Can Locking Plates Improve First MPJ Fusions?

Locking compression plates have a number of advantages over conventional plate fixation and may provide ideal fixation for fusions of the first metatarsophalangeal joint. Accordingly, these authors examine the merits of these devices and offer salient surgical pearls.

   Arthrodesis of the first metatarsophalangeal joint (MPJ) is a well-documented, reliable and reproducible procedure for many pathologies of the first MPJ. Advances in fixation technique have led to even better results over the past 10 to 15 years and the recent advent of locking compression plates (LCPs) has made an outstanding procedure even better.

   For every article on implant arthroplasty that shows good results, there are 20 articles on first MPJ arthrodesis that show good or excellent results. Implant arthroplasty has limited use for the first MPJ and the literature supports this undeniably. For those who perform first MPJ arthrodesis on a regular basis, we will offer a closer look at a superior fixation technique, which allows patients to ambulate postoperatively. For those who do more implant arthroplasty, hopefully we will influence you to take a second look at arthrodesis.

   Conventional plate fixation has greatly evolved since its introduction for fracture stabilization and anatomical reduction. The original method involved the concept of complete fracture stability in order to promote primary bone healing, which requires rigidity and little to no bony callus formation.

   Conventional plating also requires direct contact between the plate and the bone, which can result in a loss of periosteal blood supply from too much compression. This phenomenon is referred to as “early temporary porosity” or “stress shielding,” which causes the bone beneath a plate to become porous and weak.1 These bony defects could eventually cause re-fracturing or nonunions.2

Pertinent Pointers On The Unique Design Of Locking Plates

   Locking plates, in contrast to conventional plating, allow for some motion between fracture fragments or a fusion site. This motion promotes secondary bone healing and subsequent callus formation.

   A locking plate is often referred to as an internal fixator or a fixed-angle construct. It acts as a “simple beam,” which moves as one construct. The locking plate resists screw pullout and toggle, especially in osteoporotic or comminuted bone.3 The fixed angle construct is able to convert axial loads into compressive forces instead of shear frictional forces like one would see with the conventional plate.3,4

   Locked plating also stabilizes a fracture without the need of plate contouring, which again helps maintain blood supply to the bone.2 Wagner, et al., discuss initial clinical data for the use of locking plates for internal fixation of fractures. They note “excellent union rates, low rates of fixation failure and few associated complications.”2

   Locking compression plates combine conventional plating with locked plating techniques and the use of locking head screws for the ultimate fixed-angle construct.1,4,5 A threaded interface between the screw heads and the body of the plate allows for angular and axial stability. This design also prevents compression of the plate into the bone, preserving osseous blood supply. When it comes to osteoporotic bone, instead of needing the screw to engage into the bone, one securely tightens the screw into the plate itself. This reduces the chance of loosening or further damage to the already weakened bone.

   Another design unique to the locking compression plate is a combination hole. This allows the surgeon to place conventional cortical or cancellous screws on one side, and threaded conical locking screws on the other side.6 Known as the Combi hole (Synthes), the combination hole allows the surgeon to choose exactly where to place conventional screws versus locking head screws, depending on the specific fracture or joint that one is fusing.2,5,7,8

   With this combination hole, the part of the hole furthest from the middle of the plate is intended for the conventional or non-locking screw and the threaded portion of the hole, closest to the middle of the plate, is intended for locking head screws.6 Locking the screws into the plate allows for increased stability and a decreased toggle effect.2,7

   Instead of the traditional bicortical screw concept, one can now utilize a monocortical locking head screw concept with the locking compression plate. Since the locking screw is secured to the threads within the plate, a second cortex in the bone is not necessary for stability. Also keep in mind that monocortical screws are self-drilling and do not require drilling, measuring or tapping into the bone.

   The length of the plate and number of screws also affect the strength and stability of a plate. In order to function as a locked internal fixator, the length of the plate should be fairly long in regard to the joint space or fracture gap.

   Stoffel, et al., mention that one should use long plates for maximum axial stiffness. The plate span ratio is the ratio between the gap one is fusing or fixating, and the length of the plate. Usually an ideal plate length is about three times the width of a fracture or fusion gap.8

   Stoffel, et al., also discuss current results, which show that two or three screws on either side of the fracture (or joint which is to be fused) are sufficient for successful results. They also recommend that when using a locking compression plate to bridge an interfragmentary gap of less than 2 mm (such as a first MPJ), one should omit one or two plate holes superior to the fracture or fusion site. This allows slight motion and bone contact to occur.8

Why Locking Compression Plates Are A Good Fit For First MPJ Fusion

   Indications for fusion of the first MPJ include but are not limited to significant degenerative joint disease of the first MPJ and gross instability clinically and radiographically. Severe hallux abducto valgus (HAV), recurrent bunion deformities, hallux varus, severe ligamentous laxity or recurrent metatarsus adductus are additional indications for arthrodesis. Another reason for fusion is to decrease recurrence rates in a patient with underlying spasticity or neurologic disease.9-11

   Locking plates provide the stability and rigidity needed for a good fusion. Yet they also allow for micromotion between the phalanx and metatarsal head, and the formation of a bone callus. This bone callus helps reinforce the fusion site.

   Another advantage for using a locking compression plate for first MPJ fusion includes the ability to use plating in osteopenic bone. Osteopenia is not an uncommon finding in the bone of patients with severe hallux rigidus or HAV deformities. Since the surgeon tightens the locking screws into the plate as opposed to the osteopenic bone, there is a stable fixed construct, which provides rigid fixation. This reduces the risk of hardware failure and pullout of the screws.4,6,8

   Augmenting an interfragmentary compression screw obliquely across the first MPJ not only properly aligns the fusion, it also provides rigidity and compression, further stabilizing the fusion site.

   The locking compression plate gives the surgeon preference on screw choice and placement. This increases the amount of flexibility in fixation options. It also allows a surgeon to become comfortable with his or her own technique for fixation of a first MPJ fusion. It is important for the surgeon to remember that careful preoperative planning for each specific case and a good knowledge of different fixation options can facilitate maximum post-op fusion results.5

A Step-By-Step Guide To Surgical Technique

   Begin by ensuring the patient is in a supine position on the operating table. One can use monitored anesthesia care (MAC) or general anesthesia for the procedure. Prep the foot and drape it in the usual aseptic fashion. Make a dorsomedial incision extending from the midshaft of the first metatarsal to the hallux interphalangeal joint in order to ensure adequate exposure of the first MPJ. Expose the capsule and evaluate it for hypertrophy and loose bodies near the first MPJ. Make a medial incision of the capsule over the first MPJ.

   The surgeon will have an easier time reflecting the periosteum from the bone if he or she starts at the diaphyseal portion of the first metatarsal shaft and continues to the proximal phalanx. There are weaker attachments at these starting points. This also allows for good exposure of the first metatarsal head and the MPJ. This incision approach also ensures easier and improved periosteal closure.11

   Then expose the first metatarsal head. Free all plantar and medial attachments, including the flexor hallucis brevis tendon. Proceed to inspect the joint surfaces. Remove the medial eminence with a saggital saw but be careful not to stake the head. Using a rongeur, resect any osteophytes from the dorsal aspects of the proximal phalanx and the first metatarsal head.

   Use a rotating power burr to remove the cartilage on the head of the first metatarsal as well as the base of the proximal phalanx. Also use the burr to emphasize the hollowed out shape of the base of the proximal phalanx and ensure a good “ball and socket” fit between the bones. Use a McGlamry elevator to free up the plantar sesamoidal apparatus from the first metatarsal head to promote a congruous fusion.

   Use a 0.62-inch K-wire for temporary fixation. Direct the wire up the base of the proximal phalanx distally and exit the wire through the tip of the hallux. Then redirect the K-wire proximally, holding the hallux in a slightly dorsiflexed position, across the first MPJ.

   Load the foot against a flat surface, such as the lid of a screw set, to ensure dorsiflexion of the hallux at approximately 15 to 20 degrees or 2 to 4 mm. This positioning also helps to simulate weightbearing.

   Drive a second 0.62-inch K-wire obliquely across the first MPJ medially to laterally, prior to the compression screw as a guide hole. After under-drilling, proceed to countersink the bone. Then measure the hole and drive a 4.0 cortical screw across the joint in the normal surgical technique. Remove the temporary K-wire from the distal hallux.

   Assess the Synthes 2.4 six-hole or seven-hole locking plate, and dorsiflex the plate to fit the first MPJ as necessary with the bending tools included in the set. One should place the locking plate dorsally over the bone, leaving one or two central holes open. This helps prevent stress concentrations at the fusion site and allows minor motion for callus formation.

   Usual screw placement in the plate consists of two or three screws proximally in the first metatarsal and two or three screws distally in the proximal phalanx. The first screw should be a locking head screw, which one would place distally from the joint but in the most proximal hole in comparison to the fusion site.

   Pre-drill and measure the hole in the corresponding plate hole, and then insert the appropriate screw into the locking plate. The surgeon can alternate between locking head screws and non-locking screws, depending on his or her preference and the specific joint construct requirements.

   Intraoperative fluoroscopy shows positioning of the screw and plate fixation, and proper alignment. An AP view will show good frontal plane positioning of the fusion and screws, and the maintained length of the first ray. The lateral view will show good positioning and length of screws, good plantar cortical screw purchase, and a slightly dorsiflexed position of the hallux.4,11

What The Literature Reveals About Fixation And Fusion Rates

   Several types of fixation are available for first MPJ fusions. There have also been differing opinions on whether to permit weightbearing immediately after surgery. The traditional postoperative management for first MPJ fusions is four to six weeks of non-weightbearing.

   Following the aforementioned surgical technique, we have patients wear a walking cast boot for eight weeks postoperatively. They can be fully weightbearing during this time.

   Several different studies have revealed high rates of fusion for the first MPJ, regardless of fixation choice and post-op regimen. These promising results could also be associated with good surgical technique and reproducibility. However, in regard to instances of nonunions, one factor is the bone stock in these patients. Did an increase in osteopenia correlate to a higher nonunion rate?

   Mah and Banks recently reviewed the fusion rates of 22 first MPJ fusions, which surgeons fixated with two K-wires. They also allowed immediate weightbearing after surgery in a padded surgical shoe. Out of 22 fusions, the researchers noted two nonunions and one delayed union for a post-op complication rate of 13.64 percent. Their fusion rate with this fixation method and post-op regimen was 86.36 percent. Their fusion rate was similar to what other researchers have reported in studies utilizing different types of fixation and different post-op weightbearing guidelines.9

   Patil, et al., conducted a retrospective analysis of first MPJ fusions between April 2001 and December 2002. Surgeons performed a total of 56 fusions with a variety of fixation types. The fixation consisted of two-screw fixation in 31 feet, one screw in 18 feet, staples in six feet and a single K-wire in one foot. These researchers noted a 100 percent fusion rate with the two-screw technique, a 77.78 percent fusion rate with one screw and no fusions with staples or a K-wire. There were a total of 11 nonunions, eight of which were symptomatic.10

   Many other studies have looked at the fusion rates after different methods of fixation for first MPJ fusions. A large study by Coughlin revealed fusion in 1,314 of 1,451 cases (or an approximately 90 percent fusion rate) using a variety of fixation methods.12 For 30 patients, Coughlin combined cone and cup reaming with a single K-wire and a dorsal compression plate. With this approach, he reported a 100 percent fusion rate.12

   Using flat bone cuts and two compression screws for fixation, Turan found a 100 percent fusion rate in 20 patients.13

Final Notes

   Although locking plates and locking compression plates were originally designed and used in fracture repair, they may be ideal for fixating first MPJ fusions due to their superior stability and rigid properties, which help ensure a proper fusion. The combination of axial and angular stability, as well as the option to use a locking compression plate as either a compression plate or locked internal fixation, gives this fixation device great versatility.

   Locking compression plates are also advantageous in this procedure due to the population of patients requiring a first MPJ fusion. Many patients with late stages of hallux rigidus or HAV are elderly, and have decreased bone stock.

   Due to the safe and effective use of locking compression plates in osteoporotic bone, this could be a viable fixation option for these patients. Unlike original plate and screw combination methods, the locking compression plate helps to preserve periosteal bone supply, thereby increasing the chances of fusion and decreasing the need for plate removal.

Dr. DeHeer is a Fellow of the American College of Foot and Ankle Surgeons, and is a Diplomate of the American Board of Podiatric Surgery. He is also a team podiatrist for the Indiana Pacers and the Indiana Fever. Dr. DeHeer is in private practice with various offices in Indianapolis.

Dr. Achramowicz is a first-year resident at Westview Hospital in Indianapolis.

For further reading, see “A Guide To Locking Plates In Podiatric Surgery” in the April 2008 issue, “Exploring New Advances In Internal Fixation” in the May 2005 issue, and “Secrets To Managing Complications Of First MPJ Fusion” in the May 2006 issue of Podiatry Today.

To check out the archives or get information on reprints, visit www.podiatrytoday.com.

References:

1. Perren SM, Cordey J, Rahn BA, Gautier E, Schneider E. Early temporary porosis of bone induced by internal fixation implants. A reaction to necrosis, not to stress protection? Clin Orthop Relat Res. 1988; 232:139-151. 2. Wagner M, Frenk A, Frigg R. Locked plating: biomechanics and biology and locked plating: clinical indications. Techniques In Orthopaedics. December 2007; 22(4):209-218. 3. Greiwe MR, Archdeacon MT. Locking plate technology: current concepts. J Knee Surg. January 2007; 20(1): 50-55. 4. Gautier E, Sommer C. Guidelines for the clinical application of the LCP. Injury 2003; 34(suppl 2):S-B63-S-B76. 5. Wagner M, Frenk A, Frigg R. New concepts for bone fracture treatment and the locking compression plate. Surg Technol Int. 2004; 12:271-7. 6. Synthes Large Fragment LCP Instrument and Implant Set Technique Guide, pages 1-30. 7. Frigg R. Development of the locking compression plate. Injury 2003; 34 (suppl 2):S-B6-S-B10. 8. Stoffel K, Dieter U, Stachowiak G, Gächter A, Kuster MS. Biomechanical testing of the LCP – how can stability in locked internal fixators be controlled? Injury 2003; 34(suppl 2):S-B11-S-B19. 9. Mah C, Banks A. Immediate weight bearing following first metatarsophalangeal joint fusion with Kirschner wire fixation. J Foot Ankle Surg January 2009; 48(1):3-8. 10. Patil S, Chojnowski A, Albert J. A retrospective analysis of first metatarso-phalangeal joint fusions. J Foot Ankle Surg 2005 11(2):113-16. 11. Yu G, Shook J. Arthrodesis of the First Metatarsophalangeal Joint. In: A. Banks, M. Downey, D. Martin et al. (eds). McGlamry’s Comprehensive Textbook of Foot and Ankle Surgery. Vol. 1, 3rd ed. Lippincott, Williams and Wilkins, Philadelphia, 2001, pp. 581-607. 12. Coughlin MJ. Arthrodesis of the 1st MTPJ. Orthrop Rev 1990; 19(2):177-186. 13. Turan I, Lindgren U. Compression screw arthrodesis of the first metatarsophalangeal joint of the foot. Clin Orthop Relat Res. 1987; 221:292-295. Additional References 14. Dickson KF, Munz J. Locked plating: clinical indications. Techniques In Orthopaedics. September 2007; 22(3):181-185. 15. Müller ME, Allgöwer M, Schneider R and Willenegger H. AO Manual of Internal Fixation, 3rd Edition. Springer-Verlag, Berlin, 1991. 16. Rüedi TP, Murphy WM, eds. AO Principles of Fracture Management. Thieme, New York, 2000.