Surg Radiol Anat DOI 10.1007/s00276-013-1220-3
ORIGINAL ARTICLE
Bony palmar ridges of the phalanges of the human fingers Jie Meng • Inneke Willekens • Erik Cattrysse • Evie Vereecke • Caroline Geers • Toon Van Cauteren Johan de Mey • Michel De Maeseneer
•
Received: 17 April 2013 / Accepted: 26 September 2013 Springer-Verlag France 2013
Abstract Purpose On imaging studies, bony ridges can be seen at the palmar aspect of the phalanges of the fingers. Our purpose was to address the following: (1) which structures insert on to the ridges and what is the histological appearance? (2) Is there a difference between the different fingers? (3) Is there a correlation between the ridges and age? Materials and methods Two observers retrospectively evaluated 270 radiographs (135 men; 135 women; mean age 44 years), and 33 CT scans (22 men; 11 women; mean age 46 years). Three cadaveric hands were also studied.
J. Meng I. Willekens T. Van Cauteren J. de Mey M. De Maeseneer (&) Department of Radiology, University Hospital Free University Brussels, UZ Brussel, Laarbeeklaan 101, 1090 Jette, Belgium e-mail: [email protected] Present Address: J. Meng Department of Ultrasonic Diagnosis, The Second Clinical Hospital of Jilin University, Changchun, Jilin, China E. Cattrysse Department of Experimental Anatomy, Vrije Universiteit Brussel, Brussels, Belgium E. Vereecke Department of Anatomy, KULAK-Catholic University Leuven-Campus Kortrijk, Kortrijk, Belgium C. Geers Department of Pathology, University Hospital Free University Brussels, Jette, Belgium M. De Maeseneer Department of Experimental Anatomy, Free University Brussels, Jette, Belgium
The ridges were graded using a 4-point scale. A Chi-square test was used to compare the different fingers (p \ 0.05) and to study the prominence of the ridges in relation to age (p \ 0.05). Results On histology with routine stains the A2 pulley was inserted on the ridges of the proximal phalanx, and the flexor superficialis and A4 pulley on the ridges of the middle phalanx. On histology, the insertion showed a transition zone consisting of fibrocartilage. The prominence of the ridges was significantly different between fingers with III and IV categorized higher than II and III. There was a significant correlation with age for all fingers except for the middle phalanx of II and III. Conclusion The bony palmar ridges have characteristics of enthesophytes. They correspond to the insertion site of the A2 pulley, and the flexor superficialis tendon and A4 pulley, at the proximal and middle phalanx, respectively. The ridges become more prominent with age, and their prominence is different between the fingers with III and IV categorized higher than II and V. Keywords Hand radiography CT Hand enthesophytes Finger pulley Flexor digitorum superficialis tendon Normal variants
Introduction Bony excrescences can be observed in various bones and typically correspond to the normal insertion site of tendons and muscles [1–3, 10, 13]. They may also be caused by excessive traction of muscles, tendons, and ligaments. Prominent excrescences are also encountered in various bone diseases such as seronegative arthritis, DISH (diffuse idiopathic skeletal hyperostosis), certain medications, and
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occasionally in hypoparathyroidism [10]. The excrescences are an important element in the imaging diagnosis of these disorders. Osteophytes also present as excrescences but they are usually located at the margins of damaged cartilage. Osteophytes typically occur in osteoarthritis. It is debated whether enthesophytes also occur more frequently in this disorder [9, 12]. Ridges are evident on the palmar aspect of the proximal and middle phalanges of the fingers. They were mentioned in the anatomical work of Testut [8]. These authors considered that the ridges of the proximal phalanx corresponded to the insertion of the synovial sheath, and the ridges of the middle phalanx to the insertions of the flexor superficialis tendons. To our knowledge, the ridges have not been addressed in detail in the radiological literature. In our clinical practice, we observed that the prominence of these ridges is quite variable from patient to patient, and we have not observed them on imaging studies of children. When prominent the ridges could potentially be misinterpreted as a pathological bony proliferation [10]. As is the case with other bony excrescences it remains to be investigated whether these ridges could become more prominent in certain disease processes. We decided to undertake a study to address the following questions: (1) Which structures precisely insert onto the ridges and what is the histological appearance of the insertion site? (2) Is there a difference of the prominence of the ridges between the different fingers? (3) Is there a correlation between prominence of the ridges and age?
Materials and methods Radiography and CT study The IRB of our hospital approved a retrospective analysis of radiographs and CT scans of the hand, as well as an anatomical study in cadaver specimens. We retrospectively reviewed hand radiographs of 270 randomly selected patients (135 men; 135 women; mean age 44 years). The geographic origin of the patients was variable and included European and North African ethnicities. Oblique radiographs, obtained on a state of the art system (Definium 8000, GE Health Care, Milwaukee, WI, USA), were analyzed as they best showed the radial ridges. Two radiologists by consensus scored the phalanges using a 4-point grading scale. The grading scale used is shown in Table 1. We also evaluated 33 CT scans of the hand obtained on a state of the art scanner (Definition 750HD, GE Health Care, Milwaukee, WI, USA) and available on our PACS. The ridges were graded on CT scans using the same grading scale (as for the radiographs) and also in
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Table 1 Gradings of ridges Grade 1
Absent
Grade 2
Subtle (maximal thickness \0.5 mm)
Grade 3
Moderate (maximal thickness 0.5–1.5 mm)
Grade 4
Prominent (maximal thickness [1.5 mm)
consensus by 2 radiologists (22 men; 11 women; mean age 46 years). On CT images 133 ulnar ridges and 125 radial ridges were evaluated for the proximal phalanx, and 88 ulnar and radial ridges for the middle phalanx. The number of ulnar and radial ridges, and proximal and distal phalanges analyzed on CT differed because interpretation was not possible in some instances due to obliquity of the section or traumatic lesions in the region of interest. Anatomic–histologic study Three cadaveric hands were obtained from the department of anatomy. The donors had approved the use of their bodies for scientific purposes. The age at death and cause of death of the donors were not known. The palmar aspect of fingers of 1 cadaveric hand was dissected. The soft tissue structures at the palmar side of the proximal and middle phalanx of the fingers were studied macroscopically. We performed transverse slicing with a bandsaw of the fingers of 2 deep frozen hands (1 left, 1 right). The sections were 4-mm thick. They were photographed and examined by two investigators. Slices obtained at the level of the 4th finger (2 proximal phalanxes, 2 middle phalanxes) were selected for histological analysis. These slices were thawed and preserved in formaldehyde. They were decalcified for 36 h and histologic sections were then obtained with a microtome using standardized histological technique. The sections were mounted and stained with HES (hematoxylin eosin) using routine histological technique. They were examined by an experienced anatomopathologist (CG) and photographs were made without magnification, and with magnification 2.59 and 109. Statistical analysis A Chi-square or Fisher exact test was used to compare the contingency tables obtained for the ridges at the different fingers, for the proximal and middle phalanges, as well as to assess differences with age. A significance threshold of p \ 0.05 was used. A Chi-square test was also used to assess whether there was a difference between the ulnar and radial ridges on CT. Statistical analysis was performed using IBM SPSS Statistics 20.
Surg Radiol Anat
Fig. 1 Radiographs showing grades 1–4 for the proximal phalanx (arrows). a Left 4th finger in 11-year-old boy, b right 3rd finger in 53-year-old woman, c left 4th finger in 62-year-old man, d left 4th finger in 75-year-old man
Fig. 2 Radiographs showing grades 1–4 for the middle phalanx (arrows). a Left 4th finger in 11-year-old boy, b left 4th finger in 62-year-old man, c right 4th finger in 46-year-old man, d right 3rd finger in 84-year-old man
Results Radiography and CT study On imaging studies the ridges of the proximal phalanx were located at the proximal and mid diaphysis, and the ridges of the middle phalanx at the transition zone between proximal and mid diaphysis (Figs. 1, 2, 3). The gradings for radiography at the different fingers are shown in Table 2. There was a statistically significant difference between ridges at the proximal phalanx for all fingers with III and IV categorized higher than II and V, on radiography. The gradings for CT are shown in Table 3. On CT, only the ridges at the 4th finger were more prominent than the other fingers. The same trend could be observed on CT as on radiography with III and IV being more prominent than II and V. For the middle phalanx, on radiography, the ridges were also significantly different between all fingers, with III and IV categorized higher than II and III. There
were no statistically significant differences on CT, but the ridges at III and IV were also larger than at II and V. The gradings relative to age are shown in Table 4. There was a statistically significant correlation with age for all the ridges except for the 2nd and 3rd middle phalanx (p \ 0.05). For these middle phalanges a trend of increasing prominence with age could still be observed. There was no statistically significant difference between the radial and ulnar ridges, on CT, at a significance threshold of p \ 0.05 (Table 5). Anatomic–histologic study On dissection of the fingers, the soft tissues attaching to the ulnar and radial aspects of the midshaft of the diaphysis of the proximal phalanges corresponded to the A2 pulley. At the level of the middle phalanx, the flexor superficialis tendons and A4 pulleys were seen to insert on to the ridges.
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Surg Radiol Anat Table 3 Mean gradings on CT of the ridges for the proximal (P) and middle phalanx (M)
P II
1.16
P III
1.32
P IV
2.17
PV M II
0.84 0.92
M III
1.14
M IV
1.07
MV
0.84
evident. Hence, the findings were similar to those seen in enthesophytes.
Discussion
Fig. 3 CT images at the proximal phalanx (a), middle phalanx (b) and volume rendering of the entire 4th finger (c) in 53-year-old man. a Ridges at the proximal phalanx (arrows). b Ridges at the middle phalanx (arrows). In c the ridges at the proximal phalanx (thick arrows), and middle phalanx (arrows) can be seen. Also note subluxation at the PIP joint, the reason why this patient underwent imaging Table 2 Mean scores for proximal and middle phalanges for different fingers in different age groups IIp
IIm
IIIp
IIIm
IVp
IVm
Vp
Vm
0–9
0.00
0.00
0.17
0.00
0.20
0.00
0.00
0.00
10–19
0.00
0.03
0.07
0.27
0.03
0.17
0.00
0.03
20–29
0.13
0.10
0.37
0.77
0.43
0.47
0.00
0.03
30–39 40–49
0.13 0.10
0.10 0.00
0.50 0.63
0.50 0.30
0.60 0.90
0.67 0.31
0.00 0.17
0.00 0.03
50–59
0.30
0.00
0.73
0.28
0.97
0.43
0.23
0.17
60–69
0.43
0.07
1.03
0.45
1.28
0.41
0.27
0.23
70–79
0.47
0.41
1.27
1.00
1.75
1.13
0.53
0.60
80–89
0.60
0.55
1.10
1.43
1.43
1.33
0.60
1.10
IIp proximal phalanx of 2nd finger, IIm middle phalanx of 2nd finger, IIIp proximal phalanx of 3rd finger, IIIm middle phalanx of 3rd finger, IVp proximal phalanx of 4th finger, IVm middle phalanx of 4th finger, Vp proximal phalanx of 5th finger, Vm middle phalanx of 5th finger, 0–9, …, 80–89 age groups
On histological investigation of sections, bony ridges were clearly seen at both sides of the palmar aspect of the phalanx. At the proximal phalanx the A2 pulley was inserted on the ridges (Fig. 4). Histological investigation of the middle phalanx also showed ridges, and both slips of the flexor superficialis tendon were shown to insert on the mid and central aspect of the ridges, whereas the A4 pulley was seen to insert on the external aspect of the ridges (Fig. 5). At histology, a transition zone between ligament and tendon, and bone consisting of fibrocartilage was
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The palmar bony ridges are mentioned in the work of Testut [14]. These authors suggest that the synovial sheath attaches to the ridges at the proximal phalanx, and the flexor superficialis tendons to the ridges at the middle phalanx. In Gray’s anatomy the ridges are mentioned at the middle phalanx but it is not specifically addressed what inserts on them [15]. Keats [10] mentions the ridges, as a pitfall on radiographs, and suggests they correspond to variants occurring at muscle insertion sites. Excrescences are known to arise on bony surfaces due to traction of tendons and muscles. In our clinical practice, we noticed that the prominence of the palmar ridges was variable from patient to patient, and we did not seem to observe them in pediatric patients. We studied the prominence of the ridges at the level of the different fingers. We found that the prominence of the ridges was different between the fingers, being most prominent at the 3rd and 4th fingers. For the 3rd finger, this prominence is in accordance with the greater strength exerted by the flexor digitorum superficialis tendon at this level [11]. For the other fingers, correlation with flexor digitorum superficialis strength is less clear [11]. Little is known about the lifetime prevalence or age of appearance of the bony ridges. To our knowledge, only a recent investigation by Kalichman et al. [9] addressed this aspect and found that the palmar ridges become more prominent with age. We also showed that the ridges become more prominent with age, and hence, our findings are in accordance with this report. These authors further found that the correlation was higher in men than in women, and that a genetic factor may be involved. In our study, we did not address differences between men and women. We did confirm our subjective clinical observation that the ridges seemed to be absent in pediatric patients. In this study, we did not correlate the prominence of the ridges with the severity of osteoarthritis. Bony
Surg Radiol Anat Table 4 Mean scores for proximal and middle phalanx in 9 age groups and statistics 0–9
10–19
20–29
30–39
40–49
50–59
60–69
70–79
[80
p
R
IIp
0
0
0.13
0.13
0.10
0.30
0.43
0.47
0.60
0.01
0.41
IIIp
0.17
0.07
0.37
0.50
0.63
0.73
1.03
1.27
1.10
0
0.50
IVp
0.20
0.03
0.43
0.60
0.90
0.97
1.28
1.75
1.43
0.003
0.55
Vp
0
0
0
0
0.17
0.23
0.27
0.53
0.60
0
0.41
IIm
0
0.03
0.10
0.10
0
0
0.07
0.41
0.55
0.48
0.29
IIIm
0
0.27
0.77
0.50
0.30
0.28
0.45
1.00
1.43
0.31
0.38
IVm
0
0.17
0.47
0.67
0.31
0.43
0.41
1.13
1.33
0
0.45
Vm
0
0.03
0.03
0
0.03
0.17
0.23
0.60
1.10
0.01
0.47
IIp proximal phalanx of 2nd finger, IIm middle phalanx of 2nd finger, IIIp proximal phalanx of 3rd finger, IIIm middle phalanx of 3rd finger, IVp proximal phalanx of 4th finger, IVm middle phalanx of 4th finger, Vp proximal phalanx of 5th finger, Vm middle phalanx of 5th finger, 0–9, …, 80–89 age groups, p p value
Table 5 Comparison of radial and ulnar ridges, on CT (n = 33), p value \ 0.05 Proximal
Middle
Phalanx II
0.94
0.51
Phalanx III Phalanx IV
0.59 0.69
0.87 1
Phalanx V
0.76
1
Prominence of radial and ulnar ridges at the proximal and middle phalanx (p values)
excrescences are often associated with osteoarthritis. For example, an increase in size of the medial and lateral intercondylar tubercles is typical in osteoarthritis [10]. Kalichman et al. [9] in their study found a correlation between the ridges and osteoarthritis. Other researchers also have suggested that osteophytes and enthesophytes occur
Fig. 4 Anatomic slice (a) and histologic study of proximal phalanx without magnification (b), with magnification 92.5 (c) and 910 (d). a The A2 pulley (bold arrows) is seen to insert on the ridges (arrows). T flexor tendons. b Ridge (arrow, R) and A2 pulley (arrow). c Ridge
simultaneously in persons sometimes designated as ‘bone formers’. The pulleys of the fingers consist of annular and cruciform pulleys [4, 5]. Only the annular pulleys are clearly visible on dissection as 5 strong band-like structures. The pulleys keep the tendons in proximity to the bone with finger flexion. The most important pulleys are the A2 and A4 pulleys at the level of the proximal and middle phalanx, respectively [6, 8]. In our anatomic–histologic study, we found that the structure attaching at the proximal phalanx corresponded to the A2 pulley. This is similar to the suggestion by Testut [14] that the synovial sheath inserts in this location. We showed that the soft tissue structures inserting at the middle phalanx consist of the flexor superficialis tendon at the mid and central aspect of the ridge, and the A4 pulley at the external aspect of the ridge. The flexor superficialis tendon insertion takes up the major part of the ridge.
(R, arrows), tendon (T) and A2 pulley (arrow, A2). d Collagen bundles c containing small rounded cells adjacent to the ridge (arrows)
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Fig. 5 Histologic study of middle phalanx without magnification (a), and with magnification 92.5 (b). a Ridges (thick arrows), A4 pulley (arrows), and flexor superficialis tendons (FS). b Ridge (thick arrow), A4 pulley (arrow), and flexor superficialis tendon (FS)
The ridges are excrescences with characteristic similar to enthesophytes, and should not alarm the radiologist. Nevertheless, further studies could address whether in diseases that affect entheses, such as for example the seronegative rheumatoid disorders, imaging abnormalities can be seen at the level of these ridges. On imaging studies, the ridges also should not be interpreted erroneously as abnormal (periosteal) bony proliferation, but as a ‘normal’ bony excrescence related to the attachment of soft tissue structures. Further studies could also address whether the ridges can be used in the determination of bone age, and thus would have potential medicolegal, forensic, and paleopathological applications [5, 7]. Although not studied in this investigation, we have noticed in our practice that the ridges are useful bony landmarks for the identification of the insertion site on ultrasound and CT of the A2 pulley and especially the flexor superficialis tendons, which may otherwise be difficult. We acknowledge that our study has limitations. The ridges were evaluated on oblique radiographs because this shows the ridges best. Although all radiographs were obtained in our hospital using standardized positioning, it is
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possible that the obliquity of the radiographs varied slightly and this influenced the radiographic appearance of the ridges. On radiography, only the radial ridges could be evaluated. On CT, however, we showed that there was no statistically significant difference between the radial and ulnar ridges. In addition, the CT parameters were not standardized. However, routine technique on a state of the art CT scanner was used in all studies. The size of the ridges on radiographs may be different from the real size due to projection technique. We did not stratify patients in a group with manual labor or sports related stress on the hands, and a group without such activities. Thus, we could not assess the influence of this factor on the prominence of the ridges. The number of anatomical specimens is limited, and we acknowledge that our anatomical and histological findings would benefit from further study. In conclusion, we found that the bony ridges at the proximal phalanx correspond to the insertion site of the A2 pulley, and those at the middle phalanx to the insertion site of the flexor superficialis tendon and A4 pulley. The ridges become more prominent with age, and they are different between the fingers being most prominent at the 3rd and 4th finger. The ridges are not typically seen in pediatric patients. Taking into account the age of the patient, the ridges are thus a normal finding. Since we showed that the ridges are similar to enthesophytes, further studies could address whether the ridges show imaging abnormalities in specific diseases affecting the enthesis. Acknowledgments We would like to thank Erik Cattrysse, PhD, Aldo Scafoglieri, PhD, Faes Kerkhof, MD, Maryam Shahabpour, MD, Rita Bosschaert, Dirk Blommaert, and Jo De Neef. Conflict of interest None of the authors of this work has a conflict of interest or financial relation to disclose.
References 1. Abreu MR, Chung CB, Mendes L, Mohana-Borges A, Trudell D, Resnick D (2003) Plantar calcaneal enthesophytes: new observations regarding sites of origin based on radiographic, MR imaging, anatomic, and paleopathologic analysis. Skeletal Radiol 32:13–21 2. Benjamin M, McGonagle D (2009) Entheses: tendon and ligament attachment sites. Scand J Med Sci Sports 19:520–527 3. Benjamin M, Rufai A, Ralphs JR (2000) The mechanism of formation of bony spurs (enthesophytes) in the achilles tendon. Arthritis Rheum 43:576–583 4. Boutry N, Titecat M, Demondion X, Glaude E, Fontaine C, Cotton A (2005) High frequency ultrasonographic examination of the finger pulley system. J Ultrasound Med 24:1333–1339 5. Doyle JR (1989) Anatomy of the flexor tendon sheath and pulley system: a current review. J Hand Surg Am 14:349–351 6. Guntern D, Goncalves-Matoso V, Gray A, Picht C, Schnyder P, Theumann N (2007) Finger A2 pulley lesions in rock climbers:
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detection and characterization with magnetic resonance imaging at 3 Tesla—initial results. Invest Radiol 242:435–441 Halle-Selassle Y (2001) Late Miocene hominids from the middle Awash, Ethiopia. Nature 412:178–181 Hauger O, Chung CB, Lektrakul N, Botte MJ, Trudell D, Boutin RD, Resnick D (2000) Pulley system in the fingers: normal anatomy and simulated lesions in cadavers at MR imaging, CT, and US with and without contrast material distension of the tendon sheath. Radiology 217:201–212 Kalichman L, Malkin I, Kobyliansky E (2007) Hand bone midshaft enthesophytes: the influence of ages, sex, and heritability. Osteoarthritis Cartilage 15:1113–1119 Keats TE (1995) Plain film radiography: sources of diagnostic errors. In: Resnick D (ed) Diagnosis of bone and joint disorders, 3rd edn. Saunders, Philadelphia, p 49
11. Ketchum L, Brand P, Thompson D (1978) The determination of moments for extension of the wrist generated by muscles of the forearm. Hand Surg 3:205–210 12. Rogers J, Shepstone L, Dieppe P (1997) Bone formers: osteophyte and enthesophyte formation are positively associated. Ann Rheum Dis 56:85–90 13. Shaibani A, Workman R, Rothschild BM (1993) The significance of enthesopathy as a skeletal phenomenon. Clin Exp Rheumatol 11:399–403 14. Testut L (1921) Osteologie-Arthrologie-Myologie. In: Testut L (ed) Taite d’anatomie humaine, 7th edn. G Doin & Cie, Paris, pp 307–308 15. Williams PL (1995) Skeletal system. In: Gray’s Anatomy, 38th edn. Churchill Livingstone, Edinburgh, pp 657–658
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ORIGINAL ARTICLE
Bony palmar ridges of the phalanges of the human fingers Jie Meng • Inneke Willekens • Erik Cattrysse • Evie Vereecke • Caroline Geers • Toon Van Cauteren Johan de Mey • Michel De Maeseneer
•
Received: 17 April 2013 / Accepted: 26 September 2013 Springer-Verlag France 2013
Abstract Purpose On imaging studies, bony ridges can be seen at the palmar aspect of the phalanges of the fingers. Our purpose was to address the following: (1) which structures insert on to the ridges and what is the histological appearance? (2) Is there a difference between the different fingers? (3) Is there a correlation between the ridges and age? Materials and methods Two observers retrospectively evaluated 270 radiographs (135 men; 135 women; mean age 44 years), and 33 CT scans (22 men; 11 women; mean age 46 years). Three cadaveric hands were also studied.
J. Meng I. Willekens T. Van Cauteren J. de Mey M. De Maeseneer (&) Department of Radiology, University Hospital Free University Brussels, UZ Brussel, Laarbeeklaan 101, 1090 Jette, Belgium e-mail: [email protected] Present Address: J. Meng Department of Ultrasonic Diagnosis, The Second Clinical Hospital of Jilin University, Changchun, Jilin, China E. Cattrysse Department of Experimental Anatomy, Vrije Universiteit Brussel, Brussels, Belgium E. Vereecke Department of Anatomy, KULAK-Catholic University Leuven-Campus Kortrijk, Kortrijk, Belgium C. Geers Department of Pathology, University Hospital Free University Brussels, Jette, Belgium M. De Maeseneer Department of Experimental Anatomy, Free University Brussels, Jette, Belgium
The ridges were graded using a 4-point scale. A Chi-square test was used to compare the different fingers (p \ 0.05) and to study the prominence of the ridges in relation to age (p \ 0.05). Results On histology with routine stains the A2 pulley was inserted on the ridges of the proximal phalanx, and the flexor superficialis and A4 pulley on the ridges of the middle phalanx. On histology, the insertion showed a transition zone consisting of fibrocartilage. The prominence of the ridges was significantly different between fingers with III and IV categorized higher than II and III. There was a significant correlation with age for all fingers except for the middle phalanx of II and III. Conclusion The bony palmar ridges have characteristics of enthesophytes. They correspond to the insertion site of the A2 pulley, and the flexor superficialis tendon and A4 pulley, at the proximal and middle phalanx, respectively. The ridges become more prominent with age, and their prominence is different between the fingers with III and IV categorized higher than II and V. Keywords Hand radiography CT Hand enthesophytes Finger pulley Flexor digitorum superficialis tendon Normal variants
Introduction Bony excrescences can be observed in various bones and typically correspond to the normal insertion site of tendons and muscles [1–3, 10, 13]. They may also be caused by excessive traction of muscles, tendons, and ligaments. Prominent excrescences are also encountered in various bone diseases such as seronegative arthritis, DISH (diffuse idiopathic skeletal hyperostosis), certain medications, and
123
Surg Radiol Anat
occasionally in hypoparathyroidism [10]. The excrescences are an important element in the imaging diagnosis of these disorders. Osteophytes also present as excrescences but they are usually located at the margins of damaged cartilage. Osteophytes typically occur in osteoarthritis. It is debated whether enthesophytes also occur more frequently in this disorder [9, 12]. Ridges are evident on the palmar aspect of the proximal and middle phalanges of the fingers. They were mentioned in the anatomical work of Testut [8]. These authors considered that the ridges of the proximal phalanx corresponded to the insertion of the synovial sheath, and the ridges of the middle phalanx to the insertions of the flexor superficialis tendons. To our knowledge, the ridges have not been addressed in detail in the radiological literature. In our clinical practice, we observed that the prominence of these ridges is quite variable from patient to patient, and we have not observed them on imaging studies of children. When prominent the ridges could potentially be misinterpreted as a pathological bony proliferation [10]. As is the case with other bony excrescences it remains to be investigated whether these ridges could become more prominent in certain disease processes. We decided to undertake a study to address the following questions: (1) Which structures precisely insert onto the ridges and what is the histological appearance of the insertion site? (2) Is there a difference of the prominence of the ridges between the different fingers? (3) Is there a correlation between prominence of the ridges and age?
Materials and methods Radiography and CT study The IRB of our hospital approved a retrospective analysis of radiographs and CT scans of the hand, as well as an anatomical study in cadaver specimens. We retrospectively reviewed hand radiographs of 270 randomly selected patients (135 men; 135 women; mean age 44 years). The geographic origin of the patients was variable and included European and North African ethnicities. Oblique radiographs, obtained on a state of the art system (Definium 8000, GE Health Care, Milwaukee, WI, USA), were analyzed as they best showed the radial ridges. Two radiologists by consensus scored the phalanges using a 4-point grading scale. The grading scale used is shown in Table 1. We also evaluated 33 CT scans of the hand obtained on a state of the art scanner (Definition 750HD, GE Health Care, Milwaukee, WI, USA) and available on our PACS. The ridges were graded on CT scans using the same grading scale (as for the radiographs) and also in
123
Table 1 Gradings of ridges Grade 1
Absent
Grade 2
Subtle (maximal thickness \0.5 mm)
Grade 3
Moderate (maximal thickness 0.5–1.5 mm)
Grade 4
Prominent (maximal thickness [1.5 mm)
consensus by 2 radiologists (22 men; 11 women; mean age 46 years). On CT images 133 ulnar ridges and 125 radial ridges were evaluated for the proximal phalanx, and 88 ulnar and radial ridges for the middle phalanx. The number of ulnar and radial ridges, and proximal and distal phalanges analyzed on CT differed because interpretation was not possible in some instances due to obliquity of the section or traumatic lesions in the region of interest. Anatomic–histologic study Three cadaveric hands were obtained from the department of anatomy. The donors had approved the use of their bodies for scientific purposes. The age at death and cause of death of the donors were not known. The palmar aspect of fingers of 1 cadaveric hand was dissected. The soft tissue structures at the palmar side of the proximal and middle phalanx of the fingers were studied macroscopically. We performed transverse slicing with a bandsaw of the fingers of 2 deep frozen hands (1 left, 1 right). The sections were 4-mm thick. They were photographed and examined by two investigators. Slices obtained at the level of the 4th finger (2 proximal phalanxes, 2 middle phalanxes) were selected for histological analysis. These slices were thawed and preserved in formaldehyde. They were decalcified for 36 h and histologic sections were then obtained with a microtome using standardized histological technique. The sections were mounted and stained with HES (hematoxylin eosin) using routine histological technique. They were examined by an experienced anatomopathologist (CG) and photographs were made without magnification, and with magnification 2.59 and 109. Statistical analysis A Chi-square or Fisher exact test was used to compare the contingency tables obtained for the ridges at the different fingers, for the proximal and middle phalanges, as well as to assess differences with age. A significance threshold of p \ 0.05 was used. A Chi-square test was also used to assess whether there was a difference between the ulnar and radial ridges on CT. Statistical analysis was performed using IBM SPSS Statistics 20.
Surg Radiol Anat
Fig. 1 Radiographs showing grades 1–4 for the proximal phalanx (arrows). a Left 4th finger in 11-year-old boy, b right 3rd finger in 53-year-old woman, c left 4th finger in 62-year-old man, d left 4th finger in 75-year-old man
Fig. 2 Radiographs showing grades 1–4 for the middle phalanx (arrows). a Left 4th finger in 11-year-old boy, b left 4th finger in 62-year-old man, c right 4th finger in 46-year-old man, d right 3rd finger in 84-year-old man
Results Radiography and CT study On imaging studies the ridges of the proximal phalanx were located at the proximal and mid diaphysis, and the ridges of the middle phalanx at the transition zone between proximal and mid diaphysis (Figs. 1, 2, 3). The gradings for radiography at the different fingers are shown in Table 2. There was a statistically significant difference between ridges at the proximal phalanx for all fingers with III and IV categorized higher than II and V, on radiography. The gradings for CT are shown in Table 3. On CT, only the ridges at the 4th finger were more prominent than the other fingers. The same trend could be observed on CT as on radiography with III and IV being more prominent than II and V. For the middle phalanx, on radiography, the ridges were also significantly different between all fingers, with III and IV categorized higher than II and III. There
were no statistically significant differences on CT, but the ridges at III and IV were also larger than at II and V. The gradings relative to age are shown in Table 4. There was a statistically significant correlation with age for all the ridges except for the 2nd and 3rd middle phalanx (p \ 0.05). For these middle phalanges a trend of increasing prominence with age could still be observed. There was no statistically significant difference between the radial and ulnar ridges, on CT, at a significance threshold of p \ 0.05 (Table 5). Anatomic–histologic study On dissection of the fingers, the soft tissues attaching to the ulnar and radial aspects of the midshaft of the diaphysis of the proximal phalanges corresponded to the A2 pulley. At the level of the middle phalanx, the flexor superficialis tendons and A4 pulleys were seen to insert on to the ridges.
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Surg Radiol Anat Table 3 Mean gradings on CT of the ridges for the proximal (P) and middle phalanx (M)
P II
1.16
P III
1.32
P IV
2.17
PV M II
0.84 0.92
M III
1.14
M IV
1.07
MV
0.84
evident. Hence, the findings were similar to those seen in enthesophytes.
Discussion
Fig. 3 CT images at the proximal phalanx (a), middle phalanx (b) and volume rendering of the entire 4th finger (c) in 53-year-old man. a Ridges at the proximal phalanx (arrows). b Ridges at the middle phalanx (arrows). In c the ridges at the proximal phalanx (thick arrows), and middle phalanx (arrows) can be seen. Also note subluxation at the PIP joint, the reason why this patient underwent imaging Table 2 Mean scores for proximal and middle phalanges for different fingers in different age groups IIp
IIm
IIIp
IIIm
IVp
IVm
Vp
Vm
0–9
0.00
0.00
0.17
0.00
0.20
0.00
0.00
0.00
10–19
0.00
0.03
0.07
0.27
0.03
0.17
0.00
0.03
20–29
0.13
0.10
0.37
0.77
0.43
0.47
0.00
0.03
30–39 40–49
0.13 0.10
0.10 0.00
0.50 0.63
0.50 0.30
0.60 0.90
0.67 0.31
0.00 0.17
0.00 0.03
50–59
0.30
0.00
0.73
0.28
0.97
0.43
0.23
0.17
60–69
0.43
0.07
1.03
0.45
1.28
0.41
0.27
0.23
70–79
0.47
0.41
1.27
1.00
1.75
1.13
0.53
0.60
80–89
0.60
0.55
1.10
1.43
1.43
1.33
0.60
1.10
IIp proximal phalanx of 2nd finger, IIm middle phalanx of 2nd finger, IIIp proximal phalanx of 3rd finger, IIIm middle phalanx of 3rd finger, IVp proximal phalanx of 4th finger, IVm middle phalanx of 4th finger, Vp proximal phalanx of 5th finger, Vm middle phalanx of 5th finger, 0–9, …, 80–89 age groups
On histological investigation of sections, bony ridges were clearly seen at both sides of the palmar aspect of the phalanx. At the proximal phalanx the A2 pulley was inserted on the ridges (Fig. 4). Histological investigation of the middle phalanx also showed ridges, and both slips of the flexor superficialis tendon were shown to insert on the mid and central aspect of the ridges, whereas the A4 pulley was seen to insert on the external aspect of the ridges (Fig. 5). At histology, a transition zone between ligament and tendon, and bone consisting of fibrocartilage was
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The palmar bony ridges are mentioned in the work of Testut [14]. These authors suggest that the synovial sheath attaches to the ridges at the proximal phalanx, and the flexor superficialis tendons to the ridges at the middle phalanx. In Gray’s anatomy the ridges are mentioned at the middle phalanx but it is not specifically addressed what inserts on them [15]. Keats [10] mentions the ridges, as a pitfall on radiographs, and suggests they correspond to variants occurring at muscle insertion sites. Excrescences are known to arise on bony surfaces due to traction of tendons and muscles. In our clinical practice, we noticed that the prominence of the palmar ridges was variable from patient to patient, and we did not seem to observe them in pediatric patients. We studied the prominence of the ridges at the level of the different fingers. We found that the prominence of the ridges was different between the fingers, being most prominent at the 3rd and 4th fingers. For the 3rd finger, this prominence is in accordance with the greater strength exerted by the flexor digitorum superficialis tendon at this level [11]. For the other fingers, correlation with flexor digitorum superficialis strength is less clear [11]. Little is known about the lifetime prevalence or age of appearance of the bony ridges. To our knowledge, only a recent investigation by Kalichman et al. [9] addressed this aspect and found that the palmar ridges become more prominent with age. We also showed that the ridges become more prominent with age, and hence, our findings are in accordance with this report. These authors further found that the correlation was higher in men than in women, and that a genetic factor may be involved. In our study, we did not address differences between men and women. We did confirm our subjective clinical observation that the ridges seemed to be absent in pediatric patients. In this study, we did not correlate the prominence of the ridges with the severity of osteoarthritis. Bony
Surg Radiol Anat Table 4 Mean scores for proximal and middle phalanx in 9 age groups and statistics 0–9
10–19
20–29
30–39
40–49
50–59
60–69
70–79
[80
p
R
IIp
0
0
0.13
0.13
0.10
0.30
0.43
0.47
0.60
0.01
0.41
IIIp
0.17
0.07
0.37
0.50
0.63
0.73
1.03
1.27
1.10
0
0.50
IVp
0.20
0.03
0.43
0.60
0.90
0.97
1.28
1.75
1.43
0.003
0.55
Vp
0
0
0
0
0.17
0.23
0.27
0.53
0.60
0
0.41
IIm
0
0.03
0.10
0.10
0
0
0.07
0.41
0.55
0.48
0.29
IIIm
0
0.27
0.77
0.50
0.30
0.28
0.45
1.00
1.43
0.31
0.38
IVm
0
0.17
0.47
0.67
0.31
0.43
0.41
1.13
1.33
0
0.45
Vm
0
0.03
0.03
0
0.03
0.17
0.23
0.60
1.10
0.01
0.47
IIp proximal phalanx of 2nd finger, IIm middle phalanx of 2nd finger, IIIp proximal phalanx of 3rd finger, IIIm middle phalanx of 3rd finger, IVp proximal phalanx of 4th finger, IVm middle phalanx of 4th finger, Vp proximal phalanx of 5th finger, Vm middle phalanx of 5th finger, 0–9, …, 80–89 age groups, p p value
Table 5 Comparison of radial and ulnar ridges, on CT (n = 33), p value \ 0.05 Proximal
Middle
Phalanx II
0.94
0.51
Phalanx III Phalanx IV
0.59 0.69
0.87 1
Phalanx V
0.76
1
Prominence of radial and ulnar ridges at the proximal and middle phalanx (p values)
excrescences are often associated with osteoarthritis. For example, an increase in size of the medial and lateral intercondylar tubercles is typical in osteoarthritis [10]. Kalichman et al. [9] in their study found a correlation between the ridges and osteoarthritis. Other researchers also have suggested that osteophytes and enthesophytes occur
Fig. 4 Anatomic slice (a) and histologic study of proximal phalanx without magnification (b), with magnification 92.5 (c) and 910 (d). a The A2 pulley (bold arrows) is seen to insert on the ridges (arrows). T flexor tendons. b Ridge (arrow, R) and A2 pulley (arrow). c Ridge
simultaneously in persons sometimes designated as ‘bone formers’. The pulleys of the fingers consist of annular and cruciform pulleys [4, 5]. Only the annular pulleys are clearly visible on dissection as 5 strong band-like structures. The pulleys keep the tendons in proximity to the bone with finger flexion. The most important pulleys are the A2 and A4 pulleys at the level of the proximal and middle phalanx, respectively [6, 8]. In our anatomic–histologic study, we found that the structure attaching at the proximal phalanx corresponded to the A2 pulley. This is similar to the suggestion by Testut [14] that the synovial sheath inserts in this location. We showed that the soft tissue structures inserting at the middle phalanx consist of the flexor superficialis tendon at the mid and central aspect of the ridge, and the A4 pulley at the external aspect of the ridge. The flexor superficialis tendon insertion takes up the major part of the ridge.
(R, arrows), tendon (T) and A2 pulley (arrow, A2). d Collagen bundles c containing small rounded cells adjacent to the ridge (arrows)
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Surg Radiol Anat
Fig. 5 Histologic study of middle phalanx without magnification (a), and with magnification 92.5 (b). a Ridges (thick arrows), A4 pulley (arrows), and flexor superficialis tendons (FS). b Ridge (thick arrow), A4 pulley (arrow), and flexor superficialis tendon (FS)
The ridges are excrescences with characteristic similar to enthesophytes, and should not alarm the radiologist. Nevertheless, further studies could address whether in diseases that affect entheses, such as for example the seronegative rheumatoid disorders, imaging abnormalities can be seen at the level of these ridges. On imaging studies, the ridges also should not be interpreted erroneously as abnormal (periosteal) bony proliferation, but as a ‘normal’ bony excrescence related to the attachment of soft tissue structures. Further studies could also address whether the ridges can be used in the determination of bone age, and thus would have potential medicolegal, forensic, and paleopathological applications [5, 7]. Although not studied in this investigation, we have noticed in our practice that the ridges are useful bony landmarks for the identification of the insertion site on ultrasound and CT of the A2 pulley and especially the flexor superficialis tendons, which may otherwise be difficult. We acknowledge that our study has limitations. The ridges were evaluated on oblique radiographs because this shows the ridges best. Although all radiographs were obtained in our hospital using standardized positioning, it is
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possible that the obliquity of the radiographs varied slightly and this influenced the radiographic appearance of the ridges. On radiography, only the radial ridges could be evaluated. On CT, however, we showed that there was no statistically significant difference between the radial and ulnar ridges. In addition, the CT parameters were not standardized. However, routine technique on a state of the art CT scanner was used in all studies. The size of the ridges on radiographs may be different from the real size due to projection technique. We did not stratify patients in a group with manual labor or sports related stress on the hands, and a group without such activities. Thus, we could not assess the influence of this factor on the prominence of the ridges. The number of anatomical specimens is limited, and we acknowledge that our anatomical and histological findings would benefit from further study. In conclusion, we found that the bony ridges at the proximal phalanx correspond to the insertion site of the A2 pulley, and those at the middle phalanx to the insertion site of the flexor superficialis tendon and A4 pulley. The ridges become more prominent with age, and they are different between the fingers being most prominent at the 3rd and 4th finger. The ridges are not typically seen in pediatric patients. Taking into account the age of the patient, the ridges are thus a normal finding. Since we showed that the ridges are similar to enthesophytes, further studies could address whether the ridges show imaging abnormalities in specific diseases affecting the enthesis. Acknowledgments We would like to thank Erik Cattrysse, PhD, Aldo Scafoglieri, PhD, Faes Kerkhof, MD, Maryam Shahabpour, MD, Rita Bosschaert, Dirk Blommaert, and Jo De Neef. Conflict of interest None of the authors of this work has a conflict of interest or financial relation to disclose.
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