The cls uncemented stem: 15 years f-up results

Spotorno L., Grüen T., Grappiolo G., Romagnoli S., Burastero G.
II Divisione Ortopedico-Traumatologica Azienda Ospedale "S. Corona" Pietra L.. (SV)

 Communication complète

 

Purpose of the study: The results obtained with CLS stem during its 15 years of use seem to demonstrate the hypothesis that an uncemented stem can reach the "golden standard" in both quality of results and survival curve. CLS stem is of TiAlNb alloy and it has a tapered shape which is ideal to allow initial stability through press-fit. There is no macro-structuring of surface, but the bone ongrowth occurs the same on the rough sand blasted surface. The goals are to achieve and maintain the osteointegration and the proximal load transfer. Neverthless, experience shows that nowadays the limit of survival of a T.H.A. (total hip arthroplasty) derives from the loosening/wear of the acetabular component, but acetabular failure and debris production too influence the result of the femoral component. Our aim was to evaluate two surveys with similar follow-up (>10 yrs.), similar demographic data and identical stem solution (CLS) but different cup.

 

Materials and Methods:

FIRST SERIES

300 Primary T.H.A (12/1983-04/1985).

Femoral comp.: CLS stem 100%

Acetabular comp.: All-PE sockets 81%

Metal-backed sockets 19%

M 48,7% (avg 60 y) - F 51,3% (avg 57 yrs.)

SECOND SERIES

171 Primary T.H.A. (12/1984-12/ 1987).

Femoral comp.: CLS stem 100%

Acetabular comp.: CLS expansion cup 100%

M 44,6% (avg 57 y) - F 55,4% (avg 57 yrs.)

Radiographic analyses were done for both series, according to Gruen criteria on 10 yrs. minimum X-ray follow-up. Implant Bone Demarcation (I.B.D.), periprosthetic osteolysis and bone remodeling were examined. We analyse 180 cases out of the first series and 134 cases on the second series.

Survivorship analysis were done according Kaplan Meier study with 15 yrs. Follow-up.

 

Results:

Radiographic analyses:

I.B.D. was mainly present in the proximal femor (zones 1-7) but also distally (zones 3-4-5), seldom in zones 2-6.

 

I.B.D.

 

1st series

 

2nd series

None

60,9%

79,6%

Low grade (zones 1-3)

37,4%

18,8%

High grade (zones 4-6)

2,2%

1,6%

Complete (7 zones)

0,5%

0%

 

Femoral osteolyses were evaluated in the 7 zones plus the Greater Trochanter (G.T. Zone), if 5mm (criteria of Harris).

 

Osteolysis

 

1st series

 

2nd series

Total

22,8%

15,9%

Proximal

(37 cases) 21,6%

(18 cases) 15,1%

Endosteal

(2 cases) 1,2%

(1 case) 0,8%

 

Regarding the stress-shielding, we considered the cortico-cancellization (in particular in zone 7) and the cortical thinning (zones 2-3-5-6).

 

Stress shielding

 

1st series

 

2nd series

None

16,3%

37,9%

Minimal (1 zone)

62,2%

54,6%

Mild (2-3 zones)

18,8%

6,7%

Moderate (4 zones)

2,2%

0,8%

Severe (> 5 zones)

0,5%

0%

Positive bone remodeling was seen as Endosteal Bone Formation in 76,2% of cases of 1st series and 82,3% for the second series.

 

Kaplan Meier Survivorship analyses results:

 

First series:

Still Followed 226

Revisions All 69 (Fig. 1 A)

Stem only 18 (Fig. 1 B)

Deceased 45

Lost at follow -up 11

 

Second series:

Still Followed 134

Revisions All 12 (Fig. 2 A)

Stem only 2 (Fig. 2 B)

Deceased 21

Lost at follow -up 5

 

Conclusions:

As expected, high revision rate (23%) of the cementless all-PE acetabular component was due to migration and/or osteolysis, in fact all-PE sockets were discontinued in 1987, and metal-backed Expansion cup is still being used today for primary cases.

The cementless femoral prosthesis had low revision rate (6%), most were associated with proximal femoral osteolysis. Original stem design from 1983 is still being used today.

Results of ten year survival rates of 96 & 98% for the femoral components in the two series are encouraging, with little or no changes in survival rates
up to 15 years

Long-term stability with osseointegration can be achieved with use of a tapered press-fit titanium alloy stem having a corundumized surface. Osseointegration with the femoral prosthesis can preserve structural integrity of the proximal femur; despite the "abnormal" debris production, coming by fretting between the PE-Bone interface, the CLS stem seems to have a good "functional reserve" to face its challenge.

We observed minimal or no stress-shielding in both series (81 and 93%); osteointegration and adaptive bone remodeling appears to protect the proximal femur from distal endosteal osteolysis (3 and 1%).

Clinical and radiographic studies are still in progress today. We assess long-term effects of progressive osteolysis on the fixation of the stem, to assess long-term adaptive bone remodeling and corroborate with studies of the same implant from other surgeons at other centers. g-term results are very promising.

 

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