In a retrospective article comparing 27 arthrodesis procedures versus 21 hemiarthroplasties, Raikin and colleagues showed that 24 percent of the BioPro Great Toe Hemi-Implant group failed while 100 percent of the arthrodesis group achieved fusion.6 Patients in the hemiarthroplasty group had an American Orthopaedic Foot and Ankle Society-Hallux Metatarsophalangeal Interphalangeal (AOFAS-HMI) score of 71.8 percent whereas patients in the arthrodesis group had an AOFAS-HMI score of 93 percent.6 The BioPro implants showed dorsal subsidence at the final follow-up evaluation (a mean of 79.4 months). Eight of the 16 surviving implants displayed cutout of the distal portion through the plantar cortex of the proximal phalanx on the final follow-up radiographs. However, none were associated with osteolysis.
Roukis and Townley conducted a prospective study intended to report follow-up and analysis of patients who underwent surgical intervention for symptomatic hallux rigidus in the form of either a periarticular osteotomy or a resurfacing endoprosthesis.7 The AOFAS-HMI score increased by 30.2 points, from 54.4 preoperatively to 84.6 postoperatively, for the periarticular osteotomy group. The mean AOFAS-HMI score increased 26.7 points, from 51.1 preoperatively to 77.8 postoperatively, for the resurfacing endoprosthesis group.
What The Research Reveals About Other Implants
Trihedron™ Great Toe Hemi-Implant (Small Bone Innovations). Assessing the use of the Trihedron for hallux rigidus in a series of 23 cases, Sorbie and Saunders noted an average AOFAS score of 88.2 after hemiarthroplasty with an average gain of 31.4 points.8 The design of the implant included a 4-degree angle in the coronal plane to accommodate the shape of the proximal phalanx. The study authors also found no evidence of loosening or osteolysis at the last follow-up evaluation, which took place between 34 to 72 months postoperatively. One disadvantage of the study was it did not discuss range of motion over the past five years.
Futura™ Metal Hemi-Toe implant (Tornier). In 2009, Konkel and colleagues evaluated 23 patients over a six-year period with the Futura Metal Hemi-Toe implant.9 These patients suffered from grade 3 and 4 hallux rigidus, and their average age was 62 years. After assessing the outcome of these patients, the authors noted the patients had an average of 92 percent plantarflexion, average 73 percent dorsiflexion, a total average range of motion of 76 percent and an AOFAS score of 78 percent improvement.
The authors concluded that the Futura Metal Hemi-Toe implant had been used successfully with only mild lucency at the bases of the implants and no clinically visible subsidence on radiographs after an average follow-up of six years.9
HemiCAP® (Arthrosurface). The HemiCAP system addresses hallux rigidus at the metatarsal head. The implant resurfaces damaged articular surfaces and restores the patient’s own unique joint geometry. Over the years, the design has changed and the implant now includes a dorsal lip to reduce osteophyte ingrowth as with the previous design.
Carpenter and colleagues assessed the use of 32 implants in patients with hallux rigidus.10 Seventy-two percent of the study group had grade III hallux rigidus while the remaining 28 percent had grade II hallux rigidus. The average age of patients in the study was 63. The average follow-up was 27.3 months. The preoperative mean AOFAS-HMI score was 30.84 and the postoperative mean was 89.31. No implants were revised or removed, and no loosening occurred.
In July 2009, Hopson and colleagues published a single case report involving a failed HemiCAP implant.11 The authors believe the HemiCAP system does not address the proximal phalanx of the hallux and is still too new to have substantial long-term studies describing its use. Unfortunately, if this implant fails and requires removal, as was the course of events in this case study, a large bone deficit remains in the first metatarsal head.