Keywords
tendon absence - palmaris longus - flexor digitorum superficialis absence - Schaeffer's test - Baker's test - normative data
Introduction
The palmaris longus (PL) and the flexor digitorum superficialis (FDS) are the frequently absent tendons of the upper limb. Both are frequently used donors for tendon reconstruction. In addition, the absence of a functional FDS affects the outcome of isolated injury of the flexor digitorum profundus of the little finger. The prevalence of PL absence shows a wide variation among different ethnic groups.[1]
[2] The FDS of the little finger has various anatomical variations.[3] The study was conducted to determine the prevalence of the absence of the PL and functional FDS of the little finger in the Indian population.
Materials and Methods
The study was a prospective study conducted at our institute after the Institute Ethical Committee clearance. The study population was 200 volunteers who responded to the pamphlet displayed on the notice board. All of them gave informed consent for the study and inclusion of their data. The volunteers included students, staff, employees of the institute, and patient attenders, and belonged to various states of the country.
The volunteers were assessed for the presence of the PL by Schaeffer's test in both hands as shown in [Fig. 1]. Schaeffer's test was done by palpating the PL while flexing the wrist and keeping the thumb opposed to the little finger.[4]
[5]
Fig. 1 Schaeffer's test shows the presence of the palmaris longus in the left hand and its absence in the right hand.
Then the function of the FDS of the little finger was assessed by the standard test and as described by Kaplan[6] the modified test as described by Baker et al[7], and results were divided into independent, common, and absent functions.[4] The standard test as shown in [Fig. 2], was performed by asking the volunteer to flex the little finger while restraining the FDP function of other fingers. If the volunteer flexed the proximal interphalangeal (PIP) joint of the little finger more than 90 degrees, the result was termed independent.[6]
Fig. 2 The standard test shows the absence of functional flexor digitorum superficialis (FDS) of the little finger in the right hand and its presence in the left hand.
The modified test as shown in [Figs. 3] and [4], was performed by asking the volunteer to flex the little and ring fingers while restraining the FDP action of the middle and index fingers. If the volunteer was able to flex the little finger PIP more than 90 degrees with the DIP joint in neutral, the test was considered positive and the result was termed common, the inference being the little finger FDS is adherent to the ring finger FDS.[7]
Fig. 3 The modified test. The same hand in [Fig. 2] shows a functional flexor digitorum superficialis (FDS) of the little finger in the right hand on performing the modified test.
Fig. 4 (A) The standard test shows the absence of the flexor digitorum superficialis (FDS) in the little finger. (B) The modified test also shows the absence of a functional FDS in the little finger. (C) Lateral view showing the absence of the FDS in the little finger in the modified test.
All statistical tests were conducted using SPSS and the association between the absence of the PL and functional little finger FDS was assessed using the chi-squared test.
Results
Two hundred individuals aged between 21 and 60 years were examined. The mean age was 37 years. There were 84 males (42%) and 116 females (58%). The PL was absent unilaterally in 12 individuals (6%) and bilaterally in 7 individuals (3.5%). When unilaterally absent, it was absent on the right side in eight individuals and on the left side in four individuals.
Of the 400 hands examined, PL absence was seen in 26 upper limbs (6.5%). The PL was more absent in the right side and the difference in prevalence between the two sides was 1% ([Table 1]). The association between absence in the right and left sides was not statiscally significant with odds ratio of 39.5 (95% confidence interval [CI] = 9.5–163), risk ratio (Risk Ratio [RR]) = 21.5 (95% CI = 7.5–65.4), and chi-squared test value of 52 (p = 0).
Table 1
Prevalence of palmaris longus absence
|
Palmaris longus
|
Present
|
Absent
|
|
Right side (n = 200 hands)
|
185 (92.50%)
|
15 (7.50%)
|
|
Left side (n = 200 hands)
|
189 (94.50%)
|
11 (5.50%)
|
|
Total (n = 400 hands)
|
374 (93.5%)
|
26 (6.5%)
|
Of the 400 little fingers examined, FDS function was absent in 72 fingers (18%), while 67 fingers (16.75%) had a common/combined function and 261 fingers (65.25%) had an independent function ([Table 2]).
Table 2
Summary of clinical evaluation of functional FDS of the little finger
|
Standard and modified test for the FDS
|
Independent function
|
Combined function with FDS of the ring finger
|
Absent function
|
|
Right side (n = 200 hands)
|
128 (64%)
|
33 (16.5%)
|
39 (19.5%)
|
|
Left side (n = 200 hands)
|
133 (66.50%)
|
34 (17%)
|
33 (16.5%)
|
|
Total (n = 400 hands)
|
261 (65.25%)
|
67 (16.75%)
|
72 (18%)
|
The independent FDS function was bilaterally absent in 54 individuals (27%) and unilaterally absent in 31 individuals (15.5%). When unilaterally absent, it was absent on the right side in 18 individuals and on the left side in 13 individuals. The FDS of the little finger was more absent on the right side and the difference in prevalence between the two sides was 3%. The association between the absence on the right and left sides was not significant with an odds ratio of 17.6 (95% CI = 7.3–42.5), RR = 8.2 (95% CI = 4.3–15.5), and a chi-squared test value = 56 (p = 0).
Only 2% had a bilateral absence of both the PL and functional FDS tendons and 5% had a unilateral absence of both tendons.
There was no significant association between the absence of the PL and functional FDS. For the absence on the right side, the odds ratio was 3 (95% CI = 1.02–9.2) and RR was 2.2 (95% CI = 1.1–4.4) and for absence on the left side, the odds ratio was 3.1% (95% CI = 0.8–11.4) and RR was 2.3 (95% CI =1.0–5.5). The p-value was 0.03 on the right side and 0.06 on the left side.
Discussion
Prevalence of Palmaris Longus
Many textbooks quote that the PL is absent in 15% of the global population.[4] A systemic review of 32 studies by Ioannis et al showed that its absence prevalence ranges between 1.5 and 63.9%.[1]
Our study, conducted in south India, found the prevalence of absence of the PL to be 6.5%. Mugalur et al studied the population in central India and reported an absence of 19.3%.[8] Another study from central India reported unilateral absence of 16.95% and bilateral absence of 3.3%.[9] Both studies showed a higher prevalence of absence than the current study. Three further studies from India showed that the PL was absent in 264of 942 (28%) individuals studied,[10] 65 of 400 (16.25%) individuals studied,[11] and 73 of 266 (27.44%) studied.[12] Three cadaver studies were done in India. Pai et al found the absence to be 3.33%,[13] Patil et al found 16% to be absent,[14] and Lalit et al found 8.06% to be absent.[15] This emphasizes the significant variations in the prevalence of the absence of PL within our country. This sort of various prevalence within different regions in the same country is seen in the systemic review by Ioannis et al.[1]
Prevalence of Functional FDS of the Little Finger
The absence of a functional FDS of the little finger has been discussed a lot. Furnas noted that 6 of 100 cadaver forearms had no muscle belly or tendon in the wrist representing the FDS of little finger.[16] Shrewsbury and Kuczynski noted 30% absence of the FDS tendon on dissecting 23 hands.[17] Kaplan found that 30.85% of the FDS of the little finger had a connection to the FDS of the index finger and 33.6% had a connection to the FDS of the ring finger while dissecting 68 cadaver hands.[6]
On clinical examination by applying the standard and modified tests, Austin et al found that 58% had an independent function, 21% had a combined function, and 21% had no function.[18] The study done by Watanabe et al showed an independent function in 67.5%, a combined function in 12.0%, and an absent function in 20.5%.[19] Similarly, in our study, the majority of 65.25% had an independent function of the FDS of the little finger, followed by absent FDS function in 18% and a common function in 16.75%.
Association between Absence of the PL and Functional FDS of the Little Finger
There was no statistically significant association between the absence of the PL and functional FDS. This is similar to the findings in Thompson et al,[20] Alzahrani et al,[21] Kigera et al,[22] and Sebastin et al.[4]
The limitation of our study is the relatively small sample size and lack of multicentric representation.
Conclusion
The prevalence of an absent PL in our study is 6.50%. There is no association between the absence of the PL and the side of the hand. The prevalence of independent functional absence of the FDS of the little finger is 18% and there is no association with the side of the hand. Also, there is no statistically significant association between an absent PL and an absent functional FDS of the little finger.
