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Newer studies challenged the traditionally held belief that the supraspinatus inserts on the entire superior facet and the infraspinatus is attached on the entire middle facet of the greater tuberosity. They showed that the infraspinatus tendon is thicker anteriorly and can be differentiated from the posterior part of the supraspinatus. Hence, the newer studies showed that the supraspinatus attached in a much smaller area than previously thought, and infraspinatus occupied the lateral part of the superior facet of the greater tuberosity. This review aimed to present all the older and current knowledge of the rotator cuff insertion and discuss how this knowledge may affect the surgical repair of the rotator cuff tendons. Our review has synthesized and compared the differences and similarities between the older and the newer knowledge about the footprint anatomy of the cuff tendons and the capsule attachment. We have also highlighted how the newer knowledge impacts the way we treat the tears of the rotator cuff tendons.
However, several factors can affect the outcomes after the repair of the rotator cuff tendon. Restoring an anatomic footprint of the tendon is one of the crucial factors that leads to a good outcome.
Furthermore, an anatomic repair of the rotator cuff tendon is one of the few factors under the surgeon's control. Accurate knowledge of the footprint anatomy helps diagnose and treat the partial tears of the rotator cuff tendons and helps in recognizing the tear's pattern and accurately planning the surgical repair.
However, the commonly understood footprint description of the cuff was challenged in 2008, after some investigators reported newer findings in the insertion anatomy.
Subsequently, few more reports published in 2012 and 2017 added newer knowledge on the capsular and rotator cuff intricate anatomy. This difference in the anatomic insertion knowledge arose from the difficulties in separating the supraspinatus and the infraspinatus tendon near their insertion on the greater tuberosity.
However, the newer research used robust techniques to define the edges of the tendons near the insertion and accurately delineate the insertion anatomy.
This review aimed to summarize and present all the older and recent knowledge of the rotator cuff insertion and discuss how this knowledge may affect the surgical repair of the rotator cuff tendons. We hypothesized that knowledge from the newer research into the footprint anatomy of the cuff tendons would be significantly different from the older knowledge.
2. Material and methods
We searched the PubMed database in August 2020 with the following keywords (in “quotes”) connected with the Boolean operator (in all capital): “rotator cuff” OR “supraspinatus” OR “infraspinatus” OR “subscapularis” OR “teres minor,” AND “insertion” AND “anatomy.” We also screened the reference lists of the most relevant publications for additional articles. We screened the abstracts for further inclusion according to the inclusion criteria and read the full text of selected articles for inclusion into the final review. All the major findings from the articles were synthesized and presented as a narrative review.
The inclusion criteria were: English language articles with an abstract, cadaveric anatomy research articles, articles that described the insertional footprint dimensions and anatomy of the rotator cuff tendons on the greater tuberosity. The exclusion criteria were surgical technique articles, case reports, review articles, computer modeling articles, and articles not describing the footprint dimensions.
3. Results
3.1 Rotator cuff tendon insertion anatomy
3.1.1 Supraspinatus
Traditionally, it was thought that supraspinatus inserted completely on the superior-most facet of the greater tuberosity.
The anterior to posterior length measured 23 mm (range: 18–33 mm), and the average maximum medial to lateral width measured 16 mm (range: 12–21 mm) (Fig. 1a). Thus, the supraspinatus inserted in a trapezoidal fashion with a longer insertion near the cartilage than laterally. Additionally, the medial border of the supraspinatus inserted just near the humeral head cartilage, at 1 mm from the articular margin on the greater tuberosity (GT) (Fig. 1a) (Table 1).
Fig. 1aOlder concepts: Figure shows the insertion of the supraspinatus as a trapezoidal area(green), and insertion of the infraspinatus (blue) on the greater tuberosity; insertion of the capsule is indicated by black arrows, and articular margin is shaded (yellow).
In subsequent newer studies, Mochizuki et al. challenged the then existing knowledge of the trapezoidal insertion of the supraspinatus tendon; he reported that the supraspinatus inserted in a triangular fashion with its length being longer medially than laterally
(Fig. 1b). They described that its anteroposterior length measured 12.6 ± 2.0 mm at the medial margin and 1.3 ± 1.4 mm at the lateral margin, and the maximum mediolateral width measured 6.9 ± 1.4 mm. Thus, the tendon inserted in the form of a triangle and most of the lateral footprint that was earlier thought to be occupied by the supraspinatus, was described to be occupied by the infraspinatus tendon. They also showed that the medial margin of the supraspinatus inserted 4–5 mm away from the cartilage margin and some of the tendinous slips of the supraspinatus crossed the biceps groove and inserted on the lesser tuberosity (Table 1).
Fig. 1bNewer knowledge: Figure shows the insertion of the supraspinatus in a triangular area (green) on the greater tuberosity and small insertion on the lesser tuberosity; insertion of infraspinatus (blue) is on the greater tuberosity; the capsular attachment is indicated by black arrows and the articular margin is shaded (yellow).
In a separate study, the authors showed that the capsule was inserted in the area between the cartilage and the supraspinatus, which measured 5.6 ± 1.6 near the anterior margin of supraspinatus to 4.4 ± 1.2 mm near the posterior margin of the supraspinatus
It had an anteroposterior length of 29 mm (range: 20–45 mm) and a medial-lateral width of 19 mm (range: 12–27 mm). Additionally, it was believed that the insertion was near the cartilage anteriorly but tapered away posteriorly (Fig. 1a) (Table 1).
In the newer studies, Mochizuki et al. showed that infraspinatus inserted in a trapezoidal fashion, but the anterior part of the tendon curved and reached the anterolateral part of the superior facet of the greater tuberosity
(Fig. 1b). Thus, the infraspinatus occupied all of the middle facet and half of the superior facet of the greater tuberosity (GT). The maximum medial-lateral width was around 10.2 ± 1.6 mm, the maximum anteroposterior length at the medial margin was 20.2 ± 6.2 mm, and at the lateral margin was 32.7 ± 3.4 mm (Table 1).
3.1.4 Capsular attachment
In newer studies, the researchers showed that the capsule attachment was thicker and wider near the infraspinatus tendon.
The widest and thickest attachment was near the posterior border and measured around 9 mm. Near the anterior border and at the widest part of the infraspinatus, the capsular insertion ranged between 3.5 and 5.5 mm (Fig. 1a, Fig. 1b).
3.1.5 Subscapularis
In the older studies, the authors described that the subscapularis was attached medial to the biceps groove on the lesser tuberosity
(Fig. 2a). Its maximum length measured 40 mm, and its maximum width measured 20 mm. The upper part was tendinous, attached near the articular margin, and tapered away from the cartilage in its lower attachment site. The lower part of the subscapularis was inserted as an all musculocapsular structure.
(Fig. 2b). The 2nd part of the subscapularis was a tendinous structure formed by the cranial part of intramuscular tendons. The 3rd part of the attachment was also tendinous, but the lowermost part of the 4th area was in the form of muscular attachment. The medial and lateral margins of attachments measured 40.7 ± 6.9 mm and 37.6 ± 6.6 mm, respectively (Table 1).
Fig. 2bNewer knowledge: Figure shows the insertion of subscapularis: 1st part (purple) is the superior most tendon, 2nd part (orange) and 3rd part(red) are tendinous and 4th part (green) is a muscular attachment.
In the earlier published papers, the authors described that the teres minor was inserted in the form of a triangle; it started as a tendinous attachment but tapered into a largely muscular attachment in the lower part.
The average maximum length was 29 mm, and the average maximum width was 21 mm (Fig. 3a).
Fig. 3aOlder concepts: Figure shows the insertion of the teres minor (red); infraspinatus (blue); capsular attachment is indicated by black arrows and articular margin is shaded in yellow.
In the newer studies, Hamada et al. described that the muscle originated and inserted as 2 parts on the posterior part of the greater tuberosity and the adjacent part of the surgical neck
(Fig. 3b). The upper part was inserted as a circular attachment with a length of 14 ± 2 and width of 11 ± 3 mm, and the lower part inserted linearly with a length of 17 mm ± 6 mm (Table 1).
Fig. 3bNewer knowledge: Figure shows the attachment of the teres minor (red) as 2 parts; 1st part inserts in a circular manner and 2nd part inserts in a linear manner.
The newer knowledge in the insertion anatomy of the rotator cuff tendons and especially of the supraspinatus and infraspinatus tendon directly affects our understanding of the shoulder functions and our understanding of the techniques of rotator cuff repair. This review aimed to summarize and present the evolution in our understanding of the footprint insertional anatomy of the rotator cuff tendons due to the ongoing and newer research into the area.
This review should be read in the context of its limitations. The review has described the cuff tendons and capsular insertion dimensions, which are precise to small millimeters; these footprint dimensions and measurements were studied in detailed cadaveric dissection in all the included studies. We should also acknowledge that the small differences in the capsular insertion dimensions between the studies may be because different authors used different methods to separate the capsule from the tendons. Such detailed and precise delineations of the tendons and capsule are usually not possible during arthroscopic and open repairs. Hence, intraoperatively, the surgeon is best advised to judge the reparability and reduction of cuff tears in the most anatomic way possible using the knowledge of the insertional anatomy as a guideline, without attempting any finer delineations between the tendons or capsule.
The significant differences highlighted in our review were that, according to earlier reports, the supraspinatus tendon inserted in a broad area on the superior facet of GT.
In the newer studies, the infraspinatus was also shown to insert in a curvilinear fashion, extending till the anterolateral part of the superior facet and occupying a large lateral part of the superior facet of the GT that was earlier understood to be the supraspinatus insertion area. These newer findings of a reduced area of insertion of the supraspinatus and a broader area of insertion of the infraspinatus were corroborated in another cadaveric study
Nozaki et al. described the presence of a lateral impression on the GT that corresponded to the insertion region of the infraspinatus on the superior facet. The capsular insertion was earlier thought to be only 1 mm in width but was later shown as being 5–6 mm in width, with its widest area being near the posterior part of infraspinatus insertion.
But the subscapularis differentiation into 4 different parts and teres minor insertion as two parts with tendinous and muscular differentiation was a newer finding.
The differences in the anatomic description between various studies can be explained because of how the tendons were dissected. Some of the earlier authors could not separate the supraspinatus and the infraspinatus tendons,
In the newer studies, the authors separated the loose connective tissue and the coracohumeral ligament and then traced the tendons from their muscular portion to delineate the anterior and posterior margins of the tendons. A capsular separation from the underlying tendons was also performed to map the capsular insertion area, however, the methods of capsular dissection may have accounted for the observed differences between the studies.
It has been thought that the supraspinatus plays the most important role in shoulder abduction, but with an understanding of how the infraspinatus occupies most of the footprint of the superior facet of the greater tuberosity, there may be a significant role of infraspinatus in abduction movement of the shoulder. The newer findings also help us understand why infraspinatus fatty infiltration was found in the supraspinatus tears in earlier reports. Those cuff tears probably involved a large part of the infraspinatus tendon; hence infraspinatus muscle involvement was often reported.
The newer knowledge of the supraspinatus and infraspinatus attachment also directly influences the surgical repair concepts. Since the distal infraspinatus curves and attaches in the lateral and anterolateral part of the superior facet of the greater tuberosity, U-shaped tears of the cuff may result in the infraspinatus tendon being retracted medially and posteriorly.
In these circumstances, the posterior part of the cuff should be brought anterolaterally to the footprint. Furthermore, margin convergence may not be the best way to reduce a U-shaped cuff tear, even though it may reduce the size of the cuff tear and make it easier to be repaired.
The recommended technique may be to first evaluate the mobility of the torn cuff. Generally, in U-shaped tears, the posterior part of the cuff is found to be more mobile, and it is possible to convert it into L shaped tear before the repair. The rotator cuff tears often present as delaminated tears.
The concept of infraspinatus being inserted on the large anterolateral part of the GT should be kept in mind while repairing the tendon. The deeper layer of such a tear can be repaired medially near the articular margin, and the superficial layer may be repaired laterally. While en-masse repairs have also been described to yield good outcomes,
The partial tears of the rotator cuff should be appropriately diagnosed and treated while acknowledging the newer finding that the capsular insertion width can be 5–7 mm near the articular margin and that some of the partial cuff tears may represent tears of the capsule.
The other implication of the infraspinatus and supraspinatus insertion anatomy knowledge is to keep the interconnection and the intricate coalescence of the tendons at the insertion site in mind while repairing the cuff. This interconnection of the tendons means that the surgeons should try and repair the tendons as a whole unit instead of performing an anterior or posterior interval slide to aid mobilization of the retracted cuff.
In massive tears of the rotator cuff tendons, which cannot be completely repaired, it is worthwhile to reduce and repair the infraspinatus as much as possible because the infraspinatus being inserted on the larger part of the GT, its repair may balance the force couple of the shoulder.
Arthroscopic management of massive rotator cuff tears: an evaluation of debridement, complete, and partial repair with and without force couple restoration.
Several newer studies have shown us that supraspinatus inserts in a triangular manner on the superior facet of the greater tuberosity and the infraspinatus inserts on the middle facet of the greater tuberosity. The infraspinatus also curves distally to insert on the anterolateral part of the superior facet of the greater tuberosity. Therefore, a surgeon should be aware that a torn cuff may retract medially and posteriorly, and this part may need to be mobilized and repaired anterolaterally. Our review has summarized how our understanding of the rotator cuff footprint anatomy has evolved due to newer research in the last two decades and how this knowledge directly impacts the biomechanics of the rotator cuff and the concepts behind the repair techniques.
Funding
No funding was received for the study.
Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article."
No ethics approval was required in accordance with the local laws.
All the subjects gave their consent for participation.
Both authors DS, AP were involved in designing the study, methodology, writing the manuscript, statistics and reviewing and editing.
References
Curtis A.S.
Burbank K.M.
Tierney J.J.
Scheller A.D.
Curran A.R.
The insertional footprint of the rotator cuff: an anatomic study.
Arthroscopic management of massive rotator cuff tears: an evaluation of debridement, complete, and partial repair with and without force couple restoration.
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