Creator: Dr. Mohammed hutaif
Published: 2026-04-12T14:24:17.137073+00:00

Key Takeaway

Intrapelvic protrusio acetabuli, or Otto pelvis, is a chronic condition characterized by the progressive medial migration of the femoral head into the true pelvis. Surgical management primarily involves total hip arthroplasty combined with structural or morselized medial bone grafting to restore the center of rotation. Osteitis pubis, a related pelvic inflammatory condition, typically responds to conservative measures but may rarely necessitate symphyseal arthrodesis for recalcitrant instability.

INTRAPELVIC PROTRUSIO ACETABULI (OTTO PELVIS OR ARTHROKATADYSIS)

Intrapelvic protrusio acetabuli, historically referred to as Otto pelvis or arthrokatadysis, is a complex morphological deformity characterized by the chronic, progressive protrusion of the femoral head into the acetabulum and the true pelvis. Radiographically, it is defined by the medialization of the acetabular line past the ilioischial line (Kohler’s line).

Approximately two-thirds of these lesions present unilaterally. While the condition most frequently manifests in middle-aged individuals, it can develop during adolescence, particularly in the context of genetic or metabolic predispositions. The etiology is broadly categorized into primary (idiopathic) and secondary forms. Secondary protrusio acetabuli is frequently causally related to metabolic bone diseases such as osteomalacia, Paget's disease, or severe inflammatory arthropathies, most notably rheumatoid arthritis.

Biomechanics and Pathophysiology

The biomechanical consequences of protrusio acetabuli are profound. As the femoral head migrates medially, the center of rotation (COR) of the hip joint is displaced medially and superiorly. This medialization shortens the abductor moment arm, leading to significant abductor weakness, a pronounced Trendelenburg gait, and increased joint reactive forces that further accelerate medial bone loss. The femoral neck may eventually impinge on the ischium or the anterior acetabular rim, severely restricting the range of motion.

Clinical Pearl: The primary biomechanical goal in the surgical reconstruction of protrusio acetabuli is the lateralization and inferiorization of the hip's center of rotation to its anatomic origin. Failure to restore the COR will result in persistent abductor weakness, impingement, and premature component failure.

Clinical Presentation and Radiographic Evaluation

Patients typically present with an insidious onset of deep groin pain, a progressive limp, and a marked limitation in hip range of motion—particularly in abduction and rotation. Pain and functional incapacitation are the primary indications for surgical intervention.

Standard anteroposterior (AP) pelvis and lateral hip radiographs are essential. The diagnosis is confirmed when the acetabular teardrop is obliterated or when the medial wall of the acetabulum projects medial to Kohler's line.

Fig. 25-38 Intrapelvic protrusio acetabuli. Severe bilateral progressive protrusion of acetabulum with severe pain and decreased motion in both hips.

Cross-sectional imaging (CT scanning) is highly recommended for preoperative templating. A 3D CT reconstruction allows the surgeon to accurately quantify the volumetric bone loss of the medial wall, assess the integrity of the anterior and posterior columns, and determine the required volume of bone graft.

Surgical Management: Total Hip Arthroplasty (THA)

Total hip arthroplasty is the preferred and definitive treatment for protrusio acetabuli. Historically, bipolar socket hemiarthroplasty combined with bone grafting to the medial wall defect yielded acceptable results (as reported by Wilson and Scott, who noted good outcomes in 21 of 22 hips at an average of 54 months). However, modern tribology and advanced uncemented fixation have made THA the gold standard.

Ebert et al. and Gates et al. have heavily emphasized the absolute necessity of medial bone grafting when performing THA in these patients. In a long-term follow-up study averaging 12.8 years, Gates et al. demonstrated that THA combined with medial bone grafting was effective in arresting the progression of protrusio acetabuli in 90% of patients.

Step-by-Step Surgical Technique for THA in Protrusio

Surgical Approach and Exposure:
A standard posterior or direct anterior approach may be utilized. However, the surgeon must be prepared for a challenging dislocation. Because the femoral head is "captured" within the deep acetabular socket, forceful dislocation maneuvers can easily result in iatrogenic fractures of the posterior wall or the femoral shaft.
In Situ Femoral Neck Osteotomy:
If the head cannot be safely dislocated, an in situ osteotomy of the femoral neck is mandatory. The femoral neck is cut at the templated level, and the femoral head is subsequently extracted from the acetabulum using a corkscrew. In severe cases of arthrokatadysis, the head may need to be sectioned into quadrants (pie-crusting) for safe removal.
Acetabular Preparation:
The fundamental principle of acetabular reaming in protrusio is to ream the periphery, not the medial wall. The medial wall is often paper-thin or entirely deficient. Reaming should be directed laterally and inferiorly to create a bleeding peripheral rim that will support the hemispherical shell.
Medial Bone Grafting:
The medial defect must be grafted to lateralize the component. Morselized cancellous autograft (often harvested from the extracted femoral head) or allograft is packed tightly into the medial defect. Reverse reaming (running the reamer in reverse) can be used to impact the graft into a dense, supportive layer.
Component Implantation:
A multi-hole, uncemented hemispherical titanium shell is impacted into the prepared peripheral rim. The shell must achieve rigid peripheral press-fit stability. Supplemental screw fixation into the safe zones (posterosuperior quadrant) is highly recommended. If the peripheral rim is incompetent, an anti-protrusio cage (e.g., Burch-Schneider cage) or a custom triflange component may be required to span the defect and transfer loads to the intact ilium and ischium.

Surgical Warning: Never accept a medialized cup position. Placing the acetabular component directly against the thin medial wall without grafting will inevitably lead to intrapelvic migration of the prosthesis.

Alternative: Arthrodesis

While THA is the treatment of choice, hip arthrodesis should be considered in a very specific subset of patients: young, active individuals with unilateral disease who are engaged in heavy, demanding physical labor. Arthrodesis provides a stable, painless joint that can withstand extreme loading, though it sacrifices mobility and places increased stress on the lumbar spine and contralateral hip over time.

OSTEITIS PUBIS

Osteitis pubis is a painful, noninfectious, inflammatory condition involving the pubic bone, the pubic symphysis, and the surrounding myofascial structures. It represents a spectrum of anterior pelvic ring overload and instability.

Etiology and Demographics

The condition is frequently triggered by repetitive microtrauma and biomechanical overload. It is highly prevalent in athletes whose sports require repetitive kicking, pivoting, or extreme exertion, ranging from long-distance runners and soccer players to powerlifters.

Additionally, osteitis pubis has a well-documented iatrogenic etiology. It has been reported following various urological and gynecological procedures (e.g., prostatectomy, bladder suspension) where the retropubic space of Retzius is violated, leading to localized periostitis or altered symphyseal biomechanics.

Clinical Presentation and Diagnostics

The primary symptom is the gradual onset of sharp or aching pain in the pubic region. The pain frequently radiates into the groin, along the medial aspect of the thighs (following the adductor origin), or superiorly into the lower abdomen (following the rectus abdominis insertion).

As the inflammatory process progresses, increasing pain may make ambulation exceedingly difficult. Patients often develop a characteristic antalgic or waddling gait to minimize shear forces across the symphysis pubis.

Imaging Modalities:
* Radiographs: Plain radiographic changes may lag behind clinical symptoms by 2 to 3 weeks. Characteristic findings include symmetrical bone resorption at the medial ends of the pubic bones, widening or irregularity of the pubic symphysis, and reactive rarefaction or sclerosis along the pubic rami.
* Bone Scintigraphy (Technetium-99m): Bone scans are highly sensitive and will show diffuse, intense uptake in the pubis much earlier than plain radiographs.
* Magnetic Resonance Imaging (MRI): MRI is the gold standard for differentiating osteitis pubis from other causes of groin pain, such as athletic pubalgia (sports hernia), adductor tendinopathy, iliopsoas bursitis, and pubic ramus stress fractures. MRI typically reveals subchondral bone marrow edema extending from the symphysis into the pubic rami.

Nonoperative Management

Because osteitis pubis is generally a self-limiting condition, the first line of treatment is strictly nonoperative.
* Rest and Modification: Complete cessation of the offending activity is paramount.
* Pharmacotherapy: Aggressive use of nonsteroidal anti-inflammatory drugs (NSAIDs) to modulate the inflammatory cascade.
* Physical Therapy: Core stabilization and progressive adductor stretching/strengthening once acute pain subsides.
* Injections: If symptoms persist despite oral medications and rest, fluoroscopically or ultrasound-guided corticosteroid injections directly into the symphysis pubis can provide significant diagnostic and therapeutic benefit.

Operative Management

Operative treatment is rarely indicated and is reserved for patients with recalcitrant symptoms that have failed a minimum of 6 to 12 months of exhaustive nonoperative management.

Wedge Resection of the Symphysis (Historical Context)

Historically, wedge resection of the symphysis pubis was utilized. Grace et al. reported on 10 patients who underwent wedge resections for recalcitrant osteitis pubis. At an average of 14 months postoperatively, all patients showed marked improvement. However, the long-term follow-up (average 92 months) revealed a high failure rate, with three of the 10 patients dissatisfied.

Pitfall: Resection of the symphysis pubis destroys the anterior tension band of the pelvic ring. This can lead to catastrophic posterior pelvic instability. One patient in the Grace et al. series required bilateral sacroiliac arthrodeses for severe pain caused by secondary pelvic instability. Similarly, Moore, Stover, and Matta reported patients developing bilateral sacroiliac instability after wedge resection, necessitating complex posterior arthrodesis.

Symphyseal Arthrodesis (Preferred Technique)

Due to the high risk of posterior pelvic destabilization associated with resection, symphyseal arthrodesis (fusion) is now the preferred operative intervention for refractory cases. Williams, Thomas, and Downes reported excellent results after symphysis fusion in patients with osteitis pubis and documented anterior pelvic instability.

Surgical Technique for Symphyseal Arthrodesis:
1. Approach: A Pfannenstiel incision is utilized to expose the anterior pelvic ring. The rectus abdominis insertions are carefully mobilized.
2. Preparation: The fibrocartilaginous disc of the symphysis is radically excised. The hyaline cartilage endplates of the pubic bones are decorticated down to bleeding subchondral bone using curettes and a high-speed burr.
3. Grafting: Autologous cancellous bone graft, typically harvested from the anterior iliac crest, is packed tightly into the symphyseal defect.
4. Fixation: Rigid internal fixation is achieved using a multi-hole reconstruction plate (often a 3.5mm or 4.5mm pelvic plate) contoured to the superior aspect of the pubic rami. In cases of severe instability, orthogonal dual-plating (superior and anterior) may be employed to neutralize shear forces until arthrodesis is achieved.

PATHOPHYSIOLOGICAL CONSIDERATIONS IN RHEUMATOID SYNOVITIS

Given that rheumatoid arthritis (RA) is a primary driver of secondary protrusio acetabuli, a deep understanding of rheumatoid synovitis is essential for the reconstructive surgeon.

As detailed by Bondeson et al., the pathophysiology of rheumatoid joint destruction is driven by synovial macrophages and macrophage-produced cytokines (such as TNF-alpha and IL-1). These cytokines upregulate aggrecanases and matrix metalloproteinases (MMPs), leading to rapid degradation of articular cartilage and subchondral bone. This aggressive osteolysis is what permits the femoral head to migrate medially through the acetabular floor.

Synovectomy and Arthroplasty in the Rheumatoid Patient

While early arthroscopic or open synovectomy (as discussed by Krebs, Limbird, and Triantafyllou) can temporarily halt the inflammatory cascade and provide symptomatic relief in early-stage rheumatoid joints, it does not permanently prevent joint deterioration. Doets et al. demonstrated that synovectomy of the rheumatoid knee does not prevent long-term radiographic progression.

Therefore, in the setting of advanced rheumatoid arthritis with protrusio acetabuli, total joint arthroplasty remains the definitive solution. Modern literature (Creighton et al., Lachiewicz) supports the use of uncemented, porous-coated components in rheumatoid patients, provided that bone stock is adequately restored via the impaction grafting techniques described above. The surgeon must also be highly cognizant of perioperative medical management, particularly the coordination of disease-modifying antirheumatic drugs (DMARDs) and biologic agents, to balance the risks of postoperative infection against the risk of a systemic rheumatoid flare (Howe et al.). Furthermore, preoperative evaluation of the cervical spine is mandatory in all RA patients undergoing THA to rule out atlantoaxial instability prior to intubation (Collins et al.).

Authoritative Medical Review

This academic synthesis is based on established protocols from Hutaifortho's Operative Orthopaedics and has been medically reviewed by Prof. Dr. Mohammed Hutaif, Consultant Orthopedic & Spine Surgeon. It is designed to assist orthopedic residents, fellows, and practicing surgeons in surgical preparation and board reviews (AAOS, FRCS, Arab Board).

Clinical Disclaimer: The surgical techniques, indications, and medical guidance detailed herein are for advanced educational purposes only. They do not supersede institutional guidelines or independent surgical judgment.

📚 Medical References

Medically Verified Content

Prof. Dr. Mohammed Hutaif

Consultant Orthopedic & Spine Surgeon

Intrapelvic Protrusio Acetabuli and Osteitis Pubis: Comprehensive Surgical Management