THE POSTOPERATIVE COURSE OF THE SERUM LEVELS OF OSTEOPROTEGERIN, RECEPTOR ACTIVATOR FOR NUCLEAR FACTOR-{KAPPA} B LIGAND (RANKL), OSTEOCALCIN AND BONE-SPECIFIC ALKALINE PHOSPHATASE (B-ALP) FOLLOWING TOTAL HIP AND KNEE ARTHROPLASTY: A PROSPECTIVE OBSERVATIONAL, ONE-YEAR FOLLOW-UP STUDY.

Abstract

Background: The clinical significance of bone turnover markers is well recognized, at least in several diseases affecting the bone metabolism. However, their clinical significance (if any) remains still unknown in patients undergoing Total Joint Arthroplasty (TJA). Changes in the levels of some markers have been reported in the early postoperative period after Total Hip Arthroplasty; however their exact postoperative course has not been clearly documented yet. In order to assess the clinical value of biochemical markers when trying to determine the fixation of orthopaedic implants, it is necessary to clarify their normal postoperative course.

The aim of this study was to extend the evaluation of the course of bone turnover markers over a longer period (12 postoperative months) following a TJA, and to assess the postoperative course for two of them (RANKL and Osteoprotegerin) for the first time.

Methods: The serum levels of RANKL, Osteocalcin, Osteoprotegerin and bALP were determined one day preoperatively and several times during the first postoperative year in patients suffering from idiopathic osteoarthritis that underwent total knee (n=23) and hip arthroplasties (n=24).

Results: There were statistically significant changes in the serum levels of all markers over time (p< 0,001). RANKL values initially increased and then gradually decreased. Following an initial decrease, Osteocalcin values continuously increased until the 2nd postoperative month and then continuously decreased. Osteoprotegerin initially increased, then decreased until the 4th postoperative month and then increased again reaching a peak 8 months postoperatively. Bone-specific ALP decreased until the 7th postoperative day. After that time it continuously increased, reaching a peak at the 8th month, and then it gradually decreased. There were no major differences in the postoperative course of all markers between the hip and knee arthroplasties.

Conclusions: The levels of all bone markers did not uniformly ‘return’ to their preoperative values one year postoperatively. A one-year period is not enough, when assessing an orthopaedic implant’s fixation with the use of bone turnover markers.