This prospective study compares the outcome of 157 hydroxyapatite (HA)-coated tibial components with 164 cemented components in the ROCC Rotating Platform total knee replacement in 291 patients. The mean follow-up was 7.6 years (5.2 to 11). There were two revisions for loosening: one for an HA-coated and one for a cemented tibial component. Radiological evaluation demonstrated no radiolucent lines with the HA-coated femoral components. A total of three HA-coated tibial components exhibited radiolucent lines at three months post-operatively and these disappeared after three further months of protected weight-bearing. With HA-coated components the operating time was shorter (p <  0.006) and the radiological assessment of the tibial interface was more stable (p < 0.01). Using revision for aseptic loosening of the tibial component as the end point, the survival rates at nine years was identical for both groups at 99.1%.

Our results suggest that HA-coated components perform at least as well as the same design with cemented components and compare favourably with those of series describing cemented or porous-coated knee replacements, suggesting that fixation of both components with hydroxyapatite is a reliable option in primary total knee replacement.

Purpose: This comparative study of femoropatellar function in four types of total knee arthroplasty (TKA) was conducted to demonstrate the relation between the form of the femoropatellar articulation and the function outcome achieved with these prostheses.

Material and methods: Forty patients who had undergone first-intention TKA for primary degenerative joint disease were selected at random. Minimum follow-up was one year. The functional IKDC score was greater than 85/100. All TKA had been inserted without preservation of the posterior cruciate ligament. Four types of prostheses were used:

- posterior stabilised prosthesis with a fixed plateau, toric trochlea, cemented dome patella (n=10);

- TKA with a rotating platform, 2-facet trochlae, rotatory congruent patella (n=10);

- TKA with a rotating platform, 2-facet trochale, without resurfacing (n=10);

- TKA with a rotating platform, hollow anatomic trochlae (n=10).

The following parameters were studied prospectively:

- pain assessed on a visual analogue scale;

- clinical assessment of going up and down stairs (normal, step-by-step, with handrail);

- kinematic assessment of active flexion extension (0°–120°) during which the position of the patella was measured in the three planes and the trajectory of the patella was noted in comparison with the healthy side and with the moment of the quadriceps;

- efficacy of the quadriceps (Cibex).

Results: The kinematic data demonstrated a significant difference between:

- TKAs with a dome patella and those with an anatomic patella;

- TKAs with an anatomic trochlae and those with a hollow trochlae;

This difference basically involved the patellar tilt, lateral subluxation of the patella, and especially, the patellar trajectory between 20° and 90°, the toric trochlae with a dome patella having a more anterior trajectory than the normal knee.

The clinical and functional study showed that:

- the percentage of totally pain-free femoropatellar articulations was higher for the hollow anatomic trochlae (96%) than for the three other types (75%) (p = 0.04);

- the stairs function was better for all the anatomic trochlae compared with the dome trochlae (p = 0.05);

- the efficacy of the quadriceps was the same for the four types of TKA.

Discussion and conclusion: This study confirms the theoretic work reported by Walker and the clinical work reported by Andriacchi on the anterior curvature of the trochlae and the kinematic work reported by Stichl on the advantage of anatomic trochlae. These findings point out the advantage of the hollow anatomic trochlae where the patella is applied on the trochlear groove situated at the same depth as the normal trochlae, which is not the case with most TKAs. This advantage is seen by the absence of pain and by the propulsion when climbing stairs.

Purpose: The purpose of this work was to compare polyethylene (PE) wear between prostheses with similar function but different congruency of the femoral implant / PE insert and, as a corollary, the mobility of the plateau.

Material and methods: We studied two groups of knee prostheses: prostheses preserving both cruciate ligaments (n = 20), and stabilised prostheses without preservation of the cruciate ligaments (n = 20). Four representative samples of ten patients by type of total knee arthroplasty (TKA) were selected at random among a cohort of 105 patients operated on between 1994 and 1996 with a mean follow-up of five years. All patients were reviewed with AP and lateral radiographs, a view in the plateau plane, and goniometry. Using this random selection, patients in the two groups were comparable for operative age (69 years), diagnosis (degenerative disease), sex ratio, IKS score (> 80/100), and follow-up. The only difference between the two groups was the postoperative goniometry: 180±2° for fixed plateau; 178±3° for mobile plateau (p< 0.05).

Result: Penetration of the femur in the PE insert (U) (after correction for radiographic magnification) was: TKA two cruciates fixed plateau: U=3.5±1.5mm; TKA two cruciates mobile plateau: U=0±1mm (p< 0.001); TKA posterior stabilisation fixed plateau: U=2.5±1mm; TKA posterior stabilisation mobile plateau: U=0 mm (p< 0.001). A difference of more than 3° in the mechanical axis did not show detectable wear in the group of congruent prostheses while for fixed plateau prostheses, wear appeared when the mechanical axis was 180°.

Discussion: Few studies have compared PE wear of TKAs with identical form and function. The random selection allowed us to compare homogeneous groups of patients eliminating selection bias of the retrospective analysis and of the effect of patients lost to follow-up. The highly significant difference between the groups compared avoided potential ß risk. However the quality of the PE and its mode of sterilisation were not known with certainty for the tested implants.

Conclusion: This study demonstrates the importance of congruency as a factor reducing PE wear in TKA. This parameter is more favourable when the postoperative mechanical axis is perfectly corrected.