The proportion of persons older than 75 years ascribed to our hospital is slowly but steadily growing.22
There are few reports of the use of cementless femoral prostheses in this age group5–7,13,23,24
Results of cementless THAs in elderly patients
Concerns about the use of cementless stems in elderly persons are essentially based on two facts. First, the high incidence of intraoperative fractures, and second, failure to achieve good bone ingrowth in the stem. The latter is the outcome of a poorer bone tissue quality, as this factor diminishes with age.25,26
Accordingly, many surgeons consider the use of cementless stems in elderly persons inappropriate, on the grounds than an initial stem stability cannot be achieved.27,28
No intraoperative fractures were recorded in our series. The essential prerequisite for the use of a cementless stem was that the test rasp could be stably fitted without the need for a cortical contact around the entire stem periphery. Four periprosthetic fractures, three type B1 and one type B2 according to the Vancouver classification, were recorded during the follow-up, and the stems were revised because the fracture could affect the stability of the implant. In some cases we used long modular stem revision (Restoration modular system, Stryker), and in other cases we used long stem revision (Restoration HA). Stem revision for oblique or transverse B1 fractures is now considered as a viable treatment modality, as this fracture configuration is difficult to control with single plating29
(a) Radiograph of an 83-year-old man showing an oblique Vancouver B1-type fracture around the stem. The stem was unstable, and a revision with a long modular stem was done (b)
No detrimental effects of fixation were observed in terms of pain and functionality. The incidence of pain, albeit low, recorded in the middle third of the thigh (3.8%) could be due to the diameter of the distal centralizer placed at the tip of the stem. The size selected for this centralizer was a diameter of at least 1 mm less than the last rasp used to assess the canal size.
Noble et al
established a radiographic classification scheme for femur canals, which was further developed by Dorr et al
according to radiographic and histomorphometric criteria. Thus, following Noble's radiographic scheme and his premise that a single stem design would not be compatible with the different femoral canal types, we assessed the behavior of a single stem type, regardless of the morphology of the femoral canal.
In March 1997, the OMNIFLEX hip system was introduced in our Orthopedic Surgery Unit as the only uncemented femoral stem. Implants coated proximally with HA have provided good clinical outcomes, mostly in young patients.12,31,32
However, only a few studies have assessed the performance of stems whose metaphyseal portion is coated with HA, in elderly patients. The present study has analyzed patients older than 75 years undergoing surgery in 1998 (52 stems implanted in 48 patients) after the initial learning curve. The use of stems had started several months prior to this date.
Our series of patients revealed a predominance of type B femoral canals. One stem was revised because of mechanical loosening. The initial metaphyseal fill was less than 70%, and its alignment was varus by 5°. Dorr16
observed that metaphyseal fitted stems needed a fill exceeding 90% that required cortical contact. Our series of patients showed a mean metaphyseal fill of less than 90%, as we tried to avoid cortical contact over the entire periphery, to reduce the risk of intraoperative periprosthetic fracture. This could explain why HA coated stems need a lesser proximal fill.34,35
Four of the femurs were type C, for which the use of cemented stem would normally be recommended.36,37
Hence, obtaining sufficient stability for an optimal outcome of the implant of a cementless prosthesis, in this type of femur, is a particular challenge. Although the number of cases assessed here is too low to draw any valid conclusions, it would seem that the osteoconductive properties of HA might help stem ingrowth in type C femurs .
A postoperative radiograph at 10, 2 years reveals a well-fixed, primary, cementless stem in the proximal femur of type C morphology
The results obtained with the modular OMNIFLEX system have been reviewed by several authors in younger patients, but to our knowledge, no series describing the outcome of this stem have been published in elderly patients. Capello, Kitamura, and Ito38,39,40
reported poor results using first generation stems, which featured a proximally non-circumferential porous tip. However, Takahashi35
obtained good results with the use of second generation stems, with arc deposition of pure titanium on the surface of the proximal circumference, and with third generation models whose circumferential porous tip was coated with HA. No revision stem was required, and 97% of all stems showed bone ingrowth fixation. We report one revised stem (1.9%) due to aseptic loosening. Thus there are clear differences among the results obtained with the first, second, and third generation stems, with the latter showing the best outcomes. In effect, a HA-coated metaphyseal portion promotes bone ingrowth.
In our series, 22% of the stems showed a valgus or varus alignment, with no functional repercussions. This could be explained by the size of the distal centralizer used, which was at least 1 mm smaller in diameter than the size of the last rasp of the centralizer. Our findings indicated that despite mal-alignment, there was adequate metaphyseal fill and the HA coating promoted bone ingrowth, with no clinical significance . On the other hand, the present stem revised because of subsidence was attributed to a technical error in establishing a metaphyseal fill, besides its varus position. In effect, Capello38
highlighted the technical skill needed for the use of this hip system.
Bone atrophy of the proximal end of the femur following total hip arthroplasty is widely established.41
We recorded shielding-related bone atrophy in 75% of the hips. This adaptive process was observed during the first few years of follow-up, yet there was no progression thereafter. Cancellous condensation indicating osseointegration in stems, stable by bone ingrowth, mainly appeared in Gruen zones 2 and 6, which explained the high proportion of proximal bone atrophy. This behavior was typical of stems with a greater surface area for bone ingrowth, such as, extensively porous stems. Thus, we could infer that OMNIFLEX stems became more distally integrated in the host tissues despite their porous circumferential surface coated with HA, which circumscribed the metaphyseal zone, probably due mainly to the grit-blasted finish of the middle third of the stem. Takahashi35
reported proximal bone atrophy in 65% of the second generation and 68% of the third generation stems, in patients of a mean age of 64 years. The mean age of our patients was above 75 years. Younger, more active patients with better bone quality develop less atrophy due to stress shielding. The three stems showing stable fibrous ingrowth exhibited grade I atrophy, which could be attributed to the fibrous fixation. We noted atrophy below the lesser trochanter without diaphysis involvement (third grade) in 16% of the cases. This incidence was lower than that reported by others.41,42
The OMNIFLEX stem was shaped like a double wedge and was less stiff, explaining its behavior. Notwithstanding, according to the other authors,43
we were aware of the radiographic limitations of assessing bone mineral density loss, and concur with Glassman44
who stresses on the importance of the use of DEXA (dual energy X-ray absorptiometry) in this field.
Polyethylene wear was not greater in the revised stem because of mechanical loosening. As shown in other studies, neither was this PE wear greater in femurs showing atrophy due to stress shielding,45
precluding its relation with osteolysis induced by debris.
The weakness of our study is that the number of dropouts is high (11%), but that is in accordance with others studies.5
This is difficult to avoid in this elderly population who frequently have associated comorbidities. Another weakness could be the number of patients. However, despite these limitations arising from the number of patients we reviewed during the exact period of time of one year, a reliable database, medical records, and radiographs were collected to make a unique set of data that allowed us to address the survival of such an uncemented femoral stem, in different classifications of femoral bone, in elderly patients. The main strength of this study is the age of the patients, 75 years of age and older, and the follow-up mean of 10,4 years, in comparison with other reports . The findings of this study indicate that the third generation OMNIFLEX modular stem achieves adequate biological fixation, with favorable clinical–radiographic results obtained in the long-term in this cohort of 52 prostheses, in elderly patients. However, we feel the objective for which this stem was created has not been fulfilled, given the high proportion of stress shielding-induced bone atrophy observed, higher than the reported one, probably due to the patient age. We do not think this problem should affect stem stability, although it could be a concern in the long term. Based on our experience, primary arthroplasties in our unit are essentially performed using a cementless femoral stem, regardless of the patient's age and femoral canal type.