Surgeons Take a Closer Look at a Hip Replacement Implant

Hip replacement surgery has been around long enough now that there are numerous implants to choose from. Size, design, type of material, and cemented versus cementless are some of the key features that differ from one system to another.

In this study, the CementLess Spotorno System (CLS) was investigated for long-term (10 year or more) results. Like all other hip implant systems, the CLS has two basic components: the acetabular cup (socket) and the femoral head and stem. The cup and stem are made of titanium. The femoral head is ceramic.

There is a polyethylene (plastic) liner that goes inside the socket. The head of the femur fits into the liner. The liner or insert helps absorb impact on the implant so it must be as durable as possible.

Extensive wear of the liner or insert can result in failure of the entire implant, the release of debris into the joint, and osteolysis (bone loss). Too much wear of the liner or insert can result in the need for a revision surgery to remove the worn liner or insert and to replace it with a new liner or insert.

Both pieces (femoral and acetabular component parts) are press-fit into the bone. The stem fits down inside the center of the femoral shaft. The surface of the implant is coated with hydroxypatite, a compound that gives the surface a rough finish to which bone will adhere or stick.

The first hip replacements were all cemented in place. But over time, surgeons found that a cementless fixation had many advantages over a cemented implant. There are fewer cases of implant loosening with cementless implants.

If a reoperation to revise or remove and replace the implant ever becomes necessary, the cementless type is easier to work with. Best of all, the bone is less likely to be disrupted with a cementless hip implant like the CementLess Spotorno System (CLS).

Most of the patients in this study had osteoarthritis of the hip but there were a few with rheumatoid arthritis (RA) or osteonecrosis (bone death from loss of blood supply to the bone). Everyone was 66 years old or younger.

Long-term results were measured by looking at hip motion, pain, walking ability, and X-rays to look at wear and tear on the implant and any underlying bone loss. Surgeons also use type and number of complications, number of revisions, and overall survival of the implant as outcome measures.

In the final evaluation, there were 14 of the 102 patients who had a second surgery to revise the implant. Most had a loose cup without infection. Like other types of hip implant systems, the CementLess Spotorno System (CLS) had some problems with wearing of the polyethylene liner.

Analysis of the data showed that risk factors for implant failure (especially liner wear) in this group of patients included younger age at the time of surgery (more active), larger femoral head component part, smaller socket size, larger body-mass index (BMI), and male sex.

All implants did quite well during the first 10-years (first decade). Problems didn’t start to develop until the second decade (years 11 through 20). The number of CLS hip implants that were still intact and working fine after the first ten years was 92 per cent. That’s called the survival rate. Survival rate after 15 years was 78.4 per cent (good but not as good as the first decade). Survival rates past 15 years are not available yet.

The overall complication rate was 20 per cent. The most common complications included heterotopic ossification (HO) (formation of bone in the muscles and soft tissues around the joint), hip dislocations, bone fractures around the implant, infections, and deep vein thrombosis (DVTs or blood clots).

How does the CementLess Spotorno System (CLS) stack up against other similar hip implant systems? The authors say, “very favorably.” Survival rates, complication rates, and improvements in pain, motion, and function were all in the same ranges.

The biggest problem remains loosening of the cementless cup during the second decade of use. Knowing what some of the risk factors might be may help shape future patient selection and management approaches. More long-term studies following patients a full 20 years are also needed.