[Effects of changes in axis length of patella on patellofemoral contact areas and pressures].
OBJECTIVE
To explore the effects of changes in the length of the patella on patellofemoral contact areas and pressures, to provide a theoretical foundation for treatment of lower pole of patella fracture.


METHODS
Using homemade-loading equipment, pressure sensitive films of 100 mm x 100 mm in size were placed on the force platform, vertically downward load (0-19.6 N) was given. The pressure-sensitive response curve was obtained by computer image analysis of the pressure-sensitive tablets and calculation. Six male left fresh knee specimens from voluntary donation were placed in homemade-test fixed load device, and the double-layer pressure sensitive film was placed on the patellofemoral joint surface; under loading of 196 N at flexion of 0, 15, 30, 45, 60, 75, 90, 105, 120, and 135 degrees for 2 minutes, respectively, the pressure sensitive film was removed as the control group. Patellas were transected cut and in situ fixed by Kirschner wire and steel-wire as in situ fixation group. Bone fragments obtained from the corresponding 1/6 and 2/6 of contralateral patella, were embedded in the interspace between osteotomy with internal fixation with Kirschner wire and steel-wire respectively as lengthening group. Followed by the amputating patella length of 1/6, 2/6, 3/6 from proximal to distal and internal fixation with Kirschner wire and steel wire by turns as a shortening group. Repeat the above steps of each experiment. By image analysis the pressure sensitive film, the patella joint contact area were measured, and patellar contact pressure (including the peak pressure and average pressure) was calculated according to pressure-sensitive response curve.


RESULTS
The actual contact area were significantly smaller in the shortening groups than in the control group at flexion of 30-135 degrees (P < 0.05); the pressure was significantly bigger in shortening 1/6 group at flexion of 0, 15, 60, and 75 degrees, in shortening 2/6 group at flexion of 0 degrees and 75-135 degrees, and in shortening 3/6 group at flexion of 0-30 degrees and 75-135 degrees than in the control group (P < 0.05); the peak pressure was significantly bigger in shortening 1/6 group at flexion of 0, 15, and 60-105 degrees, in shortening 2/6 group at flexion of 0, 15, and 75-105 degrees, and in shortening 3/6 group at flexion of 0, 30, and 60-135 degrees than in the control group (P < 0.05). The actual contact area was significantly smaller in the lengthening groups than in the control group at flexion of 15, 60, and 90 degrees, and it was bigger at flexion of 105, 135 degrees in lengthening 2/6 group than in the control group (P < 0.05); the pressure was significantly bigger in the lengthening groups at flexion of 15-75 degrees than in the control group and it was smaller in the lengthening groups at flexion of 105, 135 degrees, and smaller in lengthening 2/6 group at flexion of 120 degrees (P < 0.05); the peak pressure was significantly smaller in lengthening 1/6 group than in the control group at flexion of 0, 90, and 105 degrees and smaller in lengthening 2/6 group at flexion of 0 degrees (P < 0.05). The actual contact area was significantly bigger in all lengthening groups than in all shortening groups at flexion of 30, 45, and 75-135 degrees (P < 0.05). The pressure was significantly bigger in shortening 1/6 group than in lengthening groups at flexion of 0, 60, and 90 degrees (P < 0.05), in shortening 2/6 group at flexion of 0, 60, and 90-120 degrees (P < 0.05), in shortening 3/6 group at flexion of 0-135 degrees (P < 0.05). The peak pressure was bigger in shortening groups than in lengthening 1/6 group at flexion of 0, 90, and 105 degrees (P < 0.05), bigger than lengthening 2/6 group at flexion of 0 degrees (P < 0.05).


CONCLUSIONS
To treat comminuted fracture of the inferior pole of patella, the partial resection or the late lengthening after preserving the patella has less effect on knee joint function, especially at the patella to be cut less than 1/6 or after surgery lengthening of less than 1/6, while the latter is better than the former. The patella should be preserved as much as possible. If the patellar partial resection is inevitable, the length resection should be less than 1/6, it also can get satisfactory results.
Zhang
Xinglin
X
Department of Orthopaedics, Yantaishan Hospitial, Yantai Shandong 264001, PR China.
Chen
Xu
X
Jiang
Junjie
J
Jia
Peitong
P
Zhou
Zhiyong
Z
Sun
Tao
T
Liu
Shaoxian
S
Chu
Kai
K
D000328:Adult; D006801:Humans; D007719:Knee Joint / Q000473:pathology* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010329:Patella / Q000033:anatomy & histology* / Q000473:pathology / Q000601:surgery; D011312:Pressure