Alphabet Soup of Limb Alignment (Frontal Plane) - Philip McClure, MD — Transcript

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1. 0:08welcome to alphabet soup of limb
2. 0:10alignment in the frontal plane
3. 0:13our objectives here are to define the
4. 0:14normal angles in the frontal plane
5. 0:17and an overview of how to draw lower
6. 0:19extremity axes and angles
7. 0:21to be used throughout the course
8. 0:25first of all normal limb alignment is
9. 0:28defined as collinearity of the hip
10. 0:30knee and ankles the mechanical axis
11. 0:34should fall through the center third of
12. 0:36the knee
13. 0:38the mechanical axis line is a straight
14. 0:40line connecting the center of two joints
15. 0:43there's a mechanical axis line of the
16. 0:45entire lower extremity as shown here
17. 0:48of just the femur and of just the tibia
18. 0:55there are also anatomic axis lines
19. 0:58there is no anatomic axis line of the
20. 1:00entire lower extremity
21. 1:02however there is one of just the femur
22. 1:04and just the tibia
23. 1:05as shown here the anatomic axis line is
24. 1:10defined
25. 1:11as a mid diaphyseal line through the
26. 1:13intramedullary canal of the bone
27. 1:18anatomic and mechanical axis lines can
28. 1:21both be used in planning
29. 1:23the anatomic and mechanical axis of the
30. 1:25femur are very different
31. 1:27while the anatomic and mechanical axis
32. 1:29of the tibia are very similar
33. 1:31we'll review this in more detail in the
34. 1:34femur
35. 1:35there's an angle known as the anatomic
36. 1:36mechanical axis angle
37. 1:39where we describe the relationship
38. 1:40between the anatomic and mechanical axes
39. 1:42of this bone segment the mechanical axis
40. 1:46of the femur goes from the center of the
41. 1:47hip joint
42. 1:48the center of the femoral head to the
43. 1:50center of the knee joint
44. 1:52splitting the condyles the anatomic axis
45. 1:56is defined as a mid diaphyseal line
46. 2:00halfway between outer cortices along the
47. 2:03axis of the bone
48. 2:05the normal anatomic mechanical axis
49. 2:07angle
50. 2:08is seven degrees and it varies between
51. 2:10five and nine degrees depending on
52. 2:12stature and several other variables
53. 2:16typically the anatomic axis of the femur
54. 2:19crosses knee joint about a centimeter
55. 2:22medial to the mechanical axis of the
56. 2:23femur
57. 2:24just off the medial femoral condyle
58. 2:30for the tibia the mechanical anatomic
59. 2:32axes are parallel
60. 2:34therefore there is no anatomic
61. 2:36mechanical angle for the tibia
62. 2:39to return the mechanical axis of the
63. 2:41entire lower extremity
64. 2:42just a reminder through the center of
65. 2:44the femoral head down to the center of
66. 2:46the ankle joint
67. 2:49in the normal limb this line passes
68. 2:52within
69. 2:52three to four millimeters of the center
70. 2:54of the knee joint
71. 2:58on average this is slightly medial to
72. 3:00the center
73. 3:01in asymptomatic patients
74. 3:06the mechanical axis is termed deviated
75. 3:08if it passes outside of the normal zone
76. 3:11valgus is present if the mechanical axis
77. 3:14passes lateral to the knee joint if the
78. 3:18mechanical axis passes medial to the
79. 3:20center of the knee then a varus
80. 3:21deformity is present
81. 3:24there are various ways of quantifying
82. 3:26this but in this course we use
83. 3:28mechanical axis deviation
84. 3:30as the primary means all of these angles
85. 3:33help to be more specific when describing
86. 3:36lower extremity
87. 3:37malalignment and the strict use of them
88. 3:40and restoration of their normal values
89. 3:42will create normal alignment as well as
90. 3:45eliminating joint line obliquity
91. 3:48these angles account for the shape of
92. 3:51the femur and tibia
93. 3:53as well as joint alignment at the hip
94. 3:54knee and angle
95. 3:57the joint line is aligned to represent
96. 3:59the orientation of the joint in space
97. 4:01for the proximal femur it goes from the
98. 4:04center of the femoral head
99. 4:05to the tip of the greater trochanter for
100. 4:07the distal femur
101. 4:08it touches the medial and lateral
102. 4:10condyles
103. 4:11for the proximal tibia a line
104. 4:13approximating the plateau
105. 4:15defines the joint line at the knee in
106. 4:18the distal tibia a line
107. 4:20approximating the plafon defines the
108. 4:22ankle joint line
109. 4:26when this joint line intersects with an
110. 4:28axis line
111. 4:29we create a joint line angle
112. 4:35we will go through the nomenclature as
113. 4:38well as naming conventions
114. 4:40shortly
115. 4:43the joint angle defines the position of
116. 4:44the joint relative to the axis of the
117. 4:46bone segment
118. 4:49you'll be hearing this a lot from us
119. 4:50analyzing the joined angles
120. 4:53is the primary means of evaluating a
121. 4:55deformity
122. 4:57to define the mechanical joint angles of
123. 4:59the femur we draw the mechanical axis of
124. 5:01the femur
125. 5:02and the joint lines of the proximal and
126. 5:03distal femur
127. 5:05to define the joint lines of the tibia
128. 5:07we draw the mechanical axis of the tibia
129. 5:13and the joint lines of the tibia both
130. 5:16approximately endlessly
131. 5:19the joint line convergence angle of the
132. 5:21knee is defined as the angle between the
133. 5:23distal femoral joint line
134. 5:25and the proximal tibial joint line to be
135. 5:27within normal limits
136. 5:28it needs to be less than two degrees
137. 5:33abnormalities in the joint line
138. 5:34congruency angle indicate soft tissue
139. 5:36laxity
140. 5:37which can be a complicating factor in
141. 5:39correcting lower extremity alignment
142. 5:45we'll now review the angle nomenclature
143. 5:48while you could choose any angle there
144. 5:51is a convention that's been established
145. 5:53over the last several decades
146. 5:55since the initial publishing of their
147. 5:56description
148. 6:00the first letter will be an a or an m
149. 6:03indicating anatomic
150. 6:04or mechanical angles
151. 6:07the second letter indicates whether it's
152. 6:10a medial or a lateral angle
153. 6:14the third letter gives you orientation
154. 6:16in space
155. 6:17of proximal or distal
156. 6:22the fourth letter defines the bone
157. 6:24segment
158. 6:26and a means angle
159. 6:30therefore the mldta is the mechanical
160. 6:33lateral distal tibial angle
161. 6:37and the aldta is the anatomic lateral
162. 6:40distal tibial angle
163. 6:41however since the tibial axes are
164. 6:43parallel we will often drop
165. 6:45the a and the m when we're describing
166. 6:47the tibia
167. 6:49the mechanical medial proximal tibial
168. 6:51angle or more commonly called
169. 6:52medial proximal tibial angle is known as
170. 6:54the mpta
171. 7:01the mechanical lateral distal femoral
172. 7:03angle or mldfa
173. 7:05averages 87 degrees and
174. 7:08is different the anatomic lateral distal
175. 7:11femoral angle
176. 7:12which averages 81 degrees we need to be
177. 7:14very careful when analyzing the femur
178. 7:17whether we're using anatomic or
179. 7:19mechanical axis planning
180. 7:20we will review this multiple times
181. 7:22throughout the course
182. 7:25the mechanical lateral proximal femoral
183. 7:28angle
184. 7:28is 90 degrees with a range of 85 to 95
185. 7:31the anatomic medial proximal femoral
186. 7:34angle is 84 degrees
187. 7:35with an average of 80 to 89 degrees the
188. 7:38decision was made
189. 7:39that the average angle would always be
190. 7:41less than 90 hence the choice of medial
191. 7:43versus lateral for these two angles
192. 7:48it may be worthwhile to take a screen
193. 7:50capture of this image
194. 7:51to keep next to you throughout the
195. 7:52course as it will help you maintain
196. 7:54a reference for normal angles as we
197. 7:56review deformity analysis
198. 7:59thank you