Abstract
Background
Patellofemoral complications have dwindled with contemporary total knee designs that market anatomic trochlear grooves that intend to preserve normal patella kinematics. While most reports of patellofemoral complications address patella and its replacement approach, they do not focus on shape of trochlear grooves in different prostheses [1]. The purpose of this study was to characterize 3D geometry of trochlear grooves of contemporary total knee designs (NexGen, Genesis II, Logic, and Attune) defined in terms of sulcus angle and medial-lateral offset with respect to midline of femoral component in coronal view and to compare to those of native femurs derived from 20 osteoarthritic patient CT scans.
Materials and Methods
Using 3D models of each implant and native femur, sulcus location and orientation were obtained by fitting a spline to connect sulcus points marked at 90°, 105°, 130°, and 145° of femoral flexion (Fig A). Implant reference plane orientations were established using inner facets of distal and posterior flanges. Reference planes of native femurs were defined using protocols developed by Eckhoff et al. [2] where coronal plane was defined using femoral posterior condyles and greater trochanter. In the coronal plane, a best fit line was used to measure sulcus angle and medial-lateral offset with respect to midline at the base of trochlear groove (Fig B).
Results
With exception to Logic (0° sulcus angle & 0 mm offset), contemporary knee designs include high valgus angulations (4° to 18°) with laterally-biased offsets (3 to 5 mm). The native sulcus angle on average was slightly valgus, but varied significantly among the cohort (−0.2° ± 4.6°). Native trochlear groove offset was biased laterally (2.5 ± 1.7 mm).
Discussion
We observed a considerable geometric deviation between native femur and implants in terms of sulcus angle while both geometries displayed comparable lateral bias at the base of trochlear groove. Similar to past studies by Iranpour et al. [4] and Feinstein et al. [5], a large variation in sulcus angle was observed among the selected native femurs with an average of small valgus angulation (Fig C). However, most contemporary trochlear grooves are biased towards higher valgus angulations. Retrieval and registry studies have shown that NexGen trochlear groove design (4° sulcus angle) has been shown to better accommodate natural patellas, which highlights that the differences among designs may be significant [5,6]. It remains unclear which features specifically translate to better patellafemoral outcomes, which is a merit for further study.
Conflict of Interest: None
Figure A. Sulcus points defined at various flexion angles. Figure B. Best fit line to measure ML-offset and sulcus angle. Figure C. Sulcus angle comparison to past studies
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