The CHI System - Pioneered by Vilex

CHI is a cannulated metallic hemi implant intended to replace the base of the proximal phalanx. Each CHI is individually machined. The articular surface is mirror finished to minimize friction and shaped to maintain range of motion without inducing pain or altering the MPJ biomechanics.

The cannulation provides a mechanism for precise positioning of the CHI and also provides a path to expel body fluids during press fit. Two 1.1 mm holes at the periphery enable the surgeon to adjust the orientation if desired.

Although bone cement is the primary method of fixation, the two positioning holes provide a mechanism for suturing(optional) the CHI to the flexor halluxis brevis or longus while osseous integration proceeds naturally.

• Hallux limitus or hallux rigidus.
• Pain due to severe hallux valgus.
• Joint deterioration.

Contraindication

• Osteoporotic or poor bone stock
• Inadequate skin or musculotendinous system
• Unrealistic patient expectations
• Poor overall patient health
• History of bone infection
• Poor or inadequate neurovascular status

• Anatomically compatible, elliptical shape with ellipsoidal articular surface
• Cannulation for precise positioning
• CoCrMo or titanium
• Suturing holes for fixation

The surgeon should evaluate the overall health of the patient. An implant site may become infected, painful, swollen, or inflamed. The status of the adjacent bone and soft tissue may be inadequate to support the implant, resulting in instability, deformity, or both.

The benefits from implant surgery may not meet patient's expectations or may deteriorate with time, requiring revision surgery which is common with implants.

Vilex does not recommend a particular surgical procedure. The general procedure to implant CHI is similar to proced- ures employed with similar im- plants.The information and protocol provide an approach and not a required procedure. This is not a training manual.

A longitudinal incision is made on the dorsal aspect of the metatarsal-phalangeal joint. The incision is deepened by sharp and blunt dissection, avoiding the exterior tendon, to the level of the joint, and the vital structures are retracted. A longitudinal capsulotomy is performed, and the joint is resected free. All hypertrophic bone is resected from both the metatarsal and phalanx. Metatarsal osteotomy is performed if deemed appropriate. The base of the proximal phalanx is completely freed of its attachments on the medial, dorsal, and lateral aspects.

The special blade guide is then utilized to resectthe base of the proximal phalanx at the appropriate level. The resection line should bypass any tendon or critical tissue. If the joint has been decompressed on themetatarsal side, only a neutral amount of bone is resected from the base of the phalanx. (If the surgeon wishes to decompress the joint on the phalangeal side, the resection line is moved distally by distally placing the k-wires holding the blade guide. A curved blade guide is also available.

Figure 1: Position Blade with K-Wires		Figure 2: Trial Sizer Positioned and K-Wire Marks the Center		Figure 3: Drive Metal Hemi Implant Into Medullary Canal.

Figure 1 shows the blade guides mentioned and the positioning of the blade guide over the base of the phalanx. After the base is resected, a trial sizer is placed over the phalanx to determine the correct size of the prosthesis. Once the correct size is selected, with the sizer in position, drive a 1.6 mm K-wire through the sizer and into the phalanx as in Figure 2.

Remove the sizer and insert the implant over the K-wire. Press fit and drive the implant into the medullary canal, Figure 3. The surgeon may adjust the orientation of the implant by backing it out slightly. If there is a gap between the back of the implant and the phalanx, the surgeon can gently impact the implant with a mallet to eliminate the gap. (This last step may not be necessary if the surgeon elects to suture the implant to the surrounding soft tissue.

To cement the implant, roughen the phalanx surface with a rasp to provide a cement mantle. The joint capsule is closed over the prosthesis and sutured. Wound closure is performed with suture of the surgeon's choice. Bandaging and post-operative management corresponds to other arthroplasty procedures.