Long-term bone remodelling around 'legendary' cementless femoral stems

Abstract

Bone remodelling around a stem is an unavoidable long-term physiological process highly related to implant design. For some predisposed patients, it can lead to periprosthetic bone loss secondary to severe stress-shielding, which is thought to be detrimental by contributing to late loosening, late periprosthetic fracture, and thus rendering revision surgery more complicated.However, these concerns remain theoretical, since late loosening has yet to be documented among bone ingrowth cementless stems demonstrating periprosthetic bone loss associated with stress-shielding.Because none of the stems replicate the physiological load pattern on the proximal femur, each stem design is associated with a specific load pattern leading to specific adaptive periprosthetic bone remodelling. In their daily practice, orthopaedic surgeons need to differentiate physiological long-term bone remodelling patterns from pathological conditions such as loosening, sepsis or osteolysis.To aid in that process, we decided to clarify the behaviour of the five most used femoral stems. In order to provide translational knowledge, we decided to gather the designers' and experts' knowledge and experience related to the design rationale and the long-term bone remodelling of the following femoral stems we deemed 'legendary' and still commonly used: Corail (Depuy); Taperloc (Biomet); AML (Depuy); Alloclassic (Zimmer); and CLS-Spotorno (Zimmer). Cite this article: EFORT Open Rev 2018;3:45-57. DOI: 10.1302/2058-5241.3.170024.

Keywords: bone remodelling; legendary stems.

Fig. 1

a) Pre-operative radiographs of a 54-year-old male patient operated in 1988 for osteoarthritis. b) Immediate post-operative control; Corail® stem KA11, ceramic-on-poly bearing was implanted with the stem in a slight varus position but with good reconstruction of the hip anatomy. c, d, e) Successive AP radiographic controls done at five years, 15 years and 20 years, respectively, showing limited resorption in the calcar region. Note the radiological ‘silence’ with no significant modification of the periprosthetic bone pattern. No osteolysis on both sides, despite significant PE wear.

Fig. 2

a) 17-year follow-up on a Taperloc® stem with evidence of distal cortical thickening. b) 12-year follow-up on a Taperloc® stem with evidence of lucent zones.

Fig. 3

Patients with AML stem and good bone quality might develop a spot weld and stress-shielding after a long time. a) Successive AP radiographs at one year, seven years and 15 years post-operatively showing a spot weld developing after seven years on the distal medial aspect of the stem. b) Later views confirm the spot weld formation.

Fig. 4

Osteoporotic patients requiring a larger diameter stem develop a spot weld and stress-shielding earlier. a) Successive AP radiographs of an AML® stem at four months, three years and ten years post-operatively showing the development of a spot weld and stress-shielding which started as early as 3 years. b) Lateral views are more sensitive in detecting these changes. c) A close-up view of the distal stem showing enlarging changes.

Fig. 5

A fibrous stable stem will be seen when bone ingrowth does not occur. Instead of a spot weld, a fibrous stable stem will develop parallel radiolucent lines. The stem is stable and does not migrate distally. No calcar hypertrophy and no distal pedestal can be seen. a) Successive AP radiographs of an AML® stem at one year, two years and ten years post-operatively showing the development of parallel radiolucent lines along the stem. b) Lateral views showing similar changes. c) A close-up view of the distal stem revealing more of these changes.

Fig. 6

A loose stem characteristic hallmark is distal stem migration. a) Successive AP radiographs of an AML® stem at four weeks, one year and six years post-operatively showing an increase in the distance between the tip of the femoral stem and the tip of the greater trochanter, indicating distal stem migration. Pedestal formation can be seen as early as one year post-operatively. b) Lateral views showing the pedestal formation. c) A close-up view of the distal stem showing more of these changes.

Fig. 7

a) Successive AP radiographs of an Alloclassic SL® stem immediately following surgery, and ten years and eleven years post-operatively, showing proximal cortical atrophy mainly in Gruen zones 1, 2, 6 and 7, indicating stress-shielding. b) Sequential AP radiographs of an Alloclassic SL® stem at three months, one year and nine years post-operatively showing cortical diaphyseal hypertrophy developing combined with proximal stress-shielding. c) Sequential AP radiographs of an Alloclassic SL® stem showing the adaptive behaviour of the stem in patients with osteoporosis.

Fig. 8

a) Successive AP radiographs of a CLS-Spotorno® stem at one-year, seven-year, 15-year and 30-year follow-up revealing no stress-shielding and distal cortical hypertrophy. b) Successive AP radiographs of a CLS-Spotorno® stem at one year, three years, seven years and after a revision surgery performed to change the worn polyethylene of the acetabular cup shows that wear-related osteolytic lesions are restricted to the proximal zones of the femur.