Hip Resurfacing Arthroplasty

Hip resurfacing arthroplasty (HRA) — the replacement of the femoral head articular surface and the acetabular articular surface while preserving the femoral head and neck — was developed as a bone-conserving alternative to conventional total hip arthroplasty (THA) for younger, more active patients with end-stage hip arthritis. By preserving the femoral head and neck, HRA maintains proximal femoral bone stock, allows a more physiological loading pattern through the proximal femur, and uses a large-diameter metal femoral head that provides exceptional jump distance and dislocation resistance. The most widely used contemporary design is the Birmingham Hip Resurfacing (BHR — Smith & Nephew), which uses a metal-on-metal (cobalt-chrome on cobalt-chrome) bearing surface.

• Advantages of HRA over conventional THA: (1) bone stock preservation — the femoral head and neck are retained; if HRA fails and revision to THA is required, a standard primary-length femoral stem can usually be used (unlike THA revision which may require longer stemmed revision implants); (2) large femoral head size — the HRA femoral component resurfaces the native femoral head (typically 44–54 mm diameter) — the largest possible femoral head; this produces a jump distance equivalent to the native hip and makes dislocation extremely rare (<0.5%); (3) physiological loading — load is transmitted through the preserved femoral head and neck to the proximal femur, maintaining normal femoral stress distribution and reducing stress shielding compared to a conventional femoral stem; (4) improved proprioception and kinematics — patients often report a more natural feeling hip with better range of motion and proprioception vs conventional THA
• The metal-on-metal bearing in HRA: the HRA femoral head is larger than any conventional THA head; at large head sizes, metal-on-metal bearings operate in the `fluid film lubrication` regime — the opposing CoCr surfaces are separated by a thin film of synovial fluid, reducing direct metal-metal contact and keeping wear rates very low; at smaller head sizes (as in conventional MoM THA bearings), fluid film lubrication is less consistent and wear rates are higher; this is why large-head MoM resurfacing was expected to have better tribological performance than small-head conventional MoM THA

• Ideal candidate for HRA: young (<55 years); male (critical — female sex is a major risk factor for ALTR in HRA, largely due to smaller femoral head size → less favourable fluid film lubrication → more wear → more ions; NICE guidance and MHRA recommend HRA only in males; multiple registries show significantly higher revision rates in females with HRA); high activity level; good bone quality (no severe osteoporosis); large femoral head size (men with larger femoral heads have better fluid film lubrication and lower ion release); no significant femoral head deformity or necrosis (AVN is a relative contraindication — the necrotic bone cannot adequately support the cemented HRA femoral component); primary osteoarthritis as indication (not inflammatory arthritis — RA bone quality is inadequate for the cemented femoral component); BMI <35 (obesity associated with higher complication rates)
• Contraindications: female sex (relative — most centres now avoid HRA in females; absolute in high-risk subgroups); severe osteoporosis (DEXA T-score <–2.5); large femoral head cysts (>1 cm — compromises the supporting bone for the cemented femoral component); femoral head avascular necrosis (Ficat III–IV); renal impairment (impaired clearance of metal ions — accelerates systemic cobalt/chromium accumulation); known metal hypersensitivity; leg length discrepancy requiring significant correction at arthroplasty (better achieved with conventional THA which allows independent femoral and acetabular reconstruction)

• The femoral component: the femoral head is prepared using a dedicated femoral head reamer and sizing guide; the femoral component is a metal cap that is press-fitted and cemented onto the prepared femoral head; the stem of the femoral component (a short central peg) is cemented into a prepared channel in the femoral head and neck; the component must be positioned in a slight valgus orientation relative to the femoral neck — a stem-shaft angle of >130° (the `valgus` position) reduces the bending stress on the femoral neck and reduces the risk of femoral neck fracture; a varus or neutral positioned component increases neck notching risk
• Notching: inadvertent notching of the superior femoral neck cortex during femoral head preparation is the most common intraoperative error; notching creates a stress riser in the femoral neck and significantly increases the risk of post-operative femoral neck fracture — the most specific complication of HRA; prevention — careful femoral head preparation technique with the appropriate sizing guide; verification of no notching before cementing the component
• The acetabular component: a cementless hemispherical metal shell (no liner — direct CoCr-to-CoCr articulation between the femoral head cap and the acetabular shell); press-fit into the reamed acetabulum; optimal position — abduction 40° and anteversion 20° (same `safe zone` principles as conventional THA); cup malposition is a significant risk factor for ALTR in HRA — a steep cup (abduction >55°) produces edge loading of the femoral component on the cup rim, generating metallic debris (stripe wear) and substantially increasing metal ion release; cup position in HRA is more critical than in conventional THA due to the absence of a polyethylene liner

• BHR outcomes in optimal patients: the Birmingham Hip Resurfacing has the best registry data of any resurfacing system; in young (<55 years) active males, the BHR has 10-year survival of approximately 95–97% in specialist high-volume centres (comparable to conventional THA in the same demographic); the NJR and AOANJRR (Australian registry) both report that in well-selected patients (young males, large femoral head, experienced surgeon), HRA revision rates approach those of conventional THA; the NJR 10-year data for BHR in males under 60 show revision rates of approximately 3–5%, comparable to conventional THA in the same group
• Surgeon volume effect: outcomes of HRA are highly volume-dependent; HRA is technically demanding and requires specific training; low-volume surgeons (<10 cases/year) have significantly higher complication and revision rates than high-volume specialists (>50 cases/year); NJR guidance recommends that surgeons perform a minimum volume of HRA to maintain competency; HRA should be concentrated in specialist centres
• Comparison with conventional THA in young males: the ongoing debate — HRA in optimal male patients produces comparable or superior functional outcomes (higher activity scores, more natural hip feel, better proprioception) and comparable revision rates to conventional THA; however, conventional THA with HXLPE has also shown excellent 15–20 year outcomes in young patients; the relative advantages of HRA (bone preservation, dislocation resistance) must be weighed against HRA-specific risks (femoral neck fracture, ALTR from MoM bearing)

• HRA ideal candidate: young (<55) active MALE; primary OA; large femoral head (≥46 mm); good bone quality; no significant AVN, large cysts, or osteoporosis; experienced high-volume surgeon
• Female sex: MAJOR risk factor for ALTR and revision in HRA (smaller head → less fluid film lubrication → more wear → more ions); NICE and MHRA guidance → HRA not recommended in females; avoid
• Femoral neck fracture: most specific HRA complication; ~1–2%; risk factors — notching (stress riser), varus orientation, female, osteoporosis, AVN, large cysts; revision to THA with standard primary stem (preserved bone stock = straightforward revision)
• Notching prevention: careful femoral preparation with sizing guide; component in valgus (stem-shaft angle >130°); intraoperative check for notching before cementing
• Cup position is critical in HRA: abduction >55° → edge loading → stripe wear → dramatically increased metal ion release; safe zone — abduction 40°, anteversion 20°; more critical than in conventional THA (no PE liner to buffer edge loading)
• ALTR / pseudotumour: same as MoM THA ALTR; more common in females + steep cup; MHRA Co/Cr monitoring (Co or Cr >7 µg/L → MARS MRI + consider revision; >4 µg/L for unilateral); cobaltism at very high Co levels
• BHR outcomes in young males: 10-year survival ~95–97% in specialist centres; comparable to conventional THA in same demographic; NJR 10-year data shows 3–5% revision in males <60 years
• Advantages of HRA: bone preservation (revision to THA = primary THA complexity); large head (jump distance = native hip → dislocation <0.5%); physiological loading (less stress shielding); better proprioception/kinematics in optimal patients
• Surgeon volume: HRA outcomes highly volume-dependent; concentrate in specialist high-volume centres; low-volume surgeons → higher complication rates