Cementless total hip replacement: past, present, and future

Abstract

Cementless total hip replacement (THR) is rapidly being accepted as the surgery for arthritic diseases of the hip joint. The bone-ingrowth rate in porous-type cementless implants was about 90% over 10 years after surgery, showing that biological fixation of cementless THR was well maintained on both the stem and cup sides. As for the stress shielding of the femur operated using a distal fixation-type stem, severe bone resorption was observed. The severe bone resorption group showed continuous progression for more than 10 years after surgery. Stem loosening directly caused by stress shielding has been considered less likely; however, close attention should be paid to bone resorption-associated disorders including femoral fracture. Cementless cups have several specific problems. It is difficult to decide whether a cup should be placed in the physiological position for the case of acetabular dysplasia by bone grafting or at a relatively higher position without bone grafting. The bone-ingrowth rate was lower in the group with en bloc bone grafting, and the reactive line was frequently noted in the bone-grafted region. Although no data indicated that en bloc bone grafting directly led to poor outcomes, such as loosening, cup placement at a higher site without bone grafting is now selected by most operators. The polyethylene liner in a cementless cup is thinned due to the metal cup thickness; however, it has been suggested that the apparent relation between the cup size and the wear rate was absent as long as a cementless cup is used. Comparative study indicated cementless THR was inferior with regard to the yearly polyethylene wear rate and incidence of osteolysis on both the stem and cup sides. Meta-analysis study on the survival rate between cement and cementless THR reported that cemented THR was slightly superior. It should be considered that specific problems for cementless THR, especially with regard to polyethylene wear, do occur.

Fig. 1

Total number of stem implants used in Japan. Squares, cementless stems; triangles, cemented stems

Fig. 2

Cementless total hip replacements (THRs) performed during the 1960s. Ring-type cementless THR was used during the 1960s. Ring-type THR adopted many points of the same concept as the current cementless THR including metal-on-metal articulation, a femoral head with a large diameter, and cup fixation with a screw using a direction and depth indicator

Fig. 3

Relation of bone, connective tissue formation, and total bone ingrowth with the pore size of the implant in an animal model. Dotted line, bone formation; dashed line, connective tissue formation; solid line, bone ingrowth

Fig. 4

Types of surface structure in bone ingrowth cementless implants. Magnified appearances of the implant surfaces are shown at the top. Ti, titanium; Co-Cr, cobalt-chromium; AML, anatomical medullary locking

Fig. 5

Results of biological fixation of AML-A stems (average 13 years after operation). Biolological fixation of the AML-A stem implant was evaluated radiologically according to the classification of Engh et al. There were 76 total joints, and the average postoperative follow-up period was 13 years

Fig. 6

Results of biological fixation of AML Tri-Lock cups (average 13 years after operation). Biological fixation of the AML Tri-Lock cup implant was evaluated radiologically according to the modified classification of Engh et al.21 There was a total of 76 joints, and the average postoperative followup period was 13 years

Fig. 7

Method for evaluating bone resorption of the proximal femur with cementless stems. The level at which the cortical bone thickness was one-half (1/2) was measured in the radiographic anteroposterior (AP) view. The medial cortical thickness in the distal region of the stem on the same side was regarded as the baseline. The most distal point in the region with reduced medial femoral cortical bone thickness to onehalf or less of the baseline was determined, and the percent ratio of the length between the distal end of the stem and this point (A) to the whole length of the stem (T) was calculated,

Fig. 8

Bone resorption in AML-A cementless stems. The “level with half cortical thickness” immediately after surgery was slightly lower than the lower margin of the lesser trochanter, showing a normal distribution-like single peak (A). In contrast, the mean “level with half cortical thickness” was 50.0% ± 11.1% at the final follow-up, showing that the level shifted toward the distal side by 14% of the whole length, compared to the level immediately after surgery (B); and the distribution showed a biphasic pattern with a boundary at 40%–44%

Fig. 9

Bone resorption in AML-A cementless stems. On a time course observation of the “level with half cortical thickness” in the severe bone resorption group, the level was increasingly lower for more than 10 years after surgery

Fig. 10

Metaphysis fracture of the femur with severe stress shielding. This 53-yearold woman with systemic lupus erythematosus was operated on using an AMLA cementless stem as the femoral endoprosthesis for the treatment of idiopathic osteonecrosis of the femoral head. She was treated with low-dose oral steroid administration. She complained of no thigh pain or hip pain at 9 years after operation. Radiological findings at 9 years after operation indicated no osteolysis or loosening; however, there were severe cortical hypertrophy and bone resorption (A). She slipped in the bathroom 10 years after her operation and felt severe thigh pain. Radiological findings showed metaphysis transverse fracture of the femur with small displacement (B)

Fig. 11

Displacement of a polyethylene liner due to failure of the locking mechanism. This 64-year-old woman with secondary hip osteoarthritis (OA) due to dysplasia was operated on using a Harris/Galante-type cementless implant 6 years earlier. She had no pain at 5 years after operation (A). However, she felt severe hip pain suddenly and could not walk (B). At revision surgery, displacement of the polyethylene liner was apparent due to failure of the locking mechanism. Metallosis was observed

Fig. 12

Biological fixation of cementless cups and en bloc bone grafting. Biological fixation of AML cementless cups (Duraloc and Tri-Loc) was evaluated according to the modified classification of Engh et al.11 There was a total of 77 joints, and the average follow-up period was 13 years. The rate of stable fibrous fixation was higher in the bone-grafted group than in the non-bone-grafted group

Fig. 13

Biological fixation of a cementless cup at the en bloc grafted bone. Cementless THR was performed for a 52-year-old woman with severe acetabular dysplasia using en bloc bone grafting with a resected femoral head. At 3 years after operation, biological fixation was evaluated as bone ingrown (A). At 11 years after operation, radiological findings indicated an apparent radiolucent line at zone 3 (arrows), and biological fixation of the cup was evaluated as fibrous fixation (B)

Fig. 14

Biological fixation of cementless cups and use of screws. Biological fixation of AML cementless cups (Duraloc and Tri-Loc) was evaluated according to the modified classification of Engh et al. There were a total of 77 joints, and the average follow-up period was 13 years. No significant differences in the biological fixation was observed between those without screws [screw (−)] and those with screws [screw (+)]

Fig. 15

Failures of cement-less cup implants after operation

Fig. 16

Failures of cement-less stem implants (arrows) after operation

Fig. 17

Meta-analysis of cement and cementless THR. The survival rates between cement and cementless THR were analyzed by metaanalysis. Regarding revision surgery on one of these devices or both the cup and the stem as failure, cemented THR was slightly superior

Fig. 18

Bone resorption after cementless THR. A marker of bone resorption (NTX-I) was measured after the THR operation. Peak bone resorption was observed at 4–5 weeks after operation. Surgical stress-induced marked bone resorption occurred immediately after surgery. In contrast, stress shielding-induced bone resorption progressed slowly but continuously