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Moberg Osteotomy - Dorsiflexion Osteotomy of Proximal Phalanx

Indications

Dorsal closing wedge osteotomy of the proximal phalanx was popularized by Moberg in 1979. [1] Although it was initially recommended for young patients (under 18 years of age), Moberg extended the indications to include adults. The Moberg osteotomy is used for hallux rigidus, grades 2 and 3, and is usually performed in conjunction with a cheilectomy and not as a stand-alone procedure. It seems to be most helpful for younger or middle-aged patients who are still active.

Preoperative Planning

Preoperatively, three views of the foot are usually sufficient. Weight-bearing views are important; non-weight-bearing views often obscure the dorsal first metatarsal osteophyte. In non-weight-bearing views, the toes are usually in passive extension, which could block the dorsal osteophyte. Also, the AP view may over-estimate the degenerative change as osteophytes may overlie the joint, creating the impression that the joint is abnormally decreased (Figure 1). CT and MRI studies may be done to elucidate the presence of suspected chondral injuries.


Figure 1. AP weight-bearing view of the foot. Note slightly narrowed first MTP joint space.


All radiographs and other imaging studies should be closely reviewed, with special attention to the lateral radiograph. This study will show the dorsal osteophytes from the distal metatarsal head and proximal phalanx (Figure 2). No specific physical examinations need to be done under anesthesia, but is important to document the passive range of motion (both dorsiflexion and plantarflexion) before the onset of the procedure.


Figure 2. Lateral weight-bearing view of the foot: Note significant dorsal metatarsal flowing osteophyte, as well as dorsal joint space loose body.


The surgeon should alert the patient that we are “stealing” motion from plantarflexion and giving it to dorsiflexion. Therefore, the motion in plantarflexion may be somewhat decreased postoperatively.

Positioning

The patient is placed supine on the operating table. Occasionally, a small bump under the patient’s buttocks may be necessary if the patient’s hip has excessive external rotation.

A Martin-type tourniquet in applied to the supramalleolar region of the ankle. Some surgeons also favor a thigh tourniquet to avoid “tethering” the tendons about the ankle and to allow good evaluation of intra-operative range of motion. It should be noted that the thigh tourniquet is more painful for the awake, alert patient.

The procedure is usually done under ankle block anesthesia. A mini C-arm is also used during the procedure and should be available. Antibiotics are given before the procedure as per protocol.

Approach

Usually a dorsomedial approach to the first MTP joint is used. The extensor hallucis longus (EHL) is retracted laterally and the dorsomedial nerve is retracted medially (Figures 3-4). This will provide good access to both the medial and lateral sides of the MTP joint. A directly medial approach to the first MTP joint can be used as well, but this approach can limit access to the lateral side of the joint and is more difficult. If a prior medial approach has been used, a parallel incision can still be made safely on the dorsum of the foot.


Figure 3. Dorsal-medial approach to the first MTP joint. Note lines on the skin to allow exact skin re-approximation.


Figure 4. In the dorsal medial approach, the EHL is retracted laterally with the dorsal capsule.

Techniques

Part One: Cheilectomy
  • Make a dorsomedial incision, taking care to identify and protect the dorsomedial cutaneous nerve. Retract the EHL laterally. Make the MTP capsulotomy in line with the skin incision; the capsule edges can be tagged with a 2-0 Vicryl suture for ease of identification later (optional).
  • Retract the capsular edges both plantarly and dorsally.
  • Inspect the MTP joint closely (Figure 5). Examine the joint surfaces for osteochondral defects or chondral flaps (especially plantarly), as well as overall degeneration within the MTP joint. Use a reciprocating saw with irrigation to remove 1 to 2 mm of the medial eminence. (This is done to promote healing of the capsule to the bone.)  If noted, osteochondral lesions are usually drilled with an 0.054-inch Kirshner-wire (K-wire) under cooling irrigation.


Figure 5. hallux rigidus -Thirty-nine year-old female with hallux rigidus and near complete loss of cartilage from the dorsal third of
the metatarsal head. EHL tendon is retracted laterally.


  • Perform a dorsal cheilectomy of the metatarsal head, as described elsewhere. In moderate cases, bone is removed flush with the surface of the dorsum of the metatarsal neck. In more severe grades, we routinely remove up to 30% of the metatarsal head, but we try to limit our resection to only the degenerated areas of the metatarsal head. All bony cuts should be made with cooling irrigation.
  • Access and inspect the lateral side of the MTP joint.
  • If present, remove osteophytes or ossicles from the proximal phalanx with a rongeur.
Part Two: Osteotomy

We now shift our attention to the proximal phalanx and the osteotomy.

  • Expose the plantar aspect of the proximal phalanx sufficiently to protect the flexor hallucis longus (FHL) tendon.
  • Place a 0.062-inch smooth K-wire transversely from medial to lateral as a guide wire. It is placed parallel and as close to the articular surface of the proximal phalanx as possible without entering the joint. Use a mini C-arm to verify the proper extra-articular placement of the K-wire. Place the guide wire such that the osteotomy is made just distal to the guide pin (Figure 6).


Figure 6. AP fluoroscopic image of K-wire placement to help ensure extra-articular osteotomy placement.


  • Once the placement of the K- wire has been verified, the osteotomy can begin.
  • To maximize the amount of dorsiflexion of the tip of the toe, make the osteotomy as close to the articular surface as feasible. However, if the proximal fragment is too small, sometimes it will fragment postoperatively. Furthermore, the osteotomy may be made more distally if the plans is to use internal fixation such a mini-plate or screw to allow more bone for fixation. If the plan is to use a plate, make sure the osteotomy is distal enough to allow for non-articular placement of the proximal screw.
  • Use an oscillating saw with a 0.5-cm blade width to make the first cut in the phalanx just distal to the surface of the K-wire with cooling irrigation (Figure 7).


Figure 7. First cut of the osteotomy. Note K-wire to demarcate and help ensure extra-articular osteotomy.


  • The initial cut is incomplete, leaving the plantar cortex intact. This protects the FHL and maintains stability in the phalanx in preparation for the second cut.
  • Make a second, oblique cut, measured about 3-5 mm distal to the first cut. In very mild cases of hallux rigidus, a 3-mm wedge is used (Figure 8).


Figure 8. Angled cut to remove a dorsal wedge of bone.


  • Keep this cut as parallel as possible to the first cut, looking at the dorsal surface. The width is measured with a sterile ruler. If the two cuts are not parallel, an angular deformity (hallux valgus or varus) can ensue. Attempt to angle the cut to meet at the plantar cortex.
  • Be careful not to sever the EHL during the osteotomy, as non-vigilant retraction can lead to this complication and slow the postop recovery. If the EHL is compromised, be sure to repair it acutely.
  • If there is significant preoperative abductus (lateral angulation), it may help the appearance of the toe to make the medial part of the wedge bigger than the lateral side. The so-called “Mo-Akin” or “Akin-berg,” depending on preference.
  • As with the first cut, it is important not to finish the osteotomy completely.
  • Weaken the remaining plantar cortex with multiple 0.062 K-wire drill holes (Figure 9). The osteotomy is then completed or “greensticked” manually with dorsally directed force.  Again, the more irrigation used the better, to keep the bone cool and prevent thermal necrosis and potentially slower healing.


Figure 9. Placement of 0.054-inch K-wire to perforate remaining plantar cortex to help "greenstick" osteotomy; cheilectomy
has already been completed.

Part Three: Fixation and Closure
  • Various types of fixation have been described for this osteotomy. We initially used 28-G wire placed through drill holes. Although inexpensive, we were concerned about initial strength of fixation. We have also used two or three K-wires (usually 0.054”) placed from medial proximal to distal plantar. These were typically removed at 3-4 weeks and do work well, but possess downsides such as pin tract infections, patient dissatisfaction with appearance, and fears of a painful removal. 
  • Furthermore, internal fixation such as a partially threaded screws, in diameter of 2.0-3.0 mm, or staples have been used. Recently we have used the Plaple (Arthrex, Naples, Florida), which combines a plate with a staple (Figures 10-11). The staple aspect is used proximally and the 2.3-mm screw is used distally to allow good compression and initial strength (Figure 12). Fortunately, the postop biomechanics of weight bearing place the toe into dorsiflexion and compression, thus adding to the healing forces added to the construct.


Figure 10. Low-lying Plaple in place.


Figure 11. AP fluoroscopic image of the Plaple in place.


Figure 12. Lateral view of foot 6 weeks from cheilectomy and Moberg osteotomy. Note generous cheilectomy and Plaple used to secure the proximal phalanx osteotomy.


  • Close the deep capsule with nonabsorbable suture, usually 2-0 in diameter. Release the tourniquet after deep closure to ensure adequate hemostasis.  
  • Try to completely cover the osteotomy site with soft tissue. Sometimes this is not possible, given the limited amount of distal capsule and thin periosteum (Figure 13). Close the skin with 4-0 nylon type suture.


Figure 13. First layer of closure. Note complete closure of deep capsule and covering of indwelling hardware.


  • Apply a soft dressing consisting of a nonadherent dressing, 4x4 gauze, and 4-inch Kling. Apply a 2- or 3-inch elastic bandage over this, and place the patient in a hard-soled postoperative shoe.

Pearls and Pitfalls

  • Indications: If the MTP joint has end-stage degeneration, the patient may have residual postoperative pain and be better served with an arthrodesis. One good pr-operative question to ask is whether the patient has pain at rest. If the answer is yes, it may be better to consider an arthrodesis.
  • Intra-articular osteotomy: Use of K-wire as a guide and a mini C-arm can decrease the incidence of an intra-articular placement of the proximal limb of the osteotomy.
  • Angular deformity after surgery: Extreme care should be taken to make the second cut of the osteotomy as parallel as possible to the first. “Parallel” is from the perspective of looking at the dorsal surface of the proximal phalanx. It is important to visualize the medial and lateral aspect of the joint and the proximal phalanx.
  • FHL injury: Careful exposure of the proximal phalanx is essential. Incomplete plantar osteotomy and “greensticking” the osteotomy after multiple drill holes.
  • EHL injury: Careful and conscious retraction is very important during the creation of the osteotomy. If mindful of the EHL, laceration is unlikely. Also, plantarflexion of the toe during the osteotomy places undue tension on the EHL, making injury more common.
  • Non-union: Rare, but bony apposition is important, as is solid fixation. Greensticking of the plantar cortex and a lot of irrigation during the bony cuts are also helpful.
  • Proximal fragment fracture: Avoid making the osteotomy too close to the articular surface, let alone cutting into the articular surface.

Postoperative Care

Postoperatively, patients are placed in a hard-soled shoe for 3-6 weeks. Weight-bearing as tolerated is allowed the day after surgery when blood coagulation is complete. We usually tell the patient to elevate the limb for the first 2-3 days.

Patients are initially seen 7-10 days after surgery. The patient is instructed to massage the operative site to desensitize the wound beginning 1 week postoperatively. Passive dorsiflexion exercises of the MTP joint are begun 1-2 weeks after surgery, depending on the fixation used.

Plantarflexion-type exercises are not started until 4 weeks postoperatively to avoid early tension on the fixation of the osteotomy site. Less emphasis is placed on plantarflexion unless the resting posture of the hallux is above ground.

Outcome

The use of a dorsal closing wedge osteotomy increases the space at the dorsal MTP joint. In effect, the osteotomy draws the dorsal aspect of the phalanx away from the dorsal aspect of the first metatarsal head. The osteotomy may reduce the joint compression force on the dorsum of the first MTP joint during the toe-off phase of gait.

In one long-term study, [2] eight women who had 10 toes treated for hallux rigidus by dorsal wedge osteotomy of the proximal phalanx were reviewed after an average follow-up of 22 years (no cheilectomies were done in this study). Five toes were symptom-free, four others did not restrict walking, and only one had required metatarsophalangeal fusion. The authors concluded that dorsal wedge osteotomy afforded long lasting benefits for hallux rigidus.

Thomas and Smith [3] reviewed 17 patients (24 feet) with radiographic Grade I or II changes at a median follow-up of 30 months. A 96% satisfaction rate was obtained without any reported complications. The authors concluded that the addition of a proximal phalanx osteotomy provided better results than cheilectomy by itself.

Blyth et al [4] reviewed 18 patients with Grade I to III hallux rigidus treated with these combined procedures. Fourteen patients demonstrated good or excellent results and a substantial improvement in motion of the MTP joint at mean follow-up of 4 years. One patient with a poor result went on to arthrodesis. Additional complications included transfer metatarsalgia and one injury of  the dorsomedial cutaneous nerve.

Complications

  • Intra-articular osteotomy
  • FHL, EHL, and dorsomedial cutaneous nerve injury and/or laceration
  • Angular deformity after surgery
  • Fragmentation of the proximal fragment of the proximal phalanx
  • Non-union
  • Malunion, including rotational malunion
  • Failure to improve, likely related to incorrect or expanded indications for this surgery

References

1. Moberg E. A simple operation for hallux rigidus. Clin Orthop 1979;142:55-6.

2. Citron N, Neil M. Dorsal wedge osteotomy of the proximal phalanx for hallux rigidus. Long-term results. J Bone Joint Surg Br 1987;69(5):8357.

3. Thomas PJ, Smith RW. Proximal phalanx osteotomy for the surgical treatment of hallux rigidus. Foot Ankle Int 1999;20(1):3-12.

4. Blyth MJ, Mackay DC, Kinninmonth AW. Dorsal wedge osteotomy in the treatment of hallux rigidus. J Foot Ankle Surg 1998;37(1):8-10.

Additional Reading

Feldman R, Hutter J, Lapow L, et al. Cheilectomy and hallux rigidus. J Foot Surg 1983;22:170-4.

Frey CC, Jahss MJ, Kummer FJ. The Akin procedure: an analysis of results. Foot Ankle Int 1991;12:1-6.

Giannestras NJ. Foot Disorders: Medical and Surgical Management, 2nd ed. Philadelphia: Lea & Febiger, 1973:400.

Gould N, Schneider W, Ashikaga T. Epidemiological survey of foot problems in the continental United States: 1978-1979. Foot Ankle Int 1980;1:8-10.

Mann RA, Clanton TO. Hallux rigidus: treatment by cheilectomy. J Bone Joint Surg Am 1988;70A:400-6.

McMaster MJ. The pathogenesis of hallux rigidus. J Bone Joint Surg Br 1978;60B:82-7.

Smith RW, Katchis SD, Ayson LC. Outcomes in hallux rigidus patients treated nonoperatively: a long-term follow-up study. Foot Ankle Int 2001;22:462-70.

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