R | Basicmedical Key

radiation emission of electromagnetic impulses from a source; e.g. visible light, ultraviolet light, infrared light, X-rays, gamma rays

radiation damage premalignant and malignant skin lesions (e.g. Bowen’s disease, basal cell carcinoma and squamous cell carcinoma during later adult life) developing subsequent to long-term exposure to ultraviolet radiation (wavelength = 180–400 nm, especially in ultraviolet B range, [~ 290 nm wavelength], i.e. sunlight)

radiation therapy radiant energy used in treatment of disease

radiculitis inflammation of a spinal nerve root, at its exit from the intervertebral foramen/incorporation into the local nerve plexus

radiculopathy pathology of spinal nerve roots, due to nerve impingement, entrapment, inflammation or trauma; presents as focal pain (i.e. pain at spinal nerve root), referred pain (i.e. pain at a distal site within the dermatome of the affected spinal nerve) and/or pseudoclaudication, with associated sensory and motor neuropathies (see Table P9)

lower-limb radiculopathy radiculopathy affecting lumbar (L4, L5) and sacral (S1 and S2) spinal nerves (see Table P9); L5 and S1 roots are especially vulnerable to radiculopathy due to articulation of the flexible lumbar spine on the inflexible sacrum

radioactive isotopes; radioisotopes elements with unstable atomic nuclei; they decompose spontaneously by emitting radiation (electrons [β-particles], helium nuclei [α-particles] and radiation [γ-rays]); decomposition proceeds at a predictable rate until stability is reached (i.e. half-life); used diagnostically to visualize soft or specific tissues under radiography; e.g. iodine-131 (¹³¹I), carbon-12 (¹²C)

radioactivity spontaneous emission of gamma rays or subatomic particles from some elements or isotopes

radiodermatitis dermatitis induced by skin exposure to ionizing radiation

radiograph (common term: X-ray) ‘negative’ shadow image of tissues, produced by the passage of ionizing radiation through body tissue; the greater the density of the tissue, the greater the tissue absorption of X-ray, so that bones appear white (i.e. are radiopaque), soft tissues show as various shades of grey, in relation to their relative densities and air shows as black (i.e. is radiolucent); Table R1; see X-rays

Table R1 Common radiographic projections of the foot and ankle

Projection	Visualization
*Foot projections*
Dorsiplantar (DP) projection or anteroposterior (AP) view	Weight-bearing with the beam directed at 15 ° to the frontal plane, to eliminate distortion due to the angulation of the metatarsals and centred on the metatarsal shafts It is used to visualize the phalanges, metatarsophalangeal joints, the metatarsals and the midfoot
Lateromedial oblique projection	Weight-bearing with the beam angled at 45 ° to the lateral side of the sagittal plane and centred on the forefoot; or non-weight-bearing, with the beam vertical and foot everted so that the plantar surface is at 45 ° to the ground surface It is used to visualize the phalanges, metatarsals, metatarsocuneiform joints and sesamoids, but tends to give an elongated image of bony architecture
Mediolateral oblique projection	Weight-bearing with the beam angled between 25 and 45 ° to the medial side of the sagittal plane and centred on the forefoot It is used to visualize the first ray and associated structures, but tends to give an elongated image of bony architecture
Lateral projection	Weight-bearing or non-weight-bearing, with the beam angled at 90 ° to the lateral aspect of the foot and centred on the mid- or hindfoot It is used to visualize the profile of the whole foot, but obscures the midtarsal joint, due to superimposition of local structures
Digital projection	The lateromedial oblique projection is useful to visualize subungual exostoses, especially when the hallux (or affected toe) is raised up on a pad
Sesamoid projection or skyline projection	Weight-bearing, with the metatarsophalangeal joints dorsiflexed to 45 ° and the beam angled to be parallel to the ground surface on the sagittal plane, and centred on the plantar aspect of the forefoot It is used to visualize the relationship of the sesamoids with the head of the first metatarsal
*Tarsal and ankle projections*
Anteroposterior view	Weight-bearing with the beam angled at 90 ° to the frontal plane and the beam centred on the ankle joint Used to visualize the ankle mortise and the trochlear surface of the talus
Axial calcaneal projection	Weight-bearing with the beam angled at 45 ° to the posterior aspect of the sagittal plane with the beam centred on the hindfoot It is used to visualize calcaneal trauma
Harris–Beath projection	Similar to the axial calcaneal projection, but the patient is positioned as if making a ski-jump, that is, weight-bearing with the foot dorsiflexed at the ankle and the beam angled at 45 ° to the posterior aspect of the sagittal plane with the beam centred on the ankle It is used to visualize the subtalar joint where talar fusions are suspected

radiographic assessment Tables R2 and R3, Figure P2

Table R2 Radiograph assessment – the logical, sequential and consistent method for interpreting a radiograph

Feature	Characteristics
*The technical quality of the radiograph*
The quality of the image	Detail of structures Contrast, allowing a clear profile of individual structures Density variation so that all features of the image are clearly defined
*Diagnostic review of the image: ABCDS approach*
Alignment	Bone alignment, apposition and angulation, joint congruity The shape of each osseous component is view-dependent: Lateral view: talus, calcaneum, navicular, first metatarsal Dorsoplantar view: foot type (supinated/pronated), calcaneum, navicular, cuneiforms, fifth metatarsal, first metatarsal, hallux, phalanges Mediolateral oblique view: cuboid, navicular, lesser metatarsals, first metatarsal Axial view: sesamoids
Architecture	Internal architecture: structure of cortex and trabeculae External architecture: integrity of bone margins, subperiosteal surfaces, subchondral bone plate, fracture, sequestrum, involucrum, cloaca, accessory ossicles, Charcot joint, osteolysis, osteoarthritis, coalitions, osteochondritis, rheumatoid disease, tumours
Bone mineralization	Increased density (sclerosis/eburnation), decreased density (osteoporosis, osteopenia, active osteomyelitis)
Cartilage space	Increased or decreased joint spaces
Distal to proximal examination	The consistent method of radiograph evaluation
Soft-tissue evaluation	Calcification or ossification of soft-tissue structures, arterial calcification, gouty tophus, oedema, infection

Table R3 Radiographic charting

Angle	Normal range	Clinical features
Boehler’s angle	20–40 °	Angle between a line drawn from the superior–posterior aspect of the calcaneum and a line drawn from the anterior dorsal aspect of the calcaneum, on a lateral radiograph
Calcaneal inclination angle		Angle between a line drawn to the undersurface of the calcaneum (on a lateral radiograph) and the support surface; the greater the calcaneal angle, the more supinated the rearfoot; the lower the angle, the more pronated the rearfoot
CYMA line		Lazy S-shaped line that forms the midtarsal joint (talonavicular and calcaneocuboid joints) on a lateral radiograph; the smoothness of the CYMA line is lost in the excessively pronated or supinated foot
Hallux abductus angle	0–20 °	Angle between the longitudinal bisection of the first metatarsal and the longitudinal bisection of the proximal phalanx of the hallux (on a dorsiplantar radiograph)
Hallux interphalangeal angle	0–10 °	Angle between the longitudinal bisection of the proximal phalanx of the hallux and the longitudinal bisection of the distal phalanx of the hallux (on a dorsiplantar radiograph)
Lesser tarsal angle	10 °	Angulation between the longitudinal bisection of the rearfoot and a longitudinal bisection of the lesser metatarsals (on a dorsiplantar radiograph). This angle is increased in a pronated foot, and decreased in a supinated foot
Metatarsus adductus angle	10–20 °	Angle between the longitudinal axis of the second metatarsal and a line perpendicular to a line drawn from reference points on the medial cuneiform to the cuboid (on a dorsiplantar radiograph)
Metatarsus adductus primus angle	8–10 °	Angulation between the bisections of the first and second metatarsal (on a dorsiplantar radiograph) >12 ° indicates pathology in a rectus foot; 10 ° indicates pathology in an adductus foot
Parallel pitch lines (PPLs)		Lines drawn on a lateral radiograph of the foot: see Figure P2 PPL 1: a line drawn at the inferior margin of the calcaneum that joins the anterior tubercle and the medial tubercle of the posterior tuberosity of the calcaneum PPL 2: a line drawn parallel to PPL 1 between the bursal projection (or posterior–superior prominence) at the superior margin of the calcaneum and the posterior lip of the talar articular facet Divergent PPLs are characteristic of a foot with Haglund’s deformity
Proximal articular set angle (PASA)	0–8 °	Angle created between a line perpendicular to the longitudinal bisection of the first metatarsal and a line drawn to represent the effective articular cartilage of the head of the first metatarsal (on a dorsiplantar radiograph)
Superior calcaneal tuberosity angle		Angle between the posterior tuberosity of posterior margin of the calcaneum and the anterior and medial tuberosities on the inferior margin of the calcaneum (on a lateral radiograph)
Talar declination angle		Angle between the longitudinal bisection of the talus and the support surface (on a lateral radiograph); the nearer to the horizontal, the more supinated the rearfoot; the greater the declination of the talus, the more pronated the rearfoot (on a dorsiplantar radiograph)
Tibial sesamoid position		Relationship of the tibial sesamoid and the longitudinal bisection of the first metatarsal; the tibial sesamoid is normally medial to the first metatarsal bisection; christa erosion is likely where the tibial sesamoid abuts or crosses to the lateral part of the first metatarsal (on a dorsiplantar radiograph)
Total angle	<75 °	Sum of the calcaneal inclination angle and superior calcaneal tuberosity angle see Figure P2

Biomechanical evaluation of plain radiographs is primarily made from dorsiplantar

radiographic assessment as part of a biomechanical evaluation transverse-plane biomechanical analysis from dorsoplantar foot views (anteroposterior projections); sagittal-plane biomechanical analysis from lateral foot views Table R3

radiographic projections of the foot and ankle Table R1

radiographic techniques to view the foot and ankle Table R1

radioimmunoassay reaction of a radioisotope-labelled agent with specific antibodies; allows light microscopy visualization of antigen–antibody complexes in tissue samples

radiolucent offering minimal obstruction to passage of X-rays

radiopaque relatively impermeable to X-rays

radiotherapy use of electromagnetic or particulate (alpha and beta) radiation to treat disease

ram’s horn nail see nail, ostler’s

ramus primary division of a nerve

random blood glucose; RBG amount of glucose dissolved in circulating blood, recorded irrespective of when food was last ingested; two consecutive RBG recordings >10 mmol/L are strongly indicative of diabetes mellitus

range of motion natural amount of movement within a joint

ranitidine; Zantac agent that prevents secretion of excess gastric acid; it reduces metabolism of local anaesthetic agents by liver enzymes

rarefaction expansion; becoming less dense

rate frequency of an event/process in relation to a fixed standard, usually expressed as a ratio i.e. a/b

ratio index; calculated comparison of two events/factors, i.e. a/b; ratio of <1 indicates b>a; ratio of >1 indicates b<a; where there is no difference, ratio = 1

ankle–brachial ratio see ankle–brachial index

heart rate ratio see manoeuvre, Valsalva’s

ray forefoot segment, composed of phalanges (of one toe), associated metatarsal, and overlying soft tissues

ray block see anaesthesia; injection

ray excision surgical removal of a toe and metatarsal; usually undertaken as a salvage procedure in digital or metatarsal osteomyelitis

Raynaud’s disease; RD see disease, Raynaud’s (Table R4)

Table R4 Disorders associated with Raynaud’s disease

Raynaud’s-associated condition	Examples
Immune-related disease states	Scleroderma (Raynaud’s disease affecting 95% of patients) Systemic lupus erythematosus (10–45% of cases) Mixed connective tissue disease (85% of patients) Sjögren’s syndrome (33% of patients) Rheumatoid arthritis (10% of patients) Cryoglobulinaemias
Drug-induced Raynaud’s	Antimigraine compounds Cytotoxic drugs Beta-blockers (especially non-selective beta-blockers)
Occupation-related	Vibration exposure (50% of workers) Cold injury (frozen-food packers) Polyvinyl chloride exposure
Obstructive vascular disease	Atherosclerosis Microemboli Thrombangiitis obliterans Thoracic outlet syndrome