Optimum interpulse interval for transcranial electrical train stimulation to elicit motor evoked potentials of maximal amplitude in both upper and lower extremity target muscles.

OBJECTIVE: The aim of this study was to determine the optimum interpulse interval (OIPI) for transcranial electrical train stimulation to elicit muscle motor evoked potentials (TES-MEP) with maximal amplitude in upper and lower extremities during intra-operative spinal cord monitoring. METHODS: Intraoperative spinal cord monitoring with TES-MEP was performed in 26 patients who had (corrective) spine surgery. Optimum interpulse interval (OIPI) were determined for the abductor pollicis brevis muscle (APB) representing the upper extremity and the anterior tibialis muscle (TA) representing the lower extremity. The IPI was varied between 0.5 and 4.0ms, where the OIPI was defined as the IPI with the highest muscle MEP amplitude for each muscle group. Differences between upper and lower extremity OIPIs were analyzed. Furthermore, the MEP amplitudes difference between the upper and lower extremity OIPIs and between the OIPI and IPI 2 ms was determined. RESULTS: The mean OIPI(APB) representing the upper extremity was 1.78 ± 1.09 ms on the left side and 1.82 ± 0.93 ms on the right side. The lower extremity showed a mean OIPI(TA) of 2.26 ± 1.16 ms on the left and 2.73 ± 0.88 ms on the right side. The mean differences between the OIPI(APB) and OIPI(TA) were significant for p=0.019 (Student's T-test). No within patient differences in OIPIs between the left and the right side were found. The mean MEP amplitude reduction, the APB amplitude at OIPI(TA) compared to the APB at OIPI(APB), was 32.5 ± 27.9%. For the TA a mean amplitude reduction of 33.4 ± 27.4% was found. The mean amplitude reduction for the OIPI amplitudes compared to the amplitudes at IPI 2 ms was 53.6 ± 25.5% for the APB and 45.8 ± 28.3% for the TA. CONCLUSION: Large intra- and interindividual differences were found between the mean OIPIs of the TA and APB muscles (range 1.78-2.73 ms) representing the upper and lower extremity. SIGNIFICANCE: Based on the results of this study, it is advisable to perform a set-up procedure for each individual patient undergoing TES-MEP to determine the optimal parameter settings when using supramaximal intensity of TES.

The anterior-posterior laxity after total knee arthroplasty inserted with a ligament tensor.

Goal of this study is to determine the anterior-posterior laxity in 30 degrees of knee flexion for a posterior cruciate retaining total knee arthroplasty with a relative dished insert and implanted with a ligament tensor. Furthermore, the correlation between these AP laxities and the postoperative range of motion (ROM) and postoperative Knee Society Score (KSS) is analysed. Fifty-one balanSys total knee arthroplasties were performed in 49 patients between 1998 and 2000. These arthroplasties are analysed with respect to AP laxity (Rolimeter), ROM and KSS with a mean follow-up of 4.6 years. The mean anterior laxity is 2.8 mm with no posterior laxities at all. The average postoperative ROM is 110 degrees with an average KSS of 142. No correlations between AP-laxity and postoperative ROM or between AP-laxity and postoperative KSS are found. A posterior cruciate retaining TKA with a relative dished insert and implanted with a tensor is very stable in the anterior-posterior direction in 30 degrees of knee flexion. This limited laxity does not seem to disadvantage the mean postoperative ROM and KSS, when compared to other TKA studies.

Time-dependent mechanical properties of HA/TCP particles in relation to morsellized bone grafts for use in impaction grafting.

In reconstructive surgery human bone defects are sometimes filled with the use of the impaction bone grafting technique. Currently different types of biomaterial particles are being developed as bone-substitute materials. Before these biomaterials can be applied their mechanical and biological behavior should be characterized. In this study the time-dependent mechanical behavior of biomaterial particles with different tri-calcium-phosphate/hydroxy-apatite (TCP:HA) ratios, particle sizes, and porosities is determined and compared to the behavior of human bone grafts, the latter being the standard material currently used to augment bone defects. The mechanical properties were assessed with the use of dynamic confined compression creep tests with a loading and unloading phase. Different graft material groups were tested, consisting of 100% human bone grafts, 100% biomaterial particles, and 50:50 weight mixtures of human grafts and biomaterial particles. No damage to the particles was observed by the impaction in the test chamber or by the dynamic load. Relative to the human graft material, the biomaterial particles hardly deformed under loading, were much stiffer, and showed almost no viscoelastic behavior. The mixtures showed intermediate results. Particle size and porosity influenced the behavior of the biomaterial particles. TCP:HA ratio did not have a great effect. The conclusion is that the application of these particles should be done with great care, as their mechanical behavior is drastically different than that of the human graft material. Mixing it with human bone grafts gave the material some biphasic, viscoelastic behavior that may be important for its biological response.