Pi2 and Nugrip are pyrocarbon implants for thumb basal joint osteoarthritis after trapeziectomy. Pi2 implant is a free spacer whereas the Nugrip is an hemiprosthesis. The author reports the results in the literature of both implants and describes Pi2 pyrocarbon implant technique for primary thumb basal joint osteoarthritis. The key points of the Pi2 procedure are: preservation of the soft tissue environment during the trapeziectomy, partial trapezoidectomy to medialize the implant, and careful capsuloplasty and ligamentoplasty to stabilize the implant.
Key wordsPyrocarbon – thumb basal joint – osteoarthritis – arthroplasty – CMC implant – trapeziectomy
19 Pi2 and Nugrip Pyrocarbon Arthroplasties of the Thumb CMC Joint
Today’s bioindustrial proficiency in pyrocarbon technology has led to its use in the field of orthopedics, most particularly in hand and wrist surgery with the development of joint prostheses or hemiprostheses and new implants. 1 , 2 , 3
19.2 Characteristic of Implants
Whright Pi2 implant is a free spacer because there is no bone or ligament fixation (Fig. 19.1). It can therefore be mobile, and its shape allows it to adapt its position to thumb movements. Implant stability is based to a large extent on the soft tissues, which prevent it from coming out of its trapezium fossa. The implant is oval with two axes. When the implant is positioned, its largest axis is perpendicular to the thumb column. The implant comes in two sizes (thickness by length): 9 × 13 mm and 9 × 15 mm. The 9-mm thickness was chosen to be slightly smaller than the trapezium height, which is on average 11 mm. The implant thus maintains a certain height in its trapezium compartment without being subjected to or subjecting the scaphoid or the metacarpal base to excessive stresses that could result in bone resorption.
Ascension NuGripTM CMC Implant is not a free spacer but a pyrocarbon hemiprosthesis. This is the second-generation PyroHemiSpher implant that has been specifically designed for the treatment of osteoarthritis in the thumb carpometacarpal joint (Fig. 19.2).
19.3 Results in the Literature
This ellipsoidal free implant was originally intended for total TMC implant failures before being routinely used as a trapezium spacer for primary treatment of TMC osteoarthritis. 4 The Pi2 implant has been afterward our technique of choice for treating TMC osteoarthritis. In a short-term prospective and comparative study, Alligand-Perrin et al 5 found earlier functional recovery and better overall patient satisfaction with the Pi2 implant than with trapeziectomy stabilization. The Ardouin and Bellemère study at 5-year follow-up 6 was supplemented by that of Agout et al 7 at a minimum of 10-year follow-up. Of the 29 implants reviewed, 96.6% of patients were satisfied or very satisfied, pain measured 1.6/10, and the QuickDASH was 19.9%, while grip strength was 24 kg and key pinch was 5.9 kg. 7 The preoperative metacarpophalangeal (MCP) hyperextension did not get worse and the thumb column’s mobility increased. 7 No implants were revised. 7 Radiologically, 4.2% of the implants were dislocated, 48.2% (29% at 5-year follow-up) had signs of bone remodeling, mainly of the scaphoid distal pole, averaging 11.2% (8.5% at 5-year follow-up) of its height, without functional repercussions. 7 These good results are unusual. Many authors 8 , 9 , 10 , 11 , 12 found an early implant dislocation rate between 12.5 and 33% and a revision rate between 4 and 33%. However, the implantation method in these studies differed from ours, either in the approach or the stabilization technique (when performed). This underlines the demanding and precise nature of this procedure, mastery of which may require a lengthy learning curve.
In a recent publication comparing the results of 47 pyrocarbon hemiarthroplasties (24 Nugrip and 23 PyroHemiSpher) with those of 40 trapeziectomies performed using Thompson technique, there was no significant difference in pain, strength, mobility, and QuickDASH scores at an average follow-up of more than 24 months. 13 PyroHemiSpher implants have a significantly better functional thumb score (Nelson score) but higher complication, revision, and failure rates. Scaphotrapeziotrapezoid (STT) osteoarthritis (OA) decompensation occurred in 23% of cases and there was a 30% revision rate mainly due to STT OA; 17% were failures revised by trapeziectomy. Radiologically, 23% of cases had signs of implant instability and 32% had radiolucent lines up to 0.5 mm thick around the stem.
Indications are basal joint osteoarthritis in patients with primarily Eaton stage III–IV arthritic changes. It can be used in stage II osteoarthritis, but as this technique involves total trapeziectomy, the scaphotrapezial joint will also be removed.
We do not have any contraindications unless hyperextension of the MCP joint is treated when preoperatively hyperextension in the MP joint is 40 degrees or more.
19.5 Pi2 Implant: Author’s Own Experience and Preferred Technique
This procedure does not simply remove the trapezium and replace it with an implant. The technique requires several surgical stages whose sequence and execution must be scrupulously respected. 14 The intervention takes place under locoregional anesthesia with a pneumatic tourniquet at the root of the arm.
19.5.1 Anteroexternal Approach
We use a modified anterior Gedda-Moberg approach (Fig. 19.3), i.e., slightly medial and centered in a V on the trapezium tubercle. It provides easy access to the abductor pollicis longus (APL) tendon as well as to the flexor carpi radialis (FCR) tendon, which will be used to stabilize the implant. The fascia of the external thenar muscles is detached on its external edge, so that the muscles can be retracted internally, and the trapeziometacarpal joint can be approached as well as the trapezium tubercle. There often is an accessory tendon of the APL, highly variable in size, which is frequently inserted on the thenar muscle fascia or more rarely on the trapezium. This accessory tendon can be left in place or resected.
19.5.2 Nontraumatic Trapeziectomy
Before proceeding to the trapeziectomy, it is important to identify the FCR tendon immediately above the trapezium tubercle. This tendon should be preserved for the duration of the trapeziectomy. This should be done as gently as possible by disinsertion of the soft peritrapezial tissues at the bone level using a no. 15 blade or a fine periosteal elevator. We use a “corkscrew” screwed into the trapezium and handled like a joystick to expose each facet of the trapezium as much as possible and release them from the surrounding soft tissue (Fig. 19.4). This allows the trapezium to be extracted in the majority of cases in a single piece. The corkscrew is never used as an extractor, which would tear and weaken soft tissue environment. The internal osteophyte of the trapezium, often fractured during trapeziectomy, is removed with the same care as the trapezium.