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Joint prep, compression, rigid fixation among keys to hallux MTP joint arthrodesis
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Hallux metatarsophalangeal joint arthrodesis is an established surgical treatment for various pathologies, including end-stage hallux rigidus, severe hallux valgus with degenerative changes, advanced inflammatory arthritis of the forefoot, neuromuscular disorders and revision bunion surgery. Studies have shown hallux MTP arthrodesis is associated with good pain relief, deformity correction and improved function when bony fusion is obtained.
Previous surgical techniques have included flat cuts on either side of the metatarsophalangeal (MTP) joint with fixation using K-wires, crossed screws or non-anatomic one-third tubular plates with screws. These earlier techniques were prone to higher nonunion rates and implant failure due to the high levels of shear stress at the hallux MTP joint.
There are a variety of anatomically contoured hallux MTP arthrodesis-specific plates with non-locking and locking screw options that have been biomechanically shown to have greater fatigue strength and stiffness in load-to-failure than non-anatomic plates. Modern techniques combine the fusion benefits of joint compression with the biomechanical advantages of low-profile rigid fixation to help improve union rates. Implant systems often include “cup and cone” reamers, lag screws, side-specific dorsal plates, plates with different amounts of MTP dorsiflexion (0°, 5°, 10°, etc.) and multiple screw-type options. However, meticulous joint preparation and compression are critical prior to rigid fixation with dorsal plating to obtain successful outcomes with hallux MTP arthrodesis.
Images: Hsu AR
Setup and approach
It is important to perform a thorough history and physical exam preoperatively to determine the nature and severity of the hallux pathology. With hallux valgus, patients typically present with difficulty wearing shoes due to a protruding medial eminence and pain at the hallux MTP joint. Compression of the medial digital nerve may also elicit pain or numbness. The physical exam should include evaluation of standing hallux alignment and assessment of MTP range of motion, first tarsometatarsal instability, callus formation and sesamoid pain, in addition to the presence of pes planus, lesser toe deformities and midfoot or hindfoot conditions (Figure 1).
Preoperative standing radiographs should be analyzed for the amount of lateral sesamoid displacement, joint congruency, degenerative changes and radiographic parameters, including hallux valgus angle (HVA), intermetatarsal angle (IMA) and distal metatarsal articular angle (DMAA). All patients should attempt a period of nonoperative treatment with modalities, such as shoes with a wide and tall toe box, toe spacers, medial eminence pads and activity modification, prior to surgical intervention.
In the OR, patients are positioned supine with the foot at the end of the bed on an elevated platform above the contralateral limb to assist with lateral fluoroscopy (Figure 2). A bump is placed under the ipsilateral hip to obtain a neutral foot rotation with the foot pointed toward the ceiling. A non-sterile thigh or ankle tourniquet can be used. A thigh tourniquet has the advantage of reducing the amount of tension placed on the hallux flexor tendons that can later influence intraoperative assessment of hallux MTP dorsiflexion and alignment.
A dorsal skin incision is made in line with the long axis of the hallux metatarsal and proximal phalanx just medial to the extensor hallucis longus (EHL) tendon. Full-thickness flaps are created with sharp dissection down to bone 1 mm to 2 mm medial to the EHL, though more distal exposure is often needed for distal plate placement and screw insertion. Subperiosteal dissection is carried along the medial eminence and lateral aspect of the joint to achieve adequate joint visualization. There are often plantar adhesions that need to be freed up using a small Hohmann or McGlamry retractor to mobilize the joint into maximum plantarflexion. Prior to joint preparation, the medial eminence is resected in its entirety with a saw and the edges are smoothed down. Removing the medial eminence helps determine the true center of the hallux metatarsal head for proper guidewire placement.
Joint preparation and alignment
A guidewire is inserted into the center of the hallux metatarsal head, then slightly laterally into the center of the metatarsal shaft (Figure 3). A small rongeur or curette can be used to preliminarily remove cartilage to assist with subsequent reaming. A cone-shaped reamer is placed over the guidewire and reaming of the metatarsal head is done in a high-to-low fashion (20 mm to 18 mm to 16 mm). Reaming should be done on full speed in a gentle, concentric tapping motion to avoid excessive bony resection and metatarsal shortening. Subchondral cysts may be encountered which require autograft or allograft packing. Once all cartilage has been removed from the metatarsal head, the guidewire can be used to create multiple subchondral perforations to assist with bony union.
Next, the joint is maximally plantarflexed and the guidewire is inserted securely into the center of the proximal phalanx. It is critical the guidewire be securely fixed into bone, otherwise subsequent reaming can eccentrically remove the base of the proximal phalanx and create a bony void. A cup-shaped reamer is placed over the guidewire, and reaming of the proximal phalanx is done in a low-to-high fashion until both the metatarsal head and proximal phalanx are matching sizes. Prior to reaming, it is critical the metatarsal head be completely out of the way of the reamer to avoid iatrogenic damage to the metatarsal head. All remaining cartilage is removed with a small rongeur and curette, and the proximal phalanx joint surface is then subchondrally perforated using the guidewire. Depending on bone quality, autograft or allograft can be added in between the articular surfaces to assist with union.
The hallux is then positioned into 0° to 5° of valgus and 0° to 10° of dorsiflexion, depending on the patient. Patients with pes planus often require less dorsiflexion, while patients with cavus alignment require more dorsiflexion. Men are typically placed in 0° of dorsiflexion, and women are commonly placed in 5° to 10° of dorsiflexion due to shoe wear needs. Careful attention to hallux position is important as excessive dorsiflexion can lead to postoperative sesamoid pain while increased plantarflexion can lead to toe-tip pain after surgery. Once the hallux is in the desired alignment, the guidewire for a cannulated 4-mm partially threaded lag screw is placed across the joint in a distal-to-proximal orientation. A flat plate should be used against the bottom of the foot to evaluate the amount of MTP dorsiflexion and plantarflexion. A fingertip should be able to easily fit under the tip of the toe. Placing a screwdriver handle between the flat plate and heel pad can simulate position of the hallux in a shoe with a 1-inch heel.
Once the hallux is confirmed to be in appropriate radiographic and clinical alignment, the guidewire is over-drilled and the 4-mm cannulated lag screw is inserted. The hallux position should be firmly held in place during lag screw insertion as the screw can slightly pull the hallux into valgus during final compression.
Plate placement and fixation
Prior to plate placement, a power saw can be used to smooth and contour the dorsal aspect of the hallux MTP joint to ensure the plate sits flush and evenly across the hallux (Figure 4). A dorsal side-specific plate with the desired amount of dorsiflexion (Ortholoc 3Di MTP Fusion Plate, Wright Medical) is inserted and centered over the MTP joint followed by provisional fixation with k-wires or plate tacks. Once appropriate plate position is confirmed on radiograph, three 2.7-mm screws (non-locking or locking, depending on bone quality) are inserted distally followed by eccentric drilling and placement of a proximal 3.5-mm non-locking screw. The proximal eccentrically placed screw increases the amount of joint compression while also allowing for increased MTP dorsiflexion as needed. Additional 3.5-mm screws are inserted proximally to complete the final construct.
Capsule is closed over the plate using 2-0 Vicryl (Ethicon) sutures with the EHL gently retracted out of the way. It is important to ensure the EHL glides easily after capsular closure so painful adhesions and stiffness do not develop postoperatively. Subcutaneous tissues are closed with 3-0 Monocryl (Ethicon) sutures, and skin is closed with 3-0 nylon sutures. Final AP and lateral radiographs are checked for joint compression, hallux alignment and rigid fixation (Figure 5). A bunion wrap is placed over the hallux, and patients are made non-weight-bearing or heel weight-bearing in a postoperative shoe for 2 weeks.
Rehabilitation
Careful postoperative wound care and protected, progressive weight-bearing are essential to successful rehabilitation after hallux MTP arthrodesis. If the incision is healed at 2 weeks, the sutures are removed and patients are made partial weight-bearing in a short or tall CAM boot. If there is any concern regarding wound healing status, sutures are maintained for an additional 1 week to 2 weeks, particularly in elderly patients and patients with rheumatoid arthritis with delicate skin.
From 2 weeks to 6 weeks after surgery, patients progressively increase their weight-bearing in a CAM boot with the goal of being full weight-bearing at 6 weeks postoperatively. Repeat standing radiographs are taken at 6 weeks to evaluate initial arthrodesis consolidation. If imaging shows early arthrodesis, patients are transitioned to a postoperative shoe from 6 weeks to 8 weeks and then a regular accommodative shoe as swelling allows. From 8 weeks to 12 weeks, patients are returned to regular activities in normal shoes as pain and swelling allows. Patients should be counseled that full return to baseline athletic activities may take a total of 4 months to 5 months after surgery.
- References:
- Hsu AR. Hallux MTP fusion and cotton osteotomy. Presented during the Instructional Course Lecture: Osteotomy and arthrodesis of the forefoot and hindfoot. Presented at: American Academy of Orthopaedic Surgeons Annual Meeting; March 1-5, 2016; Orlando, Fla.
- Hunt KJ, et al. Foot Ankle Int. 2012;doi:10.3113/FAI.2012.0984.
- Hunt KJ, et al. Foot Ankle Int. 2011;32(7):704-709.
- Kumar S, et al. Foot Ankle Int. 2010;doi:10.3113/FAI.2010.0797.
- Mayer SA, et al. Foot Ankle Int. 2014;doi:10.1177/1071100714520695.
- For more information:
- Andrew R. Hsu, MD, can be reached at University of California-Irvine Department of Orthopaedic Surgery, 101 The City Dr. South, Pavilion 3, Orange, CA 92868; email: hsuar@uci.edu.
Disclosure: Hsu reports no relevant financial disclosures.