OR3.1-3 | Musculoskeletal Infection — Glossary

A bacterial infection of bone occurring via bloodstream seeding, predominantly affecting the metaphysis of growing long bones in children, caused most commonly by Staphylococcus aureus.

The standard drug regimen for tuberculosis: 2 months of isoniazid, rifampicin, pyrazinamide, and ethambutol (HRZE), followed by 4 months of isoniazid and rifampicin (HR); extended to at least 9-12 months for skeletal TB.

The aspiration of synovial fluid from a joint using a sterile needle, performed for diagnosis (cell count, culture) and initial therapeutic decompression in suspected septic arthritis.

Abnormal fibrous tissue formation within a joint following infection, surgery, or immobilisation, leading to restricted range of motion; prevented by early passive physiotherapy after septic arthritis surgery.

Minimally invasive joint lavage using an arthroscope, inflow, and outflow cannulas to irrigate a septic joint without open arthrotomy; appropriate for the knee and shoulder but not for the paediatric hip.

Surgical incision into a joint capsule to access the joint interior for evacuation of pus (septic arthritis), debridement of infected synovium, and copious lavage.

A set of procedural practices designed to prevent the introduction of microorganisms into a sterile body cavity, including sterile gloves, skin antisepsis, sterile drapes, and avoiding contamination of the sterile field.

Death of the femoral head bone due to interruption of the lateral epiphyseal vessel blood supply; a catastrophic complication of delayed hip arthrotomy in septic arthritis, leading to femoral head collapse and secondary osteoarthritis.

Microbiological culture of a bone core sample taken intraoperatively from the infected bone wall; the gold standard for identifying the causative organism in chronic osteomyelitis, more accurate than sinus-tract swabs or blood cultures.

A localised form of subacute osteomyelitis presenting as a well-defined oval lytic cavity in the metaphysis with surrounding sclerotic rim, representing partial host containment of a low-virulence infection.

Autologous spongy bone harvested from the iliac crest, used to fill the dead space after sequestrectomy; the cancellous bone is rapidly revascularised and osteoconductive, promoting bone regeneration.

A broad-spectrum antiseptic used for skin preparation before invasive procedures; 2% chlorhexidine in 70% isopropyl alcohol is the preferred agent for arthrocentesis, with residual activity after drying.

A classification system for osteomyelitis that grades the anatomical extent (medullary, superficial, localised, diffuse) and host physiological status (A = normal, B = locally or systemically compromised, C = treatment risk outweighs benefit) to guide surgical planning.

Perforations in the involucrum through which pus and small bone fragments discharge to form sinus tracts to the skin surface.

An abscess in which the overlying skin lacks the classical acute inflammatory signs of warmth and erythema, characteristic of tuberculous infection because TB provokes granulomatous rather than acute neutrophilic inflammation.

The void left in bone or soft tissue after removal of the sequestrum and debridement; must be managed (with antibiotic beads, bone graft, or muscle flap) to prevent haematoma accumulation and re-infection.

A workplace-based assessment tool in which a supervising clinician observes a trainee performing a procedure and provides structured feedback across domains including preparation, technique, communication, and complication management.

A blood collection tube containing ethylenediaminetetraacetic acid (EDTA) anticoagulant, used for synovial fluid cell count and differential; NOT suitable for culture because EDTA inhibits bacterial growth.

A sharply angled, angular kyphotic deformity of the spine resulting from anterior vertebral body destruction in Pott's disease (TB spine), in contrast to the smooth kyphosis of senile osteoporosis.

A rapid microbiological staining technique that classifies bacteria as Gram-positive (blue-purple, thick peptidoglycan cell wall) or Gram-negative (pink, thin wall with outer membrane); sensitivity in septic arthritis is only 50-70%.

Bleeding into a joint cavity, producing a blood-stained or frankly bloody effusion; causes include acute ligament or meniscal tears, fractures (especially tibial plateau), haemophilia, and anticoagulant therapy.

The high-molecular-weight polysaccharide that gives synovial fluid its viscosity and forms the 'string' in the viscosity test; degraded by bacterial and leucocyte hyaluronidase in septic arthritis, reducing viscosity.

The posterior or anterior iliac crest used as a donor site for autologous cancellous bone graft; complications include donor-site pain, numbness (lateral cutaneous nerve of the thigh), and rarely, bowel herniation through the graft defect.

A method using an external ring fixator with transosseous wires to gradually transport a bone segment through the dead space, regenerating bone by distraction osteogenesis; used for segmental bone defects >3 cm after sequestrectomy.

A shell of reactive new bone laid down by the elevated periosteum surrounding the sequestrum in chronic osteomyelitis; the presence of involucrum is a radiological marker of chronicity.

Four clinical parameters (non-weight-bearing, ESR >40, fever >38.5°C, WBC >12,000) used to distinguish septic arthritis from transient synovitis in the paediatric hip; all four criteria carry a >99% probability of septic arthritis.

The tactile sensation of reduced needle resistance as it passes through the joint capsule into the joint cavity, signalling that the needle tip has entered the synovial space and aspiration may commence.

A squamous cell carcinoma arising in a chronic sinus tract or long-standing ulcer, a rare but important late complication of chronic osteomyelitis with discharging sinus.

The flared region of a long bone between the diaphysis (shaft) and the growth plate (physis); the preferential site of haematogenous seeding due to sluggish capillary flow and absence of phagocytic endothelial cells.

A strain of S. aureus resistant to beta-lactam antibiotics including flucloxacillin; requires vancomycin or teicoplanin for treatment; increasingly important in hospital-acquired osteomyelitis.

A section of vascularised muscle (e.g., gastrocnemius for tibial defects) transposed to fill a dead space or cover an exposed bone surface, providing a blood supply to an avascular area and improving antibiotic delivery.

In synovial fluid analysis, a neutrophil (polymorphonuclear cell) percentage >90% with a WBC >50,000/μL is the diagnostic hallmark of septic arthritis; percentages between 50-90% are consistent with inflammatory arthritis.

The surgical removal or decompression of an infected focus (abscess, sequestrum, infected joint) to eliminate the reservoir of infection that cannot be sterilised by systemic antibiotics.

Progressive degeneration of articular cartilage and subchondral bone following an episode of septic arthritis, resulting from enzymatic cartilage destruction during the infection and ongoing mechanical load on a damaged joint surface.

Polymethylmethacrylate bone cement beads loaded with heat-stable antibiotics (gentamicin, tobramycin) that release high local concentrations at the infected site over weeks; used as a temporary dead-space filler before definitive bone grafting.

A technique used to identify and characterise crystals in synovial fluid; monosodium urate crystals (gout) are needle-shaped and negatively birefringent; calcium pyrophosphate crystals (pseudogout) are rhomboid and weakly positively birefringent.

Tuberculous osteomyelitis of the spine, classically affecting the lower thoracic and thoracolumbar junction, presenting as anterior vertebral body destruction, disc space loss, gibbus deformity, and cold abscess (which may track to form a psoas abscess).

A cold abscess in the psoas muscle, most commonly arising from Pott's disease of the lumbar spine; presents as a fluctuant groin swelling and may mimic an inguinal hernia.

A surgical procedure in chronic osteomyelitis in which infected, necrotic, and sclerotic bone is removed to create an open, shallow, saucer-shaped cavity that allows drainage and granulation tissue ingrowth.

A bacterial infection of a synovial joint, representing an orthopaedic emergency because pus causes rapid enzymatic and pressure-mediated destruction of articular cartilage within hours to days.

The surgical removal of the sequestrum (dead bone) in chronic osteomyelitis, an essential step in source control since avascular bone cannot be sterilised by antibiotics.

A piece of dead, avascular cortical bone in chronic osteomyelitis, radiologically denser than surrounding living bone, which serves as a nidus of infection inaccessible to antibiotics.

An abnormal epithelium-lined channel connecting a deep infected focus (sequestrum or abscess cavity) to the skin surface, characterised by chronic purulent discharge.

An anterior surgical approach to the hip between the tensor fasciae latae and sartorius/rectus femoris; the anterior approach to hip aspiration follows this interval, entering medial to the femoral artery.

A bedside qualitative test of synovial fluid viscosity — normal fluid pulled from a syringe forms a string >5 cm before breaking; septic or inflammatory fluid snaps short due to loss of hyaluronan.

A collection of pus between the periosteum and the bone cortex, formed when intraosseous pus in osteomyelitis strips the periosteum away from the cortex; its presence is an indication for surgical drainage.

The preferred route for knee joint aspiration — needle inserted 1 cm superior and 1 cm posterior to the superolateral border of the patella, directed toward the patellofemoral joint and suprapatellar pouch.

A synovial recess extending 3-4 cm above the patella under the quadriceps tendon, which fills with fluid in a knee effusion and provides the target cavity for the superolateral aspiration approach.

A viscous, hyaluronan-rich fluid secreted by type B synoviocytes that lubricates the joint and nourishes articular cartilage; normal fluid is clear, straw-coloured, and contains <200 white cells/μL.

Laboratory examination of fluid aspirated from a joint, including gross appearance, cell count and differential, Gram stain, culture, glucose, and protein — the gold standard for diagnosing septic arthritis.

A self-limiting inflammatory condition of the hip in children aged 3-10 years, likely post-viral, causing acute hip pain and antalgic gait; must be distinguished from septic arthritis — the hip effusion shows <5,000 WBC/μL on aspiration.

Synovial fluid with reduced transparency due to elevated leucocyte count, protein, or crystal content; turbidity suggests an inflammatory or infected effusion and contrasts with the clear appearance of normal or mildly non-inflammatory fluid.

An anterolateral surgical approach to the hip passing between the tensor fasciae latae and the gluteus medius, providing anterior capsule access for hip arthrotomy and open reduction of hip dislocations.

A standardised three-stage operative safety protocol (sign-in, time-out, sign-out) that verifies patient identity, procedure, site, allergies, antibiotic prophylaxis, and instrument/swab counts — mandatory for all operative procedures.