TOTAL HIP ARTHROPLASTY WITH BIOMEC PROSTHESIS: 20-YEAR FOLLOW-UP.

OBJECTIVE: To analyze the clinical and radiological outcomes from total hip arthroplasty using the Biomec prosthesis over a 20-year period (1988 to 2009).
METHODS: The patients were evaluated clinically in accordance with the Merle d'Aubigné and Postel functional classification, and underwent anteroposterior (AP) radiography of the pelvis and the operated joint in lateral view. The variables evaluated were acetabular and femoral osteolysis, polyethylene wear, nail migration, follow-up and clinical outcomes.
RESULTS: The mean follow-up was 10.6 years (range 4 to 21 years). The sample consisted of 84 patients (32 men and 52 women) and the mean preoperative age was 47 years. We found that 88% of the results from the clinical evaluation were good or excellent. In relation to the radiological findings, 92.5% of the results were good. The mean wear on the polyethylene was 1.4 mm.
CONCLUSION: The use of the Biomec prosthesis in this cohort showed good clinical and radiographic results.

INTRODUCTION

Total hip arthroplasty (THA) was popularized by Charnley in the 1960s. At that time, metal-on-polyethylene joints fixed with surgical cement (polymethyl methacrylate, PMMA) became standard. As the use of cemented THA spread, the number of complications also increased, especially cases of aseptic loosening and osteolysis. Initially, it was thought that the problem was in the cement and, at that time, the term “cement disease舡 started to be investigated. The results from such studies showed that the reason for the failures was not just the cement, but rather, a set of factors. Whatever the cause, these events stimulated the search for biological solutions (without cement), as alternatives for performing THA3, 4.

Thus, at the end of the 1970s, the number of indications for THA using biological fixation increased. This period was marked by the emergence of a series of new types of implant based on a wide variety of concepts regarding materials, format, type of covering and fixation. Among these, the Spotorno® prosthesis, which has become established worldwide, is an example of an implant with biological fixation and a wedge-shaped quadrangular format, made of titanium (T16Al7Nb), which served as a model for developing the prosthesis examined in the present study (Biomec). Analysis on the preliminary results from various designs for uncemented implants, compared with the results achieved using adequately cemented prostheses, suggested that not all the concepts put forward could be sustained over medium-term follow-up, and this is well demonstrated by the variations in the models made by various companies that were formed at that time7, 8.

All of this motivated us to present our experience over 20 years of performing THA using the Biomec uncemented wedge-shaped quadrangular prosthesis.

The aim of this study was to show the clinical and radiographic results from the use of the Biomec uncemented prosthesis, with a mean length of follow-up of 10.6 years.

METHODS

The present study consisted of a cohort of 84 patients (93 hips) who underwent THA using the Biomec uncemented prosthesis between 1988 and 2005, with follow-up until 2008. The clinical evaluation was performed before the radiographic evaluation and was done by different examiners, with the aim of diminishing the measurement bias. The patients were called in for assessment; they gave responses according to a preestablished protocol; and they underwent radiography on the pelvis (anteroposterior view), and on the coxofemoral joint on the side affected (lateral view). The patients underwent operations consisting of an anterolateral or posterolateral approach according to the decision made by the chief surgeon and the Hip Surgery Group of our hospital.

With regard to design, the femoral component of the Biomec prosthesis is made of titanium (T16Al7Nb), with a cervical-diaphyseal angle of 145° and a wedge-shaped format in the three planes. It is fixed to the bone under pressure (pressfit) in the metaphyseal region. Proximally, the nail has anterior and posterior grooves to avoid rotational movements and favor osseointegration. The Biomec acetabulum consists of a cupola made of titanium, of hemispherical format with six expandable fins. The interchangeable head used was made of chromium-cobalt-molybdenum (CoCrMO) of diameter 28 mm.

For the clinical evaluation, the criteria proposed by D'Aubigné and Postel were used. Pain, gait and hip mobility were assessed, with a maximum score of six for each item, such that the total of 18 points represented the best result. For the purposes of statistical analysis, the results were considered good if the patients obtained scores graded as good or very good (greater than or equal to 15 points), and other results were considered unsatisfactory.

The radiographic evaluation on acetabular osteolysis was based on the criteria of Zicat et al, regarding expansive or linear type, and on De Lee and Charnley zones regarding localization. For evaluations on femoral osteolysis, the criteria of Turibio were used.

Other variables were also assessed radiographically, such as the wear on the polyethylene, migration of the femoral component (subsidence) and femoral morphocortical index. All these were measured with a transparent plastic ruler divided into millimeters.

To describe the variables, we took into consideration the arithmetic mean, standard deviation (SD), median and maximum and minimum values. In the statistical analysis on non-parametric variables, Spearman's correlation test was use, while the Mann-Whitney test was used for parametric variables. Both of these were calculated using the SPSS software for Windows, version 14.0 (SPSS Inc, Chicago, IL, USA). We took P values less than 0.05 to be significant.

Statistical correlations were investigated in relation to the following outcomes: acetabular osteolysis versus clinical outcome; clinical outcome versus follow-up, femoral migration, polyethylene wear, femoral osteolysis and acetabular osteolysis; acetabular osteolysis versus follow-up, polyethylene wear and follow-up.

RESULTS

The Biomec prosthesis was used for 100 patients between 1988 and 2001. Of these, seven died during the later postoperative period for reasons unrelated to the surgical procedure. Because there was no recent assessment for these patients, they were excluded from the study. Another nine patients could not be located for reassessment. Thus, 84 patients and 93 hips were evaluated, i.e. there were nine cases of bilateral arthroplasty. Thirty-two of the patients (38%) were men and 52 (62%) were women. The mean age before the operation was 47 years (range 19 to 77 years). The right side was operated in 49 cases (58%) and the left side in 35 cases (42%).

The mean duration of follow-up was 10 years and six months. The shortest follow-up was four months and the longest was 20 years, with a median of nine years and SD of 4.8 years.

There were three cases of failure of both components (3.2%) and four cases of failure of the acetabular component alone (4.3%).

From analysis on the clinical results in accordance with the classification of D'Aubigné and Postel, 82 hips (88%) presented good or very good results, as illustrated in Figure 1.

Figure 1

Sample distribution in accordance with the functional evaluation proposed by D'Aubigné and Postel

Osteolysis was present in 66 acetabula (75%) and was most frequently seen in the DeLee and Charnley zones two and three, as presented in Figure 2, according to their location.

Figure 2

Sample distribution according to the presence of osteolysis and location in accordance with the DeLee and Charnley zones. In this case, we considered that osteopenia was present in area II.

In Figure 3, we present a radiograph from a case with 17 years of follow-up on the right side and 16 years on the left side, without any signs of loosening of the implants. It shows signs of acetabular osteolysis, but without clinical repercussions.

Figure 3

Anteroposterior radiograph of the pelvis on a patient with 17 years of follow-up on the right side and 16 years on the left side.

Femoral osteolysis was present in 83 cases (98.8%), and it was classified in accordance with the criteria of Turibio, as illustrated in Table 1 according to its location:

Table 1

Sample distribution in relation to femoral osteolysis, in accordance with the criteria of Turibio

Turibio grade	Cases	Percentage (%)
0	1	1.20
1	29	34.50
2	42	50.00
3	10	11.90
4	2	2.40

0 – absence of osteolysis

1 – osteolysis restricted to the region of the greater trochanter

2 – osteolysis extending from the region of the greater trochanter towards the lesser trochanter

3 – osteolysis affecting both the greater and the lesser trochanter and extending to the middle third of the diaphysis

4 – osteolysis throughout the region of the femoral implant.

In Figure 4, we present an example of femoral osteolysis affecting the regions of the greater and lesser trochanter (Turibio 2), without compromising the stability of the femoral component.

Figure 4

Radiograph on the left hip demonstrating femoral osteopenia affecting the regions of the greater and lesser trochanters, without compromising the stability and fixation of the femoral implant.

Polyethylene wear was present in 69 cases (82%), with a mean of 1.4 mm (range 0 to 5). Taking the mean duration of follow-up of 10 years and six months, the mean rate of polyethylene wear was 0.13 mm per year. The statistical analysis demonstrated that the occurrences of acetabular osteolysis were related to polyethylene wear (P = 0.04). The wear on the polyethylene was also correlated with worsened clinical outcomes (P = 0.036).

Femoral nail migration or “subsidence舡 was present in 67 cases (79.7%) and absent in 17 cases (20.3%), with a mean migration distance of 2.33 mm and median of 2 mm. Figure 5 provides a better illustration of the frequency of migration. The statistical analysis did not show any worsening of the clinical outcome through femoral migration (P = 0.009).

Figure 5

Sample distribution according to the frequency and magnitude of migration of the femoral nail.

DISCUSSION

The sex distribution in our sample (38% men and 62% women) was in accordance with other reports in the literature13, 14, 15. The mean age in our study (47 years) was also similar to reports in the literature, which describe mean ages ranging from 51 to 53 years13, 14, 15, 16, 17, 18.

The clinical assessment showing that 80% of the results were good and very good was similar to what was found in a study using the Spotorno® prosthesis, a foreign model that formed the basis for the development of the prosthesis under examination here13, 14, 18, 19. In the statistical analysis on the clinical outcome over the follow-up period, it was observed that there was a gradual decrease in functional grade as the length of follow-up increased, with P = 0.008. This can be explained in terms of wear on the implant with the passage of the years, thereby leading to a gradual decrease in the clinical score.

We did not find any statistical significance with regard to analyzing the prevalence of acetabular osteolysis (75%) in relation to the clinical outcome (P = 0.001). This explains the finding of very good functional results despite the high prevalence of acetabular osteolysis. It is in line with what was reported by other authors, who did not find any relationship between acetabular osteolysis and the clinical outcome15, 18.

Femoral osteolysis presented even greater prevalence, such that it was observed in 98.8% of the cases. However, in around 85% of the cases, it only affected the regions of the greater and lesser trochanters and did not compromise the fixation and/or stability of the implant. This was demonstrated in a prospective study with evaluation of the bone mineral density around the prosthesis following Spotorno® arthroplasty, in which a significant decline in bone mass (21 %) was found in the region of the trochanters over the first two years after the operation. In the statistical analysis between femoral osteolysis and the clinical outcome, we also did not find any statistical significance (P = 0.124).

Acetabular osteolysis presented a correlation with femoral osteolysis, with greater prevalence as the femoral osteolysis became more marked (P = 0.014). This was very likely due to the accumulation of debris and penetration at the bone-implant interface.

The correlation between wear on the polyethylene and greater prevalence of acetabular osteolysis found in our study was statistically significant (P = 0.04), and this had already been demonstrated by previous studies21, 22.

The mean wear of 1.4 mm found in our series and the wear rate of 0.13 mm/year considering the mean followup of ten years and six months overlapped with the mean wear reported in the literature for cemented prostheses and was a smaller amount than shown in studies on uncemented (non-expansive) acetabula with shorter follow-up.

The migration and accommodation of the femoral nail (subsidence) in 67 cases (80%), with a mean of 2.33 mm, was in line with the biomechanical theory put forward many years ago by Spotorno for wedge-shaped nails, which is now greatly valued by advocates of cemented and polished wedge-shaped nails without collars. This makes us believe that until secondary fixation through osseointegration has been established, adjustments to the wedge-shaped quadrangular nail within the bone case.

CONCLUSION

THA using the Biomec uncemented prosthesis presented good results in 88.2% of the cases, over a mean followup of ten years and six months among this cohort.

Although we found significant numbers of cases of femoral and acetabular osteolysis among our sample, these did not have any significance regarding modification of the clinical outcome.