Short report letter: Cortical contact is unnecessary to prevent stem subsidence in cementless trapeziometacarpal arthroplasty

[Current Trends in the Implantation of the Touch Prosthesis at the Thumb Carpometacarpal Joint: Results of the 1st German-Speaking User Meeting]

The introduction of the new generation of thumb carpometacarpal (CMC I) joint implants for the treatment of CMC I osteoarthritis has significantly broadened the scope of hand surgery in recent years. However, the technical demands of the procedure and the many details that need to be considered require appropriate training and a learning curve. To share experiences with the Touch CMC I prosthesis, we held the first German-speaking CMC I joint prosthetics user meeting in Zurich. After some basic introductory lectures on biomechanics and the principles of prosthetic fitting of the CMC I joint, the various challenges associated with CMC I joint prosthetics were discussed in interactive expert panels. Subsequently, cases were discussed in small groups under expert guidance and the respective conclusions were discussed in plenary. The main results of this symposium are summarised in this manuscript.

New radiographic monitoring indices for total trapeziometacarpal prostheses

OBJECTIVE

The objective of this study is to propose and evaluate a method of monitoring implants via the calculation of a trapezial and metacarpal index from radiological measurements and to describe an initial patient analysis.

METHODS

This retrospective study describes the trapezial index which reflects the trapezial bone stock not occupied by the trapezial cup, while the metacarpal index reflects the rate of metacarpal occupation by the prosthetic stem. Those indexes were used on a series of 20 patients with a Maïa™ prosthesis with a minimum follow-up of seven years. The indexes were measured immediately postoperatively and at the various annual check-ups. Four observers measured each index on two occasions, to obtain an inter- and intra-observer correlation coefficient.

RESULTS

The average intra-observer correlation coefficient for the trapezium index was 0.94, for the metacarpal index 0.98. The inter-observer correlation coefficient was 0.93 for the trapezium index, 0.94 for the metacarpal index on average. The post-hoc calculated power was 0.98 as the number of subjects required was not usable. The mean immediate postoperative trapezial index was 45.74%, compared with a value at longest follow-up of 41.74%, reflecting a highly significant loss of height of 8,74%. The mean immediate postoperative metacarpal index was 77.69% compared with a mean value at longest follow-up of 78.99% indicating a non-significant increase in the index of 1,67%.

CONCLUSION

Proposed indexes had excellent inter- and intra-observer correlation, the metacarpal one is stable over time whereas the trapezial one reveals changes in some patients, requiring further investigations. These simple and reproducible indexes allow precise monitoring of trapeziometacarpal prostheses and identify radiographic changes that should lead to additional examinations to improve survival of implants.

LEVEL OF EVIDENCE

III, retrospective single cohort study.

Total joint replacement for osteoarthritis of the carpometacarpal joint of the thumb: why and how?

Total joint replacement has certain advantages over other surgical treatment methods for osteoarthritis of the thumb carpometacarpal joint, including restoration of thumb length and alignment, good cosmetical result, fast recovery of hand function and prevention of iatrogenic complications at neighbouring joints. Disadvantages include the technical difficulty to perform this surgery and a possible higher complication rate. A meticulous surgical technique is mandatory. Combined with a cementless and modular ball-in-socket implant with a metal-on-polyethylene friction couple, a 10-year survival rate higher than 90% can be expected. Revision surgery is possible with implant exchange or conversion to trapeziectomy.

[Experiences with arthroplasty of the basal joint of the thumb : The"mini-hip" gains ground]

The complex kinematics of the saddle joint has been a challenge in the development of trapeziometacarpal prostheses. The introduction of the dual-mobility design increases the range of motion and limits strains on the cup fixation. Therefore, rates of loosening and dislocation have been markedly reduced. Furthermore, several studies showed a similar relief of pain, range of movement and grip strength compared to the results of resection arthroplasty. The preservation of the length of the first ray as well as the more stable and functional joint can be favourable in younger and active patients. Further investigation is needed to determine whether or not those higher demands affect long-term survivorship. The high grade of patient satisfaction, the shorter recovery time and the safe surgical technique motivates considering the implantation of a total endoprosthesis with a dual-mobility cup as an attractive alternative to resection arthroplasty in the operative treatment for trapeziometacarpal osteoarthritis.