Purpose: Hip resurfacing techniques utilize mechanical jigs to align a femoral guide-pin that directs implant placement. Errors in alignment may lead to premature failure. The purpose of this study was to compare femoral guide-pin placement using a computer-assisted surgical (CAS) navigation system to a currently available manual alignment device.

Methods: A computer-assisted navigation system was developed by our group. Target guide-pin position was determined for each cadaveric hip from radiographs. A guide-pin was driven into each hip using either the CAS method or a manual alignment jig (Durom; Zimmer) by a novice or expert surgeon respectively. Radiographic pin position was compared to the target and accuracy was compared between the two techniques.

Results: Guide-pin insertion trajectory using the CAS system was significantly less variable in varus/valgus alignment than the mechanical jig (2.0° SD vs. 5.5° SD; p < 0.05). Ante/retroversion variability was also lower using CAS (4.4° SD vs. 7.7° SD) as was alignment error (CAS: 2.0° ± 2.2° SD valgus vs. Durom: 3.3° ± 5.5° SD varus, p=0.17; CAS: 0.1° ± 4.6° SD anteverted; Durom 3.2° ± 7.7° SD retroverted, p=0.48) but not significantly. Both methods proved accurate in placing the pin within 2 mm from the centre of the neck axis. Procedure time was similar between the two methods

Conclusions: Computer-assisted surgical navigation significantly improves reliability of guide-pin placement. This technique may help achieve better femoral implant alignment regardless of experience and contribute to improving hip resurfacing outcomes.

Funding : Other Education Grant

Funding Parties : Zimmer/UBC Research Fund

Patients were randomized between surgeon chosen pressure (control) and an automatically determined tourniquet pressure(study) group. Of the study group 94/106 (88.7%) had good to excellent fields compared to the control group where 100/132 (75.8%) had good to excellent fields (p< 0.05). In the study group, 5% failed to obtain an automatic pressure. Of the remainder, the average tourniquet pressure was 198 +/− 20.2 mHg compared to 259.6 +/− 4.4 mmHg for the control group (p< 0.0001). The automatic measurement of limb occlusion pressure resulted in better operative fields at a lower pressure.

To compare the quality of the operative field that results from using an automatic limb occlusion pressure measurement (study group) versus the tourniquet cuff pressure chosen by the surgeon (control group).

A module allowing rapid determination of tourniquet pressure from limb occlusion pressure was attached to a Zimmer ATS tourniquet machine. Using a coin toss, patients were randomized to the study or control groups. All patients underwent elective foot and ankle operations using a wide contoured tourniquet cuff.

Of two hundred and forty-three patients, one hundred and twelve were assigned to the study (automatic) group and one hundred and thirty-two to the control (surgeon selected) group. Six patients (5.4%) failed to obtain a limb occlusion pressure measurement due to anatomical constraints (toe or thigh shape) or equipment problems, leaving one hundred and six in the study group. The average measurement time to determine limb occlusion pressure was 20 +/− 6 seconds. The mean tourniquet pressure for the study group was 198.5 +/−20.2 mmHg, and 259.6 +/−4.4 mmHg for the control group (p< 0.0001). Of the study group 94 (88.7%) had good to excellent fields compared to the control group where one hundred (75.8%) had good to excellent fields (p< 0.05).

An automatically determined tourniquet pressure reduced the tourniquet pressure and improved the incidence of good to excellent operative fields compared to surgeon chosen pressures. The distribution curve of automatically determined tourniquet pressure indicates that 16% of patients will have a failed field if a standard pre-selected pressure of 250 mmHg is always chosen, in part explaining why pre-selected pressure may cause a poorer operative field.

Introduction and Aims: Limb occlusion pressure directly measures the cuff pressure required to occlude blood flow. We determined if a plethysmographic technique of limb occlusion pressure measurement could be used clinically and compared limb occlusion pressures for wide contoured cuffs versus standard narrow cuffs.

Method: A photoplethysmograph sensor and a handheld module containing the required hardware and software were added to a standard Zimmer ATS 2000 tourniquet. Twenty patients undergoing elective foot and ankle surgery were randomised to either a wide contoured cuff or a regular cuff. Limb occlusion pressure and quality of the bloodless surgical field were recorded. Cuff pressure was selected using an incremental increase of pressures over the limb occlusion pressure. Cuff pressures were compared between cuff types and were also compared to the cuff pressure selected by most surgeons determined by a previous survey.

Results: Three out of 40 patients had poor fields. Fifty-two patients were recruited and 12 patients were excluded due to difficulty obtaining a limb occlusion pressure measurement. The mean LOP in the wide cuff group was 36 mmHg lower than the standard cuff group (P = 0.004, 80% power to detect a reduction of 25 mmHg). The cuff pressure using the recommended tourniquet pressure (RTP) and a standard cuff was an average of 58 mmHg lower than 300 mmHg, and 108 mmHg lower than 350 mmHg. For the wide cuff and using the RTP the pressure was 98 mmHg lower than 300 mmHg, and 148 mmHg lower than 350 mmHg. There was a poor relationship between limb occlusion pressure and systolic blood pressure.

Conclusion: Tourniquet pressures can be reduced by one-third using limb occlusion pressure measurement and a wide contoured cuff without increasing the number of poor operative fields. Traditional techniques of setting the tourniquet, such as using systolic blood pressure, are likely to result in poor fields or excessive tourniquet pressures. The plethysmographic method is accurate and practical for clinical use.