Complications of Total Hip Arthroplasty (THA)

Total hip arthroplasty (THA) is one of the most successful surgical procedures in medicine, producing excellent long-term pain relief and functional improvement in the vast majority of patients. However, as with all major surgical procedures, THA carries a defined spectrum of complications ranging from common minor issues to rare but catastrophic events. Understanding the incidence, mechanisms, risk factors, prevention strategies, and management of THA complications is essential for the arthroplasty surgeon. Complications can be broadly categorised as early (within 30 days), intermediate (30 days to 2 years), and late (>2 years), though there is significant overlap.

• Overview of major THA complications by frequency: dislocation (1–3% primary THA; 10–15% revision THA); periprosthetic joint infection (PJI) — 0.5–1.5% primary THA; venous thromboembolism (DVT/PE) — DVT in up to 40–60% without prophylaxis; symptomatic PE 1–3% without prophylaxis; nerve injury — sciatic nerve palsy 0.5–2%; femoral nerve palsy <0.5%; leg length discrepancy — clinically apparent LLD in 10–30%; intraoperative periprosthetic fracture — 1–3% cementless THA; aseptic loosening — the dominant late complication; see dedicated articles for each complication type
• Mortality: 90-day mortality after elective primary THA is approximately 0.3–0.5% (NJR data); higher in older patients, those with multiple comorbidities, and emergency THA for femoral neck fracture (mortality for hemiarthroplasty for intracapsular neck of femur fracture is approximately 5–8% at 30 days and 20–30% at 1 year); the 90-day mortality of UKA is lower than THA due to lower surgical invasiveness

• Sciatic nerve palsy: the most common major nerve injury after THA (0.5–2%); risk factors — posterior approach (proximity of the sciatic nerve to the posterior capsule and short external rotators); developmental dysplasia of the hip (DDH) — the sciatic nerve is tethered and at greater risk of stretch during lengthening; revision THA; leg lengthening >2–3 cm (nerve stretch is the most common mechanism — the sciatic nerve is relatively inelastic; the rule of thumb is that limb lengthening >4% of limb length = increased nerve stretch risk); direct retractor pressure on the sciatic nerve; presentation — foot drop (common peroneal division of sciatic nerve — the most vulnerable division due to its relatively sparse blood supply and fixed position at the fibular head); management — neurophysiology assessment (EMG/NCS); positioning in slight knee flexion and foot-drop splint; most cases resolve partially or completely over 6–24 months if injury is neuropraxia/axonotmesis rather than neurotmesis
• Femoral nerve palsy: less common than sciatic nerve palsy; risk factors — anterior approach (femoral neurovascular bundle in the anterior interval); prolonged anterior retractor pressure; direct femoral nerve injury during anterior approach; presentation — quadriceps weakness, inability to extend the knee against gravity, reduced anterior thigh sensation; usually resolves with time if retractor-related
• Superior gluteal nerve: the abductor nerve supply; at risk with anterolateral (hardinge) approach if the approach extends >5 cm proximal to the tip of the greater trochanter (the superior gluteal nerve enters the gluteus medius approximately 5 cm proximal to the tip of the greater trochanter); superior gluteal nerve injury causes persistent abductor weakness — the `abductor lurch` (Trendelenburg gait); also at risk if the gluteus medius is excessively retracted or detached from the greater trochanter; the `5 cm rule` — stay within 5 cm of the trochanter tip during the anterolateral approach to avoid superior gluteal nerve injury

• LLD is a common source of patient dissatisfaction after THA — patients are often more sensitive to leg length changes than surgeons expect; true LLD (measured radiographically — differences in femoral head centre height, femoral offset, and acetabular cup position) must be distinguished from functional LLD (caused by pelvic obliquity, scoliosis, or soft tissue contracture)
• Prevention: pre-operative templating is essential — the planned femoral stem size and offset, acetabular cup position, and femoral head/neck length should be determined on calibrated standing AP pelvis X-rays; intraoperative leg length assessment — the `epicondyle level test` (assess symmetry of medial femoral condyle levels with the knee flexed in lateral decubitus); `Shuck test` — confirm appropriate soft tissue tension after trial reduction; use of anatomical landmarks (the lesser trochanter — the stem should be implanted so the lesser trochanter is at a planned height relative to the acetabular cup centre); navigation and robotics assist with leg length accuracy
• Management of post-operative LLD: a true shortening of <1 cm is generally well tolerated; 1–2 cm may require a shoe raise; >2 cm causes gait abnormality and may require revision if soft tissue balancing confirms the discrepancy is structural (not functional); revision for LLD alone is a high-risk decision and is rarely performed

• Vascular injury: rare but catastrophic; major vascular structures at risk — external iliac artery and vein (anterior approach; retraction or acetabular screw penetration through the anterior wall of the acetabulum into the pelvis); obturator artery (medial retractor displacement through the medial wall of the acetabulum); the `safe zones` for acetabular screw placement (Wasielewski zones) — Zone 1 (posterosuperior) and Zone 2 (posteroinferior) are safe for screw placement; Zone 3 (anterosuperior — external iliac vessels) and Zone 4 (anteroinferior — obturator vessels) are dangerous; always confirm screw direction and length with fluoroscopy before committing to fixation
• Intraoperative periprosthetic fracture (cementless THA): the femoral canal is reamed to the appropriate diameter and a cementless femoral stem is impacted — the press-fit can crack the femoral cortex; incidence approximately 1–3% for cementless THA; more common in osteoporotic bone, narrow femoral canals, and DDH (dysplastic femurs); an intraoperative calcar crack is managed by cerclage wiring before or after stem impaction (the wire holds the crack and prevents propagation); more extensive fractures may require a longer stem or cortical strut allograft; always check fluoroscopy after stem impaction to exclude intraoperative fracture

• THA major complications overview: dislocation (1–3% primary); PJI (0.5–1.5%); nerve injury (sciatic 0.5–2%); LLD (apparent in 10–30%); intraoperative fracture (1–3% cementless); aseptic loosening (dominant late complication); 90-day mortality ~0.3–0.5%
• Sciatic nerve palsy: most common major nerve injury (0.5–2%); posterior approach; DDH; limb lengthening >2–3 cm (stretch); common peroneal division most vulnerable → foot drop; management — EMG/NCS, foot-drop splint, knee flexion; most resolve with time
• Superior gluteal nerve: 5 cm rule — do NOT extend anterolateral approach >5 cm proximal to greater trochanter tip; injury → persistent abductor weakness + Trendelenburg gait; beware excessive retraction in hardinge approach
• LLD prevention: pre-operative templating on calibrated X-rays; intraoperative epicondyle level test + shuck test; lesser trochanter height reference; navigation/robotics for accuracy; >2 cm LLD → gait abnormality; revision rarely performed for LLD alone
• Acetabular screw safe zones (Wasielewski): Zone 1 (posterosuperior) + Zone 2 (posteroinferior) = SAFE; Zone 3 (anterosuperior — external iliac) + Zone 4 (anteroinferior — obturator) = DANGEROUS; always confirm with fluoroscopy
• Intraoperative calcar crack (cementless): cerclage wiring before/after stem impaction; more extensive fractures → longer stem; always check fluoroscopy post-impaction; more common in osteoporotic bone + narrow canal + DDH
• Bone cement implantation syndrome (BCIS): fat + air + cement monomer + marrow emboli during canal pressurisation → cardiovascular collapse; Grade 0–3; warn anaesthetist + raise FiO2 before cementing; high risk in elderly osteoporotic patients + cardiorespiratory disease
• Femoral nerve palsy: anterior approach; retractor pressure; quadriceps weakness + reduced anterior thigh sensation; usually resolves if retractor-related; distinguish from sciatic nerve (foot drop vs quad weakness)
• THA mortality: 90-day ~0.3–0.5% elective; hemiarthroplasty for NOF fracture — 30-day mortality ~5–8%, 1-year ~20–30%; UKA lower mortality than THA due to lower invasiveness