THR is one of the most successful principles in orthopaedic surgery. Cementless THR is a well-established procedure especially for younger patients. The loading of the implant and bone stock multiplies due to higher activities in younger patients. The demand for a maximal clinical outcome led to improvements in designs to gain a higher range of motion.
The present study has made a retrospective investigation on two kinds of prosthesis by radiological and clinical outcomes. Additionally, this study evaluated the survival rate of the two kinds of prosthesis. The clinical results showed that Harris Hip Score has significantly difference between cement and cementless groups. Radiological outcomes and survival rate also have shown that cementless prosthesis achieves high rate of functional restoration and a low rate of complications. The cumulative surviving proportion free from osteolysis, stem loose, linear penetration or femoral revision are much lower in cementless group compared with cement group. However, the outcomes of cemented THR procedures were markedly poor.
These poor outcomes of early cemented THR were due to the implant design and cementing technique in many cases. However, cement itself was considered the real cause, and loosening was called “cement disease”. Based on these backgrounds, cementless THR was developed.
The concept of cementless fixation of a polyethylene acetabular component for total hip arthroplasty is presented in 1982[9]. The spherical cup is fixed directly to the subchondral bone of the acetabulum by means of two pegs and screws. The polyethylene in direct contact to the bone adjusts to the deformation of the pelvis (Isoelasticity). Bone grows into the indentations of the outer surface of the implant. The elastic cup does not interfere with the physiological stress patterns of the hip joint so that a stable “biomechanical incorporation” of the implant is achieved. The early radiological results indicate that the cementless stem resulted in higher primary and secondary stability by enhanced osseous integration[10]. Sharma et al[11] described the clinical and radiological long-term outcomes of 77 primary total hip replacements in 69 patients using the fully hydroxyapatite-coated JRI (Furlong) total hip replacement. Their findings suggested that the JRI (Furlong) hip gives a durable femoral stem implant fixation, whereas the prosthesis-bone interface achieved with the acetabular component is questionable. The study made by Ishaque et al[12] showed that the long-term analysis of cementless cup leads to good clinical results and fulfils the minimum survival rate of 95% at 10 years. Stastný et al[13] also concluded that the mid-term clinical results and evidence of good osteointegration of both components five years after primary implantation of the THR. The study of Peters et al[14] has confirmed that cementless total hip replacement in patients with rapidly destructive arthropathy led to a good result in a series of eight cases at midterm follow-up. Li et al[15] conducted a study to reveal whether or not uncemented total hip arthroplasty (THA) can achieve durable fixation of implants to bone in patients on chronic hemodialysis. The results have indicated that uncemented THA shows promising medium-term results in patients receiving long-term hemodialysis.
The surface of most early cementless implants was smooth, for which strong adherence to bone, could not be expected, and a macro lock implant with a window or fin was inserted into bone by press-fitting. Some researchers also suggested that the outcomes of these smooth-surface-type cementless THRs (including bipolar-type femoral prosthesis) were poor, causing aseptic loosening several years after surgery, and many cases required revision surgery[16]. Cementless proximal porous-coated stems are a good option for elderly patients[17]. The long-term results of total hip arthroplasty using an extensively porous coated stem were acceptable, and there was no case involving the progression of proximal bone resorption[18]. The development of material engineering in recent years completely changed the condition, because these materials make the bone ingrowths became available. Animal experiments showed that the pore size of porous materials is important. Bone formation into the porous implant increased as the pore size increased, but the connective tissue amount also increased. Thus, the maximum bone ingrowth capability was obtained when the pore size was 100-200 μm[19]. Second-generation cementless femoral components designed by Archibeck et al[20] provides more reliable ingrowth and limits distal osteolysis by incorporating circumferential proximal ingrowth surfaces. The present study examined the eight to eleven-year results of THA with a cementless, anatomically designed femoral component and a cementless hemispheric acetabular component. This second-generation cementless, anatomically designed femoral component provided excellent clinical and radiographic results with a 100% survival rate at ten years. The circumferential porous coating of this implant improved ingrowth and prevented distal osteolysis at a mean of ten years after the arthroplasty. Investigations of Plötz et al[21] in human specimens and animal experiments show that prostheses with a spongy metal surface can become fixed by bony ingrowth to varying degrees. Cementless hip arthroplasty using titanium implants has an excellent outcome in the medium term[22].
Although results are exciting for cementless prosthesis, clinical and radiographic failures in different kinds of bone deficiencies have been found in many patients. In comparison with contained deficiencies, better underlying host bone quality seems an essential condition for the success of these constructs. Because this condition cannot be interpreted with preoperative diagnostic methods, we do not consider indications for use of this method to be completely elucidated. The main worry about uncemented prosthesis are stress shielding in distal fixation-type cementless stems implants are fixed to the bone tissue by bone ingrowth in cementless THR. Transmission of weight-bearing stress to the femur via the cementless stem is different from that with the cement stem, and it is impossible to avoid its influence on bone tissue within in a long-term period. A typical influence is stress shielding in distal fixation-type stems. In patients who have a distal fixation-type stem, weight-bearing stress is not transmitted in the proximal femur, and bone resorption occurs. Problems specific to cementless cups have been reported: ① failure of the locking system of polyethylene liner; ② use in patients with acetabular dysplasia (cup placement level, influence of bone transplantation; ③insufficient polyethylene thickness; and ④use of screws. Malchau et al also believed that cementless THR has specific problems, and it is inferior to cement THR with regard to at least wear of polyethylene in many reports. Because of the high incidence of liner wear and osteolysis of modular cementless cups in this series, nowadays hard-on-hard articulations were used in these patients[23]. Cemented THR has been increasingly selected in Sweden because the revision rate following cemented THR was lower than that following cementless THR[24]. The poor long-term results with these uncemented total hip arthroplasties illustrate the necessity of regular radiographic evaluation to detect osteolysis and liner failure, which are both generally asymptomatic until catastrophic failure appears[25].
Why then, do surgeon increasingly use cementless THR today? In my personal opinion, biological fixation, in which the prosthesis is directly fixed to the bone, is an ultimate fixation method; and the absence of cement may be considered to reduce a mechanically unstable interface. Long-term results must be followed. Expectation for innovations (e.g., materials, surface property, implant design) aiming at further improvement of outcomes attracts many operators. In any case, whether cementless THR remains a truly useful procedure for hip arthroplasty depends on detailed investigations by unbiased orthopedic surgeons.
In conclusion, cementless prosthesis achieves high rate of functional restoration and a low rate of complications.