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Metatarsal head resurfacing preserves motion in patients with end-stage hallux rigidus
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When doing arthroplasty for later stages of hallux rigidus (stages 2 and 3), think of the joint as an upside down knee replacement but you walk on the “patella joint.” The three keys to successful replacement are proper joint alignment, immediate rigid fixation of the components and appropriate soft tissue releases. If these three requirements are done, you and the patient will be pleased with the outcomes of joint replacement for the first metatarsophalangeal joint.
The soft tissue release (along with proper component placement) is the key to the procedure, which is no different from any other lower extremity joint replacement technique. The soft tissue releases must be in accordance with the contractures. With hallux rigidus, the majority of contractures are on the plantar surface. I have never seen a patient in my practice with an unstable first metatarsophalangeal (MTP) joint after arthroplasty; just the opposite is true, and many referrals come to me due to a stiff and contracted joint after arthroplasty. It is my belief that hallux rigidus begins with plantar contractures, which cause dorsal impaction of the joint and subsequent arthritis. If we do not address the primary contracture, then we are bound to see failures.
Figure 1. A soft tissue release of the metatarsal head to include the sesamoidal ligaments and collateral ligaments is showntincidunt lorem lobortis cursus. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer commodo placerat fermentum.
Figure 2. Complete release of all soft tissues off the metatarsal head from the joint to 3 cm proximal to the joint line is seen.
Images: Hasselman CT
Soft tissue release
The soft tissue release around the first metatarsal must include the sesamoidal ligaments, collateral ligaments and plantar plate (Figure 1). Essentially all soft tissues are released to include the distal 3 cm of the metatarsal head (Figure 2). The dissection should occur directly off the periosteum similar to a release of the medial structures in a total knee replacement for a varus knee. A curved osteotome or similar device is placed just proximal to the sesamoid articulation and the plantar plate is released from its insertion into the metatarsal (Figure 3). Since the blood supply within the bone is not disrupted with an osteotomy, the risk of avascular necrosis has not been an issue with this technique. It has been my experience with more than 500 implants that instability after the procedure is not an issue, even in the most extensive releases as long as subperosteal stripping is performed.
Figure 3. A curved osteotome is used to release the plantar plate proximal to the sesamoid articulation with the metatarsal head.
Figure 4. Subperosteal dissection of the flexor digitorum brevis and plantar plate from the proximal phalangeal base using a knife is illustrated.
The soft tissues of the proximal phalangeal base are similarly released. The collateral ligaments are released by dissection directly off the periosteum. The plantar plate and flexor hallicus brevis are released by sharp periosteal dissection. This can be done with a knife or curved osteotome (Figure 4). The key to this technique is that the release should not involve cutting of the flexor hallucis brevis but rather sharp dissection off the bone, similar to release of the hamstrings in a flexion contracture of the knee during knee replacement (Figure 5). By dissecting the flexor brevis off the bone rather than transectioning the tendon, it has been my experience that patients still keep their flexion strength but improve their overall range of motion. My rule of thumb is that at the end of the case the toe is taken through a full passive range of motion and the first MTP must extend to 90° with the ankle in neutral. If this is not achieved, I will do further stripping of the soft tissues.
Resurfacing
Figure 5. Surgeons further dissect the
flexor digitorum brevis and plantar plate
from the proximal phalangeal base using
a curved osteotome.
Sometimes the phalangeal side of the bone has significant wear as well. If there is minimal wear off the phalangeal base, then I will just remove heterotopic bone and leave this surface alone. However, if grade 2 or 3 wear had developed off the phalangeal side, then I will do a tissue transfer. After resurfacing the metatarsal head, all remaining osteophytes and any remaining medial or lateral articular surfaces are removed off the metatarsal head so that just the implant articulates with the proximal phalangeal base. This creates a moderate amount of redundant capsular surface along with the extensor hallucis brevis hood. I will often harvest a piece of the redundant dorsal capsule and secure it to the phalangeal articular surface with suture anchors. This provides a type of interpositional arthroplasty for moderate phalangeal cartilage deterioration and in my experience can reduce pain generated by the phalangeal base. In cases of severe phalangeal arthrosis as well, I will also resurface the phalangeal base with the total toe system designed by Arthrosurface to prevent impact into the arthritic phalangeal base and provide smooth glide into the joint. In cases where the sesamoids are severely damaged, a piece of collagen allograft or xenograft is placed between the sesamoids and the metatarsal head to prevent impaction of this joint; however future studies are needed to support use of this technique.
The other key is rigid fixation of the device into bone so that early range of motion can begin. There are several metatarsal head resurfacing implants on the market, but most rely on bony ingrowth to support fixation. This requires approximately 6 weeks to occur and if excessive forces are transmitted across the implant during this time then fibrous fixation of the implant will occur. This will most likely allow for early component failure due to component migration. Therefore one must pick a component that creates an immediate stable fixation during bony ingrowth into the implant. This allows for aggressive early range of motion, which is key in any arthroplasty no matter which joint it happens to be.
Although implant arthroplasty of the first metatarsophalangeal joint is still in its infancy, one must remember that there was a time where hip, knee and ankle arthroplasty were considered to be experimental. As surgeons, we need to further explore this joint as most would agree that fusion is not without its complications and we need to find options that allow pain relief without sacrificing joint motion. A stepwise approach to this joint with proper soft tissue release, immediate fixation of the implants, stepwise resurfacing of the surfaces and early rehabilitation are all key to success of long-term survival and patient satisfaction.
References:
Kline AJ. Foot Ankle Int. 2013;doi:10.1177/1071100713478930.
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Disclosure: Hasselman is a consultant for Arthrosurface, Arthrex, Synthes and Small Bone Innovations.