Treatment of arthritis at the PIP joint has remained one of the unsolved problems in hand surgery. The index and middle fingers are subject to such strong lateral forces during pinch activities that an implant at the PIP joint would need significant lateral stability for long-term survival. Arthrodesis at these joints provides good lateral stability but at the expense of motion. In contrast, although arthrodesis may be fairly well-tolerated in the index finger, fusion of the ulnar digits causes significant difficulty with power grip. Thus, surgeons have looked toward developing a durable implant that can withstand lateral forces but preserve motion.
Swanson introduced a constrained silicone implant for the PIP joint in the 1960s.10
Good pain relief has been reported from this procedure, although restoration of range of motion has been somewhat variable.1
Periprosthetic bone resorption as well as implant breakage have been noted over time in these implants.1,11
In contrast to earlier constrained implants, newer implants have been developed in order to more closely recreate the normal joint anatomy. These types of implants rely on the intact surrounding soft tissues for stability and require resection of only small amounts of bone. Minimally constrained pyrolytic carbon implants have been used as an alternative to silicone arthroplasty. Tuttle and Stern reported a total of 24 complications in 15 of these joints, with the most common being notice-able squeaking of the joint.3
Fifty percent of patients in this series had incomplete pain relief. Only two joints showed radiologic evidence of loosening. Nunley et al showed inadequate relief of pain and lack of improve-ment in range of motion in patients who underwent pyrolytic carbon arthroplasty for post-traumatic arthritis of the PIP joint.4
Interestingly, Bravo et al reported radio-graphic settling in 20 of 50 joints undergoing pyrolytic carbon arthroplasty.2
However, only four cases in this series were revised for loosening.2
These authors speculate that the implants “settle” into a stable position. Branam et al. compared the outcomes of silicone PIP implants to that of pyrolytic carbon implants.5
These authors found that both groups had good pain relief and self-reported satisfaction with similar numbers of complications.
The original version of the SR-PIP joint arthroplasty (Avanta) consisted of a chromium cobalt proximal component and a pure ultra-high molecular weight polyethylene (UHMWPE) distal component designed to be cemented. Linscheid et al reported on 66 joints at an average of 4.5 years with 32 good, 19 fair and 15 poor results.6
Interestingly, radiologic loosening was seen in only one joint This study also found that results were better using a dorsal rather than a lateral or volar approach.6
A kinematic study in cadavers of this implant also by Linscheid's group, revealed that the SR-PIP implant had a similar center of rotation and similar kinematics to a native joint.12
A later version of the implant (SBI) consisted of a distal component with a UMWPE surface with a textured titanium stem allowing for press-fit uncemented fixation. Johnstone et al compared the results of cemented versus uncemented SR-PIP arthroplasty and found that although patients had similar pain relief and gains of motion after surgery, there were significantly more cases with radio-logic evidence of loosening in the uncemented group.9
Thirteen out of 19 uncemented joints showed radiologic evidence of loosening compared with only one out of 24 cemented joints. The lead author now exclusively uses cement in his PIP joint arthroplasties.9
Jennings et al also reported increased loosening in uncemented versus cemented prosthesis with 10 of the 11 revisions in his series associated with lack of cement.7
In this series, although range of motion was not significantly improved after surgery, 88% of patients had a very satisfactory or satisfactory results.7
In the series published by Luther et al, the mean DASH score was 24 and patients had an average improvement in range of motion of 21 degrees.8
However, 14 of 24 patients required reoperations.8
Our study showed a 28-degree average gain of motion at the PIP joint as well as minimal disability as reported on the DASH questionnaire. Both results are similar to those reported by Luther et al.8
Our series was substantially smaller that the prior study; however, only one of our patients required reoperation. The MHQ showed a trend toward slightly worse scores on the operated hand; however, the small number of patients who responded to the questionnaire precludes meaningful statistical analyses.
The most striking feature in this series is the amount of subsidence seen radiologically. Early signs of subsidence were in some cases quite subtle, but careful evaluation of serial radiographs showed some subsidence in seven of 11 joints. All cases in our series were cemented in contrast to prior series which showed increased rates of radiologic subsidence or loosening mainly in their non-cemented implants.7,9
Interestingly, none of these cases has been revised for symptomatic loosening. These radiographic changes may represent stable “settling” of the implant as seen by Bravo et al in pyrolytic carbon implants, or they may represent early loosening that could eventually become symptomatic.2
In this small series of patients with SR-PIP arthroplasty, patients showed an increase in range of motion and reported fairly good function and pain relief on validated questionnaires. However, a large amount of radiographic subsidence was also seen on follow-up. Longer-term follow-up is needed to assess the survivorship of this implant.