Total Hip Arthroplasty (THA) — Indications & Outcomes

Total hip arthroplasty (THA) is one of the most successful elective surgical procedures in medicine, providing reliable and durable pain relief and functional restoration for end-stage hip arthritis and other destructive hip conditions. Over 100,000 primary THAs are performed annually in the UK (National Joint Registry data), with the majority for primary osteoarthritis. Patient selection, pre-operative optimisation, implant choice, and surgical technique all significantly influence outcomes.

• Primary osteoarthritis (OA) is the most common indication, accounting for approximately 75% of primary THA procedures; other common indications include inflammatory arthritis (RA, AS), avascular necrosis, post-traumatic arthritis, hip dysplasia, and failed hemiarthroplasty
• NJR data (UK National Joint Registry): the largest arthroplasty registry in the world; tracks implant performance and revision rates; the 10-year revision rate for primary THA is approximately 5–7% (most implants have >90% survivorship at 10 years); data used for implant surveillance and ODEP (Orthopaedic Device Evaluation Panel) ratings; surgeons are mandated to submit data to the NJR for all arthroplasty procedures in England, Wales, and Northern Ireland
• Oxford Hip Score (OHS): the most widely used patient-reported outcome measure (PROM) for THA in the UK; 12 questions, each scored 0–4, total 0–48 (48 = best); minimum clinically important difference (MCID) approximately 5 points; collected pre-operatively and at 6 months post-operatively as standard in the UK

• Indications for THA: (1) end-stage hip OA with severe pain, functional disability, and failure of non-operative management (analgesia, physiotherapy, walking aids, lifestyle modification, corticosteroid injection); (2) inflammatory arthritis with joint destruction; (3) AVN Stage IV–V; (4) post-traumatic arthritis; (5) hip dysplasia with secondary OA; (6) displaced intracapsular NOF fracture in independently mobile, cognitively intact patients (see hemiarthroplasty article); (7) failed hemiarthroplasty (acetabular erosion)
• Non-operative management should be genuinely exhausted before surgery — patient expectations management, weight management (BMI >40 is a relative contraindication — higher complication rates, lower functional gains, higher revision rates), smoking cessation (reduces wound healing complications, PJI risk, and non-union of trochanteric osteotomies)
• Absolute contraindications: active systemic or local infection; non-reconstructable bone deficiency; neurological conditions causing severe spasticity or paralysis where the hip cannot be controlled post-operatively
• Age and THA: there is no absolute lower age limit for THA; however, younger patients (<55 years) have higher revision rates due to greater activity demands and longer remaining life span; in young patients, bearing surface selection, implant fixation, and bone preservation are particularly important considerations

• Dorr classification of femoral morphology: Type A — champagne flute shape; thick cortices; narrow canal; typical in young patients; good press-fit cementless; Type B — intermediate; Type C — stovepipe shape; thin cortices; wide canal; typical in elderly osteoporotic patients; cemented stem preferred — press-fit in a Type C femur has high risk of subsidence and peri-prosthetic fracture

• Posterior approach (Moore / Southern): most widely used in the UK; excellent visualisation; extensile; posterior capsule and short external rotators divided; higher dislocation rate without posterior repair; post-operative posterior precautions (avoid flexion >90°, adduction, IR)
• Anterolateral (Hardinge / Watson-Jones): anterior split of the gluteus medius; lower posterior dislocation rate; risk of abductor weakness/Trendelenburg limp; commonly used for hip fracture work
• Direct anterior approach (DAA / Hueter): internervous plane between the tensor fascia lata (superior gluteal nerve) and sartorius (femoral nerve); true internervous plane — no muscle is cut; lower dislocation rate, no posterior precautions, faster early rehabilitation in some studies; challenges — access to the femoral canal is technically demanding, higher risk of lateral femoral cutaneous nerve (LFCN) injury (anterolateral thigh numbness — LFCN runs just medial to the approach), fluoroscopy often used intraoperatively; learning curve of approximately 100 cases

• Dislocation: most common early mechanical complication; posterior approach without repair approximately 3–5%; posterior repair reduces to 1–2%; DAA and anterolateral approach have lower dislocation rates; dual-mobility cups reduce dislocation rate significantly; risk factors — prior surgery, cognitive impairment, abductor weakness, malposition of implants
• Peri-prosthetic joint infection (PJI): deep infection around the prosthesis; early PJI (<3 months) managed with DAIR (debridement, antibiotics, implant retention) if the implant is stable; late chronic PJI managed with two-stage revision (explant, 6-week antibiotic spacer, re-implantation); the Musculoskeletal Infection Society (MSIS) criteria or ICM (International Consensus Meeting) criteria are used to define PJI; gram-positive cocci (Staph aureus, Staph epidermidis) are the most common organisms
• Aseptic loosening: most common cause of late revision; PE wear debris → macrophage activation → osteolysis → implant loosening; modern XLPE dramatically reduces this complication
• Peri-prosthetic fracture: Vancouver classification (Type A — trochanteric, B1/B2/B3 — around stem, C — distal to stem); B1 — stem stable, ORIF; B2 — stem loose, good bone stock, revision stem; B3 — stem loose, poor bone stock, revision with allograft or megaprosthesis
• Nerve injury: sciatic nerve most at risk (posterior approach, leg lengthening >4 cm); femoral nerve (anterior approach); LFCN (DAA); superior gluteal nerve (anterolateral approach)

• ODEP (Orthopaedic Device Evaluation Panel) ratings: the UK-specific evidence framework for implant evaluation; implants are rated A* (10-year data from NJR or equivalent), A (10-year data published), B (7-year data), C (3-year data); surgeons should use ODEP A* rated implants whenever possible; the NJR and ODEP together form the most rigorous implant surveillance system globally; use of implants outside these ratings requires specific justification and patient consent
• Metal on metal surveillance: all patients with metal-on-metal THA (including hip resurfacing) require annual review; serum cobalt and chromium ion levels (both <7 ppb is reassuring; either >7 ppb requires further investigation with MARS MRI); MARS MRI (Metal Artefact Reduction Sequence) is the investigation of choice for suspected ALTR/pseudotumour; MHRA guidance mandates surveillance; patients with symptoms, rising metal ions, or MARS MRI changes require revision
• The combined anteversion concept: in THA, both the acetabular cup and the femoral stem contribute to the overall anteversion of the hip construct; excessive combined anteversion increases the risk of anterior dislocation, while insufficient anteversion increases posterior dislocation risk; the safe zone for cup position (Lewinnek safe zone) is 40±10° abduction and 15±10° anteversion; combined anteversion of approximately 25–50° is generally targeted; navigation and robotic systems improve positioning accuracy

• NJR: 10-year revision rate ~5–7%; >90% survivorship at 10 years; ODEP A* = gold standard implant rating; hybrid THA most common construct in the UK
• Oxford Hip Score (OHS): 12 questions, 0–48 (48 = best); MCID ~5 points; primary PROM for THA in UK
• Dorr Type C femur: stovepipe; thin cortices; wide canal; cemented stem preferred — cementless risks subsidence and peri-prosthetic fracture
• Bearing surfaces: ceramic on XLPE — most common in UK for younger patients; CoC — lowest wear, highest squeaking/fracture risk; MoM — ALTR/pseudotumour/cobaltism — largely abandoned; metal ion surveillance mandatory for all MoM patients
• DAA: internervous (TFL vs sartorius); no muscle cut; lower dislocation rate; LFCN injury risk (anterolateral thigh numbness); learning curve ~100 cases
• PJI: DAIR for early stable implant; two-stage for late chronic PJI; Staph aureus and Staph epidermidis most common organisms
• Vancouver peri-prosthetic fracture: B1 (stable stem, ORIF); B2 (loose stem, good bone, revision); B3 (loose stem, poor bone, megaprosthesis/allograft)
• Lewinnek safe zone: cup abduction 40±10°, anteversion 15±10°; combined anteversion target ~25–50°; navigation/robotics improve accuracy
• MoM surveillance: cobalt + chromium <7 ppb reassuring; >7 ppb = MARS MRI; MHRA mandates annual review for all MoM THA and resurfacing
• Dislocation: most common early complication; posterior repair reduces rate to ~1–2%; dual-mobility cup for high-risk patients