Osteoarthritis & Rheumatological Bone Disease — Practice

Question 1

Synovial fluid from an acutely inflamed first metatarsophalangeal joint shows needle-shaped crystals that are negatively birefringent under polarised light. The diagnosis is

Accepted Answer

B

Question 2

Which biochemical pattern fits uncomplicated osteoporosis?

Accepted Answer

A

Question 3

A 60-year-old woman has painful knobbly swellings of her distal interphalangeal joints and pain at the base of the thumb. Wrists and metacarpophalangeal joints are normal. Rheumatoid factor is weakly positive. What is the diagnosis?

Accepted Answer

Osteoarthritis of the hand. The distribution decides it: distal interphalangeal involvement with Heberden nodes and first carpometacarpal disease, with sparing of the wrist and metacarpophalangeal joints.

Rheumatoid arthritis characteristically spares the distal interphalangeal joints and attacks precisely the joints that are normal here. A weakly positive rheumatoid factor is common in older people and lacks specificity; anti-CCP would be the discriminating test if genuine doubt remained.

Question 4

A 68-year-old man with Kellgren-Lawrence grade 4 knee osteoarthritis walks two kilometres daily without significant pain. Should he be offered a knee replacement?

Accepted Answer

No. Radiographic grade and symptoms correlate poorly, so the film alone is not an indication.

The indication for arthroplasty is clinical: pain and functional limitation that persist despite exercise, weight management and appropriate analgesia. Operating on a radiograph exposes a comfortable patient to surgical risk and commits him to a prosthesis with a finite lifespan, which matters more the earlier it is implanted.

Question 5

A patient established on allopurinol develops an acute flare of the first metatarsophalangeal joint. What should be done with the allopurinol, and why?

Accepted Answer

Continue it unchanged. Stopping urate-lowering therapy during a flare allows serum urate to rise again, prolongs the problem, and provokes a further flare when it is restarted.

Treat the attack itself with an NSAID, colchicine or corticosteroid selected by comorbidity. The mirror-image rule applies at initiation: when starting urate-lowering therapy, give colchicine or NSAID prophylaxis, because a falling urate level mobilises deposited crystals and precipitates attacks. Both rules follow from the same physiology, that a changing urate level in either direction destabilises crystals.

Question 6

A 55-year-old woman with a vertebral fragility fracture has calcium 7.8 mg/dL, phosphate 2.1 mg/dL, markedly raised alkaline phosphatase and raised parathyroid hormone. Is this osteoporosis, and what should be done?

Accepted Answer

No. Osteoporosis has an entirely normal biochemical panel, so this pattern excludes it as the sole diagnosis. Low calcium with low phosphate, raised alkaline phosphatase and secondary elevation of parathyroid hormone is the signature of osteomalacia from vitamin D deficiency.

Look for Looser zones on radiographs of the pubic rami, femoral neck and scapula, and ask about diffuse bone pain, proximal myopathy and difficulty rising from the floor. Measure 25-hydroxyvitamin D and correct the deficiency with calcium and vitamin D. Giving a bisphosphonate alone to a patient with unmineralised osteoid would be both ineffective and potentially harmful.

Question 7

A 28-year-old man has 8 months of low back pain worse in the second half of the night, easing when he gets up and moves, with an hour of morning stiffness and one past episode of a painful red eye. Give the diagnosis, the key investigation and the treatment sequence.

Accepted Answer

Axial spondyloarthritis, most likely ankylosing spondylitis. The pain is inflammatory rather than mechanical, being worse with rest and better with movement, and anterior uveitis is the characteristic extra-articular association of HLA-B27 disease.

Imaging of the sacroiliac joints is the key investigation, with MRI detecting active inflammation before radiographic sacroiliitis develops. Treatment begins with a structured exercise programme and NSAIDs. If disease activity remains high after two adequate NSAID trials, a biologic is indicated, either a TNF inhibitor or an IL-17 inhibitor. Conventional synthetic DMARDs would be the wrong choice for purely axial disease, though they may help if peripheral arthritis dominates.

Question 8

A woman completes five years of denosumab. Her physician plans to simply stop the drug and review her in a year. What is wrong with this plan?

Accepted Answer

Denosumab withdrawal produces a rebound increase in bone turnover, with a documented risk of multiple vertebral fractures occurring within months of the missed dose. Its effect depends on continuous RANK ligand blockade and, unlike bisphosphonates, it does not persist in the skeleton after discontinuation.

The correct approach is to follow denosumab with a bisphosphonate to consolidate the gains, and to ensure scheduled doses are never delayed while treatment continues. This contrast is the reason a drug holiday is a reasonable concept for bisphosphonates, where the drug remains bound in bone, and a dangerous one for denosumab.

Question 9

A 34-year-old man on long-term corticosteroids for systemic lupus erythematosus develops groin pain. Hip radiographs are normal. Outline the investigation and explain what changes management.

Accepted Answer

Avascular necrosis of the femoral head is the working diagnosis, since corticosteroids and lupus are both established causes, acting through marrow fat changes and through thrombosis respectively. A normal radiograph is expected early and excludes nothing.

MRI is the investigation of choice and detects the infarct before any radiographic change appears. The finding that changes management is the crescent sign, a subchondral lucency representing subchondral fracture, which marks the moment immediately before the articular surface collapses. Before collapse, joint-preserving options including core decompression are reasonable. Once the head has collapsed the articular surface is lost and arthroplasty becomes the realistic option, which is why early imaging in a high-risk patient is worth doing rather than waiting for radiographic change.

Practice — Osteoarthritis & Rheumatological Bone Disease

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