Upright CT of the knee: the effect of weight-bearing on joint alignment.
OBJECTIVE
To prospectively compare patellofemoral and femorotibial alignment in supine non-weight-bearing computed tomography (NWBCT) and upright weight-bearing CT (WBCT) and assess the differences in joint alignment.


METHODS
NWBCT and WBCT images of the knee were obtained in 26 patients (mean age, 57.0 ± 15.9 years; range, 21-81) using multiple detector CT for NWBCT and cone-beam extremity CT for WBCT. Two musculoskeletal radiologists independently quantified joint alignment by measuring femorotibial rotation, tibial tuberosity-trochlear groove distance (TTTG), lateral patellar tilt angle, lateral patellar shift, and medial and lateral femorotibial joint space widths. Significant differences between NWBCT and WBCT were sought using Wilcoxon signed-rank test (P-value < 0.05).


RESULTS
Significant differences were found for femorotibial rotation (the NWBCT mean changed from 2.7° ± 5.1 (reader 1)/2.6° ± 5.6 (reader 2) external rotation to WBCT 0.4° ± 7.7/0.2° ± 7.5 internal rotation; P = 0.009/P = 0.004), TTTG (decrease from NWBCT (13.8 mm ± 5.1/13.9 mm ± 3.9) to WBCT (10.5 mm ± 5.0/10.9 mm ± 5.2; P = 0.008/P = 0.002), lateral patellar tilt angle (decrease from NWBCT (15.6° ± 6.7/16.9° ± 7.4) to WBCT (12.5° ± 7.7/15.0° ± 6.2; P = 0.011/P = 0.188). The medial femorotibial joint space decreased from NWBCT (3.9 mm ± 1.4/4.5 mm ± 1.3) to WBCT (2.9 mm ± 2.2/3.5 mm ± 2.2; P = 0.003/P = 0.004). Inter-reader agreement ranged from 0.52-0.97.


CONCLUSIONS
Knee joint alignment changes significantly in the upright weight-bearing position using CT when compared to supine non-weight-bearing CT.


CONCLUSIONS
• Cone-beam extremity CT offers upright weight-bearing examinations of the lower extremities. • Knee alignment changes significantly in an upright position compared to supine position. • Tibial tuberosity-trochlear groove distance (TTTG) is less pronounced in a weight-bearing position. • The weight-bearing position leads to a decrease of the lateral patellar tilt angle.
Department of Radiology, Orthopedic University Hospital Balgrist, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland. anna.hirschmann@usb.ch.|Clinic of Radiology and Nuclear Medicine, University of Basel Hospital, Petersgraben 4, 4031, Basel, Switzerland. anna.hirschmann@usb.ch.
Anna
A
Hirschmann
Department of Radiology, Orthopedic University Hospital Balgrist, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland.
Florian M
FM
Buck
Orthopedic Surgery, Orthopedic University Hospital Balgrist, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland.
Sandro F
SF
Fucentese
Department of Radiology, Orthopedic University Hospital Balgrist, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland.
Christian W A
CW
Pfirrmann
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D054893:Cone-Beam Computed Tomography; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000033:anatomy & histology* / Q000502:physiology; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D010329:Patella / Q000033:anatomy & histology*; D056888:Patient Positioning; D012399:Rotation; D013977:Tibia / Q000033:anatomy & histology*; D014057:Tomography, X-Ray Computed; D016474:Weight-Bearing / Q000502:physiology; D055815:Young Adult
Cone-beam extremity CT; Knee alignment; Lateral patellar tilt angle; Tibial tuberosity-trochlear groove (TTTG); Upright weight-bearing CT