Femoral Neck Fracture — Garden/Pauwels

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

• 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

• 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

• 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

• 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

• 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