Patient-specific implants for use in hand surgery

evonos has developed two individual implants that have already been successfully used in patients. In both cases, a mediocarpal partial arthrodesis was necessary.

What is mediocarpal partial arthrodesis?

Mediocarpal partial arthrodesis is a partial stiffening of the carpal bones. This form of therapy is considered, for example, in the case of joint wear or instability of the carpal bone row close to the body and is intended to reduce the pain caused by a degenerative process, while maintaining a certain degree of mobility.

What makes the individual implant unique?

The special feature of the individual implant is that it connects the following bones: Os scaphoideum (navicular bone), Os lunatum (lunate bone), Os triquetrum (triquetral bone), Os hamatum (hamate bone) and Os capitatum (capitate bone).

Compared to the usual “four-corner fusion”, all the carpal bones are preserved with the evonos individual implant and are only debrided. The latter serves to remove degenerative changes and thus leads to improved healing.

The basic shape of the implant is reminiscent of the number eight. Both the size and the centers of the two implant halves are determined individually depending on the patient and case.

The implant is fixed with at least ten multidirectional screws, two of which are screwed into each carpal bone. The screw position and length is determined in advance using the patient-specific CT data and a 3D model of the patient’s hand.

How is the implant delivered?

We deliver the individual implant in a practical evonos tray. All the necessary instruments that the physician performing the procedure needs are within reach:

• Implant
• Milling cutter including individual milling template
• Multidirectional locking screws and cortical screws
• Drill
• Drill gauge funnel
• Screwdriver and tip
• Positioning pin for the implant

How is the implant inserted?

The cut-seam time is about 2.5 hours. Approximately 30 minutes of this are required for inserting and securing the implant.

After opening the skin and exposing the surgical field, the physician begins with the repositioning or the working on the various bones. In this process, the joint surfaces are debrided.

Once all bones are repositioned as desired, milling for the first plate can be performed. The attached image serves as a rough guide: It simulates the reposition including the implant and the screw position and screw length.

After the first milling, the second recess is milled using the milling template. The milling template is individually adapted to the implant based on the size and the distance between the two milling operations. The implant can then be inserted. At this point, subsequent milling or optimization of the position can still be carried out.

As soon as the implant is in the desired position, it is secured using a cortical screw. The implant is now securely placed, but has not yet achieved angular stability. This changes with the first multidirectional locking screw, which completely secures the implant.
The remaining screws are then fastened.

The position of the implant is then checked using an X-ray, and the surgical site is closed.

We look back on successful operations, in which we were able to satisfy both the physician performing the work and the patients. The delivery in our practical tray enables an all-round efficient performance of the operation.

This means: Save time while reducing the risk of infection. We are pleased to bring our many years of know-how in the development of complex neurosurgical individual implants to the field of hand surgery and to offer patients the highest quality of life as possible.

You can find more information about our patient-specific cranial implants on the evoShape product page.

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