It has been about six decades since surgeons started using silicone implants for the first metatarsophalangeal joint, with patients suffering from hallux rigidus being the main beneficiaries. Mohammad Salim, Elizabeth Alderton and Rajiv Limaye ask, is its use still a viable option in the 21st century?
History
As surgeons started recognising the importance of the first metatarsophalangeal joint (MTPJ) in foot function and maintaining normal gait, interest emerged in developing a functional first MTPJ prosthesis. In 1952, Swanson designed a metal hemispherical cap with a tapered stem as a first metatarsal head replacement [1]. Swanson later believed the implant failed because of the rigidity of the material [2], prompting him to design a single-stemmed intramedullary prosthesis made of only silicone in collaboration with Dow Corning in 1967 [3].
The implant took cues from the existing hand implants and was primarily designed to act as a spacer to augment the Keller’s procedure [4]. Silicone was selected as the material of choice because of its inert nature, softer composition and well-tolerated physiologic properties [5].
The hemi-implant was not free of complications however, the most worrisome being silicosis which included dentritic synovitis, silicone lymphadenopathy and silicone synovitis. This was reported by Rehman and Fagg in their study [6] in which they recommended abandoning the procedure entirely. This led to the development of the double-stemmed hinged implants, which provided better joint stability and range of motion [7]. Subsequently, titanium grommets were introduced to protect the hinged implants from bone damage [8]. This double-stemmed hinged silicone implant is still the most commonly used and accepted prosthesis with an increase in its utilisation recently [5,7].
Indications
The general patient profile for the use of the silicone MTPJ prosthesis is a middle-aged to older individual with low to moderate activity levels [7]. Hallux rigidus remains the most common indication for its use with the aim to relieve pain, maintain joint motion and maintain length [9]. Other indications include rheumatoid arthritis and hallux valgus associated with arthritis. However, it is not recommended to use the implant where the intermetatarsal angle exceeds 16-19 degrees [5]. It is also worth mentioning that smaller silicone implants have been used for treating Frieberg’s disease and second and third MTPJ arthritis as well.
Silicone implants are an interpositional arthroplasty and act as a spacer. They are not a joint replacement procedure as such [5,9]. The implant gets encapsulated and forms a capsuloligamentous system to provide stability [10]. As time goes on the joint becomes flexible and functions as a new joint.
Surgical technique
After positioning the patient supine with a tourniquet and sand bag on the ipsilateral side, a dorsomeal approach to the first MTPJ is utilised. Skin and subcutaneous dissection is carried out in line with incision up to the joint capsule.
The capsule is incised in a linear fashion and reflected to provide adequate exposure of the metatarsal head and base of the proximal phalynx.
Osteophytic over growth is excised and adequate bone cuts are taken. The phalangeal cut is performed parallel to the eponychial fold, while the metatarsal cut is performed perpendicular to its weightbearing surface. Resection must be kept to a minimum to avoid shortening and transverse metatarsalgia [5].
Initial entry into the intramedullary canal is made using a 2.5mm drill. Then the canal is prepared using an introducer and increamental broaches.
After the preparation of the canal, a trial prosthesis is inserted to judge the required size and adequacy of the resection. This is followed by implantation of the actual prosthesis. The stems of the prosthesis can be cut to allow better seating of the implan