Influence of bone morphology and femur preparation method on the primary stability of hip revision stems

Abstract

Aseptic loosening is one of the major reasons for re-revisions of cementless revision stems. Insufficient primary stability is associated with bone characteristics and the surgical process. This study aimed to investigate how femur morphology and preparation methods influence the primary stability of revision stems. The Femur morphology was described by the upper femoral curvature (UFC) and an individualized Dorr type classification based on the ratio between the canal-to-calcar ratio (CCR*) and the cortical index (CI*) introduced as the cortical-canal shape (CCS). Manual and powered reaming in combination with helical and straight reamers were used to prepare the bone cavity of 10 cadaveric human femur pairs. Forces during stem impaction were recorded (Reclaim, Depuy Synthes). Micromotion at the bone-implant interface during cyclic axial loading and torsional load to failure was determined. The CCS and impaction forces (R 2 = 0.817, p < 0.001) or torsional strength (R 2 = 0.577, p < 0.001) are inversely related. CCS did not correlate with micromotion during axial loading (R 2 = 0.001, p > 0.999), but proximal femoral curvature did (R 2 = 0.462, p = 0.015). Powered reaming and straight reamers led to an improved torsional strength (both: p = 0.043). The Individualized Dorr classification CCS and UFC allows a good estimation of the primary stability of revision stems. For severely curved Dorr type-C femurs, an alternative anchorage method should be considered clinically.

The influence of hip revision stem spline design on the torsional stability in the presence of major proximal bone defects

“…Cortical (1056 ± 62 mgHA/cm 3 ) as well as trabecular BMD (272 ± 49 mgHA/cm 3 ) were similar for both stem design groups (p cortical = 0.893, p trabecular = 0.762, independent t-test). About 70% of the bones were Dorr type C according to the adjusted definition of Konow et al [ 19 ].…”

“…Hounsfield units were converted to bone mineral density (BMD) in terms of hydroxyapatite concentrations (Structural Insight 3; University Medical Center Schleswig-Holstein [ 18 ], Kiel, Germany). Cortical BMD was determined in a 10 mm-wide ring of the femoral shaft at a distance of 5.8% body height distal to the trochanter minor [ 19 ]. An image processing algorithm was used to automatically detect the minor trochanter (threshold: [400–2000 mgHA/cm 3 ] [ 20 ]; Matlab 2022a; The Mathworks, Natick, MA).…”

Stem size and stem alignment affects periprosthetic fracture risk and primary stability in cementless total hip arthroplasty

“…Bone morphology was quantified (Matlab 2020b; The MathWorks) using the Cortical-Canal-Shape (CCS). 27 A higher CCS corresponds to an aged bone morphology.…”

“…Femur‐specific BMD was determined from a 10 mm³ cubic region of interest (ROI) in the head center (AVIZOLite 9.7.0; Thermo Fisher Scientific). Bone morphology was quantified (Matlab 2020b; The MathWorks) using the Cortical‐Canal‐Shape (CCS) 27 . A higher CCS corresponds to an aged bone morphology.…”

Small design modifications can improve the primary stability of a fully coated tapered wedge hip stem

“…The final positions of the stem and the final broach in the femur cavity were compared using superimposed laser-scans to compare the seating behavior of the stems quantified by the angle between the broach and implant axis (seating rotation) and the height difference of stem and broach (seating depth). The final position of the implant (varus / valgus tilt) and the canal-fill-ratio was also determined [ 36 ]. The canal-fill-ratio is the ratio between the stem area and the cavity area in a sagittal section of the implanted femur averaged along the entire stem [ 36 ].…”