A Randomized Clinical Trial of Cementless Femoral Stems With and Without Hydroxyapatite/Tricalcium-Phosphate Coating. An 8- to 12-Year Follow-Up Study

Abstract

We appreciate Dr Hernandez-Vaquero and colleagues' interest and concern in our study. As they mentioned, the survival of non–hydroxyapatite-coated stems was similar to hydroxyapatite-coated stems; and apparently, hydroxyapatite coating did not seem to have an advantageous effect in terms of fixation and survival of stem in our study. The HG Multilock porous-coated stem (Zimmer, Warsaw, Ind), which was used in our study, has circumferential titanium fiber mesh in the proximal portion. This stem design has been known to achieve excellent clinical results and demonstrable biological fixation [1Sinha R.K. Dungy D.S. Yeon H.B. Primary total hip arthroplasty with a proximally porous-coated femoral stem.J Bone Joint Surg Am. 2004; 86: 1254Crossref PubMed Scopus (26) Google Scholar]. Thus, hydroxyapatite coating on the fiber mesh appeared to have no additional advantage compared with simple porous coating. The incidence of thigh pain was rather high in both groups of our study (8.1% in the coated group and 7.1% in the noncoated group). The reported prevalence of thigh pain after cementless total hip arthroplasty ranges from 0.5% to 40% [2Brown T.E. Larson B. Shen F. Moskal J.T. Thigh pain after cementless total hip arthroplasty: evaluation and management.J Am Acad Orthop Surg. 2002; 10: 385Crossref PubMed Scopus (142) Google Scholar]. A number of factors have been attributed to this problem, including the geometry and the size of the stem. The incidence of thigh pain after total hip arthroplasties with a nontapered stem design is higher than that with a tapered stem design. The HG Multilock stem has smooth, cylindrical, and nontapered distal region with flutes. This implant requires diaphyseal reaming for insertion to obtain diaphyseal contact and to provide rotational stability. The relatively high prevalence of thigh pain in our patients seems to be associated with the prosthetic design with a lack of taper angle in the distal region. Sinha et al, in a study of 123 hips that had been operated on with the HG Multilock stem, reported an 11% rate of thigh pain after an average duration of follow-up of 6.5 years [1Sinha R.K. Dungy D.S. Yeon H.B. Primary total hip arthroplasty with a proximally porous-coated femoral stem.J Bone Joint Surg Am. 2004; 86: 1254Crossref PubMed Scopus (26) Google Scholar]. The densification in the metaphyseal zone, which Dr Hernandez-Vaquero and colleagues have mentioned [3Hernández-Vaquero D. Murcia-Mazón A. Paz-Jimenez J. et al.Behavior of the femoral stem in the Bihapro hip prosthesis.Orthopedics. 1999; 22: 1049PubMed Google Scholar], seems to be “spot weld” or “endosteal bone formation,” which is a radiographic evidence of bone-ingrown stability of the femoral stem. We have already described this finding as endosteal bone formation in the results of our article. Dr Hernandez-Vaquero and colleagues favored a stem design with close metaphyseal anchoring and a polished and tapered distal end, which is the so-called third-generation cementless total hip arthroplasty. We agree with them that the third-generation stem design provides an excellent mechanical fixation and low prevalence of thigh pain [4Kim Y.H. Cementless total hip arthroplasty with a close proximal fit and short tapered distal stem (third-generation) prosthesis.J Arthroplasty. 2002; 17: 841Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar].