Periprosthetic bone loss of the acetabulum. Classification and management.

Periprosthetic bone loss, associated with failed acetabular implants, results in disruption of hip mechanics and complicates further reconstruction. To restore normal biomechanics and idealize implant loads, restoration of the normal center of rotation of the hip is recommended. Johnston et al have shown that medial, inferior, and anterior placement of the acetabular component minimizes prosthetic loading, whereas lateralizing the socket relative to the normal center greatly increases joint reactive forces. Since 1984, I have made every effort to restore the normal hip center, within reason, when dealing with the bony deficient acetabulum. In most every socket revision performed during this period, cavitary lesions have been addressed simply with particulate bone grafting or a larger component. To justify the use of structural allografts for the management of segmental defects, I believe the defect must involve the supporting rim, comprise the ability to obtain prosthetic stability, compromise the ability to restore normal hip mechanics, and be located in a high-stress area, i.e., posterior or posterior-superior. Smaller rim defects, in particular those located superior and anterior, can be ignored if they do not lead to prosthetic instability. Some alteration in hip mechanics can be tolerated to avoid structural allografting, but I have elected not to accept a superior translation of greater than 2 cm nor a medial defect that compromises the ability to lateralize the prosthesis adequately towards the normal center. When segmental defects exist while the prosthesis is well contained and stable in host bone (particularly superior and posterior), structural allografts are not necessary. A possible need for bone graft exists when there is questionable stability of the implant, i.e., a segmental defect combined with poor quality host bone, and when a major part of the posterior or superior rim of the component remains uncovered. The age and activity level of the patient enter into this formula at this point, and when the question exists in a younger patient, bone grafting should be performed. A definite need for structural allografting exists when component stability cannot be obtained in host bone, when there is a loss of the weight-bearing portion of the acetabular, particularly posterior, superior, or both, and when a major alteration of hip mechanics has occurred where no medial support or superior translation of greater than 2 cm has occurred. Prosthetic selection can affect the long-term results of acetabular reconstruction. Smooth-threaded components and bipolars have not performed well in revision acetabular surgery.(ABSTRACT TRUNCATED AT 400 WORDS)