Overview & Epidemiology
Femoral neck fractures are among the most clinically significant injuries in orthopaedics, disproportionately affecting the elderly osteoporotic population and carrying a one-year mortality of 20–35%. They represent a unique fracture where the choice of surgical treatment — internal fixation to preserve the femoral head vs arthroplasty to replace it — is critically dependent on the patient`s age, physiological status, degree of displacement, and pre-existing hip disease. The two most widely used classification systems — Garden (displacement) and Pauwels (fracture angle) — directly guide this decision-making.
- Epidemiology: approximately 76,000 hip fractures per year in the UK; femoral neck fractures account for ~45–50% (the remainder being intertrochanteric and subtrochanteric); female:male ratio 3:1; mean age ~80 years; the one-year mortality of 20–35% reflects the frailty of the patient population rather than the fracture per se; approximately 50% never return to their pre-fracture level of function
- Vascular anatomy — the key to understanding AVN risk: the femoral head is supplied by three sources: (1) the medial femoral circumflex artery (MFCA — the dominant supply via the retinacular vessels running along the femoral neck beneath the synovium — the posterosuperior and posteroinferior retinacular arteries; the MFCA arises from the profunda femoris); (2) the lateral femoral circumflex artery (LFCA — minor contribution); (3) the artery of the ligamentum teres (obturator artery — minor, but the ONLY supply to the femoral head in infancy); displacement of the femoral neck fracture tears or kinks the retinacular vessels, interrupting the dominant MFCA supply → avascular necrosis (AVN) of the femoral head; the risk of AVN is directly proportional to the degree of displacement
- Non-union and AVN: the two most important complications of femoral neck fractures managed with internal fixation; AVN rate: undisplaced (Garden I/II) ~10–15%; displaced (Garden III/IV) ~20–30% with modern fixation; non-union rate: undisplaced ~5%; displaced ~20–30%; these high rates of failure with internal fixation in displaced fractures in elderly patients drove the shift to primary arthroplasty
Garden Classification (Displacement)
| Garden Grade | Description | AP X-ray Finding | AVN Risk |
|---|---|---|---|
| Grade I — Incomplete / valgus impacted | Incomplete fracture; the inferior cortex is intact; the femoral head is tilted into valgus; the trabecular pattern is malaligned but the fracture is stable; the head is impacted superiorly | Valgus tilt of femoral head; trabeculae of femoral head appear more vertical than normal; incomplete fracture line visible inferiorly | Low (~10%); retinacular vessels are unlikely to be fully disrupted in an impacted valgus fracture |
| Grade II — Complete, undisplaced | Complete fracture through the femoral neck but WITHOUT displacement; the trabecular pattern remains aligned (trabeculae of femoral head are continuous with those of the acetabulum); no varus or valgus tilt | Complete fracture line; normal trabecular alignment; no displacement | Low–moderate (~10–15%); vessels intact but at risk from haematoma pressure |
| Grade III — Complete, partially displaced | Complete fracture with partial displacement; the femoral head is rotated into varus; the trabecular pattern is MALALIGNED — the trabeculae of the femoral head are no longer continuous with those of the acetabulum; posterior capsule remains partially intact | Varus tilt of femoral head; trabecular malalignment; partial displacement; head rotates into apparent abduction | High (~20–30%); retinacular vessels likely kinked or partially torn |
| Grade IV — Complete, fully displaced | Complete fracture with full displacement; the femoral head lies free in the acetabulum (no soft tissue attachment restraining it); the trabecular pattern paradoxically REALIGNS (the femoral head reorients to the acetabulum due to the capsular detachment) — this `realignment` on the AP view in a displaced fracture = Grade IV | Full displacement; the femoral head trabeculae paradoxically re-align with the acetabulum (head is free and reorients); the femoral shaft is proximally migrated and externally rotated | Very high (~30%); retinacular vessels fully torn; head is devascularised |
- Practical Garden simplification: in clinical practice, Garden is simplified to two groups — undisplaced (Garden I + II) and displaced (Garden III + IV); this binary classification directly guides treatment: undisplaced = internal fixation in all age groups; displaced in the elderly = arthroplasty (hemiarthroplasty or THA); displaced in the young = urgent anatomical reduction and internal fixation (preserve the head)
- The paradox of Grade IV trabecular alignment: in Garden IV, the femoral head is completely detached from the neck and free in the acetabulum; it rotates to align its trabeculae with the acetabular trabeculae — this paradoxical `alignment` on the X-ray actually indicates maximum displacement and is NOT reassuring; recognising this is a key exam point
Pauwels Classification (Fracture Angle)
| Pauwels Type | Fracture Angle (from horizontal) | Biomechanical Forces | Stability & Clinical Significance |
|---|---|---|---|
| Type I | <30° from horizontal | Compressive forces predominate across the fracture; the fracture line is nearly horizontal; compressive load drives the fragments together; inherently stable | Most stable; good healing potential; low non-union rate; compression load promotes union; internal fixation straightforward |
| Type II | 30–50° from horizontal | Mixed compressive and shear forces; moderate obliquity; intermediate stability | Moderate stability; reasonable healing potential with adequate fixation; intermediate non-union risk |
| Type III | >50° from horizontal (approaching vertical) | Shear forces predominate; the fracture line is steep/vertical; axial load produces shear across the fracture rather than compression; the fragments tend to slide past each other rather than being compressed together; mechanically very unstable | Most unstable; highest non-union rate; internal fixation is most at risk of failure; shear forces cause hardware to cut out; Pauwels III in a young patient is a technically demanding fixation problem; valgus intertrochanteric osteotomy may be used to convert the shear forces to compression in selected cases |
- The Pauwels angle is measured on the AP radiograph between the fracture line and the horizontal; a more vertical fracture line = higher Pauwels type = more shear force = more unstable = higher non-union risk; the Pauwels classification is most clinically relevant in young patients where internal fixation is the goal — a Pauwels III fracture in a young patient requires a more aggressive fixation strategy (blade plate, dynamic hip screw with derotation screw, or valgus osteotomy) than a Pauwels I fracture treated with cannulated screws alone
Management Algorithm
| Patient Group | Fracture | Treatment of Choice | Rationale |
|---|---|---|---|
| Elderly (>65), low-demand, undisplaced (Garden I/II) | Garden I / II | Cannulated cancellous screws (3 screws in inverted triangle configuration); or dynamic hip screw (DHS) with derotation screw | Low AVN risk; fixation preserves the native femoral head; shorter operation; less morbidity than arthroplasty in low-demand elderly patient |
| Elderly (>65), low-demand, displaced (Garden III/IV) | Garden III / IV | Hemiarthroplasty (HA) — cemented Austin-Moore or Thompson (older, unipolar), or cemented bipolar HA (Charnley-Hastings) | High AVN/non-union rate with fixation in displaced fractures; hemiarthroplasty eliminates the risk of AVN and non-union; cement fixation faster rehabilitation and lower peri-prosthetic fracture risk; bipolar HA reduces acetabular erosion vs unipolar |
| Active, independent elderly (>65), displaced (Garden III/IV) | Garden III / IV | Total hip arthroplasty (THA) — NICE guideline recommends THA over HA for patients who were able to walk independently and have no cognitive impairment; cemented femoral stem preferred in elderly (lower peri-prosthetic fracture risk); standard bearing surfaces | HEALTH and HIP ATTACK trials demonstrate superior functional outcomes (Harris Hip Score, Oxford Hip Score) and lower re-operation rates with THA vs HA in fit elderly patients; NICE NG124 (2020) recommends THA for patients meeting activity and cognition criteria; dislocation risk of THA is the main disadvantage |
| Young patient (<60), any displacement | Garden I–IV | Urgent anatomical reduction + internal fixation; displaced fractures require URGENT reduction (within 6–12 hours) to restore blood supply and reduce AVN risk; cannulated screws or sliding hip screw + derotation screw; Pauwels III may require valgus osteotomy or blade plate; the femoral head MUST be preserved in young patients | The young patient has decades of life ahead — arthroplasty is NOT an appropriate primary treatment; THA has a finite implant life and revision arthroplasty at age 40–50 carries high morbidity; every effort must be made to preserve the native femoral head even if AVN risk is high; AVN can be managed with core decompression, vascularised fibula graft, or eventual THA later |
Internal Fixation Technique
- Cannulated cancellous screws (3 screws): the standard fixation for undisplaced femoral neck fractures; three 6.5 mm or 7.3 mm partially threaded cannulated screws placed in an inverted triangle (apex inferior) configuration; the inferior screw should lie along the calcar (inferior cortex of the femoral neck) to maximise stability and resist varus collapse; all screws must engage the subchondral bone of the femoral head without penetrating the articular surface; parallel screw placement allows `sliding` of the fracture surfaces as the fracture settles, promoting union; the `inverted triangle` configuration is more stable than a straight horizontal line configuration
- Dynamic hip screw (DHS): a sliding hip screw placed in the inferior femoral neck with a derotation screw placed superiorly; the DHS allows controlled collapse of the fracture which promotes union (unlike screws which can `cut out` if collapse occurs without controlled sliding); the lag screw tip-apex distance (TAD) must be <25 mm to prevent cut-out (Baumgaertner 1995); the TAD is the sum of the distance from the tip of the screw to the apex of the femoral head on the AP and lateral views; TAD >25 mm = dramatically increased cut-out risk
- Tip-apex distance (TAD): one of the most important concepts in proximal femoral fixation; TAD = AP distance (tip to apex on AP) + lateral distance (tip to apex on lateral), both corrected for magnification; TAD <25 mm = low cut-out risk; TAD >25 mm = exponentially increasing cut-out risk; applies to DHS for femoral neck AND intertrochanteric fractures; the screw should be central-central or slightly inferior-central on the AP view, and central on the lateral view
Timing of Surgery & Perioperative Considerations
- NICE NG124 (2020) — best practice tariff standard: all patients with hip fractures should receive surgery within 36 hours of admission and within 48 hours of injury; delays beyond 36 hours are associated with increased mortality, pressure sores, DVT, pulmonary complications, and delirium; `time to theatre` is an NHS best practice tariff quality indicator and is audited nationally via the National Hip Fracture Database (NHFD); the 36-hour target should not be delayed for reversible medical issues (anaemia, electrolyte abnormalities, anticoagulation reversal where possible) but should proceed promptly once the patient is medically optimised
- Anticoagulation management: patients on warfarin — reversal with vitamin K ± prothrombin complex concentrate (PCC) to allow surgery; patients on DOACs (apixaban, rivaroxaban, dabigatran) — stop DOAC; time to acceptable surgical levels depends on the agent and renal function (typically 24–48 hours); do NOT delay for >24 hours for anticoagulation alone unless INR is markedly elevated (>1.5 for spinal); the mortality benefit of timely surgery outweighs the bleeding risk in most cases
- The `orthogeriatric` model: multidisciplinary management by orthogeriatricians, orthopaedic surgeons, anaesthetists, physiotherapists, and occupational therapists; reduces mortality, length of stay, and delirium; now the standard of care in the UK hip fracture pathway
Exam Pearls
- Garden classification: I (incomplete, valgus impacted, low AVN risk); II (complete, undisplaced, normal trabecular alignment); III (displaced, trabecular malalignment, partial displacement); IV (fully displaced — paradoxical trabecular realignment as head is free in acetabulum); simplified in practice to undisplaced (I+II) vs displaced (III+IV)
- Garden IV paradox: the femoral head is completely free — it reorients its trabeculae to align with the acetabulum on the AP view; this `realignment` = maximum displacement = NOT reassuring; a common exam trap
- Pauwels classification: angle of fracture line from horizontal; Type I <30° (compressive, stable, good healing); Type II 30–50° (mixed); Type III >50° (shear forces, unstable, highest non-union risk); Pauwels III in young patient = most demanding fixation challenge
- Vascular supply: MFCA (via retinacular vessels) = dominant supply to femoral head; displaced fracture tears retinacular vessels; AVN risk proportional to displacement; Garden III/IV = 20–30% AVN risk with modern fixation
- Treatment: undisplaced (Garden I/II) ALL ages = cannulated screws or DHS; displaced elderly (>65) = HA (low demand) or THA (active, independent — NICE NG124); displaced young (<60) = URGENT anatomical reduction + internal fixation within 6–12 hours
- NICE NG124 (2020): THA superior to HA for active, independent, cognitively intact patients with displaced femoral neck fractures; HEALTH and HIP ATTACK RCTs support this; cemented femoral stem preferred in elderly
- Tip-apex distance (TAD): <25 mm = low cut-out risk; >25 mm = high cut-out risk (exponential increase); sum of AP + lateral tip-to-apex distances corrected for magnification; most important technical parameter for DHS fixation
- NICE NG124 timing: surgery within 36 hours of admission; delay beyond 36 hours = increased mortality, pressure sores, DVT; NHS Best Practice Tariff standard; NHFD audits compliance nationally
- 3-screw inverted triangle: standard for undisplaced femoral neck fractures; inferior screw along calcar; parallel placement allows controlled collapse; TAD <25 mm for each screw