Superior Capsule Reconstruction: A Comprehensive Overview

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Superior Capsule Reconstruction: A Comprehensive Overview

Shoulder injuries are common, and rotator cuff tears (RCTs) are a significant concern. Rotator cuff tendons are subjected to continuous loading, making RCTs the most prevalent musculoskeletal injury of the shoulder. Massive RCTs, defined as tears of >5 cm or involving two or more rotator cuff tendons, can be particularly challenging. When these massive RCTs are irreparable, meaning direct tendon-to-bone repair is not feasible, patients often face poor functional outcomes.

Conventional surgical approaches for irreparable massive RCTs include various techniques such as debridement, biceps tenotomy, partial rotator cuff repair, bridging patch grafts, tendon transfers, and reverse total shoulder arthroplasty. However, in 2012, Mihata et al introduced superior capsule reconstruction (SCR) as an alternative. SCR aims to restore the superior stability of the shoulder joint, and it has been gaining popularity among orthopedic surgeons. But with its use, questions about graft healing and variable clinical outcomes have emerged. Let’s explore the anatomy, biomechanics, indications, and graft treatment aspects of SCR.

Anatomy of the Superior Capsule

The superior capsule is a relatively thin fibrous structure attached to the undersurface of the supraspinatus and infraspinatus muscle-tendon units. Its thickness varies between 0.40 mm and 4.47 mm in different parts. Notably, it is thicker than the posterior and inferior parts of the shoulder capsule and also thicker in the medial aspect compared to the lateral. The superior capsule intermingles with the coracohumeral ligament, envelops the anterior edge of the supraspinatus, and attaches to the greater tuberosity. The fibers of the superior capsule, superior glenohumeral ligament, and rotator cuff crosslink to form a functional unit, which can be referred to as the “superior capsular complex.” This concept helps in understanding the pathology related to internal impingement and articular-sided RCTs.

Biomechanics of SCR

The superior capsule acts as one of the static stabilizers of the glenohumeral joint, providing superior stability at extreme ranges of motion. When the shoulder is abducted, the superior capsule becomes lax, but contraction of the rotator cuff muscles causes tensile stiffening. In maximum shoulder abduction, the superior capsule is relaxed, while the inferior capsule is taut. In a cadaveric biomechanical test, Itoi found that the posterior capsule had the greatest strength and modulus of elasticity, and the superior capsule showed the least strength. The most common failure mode of cadaveric shoulder capsules was a tear at the mid-substance, followed by a tear at the detachment from the humerus.

In irreparable massive RCTs, when both the supraspinatus tendon and superior capsule are destroyed, the shoulder joint loses superior stability. This loss is the theoretical basis for the high failure rates of conventional surgical techniques in such cases. Superior stability is disrupted not only in irreparable massive RCTs but also in medium to large (full-thickness) RCTs. Using a graft in SCR reinforces the superior capsule, providing the leverage and support to the proximal humerus that was previously provided by the supraspinatus tendon and the native superior capsule. For example, partial articular supraspinatus tendon avulsion (PASTA), a type of partial-thickness RCT in the joint side, likely starts from a superior capsular tear. The superior capsule creates a stable fulcrum for glenohumeral joint motion, allowing the remaining intrinsic and extrinsic force couples to act around it. In rotator cuff dysfunction, this static stabilization is disrupted, and the main goal of SCR is to preserve the centered position of the humeral head and restore superior stability.

Indications for SCR

  • Irreparable massive RCTs: These show progressive radiographic changes like bone loss and narrow joint space. By restoring superior stability, SCR can potentially delay or halt these processes. Most orthopedic surgeons consider irreparable massive RCTs without severe glenohumeral arthritis as the prime indication. Irreparable massive RCTs negatively impact patients’ functional mobility and quality of life, and there is insufficient rotator cuff remnant for repair. Compared to partial rotator cuff repair or conservative treatment, the outcome after SCR is more predictable. Reverse shoulder arthroplasty (RSA) is an alternative for Grade 4 or 5 (Hamada classification) massive RCTs, but there is an ongoing debate about whether SCR combined with anatomy totals shoulder arthroplasty or RSA is better for irreparable massive RCTs with severe arthropathy. More high-quality studies are needed.
  • Severely degenerated medium to large RCTs: Some chronic medium to large RCTs, especially in geriatric patients, show structural degeneration of the rotator cuff, such as fatty infiltration, loss of muscle volume, subtraction of sarcomeres, and sometimes profound muscle weakness. The limited healing potential of injured rotator cuff tendons may lead to retear or non-healing. Mihata classified muscle degeneration, tendon degeneration, and tendon retraction into mild, moderate, and severe types based on pre-operative magnetic resonance imaging findings.
  • Delaminated RCTs: Delamination is a horizontal tear between the layers of the rotator cuff. It is common in large-sized tears, limited to the posterior part of the rotator cuff, and affects the thicker deep layers. Delaminated RCTs are associated with diminished healing and worse clinical outcomes after repair. Dual-layer rotator cuff repair based on the retraction pattern of delamination has been recommended, but it is difficult to simultaneously restore appropriate tensioning of dual layers without causing tendon fiber cleavage. In such cases, SCR-reinforcement may be the right choice.
  • Pseudoparalysis caused by massive RCTs: Pseudoparalysis from irreparable massive RCTs is a tough challenge for shoulder surgeons and is related to superior instability. Mihata reported that SCR reversed pseudoparalysis in 96% (27/28) and 93% (14/15) of patients with moderate and severe pre-operative pseudoparalysis, respectively. If the deltoid muscle is functional, pseudoparalysis from irreparable massive RCT is a valid indication for SCR.

Graft Treatment for SCR

To achieve the best long-term clinical outcome based on biomechanical rationale, two important principles are involved: enhancing graft-bone healing in the short term and preventing graft retear in the long run.

  • Enhanced graft-bone healing: Originally, Mihata’s group used fascia lata autograft. Now, various grafts like human dermal allograft, long head of biceps, and autologous hamstring graft are used. The main concern is achieving positive biomechanical outcomes, such as restoring the position of the humeral head and decreasing the acromial-humeral distance. So, attaining graft-bone healing in both the glenoid and rotator cuff footprint is crucial.
  • Decreased possibility of graft retear:
    • Appropriate thickness: Superior capsule reconstruction was originally tested with a 5-mm folded fascia lata autograft. Mihata used 6 to 8-mm-thick grafts clinically. Sutter reported excellent biomechanical properties of a 3.5-mm-thick dermal allograft. Grafts thicker than 8 mm may not strike the right balance between mechanical advantage and avoiding subacromial impingement.
    • Appropriate graft tension: Graft tension depends on factors like accurate measurement of anchor distances and arm position. Sutter reported the ideal arm position as 30° of abduction, 20° of forward flexion, and 10° of external rotation. Passive external rotation can cause graft strains and failure, so fixing the graft in passive internal rotation biomechanically is preferable. Different abduction angles change the distance between the glenoid and the greater tuberosity asymmetrically.
    • Better continuity: Ensuring better continuity between the graft and infraspinatus tendon is vital. Side-to-side suturing between the graft and infraspinatus tendon remnants increases superior stability. However, anterior side-to-side sutures do not change measurements compared to posterior side-to-side suturing.

In conclusion, SCR is a valuable surgical option. It can restore the superior stability of the shoulder joint. It is a well-established joint-preserving option for irreparable massive RCT and/or pseudoparalysis associated with massive RCT without glenohumeral joint arthritis. SCR reinforcement may also be indicated for severely degenerated rotator cuff and/or delaminated medium to large RCT. Improving the quality of degenerated rotator cuff and decreasing retear rates have broadened its scope. Graft treatment is a key step, and selecting an appropriate thickness, fixing with correct tension, and ensuring improved capsular continuity are essential for successful outcomes.

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