The goal of this master thesis is to design an instrument which is able to insert an implant called a spinal cage, designed by M. Ahmadi, between two vertebrae. The spinal cage is of a new hinged, and spring loaded design, requiring a new insertion instrument, since no existing instruments are able to place the implant. The implant is used in a PLIF (Posterior Lumbar Interbody Fusion) surgery. The goal of this surgery is to relieve patients from their symptoms when suffering from a hernia. The new applicator is designed to have a workflow which induces a low workload. To gain information on the current surgery, two observations in the operating theatre are made and a workflow analysis is performed. After the initial analysis a lean startup process is used to create iterations of the new spinal cage applicator. This method is used because it is found to better suit the already largely defined context of the project. A test with the first design shows that the multi-segment spinal cage was difficult to load into the applicator, therefore a solution is found by creating a cartridge which contains the spinal cage and allows for a quick and easy insertion. A connection between the spinal cage and the part which pushes the implant into the body is added as well to allow for a controlled insertion. The second design is tested on a simulated anatomical setup. This user test shows that the connection between spinal cage and pusher, and markings indicating the correct insertion orientation requires improvement. The third design is tested to evaluate the workflow. It is found that the workflow induces a low to moderate workload. It is found that the applicator still blocks the surgical view too much. The final design, called ClearFix, is a disposable applicator made from clear polycarbonate to increase the surgeons view on the surgical area. Surgeons state that the ClearFix is easy and intuitive to use, and would use the ClearFix if it were available.