We present a retrospective series of 170 cemented titanium straight-stem femoral components combined with two types of femoral head: cobalt-chromium (CoCr) alloy (114 heads) and alumina ceramic (50 heads). Of the study group, 55 patients (55 stems) had died and six (six stems) were lost to follow-up. At a mean of 13.1 years (3 to 15.3) 26 stems had been revised for aseptic loosening. The mean follow-up time for stable stems was 15.1 years (12.1 to 16.6).

Survival of the stem at 15 years was 75.4% (95% confidence interval (CI) 67.3 to 83.5) with aseptic failure (including radiological failure) as the end-point, irrespective of the nature of the head and the quality of the cement mantle. Survival of the stem at 15 years was 79.1% (95% CI 69.8 to 88.4) and 67.1% (95% CI 51.3 to 82.9) with the CoCr alloy and ceramic heads, respectively. The quality of the cement mantle was graded as a function of stem coverage: stems with complete tip coverage (type 1) had an 84.9% (95% CI 77.6 to 92.2) survival at 15 years, compared with those with a poor tip coverage (type 2) which had a survival of only 22.4% (95% CI 2.4 to 42.4). The poor quality of the cement mantle and the implantation of an alumina head substantially lowered the survival of the stem.

In our opinion, further use of the cemented titanium alloy straight-stem femoral components used in our series is undesirable. Titanium alloys are widely used for the manufacture of orthopaedic implants in total hip replacement (THR), for both cemented and cementless prostheses. The properties of titanium alloys include good biocompatability, low modulus of elasticity and resistance to fatigue and corrosion. The ability to accept bone on-growth makes titanium alloy favourable for cementless fixation. According to the literature, cementless stems produce less osteolysis and suffer fewer mechanical failures than similar cemented stems.2-4 However, the use of titanium for articulating surfaces is not recommended because of their low wear resistance.5

Cemented titanium alloy monoblock stems were introduced in the 1970s6 and initial results proved encouraging. Sarmiento and Gruen7 reported good short-term radiological results for cemented titanium alloy straight stems. Additional reports for other cemented titanium alloy stems with cobalt-chromium (CoCr) heads quote survival rates of 97% at 7.5 years8 and ten years.9

Straight Müller stems (Proteck, Freiburg, Germany) made of titanium-aluminium-niobium (TiA1Nb) with a ceramic head had a revision rate of 2.5% at a mean of six years' follow-up.10 The patient's weight was considered to he a factor affecting loosening. Good long-term results with 87.3% survival at 20 years were reported with 89 Ceraver Osteal (Ceraver Osteal, Roissy, France) polished titanium-aluminium-vanadium (TiAl^sub 6^V^sub 4^) cemented stems when combined with an alumina-on-aluniina coupling.11

Manner et al12 reported increased loosening of cemented straight Millier stems made of titanium alloy compared with cobalt-nickelchromium (CoNiCr) alloy stems at a median follow-up of 7.7 years, and noted that smaller titanium stem sizes, male gender and increased physical activity were associated with an increased risk of failure. Failure rates of 4.5%,13 and 9%14 at five years and 11.5% at 5.5 years,15 have been reported for titanium alloy cemented stems. The report from Jacohsson et al14 found that most failures occurred with smaller stems, especially in heavier patients, implicating the influence of the modulus of elasticity. The results of the Capital modular titanium alloy stems (3M, Loughborough, United Kingdom) with either CoCr or nitride-coated titanium heads were poor, with loosening of 16% of the femoral components at a mean follow-up of 26 months.16

The cemented modular Müller self-locking titanium alloy straight stem was introduced in 1984.12 We have retrospectively examined the outcome of 164 self-locking titanium alloy straight stems combined with either a CoCr alloy or an alumina head, implanted in patients between June 1986 and June 1988.

Patients and Methods

During the study period 386 THRs were performed in our hospital, of which 170 consecutive cemented titanium alloy straight Millier-style stems were implanted. Although 62 patients had bilateral THRs during this period, none had self-locking stems bilaterally. Six patients were lost to follow-up, leaving a final study group of 164 patients (164 hips).

The mean age of the patients was 64.9 years (48 to 80), with three less than 50 vears old at the time of operation, There were 114 women and 50 men. The pre-operative diagnosis was primary osteoarthritis in 139 hips, rheumatoid arthritis in six, avascular necrosis in eight, osteoarthritis secondary to dysplasia in four, and post-traumatic osteoarthritis in seven. There were 80 left and 84 right THRs.

The self-locking stem (Lima-Lto, Udine, Italy) is a Müller-style cemented straight stem made of a titanium alloy (TiA1^sub 6^V^sub 4^) which relies on a biomechanical self-locking mechanism. The surface of the stem is roughened by grit-Blasting. The surface roughness of retrieved components was measured at rhrec sites on the surface with a diamond stylus profilometer using a 2 mm evaluation length and a 0.25 mm cut-off length (Taylor-Hobson Form Talysurf Series 2; Leicester, United Kingdom). The mean surface roughness (Ra) was 1.72 µm (1.30 to 2.5). The tapered stem is flattened anteropusteriorly and primary stability is achieved by impaction into the broached femoral canal. Introduction of the stem and the extrusion of excess cement is facilitated by a groove on the anterior and posterior surfaces (Fig. 1). The stem is available in seven different sizes, with a 14/16 morse taper and can he coupled with a 32 mm diameter cobalt-based alloy (CoCr) or an alumina (Al^sub 2^O^sub 3^) ceramic head. The polyethylene cemented acetahular components obtained from the same manufacturer were sterilised in ethyleneoxide.