A Closer Look At A First MPJ Hemi-Implant For The Treatment Of Hallux Limitus/Rigidus

This author explores the potential of a new design for a first metatarsophalangeal joint implant, citing initial study results in using the implant for patients with hallux limitus and hallux rigidus.

Hallux limitus, hallux rigidus, arthritic changes and post-traumatic first metatarsophalangeal (MPJ) injuries are common problems. We continue to see journal articles encompassing varied treatment plans and outcomes for these pathologies. With this in mind, I will present a closer look at an emerging first MPJ hemi-implant for the treatment of stages 2, 3 and, in some cases, stage 4 hallux limitus/rigidus, and how this implant can reduce potential issues with currently available implants.

There are a variety of surgical options for this pathology with the two most popular being first MPJ implant surgery and arthrodesis. Each may work well in a particular surgeon’s hands and both can present complications. The primary goal of both procedures is relief of pain. There are also two schools of surgical philosophies: those who are satisfied with absence of joint motion (i.e. fusion) and those who seek to preserve joint motion (i.e. implant surgery).

Hemi-implant surgery is a relatively easy procedure and one may combine it with adjunctive procedures if necessary. However, outcomes vary with different surgeons along with patient follow-up and adherence to postoperative protocols. The basic design of phalangeal-based hemi-implants has not changed in over 60 years. The articulating surfaces are basically the same in all implants with variances in stem design, thickness and angulation. Potential issues may be related to surgical technique, implant sizing and/or placement, implant deviation or telescoping, and bone overgrowth reducing the functionality of the joint.

The HemiEdge First MPJ Implant (BioPro) was designed to address these potential issues and help afford the patient a longer functional joint life. The HemiEdge implant has been in use during the trial phase since 2011. From 2011 to 2014, surgeons have inserted nine implants. 

The first three patients received the initial implant design with modifications in technique and instrumentation. The technique and design subsequently changed, and the remaining six patients had the current HemiEdge implant.

What Preliminary Long-Term Outcomes With The Implant Revealed

In my initial study, there were a limited number of patients. Much greater numbers and in-depth reviews and analysis will be forthcoming proportional to the amount of implants used and length of time. General symptom analysis revealed all patients had daily first MPJ pain, very limited motion, bone proliferation, and the inability to do certain physical activities without discomfort. Out of the six patients with the current HemiEdge implant, four patients agreed to participate in the study. All of the patients were 2.5 to three years post-surgery. This study included simple subjective survey questions as well as review of pre-op and current X-rays, objective X-ray parameters, and first MPJ functionality.

I used a modified version of the American College of Foot and Ankle Surgeons (ACFAS) Universal Evaluation questionnaire. In regard to subjective findings, the patients postoperatively related that over the previous month, they had no foot pain with normal activities. All were satisfied with the appearance of their big toe joints. All were able to wear any type of shoe continuously.

As far as objective findings go, all the patients’ hallux abductus angles were between 0 and 20 degrees and their intermetatarsal angles were all below 10 degrees. One patient had an elevatus, which required a Youngswick procedure.

Patients took the paper pullout test to rate their hallux purchase. Three of the four patients scored “non-movable” and one patient scored “easy.” The one patient that scored “easy” stated that he did not follow the required post-op protocol. Three of the patients had a post-op range of motion for the first MPJ that ranged between 45 to 59 degrees whereas the fourth patient’s post-op range of motion for the first MPJ was below 36 degrees.

All patients said they would have the surgery again and would also recommend the surgery to a friend who was having the same problem.

What Advantages Does The Implant’s New Design Offer?

The HemiEdge implant maintains the successful longstanding articulation and stem design.

The design change incorporates an “edge” extending dorsally, medially and laterally around 60 percent of the implant with no change plantarly to allow for the flexor hallucis brevis pathway. The dorsal edge incorporates two windows or portals to view proper implant seating at the bone/implant interface. With this unique design, the HemiEdge helps reduce or eliminate the following potential complications:

1. Abnormal placement or insertion. The edge on the implant ensures one can only insert the implant in the proper orientation, avoiding angled insertions.
2. Abnormal implant size selection. Improperly sized implants will not fit properly.
3. Elimination of shift or deviation. The edge assists in maintaining proper position and stabilizing the implant.
4. Compression or telescoping of the implant into the phalanx. The implant is larger than the peripheral cortices to maintain implant stability.
5. Abnormal bone overgrowth or impingement. The HemiEdge encompasses the dorsal, medial and lateral sides of the proximal phalanx, assisting in reducing or eliminating bone overgrowth.

In Summary

The HemiEdge implant is a design update to an implant design surgeons have used for over 60 years. The implant is designed to address potential problems while maintaining the current instrumentation and implantation techniques. One more procedural step is required with the addition of the HemiEdge sizers. First MPJ implant surgery for hallux limitus/rigidus is an easy surgical procedure with quick healing (and an absence of adjunctive procedures). It is a great choice for all patients wishing to maintain first MPJ motion.