How I Put In an Uncemented Acetabular Component

Faculty Operative Technique & Master Lecture: Uncemented Acetabular Component Placement in Total Hip Arthroplasty.

1. High-Yield Summary

Uncemented hemispherical acetabular component placement represents the international gold standard for acetabular reconstruction in primary total hip arthroplasty (THA). The biological foundation of cementless acetabular fixation relies on achieving immediate, rigid mechanical press-fit stability within the prepared osseous cotyloid cavity, converting equatorial frictional interference into primary stability that limits interfacial micromotion below the critical 40 to 150 micrometer threshold. This rigid mechanical environment facilitates secondary biological intramembranous osseointegration via bone ingrowth or ongrowth into porous titanium or tantalum coatings. Achieving reproducible cup positioning demands disciplined identification of native patient-specific anatomical landmarks, most notably the transverse acetabular ligament (TAL) and the medial cotyloid floor, rather than reliance on variable operating table orientation.

• Primary Clinical Indication: End-stage degenerative joint disease of the hip (primary osteoarthritis, secondary osteoarthritis due to developmental dysplasia or trauma, avascular necrosis, and inflammatory arthropathies) with adequate pelvic bone stock and supportive anterior and posterior acetabular columns.
• Fixation Mechanism: Equatorial interference press-fit generated by under-reaming the acetabular cavity by 1 to 2 mm relative to the nominal outer diameter of a porous-coated hemispherical shell, delivering circumferential frictional scratch-fit across the anterior and posterior columns and the subchondral dome, followed by secondary osseointegration into micro-porous or trabecular metallic coatings.
• The Single Critical Move: Systematic clearance of the pulvinar to visualize the true medial cotyloid floor, followed by sequential reaming referencing the transverse acetabular ligament (TAL) to guide cup orientation to 40 degrees of inclination and 15 to 20 degrees of anteversion, culminating in coaxial impaction until polar bottoming is verified by an acoustic pitch transition and apex hole inspection.
• Neurovascular Danger Zones: Wasielewski anterior-superior quadrant (external iliac artery and vein); anterior-inferior quadrant (obturator neurovascular bundle); posterior-superior sciatic notch margin (superior gluteal nerve and vessels); and posterior acetabular wall corridor (sciatic nerve).
• Catastrophic Technical Errors to Avoid: First, cup over-inclination (>45 to 50 degrees) or malversion resulting from spatial disorientation or unrecognized pelvic roll, predisposing to accelerated polyethylene edge-loading, squeaking in ceramic bearings, stripe wear, and recurrent prosthetic dislocation. Second, aggressive medial reaming violating Kohler’s line and breaching the medial wall, causing intrapelvic cup migration or anterior/posterior column discontinuity. Third, uncontained equatorial binding where an oversized shell wedges at the peripheral rim with a persistent apical gap, resulting in excessive interfacial micromotion and early fibrous loosening. Fourth, placing supplemental transacetabular screws outside the safe posterior quadrants, risking life-threatening external iliac vascular laceration or obturator nerve palsy. Fifth, incomplete or canted modular liner insertion, leading to locking mechanism fracture, malseating wear, or catastrophic ceramic liner fracture.

2. Indications

Uncemented hemispherical acetabular shells are indicated for primary reconstructive hip surgery where native pelvic bone stock provides supportive anterior and posterior column architecture capable of resisting multiplanar physiological joint reaction forces.

Absolute Indications

• Primary Hip Osteoarthritis: Severe symptomatic osteoarthritis (Kellgren-Lawrence Grade 3 or 4) with debilitating pain, joint space obliteration, and functional limitation refractory to comprehensive non-operative interventions.
• Avascular Necrosis of the Femoral Head: Advanced osteonecrosis (Ficat-Arlet Stage III or IV; Steinberg Stage IV to VI) with secondary acetabular cartilage ulceration, subchondral sclerosis, and acetabular cotyloid changes.
• Post-Traumatic Osteoarthritis: Secondary degenerative arthritis following prior acetabular fractures or traumatic hip dislocations where pelvic columns have healed in an anatomical or near-anatomical alignment with preserved column continuity.
• Inflammatory Arthropathies: Rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis, and systemic lupus erythematosus presenting with progressive joint destruction and structurally intact pelvic columns.
• Developmental Hip Dysplasia: Secondary degenerative joint disease secondary to developmental dysplasia of the hip (Crowe Type I or II) where superior and posterior column coverage of the trial shell achieves at least 70% native host bone contact.

Relative Indications & Patient Selection

• Young and Active Patients: Individuals under 65 to 70 years of age with high functional demands, where long-term biological osseointegration and preservation of pelvic bone stock for future reconstructive procedures are critical.
• Paprosky Type I and II Acetabular Bone Loss: Mild to moderate cavitary or mild segmental rim bone deficiencies where rigid equatorial press-fit can be established against intact columns and supplemented with transacetabular cancellous screws.
• Altered Spinopelvic Mobility: Patients with rigid lumbar spinal fusions, ankylosing spondylitis, or flatback deformity, requiring customized functional cup positioning or dual-mobility articulations to prevent dynamic prosthetic impingement.

Contraindications

• Active Infection: Active septic arthritis of the hip joint, adjacent soft-tissue phlegmon, pelvic osteomyelitis, or active systemic bacteremia. Uncemented porous shell placement in an infected environment is strictly contraindicated.
• Severe Pelvic Column Discontinuity & Paprosky Type IIIB Defects: Complete loss of anterior and posterior column structural integrity, pelvic discontinuity, or massive circumferential wall deficiencies exceeding 50% of the acetabular rim where a standard hemispherical press-fit shell cannot achieve primary rigid stability. Such scenarios necessitate modular porous metal augments, cup-cage reconstruction, double-column plating, or custom triflange acetabular components.
• Prior Pelvic Radiation Therapy: High-dose therapeutic pelvic irradiation resulting in profound vascular obliteration and osteonecrosis of the iliac and ischial columns, severely compromising osteoblast recruitment and biological osseointegration. Cemented fixation or highly porous structural tantalum with extensive multi-screw fixation represents the preferred alternative.
• Neuropathic Arthropathy: Charcot neuroarthropathy or profound neuromuscular disorders with complete abductor paralysis and lack of protective proprioception, where extreme dislocation and loosening risks require specialized constrained or dual-mobility reconstruction.

3. Preoperative Planning

Rigorous preoperative radiographic templating and spinopelvic kinematic evaluation are mandatory prerequisites to predict acetabular component dimensions, restore the anatomical center of rotation, and account for functional pelvic tilt changes between standing and sitting postures.

Imaging Review

• Standard Radiographic Series: Calibrated anteroposterior (AP) pelvis radiograph centered over the pubic symphysis with both lower limbs internally rotated 15 degrees to optimize neck-shaft geometry; dedicated high-resolution AP view of the operative hip; and a true lateral radiograph (cross-table lateral or 45-degree Dunn view).
• Radiographic Acetabular Landmarks: Meticulous evaluation of the radiographic U-shaped teardrop (the floor of the acetabular fossa), Kohler’s line (the ilioischial line representing the medial wall of the acetabulum), the iliopubic line (anterior column), the ilioischial line (posterior column), and the superior subchondral dome.
• Center of Rotation Restoration: Identification of the native anatomical hip center of rotation (COR). Digital templating establishes the target medialization boundary at the lateral border of the teardrop floor, avoiding superior or lateral migration (“high hip center”) that shortens the abductor moment arm and increases joint reaction forces.
• Acetabular Sizing & Bone Coverage: Selection of the templated cup diameter to match the true subchondral bony diameter between the anterior and posterior columns. Coverage of at least 70% host bone is verified; any anticipated superior-lateral uncovered bone (>30%) indicates the need for medialized reaming, a cotyloid osteophyte resection, or augment planning.
• Spinopelvic Mobility & Functional Pelvic Tilt: Standing and relaxed sitting lateral radiographs of the spine and pelvis are evaluated to classify spinopelvic kinematics. Pelvic incidence (PI), sacral slope (SS), and pelvic tilt (PT) are quantified. In a normal flexible spine, sitting causes the lumbar spine to flatten (decreased lordosis) and the pelvis to tilt posteriorly (sacral slope decreases by >10 degrees, pelvic tilt increases), which dynamically increases acetabular anteversion and inclination by approximately 1 degree for every 1 degree of posterior pelvic tilt. In patients with a “stiff spine” (prior multi-level lumbar fusion or severe spondylosis) who are stuck in a standing lordotic posture, the pelvis cannot tilt posteriorly when sitting, leaving the functional cup retroverted and predisposing to anterior prosthetic impingement and posterior dislocation. Conversely, a pelvis stuck in sitting kyphosis fails to tilt anteriorly upon standing, exposing excessive functional anteversion and inclination that provokes anterior dislocation. Cup target angles must be individualized based on spinopelvic classification.

Equipment Checklist

• Hemispherical Acetabular Reamers: Complete set of low-profile hemispherical reamers ranging from 38 mm to 64 mm in 1-mm increments, ensuring sharp, balanced cutting flutes.
• Reamer Handles: Straight reamer drive handles and 45-degree offset or curved drive handles for direct anterior and minimally invasive posterior approaches to clear the soft-tissue envelope.
• Trial Acetabular Cups: Sized hemispherical trial cups equipped with peripheral observation windows and a threaded apex apical hole for direct visualization of the cotyloid floor.
• Component Introducer & Impactors: Rigid, threaded cup introducer handles with modular external mechanical alignment guides (set to 40 degrees inclination and 15 to 20 degrees anteversion); dedicated heavy mallets (2 to 3 lb).
• Transacetabular Screw Instrumentation: Curved and straight drill guides with depth stops (25 mm, 30 mm, 35 mm, 40 mm); flexible and straight 3.2-mm drill bits; calibrated modular depth gauge; universal-joint and ball-hex screwdrivers; screw-holding forceps.
• Definitive Shells & Fixation Hardware: Porous-coated titanium or trabecular metal hemispherical cups (solid-back and multi-hole configurations); 6.5-mm self-tapping cancellous bone screws (lengths 15 mm to 45 mm).
• Modular Liners: Highly cross-linked polyethylene (HXLPE) liners (neutral, 10-degree elevated rim/hooded, and lateralized/offset options) and ceramic liners (biolox delta) matching the shell diameter; dedicated concentric suction cup and mechanical seating impactor heads.
• Acetabular Retractor Tray: Sharp and blunt anterior Hohmann retractors; two-pronged inferior retractor (TAL / obturator foramen retractor); posterior wall / ischial retractor; and superior dome retractor.

Examination Under Anesthesia (EUA)

• Passive Arc of Motion: Assessment of maximal flexion, extension, abduction, adduction, internal rotation, and external rotation with the patient relaxed under general or regional anesthesia to identify structural contractures.
• Contracture Testing: Performance of the Thomas test to evaluate fixed hip flexion contractures and evaluation of tight adductor or abductor myofascial bands that may distort pelvic orientation on the operating table.
• Clinical Limb Length & Pelvic Obliquity: Direct palpation of bilateral anterior superior iliac spines (ASIS), patellar poles, and medial malleoli to confirm true versus apparent leg length discrepancy prior to draping.

4. Patient Positioning & Setup

Reproducible, rigid patient positioning is the primary surgical safeguard against spatial disorientation. An undetected shift in pelvic tilt or rotation during reaming directly causes component malposition.

Patient Orientation & Operating Room Setup

• Lateral Decubitus Position (Posterior & Direct Lateral Approaches): The patient is positioned on a radiolucent operating table. Rigid pelvic fixation is secured using well-padded anterior pubic symphysis and posterior sacral positioners (e.g., pegboard, Stulberg positioner, or three-point rigid clamps). The operative pelvis must be secured strictly perpendicular (90 degrees) to the floor in both coronal and transverse planes. Any inadvertent anterior pelvic tilt (rolling forward) creates a visual illusion of excessive anteversion, tempting the surgeon to retrovert the cup; rolling backward (posterior tilt) induces under-estimation of anteversion, driving excessive cup anteversion.
• Supine Position (Direct Anterior Approach): The patient is placed supine on a specialized orthopaedic traction table (e.g., Hana table) or a standard radiolucent operating table. Both ASIS are palpated and leveled horizontally, ensuring the pelvis is parallel to the floor without coronal tilt. The abdomen and pubic area are draped to allow direct trans-operative palpation of both ASIS as an immutable pelvic reference plane.
• Pressure Point Protection: A dedicated axillary roll is placed one handbreadth inferior to the dependent axilla to protect the brachial plexus. The dependent peroneal nerve is cushioned at the fibular head with foam padding, and dependent bony prominences (malleoli, knees, trochanter) are safeguarded.
• Surgical Field Draping: Wide sterile preparation and draping of the operative hemipelvis and lower extremity from the costal margin to the mid-calf or foot, providing full, unrestricted limb mobility for dynamic trialing and stability assessments.

Safety Check

• Positioner Rigidity Verification: Prior to sterile incision, vigorous manual force is applied to the pelvis in anterior, posterior, and cephalad directions to confirm absolute stability without translational slippage within the clamping system.
• Range of Motion Arc Check: Confirming that the draped limb can be flexed to 90 degrees, internally rotated to 90 degrees, and adducted across the table without contacting unsterile draping poles or mayo stands.
• Fluoroscopy Clearance: When intraoperative fluoroscopy or C-arm imaging is planned (e.g., direct anterior approach), the C-arm is brought into the field to confirm unobstructed AP pelvis and hip visualization prior to surgical incising.

5. Surgical Approach & Exposure

Exposure of the acetabulum requires systematic capsular releases and strategic 360-degree retractor placement around the bony perimeter, isolating the cotyloid rim without compromising adjacent neurovascular structures.

Named Surgical Approaches

• Posterior Approach (Moore / Southern): The patient is in the lateral decubitus position. The fascia lata is incised longitudinally, and the gluteus maximus is bluntly split in line with its fibers. The piriformis and conjoint tendons (obturator internus and gemelli) are identified, tagged with heavy stay sutures for later anatomical repair, and reflected sharply from their trochanteric insertion. A broad, medially hinged posterior capsular flap is developed, exposing the femoral head and acetabular rim. Following femoral head dislocation and neck resection, the proximal femur is mobilized anteriorly to provide wide acetabular visualization.
• Direct Anterior Approach (Smith-Petersen / Hueter Interval): The patient is positioned supine. Dissection enters the intermuscular and internervous interval between the tensor fasciae latae laterally and the sartorius / rectus femoris medially. The ascending branch of the lateral circumflex femoral artery is coagulated. An anterior capsulotomy is performed, the femoral neck is osteotomized in situ, and the femoral head is extracted with a corkscrew. The proximal femur is retracted laterally, exposing the acetabular rim directly.
• Direct Lateral Approach (Hardinge): The patient is positioned in lateral decubitus. The fascia lata is split, and the anterior one-third of the gluteus medius and vastus lateralis are elevated in continuity off the greater trochanter as a single tendinous sleeve. An anterior capsulotomy provides direct in-line visualization of the acetabulum.

Internervous & Intermuscular Planes

• Posterior Approach Interval: Lacks a true internervous plane. The gluteus maximus is split along its muscular fibers, innervated entirely by the inferior gluteal nerve (L5, S1, S2). The short external rotators are detached near their insertion, protecting the sciatic nerve located posteromedially.
• Direct Anterior Approach Interval: Utilizes a true internervous and intermuscular plane. Superficial interval lies between the tensor fasciae latae (superior gluteal nerve, L4, L5, S1) and the sartorius (femoral nerve, L2, L3, L4). Deep interval lies between the tensor fasciae latae / gluteus medius (superior gluteal nerve) and the rectus femoris (femoral nerve).
• Direct Lateral Approach Interval: Intermuscular, non-internervous interval splitting the abductor mechanism. The gluteus medius is supplied by the superior gluteal nerve, and the vastus lateralis is supplied by the femoral nerve. Proximal dissection must remain strictly within 3 cm of the trochanteric tip to protect the main trunk of the superior gluteal nerve.

Soft-Tissue Releases & Acetabular Retractor Placement

• Anterior Hohmann Retractor: Placed over the anterior acetabular wall, resting directly on the sub-iliopsoas anterior bony rim or pubic ramus. The retractor tip must remain strictly on bone under direct visualization; never allow the tip to plunge into the pelvic basin, which risks laceration of the external iliac artery or vein. This retractor retracts the anterior capsule and proximal femur forward.
• Inferior Retractor (Transverse Acetabular Ligament Retractor): A two-pronged or curved Hohmann retractor is positioned under the inferior margin of the transverse acetabular ligament into the obturator foramen or sub-cotyloid notch. This retractor depresses the inferior capsule and proximal femur away from the cotyloid notch, fully exposing the inferior margin and TAL.
• Posterior Retractor: Placed behind the posterior acetabular wall, resting securely on the ischial column. It retracts the posterior capsule and protects the sciatic nerve from reamer blades.
• Superior Dome Retractor: An optional sharp or blunt Hohmann retractor placed superior to the acetabular dome beneath the reflected abductor muscles, elevating the soft tissues to confirm full visualization of the superior subchondral rim.

6. Technique: Step-by-Step Operative Method

Implantation of an uncemented acetabular shell requires disciplined, sequential execution across six standardized phases, balancing osseous conservation with circumferential press-fit engagement.

Step 1: Acetabular Labral Excision & Fossa Clearance

• Excise the complete circumferential labrum sharply around the entire bony rim using a curved scalpel (No. 15 blade) or electrocautery, peeling fibrocartilage down to bleeding subchondral bone.
• Identify and strictly preserve the transverse acetabular ligament (TAL). The TAL spans the inferior cotyloid notch, representing the native anatomical guide for cup anteversion and inclination. Do not transect or release the TAL.
• Debride the fibrofatty pulvinar tissue completely from the cotyloid fossa using a curved rongeur and heavy curette. Continue debridement down to the hard, pale cortical floor of the cotyloid fossa. This medial wall represents the true medial boundary of the acetabulum.
• Resect peripheral osteophytes from the anterior, posterior, and superior rims using a curved osteotome or rongeur. Remove large inferior teardrop osteophytes that can falsely elevate the reamer or cause premature component impingement.

Step 2: Sequential Acetabular Reaming

• Medialize the cavity using a small hemispherical starter reamer (typically 40 to 44 mm, or 4 to 6 mm smaller than the anticipated definitive shell). Direct the reamer at 45 degrees of inclination and 20 degrees of anteversion, aiming toward the cotyloid floor. Ream medially until the reamer just touches the cortical bone of the medial cotyloid floor. This critical step medializes the hip center to its anatomical position and prevents lateralized high hip center positioning. Do not violate Kohler’s line.
• Reorient the reamer trajectory to the definitive planned component alignment: 40 degrees of inclination and 15 to 20 degrees of anteversion, aligned strictly parallel to the plane of the transverse acetabular ligament.
• Expand the reamer sequentially in 1-mm to 2-mm increments. Maintain constant coaxial alignment without toggling or levering the reamer handle, which can create an oval or eccentric cavity.
• Prepare the anterior and posterior columns. Ream until the reamer blades bite simultaneously into the anterior column, posterior column, and superior dome, exposing a uniform bed of viable, bleeding cancellous bone.
• Preserve subchondral bone. Stop reaming when a uniform hemispherical envelope is created with intact anterior and posterior cortical walls. Over-reaming weakens cortical column support, risking intraoperative fracture or intrapelvic cup migration.

Step 3: Acetabular Trialing & Bone Bed Inspection

• Introduce a trial acetabular cup matching the diameter of the last reamer used (or 1 mm smaller, depending on system under-reaming convention).
• Assess equatorial bite: Apply rotational and levering forces to the trial cup handle. The trial shell must demonstrate immediate frictional scratch-fit against the anterior and posterior columns without toggle or rocking.
• Check for polar bottoming out: Inspect the cotyloid floor directly through the trial shell’s apical hole and peripheral observation windows. Confirm that the apex of the trial contacts the medial cotyloid floor without an apical gap. An apical gap (>1 to 2 mm) indicates peripheral rim hanging, requiring further sequential reaming.
• Evaluate host bone coverage: Verify that at least 70% to 80% of the trial cup surface is supported by native subchondral and cancellous bone, with intact column purchase.
• Confirm anatomical orientation: Verify that the inferior face of the trial cup is parallel to the plane of the transverse acetabular ligament (TAL) and recessed 1 to 2 mm within the bony rim.

Step 4: Component Positioning, Press-Fit Impaction & Fixation

• Determine press-fit under-reaming: In standard non-sclerotic bone, under-ream the acetabulum by 1 to 2 mm relative to the nominal outer diameter of the definitive hemispherical shell (e.g., prepare the bone with a 52-mm reamer for a 54-mm porous cup). In dense, sclerotic bone or irradiated pelves, ream line-to-line (0 to 1 mm under-ream) to prevent acetabular fracture during impaction.
• Align the component: Thread the definitive porous-coated titanium or trabecular shell securely onto the introducer handle. Orient the mechanical alignment guide to achieve 40 degrees of inclination (abduction) relative to the longitudinal body axis and 15 to 20 degrees of anteversion. Directly cross-reference the inferior rim against the transverse acetabular ligament, positioning the shell parallel to the TAL and recessed 1 to 2 mm superiorly.
• Deliver the shell into the prepared acetabular cavity, ensuring the peripheral porous coating does not skive or hang up on the anterior bony rim.
• Impact the cup coaxially using disciplined, solid blows with a heavy mallet (2 to 3 lb). Maintain unwavering directional alignment throughout impaction.
• Monitor acoustic feedback: Listen intently to the mallet strikes. The acoustic pitch changes from an initial dull, low-frequency thud to a crisp, high-frequency metallic ring as the shell achieves intimate contact with the subchondral bone. Cessation of cup advancement coincides with this acoustic pitch transition.
• Verify polar contact: Disengage the introducer handle. Introduce a curved depth probe or direct light source through the apical portal. Confirm direct bone-to-implant contact between the shell apex and the medial cotyloid floor (zero apical gap). If an apical gap persists, re-attach the introducer and deliver additional controlled strikes; if advancement has halted, confirm absence of peripheral osteophyte block.
• Confirm mechanical rigidity: Manually test cup stability by levering firmly against the rim in multiple vectors. The shell must demonstrate absolute three-dimensional stability with zero toggle, rock, or rotation.

Step 5: Supplemental Screw Fixation (Wasielewski Quadrants)

Supplemental screw fixation is indicated when host bone quality is compromised, when minor cavitary defects reduce contact area, or when additional rotational and shear resistance is required to facilitate osseointegration.

• Map the Wasielewski Quadrants: Construct a reference line from the anterior superior iliac spine (ASIS) through the center of the acetabulum to the fovea/ischial spine. Bisect this line with a perpendicular line through the center of the acetabulum, dividing the pelvic cotyloid envelope into four distinct quadrants:
  • Posterior-Superior Quadrant (“Safe Zone”): Encompasses the dense, thick bone of the posterior iliac wing and sciatic buttress, offering 25 to 35 mm of osseous depth. Screws placed here engage the iliac pillar directed toward the sacroiliac joint. Screws longer than 35 to 40 mm risk exiting the greater sciatic notch, endangering the superior gluteal vessels and nerve.
  • Posterior-Inferior Quadrant (“Caution / Safe Zone”): Corresponds to the ischial column, offering 15 to 25 mm of bone depth. Safe for short screws (15 to 20 mm). Screws exceeding 25 mm risk exiting into the lesser sciatic notch, threatening the internal pudendal neurovascular bundle.
  • Anterior-Superior Quadrant (“Absolute Danger Zone”): Thin bone overlying the external iliac artery and vein. Screw drilling or insertion in this quadrant carries extreme risks of catastrophic retroperitoneal vascular laceration. Transacetabular screws must never be inserted here.
  • Anterior-Inferior Quadrant (“Danger Zone”): Overlies the obturator foramen and obturator neurovascular bundle. Screw placement carries high risks of obturator nerve and vessel transection. Transacetabular screws must never be inserted here.
• Drill screw corridors: Position a drill guide with a mechanical safety stop (typically 25 to 30 mm) into a selected screw hole within the posterior-superior safe quadrant. Use a flexible drill shaft and a 3.2-mm drill bit. Drill under tactile control, feeling the drill bit penetrate the near cortex, traverse cancellous bone, and just engage the far cortex without plunging.
• Measure & Insert: Measure bone depth using a calibrated depth gauge, feeling the far cortical edge. Introduce a 6.5-mm self-tapping cancellous bone screw using a ball-hex screwdriver. Drive the screw until it achieves solid compression against the shell.
• Verify countersinking: Ensure the screw head is completely recessed within the spherical contour of the shell’s screw hole. A proud screw head will prevent full concentric seating of the modular liner, causing liner malseating, edge tilt, or mechanical failure.

Step 6: Liner Insertion & Seating

• Debride & Irrigate: Thoroughly irrigate the interior of the metal shell with pulsed saline lavage. Meticulously inspect and dry the inner locking taper, dome, and rim using dry laparotomy sponges. Ensure complete absence of bone reamings, soft-tissue tags, blood clot, or foreign debris. A single microscopic bone particle trapped behind the liner will cause liner tilting, incomplete lock engagement, or backside wear.
• Select modular liner design: Highly cross-linked polyethylene (HXLPE) or ceramic (biolox delta). Select a neutral liner for unrestricted range of motion and anatomical impingement clearance. Select a 10-degree elevated rim/hooded liner to augment posterior-superior coverage if joint laxity or borderline posterior instability is encountered. Select a lateralized (+4 mm) liner if increased femoral offset and soft-tissue tensioning are required.
• Align anti-rotational tabs: Align the anti-rotational splines or tabs of the liner with the mating scallops on the inner circumference of the metallic shell.
• Engage & Impact: Push the liner concentrically into the shell by hand. Mount the dedicated manufacturer liner impactor with a matching hemispherical face. Deliver several firm, coaxial mallet blows directly perpendicular to the face of the shell.
• Verify concentric flush seating: Run a fine hook probe or nerve hook 360 degrees around the entire circumferential junction between the liner and the metal shell rim. Confirm that the liner is completely flush, concentric, and fully engaged within the locking mechanism. There must be zero canting, step-off, or proud rim segment. For ceramic liners, incomplete or canted seating results in catastrophic ceramic chipping or liner fracture upon reduction.

The Critical Move: Achieving Rigid Press-Fit & Anatomical Orientation

The definitive biomechanical success of an uncemented acetabular reconstruction hinges entirely upon achieving immediate equatorial interference fit and anatomical spatial orientation while eliminating apical gaps. The critical move represents the seamless synchronization of four mandatory technical elements: systematic medialization to the cotyloid floor, orientation referencing the transverse acetabular ligament (TAL), disciplined coaxial impaction until the acoustic pitch transitions to a high-frequency metallic ring, and visual verification of zero apical gap through the dome portal.

The irreversible point of no return occurs during the final 2 to 3 millimeters of shell impaction. If an oversized cup wedges at the peripheral rim before bottoming out against the medial floor, continued aggressive impaction will not seat the cup deeper; instead, excessive hoop tensile stresses will instantaneously split the anterior or posterior column. Conversely, accepting an apical gap leaves the shell supported only by a fragile equatorial rim wedge, predisposing to cyclic toggling, interfacial micromotion exceeding 150 micrometers, fibrous tissue interposition, and early aseptic loosening. The master surgeon achieves intimate polar contact and rigid circumferential stability, verifying that the shell cannot be dislodged before placing supplemental screws or the modular liner.

7. Pearls and Pitfalls

Meticulous intraoperative execution and rapid recognition of anatomical pitfalls distinguish experienced hip surgeons and ensure durable long-term implant survival.

Surgical Pearls

• Anatomical Referencing via the TAL: Always identify the transverse acetabular ligament (TAL) before reaming. Aligning the inferior face of the reamer and definitive cup parallel to the TAL provides a patient-specific guide that eliminates visual errors caused by pelvic tilt or table roll.
• Find the Cotyloid Floor Early: Never skip the starter medialization reaming step. Using a small reamer (40 to 44 mm) to expose the cortical floor of the cotyloid fossa establishes the true anatomical depth and prevents lateralized high hip center placement.
• Preserve Subchondral Bleeding Bone: Ream conservatively. Do not excavate subchondral bone down to soft, unsupportive cancellous bone across the dome. Dense subchondral bone provides the structural stiffness needed to support press-fit hoop stresses.
• Acoustic Feedback Surveillance: Train the surgical ear to detect the pitch change during cup impaction. When the mallet strike transitions from a dull thud to a crisp, high-pitched ring, the shell has achieved full cortical engagement; stop impaction immediately to avoid column fracture.
• Apical Hole Inspection: Always look directly through the apex portal with a probe or light source before placing screws. Polar contact with zero apical gap is mandatory for primary stability and secondary osseointegration.
• Meticulous Shell Debris Clearance: Irrigate and dry the inner shell locking taper thoroughly. A single trapped bone fragment will prevent concentric liner locking, predisposing to liner dissociation or catastrophic ceramic fracture.

Technical Pitfalls & Rescue Maneuvers

• Pitfall: Cup Over-Inclination / Vertical Placement (>45 to 50 Degrees):
  Mechanism: The patient rolls forward during lateral decubitus positioning, or the surgeon references the operating table rather than the pelvic skeleton, placing the cup too vertical.
  Rescue Maneuver: Recognize the error prior to liner insertion. Remove the shell using a dedicated extraction handle. Re-evaluate the transverse acetabular ligament and the superior bony rim. Ream the superior-lateral dome slightly if needed, and re-impact the shell at 40 degrees of inclination. If equatorial press-fit is diminished, place two or three 6.5-mm cancellous screws into the posterior-superior safe quadrant to secure primary stability.
• Pitfall: Intraoperative Acetabular Rim or Column Fracture:
  Mechanism: Aggressive under-reaming (e.g., >2 to 3 mm press-fit) in stiff, sclerotic bone, or forceful off-axis mallet impaction.
  Rescue Maneuver: Carefully extract the cup and inspect the anterior and posterior columns. If a non-displaced rim crack occurs with stable columns, re-ream the acetabulum line-to-line, re-impact the cup gently, and secure rigid fixation with multiple (3 to 4) divergent cancellous screws into the posterior-superior and posterior-inferior columns. Restrict postoperative weight-bearing to 50% for 6 weeks. If a complete, displaced column fracture occurs, perform open reduction and internal fixation of the column using a 3.5-mm reconstruction plate before re-implanting the cup, or convert to a porous metal augment construct.
• Pitfall: Medial Wall Breach / Intrapelvic Perforation:
  Mechanism: Overzealous reaming directed too medially with small reamers, violating the cotyloid floor and breaching Kohler’s line.
  Rescue Maneuver: Cease medial reaming immediately. Assess column stability: if the anterior and posterior columns remain completely intact, the medial defect is contained. Harvest autologous cancellous bone from the femoral head reamings and densely pack the medial floor defect (reverse bone grafting). Seat a hemispherical cup that spans the defect, obtaining rigid press-fit across the intact anterior and posterior columns, and secure with multiple screws into the posterior-superior safe zone.
• Pitfall: Malseated Modular Liner:
  Mechanism: Off-axis liner impaction, soft-tissue interposition, or trapped bone debris within the peripheral locking groove.
  Rescue Maneuver: If circumferential probing reveals an asymmetric step-off or incomplete seating, remove the liner immediately. Never attempt to force a malseated liner down with heavier blows. Copiously irrigate the shell, inspect locking mechanisms, and re-insert a pristine liner under direct, coaxial visualization. Confirm 360-degree flush alignment before proceeding.

8. Postoperative Care & Rehabilitation

Modern postoperative management for uncemented acetabular components emphasizes immediate full weight-bearing, multimodal opioid-sparing analgesia, and structured physical therapy to restore pelvic stability and functional ambulation.

Immediate Postoperative Protocol

• Weight-Bearing Status: Weight-bearing as tolerated (WBAT) with an assistive device (walker or two crutches) is initiated on postoperative day 0 for patients with rigid, uncomplicated press-fit cup fixation. Immediate physiological axial loading stimulates trabecular bone remodeling and osteoblast osseointegration. Protected partial weight-bearing (50% flat-foot load) for 4 to 6 weeks is reserved for cases involving intraoperative rim microfractures, structural bone grafting, or extensive screw supplementation in osteopenic bone.
• Multimodal Pain Management: Comprehensive multimodal analgesia combining oral acetaminophen (1000 mg q8h), celecoxib (200 mg q12h) or meloxicam, gabapentinoids, local infiltration analgesia (LIA with ropivacaine, epinephrine, and ketorolac), and cryotherapy to eliminate intravenous opioid reliance.
• Venous Thromboembolism (VTE) Prophylaxis: Stratified chemoprophylaxis per AAOS and CHEST guidelines. Standard-risk patients receive enteric-coated aspirin 81 mg twice daily for 4 to 6 weeks. High-risk patients (prior VTE, active malignancy, severe obesity) receive direct oral anticoagulants (DOACs, e.g., rivaroxaban 10 mg daily or apixaban 2.5 mg twice daily) or low-molecular-weight heparin for 35 days.
• Early Ambulation & Rapid Recovery: Mobilization within 4 to 6 hours postoperatively reduces cardiopulmonary complications, urinary retention, and venous thromboembolism, enabling safe same-day or next-day hospital discharge.

Structured Rehabilitation Timeline

Rehabilitation Phase	Timeframe	Primary Clinical Goals	Permitted Exercises & Modalities	Precautions & Milestones
Phase I: Acute Protection & Activation	Weeks 0 to 2	Edema control, quadriceps and abductor activation, safe bed transfers, independent ambulation with walker.	Ankle pumps, isometric quadriceps sets, gluteal sets, assisted heel slides, seated knee extension.	WBAT with walker/crutches; approach precautions (posterior: avoid flexion >90°, adduction past midline, internal rotation; anterior: avoid hyperextension, external rotation).
Phase II: Gait Normalization & Endurance	Weeks 2 to 6	Wean from walker to single cane, restore symmetrical stance phase, improve pelvic abductor endurance.	Stationary cycling with light resistance, terminal knee extensions, standing hip abduction, mini-squats.	Discontinue walker; progress to unassisted ambulation when Trendelenburg sign resolves; drive when off opioids.
Phase III: Dynamic Strengthening & Balance	Weeks 6 to 12	Restore full active range of motion, muscle hypertrophy, proprioception, and stair ascent/descent.	Closed-chain leg press, step-ups, resistance band lateral walks, single-leg balance boards, elliptical trainer.	Full unassisted ambulation; return to unrestricted occupational activities; low-resistance gym training.
Phase IV: Functional Return & Athletics	>12 Weeks	Consolidate biological osseointegration, return to low-impact sports and recreational activities.	Swimming, doubles tennis, golf, road cycling, hiking, progressive resistance training.	Avoid high-impact running and contact sports; routine clinical and radiographic surveillance at 1, 5, and 10 years.

9. Outcomes & Long-Term Survivorship

Uncemented hemispherical acetabular components demonstrate exceptional long-term survivorship and predictable clinical performance across multiple international joint registries and multi-decade cohort investigations. Long-term cup survivorship free from revision for aseptic loosening consistently exceeds 95% to 99% at 15 to 25 years of clinical follow-up.

Radiostereometric analysis (RSA) and sequential dual-energy X-ray absorptiometry (DXA) studies confirm that press-fit porous-coated shells achieve rapid primary mechanical stability with minimal early proximal migration (<0.2 mm at 2 years). This initial stability fosters durable secondary osseointegration, characterized by dense trabecular condensation and spot welds in DeLee-Charnley zones I, II, and III without progressive radiolucent lines. Furthermore, periprosthetic acetabular bone mineral density is well-preserved over time, demonstrating physiological compressive load transfer across the columns.

The widespread clinical adoption of highly cross-linked polyethylene (HXLPE) and contemporary ceramic-on-ceramic bearings has virtually eliminated periacetabular osteolysis and catastrophic polyethylene wear. Volumetric wear rates for HXLPE routinely measure below 0.02 mm/year, well below the osteolysis threshold of 0.1 mm/year. Patient-reported outcome measures, including the Harris Hip Score (HHS), Oxford Hip Score, and Forgotten Joint Score, show rapid, durable improvements, with mean postoperative Harris Hip Scores consistently surpassing 90 to 95 points.

10. Complications & Risk Mitigation

Complications involving uncemented acetabular components can be mitigated through disciplined surgical exposure, anatomical landmark referencing, and systematic salvage strategies.

Complication	Reported Incidence / Risk Factors	Pathophysiologic Mechanism	Intraoperative Prevention & Avoidance Strategy	Diagnostic Workup & Salvage Algorithm
Intraoperative Acetabular Fracture	0.5% to 2.0%; osteopenia, dense sclerotic bone, excessive under-reaming (>2 mm), aggressive impaction.	Excessive radial hoop tensile stresses generated during press-fit cup impaction exceeding column tensile strength.	Ream line-to-line in sclerotic bone; clear peripheral osteophytes; monitor acoustic pitch during impaction.	Direct inspection; non-displaced crack: multiple screws into columns and 50% WB for 6 wks; displaced fracture: column reconstruction plating.
Medial Wall Breach / Perforation	0.5% to 1.5%; small reamers, medialized reaming vector, severe osteopenia, revision surgery.	Overzealous medial reaming directed through the cotyloid fossa violating Kohler’s line into the pelvic cavity.	Identify cotyloid floor before reaming; stop medialization when cortical floor is touched; avoid small deep reaming.	Evaluate column integrity. If columns intact: pack autologous bone reamings into floor, span with press-fit cup, and secure with safe-zone screws.
Neurovascular Injury (External Iliac / Obturator)	0.1% to 0.5%; anterior retractor slippage, screw placement in anterior quadrants, intrapelvic drill plunging.	Direct laceration, compression, or puncture of external iliac vessels (anterior-superior) or obturator bundle (anterior-inferior).	Keep anterior retractors strictly on bone; drill only in posterior-superior safe quadrant; use drill depth stops (<30 mm).	Vascular emergency: immediate surgical exposure, vascular surgery consultation, tamponade, and vessel repair; angiographic embolization.
Prosthetic Hip Dislocation	1.0% to 3.0%; component malposition (vertical/retroverted cup), spinopelvic stiffness, abductor deficiency.	Prosthetic or bony impingement causing femoral head levering out of the acetabular liner during physiological motion.	Position cup at 40° inclination and 15-20° anteversion using TAL; optimize offset; assess combined anteversion (25°-45°).	Closed reduction under conscious sedation. Recurrent instability: CT spinopelvic scan; revise cup version, use elevated liner, or convert to dual-mobility.
Modular Liner Malseating / Dissociation	0.2% to 1.0%; trapped bone debris, off-axis impaction, soft-tissue interposition, defective locking mechanism.	Incomplete engagement of peripheral locking tabs leading to liner tilt, micromotion, dissociation, or ceramic fracture.	Copiously irrigate and dry shell; inspect locking grooves; seat coaxially; verify 360° flush seating with fine probe.	Plain radiographs reveal eccentric liner step-off or dissociation. Surgical revision: shell debridement, exchange liner, or revise shell.
Aseptic Loosening / Fixation Failure	0.5% to 2.0% at 10-15 years; poor initial press-fit, apical gap >2 mm, severe osteopenia, pelvic irradiation.	Interfacial micromotion exceeding 150 micrometers preventing secondary osseointegration, leading to fibrous membrane encapsulation.	Achieve rigid primary press-fit; confirm zero apical gap; place supplemental screws in questionable bone quality.	Serial radiographs show progressive radiolucent lines (>2 mm) in DeLee-Charnley zones I-III or cup migration. Salvage: revision THA with porous augments.
Periprosthetic Joint Infection (PJI)	0.5% to 1.5%; diabetes, obesity, immunosuppression, prolonged operative time, hematoma.	Bacterial contamination and biofilm formation across metallic and polyethylene implant surfaces.	Laminar airflow, prophylactic IV antibiotics within 60 minutes of incision, dilute betadine lavage, watertight closure.	Serum ESR, CRP, joint aspiration (cell count, alpha-defensin, culture). Acute (<4 wks): DAIR with modular exchange; Chronic: two-stage revision.

11. Neurovascular Danger Zones & Anatomical Corridors

Acetabular exposure, reaming, and transacetabular screw fixation place four major neurovascular bundles at direct risk of mechanical injury, traction neurapraxia, or life-threatening vascular transection.

External Iliac Vessels (Anterior-Superior Corridor)

The external iliac artery and vein lie directly over the anterior pelvic brim, resting on the iliopubic ramus and psoas major muscle belly immediately anterior and superior to the acetabulum. The average distance from the inner pelvic cortex of the anterior-superior acetabulum to the external iliac vein is less than 5 to 7 millimeters, separated only by thin pelvic cortical bone and the iliopsoas muscle. Drilling or placing transacetabular screws in the Wasielewski anterior-superior quadrant carries an extreme risk of penetrating the pelvic cortex and lacerating the external iliac vessels, producing catastrophic retroperitoneal hemorrhage that is difficult to control from an intra-articular hip exposure. Furthermore, sharp anterior Hohmann retractors placed over the anterior rim that slip or plunge deep to the iliopsoas can directly compress or tear these vessels. Anterior retractors must be placed under direct vision, maintaining intimate bone contact beneath the capsular sleeve.

Obturator Neurovascular Bundle (Anterior-Inferior Corridor)

The obturator nerve, artery, and vein traverse the pelvis along the lateral pelvic wall and exit through the superior aspect of the obturator foramen, located immediately anterior and inferior to the cotyloid notch. Inserting screws through the anterior-inferior quadrant of the acetabular shell risks direct penetration into the obturator canal, resulting in obturator vessel laceration, intrapelvic hematoma, or obturator nerve palsy with profound adductor muscle denervation. Similarly, inferior Hohmann retractors positioned around the transverse acetabular ligament must not be driven deeply through the obturator membrane; retractors should hug the inferior bony cotyloid notch to protect the obturator bundle.

Sciatic Nerve (Posterior Corridor)

The sciatic nerve exits the greater sciatic notch inferior to the piriformis muscle and courses distally along the posterior surface of the short external rotators, separated from the posterior acetabular wall by the gemelli and obturator internus muscle bellies. During posterior acetabular exposure and reaming, the sciatic nerve is vulnerable to direct compression from posterior capsular retractors, traction injury from forceful limb internal rotation, or laceration from spinning reamer teeth if a posterior wall defect exists. Protecting the nerve requires tagging and reflecting the short external rotators posteriorly to form a protective soft-tissue cushion, keeping retractors strictly on the ischial bone, and flexing the knee during posterior hip positioning to alleviate sciatic nerve tension.

Superior Gluteal Vessels & Nerve (Posterior-Superior Sciatic Notch)

The superior gluteal nerve and vascular bundle exit the pelvis through the greater sciatic notch superior to the piriformis muscle, arborizing laterally between the gluteus medius and gluteus minimus muscles. When drilling and placing cancellous screws in the posterior-superior safe quadrant, screws directed too far posteriorly or screws exceeding 35 to 40 mm in length can exit the inner cortex of the greater sciatic notch, directly injuring the superior gluteal vessels and nerve. Transection of the superior gluteal artery can lead to massive pelvic hemorrhage and retroperitoneal hematoma, while superior gluteal nerve injury denervates the abductor musculature, causing a permanent, disabling Trendelenburg gait. Screws in the posterior-superior quadrant must be directed superiorly and medially toward the sacroiliac joint, utilizing drill stops to avoid sciatic notch exit.

12. Classification of Acetabular Bone Loss & Host Morphology

The Paprosky classification of acetabular bone deficiency evaluates structural column integrity and radiographic osteolysis landmarks, providing a reliable algorithm for determining the suitability of uncemented press-fit fixation.

Paprosky Classification	Anatomical Defect Pattern	Column Structural Integrity	Radiographic Landmarks (Teardrop & Kohler’s)	Acetabular Fixation Strategy
Type I	Minimal bone loss; intact acetabular rim and circular geometry; small focal cavitary defects.	Anterior and posterior columns completely intact; rigid 3-point support.	Teardrop normal; Kohler’s line intact; zero superior migration of hip center.	Standard uncemented hemispherical press-fit cup (1 to 2 mm under-ream); optional single screw fixation.
Type IIA	Superior-lateral cavitary defect; intact rim with oval cavity; mild superior dome bone loss.	Both columns structurally intact; intact peripheral rim envelope.	Teardrop intact; Kohler’s line intact; superior hip center migration <1 cm.	Hemispherical press-fit cup; medialized reaming to cotyloid floor; supplemental safe-zone screws.
Type IIB	Superolateral rim defect involving less than one-third of the circumference; dome osteolysis.	Columns intact; compromised superior rim coverage (>30% uncontained dome).	Teardrop intact; Kohler’s line intact; superior migration 1 to 2 cm.	Hemispherical press-fit cup; 2 to 4 cancellous screws; consider modular porous metal augment if coverage <70%.
Type IIC	Medial wall defect; osteolysis extending medial to the ilioischial line; columns intact.	Anterior and posterior columns completely intact; lost medial cotyloid floor.	Teardrop osteolysis/destruction; Kohler’s line violated medially; normal vertical height.	Reverse medial bone grafting with reamings; press-fit hemispherical cup bridging columns; multiple safe-zone screws.
Type IIIA	Severe superior-lateral bone loss (“flying saucer” defect); severe dome and column osteolysis.	Moderate column deficiency; >50% rim uncontained; intact posterior column buttress.	Teardrop severely compromised; Kohler’s line intact; superior migration >3 cm.	Modular porous metal augments with hemispherical cup; jumbo cup; multi-screw iliac pillar fixation.
Type IIIB	Catastrophic bone loss; massive anterior and posterior column destruction; pelvic discontinuity.	Gross column discontinuity; anterior and posterior columns non-supportive.	Teardrop destroyed; Kohler’s line broken; superior-medial migration >3 cm.	Cup-cage construct, custom triflange acetabular component, or dual-column plating with trabecular metal revision.

13. Evidence-Based Synthesis

Modern clinical decision-making is grounded in high-quality randomized controlled trials and prospective registry analyses, corroborated by seminal biomechanical and anatomical descriptions.

Clinical Question / Investigation	Level of Evidence	Pivotal Landmark Study	Study Design & Methodology	Cohort Size / Follow-up	Primary Outcome / Effect Size	DOI
Does computer navigation improve accuracy of acetabular cup placement compared to manual instrumentation?	Level I	Bernsmann K, Langlotz U, Ansari B et al (2001)	Randomized Controlled Trial	60 patients randomized to CT-free computer-assisted navigation vs conventional freehand cup placement	Navigation significantly narrowed radiographic cup inclination variance and reduced outlier rates (>45° abduction or <10° anteversion) from 27% to 3% (p < 0.01).	DOI
How does uncemented press-fit cup fixation affect periprosthetic acetabular bone mineral density over time?	Level I	Digas G, Kärrholm J, Thanner J (2006)	Randomized Controlled Trial	96 hips randomized to uncemented press-fit porous-coated cups vs cemented all-polyethylene cups, evaluated with sequential DXA and RSA at 2- and 5-year intervals	Uncemented press-fit cups achieved rigid primary mechanical stability with physiological trabecular bone preservation in periacetabular DeLee-Charnley Zone II and Zone III, without progressive radiolucent line migration.	DOI
What surgical and demographic factors predict acetabular cup malposition outside defined safe zones in high-volume arthroplasty?	Level III	Callanan MC, Jarrett B, Bragdon CR et al (2011)	Prospective Registry Comparative Cohort Study	2,077 consecutive primary total hip arthroplasties evaluated for cup inclination and anteversion using postoperative CT and validated radiographic protocols	Identified that surgical approach, lower surgeon procedural volume, and patient obesity significantly increased the odds ratio of cup malposition outside the modified safe zone (30°-45° abduction, 5°-25° anteversion; overall 50% malposition rate with freehand technique).	DOI
What are the anatomical safe and danger zones for transacetabular screw fixation in uncemented cups?	Level IV	Wasielewski RC, Cooperstein LA, Kruger MP et al (1990)	Landmark Anatomical & Morphometric Study	32 human cadaveric hemipelves analyzed with high-resolution radiography, axial CT, and direct anatomical dissection for transacetabular screw corridors	Defined the 4 acetabular quadrants: posterior-superior and posterior-inferior quadrants offer safe osseous corridors (ischial and iliac columns) with greatest bone depth; anterior-superior quadrant presents extreme external iliac vessel laceration risk; anterior-inferior quadrant risks obturator neurovascular injury.	DOI
Does historic Lewinnek safe zone positioning reliably prevent prosthetic hip dislocation?	Level IV	Abdel MP, von Roth P, Jennings MT et al (2015)	Landmark Retrospective Cohort Study	9,784 primary total hip arthroplasties with 206 dislocated hips compared against an institutional registry control cohort	58% of dislocated THAs had acetabular components positioned strictly within the Lewinnek safe zone (40° ± 10° inclination, 15° ± 10° anteversion), proving that rigid static 2D target zones fail to account for dynamic spinopelvic mobility, pelvic tilt, and functional impingement.	DOI
How does intraoperative fluoroscopic guidance during direct anterior THA influence acetabular cup orientation and leg length restoration?	Level IV	Matta JM, Shahrdar C, Ferguson TA (2005)	Landmark Surgical Technique Cohort Study	494 consecutive primary THAs performed through the direct anterior intermuscular Hueter interval using traction table and intraoperative fluoroscopy	Demonstrated 96% accuracy in placing the acetabular cup within 5 degrees of planned inclination and anteversion; dislocation rate was 0.61% without formal posterior capsular disruption.	DOI

14. References

• Bernsmann K, Langlotz U, Ansari B et al. Computer-assisted navigated cup placement of different cup types in hip arthroplasty: a randomised controlled trial. Z Orthop Ihre Grenzgeb. 2001. doi:10.1055/s-2001-19233 [Level I: Randomized Controlled Trial]
• Digas G, Kärrholm J, Thanner J. Different loss of BMD using uncemented press-fit and whole polyethylene cups fixed with cement: repeated DXA studies in 96 hips randomized to 3 types of fixation. Acta Orthop. 2006. doi:10.1080/17453670610045948 [Level I: Randomized Controlled Trial]
• Callanan MC, Jarrett B, Bragdon CR et al. The John Charnley Award: Risk Factors for Cup Malpositioning: Quality Improvement Through a Joint Registry at a Tertiary Hospital. Clin Orthop Relat Res. 2011. doi:10.1007/s11999-010-1487-1 [Level III: Prospective Registry Comparative Cohort Study]
• Wasielewski RC, Cooperstein LA, Kruger MP et al. Acetabular anatomy and the transacetabular fixation of screws in total hip arthroplasty. J Bone Joint Surg Am. 1990. doi:10.2106/00004623-199072040-00005 [Level IV: Landmark Anatomical & Morphometric Study]
• Abdel MP, von Roth P, Jennings MT et al. What Safe Zone? The Vast Majority of Dislocated THAs Are Within the Lewinnek Safe Zone for Acetabular Component Position. Clin Orthop Relat Res. 2015. doi:10.1007/s11999-015-4432-5 [Level IV: Landmark Retrospective Cohort Study]
• Matta JM, Shahrdar C, Ferguson TA. Single-incision Anterior Approach for Total Hip Arthroplasty on an Orthopaedic Table. Clin Orthop Relat Res. 2005. doi:10.1097/01.blo.0000194309.70518.cb [Level IV: Landmark Surgical Technique Cohort Study]

15. Master Class Pro-Tip

The definitive mastery of uncemented acetabular placement hinges upon two non-negotiable anatomical imperatives: never reference the operating room environment for cup orientation, and never accept an equatorial bite without true polar bottoming. Operating table tilt, patient pelvic roll in lateral decubitus, and variations in lumbar lordosis create profound spatial illusions that cause even experienced surgeons to place vertical or retroverted cups. The transverse acetabular ligament (TAL) represents the immutable, patient-specific anatomical compass: orienting the shell’s inferior rim strictly parallel to the TAL and recessed 1 to 2 millimeters within the bony cotyloid margin guarantees an anatomical version and inclination tailored to that specific pelvis. During impaction, listen intently to the acoustic resonance. The mallet blow must transform from an initial dull, low-frequency thud into a sharp, high-frequency metallic ring. The moment this acoustic pitch transition occurs, stop impaction and look directly through the apex portal with a probe. You must visually confirm direct bone-to-implant contact against the medial cotyloid floor. A shell that binds equatorially at the peripheral rim while leaving an apical gap will inevitably experience microscopic toggling, interfacial shear stress exceeding 150 micrometers, and failure of secondary osseointegration. Conversely, continuing to batter a shell after axial advancement has ceased will instantaneously fracture an osteopenic column. Polar contact, verified by acoustic pitch elevation and direct apex inspection, is the definitive hallmark of permanent mechanical press-fit.

Master Class Surgical Pearl: Uncemented Acetabular Component Placement