How to Read a Hip X-Ray — Systematic Approach

Why a Systematic Approach Matters

The hip radiograph is one of the most frequently requested and most information-rich plain films in orthopaedic practice. A poorly interpreted hip X-ray leads to missed diagnoses, inappropriate management, and avoidable harm. The key to reliable interpretation is a reproducible, systematic approach — examining every film in the same sequence regardless of the presenting complaint, ensuring that incidental findings and subtle pathology are not missed. This article presents a step-by-step framework for reading the hip X-ray, from assessing film quality through to identifying specific pathological patterns.

Standard hip radiograph views: (1) AP pelvis (anteroposterior pelvic view — both hips on one film; the standard initial view for all hip pathology; allows comparison between sides); (2) Lateral hip (true lateral or frog-leg lateral — demonstrates the femoral head, neck, and proximal femur in a second plane); (3) Cross-table lateral (for trauma — avoids moving the injured leg; the X-ray beam passes horizontally across the table); always review BOTH views before interpreting the hip; the AP pelvis provides broad pelvic ring, acetabular, and bilateral hip information; the lateral reveals anterior/posterior relationships of the femoral head and neck, and is essential for assessing femoral neck fractures, slipped upper femoral epiphyses (SUFE), and cam deformity
The systematic approach — 10 steps: (1) Film adequacy and patient identification; (2) Bony alignment and symmetry; (3) Shenton`s line; (4) Neck-shaft angle; (5) Acetabular assessment (depth, version, inclination, coverage); (6) Femoral head assessment (shape, sphericity, density, congruency); (7) Joint space; (8) Periarticular structures (trochanters, lesser trochanter, pubic rami, ischium, sacrum); (9) Soft tissues; (10) Named lines and angles

Step 1 — Film Adequacy & Patient Identification

Parameter	What to Check	Adequate Film Criteria	Consequence of Poor Quality
Patient identification	Name, date of birth, date of film; left/right marker	Correct patient; date confirmed; R/L marker present	Wrong-side surgery is a catastrophic never event; always check the R/L marker AND the clinical context
Rotation	The obturator foramina should be symmetric; the coccyx should be aligned with the pubic symphysis midline; the iliac crests should be symmetric; slight internal rotation of the legs (10–15°) is standard positioning for AP pelvis to profile the femoral neck	Symmetric obturator foramina; coccyx overlying the symphysis midline; symmetric iliac wings	Rotation alters the apparent neck-shaft angle and makes Shenton`s line unreliable; a rotated pelvis may make a normal hip appear dysplastic or vice versa
Tilt (pelvic tilt)	The distance from the top of the pubic symphysis to the coccyx tip should be 1–3 cm (women) or 0–2 cm (men); excessive tilt alters acetabular version appearance	Symphysis-to-coccyx distance within normal range; neutral pelvic tilt	Posterior pelvic tilt = acetabulum appears retroverted (crossover sign may be artifactually positive); anterior tilt = acetabulum appears anteverted; pelvic tilt is the most common source of error in acetabular version assessment
Exposure	Bony cortices clearly visible; trabecular pattern visible within the femoral head and acetabulum; not overexposed (washed out) or underexposed (too dense)	Adequate penetration to see trabecular detail in the femoral head AND the pelvis	Subchondral bone and trabecular detail are lost in poor exposure — early AVN, stress fractures, and subtle bone lesions are missed
Femoral rotation	Lesser trochanter should be visible as a small medial profile; minimal lesser trochanter profile = correct neutral to slight internal rotation; large lesser trochanter profile = external rotation (common in hip fractures)	Small/minimal lesser trochanter profile = neutral/internal rotation — standard for AP pelvis	External rotation (visible large lesser trochanter) foreshortens the femoral neck on AP view, making undisplaced fractures harder to see and altering the apparent neck-shaft angle

Step 2 — Alignment & Symmetry

Overall alignment: assess the pelvis as a ring — the two innominate bones and the sacrum form a continuous ring; any disruption of this ring is significant; check the sacroiliac joints (should be symmetric; fusion or widening suggests sacroiliitis — ankylosing spondylitis; widening in trauma suggests SI joint disruption); check the pubic symphysis (normal width <5 mm in adults; >5 mm = symphyseal diastasis; >10 mm = significant pelvic ring disruption; in pregnancy, up to 9 mm is physiological); assess the pubic rami (fractures of the superior and inferior pubic rami are common in low-energy pelvic fractures in the elderly)
Bilateral comparison: always compare the symptomatic hip to the asymptomatic side; bilateral symmetry allows detection of subtle unilateral abnormalities (asymmetric joint space, asymmetric femoral head shape, asymmetric offset) that would be difficult to recognise without comparison

Step 3 — Shenton`s Line

Shenton`s line: a continuous arc drawn from the inferior border of the femoral neck, sweeping medially to become continuous with the superior border of the obturator foramen; in a normal hip, this arc is smooth, unbroken, and graceful; a broken or disrupted Shenton`s line indicates: (1) femoral neck fracture (even if the fracture line is not clearly visible on the AP view, a broken Shenton`s line alerts the clinician to the diagnosis); (2) hip dislocation (the femoral head is no longer congruent in the acetabulum); (3) DDH (developmental dysplasia of the hip — the femoral head is subluxed or dislocated superolaterally, breaking the line); (4) coxa vara (the neck-shaft angle is reduced, dropping the lesser trochanter and disrupting the line); Shenton`s line should be assessed on every hip X-ray as a standard step

Step 4 — Neck-Shaft Angle (Collodiaphyseal Angle)

Measurement	Normal Value	Abnormal (Low)	Abnormal (High)
Neck-shaft angle (NSA)	Adults: 125–135°; children: wider (140–150° at birth, reduces with growth)	Coxa vara: NSA <120°; the femoral neck is in more varus than normal; Shenton`s line is broken; limb shortening; Trendelenburg gait; causes: congenital, Paget`s, rickets, post-fracture malunion, Perthes`; coxa vara reduces the lever arm of the hip abductors → Trendelenburg gait	Coxa valga: NSA >140°; the femoral neck is in more valgus; associated with hip dysplasia; reduces the mechanical advantage of the abductor muscles; increases joint reaction force
Anteversion	Femoral neck anteversion normal = 10–15° in adults; assessed on CT scanogram (femoral neck axis vs knee epicondyle axis); on plain AP X-ray — cannot directly measure anteversion; external rotation of the leg profiles the femoral neck better on AP (used clinically in SUFE)	Increased anteversion (>20°) = in-toeing; associated with cerebral palsy; reduced anteversion/retroversion = out-toeing; rotational deformity cannot be reliably assessed on plain AP — requires CT	N/A

Step 5 — Acetabular Assessment

Parameter	How to Measure	Normal	Abnormal & Clinical Significance
Acetabular index (AI) — Hilgenreiner`s angle	In children: the angle between Hilgenreiner`s line (horizontal line through both triradiate cartilages) and a line from the triradiate cartilage to the lateral edge of the acetabulum; measures the slope of the acetabular roof	Newborn: <30°; 1 year: <25°; 2 years: <20°; progressive decrease with normal development	AI >30° at any age suggests acetabular dysplasia; a steep acetabular roof indicates inadequate coverage of the femoral head; seen in DDH, neuromuscular conditions (CP — acetabular dysplasia from reduced joint loading)
Lateral centre-edge angle (LCEA — Wiberg angle)	In adults: the angle between a vertical line through the centre of the femoral head and a line from the centre of the femoral head to the lateral edge of the acetabular sourcil (weight-bearing zone); measures lateral coverage of the femoral head	Normal: ≥25°; borderline: 20–25°; dysplastic: <20°	LCEA <20° = acetabular dysplasia — the femoral head is inadequately covered laterally; causes early OA from edge loading; indication for periacetabular osteotomy (PAO — Ganz osteotomy) in symptomatic adults; LCEA >40° = acetabular overcoverage (pincer morphology — FAI)
Anterior centre-edge angle (ACEA)	Measured on the false profile view (a lateral oblique view at 65°); vertical line through the centre of the femoral head and a line from the centre to the anterior acetabular rim; measures ANTERIOR coverage	Normal: ≥25°; <20° = anterior dysplasia	Anterior undercoverage predisposes to anterior subluxation and anterior labral tears; not assessable on standard AP view — false profile view required
Acetabular version (crossover sign)	On a correctly positioned AP pelvis (neutral tilt): normally the anterior acetabular wall (inner line) runs medial to the posterior acetabular wall (outer line) throughout; a `crossover sign` is POSITIVE when the anterior wall line crosses LATERAL to (over) the posterior wall line superiorly — indicating acetabular retroversion (the acetabulum faces posteriorly rather than anteriorly-laterally); the `ischial spine sign` (prominent ischial spine visible medially within the pelvic brim) is a secondary sign of retroversion; the `posterior wall sign` (the posterior wall passes medial to the centre of the femoral head) indicates posterior undercoverage	Normal: anterior wall medial to posterior wall throughout; no crossover; ischial spine not prominent; posterior wall passes through or lateral to the centre of the femoral head	Positive crossover sign = acetabular retroversion = pincer-type FAI; the anteriorly projecting retroverted acetabulum impinges on the femoral head-neck junction in flexion/IR; associated with deep hip pain, restricted flexion/IR, and anterior labral tears; NB: pelvic tilt MUST be correct before interpreting the crossover sign (posterior tilt = artifactual retroversion)
Sourcil (weight-bearing zone)	The subchondral sclerosis of the acetabular roof — the `sourcil` (French for `eyebrow`); should be horizontal and uniform; the medial edge should reach the medial edge of the femoral head; the lateral edge should have a sharp `lateral sourcil angle`	Horizontal, uniform subchondral density; extends adequately over the femoral head	Steep sourcil (slopes laterally) = dysplasia; non-uniform sourcil (focal sclerosis or cyst) = OA or avascular necrosis of the acetabular roof; loss of the sharp lateral angle = loss of lateral coverage

Step 6 — Femoral Head Assessment

Feature	Normal	Abnormal	Diagnosis
Sphericity	Smooth, round arc — the femoral head should form a portion of a perfect sphere; the articular surface should be convex and smooth	Loss of sphericity; flattening (coxa plana); irregular outline	Perthes` disease (femoral head flattening — `mushroom deformity` — coxa plana); AVN (segmental collapse — `crescent sign`); OA (flattening of superior femoral head from wear); cam morphology (non-spherical head-neck junction)
Alpha angle (cam morphology)	Measured on axial or Dunn lateral view: a circle is drawn fitting the femoral head; a line from the centre of the femoral head to the centre of the femoral neck; a second line from the centre of the head to the point where the bone exits the circle (the cam bump); the angle between these lines = alpha angle	Normal: <55°; borderline: 55–60°; cam morphology: >60°	Cam-type FAI (femoroacetabular impingement) — the non-spherical femoral head-neck junction (cam bump) jams into the acetabulum in flexion/IR, shearing the labrum and cartilage from the acetabular rim; best seen on Dunn lateral (45° or 90° flexion lateral); on AP view, the `pistol grip` deformity of the femoral head-neck junction is visible
Bone density within the femoral head	Uniform trabecular pattern throughout the femoral head and neck	Sclerosis (white, dense area); lysis (dark area); subchondral collapse (crescent sign); mixed density	AVN: subchondral crescent sign (a thin radiolucent line below the subchondral bone = subchondral fracture = Ficat Stage III); sclerosis surrounding a lucent necrotic segment; late: femoral head collapse and flattening; Transient osteoporosis of the hip: diffuse osteopenia of the femoral head and neck on X-ray (best seen on MRI as STIR high signal marrow oedema); Mets/tumour: focal lytic or sclerotic lesion within the femoral head or neck
Head-neck offset	The femoral head should be wider (more prominent) anteriorly than the femoral neck — creating an `offset`; measured as the difference between the radius of the femoral head and the radius of the femoral neck on the lateral view	Offset ratio <0.17 = reduced offset; cam deformity	Reduced head-neck offset = cam FAI; the lack of offset means the non-spherical head-neck junction contacts the acetabular rim in flexion; offset restoration (femoral osteochondroplasty / cam resection) is the surgical treatment

Step 7 — Joint Space Assessment

Normal joint space: the hip joint space (the radiolucent gap between the femoral head and the acetabular sourcil) should be 4–5 mm in young adults; it should be uniform (equal width medially and superiorly); the joint space represents the combined thickness of the articular cartilage on both the femoral head and acetabular surfaces; since articular cartilage is not visible on plain X-ray, joint space narrowing is used as a surrogate marker for cartilage loss
Patterns of joint space loss (Kellgren-Lawrence grading is used for OA, but pattern of loss gives additional diagnostic information):

Pattern of Joint Space Loss	Diagnosis	Additional Features
Superior (superolateral) joint space loss	Primary osteoarthritis (most common pattern); the weight-bearing zone is the superolateral aspect of the hip — OA preferentially destroys this area first; the femoral head migrates superolaterally	Subchondral sclerosis (eburnation); osteophytes (femoral head and acetabular rim); subchondral cysts; femoral head superolateral migration
Medial joint space loss (axial migration)	Inflammatory arthritis (rheumatoid arthritis — characteristically causes axial/medial migration of the femoral head; protrusio acetabuli — the femoral head protrudes medially through the acetabular floor); also secondary OA after DDH	Uniform joint space loss (RA — all compartments lost equally); periarticular osteoporosis; protrusio (femoral head crosses the ilioischial line); bilateral and symmetric in RA
Concentric (uniform) joint space loss	Inflammatory arthritis (RA, ankylosing spondylitis); septic arthritis (rapid concentric loss); AVN (late); DDH secondary OA	Inflammatory arthritis: periarticular osteoporosis without osteophytes; septic arthritis: very rapid loss + periarticular osteoporosis; ankylosing spondylitis: bilateral, may progress to bony ankylosis
Inferior joint space loss	Rare; inferior femoral head OA; inferior osteophytes	Less common pattern; may be associated with vascular necrosis of the inferior femoral head

Kellgren-Lawrence Grade	Radiological Features	Clinical Correlation
Grade 0	Normal — no radiological features of OA	No OA
Grade 1	Possible osteophytes only; joint space normal; doubtful narrowing	Equivocal OA
Grade 2	Definite osteophytes; possible joint space narrowing; no subchondral sclerosis	Mild OA — conservative management; analgesics; physiotherapy
Grade 3	Moderate joint space narrowing; subchondral sclerosis; osteophytes; possible deformity	Moderate OA — consider specialist referral; injection therapy; weight loss
Grade 4	Severe joint space narrowing (bone-on-bone); marked osteophytes; subchondral sclerosis; cysts; gross deformity of femoral head	Severe OA — THA if functionally limited; X-ray grade alone is NOT the indication for surgery (must correlate with symptoms)

Step 8 — Periarticular Structures

Greater trochanter: avulsion fractures of the greater trochanter (abductor avulsion — gluteus medius and minimus); heterotopic ossification around the greater trochanter; trochanteric bursitis (not visible on X-ray but can show a soft tissue density); trochanteric stress fractures (rare); check for calcific tendinitis over the greater trochanter
Lesser trochanter: prominence of the lesser trochanter on the AP view indicates external rotation of the femur; avulsion of the lesser trochanter occurs from the pull of the iliopsoas tendon — in young athletes, this is a typical sports injury; in adults over 40, lesser trochanter avulsion is a pathological fracture through metastatic bone disease until proven otherwise — a spontaneous lesser trochanter avulsion in an adult IS A RED FLAG for malignancy (typically metastatic carcinoma, most commonly prostate or breast; or myeloma) and requires urgent staging CT and MRI
Pubic rami: pubic rami fractures are the most common insufficiency fracture in elderly osteoporotic women; often bilateral (anterior pelvic ring fracture pattern); may be associated with sacral fractures (H-pattern sacral fracture in pelvic insufficiency); look for superior AND inferior rami fractures; always assess the AP pelvis for pubic rami fractures when examining hip X-rays in the elderly — these fractures can be extremely subtle and are easily missed
Ischium: ischial tuberosity avulsion (hamstring origin) — adolescents; subchondral insufficiency fracture of the ischium (elderly); ischial osteomyelitis (rare)
Sacrum and sacroiliac joints: check for sacral fractures (Denis Zone I, II, III — see pelvic ring article); SI joint widening (traumatic disruption; sacroiliitis in ankylosing spondylitis — bilateral symmetric SI joint sclerosis and eventual fusion `bamboo spine`); SI joint sclerosis on one side = osteitis condensans ilii (benign; pregnancy-related; triangular sclerosis on the iliac side only)

Step 9 — Soft Tissues

Fat planes: the obturator internus fat stripe is visible on a well-exposed AP pelvis as a fat lucency medial to the hip joint; effacement (obliteration) of this fat stripe suggests a hip joint effusion or pericapsular soft tissue swelling (septic arthritis, haemarthrosis, trauma); in paediatric practice, the `teardrop distance` (distance between the base of the `teardrop` — formed by the medial acetabular wall and the medial wall of the obturator foramen — and the medial cortex of the femoral neck) is used to assess for hip effusion; an increased teardrop distance suggests effusion
Calcifications: iliopectineal bursa calcification (from gout, CPPD, or calcific tendinitis); trochanteric bursa calcification; loose bodies within the joint (os acetabuli; osteochondral loose bodies from synovial chondromatosis — multiple calcified loose bodies within the joint space = synovial chondromatosis until proven otherwise); calcification within the femoral head (rare — dystrophic calcification after AVN or tumour)
Gas within the joint: pneumarthrosis — air within the hip joint; may be iatrogenic (post-injection), traumatic, or rarely from a gas-producing infection; vacuum phenomenon (gas in the joint space — especially the hip — is common in degenerative joints; it represents nitrogen gas drawn into the space during traction/positioning)

Step 10 — Key Lines, Angles & Measurements Summary Table

Line / Angle / Measurement	How Drawn / Measured	Normal Value	Abnormal = Diagnosis
Shenton`s line	Continuous arc — inferior femoral neck to superior obturator foramen	Smooth, unbroken arc	Broken = femoral neck fracture, hip dislocation, DDH, coxa vara
Neck-shaft angle (NSA)	Angle between femoral neck axis and femoral shaft axis	125–135° (adults)	<120° = coxa vara; >140° = coxa valga
Lateral centre-edge angle (LCEA / Wiberg)	Vertical line through femoral head centre → line to lateral acetabular sourcil edge	≥25°	<20° = dysplasia; >40° = overcoverage (pincer FAI)
Acetabular index (AI / Hilgenreiner)	Angle between Hilgenreiner`s line and acetabular roof line (children)	<30° (newborn); <20° (2 years)	>30° = acetabular dysplasia (DDH)
Alpha angle (cam morphology)	On Dunn lateral view: angle from femoral head centre to neck axis vs centre to cam bump	<55°	>60° = cam FAI; 55–60° = borderline
Crossover sign (acetabular version)	Anterior wall line crosses LATERAL to the posterior wall line superiorly on AP pelvis	Negative (anterior wall medial throughout)	Positive = acetabular retroversion = pincer FAI (check pelvic tilt first)
Hilgenreiner`s line	Horizontal line through both triradiate cartilages (children)	Both femoral head ossific nuclei at or below this line	Femoral head ossific nucleus above = dislocated hip (DDH)
Perkin`s line	Vertical line drawn perpendicular to Hilgenreiner`s through the lateral edge of the acetabulum	Ossific nucleus in the inner lower quadrant	Ossific nucleus in outer quadrant = subluxed/dislocated (DDH)
Ilioischial line (Köhler`s line)	A straight line tangential to the inner surface of the ilium and the inner surface of the ischium; forms the medial wall of the acetabulum	Femoral head medial margin does not cross this line	Femoral head crossing ilioischial line = protrusio acetabuli (medial migration — RA, Paget`s, Otto pelvis — idiopathic protrusio)
Iliopectineal line	Line along the pectineal eminence — marks the anterior column of the acetabulum; disruption = anterior column acetabular fracture	Intact continuous line	Disrupted = anterior column acetabular fracture; both lines disrupted = complex fracture
Symphysis pubis width	Width of the pubic symphysis gap	<5 mm adults; up to 9 mm in pregnancy	>5 mm = diastasis; >10 mm = significant pelvic ring disruption (APC II/III)
Teardrop (Köhler`s teardrop)	The `U`-shaped radiodense structure formed by the medial acetabular floor and the medial wall of the obturator foramen on AP pelvis; its lateral limb = medial acetabular wall	Symmetric bilaterally; clearly visible as a `teardrop` shape	Medialisation of teardrop = protrusio acetabuli; asymmetry = acetabular trauma; used as reference in THA (cup position should not violate the medial wall of the teardrop)

Common Conditions — Radiological Pattern Recognition

Condition	Key Radiological Features on Hip X-Ray	Memory Aid
Osteoarthritis (OA)	Superior joint space loss; subchondral sclerosis (eburnation); osteophytes (femoral head, acetabular rim, inferior femoral head — `femoral head collar`); subchondral cysts; femoral head superolateral migration	LOSS: Loss of joint space, Osteophytes, Sclerosis, Subchondral cysts
Rheumatoid arthritis (RA)	Concentric (uniform) joint space loss; periarticular osteoporosis; NO osteophytes (early); axial/medial migration; protrusio acetabuli in severe disease; bilateral and symmetric; may see erosions	Uniform loss + osteoporosis + NO osteophytes + medial migration = RA
Avascular necrosis (AVN)	Ficat stages: I = normal X-ray (MRI positive); II = sclerosis or lysis in the femoral head (subchondral); III = crescent sign (subchondral fracture — thin radiolucency below the subchondral plate); IV = femoral head collapse (flattening of the articular surface); V = secondary OA (joint space loss); the `crescent sign` is pathognomonic of impending collapse	Crescent sign = subchondral fracture = Ficat III = impending collapse → THA
Developmental dysplasia of hip (DDH) — adult	LCEA <20°; steep acetabular roof; shallow acetabulum; superolateral femoral head subluxation (broken Shenton`s line); secondary OA changes (superolateral joint space loss, osteophytes at the uncovered femoral head); false acetabulum may form superolaterally where the femoral head has been resting	Low LCEA + steep sourcil + broken Shenton`s = DDH
Cam FAI	Non-spherical femoral head-neck junction; `pistol grip` deformity on AP view (bony prominence at the anterosuperior head-neck junction); alpha angle >60° on Dunn lateral; reduced head-neck offset; associated superior acetabular cartilage damage and labral tears (on MRI)	Pistol grip deformity + alpha >60° = cam FAI; young active male (most common); arthroscopic or open cam resection
Pincer FAI	Positive crossover sign (retroversion); LCEA >40° (overcoverage); deep acetabulum (coxa profunda); os acetabuli (ossicle at the anterosuperior acetabular rim — from repetitive impingement avulsion); posterior wall sign negative; os acetabuli and acetabular version are the key X-ray features	Positive crossover sign + LCEA >40° + os acetabuli = pincer FAI; middle-aged active female (most common)
Perthes` disease (children)	Early: increased density of femoral head (sclerosis); widened joint space (effusion); later: fragmentation of femoral head; flattening (coxa plana); eventually: healing with variable head deformity; classification — Catterall (I–IV — extent of head involvement); Herring lateral pillar (A/B/C — height of lateral pillar); `sagging rope sign` (crescentic radiolucency in the subchondral bone)	Flat dense sclerotic fragmented femoral head in a child 4–10 years = Perthes`; Herring B or B/C = surgical containment (varus osteotomy)
SUFE (Slipped upper femoral epiphysis)	Widening and irregularity of the proximal femoral physis; the femoral epiphysis slips posteriorly and medially (inferiorly on AP view); on AP view: `Klein`s line` (a line drawn along the superior surface of the femoral neck should intersect the epiphysis by approximately 20% — if it does not intersect, or intersects less than normal, the epiphysis has slipped); on lateral view: the posterior slip is most evident; the `ice cream scoop falling off the cone` description	Klein`s line failure to intersect epiphysis = SUFE; obese male adolescent 10–16 years; urgent stabilisation (percutaneous pin fixation in situ); manipulate ONLY in acute unstable SUFE — risk of AVN
Femoral neck fracture	Disruption of Shenton`s line; fracture line through the femoral neck; loss of trabecular alignment (Garden alignment indices); impaction (valgus impacted = Garden I — subtle); displacement (Garden III/IV — obvious); cortical step at the inferior femoral neck; Garden alignment: normal trabeculae in the femoral head run at 160° to the femoral neck axis (Ward`s trabecular index); in Garden I, the medial trabeculae of the head are malaligned with the pelvis (misalignment despite apparent impaction)	Always check Shenton`s line for subtle undisplaced femoral neck fractures in elderly patients with hip pain after a fall; if X-ray negative but clinical suspicion high → MRI (STIR — bone marrow oedema positive within 24 hours)
Intertrochanteric fracture	Fracture line extending from the greater to lesser trochanter; extracapsular (distal to the capsular insertion at the intertrochanteric line); variable comminution; classify by AO/OTA or Evans system; greater trochanter fragment; lesser trochanter avulsed separately in unstable patterns; loss of medial cortical buttress (calcar) = unstable = reverse oblique	Extracapsular = DHS or cephalomedullary nail; unstable patterns (reverse oblique, subtrochanteric extension) = long cephalomedullary nail

Post-Arthroplasty Hip X-Ray Assessment

Parameter	Normal / Acceptable	Concerning / Abnormal	Clinical Significance
Acetabular cup inclination (abduction angle)	Measured on AP pelvis as the angle between the cup rim and the horizontal; target: 40° ± 10° (30–50°); the `safe zone` of Lewinnek	>50° (excessively vertical / `steep cup`) = increased dislocation risk (superior dislocation); increased edge loading on the polyethylene; increased wear; <30° (horizontal cup) = posterior impingement; edge loading medially	Malpositioning is the most common cause of early THA dislocation; revision for recurrent dislocation addresses cup orientation
Cup anteversion	Target: 15° ± 10° (5–25°) of anteversion; cannot be accurately measured from AP film alone; requires lateral view or CT; on AP film — if the cup opening ellipse is visible anteriorly (the anterior opening is visible), the cup is anteverted; if posteriorly visible = retroverted	Cup retroversion = posterior dislocation risk; cup excessive anteversion = anterior dislocation risk; combined anteversion (stem + cup) should total 40° ± 10°	CT is the definitive assessment for cup version post-THA
Femoral stem alignment	Stem should be in neutral or slight valgus within the femoral canal; the stem axis should parallel the medullary canal axis; collar (if present) should be flush with the calcar	Varus stem: tip contacts the lateral cortex; risk of periprosthetic fracture; suboptimal fixation in cementless stems; may indicate undersized stem or abnormal femoral anatomy	Calcar resorption in cementless stems = normal stress shielding; diaphyseal fixation zone integration (spot welds)
Cement mantle quality	Uniform white cement mantle ≥2–3 mm thickness circumferentially; no voids, cracks, or thin areas; Barrack grading: A (white-out — all interfaces); B (slight radiolucency); C (>50% radiolucency); D (massive defect/debonding)	Barrack C or D cement mantle = increased risk of aseptic loosening; cement cracks = fracture and fatigue failure; cement radiolucencies at the cement-bone interface (>2 mm wide progressive) = loosening	Bone-cement interface radiolucency: non-progressive thin lucency = fibrous membrane (may be stable); progressive widening = loosening; localised lucency at the tip = stem toggle
Leg length	The lesser trochanters should be at the same height bilaterally (as a reference); templating pre-operatively identifies the target leg length restoration	Leg length discrepancy (LLD) >1 cm = symptomatic (limp, back pain, nerve stretch — sciatic nerve); LLD is one of the most common causes of patient dissatisfaction after THA	Measure from lesser trochanter to ischial tuberosity (or teardrop) on both sides as a reproducible reference; pre-operative templating reduces LLD risk
Osteolysis / loosening	No radiolucency at implant-bone or cement-bone interfaces; no periimplant lytic lesions; stable implant position over serial films	Progressive radiolucency (>2 mm, progressive) = aseptic loosening; `balloon` osteolysis = focal expansile lytic lesions around acetabular cup or femoral stem from polyethylene wear debris (osteoclastic osteolysis from particle disease); migration of the cup (change in cup inclination or position on serial films) = loosening	Aseptic loosening is the most common cause of THA revision; serial X-rays every 5 years (or sooner if symptoms develop) are standard follow-up for well-functioning THA

Exam Pearls — High-Yield Hip X-Ray Facts

Shenton`s line: broken = femoral neck fracture / hip dislocation / DDH / coxa vara; assess on EVERY hip film; if subtle fracture suspected and X-ray negative → MRI STIR within 24 hours
LCEA (Wiberg angle): <20° = dysplasia → PAO (periacetabular osteotomy) if symptomatic; >40° = overcoverage (pincer FAI); the most important single measurement in adult hip dysplasia assessment
Crossover sign: positive = acetabular retroversion = pincer FAI; BUT always check pelvic tilt (symphysis-to-coccyx distance); posterior tilt = artifactual positive crossover; the ischial spine sign and posterior wall sign are supporting features
Alpha angle >60° on Dunn lateral = cam FAI; `pistol grip` deformity on AP; young active male; anterior-superior acetabular cartilage and labral damage from shear in flexion/IR
AVN crescent sign: subchondral radiolucent line = Ficat III = subchondral fracture = impending collapse; X-ray-positive AVN with crescent sign → THA; early AVN (X-ray normal) → MRI STIR: T1 dark + STIR bright + double line sign on T2 = pathognomonic
Lesser trochanter avulsion in adult (>40 years) = pathological fracture from metastatic bone disease until proven otherwise; urgent staging CT + MRI; do NOT dismiss as a sporting injury in an adult
Klein`s line (SUFE): line along superior femoral neck should intersect the epiphysis by ~20%; if it does not intersect the epiphysis (or intersects less) = slipped epiphysis; always assess the AP AND lateral; obese adolescent male 10–16 years; stabilise in situ with cannulated screw; check the contralateral hip (25% bilateral)
THA cup inclination: target 40° ± 10° (Lewinnek safe zone); >50° = steep cup = increased dislocation and wear risk; cup version requires lateral view or CT; combined anteversion (stem + cup) target = 40° ± 10°
Ilioischial line (Köhler): femoral head crossing the ilioischial line = protrusio acetabuli; causes: RA, Paget`s, osteomalacia, idiopathic (Otto pelvis — young women); THA for protrusio requires acetabular reconstruction with bone grafting of the medial wall
Radiological OA does NOT = indication for surgery; Grade 4 Kellgren-Lawrence must be correlated with symptoms, functional limitation, and failed conservative management before recommending THA

How to Read a Hip X-Ray — Systematic Approach

References

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