Transverse Z-Osteotomy: Is It A Viable Adjunctive Option For Hallux Limitus?

Author(s): 
By Daniel K. Lee, DPM, and Gregory E. Tilley, DPM

   There have been many surgical treatment modalities described in the podiatric and orthopedic literature for the correction of hallux limitus.1-5 Since the Regnauld procedure was introduced in 1968, surgeons have used it in the treatment of a pathologically long proximal phalanx and hallux limitus.6 However, since its development, this procedure has been characterized as a technically challenging procedure for the treatment of hallux limitus with or without moderate degenerative arthritis.7-10    In 1995, Kissel, et. al., and Hodor, et. al., introduced the sagittal Z-osteotomy, and Gusman, et. al., introduced the Newell decompression osteotomy for the proximal phalanx of the hallux. These authors described the two procedures as alternatives to the Regnauld procedure and included a compilation of indications, advantages and disadvantages.11-13    We believe the transverse Z-osteotomy offers another suitable osteotomy for the proximal phalanx when it comes to joint preservation and correction of hallux limitus in conjunction with a first metatarsal osteotomy.    In previous studies, Kessel and Youngswick emphasized the importance for a first metatarsal decompression osteotomy in treating hallux limitus.14,15 The articles by Hodor and Gusman have also reported using a first metatarsal osteotomy in conjunction with a hallux osteotomy.11,13    A complete discussion of hallux limitus pathomechanics is beyond the scope of this article and has been published extensively in the past. However, it is important to note that the lack of appreciation to these pathomechanics will lead to surgical failure. Durrant and Siepert offered an elegant guide to the understanding of the mechanical criteria and soft tissue involvement around the first metatarsophalangeal joint (MTPJ) in hallux limitus.16    While this is by no means an exhaustive list, here are some proposed indications, advantages and disadvantages for the transverse Z-osteotomy.    Indications for the transverse Z-osteotomy include: mild to moderate degenerative joint disease of the first metatarsophalangeal joint; a painful first metatarsophalangeal joint; excessive retrograde pressure of the hallux on the head of the first metatarsal; a pathologically long proximal phalanx; cosmetic improvement of an excessively long hallux; and a reduction in range of motion at the first metatarsophalangeal joint.

Assessing The Pros And Cons Of The Procedure

The advantages of the procedure include:    • complete anatomical protection for the attachments of the adductor hallucis, abductor hallucis, flexor hallucis brevis, capsule and ligamentous attachments;    • correction of a pathologically long proximal phalanx of the hallux;    • correction of a pathologic hallux abductus interphalangeus or hallux equinus, sparing the first metatarsophalangeal joint;    • excellent stability along the osteotomy site;    • increased range of motion at the first metatarsophalangeal joint by relaxing the muscular, capsular and ligamentous structures after shortening of the proximal phalanx;    • no contraindication with mild osteopenia;    • an immediate return to weightbearing assuming no contraindicating proximal procedure;    • a procedure that is technically less difficult than the Regnauld procedure;    • a lack of complications associated with an autogenous bone graft;    • the ability to use a Kirschner wire osteotomy guide to ensure accurate and reproducible osteotomies;    • a reduced risk of avascular necrosis; and    • an excellent extraarticular, joint sparing osteotomy alternative for the young patient.    Disadvantages include the requirement of internal fixation and all complications inherent with any osteotomy.    In addition to all the advantages of other classic hallux osteotomies over the Regnauld procedure, the transverse Z-osteotomy, by design, provides complete anatomical protection of the sesamoidal apparatus attachments in the plantar base of the proximal phalanx. This may or may not contribute to good mobility of the sesamoidal apparatus. Also, this procedure includes the ability to correct for transverse plane deformities of the hallux or a pathologic hallux abductus interphalangeus.17-22

A Step-By-Step Guide To The Procedure

   The surgeon makes a skin incision, usually as a distal extension of the bunionectomy incision, over the medial aspect of the proximal phalanx. One would deepen the incision through the subcutaneous tissues to the level of the periosteum. Dissection exposes the medial head, shaft and the medial base of the proximal phalanx. Surgeons would proceed to insert two 0.045-inch smooth Kirschner wires in a parallel manner in the transverse plane, perpendicular to the long axis of the proximal phalanx, and into the center of the base and the head of the proximal phalanx.    Using an oscillating saw, one can perform the first osteotomy transversely between and in the same plane with the Kirschner wires through the medial and lateral cortices. Place the second osteotomy in the frontal plane at the distal Kirschner wire plantar to the K-wire. Surgeons can place the third osteotomy parallel and proximal to the second. One would place the fourth osteotomy distal to the proximal Kirschner wire and equal to the distance between the second and third osteotomies. This fourth osteotomy is parallel to the proximal Kirschner wire and through the dorsal aspect of the bone. The fifth osteotomy is at the site of and parallel to the proximal Kirschner wire.    Proceed to remove the resulting portions of bone. The distal and proximal fragments are apposed, and one would employ a bone clamp to maintain reduction. Using proper AO technique, one may place two 2.0-mm cortical screws from dorsal to plantar through the proximal phalanx to achieve permanent fixation. Then the surgeon can irrigate, close and dress the site as per his or her preference.    To correct for a pathologic hallux abductus interphalangeus, as in the Akin procedure for the transverse plane correction, one would perform the second and fourth osteotomies perpendicular to the long axis of the distal phalanx whereas the third and fifth osteotomies are the same as described above.    Intraoperatively and postoperatively, we have consistently noticed increased range of motion and increased space in the first metatarsophalangeal joint on radiographs.    When it comes to postoperative weightbearing, this is determined by any proximal procedures one performs concomitantly. Without any proximal osteotomies that would contraindicate weightbearing, the patient may initially bear weight in a wooden post-op shoe. We emphasize an early, aggressive return to passive range of motion regardless of any other procedures performed. We recommend 20 minutes of passive range of motion (ROM) three times a week in the office with dressing changes prior to suture removal. We also recommend referring patients to physical therapy to facilitate passive and subsequently active range of motion with appropriate precautions.

Pertinent Biomechanical Considerations

   After one has performed the first metatarsal decompression osteotomy, the subsequent transverse Z-osteotomy is designed to decrease the torque about the first MTPJ in hallux limitus during the propulsive phase of gait. Clinically, this translates in reducing the jamming effect at the first MTPJ by decreasing both the lever arm (hallux) distal to the first MTPJ and the tension of both the extensor and flexor hallucis longus.    In hallux limitus, the predominant plane of motion of the joints is in the sagittal plane. During the propulsive phase of gait, beginning with heel-off, the knee is extended to about 180 degrees while the ankle dorsiflexes to 10 degrees and the first metatarsophalangeal joint is about 20 degrees dorsiflexed. At toe-off, the knee is flexed to about 140 degrees while the ankle plantarflexes to about 20 degrees and the first MTPJ dorsiflexes to about 60 degrees.23 Accordingly, as propulsion continues toward toe-off, the first MTPJ becomes a hinge through which there is an increasing dorsiflexion momentum and the hallux becomes the lever arm through which ground reactive forces are acted upon.    As these joints move in concert throughout propulsion and just before proceeding to the swing phase of gait, the first MTPJ becomes the last anatomical hinge through which the entire lower extremity rotates.    Given the limited ROM at the first MTPJ with hallux limitus, there is higher torque at the first MTPJ than in the non-pathologic foot, whether it is secondary to an abnormally long proximal phalanx or to the increasing jamming effect caused by metatarsus primus elevatus.24,25    By reducing the total length of the hallux or the lever arm with our adjunctive procedure for hallux limitus, one may facilitate decreased torque at the first MTPJ at the end of propulsion. Reducing the total length of the hallux leads to a shorter lever arm, which rotates around the hinge during the end propulsion phase of gait. It also decreases the intraarticular pressure and the dorsal articular lip impaction within the first MTPJ.    Torque is directly proportional to the angular acceleration about its axis of rotation or hinge. It is defined as the product of applied force and lever arm or distance.26 One can reduce the torque by reducing either the applied force or the lever arm. One can accomplish a reduction of force by evenly distributing the ground reactive forces through the use of orthoses and reducing the weight of the patient. As noted above, we chose to manipulate the lever arm in order to decrease the torque.

In Conclusion

   Using this osteotomy in conjunction with a first metatatarsal decompression osteotomy provides inherent stability and may possibly decrease the complications and shortcomings of other previously described osteotomies. This combination of procedures can preserve the first metatarsophalangeal joint and correct for hallux limitus or rigidus in stage I, II and possibly III.    We would like to see further biomechanical studies to further determine the efficacy of this procedure in correcting hallux limitus or rigidus in all the stages, and to help analyze the abnormal length proportions between the proximal phalanx and the first ray structures. Dr. Lee is an Assistant Clinical Professor and the Director of Foot and Ankle Surgery in the Department of Orthopaedic Surgery at the University of California in San Diego. Dr. Tilley is the Chief of Podiatric Service within the Division of Orthopedics at the USC Medical Center in Los Angeles. Dr. Burks is a Fellow of the American College of Foot and Ankle Surgeons, and is board-certified in foot and ankle surgery. Dr. Burks practices in Little Rock, Ark.
 

 

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