The Relationship between Frontal, Axial Leg Alignment, and Ankle Joint Line Orientation-a Radiographic Analysis of Healthy Subjects

OBJECTIVE

Ankle joint line orientation (AJLO) is influenced by the subtalar foot and frontal leg alignment. However, the influence of axial leg alignment on AJLO remains unclear. The study aimed to analyze the influence of frontal, axial leg alignment on AJLO in healthy subjects.

METHODS

Thirty healthy subjects (60 legs) without prior surgery underwent standing biplanar long leg radiograph (LLR) between 2016 and 2020. AJLO was measured in standing long-leg radiographs relative to the ground. Meary's angle and calcaneal pitch were measured. Hip-knee-ankle angle (HKA), femoral antetorsion, and tibial torsion were assessed with SterEOS software (EOS Imaging, Paris, France). LLR was acquired with the feet directing straight anteriorly, which corresponds to a neutral foot progression angle (FPA). The influence of subtalar, frontal, and axial alignment on AJLO was analyzed in a multiple regression model.

RESULTS

An increase in knee valgus increased relative valgus AJLO by 0.5° (95% CI: 0.2° to 0.7°) per 1° (P < 0.001). A decrease in femoral antetorsion increased relative valgus AJLO by 0.2° (95% CI: 0.1° to 0.2°) per 1° (P < 0.001), whereas Meary's angle and calcaneal pitch did not influence AJLO.

CONCLUSION

A link between frontal, axial leg alignment, and AJLO could be demonstrated, indicating that a valgus leg alignment and relative femoral retrotorsion are associated with an increase of valgus AJLO in healthy subjects when placing their feet in a neutral position. Alteration of the frontal, or rotational profile after realignment surgery or by implant positioning might influence the AJLO, when the FPA is kept constant.

Joint line position in revision total knee arthroplasty: the role of posterior femoral off-set stems

BACKGROUND

Elevation of the joint line frequently occurs in revision total knee arthroplasty (RTKA) because of a wider flexion space than extension space. One solution to balance this flexion-extension space involves the introduction of couplers between the stem and femoral components, and the use of posteriorly offset femoral stems that we hypothesized would improve gap balancing and facilitate joint line restoration.

METHODS

We retrospectively reviewed a selected series of 43 RTKA. Postoperative joint line height was subtracted from intended height using postoperative lateral radiographs. The value was negative if the joint line position was lowered, and positive if raised.

RESULTS

Forty knees were followed for a mean of 3.5years. Mean postoperative joint line position change from intended position was 1.5mm (range -2.5-7.5mm). In 28 knees (70%), the joint line position was restored to within ±2mm of the intended position; in eight knees (20%), from 2-4mm; and in four knees (10%), >4mm. Joint line position was raised in 32 knees (80%) and lowered in eight (20%). In the offset stem knees, the intended joint line position was 0.9mm (range -1.2-3.4mm) as compared with 3.2mm (range -2.5-7.5mm) for the straight stem knees.

CONCLUSIONS

A coupler system between the femoral stem and femoral component restored the joint line in 70% of cases. The posterior offset stem provided increased posterior condylar offset, addressed the wider flexion space, provided better positioning of the stem, and restored the joint line.

LEVEL OF EVIDENCE

Therapeutic Study Level IV.