Seinsheimer Classification — Subtrochanteric Femur

Overview — Subtrochanteric Femur Fractures

Subtrochanteric femur fractures are fractures occurring in the region between the lesser trochanter and a point 5 cm distal to it (the `subtrochanteric zone`). They are mechanically challenging fractures for several reasons: (1) the subtrochanteric region bears the highest mechanical stress per unit area of any long bone in the body — the bending moment is maximised here; (2) the cortical bone of the subtrochanteric region is thicker (cortical dominance) — making fractures here prone to non-union; (3) strong deforming forces from the hip muscles create characteristic deformity (flexion, abduction, and external rotation of the proximal fragment); (4) they carry a high risk of implant failure if the medial cortex is not restored. The Seinsheimer classification (1978), developed by F. Seinsheimer, grades subtrochanteric fractures by the number of bony fragments and the fracture pattern, directly predicting stability and guiding fixation choice.

Deforming forces at the subtrochanteric level: the proximal fragment is subjected to: (1) FLEXION — from the iliopsoas (L2/3 nerve supply — inserts onto the lesser trochanter) pulling the proximal fragment into FLEXION; (2) ABDUCTION — from the hip abductors (gluteus medius + minimus — inserting onto the greater trochanter) pulling the proximal fragment into ABDUCTION; (3) EXTERNAL ROTATION — from the short external rotators (piriformis, obturators, gemelli) inserting onto the posterior greater trochanter; these three forces combine to give the characteristic deformity: the proximal fragment is flexed, abducted, and externally rotated relative to the shaft; this deformity must be corrected at the time of nailing (the nail is inserted while the hip is in flexion, abduction, and external rotation to match the proximal fragment position)
Epidemiology: subtrochanteric fractures occur in two distinct populations — (1) young adults from high-energy trauma (road traffic accidents, falls from height); (2) elderly patients from low-energy falls (particularly those with osteoporosis or Paget`s disease); a specific and important subgroup is atypical subtrochanteric fractures associated with bisphosphonate therapy (long-term bisphosphonate use causes stress fractures at the subtrochanteric region from suppression of bone remodelling)

Seinsheimer Classification

Seinsheimer Type	Fragment Count / Pattern	Description	Stability	Management
Type I — Undisplaced	2 fragments; <2 mm displacement	An undisplaced or minimally displaced fracture (displacement <2 mm); ANY pattern but no significant displacement; rare in clinical practice as most subtrochanteric fractures present with some displacement	STABLE — the cortical contact maintains the fracture position; minimal deforming forces acting across an undisplaced fracture	Non-operative is possible but intramedullary nailing is usually preferred (patients are mobilised earlier and there is no risk of late displacement with the nail); protected weight-bearing with a nail provides early functional recovery
Type II — Two-part (transverse/spiral)	2 fragments	A two-part fracture; subtypes: IIA (two-part transverse fracture); IIB (two-part spiral fracture, with the lesser trochanter on the PROXIMAL fragment — the lesser trochanter remains part of the proximal piece); IIC (two-part spiral fracture, with the lesser trochanter on the DISTAL fragment — the lesser trochanter is on the shaft side)	VARIABLE: IIA (transverse) — moderately stable if medial cortex contacts; IIB — the proximal fragment includes the lesser trochanter and its iliopsoas attachment (flexion deformity is magnified in IIB); IIC — the proximal fragment does NOT include the lesser trochanter (there is no flexion deformity from the iliopsoas); recognising whether the lesser trochanter is on the proximal or distal fragment has practical implications for reduction technique	IM cephalomedullary nail (reconstruction nail with a proximal interlocking screw directed into the femoral head — `reconstruction nail` or `long Gamma nail`); the nail enters the medullary canal from the proximal femur (greater trochanteric entry), bypasses the fracture, and is locked distally; the cephalic interlocking screw prevents proximal fragment rotation; the nail must span the entire fracture zone with adequate proximal and distal fixation
Type III — Three-part	3 fragments (two fracture lines)	A three-part fracture: IIIA (spiral fracture + a separate third fragment — a `butterfly` fragment — that includes the lesser trochanter as a separate piece; the posteromedial wall is lost as the third fragment; the medial cortex is disrupted); IIIB (comminuted fracture — a comminuted butterfly fragment in the subtrochanteric region; the third fragment is comminuted)	UNSTABLE — the third fragment (which often includes the posteromedial cortex) is detached; there is no medial cortical support; varus collapse tendency is highest in IIIA; the loss of the lesser trochanter fragment removes the iliopsoas attachment from the main proximal fragment (but a separate IIIA fragment with the lesser trochanter creates instability)	IM cephalomedullary nail; cerclage wiring of the butterfly fragment to restore medial cortical continuity before nailing is occasionally used; the medial cortical defect must be addressed — if the posteromedial fragment cannot be reduced to bony contact, the nail bears the entire load and is prone to fatigue failure; bone grafting of the medial defect reduces non-union risk
Type IV — Comminuted (≥4 fragments)	≥4 fragments	A comminuted fracture with 4 or more fragments; the subtrochanteric region is extensively comminuted; ALL four criteria for subtrochanteric instability may be present: complete loss of medial cortical support; multiple free fragments; loss of femoral neck-shaft alignment; maximum deforming force exposure; there is NO remaining bony continuity at the fracture site	VERY UNSTABLE — no medial cortical support anywhere; high risk of varus collapse and implant fatigue failure without biological healing; the nail must span a long comminuted zone; bridge plating technique	IM cephalomedullary nail (bridge the comminuted zone — do NOT attempt to reconstruct the fragments individually); bone grafting of the medial cortical defect; cerclage wires to consolidate the fragments around the nail before nailing (in selected cases); biological approach — minimise soft tissue stripping; allow secondary callus formation to bridge the comminuted zone; patience — these fractures are slow to heal
Type V — Involving the lesser trochanter + subtrochanteric zone	Subtrochanteric fracture extending INTO the greater trochanter region (reverse oblique pattern OR fracture extending proximally to involve the greater trochanter)	A subtrochanteric fracture that extends proximally into the intertrochanteric region, involving the greater trochanter; the fracture has both a subtrochanteric and an intertrochanteric component; this includes the `reverse oblique intertrochanteric` fracture with subtrochanteric extension	HIGHLY UNSTABLE — the greater trochanter involvement further destabilises the proximal fragment; the hip abductors lose their bony attachment; this is the most proximal and unstable Seinsheimer type	Long IM cephalomedullary nail to bypass the fracture; the proximal segment may be very short — careful planning for cephalic screw placement; in very proximal fractures with minimal bone above the nail entry, a `trochanteric nail` variant is used to provide more distal entry and longer proximal purchase

Atypical Femoral Fractures (Bisphosphonate-Associated)

Atypical femoral fractures (AFFs): a specific subtype of subtrochanteric (and occasionally distal diaphyseal) fracture occurring in patients on long-term bisphosphonate therapy; bisphosphonates suppress osteoclastic bone remodelling — leading to accumulated micro-damage and stress fractures that cannot be repaired; the fractures typically occur in the subtrochanteric or mid-diaphyseal region of the femur; characteristic features on plain X-ray: (1) transverse fracture with a `medial spike` or `beaked` pattern on one cortex; (2) `lateral cortical thickening` on the plain AP X-ray (a periosteal reaction on the lateral femoral cortex — a `dreaded black line` equivalent); (3) bilaterality (bilateral AFFs in 40–50% of patients); (4) minimal or no trauma history; (5) prodromal thigh pain weeks-months before fracture
Management of AFFs: (1) cessation of bisphosphonate therapy (the most important intervention — consider alternative bone protection such as denosumab or teriparatide after discussion with endocrinology); (2) for incomplete fractures (stress reaction with thigh pain and lateral cortical thickening but no complete fracture) — IM prophylactic nailing is recommended before complete fracture occurs; (3) for complete fractures — IM cephalomedullary nailing; healing is slow (6–12+ months) due to the suppressed bone remodelling; teriparatide (PTH analogue) may be used post-operatively to stimulate healing; (4) contralateral femur assessment (bilateral in ~40–50% — plain X-ray of the contralateral femur to detect an incomplete AFF; prophylactic nailing if lateral thickening is present)

Exam Pearls

Seinsheimer: I (undisplaced); II (two-part — A transverse, B spiral lesser trochanter on proximal, C spiral lesser trochanter on distal); III (three-part — A butterfly with lesser trochanter, B comminuted); IV (≥4 fragments — highly comminuted); V (subtrochanteric + intertrochanteric extension)
Deforming forces: flexion (iliopsoas — lesser trochanter); abduction (hip abductors — greater trochanter); external rotation (short external rotators); the proximal fragment is flexed, abducted, and externally rotated; the nail is inserted with the hip in this position to match the deformity, then the nail corrects alignment as it passes down the canal
IM cephalomedullary nail for all displaced subtrochanteric fractures: standard treatment; reconstruction nail or long Gamma nail; cephalic screw into the femoral head prevents proximal fragment rotation; DHS is CONTRAINDICATED for subtrochanteric fractures (too much bending moment on the plate)
Medial cortical integrity: the most important determinant of stability and prognosis; loss of medial cortex = tendency to varus collapse; restoring medial cortical contact at nailing (by reduction) reduces implant stress; bone grafting of the medial defect promotes union in severely comminuted fractures
Atypical femoral fractures (bisphosphonates): transverse fracture with medial spike; lateral cortical thickening; bilateral in 40–50%; prodromal thigh pain; cease bisphosphonates; IM prophylactic nailing for incomplete AFFs; slow healing; teriparatide post-op; screen contralateral side
IIB vs IIC distinction: IIB — lesser trochanter on the PROXIMAL fragment → iliopsoas acts on the proximal fragment, magnifying the flexion deformity of the proximal fragment → more difficult reduction; IIC — lesser trochanter on the DISTAL fragment → no flexion deformity from iliopsoas on the proximal fragment → easier reduction
Seinsheimer IIIA: butterfly fragment with the lesser trochanter as the third piece — the posteromedial wall (calcar) is the butterfly fragment; this creates the classic three-part subtrochanteric fracture with loss of medial support; cerclage wiring of the fragment to restore medial contact, then IM nail

Seinsheimer Classification — Subtrochanteric Femur

References

Share Wiki