Femoral Neck Fracture - Dynamic Hip Screw (DHS) Fixation

Primary indication. The dynamic hip screw (DHS) is most strongly indicated for a basicervical femoral neck fracture - a fracture at the base of the femoral neck, immediately proximal to the intertrochanteric line, with little or no medial metaphyseal buttress and a short, rotationally unstable proximal fragment. Biomechanically it behaves between a true femoral neck fracture and an unstable intertrochanteric fracture, with high varus and shear forces. Cannulated screws alone fail here through rotational instability and varus collapse; the DHS lateral side-plate directly buttresses the varus moment. In the FAITH randomised controlled trial (Lancet 2017) the sliding hip screw showed no overall reoperation advantage over cancellous screws across all hip fractures, but the pre-specified subgroups of base-of-neck (basicervical) fractures and smokers appeared to benefit from the sliding hip screw. The trade-off to disclose is that avascular necrosis was slightly more common with the sliding hip screw. Other indications.

What it is NOT for. A posterior (Moore) approach gives inadequate access for lateral plate placement and is not used for a DHS. A cephalomedullary nail is the main alternative many surgeons now prefer for basicervical and subtrochanteric-extension patterns, because the short unstable proximal fragment behaves like an unstable trochanteric fracture (Matre, Norwegian Hip Fracture Register). Patient factors and consent. Counsel for implant prominence and lateral thigh pain, and for the small but real risks of cut-out, non-union, avascular necrosis (related chiefly to the injury rather than the surgery), infection, and periprosthetic femoral shaft fracture, plus the prolonged protected weight-bearing. For displaced fractures in older, lower-demand patients, arthroplasty (hemiarthroplasty or total hip arthroplasty) is usually preferred over fixation - both NICE and the AAOS recommend this. Head-preserving fixation is favoured in younger patients (under about 60-65 years) regardless of displacement. Setup. Supine on a fracture table with a well-padded perineal post (check distal pulses and padding to protect the pudendal nerve). The uninjured leg is flexed 90 degrees at hip and knee, abducted and held in a leg holder to allow C-arm access from the opposite side. The injured leg sits in 10-15 degrees of abduction and neutral to slight (5-10 degrees) internal rotation to correct posterior tilt, with gentle longitudinal traction of 10-20kg. Confirm acceptable reduction on AP and lateral fluoroscopy BEFORE prepping.

The goal is to anatomically reduce the fracture, place a lag screw centrally in the femoral head with a tip-apex distance under 25mm, seat a 135-degree barrel plate flush on the lateral cortex, apply interfragmentary compression, and - for basicervical patterns - add an anti-rotation screw. The exposure is a direct lateral approach to the proximal femur, elevating vastus lateralis off the lateral cortex to seat the plate; the Watson-Jones (anterolateral) and Hardinge (direct lateral, muscle-splitting) intervals are the relevant surgical planes (detailed in Background and Evidence).

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Rehabilitation | Phase | Timing | Weight-bearing | Focus | |-------|--------|----------------|-------| | Immediate | 0-2 weeks | Touch weight-bearing (foot flat, no push-off), walking frame | Day-1 mobilisation; sit out, transfer; DVT prophylaxis (LMWH e.g. enoxaparin 40mg daily), extended to 28-35 days per NICE, AAOS and ACCP | | Early | 2-6 weeks | Touch WB, progress to partial (20-30kg) at 4-6 weeks if healing | Wound check at 2 weeks; hip ROM (avoid forced internal rotation and adduction); continue LMWH to 6 weeks | | Intermediate | 6-12 weeks | Weight-bearing as tolerated if callus visible and pain-free | Full ROM, abductor strengthening, gait re-education; basicervical patterns may progress earlier | | Late | 3-6 months | Full unrestricted WB by 10-12 weeks if union | Bridging callus on 3 cortices; graded return by bone quality | | Long-term | 6-24 months | Full | AVN surveillance (can present up to 3 years); osteoporosis management (DEXA, bisphosphonates e.g. alendronate 70mg weekly, or denosumab 60mg 6-monthly) | Avoid NSAIDs for the first 6 weeks, as they may impair fracture healing. Undisplaced fractures fixed with DHS return toward roughly 70-80 percent of pre-fracture function by one year; one-year mortality for fragility hip fractures is about 20-30 percent, driven chiefly by comorbidity rather than implant choice. Complications The commonest pathway to mechanical failure is a preventable technical error: malreduction accepted (varus under 160 degrees or posterior tilt under 160 degrees), poor guide-wire position (superior on AP, posterior on lateral, or TAD over 25mm), a plate not flush on the lateral cortex, or inadequate or over-compression.

Epidemiology and outcomes. Femoral neck fractures are typical fragility fractures of the elderly. One-year mortality for fragility hip fractures is about 20-30 percent, driven predominantly by patient comorbidity rather than implant choice. Undisplaced fractures fixed with DHS return toward roughly 70-80 percent of pre-fracture function by one year, best when reduction is anatomic and mobilisation is early. Predictors of a good outcome are a younger physiological age, an undisplaced pattern, anatomic reduction (low posterior tilt), a TAD under 25mm, and early weight-bearing. Fixation versus arthroplasty (global guidance). Both NICE (UK) and the AAOS (US) recommend arthroplasty for most DISPLACED intracapsular fractures in older patients, and internal fixation for UNDISPLACED fractures with acceptable posterior tilt. In younger patients (under about 60-65 years) head-preserving anatomic reduction and fixation is favoured regardless of displacement, with arthroplasty reserved for salvage. The DHS is one fixation option in this paradigm; cannulated screws, cephalomedullary nails and fixed-angle devices are the alternatives. Femoral head blood supply. The medial femoral circumflex artery (MFCA) is the dominant supply (60-80 percent of the head); its deep branch passes posteriorly under piriformis and the ascending cervical (lateral epiphyseal) branches course along the posterosuperior neck - these are the vessels disrupted by a displaced fracture. The lateral femoral circumflex artery contributes 20-30 percent via ascending branches along the anterior capsule. The artery of the ligamentum teres is a minor contributor in adults (5-10 percent, more important in children). The intracapsular retinacular vessels ascend beneath the synovial reflection and enter the head at the subcapital junction; the posterosuperior retinacular vessels are the most vulnerable. AVN risk by Garden grade: I 0-5 percent, II 5-10 percent, III 20-30 percent, IV 25-40 percent. Proximal femur landmarks. The vastus ridge (tubercle), 2-3cm distal to the GT tip on the lateral cortex, is the guide-wire entry point. The calcar femorale is the dense vertical medial cortex providing medial support; Ward's triangle is the relatively weak area in the neck trabeculae. The compressive trabeculae run from the medial cortex to the superior head (the basis of the Garden alignment index); the tensile trabeculae run from the lateral cortex to the inferior head. Garden classification.

Pauwels classification (biomechanical). Based on the angle of the fracture line from the horizontal: Pauwels I (less than 30 degrees) - stable, mainly compression; Pauwels II (30-50 degrees) - intermediate, mixed compression and shear; Pauwels III (greater than 50 degrees) - unstable, mainly shear, high failure risk. A higher Pauwels angle increases shear across the fracture and raises non-union and cut-out risk with any fixation method. Surgical approach planes. The DHS is placed through a direct lateral approach, elevating vastus lateralis off the lateral femur. The relevant named intervals are the Watson-Jones (anterolateral) approach, working between tensor fascia lata and gluteus medius (both supplied by the superior gluteal nerve, L4-S1 - not a true internervous plane, but more anatomic with less muscle splitting); the direct lateral (Hardinge) approach, splitting the anterior third of gluteus medius and minimus for direct access (simpler, but with abductor damage and a Trendelenburg risk if split excessively); and the posterior (Moore) approach, which is NOT used for a DHS because access is inadequate for a lateral plate.