Systemic Lupus Erythematosus - Musculoskeletal

Musculoskeletal complaints are the most common reason a patient with SLE first presents to a clinician, and they remain the leading cause of morbidity through the disease course. The orthopaedic surgeon meets SLE in three principal scenarios: a hand deformity that mimics rheumatoid arthritis (Jaccoud arthropathy), avascular necrosis of the femoral head in a young patient on steroids, and the perioperative management of an SLE patient listed for arthroplasty or fracture fixation.

Who. SLE affects roughly 30-50 per 100,000 adults worldwide, with a 9:1 female-to-male ratio and peak onset in the second to fourth decade.

Symptom or sign. Joint symptoms reach 90% or more across the disease course, and that is the figure usually quoted, but it is arthralgia, and arthralgia is not synovitis. In the 1,000-patient European cohort followed prospectively for 10 years, objective arthritis occurred in 48.1%, still the commonest single manifestation of the disease, ahead of malar rash (31.1%) and nephropathy (27.9%). Quote whichever endpoint the question asks for, and never treat a 90% symptom figure as a licence to call a painful lupus joint inflamed.

Bone and hand. The cumulative incidence of symptomatic AVN in SLE cohorts is 5-15%. Asymptomatic MRI-detected lesions are found in up to 40%, a different endpoint and not a range with the symptomatic figure. AVN is the dominant musculoskeletal cause of disability. Jaccoud arthropathy affects 5-12% of patients, increasing with disease duration and severity.

What kills them. In the same European cohort, deaths divided almost evenly between active SLE (26.5%), thrombosis (26.5%) and infection (25%), and thrombosis became the commonest cause in the second 5 years as inflammatory manifestations settled and vascular ones did not. The surgical corollary is that thromboprophylaxis deserves the same seriousness as infection prophylaxis, not less.

Two mechanisms. The orthopaedic phenotypes of SLE arise from two separable but overlapping mechanisms. Inflammatory capsuloligamentous laxity, from immune complex deposition in synovium and peri-articular soft tissues, underlies Jaccoud arthropathy and is the principal driver of hand deformity. Ischaemic bone death, from corticosteroid-induced adipocyte hypertrophy, a rise in intraosseous pressure and microvascular thrombosis from antiphospholipid antibodies, underlies avascular necrosis. The two are not mutually exclusive: a patient may have Jaccoud hands and bilateral femoral head AVN.

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How the Jaccoud hand deforms. The synovitis is immune-complex driven and often transient. The deformity comes from what chronic inflammation does to the soft tissues around the joint:

1. The capsuloligamentous structures weaken: the MCP volar plate, the PIP collateral ligaments and the extensor hood
2. The extensor tendons slip ulnarly at the MCP joints and the intrinsic muscles shorten
3. Ulnar deviation, swan-neck and boutonniere deformities follow, all passively correctable early

The articular cartilage is preserved despite the deformity, and there is no bony erosion. Ultrasound or MRI may show non-erosive synovitis. The hand looks rheumatoid and is structurally different.

How the bone dies. Beyond the marrow fat and thrombosis in the table, osteocytes and adipocytes in the subchondral bone undergo apoptosis, and fat emboli from steroid-induced marrow change may play a part. The end result is subchondral fracture, femoral head collapse and secondary OA.

Who gets AVN. Cumulative steroid dose is the dominant modifiable risk factor. The risk factors to recall:

• Cumulative dose greater than 3-5 g prednisolone equivalent
• Daily dose greater than 20 mg, pulse therapy, higher peak doses and rapid tapering
• Elevated disease activity: vasculitis, renal disease and Raynaud phenomenon, which compromises the microvasculature of bone
• Antiphospholipid antibodies, through thrombosis of subchondral vessels
• Disease duration, since longer disease means a longer exposure window

History. Establish the lupus, its activity and its complications as well as the joint:

• Lupus features: malar rash, photosensitivity, oral ulcers, serositis, renal disease, cytopenias, neurological involvement
• Disease activity: SLEDAI score, BILAG index and current immunosuppression
• Joints: pain, swelling and morning stiffness, usually minutes rather than the hours of RA
• AVN: groin, buttock, knee or shoulder pain, especially after steroid bursts
• Thrombosis: DVT, PE, stroke, transient ischaemic attack, pregnancy morbidity

Examination. Look beyond the painful joint:

• Hands: the pattern of deformity (reducible ulnar deviation, swan-neck, boutonniere), the squeeze test, FDS and FDP function
• Skin: periungual erythema, livedo reticularis, digital ulceration, Raynaud
• Hips, knees and shoulders: log roll, FABER, FADIR, range of movement, antalgic gait, limb length, and the contralateral joint whenever one AVN site is found
• System screen: blood pressure, urine dipstick, fundoscopy, lymphadenopathy

The Jaccoud hand. Inspect the hand at rest, where ulnar deviation, swan-neck and boutonniere may be obvious. Then correct the deformity passively: the examiner can straighten a Jaccoud hand, whereas the rheumatoid deformity is fixed, resists correction and shows erosions on X-ray. This is the key clinical sign that separates the two.

Then test function. Despite dramatic-looking deformity, Jaccoud hands often retain good grip and key-pinch, and a Jaccoud hand may function better than an RA hand with less obvious deformity.

Screening for AVN. The bedside tests and the imaging that follows them:

Immunology. The core panel is ANA, anti-dsDNA, anti-Smith and anti-SSA/SSB, with complement: C3 and C4 are low in active disease. The table sets out what each antibody means to the surgeon.

Antiphospholipid screen. The screen is lupus anticoagulant (a functional assay), anti-cardiolipin IgG and IgM, and anti-beta2 glycoprotein I, and a positive result is confirmed after 12 weeks.

Inflammatory markers. The ESR is often raised. The CRP is variable, and often normal even with active disease.

Imaging. Radiographs of symptomatic joints are often normal early. MRI is the gold standard for AVN: it detects pre-collapse disease while joint-preserving surgery is still possible. It shows:

• Bone marrow oedema
• The double-line sign on T2: a low-signal outer band and a high-signal inner band
• A geographic subchondral lesion

Where AVN occurs. The femoral head is the commonest site (90%), followed by the femoral condyles, humeral head, talus and lunate. The ARCO or Ficat stage dictates the choice between joint preservation and arthroplasty.

Spontaneous tendon rupture. A steroid-treated lupus patient who ruptures a major tendon after trivial or no trauma is a classic viva trap. Chronic steroid use plus a lupus enthesopathy degrades the tendon-bone junction, so ruptures are typically at the insertion and the tendon quality is poor.

Where and how it presents. The extensor mechanism is classic: the patellar, quadriceps and Achilles tendons, and the finger extensors. Bilateral and multiple ruptures are characteristic and a strong clue to the diagnosis. The story is a sudden extensor lag, a palpable gap and inability to straight-leg-raise after a minor stumble; because simultaneous or sequential bilateral rupture is described, always examine and image the contralateral side.

Repair. Surgical repair is harder than in normal tendon, with friable tissue and a high re-rupture rate. Use augmentation or reinforcement, protect the repair with longer immobilisation, and optimise the steroid dose first. A missed or late repair retracts and becomes a reconstruction.

Glucocorticoid-induced osteoporosis. AVN gets the attention, but the same steroids cause GIOP, the commonest cause of secondary osteoporosis and a distinct complication that must not be conflated with AVN. Glucocorticoids suppress osteoblasts and prolong osteoclast survival, causing rapid bone loss in the first 3-6 months of therapy that falls disproportionately on trabecular bone (vertebrae, femoral neck), so fractures occur at a higher bone density than in postmenopausal osteoporosis.

The fractures. The result is vertebral fragility fractures, often atraumatic or asymptomatic, and hip and wrist fractures. Lupus adds inflammation, renal impairment, low vitamin D and reduced mobility on top of the steroid effect.

Prevention and treatment. Start with the steroid dose itself:

• The lowest effective steroid dose
• Calcium and vitamin D
• Fracture risk assessed with FRAX (with the glucocorticoid adjustment) and DXA
• A bisphosphonate (or denosumab) for patients on significant ongoing steroids or with a prior fragility fracture, per glucocorticoid-osteoporosis guidance

GIOP or AVN. GIOP is generalised low bone mass with fragility fracture, assessed by DXA and vertebral imaging. AVN is focal subchondral bone death, shown on MRI by the double-line sign. Both are steroid-driven and can coexist, so a steroid-treated lupus patient needs both a bone-protection plan and AVN vigilance.

Prognosis. The good prognostic markers are early hydroxychloroquine, a low cumulative steroid dose, quiescent disease at the time of surgery, normal renal function and no APS antibodies. The adverse markers are cumulative prednisolone greater than 5 g, lupus nephritis, positive lupus anticoagulant, multifocal AVN, recurrent infection and active serositis at the time of surgery.