Hip Resurfacing Case Presentations and Discussion

Archival Presentation Notice: This article modernizes the multimedia presentation “Hip Resurfacing Case Presentations and Discussion” originally presented by Thomas Parker Vail, MD (Professor and Chairman, Department of Orthopaedic Surgery, University of California, San Francisco). The historical Flash lecture has been reconstructed into the synchronized video slide presentation above, with the original file preserved in the digital archives (session_2_case_presentations_vail.swf).

1. High-Yield Summary

Hip resurfacing arthroplasty (HRA) represents a specialized bone-conserving alternative to conventional total hip arthroplasty (THA) designed primarily for young, active patients with end-stage hip osteoarthritis:

• Proximal Femoral Bone Preservation: The femoral head is sculpted and capped with a cobalt-chromium alloy shell rather than resected, completely sparing the femoral canal, maintaining physiologic proximal metaphyseal loading, and preserving native bone stock for subsequent revision.
• Enhanced Biomechanical Stability: Anatomical large-diameter femoral head sizes (typically 46 mm to 56 mm) yield a near-physiologic head-to-neck ratio and substantial jump distance, virtually eliminating prosthetic dislocation and enabling unconstrained return to vigorous physical activity.
• Stringent Candidate Selection: Optimal survivorship is strictly limited to young ( -1.0), femoral head diameter ≥48 mm, and normal proximal femoral morphology.
• Critical Contraindications: Female gender of childbearing age (placental cobalt/chromium transfer), renal insufficiency (impaired heavy metal excretion), osteopenia or osteoporosis, cystic collapse involving >30% of the femoral head, and severe acetabular dysplasia.
• Surgical Precision Imperative: Implant survival is highly operator-dependent. Essential surgical imperatives include avoiding femoral neck notching, aligning the femoral component in neutral to 5°–10° of relative valgus, and seating the acetabular component at 40°–45° inclination and 15°–20° anteversion to prevent edge loading.

2. Applied Surgical Anatomy & Biomechanics

Vascular Anatomy of the Femoral Head

The blood supply to the proximal femur is vital to the success of surface arthroplasty. The deep branch of the medial circumflex femoral artery (MCFA) gives rise to the subsynovial ascending retinacular arteries (predominantly the lateral retinacular arterial group), which travel along the posterosuperior and posteroinferior aspects of the femoral neck. During surgical exposure, extensive posterior capsular dissection must balance joint mobilization against devascularization of the femoral neck and remaining head core. Preservation of the inferior retinacular vessels and careful handling of the lateral retinaculum minimize the risk of secondary femoral head avascular necrosis.

Surgical Approaches & Internervous Planes

• Posterior (Moore / Southern) Approach: The most widely adopted approach for HRA. Employs the plane through the gluteus maximus (inferior gluteal nerve) with retroperitoneal protection of the sciatic nerve. Offers circumferential 360° access to the acetabulum and femoral neck, though meticulous repair of the short external rotators and posterior capsule is required to protect stability.
• Direct Lateral (Hardinge) Approach: Utilizes the internervous plane of the superior gluteal nerve within the split gluteus medius and vastus lateralis. Eliminates posterior dislocation risk and preserves the posterior retinacular blood supply, but risks superior gluteal nerve traction and postoperative abductor lurch.
• Anterior (Smith-Petersen) / Anterolateral (Watson-Jones) Approaches: Internervous plane between the tensor fasciae latae (superior gluteal nerve) and sartorius/rectus femoris (femoral nerve). Technically challenging for large-diameter component insertion due to restricted femoral neck reaming trajectories.

Biomechanical Load Transfer & Jump Distance

Unlike stemmed femoral prostheses that transfer weight-bearing stress distally to the femoral diaphysis (causing proximal stress shielding and calcar resorption), hip resurfacing retains physiologic compressive load transmission through the femoral trabeculae and medial calcar. Furthermore, restoring the anatomical femoral head diameter (48–56 mm) markedly expands the jump distance—the vertical translation required for the femoral head center to escape the acetabular rim. This high jump distance, coupled with native head-to-neck ratio restoration, confers unmatched joint stability during high-flexion and rotational athletic maneuvers.

3. Pathophysiology of Surface Replacement & Metal-on-Metal Tribology

Modern metal-on-metal (MoM) hip resurfacing relies on high-carbon (>0.20% C) as-cast cobalt-chromium-molybdenum (CoCrMo) alloy. The tribological behavior of these bearings operates under two distinct regimes:

• Fluid-Film Lubrication: Under dynamic walking conditions, the hydrodynamic pressure generated within the synovial fluid exceeds contact pressure, creating a micro-layer (5–20 nm) that separates the metal surfaces. In well-designed bearings with correct clearance (100–200 μm) and ideal cup inclination (<45°), volumetric wear decreases dramatically after the initial run-in period (first 1–2 years), dropping to steady-state rates <0.5 mm³/year.
• Boundary Lubrication and Edge Loading: When the acetabular component is placed with steep inclination (>50°–55°) or excessive anteversion/retroversion, the fluid-film layer breaks down at the cup margin. The femoral head contacts the rim (edge loading), switching the lubrication regime to boundary friction. This triggers accelerated volumetric wear, generating billions of submicron Co and Cr nanoparticles.
• Biological Host Response (ALVAL & ARMD): Nanoparticulate wear debris and soluble metal ions (Co²⋅, Cr³⋅) phagocytosed by macrophages stimulate pro-inflammatory cytokine cascades (TNF-α, IL-1β, IL-6). In susceptible individuals, a delayed-type (Type IV) cell-mediated hypersensitivity reaction develops. Histologically termed Aseptic Lymphocytic Vasculitis-Associated Lesions (ALVAL), this condition is characterized by perivascular lymphocytic cuffing, extensive soft-tissue necrosis, osteolysis, and sterile inflammatory cystic masses termed pseudotumors.

4. Patient Selection & Candidate Stratification

Rigorous candidate stratification is the decisive factor dictating long-term implant survival. The wide disparity between single-center designer series and multi-center registry outcomes is primarily explained by patient selection criteria.

5. Clinical Presentation & Physical Examination

History & Symptom Localization

Candidates for hip resurfacing present with classic mechanical groin pain radiating down the anterior thigh toward the knee. Patients typically report stiffness during transition from sitting to standing, progressive restriction in athletic or occupational endeavors, and difficulties with footwear and socks. Night pain and rest pain herald advanced cartilage loss. Clinicians must specifically inquire about occupational impact demands, athletic expectations, renal disease, and prior cutaneous reactions to metal jewelry or watchbands.

Physical Examination Maneuvers

• Flexion-Adduction-Internal Rotation (FADIR) Test: The hip is flexed to 90°, adducted, and internally rotated. Positive finding is acute groin pain, demonstrating anterior femoral head-neck junction impingement against the acetabular rim.
• Patrick / FABER (Flexion-Abduction-External Rotation) Test: The ipsilateral ankle is rested on the contralateral knee while the examiner exerts gentle downward pressure on the knee. Groin pain confirms intra-articular pathology; posterior sacroiliac pain indicates pelvic ring involvement.
• Stinchfield Maneuver: Resisted active straight-leg raise at 30° of hip flexion. Deep groin discomfort indicates joint loading against an irritated, arthritic articular surface.
• Trendelenburg Test & Gait Assessment: Evaluates abductor lever-arm integrity. Pelvic sag toward the unsupported swing limb indicates abductor insufficiency or biomechanical lever-arm shortening.

6. Diagnostic Imaging & Radiographic Planning

Accurate preoperative radiographic templating is essential to verify anatomical suitability, bone stock sufficiency, and component dimensions:

• Standard Radiographic Series: Low anteroposterior (AP) pelvis centered over the superior pubic symphysis, cross-table true lateral hip, and Dunn 45°/90° views to assess anterior head-neck offset and asphericity.
• Radiographic Neck-Shaft Angle: Normal range 125°–135°. Coxa vara (135°) facilitates valgus component placement.
• Lateral Center-Edge Angle (LCEA): Normal 25°–40°. Angles <20° indicate acetabular dysplasia requiring supplemental cup coverage or conversion to stemmed THA.
• Femoral Head Cystic Involvement: Subchondral cysts >1 cm or occupying >30% of the femoral head core undermine cement interdigitation and carry high early collapse rates.
• Dual-Energy X-ray Absorptiometry (DEXA): Mandatory in borderline cases or older candidates. A proximal femur T-score < -1.5 is an absolute contraindication to resurfacing due to unacceptably high risks of periprosthetic femoral neck fracture.
• MARS MRI (Metal Artifact Reduction Sequence): Gold standard for evaluating symptomatic postoperative resurfacings. Detects periprosthetic fluid collections, abductor tendon avulsion, and soft-tissue pseudotumors.
• High-Resolution Computed Tomography (CT): Pelvic CT evaluates 3D acetabular bone volume, version, and focal femoral head-neck cysts.
• Serum Metal Ion Testing: Whole blood or serum inductively coupled plasma mass spectrometry (ICP-MS) for cobalt and chromium. Thresholds >7 μg/L (parts per billion) correlate with edge loading, adverse local tissue reactions, or early implant failure.

7. Classification Systems

Standardized diagnostic classifications establish clinical severity and guide surgical decision-making:

8. Operative Principles & Technique Pearls

Surface arthroplasty requires unforgiving technical precision across both the femoral and acetabular components:

Femoral Head Sculpting & Guide Pin Placement

The guide wire dictates the ultimate orientation of the femoral component. The alignment pin must be positioned strictly along the central axis of the femoral neck in both AP and lateral planes, intentionally biasing toward 5°–10° of relative valgus compared to the native neck-shaft angle. Varus positioning is catastrophic, exponentially increasing tensile stress along the superior femoral neck cortex and predisposing to acute fracture. Cylindrical reaming must respect the native neck cortex; any accidental notching (>1 mm) of the superior femoral neck cortex requires immediate conversion to a stemmed primary THA.

Acetabular Preparation & Orientation

The acetabular cup is a monobloc, thin-walled CoCr component coated with porous titanium or hydroxyapatite for press-fit fixation. Because the cup has no modular liner, its rim profile is shallow to preserve range of motion. Acetabular reaming must be line-to-line or under-reamed by 1 mm depending on bone density. Target orientation is strictly 40°–45° inclination (abduction) and 15°–20° anteversion. Steep inclination (>50°) dramatically shrinks the contact area, shifting bearing contact to the rim and precipitating edge loading, accelerated ion production, and early failure.

Femoral Component Cementation

Low-viscosity polymethylmethacrylate (PMMA) bone cement is utilized to seat the femoral shell. Cement must be applied exclusively into the internal dome of the component, leaving the cylindrical sleeve free of pressurization. This strategy prevents cement extrusion down the femoral neck cortex, which can cause thermal osteonecrosis of the retinacular vessels or circumferential stress risers.

9. Clinical Outcomes & Long-Term Registries

Long-term registry data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) and the UK National Joint Registry (NJR) demonstrate clear dichotomies in implant durability:

• Male Patient Cohorts: In males under 55 years receiving large-diameter (≥50 mm) components, 10- and 15-year survivorship exceeds 94%–96%, matching or exceeding contemporary conventional THA cohorts. High UCLA activity scores (≥8) and return to vigorous sports (running, hockey, martial arts) are consistently reported.
• Female Patient Cohorts: Across all international registries, female patients experienced significantly higher cumulative revision rates (up to 3–4 times higher than males), driven by smaller head sizes (≤46 mm), shallower acetabular coverage, increased rates of metal hypersensitivity, and thinner femoral neck architecture. These findings led regulatory agencies worldwide to contraindicate HRA in women.
• Registry Revision Causes: The primary indications for revision include adverse reaction to metal debris (ALTR/ARMD) (40–50%), femoral neck fracture (15–20%), aseptic femoral loosening (15%), and infection (5%). Notably, revision for prosthetic dislocation remains <1%, dramatically lower than conventional THA.

10. Complications & Failure Modes

Complications in hip resurfacing encompass mechanical, biological, and technical failure patterns:

11. Pearls and Pitfalls

Technical Pearls

• Valgus Alignment Target: Always insert the femoral guide wire in 5°–10° of relative valgus to the native femoral neck axis. This reorients joint reaction forces into compression along the medial calcar and eliminates superior tensile strains.
• Circumferential Neck Inspection: After completing cylindrical reaming and barrel chamfering, palpate 360° around the femoral neck. Ensure zero cortex notching exists before cementing.
• Dome-Only Cement Pressurization: Place cement solely into the internal dome of the femoral component. Never pack cement around the cylindrical neck sleeve to avoid thermal retinacular injury.
• Rigid Cup Inclination Control: Target 40°–45° inclination and verify with mechanical alignment guides or intraoperative fluoroscopy to guarantee fluid-film lubrication.

Clinical Pitfalls

• Yielding to Patient Demand in High-Risk Cohorts: Agreeing to perform resurfacing in small-statured individuals, osteopenic patients, or women of childbearing age based on lifestyle desires rather than strict anatomical guidelines.
• Ignoring Asymptomatic Elevated Metal Ions: Failing to perform routine annual surveillance of blood Co/Cr levels; ions >7 μg/L can silently cause asymptomatic abductor muscle necrosis and massive pseudotumor formation.
• Under-Reaming Soft Acetabular Bone: In young patients with dense bone, aggressive under-reaming can cause acetabular ring fracture or incomplete component seating with dome gaps.

12. Clinical Controversies: Resurfacing vs. Conventional THA

The contemporary role of hip resurfacing remains one of the most vigorously debated topics in reconstructive surgery. Proponents highlight superior proprioception, natural gait kinematics, minimal dislocation risk, and the ease of femoral revision to standard primary stems without femoral osteotomy. Conversely, critics point to the technological maturation of conventional THA—specifically 36 mm and 40 mm delta ceramic heads on highly cross-linked polyethylene (HXLPE) or dual-mobility bearings—which offer comparable low dislocation rates and high activity tolerance without the biological hazards of cobalt-chromium release, pseudotumors, or systemic metallosis. Furthermore, emerging investigations into ceramic-on-ceramic resurfacing designs seek to deliver bone conservation while completely eliminating metal ion wear debris.

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.

14. References

• Daniel J, Pynsent PB, McMinn DJ. Metal-on-metal resurfacing of the hip in patients under the age of 55 years with osteoarthritis. J Bone Joint Surg Br. 2004. doi:10.1302/0301-620x.86b2.14600 [Level IV: Prospective Cohort Study]
• Smith AJ, Dieppe P, Howard PW et al. Failure rates of metal-on-metal hip resurfacings: analysis of data from the National Joint Registry for England and Wales. Lancet. 2012. doi:10.1016/S0140-6736(12)60989-1 [Level II: National Joint Registry Comparative Cohort Analysis]
• Treacy RB, McBryde CW, Pynsent PB. Birmingham hip resurfacing arthroplasty. A minimum follow-up of five years. J Bone Joint Surg Br. 2005. doi:10.1302/0301-620x.87b2.15030 [Level IV: Prospective Clinical Cohort Study]
• Za P, Casciaro C, Papalia GF et al. Hip resurfacing versus total hip arthroplasty: a systematic review and meta-analysis of randomized clinical trials. Int Orthop. 2024. doi:10.1007/s00264-024-06269-3 [Level I: Systematic Review / Meta-Analysis]
• Gustafson K, Jakobsen SS, Lorenzen ND et al. Metal release and metal allergy after total hip replacement with resurfacing versus conventional hybrid prosthesis. Acta Orthop. 2014. doi:10.3109/17453674.2014.922730 [Level I: Randomized Controlled Trial]

15. Master Class Pro-Tip

The single most catastrophic intraoperative error in hip resurfacing is cortical notching of the superior femoral neck during cylindrical reaming. When setting the alignment pin, always position the guide wire in 5° to 10° of relative valgus compared to the anatomical neck-shaft angle, and intentionally favor slight anterior positioning over posterior deviation. If post-reaming tactile inspection reveals even a 1-mm notch on the superior neck cortex, never proceed with surface capping under the presumption that bone cement will bridge the defect—the notch creates a lethal stress concentration zone that will fracture under cyclic gait loading within 6 to 12 weeks. Abort the resurfacing and convert immediately to a primary stemmed femoral component.

Master Class Surgical Pearl: Cylindrical Femoral Neck Reaming and Varus Avoidance