Orientación del componente femoral en artroplastia parcial de cadera. (Inglés)

Paul E. Beaulé, MD, FRCSC1, Jessica L. Lee, MS2, Michel J. Le Duff, MA1, Harlan C. Amstutz, MD1 and Edward Ebramzadeh, PhD3

1 Joint Replacement Institute at Orthopaedic Hospital, 2400 South Flower Street, Los Angeles, CA 90007. E-mail address for P.E. Beaulé: pbeaule@laoh.ucla.edu 2 Department of Biomedical Engineering, University of Southern California, OHE 500, MC1451, University Park, Los Angeles, CA 90007. E-mail address: jessicll@usc.edu 3 Biomechanics Laboratory, Orthopaedic Hospital, 2400 South Flower Street, Los Angeles, CA 90007-2697

Investigation performed at the Joint Replacement Institute and the J. Vernon Luck Sr., MD, Orthopaedic Research Center, Orthopaedic Hospital/UCLA, Los Angeles, California

Background:
Although the orientation of the femoral component has been shown to influence the outcome of total hip replacement, its effect on the clinical outcome of surface arthroplasty has not been studied, to our knowledge. The purpose of this study was to examine the relationship between femoral component positioning and the outcome of a surface arthroplasty of the hip.

Methods:
We reviewed the results of ninety-four hybrid metal-on-metal surface arthroplasties in patients who were forty years old or younger at the time of the operation and were followed for a minimum of two years or until the prosthesis failed. Measurements of the hip reconstruction were made on the anteroposterior pelvic radiograph. The correlation between the orientation of the femoral component and the outcome of the arthroplasty was evaluated, as were stresses within the resurfaced femoral head as a function of the orientation of the femoral component.

Results:
The mean duration of follow-up was 4.2 years. Thirteen hips had an adverse outcome, defined as conversion to a total hip replacement, radiolucency of >1 mm in thickness adjacent to the femoral stem, or narrowing of the femoral neck of >10%. The mean femoral stem-shaft angle in the coronal plane was 138°, with the hips that had an adverse outcome having a significantly lower mean angle than the rest of the cohort (133° compared with 139°, p = 0.03). Hips with an angle of 130° had an increase in the relative risk of an adverse outcome by a factor of 6.1 (p < 0.004). In the entire cohort, stresses in the superior aspect of the resurfaced femoral head were substantially lower during slow walking than they were during fast walking (7.1 N/mm2 compared with 14.2 N/mm2).

Conclusions:
Optimizing the femoral stem-shaft angle toward a valgus orientation during the preparation of the femoral head is important when a hip is being reconstructed with a surface arthroplasty because the resurfaced hip transmits the load through a narrow critical zone in the femoral head-neck region and the valgus angulation may reduce these stresses.