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The effect of flexor digitorum profundus quadriga on grip strength
ARTICLE IN PRESS THE EFFECT OF FLEXOR DIGITORUM PROFUNDUS QUADRIGA ON GRIP STRENGTH T. C. HORTON, S. SAUERLAND and T. R. C. DAVIS From the Department of Trauma and Orthopaedics, Queens Medical Centre, Nottingham, UK and the Institute for Research in Operative Medicine, University of Witten/Herdecke, Germany
This study evaluated the flexor digitorum profundus quadriga effect by mimicking stiffness of one finger and observing its effect on the strengths of the other three fingers of the same hand. Thermoplastic wedges were used to simulate mild, moderate and severe stiffness of each finger and the individual strengths of each finger during power grip were measured using a digit-gripTM dynamometer in ten healthy adult volunteers. Middle, ring, and little fingers strength diminished significantly (Po0.05) when each of the other fingers, including the index, was stiffened. Index finger strength was largely unaffected by simulated stiffness of the other fingers. The degree of simulated stiffness influenced the strength of the other fingers, but there was considerable intersubject variability, suggesting that the significance of the quadriga effect varies between individuals. An anatomical basis for our findings is suggested. Journal of Hand Surgery (European Volume, 2007) 32E: 2: 130–134 Keywords: quadriga, flexor digitorum profundus, grip strength, finger stiffness
The quadriga, or profundus tendon blockage phenomenon, occurs most commonly when full proximal excursion of one of the finger flexor digitorum profundus (FDP) tendons is prevented by finger stiffness or adhesions. This prevents full FDP excursion and, thus, full flexion of the remaining fingers because the FDP tendons to the middle, ring and little fingers share a common muscle belly. The patient may also experience a loss of grip strength that exceeds the lost contribution of the stiff finger alone because of weakness of the adjacent fingers as a result of their restricted finger flexion (Bunnell, 1924; Verdan, 1960). As the index finger FDP tendon has its own muscle belly, stiffness of the index finger should not have any effect on the function of the middle, ring and little fingers and stiffness of one or more of the ulnar three fingers should have no effect on the strength of the index finger. Although the quadriga syndrome occurs commonly in clinical practice, its effect on hand strength is unknown and the relationship between the degree of finger stiffness and the loss of grip strength remains undefined. It is also not known whether the quadriga effect varies depending upon which finger is stiff, or whether certain fingers are more susceptible than others to weakness due to this phenomenon. Although the effect is expected to be different for the index finger, this has not been investigated. Finally, it is not known if all patients are equally at risk of developing the quadriga effect, or whether anatomical, or physiological, variations place some at high risk of developing a clinically significant effect, whereas others are relatively immune to the problem. This experimental study aimed to evaluate the effect of blocking full flexion of one finger on the strengths of the other three fingers of the same hand in ten healthy volunteers.
SUBJECTS AND METHODS Ten healthy adult volunteers with a mean age of 45 (range 32–63) years were recruited to the study. Exclusion criteria included a history of significant upper limb trauma or pathology and current upper limb weakness, pain or stiffness. Six of the volunteers were women and four were men. Nine were right hand dominant. The group consisted of four manual, two office and four fine skilled workers. We used a recently calibrated digit-gripTM dynamometer (NK Biotechnical Corporation, Minneapolis, USA) which has four force meters, one for each individual finger, such that it measures the individual strength of each finger during power grip (Fig 1). All measurements were performed with the handle on the first setting, which is equivalent to a grip width halfway between the second and third settings of a JAMAR dynamometer (Jamar, Jackson, Mississippi). Three thermoplastic wedges were designed to fit onto the handle of the dynamometer and cover the force meter of a single finger. These wedges simulated finger stiffness by providing a block to flexion for a single digit. They also prevented measurement of the strength of the ‘‘blocked’’ digit. The smallest wedge simulated mild stiffness and increased fingertip to distal palmar crease distance by 0.5 cm. The medium wedge simulated moderate stiffness, increasing fingertip to distal palmar crease distance by 1.5 cm. The largest wedge simulated severe stiffness, with an increased fingertip to distal palmar crease distance of 2.0 cm. The individual strengths of the fingers during power grip were measured in the dominant hand of each volunteer in a standardised manner during four sessions, which were held on different days in order to reduce fatigue bias. Twelve measurements of grip strength were 130
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131
Fig 1 The digit-gripTM dynamometer which has four force meters, one for each individual finger. (a) In this illustration, the strengths of all four fingers is measured without simulated stiffness of any finger; (b) in this illustration, the strengths of the index, ring and little fingers are measured after a wedge has been placed on the force meter for the middle finger, in order to simulate stiffness of the middle finger.
performed during each session with rest periods of 2 minutes after each grip, such that each session lasted approximately 30 minutes. The volunteer stood with the elbow flexed to 901 and the forearm in neutral rotation, holding the digit-gripTM dynamometer. The position of the fingertips on the receptor pads was checked to eliminate overlap of the fingers and the volunteer was then asked to grip the dynamometer as hard as possible. During each of the four 30 minute assessment sessions, the effect of blocking full flexion of one particular finger was investigated. The order of the sessions in which each of the four fingers of each patient was blocked was random and, thus, varied from subject to subject. In each session, the strengths of the three fingers which were not ‘‘blocked’’ were measured on three occasions in the following four situations: finger strength with no block to finger flexion; finger strength with one finger blocked using the smallest wedge; finger strength with the same finger blocked using the medium wedge and finger strength with the same finger blocked using the largest wedge. The order in which the wedges were applied was varied and the three measurements of the strength of each finger in each situation were averaged. This data established the effect of ‘‘blocking flexion’’ (simulated stiffness) of a single finger on the strengths of the other ‘‘normal’’ fingers. Statistical analysis An analysis of variance (ANOVA) for multiply repeated measures was used for the statistical analysis of finger
strength. This analysis included three independent variables: firstly, the finger whose strength was measured; secondly, the finger which was blocked and, thirdly, the degree of blocking (on a linear scale from 0 to 3). Since sphericity of data (i.e. multidimensional normal distribution) was not fully given (P ¼ 0:037 by Mauchly’s test), degrees of freedom were corrected by Greenhouse–Geisser’s epsilon before obtaining multivariate P values. The general linear model also included three quadratic and one cubic interaction terms. After overall data analysis, effects were examined for each single finger, again using repeated measures ANOVA. P values of less than 0.05 were considered significant.
RESULTS As expected, finger strength differed between the different fingers (P ¼ 0:001 by ANOVA) and it was also affected by the degree of blocking (Po0.001). With regard to finger strength, it was generally not important which other finger was blocked ðP ¼ 0:72Þ: However, there was a significant interaction between ‘‘finger examined’’ and ‘‘finger blocked’’ ðP ¼ 0:035Þ; indicating a specific relationship in some, but not all, fingers. As shown in Fig 2, the strength of the index finger was largely unaffected by blocking flexion of other fingers, whereas the middle, ring, and little fingers exhibited reduced strength when any other finger, including the index, was blocked. The interaction term between ‘‘finger examined’’ and ‘‘degree of stiffness’’ was also significant ðP ¼ 0:008Þ:
ARTICLE IN PRESS 132
THE JOURNAL OF HAND SURGERY VOL. 32E No. 2 APRIL
2007
Finger Strength (Kg) Middle
Index
Index
Ring 15
15
10
10
10
5
5
5
0
Middle Blocked Finger
1
2
3
0
1
2
3
15
15
15
10
10
10
5
5
5
0 1
2
3
0
1
2
3
15
15
15
10
10
10
5
5
5
0
0 0
1
2
3
1
2
3
0
1
2
3
0
1
2
3
0 0
1
2
3
15
15
15
10
10
10
5
5
5
0
0
0
0 0
Ring
0
0 0
Little
Little
15
0 0
1
2
3
0
1
2
3
0
1
2
3
Fig 2 Grip strength of each finger with each of the other fingers blocked. The columns show the fingers being measured (first column for index finger, second for middle finger, etc.) and rows are for fingers being blocked (top row – index finger, second row – middle finger, etc.). In each graph, the different degrees of immobilisation (0 ¼ none, 1 ¼ smallest block, 3 ¼ largest block) are shown on the X-axis. Data are given as mean values with standard deviations. Each mean represents measurements from ten individuals.
This was possibly because the linear relationship between degree of blocking and strength was more consistent for the middle and ring fingers. The index and little fingers show only marginal signs of an association with degree of simulated stiffness. When restricting analysis to each of the fingers, there was no significant effect detectable in the index finger when any other finger was blocked ðP ¼ 0:12Þ: For the middle, ring and little fingers, it did not matter which other finger was blocked (P ¼ 0:64; 0.16 and 0.31, respectively), but the effect of simulated stiffness on finger strength was clearly detectable (Po0.001 for all). None of the interaction terms reached significance. There was considerable variability of the effect of
blocking finger flexion on the strengths of the other fingers between the 10 subjects (Table 1).
DISCUSSION Quadriga was first described by Bunnell (1924), who observed ‘‘As the flexor tendons arise from practically a common muscle belly, the function of one tendon limits the excursion of the rest of the tendons’’. This was noted in relation to a technique of finger amputation in which the FDP tendon was sutured to the extensor tendon over the end of the bone. The phenomenon was termed ‘‘Quadriga’’ by Verdan (1960), who compared it to the
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Table 1—Finger strength expressed as a percentage of normal (100%) Finger with stiffness and degree of stiffness (0–3)
Finger strength
Index
Middle
Index 1 2 3
85 60 50
28–115 18–115 15–108
Middle 1 2 3
91 79 92
57–143 45–162 8–127
Ring 1 2 3
83 100 116
51–135 45–187 6–204
82 77 72
38–139 36–156 12–126
Little 1 2 3
85 77 94
62–310 5–390 0–305
84 80 70
40–117 25–108 31–170
Ring
Little
78 51 48
30–124 19–95 8–95
73 48 63
17–105 17–113 14–93
85 84 52
51–99 34–150 17–101
84 90 42
22–143 37–135 19–130
81 66 31
45–108 9–118 31–74
111 98 69
28–262 72–600 54–469
Data are median values and ranges. 1 ¼ small wedge; 2 ¼ medium wedge; 3 ¼ large wedge.
Roman four horse chariot, the Quadriga. His original description cannot be bettered: ‘‘The muscular bodies of the flexors can be compared to the driver of a Roman chariot, the auriga, whereas the reins of his four horses are like the flexor tendons, two reins per horse and two tendons per finger. Now, we know that the drivers of quadrigas did not hold their reins in their hands, which they had to keep free for the whip or for grasping the bar of the chariot during racing in the Circus Maximus. The reins were wound around the charioteer’s body and the auriga curbed, or guided, his horses by bending his body backward, or to either side, while stressing his action by the motion of his left hand on certain reins. I am fond of comparing that performance to the effect of the common muscular body upon the flexor tendons, whose functional individuality is limited. As a matter of fact, the muscular body can act efficiently only if the gliding amplitude of each of the four tendinous reins is normal.’’ In addition, Verdan observed that patients with quadriga also complained of a lack of prehensile power. Quadriga occurs because the ulnar three fingers are flexed by a single ulnar belly of the FDP muscle, whose origin is on the flexor aspect of the ulna and the interosseous membrane. Seven to 12 tendon units, clearly linked together, arise from the ulnar belly of the muscle. Distally these units form the three definitive tendons for the middle, ring and little fingers. This ulnar muscle belly is distinct from the smaller radial muscle
belly of the FDP muscle, which provides a single tendon for the index finger alone. The three ulnar tendons are also joined at the base of the palm by the origins of the third and fourth lumbrical muscles. Motion of the FDP tendon to the index finger may not be entirely independent of that of the other FDP tendons, as all four FDP tendons are loosely tethered together by the synovium of the carpal tunnel which envelops all of the profundi tendons and loosely attaches them to the sides and floor of the carpal tunnel (Fahrer, 1979). The Quadriga syndrome can occur as a consequence of trauma to any of the three ulnar fingers, if this causes joint stiffness or tendon adhesions resulting in restricted flexion. Restricted flexion of one or more of these digits prevents full contraction of the shared ulnar belly of the FDP muscle, causing restricted FDP gliding and reduced finger flexion and strength of flexion in the other two ulnar digits. The patient may present with loss of flexion in the normal fingers or weakness of grip, particularly for small objects, which exceeds the weakness expected as a result of the lost contribution of the stiff finger alone. The results of this study demonstrate the existence of the quadriga effect when a finger is blocked to prevent full flexion. The study also demonstrates that the index finger with its apparently independent FDP muscle belly is not entirely independent from the FDP musculotendinous unit for the ulnar three digits in that the strengths of the middle, ring and little finger are reduced by simulated stiffness of the index finger. However, the strength of the index finger is not reduced by simulated stiffness of any other digit. This finding could be
ARTICLE IN PRESS 134
Fig 3 An oblique fibrous band (a) connecting the index FDP musculotendinous unit to the combined FDP musculotendinous unit for the middle, ring and little fingers would explain the findings of the present study. Flexion of the index finger is not prevented by restricted flexion of the other digits as the connecting band will then become lax. However, the band becomes tight if index finger flexion is restricted during flexion of any of the other digits.
explained on an anatomical basis by the presence of an oblique connection between the index and the combined middle, ring and little finger musculotendinous units which becomes lax when the index finger is flexed relative to the other digits and tight when the other digits are flexed relative to the index finger (Fig 3). This structure could be soft tissue connections between the radial and ulnar bellies of the FDP muscle, a tendinous band between the index and middle finger FDP tendons, or the synovium of the carpal tunnel, as suggested by Fahrer (1979). Linburg and Comstock (1979) and Slater (2001) have described a ‘‘quadriga’’ type of link between the thumb and the index and middle fingers as a result of two anomalous tendons joining the flexor pollicis longus to the index and middle finger FDP tendons. As all of these muscle arise from a common mesodermal mass (Kaplan and Riordan, 1984; Mangini, 1960), muscular, or tendinous, interconnections between the index and middle finger FDP tendons are a likely anomaly. We do not consider that our findings for the index finger could have been created artefactually by our study design as systematic bias was avoided by randomly selecting the order in which the fingers were blocked in each subject.
THE JOURNAL OF HAND SURGERY VOL. 32E No. 2 APRIL
2007
The effect of blocking flexion of one finger on the other digits varied considerably between individuals. Some of this variability could be explained by the random sequence in which the different sized wedges were introduced to block finger flexion, such that any muscle fatigue would have different effects on the results of different subjects. In addition, the increased strength measurements which were, sometimes, observed in fingers with blocking of the other digits does suggest some variability in the ability of the subject to grip the measuring instrument as hard as possible or, possibly, some error in the accuracy of the instrument, even although this was calibrated at the start of each measurement session. However, the potential for muscle fatigue was reduced by performing the measurements in four sessions on different days and allowing 2 minute rest intervals between each of the four sets (no blocking and small, medium and large wedges) of three grip measurements. We suggest that, at least, some of the intersubject variability was due to different levels of development of interconnections between the musculotendinous units of the index and the ulnar three fingers, and, also, possibly, because some individuals have middle, ring and little finger musculotendinous units which are firmly bound together while other have more lax connections, which allow some independent movements of their FDP tendons. Whatever the cause, the intersubject variability in the quadriga effect which we observed prevents the prediction of the effect of stiffness or reduced tendon gliding in one finger on the strengths of the hand and the other three digits. References Bunnell S (1924). Reconstructive surgery of the hand. Surgery Gynecology and Obstetrics, 34: 259–274. Fahrer M. In: Verdan C (Ed) Tendon surgery of the hand, Edinburgh, Churchill Livingstone, 1979: 17–24. Kaplan EB, Riordan DC. The Thumb. In: Spinner M (Ed) Kaplan’s functional and surgical anatomy of the hand, Philadelphia, JB Lippincott, 1984: 125. Linburg RM, Comstock BE (1979). Anomalous tendon slips from the flexor pollicis longus to the flexor digitorum profundus. Journal of Hand Surgery, 4: 79–83. Mangini U (1960). Flexor pollicis longus muscle: its morphology and clinical significance. Journal of Bone and Joint Surgery, 42A: 467–470. Slater RR (2001). Flexor tendon anomalies in a patient with carpal tunnel syndrome. Journal of Hand Surgery, 26B: 373–376. Verdan C (1960). Syndrome of the quadriga. Surgical Clinics of North America, 40: 425–426. Received: 18 February 2006 Accepted after revision: 8 November 2006 Prof TRC Davis, Department of Trauma and Orthopaedics, Queens Medical Centre, Nottingham, NG7 2UH, UK. Tel.: +44 1159 249924x44337; fax: +44 1159 209921. E-mail: [email protected]
r 2006 The British Society for Surgery of the Hand. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.jhsb.2006.11.005 available online at http://www.sciencedirect.com
This study evaluated the flexor digitorum profundus quadriga effect by mimicking stiffness of one finger and observing its effect on the strengths of the other three fingers of the same hand. Thermoplastic wedges were used to simulate mild, moderate and severe stiffness of each finger and the individual strengths of each finger during power grip were measured using a digit-gripTM dynamometer in ten healthy adult volunteers. Middle, ring, and little fingers strength diminished significantly (Po0.05) when each of the other fingers, including the index, was stiffened. Index finger strength was largely unaffected by simulated stiffness of the other fingers. The degree of simulated stiffness influenced the strength of the other fingers, but there was considerable intersubject variability, suggesting that the significance of the quadriga effect varies between individuals. An anatomical basis for our findings is suggested. Journal of Hand Surgery (European Volume, 2007) 32E: 2: 130–134 Keywords: quadriga, flexor digitorum profundus, grip strength, finger stiffness
The quadriga, or profundus tendon blockage phenomenon, occurs most commonly when full proximal excursion of one of the finger flexor digitorum profundus (FDP) tendons is prevented by finger stiffness or adhesions. This prevents full FDP excursion and, thus, full flexion of the remaining fingers because the FDP tendons to the middle, ring and little fingers share a common muscle belly. The patient may also experience a loss of grip strength that exceeds the lost contribution of the stiff finger alone because of weakness of the adjacent fingers as a result of their restricted finger flexion (Bunnell, 1924; Verdan, 1960). As the index finger FDP tendon has its own muscle belly, stiffness of the index finger should not have any effect on the function of the middle, ring and little fingers and stiffness of one or more of the ulnar three fingers should have no effect on the strength of the index finger. Although the quadriga syndrome occurs commonly in clinical practice, its effect on hand strength is unknown and the relationship between the degree of finger stiffness and the loss of grip strength remains undefined. It is also not known whether the quadriga effect varies depending upon which finger is stiff, or whether certain fingers are more susceptible than others to weakness due to this phenomenon. Although the effect is expected to be different for the index finger, this has not been investigated. Finally, it is not known if all patients are equally at risk of developing the quadriga effect, or whether anatomical, or physiological, variations place some at high risk of developing a clinically significant effect, whereas others are relatively immune to the problem. This experimental study aimed to evaluate the effect of blocking full flexion of one finger on the strengths of the other three fingers of the same hand in ten healthy volunteers.
SUBJECTS AND METHODS Ten healthy adult volunteers with a mean age of 45 (range 32–63) years were recruited to the study. Exclusion criteria included a history of significant upper limb trauma or pathology and current upper limb weakness, pain or stiffness. Six of the volunteers were women and four were men. Nine were right hand dominant. The group consisted of four manual, two office and four fine skilled workers. We used a recently calibrated digit-gripTM dynamometer (NK Biotechnical Corporation, Minneapolis, USA) which has four force meters, one for each individual finger, such that it measures the individual strength of each finger during power grip (Fig 1). All measurements were performed with the handle on the first setting, which is equivalent to a grip width halfway between the second and third settings of a JAMAR dynamometer (Jamar, Jackson, Mississippi). Three thermoplastic wedges were designed to fit onto the handle of the dynamometer and cover the force meter of a single finger. These wedges simulated finger stiffness by providing a block to flexion for a single digit. They also prevented measurement of the strength of the ‘‘blocked’’ digit. The smallest wedge simulated mild stiffness and increased fingertip to distal palmar crease distance by 0.5 cm. The medium wedge simulated moderate stiffness, increasing fingertip to distal palmar crease distance by 1.5 cm. The largest wedge simulated severe stiffness, with an increased fingertip to distal palmar crease distance of 2.0 cm. The individual strengths of the fingers during power grip were measured in the dominant hand of each volunteer in a standardised manner during four sessions, which were held on different days in order to reduce fatigue bias. Twelve measurements of grip strength were 130
ARTICLE IN PRESS THE EFFECT OF FLEXOR DIGITORUM PROFUNDUS QUADRIGA
131
Fig 1 The digit-gripTM dynamometer which has four force meters, one for each individual finger. (a) In this illustration, the strengths of all four fingers is measured without simulated stiffness of any finger; (b) in this illustration, the strengths of the index, ring and little fingers are measured after a wedge has been placed on the force meter for the middle finger, in order to simulate stiffness of the middle finger.
performed during each session with rest periods of 2 minutes after each grip, such that each session lasted approximately 30 minutes. The volunteer stood with the elbow flexed to 901 and the forearm in neutral rotation, holding the digit-gripTM dynamometer. The position of the fingertips on the receptor pads was checked to eliminate overlap of the fingers and the volunteer was then asked to grip the dynamometer as hard as possible. During each of the four 30 minute assessment sessions, the effect of blocking full flexion of one particular finger was investigated. The order of the sessions in which each of the four fingers of each patient was blocked was random and, thus, varied from subject to subject. In each session, the strengths of the three fingers which were not ‘‘blocked’’ were measured on three occasions in the following four situations: finger strength with no block to finger flexion; finger strength with one finger blocked using the smallest wedge; finger strength with the same finger blocked using the medium wedge and finger strength with the same finger blocked using the largest wedge. The order in which the wedges were applied was varied and the three measurements of the strength of each finger in each situation were averaged. This data established the effect of ‘‘blocking flexion’’ (simulated stiffness) of a single finger on the strengths of the other ‘‘normal’’ fingers. Statistical analysis An analysis of variance (ANOVA) for multiply repeated measures was used for the statistical analysis of finger
strength. This analysis included three independent variables: firstly, the finger whose strength was measured; secondly, the finger which was blocked and, thirdly, the degree of blocking (on a linear scale from 0 to 3). Since sphericity of data (i.e. multidimensional normal distribution) was not fully given (P ¼ 0:037 by Mauchly’s test), degrees of freedom were corrected by Greenhouse–Geisser’s epsilon before obtaining multivariate P values. The general linear model also included three quadratic and one cubic interaction terms. After overall data analysis, effects were examined for each single finger, again using repeated measures ANOVA. P values of less than 0.05 were considered significant.
RESULTS As expected, finger strength differed between the different fingers (P ¼ 0:001 by ANOVA) and it was also affected by the degree of blocking (Po0.001). With regard to finger strength, it was generally not important which other finger was blocked ðP ¼ 0:72Þ: However, there was a significant interaction between ‘‘finger examined’’ and ‘‘finger blocked’’ ðP ¼ 0:035Þ; indicating a specific relationship in some, but not all, fingers. As shown in Fig 2, the strength of the index finger was largely unaffected by blocking flexion of other fingers, whereas the middle, ring, and little fingers exhibited reduced strength when any other finger, including the index, was blocked. The interaction term between ‘‘finger examined’’ and ‘‘degree of stiffness’’ was also significant ðP ¼ 0:008Þ:
ARTICLE IN PRESS 132
THE JOURNAL OF HAND SURGERY VOL. 32E No. 2 APRIL
2007
Finger Strength (Kg) Middle
Index
Index
Ring 15
15
10
10
10
5
5
5
0
Middle Blocked Finger
1
2
3
0
1
2
3
15
15
15
10
10
10
5
5
5
0 1
2
3
0
1
2
3
15
15
15
10
10
10
5
5
5
0
0 0
1
2
3
1
2
3
0
1
2
3
0
1
2
3
0 0
1
2
3
15
15
15
10
10
10
5
5
5
0
0
0
0 0
Ring
0
0 0
Little
Little
15
0 0
1
2
3
0
1
2
3
0
1
2
3
Fig 2 Grip strength of each finger with each of the other fingers blocked. The columns show the fingers being measured (first column for index finger, second for middle finger, etc.) and rows are for fingers being blocked (top row – index finger, second row – middle finger, etc.). In each graph, the different degrees of immobilisation (0 ¼ none, 1 ¼ smallest block, 3 ¼ largest block) are shown on the X-axis. Data are given as mean values with standard deviations. Each mean represents measurements from ten individuals.
This was possibly because the linear relationship between degree of blocking and strength was more consistent for the middle and ring fingers. The index and little fingers show only marginal signs of an association with degree of simulated stiffness. When restricting analysis to each of the fingers, there was no significant effect detectable in the index finger when any other finger was blocked ðP ¼ 0:12Þ: For the middle, ring and little fingers, it did not matter which other finger was blocked (P ¼ 0:64; 0.16 and 0.31, respectively), but the effect of simulated stiffness on finger strength was clearly detectable (Po0.001 for all). None of the interaction terms reached significance. There was considerable variability of the effect of
blocking finger flexion on the strengths of the other fingers between the 10 subjects (Table 1).
DISCUSSION Quadriga was first described by Bunnell (1924), who observed ‘‘As the flexor tendons arise from practically a common muscle belly, the function of one tendon limits the excursion of the rest of the tendons’’. This was noted in relation to a technique of finger amputation in which the FDP tendon was sutured to the extensor tendon over the end of the bone. The phenomenon was termed ‘‘Quadriga’’ by Verdan (1960), who compared it to the
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133
Table 1—Finger strength expressed as a percentage of normal (100%) Finger with stiffness and degree of stiffness (0–3)
Finger strength
Index
Middle
Index 1 2 3
85 60 50
28–115 18–115 15–108
Middle 1 2 3
91 79 92
57–143 45–162 8–127
Ring 1 2 3
83 100 116
51–135 45–187 6–204
82 77 72
38–139 36–156 12–126
Little 1 2 3
85 77 94
62–310 5–390 0–305
84 80 70
40–117 25–108 31–170
Ring
Little
78 51 48
30–124 19–95 8–95
73 48 63
17–105 17–113 14–93
85 84 52
51–99 34–150 17–101
84 90 42
22–143 37–135 19–130
81 66 31
45–108 9–118 31–74
111 98 69
28–262 72–600 54–469
Data are median values and ranges. 1 ¼ small wedge; 2 ¼ medium wedge; 3 ¼ large wedge.
Roman four horse chariot, the Quadriga. His original description cannot be bettered: ‘‘The muscular bodies of the flexors can be compared to the driver of a Roman chariot, the auriga, whereas the reins of his four horses are like the flexor tendons, two reins per horse and two tendons per finger. Now, we know that the drivers of quadrigas did not hold their reins in their hands, which they had to keep free for the whip or for grasping the bar of the chariot during racing in the Circus Maximus. The reins were wound around the charioteer’s body and the auriga curbed, or guided, his horses by bending his body backward, or to either side, while stressing his action by the motion of his left hand on certain reins. I am fond of comparing that performance to the effect of the common muscular body upon the flexor tendons, whose functional individuality is limited. As a matter of fact, the muscular body can act efficiently only if the gliding amplitude of each of the four tendinous reins is normal.’’ In addition, Verdan observed that patients with quadriga also complained of a lack of prehensile power. Quadriga occurs because the ulnar three fingers are flexed by a single ulnar belly of the FDP muscle, whose origin is on the flexor aspect of the ulna and the interosseous membrane. Seven to 12 tendon units, clearly linked together, arise from the ulnar belly of the muscle. Distally these units form the three definitive tendons for the middle, ring and little fingers. This ulnar muscle belly is distinct from the smaller radial muscle
belly of the FDP muscle, which provides a single tendon for the index finger alone. The three ulnar tendons are also joined at the base of the palm by the origins of the third and fourth lumbrical muscles. Motion of the FDP tendon to the index finger may not be entirely independent of that of the other FDP tendons, as all four FDP tendons are loosely tethered together by the synovium of the carpal tunnel which envelops all of the profundi tendons and loosely attaches them to the sides and floor of the carpal tunnel (Fahrer, 1979). The Quadriga syndrome can occur as a consequence of trauma to any of the three ulnar fingers, if this causes joint stiffness or tendon adhesions resulting in restricted flexion. Restricted flexion of one or more of these digits prevents full contraction of the shared ulnar belly of the FDP muscle, causing restricted FDP gliding and reduced finger flexion and strength of flexion in the other two ulnar digits. The patient may present with loss of flexion in the normal fingers or weakness of grip, particularly for small objects, which exceeds the weakness expected as a result of the lost contribution of the stiff finger alone. The results of this study demonstrate the existence of the quadriga effect when a finger is blocked to prevent full flexion. The study also demonstrates that the index finger with its apparently independent FDP muscle belly is not entirely independent from the FDP musculotendinous unit for the ulnar three digits in that the strengths of the middle, ring and little finger are reduced by simulated stiffness of the index finger. However, the strength of the index finger is not reduced by simulated stiffness of any other digit. This finding could be
ARTICLE IN PRESS 134
Fig 3 An oblique fibrous band (a) connecting the index FDP musculotendinous unit to the combined FDP musculotendinous unit for the middle, ring and little fingers would explain the findings of the present study. Flexion of the index finger is not prevented by restricted flexion of the other digits as the connecting band will then become lax. However, the band becomes tight if index finger flexion is restricted during flexion of any of the other digits.
explained on an anatomical basis by the presence of an oblique connection between the index and the combined middle, ring and little finger musculotendinous units which becomes lax when the index finger is flexed relative to the other digits and tight when the other digits are flexed relative to the index finger (Fig 3). This structure could be soft tissue connections between the radial and ulnar bellies of the FDP muscle, a tendinous band between the index and middle finger FDP tendons, or the synovium of the carpal tunnel, as suggested by Fahrer (1979). Linburg and Comstock (1979) and Slater (2001) have described a ‘‘quadriga’’ type of link between the thumb and the index and middle fingers as a result of two anomalous tendons joining the flexor pollicis longus to the index and middle finger FDP tendons. As all of these muscle arise from a common mesodermal mass (Kaplan and Riordan, 1984; Mangini, 1960), muscular, or tendinous, interconnections between the index and middle finger FDP tendons are a likely anomaly. We do not consider that our findings for the index finger could have been created artefactually by our study design as systematic bias was avoided by randomly selecting the order in which the fingers were blocked in each subject.
THE JOURNAL OF HAND SURGERY VOL. 32E No. 2 APRIL
2007
The effect of blocking flexion of one finger on the other digits varied considerably between individuals. Some of this variability could be explained by the random sequence in which the different sized wedges were introduced to block finger flexion, such that any muscle fatigue would have different effects on the results of different subjects. In addition, the increased strength measurements which were, sometimes, observed in fingers with blocking of the other digits does suggest some variability in the ability of the subject to grip the measuring instrument as hard as possible or, possibly, some error in the accuracy of the instrument, even although this was calibrated at the start of each measurement session. However, the potential for muscle fatigue was reduced by performing the measurements in four sessions on different days and allowing 2 minute rest intervals between each of the four sets (no blocking and small, medium and large wedges) of three grip measurements. We suggest that, at least, some of the intersubject variability was due to different levels of development of interconnections between the musculotendinous units of the index and the ulnar three fingers, and, also, possibly, because some individuals have middle, ring and little finger musculotendinous units which are firmly bound together while other have more lax connections, which allow some independent movements of their FDP tendons. Whatever the cause, the intersubject variability in the quadriga effect which we observed prevents the prediction of the effect of stiffness or reduced tendon gliding in one finger on the strengths of the hand and the other three digits. References Bunnell S (1924). Reconstructive surgery of the hand. Surgery Gynecology and Obstetrics, 34: 259–274. Fahrer M. In: Verdan C (Ed) Tendon surgery of the hand, Edinburgh, Churchill Livingstone, 1979: 17–24. Kaplan EB, Riordan DC. The Thumb. In: Spinner M (Ed) Kaplan’s functional and surgical anatomy of the hand, Philadelphia, JB Lippincott, 1984: 125. Linburg RM, Comstock BE (1979). Anomalous tendon slips from the flexor pollicis longus to the flexor digitorum profundus. Journal of Hand Surgery, 4: 79–83. Mangini U (1960). Flexor pollicis longus muscle: its morphology and clinical significance. Journal of Bone and Joint Surgery, 42A: 467–470. Slater RR (2001). Flexor tendon anomalies in a patient with carpal tunnel syndrome. Journal of Hand Surgery, 26B: 373–376. Verdan C (1960). Syndrome of the quadriga. Surgical Clinics of North America, 40: 425–426. Received: 18 February 2006 Accepted after revision: 8 November 2006 Prof TRC Davis, Department of Trauma and Orthopaedics, Queens Medical Centre, Nottingham, NG7 2UH, UK. Tel.: +44 1159 249924x44337; fax: +44 1159 209921. E-mail: [email protected]
r 2006 The British Society for Surgery of the Hand. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.jhsb.2006.11.005 available online at http://www.sciencedirect.com