chapter 4:imaging the patellofemoral joint

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Figure 4.1. AP radiograph of the knee. The patella is well seen, but its functional relationship to the remainder of the knee cannot be assessed. Rotation can introduce considerable artifact. Tension on the quadriceps will also change its position compared with the resting position. Factors concerning patellofemoral function such as varus or valgus can be assessed. PW, patella width; PH, patella height; CW, condylar width; CH, condylar height. Tibial plateau dimensions and tibial spine dimensions and relationships can also be assessed.

Figure 4.2. Lateral radiograph of the knee.

Figure 4.3. A, Normal alignment; B, lateral facet line and central ridge overlap; C, gross subluxation of patella. Illustrations courtesy of JY Dupont, Quimper, France.

Figure 4.3. Continued.

Figure 4.4. Lateral view of the patellofemoral joint, posterior condyles overlapped. Small arrow denotes central trochlea, large arrow shows medial condyle, and open arrow shows a shallow dysplastic lateral condyle (note that the proximal edge of the lateral condyle line crosses the central trochlea [star] as described by Dejour et al [7]). Illustrations courtesy of JY Dupont, Quimper, France.

Figure 4.5. Lateral radiograph of the knee in 30 degrees of flexion. Blumensaat's line (BL) is marked. The method of Insall and Salvati comparing patellar length (LP) and patellar tendon (LT) is perhaps less accurate than other alternative measurements when evaluating the patellofemoral articular relationship.

Figure 4.6. A, The morphology ratio described by Grelsamer relates the length of patella articular surface to the overall patella length. B to D, patella types as determined using Grelsamer's morphology ratio. Reprinted with permission from Grelsamer RP, Proctor CS, Bazos AN. Evaluation of patellar shape in the sagittal plane. A clinical analysis. Am J Sports Med 1994;22(1):61‑66.

Figure 4.6. Continued.

Figure 4.7. The Blackburne and Peel index has also been described by Caton. This illustration demonstrates the importance of considering articular length in evaluating patellar height. Reprinted with permission from Caton J, Deschamps G, Chambat P, Lerat JL, Dejour H. Les Rotules Basses. A Propos de 128 Observations. Rev Chir Orthop 1982; 68:317‑325.

Figure 4.8. A, Bernageau pointed out the impor­tance of describing the patella articular surface as it relates to the proximal, central trochlea. B, Patella in­fera. C, Patella alta.

Figure 4.9. A, Some techniques for obtaining axial patellofemoral radiographs. B‑D, Comparison of three techniques on the same knee shows the variation of images caused by position (B and D) and distortion (C).

Figure 4.10. The Laurin 20‑degree tangential view is difficult to obtain but will provide useful information.

Figure 4.11. The lateral patellofemoral angle of Laurin should open laterally (L). This measurement is help­ful in screening patients for patellar tilt.

Figure 4.12. Functional relationship. TO, neutral reference line bisecting angle E'TI'. RT, line connecting median ridge to trochlear depth. Adapted from Merchant AC, Mercer R L, Jacobsen RH, Cool, CR. Roentgenographic analysis of patello‑femoral congruence. J Bone Joint Surg 1974;56A:1391‑1396.

Figure 4.13. Normal patellofemoral indices.

Figure 4.14. This CT image demonstrates the precision possible with tomographic slices centered on the mid­transverse patella. Because there is no image overlap, a true picture of patellofemoral congruity is possible.

Figure 4.15. The posterior femoral condyles of this CT image are anatomically very consistent and provide a reliable reference plane for evaluating patellar tilt. The angle formed by the lateral facet and posterior condyle lines is the patellar tilt angle.

Figure 4.16. When the anterior trochlear line is used to determine tilt, there is a much greater chance of inaccuracy. Reprinted with permission from Fulkerson JP, Schutzer SF, Ramsby GR, Bernstein RA. Computerized tomography of the patellofemoral joint before and after lateral release or realignment. Arthroscopy 1987;3(1):19‑24.

Figure 4.17. Malalignment patterns determined by CT. It is most important to recognize that tilt may occur with or without subluxation. Reprinted with permission from Schutzer S F, Ramsby G R, Fulkerson JP. Computed tomographic classification of patellofemoral pain patients. Orthop Clin North Am 1986;17(2): 235‑248.

Figure 4.18. There are many patellofemoral pain patients whose patellae are relatively subluxated when compared with controls. Reprinted with permission from Schutzer SF, Ramsby GR, Fulkerson JP. Computed tomographic classification of patellofemoral pain patients. Orthop Clin North Am 1986;17(2):235‑248.

Figure 4. I 9. Note that patellar tilt tends to be somewhat progressive in patellofemoral pain patients. Reprinted with permission from Schutzer SF, Ramsby GR, Fulkerson JP. Computed tomographic classification of patellofemoral pain patients. Orthop Clin North Am 1986;17(2):235‑248.

Figure 4.20. A high‑quality tomographic study of the patellofemoral joint should include adequate delineation of the femoral sulcus and posterior condyles, and must be centered on the midtransverse patella.

Figure 4.21. A and B, The posterior femoral condyles provide a reliable reference plane for evaluating patellar tilt.

Figure 4.22. A, The patellar tilt angle is more reliable when determined in this manner. The anatomy of the anterior femoral trochlea changes considerably as the patella moves through flexion, but the posterior condyles provide a stable reference line. B, This CT image demonstrates a normal patellar tilt angle (PTA) at 20 degrees of knee flexion (PTA = 18 degrees).

Figure 4.24. A, A line drawn to the tip of the patella (point R) forms line F. B, This CT image demonstrates a normal (≤0) CT congruence angle at 20 degrees of knee flexion.

Figure 4.25. The congruence angle (α) is used to evaluate subluxation of the patella. If α is medial to line E, it is negative. If a is lateral to line E, it is positive.

Figure 4.26. A, Good quality arthrogram showing the joint line well delineated. B, The radiograph beam has been angled 5 degrees differently from A (same knee), showing that precision is necessary in order to have an interpretable arthrogram.

Figure 4.27. Axial view of a 3‑year‑old child. The patella is not visible, but the trochlear sulcus is seen in the femoral ossific nucleus.

Figure 4.28. Axial view of a 6‑year‑old child in which the patella ossific nucleus is seen to be well centered in the cartilaginous anlage.

Figure 4.29. Axial view of an 11‑year‑old in which the adult patella form is evident, although the joint line is still considerably thicker than it eventually will be.

Figure 4.30. Magnetic resonance provides the advantage of soft tissue and cartilage imaging. This is particularly beneficial when evaluating articular cartilage of the patella or trochlea.

Figure 4.31. These magnetic reso­nance images of the peripatellar quadriceps muscle demonstrate a he­mangioma (later removed) that had caused resistant anterior knee pain. Photos courtesy of John Elliott., Westerly, Rhode Island.

Figure 4.32. Technetium 99m radionuclide scan will detect significant intraosseous remodeling of patellar or trochlear bone in response to injury, excessive pressure, or arthrosis. Scan courtesy of Scott Dye, San Francisco, California.

Figure 4.33. Three‑dimensional reconstruction of the patellofemoral joint using computerized tomography may be particularly helpful in difficult cases involving fracture, dysplasia, or deformity.


        

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