Aim: To study the influence of cement restrictors on the thickness and quality of femoral cement mantle.

Methods: In this prospective study, there are 49 cases of Hardinge restrictor and 33 cases bone block restrictor were used for Charnley hip replacement. The operation was carried out by one surgeon on 78 patients between 1 March 2003 and 30th April 2004. Each preoperative X-rays were templated for the placement of restrictor. Intraoperatively, a calibrated holder for the cement restrictor was used aiming at keeping the distal cement height within 2-3 cm of the tip of the femoral prosthesis. Postoperative X-rays were checked for cement mantle thickness and quality.

Results: The preoperative target of having a distal cement height of 2-3 cm was achieved as seen on postoperative X-ray in only 60.6% of the bone block group and 30.6% of the Hardinge group. Distal migration of the restrictors was associated with non-homogenous cement mantle in zones 3, 4 and 5 but did nor affect zone 2, 6, or7. As the restrictor remained within 20-30 mm, the thickness of mantle is maintained between 9mm and 21mm in zone 4. This finding is statistically significant with the p value of 0.001.

Conclusion: Though the bone block was marginally better than Hardinge restrictor, we conclude that the current available cement restrictors are not sufficiently good enough to offer a good cavity for cement intrusion in to the bone; further restrictors need to be developed and tested before clinical use.

There are good evidence that the distal canal restrictor improves pressurisation. Bone block and Hardinge restrictors are among the commonly used restrictors in UK.

During the introduction of cement, the restrictors tend to migrate. The effect may cause significant change in the size and thickness of the cement mantle. One of the determinants of early dramatic failure is the size of the cement mantle.

In our study, we compared the cement mantle thickness and amount of migration with Bone block restrictor and with Hardinge restrictor. The measurements were done in the standard AP x-ray of the hip taken in the post operative period. All cases were operated by one surgeon. The position of the either of the restrictor were maintained in all cases to 1.5 cm below the tip of the stem. Measurements were made for the cement mantle thickness, the distance between the tip of the stem and restrictor and canal diameter.

One observer who was not involved in the operative procedure evaluated 69 x-rays. Twenty seven cases of bone block restrictor and 42 cases of Hardinge restrictors were used.

At the end of our study, we conclude that both restrictors migrate with pressurisation. The amount of migration with Hardinge restrictor is more than bone block restrictor (21.5mm Vs 14.4mm) which is significant (p-0.007). The amount of migration had not affected the zone-4 cement mantle thickness (p-0.450). With the use of either restrictors, migration was influenced by the canal diameter (p-0.00). Canal diameter did not affect the cement mantle thickness ( p-0.368). We conclude that bone block restrictor is superior in withstanding pressurisation