Prevalence and risk factors for development of subscapularis and biceps pathology in shoulders with degenerative rotator cuff disease: A prospective cohort evaluation.

Abstract

Purpose

To describe prevalence of subscapularis and long head of biceps tendon (LHB) pathology in relation to presence and severity of degenerative posterosuperior (PS) rotator cuff disease in a prospective cohort.

Methods

Subjects with asymptomatic rotator cuff tears were enrolled for this prospective longitudinal study (n=354) and followed annually with shoulder ultrasonography and clinical evaluations to assess for presence of subscapularis, LHB, and PS rotator cuff pathology and pain development.

Results

Subscapularis pathology developed in 14% of shoulders over a median follow-up of 5 years, with partial-thickness tearing occurring most commonly (83%). Age, gender, and hand dominance were not associated with subscapularis pathology. A greater proportion of concomitant full-thickness PS cuff tears was observed in shoulders that developed subscapularis tears (76% vs. 50%;p=0.002). PS cuff tear width (10mm vs. 14mm,p=0.01) at time of enrollment and both tear width (10mm vs. 15mm,p=0.003) and length (12mm vs. 15.5mm,p=0.02) at time of diagnosis of subscapularis pathology were greater in subscapularis-torn shoulders. LHB pathology was prevalent in 34% of shoulders, with dislocation/subluxation occurring in 63%, and higher prevalence in subscapularis-torn shoulders (71% vs. 12%;p<0.01). Subscapularis-torn shoulders were more likely to develop pain (67% vs. 45%,p=0.004), and concomitant PS cuff tear enlargement was associated with greater risk for pain development (76% vs. 36%;p=0.01).

Conclusions

The development of subscapularis and LHB pathology is significantly related to the size of the posterosuperior cuff tear. Subscapularis involvement is associated with greater risk of pain development in degenerative rotator cuff disease.

INTRODUCTION

The prevalence and evolution of subscapularis and long head of biceps (LHB) pathology in shoulders with degenerative posterosuperior (PS, supraspinatus and infraspinatus) cuff tears is unknown. The understanding of the natural history of degenerative rotator cuff tears has significantly evolved over the past few decades.^{11; 38} The majority of natural history studies, however, have focused on pathology involving the supraspinatus and infraspinatus tendons. The identification of risk factors for the presence and development of subscapularis tears in shoulders with degenerative PS cuff tears has not been studied. Clinically, it is not uncommon to observe subscapularis and LHB disease at the time of surgery for the treatment of both full-thickness and partial thickness PS cuff tears.^{2; 3; 5; 7; 8; 10; 14; 22; 24; 27; 29; 30} In these shoulders, pathology within the subscapularis and LHB likely represent significant secondary pain generators.

The subscapularis is the largest rotator cuff muscle and imparts significant strength and stability to the glenohumeral joint.¹⁹ A powerful internal rotator of the glenohumeral joint, the subscapularis also provides stability against anteroinferior translation primarily in the mid-range of glenohumeral elevation in neutral rotation.²⁸ Furthermore, the subscapularis is an important contributor to the rotator cuff force couple, along with the posterior cuff, to assist with shoulder elevation and promote humeral centering.³⁵ Subscapularis tendon tears have been described to occur in isolation and combined with tears of the PS cuff.^{3; 5; 6; 16; 23; 24} The etiology of these tears may be traumatic or possibly degenerative. The correlation of subscapularis tendon tears with the presence and severity of PS cuff tears is not well described. This is clinically relevant given the high association of subscapularis disease and LHB instability.^{1; 2; 15; 25; 32; 36} Furthermore, there is evidence that the clinical outcomes of combined repairs of the subscapularis and PS cuff may be inferior to those of isolated PS repairs.^{18; 31}

The LHB shares an intimate anatomic relationship with the supraspinatus and subscapularis tendons. Stability of the LHB in the groove is conferred by a sling-like confluence of fibers originating from the coracohumeral ligament, superior glenohumeral ligament, joint capsule, and supraspinatus and subscapularis tendons.^{17; 37} Upper subscapularis tendon tears are frequently associated with LHB instability and pain.^{25; 36} Although the LHB is commonly diseased in patients with rotator cuff tears, the prevalence of LHB pathology in relation to the severity of PS cuff tears with or without subscapularis tendon disease has also not been well studied.

While concomitant pathology of the subscapularis and degeneration of the LHB are commonly seen at the time of arthroscopic cuff repair surgery, the occurrence of the subscapularis and LHB in relation to the severity of posterosuperior cuff disease is unknown. The primary purpose of the present study was to examine the prevalence of subscapularis pathology in relation to the presence and severity of degenerative posterosuperior rotator cuff disease in prospective cohort. It was hypothesized that subscapularis tears correlate with the severity of PS rotator cuff tears and LHB pathology to be associated with the presence of a subscapularis tear.

MATERIALS & METHODS

IRB approval was obtained prior to and maintained throughout this study (IRB#201103230). This study is a retrospective review of prospective, longitudinally collected data. Subjects included patients with an asymptomatic rotator cuff tear of the PS cuff identified with shoulder ultrasound while undergoing treatment for painful rotator cuff disease in the contralateral shoulder. Inclusion criteria included: 1) bilateral shoulder ultrasonography investigating unilateral shoulder pain, 2) painful rotator disease in the non-study shoulder, 3) documentation of rotator cuff integrity in the asymptomatic study shoulder (full-thickness, partial-thickness and control (no tear)), 4) verified as asymptomatic at enrollment in the study shoulder, 5) no history of trauma to either shoulder and remained free of trauma throughout the study follow-up. Exclusion criteria included: 1) previous history of pain in the currently asymptomatic shoulder, 2) continuous use of narcotic or nonsteroidal anti-inflammatory medication from 3 months before to enrollment, 3) history of trauma in the asymptomatic shoulder, 4) inflammatory arthritis, 5) radiographic osteoarthritis in the asymptomatic shoulder, 6) upper extremity weight bearing demands, 7) isolated subscapularis tears in the asymptomatic shoulder.

Subjects underwent an enrollment and subsequent yearly surveillance examinations consisting of shoulder ultrasound, radiographs, physical examination and assessment of shoulder pain. Additionally, patients were instructed to contact the study coordinator if they developed shoulder pain at any time between study visits, at which time, they would return for repeat clinical examination with a treating physician. New shoulder pain was defined by any of the following criteria: 1) shoulder pain >=3 on a 10 point scale lasting for 6 weeks or longer, 2) pain requiring formal consultation with a physician who administered pain medication or treatment 3) night pain affecting sleep. Demographic data was collected including age, sex, hand dominance and retrospective assessment of work status (working or retired) and occupational demand classified as “sedentary”, “labor” and “in between”. All physical examinations were performed by trained research staff. Questionnaires were completed consisting of a numeric pain scale (0–10), components of the American Shoulder and Elbow Surgeon (ASES) Score at each visit. Enrolled participants were retained in the annual protocol for ongoing evaluation regardless of pain development or tear enlargement.

Shoulder ultrasonography was performed by one of four experienced radiologists according to previously described protocol which describes the characterization of both partial and full-thickness cuff tears.^{33; 34} Partial thickness subscapularis tears were defined as attenuation and thinning of the upper border of the tendon. The maximum anteroposterior dimension of the tear was measured in transverse views (perpendicular to the long axis of the cuff) and designated as the tear width. The maximum degree of retraction was measured in longitudinal views (parallel to the long axis of the cuff) and designated as tear length. These tear dimension definitions were used for both PS cuff and subscapularis tendon assessment. Tear dimensions are provided for full tears that are not massive in size. Tear progression was defined as tear enlargement or conversion to a more severe tear type (partial to full-thickness or control to partial or full-thickness defect). Partial and full-thickness tears were considered enlarged if the tear size increased 5 mm or greater in any dimension compared to baseline. A partial-thickness tear was also considered enlarged if it converted to a full-thickness defect regardless of tear size compared to baseline. The LHB was described as normal, partially torn, absent (not visible), or dislocated/subluxated from the biceps groove. At the time of diagnosis of subscapularis and/or LHB pathology, the condition of the PS rotator cuff was assessed as either normal, partial-thickness, or full-thickness. If torn, the length and width of the PS rotator cuff tear was recorded. At the time of diagnosis of a subscapularis tear, the condition of the LHB was noted as described previously.

Statistical analysis was performed using SAS/STAT software, version 9.4 of the SAS System for Linux (SAS Institute Inc., Cary, NC, USA). According to their distribution, continuous data were reported as mean ± standard deviation or median. Continuous data were compared using unpaired t-tests for normally distributed variables and Wilcoxon rank-sum test for nonparametric data. Categorical data were compared across groups using the chi-square test except for when sample sizes were small in which case Fisher exact test was used. The level of significance for all tests was established at α=0.05.

RESULTS

Of 395 subjects enrolled in the study. Forty-one subjects were excluded due to no ultrasound after baseline. Therefore, 354 met inclusion criteria for the present study. The median duration of follow-up for this cohort was 5 years (range 0.5 to 13.1 years).

Analysis of subscapularis pathology

The subscapularis was noted to be torn in 49 shoulders (14%), of which 11 were identified at the time of enrollment and 38 tears were identified during the follow-up. Four shoulders with subscapularis tears had missing data regarding the subscapularis at enrollment. The median time to identification of a subscapularis tear from enrollment was 2.1 years (range 0–9.7 years). Of the 41 shoulders with subscapularis tears and non-missing tear type, 34 (83%) were classified as partial-thickness tears and 7 (17%) were full-thickness tears.

When comparing the shoulders with and without subscapularis tears, the age at enrollment, sex, and hand-dominance distributions were comparable (Table I). A significantly greater proportion of full-thickness PS rotator cuff tears was observed in shoulders that developed subscapularis tears during surveillance (n=37, 76%) compared to those that did not develop a subscapularis tear (n=154, 50%) (p=0.002). However, at the time of enrollment the tear distribution types were similar between groups. In comparing shoulders that developed a subscapularis tear to those that did not, a larger PS rotator cuff tear width was observed at the time of enrollment in subscapularis torn shoulders (10mm vs. 14mm, p=0.01) while tear length was not significantly different (12mm vs. 11mm, p=0.25). At the time subscapularis tears were identified, a significant difference was noted between subscapularis intact vs. subscapularis torn shoulders with respect to PS rotator cuff tear width (10mm vs. 15mm, p=0.003) and tear length (12mm vs. 15.5mm, p=0.02). These data are summarized in Tables II & III.

Table I.

Patient demographics

	Subscapularis tear		P-value
	absent (n=305)	present (n=49)
Age at enrollment (SD)	62.0 (9.1)	63.6 (9.6)	0.24
Gender			0.78
Male	174 (57%)	29 (59%)
Female	131 (43%)	20 (41%)
Dominant study side	113 (37%)	22(45%)	0.29

Table II.

Characteristics of subscapularis and biceps pathology

Subscapularis pathology
Prevalence (end of surveillance)	49/354 (14%)
Present at enrollmentA	11/45 (24%)
Identified during study periodA	38/49 (78%)
Median time to identification of tear	2.1 years
Tear typeB
partial thickness	34/41 (83%)
full thickness	7/41 (17%)
Biceps pathology
Prevalence	121/353 (34%)
Present at enrollmentC	56/118 (47%)
Identified during study periodC	65/121 (54%)
Median time to identification of tear	0.9 year
Tear type
partial thickness	16/121 (13%)
completely ruptured/not visualized	29/121 (24%)
dislocated/subluxated	76/121 (63%)
Status of posterosuperior rotator cuff at time of diagnosis of biceps pathology
intact (control)	8/121 (7%)
partial thickness tear	25/121 (21%)
full thickness tear	88/121 (73%)

^AFour subjects are missing subscapularis pathology at enrollment (and are not included in the enrollment denominator), but subscapularis presence was identified during the study period (and are included in the during study period denominator).

^BEight subjects have missing data and are not included in the denominator.

^CThree subjects are missing biceps pathology at enrollment (and are not included in the enrollment denominator), but biceps pathology was identified during the study period (and are included in the during study period denominator).

Table III.

Statistical comparison of characteristics of posterosuperior rotator cuff tears in subjects with and without subscapularis tears

Characteristic of posterosuperior rotator cuff tear	Subscapularis tear		P-value
	absent (n=305)	present (n=49)
Tear type
no tear (control)	61 (20%)	2 (4%)	0.002
partial thickness	90 (30%)	10 (20%)
full thickness	154 (50%)	37 (76%)
Full thickness tear median size at enrollment (mm)†
length	12.0A	11.0B	0.25
width	10.0C	14.0D	0.01
Full thickness tear median size at time of subscapularis tear identification (mm)†
length	12.0A	15.5E	0.02G
width	10.0C	15.0F	0.003G

^†Due to inability to measure tear size in massive rotator cuff tears with significant retraction using ultrasound, there is missing data for this variable that is not included in the analysis.

^AEight subjects have missing data and are not included in the analysis.

^BTwo subjects of 29 full tears at enrollment have missing data and are not included in the analysis.

^CSix subjects have missing data and are not included in the analysis.

^DOne subject of 29 full tears at enrollment has missing data and is not included in the analysis.

^ENine subjects have missing data and are not included in the analysis.

^FSix subjects have missing data and are not included in the analysis.

^GComparison of full thickness tear size at enrollment in subjects without subscapularis tears to tear size at time of subscapularis tear identification in subjects with subscapularis tears.

Analysis of LHB pathology

LHB pathology was observed in 121 shoulders (34%). Of these, 56 (16%) of shoulders demonstrated LHB pathology at the time of enrollment. Three shoulders with LHB tears had missing data at enrollment and one shoulder had missing data at enrollment and during the study period. Sixty-five shoulders had LHB pathology identified during the study period. The median time to the identification of LHB pathology from enrollment was 0.9 year (range 0 to 10.1 years). The LHB was partially torn in 16 patients (13%), completely ruptured and not visualized in 29 patients (24%), and found to be dislocated or subluxated in 76 patients (63%). At the time of diagnosis of LHB pathology, the condition of the PS rotator cuff was noted as follows: intact in 8 patients (7%), partial-thickness tear in 25 patients (21%), and full-thickness tear in 88 patients (73%). The characteristics of biceps pathology is summarized in Table II.

A significantly greater proportion of LHB pathology was noted in shoulders with subscapularis tears (n=35, 71%) compared to those with an intact subscapularis (n=36, 12%) (p<0.01). The most common LHB pathology observed with subscapularis tears was dislocation/subluxation of the LHB, representing 74% of of LHB disease in subscapularis torn shoulders compared to 56% in subscapularis intact shoulders. These data are summarized in Table IV.

Table IV.

Statistical comparison of characteristics of biceps pathology in subjects with and without subscapularis tears

Biceps tendon†	Subscapularis tear		P-value
	absent (n=301)	present (n=49)
normal	265 (88%)	14 (29%)	<0.0001
abnormal	36 (12%)	35 (71%)
partial tear	4/36 (11%)	2/35 (6%)
absent	12/36 (33%)	7/35 (20%)
dislocated/subluxated	20/36 (56%)	26/35 (74%)

^†Missing data (n=4) was not included in the analysis.

Analysis of pain development

Of the 354 subjects included in this study, 170 shoulders (48%) became symptomatic while 184 remained asymptomatic. The median time to development of pain was 2.6 years (range 0.4 to 10.2 years). Tear enlargement of the PS cuff was more common in shoulders that developed pain (111/170 (65%)) during surveillance than those that remained asymptomatic (77/184 (42%), p<0.0001). Additionally, a significantly greater proportion of shoulders with subscapularis tears (n=33/49, 67%) became painful compared to subjects with an intact subscapularis (n=137/305, 45%) (p=0.004). Combined tear analysis showed the risk of pain development for shoulders with subscapularis pathology combined with enlargement of the PS cuff (29/38 (76%)) was greater compared to shoulders with enlargement of the PS cuff without subscapularis pathology (82/150 (55%), p=0.02). Likewise, the risk of pain development for shoulders with subscapularis pathology combined with enlargement of the PS cuff (29/38 (76%) was greater than shoulders with subscapularis tears that demonstrated no enlargement of the PS cuff during surveillance (4/11 (36%), p=0.01). Tables V and VI summarize the analysis of pain development in this cohort.

Table V.

Risk factors for pain development

Variable	Remained asymptomatic (n=184)	Became symptomatic (n=170)	P-value
Subscapularis pathology
no (n=305)	168 (91%)	137 (81%)	0.004
yes (n=49)	16 (9%)	33 (19%)
Posterosuperior cuff tear enlargement
no (n=166)	107 (58%)	59 (35%)
yes (n=188)	77 (42%)B	111 (65%)	<0.0001

Table VI.

Analysis of the association of posterosuperior cuff tear enlargement and subscapularis pathology in pain development

Shoulders with posterosuperior cuff tear enlargement (n=188)
Variable	Remained asymptomatic (n=77)	Became symptomatic (n=111)	P-value
intact subscapularis (n=150)	68 (88%)	82 (74%)	0.02
subscapularis pathology (n=38)	9 (12%)	29 (26%)
Shoulders with subscapularis tear pathology (n=49)
Variable	Remained asymptomatic (n=16)	Became symptomatic (n=33)	P-value
absence of enlargement of posterosuperior tear (n=11)	7 (44%)	4 (12%)	0.01
presence of enlargement of posterosuperior tear (n=38)	9 (56%)	29 (88%)

DISCUSSION

The present study is the first to prospectively evaluate the prevalence of subscapularis tears in reference to existing posterosuperior degenerative rotator cuff tears. The prevalence of subscapularis pathology was noted to be 14% in this cohort study, with partial-thickness tearing being the most common subscapularis tear type. Analysis of demographic data showed that age, gender, and hand dominance were not associated with the presence of a subscapularis tear. A larger PS cuff tear at baseline and the development of a full-thickness tear during surveillance were noted to be risk factors for the development of a subscapularis tear. A full-thickness PS rotator cuff tear was observed in 76% of shoulders that developed a subscapularis tear during the study period. Similar to previous studies, the development of LHB disease (particularly instability) was linked to the development of subscapularis tendon tears. Importantly, from a clinical standpoint, the risk of pain development in shoulders with asymptomatic tears was found to be related to the development of subscapularis disease regardless of enlargement of the PS cuff; however, magnified by concomitant enlargement of the PS cuff.

The true prevalence of subscapularis tears in the aging shoulder is unknown as most studies document subscapularis disease based upon intraoperative findings in shoulders with painful cuff disease. DePalma et al.¹² observed subscapularis pathology in 21% of cadaveric shoulders. The prevalence of subscapularis pathology noted during rotator cuff surgery has ranged from 8–52%.^{2; 3; 5; 7; 14; 22; 24; 27; 30} This variable range likely reflects differing patient populations, age groups and tear etiologies (traumatic vs. degenerative) as well as variable thresholds for identifying partial-thickness tears at the time of surgery. Additionally, these studies represent a single evaluation point and do not describe the risk factors for the development of and prevalence of subscapularis tears in relation to PS cuff disease severity. The current study suggests a relatively low prevalence of subscapularis pathology (14%), the majority of which were partial-thickness (83%) tears. Other studies have also found partial subscapularis tears to be more frequent than full-thickness tears suggesting a progressive degenerative etiology for many of these tears.^{3; 13; 22} Our findings regarding the prevalence of subscapularis tears must be interpreted with caution as isolated subscapularis tears and a history of shoulder trauma were exclusion criteria at the outset of the study. Given the initial purpose of this cohort was to study the progression of degenerative tears of the PS cuff, the current study findings likely underestimate the true prevalence of subscapularis pathology.

Previous research has consistently demonstrated that most subscapularis tears do not occur in isolation but combined with pathology of the PS cuff (supraspinatus and/or infraspinatus tears)^{3; 5; 14; 24; 25; 27; 30}. Subscapularis tears have been noted to occur in isolation in only 1.4 – 21% of shoulders in previous studies.^{5; 14; 24; 25; 27; 30} The etiology of subscapularis tears is not known, but the frequent involvement of the PS rotator cuff suggests a potential relationship between disease of anterior and PS cuff. The present study is the first to prospectively report on the prevalence of subscapularis tears in a cohort of subjects with known PS cuff disease. While age and sex were not found to be significant, the current study demonstrated that the development of a full-thickness tear of the PS cuff to be a risk factor for the future development of a subscapularis tear. Additionally, larger PS tears had a greater risk of development of a subscapularis tear. This observation suggests larger PS cuff tears may propagate into and disrupt the anterior rotator cable. The rotator cable is a thickening of cuff tissue that arcs from the inferior infraspinatus to the anterior supraspinatus and anteriorly is continuous with the coracohumeral ligament blending with the upper subscapularis.⁹ Previous research has shown approximately 30% of degenerative cuff tears involve the anterior cable as defined as tear propagation to within 3mm posterior to the LHB.²¹ A larger tear size with cable disruption could allow for propagation of the tear anteriorly to involve the upper subscapularis tendon, as observed in the present study. This finding is clinically relevant, particularly at the time of surgical management of larger full thickness tears as subscapularis pathology should to be carefully identified and addressed. Further studies are warranted to determine if cable disruption into the subscapularis is the primary means of subscapularis damage or if the presence of a larger PS tear is an independent risk factor for subscapularis disease regardless of the integrity of the anterior cable.

The studied cohort consisted of asymptomatic tears at baseline which were originally assembled to prospectively assess for pain development, tear enlargement and progression of muscle degeneration of the PS cuff. Previous studies related to this cohort has shown the only identifiable risk factor for pain development was enlargement of the PS cuff.^{20; 26} Findings of the current study suggest that the development of subscapularis tendon tears may also correlate with pain development. The risk of pain development was 45% for shoulders with an intact subscapularis compared to 67% for shoulders that developed a subscapularis tear. To control for the effects of enlargement of the PS cuff the current study examined pain development with two methods. The risk of pain development was greater in shoulders with a subscapularis tear and enlargement of the PS cuff (76%) compared to shoulders with a subscapularis tear and no enlargement of the PS cuff (36%). Likewise, pain development occurred in 55% of shoulders without subscapularis tears with enlargement of the PS cuff compared to the prior noted 76% of shoulders that developed a subscapularis tear and demonstrated enlargement of the PS cuff. The relative importance of the PS cuff and subscapularis as related to pain development cannot be fully elucidated unfortunately due to the high percentage of shoulders with overlapping disease. The mechanism of pain development in shoulders with subscapularis tears is unknown and possibly related to concomitant LHB disease which was seen in 71% of shoulders with subscapularis tears. One argument against this hypothesis; however, was the fact that 47% of the shoulders with biceps disease had LHB disease at enrollment and were asymptomatic at that time point. Limited sample size precluded subgroup analysis regarding the independent association of LHB disease and pain development while controlling for confounding variables.

The prevalence of LHB disease increased from 16 to 34% during the course of surveillance. As expected, the presence of LHB disease was associated with the presence of a subscapularis tear seen in 71% of shoulders compared to 12% without subscapularis involvement. The most common pathology (63%) seen on ultrasound was medial subluxation/dislocation. Subluxation or dislocation of the LHBT has previously been associated with rotator cuff pathology, particularly with involvement of the subscapularis.^{1; 2; 15; 25; 32; 36} The medial border of the biceps pulley is formed by the attachment of the subscapularis tendon at the lesser tuberosity and disruption results in medial subluxation of the LHB tendon over the lesser tuberosity. The current study findings corroborate multiple previous studies which has strongly associated LHB disease to the presence of subscapularis pathology.^{2; 3; 21; 25; 36} Given the high percentage of partial subscapularis tears in the current study, potentially clinically relevant LHB disease can exist with minimal subscapularis tendon pathology. Further studies with larger cohorts may better define the role of the LHB as a pain generator in shoulders with degenerative cuff tears.

This is the first study to describe the natural history of subscapularis tears and LHB pathology in relation to degenerative rotator cuff disease in a large, prospective cohort. The methodology employed is unique in that serial annual surveillance examinations were performed rather than analysis at a single point in time. Furthermore, strict criteria for pain development were defined to allow for careful assessment and reporting. There are several study limitations that are worth mentioning. First, the diagnosis of subscapularis and LHB pathology is solely based on ultrasound findings, and there is no report of clinical exam findings. Physical examination findings would have been helpful to tease out the subscapularis and LHB tendon as a clinically relevant pain generator. Although ultrasound has been shown to be accurate for the diagnosis of full-thickness tears, similar to MRI, the accuracy for detection of partial tears is lower.^{33; 34} Previous research has shown an overall accuracy of ultrasound for the detection of subscapularis tears to be 76% with improved accuracy for larger tears. The primary limitation of ultrasound was shown to be limited sensitivity of for smaller tears (43%) compared to larger tears (79%).³⁰ The current study protocol allows serial examinations of a given shoulder at annual visits which likely improves the accuracy of identifying changes in the subscapularis over time compared to a single point in time assessment. Despite the implementation of a defined ultrasound protocol with experienced Radiologists, it is likely that the true prevalence of subscapularis disease is under reported in this cohort. This is likely a problem with any study relying on imaging findings compared to operative findings and must be considered when interpreting the actual prevalence of subscapularis tears in this cohort. We do not feel that this limitation affects conclusions regarding the relationship of subscapularis tears to posterosuperior cuff tears and pain development. The reporting of LHB disease has been performed in a categorical manner, with a limited description or quantification of the specific pathology. Ultrasound has been shown to be very accurate for the diagnosis of rupture, subluxation or dislocation but has limited accuracy for the detection of partial tears compared to operative findings.⁴ Therefore, this study may also under estimate the true prevalence of biceps disease. The exclusion of isolated subscapularis tears at enrollment likely underestimates the true prevalence of subscapularis disease. However, the purpose of the study was to examine the importance of PS cuff disease on the presence of and the development of subscapularis pathology, which the current study design allows. Additionally, this study did not examine the timing of pain development in relation to the timing of enlargement of subscapularis or posterosuperior cuff tears that would potentially provide insight regarding the temporal relationship of pain development. Given the multitude of potential pain generators examined in this study, it is difficult to determine the true etiology of pain associated with subscapularis disease, either from the subscapularis or related to LHB pathology and the relative contribution of the PS cuff in pain development. A much larger cohort would be needed to examine these potential pain generators independently. Lastly, this study can only describe associations rather than cause and effect of the influence of PS cuff disease on the development of subscapularis tears. It remains unclear if anterior cable disruption allows propagation into the subscapularis or if disease of the tendons occurs independently.

CONCLUSION

This prospective cohort study provides a better understanding of the occurrence of subscapularis and LHB pathology in relation to the severity of posterosuperior cuff disease. While age, gender, and hand dominance were not associated with the presence of subscapularis pathology, a larger PS cuff tear at baseline and development of a full-thickness tear during surveillance were significant risk factors for the development subscapularis pathology. Biceps disease was confirmed to have a strong association with subscapularis pathology. Furthermore, subscapularis involvement was linked to pain development in shoulders with asymptomatic tears regardless of the presence of PS cuff tear enlargement. Taken together, findings from this study provide an improved understanding of the natural history of degenerative rotator cuff disease which can be valuable in diagnosing and treating this common clinical entity.