Total Hip Replacement with Dual Mobility Cup

A dual mobility cup is chosen whenever the patient's dislocation risk outweighs the small added complexity of a dual-articular bearing. The bearing reduces dislocation by increasing the effective head size and jump distance; it does not improve all-cause survivorship, so the decision is framed around dislocation-risk reduction, not implant longevity.

Pre-operative planning. Document the dislocation history (number, direction, mechanism), neuromuscular and cognitive status, spine symptoms or prior fusion, compliance concerns and previous hip surgery. Examine abductor strength (Trendelenburg test), leg-length discrepancy, range of motion and spinopelvic mobility (the sit-to-stand test). Image with an AP pelvis and lateral of the affected hip; add full-spine standing radiographs if spinopelvic pathology is suspected, and a CT pelvis with 3D reconstruction in revision cases to map acetabular defects. Templating. Dual mobility cups typically measure 50–62 mm outer diameter (smaller than standard cups because of the thick polyethylene liner). Template to the anatomic hip center (medialize to the true floor at the transverse ligament/teardrop), plan 40–45 degrees inclination and 15–20 degrees anteversion, and confirm intact 360-degree rim support. The femoral side accepts any compatible stem (standard, modular or revision); template stem size, offset and neck length with 10–15 degrees stem anteversion (combined anteversion 25–35 degrees with the cup). Measure the leg-length discrepancy and plan correction to within 1 cm. In every revision, failed hemiarthroplasty conversion, or patient with risk factors, perform an infection workup — ESR and CRP, and hip aspiration for cell count, differential and culture (holding antibiotics for two weeks beforehand); add alpha-defensin or synovial CRP where available. Counsel the patient honestly.

Setup and positioning. The posterior (Moore/Southern) approach is used here and is the operation described below; the anterior (Smith-Petersen) approach is a valid alternative noted where it differs. For the posterior approach the patient is in lateral decubitus, affected hip uppermost, held rigidly with an anterior support at the pubic symphysis/ASIS and a posterior support at the sacrum so the pelvis is perpendicular to the table — verify this with a spirit level before draping, because pelvic tilt is the commonest source of cup malposition and dual mobility does not forgive it. Flex the hip and knee to relax the sciatic nerve. For the anterior approach the patient is supine on a radiolucent table with a small bump under the ipsilateral pelvis and the contralateral leg abducted for C-arm access.

The goal is to expose the hip, remove the femoral head, prepare an acetabulum with an intact rim, implant the cup in the Lewinnek safe zone, assemble the mobile dual-articular bearing, restore offset and leg length, and close the soft tissues — above all protecting the sciatic nerve and ensuring the liner and head are fully seated. The exposure is laid out in full below (and in depth on the posterior approach to the hip page).

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Immediate recovery (day 0–2). Check neurovascular status (dorsalis pedis and posterior tibial pulses, sensation, motor) before the neuraxial block wears off, use multimodal analgesia, and keep an abduction pillow between the legs. Start DVT prophylaxis at 12–24 hours (LMWH such as enoxaparin 40 mg subcutaneously daily, or a DOAC such as rivaroxaban 10 mg daily) for 4–6 weeks, with TED stockings and sequential compression until mobile. Mobilise on day 1–2: sit to stand, walk with a frame, gait train and practise stairs before discharge. Weight-bearing and precautions. Weight-bear as tolerated immediately (both cemented and cementless dual mobility allow this) — early mobilisation is critical in the elderly to prevent deconditioning. Hip precautions for six weeks remain my practice to allow soft-tissue healing: no flexion past 90 degrees (raised toilet seat, no low chairs), no adduction across the midline, and no internal rotation after a posterior approach. Some surgeons use minimal or no precautions, leveraging the dual mobility's inherent stability; there is no consensus. Follow-up. | Time | Assessment | |------|------------| | 6 weeks | Wound, mobility, pain; AP pelvis and lateral hip; advance activities, may resume driving if safe | | 3 months | Function (Oxford Hip Score, HOOS) and range of motion | | 1 year | AP pelvis and lateral hip for wear, osteolysis, loosening, heterotopic ossification; full activities | | Long-term | Every 2 years with radiographs; monitor for late wear, loosening and the rare intraprosthetic dislocation | Complications. Dislocation still occurs (0.5–3 percent) — usually from malposition, soft-tissue failure or impingement — and is closed-reduced under sedation, then assessed for cause. The dual-mobility-specific failure is intraprosthetic dislocation (0.5–1 percent): the inner bearing dissociates, producing a "double density" sign on the radiograph, and it cannot be closed-reduced — it needs open reduction and liner revision.

Concept and history. The dual-articular cup was introduced by Gilles Bousquet in France in the 1970s, giving the French experience the longest clinical follow-up of any dual mobility series. Early adoption was held back — especially in the USA — by high rates of intraprosthetic dislocation with the first-generation, non-cross-linked polyethylene designs. Modern improvements (better retentive head-capture rims, chamfered liner geometry and highly cross-linked polyethylene) have reduced intraprosthetic dislocation to about 0.3–1 percent and broadened use into high-risk primary arthroplasty. The mechanism. A dual mobility construct has two concentric, independent articulations. The small inner bearing is the femoral head (22–28 mm) captured inside a mobile polyethylene liner; the large outer bearing is that liner's convex surface moving against the polished metal shell, with an effective outer diameter matching the cup (38–60 mm). There is no liner-to-shell locking mechanism — that distinguishes it from a standard fixed liner. The large effective head raises the head-to-neck ratio, increases the jump distance from about 10 mm (a standard 32 mm head) to 15–20 mm, and widens the range of motion before impingement — the biomechanical basis of dislocation reduction. The trade-off is a smaller usable head for a given acetabulum (because of the thick polyethylene), relevant in small acetabulae.

Intraprosthetic dislocation — modern versus historical.

The honest evidence position. The strongest current data are large registry and meta-analytic studies, not completed randomised trials. For femoral neck fracture, Farey pooled six national registries (Australia, Denmark, Sweden, Netherlands, UK, USA — 15,024 dual mobility versus 97,200 conventional THAs) and found dual mobility lowered revision for dislocation (0.9 percent versus 1.4 percent) but did NOT reduce all-cause revision (HR 0.96, 95% CI 0.86–1.06) and carried MORE revision for infection (1.2 percent versus 0.8 percent). The honest exam position is to support dual mobility in the high-risk elderly fracture patient for its dislocation benefit, but NOT to claim a proven all-cause survivorship advantage. For primary THR in high-risk patients, pooled survivorship is acceptable (Gardner 2023: 95.7 percent at 10 years, about 77 percent at 20 years), justifying liberal use framed as dislocation-risk reduction. For revision instability, dual mobility is increasingly first-line (re-dislocation 3–5 percent versus 8–12 percent for a constrained liner, and it preserves range of motion). The definitive randomised trial — the registry-nested cluster-randomised DISTINCT trial — is ongoing and powered for one-year dislocation. Current controversies. In young active patients (under 55–60) long-term data are limited and intraprosthetic dislocation remains a theoretical concern, so dual mobility is not recommended for routine primary use in the low-risk young, though modern HXLPE data to 10–15 years are reassuring. Hip precautions are debated: traditional six-week precautions versus no precautions leveraging the dual mobility's inherent stability — there is no consensus, and many surgeons (myself included) still use six weeks to allow soft-tissue healing. Against the constrained liner for revision instability, dual mobility offers lower re-dislocation and preserved range of motion; the constrained liner is simpler (liner exchange, keep a well-fixed cup) and is reserved for cases where a dual mobility cup cannot be revised.

Further reading 1. Grazioli A, Ek ET, Rudiger HA. Biomechanical concept and clinical outcome of dual mobility cups. Int Orthop. 2012;36(12):2411-2418. doi:10.1007/s00264-012-1678-3 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. doi:10.1016/j.otsr.2009.04.016 3. Chalmers BP, Syku M, Sculco TP, Jerabek SA, Mayman DJ, Westrich GH. Dual-mobility constructs in primary total hip arthroplasty in high-risk patients with spinal fusions: our institutional experience. Arthroplast Today. 2020;6(4):749-754. doi:10.1016/j.artd.2020.07.024 (PMID 32923563) 4. Farey JE, Hooper T, Alland T, et al. Dual mobility versus conventional total hip arthroplasty in femoral neck fractures (DISTINCT): protocol for a registry-nested, open-label, cluster-randomised crossover trial. BMJ Open. 2022;12(9):e064478. doi:10.1136/bmjopen-2022-064478 5. International Society of Arthroplasty Registries (ISAR) member reports — NJR (UK), AOANJRR (Australia), Swedish Hip Arthroplasty Register, Danish Hip Arthroplasty Register, Dutch Arthroplasty Register (LROI) and AJRR (USA) — provide the registry evidence pooled in the meta-analyses above.