Calculation of the true first intermetatarsal angle based

Calculation of the true first intermetatarsal angle based on the metatarsus adductus angle and Engel’s angle. Whitney Ellis-Mc. Connell, DPMa, Vanessa Cardenas, DPMa, Kieran T. Mahan, DPMb, and Andrew J. Meyr, DPMc a. Resident, Temple University Hospital Podiatric Surgical Residency Program, Philadelphia, Pennsylvania b. Professor, Department of Surgery, Temple University School of Podiatric Medicine, Philadelphia, Pennsylvania b. Associate Professor and Residency Program Director, Department of Podiatric Surgery, Temple University School of Podiatric Medicine and Temple University Hospital, Philadelphia, Pennsylvania (AJMeyr@gmail. com)* *Please don’t hesitate to contact AJM with any questions/concerns. He’s happy to provide you with a. pdf of this poster if you email him. Statement of Purpose and Literature Review Results Discussion The correction of hallux abductovalgus (HAV) is among the most frequently performed podiatric surgical procedures. Although numerous clinical and radiographic factors are utilized with respect to pre-operative surgical decision making, identification and measurement of the first intermetatarsal angle represents a near universal tenet of determining HAV deformity severity [1 -5]. However, the presence of the metatarsus adductus deformity has a tendency to artificially decrease measurement of the first intermetatarsal angle because of the relative adducted position of the 2 nd metatarsal. For this reason, it is recommended to calculate a “true” first intermetatarsal angle in cases of metatarsus adductus with the following formula [1]: True first intermetatarsal angle = First intermetatarsal angle + metatarsus adductus angle - 15°. Despite this, we have noticed that many people choose to define the presence of metatarsus adductus in clinical practice with Engel’s angle due to its relatively simpler calculation when compared to the metatarsus adductus angle [5]. We are unaware of any investigation which has specifically compared Engel’s angle to the metatarsus adductus angle with respect to the diagnosis of metatarsus adductus or with respect to the calculation of the true first intermetatarsal angle. We measured radiographs from 140 feet, 111 (79. 3%) of which demonstrated evidence of metatarsus adductus based on either the metatarsus adductus angle or Engel’s angle. Metatarsus adductus was identified based on the metatarsus adductus angle alone in 54. 1% of cases, Engel’s angle alone in 7. 2% of cases, and by both measurements in 38. 7% of cases. In the cohort with metatarsus adductus a mean ± standard deviation (range) age of 44. 38 ± 15. 12 (18 -77) years was observed. Twenty two (19. 8%) of the 111 were males and 72 (64. 9%) were right feet. The mean ± standard deviation (range) first intermetatarsal angle was 11. 40 ± 3. 25° (4 -22°), metatarsus adductus angle was 19. 97 ± 5. 15° (9 -41°), and Engel’s angle was 22. 99 ± 4. 38° (10 -37°). The mean ± standard deviation (range) true first intermetatarsal angle calculated based on the metatarsus adductus angle was 16. 37 ± 6. 33° (240°), while calculation based on Engel’s angle_21 was 13. 39° ± 4. 96° (025°), and Engel’s angle_24 was 10. 39° ± 4. 96° (-3 -22°). The difference between calculation of the true first intermetatarsal angle based on the metatarsus adductus angle or either Engel’s angle was found to be statistically significant (p<0. 001). As with any scientific investigation, critical readers are encouraged to review the study design and results and reach their own conclusions, while the following represents our conclusions based on the specific results. As scientists, we also never consider data to be definitive, but do think that these results are worthy of attention and future investigation. The objective of this investigation was to evaluate calculation of the true first intermetatarsal angle based on both the metatarsus adductus angle and Engel’s angle. Methodology Following IRB approval, pre-operative radiographs of consecutive patients undergoing elective reconstruction of the first metatarsalphalangeal joint were evaluated for measurement of the first intermetatarsal angle, metatarsus adductus angle, and Engel’s angle. The first intermetatarsal angle was defined as the resultant angulation between the longitudinal bisection of the first and second metatarsals (Figure 1). Engel’s angle was defined as the resultant angulation between the longitudinal axis of the second metatarsal and longitudinal axis of the intermediate cuneiform (Figure 2). The metatarsus adductus angle was defined as the resultant angulation between the longitudinal axis of the lesser tarsus and the longitudinal axis of the second metatarsal (Figure 3). In cases of associated metatarsus adductus (defined as either a metatarsus adductus angle ≥ 15 degrees and/or an Engel’s angle ≥ 24 degrees), a calculation of the true first intermetatarsal angle was performed based on both the metatarsus adductus angle (first intermetatarsal angle + metatarsus adductus angle – 15 degrees) and Engel’s angle (first intermetatarsal angle + Engel’s angle – 24 degrees). Descriptive statistics of the angular measurements were performed and included the mean, standard deviation and range, in addition to a comparison of the two calculations of the true first intermetatarsal angle with a paired student t-test. Figure 1: First Intermetatarsal Angle The first intermetatarsal angle was defined as the resultant angulation between the longitudinal axis of the first metatarsal and the longitudinal axis of the second metatarsal. Measurements were performed by two researchers (WE and VC) with computerized radiology software which measures to a precision of 0. 1°. Figure 2: Engel’s Angle Engel’s angle was defined as the resultant angulation between the longitudinal axis of the second metatarsal and the longitudinal axis of the intermediate cuneiform [5]. In their original publication, Engel et al found an average measurement of 21° in their cohort and defined an abnormal measurement as one greater than 24°. For this investigation we calculated a measurement of the true first intermetatarsal angle based on Engel’s angle utilizing both 21° and 24°. Figure 3: Metatarsus Adductus Angle The metatarsus adductus angle was defined as the resultant angulation between the longitudinal axis of the lesser tarsus and the longitudinal axis of the second metatarsal [3, 4]. A normal value for this measurement is defined as < 15° with measurements ≥ 15° defined metatarsus adductus. The “true” first intermetatarsal angle is defined as the first intermetatarsal angle + the metatarsus adductus angle - 15°. First Intermetatarsal Angle Metatarsus Adductus Angle Engel’s Angle [Mean ± Standard Deviation (Range)] Descriptive statistics in all cases with metatarsus adductus (N= 111) Calculation of the True First Intermetatarsal Angle 11. 40 ± 3. 25° (4 -22°) 19. 97 ± 5. 15° (9 -41°) 22. 99 ± 4. 38° (10 -37°) 1 st IMA + MAA -15° = 1 st IMA + Engel’s-21° = 16. 37 ± 6. 33° (2 -40°) 13. 39° ± 4. 96° (0 -25°)* 1 st IMA + Engel’s- 24° = 10. 39° ± 4. 96° ( -3 -22°)* *Indicates statistical significance (p<0. 001) when compared to the true IMA calculation based on the MAA with a paired student t-test. -First, results of this investigation demonstrate that the metatarsus adductus angle might be a more sensitive diagnostic measure of underlying metatarsus adductus deformity compared to Engel’s angle in adult patients with pathology of the first metatarsophangeal joint. In our cohort, 54. 1% of patients had an increased metatarsus adductus angle with a normal Engel’s angle. Conversely, only 7. 2% of patients had an increased Engel’s angle with a normal metatarsus adductus angle. 38. 7% of patients demonstrated increases in both measurements. With that being said, however, a limitation of this or any investigation involving radiographic parameters is their definition of normal values. We choose to define metatarsus adductus as a metatarsus adductus angle >15°, but some sources have defined the diagnostic threshold based on this angle as low as 10° or as high as 20° [15]. Utilizing 10° or 20° instead of 15° as a diagnositic threshold would have obviously changed the outcomes of this investigation. In the same way, Engel’s original study found a mean measurement of 21° (which does not necessarily imply “normal”) and did not utilize any quantitative means to define an “abnormal” measurement of 24°. Also of interest, we found little correlation between measurement of the metatarsus adductus angle when plotted against measurement of Engel’s angle (R 2 = 0. 00). -Second, results of this investigation demonstrate that calculation of the true first intermetatarsal angle based on the metatarsus adductus angle resulted in a higher result than calculation of the true first intermetatarsal angle based on Engel’s angle (16. 37° vs. 13. 39°). This finding was both statistically significant (p<0. 0001 with a paired student t-test) and clinically significant as one measurement recorded in the “severe IMA” category and the other in the “moderate IMA” category. This implies that it would be more clinically conservative to calculate the true first intermetatarsal angle based on the metatarsus adductus angle when compared to Engel’s angle. We hope that the results of this investigate add to the body of knowledge with respect to the radiographic evaluation of the forefoot, particularly as it related to the hallux abductovalgus and metatarsus adductus deformities. References [1] Martin DE, Pontious J. Introduction and evaluation of hallux abductovalgus. In Mc. Glamry’s Comprehensive Textbook of Foot and Ankle Surgery, pp 485 -491, edited by AS Banks, MS Downey, DE Martin, SJ Miller, Lippincott, Williams and Wilkins, Philadelphia, 2000. [2] Coughlin MH, Mann RA. Hallux valgus. In Surgery of the Foot and Ankle, pp 183 -362, edited by MJ Coughlin, RA Mann, Mosby Elsevier, Philadelphia, 2007. [3] Sanner WH. Foot segmental relationships and bone morphology. In Foot and Ankle Radiology, pp 272302, edited by RA Christman, Churchill Livingstone, St. Louis, Missouri, 2003. [4] Yu GV, Johng B, Freireich R. Surgical management of metatarsus adductus deformity. Clin Podiatr Med Surg. 1987 Jan; 4(1): 207 -32. [5] Engel E, Erlick N, Krems I. A simplified metatarsus adductus angle. J Am Podiatry Assoc. 1983 Dec; 73(12): 620 -8.