TIME COURSE OF PERIPROSTHETIC BONE MINERAL DENSITY AFTER SHORT-STEM HIP ARTHROPLASTY
Volga District Medical Centre under Federal Medical and Biological Agency,
Nizhny Novgorod, Russia
Hip joint replacement is one of the most popular and successful operations in treatment of degenerative and inflammatory diseases, and consequences of hip joint injuries. A demand for such surgery is 52 per 100,000 of the population in Russia; it is higher than the real volume – 40 per 100,000 [1]. Currently, there are two concepts in hip joint replacement: cement and cementless techniques. Since the time of J. Charney the gold standard exists. It is cement endoprosthetics of the hip joint confirmed by the long term studies [2, 3]. A new concurrent concept, i.e. hip joint cementless replacement, has appeared in 90s of the 20th century, and its first results were excellent [4]. During the following years this approach became popular [5, 6].
The supporters of cementless replacement stood for more young population of patients who need for hip joint replacement, as well as for increasing life span with the increasing possibility of revision surgery for the hip joint [7]. The main idea of the first generation of cementless endoprosthetics consisted in tight introduction of an implant into the shaft of the femur (press fit) [4]. However further studies identified the resorption in the proximal femur because of tight contact between the distal end of the cementless implant and the diaphyseal cortical bone (stress-shielding syndrome) and load transfer to the calcar region [8] that results in loosening of the endoprosthesis. The further studies were oriented to improving the shape of the cementless implant with maximal preservation of bone tissue, decreasing the risk of stress-shielding syndrome and prevention of loosening.
One of the ways of development of cementless endoprosthetics is production and improvement of short femoral stems. Such implants were firstly reported by d’Imporzano & Pierannunzii (2006) and Renkawitz (2008) [9, 10], but the authors noted higher risk of displacement of the femoral component. However the comparative study (Westphal et al., 2006) of the standard femoral components showed the comparable results according to the level of migration of implants in case of correct positioning (the contact with the cortical layer) and good quality of bone tissue [11]. The researchers stated that adaptive remodeling of bone tissue around the short femoral implant was accompanied by less loss of bone mineral density in the proximal femur [12]. But other authors stated insufficient osteointegration and high risk of displacement of the endoprosthesis because of less square of contact between the implant and the bone in comparison with the standard stems (Reimeringer M. et al., 2013) [13].
The stability of the components of the endoprosthesis is estimated in concordance with qualitative and quantitative signs. The state of bone tissue around the femoral component is analyzed in 7 regions of the femoral bone according to Gruen et al. [14].
Some qualitative signs can be noted in the standard X-ray images. The femoral component is unstable, if one of the following criteria exists: 1 – implant displacement over a distance not less than 5 mm or change in its position compared with the basic state that is identified in X-ray images performed in dynamics; 2 – a fracture of a stem of the endoprosthesis; 3 – crevices in cement surface, if fixation is done with cement; 4 – presence of radiologic region of clarification along the line of metal-bone or cement-bone which is absent in primary X-ray images (Harris and McGann) [14].
The quantitative estimation of bone mineral density around the endoprosthesis is conducted with two energy X-ray absorptiometry. The special software estimates the loss or growth of bone tissue around the endoprosthesis. According to the data from B.J. Kiratli, J.P. Heiner è A.A. McBeath [14], by the end of the first year postsurgery the loss of bone mineral density is 25-32 % with more intensive processes during 6 months after surgery. Thereafter the intensity of resorption significantly decreases, but decrease in bone mineral density still continues. One believe that destruction of a bone at the boundary of the prosthesis can be result of fractures of bone trabecules under the influence of mechanical load and as result of a biological response, when bone resorption is stimulated by the cellular response to development of specific particles (cement, polyethylene), fragments and metal ions [14].
The objective was to study the time course of bone mineral density around the various short-stem component of the hip joint after 6, 12 and 24 months after surgery by means of dual-energy X-ray absorptiometry (DEXA), to estimate the function of an operated joint (Harris hip score) and complications.
MATERIALS AND METHODS
The prospective non-randomized single-center study included 100 patients (men and women) with posttraumatic and idiopathic coxarthrosis and septic necrosis of the femoral head. The age of the patients was 25-68. In 2011-2013 they received hip joint replacement with short femoral components.
The ethical standards of the study corresponded to the standards of the committee of Volga District Medical Centre under Federal Medical and Biological Agency. The study protocol was approved by the ethical committee.
The inclusion criteria were young age (before 68), absence of previous osteoporosis or septic necrosis of the femoral head, absence of dysplastic changes in the hip joint, the femoral canal of types A and B according to Dorr, absence of significant obesity (BMI < 40).
The exclusion criteria were patient’s age > 68, previous diagnosed osteopenia or osteoporosis (SD > 2.5), inflammatory and autoimmune diseases of the hip joint, fractures in the region of the hip joint, hip dysplasia, previous surgery of the hip, obesity (BMI > 40), type C of the femoral canal according to Dorr.
At the stage of presurgical planning all patients received the clinical examination, X-ray examination of the hip in two views, densitometry, estimation of the functional status of the hip (Harris hip score).
The clinical examination included collection of complaints and anamnesis data, estimation of the locomotor system. Pain intensity was assessed with visual analog scale (VAS), where 0 – absence of pain, 100 – maximal pain.
According to the standard frontal and lateral views, the pathologic changes in the hip joint, the femoral bone and the acetabulum were estimated. The coxarthrosis changes were estimated according to the classification by N.S. Kosinskaya (1961), the changes in aseptic femoral head necrosis – with FICAT (1985).
The quality of bone tissue was estimated in 7 regions according to Gruen. The cortical index and the type of the femoral diaphysis were estimated according to Dorr (A, B and C) (Fig. 1). The type A – narrow femoral canal, thick cortical walls, the cortical index (the relationship between minimal and maximal sizes of the femoral canal) < 0.5. The type B – moderate development of cortical layers and the femoral canal, the cortical index – 0.5-0.75. The type C – wide canal of the femoral bone, thin cortical walls, the cortical index > 0.75. The choice of the size and the type of an endoprosthesis was done according to the standard X-ray images with match templates.
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Figure 1 The regions of the femoral bone according to Gruen for estimation of bone mineral density |
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The control radiography was conducted within 24 hours after surgery, and in 3, 6, 12 and 24 months after surgery.
The quantitative estimation of bone mineral density was realized with assessment of bone mineral density around the endoprosthesis. For this purpose all patients received dual-energy X-ray densitometry according to the orthopedic program. BMD was estimated around the femoral and acetabular components of the endoprosthesis. BMD was estimated in the region of the femoral component of the prosthesis in 7 zones described by Gruen et al. The results were assessed before surgery and in 6, 12 and 24 months after it. The examination was conducted with X-ray bone densitometer DMS (Diagnostic Medical Systems) (DEXA, France Challenger).
The presurgical functional condition of the patients and the analysis of time course of the function after total hip replacement were performed with Harris hip score. Results are estimated with 100-point scale with consideration of activity of a patient, ability to walking for a distance, upstairs, sitting in the chair and standing up. From 100 points the level of daily activity is 47 points, pain intensity – 44, volume of motions in the joint – 5, deformation of the joint and contracture – 4. The total sum of 90-100 is considered as excellent result, 80-89 – as good one, 70-79 – as satisfactory one. A result is estimated as unsatisfactory, if the total sum of points is lower than 70. Estimation of the results was conducted in 3, 6, 12 months and annually after surgery.
The study used cementless endoprosthesis with short femoral stems produced by Zimmer, Smith and Nephew, Biomet.
The femoral stem Fitmore is a curved cementless stem with trapezoidal transverse section, with Ti-VPS coverage in the proximal part (titanium plasma sputtering), with asperity in the distal part. The system of the stems includes 56 sizes including 3 groups of stems A, B and C (the group B with two types of offset) (Fig. 2).
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Figure 2 The femoral component Zimmer Fitmore
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2 |
The femoral stem SMF is a short curved stem made of Ti-6Al-4V, with trapezoid section, with STIKTITE alloy (pore size up to 200 µm) in the proximal part (plasma spray technique) that increases primary stability. It is possibly to use both the monoblock and exchangeable module necks.
The femoral stem Taperlock short is a short version of the well-known stem Taperlock, with wedge shape. It is made of Ti-6Al-4V, with Bonemaster sputter in the proximal part. There is a standard type of the neck-shaft angle 133 and different types of changed offset.
All operations with short stem components were performed with the anterior approach. A lineal incision (7 cm) was made along the anterior surface of the hip joint. The fascia was dissected. The gluteus medius muscle was sutured and intersected. The hip joint capsule was exposed and dissected in T-shape. Then the standard stages of hip replacement were performed.
Statistical analysis
The mean (M) and standard deviation (SD), confidence interval (CI) of the age and of bone mineral density, mean Harris hip score, pain level (VAS, mm) were estimated with Statistica 7.0 before surgery. The changes in bone mineral density (according to the Gruen regions) were estimated with confidence intervals, where CI is made up at the level of +1.96 of standard error; such interval includes 95 % of data. The time trends of Harris hip score and pain (VAS) were estimated with the paired t-test, with p ≤ 0.05 as reliable result.
RESULTS
The study group (100 patients, 100 hips) included 68 % of women (68 women and 32 men), the mean age of 50.2 (20-68). Most patients (82 %) suffered from coxarthrosis (idiopathic or posttraumatic) or aseptic necrosis of the femoral head (18 %). 73 operations were conducted for the right hip joint, 27 operation –for the left one. 40 % of the cases were operated with Fitmore Zimmer, 20 % - with SMF Smith and Nephew, 20 % - with Taperlock Short Biomet.
12 patients did not visit the control examinations. Their outcomes were estimated as satisfactory.
The mean BMD was 0.2 in the neck of the femur in the study group before treatment. The first control examination in 6 months after hip replacement showed the significant improvement in BMD in all regions of the femoral bone. In the region 1 BMD increased to 0.76, in the region 2 – to 1.56, in the region 3 – to 1.6, in the region 4 – to 1.7, in the region 5 – to 1.75, in the region 6 – to 1.35, in the region 7 – to 1.3.
The following control examinations after 12 and 24 months showed only insignificant changes in Gruen regions with increasing BMD in the regions 1-2 and 4-7. In the region 1 BMD increased to 0.80, in the region 2 – to 1.56, in the region 4 – to 1.75, in the region 5 – to 1.80, in the region 6 – to 1.44, in the region 7 – to 1.43, whereas BMD was without any changes in the region 3 (the table).
Table
| Time course of bone mineral density of the femoral bone after endoprosthetics in the study group |
| Gruen regions | 6th month M (CI) | 12th month M (CI) | 24 month M (CI) |
| 1 | 0.76 (0.64-0.84) | 0.76 (0.63-0.80) | 0.8 (0.65-0.87) |
| 2 | 1.5 (1.3-1.6) | 1.58 (1.41-1.62) | 1.56 (1.45-1.72) |
| 3 | 1.6 (1.56-1.82) | 1.7 (1.51-1.83) | 1.60 (1.56-1.82) |
| 4 | 1.7 (1.52-1.81) | 1.7 (1.52-1.81) | 1.75 (1.56-1.86) |
| 5 | 1.75 (1.63-1.83) | 1.79 (1.65-1.87) | 1.80 (1.67-1.84) |
| 6 | 1.35 (1.28-1.58) | 1.34 (1.28-1.6) | 1.44 (1.31-1.63) |
| 7 | 1.3 (1.21-1.51) | 1.37 (1.23-1.54) | 1.43 (1.24-1.64) |
Before surgery the patients of the control group had some functional disorders of the hip joint. The mean value of Harris hip score was 39.7. Within the first 6 months one could observe the significant improvement in functional outcomes. The control examination showed the mean HHS of 71.9 (p ≤ 0.05). The subsequent control examinations showed the stable improvement in the functional status: in 12 months – 76.8 (p ≤ 0.05 as compared with the basic value), in 24 months – 75.4 (p ≤ 0.05 as compared with the basic value) (Fig. 3).
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Figure 3 Time course of the functional status after hip replacement in the patients in the study group (Harris hip score)
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3 |
The postsurgical period showed the decrease in pain according to VAS from 81.3 mm to 21.8 mm (p ≤ 0.05) in 6 months after surgery. The improvement persisted by the moment of 12th month and 24th month: 15.6 mm (p ≤ 0.05 as compared with the basic value) correspondingly.
COMPLICATIONS
We observed some signs of aseptic loosening in 2 patients of the study group. It required revision surgery. Aseptic instability developed within 6-12 months after surgery, but the patients did not demonstrate any decrease in BMD because of compensatory sclerosis around the endoprosthesis.
DISCUSSION
In 2009 Albanese et al. [15] firstly published the results of the study of bone mineral density around short femoral components of the hip joint endoprosthesis. The authors noted that the short construction of the endoprosthesis was associated with increasing load to the proximal hip, efficient preservation of bone mass in the femoral metaphysis. The results were confirmed by the data of densitometry: increasing BMD in all Gruen regions. The results of our study were comparable with the results by Albanese et al.
The study by Götze C. et al. [16] showed the good functional outcomes (increasing HHS from 43.1 to 95.6), absence of revision with regard to aseptic loosening of the components. However the data of densitometry varied: the authors noted the decrease in BMD in the regions 1 and 7 (by 7.2 %), increasing BMD in the region 2 (up to 9.7 %), with no statistically significant changes in the regions 3-6.
The study by Schmidt R [17] showed the good functional results (increasing HHS from 45 to 93), but they noted the progressive decrease in bone mineral density according to Gruen: by 8 % in 12 months, by 22 % in 3 years. However it did not influence on the good clinical outcome of surgical treatment.
CONCLUSION
1. Use of short femoral components of the hip joint endoprosthesis is appropriate for young patients with osteoarthrosis or aseptic necrosis of the femoral head in absence of osteoporosis or osteopenia that confirmed by good survival within 24 months after surgery.
2. The most significant changes in bone mineral density around the femoral component, as well as changes in the functional status, were observed within 6 months after surgery.
3. Aseptic loosening of the stem was observed within the first year after surgery. Realization of densitometry do not influence on the rate of identification of aseptic loosening.