Abstract
Strength is regarded as normal in patients with an opposable triphalangeal thumb. Our clinical impression is, however, that intrinsic musculature is probably affected in all forms of triphalangeal thumb. Therefore, we established the strength of 38 thumbs in patients with a triphalangeal thumb. Patients were excluded if the intrinsic musculature was enhanced or if osteotomies of the first metacarpal were performed. On average, strength of all thumb functions was significantly diminished, up to 63% for opposition strength. Strength of the power grip was on average 70%. As shown in this study, strength of the musculature of the thumb is affected in all types of triphalangeal thumb. Although strength of the thumb is diminished, in the investigated group it is apparently sufficient in daily life, as these individuals did not seek surgical enhancement. However, reconstructive procedures that enhance intrinsic musculature must be considered in all types of triphalangeal thumb.
Introduction
Triphalangeal thumb is a congenital hand anomaly with a heterogenic occurrence, ranging from less complex, with only an extra phalanx at the interphalangeal joint, to a five-fingered hand with absent thenar musculature and therefore no opposition (Hovius et al., 2004; Upton and Shoen, 2000). In Buck-Gramcko’s extensive classification of triphalangeal thumb, absent or hypoplastic thenar musculature is only assigned to the types with the larger transitional extra phalanges and long rectangular middle phalanx (Buck-Gramcko, 2002), which is comparable with Wood’s full type (Wood, 1976). In all others types, no aberrant thenar musculature is mentioned, suggesting a normal thenar musculature is present.
In the literature, no involvement of intrinsic musculature in the delta-type triphalangeal thumb, trapezoid-shaped extra phalanx, short rudimentary phalanx, or short triangular bone has been described. However, our clinical impression was that intrinsic musculature is probably affected in more types of triphalangeal thumb. Therefore, we established the strength of specific thumb functions in patients with delta and trapezoid types of triphalangeal thumb.
Methods
Patient characteristics
Between 1980 and 2006, 90 patients with a triphalangeal thumb visited the Erasmus Medical Centre, Rotterdam, the Netherlands. Patients with disorders affecting general strength, peripheral nerve injuries, or other disorders disturbing hand strength were excluded. Patients not able to perform the required motion as a result of joint limitations, stiffness, or laxity were also excluded. Patients who had been treated with pollicization, first metacarpal reduction osteotomy, opponensplasty, or any other form of tendon transfer to enhance thumb function, or reinsertion of intrinsic musculature were excluded as well. Patients under the age of 4 years were excluded, because of the impossibility to perform the strength tests. Of the remaining 23 patients that were included, there were 7 male and 16 female, aged 7–64 (mean 34) years, and three persons were left dominant (Table 1).
Characteristics of patients with triphalangeal thumb, operated or non-operated, without tendon transfer or reinsertion of intrinsic musculature (N = 23, H = 38)
DEL = removal of extra phalanx if combined with reconstruction of the collateral ligaments; DIPRAD = distal interphalangeal joint combined reduction osteotomy and arthrodesis according to the technique described by Peimer for triphalangeal thumb; PIPRAD = proximal interphalangeal combined reduction osteotomy and arthrodesis, a variation of the above mentioned technique.
Medical data
All patient files were retrieved and patient characteristics, dominance, type of triphalangeal thumb, and surgical data were scored. Patients were classified by type of triphalangeal thumb using Wood’s classification (1976) of the shape of the extra phalanx: delta, trapezoid, and full-type triphalangeal thumb. In addition, we used Buck-Gramcko’s classification of the treatment options (2002).
Strength measurements
Intrinsic hand strength was measured using the Rotterdam Intrinsic Hand Myometer (RIHM). The RIHM has proven to be a reliable instrument for strength measurements of the individual thumb and fingers in healthy controls (Molenaar et al., 2008) and a number of patients groups (Schreuders et al., 2004; Selles et al., 2006). Individual measurements were performed for the strength of opposition, flexion of the metacarpophalangeal joint of the thumb, anteposition, and radial abduction of the index finger. The mean of three repeated measurements was registered.
Maximal isometric grip, pinch, and tip strength were measured using the Jamar dynamometer and pinch gauge (Sammons Preston, Bolingbrook, Illinois). Measurements using the Jamar dynamometer were performed with the handle in the second position, and all persons were seated in the position suggested by the American Society of Hand Therapists, with the shoulder in rest, the elbow in 90° of flexion, and the wrist in neutral position (Fess, 1992). The mean of three repeated measurements was recorded.
Because of the wide age range in this group, and therefore wide variability in normal values, measurements from both instruments were presented in percentages of the age- and sex-specific reference values (Mathiowetz et al., 1985; 1986; Molenaar et al., 2008; Schreuders and Selles, 2008).
Statistical analysis
Data were analyzed as frequencies and percentages or means and ranges. To detect differences between the study group and normal population (100%), a one-sample t-test was used. A p value < 0.05 was accepted as statistically significant.
Results
All strength measurements were significantly reduced compared with age-specific reference values. Mean strength for opposition was 63% (p < 0.05) (SD 19, range 26–121). Mean strength for flexion of the metacarpophalangeal thumb was 62% (SD 16, range 26–97) (p < 0.05). Anteposition of the thumb had a mean strength of 76% (SD 25, range 26–121) (p < 0.05). Mean strength of radial abduction of the index finger was 88% (SD 26, range 48–160) (p 0.01) (Figure 1). Mean strength of power grip was 69% (SD 33, range 22–142) (p < 0.05). Strength of the pinch grip was 84% (SD 25, range 27–145) (p < 0.05) and of key grip was 73% (SD 19, range 21–107) (p < 0.05) (Figure 2). In patients who were affected unilaterally (n = 8), the hand with the triphalangeal thumb was compared with the non-affected hand. For all measurements, the non-affected hand was stronger, although this was not statistically significant.
Boxplot of thumb strength in different directions as a percentage of the age-specific reference values. Measurements of the normal population are indicated as 100% (dotted line) (Molenaar et al., 2008; Schreuders and Selles, 2008). All measurements were significantly lower compared with reference values.
Boxplot of the power grip, key pinch, and tip pinch as a percentage of the age-specific reference values. Measurements of the normal population are indicated as 100% (dotted line) (Mathiowetz et al., 1985; 1986). All measurements were significantly lower compared with reference values.
Discussion
Our clinical impression was that strength of the thumb is affected in all types of triphalangeal thumb, besides the well-known diminished strength in the five-fingered hand. Therefore, thumb strength in the 23 patients with delta and trapezoid types of triphalangeal thumb was established. The strength of thumb and hand functions (opposition, flexion of the metacarpophalangeal joint, anteposition, and radial abduction of the index finger) was significantly lower compared with a normal population. Strength of power, pinch, and key grip was also significantly diminished.
Intrinsic hand function strength is difficult to measure. The Rotterdam Intrinsic Hand Myometer is the only capable and validated instrument for adults and children, although it has its limitations. One limitation is that it measures a function rather than a specific muscle. Another study limitation was the inclusion of patients who had had their thumb operated on. Although no procedures that enhanced or recreated intrinsic hand function were performed, alterations of the thumb had been performed. These procedures (e.g. removal of extra additional rays, correction of the extra phalanx) are not focused on enhancing muscle strength, although a small effect cannot be excluded. To investigate a possible difference between the operated and non-operated group, a subgroup analysis was performed. Both groups had statistically diminished strength for all measurements compared with a normal population (data not shown). Also older (i.e. adults) were included. These patients could have had diminished strength as a result of disuse of specific thumb functions. All adults, however, were bilaterally affected and the strength of both hands was diminished in all.
Triphalangeal thumb has a heterogenic presentation, from a small extra phalanx to a non-opposable thumb, and everything in-between. Therefore, it is difficult to make classifications with clear cut-off points. Wood classified the triphalangeal thumb by the shape of the extra phalanx. Besides the shape of the extra phalanx, Buck-Gramcko also included the associated duplications and degree of development of the thumb; the hypoplastic type. The present classifications of the triphalangeal thumb (Wood, 1976) use severity; however, in both classifications the presence of absent or hypoplastic intrinsic musculature is only attributed to the more severe types (for Wood, full type; Buck-Gramcko, larger transitional and long rectangular). A classification suitable for all types of triphalangeal thumb with their wide variety would probably be unusable.
This study enhances our clinical experience that thumb function and intrinsic hand function strength is affected in all types of triphalangeal thumb. Although the strength of the different thumb functions is on average diminished in all types of triphalangeal thumb, it is apparently sufficient in daily life, at least in the researched group. Persons with untreated triphalangeal thumbs probably have developed skills to perform daily life tasks with diminished strength. It is not necessary to recreate or enhance intrinsic hand function in all patients with triphalangeal thumbs, although it must be considered in all the different variations and types.
Footnotes
Conflict of interests
None declared.
Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.