Tendons are robust bands of dense fibrous connective tissue that connect muscle to bone. They transmit the force generated by muscle contraction to the skeleton, facilitating movement and joint stability. A severe injury can cause a tendon to completely pull away from its bony attachment point, a detachment known as an avulsion. This detachment often requires a surgical procedure to physically reattach the soft tissue back to the bone surface.
Identifying Injuries Requiring Reattachment
Surgical reattachment is necessary when a tendon has completely detached from the bone, resulting in a significant loss of function. These injuries often occur due to high-impact acute trauma, where a sudden, forceful load overwhelms the tendon’s strength. Common examples include a complete Achilles tendon rupture or a quadriceps tendon tear resulting from sports or a fall.
Reattachment is also required for degenerative tears, where chronic wear weakens the tendon until it detaches. Rotator cuff tears in the shoulder are the most common example, involving one or more tendons pulling away from the humeral head. Diagnosis is established using imaging modalities, such as Magnetic Resonance Imaging (MRI) or ultrasound, to determine the extent of the tear and the degree of tendon retraction.
Preparing the Surgical Site for Fixation
Before mechanical fixation, the surgeon must prepare both the bone and the detached tendon end. The bony attachment site, known as the footprint, is carefully debrided to remove any remnants of damaged tendon tissue. This cleaning process involves lightly abrading the cortical bone surface to expose the underlying cancellous bone, creating a fresh, bleeding bed. This exposure stimulates a localized healing response by allowing stem cells and growth factors from the bone marrow to migrate to the repair site.
The detached end of the tendon also requires preparation to create a strong anchor point for fixation. Frayed or damaged tendon tissue is trimmed away to expose a healthy, robust edge. High-strength, non-absorbable sutures are often pre-placed into the tendon end using specialized patterns, such as the Krackow or locking-loop technique, to distribute tension. These sutures are used to pull the tendon back down and secure it firmly against the bone surface.
Mechanical Methods of Tendon-to-Bone Fixation
The physical reattachment of the tendon relies on several mechanical techniques, aiming to hold the tendon securely against the prepared bony bed for biological healing. Suture anchors represent the most common modern method, functioning as small implants drilled directly into the bone. These anchors are preloaded with durable, high-tensile strength sutures passed through the prepared end of the tendon.
Once tensioned, the tendon is cinched down onto the bone surface, and the sutures are tied or locked into the anchor, securing the repair. Anchors may be made of non-absorbable materials like titanium or absorbable polymers that dissolve over time as the tendon heals. Suture anchors offer the advantage of a minimally invasive approach and generally result in less gapping at the repair site during early post-operative motion.
An alternative, traditional approach involves transosseous tunnels, where the bone is pierced with small drill holes. These tunnels allow the pre-placed sutures to pass from the tendon, through the bone, and out the opposite side. The sutures are then tightly tied over a bridge of bone or a button, creating mechanical compression of the tendon against its footprint. This method secures the tendon firmly without applying excessive tension that could cause the sutures to pull through the soft tissue.
The Biological Process of Reintegration
Following mechanical fixation, the tendon must undergo a complex biological process called enthesis healing to truly bond with the bone. The native junction between tendon and bone, known as the enthesis, is a specialized transition zone that includes uncalcified fibrocartilage, calcified fibrocartilage, and bone. During surgical reattachment, this complex structure is not immediately recreated; instead, a more fibrous connection forms initially.
The healing process begins with inflammation and the formation of a hematoma, followed by the proliferation of cells and the deposition of new collagen fibers at the interface. Over a period of several weeks to months, mesenchymal stem cells differentiate into cells that lay down a new matrix, eventually leading to the formation of fibrocartilage. The ultimate sign of successful biological reintegration is the formation of Sharpey’s fibers. These new collagen fibers grow directly from the tendon matrix into the new bone matrix, physically anchoring the soft tissue. This slow, organized remodeling ultimately restores the structural and functional integrity of the tendon-to-bone connection.