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Journal of Medical Cases

Case Report

Volume 1, Number 2, October 2010, pages 68-70

Anomalous V-shape Palmaris Longus Tendon: Two Cases

The Palmaris Longus (PL) is the most variable muscle in the human arm and one of the most variable muscles in the human body [1, 2]. This variability has formed the base for many medical literatures. Although the PL muscle of little functional importance, it assumes great surgical importance since it is the first option in tendon graft procedures, for it is readily detected in vitro and easy surgical accessibility as well, which make harvesting its tendon much easier than its counterpart, the Plantaris muscle in the leg [3, 4]. The awareness of PL absence and the anomalous presentation is highly warranted. Reimann et al examined 1,600 extremities and found incidence rate of other anomalies apart from absence was 9% [5]. Furthermore concomitant anomalies in the soft tissue of the upper limb which share same embryonic origin (mesoderm) have been recorded as well [6-8]; these include nerves, arteries and other muscles. Therefore, knowledge of these anomalous structures, although rare, is important not only to anatomists but also to clinicians in their routine practice. The morphologic aspect of V-shape anomalous tendon and literatures review is presented with special emphasis on clinical significance of this anomalous finding.

A prospective study to identify prevalence of absence of PL muscle among the medical school students of Faculty of Medicine, University Technology Mara were conducted, the examined sample of subjects: n = 253; hands: n = 506; the age ranged 19 - 22 years with the mean of 21 and the Male/Female ratio 1:3. Two asymptomatic cases were incidentally found during in vitro clinical examination by Schaeffer’s test (Fig. 1), while Thompson’s and Mishra’s test failed to demonstrate the anomalous tendon. The morphologic feature of the anomalous tendon was V-shape bifid distal part of PL tendon. Both slips run superficially crossing the wrist creases to be inserted into the palm onto palmer aponeurosis, the central tendoneus slip runs towards a groove created by the two eminences, in the mid-palm while the other lateral slip was radial directed towards the thenar eminence. This bifidity of the PL tendon was confirmed by wrist ultrasonography.

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Figure 1. Anomalous V-shaped PL identified in Schaeffer’s and not in Thompson’s or Mishra’s.

Palmaris Longus is often described as one of the most variable muscles in the human body and is classified as a phylogenetically retrogressive muscle, in other words, a short belly with a long tendon [9]. The PL absence is easy to detect in vitro by Schaeffer’s, Thompson’s and Mishra’s tests. Its absence ranged between 2.8-24% in different races [1, 2], but the reported incidence of other anomalies in the PL was still 9% (Table 1), including inverted PL [10, 11], three headed reversed [12], epifasial accessory [13], duplicate [14-16]. The muscle belly may be central, distal or digastrics or may be completely muscular [15]. According to Paraskevas et al, the duplication of palmaris longus vary between 0.8-3.1% [17].

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Table 1. Types of Anomalies in Palmaris Longus

The clinical significance of the anomalous PL was reported in numerous literatures. There are many reports of median and/or ulnar nerve compression due to the existence of a variant PL [18-20]. In clinical practice, the aberrant PL could also be incidentally found during clinical examination without provoking any clinical symptoms like our cases [18].

The PL tendon is often considered as an ideal donor tendon in hand surgery. It’s the first option in tendon grafts procedure of the long flexors, extensor tendons of the fingers, flexor pollicis longus tendon and extensor tendon defects as well. It can be used in tendon transfer procedure [13]. It is also utilized as a simple static support in the treatment of facial paralysis, and some surgeon utilize the tendon in digital pulley reconstruction [21], lip augmentation, and in various nerve palsies.

This unique V-shape arrangement of PL tendon makes it a potential source to provide V-shape splint in selected reconstructive procedures, oral and lid angle in facial palsy or any other reconstructive procedures where a V-shaped splint is required. Therefore, surgeon awareness of this anomaly, as well as pre-operative identification is warranted when such type of splint is indicated, and it can be easily distinguished from the normal PL tendon(Fig. 2).

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Figure 2. Single PL identified in Schaeffer’s test.

In conclusion, the V-shape PL tendon represent potential donor splint in selected surgical procedures. Therefore surgeon awareness and pre-operative identification of this anomalous tendon is warranted.

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