Pyrocarbon Disc Interposition Arthroplasty (PyroDisk) for the Treatment of Carpometacarpal Thumb Joint Osteoarthritis
Authors: van der Heijden Brigitte E.P.A. , van Laarhoven Cecile M.C.A. 
Published: November 2022

Background:
In cases of isolated carpometacarpal (CMC) thumb joint osteoarthritis, a hemitrapeziectomy can be performed. To address the risk of subsidence of the first metacarpal, a pyrocarbon disc has been designed as an interposition prosthesis. The disc is made of pyrolytic carbon with the same elastic modulus as cortical bone, making it resistant to wear from surrounding bone. This property contributes to preservation of thumb length and prevents subsidence. The present video article shows the pyrocarbon disc interposition arthroplasty step by step. The procedure results in substantial pain reduction with good function and strength at long-term follow-up. The complication rate is comparable with that of other surgical tendinoplasties for CMC thumb joint osteoarthritis. The survival rate has been reported to be 91% at a minimum follow-up of 5 years
1–3
.
CMC thumb joint osteoarthritis is a common pathology. If symptoms remain despite splinting and hand therapy, surgical treatment is often performed. The simple trapeziectomy is seen as the reference standard, with good results and fewer complications compared with other surgical procedures
4–6
. Despite this fact, many surgeons still prefer to combine trapeziectomy with a tendinoplasty in order to reduce the risk of proximal migration and impingement of the first metacarpal on the scaphoid
7–9
. However, the volume and stiffness of autologous tendons are far less than that of the trapezial bone. This might be one of the reasons that trapeziectomy with tendinoplasty does not lead to better results than simple trapeziectomy. To overcome the disadvantages of a tendinoplasty, the PyroDisk (Integra LifeSciences) was introduced for CMC thumb joint osteoarthritis to preserve thumb length and provide more stability than other traditional techniques. The disc is designed to be utilized after a distal hemitrapeziectomy for patients with CMC thumb joint osteoarthritis without involvement of the scaphotrapeziotrapezoid (STT) joint.

Description:
Preoperatively, review radiology images to confirm that the osteoarthritis is limited to the thumb CMC joint and that all appropriate tools for inserting the disc are available before beginning surgery. Next, the patient is placed with their arm on an arm rest. The CMC thumb joint is exposed via a dorsal longitudinal skin incision, sparing the dorsal radial nerve branches and the radial artery and accompanying venes. The capsule is opened with an H-incision. With 2 parallel cuts to the joint surface, the articular surfaces of the joint are removed. After resection of the articular joint surfaces, the residual width and height of the joint space after resection are measured. The central point in the joint surfaces is marked for the bone tunnels. With an awl, tunnels are created from the center of the joint surface to the proximal (trapezial bone) and distal (first metacarpal bone) and the dorsal side. The implant size is measured with the trial implants for correct size of the disc. A tendon strip of either APL (abductor pollicis longus) or FCR (flexor carpi radialis) tendon is harvested for use securing the disc. The disc is secured with the tendon strip from proximal through the trapezium, through the disc and distal through the first metacarpal, and is secured to itself at the trapezial bone. The position is checked under fluoroscopy. When the disc in the right position, the joint capsule and skin are closed and a plaster cast is applied with the thumb in abduction.

Alternatives:
Alternative treatments include hemitrapeziectomy without interposition; full trapeziectomy, with or without ligament reconstruction and/or tendon interposition; and joint resurfacing prostheses.

Rationale:
The advantage of pyrocarbon disc interposition arthroplasty over other treatment options is the preservation of the STT joint
1
. Therefore, the procedure is minimally harming the surrounding anatomy despite open surgery and has a high success rate in reducing pain while preserving function and strength. The risk of complications is comparable with that of other CMC joint arthroplasty techniques. A relatively high survival rate has been reported at a mean follow-up of 7 years (range, 5 to 12 years). In cases of recurrent pain, all other surgical options remain possible (“no bridges are burned”). The main disadvantage is the cost of the disc.

Expected Outcomes:
Our recent study of this technique showed good patient-reported outcomes, pain reduction, patient satisfaction, and preservation of strength and range of motion at a mean follow-up of 7 years
1,2
. The survival rate was 91%, with 3% failing as a result of disc dislocation. Other reasons of failure were STT osteoarthritis and pain without a specific cause.

Important Tips:

Preoperatively, make sure that only the CMC thumb joint has osteoarthritis and that the STT joint does not. In cases in which it is unclear whether the osteoarthritis is isolated to the CMC thumb joint, perform computed tomography to make certain
10
.Only a few millimeters of bone must be resected from the first metacarpal base and the distal trapezium. Both bone cuts must be made parallel to each other and perpendicular to the longitudinal axis of the first metacarpal bone.Bone tunnels must be exactly centered in the cut joint surfaces for proper implant positioning and to decrease the chance of subluxation.Size the implant properly and check movement and stability.

Acronyms and Abbreviations:

OR = operating roomFCR = flexor carpi radialisAPL = abductor pollicis longusPRWHE = Patient-Rated Wrist and Hand EvaluationDASH = Disabilities of the Arm, Shoulder and Hand QuestionnaireMHQ = Michigan Hand QuestionnaireROM = range of motionFU = follow-upCRPS = complex regional pain syndromeLRTI = ligament reconstruction and tendon interpositionMRI = magnetic resonance imagingCT = computed tomography