We observed a low frequency of osteolysis that was similar (p = 0.8130) among the three bone classes. The overall incidence of osteolysis at last followup of all three classifications was 1.4% (33 of 2321 hips); femoral osteolysis was identified in 10 Class A hips (1.6%), 20 Class B hips (1.3%), and three Class C hips (2.4%). Radiolucent lines were generally small. At most recent followup, two patients (7 years followup) with Class A bone had a nonprogressive radiolucency line measuring less than 1 mm in Zone 1. One patient (3 years followup) had a radiolucency line of less than 1 mm in both Zones 1 and 7, whereas another (1-year followup) had a 3-mm line within Zone 1. In the Class B cohort, two patients (2 and 3 years followup) had a less than 1-mm radiolucency line in Zone 1 and one other patient (2 years followup) had it in Zone 7. One patient (3 years followup) had a less than 1-mm radiolucency line in both zones. Only one Class B bone patient (8 years followup) had a substantial radiolucent progression of 3 mm in Zone 1. One patient with Class C bone had a less than 1-mm radiolucency line in Zone 1 at 3 years followup. We identified no substantial radiolucencies in patients with Class C bone.
Aseptic loosening is a major mechanism of failure in TKA with regard to cementless stems [1, 3, 9, 11-13] and depreciated bone . As a result of improved bone ingrowth in new-generation implants, attributed to cementless femoral stems, the fear of aseptic loosening has decreased . Our primary aims were therefore to (1) determine the survivorship of a cementless Bi-Metric femoral component in all three classes of bone, especially those with osteoporotic bone (Dorr et al. , Class C), (2) describe the hip function and pain scores, and (3) determine whether the frequency of osteolysis and size of radiolucencies differed among the classes of bone.
The study's limitations are as follows. First, the study was a retrospective review of a previously collected database. With the study's intermediate followup of approximately 6 years and a similar Class C case count after 10 years to those reported in literature [1, 2, 12], we were able to attain adequate analysis on implant survivability. Second, we had 22% loss to followup. Third, the surgeries were performed by one group of physicians, all with possible bias in surgical procedure, decision-making, and approaches. We believe with a moderately high number of hips included in the study, the power should overcome potential confounding variables and differences in surgical preference between physicians. Fourth, two surgeons evaluated the patient's radiographs for bone class, so there may be variation in measurements and observations. The evaluation was by visual observation with Class A hips maintaining a narrow canal isthmus and Class C hips showing substantial osteoporotic degradation of the cortices. This would not alter the conclusions because failures occurred only in Class B hips. These failures, on observation, did not have a narrow canal isthmus (Class A) nor were they depreciated enough to lack any sort of structural integrity (Class B). Despite these limitations, we reviewed a reliable database, medical records, and radiographs to collect a unique set of data that allows us to address the survival of such an uncemented femoral stem in different classifications of femoral bone.
Overall, the survivability and performance of cementless proximally plasma-sprayed, porous-coated, straight-stemmed, titanium alloy femoral stems at a minimum of 2 years followup was excellent in all three bone classes. Within the study, there were only two patients who experienced loosening of their cementless femoral stems, which resulted in revision of the primary THA, and both were among those in the Class B cohort. No Class A or C hip implants were reported as being aseptically loose at most recent followup. These low failure rates resulting from overall complications and aseptic loosening, along with low incidence of femoral osteolysis, are similar to those reported in the literature (Table 6).
By means of clinical assessment (eg, Harris hip score and pain) and radiographic analysis, all three classes showed high clinical scores and well-intact implant condition with no difference among biologically active (Class A), moderately active (Class B), and poorly active bone (Class C). Kelly et al.  reported similarly high clinical scores (median Harris hip score, 94.5) and no femoral fixation failures in 15 Class C bone patients with a minimum of a 9-year followup (average, 11.5 years; range, 9-14 years) and the use of a hydroxyapatite-coated cemented stem. While they had a longer mean followup, our data, with 127 patients with Class C bone confirm their findings.
Although our study's demographics are similar, especially in regard to age and body mass index, to those reported by Dorr et al. , we saw no major difference among the three classifications of bone with consideration to clinical and radiographic success and adequate results with regard to the morphologically depreciated Class C bone. This could be attributed to numerous surgical reasons that not only affect clinical outcome, but also the formation of femoral osteolysis. Our study's 1.4% incidence of femoral osteolysis is similar to those reported by Parvizi et al.  (2.3%) and Berend et al.  (0% distal, 2.3% focal). Our institutional standardized procedure of using a proximally coated porous coating along with a titanium alloy component allowed for an improved prosthesis-bone interface, which in turn increased bone ingrowth and promoted implant stability. Several other studies have reported surgical practices that have improved the way cementless femoral components are implemented in THA, including plasma spray (eg, hydroxyapatite) of the femoral stem , a straight-stem and/or short-stem component design [11, 12], and the addition of proximal-to-distal coronal and sagittal tapers . The obstacle of finding an adequate prosthesis design to prevent aseptic loosening in osteoporotic bone (Class C) was addressed with the use of a collarless stem, which has been reported to reduce the loss of cortical density of the metadiaphyseal bone . By maintaining the cortical density, the bone is able to maintain initial fixation between it and the prosthesis, creating an interface that promotes implant stability .
We observed radiolucencies greater than 2 mm in two hips: one Class A and one Class B. Although relatively low in cohort size (127 hips), the Class C hips had no radiographic evidence of progression of radiolucency in both growth regions (Zones 1 and 7). We observed femoral osteolysis was identified in 33 of the 2321 hips (1.4%) with no difference in the frequency of osteolysis among the three cohorts. As suggested in our previous study , we presumed circumferential porous coating obstructs the movement of particles within the intramedullary canal, which in turn prevents the formation of lytic lesions. We believe this “sealing of the femoral canal” allows for cementless fixation of the femoral stem  to decrease the chance of osteolysis formation without other means of fixation such as cement, which could compromise function and increase radiolucency.
With recent alterations in implant composition, cementless stem fixation, and porous coating to enhance bone ingrowth, the use of cementless stems, including those with osteoporotic bone (Class C), has greatly increased [1, 3, 6, 9-13]. We reviewed a large population of a cementless proximally porous-coated, straight-stemmed, titanium alloy component in patients with Class A, B, and C bone showing secure long-term fixation along with adequate clinical and radiographic assessment.
We thank Dr Michael E. Berend, Dr Robert A. Malinzak, Dr E. Michael Keating, Dr Philip M. Faris, and Matthew J. Brunsman, MS, for their assistance.
1. Berend, KR., Lombardi, AV., Mallory, TH., Dodds, KL. and Adams, JB. Cementless double-tapered total hip arthroplasty in patients 75 years of age and older. J Arthroplasty.
2004; 19: 288-295. 10.1016/j.arth.2003.11.002
2. Burt, CF., Garvin, KL., Otterberg, ET. and Jardon, OM. A femoral component inserted without cement in total hip arthroplasty. A study of the Tri-Lock component with an average ten-year duration of follow-up. J Bone Joint Surg Am.
1998; 80: 952-960.
3. Clohisy, JC. and Harris, WH. The Harris-Galante uncemented femoral component in primary total hip replacement at 10 years. J Arthroplasty.
1999; 14: 915-917. 10.1016/S0883-5403(99)90003-7
4. Dorr, LD., Faugere, MC., Mackel, AM., Gruen, TA., Bognar, B. and Malluche, HH. Structural and cellular assessment of bone quality of proximal femur. Bone.
1993; 14: 231-242. 10.1016/8756-3282(93)90146-2
5. Edidin, AA., Merritt, PO., Hack, BH. and Manley, MT. A ported, proximally-cemented femoral stem for total hip arthroplasty. Development and clinical application. J Bone Joint Surg Br.
1998; 80: 869-875. 10.1302/0301-620X.80B5.8670
6. Emerson, RH., Sanders, SB., Head, WC. and Higgins, L. Effect of circumferential plasma-spray porous coating on the rate of femoral osteolysis after total hip arthroplasty. J Bone Joint Surg Am.
1999; 81: 1291-1298.
7. Gruen, TA., McNeice, GM. and Amstutz, HC.‘Modes of failure’ of cemented stem-type femoral components: a radiographic analysis of loosening. Clin Orthop Relat Res.
1979; 141: 17-27.
8. Harris, WH. Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty. An end-result study using a new method of result evaluation. J Bone Joint Surg Am.
1969; 51: 737-755.
9. Hozack, WJ., Rothman, RH., Eng, K. and Mesa, J. Primary cementless hip arthroplasty with a titanium plasma sprayed prosthesis. Clin Orthop Relat Res.
1996; 333: 217-225. 10.1097/00003086-199612000-00023
10. Kelly, SJ., Robbins, CE., Bierbaum, BE., Bono, JV. and Ward, DM. Use of a hydroxyapatite-coated stem in patients with Class C femoral bone. Clin Orthop Relat Res.
2007; 465: 112-116.
11. Meding, JB., Keating, EM., Ritter, MA., Faris, PM. and Berend, ME. Minimum ten-year follow-up of a straight-stemmed, plasma-sprayed, titanium-alloy, uncemented femoral component in primary total hip arthroplasty. J Bone Joint Surg Am.
2004; 86: 92-97.
12. Morrey, BF. Short-stemmed uncemented femoral component for primary hip arthroplasty. Clin Orthop Relat Res.
1989; 249: 169-175.
13. Parvizi, J., Keisu, KS., Hozack, WJ., Sharkey, PF. and Rothman, RH. Primary total hip arthroplasty with an uncemented femoral component: a long-term study of the Taperloc stem. J Arthroplasty.
2004; 19: 151-156. 10.1016/j.arth.2003.10.003
14. Rasquinha, VJ. and Ranawat, CS. Durability of the cemented femoral stem in patients 60 to 80 years old. Clin Orthop Relat Res.
2004; 419: 115-223. 10.1097/00003086-200402000-00019
© 2010 Lippincott Williams & Wilkins, Inc.
15. Williams, HD., Browne, G., Gie, GA., Ling, RS., Timperley, AJ. and Wendover, NA. The Exeter universal cemented femoral component at 8 to 12 years. A study of the first 325 hips. J Bone Joint Surg Br
2002; 84: 324-334. 10.1302/0301-620X.84B3.12261