Subsidence of the Femoral Stem

Subsidence refers to the downward (axial) migration of the femoral prosthesis stem within the femoral canal following total hip arthroplasty (THA). It is one of the most important radiographic indicators of implant fixation status.

How It Is Measured

Subsidence is quantified by measuring the distance between a fixed point on the stem and a radiographic landmark such as:

A trochanteric wire or cable
A bony prominence (lesser or greater trochanter)

Serial radiographs are essential - single films are insufficient because differences in magnification and positioning can mimic or mask migration.

Campbell's Operative Orthopaedics 15th Ed 2026, p. 325

Subsidence in Cemented Femoral Stems

Subsidence of a cemented stem is one of the cardinal signs of loosening. The full list of loosening signs includes:

Radiolucency between the superolateral stem (Gruen zone 1) and cement mantle - indicates debonding and possible stem deformation
Radiolucency between the cement mantle and surrounding bone
Subsidence of the stem alone, or stem + cement mantle together
Change into varus position
Fragmentation of cement (especially Gruen zone 7, superomedial)
Fracture of the cement mantle (especially Gruen zone 4, near tip)
Deformation of the stem
Fracture of the stem

Harris Radiographic Grading of Loosening:

Grade	Criteria
Definite loosening	Migration of the component or cement
Probable loosening	Complete radiolucency around cement mantle
Possible loosening	Incomplete radiolucency >50% of cement

Subsidence may not be noticed unless serial films are carefully compared. The stem may subside within the cement (often with cement fracture near the tip), or the entire cement-stem construct may subside together.

Technical factors predisposing to loosening/subsidence:

Failure to remove soft cancellous bone from medial femoral neck
Inadequate cement mantle thickness
Inadequate cement quantity or pressurization
Stem motion during cement hardening
Malalignment (non-neutral positioning)
Cement voids from poor mixing technique
Campbell's Operative Orthopaedics 15th Ed 2026, pp. 324-326

Subsidence in Cementless Femoral Stems

Engh Classification of Cementless Fixation

Engh et al. proposed a 3-category radiographic classification:

Category	Criteria
Bone Ingrowth	No subsidence, minimal/no radiopaque lines, spot welds present, possible cortical hypertrophy distally and proximal stress shielding
Stable Fibrous Fixation	No progressive migration, but extensive parallel radiopaque lines ~1 mm from stem surface; no cortical hypertrophy
Unstable	Progressive subsidence/migration, divergent radiopaque lines (wider at extremities), increased cortical density beneath collar and at stem tip

Fig. 4.130 - Unstable cementless stem with subsidence and circumferential radiolucencies (shown below):

Unstable cementless femoral stem with subsidence and circumferential radiolucencies surrounding the entire stem

Early vs. Late Subsidence - Key Distinction:

Early subsidence (shortly after surgery): May actually be beneficial - it allows the stem to seek a more stable position within the canal. Bone ingrowth can still occur, and early subsidence is compatible with durable fixation.
Late subsidence (months to years post-op): Implies unstable fixation. A bony pedestal often develops at the stem tip (Gruen zone 4) - evidence of pistoning.

Other radiographic signs of cementless instability:

Progressive bead shedding from porous coating on serial films = micromotion at bone-implant interface
Neocortex formation (cortical bone around smooth distal portion of proximally-coated stem) - when seen without subsidence, it is a variant of normal fixation seen with tapered wedge designs
Calcar atrophy/rounding - paradoxically, a sign of good proximal osseointegration (stress transfer to proximal stem)
Campbell's Operative Orthopaedics 15th Ed 2026, pp. 325-326

Collar vs. Collarless Stems and Subsidence

The role of a collar in preventing subsidence is debated:

A collarless stem may allow small amounts of early subsidence, enabling better canal fit and promoting bone ingrowth
A collar might resist subsidence but can also prevent optimal seating
Campbell's Operative Orthopaedics 15th Ed 2026, p. 283 (Classification of Cementless Stem Designs)

Subsidence in Revision Surgery (Impaction Bone Grafting)

In femoral impaction grafting for revision THA, a small degree of subsidence of the collarless polished tapered stem is expected and acceptable. The graft consolidates as the stem subsides slightly, restoring bone stock.

A 2025 meta-analysis of 2,514 hips specifically examined graft incorporation and stem subsidence in femoral impaction bone grafting, confirming that measured subsidence is a routine part of the technique's outcome assessment.

Recent Evidence (2026 Meta-Analysis)

A landmark 2026 systematic review and meta-analysis (Van der Water et al., Acta Orthopaedica, PMID 41989304) of 73 studies, 2,970 uncemented stems measured by radiostereometric analysis (RSA) found:

Time point	Pooled subsidence	Pooled retroversion
3 months	0.29 mm (95% CI 0.19-0.39)	0.51° (CI 0.33-0.70)
2 years	0.32 mm (CI 0.21-0.43)	0.70° (CI 0.48-0.93)

Key findings:

Most subsidence occurs within the first 3 months, then stabilizes
Hydroxyapatite (HA)-coated stems showed the least migration (0.26 mm)
Anterior approach showed significantly more migration (1.04 mm at 3 months) than other approaches
Migration patterns differ based on stem type, coating, surgical approach, and timing of baseline measurement

Clinical Significance Summary

Scenario	Interpretation
Early, self-limited subsidence (cementless)	Likely benign; stem seeking stable position
Progressive subsidence months-years later	Unstable fixation; consider revision
Subsidence + pedestal at tip (zone 4)	Pistoning - definite instability
Subsidence + cement migration (cemented)	Definite loosening (Harris criteria)
Subsidence in impaction grafting revision	Expected; part of normal graft consolidation

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