[Braking capacity after hip arthroplasty - effect of prosthesis design and preoperative status]

Driving a car is an important everyday activity. However, the patients' desire to resume driving at an early stage after hip arthroplasty is often faced by the uncertainty about their driving ability. Only little evidence is available to support the clinical decision-making with regard to driving competence after conventional total hip arthroplasty (THA). However, there is no proof that the results observed after THA can be transferred to hip resurfacing arthroplasty (HRA) patients. Due to physiological advantages, i.e., patient age and activity, as well as the special biomechanical implant characteristics, HRA patients could be expected to achieve normal braking capacity at an earlier stage in the rehabilitation process than THA patients. This could be achieved by an accelerated postoperative recovery or could depend on the preoperative vantage point concerning the patients' braking capacity.

To verify this hypothesis HRA and THA patients were compared to healthy subjects concerning their ability to perform an emergency braking manoeuvre in a car simulator before surgery, and at 6 weeks and 3 months after operation. Furthermore, postoperative recovery rates were compared between the two groups of patients. In addition, correlations between pre- and postoperative braking capacity were tested. Reaction time, movement time and force-time integral on the brake pedal were analysed.

Except for a deficient preoperative force-time integral, no significant differences were detected in HRA patients compared to healthy controls. In contrast THA patients required, pre- as well as postoperatively, a longer movement time and exhibited a smaller force-time integral. The two patient groups did not show any significant difference in recovery rates of movement time and force-time integral. However, considering the two patient groups as a whole, a significant correlation was detected between existing pre- and postoperative deficits.

In conclusion, it can be confirmed that HRA patients resume normal braking capacity at an earlier stage in their rehabilitation process than THA patients. Patients recommended for HRA recover braking capacity at the latest six weeks after surgery. This capacity clearly depends on the better preoperative status of the HRA patients and is not determined by a faster recovery rate. General patient-related advantages as well as biomechanical aspects of HRA have thus no influence on the recovery rates of braking capacity during the first three months after surgery. Due to the increasing outpatient rehabilitation regime after HRA, further studies are necessary to detect the turning point after surgical impairment within the first six weeks after surgery. Concerning the THA patients we recommend a longer safety distance when driving a car for up to three months after the operation. However, patients, especially those assigned to THA, should be made aware of their most likely already existing preoperative deficit. For clinical practice a rough estimation of postoperative braking capacity seems to be possible based on group assignment (HRA/THA). Nevertheless, deviators cannot be detected by this group classification. As driving simulator systems usually are not available in hospitals, a more accurate prognosis, i.e., based on established clinical scores, would be helpful.