Erratum

To the Editor

During the preparation of a further study on urinary cross-link levels in asepticloosening, we noted a fault in the procedure we used to input data forcomputerized calculations in our original study. (‘‘Increased Urinary CrosslinkLevels in Aseptic Loosening of Total Hip Arthroplasty.’’ J Arthroplasty 13:687,1998.) We now write to correct errors in the original data.

We have now excluded 13 patients from the original patient population(n 5 100) for whom we consider data to be uncertain. The results of the reanalysisof the reliable data (n 5 87) are as follows. There was no significant differencebetween the loose and the control group with respect to serum levels ofprocollagen type 1, alkaline phosphatase, calcium, and creatinine. There was nodifference between cemented, uncemented, and hybrid implants with respect toincreased levels of the markers deoxypyridinoline (DPYD) and collagen n-telopeptide (NTX). The evaluation of the most sensitive markers DPYD and NTXstill showed a significant increase in the loose group (Table 1). The overall accuracyof NTX and DPYD as markers for implant loosening was reduced; however: Bothnow show only weak or clear concordance (Table 2).

Having reworked our data, we conclude that the predictive power of urinarycross-link levels is less strong than we had originally supposed. Further studies arenecessary to determine a possible value of these markers in the diagnosis anddetection of aseptic loosening in total hip arthroplasty.

We apologize for this error.Ulrich Schneider

Steffen J. BreuschMarc Thomsen

Silke SimankDario R. C. Brocai

Fritz-Uwe NiethardChristian Kasperk

Departments of Orthopedic Surgery and Internal Medicine,University of Heidelberg, Heidelberg;

and the Department of Orthopedic Surgery,University of Aachen, Aachen, Germany

The Journal of Arthroplasty Vol. 15 No. 5 2000

679

Table 1. Statistical Analysis of Deoxypyridinoline (DPYD) and Collagen n-Telopeptide(NTX) in the Control and Loosening Groups

Control Group Loosening Group U 5 Test

DPYD* 6.84 (2.04–17.65) 11.89 (1.26–69.2) n 5 35/n 5 35NTX† 40 (16–117) 71 (27–220) n 5 45/n 5 35

U-Test: p , 0.001

NOTE. Values are median (range).*n 5 35 (control); n 5 35 (loosening).†n 5 45 (control); n 5 35 (loosening).

Table 2. Sensitivity, Specificity, and Overall Accuracy of n 5 Telopeptide (NTX)and Deoxypyridinoline (DPYD)

ThresholdSensitivity (%)

(n 5 35)Specific (%)

(n 5 35)

OverallAccuracy (%)

(n 5 70) Kappa Concordance

NTX 26.5 100 18 54 0.159 Weak50.5 77 69 73 0.452 Clear

117.5 20 100 65 0.220 WeakDYPD 1.250 100 0 50 Not calculated

9.730 69 74 71 0.429 Clear17.680 29 100 64 0.286 Weak

680 The Journal of Arthroplasty Vol. 15 No. 5 August 2000