SCIENTIFIC ARTICLE A Modular Surface Gliding Implant (CapFlex-PIP) for Proximal Interphalangeal Joint Osteoarthritis: A Prospective Case Series Stephan F. Schindele, MD, Stefanie Hensler, MSc, Laurent Audigé, DVM, PhD, Miriam Marks, PhD, Daniel B. Herren, MD, MHA Purpose To evaluate the one-year postoperative clinical and patient-rated outcomes in patients receiving proximal interphalangeal (PIP) joint arthroplasty with a modular surface gliding implant, CapFlex-PIP. Methods 10 patients each with primary osteoarthritis of a single PIP joint were assessed preoperatively (baseline), at 6 weeks, and 3, 6, and 12 months after CapFlex-PIP arthroplasty for lateral stability and range of motion of the affected digit. In addition, patients rated their pain using a numeric rating scale and function and overall assessment of their treatment and condition using the quick Disabilities of the Arm, Shoulder and Hand (QuickDASH) and Patient Evaluation Measure (PEM) questionnaires, respectively. Results The mean baseline active mobility of the affected PIP joint increased from 42 to 51 by one year, although this change was not significant. Patients reported reduced pain at one year, which was statistically significant. There was also a significant improvement between baseline and one-year QuickDASH (43 points vs 15 points, respectively) and PEM scores (51 vs 25 points, respectively). Absent or low lateral instability was observed in 9 joints at follow-up. All implants remained intact over the one-year postoperative period and there was no migration, osteolysis, or implant fracture. After study completion, 2 patients underwent tenolysis. Conclusions Patients experienced a significant reduction in pain and a trend towards increased mobility. All implants showed complete osteointegration without evidence of radiological migration. Lateral stability improved. (J Hand Surg Am. 2015;40(2):334e340. Copyright Ó 2015 by the American Society for Surgery of the Hand. All rights reserved.) Type of study/level of evidence Therapeutic IV. Key words Arthroplasty, case-series, proximal interphalangeal joint, surface replacement. 1e3 N CONTRAST TO OSTEOARTHRITIS of the distal in- interphalangeal (PIP) joints. Lateral stability of terphalangeal joints, where arthrodesis is the the PIP joint is an important aspect for preserving I treatment of choice for most patients, most sur- function, especially of the index and middle fingers, geons prefer to preserve motion of the proximal which, together with the thumb, are responsible for From the Department of Upper Extremities and Hand Surgery and the Department of Research further financial payments or benefits from any other commercial entity related to and Development, Schulthess Clinic, Zurich, Switzerland. the subject of this article. The implants used in this study were funded by the KLS Received for publication April 24, 2014; accepted in revised form October 23, 2014. Martin Group. The authors thank Prof. Dr. Maja Bürgi and her team from the School of Engineering, Zurich Corresponding author: Stephan F. Schindele, MD, Schulthess Clinic, Department of Upper University of Applied Sciences Winterthur, for their support in the development and Extremities and Hand Surgery, Lengghalde 2, 8008 Zurich, Switzerland; e-mail: Stephan. manufacturing of the prosthesis and Dr. Melissa Wilhelmi for the copyediting of this [email protected]. manuscript. 0363-5023/15/4002-0022$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2014.10.047 The two senior authors (S.F.S. and D.B.H.) received royalties from the KLS Martin Group, Tuttlingen, Germany. These authors and their families did not receive any 334 r Ó 2015 ASSH r Published by Elsevier, Inc. All rights reserved. CAPFLEX-PIP ARTHROPLASTY 335 grasping and pinching. Joint stability is influenced by several factors including the integrity of the joint surface, the flexor and extensor tendons, capsular and ligamentous structures, and the intraarticular versus external pressure difference.4 The requirements for replacement of a well-functioning joint are defined by these factors and must be taken into consideration when designing an implant. Silicone implants have been most widely used for PIP joint arthroplasty and act as a spacer to prevent bony contact or impingement.5 Alternately, several anatomically designed metal,6,7 pyrocarbon,8 and ceramic9 implants are total joint arthroplasties directed at restoring joint function. None of these FIGURE 1: CapFlex-PIP implant. The proximal and distal cobalt- implants, however, fulfill all the requirements for chrome alloy components (distal 2 out of 3 sizes) with pure tita- adequate PIP joint replacement. Silicone implants nium coating on backside and inserted polyethylene components. may break or dislocate and, especially on the radial fi rays, cannot restore suf cient lateral stability to committee and all included patients gave their written 10,11 achieve a powerful pinch. Ceramic and pyro- informed consent. carbon implants fail to show osteointegration with possible secondary migration.12e14 In addition, implant revision remains challenging because most The modular implant, CapFlex-PIP implants require generous bone resection including The CapFlex-PIP implant (Fig. 1) is a modular partial or full release of the collateral ligaments.15,16 gliding surface PIP joint prosthesis consisting of 2 In order to address these limitations, a modular components. The proximal component is a bicondylar prosthesis for PIP joint arthroplasty (CapFlex-PIP; cap of cobalt-chrome alloy, and the distal component KLS Martin Group, Tuttlingen, Germany) was has an articular surface of ultra-high-molecular- developed to offer primary solid bone anchorage weight polyethylene. Both components have a tita- with limited bone resection and improved lateral nium pore base for cement-free osteointegration. This joint stability as a result of the implant’s anatomical design provides a classic polyethylene-metal gliding congruent joint surfaces and because collateral liga- surface known from other implant arthroplasties, ments are preserved during implantation. This pilot although the CapFlex-PIP components have only investigation aimed at evaluating the clinical and short pins for endomedullary fixation. The design of patient-rated outcomes with this new surface gliding CapFlex-PIP corresponds to the anatomical shape of implant one year after surgery. Our hypothesis was a PIP joint with relatively high contact constraint. that stable osseous integration of the implant would The varying height of the polyethylene articular be apparent without radiological signs of loosening, surfaces (ie, 2.1 mm, 3.0 mm, and 4.4 mm) allows for migration, or osteolysis in the first 12 months. modular adaption of joint stability based on the intraoperative findings to provide ideal collateral ligament tension. In addition, the polyethylene inlay METHODS can be changed in cases of revision without removal Between September 2010 and November 2011, we of the entire distal component. selected 10 patients with primary osteoarthritis of a Before its first clinical use, the CapFlex-PIP single PIP joint for surgical implantation with the implant was tested at the Zurich University of CapFlex-PIP prosthesis. Based on the lack of clinical Applied Sciences (ZHAW) (Winterthur, Switzerland) experience with this new implant, the exclusion laboratory. Biomechanical analysis and primary press criteria were radiographically fixed deviation of the fit experiments with a custom simulator were per- longitudinal axis in the frontal plane of more than 20 formed and compared with another approved implant. and lateral instability to the ulnar or radial side of The CapFlex-PIP implant showed a two-times higher more than 15; range of motion (ROM) of less than pullout force than the other implant. Furthermore, the 20; extensor or flexor tendon dysfunction; severe abrasion behavior and wear of the sliding alloy metal- cyst formation; and severe bony defect of the affected polyethylene pair surfaces were checked by simulator joint. The study was approved by the local ethics testing with one million cycles in liquid medium. J Hand Surg Am. r Vol. 40, February 2015 336 CAPFLEX-PIP ARTHROPLASTY FIGURE 2: Implantation of the CapFlex-PIP prosthesis. A Initial minimal distal cut at the head with primary resection guide under protection of the collateral ligaments. B Shaping for the inner contour with a hollow compactor after performing all resection cuts. C Trial proximal component and sizer for determining the correct size of the distal component. D Original implanted components. * ¼ collateral ligament. Finite-element and risk analyses were also success- All patients followed a standard rehabilitation fully conducted. Together with the risk analysis protocol involving 3 weeks of postoperative orthosis conducted by ZHAW and the KLS Martin Group, followed by active mobilization therapy. European Conformity certification for the European market was obtained. Clinical and patient-rated assessments The patients were assessed preoperatively, after 6 Surgical technique weeks, and 3, 6, and 12 months following surgery. All surgeries were performed by the 2 senior authors Lateral stability was judged by the treating surgeon (SFS and DBH) using the dorsal approach described using the valgus-varus method; 3 categories in- by Chamay.17 Figure 2 depicts the steps. Using cluding no, low, and high radial or ulnar instability special resection devices, 3 small cuts are performed described the degree of instability, which was at the head of the proximal