Uncemented fully hydroxyapatite-coated hip stem for intracapsular femoral neck fractures in osteoporotic elderly patients: a multicenter study.

There is still debate over the limits of age and bone stock quality of patients on whom to use an un-cemented straight stem coated with hydroxyapatite (HA). We studied a group of 244 patients with a displaced intracapsular fracture of the femoral neck who underwent cementless hemiarthroplasty or total hip arthroplasty. 143 patients were reviewed at the two-year follow up. A fully HA-coated stem for intracapsular hip fracture results in a satisfactory return to pre-injury mobility and a low complications rate. The advantage reported in the literature of a low mortality rate with use of an un-cemented implant in elderly patients was shown to be greater still on finding an immediate primary stability and rapid osteointegration of the implant.

Introduction

The concept of full coating to fixate a prosthetic stem whose geometry affords a reduction in proximal-distal rigidity was introduced 25 years ago [1], [2]. Despite good results documented in the literature however, the ideal type of coating and prosthetic design are still under discussion. The problem is even more evident if the host bone has osteoporotic characteristics.

The critical issues are primary fixation and osteointegration. The stability of the primary fixation depends on the prosthesis design and coating material. Radiostereometric analysis (RSA) studies of stem migration have shown precocious and definitive stability of fully coated implants and better results compared to porous metal-coated implants of similar geometry [3], [4]. Osteointegration is enabled by the interaction of the bone stock and the inert material coating of the prosthesis [5]. This phenomenon is not transitory but is seen throughout the entire duration of the arthroprosthesis in a process of periprosthetic remodeling. The quality of the bone is therefore vitally important for the short- and long-term survival of the implant. The use of an uncemented straight stem coated with hydroxyapatite (HA) in young, active patients with good bone quality is an indication endorsed in the literature [6], [7], [8]. There is still debate, on the other hand, over the limits of age and bone stock quality of patients on whom to use this type of prosthetic solution.

In light of this, we studied a group of patients having intracapsular hip fractures treated with a collarless fully HA-coated stem as a prosthetic solution and analyzed their clinical and X-ray results over a 2-year follow-up.

Material and methods

We retrospectively reviewed a group of 244 patients with a displaced intracapsular fracture of the femoral neck who underwent cementless hemiarthroplasty or total hip arthroplasty with a collarless fully HA-coated right stem. Our group of study consisted of all patients admitted with a diagnosis of intracapsular hip fracture between April 2011 and July 2012. The exclusion criteria for our study were: patients with arthritic changes involving the acetabulum and pathological fractures. Informed written consent from all patients was obtained prior to any intervention. Degree of Osteoporosis was evaluated measuring Cortical Thickness Index (CTI) according to Dorr [9]. CTI was assessed by examination of opposite femur on routine pelvis radiograph for preoperative planning. All surgical operations were done under spinal or epidural anesthesia at the discretion of the anesthetist. A lateral approach to the hip was used in 186 patients and a posterior approach was used in 58 patients, according to the surgeon's preference. Ultra short-term antibiotic prophylaxis was performed in all patients. Prophylaxis against heterotopic ossifications was done by administration of nonsteroidal anti-inflammatory drugs. All patients received a collarless fully HA-coated Korus stem (Gruppo Bioimpianti, Peschiera Borromeo, MI, Italy) (Fig. 1). The Korus stem, made of a titanium-substrate, has a triple-tapered design, being tapered in the anterior-posterior (AP) dimension and from lateral to medial. The stem features both horizontal and vertical grooves to increase both rotational and axial stability after implantation. Both the 135° and 125° CCD angle neck stems are coated with a layer of Osprovit hydroxyapatite (HA) of approximately 150 μm thickness. The combination of the macrostructure tapering, horizontal and vertical grooves and the HA coating was devised to promote implant stability. The Korus stem should be implanted with either a collarless or collared stem, depending on the surgeon's preference and estimations of bone quality. In 181 cases patients received a bipolar cup (Janus cup, Gruppo Bioimpianti, Peschiera Borromeo, MI, Italy), in 14 cases a traditional cup (Fin II cup, Gruppo Bioimpianti, Peschiera Borromeo, MI, Italy) (Figs. 2 and 3), and in 49 cases a dual mobility cup (Dualis cup, Gruppo Bioimpianti, Peschiera Borromeo, MI, Italy). Pre-operative indication of the use of coupling with a different type of acetabular component was as follows: a traditional cup in patients under 80 not showing co-morbidity with pre-fracture unaided walking; a bipolar cup for patients over 80 or in those under 80 but with low capacity to walk unaided; use of a dual mobility cup in patients with neuromuscular disorders or cognitive dysfunction, and for patients under 75 if at risk of falls and early dislocation. To calculate fall risk status we used the Morse Fall Scale (MSF) [10] upon patient admission. MFS > 45 was indicative of high risk.

Figure 1

Photograph of an uncemented fully coated Korus stem (Gruppo Bioimpianti, Peschiera Borromeo, MI, Italy).

Figure 2

AP hip radiograph of a 79 year-old with an intracapsular left hip fracture.

Figure 3

AP hip radiograph of the same patient 2 years after total uncemented total hip arthoplasty with a fully coated stem.

Information collected included the patient's age, gender, pre-fracture mobility status and co-morbidity. Surgical parameters recorded were operative time, intra-operative complications and postoperative complications. Complications included fracture of the proximal femur, infection, hematoma and dislocation. Regular clinical and radiological follow up of all cases was done at 6 weeks, 3 months, 6 months, 12 months and two years. At each follow up, patients were evaluated clinically using the Harris Hip Score (HHS) [11] and radiologically to detect any loosening, heterotopic ossification, subsidence of the prosthesis, acetabular erosion or protrusion acetabuli.

Results

244 patients were treated with a collarless Korus uncemented fully HA-coated stem for a fractured femur neck. 156 patients (59%) were women. 30 patients had an opposite hip arthroplasty for a previous hip fracture. 3 pre-operative pelvis radiographs was lost at time of our study. 211 pre-operative pelvis radiographs was available to calculate CTI. Mean CTI was 0.49 (SD = 0.03; range = 0.39–0.54), supporting a poor quality of bone of patients treated [12]. In 49 cases the MFS score was 45 or more and a dual mobility cup was implanted due to high risk of fall or dislocation. 41 patients died during the first year follow up period. 87 patients died and 14 were lost to final follow up. 143 patients were reviewed at the two-year follow up. At surgery time, mean age was 83.7 years (SD = 6.66; range = 66–100). 201 (82.3%) patients had at least one systemic disease, the commonest being hypertension (172 patients, 70.4%). One-year mortality rate was 16.8% (41 patients).

There were four cases of intraoperative trochanteric fractures managed by trochanteric cable fixation. Postoperatively, shortening of >15 mm was observed in five patients. Superficial infection in the form of a wound dehiscence was seen in three patients, one of whom was a diabetic. Two patients were managed by debridement and appropriate intravenous antibiotics. One case was managed with intravenous antibiotics. The infection resolved without any sequelae in all cases. Four patients had a deep vein thrombosis post-operatively. We observed two cases of dislocations. The first one was due to instability and the second to early loosening of the stem. In the second case, an undersized stem compared to the one chosen in pre-operative planning was implanted. Two patients were managed, respectively, with acetabular revision with a dual mobility cup and stem revision with an uncemented oversized stem. The rate of peri-operative complications was 7.3% (18 patients). One patient sustained a peri-prosthetic Vancouver B1 fracture after a fall six months after surgery which was successfully fixed internally with a plate and cabling.

The average HHS at 6 weeks after surgery was 52.16 (43.33–68.65), at 3 months 69.45 (49.62–81.28), and at 6 months 79.12 (54.55–87.81). At one year, the average score rose to 79.64 (55.80–88.96) and at the final two year follow up it was 81.14 (56.21–94.32). In 4 cases (1.6%) a subsidence of >3 mm was observed at the at the 6 week and 3 month follow-ups. In none of these cases there were any pain symptoms relative to subsidence and no further subsidence of the stem was seen at the next X-ray tests. One year radiological follow up revealed 14 (6.8%) cases of Brooker Grade I heterotopic calcifications, 8 cases (3.9%) of Brooker Grade II heterotopic calcifications and 2 cases (0.9%) of Brooker Grade III heterotopic calcifications [13]. Four cases (2.7%) of bone resorption on Gruen zone 7 was observed at the two-year follow up.

There were no additional late postoperative complications such as loosening, acetabular erosion, calcar resorption or protrusio acetabuli noted at two years.

Discussion

Many studies indicate that the ideal treatment for patients over 65 with an intracapsular hip fracture is total hip arthroplasty or hemiarthroplasty. In the literature the discussion is open over use of cemented or uncemented stem. Short-term results, at 1 year from surgery, indicate a higher rate of mortality in patients treated with a cemented stem [14]. Numerous possible complications are cited to explain this phenomenon: embolization of fat, bone marrow, and cement particles [15]. And now even the lower cost of a cemented compared to an uncemented stem, which has always been seen as an advantage of cemented over uncemented stems, has been challenged [16].

In light of these considerations we started using a collarless, fully HA-coated stem to treat subcapital fractures in patients over 65. Although the group of patients under study hadn't recently undergone instrumental tests to quantify their degree of osteoporosis, advanced age and subcapital fracture of the femur may be considered indicative of bone quality that is not good.

The use of a fully HA-coated stem also seemed justified by the results obtained by this type of implant following the study of the long-term stability of the stem of cementless femoral implants with differing surface configurations. Hamadouche et al. [17], in fact, in describing a study of stem migration using Ein Bild Roentgen Analyse femoral component analysis (EBRA-FCA), refer to an average migration of 1.26 mm over 8 years in a group of patients treated with an HA-coated stem against a migration of 2.57 mm (p = 0.04) in a group of patients treated with a grit-blasted stem of the same design. The authors conclude that the HA coating increases the stability of the stem, design being equal.

Von Schewelov et al. [18] report the results of a study carried out on a group of 38 patients with subcapital fractures of the femur. Measurement of stem migration is by roentgen stereophotogrammetric analysis (RSA), the most accurate method currently available for measuring the migration of prosthetic components [17]. The Authors divide the patients under study into two groups. The first group includes patients implanted with a stem of a smaller size than had been calculated in preoperative planning. The second group includes patients implanted with a stem of the same or a larger size than had been calculated in preoperative planning. The average migration of the undersized stems was 5.7 mm. The average migration of the stems that were as planned or oversized was 2.0 mm. The findings of the study show it is possible to achieve a stable implant of a fully coated uncemented stem in patients with a bone stock deficit but also that there is a bigger risk of migration in the case of stem undersizing.

Despite the demonstrated immediate stability of a coated stem, it must in any case be kept in mind that certain potential effects of bone-coating interaction may jeopardize the duration of the implant [19], [20], [21], [22]. HA coating loss may have various causes, such as osteoclastic resorption during bone remodeling, abrasion, chemical dissolution or delamination. The effect of resorption and dissolution can actually be observed during the process of periprosthetic bone remodeling. It has been recognized, however, that in the periprosthetic bone zones under load this phenomenon is followed by the depositing of lamellar bone that replaces the coating and guarantees long-term osteointegration [18], [20]. The formation of a third body resulting from delamination fragments represents a theoretical problem as yet to be proven. A third body migrating into the joint space could be a cause of polyethylene wear, but the reported wear rates in all series of long-term follow-ups of HA implants are not significantly different from those reported in other types of arthroplasties [23].

The results of osteointegration studies are consistent with the good survivorship results for this type of stem. One study of bone response to implants evaluated 245 patients (291 hips) implanted with a collarless HA-coated stem for a mean of 10 years, and found a small amount of proximal bone loss (37/291) as well as a low incidence of distal hypertrophy (23/291 hips). The investigators concluded that the changes in bone confirmed that the femoral component of the implant was well fixed [24].

In our experience we have always used the collarless Korus stem. The use of a stem with a collar is recommended by certain authors [2], [15] in the case of osteopenic bone. Use of a collared stem in such cases may afford additional stability and reduced subsidence. In our study group, however, we observed only one case of precocious mobilization caused by a subsidence of >3 mm. Precocious mobilization is explained, on the other hand, by the implanting of a stem undersized with respect to one calculated in pre-operative planning, as reported by Hamadouche et al. [17]. Another 4 cases of subsidence of >3 mm – non symptomatic and then stabilized – were found by X-ray testing at the 6 week and 3 month follow-ups. We may therefore conclude that the use of a collarless stem in any case guarantees very good primary stability even in the case of osteopenic bone.

While mortality at two years cannot be estimated because 14 patients were lacking at the final follow-up, the 1-year mortality rate in our study group was 16.8%. Our results therefore confirm the efficacy of the uncemented stem in reducing post-operative mortality compared to cemented implants [25], [26]. The percentage of perioperative complications was also acceptable, above all when considering the high incidence of co-morbidity on the admission of elderly patients with intracapsular hip fracture. Despite the fact that the incidence of periprosthetic fractures is greater in patients treated with uncemented stems than in those treated with cemented stems [27], [28], we only saw one case of periprosthetic fracture, thus recording an incidence of this complication comparable to that seen for patients treated with a cemented stem [26], [27].

Conclusions

A fully HA-coated stem for intracapsular hip fracture results in a satisfactory return to pre-injury mobility and a low complications rate. The advantage reported in the literature [15], [28] of a low mortality rate with use of an uncemented implant in elderly patients was shown to be greater still on finding an immediate primary stability and rapid osteointegration of the implant.