Trauma · Classification
Pauwels Classification of Femoral Neck Fractures
Pauwels (1935) grades intracapsular femoral neck fractures by the angle the fracture line makes with the horizontal on an AP radiograph — Type I under 30°, Type II 30–50°, Type III over 50°. The principle is biomechanical: as the line tilts toward vertical, an increasing share of the load becomes a SHEAR force that slides the proximal fragment downward, so higher grades carry higher rates of varus collapse, nonunion and fixation failure. The classification therefore drives fixation: low-angle fractures heal with parallel screws or a sliding hip screw; high-angle vertical fractures need a construct that resists shear (a valgus-angled/fixed-angle device, a medial buttress plate, or a cephalomedullary nail) — or, in the older patient, primary arthroplasty. A Pauwels III fracture in a young patient is an emergency: urgent anatomical reduction and stable fixation to protect the femoral-head blood supply.
3 gradesBy fracture-line angle from horizontal
under 30° / 30–50° / over 50°Type I (compression) → III (shear)
Type IIIHigh shear → high nonunion/AVN
Young IIIEmergency: urgent anatomical ORIF
Bottom lineHigher angle = more shear = worse prognosis. State the angle, the type, the biomechanics, then a shear-appropriate fixation: Type I/II → screws ± valgus orientation or SHS; Type III young → urgent anatomical reduction + fixed-angle/medial-buttress/CMN; Type III elderly → primary arthroplasty. Combine with the Garden (displacement) classification.
Traps that cost marks
- Forgetting it's an AP measurement. The Pauwels angle is measured on the AP radiograph against a horizontal pelvic reference — the lateral view shows sagittal displacement, not the Pauwels angle. Inter-observer reliability is only moderate, and minor rotation shifts the type.
- Fixing a young Pauwels III with parallel screws alone. Vertical (high-shear) fractures fail with simple screws — use a shear-resisting construct (fixed-angle device, medial buttress plate, cephalomedullary nail). A young Pauwels III is an emergency: urgent anatomical reduction.
- Fixing a displaced Pauwels III in elderly osteoporotic bone. Fixation failure rates are unacceptable — choose primary arthroplasty (THA for the active patient).
- Quoting Pauwels alone. It captures angle only — combine with the Garden (displacement) classification, plus age and bone quality, for the real prognosis.
- Blaming the angle for AVN. AVN follows displacement and the vascular insult to the retinacular vessels, not the fracture angle per se — so an anatomical reduction (and protecting those vessels) matters more than the number.
The Pauwels classification system
Pauwels divided femoral neck fractures into three types based on the inclination of the fracture line measured from the horizontal on a standard AP pelvic radiograph.
I
- Angle from horizontal
- Less than 30 degrees
- Dominant force
- Compression (axial load)
- Healing prognosis
- Favourable — compression promotes healing
II
- Angle from horizontal
- 30 to 50 degrees
- Dominant force
- Mixed compression and shear
- Healing prognosis
- Intermediate — shear begins to jeopardise stability
III
- Angle from horizontal
- Greater than 50 degrees
- Dominant force
- Shear (vertical force)
- Healing prognosis
- Unfavourable — shear displaces the fracture, high nonunion risk
How to measure the Pauwels angle
Draw a horizontal reference line (along the superior margin of the sacral ala or the ischial tuberosities), then a line along the fracture plane; the angle between them is the Pauwels angle. A more vertical fracture is a higher type with a worse prognosis. Always measure on the AP radiograph — the lateral view assesses sagittal-plane displacement, not the Pauwels angle. Note that inter-observer reliability is only moderate, and minor hip/pelvis rotation can shift the measured type.
Biomechanics — why the angle matters
The femoral neck is loaded in compression during weight-bearing. A horizontal (low-angle) fracture is held together by axial compressive forces — the same force that drives healing. As the fracture line tilts toward vertical, an increasing component of the load becomes a shear force that slides the proximal fragment downward along the fracture plane.
- Type I (under 30 degrees): compression across the fracture exceeds shear; the surfaces are pressed together, promoting stability and union. Standard fixation (cannulated screws or sliding hip screw) works reliably.
- Type II (30 to 50 degrees): shear is significant; the fracture tends to displace inferoposteriorly. Fixation should add shear resistance — parallel cannulated screws in a valgus orientation, or a sliding hip screw with a derotation screw.
- Type III (over 50 degrees): shear dominates; the proximal fragment slides down and medially, causing varus collapse and screw cut-out. Simple parallel screws have a high failure rate; fixation must actively resist shear — a valgus-angled/fixed-angle device, a medial buttress plate, a cephalomedullary nail, or (in older patients) primary arthroplasty.
Shear vs compression
As the fracture line approaches vertical, the resolved shear component of joint load rises and the compressive component falls. This biomechanical shift is why Type III fractures fail with simple screw fixation — the screws are loaded in bending/shear and cut out, rather than being loaded in compression across an apposed fracture.
Implications for the retinacular vessels
Higher shear means greater displacement risk, and each episode of displacement threatens the superior retinacular vessels (the main supply to the femoral head). This is the pathway to avascular necrosis: it is the displacement and vascular insult, more than the fracture angle itself, that drives AVN.
The femoral head blood supply — what the fracture threatens
The topic invokes "the retinacular vessels" and "vascular insult" — here is the supply they refer to:
- The medial femoral circumflex artery (MFCA) is the dominant supply to the adult femoral head: its deep branch ascends along the posterosuperior neck and gives the lateral epiphyseal / superior retinacular vessels (running in the retinacula of Weitbrecht beneath the synovial reflection) that feed the weight-bearing head.
- The lateral femoral circumflex artery contributes less (anterior/inferior neck and head); both arise from the profunda femoris and form an extracapsular ring at the neck base feeding the ascending cervical (retinacular) branches.
- The artery of the ligamentum teres (foveal) is a minor adult supply — more important in children.
- Why an intracapsular fracture threatens the head two ways: (1) direct disruption of the retinacular vessels by the fracture/displacement, and (2) the intracapsular haematoma raising pressure (tamponade) that can further compromise retinacular flow — the rationale (debated) for early reduction and capsular decompression. This is why displacement and the vascular insult, more than the Pauwels angle, drive AVN.
Fixation strategy by Pauwels type
Choosing fixation for a femoral neck fracture
- 1Measure the angle and assign the typeAP radiograph: under 30° = I, 30–50° = II, over 50° = III. Also note displacement (Garden) and bone quality — they matter as much as the angle.
- 2Match the construct to the shearType I/II → parallel cannulated screws (inverted triangle) ± valgus orientation, or a sliding hip screw + derotation screw. Type III → a shear-resisting construct: fixed-angle device, medial buttress plate, or cephalomedullary nail.
- 3Young Type III = emergencyUrgent anatomical reduction (open if closed fails) and stable fixation as soon as the patient is fit — protect the retinacular blood supply; accept nothing less than an anatomical reduction.
- 4Elderly displaced = arthroplastyIn osteoporotic bone, fixation of a displaced Pauwels III has unacceptable failure rates — choose total hip arthroplasty for the active patient, hemiarthroplasty for the low-demand patient; aim for surgery within ~36 h.
Bottom lineThe angle tells you how much shear the construct must resist; the patient's age, displacement and bone quality tell you whether to fix or replace.
I (under 30 degrees)
- Young patient (under 60)
- Three parallel cannulated screws (inverted triangle)
- Elderly patient (over 65)
- Cannulated screws or sliding hip screw; consider arthroplasty if displaced or osteoporotic
II (30 to 50 degrees)
- Young patient (under 60)
- Cannulated screws with valgus orientation, or sliding hip screw + derotation screw
- Elderly patient (over 65)
- Sliding hip screw with anti-rotation screw; low threshold for hemi- or total arthroplasty
III (over 50 degrees)
- Young patient (under 60)
- Urgent anatomical reduction + fixed-angle device, medial buttress plate, or cephalomedullary nail
- Elderly patient (over 65)
- Primary total hip arthroplasty (cemented or uncemented); hemiarthroplasty if low demand
Caution
A Pauwels Type III fracture in a young patient is an orthopaedic emergency. Urgent anatomical reduction (open if necessary) and stable internal fixation should be performed as soon as the patient is fit for surgery. Delay and a non-anatomical reduction both increase the risk of avascular necrosis — the blood supply to the femoral head depends on restoring the anatomy.
Judging the 'anatomical reduction' — Garden alignment index & Lowell's lines
The topic demands an "anatomical reduction" — the examiner wants the objective criteria for it:
- Garden alignment index: on the AP, the principal compression trabeculae of the head should meet the medial femoral cortex at about 160°; on the lateral they should be roughly colinear (about 180°). An acceptable reduction sits about 155 to 180° on both views; varus (under about 155°) or marked deviation predicts fixation failure and AVN.
- Lowell's lines: the cortical outlines of the head and neck should form continuous, smooth S- and reversed-S curves where a convex meets a concave; a tangency or cusp (two curves meeting at a point) signals malreduction.
- Also restore Shenton's line and avoid residual varus or posterior tilt.
- Quality over clock: reduction quality is the strongest surgeon-controllable predictor of union/AVN (in Liporace's series failures occurred even with good reduction — so accept nothing less than anatomical). A displaced fracture in a young patient is a surgical urgency: most advocate prompt reduction and fixation (commonly within about 24 hours, sooner where feasible) to limit AVN, though the exact time threshold remains debated.
Limitations & practical considerations
- Inter-observer reliability is moderate at best. Different surgeons measure the Pauwels angle differently on the same radiograph, and the same fracture can shift types with minor rotation of the hip or pelvis.
- The classification is purely biomechanical and does not account for patient age, bone quality, displacement, timing of surgery, or vascularity — all of which influence outcome as much as, or more than, the angle alone.
- Combine with the Garden (displacement) classification. A fully displaced (Garden IV) low-angle fracture may carry a worse prognosis than an undisplaced (Garden I) high-angle fracture treated urgently.
- Modern angular-stable implants have narrowed the outcome gap between types — locking plates, fixed-angle devices, medial buttress plates and cephalomedullary nails provide shear resistance that screw-only constructs could not.
- CT is increasingly used to define the fracture geometry more precisely than plain radiographs, especially for vertically oriented fractures where surgical planning depends on the exact geometry.
Viva practice
Exam viva
Practise clinical reasoning and management decisions out loud
Viva scenarioStandard
Clinical prompt
“A 32-year-old man is involved in a high-speed motor vehicle collision. Radiographs show a vertical fracture line through the femoral neck, measured at 55 degrees from the horizontal. The fracture is minimally displaced. How do you classify and manage this?”
Viva scenarioAdvanced
Clinical prompt
“A 68-year-old active woman sustains a fall at home. Radiographs show a femoral neck fracture with a Pauwels angle of 60 degrees and the fracture is displaced. She is independent, mobilises with no aids, and has mild osteoporosis (T-score minus 2.5). Discuss your management.”
Exam cheat sheet
Mnemonic
30–50The three angles
I
Under 30° — low angle, compression-dominated, favourable
II
30 to 50° — intermediate, mixed compression and shear
III
Over 50° — high angle, shear-dominated, high nonunion/AVN
Hook:As the angle climbs from horizontal toward vertical, shear climbs with it and prognosis worsens — 'Vertical is Villain'.
The points that win marks
- Type I under 30° (compression), II 30–50° (mixed), III over 50° (shear). Higher angle = more shear = worse prognosis.
- Measure on the AP with a horizontal pelvic reference; reliability is only moderate.
- Young Pauwels III is an emergency — urgent anatomical reduction + shear-resisting fixation (fixed-angle device, medial buttress plate, CMN).
- Elderly displaced Pauwels III → primary arthroplasty (THA for the active patient).
- AVN follows displacement and vascular insult, not the angle alone; counsel on the substantial AVN/nonunion risk.
- Combine Pauwels (angle) with Garden (displacement) for the full picture.
Exam day cheat sheet
Pauwels classification — one-screen revision
The three types (angle from horizontal)
- Type I: less than 30 degrees — compression-dominated, favourable healing
- Type II: 30 to 50 degrees — mixed forces, intermediate risk
- Type III: greater than 50 degrees — shear-dominated, high nonunion and AVN risk
Fixation by type
- Type I: parallel cannulated screws or sliding hip screw
- Type II: cannulated screws with valgus orientation or SHS plus derotation screw
- Type III young: urgent anatomical reduction, shear-resisting fixation (fixed-angle device, medial buttress plate, CMN)
- Type III elderly: primary total hip arthroplasty (fixation failure rate too high)
Key principles for the exam
- Higher angle equals more shear equals worse prognosis
- Young Pauwels III is an emergency — urgent reduction, protect retinacular vessels
- Always state angle, type, biomechanical implication, and fixation rationale
- Pauwels measures angle only — combine with Garden (displacement)
- AVN risk depends on displacement and vascular insult, not the angle alone
Evidence Base
Evidence
Results of internal fixation of Pauwels type-3 vertical femoral neck fractures
Liporace F, Gaines R, Collinge C, Haidukewych GJ • J Bone Joint Surg Am (2008)
Key Findings:
- Multicentre series of 76 high-shear-angle (Pauwels type-3) femoral neck fractures (mean age 42); 62 followed to union or revision.
- Despite good-to-excellent reduction in 95%, the nonunion rate was 19% with cannulated screws alone versus 8% with a fixed-angle device (a difference that did not reach statistical significance).
- Osteonecrosis occurred in 11%; the authors concluded the ideal implant for this challenging pattern remains undefined.
Clinical implication: Pauwels type-3 fractures carry a high risk of fixation failure even with good reduction; a fixed-angle construct numerically outperformed screws alone, supporting shear-resisting fixation.
Limitation: Retrospective multicentre design; heterogeneous fixation methods; the screw-vs-fixed-angle difference was not statistically significant.
Source: J Bone Joint Surg Am 2008;90(8):1654-9
Evidence
Efficacy of four internal fixation devices on femoral neck fractures in young adults: a systematic review and network meta-analysis
Yuan D, Zhang Z, Wang X, Chang W, Xie W, Zhang Y • Medicine (Baltimore) (2024)
Key Findings:
- Network meta-analysis of 34 studies (2291 young-adult femoral neck fractures) comparing internal-fixation devices.
- The medial buttress plate ranked best for Harris hip score, lowest complication rate and fastest fracture healing; the femoral neck system ranked best for operation time and least neck shortening.
- Inverted triangular cannulated screws had the lowest intraoperative bleeding — i.e. no single device wins on every metric, but augmented/angular-stable constructs lead on function and complications.
Clinical implication: In young adults, augmented constructs (especially the medial buttress plate) outperform plain parallel screws on hip function and complications — consistent with the Pauwels shear principle.
Limitation: Network meta-analysis of heterogeneous studies; limited head-to-head RCT data; 'young adult' defined variably across studies.
Source: Medicine (Baltimore) 2024;103(45):e40265
How to read this evidence
According to PubMed, the high failure rate of screw-only fixation in vertical fractures comes from Liporace et al. 2008 (DOI), the valgus-osteotomy head-preserving option from Magu et al. 2005 (DOI), the appraisal of the classification's reliability from Nandi 2021 (DOI), and the medial-buttress-plate advantage from Giordano et al. 2019 (DOI) and Yuan et al. 2024 (DOI).