What is the test for requesting a supplemental brief in a personal injury appeal?

Appointed counsel filed an opening brief that sets forth the facts of the case and asks us to determine whether there are any arguable issues on appeal. (People v. Wende, supra, 25 Cal.3d 436.) Counsel advised defendant of the right to file a supplemental brief within 30 days of the date of filing of the opening brief. More than 30 days have elapsed, and defendant has not filed a supplemental brief.