Subtrochanteric varisation explains age-related changes in proximal femoral morphology and has implications for hip arthroplasty and trauma surgery

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BACKGROUND: Age-related varus remodeling of the proximal femur is well recognized, but its anatomical center of rotation remains unclear. Varus proximal femoral morphology plays a relevant role in fracture patterns, implant positioning, and surgical exposure in geriatric trauma surgery. We investigated whether correlations between the caput-collum-diaphyseal angle (CCD) and trochanteric rotation/offset parameters indicate a subtrochanteric origin of femoral varisation. METHODS: 100 CT angiographies of the pelvis-leg axis from patients of different ages were analyzed. CCD and the critical trochanter angle (CTA) were assessed in their conventional and modified forms (mCCD/mCTA). Additional parameters included greater (OGT/OGTI) and lesser trochanter offsets (OST/OSTI), femoral antetorsion, and trochanteric anteversion/retroversion. Bone quality was classified according to Dorr. RESULTS: mCCD showed a significant negative correlation with age, confirming increasing varus alignment in older individuals. CTA and mCTA positively correlated significantly with both CCD and mCCD (CTA/CCD: p = 0.005 and CTA/mCCD p < 0.001; mCTA: with both CCD & mCCD p < 0.001), indicating that increased medial trochanteric overhang is strongly associated with varus morphology. OGT and OGTI demonstrated strong positive correlations with CCD and mCCD (OGT: with both p < 0.001, OGTI: with both p = 0.001), whereas OST and OSTI correlated negatively with CCD (p = 0.032 and p = 0.02), reflecting a decrease in greater trochanter offset and an increase in lesser trochanter offset with progressive varisation. Posterior trochanteric orientation (PTO) of the greater trochanter correlated positively with CCD/mCCD, indicating reduced retroversion in varus hips. In contrast, femoral neck anteversion and anterior trochanteric anteversion showed no significant correlation with CCD parameters (p = 0.889 and p = 0.125). Lower CCD values were significantly associated with more osteoporotic Dorr types (Kendall's Tau: -0.212 for CCD, p = 0.008; -0.197 for mCCD, p = 0.014). CONCLUSION: Correlation patterns suggest that age-dependent varisation occurs predominantly in the subtrochanteric region. This morphology may complicate exposure and stem alignment in total hip arthroplasty in varus hips and should influence implant selection, stem design and fracture-related implant strategies in elderly patients.

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