Here is a quick snippet that demonstrates how you can invoke a parametrized stored procedure with PowerShell:
$CreateTraceCommand = $SqlConnection.CreateCommand();
$CreateTraceCommand.CommandType = [System.Data.CommandType] "StoredProcedure";
$CreateTraceCommand.CommandText = "sp_trace_create";
$TraceIdParameter = $CreateTraceCommand.Parameters.Add("@traceid", [System.Data.SqlDbType] "Int");
$TraceIdParameter.Direction = [System.Data.ParameterDirection] "Output";
$OptionParameter = $CreateTraceCommand.Parameters.Add("@options", [System.Data.SqlDbType] "Int");
$OptionParameter.Value = [int] 2;
$TraceFileParameter = $CreateTraceCommand.Parameters.Add("@tracefile", [System.Data.SqlDbType] "NVarChar");
$TraceFileParameter.Value = [string] "c:\temp\test";
[void] $CreateTraceCommand.ExecuteNonQuery();
$TraceId = $TraceIdParameter.Value;
Write-Host "You created a trace with id: $TraceId";