Press-fit acetabular reconstructions have become the standard THA; however, controversies remain. The purpose of this study was to critically evaluate serial radiographs for initial cup stability, i.e. gaps and signs of periacetabular interface changes for a porous tantalum monoblock socket.

A multicenter study evaluating 574 primary THRs (542 patients) performed by 9 surgeons at 7 hospitals, all with a monoblock cup without screws. Analyses included clinical outcomes and detailed 2-year minimum radiographic evaluation by one independent observer (mean follow-up, 33 months).

Complications included 9 intra-operative acetabular fractures. Among the 123 cases excluded from radiographic evaluations: deceased (19), lost-to-follow-up (8), 7 early revisions (recurrent dislocations (6) and one trauma-related loosening), and sepsis (3). Patient demographics (414 hips): mean age 65 years (19–93); 58 percent females. Baseline radiographs revealed 113 zones in 85 hips (21 percent) with acetabular gaps; 36 in zone I, 72 in zone II, and 5 in zone III. Of these radiolucencies, 57 zones were 1 mm or less and 56 zones ranged from 2 to 5 mm. At last follow-up, 64 hips (75 percent) had complete gap fill-in, including 100 percent of gaps greater than 3 mm.

There were no socket migrations, no evidence of lysis, no revisions for loosening, and no complete periacetabular interface radiolucencies. The fill-in of preexisting OA cysts and gaps is attributed to adequate initial stability and osteointegration into the porous tantalum. These results suggest that a monoblock cup without screws is an attractive option in THA.

We describe the natural history of a rabbit knee model of permanent post-traumatic joint contractures. Twenty-four skeletally mature female NZW rabbits had five-mm-squares of cortical bone removed from both femoral condyles. An extra-articular K-wire immobilized the knee joint in flexion. The K-wire was removed eight weeks later and the rabbits were divided into four groups depending on the remobilization time. The average extension loss for the experimental knees in the zero, eight, sixteen and thirty-two weeks remobilization groups was thirty-eight, thirty-two, twenty-one and twenty degrees, respectively. The motion loss stabilized in the later time intervals suggesting permanent contractures had developed. The contralateral unoperated knees average extension loss was nine degrees.

The purpose of this study was to develop a rabbit knee model of post-traumatic contractures.

A simulated intra-articular fracture plus eight weeks of immobilization leads to a permanent joint contracture even after thirty-two weeks of remobilization.

This animal model of human post-traumatic joint contractures will allow further studies investigating mechanisms underlying the process.

Twenty-four skeletally mature female NZW rabbits had 5 mm squares of cortical bone removed from both femoral condyles. An extra-articular Kirschner wire (K-wire) immobilized the knee in flexion. A second operation was performed eight weeks later to remove the K-wire. The rabbits were divided into four groups. Hind limbs were dissected, preserving the joint capsule. A device allowing six degrees-of-freedom coupled to a material testing system which applied a 0.2 Nm torque measured joint angles. Statistical analysis was performed using ANOVA with a posthoc Student-Newman-Keuls test. Data are presented as mean ± SD.

The loss of extension for the experimental knees in the zero and eight weeks remobilization groups was significantly greater than the values of all contralateral unoperated knees. The loss of extension for the experimental knees in the sixteen and thirty-two weeks remobilization groups was also greater than the contralateral knees, although it was not statistically significant (p = 0.07). With this model, the severity of the contracture decreased with time of remobilization. However, the degree of contracture stabilized between sixteen and thirty-two weeks of remobilization, suggesting that the joints had developed a permanent contracture. This mimics the human scenario of permanent post-traumatic joint contractures.

Funding: has not been received from a commercial party. This work was supported by The Alberta Heritage Foundation for Medical Research.

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