William Montross, DPM, Front Range Orthopedics Colorado Springs, CO

Introduction: The current treatment options for the 4th and 5th tarsometatarsal (TMT) joint include non-operative modalities, anti-inflammatory injections, excision, fusion, and interpositional arthroplasty.¹ In cases with severe arthritis in the TMT joint, fusion has proven to be less than adequate in the 4th and 5th TMT due to the limited motion at the lateral column of the foot necessary for normal biomechanics and gait. The fixation of a fusion must also be rigid enough to prevent transverse plane and dorsoplantar motion and must be maintained for at least 12-16 weeks. Since the 4th and 5th TMT joint has more mobility than the medial column, rigid fixation is more likely to result in symptomatic stiffness.² Moreover, fusions have been difficult to achieve in this area. Nonunion as well as hardware breakage rates are high.³

This surgeon’s goal is to maintain motion of the midfoot for optimal clinical results while decreasing pain. The Ascension® PyroSphere® TMT, composed of PyroCarbon, is indicated for treatment where degenerative or post-traumatic arthritis presents decreased motion, arthritic changes, subluxation, instability, stiffness, and/or degenerative joint disease of the midfoot associated with pain.

Surgical Technique: The patient is positioned in the supine position. A longitudinal incision is made over the 4th and 5th metatarsal cuboid joint. FIGURE 2. Joint exposure is performed by sharp and blunt dissection. FIGURE 3. Once the joint is exposed, the correct implant size is determined by using the implant sizer. FIGURE 4. The circumference of the implant should buttress against the cortical bone on the base of the 4th and 5th metatarsals. With the implant size chosen, proceed to burr and ream up to the corresponding implant size to prepare for insertion of the implant trial. FIGURE 5. Utilizing a joint distractor is essential for optimal sizing and burring of this joint. To attempt this procedure without proper distraction of the joint will lead to frustration and failure. To achieve a true interpositional arthroplasty, it is important to have 1/3 of the trial seated in the cuboid, 1/3 exposed, and 1/3 seated in the metatarsal. This can be confirmed using the trial sizer. FIGURE 6. The final implants are inserted and the capsule is closed. FIGURE 7. Intraoperative X-rays are taken during the trialing and implant placement to confirm proper implant positioning and size. FIGURE 8.

Postoperative Care: The postoperative protocol for isolated 4th and 5th TMT arthroplasty is to immobilize patients for 14 days with no weight bearing. At 14 days, the patient may progress to full weight bearing using a removable walker boot. At 6 weeks, the patient may wear an accommodative shoe with arch support. If a concomitant medial column arthrodesis is performed, follow standard arthrodesis protocol.

Results: At 8 weeks, the patient had less pain postoperatively than prior to surgery. Within several more weeks, the patient was near pain-free. This is the author’s experience with 10 other cases.

Discussion: Historically, treatment options have been limited for lateral column pain, particularly at the 4th and 5th metatarsal cuboid articulation. Dr. Myerson noted this is a difficult area to treat, particularly with fusion.⁴ Fusion rates are less than satisfactory. Interpositional arthroplasty using soft tissue materials such as allograft or autograft have had similar results with this author. In contrast, PyroCarbon spherical implants have been successfully used by this author to reconstruct the TMT joints. Materials other than PyroCarbon present a high degree of long-term uncertainty when used in the TMT joints. A spherical thumb basal joint implant made of a ceramic material (yttrium-stabilized zirconia) has been reported to result in an unacceptable degree of subsidence into the trapezium resulting in pain, weakness and stiffness.⁵ Biomechanics of the foot present greater loading conditions than the hand, and one can assume a similar fate for the use of ceramic spherical arthoplasty in the foot. This author has encountered several cases of subsidence failure of ceramic spherical implants in the lateral column. Spherical PyroCarbon implants have been used successfully for thumb basal joint of the hand and have potential for application in the foot. Preclinical animal implant studies demonstrate a 92% probability of cartilage survival in hemiarthroplasty contact compared to a 20% probability of cartilage survival with metal implants.⁶ Laboratory wear testing has shown PyroCarbon results in dramatically less bone damage than ceramic.⁷ FIGURE 9. PyroCarbon has a 40-year history of successful use in mechanical cardiac valves and decades of use in orthopedic implants.^8,9 PyroCarbon is a chemically inert, strong and durable material having outstanding wear and fatigue resistance, a low coefficient of friction and an elastic modulus similar to cortical bone. The combination of material properties and favorable wear characteristics of PyroCarbon with native joint tissues of cartilage and bone suggest PyroCarbon is well suited as a spherical implant for reconstruction of the TMT joint. Mechanical testing demonstrated PyroCarbon spherical TMT specimens withstood loads of 540 lbs. without occurrence of damage – indicating the implant is capable of supporting the biomechanical forces of the TMT joint.

The use of PyroCarbon in the human body goes back to the 1970s. Thus, it has proven to be biocompatible, capable of supporting biologic demands and well tolerated in the body. The use of the Ascension® PyroSphere® TMT in the foot is proving to be effective. Future evaluations are needed to confirm these results.

References:

1. Shawen, Scott B.; Anderson, Robert B.; Cohen, Bruce E.; Hammit, Matthew D.; Hodges, Davis W. Spherical Ceramic Interpositional Arthroplasty for Basal�Fourth and Fifth Metatarsal Arthritis. Foot & Ankle International. Vol. 28, No.8/August 2007.
2. Komenda GA, Myerson MS, Biddinger KR: Results of arthrodesis of the tarsometatarsal joints after traumatic injury. J Bone Joint Surg in press: 1996.
3. Steven M. Raikin, M.D.; Lew C. Schon, M.D. Arthrodesis of the Fourth and FifthTarsometatarsal Joints of the Midfoot. Foot and Ankle Int. 2003. Vol. 24, No. 8/August 584-590.
4. Mark S. Myerson, MD. Tarsometatarsal Arthrodesis: Technique and Results of Treatment After Injury. https://footandankle.mdmercy.com/research_pubs/pressItem54.html. April 5th, 1996.
5. Athwal GS, Chenkin J, King GJ Pichora DR, Early Failures with a Spheric Interposition Arthroplasty of the Thumb Basal Joint, J Hand Surg, Vol 29A, No 6, 6 November 2004.
6. Cook SD, Thomas KA and Kester MA, Wear�Characteristics of the Canine Acetabulum Against Different Femoral Prostheses, JBJS Vol. 71-B, No.2, Mar 1989.
7. Strzepa P, Klawitter J, Ascension PyroCarbon Hemisphere Wear Testing Against Bone, Poster No. 0897, 51st Annual Meeting of the Ortho Res Society.
8. Cook SD, Beckenbaugh RD, Redondo J, Popich LS, Klawitter JJ, Linscheid RL, �Long term follow-up of pyrolytic carbon metacarpophalangeal implants,� J Bone and Joint Surg, Vol. 81-A, No. 5, 635-648, 1999.
9. Stanley J, Klawitter J, More R, Replacing joints with pyrolytic carbon, Joint Replacement Technology, Chapter 26, P Revell (ed) Woodhead Publishing Cambridge, England and CRC Press

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PyroSphere ® TMT PyroCarbon is Bone Friendly! The elastic modulus of PyroCarbon is very similar to cortical bone resulting in biomechanical compatibility with bone. Unlike surgical grade metals, PyroCarbon transfers load from implant to bone more effectively, thus reducing stress shielding and potential bone resorption.

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