Anatomy for Total Hip Replacement
The understanding of hip anatomy is critical for successful total hip replacement surgery, which involves replacing both the acetabulum and femoral head components to restore function and relieve pain.
Osseous Anatomy
Acetabulum
- Forms the socket portion of the ball-and-socket hip joint
- Composed of three pelvic bones: ilium, ischium, and pubis
- Oriented anteriorly, laterally, and inferiorly
- Depth increased by the fibrocartilaginous labrum around the rim
- Articular cartilage covers the lunate surface (horseshoe-shaped)
- Central portion (acetabular fossa) contains fat pad and ligamentum teres
Proximal Femur
- Femoral head: spherical structure that articulates with the acetabulum
- Femoral neck: connects the head to the shaft at an angle of 125-135° (anteversion 10-15°)
- Greater trochanter: lateral prominence for muscle attachment
- Lesser trochanter: posteromedial prominence for iliopsoas attachment
- Intertrochanteric line (anterior) and crest (posterior): connect the trochanters
- Calcar femorale: dense bone in the posteromedial aspect of the femoral neck
Soft Tissue Anatomy
Joint Capsule
- Dense fibrous capsule surrounds the hip joint
- Reinforced by iliofemoral (Y-shaped), pubofemoral, and ischiofemoral ligaments
- Zona orbicularis: circular fibers that form a collar around the femoral neck
Muscles
- Anterior: iliopsoas, rectus femoris, sartorius
- Lateral: gluteus medius, gluteus minimus, tensor fascia lata
- Posterior: gluteus maximus, piriformis, short external rotators (gemelli, obturator internus/externus, quadratus femoris)
- Medial: adductor muscles (longus, brevis, magnus, pectineus, gracilis)
Neurovascular Structures
- Femoral nerve: anterior approach risk, supplies quadriceps
- Sciatic nerve: posterior approach risk, passes below piriformis
- Superior gluteal nerve: lateral approach risk, supplies abductors
- Femoral artery and vein: anterior approach risk
- Medial and lateral femoral circumflex arteries: supply femoral head and neck
Surgical Approaches
Posterior Approach
- Patient positioned in lateral decubitus
- Incision along posterior aspect of greater trochanter
- Splits gluteus maximus fibers
- Requires detachment of short external rotators and posterior capsule
- Provides excellent exposure of femur
- Risk to sciatic nerve
Direct Lateral Approach
- Patient positioned in lateral decubitus
- Incision centered over greater trochanter
- Splits gluteus medius and minimus
- Risk to superior gluteal nerve
- Lower dislocation rates 1
Direct Anterior Approach
- Patient positioned supine
- Incision along the internervous plane between tensor fascia lata and sartorius
- True intermuscular and internervous approach
- Preserves posterior capsule and external rotators
- Allows faster recovery and reduced postoperative pain 2
- Technically more challenging with risk to lateral femoral cutaneous nerve
Implant Considerations
Acetabular Component
- Positioned with 40° of abduction and 15-20° of anteversion
- Requires adequate bone stock for fixation
- Can be cemented or uncemented (press-fit)
- Modern components typically include a metal shell with polyethylene, ceramic, or metal liner
Femoral Component
- Positioned to restore proper leg length, offset, and anteversion
- Requires proper preparation of femoral canal
- Can be cemented or uncemented
- Various stem designs: straight, anatomic, short, modular
Clinical Implications
Biomechanical Considerations
- Restoration of hip center of rotation is critical
- Proper femoral offset helps restore abductor tension and stability
- Leg length discrepancy must be minimized
- Component positioning affects range of motion and stability
Common Pitfalls
- Improper component positioning leading to impingement or dislocation
- Inadequate soft tissue tension leading to instability
- Excessive soft tissue tension causing pain and limited motion
- Neurovascular injury during surgical approach
Conclusion
Understanding the complex anatomy of the hip joint is essential for successful total hip replacement. The choice of surgical approach should be based on surgeon experience and patient factors 1, with each approach having specific anatomical considerations and risks. Proper component positioning and soft tissue handling are critical for optimal outcomes in terms of function, stability, and longevity of the implant.