Clinical Orthopaedics and Related Research®
Clin Orthop Relat Res DOI 10.1007/s11999-014-3651-5
A Publication of The Association of Bone and Joint Surgeons®
BASIC RESEARCH
Carpal Tunnel Syndrome Impairs Thumb Opposition and Circumduction Motion Tamara L. Marquardt BS, Raviraj Nataraj PhD, Peter J. Evans MD, PhD, William H. Seitz Jr MD, Zong-Ming Li PhD
Received: 17 December 2013 / Accepted: 11 April 2014 Ó The Association of Bone and Joint Surgeons1 2014
Abstract Background Carpal tunnel syndrome is associated with sensory and motor impairments resulting from the compressed and malfunctioning median nerve. The thumb is critical to hand function, yet the pathokinematics of the thumb associated with carpal tunnel syndrome are not well understood. Questions/purposes The purpose of this study was to evaluate thumb motion abnormalities associated with carpal tunnel syndrome. We hypothesized that the ranges of translational and angular motion of the thumb would be reduced as a result of carpal tunnel syndrome. Methods Eleven patients with carpal tunnel syndrome and 11 healthy control subjects voluntarily participated in this Funding for this study was received from the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health (Award Number R01AR056964) (ZML). All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request. Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained. T. L. Marquardt, R. Nataraj, Z.-M. Li (&) Hand Research Laboratory, Department of Biomedical Engineering, Cleveland Clinic, 9500 Euclid Avenue, ND20, Cleveland, OH 44195, USA e-mail: [email protected]; [email protected] P. J. Evans, W. H. Seitz Jr, Z.-M. Li Department of Orthopaedic Surgery, Cleveland Clinic, Cleveland, OH, USA Z.-M. Li Department of Physical Medicine and Rehabilitation, Cleveland Clinic, Cleveland, OH, USA
study. Translational and angular kinematics of the thumb were obtained using marker-based video motion analysis during thumb opposition and circumduction movements. Results Motion deficits were observed for patients with carpal tunnel syndrome even though maximum pinch strength was similar. The path length, normalized by palm width of the thumb tip for the patients with carpal tunnel syndrome was less than for control participants (opposition: 2.2 palm width [95% CI, 1.8–2.6 palm width] versus 3.1 palm width [95% CI, 2.8–3.4 palm width], p \ 0.001; circumduction: 2.2 palm width [95% CI, 1.9–2.5 palm width] versus 2.9 palm width [95% CI, 2.7–3.2 palm width], p \ 0.001). Specifically, patients with carpal tunnel syndrome had a deficit of 0.3 palm width (95% CI, 0.04–0.52 palm width; p = 0.022) in the maximum position of their thumb tip ulnarly across the palm during opposition relative to control participants. The angular ROM also was reduced for the patients with carpal tunnel syndrome compared with the control participants in extension/flexion for the metacarpophalangeal (opposition: 34° versus 58°, p = .004; circumduction: 33° versus 58°, p \ 0.001) and interphalangeal (opposition: 37° versus 62°, p = .028; circumduction: 41° versus 63°, p = .025) joints. Conclusions Carpal tunnel syndrome disrupts kinematics of the thumb during opposition and circumduction despite normal pinch strength. Clinical Relevance Improving understanding of thumb pathokinematics associated with carpal tunnel syndrome may help clarify hand function impairment associated with the syndrome given the critical role of the thumb in dexterous manipulation. Introduction Carpal tunnel syndrome is the most common peripheral compression neuropathy, resulting from median nerve
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compression at the wrist. Its symptoms include sensory impairments (eg, numbness and paresthesias) and motor deficits in the abductor pollicis brevis, opponens pollicis, and the superficial belly of the flexor pollicis brevis, which are the intrinsic median-innervated muscles. Prolonged compression of the median nerve potentially disturbs motor function of the thenar muscles, and in patients with severe carpal tunnel syndrome, atrophy of the thenar muscles may result. The thumb is considered the central component in human hand dexterity because its function accounts for 40% to 50% of the hand’s usefulness [30, 33]. While completing functional tasks, the thumb is required to move in multiple directions through coordinated articulations at the carpometacarpal (CMC), metacarpophalangeal (MCP), and interphalangeal (IP) joints [14]. The thenar muscles contribute to thumb flexion, abduction, and pronation of the CMC joint; flexion and ulnar deviation of the MCP joint; and extension of the IP joint [11]. However, disruption in these movements may result when involved nerves and muscles are impaired [1]. During activities of daily living, patients with carpal tunnel syndrome often experience unintentional dropping of objects and clumsiness, but identifying and quantifying these motor deficits are challenging. Current evaluation approaches of carpal tunnel syndrome-related motor impairments include strength testing (ie, pinch [2, 4, 5], grip [2, 4], and thumb abduction [16, 23]) and questionnaire assessments (eg, Boston Carpal Tunnel Questionnaire [12]). The outcomes of these commonly used clinical evaluations are reflective of synergistic muscles innervated by several nerves which may not isolate the deficiencies specific to carpal tunnel syndrome [13]. Traditional goniometry also is used to assess static ROM, but it can be imprecise and unable to determine multiple degrees of freedom movement of the individual joints [32]. Three-dimensional (3-D) video motion analysis, using surface markers, has been used to capture thumb kinematics during dynamic movements in healthy populations and those with osteoarthritis [6, 14, 15, 18, 32, 35, 39]. Such an advanced motion analysis method has the potential to identify subtle kinematic changes associated with pathological hand conditions. For example, it has been shown that osteoarthritis of the thumb CMC joint results in reduced adduction and extension in the affected joint [6, 18] and that MCP joint extension precedes the sudden extension of the distal and proximal IP joints in trigger finger [17]. Using similar motion analysis methods to investigate carpal tunnel syndrome-related impairments may quantify abnormalities that potentially are undetectable using traditional approaches. Opposition and circumduction require well-coordinated, simultaneous movements across each of the three thumb
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joints; these motion patterns may be disrupted by carpal tunnel syndrome. The aim of our study was to investigate the motion deficits of the thumb associated with carpal tunnel syndrome during tasks of thumb opposition and circumduction. We hypothesized that carpal tunnel syndrome would lead to reduced translational and angular motion of the thumb.
Materials and Methods Human Subjects Twenty-two volunteers (11 patients with carpal tunnel syndrome, aged 50 ± 10 years; 11 control subjects, aged 49 ± 8 years) participated in this study; each group consisted of nine females and two males. All participants were right hand-dominant, as verified by the Edinburgh Handedness Inventory [22]. The diagnosis of carpal tunnel syndrome was made based on clinical discretion [10] and satisfied at least three of the following criteria: The patient had (1) a history of paresthesias, pain, and/or numbness in the median innervated hand territory persisting for at least 3 months; (2) positive provocative maneuvers (Tinel’s sign, Phalen’s test, and/or median nerve compression test); (3) abnormal electrodiagnostic testing consistent with median nerve neuropathy at/or distal to the wrist [31]; and (4) an overall carpal tunnel syndrome Symptom Severity Scale score [12] greater than 1.5. The participants in the control group reported no history of neuromusculoskeletal disorders affecting the right upper extremity, and apart from carpal tunnel syndrome, the patients had no other neuromuscular disorders in the affected upper extremity. For both groups, exclusion criteria included diabetes mellitus, gout, previous trauma to the right hand, pregnancy, rheumatoid arthritis, and osteoarthritis in the hand or wrist. Before experiment participation, each participant signed a consent form approved by the institutional review board.
Marker Placement Three-dimensional kinematics of the right thumb were obtained using a retroreflective surface-based marker method (Fig. 1). A nail-marker cluster [28] consisting of three markers (N1, N2, N3) was attached to the thumb nail. Additionally, two markers each were attached to the dorsal surface of the proximal phalanx (P1 and P2) and the first metacarpal (M1 and M2) of the thumb. A cluster with three markers (H1, H2, H3) was aligned longitudinally along the second metacarpal and placed in a stable location on the dorsal surface of the hand in accordance with the International Society of Biomechanics convention [38]. All
Thumb Motion and Carpal Tunnel Syndrome
counterclockwise direction (viewed proximal to distal) from the starting position of full thumb extension and were encouraged to explore the maximum amount of space with their thumb tip. Two sets, each consisting of five circumductions, were performed. Each task was performed at the participant’s self-selected pace with 1-minute resting intervals between consecutive sets. After completing the thumb opposition and circumduction tasks, the retroreflective markers were removed and participant-specific measurements of maximal voluntary pinch force were obtained. Study participants were asked to apply maximal force to a pinch gauge (Baseline Corporation, Irvington, NY, USA) using the pulps of their thumb and index finger within 5 seconds. Maximum pinch strength was repeated three times with 2 minutes of rest between consecutive trials. Fig. 1 The reflective nail markers (N1, N2, N3), proximal phalanx markers (P1, P2), first metacarpal markers (M1, M2), and hand markers (H1, H2, H3) used to obtain thumb kinematics are shown. The origins of local coordinate systems of the thumb segments, distal phalanx (DP), proximal phalanx (PP), and first metacarpal (MC), were at the determined proximal joint centers (dashed circles) and the origin of (H) was at the average position of the hand cluster markers (H1, H2, and H3). X = ulnar/radial axis; Y = dorsal/palmar axis; Z = proximal/distal axis.
markers and clusters were fixed to a flexible plastic base and attached to the participant using double-sided adhesive tape. During experimentation, the 3-D positions of the retroreflective markers were tracked with a motion capture system (Model 460; Vicon Motion Systems Ltd, Oxford, UK) at a sampling rate of 100 Hz.
Experimental Procedures Participants were seated in a height-adjustable chair and comfortably rested their right elbow on the testing table. Throughout testing, each participant was instructed to keep the four fingers of their right hand in full extension and their palm flat. At the beginning of each trial, participants positioned their thumb in maximal voluntary extension. Two thumb motion tasks were completed: (1) opposition and (2) circumduction. Before data collection, each participant was provided task instructions and permitted practice trials. For opposition, a cycle included beginning with the thumb in full extension, moving the tip of the thumb toward the distal palmar crease of the fifth digit (opposition), and then returning the thumb to the starting position (retroposition). Two sets of 10 cycles each were completed. During the circumduction task, participants were asked to move the thumb circumferentially in a
Data Analysis The functional joint centers of the IP, MCP, and CMC joints of the thumb were identified as previously described [21]. The local coordinate system of the distal phalanx was defined by the nail marker cluster and its origin was located at the determined functional joint center of the IP joint. The joint centers of the IP and the MCP joints were used in conjunction with the two surface markers on each segment to define the local coordinate systems of the proximal phalanx and the first metacarpal, respectively. The origins of proximal phalanx and metacarpal were located at the proximally located functional joint centers of each segment, respectively. The skin-marker cluster on the hand served as the local reference coordinate system, and its origin was calculated as the average position of the three markers of the cluster (Fig. 1). All marker data were lowpass filtered at 10 Hz using a third-order Butterworth filter. For each task, translational motion metrics of the thumb tip were examined for comparison between patients with carpal tunnel syndrome and control participants. The path length was calculated as the 3-D, curvilinear distance traveled by the thumb tip during each movement (opposition, circumduction) cycle. Additionally, the thumb tip’s 3-D position was analyzed to determine directional-specific deficiencies relative to the hand reference coordinate system, including its range and its positional extremes during opposition in the ulnar/radial (X-axis), dorsal/palmar (Y-axis), and proximal/distal (Z-axis) directions. All translational metrics were normalized by participant-specific palm width. Joint angles were determined according to an X-Y0 -Z00 Euler angle rotation sequence. The angular motion of the CMC, MCP, and IP joints was calculated following the convention of distal relative to the proximal segment
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motion. The rotations about the X, Y, and Z axes of each coordinate system were assumed to correspond to extension (+)/flexion (), abduction (+)/adduction (), and supination (+)/pronation (), respectively. Six rotational degrees of freedom were examined to represent the angular motion of the thumb during opposition and circumduction, specifically extension/flexion, abduction/adduction, and supination/pronation of the CMC joint, extension/flexion and abduction/adduction of the MCP joint, and extension/ flexion of the IP joint. The motion of the CMC joint, specifically motion of the first metacarpal with respect to the trapezium, was not directly measured. Rather, the second metacarpal was used as a surrogate for the trapezium under the assumption that relative changes in orientation between the trapezium and the second metacarpal would be minimal to sufficiently estimate CMC joint rotation [21]. For each of the six angular degrees of freedom, the ROM was calculated for both tasks (opposition, circumduction). For each task, the first and last cycles of each set were excluded from data analysis. Unpaired t-tests were used to compare the metrics in a given task between the patients with carpal tunnel syndrome and the control participants, and the pinch strength between the two groups. For the circumduction task, the MCP joint ROM in extension/
Fig. 2A–B The path lengths (solid line) of the thumb tip during (A) opposition and (B) circumduction for control participants and patients with carpal tunnel syndrome (CTS) normalized according to
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flexion failed normality and therefore the Mann Whitney rank-sum test was used. For statistical comparisons, a p value less than 0.05 was considered significant. Statistical analysis was performed using SigmaStat 3.4 (Systat Software Inc, San Jose, CA, USA).
Results Overall, carpal tunnel syndrome adversely affected thumb motion during opposition and circumduction; however, maximum voluntary pinch force was preserved for patients with carpal tunnel syndrome in comparison to control participants (53 N and 57 N, respectively; p = 0.6). The palm widths for the patients and control participants were 81 mm and 78 mm, respectively. The path lengths for the patients with carpal tunnel syndrome were 2.2 palm width (95% CI, 1.8–2.6 palm width) and 2.2 palm width (95% CI, 1.9–2.5 palm width) for opposition and circumduction, respectively. These were smaller than the path lengths for the control participants for opposition (3.1 palm width; 95% CI, 2.8–3.4 palm width; p \ 0.001) and circumduction (2.9 palm width; 95% CI, 2.7–3.2 palm width; p \ 0.001) (Fig. 2). In comparison to the control group, the ranges of thumb tip positional extremes during an
participant-specific palm width are shown. The SD about the mean is represented by the dashed lines.
Thumb Motion and Carpal Tunnel Syndrome
opposition cycle for the patients with carpal tunnel syndrome were smaller in the ulnar/radial (X-axis) and proximal/distal (Z-axis) directions with differences of 0.4 palm width (95% CI, 0.15–0.67 palm width; p = 0.004) and 0.2 palm width (95% CI, 0.11–0.35 palm width; p \ 0.001), respectively (Fig. 3). The range of the thumb tip position extremes in the dorsal/palmar (Y-axis) direction was not different between the two groups (p = 0.873). Specifically, the patients with carpal tunnel syndrome exhibited an inability to ulnarly reach a similar maximum position of their thumb tip with a deficit of 0.3 palm width in comparison to the control participants (95% CI, 0.04–0.52 palm width; p = 0.022). There was a smaller angular ROM for the patients with carpal tunnel syndrome in comparison to the control participants, although the thumb moved across all six angular degrees of freedom throughout both tasks (Fig. 4). During opposition, the largest ROM for patients with carpal tunnel syndrome and control participants occurred at the IP joint in extension/flexion; however, ROM at this joint for patients with carpal tunnel syndrome was less than that of the control participants (37° [95% CI, 21°–54°] versus 62° [95% CI, 46°–79°]; p = 0.028). Similarly, patients with carpal tunnel syndrome had less ROM of the MCP joint in extension/flexion during opposition, displaying 59% of the ROM of the control participants (34° [95% CI, 22°–46°]
versus 58° [95% CI, 47°–68°]; p = 0.004). The abduction/ adduction ROM of the MCP joint for the opposition task was relatively small and comparable for patients with carpal tunnel syndrome and control participants (10° [95% CI, 7°–14°] and 9° [95% CI, 5°–13°]; p = 0.675), respectively. In the CMC joint, patients with carpal tunnel syndrome did not show any differences in ROM for any of its angular rotations during opposition. For the circumduction task, ROM was the largest in extension/flexion at the IP and MCP joints. For patients with carpal tunnel syndrome, the IP joint ROM was 41° (95% CI, 23°–58°), which was less than ROM of the control participants (63°; 95% CI, 51°–76°; p = 0.025). Patients with carpal tunnel syndrome also had reduced ROM in MCP extension/flexion with median values of 33° and 58° for control participants (p \ 0.001). For the MCP joint, abduction/adduction ROM was relatively small, 31% and 26% of extension/flexion ROM for the patients and the control participants, respectively. During circumduction, the CMC joint ROM for each of the three angular rotations was between 30° and 31° for the patients and 29° and 40° for the control participants. Although no statistical differences were found among the angular degrees of freedom in the CMC joint, there was a trend of reduced ROM for patients with carpal tunnel syndrome in extension/flexion and supination/pronation (Fig. 4).
Fig. 3A–B The (A) X-Y (ulnar/radial-dorsal/palmar) and (B) X-Z (ulnar/radial-proximal/distal) positions of the thumb tip for a representative control participant and a patient with carpal tunnel
syndrome (CTS) during a cycle of opposition normalized by participant specific palm width are shown.
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Clinical Orthopaedics and Related Research1
Fig. 4 The thumb ROMs during opposition and circumduction for control participants and patients with carpal tunnel syndrome (CTS) in each of the six angular degrees of freedom are shown. *p \ 0.05;
**p \ 0.01; ***p \ 0.001; CMC = carpometacarpal; MCP = metacarpophalangeal; IP = interphalangeal.
Discussion
surrogate for the trapezium in CMC joint motion calculation. The use of this surrogate might have biased the absolute joint angle outcome, but the ROM should not be affected by this assumption. Third, there are known anatomic variations regarding innervations of the thenar muscles [11]. In our study, identification of participant-specific innervations of the thenar muscles was not done. It was assumed that all participants exhibited the most common innervation pattern. Fourth, the study sample size (11 patients with carpal tunnel syndrome and 11 control participants) was relatively small and a larger sample size may have revealed differences in parameters that show statistical insignificance but a trend. For example, post hoc power analysis revealed that 30 patients with carpal tunnel syndrome and control participants per group are needed to detect an 8° ROM difference at the CMC joint in the extension/flexion with 80% power during circumduction. Finally, the inclusion criteria for the patients with carpal tunnel syndrome did not control for varying disease severities. All patients with carpal tunnel syndrome were clinically diagnosed; however, symptom duration and impairment level varied. A future study may be done to examine the relationship between motion impairment and carpal tunnel syndrome severity. In this study, impaired translational and angular motions were observed to be associated with carpal tunnel
As a compression neuropathy of the median nerve, symptoms of carpal tunnel syndrome often include impaired motor function during activities of daily living. Patients experience impairments such as the inability to complete tasks because of unintentionally dropping objects or clumsiness. Currently, the commonly used approaches to evaluate these motor impairments, including strength measurements and static goniometry, are potentially unspecific in detecting pathologic changes associated with carpal tunnel syndrome. In this study, we aimed to reveal kinematic deficits of the thumb associated with carpal tunnel syndrome using a retroreflective surface-based marker method during thumb opposition and circumduction. The limitations of this study should be considered while interpreting its results. First, skin movement artifact may occur when using a surface-based marker method to quantify kinematics; however, this method is considered effective for evaluating thumb motion [6, 15], and care was taken to place each marker or cluster in a stable location to minimize potential artifact. Second, the CMC joint motion quantified by this method assumed that the relative changes between the trapezium and second metacarpal were minimal, and therefore the motion of the second metacarpal was used as a
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syndrome although there were no differences in maximum pinch strength between the two groups. Strength has been used to assess carpal tunnel syndrome-related impairment, but its outcomes have been mixed [2, 4, 13], and it has been shown that normal muscle strength does not necessarily translate to normal motor function [8, 20]. The reduction in thumb tip path length and maximum position indicate that patients with carpal tunnel syndrome had less overall thumb motion. Specifically, the deficit in maximum ulnar position, across the palm, of the thumb tip for patients with carpal tunnel syndrome during opposition may help to explain impaired grip function because it is essential to properly position the thumb during prehensile activities [25]. The reduced angular ROM for patients with carpal tunnel syndrome in IP and MCP joint extension/flexion may reveal an inhibition of the patients to tension the extrinsic flexor pollicis longus muscle whose tendon passes through the carpal tunnel to aid in flexing the thumb’s IP and MCP joints [7]. Active thumb IP joint flexion has been found to result in flexor pollicis longus tendon force of nearly 35 N [27], and loading the tendons that pass through the carpal tunnel have been shown to increase carpal tunnel pressure [9]. Furthermore, ultrasound examination of the carpal tunnel contents revealed that during thumb flexion, the flexor pollicis longus tendon moves palmarly and compresses the median nerve [37]. Therefore, patients with carpal tunnel syndrome may limit their IP and MCP joint motion to mitigate carpal tunnel pressure increases or additional median nerve impingement that may aggravate symptoms and add discomfort. In general, the angular ROMs observed in the control participants in our study were smaller for the CMC joint and larger for the IP joint than those previously reported [14]. These differences may be attributed to variations in instructions provided to participants completing the experimental tasks. For example, our participants were encouraged to use all thumb joints to complete the tasks, whereas in another study, maintaining MCP and IP joint extension during opposition and circumduction were explicitly prescribed [3]. In agreement with results of a previous study, both groups had increased ROM during circumduction in comparison to opposition [14]. One may have expected the greatest deficits to be in the CMC joint because of the role of the median innervated thenar muscles in its motion; however, CMC joint motion impairment was found to be insignificant. This may be attributable to the thumb’s complex network of intrinsic and extrinsic musculature that works together throughout thumb movements. Multiple muscles may act on each joint and their motor innervations can include the radial and ulnar nerves in addition to the median nerve [36]. Another factor that may have contributed to this finding is the
absence of atrophy of the thenar muscles in this patient group. Thenar muscle atrophy is a reliable sign of significant motor denervation and usually occurs in longstanding and severe cases of carpal tunnel syndrome [24]. It is expected that deficits in thumb kinematics would be greater in patients with advanced or severe carpal tunnel syndrome, including potentially significant changes in CMC joint motion. This notion may be explored in future studies. Additional factors such as pain and impaired proprioception also may have contributed to deficits in carpal tunnel syndrome thumb motion. Patients with carpal tunnel syndrome often have chronic pain and tingling, which can result in passive tissue rigidity and less of a likelihood to reach extreme ROM during functional tasks [29, 34]. It also is accepted that sensory impairment often precedes motor impairment in patients with carpal tunnel syndrome as sensory nerve fibers are more susceptible to injury from compression than motor fibers [19]. Sensory disturbance of the median nerve may affect the proprioception of patients with carpal tunnel syndrome, and proprioceptive impairment has been shown to interfere with upper extremity joint motion [26]. Our study showed that carpal tunnel syndrome is associated with kinematic abnormalities during thumb opposition and circumduction. Even when traditional measurements such as pinch strength do not indicate weakness, deficient motor capabilities may be present and interfere with successful completion of dexterous tasks. Future studies may explore severity specific deficiencies in thumb motion during opposition and circumduction associated with carpal tunnel syndrome. Given the critical role of the thumb in dexterous manipulation, improving the understanding of thumb pathokinematics may help to clarify the functional impairment of the hand associated with carpal tunnel syndrome. Moreover, the advanced kinematic analysis may be used to assess functional improvement of the thumb after carpal tunnel syndrome interventions.
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Clin Orthop Relat Res DOI 10.1007/s11999-014-3651-5
A Publication of The Association of Bone and Joint Surgeons®
BASIC RESEARCH
Carpal Tunnel Syndrome Impairs Thumb Opposition and Circumduction Motion Tamara L. Marquardt BS, Raviraj Nataraj PhD, Peter J. Evans MD, PhD, William H. Seitz Jr MD, Zong-Ming Li PhD
Received: 17 December 2013 / Accepted: 11 April 2014 Ó The Association of Bone and Joint Surgeons1 2014
Abstract Background Carpal tunnel syndrome is associated with sensory and motor impairments resulting from the compressed and malfunctioning median nerve. The thumb is critical to hand function, yet the pathokinematics of the thumb associated with carpal tunnel syndrome are not well understood. Questions/purposes The purpose of this study was to evaluate thumb motion abnormalities associated with carpal tunnel syndrome. We hypothesized that the ranges of translational and angular motion of the thumb would be reduced as a result of carpal tunnel syndrome. Methods Eleven patients with carpal tunnel syndrome and 11 healthy control subjects voluntarily participated in this Funding for this study was received from the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health (Award Number R01AR056964) (ZML). All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request. Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained. T. L. Marquardt, R. Nataraj, Z.-M. Li (&) Hand Research Laboratory, Department of Biomedical Engineering, Cleveland Clinic, 9500 Euclid Avenue, ND20, Cleveland, OH 44195, USA e-mail: [email protected]; [email protected] P. J. Evans, W. H. Seitz Jr, Z.-M. Li Department of Orthopaedic Surgery, Cleveland Clinic, Cleveland, OH, USA Z.-M. Li Department of Physical Medicine and Rehabilitation, Cleveland Clinic, Cleveland, OH, USA
study. Translational and angular kinematics of the thumb were obtained using marker-based video motion analysis during thumb opposition and circumduction movements. Results Motion deficits were observed for patients with carpal tunnel syndrome even though maximum pinch strength was similar. The path length, normalized by palm width of the thumb tip for the patients with carpal tunnel syndrome was less than for control participants (opposition: 2.2 palm width [95% CI, 1.8–2.6 palm width] versus 3.1 palm width [95% CI, 2.8–3.4 palm width], p \ 0.001; circumduction: 2.2 palm width [95% CI, 1.9–2.5 palm width] versus 2.9 palm width [95% CI, 2.7–3.2 palm width], p \ 0.001). Specifically, patients with carpal tunnel syndrome had a deficit of 0.3 palm width (95% CI, 0.04–0.52 palm width; p = 0.022) in the maximum position of their thumb tip ulnarly across the palm during opposition relative to control participants. The angular ROM also was reduced for the patients with carpal tunnel syndrome compared with the control participants in extension/flexion for the metacarpophalangeal (opposition: 34° versus 58°, p = .004; circumduction: 33° versus 58°, p \ 0.001) and interphalangeal (opposition: 37° versus 62°, p = .028; circumduction: 41° versus 63°, p = .025) joints. Conclusions Carpal tunnel syndrome disrupts kinematics of the thumb during opposition and circumduction despite normal pinch strength. Clinical Relevance Improving understanding of thumb pathokinematics associated with carpal tunnel syndrome may help clarify hand function impairment associated with the syndrome given the critical role of the thumb in dexterous manipulation. Introduction Carpal tunnel syndrome is the most common peripheral compression neuropathy, resulting from median nerve
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compression at the wrist. Its symptoms include sensory impairments (eg, numbness and paresthesias) and motor deficits in the abductor pollicis brevis, opponens pollicis, and the superficial belly of the flexor pollicis brevis, which are the intrinsic median-innervated muscles. Prolonged compression of the median nerve potentially disturbs motor function of the thenar muscles, and in patients with severe carpal tunnel syndrome, atrophy of the thenar muscles may result. The thumb is considered the central component in human hand dexterity because its function accounts for 40% to 50% of the hand’s usefulness [30, 33]. While completing functional tasks, the thumb is required to move in multiple directions through coordinated articulations at the carpometacarpal (CMC), metacarpophalangeal (MCP), and interphalangeal (IP) joints [14]. The thenar muscles contribute to thumb flexion, abduction, and pronation of the CMC joint; flexion and ulnar deviation of the MCP joint; and extension of the IP joint [11]. However, disruption in these movements may result when involved nerves and muscles are impaired [1]. During activities of daily living, patients with carpal tunnel syndrome often experience unintentional dropping of objects and clumsiness, but identifying and quantifying these motor deficits are challenging. Current evaluation approaches of carpal tunnel syndrome-related motor impairments include strength testing (ie, pinch [2, 4, 5], grip [2, 4], and thumb abduction [16, 23]) and questionnaire assessments (eg, Boston Carpal Tunnel Questionnaire [12]). The outcomes of these commonly used clinical evaluations are reflective of synergistic muscles innervated by several nerves which may not isolate the deficiencies specific to carpal tunnel syndrome [13]. Traditional goniometry also is used to assess static ROM, but it can be imprecise and unable to determine multiple degrees of freedom movement of the individual joints [32]. Three-dimensional (3-D) video motion analysis, using surface markers, has been used to capture thumb kinematics during dynamic movements in healthy populations and those with osteoarthritis [6, 14, 15, 18, 32, 35, 39]. Such an advanced motion analysis method has the potential to identify subtle kinematic changes associated with pathological hand conditions. For example, it has been shown that osteoarthritis of the thumb CMC joint results in reduced adduction and extension in the affected joint [6, 18] and that MCP joint extension precedes the sudden extension of the distal and proximal IP joints in trigger finger [17]. Using similar motion analysis methods to investigate carpal tunnel syndrome-related impairments may quantify abnormalities that potentially are undetectable using traditional approaches. Opposition and circumduction require well-coordinated, simultaneous movements across each of the three thumb
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joints; these motion patterns may be disrupted by carpal tunnel syndrome. The aim of our study was to investigate the motion deficits of the thumb associated with carpal tunnel syndrome during tasks of thumb opposition and circumduction. We hypothesized that carpal tunnel syndrome would lead to reduced translational and angular motion of the thumb.
Materials and Methods Human Subjects Twenty-two volunteers (11 patients with carpal tunnel syndrome, aged 50 ± 10 years; 11 control subjects, aged 49 ± 8 years) participated in this study; each group consisted of nine females and two males. All participants were right hand-dominant, as verified by the Edinburgh Handedness Inventory [22]. The diagnosis of carpal tunnel syndrome was made based on clinical discretion [10] and satisfied at least three of the following criteria: The patient had (1) a history of paresthesias, pain, and/or numbness in the median innervated hand territory persisting for at least 3 months; (2) positive provocative maneuvers (Tinel’s sign, Phalen’s test, and/or median nerve compression test); (3) abnormal electrodiagnostic testing consistent with median nerve neuropathy at/or distal to the wrist [31]; and (4) an overall carpal tunnel syndrome Symptom Severity Scale score [12] greater than 1.5. The participants in the control group reported no history of neuromusculoskeletal disorders affecting the right upper extremity, and apart from carpal tunnel syndrome, the patients had no other neuromuscular disorders in the affected upper extremity. For both groups, exclusion criteria included diabetes mellitus, gout, previous trauma to the right hand, pregnancy, rheumatoid arthritis, and osteoarthritis in the hand or wrist. Before experiment participation, each participant signed a consent form approved by the institutional review board.
Marker Placement Three-dimensional kinematics of the right thumb were obtained using a retroreflective surface-based marker method (Fig. 1). A nail-marker cluster [28] consisting of three markers (N1, N2, N3) was attached to the thumb nail. Additionally, two markers each were attached to the dorsal surface of the proximal phalanx (P1 and P2) and the first metacarpal (M1 and M2) of the thumb. A cluster with three markers (H1, H2, H3) was aligned longitudinally along the second metacarpal and placed in a stable location on the dorsal surface of the hand in accordance with the International Society of Biomechanics convention [38]. All
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counterclockwise direction (viewed proximal to distal) from the starting position of full thumb extension and were encouraged to explore the maximum amount of space with their thumb tip. Two sets, each consisting of five circumductions, were performed. Each task was performed at the participant’s self-selected pace with 1-minute resting intervals between consecutive sets. After completing the thumb opposition and circumduction tasks, the retroreflective markers were removed and participant-specific measurements of maximal voluntary pinch force were obtained. Study participants were asked to apply maximal force to a pinch gauge (Baseline Corporation, Irvington, NY, USA) using the pulps of their thumb and index finger within 5 seconds. Maximum pinch strength was repeated three times with 2 minutes of rest between consecutive trials. Fig. 1 The reflective nail markers (N1, N2, N3), proximal phalanx markers (P1, P2), first metacarpal markers (M1, M2), and hand markers (H1, H2, H3) used to obtain thumb kinematics are shown. The origins of local coordinate systems of the thumb segments, distal phalanx (DP), proximal phalanx (PP), and first metacarpal (MC), were at the determined proximal joint centers (dashed circles) and the origin of (H) was at the average position of the hand cluster markers (H1, H2, and H3). X = ulnar/radial axis; Y = dorsal/palmar axis; Z = proximal/distal axis.
markers and clusters were fixed to a flexible plastic base and attached to the participant using double-sided adhesive tape. During experimentation, the 3-D positions of the retroreflective markers were tracked with a motion capture system (Model 460; Vicon Motion Systems Ltd, Oxford, UK) at a sampling rate of 100 Hz.
Experimental Procedures Participants were seated in a height-adjustable chair and comfortably rested their right elbow on the testing table. Throughout testing, each participant was instructed to keep the four fingers of their right hand in full extension and their palm flat. At the beginning of each trial, participants positioned their thumb in maximal voluntary extension. Two thumb motion tasks were completed: (1) opposition and (2) circumduction. Before data collection, each participant was provided task instructions and permitted practice trials. For opposition, a cycle included beginning with the thumb in full extension, moving the tip of the thumb toward the distal palmar crease of the fifth digit (opposition), and then returning the thumb to the starting position (retroposition). Two sets of 10 cycles each were completed. During the circumduction task, participants were asked to move the thumb circumferentially in a
Data Analysis The functional joint centers of the IP, MCP, and CMC joints of the thumb were identified as previously described [21]. The local coordinate system of the distal phalanx was defined by the nail marker cluster and its origin was located at the determined functional joint center of the IP joint. The joint centers of the IP and the MCP joints were used in conjunction with the two surface markers on each segment to define the local coordinate systems of the proximal phalanx and the first metacarpal, respectively. The origins of proximal phalanx and metacarpal were located at the proximally located functional joint centers of each segment, respectively. The skin-marker cluster on the hand served as the local reference coordinate system, and its origin was calculated as the average position of the three markers of the cluster (Fig. 1). All marker data were lowpass filtered at 10 Hz using a third-order Butterworth filter. For each task, translational motion metrics of the thumb tip were examined for comparison between patients with carpal tunnel syndrome and control participants. The path length was calculated as the 3-D, curvilinear distance traveled by the thumb tip during each movement (opposition, circumduction) cycle. Additionally, the thumb tip’s 3-D position was analyzed to determine directional-specific deficiencies relative to the hand reference coordinate system, including its range and its positional extremes during opposition in the ulnar/radial (X-axis), dorsal/palmar (Y-axis), and proximal/distal (Z-axis) directions. All translational metrics were normalized by participant-specific palm width. Joint angles were determined according to an X-Y0 -Z00 Euler angle rotation sequence. The angular motion of the CMC, MCP, and IP joints was calculated following the convention of distal relative to the proximal segment
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motion. The rotations about the X, Y, and Z axes of each coordinate system were assumed to correspond to extension (+)/flexion (), abduction (+)/adduction (), and supination (+)/pronation (), respectively. Six rotational degrees of freedom were examined to represent the angular motion of the thumb during opposition and circumduction, specifically extension/flexion, abduction/adduction, and supination/pronation of the CMC joint, extension/flexion and abduction/adduction of the MCP joint, and extension/ flexion of the IP joint. The motion of the CMC joint, specifically motion of the first metacarpal with respect to the trapezium, was not directly measured. Rather, the second metacarpal was used as a surrogate for the trapezium under the assumption that relative changes in orientation between the trapezium and the second metacarpal would be minimal to sufficiently estimate CMC joint rotation [21]. For each of the six angular degrees of freedom, the ROM was calculated for both tasks (opposition, circumduction). For each task, the first and last cycles of each set were excluded from data analysis. Unpaired t-tests were used to compare the metrics in a given task between the patients with carpal tunnel syndrome and the control participants, and the pinch strength between the two groups. For the circumduction task, the MCP joint ROM in extension/
Fig. 2A–B The path lengths (solid line) of the thumb tip during (A) opposition and (B) circumduction for control participants and patients with carpal tunnel syndrome (CTS) normalized according to
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flexion failed normality and therefore the Mann Whitney rank-sum test was used. For statistical comparisons, a p value less than 0.05 was considered significant. Statistical analysis was performed using SigmaStat 3.4 (Systat Software Inc, San Jose, CA, USA).
Results Overall, carpal tunnel syndrome adversely affected thumb motion during opposition and circumduction; however, maximum voluntary pinch force was preserved for patients with carpal tunnel syndrome in comparison to control participants (53 N and 57 N, respectively; p = 0.6). The palm widths for the patients and control participants were 81 mm and 78 mm, respectively. The path lengths for the patients with carpal tunnel syndrome were 2.2 palm width (95% CI, 1.8–2.6 palm width) and 2.2 palm width (95% CI, 1.9–2.5 palm width) for opposition and circumduction, respectively. These were smaller than the path lengths for the control participants for opposition (3.1 palm width; 95% CI, 2.8–3.4 palm width; p \ 0.001) and circumduction (2.9 palm width; 95% CI, 2.7–3.2 palm width; p \ 0.001) (Fig. 2). In comparison to the control group, the ranges of thumb tip positional extremes during an
participant-specific palm width are shown. The SD about the mean is represented by the dashed lines.
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opposition cycle for the patients with carpal tunnel syndrome were smaller in the ulnar/radial (X-axis) and proximal/distal (Z-axis) directions with differences of 0.4 palm width (95% CI, 0.15–0.67 palm width; p = 0.004) and 0.2 palm width (95% CI, 0.11–0.35 palm width; p \ 0.001), respectively (Fig. 3). The range of the thumb tip position extremes in the dorsal/palmar (Y-axis) direction was not different between the two groups (p = 0.873). Specifically, the patients with carpal tunnel syndrome exhibited an inability to ulnarly reach a similar maximum position of their thumb tip with a deficit of 0.3 palm width in comparison to the control participants (95% CI, 0.04–0.52 palm width; p = 0.022). There was a smaller angular ROM for the patients with carpal tunnel syndrome in comparison to the control participants, although the thumb moved across all six angular degrees of freedom throughout both tasks (Fig. 4). During opposition, the largest ROM for patients with carpal tunnel syndrome and control participants occurred at the IP joint in extension/flexion; however, ROM at this joint for patients with carpal tunnel syndrome was less than that of the control participants (37° [95% CI, 21°–54°] versus 62° [95% CI, 46°–79°]; p = 0.028). Similarly, patients with carpal tunnel syndrome had less ROM of the MCP joint in extension/flexion during opposition, displaying 59% of the ROM of the control participants (34° [95% CI, 22°–46°]
versus 58° [95% CI, 47°–68°]; p = 0.004). The abduction/ adduction ROM of the MCP joint for the opposition task was relatively small and comparable for patients with carpal tunnel syndrome and control participants (10° [95% CI, 7°–14°] and 9° [95% CI, 5°–13°]; p = 0.675), respectively. In the CMC joint, patients with carpal tunnel syndrome did not show any differences in ROM for any of its angular rotations during opposition. For the circumduction task, ROM was the largest in extension/flexion at the IP and MCP joints. For patients with carpal tunnel syndrome, the IP joint ROM was 41° (95% CI, 23°–58°), which was less than ROM of the control participants (63°; 95% CI, 51°–76°; p = 0.025). Patients with carpal tunnel syndrome also had reduced ROM in MCP extension/flexion with median values of 33° and 58° for control participants (p \ 0.001). For the MCP joint, abduction/adduction ROM was relatively small, 31% and 26% of extension/flexion ROM for the patients and the control participants, respectively. During circumduction, the CMC joint ROM for each of the three angular rotations was between 30° and 31° for the patients and 29° and 40° for the control participants. Although no statistical differences were found among the angular degrees of freedom in the CMC joint, there was a trend of reduced ROM for patients with carpal tunnel syndrome in extension/flexion and supination/pronation (Fig. 4).
Fig. 3A–B The (A) X-Y (ulnar/radial-dorsal/palmar) and (B) X-Z (ulnar/radial-proximal/distal) positions of the thumb tip for a representative control participant and a patient with carpal tunnel
syndrome (CTS) during a cycle of opposition normalized by participant specific palm width are shown.
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Fig. 4 The thumb ROMs during opposition and circumduction for control participants and patients with carpal tunnel syndrome (CTS) in each of the six angular degrees of freedom are shown. *p \ 0.05;
**p \ 0.01; ***p \ 0.001; CMC = carpometacarpal; MCP = metacarpophalangeal; IP = interphalangeal.
Discussion
surrogate for the trapezium in CMC joint motion calculation. The use of this surrogate might have biased the absolute joint angle outcome, but the ROM should not be affected by this assumption. Third, there are known anatomic variations regarding innervations of the thenar muscles [11]. In our study, identification of participant-specific innervations of the thenar muscles was not done. It was assumed that all participants exhibited the most common innervation pattern. Fourth, the study sample size (11 patients with carpal tunnel syndrome and 11 control participants) was relatively small and a larger sample size may have revealed differences in parameters that show statistical insignificance but a trend. For example, post hoc power analysis revealed that 30 patients with carpal tunnel syndrome and control participants per group are needed to detect an 8° ROM difference at the CMC joint in the extension/flexion with 80% power during circumduction. Finally, the inclusion criteria for the patients with carpal tunnel syndrome did not control for varying disease severities. All patients with carpal tunnel syndrome were clinically diagnosed; however, symptom duration and impairment level varied. A future study may be done to examine the relationship between motion impairment and carpal tunnel syndrome severity. In this study, impaired translational and angular motions were observed to be associated with carpal tunnel
As a compression neuropathy of the median nerve, symptoms of carpal tunnel syndrome often include impaired motor function during activities of daily living. Patients experience impairments such as the inability to complete tasks because of unintentionally dropping objects or clumsiness. Currently, the commonly used approaches to evaluate these motor impairments, including strength measurements and static goniometry, are potentially unspecific in detecting pathologic changes associated with carpal tunnel syndrome. In this study, we aimed to reveal kinematic deficits of the thumb associated with carpal tunnel syndrome using a retroreflective surface-based marker method during thumb opposition and circumduction. The limitations of this study should be considered while interpreting its results. First, skin movement artifact may occur when using a surface-based marker method to quantify kinematics; however, this method is considered effective for evaluating thumb motion [6, 15], and care was taken to place each marker or cluster in a stable location to minimize potential artifact. Second, the CMC joint motion quantified by this method assumed that the relative changes between the trapezium and second metacarpal were minimal, and therefore the motion of the second metacarpal was used as a
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syndrome although there were no differences in maximum pinch strength between the two groups. Strength has been used to assess carpal tunnel syndrome-related impairment, but its outcomes have been mixed [2, 4, 13], and it has been shown that normal muscle strength does not necessarily translate to normal motor function [8, 20]. The reduction in thumb tip path length and maximum position indicate that patients with carpal tunnel syndrome had less overall thumb motion. Specifically, the deficit in maximum ulnar position, across the palm, of the thumb tip for patients with carpal tunnel syndrome during opposition may help to explain impaired grip function because it is essential to properly position the thumb during prehensile activities [25]. The reduced angular ROM for patients with carpal tunnel syndrome in IP and MCP joint extension/flexion may reveal an inhibition of the patients to tension the extrinsic flexor pollicis longus muscle whose tendon passes through the carpal tunnel to aid in flexing the thumb’s IP and MCP joints [7]. Active thumb IP joint flexion has been found to result in flexor pollicis longus tendon force of nearly 35 N [27], and loading the tendons that pass through the carpal tunnel have been shown to increase carpal tunnel pressure [9]. Furthermore, ultrasound examination of the carpal tunnel contents revealed that during thumb flexion, the flexor pollicis longus tendon moves palmarly and compresses the median nerve [37]. Therefore, patients with carpal tunnel syndrome may limit their IP and MCP joint motion to mitigate carpal tunnel pressure increases or additional median nerve impingement that may aggravate symptoms and add discomfort. In general, the angular ROMs observed in the control participants in our study were smaller for the CMC joint and larger for the IP joint than those previously reported [14]. These differences may be attributed to variations in instructions provided to participants completing the experimental tasks. For example, our participants were encouraged to use all thumb joints to complete the tasks, whereas in another study, maintaining MCP and IP joint extension during opposition and circumduction were explicitly prescribed [3]. In agreement with results of a previous study, both groups had increased ROM during circumduction in comparison to opposition [14]. One may have expected the greatest deficits to be in the CMC joint because of the role of the median innervated thenar muscles in its motion; however, CMC joint motion impairment was found to be insignificant. This may be attributable to the thumb’s complex network of intrinsic and extrinsic musculature that works together throughout thumb movements. Multiple muscles may act on each joint and their motor innervations can include the radial and ulnar nerves in addition to the median nerve [36]. Another factor that may have contributed to this finding is the
absence of atrophy of the thenar muscles in this patient group. Thenar muscle atrophy is a reliable sign of significant motor denervation and usually occurs in longstanding and severe cases of carpal tunnel syndrome [24]. It is expected that deficits in thumb kinematics would be greater in patients with advanced or severe carpal tunnel syndrome, including potentially significant changes in CMC joint motion. This notion may be explored in future studies. Additional factors such as pain and impaired proprioception also may have contributed to deficits in carpal tunnel syndrome thumb motion. Patients with carpal tunnel syndrome often have chronic pain and tingling, which can result in passive tissue rigidity and less of a likelihood to reach extreme ROM during functional tasks [29, 34]. It also is accepted that sensory impairment often precedes motor impairment in patients with carpal tunnel syndrome as sensory nerve fibers are more susceptible to injury from compression than motor fibers [19]. Sensory disturbance of the median nerve may affect the proprioception of patients with carpal tunnel syndrome, and proprioceptive impairment has been shown to interfere with upper extremity joint motion [26]. Our study showed that carpal tunnel syndrome is associated with kinematic abnormalities during thumb opposition and circumduction. Even when traditional measurements such as pinch strength do not indicate weakness, deficient motor capabilities may be present and interfere with successful completion of dexterous tasks. Future studies may explore severity specific deficiencies in thumb motion during opposition and circumduction associated with carpal tunnel syndrome. Given the critical role of the thumb in dexterous manipulation, improving the understanding of thumb pathokinematics may help to clarify the functional impairment of the hand associated with carpal tunnel syndrome. Moreover, the advanced kinematic analysis may be used to assess functional improvement of the thumb after carpal tunnel syndrome interventions.
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