Shoulder anchors are small, specialized medical devices used during arthroscopic procedures to reattach soft tissues, such as torn tendons or ligaments, back to the bone. These devices have become indispensable tools in modern orthopedic surgery, providing the stable fixation necessary for healing. Shoulder repair relies on these implants to secure soft tissue until the body’s natural biological processes establish a solid connection. Their use is foundational to common shoulder operations, including those for rotator cuff tears and labral instability.
The Role of Anchors in Shoulder Repair
The primary mechanical function of a shoulder anchor is to serve as a fixed point within the bone to hold attached sutures under tension. The surgeon drills a small channel into the bone, typically the humeral head or the glenoid rim, and inserts the anchor into this prepared bed. Once seated, the anchor secures a strong suture, which is then passed through the damaged soft tissue, such as the rotator cuff tendon.
The anchor’s design, often featuring threads or barbs, ensures it resists pull-out forces, maintaining the tendon’s position against the bone surface. This secure reattachment is maintained throughout the 12 to 24-week period when the tendon begins to heal and integrate with the bone. The anchor acts as internal scaffolding, stabilizing the repair until the patient’s own biology takes over.
Types of Permanent Anchor Materials
Anchors designed to remain in the body indefinitely are constructed from materials chosen for their strength, biocompatibility, and stability. The earliest and most proven materials are metals, primarily titanium and sometimes stainless steel. Titanium anchors are favored for their superior tensile strength and rigidity, offering robust fixation, especially in bone of suboptimal quality. This metallic composition ensures the anchor is resistant to fatigue and provides a lasting mechanical presence within the bone structure.
A widely used non-metallic alternative is Polyether Ether Ketone (PEEK), a high-performance, inert polymer. PEEK anchors provide mechanical strength comparable to metal anchors but possess a lower modulus of elasticity, meaning their stiffness is closer to that of natural cortical bone. A primary advantage of PEEK is its radiolucency; the anchor does not appear bright white on X-rays and minimizes imaging artifacts that can obscure tissue on magnetic resonance imaging (MRI). This polymer is biologically inert, preventing chemical degradation and offering a non-metal option for patients with metal sensitivities.
Types of Bioabsorbable Anchor Materials
A newer generation of shoulder anchors is fabricated from polymers designed to degrade and be absorbed by the body over time, eliminating the need for a permanent implant. These bioabsorbable devices are primarily made from Polylactic Acid (PLA) or its stereoisomer, Poly-L-Lactic Acid (PLLA). The degradation process, known as hydrolysis, involves water slowly breaking down the polymer chains into simpler, biocompatible compounds like lactic acid, which the body can metabolize.
Poly-L-Lactic Acid is characterized by its slow degradation kinetics, with complete resorption taking between two and five years, depending on the formulation. This extended timeline ensures the anchor maintains its mechanical strength throughout the healing phase. Older materials, such as Polyglycolic Acid (PGA), degraded too rapidly, often within weeks, causing fixation failure and inflammatory reactions.
To improve mechanical properties and bone integration, current bioabsorbable anchors often utilize copolymers like PLGA (a blend of PLA and PGA) combined with osteoconductive agents like beta-tricalcium phosphate (β-TCP). These biocomposite anchors are designed not only to be absorbed, typically within three years, but also to promote the ingrowth of new bone into the anchor site as the polymer degrades. This advanced material approach aims to fully replace the implant volume with native bone, a process known as osseointegration.
Long-Term Interaction Between Anchors and the Body
The choice of anchor material has distinct implications for the patient’s post-operative experience and future medical imaging. Permanent metal anchors, while durable, can create significant signal voids and scatter artifacts on follow-up MRI scans, making it difficult to assess the condition of the repaired soft tissues. Conversely, PEEK and bioabsorbable polymers are radiolucent, minimizing these artifacts and allowing for clearer post-operative evaluation of the tendon and bone.
Permanent metal implants are designed to be left in place unless they cause issues, such as migration or local irritation, which would necessitate a removal procedure. Bioabsorbable anchors avoid this concern entirely, as they are gradually metabolized by the body over several years. However, the breakdown of some bioabsorbable materials can lead to localized biological responses, including transient inflammatory reactions or the formation of benign fluid-filled cysts around the implant site. These complications, while usually self-limiting, highlight the trade-off between the stability of permanent materials and the resorption of bioabsorbable options.