Revision Total Hip Replacement for Recurrent Instability

Primary indications. Recurrent dislocation (two or more episodes) after primary THR despite closed reduction and rehabilitation; chronic instability affecting quality of life and activities of daily living; failed conservative management (bracing, activity modification, physiotherapy); and an identifiable, correctable cause (component malposition, soft-tissue deficiency). Relative indications. A single dislocation with an identifiable mechanical cause (malpositioned components); persistent painful subluxation or apprehension; patient request after a single traumatic dislocation in the context of high-risk activities. Contraindications. Active infection — stage with explant and spacer first; medical comorbidities precluding major revision surgery; severe abductor deficiency with no reconstruction option (consider expectant management); a neuromuscular disorder driving the instability (Parkinson disease, seizures) where surgery may not solve the problem; and patient non-compliance with post-operative precautions (relative). Preoperative assessment — rule out infection, then find the cause. History: the number of dislocations and their direction (posterior 80 percent, anterior 15 percent, superior 5 percent); provocative activities (bending, low chairs); timing relative to the primary (early is less than 6 weeks, late is more than 6 weeks); previous closed reductions and conservative attempts; and the impact on quality of life. Examination: Trendelenburg test for abductor integrity, hip range of motion and stability, leg-length assessment, gait, and a baseline neurovascular record. Imaging: an AP pelvis to measure cup inclination (normal 40–45 degrees — more than 50 degrees gives superior escape, less than 35 degrees gives instability); a lateral or cross-table lateral for anteversion (normal 15–25 degrees); and a CT with 3D reconstruction, which is essential for precise cup and stem version and for impingement assessment. Consider MRI for abductor integrity, fatty infiltration and capsular deficiency. Laboratory — mandatory infection workup: ESR, CRP and joint aspiration. Aspiration cell count greater than 3000 is concerning, a differential greater than 80 percent PMNs is concerning, with 14-day culture and alpha-defensin (or synovial CRP or IL-6). You cannot proceed without excluding infection. Component assessment: cup position against the Lewinnek safe zone; cup type and liner wear pattern; stem version and offset restoration; head size (heads smaller than 32 mm carry higher risk); and impingement signs such as eccentric wear. The one decision that matters — what to rebuild. Every case begins by correcting the underlying cause. The construct is then chosen on top of that:

Consent specifically for recurrent dislocation despite reconstruction (re-dislocation rates rise with each revision), sciatic nerve palsy (2–7 percent), infection (2–5 percent, higher than primary), leg-length change, and the prolonged hip-precaution and bracing period. Setup. Lateral decubitus on a radiolucent table with the affected side up; pelvic stabilisation with anterior ASIS and posterior sacral supports; all bony prominences padded. A cell saver is recommended (typical blood loss 400–800 mL).

The goal is to re-establish stability by correcting the cause and then building a stability-enhancing construct — most often a dual mobility cup — while protecting the sciatic nerve and restoring soft-tissue tension. The exposure is laid out in full as the first steps below (and in depth on the posterior (Moore/Southern) approach to the hip page).

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Rehabilitation & follow-up

Hip precautions — strict for a minimum of 12 weeks (longer than a primary, because the soft tissues are compromised): no hip flexion past 90 degrees (raised toilet seat, no low chairs, no bending to the floor); no adduction past midline (no crossing legs, a pillow between the legs in bed); no internal rotation after a posterior approach (or external rotation after an anterior approach); sleep supine or on the operative side with a pillow between the legs. Medications. VTE prophylaxis is essential (3–5 percent risk even with prophylaxis): LMWH (enoxaparin 40 mg subcutaneously daily) or a DOAC (apixaban 2.5 mg orally twice daily) for 4–6 weeks, with TED stockings and mechanical compression. Antibiotics: IV cefazolin 2 g every 8 hours (or vancomycin) for 24–48 hours. Multimodal analgesia (paracetamol, NSAIDs if not contraindicated, opioids as needed). Transfuse for haemoglobin less than 70–80 g/L or if symptomatic. Long-term outcomes. Re-dislocation with dual mobility is 5–15 percent across registries (1–5 percent in dedicated revision series), a 60–80 percent reduction versus standard revision, with most recurrences in the first 6 months. Function improves markedly from the chronically unstable state — though not to the level of an uncomplicated primary — with hip scores rising an average of 30–40 points. Ten-year implant survival is 85–90 percent (failure from loosening, infection or recurrent instability), and 70–80 percent of patients are satisfied or very satisfied. Complications

Why hips dislocate after primary THR. Dislocation is the commonest complication of revision THR (around 9.8 percent in a large series). Recurrent instability is rarely a single-factor problem — the cause is usually a combination of component position, soft-tissue tension, impingement and patient factors, which is why correcting the cup angle alone is often insufficient. The practical breakdown of causes in recurrent dislocators is:

The Lewinnek safe zone — a guide, not a guarantee. Lewinnek and colleagues (1978) defined the targets of 40 plus or minus 10 degrees inclination and 15 plus or minus 10 degrees anteversion from a primary-THR dislocation analysis. The targets remain a useful planning guide, but Abdel and colleagues (2016) showed the limits of relying on cup angles alone: of 206 dislocated THAs from a cohort of 9784 primaries, 58 percent had a socket WITHIN the Lewinnek safe zone (84 percent within the inclination target, 69 percent within the anteversion target), with mean inclination 44 plus or minus 8 degrees and anteversion 15 plus or minus 9 degrees — squarely in the classic targets. Posterior-approach hips were more often inside the combined zones yet still dislocated more than anterolateral hips. The implication for revision is clear: restore the angles but also address combined version, offset, head size and jump distance, and the soft tissues, and add a stability-enhancing bearing when risk factors persist. Why dual mobility works. The dual mobility (tripolar) construct has two articulations — a large outer polyethylene bearing (46–54 mm) that moves against a metal shell, and a small inner head (28–32 mm) within it. The large effective head size maximises the head-to-neck ratio (less impingement) and the jumping distance (the distance the head must travel to escape the socket), which is the mechanical basis for the low re-dislocation rates seen in revision series. The device-specific failure is intraprosthetic dislocation — the inner bearing escapes the outer head (less than 1 percent, usually from technical error in seating or impingement) — which cannot be reduced closed and needs open revision. Constrained liner — when and why not first. A constrained liner mechanically captures the head with a locking ring, giving excellent initial stability, but it transmits dislocating force to the cup-bone interface as torque, which drives higher loosening (15–20 percent at 5 years) and risks locking-mechanism failure (liner dissociation, 3–8 percent). It is reserved for true abductor deficiency, dual-mobility failure or unavailability, or severe bone loss — and it requires secure screw fixation. Registry evidence. National joint replacement registries — the National Joint Registry (NJR, UK), the American Joint Replacement Registry (AJRR, US), the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), and the Swedish Arthroplasty Register (SHAR) — publish converging evidence on dual mobility and revision for instability, documenting implant survival and revision-for-instability rates in their annual reports.

Further reading 1. Lewinnek GE, Lewis JL, Tarr R, Compere CL, Zimmerman JR. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am. 1978;60(2):217–220. PMID: 641088 2. Philippot R, Adam P, Reckhaus M, et al. Prevention of dislocation in total hip revision surgery using a dual mobility design. Orthop Traumatol Surg Res. 2009;95(6):407–413. PMID: 19656750 3. Biedermann R, Tonin A, Krismer M, Rachbauer F, Eibl G, Stöckl B. Reducing the risk of dislocation after total hip arthroplasty: the effect of orientation of the acetabular component. J Bone Joint Surg Br. 2005;87(6):762–769. PMID: 15911655 4. Springer BD, Fehring TK, Griffin WL, Odum SM, Masonis JL. Why revision total hip arthroplasty fails. Clin Orthop Relat Res. 2009;467(1):166–173. PMID: 18975043 5. De Martino I, Triantafyllopoulos GK, Sculco PK, Sculco TP. Dual mobility cups in total hip arthroplasty. World J Orthop. 2014;5(3):180–187. PMID: 25035820 6. Murray TG, Wetters NG, Moric M, Sporer SM, Paprosky WG, Della Valle CJ. The use of abduction bracing for the prevention of early postoperative dislocation after revision total hip arthroplasty. J Arthroplasty. 2012;27(8 Suppl):126–129. PMID: 22608688 7. National joint replacement registries — National Joint Registry (NJR, UK), American Joint Replacement Registry (AJRR, US), Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), and Swedish Arthroplasty Register (SHAR). Annual reports document implant survival and revision-for-instability rates.