High Yield Overview

TOTAL HIP ARTHROPLASTY - PRIMARY (UNCEMENTED)

Posterior approach (Moore/Southern) most common in Australia - curved incision centered over greater trochanter, extended posteriorly. Split gluteus maximus. Expose short external rotators. Alternatively: Anterolateral (Watson-Jones/Hardinge), Direct Anterior (muscle-sparing), or Lateral (Hardinge) approaches. | advanced

Critical Danger Structures

Danger 1

Sciatic nerve. Location: Posterior to hip joint, courses 15-30mm posterior to posterior capsule. Protection: Avoid excessive posterior retraction, gentle tissue handling, identify nerve in revision cases, avoid prolonged abnormal positioning during dislocation, limit leg lengthening to less than 15mm

Danger 2

Superior gluteal nerve and vessels. Location: Exit pelvis through greater sciatic notch above piriformis, run between gluteus medius and minimus. Protection: Limit dissection to less than 5cm proximal to greater trochanter tip, avoid superior retractor migration, identify before extending incision proximally

Danger 3

Femoral neurovascular bundle. Location: Anterior to hip joint, medial to anterior hip capsule and femoral neck. Protection: Careful placement of anterior acetabular retractor (stay on bone, not into pelvis), avoid anterior perforation during acetabular reaming, gentle medial capsular release

Danger 4

Obturator neurovascular bundle. Location: Passes through obturator foramen inferior-medial to acetabulum. Protection: Avoid inferior acetabular retractor migration medially, careful inferior reaming, avoid screws in inferior quadrant

Danger 5

External iliac vessels. Location: Anterior to hip joint along pelvic brim, at risk with anterior acetabular screws. Protection: Safe screw zones are anterosuperior (10-2 o'clock) and posterosuperior - avoid anterior horizontal screws, limit screw penetration to 20mm beyond cortex, use fluoroscopy for anterior screws

Mnemonic

LEWINNEKLEWINNEK Safe Zone for Cup Positioning

Mnemonic

ACETABULARACETABULAR Reaming Principles

Positioning and Preparation

Patient Position: Lateral decubitus position with affected side up. Pelvis stabilized with anterior support against pubis and posterior support against sacrum - must be perpendicular to floor (verify with level). All bony prominences well-padded including axillary roll caudal to axilla (not in axilla to avoid brachial plexus injury), pillows between knees, fibular head padding. Arms positioned on arm boards or chest support. Contralateral leg slightly flexed at hip and knee.

Surgical Approach: Posterior approach (Moore/Southern) most common in Australia (approximately 60% per AOANJRR). Alternatively: Direct Anterior (20%), Hardinge lateral (15%), Watson-Jones anterolateral (5%). Posterior approach advantages: familiar anatomy, extensile, spares abductors. Disadvantages: higher dislocation risk without repair (10-15% vs 2-5% anterior), requires robust soft tissue repair.

Incision: Curved incision centered over greater trochanter, extending 8-10cm proximally-posteriorly along gluteus maximus fibers, then 3-5cm distally along femoral shaft. Mark incision with skin marker before draping.

Acetabular Exposure and Reaming Technique

Exposure Principles

Complete acetabular exposure requires three retractors in standard positions:

Anterior retractor (12 o'clock): Hohmann over anterior wall - stay on bone to avoid femoral vessels

Inferior retractor (3 o'clock left hip, 9 o'clock right hip): Broad retractor over inferior wall - protect obturator neurovascular bundle

Posterior retractor (6 o'clock): Hohmann around posterior wall - avoid excessive retraction (sciatic nerve 15-30mm posterior)

Sequential Reaming Steps

Remove all soft tissue: Labrum circumferentially, osteophytes (especially posterior-inferior), ligamentum teres remnant, transverse acetabular ligament (TAL) can be preserved as version guide
Start small: Initial reamer 38-40mm typically, engage all quadrants
Incremental progression: Ream 2mm at a time until bleeding subchondral bone visible over greater than 70% of hemisphere
Orientation: 40-45° inclination (from horizontal), 15-20° anteversion (middle of safe zone is safest)
Final size: Under-ream by 1-2mm for press-fit (e.g., if final reamer is 56mm, use 54-55mm cup)

Anatomic Landmarks for Version

Transverse acetabular ligament (TAL): Connects anterior and posterior horns of acetabulum, typically oriented 15-25° anteverted - useful intraoperative reference

Patient position: If pelvis perpendicular to floor, cup aimed 15-20° anterior to coronal plane

Lateral decubitus reference: Some surgeons use 45° from vertical as target (combines inclination and version)

Exam Pearl

Technical Tip: EXAM KEY - Acetabular reaming goals are threefold: 1) Create hemisphere of bleeding subchondral bone for biological fixation (bony ingrowth), 2) Achieve accurate orientation within Lewinnek safe zone (30-50° inclination, 10-30° anteversion), 3) Maximize bone preservation (stay lateral to medial wall, avoid over-reaming). Common errors: medialization through floor (alters biomechanics, risks pelvic structures), excessive inclination over 50° (edge loading, accelerated wear), inadequate exposure (malposition).

Press-Fit Principles

Modern uncemented cups rely on initial press-fit stability (micromotion less than 50 microns allows ingrowth). Under-reaming by 1-2mm creates interference fit. Porous coating or hydroxyapatite promotes ingrowth. Supplemental screws provide initial stability but do not improve long-term fixation per AOANJRR data - use 2-3 screws in safe zones if concerned about initial stability.

Acetabular Reaming Dangers

Medialization through medial wall into pelvis (vascular injury, protrusio) - especially thin bone in inflammatory arthritis, protrusio, osteoporosis
Anterior retractor migration into pelvis (external iliac vessels, obturator vessels)
Excessive inclination over 50° (edge loading, increased wear, squeaking with ceramic)
Inadequate inclination under 30° (posterior instability, reduced cup coverage)
Excessive anteversion combined with anteverted stem (anterior instability)
Inadequate anteversion with retroverted stem (posterior instability)

Complications - Recognition and Management

Major THA Complications

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

EXAMINER

"A 68-year-old woman with severe hip osteoarthritis asks about total hip replacement. Describe the Lewinnek safe zone and explain its clinical significance in preventing dislocation."

EXCEPTIONAL ANSWER

The Lewinnek safe zone describes optimal acetabular cup positioning to minimize dislocation risk in total hip arthroplasty. It was defined by Lewinnek in 1978 based on radiographic analysis of 300 THAs. The safe zone parameters are: 40 degrees inclination (with acceptable range 30-50 degrees from horizontal) and 20 degrees anteversion (with acceptable range 10-30 degrees). Lewinnek's original study showed dislocation rate of 4% when cups positioned within the safe zone versus 15% when outside the zone - nearly 4-fold increase in dislocation risk. However, I would explain that modern understanding recognizes the safe zone as necessary but not sufficient - other factors also critical for stability including combined anteversion concept (femoral plus acetabular version should total 25-50 degrees per Ranawat), soft tissue repair quality especially in posterior approach, restoration of femoral offset and leg length, head size (larger heads 32-36mm more stable than 28mm), and patient-specific spinopelvic mobility. Current AOANJRR data confirms cup malposition remains leading cause of early dislocation requiring revision, emphasizing importance of accurate cup placement within safe zone.

VIVA SCENARIOStandard

EXAMINER

"You are planning primary THA for a 55-year-old active male with osteoarthritis. What does the AOANJRR data show regarding implant selection, specifically comparing cemented versus uncemented fixation and polyethylene options?"

EXCEPTIONAL ANSWER

The Australian Orthopaedic Association National Joint Replacement Registry is the world's leading registry tracking all joint replacements in Australia since 1999. For primary THA in a 55-year-old active male, AOANJRR data provides strong evidence for implant selection. For acetabular fixation, uncemented cups significantly outperform cemented cups - at 15 years, uncemented cups have cumulative revision rate approximately 5% versus cemented cups 10-15%, with hazard ratio of 2.5 favoring uncemented. For femoral fixation in patients under 65, both cemented and modern uncemented stems perform excellently with survivorship over 95% at 15 years, though uncemented stems have slightly higher early periprosthetic fracture risk (1-3%) especially in osteoporotic bone. For bearing surface, highly cross-linked polyethylene has revolutionized outcomes - AOANJRR shows 30% reduction in revision rate compared to standard polyethylene at 10 years, with annual wear less than 0.05mm versus 0.1-0.2mm for standard PE. For head size, 32mm and 36mm heads show similar low revision rates and both are acceptable - 36mm provides better stability but minimal wear difference with HXLPE. For this 55-year-old active patient, I would recommend: uncemented acetabular cup, uncemented femoral stem (if good bone stock), 32 or 36mm head, highly cross-linked polyethylene liner - this combination has best evidence for longevity per AOANJRR.

VIVA SCENARIOStandard

EXAMINER

"Describe your systematic approach to trialing and stability assessment during primary THA via posterior approach. What would you do if the hip feels unstable posteriorly during trialing?"

EXCEPTIONAL ANSWER

Trialing is the most critical intraoperative step for ensuring successful THA outcome - this is when I determine final implant sizes, confirm stability, and verify restoration of anatomy before committing to final components. My systematic approach includes three key assessments. First, stability testing - with hip in extension and neutral rotation, I perform the shuck test by applying posterior translation force on the femur, assessing excursion before dislocation. Normal hip should have 40-50mm of translation before dislocating posteriorly. I then test impingement: flex hip 90 degrees, adduct 15 degrees, internally rotate to 70 degrees - should not dislocate or impinge posteriorly. For anterior stability, extend hip and externally rotate 40 degrees - should not dislocate anteriorly. Second, leg length measurement - I compare knee heights with legs parallel and pelvis level, and measure ASIS to medial malleolus bilaterally, targeting equal length or up to 5mm lengthening. Third, offset assessment - I assess abductor tension by pulling leg inferiorly feeling for firm resistance, indicating appropriate soft tissue envelope. If the hip feels unstable posteriorly during trialing, I have systematic algorithm: increase offset using longer neck trial (improves soft tissue tension and jump distance), check cup position is not excessively retroverted (should be 15-20 degrees anteversion), consider larger head size (36mm instead of 32mm increases jump distance), verify femoral version is not excessive (combined anteversion should be 25-50 degrees), and if still unstable consider constrained liner or dual-mobility cup. I do NOT accept instability and close - this will result in postoperative dislocation.