Introduction: With the development of powerful computing tools, it is now possible to quantify variations in skeletal morphology using standardized analytical protocols. In this presentation, we describe the development of computer-based tools to analyze components of femoral deformity in developmental hip dysplasia (DDH) and femoro-acetabular impingement (FAI).

Methods: Typically, three dimensional surface-splined computer models of bones are generated by reconstructing CT scan data. The models generated are then segmented into discrete objects (e.g. the femoral head, neck, shaft, condyles, sulcus, and apophyses) and a coordinate system is attached to each anatomic object to define its relative position and orientation in space. The size of each object can be described by characteristic parameters (eg height, length, width), and its shape with dimensionless ratios (eg width/length). Other methods include principal component analysis which expresses te principal sources of statistical variation in object dimensions, and correspondence analysis, which describes the variation of each point on the surface of a bone compared to the average specimen in the observed population.

Illustrative Applications:

DDH

These methods have been applied to examine systematic variations in the shape and dimensions of the dysplastic femur through reference to data from 171 dysplastic and 84 skeletally normal patients. Of the 171 dysplastic femora, 74 (43%) were graded as Crowe I, 82 (48%) as Crowe stages II or III, and 15 (9%) as Crowe IV. The change in femoral morphology was quantified as a function of the grade of deformity in comparison with normal controls. The principal sources of deformity were also identified.

Results: The results of these analyses will be presented during the lecture.

Conclusions: Mathematical analysis of the shape of bones allows us to describe the type and severity of skeletal deformities in precise quantitative terms. This leads to new, three-dimensional definitions of skeletal phenotypes, and allows automated screening and classification of imaging data sets for the detection of dysmorphic conditions. This approach also has the potential to provide new insights into the true nature of complex deformities presenting for orthopedic treatment.

We report the radiological and clinical outcome of a press-fit (SLF) acetabular component at two to three years in two groups of patients having primary total hip replacement. In 69 the implant was coated with hydroxyapatite (HA) and in 40 it was uncoated. The stability of the cup was assessed by measurement of proximal migration and change in the angle of inclination.

The clinical results in the two groups did not differ significantly, and the mean proximal linear wear was similar in both. Fewer radiolucent lines (RLLs) were seen on the radiographs of cups coated with HA.

The mean proximal migration was studied by calculating regression lines for each patient using migration measurements: for the SLF+HA group the mean slope was 0.06 mm/year and for the SLF–HA group 0.20 mm/year (p = 0.22). The change in the angle of inclination during follow-up was also consistently smaller in HA–coated cups. Using regression methods the SLF+HA group had a mean slope of 0.08°/year and the SLF-HA group 0.44°/year (p = 0.023).

Partial HA coating appeared to have no effect on the clinical outcome or on the rate of wear of polyethylene, but there was a trend towards a reduced rate of proximal migration, and a significant reduction in rotational migration and the number of radiolucent lines. This suggests that HA coating enhances the stability of this acetabular component.