The first-second intermetatarsal angle was not significantly different between the study group (average, 9.5° ± 3.1°) and the control group (average, 8.4° ± 2.6°).
This study suggests an association between an anatomic variant, a high second metatarsal to first metatarsal length ratio, and an uncommon disease. Midfoot arthrosis is so uncommon that most clinicians never have the opportunity to observe this association. How this anatomic variation relates to primary arthrosis of the midfoot is unclear, but a short first metatarsal or a long second metatarsal is associated with midfoot arthritis.
Primary arthrosis of the midfoot has not been discussed much in the literature, and etiological factors have not been identified, to our knowledge. It has been suggested9 that patients with a functionally short first ray (or a functionally long second ray) have radiographic evidence of overload stresses on the second metatarsal segment, consisting of thickening of the cortices and/or shaft or a gap between the first and second cuneiforms. Morton9 noted that the second tarsometatarsal joint was not built to bear this extra stress, as its vertical depth is half that of the first tarsometatarsal joint and its morphology is substantially dissimilar. Early in the disease process, pain at the so-called Morton's point9 may be the first evidence that the second tarsometatarsal joint is being overloaded and that synovitis is developing. The increased stresses on the second metatarsal and second tarsometatarsal joint may accumulate over time and result in arthrosis.
A shortcoming of this study is its small sample size, which was due to the uncommon nature of the problem. The patients were entered into the study over a three-year period. The restrictive nature of patient privacy regulations blocked our access to patients prior to that time period, as prior approval from those patients had not been obtained. Another shortcoming of the study is the limitation of imaging in a retrospective study. While the technique was standardized, the technicians and patients were not. We tried to minimize variations due to radiographic technique by using the same x-ray machine in the same manner for all subjects. Also, the analyzed data were all relative measurements with internal controls.
Another potential area of concern was whether a two-dimensional measurement might be inadequate for a three-dimensional structure. A metatarsal that is more sharply angled relative to the floor might measure shorter than one parallel to the floor on plain weight-bearing radiographs. This concern was addressed by comparing plain radiographic measurements with those made on computed tomography scans, and we found no significant difference in the length of the first or second metatarsal between the radiographic and computed tomography measurements of the same foot. In addition, ratios of the lengths measured on the computed tomography scans did not differ from the same ratios measured on plain radiographs. The computed tomography measurements of the fourth metatarsal, however, appeared to differ from the lengths measured on the radiographs. This slight difference might be explained by the fact that the fourth metatarsal was more difficult to measure than the first three metatarsals on plain radiographs as it is on the downward slope of the transverse metatarsal arch. Its proximal end is partially obscured and out of plane on the anteroposterior radiograph. It might be more accurately measured on an oblique radiograph. However, the first and second metatarsals were the focus of this study, and they are not easily measured on an oblique radiograph.
A widened first-second intermetatarsal angle would theoretically affect the measurement of the second metatarsal length. We addressed this issue by measuring the functional length, which we defined as the length of the first metatarsal as projected along the axis of the second metatarsal. This measurement showed the same results as the actual length measures. In addition, there was no significant difference between the two groups with regard to the intermetatarsal angle, so the groups can be compared without using the functional lengths.
The patients in our study group were an average of 64.2 years of age and had no history of trauma or inflammatory arthritis. The functional length of the second metatarsal in those patients was approximately 9 mm longer than that in the control group. Also, in comparison with the fourth metatarsal, the first metatarsal was short and the second metatarsal was long. While this study does not prove that the functionally long second metatarsal predisposes the midfoot to arthrosis, it does demonstrate a clear association between midfoot arthrosis and a functionally long second metatarsal and suggests a possible mechanical etiology for midfoot arthrosis. We cannot make concrete suggestions for prevention of the disease process, but the first step in developing prevention strategies is to identify risk factors involved in the disease.
Specific data from the radiographs of all subjects are available with the electronic versions of this article, on our web site at jbjs.org (go to the article citation and click on “Supplementary Material”) and on our quarterly CD-ROM (call our subscription department, at 781-449-9780, to order the CD-ROM). ▪
The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.
Investigation performed at the Department of Orthopaedics and Sports Medicine, University of Washington, Harborview Medical Center, Seattle, Washington
1. , Tejwani NC, Digiovanni CW, Holt SK, Benirschke SK, Hansen ST Jr, Sangeorzan BJ. Outcome after open reduction and internal fixation of Lisfranc joint injuries. J Bone Joint Surg Am. 2000;82: 1609-18.
2. , Olney BW. Deformity correction and arthrodesis of the midfoot with a medial plate. Foot Ankle. 1993;14: 493-9.
3. , Iorio LJ. Rheumatoid arthritis of the foot and ankle. J Am Acad Orthop Surg. 1994;2: 326-32.
4. , Meyerson MS, Biddinger KR. Results of arthrodesis of the tarsometatarsal joints after traumatic injury. J Bone Joint Surg Am. 1996;78: 1665-76.
5. , Simkin P, Kravette M, Lowe P, Gardner G. The posterior tibial tendon and the tarsal sinus in rheumatoid flat foot: magnetic resonance imaging of 40 feet. J Rheumatol. 1999;26: 289-93.
6. , Vargo R, Alexander IJ. Late reconstruction of the midfoot and tarsometatarsal joints after trauma. Orthop Clin North Am. 1995;26: 393-406.
7. , Veith RG, Hansen ST Jr. Salvage of Lisfranc's tarsometatarsal joint by arthrodesis. Foot Ankle. 1990;10: 193-200.
8. , Johnson KA. Dowel arthrodesis for degenerative arthritis of the tarsometatarsal (Lisfranc) joints. Foot Ankle. 1986;6: 243-53.
Copyright 2005 by The Journal of Bone and Joint Surgery, Incorporated
9. . The human foot; its evolution, physiology and functional disorders. New York: Columbia University Press; 1935. p 153-86.