. In cases of disagreement, a consensus was reached. Patients were dichotomized into an Early FI Group (Goutallier Grade 0 or 1) and an Advanced FI Group (Goutallier Grade ≥ 2).

Fig. 2.

Representative oblique sagittal T1-weighted MRI scans illustrating Goutallier Grades of fatty infiltration of the supraspinatus muscle. a Goutallier Grade 0: No fatty infiltration. b Goutallier Grade 1: Some fatty streaks. c Goutallier Grade 2: More muscle than fat. d Goutallier Grade 3: Equal amounts of muscle and fat. e Goutallier Grade 4: More fat than muscle

Surgical technique and postoperative rehabilitation

All surgeries were performed by a single senior surgeon using a standard arthroscopic technique. Patients underwent double-row suture bridge repair for the supraspinatus tear. Acromioplasty was performed if impingement was evident. Postoperatively, all patients followed a standardized rehabilitation protocol. Patients were immobilized in an abduction sling for 6 weeks. During this 6-week immobilization phase, limited passive range of motion (PROM) exercises were permitted within a pain-free or mildly painful range. The sling was discontinued at postoperative week 7, at which point patients began progressive active range of motion (AROM) exercises and training for activities of daily living (ADL). Comprehensive muscle strengthening exercises commenced at 12 weeks (3 months) postoperatively.

Study measures and data collection

Clinical data were collected through a retrospective chart review. Demographic data included gender, age, body mass index (BMI), involved side, smoking history, and comorbidities such as diabetes and hypertension. Clinical information included the history of trauma and duration of symptoms.

Functional outcomes were assessed preoperatively and at the final follow-up using the Visual Analog Scale (VAS) for pain, American Shoulder and Elbow Surgeons’ Scale(ASES) [18], and the University of California, Los Angeles (UCLA) shoulder rating scale [19]. Active range of motion (AROM), including forward flexion (FF) and external rotation (ER), was also recorded. Postoperative complications at 6 months, including rotator cuff retear and joint stiffness, were documented. Joint stiffness was defined according to the criteria by Oh et al. [20] as passive FF < 120° or passive ER < 30° at 6 months post-surgery.

Statistical analysis

Statistical analyses were performed using SPSS Version 26.0 (IBM Corp, Armonk, NY, USA). Continuous variables were tested for normality using the Shapiro-Wilk test. Normally distributed data are presented as mean ± standard deviation (SD) and compared using independent t-tests. Non-normally distributed data are presented as median (interquartile range) and compared using the Mann-Whitney U test. Categorical variables were compared using the Chi-square test or Fisher’s exact test.

To determine independent predictors of poor outcomes (UCLA < 29) [21, 22], variables with p < 0.10 in univariate analysis were entered into a multivariate binary logistic regression model. Results are reported as Odds Ratios (OR) with 95% Confidence Intervals (CI). A Receiver Operating Characteristic (ROC) curve analysis was conducted to evaluate the predictive value of Goutallier grading. A p value < 0.05 was considered statistically significant.

Results

Patient demographics and preoperative characteristics

Finally, a total of 386 patients were included. This cohort consisted of 132 patients (34.2%) in the Traumatic group and 254 patients (65.8%) in the Degenerative group. Significant differences were observed in the distribution of Goutallier Grades between the two groups (p = 0.013). The traumatic group had a higher proportion of patients with Goutallier Grade 0 and 1 (34.09% and 41.67%) compared to the degenerative group (19.29% and 44.49%). In contrast, the degenerative group had a higher prevalence of Goutallier Grades 2, 3, and 4. For muscle atrophy, no significant differences were observed in Warner Grade (p = 0.056) or the tangent sign (p = 0.152)(Fig. 3).

Fig. 3.

Fatty infiltration and muscle atrophy conditions of the supraspinatus in patients with traumatic and degenerative rotator cuff injuries. a Goutallier Grade: Shows the percentage distribution of Goutallier stages in both patient groups. A statistically significant difference was observed between the traumatic and degenerative groups (Chi-square test, p = 0.007). b Warner Stage: Displays the percentage distribution of Warner stages (0–3) in both patient groups. No statistically significant difference was found (Chi-square test, p = 0.056). c Tangent Sign of the Supraspinatus: Presents the percentage of patients testing positive or negative for the tangent sign in both groups. No statistically significant difference was observed (Chi-square test, p = 0.152)

Within the traumatic group, there were no significant differences in any demographic or clinical variables between the Early FI and Advanced FI subgroups (all p > 0.05). In contrast, within the degenerative group, patients with Advanced FI were significantly older (58.78 ± 8.62 vs. 51.79 ± 6.14 years, p < 0.001), had a higher BMI (26.19 ± 2.56 vs. 25.25 ± 2.62 kg/m², p = 0.005), and reported a longer duration of symptoms (4.85 ± 2.80 vs. 3.00 ± 2.19 months, p < 0.001), compared to those with Early FI(Table 1).

Table 1.

Baseline characteristics of patients with trauma and degenerative RCI in the early and advanced FI groups

	Early FI Group	Advanced FI Group	p Value
Traumatic, n = 132
Gender			0.862
Male, n (%)	42(42)	14(43.75)
Female, n (%)	58(58)	18(56.25)
Age, years	53.54 ± 6.98	56.00 ± 7.27	0.089
BMI	25.31 ± 2.71	24.76 ± 2.74	0.255
Involved side			0.949
Left shoulder, n (%)	35(35.00)	11(34.38)
Right shoulder, n (%)	65(65.00)	21(65.62)
Tobacco use, n (%)	11(11.00)	4(12.50)	0.816
Diabetes, n (%)	12(12.00)	6(18.75)	0.333
Hypertension, n (%)	34(34.00)	13(40.63)	0.496
Illness duration, months	3.02 ± 2.04	4.13 ± 2.78	0.067
Follow-up time, years	4.05 ± 1.28	4.08 ± 1.29	0.842
Degenerative, n = 254
Gender			0.099
Male, n (%)	68(41.98)	29(31.52)
Female, n (%)	94(58.03)	63(68.48)
Age, years	51.79 ± 6.14	58.78 ± 8.62	< 0.001
BMI	25.25 ± 2.62	26.19 ± 2.56	0.005
Involved side			0.828
Left shoulder, n (%)	55(33.95)	30(32.61)
Right shoulder, n (%)	107(66.05)	62(67.39)
Tobacco use, n (%)	18(11.11)	7(7.61)	0.368
Diabetes, n (%)	15(9.26)	11(11.96)	0.495
Hypertension, n (%)	61(37.65)	37(40.22)	0.687
Illness duration, months	3.00 ± 2.19	4.85 ± 2.80	< 0.001
Follow-up time, years	4.31 ± 1.29	4.25 ± 1.31	0.754

Influence of FI severity on outcomes within each etiology

In the traumatic cohort, patients with Advanced FI had significantly worse preoperative VAS, ASES, and UCLA scores compared to those with Early FI (p = 0.035, p = 0.030, and p = 0.006, respectively). Postoperatively, this group continued to show significantly worse outcomes across all scores: VAS (1.96 ± 0.98 vs. 1.32 ± 0.67, p = 0.002), ASES (76.66 ± 9.45 vs. 84.31 ± 2.90, p < 0.001), and UCLA (27.69 ± 3.27 vs. 30.38 ± 1.70, p < 0.001). Furthermore, the Advanced FI subgroup experienced significantly higher rates of postoperative joint stiffness (31.25% vs. 13.00%, p = 0.018) and rotator cuff retear (18.75% vs. 6.00%, p = 0.029). Similarly, in the degenerative cohort, the Advanced FI subgroup presented with worse preoperative VAS and UCLA scores (p = 0.001 and p = 0.038, respectively). Postoperatively, they also demonstrated significantly inferior outcomes in VAS, ASES, and UCLA scores (all p ≤ 0.001). The Advanced FI group achieved lower rates of satisfactory AROM for both FF > 120° (65.22% vs. 82.10%, p = 0.002) and ER > 30° (69.57% vs. 85.80%, p = 0.002), and had a significantly higher incidence of joint stiffness (31.52% vs. 13.58%, p = 0.001). The retear rate was higher but did not reach statistical significance (p = 0.055) (Table 2).

Table 2.

Preoperative and postoperative results of patients with traumatic and degenerative RCI in the early and advanced FI groups

	Preoperative			Postoperative
	Early FI Group	Advanced FI Group	p Value	Early FI Group	Advanced FI Group	p Value
Traumatic, n = 132
VAS score	4.77 ± 0.71	5.07 ± 0.72	0.035	1.32 ± 0.67	1.96 ± 0.98	0.002
ASES score	40.78 ± 4.23	38.69 ± 5.00	0.030	84.31 ± 2.90	76.66 ± 9.45	< 0.001
UCLA score	14.05 ± 1.40	12.88 ± 2.20	0.006	30.38 ± 1.70	27.69 ± 3.27	< 0.001
Number of patients with AROM FF > 120°, n (%)	39(39.00)	11(34.38)	0.639	81(81.00)	21(65.63)	0.071
Number of patients with AROM ER > 30°, n (%)	47(47.00)	15(46.88)	0.990	83(83.00)	22(68.75)	0.082
Number of patients with joint stiffness, n (%)				13(13.00)	10(31.25)	0.018
Number of patients with rotator cuff retear, n (%)				6(6.00)	6(18.75)	0.029
Degenerative, n = 254
VAS score	4.52 ± 0.65	4.83 ± 0.66	0.001	1.46 ± 0.44	1.77 ± 0.75	0.001
ASES score	47.50 ± 5.27	46.26 ± 5.27	0.051	83.78 ± 2.33	80.08 ± 5.01	< 0.001
UCLA score	16.43 ± 1.85	15.87 ± 1.62	0.038	30.41 ± 2.17	28.38 ± 2.56	< 0.001
Number of patients with AROM FF > 120°, n (%)	62(38.27)	29(31.52)	0.281	133(82.10)	60(65.22)	0.002
Number of patients with AROM ER > 30°, n (%)	79(48.77)	36(39.13)	0.138	139(85.80)	64(69.57)	0.002
Number of patients with joint stiffness, n (%)				22(13.58)	29(31.52)	0.001
Number of patients with rotator cuff retear, n (%)				11(6.79)	13(14.13)	0.055

Risk factors for poor functional outcome

Patients were dichotomized based on their 6-month postoperative UCLA score into an Excellent recovery group (UCLA ≥ 29) and a Poor recovery group (UCLA < 29). Univariate analysis revealed that patients in the Poor recovery group were significantly older (p = 0.034), had a longer duration of symptoms (P = 0.004), a higher prevalence of diabetes (p = 0.001), and a significantly higher rate of advanced FI (p < 0.001)(Table 3).

Table 3.

Comparison of demographic and clinical differences between the University of California, Los Angeles (UCLA) scored excellent and poor groups

	Excellent recovery group, n = 267	Poor recovery group, n = 119	p Value
Gender			0.475
Male, n (%)	109(40.82)	44(36.97)
Female, n (%)	158(59.18)	75(63.03)
Age, years			0.034
≤ 50	99(37.08)	31(26.05)
> 50	168(62.92)	88(73.95)
Illness duration, months			0.004
≤ 3 months	143(53.56)	45(37.82)
> 3 months	124(46.44)	74(62.18)
Involved side			0.210
Left shoulder, n (%)	96(35.96)	35(29.41)
Right shoulder, n (%)	171(64.04)	84(70.59)
BMI			0.192
≥ 24	175(65.54)	86(72.27)
<24	92(34.46)	33(27.73)
Tobacco use, n (%)			0.335
Yes	25(9.36)	15(12.61)
No	242(90.64)	104(87.39)
Diabetes, n (%)			0.001
Yes	21(7.87)	23(19.33)
No	246(92.13)	96(80.67)
Hypertension, n (%)			0.946
Yes	100(37.45)	45(37.82)
No	167(62.55)	74(62.18)
History of trauma, n (%)			0.120
Yes	98(36.70)	34(28.57)
No	169(63.30)	85(71.43)
Fatty Infiltration, n (%)			< 0.001
Goutallier grade ≥ 2	61(22.85)	63(52.94)
Goutallier grade< 2	206(77.15)	56(47.06)

Multivariate logistic regression analysis was performed to identify independent predictors of poor recovery. The results showed that diabetes mellitus (OR = 2.893, 95% CI: 1.475–5.671, p = 0.002) and advanced fatty infiltration (Goutallier Grade ≥ 2) (OR = 3.316, 95% CI: 2.049–5.368, p < 0.001) were significant independent risk factors for a poor postoperative outcome, while the history of trauma was not a significant predictor (Table 4).

Table 4.

Multivariate binary logistic analyses examined risk factors associated with postoperative scores at the University of California, Los Angeles (UCLA)

Variable	Odds ratio	95% confidence interval		p Value
		Lower	Upper
Age, years (> 50 vs. ≤50)	1.391	0.819	2.363	0.222
Illness duration, months (> 3 vs. ≤ 3)	1.479	0.920	2.379	0.107
Diabetes (Yes vs. No)	2.893	1.475	5.671	0.002
Fatty Infiltration (≥ 2 vs. <2)	3.316	2.049	5.368	< 0.001

Optimal cutoff thresholds

To assess the predictive ability of preoperative Goutallier Grade for poor postoperative UCLA scores, a Receiver Operating Characteristic (ROC) curve analysis was conducted. We evaluated two representations of Goutallier Grade: as a continuous ordinal variable (GG(0–4)) and as a dichotomous variable (GG ≥ 2 vs. < 2).The ROC curve for Goutallier Grade as a continuous ordinal variable resulted in an Area Under the Curve (AUC) of 0.715 (p < 0.001, 95% CI: 0.660–0.770). And the ROC curve of Goutallier Grade as a dichotomous variable showed an AUC of 0.650 (p < 0.001, 95% CI: 0.589–0.712). This suggests that although both methods demonstrated the ability to distinguish poor functional outcomes, using the full spectrum of Goutallier Grades (GG (0–4)) provides better discriminative power than a simple binary classification (GG ≥ 2 vs. < 2)(Fig. 4).

Fig. 4.

Receiver Operating Characteristic (ROC) Curve Analysis for Goutallier Grade (GG). GG, Goutallier Grade; AUC, area under curve; 95% CI, 95% confidence interval

Discussion

Our study aimed to disentangle the influence of tear etiology from muscle quality on functional outcomes after arthroscopic rotator cuff repair. We found that advanced fatty infiltration is significantly associated with poorer functional outcomes and higher complication rates, regardless of whether the tear is traumatic or degenerative. In addition, our multivariate analysis further confirmed that preoperative fatty infiltration serves as a significant independent predictor of poor outcomes, whereas the history of trauma itself does not.

As highlighted by Abechain et al. [9], traumatic rotator cuff tears are widely believed to possess superior healing potential because they are thought to lack the progressive tissue deterioration that is essential to the pathogenesis of degenerative tears. This perspective is supported by several biological and biomechanical observations. Shibata et al. [23] demonstrated that even in elderly populations, traumatic tears retain significantly greater musculotendinous elasticity and exhibit milder degeneration of surrounding structures such as the coracoacromial ligament compared to chronic tears. Furthermore, Aagaard et al. [24] noted that while both etiologies may share a similar degree of pre-existing histopathological degeneration, traumatic tears show a more active biological state characterized by higher indices of cellular apoptosis and proliferation. However, despite these inherent differences, clinical studies comparing repair outcomes have yielded conflicting results. While some authors suggest that traumatic tears achieve superior outcomes despite worse preoperative baselines [25], others report comparable healing rates and functional scores between the two groups [5, 7, 22, 26]. This is further supported by a recent large-scale analysis of 2335 patients by Hayek et al. [27], which found no significant difference in retear rates between traumatic and atraumatic tears. A critical confounding variable in these comparisons is muscle quality. For instance, Godshaw et al. [25] found better outcomes in traumatic tears but noted that these cohorts were characterized by minimal and comparable fatty infiltration. In contrast, when strict exclusion criteria for advanced fatty infiltration (Goutallier Grade ≥ 2) are applied, as demonstrated by Guevara-Alvarez et al. [5], the prognostic differences between etiologies disappear. Our findings reinforce this latter perspective. By identifying advanced fatty infiltration as an independent risk factor for poor prognosis [22], our data suggest that the “traumatic advantage” observed in some studies may partially reflect underlying differences in patient demographics and baseline muscle health. Specifically, traumatic patients frequently present at a younger age with better preserved muscle quality, which likely contributes more significantly to their favorable functional recovery than the acute injury mechanism itself.

Our study confirms that preoperative muscle quality is a potent negative predictor of surgical success. Regardless of etiology, patients with advanced fatty infiltration (Goutallier Grade ≥ 2) exhibited worse preoperative deficits and achieved significantly poorer postoperative recovery. Furthermore, advanced fatty infiltration was consistently associated with higher rates of postoperative complications across both etiologies. It significantly increased the incidence of joint stiffness in both traumatic and degenerative cohorts, and was linked to elevated retear rates, which reached statistical significance particularly in the traumatic group. This aligns with evidence suggesting that severe fatty infiltration reflects an irreversible compromise of the muscle’s functional potential, creating a biological ceiling that anatomical repair cannot overcome [28].

The irreversibility of this biological ceiling may explain why it remains a dominant prognostic factor. The progression of fatty infiltration is driven by the pathological differentiation of fibroadipogenic progenitor cells (FAPs) [26], a process influenced by mechanical unloading and inflammation [28]. These progenitors differentiate into adipocytes and fibroblasts, replacing contractile tissue with non-functional fat and fibrosis [29]. This process is regulated by complex signaling networks, including Wnt/β-catenin, Akt/mTOR, TGF-β, and NF-κB pathways [30–34]. Once established, this architectural change impairs the muscle’s capacity to generate force and support tendon-bone healing [35]. Animal models suggest this process is largely irreversible [36, 37], effectively setting a functional limit that persists regardless of whether the initial tendon failure was acute or chronic.

In our degenerative group, advanced fatty infiltration correlated with older age and longer symptom duration, consistent with a chronic, cumulative process [38, 39]. However, in the traumatic group, advanced fatty infiltration did not correlate with these traditional demographics, suggesting it may stem from the severity of the initial injury or a rapid biological response to trauma. Regarding predictive modeling, our ROC analysis showed that while the dichotomized Goutallier classification (Grade ≥ 2) is clinically practical for identifying high-risk patients, the continuous scale (Grades 0–4) offered superior discriminative ability (AUC 0.715 vs. 0.650). This suggests that while the “Grade 2 threshold” is a useful heuristic, future predictive models and research should utilize the full spectrum of muscle quality or quantitative MRI methods [40] to refine prognostic accuracy.

Collectively, our findings have important implications for patient counseling. Patients with acute traumatic tears often harbor high expectations for a “complete return to normal” because they perceive their injury as an isolated event. Our data suggest that surgeons should caution patients who present with acute trauma but concomitant advanced FI, as this presentation may represent an acute-on-chronic pathology. In such cases, the prognosis should be guarded, similar to that of a chronic degenerative tear with poor muscle quality. Conversely, for degenerative tears with preserved muscle quality (Early FI), the prognosis remains promising and relies heavily on successful anatomical repair. Therefore, preoperative counseling should focus primarily on the individualized assessment of fatty infiltration rather than relying strictly on the etiology of the tear.

This study has several limitations. First, our minimum follow-up was relatively short; future prospective studies with extended follow-up are warranted to fully evaluate long-term structural integrity. Second, regarding clinical complications, while we observed a higher trend of retear in the degenerative group with advanced fatty infiltration, the difference did not reach statistical significance (p = 0.055). This may be attributed to a Type II error, as our sample size in these specific subgroups might have been insufficient to detect subtle differences in structural healing. Third, the retrospective design introduces inherent selection bias, although we attempted to control for this with strict inclusion criteria and multivariate analysis. Fourth, we used the Goutallier classification on MRI, which is qualitative and subject to observer variability, although our inter-observer reliability was acceptable. Quantitative methods, such as Dixon sequencing for fat fraction analysis, would provide greater precision in future studies [40]. Finally, our definition of “traumatic” relied on patient history, which can be subject to recall bias; some “traumatic” tears may have been acute-on-chronic injuries.

Conclusion

Preoperative fatty infiltration is a more critical determinant of functional recovery than the etiology of the tear. While the injury mechanism provides important clinical context, our findings demonstrate that advanced fatty infiltration serves as an independent predictor of poor postoperative outcomes. Consequently, surgeons should place greater emphasis on the comprehensive evaluation of individual muscle quality when determining prognoses and counseling patients.

Abbreviations

ADL

Activities of daily living

ARCR

Arthroscopic rotator cuff repair

AROM

Active range of motion

ASES

American Shoulder and Elbow Surgeons score

AUC

Area under the curve

BMI

Body mass index

CI

Confidence interval

ER

External rotation

FAPs

Fibroadipogenic progenitor cells

FF

Forward flexion

FI

Fatty infiltration

GG

Goutallier Grade

MRI

Magnetic resonance imaging

OR

Odds ratio

PROM

Passive range of motion

RCI

Rotator cuff injury

RCT

Rotator cuff tear

ROC

Receiver operating characteristic

SD

Standard deviation

SPSS

Statistical Package for the Social Sciences

UCLA

University of California, Los Angeles shoulder score

VAS

Visual analogue scale

Authors’ contributions

YC proposed the study concept, performed the statistical analysis, and wrote the original draft of the manuscript. YL, SS, JQ, JW assisted in data collection and data curation. JS and JL supervised the study, provided critical feedback, and revised the manuscript for important intellectual content. All authors read and approved the final manuscript.

Funding

This work was supported by The National Natural Science Foundation of China (No. 82202776, 82272557), the Youth Fund of Natural Science Foundation of Jiangsu Provincial Department of Science and Technology (BK20230841), and the Research Personnel Cultivation Programme of Zhongda Hospital Southeast University (CZXM-GSP-RC44).

Data availability

The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study was approved by the Ethics Committee of Zhongda Hospital, Southeast University (Project number: 2020ZDSYLL076-P01). All procedures involving human participants were performed in accordance with the Declaration of Helsinki and relevant institutional guidelines. The requirement for informed consent was waived due to the retrospective nature of the study.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.