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Linear influence of distal femur osteotomy on the Q-angle: one degree of varization alters the Q-angle by one degree

A Flury, Lukas Jud, A Hoch, R S Camenzind & S F Fucentese

abstract

PURPOSE
The effect of a distal femur varization osteotomy on patellofemoral biomechanics in genu valgum is unknown. The purpose of this study was to quantify the influence of frontal leg axis correction on the Q-angle with a novel three-dimensional (3-D) measurement method.

METHODS
3-D surface models of ten lower extremities were generated using patient computed tomography (CT) data. The preoperative 3-D Q-angle was measured using a novel defined and validated 3-D measurement method. Biplanar supracondylar osteotomies were simulated with different degrees of varus correction (from 1° to 15°) in one-degree steps beginning from the preoperative valgus deformity, resulting in a total of 150 simulations. Additionally, mechanical leg axis and 3-D Q-angle measurements were performed on 3-D surface models of the postoperative CT scans of the same individuals. Further, pre- and postoperative TT-TG distance was measured.

RESULTS
Mean preoperative Q-angle was 15.8 ± 3.9° (range 10°-21.4°) with a mean preoperative mechanical leg axis of 6.5° ± 2.4 valgus (range 3.8°-11.6° valgus). The Q-angle changed linearly 0.9 ± 0° per 1° of varization. No difference was detected between simulated 3-D Q-angles and effectively corrected postoperative values (n.s.). TT-TG distance changed irregularly and minimally, and with no correlation to the degree of varization.

CONCLUSION
Distal femur varization osteotomy has a linear effect on the Q-angle with a change of 1° per 1° of varization. The difference in TT-TG distance was mainly due to an unintentional rotational component implemented during surgery.
   
citation Flury A, Jud L, Hoch A, Camenzind R S, Fucentese S F. Linear influence of distal femur osteotomy on the Q-angle: one degree of varization alters the Q-angle by one degree. Knee Surg Sports Traumatol Arthrosc 2020; 29:540-545.
   
type journal paper/review (English)
date of publishing 09-04-2020
journal title Knee Surg Sports Traumatol Arthrosc (29/2)
ISSN electronic 1433-7347
pages 540-545
PubMed 32274549
DOI 10.1007/s00167-020-05970-1