Sacralization is an anatomical variation where the lowest lumbar vertebra, L5, fuses partially or completely with the sacrum, a triangular bone at the base of the spine. This congenital condition is present from birth, resulting from fetal developmental processes. While it represents a structural change in the spine’s typical configuration, sacralization is not inherently a disease. It signifies a deviation from the usual five separate lumbar vertebrae, where L5 integrates with the sacrum, which normally consists of five fused vertebrae. This structural difference can impact spinal mechanics, though it often remains without symptoms.
What Sacralization Is
The human spine typically consists of five separate, mobile lumbar vertebrae (L1-L5), with intervertebral discs between them for flexibility. Below the lumbar spine lies the sacrum, a single bone formed by the fusion of five sacral vertebrae (S1-S5). In sacralization, the L5 vertebra connects to the sacrum or the iliac crest, which is part of the pelvis. This connection can be a partial or complete fusion, meaning L5 and the sacrum join to varying degrees.
Sacralization is a congenital anomaly, developing before birth when vertebrae form. It results in L5 being totally or partially connected to the pelvis, sometimes with a partial disc or no disc at all between the bones. The bony protrusions on the sides of L5, called transverse processes, can also connect to the pelvis. This anatomical variation can occur in several forms, classified based on the extent and side of fusion.
Types of sacralization include unilateral fusion, where L5 connects on one side, or bilateral fusion, where it connects on both sides. The fusion can also be complete, involving a solid bony union, or incomplete, where a “pseudo joint” or false joint forms between L5 and the sacrum or ilium. Castellvi classification categorizes these variations, describing types from enlarged transverse processes to complete osseous fusion, or a combination of partial and complete fusions. When this anatomical variation causes pain, it is referred to as Bertolotti’s Syndrome.
Bertolotti’s Syndrome arises when the enlarged transverse process of L5 articulates with the sacrum or ilium, leading to mechanical stress and associated pain. This syndrome highlights that while sacralization itself is a structural variation, it can become clinically significant if it leads to discomfort. The presence of sacralization can alter the biomechanics of the lower spine, potentially contributing to degenerative changes or issues at adjacent spinal segments. This condition is not considered disabling, and many individuals with sacralization do not experience any symptoms.
How Sacralization is Identified
Sacralization often remains asymptomatic; individuals may not experience any related discomfort or symptoms. In many instances, this anatomical variation is discovered incidentally during medical imaging performed for other reasons, such as investigating lower back pain. When sacralization does lead to symptoms, typically as part of Bertolotti’s Syndrome, the primary complaint is localized lower back pain. This pain can manifest as chronic or occasional discomfort in the lower back, particularly around the affected vertebral area.
Individuals with symptomatic sacralization might experience stiffness and a limited range of motion in their lower back, making bending or twisting movements challenging. The pain might be felt in the pelvis or above the hips, and some people find that sitting or lying down provides some relief. In certain cases, nerve compression can occur, leading to sciatica-like pain radiating down the leg, or numbness, tingling, and weakness in the legs or feet. These symptoms often appear in a person’s 20s or 30s.
The definitive diagnosis of sacralization relies on imaging techniques. X-rays of the lumbar spine are typically the initial diagnostic tool, clearly showing the presence and degree of fusion between L5 and the sacrum. More detailed images can be obtained through Computed Tomography (CT) scans, which offer a comprehensive view of the bony structures and the extent of fusion. Magnetic Resonance Imaging (MRI) scans also assess sacralization, providing insight into soft tissues, potential nerve compression, or disc degeneration.
While physical examination may reveal tenderness, limited movement, or altered gait, imaging is essential for confirming sacralization. During a physical assessment, a healthcare professional might evaluate the lower back for stiffness, restricted motion, or signs of nerve involvement. Diagnostic injections, such as local anesthetics or steroids into the affected joint, can also help determine if sacralization is the source of pain by providing temporary relief.
Managing Sacralization
For individuals with sacralization who do not experience any symptoms, specific medical treatment is generally not required. The focus of management shifts to symptomatic cases, particularly those diagnosed as Bertolotti’s Syndrome, where the anatomical variation causes discomfort. The initial approach for managing pain involves conservative treatments to reduce discomfort and improve function.
Conservative management often includes physical therapy, which helps strengthen core muscles, improve flexibility, and enhance posture and movement coordination. Therapies such as the Alexander technique or Pilates can retrain muscles and stabilize the pelvic-lumbar region. Pain medication, including over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs) or muscle relaxants, may be prescribed to alleviate pain and inflammation. Applying heat or cold to the affected area and modifying activities that aggravate symptoms can also provide relief.
If conservative measures are insufficient, injections may be considered. Corticosteroid injections, often guided by fluoroscopy, can be administered into the affected joint or pseudoarthrosis to reduce inflammation and pain. These injections can offer temporary, significant pain relief. In some instances, radiofrequency ablation, which uses heat to target affected nerves around the pseudo-joint, may also provide pain reduction.
Surgical intervention for sacralization is a last resort, reserved for individuals who have not found relief through extensive conservative treatments and injections. Surgical goals may include resecting, or removing, the enlarged transverse process that causes irritation or performing spinal fusion to stabilize the affected area. However, surgery carries inherent risks and is not the first line of treatment. Most individuals with symptomatic sacralization can effectively manage their condition with conservative care, leading to a favorable prognosis for pain control and functional improvement.