IN BRIEF

Linburg-Comstock Anomaly Stephanie M. Gancarczyk, MD, Robert J. Strauch, MD BACKGROUND Linburg-Comstock anomaly consists of tendinous interconnections between the flexor pollicis longus (FPL) muscle belly or tendon and the flexor digitorum profundus (FDP), usually of the index finger.1 Tendon slips connecting the FPL and the FDP were recognized by anatomists as early as the 1800s.1 In 1979, Linburg and Comstock1 found the variant unilaterally in 31% of their study population and bilaterally in 16%. The tendinous interconnection can range in size from 1 mm to a diameter comparable with that of the FDP tendon itself, and typically, it is hidden within a common, thickened tenosynovium.1 This connection prevents independent flexion of the thumb interphalangeal (IP) joint and the index finger distal interphalangeal (DIP) joint, occasionally the middle and ring fingers are also involved.1,2 Typically, this variant does not cause symptoms.1,3 In a study by Low et al,4 35% of patients were found to have the variant, and none of these patients had recognized the lack of independent thumb flexion prior to participation in the study. CLINICAL PRESENTATION Although usually asymptomatic, some published case reports suggest symptoms can develop following forceful index finger hyperextension with the thumb in a flexed position, in individuals who require heavy and repetitive use of the wrist and forearm, or in those who require fine and independent motor control of the fingers, such as musicians, law enforcement officials, artists, and carpenters.5e7 These mechanisms increase traction on the tendinous interconnection and may cause tenosynovitis adjacent to the intertendinous bridge.3,8 In addition, it is hypothesized that local From the Department of Orthopaedic Surgery, Columbia University Medical Center, New York, NY. Received for publication January 21, 2014; accepted in revised form February 21, 2014. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Corresponding author: Robert J. Strauch, MD, Department of Orthopaedic Surgery, Columbia University Orthopaedic Surgery, 622 West 168th St., PH1119, New York, NY 10032; e-mail: [email protected]. 0363-5023/14/---0001$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2014.02.022

injury or post-traumatic FPL tenosynovitis can cause Linburg-Comstock syndrome owing to adhesion formation.3,8,9 In a study by Ortak et al,7 of 108 security personnel studied, 2 unwillingly pressed the trigger of a firearm with the index finger while pulling back the hammer with a thumb flexed at the IP joint. Two others forced themselves not to press the trigger and experienced severe wrist pain as a result.7 When patients are symptomatic, they will typically describe a tearing-like pain during movements that would require independent excursion of the FPL and FDP tendons.8 In addition, they may complain of being unable to independently move their fingers, resulting in difficulty with tasks such as using chopsticks, tying shoelaces, or writing.2 On examination, active flexion of the thumb will cause simultaneous flexion of the DIP joint of the index finger and, occasionally, other DIP joints as well (Fig. 1).1,8 Because the tendinous connection is usually oblique and proximally based on the FPL, independent flexion of the index, middle, or ring fingers may not provoke simultaneous flexion of the thumb.8 The diagnostic test described by Linburg and Comstock is performed by restricting index finger DIP flexion in conjunction with attempting active thumb flexion. A positive test produces a sharp pain in the wrist or distal forearm.1 Studies have shown it to be positive in as many as 60% to 70% of patients.10 Injections of fast-acting analgesics around the FPL sheath have been reported to eliminate symptoms temporarily and assist in diagnosis.8 Patients with Linburg-Comstock may also complain of median nerve neuropathy, which may or may not be related to the increased contents of the carpal tunnel owing to the accessory tendon slips.11 Of the 4 original cases presented by Linburg and Comstock in 1979,1 3 patients had symptoms consistent with median nerve neuropathy and underwent subsequent carpal tunnel release. In a study by Lombardi et al,3 31 of 33 patients with Linburg-Comstock syndrome were found to have symptoms consistent with median nerve neuropathy, although these symptoms were of secondary importance to the distal forearm activitye related pain attributed to the intertendinous connections between the FPL and the FDP.

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FIGURE 1: A Independent thumb flexion. B Simultaneous finger and thumb IP joint flexion bilaterally, as seen in Linburg-Comstock anomaly.

to independently flex the thumb and index finger. Nonsteroidal anti-inflammatory medications, splints, stretching exercises, and steroid injections have been attempted, but seem unsuccessful at relieving wrist and forearm pain.3,8 Surgical intervention consists of excising or splitting the intertendinous connections, depending on the nature of the link.8 The most commonly described finding is a fibrous band of thickened synovial tissue, but a common muscle belly or anomalous muscle may also be seen.8

In addition, recognition of Linburg-Comstock anomaly is helpful in the setting of FPL repair. Careful attention should be paid to avoid active, independent index finger flexion, which may put excessive tension on the FPL repair.12,13 IMAGING Linburg-Comstock is a clinical diagnosis and further testing is rarely needed unless additional pathology is suspected or surgical intervention is planned. Ultrasound can reveal the interconnections between the FPL and the FDP, and it can be used to demonstrate the resultant simultaneous flexion of the FPL and FDP tendons.5,14 It has been suggested that magnetic resonance imaging (MRI) may be useful for preoperative planning, enabling smaller incisions and shorter operative time.15 In a study by Karalezli et al,15 9 of 52 patients were found to have Linburg-Comstock syndrome, and each of these patients underwent bilateral wrist MRI. Tendinous interconnections were clearly seen on axial plane images and length was calculated on coronal plane images.15 Other investigators have observed abnormal signal around the FPL tendon or an anomalous tendon signal between the FPL and the FDP, but findings were not confirmatory.2,9

OUTCOMES The results of surgical intervention are mixed, but usually enable return to pain-free activity.1,5 Linburg and Comstock1 presented 4 cases, all of which had complete relief of symptoms after surgical intervention. Lombardi et al3 followed 17 patients for 6 or more months and found that 13 patients had good results, 2 had fair results, and 2 had poor results, defined as frequent pain or swelling and inability to perform all normal activities. In a study by Badhe et al,8 11 patients presented with pain in the volar forearm and examination findings consistent with Linburg-Comstock syndrome; all failed conservative management and underwent surgical intervention. Ten patients had excellent improvement in pain, demonstrated independent excursion of the FPL and FDP tendons, and were able to return to daily activities pain-free.8 One patient developed complex regional pain syndrome that improved with physical therapy.8

TREATMENT OF SYMPTOMATIC LINBURG-COMSTOCK ANOMALY The goal of nonsurgical management is to alleviate painful symptoms and to increase a patient’s ability J Hand Surg Am.

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DISCUSSION The anatomy of the FPL and FDP differs between humans and our ape ancestors. Apes have a large tendon inserting on the index finger and a small tendon on the thumb, with most species having a common muscle belly between the FPL and the FDP.8 The presence of a separate FPL is an evolutionary change, with many normal variants existing on this spectrum. A link between the FPL and the FDP has been found to increase pinch strength in humans and may enhance the ability to exert a pinch precision grip.4,8 As many as 30% to 60% of the population has a positive Linburg-Comstock test, with the vast majority asymptomatic at baseline.1,10 The pathological syndrome arises when tenosynovitis, and subsequent pain, develops that interferes with daily functioning. In this scenario, nonsurgical treatment is typically unsuccessful, and surgical intervention has been found to be effective at reducing symptoms in most patients.

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REFERENCES

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1. Linburg RM, Comstock BE. Anomalous tendon slips from the flexor pollicis longus to the flexor digitorum profundus. J Hand Surg Am. 1979;4(1):79e83. 2. Yoon HK, Kim CH. Linburg-Comstock syndrome involving four fingers: a case report and review of the literature. J Plast Reconstr Aesthet Surg. 2013;66(9):1291e1294. 3. Lombardi RM, Wood MB, Linscheid RL. Symptomatic restrictive thumb-index flexor tenosynovitis: incidence of musculotendinous

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anomalies and results of treatment. J Hand Surg Am. 1988;13(3): 325e328. Low TH, Faruk Senan NA, Ahmad TS. The Linburg-Comstock anomaly: incidence in Malaysians and effect on pinch strength. J Hand Surg Am. 2012;37(5):930e932. Furukawa K, Menuki K, Sakai A, Oshige T, Nakamura T. LinburgComstock syndrome: a case report. Hand Surg. 2012;17(2): 217e220. Takami H, Takahashi S, Ando M. The Linburg Comstock anomaly: a case report. J Hand Surg Am. 1996;21(2):251e252. Ortak T, Uraloglu M, Orbay H, Koc MN, Sensoz O. LinburgComstock anomaly: seems to be harmless but may be fatal. Plast Reconstr Surg. 2007;119(6):1976e1977. Badhe S, Lynch J, Thorpe SKS, Bainbridge LC. Operative treatment of Linburg-Comstock syndrome. J Bone Joint Surg Br. 2010;92(9): 1278e1281. Lin B, Sreedharan S, Chin AY. Linburg-Comstock phenomenon following forearm laceration. Hand Surg. 2012;17(2):221e224. Miller G, Peck F, Brain A, Watson S. Musculotendinous anomalies in musician and nonmusician hands. Plast Reconstr Surg. 2003;112(7):1815e1824. Slater RR. Flexor tendon anomalies in a patient with carpal tunnel syndrome. J Hand Surg Br. 2001;26(4):373e376. Barabas AG. Flexor pollicis longus tendon repair in patients with Linburg-Comstock anomaly. J Hand Surg Eur Vol. 2013;38(2): 203e204. Stahl S, Stahl S, Calif E. Failure of flexor pollicis longus repair caused by anomalous flexor pollicis longus to index flexor digitorum profundus interconnections: a case report. J Hand Surg Am. 2005;30(3):483e486. Old O, Rajaratnam V, Allen G. Traumatic correction of LinburgComstock anomaly: a case report. Ann R Coll Surg Engl. 2010;92(4): W1eW3. Karalezli N, Karakose S, Haykir R, Yagisan N, Kacira B, Tuncay I. Magnetic resonance imaging in Linburg-Comstock anomaly. Acta Radiol. 2006;47(4):366e368.

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