Congenital hip disease in adults. Classification of acetabular deficiencies and operative treatment with acetabuloplasty combined with total hip arthroplasty.

We describe three distinct types of congenital hip disease in adults. The first type is dysplasia, in which the femoral head is contained within the original true acetabulum. The second type is low dislocation, in which the femoral head articulates with a false acetabulum, the inferior lip of which contacts or overlaps the superior lip of the true acetabulum, giving the appearance of two overlapping acetabula. The third type is high dislocation, in which the femoral head has migrated superoposteriorly and there is no contact between the true and the false acetabulum. We describe and classify the acetabular abnormalities and deficiencies found with these three types. If the anterior, posterior, and superior aspects of the acetabular component cannot be covered during a total hip arthroplasty because of a deficient acetabulum in an adult who has congenital hip disease, we advocate and acetabuloplasty technique (which we have named a cotyloplasty) that involves medial advancement of the acetabular floor by the creation of a controlled comminuted fracture of its medial wall, autogenous bone-grafting, and the implantation of a small acetabular component with cement. This procedure was performed in sixty-six patients (eighty-six hips). Forty-nine of the hips had a high dislocation, thirty-one had a low dislocation, and six were dysplastic. Two to fifteen years (mean, seven years) after the operation, the clinical and radiographic results were satisfactory. Only two acetabular components needed to be revised for aseptic loosening, at 5.3 and 7.5 years postoperatively. Moreover, the cumulative success rate for the acetabular components was 100 percent at five years and 93.2 percent at ten years.

Low friction arthroplasty for old untreated congenital dislocation of the hip.

We report the replacement of 42 hips in 34 adults with untreated congenital dislocation. We used Charnley low friction implants, cementing the cup at the level of the true acetabulum after deepening and enlarging it by our own technique of cotyloplasty. Results were evaluated in 38 hips after a mean of 5.5 years. All the patients showed marked improvement, with no infection and, as yet, no late revision. The technical difficulties of the operation and the complications are discussed.

Long-term behaviour of the Charnley offset-bore acetabular cup.

We report the long-term radiological results of 58 total hip arthroplasties (THA) using the Charnley offset-bore acetabular socket. Wear was measured at four sites and radiolucent lines and possible migration were recorded. Four cups were retrieved at revision and were examined using light microscopy, SEM and X-ray microanalysis. At a mean follow-up of seven years the mean wear in the DeLee and Charnley zone I was 0.4 mm and in zone II 0.26 mm. The wear rate was 0.06 and 0.04 mm/year, respectively. Progression of radiolucent lines was seen in five cases (8.6%). Three sockets (5.2%) were revised because of aseptic migration at a mean follow-up of 9.8 years and one socket for infection at two years. The offset-bore acetabular cup had excellent wear behaviour and a low migration and revision rate. We recommend that it should be considered in THA since the use of small cups is increasing, particularly in revision cases.

Detrimental effect of aging on the endurance of bone cement. An in vivo and in vitro study in rabbits.

We investigated the effect of aging on the compressive strength of bone cement under in vivo and in vitro conditions. Cement molds were implanted in the dorsum of rabbits and other molds were kept under stable conditions and in darkness. Comparative measures taken at 15 days and 1, 3, 6, 12 and 24 months showed lower endurance of the implanted molds (p < 0.001). A reactive capsule surrounded the bone cement in vivo up to the 3rd month, its cellularity increased, and then almost disappeared by 1 year. Macrophages and foreign body cells reappeared at 2 years, indicating a "chemical aging" effect in the in vivo environment. Our findings suggest that aging may play an important role in the amelioration of the mechanical properties of bone cement.

Offset acetabular cups: A solution to wear?

Change of tribological properties has been the main goal in the effort to augment the longevity of total hip arthroplasty, while the reduction of forces acting across the artificial joint space has received little attention. Spurred by recent reports of wear behaviour and good clinical results of the offset low friction arthroplasty cups, the authors, using the simplified free body technique, estimated the resultant hip joint reaction force and the angle of its application on 100 individual anteroposterior pelvic radiographs, by templating on the same hip a conventional concentric cup and an offset eccentric one. The results showed a highly significant reduction (p<0.0001) of the resultant hip joint reaction force in the offset group by 28.8% or 1.02 body weight and of the angle of the hip joint reaction force by 2.8 degrees. The authors believe that the reduction of the resultant hip joint reaction force in the offset cup group is the result of lowering and medialising the centre of rotation of the hip, a previously reported fact on non-clinically applicable conditions. They are also tempted to propose the generalized use of the offset type acetabular cup, since adverse events are not anticipated. (Hip International 2005; 15: 149-54).

Fifteen years' experience with Charnley low-friction arthroplasty.

In the years from 1973 to 1986, 359 low-friction hip arthroplasties were performed by the precise Charnley technique in 310 patients. Three hundred seventeen hips were reexamined both clinically and roentgenologically. Clinical evaluation was performed according to follow-up time, separating the total number of hips into three groups. In Group A, 78.49% of the reevaluated hips remained asymptomatic ten to 14 years postoperatively, a percentage that has risen to 92.02% in Group B (studied five to nine years postoperatively) and 98.38% in Group C (studied one to four years postoperatively). The infection rate was 9.6% in Group A hips, 4.7% in Group B hips, and inconsequential in Group C hips. The roentgenographic study included 96 asymptomatic hips with a follow-up period of six to 11 years (mean, 8.3%). A radiolucent line was present in the acetabulum in 40.6% of cases; cortical hypertrophy at the tip of the stem was present in 48.8% of cases. Cup wear of more than 1 mm was measured in 41.3% of hips and was correlated with longer follow-up times and younger patient age. The results are encouraging for the continuation of arthroplasty by this method.