Conversion Total Hip Arthroplasty After Failed Proximal Femoral Fracture Fixation

Cut-out — varus collapse with superolateral migration of the lag screw through the femoral head. The dominant mechanical failure of intertrochanteric fixation.

• Risk factors: tip-apex distance greater than 25 mm, poor reduction (varus, posterior sag), unstable fracture patterns (reverse obliquity, subtrochanteric extension), osteoporosis, superior/anterior screw placement
• Reconstructive consequences: destroyed head and often acetabular scoring; varus proximal femur with medialised shaft; shortened, low-offset hip; greater trochanter may be non-united, migrated or fragmented

Cut-through (axial migration, "medial migration", Z-effect in dual-screw nails) — the screw perforates the head centrally into the acetabulum without varus collapse. Acetabular cartilage and medial wall damage is typically worse than cut-out; assess for protrusio.

Non-union — persistent pain, hardware fatigue (broken lag screw or nail at the aperture), progressive deformity. In the elderly, conversion arthroplasty is usually preferred over revision fixation; in the young, revision fixation with valgus osteotomy and grafting is considered first for intertrochanteric non-union.

Failure modes after in-situ or reduced fixation of femoral neck fractures:

• Non-union (roughly 10 to 30 percent in displaced fractures treated with screws) — shortening, varus, screw back-out with lateral prominence and trochanteric bursitis
• Avascular necrosis — may present 1 to 3 years later with segmental collapse; screws may still be well fixed
• Fixation failure with displacement — early loss of reduction

Conversion after screws is technically the most benign scenario: the trochanter is usually intact, the abductors undisturbed if percutaneous fixation was used, and the canal has no large void. The main issues are the lateral cortical screw holes (stress risers) and retained broken screw fragments in the head/neck, which are removed with the head.

• Conversion THA — workhorse in the elderly and in any patient with head or acetabular damage
• Conversion hemiarthroplasty — occasionally in the very frail with a pristine acetabulum, but instability and acetabular erosion make THA preferred in most modern practice
• Revision fixation with or without valgus osteotomy and bone graft — young patients with viable head and salvageable non-union
• Excision arthroplasty (Girdlestone) — end-stage salvage in the unreconstructable or persistently infected non-ambulator

Every failed fixation must be presumed potentially septic until worked up. Low-grade infection with organisms such as coagulase-negative staphylococci or Cutibacterium acnes commonly presents purely as mechanical failure.

Universal screening

• History: wound problems, prolonged drainage, antibiotics after the index surgery, night pain, systemic symptoms
• CRP and ESR in all patients. Normal values are reassuring but do not fully exclude low-grade infection
• Plain radiographs: lucency around screws or nail, periosteal reaction, sequestrum

Escalation — when to aspirate

• Raised CRP/ESR without another explanation
• Early failure (within months) or atypical failure pattern
• Any wound history, sinus or draining scar
• Aspirate sent for cell count, differential and culture (hold 14 days for slow-growing organisms). Some units aspirate around the nail or perform image-guided biopsy of the non-union site

Intraoperative strategy

• Send a minimum of 3 to 5 tissue samples from the fracture/implant interface with separate clean instruments; do not rely on swabs
• Frozen section where available: greater than 5 polymorphonuclear cells per high-power field in at least 5 fields suggests infection
• If overt infection is found intraoperatively: abandon single-stage conversion; debride, remove hardware, place an antibiotic spacer, and stage the arthroplasty
• If cultures return positive after an implanted conversion (unexpected positive cultures, reported in 5 to 15 percent), treat as early prosthetic joint infection with targeted antibiotics, with or without DAIR depending on organism, number of positive samples and clinical picture

• Greater trochanter: united, non-united, migrated or fragmented? Palpate; assess abductor power and Trendelenburg sign (patient standing, examiner behind, patient lifts contralateral foot; pelvis drops to the unsupported side or trunk lurches to the stance side in abductor insufficiency). A migrated trochanter more than 2 cm proximal is hard to reduce and fix
• Abductor quality: prior lateral (Hardinge) approaches and repeated surgery scar the abductors; MRI (metal artefact reduction) can grade fatty atrophy if reconstruction decisions hinge on it
• Femoral deformity: varus malunion medialises the shaft and may block straight-stem passage; measure neck-shaft angle and canal diameter on calibrated AP pelvis and full-length femur views
• Leg lengths: block test clinically; radiographic leg length from inter-teardrop line to lesser trochanters. Collapse typically shortens the limb 1 to 2 cm — patients expect correction; warn about sciatic stretch limits (avoid acute lengthening much beyond 3 to 4 cm)

• AP pelvis (calibrated), AP and lateral hip, full-length femur — mandatory. The full-length film shows nail length, distal locking screws and canal geometry
• CT pelvis/hip when a screw has penetrated the joint: quantifies acetabular defect, medial wall integrity, protrusio; CT also confirms trochanteric non-union and union status of the fracture
• Templating:
  • Cup: restore native centre of rotation; anticipate medial defect after cut-through — template a multihole shell and screws
  • Stem: choose length to bypass the most distal empty screw hole (lag screw hole in the lateral cortex and distal locking holes) by at least two cortical diameters; template offset against the contralateral hip because varus collapse falsely reduces apparent offset on the affected side
  • Plan leg length correction from the un-fractured side
• Cross-match blood; conversion cases bleed substantially more than primaries; consider cell salvage and tranexamic acid per protocol

Position — lateral decubitus on a pegged table for posterior or anterolateral approach. The posterior approach gives extensile access to the femur and avoids further abductor injury but carries the higher baseline dislocation risk — a reason many surgeons pair it with dual mobility in conversions.

Imaging and equipment — image intensifier available (confirm complete hardware removal, stem position, bypass length). Universal screw removal set, carbide-tipped extraction bits, trephines matched to screw diameter, reverse-threaded extractors, metal-cutting burr, nail-specific extraction jig if identifiable from records, cerclage cables, claw/hook plate, revision stem inventory (long cementless and cemented options), multihole acetabular shells, dual mobility, allograft.

Preparation — identify the exact implant from operative notes before surgery; hold antibiotics until deep cultures taken if infection workup was equivocal, otherwise standard prophylaxis; tranexamic acid; cell salvage for anticipated blood loss.

Approach and dissection — incorporate or extend the previous lateral scar where practical. Expect scarred, distorted planes; identify the sciatic nerve deliberately in posterior approaches (scar tethers it closer than expected). Release adhesions before attempting dislocation — a stiff, screw-hole-riddled femur fractures with forced rotation.

• DHS/sliding hip screw: remove side-plate screws distal to proximal, then plate, then back the lag screw out; if the head is grossly damaged, perform the neck osteotomy first and deliver the head with the lag screw inside it — quicker and less traumatic
• Cephalomedullary nail: remove distal locking screw(s) under image, then set screw, lag screw, then nail with its extraction jig. A neck cut before lag screw removal again simplifies delivery of the head
• Cannulated screws: often removed after the neck osteotomy — the head with embedded screw tips comes out en bloc; lateral screw heads back out through the original stabs or the main wound
• Stripped/cold-welded screws: escalate stepwise — new driver with firm axial load, carbide extraction bit, conical reverse-threaded extractor, trephine over the shank, finally burr off the head and trephine the shank after plate removal. Retained deep broken fragments distal to the planned stem may be left if sterile and not obstructing the canal — removal must not cost more bone than it saves
• Take deep tissue cultures at hardware removal before systemic antibiotics if any residual suspicion of infection

The stress-riser rule — the stem tip must bypass the most distal cortical defect (lateral lag screw hole, most distal plate screw hole, distal locking holes) by at least two cortical diameters (some teach two shaft diameters). Empty holes take 8 to 12 weeks or more to regain torsional strength.

Stem selection

• Cementless tapered or fit-and-fill — younger patients, good bone. A conventional-length stem suffices after cannulated screws if bypass is achieved; after DHS/nail, a longer primary or revision-length tapered stem is often needed. Beware the sclerotic lag screw track deflecting broaches into varus
• Long cementless (modular fluted tapered or fully coated) — proximal bone loss, trochanteric fragmentation, long lateral defects, or when distal fixation must be relied upon
• Cemented long stem — elderly osteoporotic wide canals, especially after nail removal where proximal fit is poor. Occlude screw holes (bone plugs, finger pressure, cement restrictor technique) to prevent cement extrusion and preserve pressurisation; a cement mantle bridging holes also restores torsional strength immediately, allowing unrestricted weight bearing
• Prophylactic cerclage cable just proximal to the calcar or around defect zones before broaching in fragile bone; gentle in-line rotation during dislocation and preparation

At-risk structures — sciatic nerve (posterior scar), femoral cortex (fracture through holes), abductors and superior gluteal neurovascular bundle (proximal trochanteric work).

Acetabulum after cut-out/cut-through

• Inspect for cartilage scoring, screw-track defects, medial wall thinning and protrusio
• Ream cautiously, working peripherally to preserve the medial wall; impaction graft contained medial defects with autograft head (if uninfected and viable) or allograft
• Multihole cementless shell with supplementary screws is the default; highly porous shells for compromised bleeding bone; cemented cup acceptable in the elderly with adequate rim

Bearing and stability

• Dual mobility or a 36 mm head in most conversions — abductor compromise, prior posterior scarring and altered proximal anatomy justify it; constrained liners reserved for salvage of an unreconstructable abductor mechanism in low-demand patients
• Meticulous restoration of offset and length; trial and test stability through full range including flexion-internal rotation and extension-external rotation

Trochanteric non-union

• Mobilise, debride the pseudarthrosis, reduce to the lateral femur, fix with a trochanteric claw/hook plate and cables (cables passed proximal to the lesser trochanter, protecting the medial femoral circumflex/perforator zone and, anteriorly, avoiding over-tight cerclage on the nerve-free windows)
• Non-union rates of trochanteric fixation remain substantial (roughly a third in some series); even a fibrous union in a reduced position improves stability versus escape
• Protect abductor repair: abduction pillow or hip abduction brace and limited active abduction for 6 weeks

Closure and aftercare — layered closure over drains only if bleeding demands; weight bearing as tolerated with a cemented or well-fixed bypassing cementless stem, protected weight bearing 6 weeks if bone quality or trochanteric fixation is tenuous; posterior precautions per approach and bearing; radiograph before discharge to confirm bypass and no fracture; 14-day cultures reviewed and unexpected positives managed with infection team input.