Distal femoral bone mineral density decreases following patellofemoral arthroplasty: 1-year follow-up study of 14 patients.
BACKGROUND
The bone mineral density (BMD) of the distal femur decreases by 16-36% within one year after total knee arthroplasty (TKA) because of the femoral component's stress-shielding effect. The aim of this prospective study was to determine the quantitative change from the baseline BMD in the distal femur 1 year after patellofemoral arthroplasty using dual-energy X-ray absorptiometry (DXA).


METHODS
Between December 2007 and December 2008, 14 patients had patellofemoral arthroplasty for isolated patellofemoral osteoarthritis. Distal femoral BMD was assessed using DXA in 2 regions of interest (ROI) on the lateral view 2 weeks before and 12 months after patellofemoral arthroplasty. The contra-lateral knee was used as a control, with BMD measurements performed in identical ROIs.


RESULTS
The mean change from baseline BMD in the operated knees after 1 year was -0.169 g/cm2 (95% CI: -0.293 to -0.046 g/cm2) behind the anterior flange (-15%), and -0.076 g/cm2 (95% CI: -0.177 to 0.024 g/cm2) in the supracondylar area 1 cm above the prosthesis (-8%) (p = 0.01 and p = 0.13, respectively). The mean change from baseline BMD in the non-operated knees after 1 year was 0.016 g/cm2 (95% CI: -0.152 to 0.185 g/cm2) behind the anterior flange (2%), and 0.023 g/cm2 (95% CI: -0.135 to 0.180 g/cm2) in the supracondylar area 1 cm above the prosthesis (2%) (p = 0.83, and p = 0.76, respectively).


CONCLUSIONS
Our findings suggest that patellofemoral arthroplasty results in a statistically significant decrease in BMD behind the anterior flange.
van Jonbergen
Hans-Peter W
HP
Department of Orthopedic Surgery, Deventer Hospital, Nico Bolkesteinlaan 75, 7416 SE Deventer, The Netherlands. vanjonbergen@dz.nl
Koster
Kenneth
K
Labey
Luc
L
Innocenti
Bernardo
B
van Kampen
Albert
A
D015502:Absorptiometry, Photon; D000328:Adult; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects*; D001696:Biomechanical Phenomena / Q000502:physiology; D001862:Bone Resorption / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology*; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D005500:Follow-Up Studies; D006801:Humans; D007049:Iatrogenic Disease / Q000517:prevention & control; D008297:Male; D008875:Middle Aged; D010329:Patella / Q000601:surgery; D011183:Postoperative Complications / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology*; D011446:Prospective Studies; D013314:Stress, Mechanical; D013995:Time; D013997:Time Factors; D016474:Weight-Bearing / Q000502:physiology
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