Linburg-Comstock anomaly: seems to be harmless but may be fatal

The Linburg-Comstock Anomaly: A Study on Prevalence and Effect on Various Strength Metrics

BACKGROUND

The Linburg-Comstock (LC) anomaly is a common tendinous connection between the flexor pollicis longus and flexor digitorum profundus (FDP), most frequently to the FDP of the index finger. The purpose of this study was to obtain epidemiologic data on the LC anomaly in a healthy, ethnically diverse population and to study the effect of the LC anomaly on grip strength, tip pinch strength, key pinch strength, and chuck pinch strength.

METHODS

We examined 500 healthy subjects (292 females and 208 males) bilaterally for the presence of the LC anomaly. Each subject had their grip strength, tip pinch strength, key pinch strength, and chuck pinch strength measured bilaterally using a dynamometer for grip strength and a pinch meter for all pinch strength measurements.

RESULTS

The LC anomaly was present in 213 of the 500 subjects (43%). One hundred one subjects (47%) had a unilateral presentation, and 112 (53%) subjects had a bilateral presentation. The LC anomaly was associated with a weaker tip pinch strength. When examining the LC anomaly among different ethnic groups, the highest prevalence was found in the Hispanic (57%) population followed by Caucasian (50%), Asian (41%), and African American (31%) populations.

CONCLUSIONS

The LC anomaly has different prevalence according to ethnicity, with a higher prevalence in the Hispanic and Caucasian populations and a lower overall prevalence in the African American populations. The LC anomaly can also result in weaker tip pinch strength.

An investigation into the reliability and methodology of the Linburg-Comstock anomaly clinical test

STUDY DESIGN

This is a cross-sectional study.

INTRODUCTION

An intertendinous connection between the flexor pollicis longus (FPL) and index flexor digitorum profundus (IFDP) tendons causes involuntary index flexion during active thumb flexion and has been named the Linburg-Comstock anomaly (LCA). It may become symptomatic or cause functional limitations. Literature has documented the prevalence to range from 13% to 70%. Cadaver studies have reported an anatomical connection in 5% to 25%.

PURPOSE

This study aimed to examine the methodology and reliability of the LCA clinical diagnostic test and to explore the wide range of reported incidence and the discrepancy between cadaver and subject prevalence.

METHODS

Two examiners observed for the presence of involuntary index flexion during 3 separate variations of thumb flexion in 67 subjects (134 limbs); results were considered positive if involuntary flexion occurred at either index interphalangeal joint. Intertester reliability was assessed using Cohen's kappa coefficient. The volar forearm and wrist of 53 cadavers (106 limbs) were dissected and assessed for an observable and mechanical tendinous connection between the FPL and IFDP tendons.

RESULTS

Prevalence for subjects (5%-32%) was at the lower end of the range of previously reported values; results differed with altering thumb flexion motion. Observation for the presence of an intertendinous connection between the FPL and IFDP tendons in cadaver specimens (23%) fell within previously reported ranges. Intertester reliability coefficients ranged from no to weak agreement and varied according to specific thumb flexion motion performed during the test.

CONCLUSIONS

The identification of index finger flexion during thumb flexion varied both with thumb flexion motions and with whether flexion was assessed at the index proximal interphalangeal or distal interphalangeal joint. Intertester reliability was low for all variations of the LCA clinical test performed. The wide range in previously reported LCA incidence may be due to variability in testing procedure, and there is a need to establish a reliable and valid clinical test for this potentially symptomatic anatomic anomaly.

Prevalence of the Linburg-Comstock Anomaly in a Brazilian Population Sample

Objective  To determine the prevalence of the Linburg-Comstock anomaly in a Brazilian population sample. Methods  A cross-sectional observational study was carried out between October 2017 and April 2018. We included male and female volunteers aged 18 years or older. The presence of the Linburg-Comstock anomaly was determined by performing the clinical tests described by Linburg and Comstock. The data were analyzed using the GraphPad Prism software, and we considered differences with p  < 0.05. Results  The study analyzed 1,008 volunteers (2,016 hands) with a mean age of 38.3 years, 531 (52.67%) of which were male, and 477 (47.33%) were female. The Linburg-Comstock anomaly was diagnosed in 564 (55.95%) individuals, and it was bilateral in 300 (53.2%) of them, right-sided in 162 (28.72%), and left-sided in 102 (18.08%). No significant differences were found when comparing the prevalence between genders. However, a the prevalence of the right-sided anomaly in the male population (n = 99; 70.21%) was higher than in the female one (n = 63; 51.21%), with p  = 0.0016. In addition, the presence of pain by the maneuver described by Linburg and Comstock was more prevalent in women (n = 150; 54.94%) than in men (n = 105; 36.08%), with p  = 0.0001. These results show the importance of epidemiological studies on the Linburg-Comstock anomaly, mainly in order to investigate the presence of associated conditions. Conclusion  The prevalence of the Linburg-Comstock anomaly in the studied population was of 55.95%, and it was bilateral in 53.2% of the volunteers. The presence of the connection was observed more frequently in the right side and among men, but the pain symptom was more frequent among women.

Prevalence of the Linburg-Comstock variation through clinical evaluation

INTRODUCTION

Linburg-Comstock variation, the tendinous interconnection between flexor pollicis longus and flexor digitorum profundus, is known to have a wide frequency range. Its prevalence is reported with a range of 13-66%. The aim of the study was to assess this variation in general population and to correlate it with gender and side.

MATERIAL AND METHODS

This prospective study included 215 subjects (82 males and 133 females). Two clinical tests were conducted to diagnose the variation and to detect any related symptomatology. The primary outcome was set to be the prevalence of Linburg-Comstock variation. Secondary outcomes were defined as gender-based prevalence, side-based prevalence, and Linburg-Comstock variation prevalence association with gender and side.

RESULTS

Linburg-Comstock variation was clinically diagnosed in 130 (60.47%) participants. Unilateral and bilateral prevalence were of 17.21% and 43.26%, respectively, yielding a statistically significant difference. Right-sided and left-sided presence were calculated at 7.44% and 9.77%. Bilateral prevalence was statistically more common in females. Right-sided variation was found to be more frequent in males while left-sided variation was more prevalent in females. The index finger was the most commonly involved with prevalence of 91.03%. Symmetry was noted in 67.74% of subjects.

CONCLUSION

The results of our study demonstrated a relatively high prevalence of the Linburg-Comstock variation in Serbian population. We noted a few unusual cases and this finding point to the existence of the broader spectrum of Linburg-Comstock variation, and complexity of the flexor apparatus of the hand, so, further investigations about this topic are needed to improve our knowledge. Due to the possibility of false-positive result during clinical testing we suggest to use expanded clinical method.

Linburg-Comstock: Is Overuse an Etiological Factor?

Background

Linburg-Comstock anomaly is typically defined as a tenosynovial interconnection between flexor pollicis longus and flexor digitorum profundus tendon of the second finger. There are several studies stating that the current anomaly is congenital or acquired. The aim of this study is to reveal whether overuse, which is mostly reported as an acquired etiologic factor, effective in development of the current anomaly.

Methods

Three hundred thirteen medical secretaries who work with computer keyboard at least 6 hours a day were defined as study group. Three hundred twenty-three volunteers without jobs who necessitate continuous and repetitive hand and finger activities were defined as control group. All individuals were examined by an orthopaedic surgeon. Additionally, cases with Linburg-Comstock anomaly were evaluated in respect of forearm pain and subjective findings of carpal tunnel syndrome.

Results

Linburg-Comstock anomaly was determined in 27.8% cases of medical secretary group and in 32.2% of healthy control group. In medical secretaries with Linburg-Comstock anomaly, 25.3% had forearm pain and 5.7% had findings of carpal tunnel syndrome. In control group with Linburg-Comstock anomaly, 21.2% had forearm pain and 13.5% had findings of carpal tunnel syndrome. No relationship was found between overuse of the hand and Linburg-Comstock anomaly and the symptoms accompanying the anomaly.

Conclusions

The current study reveals that overuse is not an etiologic factor in Linburg-Comstock anomaly existence and related symptoms. We think that the current anomaly develops on congenital basis rather than acquired factors.

The Linburg-Comstock anomaly: incidence in Malaysians and effect on pinch strength

PURPOSE

To obtain epidemiologic data on the Linburg-Comstock anomaly in Malaysia and to study the effect of the anomaly on key pinch strength.

METHODS

We examined 292 healthy subjects (162 female and 130 male) bilaterally for the presence of the Linburg-Comstock anomaly. Each subject's key pinch strength was measured bilaterally using a pinch meter.

RESULTS

The Linburg-Comstock anomaly was present in 101 of the 292 subjects (35%). Sixty-five subjects (22%) had it unilaterally, and 36 subjects (6%) had it bilaterally. The anomaly was associated with superior key pinch strength.

CONCLUSIONS

The study provides epidemiologic data of this anomaly in Malaysia and considers its anatomical influence on key pinch strength.

TYPE OF STUDY/LEVEL OF EVIDENCE

Prognostic IV.

Traumatic correction of Linburg-Comstock anomaly: a case report

Linburg-Comstock anomaly describes an anatomical variant of flexor tendons of the hand. Flexor pollicis longus (FPL) sends a connecting tendon to flexor digitorum profundus (FDP), causing simultaneous flexion at the distal interphalangeal joint (DIPJ) of the index finger when the interphalangeal joint (IPJ) of the thumb is flexed. Epidemiological studies have revealed a unilateral prevalence as high as 31% of individuals; however, the condition rarely causes symptoms. The anomaly can present with a restrictive flexor tenosynovitis, requiring explorative surgery to confirm the diagnosis and disconnection of the anomalous tendon slip to relieve symptoms. We describe the case of a rock climber who suffered a forced extension injury to the DIPJ of the right index finger, resulting in traumatic rupture of his anomalous FPL-FDP connecting tendon. This is the first reported case of rupture of a Linburg-Comstock anomaly. Through rupture of this anomalous tendon, the patient can be viewed as having corrected his aberrant tendon to conform with the more prevalent anatomical configuration and function. We identified the rupture using dynamic ultrasound of the wrist; to our knowledge, this technique has not been described previously in the literature. We recommend the use of this imaging modality to confirm diagnosis, thus avoiding explorative surgery.