Transverse Z-Osteotomy: Is It A Viable Adjunctive Option For Hallux Limitus?
- Volume 19 - Issue 7 - July 2006
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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.
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.