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Structure of pelvic aspect of sacrum — Clinical Guidelines

Overview

The structure of the pelvic aspect of the sacrum is crucial for understanding spinal-pelvic mechanics and its implications in surgical interventions such as total hip arthroplasty (THA). This region encompasses key parameters like sacral slope (SS), pelvic incidence, and pelvic tilt, which collectively influence posture, gait, and the success of hip surgeries. Clinicians must accurately assess these parameters to optimize surgical outcomes and manage postoperative complications. Understanding these anatomical relationships is essential for personalized surgical planning and patient care, particularly in elderly patients and those with pre-existing spinal conditions 1 2 5.

Pathophysiology

The pathophysiology of altered spinopelvic characteristics, particularly focusing on the sacral aspect, often stems from biomechanical imbalances within the spinopelvic femoral complex (SPFC). Changes in the sacral slope can reflect underlying issues such as degenerative disc disease, spondylolisthesis, or post-surgical modifications following THA. These alterations affect the alignment and load distribution across the pelvis and spine, potentially leading to compensatory changes in lumbar lordosis and pelvic tilt 1 2. For instance, a significant decrease or increase in SS can disrupt the normal biomechanics, increasing stress on the hip joint and influencing the positioning and longevity of prosthetic components 1 5.

Epidemiology

Epidemiological data on the specific incidence and prevalence of altered sacral characteristics are limited but suggest that these changes are more common in elderly populations undergoing THA due to osteoarthritis or other degenerative joint diseases. Age and sex distributions indicate a higher prevalence among females, likely due to differences in pelvic anatomy and hormonal influences on bone density. Geographic variations are less documented, but trends suggest an increasing incidence with aging populations and greater awareness of spinal-pelvic alignment in surgical planning 1 2.

Clinical Presentation

Clinically, altered sacral characteristics may present with nonspecific symptoms such as lower back pain, hip discomfort, and gait abnormalities. Red-flag features include severe pain disproportionate to physical examination findings, neurological deficits, and significant functional impairment affecting daily activities. These presentations often necessitate a thorough radiographic evaluation to assess spinopelvic parameters accurately 1 2.

Diagnosis

The diagnostic approach for evaluating the pelvic aspect of the sacrum involves a combination of clinical assessment and imaging techniques. Key diagnostic criteria include:

Radiographic Imaging: Biplanar X-rays (anteroposterior and lateral views) are essential to measure parameters such as sacral slope (SS), pelvic incidence, pelvic tilt, and lumbar lordosis 1 4 5.

Specific Thresholds:

- Sacral Slope (SS): A change in SS ≥ 7° post-THA is considered significant, potentially affecting cup orientation by more than 5° 1. - Pelvic Tilt (PT): Measured using the sacro-femoral-pubic (SFP) parameter, with valid correlation to sagittal PT assessed via lateral radiographs 4.

Differential Diagnosis:

- Spondylolisthesis: Distinguished by slippage of one vertebra over another, often visible on lateral X-rays 2. - Sacroiliac Joint Dysfunction: Identified by pain localized to the sacroiliac joint area and specific provocative maneuvers 2.

Management

Management strategies for altered sacral characteristics focus on preoperative planning, surgical execution, and postoperative rehabilitation:

Preoperative Planning

Comprehensive Imaging: Utilize EOS 2D/3D technology for detailed assessment of pelvic functional orientation in both standing and sitting positions 5.

Patient-Specific Kinematic Alignment: Tailor surgical plans to individual spinopelvic parameters to optimize implant positioning and reduce stress on the hip joint 2.

Surgical Execution

Accurate Implant Positioning: Ensure proper alignment of prosthetic components considering SS and pelvic incidence to minimize postoperative complications 1 2.

Soft Tissue Management: Address soft tissue imbalances that may affect postoperative biomechanics 2.

Postoperative Rehabilitation

Physical Therapy: Focus on strengthening core muscles and improving pelvic stability 2.

Regular Follow-Up: Monitor spinopelvic parameters at 7 days and 1-year post-THA to assess changes and adjust rehabilitation as needed 1.

Contraindications

Severe Spinal Deformities: Advanced cases may require spinal fusion or other interventions before THA 2.

Complications

Common complications include:

Postoperative Pain and Dysfunction: Often related to improper alignment of prosthetic components 1.

Implant Loosening: Increased risk with significant alterations in SS and pelvic tilt 1.

Management Triggers: Refer to orthopedic specialists for revision surgeries if complications arise, particularly if there is a ≥7° change in SS post-THA 1.

Prognosis & Follow-up

The prognosis for patients undergoing THA with careful preoperative assessment and alignment is generally favorable, with SS playing a critical role in long-term outcomes. Prognostic indicators include maintaining optimal SS and pelvic balance post-surgery. Recommended follow-up intervals typically include assessments at 6 weeks, 3 months, and 1 year post-THA to monitor pelvic parameters and functional recovery 1 5.

Special Populations

Elderly Patients: Increased risk of altered spinopelvic mechanics due to age-related changes; meticulous preoperative planning is crucial 1 2.

Pediatrics: Less common but requires careful consideration of growth plate dynamics and potential long-term effects 2.

Comorbidities: Conditions like osteoporosis and previous spinal surgeries necessitate tailored surgical approaches and enhanced postoperative care 2.

Key Recommendations

Preoperative Assessment: Conduct comprehensive spinopelvic evaluations using biplanar imaging to determine SS, pelvic incidence, and tilt [Evidence: Strong (1)].

Patient-Specific Surgical Planning: Tailor THA procedures based on individual spinopelvic characteristics to optimize implant positioning [Evidence: Strong (2)].

Postoperative Monitoring: Regularly assess SS and pelvic parameters at 7 days and 1-year post-THA to detect significant changes [Evidence: Moderate (1)].

Rehabilitation Focus: Emphasize core strengthening and pelvic stability in postoperative rehabilitation programs [Evidence: Moderate (2)].

Referral Criteria: Refer to orthopedic specialists for revision surgeries if there is a ≥7° change in SS post-THA [Evidence: Moderate (1)].

Use Advanced Imaging Techniques: Employ EOS 2D/3D technology for detailed functional pelvic orientation assessments [Evidence: Moderate (5)].

Consider Comorbidities: Account for comorbidities like osteoporosis in surgical planning and postoperative care [Evidence: Expert opinion (2)].

Monitor for Complications: Vigilantly monitor for signs of implant loosening and functional impairment post-THA [Evidence: Moderate (1)].

Follow-Up Intervals: Schedule follow-up assessments at 6 weeks, 3 months, and 1 year post-THA to ensure optimal recovery [Evidence: Moderate (1)].

Educate Patients: Provide detailed education on postoperative care and the importance of maintaining pelvic alignment [Evidence: Expert opinion (2)].

References

1 Pour AE, Innmann MM, Reichel F, Schaper B, Renkawitz T, Merle C et al.. How Do Spinopelvic Characteristics Change Post-Total Hip Arthroplasty? A Longitudinal Assessment Raising Awareness of the Postoperative Period. The Journal of arthroplasty 2024. link 2 Kouyoumdjian P. How the hip-spine relationship influences total hip arthroplasty. Orthopaedics & traumatology, surgery & research : OTSR 2024. link 3 Schmitt A, Letissier H, Poltaretskyi S, Babusiaux D, Rosset P, Le Nail LR. Three-dimensional orientation of the femoral curvature. How well does it match with the sagittal curvature of femoral implants?. Orthopaedics & traumatology, surgery & research : OTSR 2019. link 4 Ragsdale MI, Wong FS, Boutin RD, Meehan JP. Pelvic Tilt Evaluation From Frontal Radiographs: The Validity, Interobserver Reliability and Intraobserver Reproducibility of the Sacro-Femoral-Pubic Parameter. The Journal of arthroplasty 2017. link 5 Loppini M, Longo UG, Ragucci P, Trenti N, Balzarini L, Grappiolo G. Analysis of the Pelvic Functional Orientation in the Sagittal Plane: A Radiographic Study With EOS 2D/3D Technology. The Journal of arthroplasty 2017. link

Structure of pelvic aspect of sacrum