High Yield Overview

MINIMALLY INVASIVE POSTERIOR THA

Mini-posterior approach | Arthroplasty

Mnemonic

POGO-Q

Mnemonic

REPAIR

Critical Danger Structures

Sciatic Nerve

Posterior to short external rotators. Location: Exits pelvis below piriformis, runs over gemelli and obturator internus, then over quadratus femoris. Protection: KNEE FLEXION relaxes nerve; release rotators at femoral insertion (not proximally); avoid aggressive posterior retraction; maintain awareness during all steps.

Superior Gluteal Neurovascular Bundle

Above piriformis. Location: Exits greater sciatic notch superior to piriformis, courses between gluteus medius and minimus. Protection: Do NOT extend gluteus maximus split more than 5cm above greater trochanter; avoid forceful proximal retraction.

Inferior Gluteal Nerve and Vessels

Below piriformis. Location: Exits below piriformis, supplies gluteus maximus. Protection: Careful dissection near piriformis; avoid blind dissection posterior to rotators; preserve to maintain gluteus maximus function.

Medial Circumflex Femoral Artery

Deep to quadratus femoris. Location: Branch of profunda femoris, passes between quadratus femoris and adductor magnus, supplies femoral head. Protection: Avoid aggressive deep retraction below quadratus femoris; gentle quadratus release if needed.

Femoral Nerve and Vessels

Anterior to hip capsule. Location: Femoral nerve, artery, vein in femoral triangle anteriorly. Protection: Avoid overly anterior acetabular retractor placement; check retractor position during cup insertion; protect with anterior labrum.

Comparison: Minimally Invasive vs Standard Posterior Approach

Feature	MIS Posterior	Standard Posterior
Incision length	6-10cm	15-20cm
Muscle approach	Gluteus maximus split	Same
Rotator management	Tag and repair	Same (essential)
Visualization	Specialized retractors, lighting	Direct
Learning curve	Steeper	Established
Complications	Same when done well	Same
Recovery	Possibly faster early	Standard

Key Points:

Same surgical principles apply to both
Posterior repair ESSENTIAL in both
MIS requires specialized instrumentation
Cosmetic benefit but no proven long-term advantage
Surgeon experience more important than incision length

Evidence:

No significant difference in long-term outcomes
Early recovery advantages debated
Learning curve associated with higher early complication rates

Positioning and Preparation

Patient Position: Lateral decubitus on standard operating table

Setup:

Bean bag or pelvic posts for stable pelvic positioning
Operative leg freely draped for full mobility
Ensure pelvis is truly vertical - affects cup orientation
Arm support and all pressure points padded

Key Considerations:

Pelvic tilt DIRECTLY affects cup orientation measurements
Tilted pelvis causes malpositioned cup if not recognized
Mark bony landmarks before draping (ASIS, GT, posterior iliac spine)
Confirm leg length markers before incision

Operative Technique

Step 1: POSITIONING AND LANDMARKS

POSITIONING: Lateral decubitus with pelvis stabilized by anterior and posterior posts or bean bag. Confirm pelvis is vertical - any tilt affects cup orientation. Operative leg freely mobile for dislocation and manipulation. Mark greater trochanter and intended incision line.

Exam Pearl

Technical Tip: EXAM KEY: LATERAL DECUBITUS is standard for posterior approach. PELVIC TILT directly affects cup position - if tilted anteriorly, measured anteversion will be LESS than actual. Ensure true vertical pelvis positioning.

Dangers at this step

Pelvic tilt causing cup malposition (unrecognized tilt = maloriented cup)
Inadequate stabilization allowing pelvic movement
Pressure injuries from prolonged positioning

Step 2: INCISION AND SUPERFICIAL DISSECTION

INCISION: MIS posterior = 6-10cm (vs 15-20cm standard). Centered over or slightly posterior to greater trochanter. Oblique direction from posterosuperior to anteroinferior, following gluteus maximus fibers. Incise skin and subcutaneous tissue. Identify fascia lata and gluteus maximus fascia.

Exam Pearl

Technical Tip: EXAM KEY: MINI-POSTERIOR = 6-10cm incision. Same surgical principles as standard posterior - just smaller window. Requires specialized retraction and lighting. Do NOT compromise on safety for incision size.

Dangers at this step

Incision too small limiting visualization and increasing tissue trauma
Excessive skin retraction causing edge necrosis
Wrong incision placement compromising exposure

Step 3: GLUTEUS MAXIMUS SPLIT

GLUTEUS MAXIMUS: Incise gluteus maximus fascia in line with muscle fibers. Split gluteus maximus BLUNTLY between fibers - this is muscle-splitting, NOT detachment. Limit split to 5cm above greater trochanter to protect SUPERIOR GLUTEAL NEUROVASCULAR BUNDLE. Insert self-retaining or specialized MIS retractors.

Exam Pearl

Technical Tip: EXAM KEY: GLUTEUS MAXIMUS SPLIT - blunt dissection in line with fibers. Do NOT extend more than 5cm proximal to GT - superior gluteal nerve exits above piriformis and courses between glut med/min. Injury causes Trendelenburg gait.

Dangers at this step

Superior gluteal nerve injury from excessive proximal split
Excessive muscle damage from forceful retraction
Gluteus maximus denervation from inferior gluteal nerve injury

Step 4: IDENTIFY SHORT EXTERNAL ROTATORS

IDENTIFY SHORT EXTERNAL ROTATORS: Expose posterior hip capsule and overlying short external rotators. From superior to inferior: piriformis (key landmark), gemelli with obturator internus between, quadratus femoris. Sciatic nerve exits BELOW piriformis and runs posterior to these muscles.

Exam Pearl

Technical Tip: EXAM KEY: POGO-Q mnemonic for rotators (Piriformis, Obturator internus, Gemelli, Obturator externus, Quadratus). SCIATIC NERVE exits inferior to piriformis in 90% (may split piriformis in 10%). Always know its location.

Dangers at this step

Sciatic nerve injury from blind dissection
Failure to identify correct anatomy
Damage to inferior gluteal nerve and vessels

Step 5: TAG AND RELEASE SHORT EXTERNAL ROTATORS

TAG AND RELEASE ROTATORS: Place tagging sutures in piriformis and conjoined tendon (superior gemellus, obturator internus, inferior gemellus) BEFORE release. Incise rotators close to their femoral insertion (away from sciatic nerve). Protect quadratus femoris if possible (MCFA runs deep to it). Maintain knee flexed to relax sciatic nerve.

Exam Pearl

Technical Tip: EXAM KEY: TAG rotators with sutures BEFORE cutting - this is CRITICAL for repair. Release at femoral insertion, NOT proximally near nerve. Piriformis + conjoined tendon most important for repair. Knee flexion protects sciatic nerve.

Dangers at this step

Inadequate tagging preventing later repair (increases dislocation)
Sciatic nerve injury during rotator release (release close to femur)
MCFA injury with aggressive quadratus release

Step 6: CAPSULOTOMY

CAPSULOTOMY: Expose posterior capsule. Perform T-shaped or L-shaped capsulotomy. TAG capsule edges for repair. Clear capsule from acetabular rim as needed for exposure. The capsule is an important stabilizer - preserve for repair.

Exam Pearl

Technical Tip: EXAM KEY: TAG CAPSULE for repair - capsular repair + rotator repair together reduce dislocation to less than 1-2%. T-capsulotomy: vertical along margin, horizontal at neck. Both capsule AND rotators must be repaired.

Dangers at this step

Failure to tag capsule preventing repair
Excessive capsule excision compromising repair
Injury to labrum affecting press-fit stability

Step 7: HIP DISLOCATION

HIP DISLOCATION: Dislocate hip posteriorly with flexion, adduction, internal rotation. May use corkscrew device in femoral head to control dislocation. Controlled dislocation prevents fracture. Remove femoral head after neck osteotomy if preferred.

Exam Pearl

Technical Tip: EXAM KEY: POSTERIOR DISLOCATION = FLEXION, ADDUCTION, INTERNAL ROTATION. Controlled technique prevents fracture. Some surgeons prefer neck cut in situ then extraction. Corkscrew provides control during dislocation.

Dangers at this step

Uncontrolled dislocation causing soft tissue damage
Femoral neck fracture with forceful dislocation
Acetabular rim fracture with leveraging

Step 8: FEMORAL NECK OSTEOTOMY AND HEAD REMOVAL

FEMORAL NECK OSTEOTOMY: Neck cut with oscillating saw per template. Standard 45° angle from lesser trochanter. Remove femoral head. Excellent visualization of femoral canal is a KEY ADVANTAGE of posterior approach.

Exam Pearl

Technical Tip: EXAM KEY: FEMORAL EXPOSURE is EXCELLENT in posterior approach - major advantage over anterior approaches. Direct visualization of canal for accurate broaching and stem placement. Version typically 10-15° anteversion.

Dangers at this step

Incorrect neck cut level affecting leg length/offset
Femoral calcar fracture during head removal
Inadequate bone removal causing femoral fracture during broaching

Step 9: FEMORAL PREPARATION

FEMORAL PREPARATION: Box osteotome to open canal. Sequential broaching with trial stems. Ensure appropriate version (10-15° anteversion typically). Posterior approach allows direct visualization of canal and version. Confirm stable broach seating before final implant.

Exam Pearl

Technical Tip: EXAM KEY: Femoral version is DIRECTLY visualized in posterior approach - align with posterior femoral condyles as reference. Canal preparation straightforward with direct visualization. Avoid varus or retroversion.

Dangers at this step

Incorrect version (excessive anteversion increases anterior dislocation risk)
Femoral fracture from aggressive broaching
Varus stem positioning from inadequate lateralization

Step 10: ACETABULAR EXPOSURE AND PREPARATION

ACETABULAR EXPOSURE: Retractors around acetabulum - anterior (inferior to ASIS), inferior (in obturator foramen), posterior as needed. Retract femur anteriorly with bone hook or dedicated retractor. Sequential reaming to bleeding subchondral bone. Maintain peripheral rim for press-fit.

Exam Pearl

Technical Tip: EXAM KEY: Femur must be retracted ANTERIORLY for acetabular visualization. Target cup position: 40° ± 10° inclination, 15° ± 10° anteversion (Lewinnek). Combined anteversion (cup + stem) = 25-45° for stability.

Dangers at this step

Cup malposition (most common technical error in THA)
Anterior wall perforation with over-medialization
Femoral nerve injury from aggressive anterior retraction

Step 11: ACETABULAR COMPONENT IMPLANTATION

ACETABULAR IMPLANTATION: Press-fit cup with 1-2mm under-ream. Confirm position before final impaction. Supplemental screws if questionable fixation. Insert liner (polyethylene, ceramic, or dual mobility per plan).

Exam Pearl

Technical Tip: EXAM KEY: Cup orientation by direct visualization or with guides. In lateral decubitus, account for pelvic position. Navigation can improve accuracy if available. Confirm rigid fixation before liner insertion.

Dangers at this step

Cup malposition causing impingement or dislocation
Inadequate press-fit (consider screws if any movement)
Liner malseating

Step 12: FEMORAL COMPONENT IMPLANTATION

FEMORAL IMPLANTATION: Insert final femoral stem (cemented or press-fit per plan). Confirm version and stable seating. Trial head for stability and leg length assessment.

Exam Pearl

Technical Tip: EXAM KEY: Posterior approach allows excellent femoral component insertion. Confirm appropriate version by aligning with posterior condyles. Trial extensively before final head placement.

Dangers at this step

Incorrect version (critical for stability)
Periprosthetic fracture during insertion
Cement extravasation (if cemented technique)

Step 13: TRIAL REDUCTION AND STABILITY TESTING

TRIAL REDUCTION: Reduce hip with trial head. Test stability in ALL positions, especially the POSTERIOR DISLOCATION POSITION - flexion, adduction, internal rotation. This is the position of risk with posterior approach. Assess leg length with contralateral comparison. Confirm adequate soft tissue tension.

Exam Pearl

Technical Tip: EXAM KEY: CRITICAL to test stability in POSTERIOR DISLOCATION POSITION - flexion past 90°, adduction, internal rotation. If unstable: larger head, higher offset, constrained liner, or adjust components. Document stable ROM achieved.

Dangers at this step

Unrecognized instability (will dislocate postoperatively)
Leg length discrepancy (measure carefully)
Over-lengthening (sciatic nerve risk if more than 4cm)

Step 14: FINAL COMPONENTS AND REDUCTION

FINAL COMPONENTS: Insert definitive head. Reduce hip. Final stability check. Confirm leg length and offset acceptable. Irrigate joint thoroughly.

Exam Pearl

Technical Tip: EXAM KEY: Final components should replicate trial findings. Head size affects stability - larger heads (32mm, 36mm) more stable. Adequate offset restores abductor tension and posterior soft tissue tension.

Dangers at this step

Component mismatch from trial
Inadequate irrigation leaving debris
Failure to confirm final stability

Step 15: POSTERIOR REPAIR - CRITICAL STEP

POSTERIOR REPAIR: THE KEY TO MODERN POSTERIOR APPROACH SUCCESS. Create 2-3 drill holes in posterior facet of greater trochanter. Pass transosseous sutures. First repair posterior capsule to bone. Then repair short external rotators (piriformis + conjoined tendon) over capsule as second layer. Creates posterior soft tissue tension band preventing posterior dislocation.

Exam Pearl

Technical Tip: EXAM KEY: POSTERIOR REPAIR = CAPSULE + ROTATORS through bone tunnels. Reduces dislocation from 4-5% to 1-2%. This is THE difference in modern posterior approach. Both layers important - capsule first, then rotators over top.

Dangers at this step

Inadequate repair strength (use transosseous, not soft tissue only)
Failure to repair one or both layers
Trochanter fracture from aggressive drilling

Closure and Post-operative

Closure:

Irrigate wound thoroughly (minimum 3L)
Gluteus maximus fascia reapproximated
Subcutaneous closure with absorbable sutures
Skin closure (staples or subcuticular)
Sterile dressing

Post-operative Care:

Weight bearing as tolerated immediately
Hip precautions 6-12 weeks:
- Avoid flexion more than 90°
- Avoid adduction past midline
- Avoid internal rotation
VTE prophylaxis per institutional protocol
Standard THA rehabilitation pathway

Complications

Minimally Invasive Posterior THA Complications

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

EXAMINER

"You are performing a posterior approach THA. Describe the importance of posterior repair and your technique for performing it."

EXCEPTIONAL ANSWER

Posterior repair of the capsule and short external rotators is THE critical step that has transformed the posterior approach from a high dislocation rate (4-5%) to comparable rates with other approaches (1-2%). My technique: First, I TAG the piriformis and conjoined tendon with sutures BEFORE releasing them at their femoral insertion. After completing the arthroplasty, I create 2-3 drill holes in the posterior facet of the greater trochanter. I then repair in TWO layers - first the posterior capsule is sutured through the bone tunnels, then the short external rotators are repaired OVER the capsule as a second layer. This creates a posterior soft tissue tension band that resists the posterior dislocation vector of flexion, adduction, and internal rotation.

VIVA SCENARIOStandard

EXAMINER

"How do you protect the sciatic nerve during the posterior approach to the hip?"

EXCEPTIONAL ANSWER

The sciatic nerve is the main neurological structure at risk in the posterior approach. It lies posterior to the short external rotators and exits the greater sciatic notch below the piriformis in 90% of patients. My protection strategies include: First, I keep the KNEE FLEXED throughout the procedure - this relaxes the nerve and reduces stretch injury risk. Second, I release the short external rotators CLOSE TO THEIR FEMORAL INSERTION, keeping the dissection away from the nerve proximally. Third, I avoid aggressive posterior retraction, as the nerve is immediately posterior to the rotators. Fourth, I limit lengthening to less than 4cm, as excessive lengthening significantly increases neuropraxia risk. Finally, I maintain constant awareness of the nerve's location even though I don't formally identify it in every case.

VIVA SCENARIOStandard

EXAMINER

"Compare the posterior approach to the direct anterior approach for primary THA. When would you choose each?"

EXCEPTIONAL ANSWER

Both are excellent approaches when performed well. POSTERIOR advantages: Excellent femoral exposure (best of any approach), familiar to most surgeons, versatile for complex anatomy, easier in obese patients. Disadvantages: Requires hip precautions, historically higher dislocation (though with repair now 1-2%). DIRECT ANTERIOR advantages: No muscles cut (internervous interval), lowest dislocation rate (0.5-1%), often no precautions, supine positioning allows intraoperative imaging. Disadvantages: LFCN injury 10-15%, challenging femoral exposure especially in muscular patients, significant learning curve. I would choose POSTERIOR for: revision surgery, dysplastic hips, obese patients, or when I need excellent femoral exposure. I would choose ANTERIOR for: standard primary THA in appropriate body habitus where minimal restrictions are prioritized.