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Thenar insertion of abductor pollicis longus accessory tendons and thumb carpometacarpal osteoarthritis
Thenar Insertion of Abductor Pollicis Longus Accessory Tendons and Thumb Carpometacarpal Osteoarthritis Michael S. Roh, MD, Robert J. Strauch, MD, Liangfeng Xu, PhD, Melvin P. Rosenwasser, MD, Robert J. Pawluk, MBA, Van C. Mow, PhD, New York, NY Although the etiology of osteoarthritis of the thumb carpometacarpal (CMC) joint remains unclear, some theories have focused on variations in the local anatomy of the abductor pollicis longus tendon insertion. This cadaver study of 68 specimens analyzed the relationship between a thenar insertion of an accessory abductor pollicis longus tendon and the presence and severity of thumb CMC osteoarthritis. The joint cartilage surfaces were visually graded for degenerative changes. Thirty-five of 68 specimens (51%) had a thenar insertion, most frequently inserting on either the abductor pollicis brevis or opponens pollicis fascia or muscle belly. No significant association between a thenar insertion and thumb CMC arthritis was observed. Conversely, increasing age was noted to have a significant association with degenerative joint disease. Thus, these findings indicate that a thenar slip of the abductor pollicis longus tendon does not correlate with the presence or severity of CMC osteoarthritis. (J Hand Surg 2000;25A:458 – 463. Copyright © 2000 by the American Society for Surgery of the Hand.) Key words: Thumb, carpometacarpal, osteoarthritis, thenar, tendon.
Osteoarthritis of the thumb carpometacarpal (CMC) joint is a common and painful disease that often carries considerable disability. Although numerous theories have been proposed, including ligaFrom the Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Columbia University College of Physicians and Surgeons, Columbia-Presbyterian Medical Center, New York, NY. Supported in part by National Institutes of Health Grant No. AR41 020. Received for publication June 8, 1998; accepted in revised form December 29, 1999. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Van C. Mow, PhD, Orthopaedic Research Laboratory, Columbia University School of Physicians and Surgeons, 630 W 168th St, BB-1412, New York, NY 10032. Copyright © 2000 by the American Society for Surgery of the Hand 0363-5023/00/25A03-0009$3.00/0 doi: 10.1053/jhsu.2000.6463
458 The Journal of Hand Surgery
mentous laxity,1,2 joint incongruence,3,4 hormonal effects,5 obesity,6 muscle imbalance,7 and anomalous abductor pollicis longus (APL) tendon insertion,8 the precise etiology remains unclear. One hypothesis of the etiology of osteoarthritis in this joint focuses on the anatomic variations of the APL tendon inserting at and around the thumb CMC joint.9 –26 Zancolli and Cozzi8 have suggested that accessory slips of the APL tendon inserting on the thenar musculature (most often the abductor pollicis brevis) increase joint compressive forces and thus accelerate the degeneration of the thumb CMC joint cartilage. Release of these accessory tendons has been recommended for the treatment of early (Eaton and Glickel27 stages I and II) CMC arthritis.8 This study investigates the relationship between thenar insertion of accessory APL tendons and CMC osteoarthritis.
The Journal of Hand Surgery / Vol. 25A No. 3 May 2000 459
Table 1. Grading System of the Carpometacarpal Articular Cartilage28 Grade 1: Normal cartilage Smooth, shiny, intact surface Grade 2: Early cartilage degeneration Fibrillation Localized pitting ⱕ25% of full thickness Grade 3: Progressive cartilage degeneration Exposed bone Deep fissures or clefts Localized pitting ⬎25% of full thickness Grade 4: End-stage cartilage degeneration Eburnated bone
Materials and Methods Sixty-eight unmatched cadaver hands were radiographically staged (using the criteria of Eaton and
Glickel27) and dissected. There were 31 women with a mean age of 56 years (range, 18 – 88 years) and 37 men with a mean age of 60 years (range, 28 –79 years). During antegrade dissection, the tendon of the APL muscle was carefully examined and the presence or absence of a thenar slip was noted. The thumb CMC joint was then opened and the articular surfaces of the metacarpal and trapezium were visually graded for osteoarthritic involvement (Table 1). The overall condition of the joint was assigned the pathologic grade that matched the worst area of cartilage degeneration noted on either articular surface (Fig. l).28 To facilitate correlation, specimens were divided into 3 age groups: those aged 40 years and younger, those aged 41 to 60 years, and those aged 61 years and older. Using 3-way ANOVA and Student-Neu-
Figure 1. The mating surfaces of the trapezium and metacarpal were graded for severity of cartilage degeneration. In this left-hand specimen the joint has been disarticulated, leaving only the dorsal attachments intact (d). Volar (v), radial (r), and ulnar (u) markers are provided for orientation. On the left, the trapezial articular surface (TM) is mostly fibrillated (grade 2), with an area of exposed bone on the dorsoradial region (grade 3, solid arrows, top left). On the right, the matching metacarpal articular surface (MC) shows similar cartilage fibrillation (grade 2), with exposed bone in the volar-radial region (grade 3; solid arrows, top right). Therefore, this overall joint was classified as grade 3.
460 Roh et al / Thenar APL Tendon Insertion & Thumb CMC OA
man-Keuls test, the presence and severity of osteoarthritis were correlated with age group, gender, and the presence of an accessory thenar tendon. Power analysis revealed a power of 0.80 to 0.88 with an effect size of 0.4. Osteoarthritis was considered to be present with a visual or radiographic stage of II or greater.
Results Thirty-five of 68 specimens (51%) had an accessory thenar insertion of the APL tendon. Most frequently, the thenar tendon inserted on the fascia or muscle belly of either the abductor pollicis brevis or opponens pollicis muscles (Fig. 2). As shown in Table 2, no significant correlation with the presence or severity of osteoarthritis was noted, as assessed by radiographic stage or visual pathologic grade (p ⫽ .30, power 0.88). Age had a clearly significant and direct correlation with the severity of osteoarthritis of the thumb CMC joint (p ⬍ .00l). Under the grading
system used gender did not seem to have an effect on the severity of osteoarthritis in this group of specimens.
Discussion A considerable number of studies have convincingly demonstrated that the tendinous anatomy of the APL is extremely variable, as are the sites of insertion.9 –26 Most frequently, 2 to 4 tendinous slips are present in the first dorsal compartment,15 although as many as 7 have been reported.16 This study focused on APL tendon slip insertion into the thenar musculature; the results (51%) are comparable with those of previous studies (Table 3). These anatomic variations usually are asymptomatic and found only as incidental intraoperative findings or in postmortem dissection. In some cases, however, anatomic anomalies of the APL muscle, tendon, and sheath can become clinically important, presenting as bilateral trapeziometacarpal subluxa-
Figure 2. This right-hand specimen is oriented with the fingers pointing upward and the thumb closest to the camera. Dissection reveals 1 tendinous slip from the APL (arrows) inserting on the abductor pollicis brevis muscle. The remaining 2 slips of tendon insert on the proximal portion of the first metacarpal.
The Journal of Hand Surgery / Vol. 25A No. 3 May 2000 461
Table 2. Summary of Data Total specimens Male Female Specimen ages Group 1 (⬍40 yr) Group 2 (40–60 yr) Group 3 (⬎60 yr) Specimens with thenar insertion Male Female Cartilage grade 1 2 3 4 Mean Radiographic stage 1 2 3 4 Mean Specimens without thenar insertion Male Female Cartilage grade 1 2 3 4 Mean Radiographic stage 1 2 3 4 Mean
68 31 37 58 (mean age) 7 32 29 35 19 16 1 9 18 7 2.88 12 16 3 4 1.97 33 18 15 2 11 14 6 2.73 15 12 2 2 1.71
tion,17 persistent CMC pain,18 de Quervain’s disease,19 –20 or a painful forearm mass.21 The question remains whether accessory APL tendons to the thenar muscles truly have any significant effect on CMC mechanics. Imaeda et al29 contend that these thenar insertions into the abductor pollicis brevis assist in thumb abduction. Brunelli and colleagues7,14 concluded that thenar insertions have no influence on CMC stability as long as a concomitant trapezial insertion is present, whereas in the absence of a trapezial insertion these thenar insertions, along with the entire APL complex, act to destabilize the CMC joint. In their series, CMC arthritis was identified in 19 of 71 joints with a trapezial insertion of APL tendon, the so-called “abductor carpi.”14 In contrast, these investigators found that in 21 of 29 patients with no such trapezial insertion, CMC arthritis was present. They went on to report either
CMC arthritis or instability in nearly all cases in which they found no trapezial insertion. Brunelli and colleagues’ study, however, comprised a heterogeneous group of 100 specimens, with 25 surgical releases of de Quervain’s disease, 31 surgical procedures to treat CMC arthritis, and 44 postmortem dissections. In addition, a radiographic staging system was used rather than direct inspection. Furthermore, some investigators believe that the overall effect of the APL is not to destabilize, but to add stability to the CMC joint.22,25,29 With regard to whether the thenar insertion may be considered independently, however, our results are consistent with those of Brunelli and colleagues. No association was found between the presence of thenar insertion and the presence or severity of thumb CMC osteoarthritis. Alternatively, Zancolli and Cozzi8 hypothesized that the thenar insertions act to increase the magnitude of the transarticular compressive force along the column of the thumb. This increased force, combined with repeated thumb use in unstable positions, is believed to be responsible for the onset of the degenerative process.8 The APL, however, has not been shown to be a primary muscle involved in pinch and grasp, as illustrated by electromyographic analysis.30 Nonetheless, Zancolli and Cozzi8 reported satisfactory results in 20 of 23 patients after excision of accessory APL tendons for painful, early (Eaton and Glickel stages I and II) CMC osteoarthritis. Evidence does exist that supports a claim for separate and possibly independent function of the accessory musculotendinous units. Both anatomic and electromyographic data have shown that the multiple
Table 3. Previous Reports of Abductor Pollicis Longus Thenar Insertion Source
Series Reported
10
86 of 134 in APB 59 of 100 in APB
64 59
15 of 100 in OPP 107 of 150 in thenar muscle 24 of 38 in APB 75 of 127 in APB 20 of 127 in OPP 35 of 84 in thenar muscle 94 of 104 in thenar muscle
15 71
Baba (1954) Brunelli and Brunelli (1991)14 Elliott (1992)13 Lacey et al (1951)11 Loomis (1951)9 Stein (1951)12 Zancolli and Cozzi (1992)8
Percentage
APB, abductor pollicis brevis; OPP, oppenens pollicis.
63 59 16 42 90
462 Roh et al / Thenar APL Tendon Insertion & Thumb CMC OA
muscle bellies are innervated separately by small but distinct branches of the posterior interosseous nerve.23,24 A bursa has been identified between the deep and superficial tendons, implying independent contractile action causing intertendinous shifts.15,25 In addition, successful transfer of an accessory APL musculotendinous unit for extensor pollicis longus rupture has been reported with good success.26 The precise effects of the individual APL musculotendinous subunits will require further study before their etiologic role, if any, is identified. Our findings, however, do not support the involvement of thenar APL insertion in osteoarthritis of the thumb CMC joint. Age is clearly shown to be a significant factor, which is quite consistent with existing clinical and epidemiologic data. The absence of an association between CMC arthritis and female gender is puzzling, although a similar lack of association has been reported.31 Although this study was not able to demonstrate a relationship between the presence of a thenar APL insertion and the presence or severity of osteoarthritis, it is still possible that there is a correlation with symptomatic osteoarthritis. Data concerning the presence or absence of thumb symptoms in our cadaver population were not available. It has been shown that approximately 30% of isolated CMC osteoarthritis in postmenopausal women is symptomatic32 and the incidental radiographic finding of asymptomatic thumb CMC osteoarthritis is common. No scientific rationale is currently available to account for the presence or absence of pain in association with thumb CMC osteoarthritis. Only a large clinical study of patients undergoing surgery for symptomatic CMC osteoarthritis could analyze the association of a thenar APL insertion with painful CMC osteoarthritis. Therefore, while this study finds no association between the presence of a thenar APL insertion and radiographic or visual CMC osteoarthritis, it cannot preclude an association between the presence of a thenar APL insertion and symptomatic osteoarthritis.
3.
4.
5.
6.
7. 8. 9.
10. 11.
12.
13. 14.
15. 16.
17.
18.
19. The authors thank Chris S. Ahmad, MD, and John S. Bucchieri, MD, for their contributions.
20.
References 1. Eaton RG, Littler JW. Ligament reconstruction for the painful thumb carpometacarpal joint. J Bone Joint Surg 1973;55A:1655–1666. 2. Pellegrini VD Jr. Osteoarthritis of the trapeziometacarpal
21.
22.
joint: the pathophysiology of articular cartilage degeneration. I. Anatomy and pathology of the aging joint. J Hand Surg 1991;16A:967–974. Aune S. Osteo-arthritis in the first carpo-metacarpal joint. An investigation of 22 cases. Acta Chir Scand 1955;109: 449-456. North ER, Rutledge WM. The trapezium-thumb metacarpal joint: the relationship of joint shape and degenerative joint disease. Hand 1983;15:201–206. Spector TD, Hart DJ, Brown P, et al. Frequency of osteoarthritis in hysterectomized women. J Rheumatol 1991;18: 1877–1883. Hart DJ, Spector TD. The relationship of obesity, fat distribution and osteoarthritis in women in the general population: the Chingford study. J Rheumatol 1993;20: 331–335. Brunelli G, Monini L, Brunelli F. Stabilisation of the trapeziometacarpal joint. J Hand Surg 1989;14B:209 –212. Zancolli EA, Cozzi EP. Atlas of surgical anatomy of the hand. New York: Churchill Livingstone, 1992:442– 444. Loomis LK. Variations of stenosing tenosynovitis at the radial styloid process. J Bone Joint Surg 1951;33A:340 – 346. Baba MA. The accessory tendon of the abductor pollicis longus muscle. Anat Rec 1954;119:541–547 Lacey T II, Goldstein LA, Tobin CE. Anatomical and clinical study of the variations in the insertions of the abductor pollicis longus tendon, associated with stenosing tendovaginitis. J Bone Joint Surg 1951;33A:347–350. Stein AH Jr. Variations of the tendons of insertion of the abductor pollicis longus and the extensor pollicis brevis. Anat Rec 1951;110:49 –55. Elliott BG. Abductor pollicis longus: a case of mistaken identity. J Hand Surg 1992;17B:476 – 478. Brunelli GA, Brunelli GR. Anatomical study of distal insertion of the abductor pollicis longus. Concept of a new musculo-tendinous unit: the abductor carpi muscle. Ann Hand Surg 1991;10:569 –576. van Oudenaarde E. Structure and function of the abductor pollicis longus muscle. J Anat 199l;174:221–227. Melling M, Wilde J, Schnallinger M, Schweighart W, Panholzer M. Supernumerary tendons of the abductor pollicis. Acta Anat 1996;155:291–294. Martinez R, Omer GE Jr. Bilateral subluxation of the base of the thumb secondary to an unusual abductor pollicis longus insertion: a case report. J Hand Surg 1985;10A: 396 –398. Rayan GM, Mustafa E. Anomalous abductor pollicis longus insertion in the thenar muscles. J Hand Surg 1989;14A: 550 –552. Gonzalez MH, Sohlberg R, Brown A, Weinzweig N. The first dorsal extensor compartment: an anatomic study. J Hand Surg 1995;20A:657– 660. Leslie BM, Ericson WB Jr, Morehead JR. Incidence of a septum within the first dorsal compartment of the wrist. J Hand Surg 1990;15A:88 –91. Patel MR, Desai SS. Anomalous muscles of the first dorsal compartment of the wrist. J Hand Surg 1988;13A:829 – 831. van Oudenaarde E. The function of the abductor pollicis
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23.
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27.
longus muscle as a joint stabiliser. J Hand Surg 1991;16B: 420 – 423. van Oudenaarde E, Oostendorp R. Significance of the innervation pattern of the human abductor pollicis longus muscle. J Anat 1992;181:155–159. van Oudenaarde E, Oostendorp RAB. Functional relationship between the abductor pollicis longus and abductor pollicis brevis muscles: an EMG analysis. J Anat 1995; 186:509 –515. Kauer JMG. Functional anatomy of the carpometacarpal joint of the thumb. Clin Orthop 1987;220:7–13. Backhouse KM. Abductor pollicis longus musculo-tendinous split as a replacement motor for ruptured extensor pollicis longus. Hand 1981;13:271–275. Eaton RG, Glickel SZ. Trapeziometacarpal osteoarthritis: staging as a rationale for treatment. Hand Clin 1987;3:455– 469.
28. Xu L, Strauch RJ, Ateshian GA, Pawluk RJ, Mow VC, Rosenwasser MP. Topography of the osteoarthritic thumb carpometacarpal joint and its variations with regard to gender, age, site, and osteoarthritic stage. J Hand Surg 1998;23A:454 – 464. 29. Imaeda T, An K-N, Cooney WP III. Functional anatomy and biomechanics of the thumb. Hand Clin 1992;8:9 – 15. 30. Cooney WP III, An K-N, Daube JR, Askew LJ. Electromyographic analysis of the thumb: a study of isometric forces in pinch and grasp. J Hand Surg 1985;10A: 202–210. 31. Bade H, Koebke J. Arthrosis in the peritrapezial joints of the hand. Surg Radiol Anat 1996;18:209 –214. 32. Armstrong AL, Hunter JB, Davis TRC. The prevalence of degenerative arthritis of the base of the thumb in postmenopausal women. J Hand Surg 1994;19B:340 –341.
Osteoarthritis of the thumb carpometacarpal (CMC) joint is a common and painful disease that often carries considerable disability. Although numerous theories have been proposed, including ligaFrom the Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Columbia University College of Physicians and Surgeons, Columbia-Presbyterian Medical Center, New York, NY. Supported in part by National Institutes of Health Grant No. AR41 020. Received for publication June 8, 1998; accepted in revised form December 29, 1999. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Van C. Mow, PhD, Orthopaedic Research Laboratory, Columbia University School of Physicians and Surgeons, 630 W 168th St, BB-1412, New York, NY 10032. Copyright © 2000 by the American Society for Surgery of the Hand 0363-5023/00/25A03-0009$3.00/0 doi: 10.1053/jhsu.2000.6463
458 The Journal of Hand Surgery
mentous laxity,1,2 joint incongruence,3,4 hormonal effects,5 obesity,6 muscle imbalance,7 and anomalous abductor pollicis longus (APL) tendon insertion,8 the precise etiology remains unclear. One hypothesis of the etiology of osteoarthritis in this joint focuses on the anatomic variations of the APL tendon inserting at and around the thumb CMC joint.9 –26 Zancolli and Cozzi8 have suggested that accessory slips of the APL tendon inserting on the thenar musculature (most often the abductor pollicis brevis) increase joint compressive forces and thus accelerate the degeneration of the thumb CMC joint cartilage. Release of these accessory tendons has been recommended for the treatment of early (Eaton and Glickel27 stages I and II) CMC arthritis.8 This study investigates the relationship between thenar insertion of accessory APL tendons and CMC osteoarthritis.
The Journal of Hand Surgery / Vol. 25A No. 3 May 2000 459
Table 1. Grading System of the Carpometacarpal Articular Cartilage28 Grade 1: Normal cartilage Smooth, shiny, intact surface Grade 2: Early cartilage degeneration Fibrillation Localized pitting ⱕ25% of full thickness Grade 3: Progressive cartilage degeneration Exposed bone Deep fissures or clefts Localized pitting ⬎25% of full thickness Grade 4: End-stage cartilage degeneration Eburnated bone
Materials and Methods Sixty-eight unmatched cadaver hands were radiographically staged (using the criteria of Eaton and
Glickel27) and dissected. There were 31 women with a mean age of 56 years (range, 18 – 88 years) and 37 men with a mean age of 60 years (range, 28 –79 years). During antegrade dissection, the tendon of the APL muscle was carefully examined and the presence or absence of a thenar slip was noted. The thumb CMC joint was then opened and the articular surfaces of the metacarpal and trapezium were visually graded for osteoarthritic involvement (Table 1). The overall condition of the joint was assigned the pathologic grade that matched the worst area of cartilage degeneration noted on either articular surface (Fig. l).28 To facilitate correlation, specimens were divided into 3 age groups: those aged 40 years and younger, those aged 41 to 60 years, and those aged 61 years and older. Using 3-way ANOVA and Student-Neu-
Figure 1. The mating surfaces of the trapezium and metacarpal were graded for severity of cartilage degeneration. In this left-hand specimen the joint has been disarticulated, leaving only the dorsal attachments intact (d). Volar (v), radial (r), and ulnar (u) markers are provided for orientation. On the left, the trapezial articular surface (TM) is mostly fibrillated (grade 2), with an area of exposed bone on the dorsoradial region (grade 3, solid arrows, top left). On the right, the matching metacarpal articular surface (MC) shows similar cartilage fibrillation (grade 2), with exposed bone in the volar-radial region (grade 3; solid arrows, top right). Therefore, this overall joint was classified as grade 3.
460 Roh et al / Thenar APL Tendon Insertion & Thumb CMC OA
man-Keuls test, the presence and severity of osteoarthritis were correlated with age group, gender, and the presence of an accessory thenar tendon. Power analysis revealed a power of 0.80 to 0.88 with an effect size of 0.4. Osteoarthritis was considered to be present with a visual or radiographic stage of II or greater.
Results Thirty-five of 68 specimens (51%) had an accessory thenar insertion of the APL tendon. Most frequently, the thenar tendon inserted on the fascia or muscle belly of either the abductor pollicis brevis or opponens pollicis muscles (Fig. 2). As shown in Table 2, no significant correlation with the presence or severity of osteoarthritis was noted, as assessed by radiographic stage or visual pathologic grade (p ⫽ .30, power 0.88). Age had a clearly significant and direct correlation with the severity of osteoarthritis of the thumb CMC joint (p ⬍ .00l). Under the grading
system used gender did not seem to have an effect on the severity of osteoarthritis in this group of specimens.
Discussion A considerable number of studies have convincingly demonstrated that the tendinous anatomy of the APL is extremely variable, as are the sites of insertion.9 –26 Most frequently, 2 to 4 tendinous slips are present in the first dorsal compartment,15 although as many as 7 have been reported.16 This study focused on APL tendon slip insertion into the thenar musculature; the results (51%) are comparable with those of previous studies (Table 3). These anatomic variations usually are asymptomatic and found only as incidental intraoperative findings or in postmortem dissection. In some cases, however, anatomic anomalies of the APL muscle, tendon, and sheath can become clinically important, presenting as bilateral trapeziometacarpal subluxa-
Figure 2. This right-hand specimen is oriented with the fingers pointing upward and the thumb closest to the camera. Dissection reveals 1 tendinous slip from the APL (arrows) inserting on the abductor pollicis brevis muscle. The remaining 2 slips of tendon insert on the proximal portion of the first metacarpal.
The Journal of Hand Surgery / Vol. 25A No. 3 May 2000 461
Table 2. Summary of Data Total specimens Male Female Specimen ages Group 1 (⬍40 yr) Group 2 (40–60 yr) Group 3 (⬎60 yr) Specimens with thenar insertion Male Female Cartilage grade 1 2 3 4 Mean Radiographic stage 1 2 3 4 Mean Specimens without thenar insertion Male Female Cartilage grade 1 2 3 4 Mean Radiographic stage 1 2 3 4 Mean
68 31 37 58 (mean age) 7 32 29 35 19 16 1 9 18 7 2.88 12 16 3 4 1.97 33 18 15 2 11 14 6 2.73 15 12 2 2 1.71
tion,17 persistent CMC pain,18 de Quervain’s disease,19 –20 or a painful forearm mass.21 The question remains whether accessory APL tendons to the thenar muscles truly have any significant effect on CMC mechanics. Imaeda et al29 contend that these thenar insertions into the abductor pollicis brevis assist in thumb abduction. Brunelli and colleagues7,14 concluded that thenar insertions have no influence on CMC stability as long as a concomitant trapezial insertion is present, whereas in the absence of a trapezial insertion these thenar insertions, along with the entire APL complex, act to destabilize the CMC joint. In their series, CMC arthritis was identified in 19 of 71 joints with a trapezial insertion of APL tendon, the so-called “abductor carpi.”14 In contrast, these investigators found that in 21 of 29 patients with no such trapezial insertion, CMC arthritis was present. They went on to report either
CMC arthritis or instability in nearly all cases in which they found no trapezial insertion. Brunelli and colleagues’ study, however, comprised a heterogeneous group of 100 specimens, with 25 surgical releases of de Quervain’s disease, 31 surgical procedures to treat CMC arthritis, and 44 postmortem dissections. In addition, a radiographic staging system was used rather than direct inspection. Furthermore, some investigators believe that the overall effect of the APL is not to destabilize, but to add stability to the CMC joint.22,25,29 With regard to whether the thenar insertion may be considered independently, however, our results are consistent with those of Brunelli and colleagues. No association was found between the presence of thenar insertion and the presence or severity of thumb CMC osteoarthritis. Alternatively, Zancolli and Cozzi8 hypothesized that the thenar insertions act to increase the magnitude of the transarticular compressive force along the column of the thumb. This increased force, combined with repeated thumb use in unstable positions, is believed to be responsible for the onset of the degenerative process.8 The APL, however, has not been shown to be a primary muscle involved in pinch and grasp, as illustrated by electromyographic analysis.30 Nonetheless, Zancolli and Cozzi8 reported satisfactory results in 20 of 23 patients after excision of accessory APL tendons for painful, early (Eaton and Glickel stages I and II) CMC osteoarthritis. Evidence does exist that supports a claim for separate and possibly independent function of the accessory musculotendinous units. Both anatomic and electromyographic data have shown that the multiple
Table 3. Previous Reports of Abductor Pollicis Longus Thenar Insertion Source
Series Reported
10
86 of 134 in APB 59 of 100 in APB
64 59
15 of 100 in OPP 107 of 150 in thenar muscle 24 of 38 in APB 75 of 127 in APB 20 of 127 in OPP 35 of 84 in thenar muscle 94 of 104 in thenar muscle
15 71
Baba (1954) Brunelli and Brunelli (1991)14 Elliott (1992)13 Lacey et al (1951)11 Loomis (1951)9 Stein (1951)12 Zancolli and Cozzi (1992)8
Percentage
APB, abductor pollicis brevis; OPP, oppenens pollicis.
63 59 16 42 90
462 Roh et al / Thenar APL Tendon Insertion & Thumb CMC OA
muscle bellies are innervated separately by small but distinct branches of the posterior interosseous nerve.23,24 A bursa has been identified between the deep and superficial tendons, implying independent contractile action causing intertendinous shifts.15,25 In addition, successful transfer of an accessory APL musculotendinous unit for extensor pollicis longus rupture has been reported with good success.26 The precise effects of the individual APL musculotendinous subunits will require further study before their etiologic role, if any, is identified. Our findings, however, do not support the involvement of thenar APL insertion in osteoarthritis of the thumb CMC joint. Age is clearly shown to be a significant factor, which is quite consistent with existing clinical and epidemiologic data. The absence of an association between CMC arthritis and female gender is puzzling, although a similar lack of association has been reported.31 Although this study was not able to demonstrate a relationship between the presence of a thenar APL insertion and the presence or severity of osteoarthritis, it is still possible that there is a correlation with symptomatic osteoarthritis. Data concerning the presence or absence of thumb symptoms in our cadaver population were not available. It has been shown that approximately 30% of isolated CMC osteoarthritis in postmenopausal women is symptomatic32 and the incidental radiographic finding of asymptomatic thumb CMC osteoarthritis is common. No scientific rationale is currently available to account for the presence or absence of pain in association with thumb CMC osteoarthritis. Only a large clinical study of patients undergoing surgery for symptomatic CMC osteoarthritis could analyze the association of a thenar APL insertion with painful CMC osteoarthritis. Therefore, while this study finds no association between the presence of a thenar APL insertion and radiographic or visual CMC osteoarthritis, it cannot preclude an association between the presence of a thenar APL insertion and symptomatic osteoarthritis.
3.
4.
5.
6.
7. 8. 9.
10. 11.
12.
13. 14.
15. 16.
17.
18.
19. The authors thank Chris S. Ahmad, MD, and John S. Bucchieri, MD, for their contributions.
20.
References 1. Eaton RG, Littler JW. Ligament reconstruction for the painful thumb carpometacarpal joint. J Bone Joint Surg 1973;55A:1655–1666. 2. Pellegrini VD Jr. Osteoarthritis of the trapeziometacarpal
21.
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