A Guide To First MPJ Head Resurfacing

By Bora Rhim, DPM

     Hallux rigidus of the first metatarsophalangeal joint (MPJ) is the most common form of osteoarthritis of the foot.1 Hallux rigidus is defined as a progressive arthritic process of the first MPJ that causes pain, stiffness and enlargement of the joint.1      There are numerous surgical procedures to help address the pain and stiffness of this joint. These procedures include cheilectomy, osteotomies, resection arthroplasty, interpositional arthroplasty, hemiarthroplasty, total joint arthroplasty and arthrodesis.      Although cheilectomy and osteotomies are considered first line surgical treatments for early stages of hallux rigidus, these procedures are not recommended for more advanced stages.2 Transfer metatarsalgia, postoperative deformities and loss of push-off strength are commonly associated with resection arthroplasty, and are recommended only for elderly and sedentary patients.3      Recently, interpositional arthroplasties have gained some popularity but long-term follow-up studies are lacking.4 Metallic hemiarthroplasties that resurface the proximal phalangeal base of hallux have shown promise but researchers have found the clinical and functional results to be significantly inferior to those obtained with arthrodesis of the first MPJ.5 Total joint arthroplasties have been associated with loosening and malalignment, leading to subsequent revisional surgeries.      Currently, the gold standard treatment for advanced hallux rigidus is arthrodesis of the first MPJ. Postoperatively, however, these patients have experienced limitations in shoe wear, complications of malunion or nonunion, or require permanent activity modifications. Accordingly, the first MPJ arthrodesis is less attractive for many active individuals.6 An alternative procedure that relieves pain and maintains motion without affecting strength or stability of the hallux is necessary.

Is There An Alternative Treatment For Active Patients?

The HemiCAP System (Arthrosurface) first debuted in 2002 and this implant was indicated for use in the shoulder, hip and knee with positive clinical outcomes.7 This implant resurfaces the damaged articular surface and restores the patient’s joint geometry with minimal bone resection.      Three years later, this device received approval for resurfacing of the metatarsal head in hallux rigidus. The implant is composed of a cobalt chromium alloy for the articular portion and attaches to a titanium alloy taper fixation post via a Morse taper. In advanced stages of hallux rigidus, in which there is denuded or damaged cartilage on the head of the metatarsal, this metallic implant resurfaces the metatarsal head with minimal bone resection and without altering the sesamoid articulation. The advantage of this implant is that it does not interfere with the normal balance of the flexor-extensor tendons, plantar plate or adductor-abductor mechanisms.

Emphasizing Proper Patient Selection

One should only consider HemiCAP implantation for a patient who has advanced stages of the hallux rigidus, displays symptoms of pain all through range of motion at the joint, has dorsal pain of the first MPJ with increased activities, or has difficulty with walking barefoot or in soft sole shoes. Before physicians consider utilizing the implant, the patients must have previously failed conservative treatments including nonsteroidal anti-inflammatory medications, physical therapy, activity alteration, orthotic therapy and shoe wear modifications.      The ideal patient for this procedure is one who demonstrates the aforementioned signs and symptoms, but expects to remain active after the surgical procedure and maintain motion at the first MPJ. Surgeons can also consider this procedure for patients who previously failed cheilectomy of the first MPJ with adequate soft tissue coverage.      When having a consultation with the patient regarding this procedure, it is essential to inform the patient that this technique is relatively new. While early results are promising, the long-term outcomes are still lacking.8      Patients with bone demineralization or inadequate bone stock, metal allergies and/or a history of osteomyelitis or persistent infection are not candidates for this procedure. Patients with infection at a remote site that may spread to the implant should only be candidates for surgery once the infection has resolved completely. Some may consider gout and inflammatory arthritis to be relative contraindications. While researchers have found these patients to have less postoperative range of motion, their motion has been adequate for activities of daily living.8      During the lower extremity physical examination, podiatrists should assess for range of motion, strength and gait. In order to evaluate joint integrity and alignment, one should look at preoperative weightbearing on anteroposterior, oblique and lateral radiographs.      There are no published age limitations for this implant. If there is an increased intermetatarsal angle with hallux valgus deformity, one must do alignment correction of the joint either in conjunction with or before the HemiCAP arthroplasty.      It is important to consider intraoperative assessment of the first metatarsal articular surface as a guide to the surgical management plan. Intraoperatively, if less than 50 percent of the metatarsal head is denuded of its cartilage and good cartilage remains plantarly at the metatarsal head, one should perform a cheilectomy. If more than 50 percent of the articular cartilage is lost, then HemiCAP implantation is indicated.

Step-By-Step Insights On The Surgical Procedure

In regard to the HemiCAP implant, the surgeon can perform this procedure with either a regional popliteal block or an ankle block with an ankle or calf tourniquet. Make an incision dorsal medial to the extensor hallucis longus tendon over the MPJ and take care to avoid the dorsomedial cutaneous nerve. Proceed to expose the dorsal joint capsule, retract the extensor hallucis longus tendon laterally to keep the tendon within its sheath and make an arthrotomy. Elevate the capsule off the bone. Perform a complete release of the capsule, collateral ligaments and sesamoidal ligaments so you can visualize the entire joint, including the sesamoids.      Utilize a McGlamry elevator to release adhesed sesamoids and flexor hallucis brevis tendons. If one does not release these structures, they will have fibrotic adhesions to the metatarsal head that will limit dorsiflexion postoperatively. However, take care to avoid damaging the metatarsal-sesamoid articulation. I discourage performing a cheilectomy at this time in order to avoid over-correction of bone.      After exposing the first metatarsal joint, one can implant the HemiCAP following the stepwise arrangement of the instrument set from the system tray.      First, insert a guide wire perpendicular into the center of the metatarsal head. Using fluoroscopy, obtain anteroposterior and lateral views to ensure that the guide wire is in the center of the shaft of the first metatarsal in both the dorsal to plantar and medial to lateral directions. Use a cannulated double-step drill over the guide wire until the plantar articular surface of the metatarsal head is flush with the proximal shoulder of the drill. Use the plantar cartilage as the reference for depth determination since this cartilage is the only normal articular surface remaining.      Proceed to insert a cannulated tap and tap it until the etched depth mark on the tap is flush with the plantar articular surface of the metatarsal head. Insert the taper post over the guide wire until the etched line on the driver is flush with the articular surface. Use the trail cap with the taper post at this time to check the apex height of the final implant relative to the native articular surface.      Once the taper post is in place, utilizing three-dimensional mapping of the metatarsal head can help establish the curvature of the patient’s metatarsal head surface geometry. After fully seating the centering shaft in the cleaned taper of the fixation component, place the contact probe over the centering shaft and use the probe tip to map the normal articular surface of the metatarsal head. There are four contact areas (dorsal, plantar, medial and lateral). Usually the plantar surface and either the medial or lateral side of the joint still have healthy articular cartilage. Now proceed to measure dimensions of the joint offsets in the plantar and medial/lateral surfaces.      The product comes with a sizing card with offset measurements, which one uses to select the appropriate shaped implant and corresponding reamer. One would reinsert the guide pin into the taper post after removing the centering shaft and contact probe.      Prepare the implant bed in the metatarsal head by using the corresponding reamer based on the offset measurements. When one places the reamer over the guide pin, it is important that the reamer is running at full speed before contacting the metatarsal head. This prevents shearing or shattering of the bone or remaining articular surface.      Slowly advance the reamer over the guide pin while maintaining a proper axis to prevent bending of the wire. Exert gentle pressure to prevent aggressive reaming and the reaming will stop upon contact with the top of the taper post. Remove the guide pin and reamer, and clean the taper and the frayed edges of the articular surface.      Place a trial implant that matches the offset measurement into the taper post to ensure proper fit and orientation of the implant. Confirm the fit of the trial implant by ensuring that it is equal with the edges of the surrounding articular surfaces (i.e. the plantar and medial/lateral surfaces).      If one desires decompression of the joint, drive the taper post deeper into the metatarsal head by placing the taper post driver back onto the taper post and turning it clockwise. The taper post moves 1 mm proximal for every quarter turn of the driver. It is recommended that the surgeon decompress the joint no more than 2 or 3 mm to avoid altering the sesamoid articulation. Proceed to repeat the reaming step to make certain the articular component is fully seated in the taper post and the metatarsal head.      The HemiCAP implant is available in 12- and 15-mm diameter sizes to accommodate most metatarsal heads. Surgeons have used a 15-mm implant most commonly. Once one has confirmed the proper fit of the trial implant, remove the trial implant and clean the area again by focusing on the taper to ensure proper seating of the final implant. Perform a cheilectomy of the metatarsal head over the trial implant to avoid damaging the actual implant.      A suction-holding device holds the actual implant device with correct medial to lateral and dorsal to plantar orientation. After placing the implant, use an impactor to seat the implant completely on the taper post and bone bed. Once again, check the metatarsal head to determine if there is adequate bone resection.      For the proximal phalanx pathology, some surgeons perform a cheilectomy at the base of the proximal phalanx. Some surgeons combine the HemiCAP implant with a soft tissue resurfacing of the proximal phalanx when more than 50 percent of the proximal surface is involved. After resecting the dorsal osteophyte, suture either an excised portion of the dorsal capsule or an acellular dermal graft to the base of the proximal phalanx by using bioabsorbable suture anchors.      Proceed to test the MPJ for range of motion intraoperatively. One should achieve approximately 80 to 90 degrees of dorsiflexion at the MPJ since some degree of dorsiflexion is expected to be lost postoperatively. One would close the incision site in layers and the skin suture can be either subcuticular absorbable stitch or non-absorbable stitch. Apply a compressive dressing and allow the patient to bear weight postoperatively from day one.

What You Should Know About Post-Op Care And Potential Complications

Place the patient in a soft dressing with a stiff-soled shoe for ambulation. Instruct the patient on passive and active dorsiflexion, and plantarflexion of the joint one week postoperatively to prevent the dorsal capsule from scarring down. This early joint mobilization has not interfered with normal wound healing and few wound complications have occurred with early mobilization of the joint.      Once the dorsal incision site has healed, prescribe formal physical therapy for range of motion and strengthening as needed. One should also prevent patients from walking on the lateral column of the foot. Take serial weightbearing postoperative radiographs of the foot to ensure appropriate alignment and to monitor for any signs of loosening of the implant.      The most common complication surgeons have seen with this implant has been loss of intraoperative dorsiflexion. Even with the decrease in range of motion that occurs postoperatively, the patients maintain adequate range of motion without limited activity or pain. No loosening of the implants has occurred in any published studies. Other complications include local wound infection, which one should treat aggressively with oral antibiotics with local wound care to prevent further spread of the infection into bone at the surgical site.      Hasselman has reported a complication in using the metallic suture anchors with the HemiCAP implant.8 Previously, he had used metallic suture anchors to secure the capsule, the suture anchors contacted the implant, and a metallosis reaction occurred that required removal of the implant.      Several months after the procedure, some patients may complain of mild to moderate plantar pain from sesamoid pain or flexor tendonitis. This tenderness usually resolves after two to three months. If pain and swelling continue to persist, and you have ruled out the possibility of infection, you may consider surgical options including the Keller resection arthroplasty, the primary bone apposition using conical reamers or bone block interposition arthrodesis of the first MPJ.

What The Literature Reveals

Hasselman and Shields have published the largest study to date involving patients who had undergone hemiarthroplasty of the first MPJ using the HemiCAP prosthesis.8 These patients were treated for hallux rigidus, arthritis hallux valgus, failed previous first MPJ surgery, avascular necrosis of the metatarsal head and failed fusion.8 Out of 100 patients, the authors reported two failures, one from infection and the other from metallosis.      The mean postoperative increase in range of motion of the joint was 42 degrees at the mean follow-up of 20 months. The mean American Orthopaedic Foot and Ankle Society (AOFAS) and 36-item Short-Form Health Survey Questionnaire scores were 82.1/100 and 96.1/100. All patients reported satisfaction with their surgical results and said they would undergo the procedure again.8      Botto-van Bemden and SanGiovanni published their results of 24 patients who were treated with HemiCAP due to advanced hallux rigidus.9 The authors performed concomitant osseous and soft tissue procedures for the correction of deformity and improvement of dorsiflexion motion. The researchers performed a 12-month follow-up and observed a 54.7 AOFAS preoperative score that increased to 70 postoperatively. The visual analog pain score decreased from 6.4 to 3.5 and the average dorsiflexion range of motion increased by 30 degrees.      The authors of the study concluded that the HemiCAP implant technique is a reliable alternative for the treatment of hallux rigidus. However, they recommended reserving this prosthesis mainly for painful MPJ arthritis rather than for the restoration of motion.9

Assessing Benefits And Raising Questions On First Metatarsal Head Resurfacing

The first metatarsal head resurfacing implant appears to be a novel approach in the treatment of the first MPJ. Currently, all hemiarthroplasty implants other than the HemiCAP prosthesis resurface the base of the proximal phalanx. Even though pain and stiffness is less severe with the proximal phalanx implant, former symptoms persist well after surgeons have performed the procedure.10 Some believe that in hallux rigidus, primary cartilage loss occurs on the metatarsal head rather than the base of the proximal phalanx.      Resurfacing the head of the first metatarsal removes the damaged cartilage and creates a new joint. Hemiarthroplasty techniques that resurface the base of proximal phalanx still leave damaged metatarsal cartilage.      Hasselman’s study of the HemiCAP implant revealed superior postoperative range of motion and pain reduction in comparison with other implant hemiarthroplasties.8 Metatarsal head resurfacing may be the surgery of choice to improve postoperative pain relief in hallux rigidus patients. However, long-term follow-up studies on the durability of the implant and functional outcomes with optimal procedures to address coexisting phalangeal pathology are still lacking.      The jamming of the first MPJ from the impaction of the proximal phalanx on the metatarsal head is considered to be the other etiology of hallux rigidus. The impaction of the implant onto the remaining damaged metatarsal head could be an important cause for persistent pain after proximal phalanx resurfacing. With repetitive dorsiflexion at the MPJ, there is an increase in shear stresses in the proximal phalanx and this may lead to implant loosening, or the inhibition of proper bony ingrowth early in the postoperative period.10      Traditionally, the total metallic implants that resurface both sides of the joint have been prone to loosening. There is less shear stress on the metatarsal side of the bone implant interface, which may explain the improved fixation and osseous integration of the first metatarsal head resurfacing implant. However, further studies are needed to explore this likelihood. Also, the high-pitched screw fixation component of the HemiCAP implant may provide a stronger construct than a pegged technique. This implant design may prevent loosening in the condition of repetitive stresses.

In Conclusion

The HemiCAP technique is easy to perform and is minimally invasive with a low learning curve. This implant requires minimal resection of subchondral bone and it preserves viable bone stock for future treatment options. Should the need arise, this procedure allows surgeons the possibility of future treatment options including joint fusion or resection arthroplasty. In hallux rigidus, the use of the HemiCAP implant to resurface the metatarsal head has shown promising short-term results. Dr. Rhim is an Associate of the University Foot and Ankle Institute, and is in practice in Rancho Cucamonga, Ca.



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