119 Pictorial Essay H............ - Hallux Valgus Deformity: Preoperative Radiologic Assessment David Karasick1 and Keith L. Wapner An estimated 40% of the American adult population experiences foot problems, especially bunions with hallux valgus and hammer toes. The noted predominance among females usually is attributed to a choice of footwear. Hallux valgus is defined as static subluxation of the first metatarsophalangeal joint with lateral deviation ofthe great toe and medial deviation of the first metatarsal. With more than 1 00 surgical procedures developed for the repair of hallux valgus and the increasingly sophisticated techniques available, a thorough understanding of the radiologic criteria involved in the assessment of these foot deformities is needed. Proper technique consists of obtaining radiographs while the patient is standing erect and bearing weight on the foot. An anteroposterior or a dorsoplantar view is obtained with 1 5#{176} of cephalic angulation of the tube at exposure factors of 6 mas and 50 kv. A lateral view is obtained without angulation of the tube at 9.5 mas and 55 kv; this view enables proper evaluation of pes planus, or flatfoot. An accompanying oblique radiograph is obtained without tube angulation; exposure factors are similar to those for the anteroposterior view. The source-to-image distance is 40 in. (1 01.6 cm). At our institution, DuPont Quanta detail screens (Du Pont, Clifton, NJ) are used with Agfa Gevaert MR 4 film (Agfa-Gevaert Rex, Secaucus, NJ). A thorough knowledge and understanding ofthe pathologic conditions present with hallux valgus deformity are essential to better differentiate normal from abnormal measurements on radiographs. Hallux valgus deformity consists of lateral deviation of the proximal phalanx on the metatarsal head with accompanying medial deviation of the first metatarsal. As the deformity progresses, the first metatarsal head slides medially off the sesamoids, which are anchored to the second metatarsal by the transverse metatarsal ligament. Enlargement of the medial bony eminence of the first metatarsal head and attenuation of medial capsular tissues occurs. Bursal thickening or inflammatory bursitis overlying the first metatarsal head can accentuate this medial eminence. The pressure of the great toe against the second toe may lead to abnormal alignment, subluxation, or dislocation of the second metatarsophalangeal joint [1]. Given these pathologic developments in hallux valgus, certam measurements made on radiographs of the weight-bearing foot are essential for proper surgical correction [2-4]. These include the hallux interphalangeus angle, hallux valgus angle, metatarsus primus varus angle, and first intermetatarsal angle (Fig. 1). The other important measurements are the tibial sesamoid position (Fig. 2) and the relative lengths of the first and second metatarsals (Fig. 3). Additional criteria concern congruency of the first metatarsophalangeal joint (Fig. 4), shape of the first metatarsal head (Fig. 5), orientation of the first metatarsal-cuneiform joint (Fig. 6), existence of a lateral facet (Fig. 7), size of the medial eminence (Fig. 8), Received January 23, 1990; accepted after revision February 27, 1990. I Department of Radiology, Jefferson Medical College, Thomas Jefferson University Hospital, 1 1 1 5. 11th St., Ste. 3607, Philadelphia, PA 191 07. Address reprint requests to D. Karasick. 2 Department of Orthopedic Surgery. Jefferson Medical College, Thomas Jefferson University Hospital, Philadelphia, PA 19107. AJR 155:119-123, July 1990 0361-803X/90/1 551-01 19 American Roentgen Ray Society
120 KARASICK AND WAPNER AJR:155, July 1990 Fig. 1.-Normal (N) angles in anteroposterior erect foot as measured on radiographs. 1, Hallux interphalangeus angle: angle between long axes of first proximal phalanx and first distal phalanx (N < 8#{176}). 2, Hallux valgus angle: angle between long axes of first proximal phalanx and first metatarsal(n < 15#{176}). Hallux valgus can be mild(16-25#{176}),moderate (26-35#{176}), or severe (>35#{176}). 3, Metatarsus primus varus angle: angle between long axes of medial cuneiform and first metatarsal (N < 25#{176}). 4, First intermetatarsal angle: angle between long axis of first and second metatarsals (N < 10#{176}). degree of degenerative joint disease (Fig. 9), degree of pronation of the hallux (Fig. 10), subluxation or dislocation of the lesser metatarsophalangeal joints (Fig. 10), and presence of crossover second toe deformity (Fig. 1 1). The radiologist s role in the basic decision-making process for selecting the corrective procedure for hallux valgus is important. The surgical treatment can be divided into seven categories [1]: (1) Simple exostectomy is indicated for a large medial eminence without significant valgus deformity. (2) Softtissue repair is indicated for mild to moderate hallux valgus less than 35#{176} with an intermetatarsal angle less than 1 5#{176}. (3) Proximal first metatarsal osteotomy (Mann crescentic osteotomy) is indicated for moderate to severe hallux valgus when the first metatarsal cannot be reduced to the second metatarsal (intermetatarsal angle greater than 1 5#{176}). (4) Distal first metatarsal osteotomy (Mitchell procedure) is indicated for moderate hallux valgus, when the first metatarsal is not shorter than the second metatarsal. Metatarsalgia, especially of the second metatarsal, may develop postoperatively if this surgery is performed on a short first metatarsal. (5) Resection arthroplasty (Keller proximal phalanx resection) is indicated in older patients for whom extensive surgery is contraindicated or in whom hallux rigidus is not amenable to treatment by cheilectomy, arthrodesis, or Silastic implant. It also is mdicated as a salvage procedure for failed bunion surgery. (6) Proximal phalangeal osteotomy (Akin procedure) is indicated for hallux valgus interphalangeus and for mild to moderate hallux valgus with a congruent joint. (7) Metatarsophalangeal joint arthrodesis is indicated for advanced degenerative or rheumatoid arthritis with hallux valgus deformity. It also is indicated with failed implant or as a salvage procedure for recurrent hallux valgus. In summary, hallux valgus deformity is not difficult to diagnose, but it must be evaluated carefully on radiographs to ensure use of the most efficacious surgical procedure for each patient. Fig. 2.-Tibial sesamoid position (four-grade classification). A, Grade 0: no displacement of sesarnold relative to reference line, which bisects long axis of first metatarsal shaft. B, Grade 1: overlap of less than 50% of sesamold to reference line. C, Grade 2: overlap of greater than 50% of sesamold to reference line. 0, Grade 3: complete displacement of tiblal sesamoid beyond reference line laterally.
AJR:155, July 1990 HALLUX VALGUS DEFORMITY 121 Fig. 3.-Relative lengths of first and second metatarsals: bisecting vertical line is drawn in second metatarsal bone and connected to perpendicular horizontal line drawn from second metatarsal head to first metatarsal head. A, Short first metatarsal (minus rating): horizontal line extends distal (>2 mm) to first metatarsal head. B, Equal metatarsal lengths: honzontal line intersects first metatarsal head within 2 mm. C, Long first metatarsal(plus rating): horizontal line extends proximal (> 2 mm) to first metatarsal head. Fig. 4.-Congruence of first metatarsophalangealjoint: two straight lines are drawn representing effective articulating surface of first metatarsal head and effective articular cartilage at base of first proximal phalanx. A, Congruent joint: proximal and distal articulating surfaces are aligned (parallel lines). B, Deviated joint: distal articulating surface is deviated lateral to proximal articulating surface, leaving medial border of proximal surface exposed (lines converge outside joint). C, Subluxed joint: base of proximal phalanx is subluxed laterally with respect to metatarsal head (lines intersect within joint). An incongruous articulation appears to be at significant risk for later metatarsophalangeal decompensation. Fig. 5.-Shape of first metatarsal head. A, Flat head: resists hallux valgus deformity. B, Round head: predisposes to hallux valgus deformity. C, Dome-shaped head with central bulge: exhibits stability postoperatively.
122 KARASICK AND WAPNER AJR:155, July 1990 A B C Fig. 6.-First metatarsal-cuneiform joint orientation. A, Flat or horizontal joint: resists increase in intermetatarsal angle. B, Oblique joint less stable and prone to deformity. c, Round joint: enhances mobility of joint and medial deviation of metatarsal. Fig. 7.-Lateral facet at base of first metatarsal bone: its presence (arrowheads) can mechanically impair successful realignment unless an osteotomy of first metatarsal is performed. Fig. 8.-Large medial eminence: size of this bony outgrowth on medial aspect of first metatarsal head can range from 1 to more than 5 mm in width. Degree of hallux valgus does not necessarily correlate with size of this medial eminence. Fig. 9.-Degenerative joint disease at first metatarsophalangeal joint: degree of joint-space narrowing, osteophytic spurs, and rigidity can determine surgical corrective procedure. Patients with hallux valgus and significant degenerativejoint disease may be treated with arthrodesis.
AJR:155, July 1990 HALLUX VALGUS DEFORMITY 123 Fig. 10.-Severe hallux valgus with pronated hallux and dislocations of second and third metatarsophalangeal joints: with increasing hallux valgus, lateral shift of lesser toes occurs as well as pronation of great toe. This can result in subluxation or dislocation of adjacent metatarsophalangeal joints, especially the second. Fig. I 1.-Crossover second toe doformity: with severe hallux valgus, second toe can overlap great toe, resulting in significant deformity. REFERENCES 10 11 1. Mann RA, Coughlin MJ. Hallux valgus and complications of hallux valgus. In: Mann RA, ed. Surgery of the foot, 5th ed. St. Louis: Mosby, 1986: 65-131 2. LaPorta G, Melillo T, Olinsky D. X-ray evaluation of hallux abducto valgus deformity. J Am Podiatr Med Assoc 1974;64:544-566 3. Spinner SM, Lipsman 5, Spector F. Radiographic criteria in the assessment of hallux abductus deformities. J Foot Surg 1984:23:25-30 4. Smith RW, Reynolds JC, Stewart MJ. Hallux valgus assessment: report of research committee of American Orthopaedic Foot and Ankle Society. Foot Ankle 1984:5:92-102