Title: 6 case of posterior 1st Carpometacarpal dislocation and review literature
Author(s): Lahiji FA MD*, Zandi R MD, Maleki A MD, Ashoori K MD, Bagheri F MD
Affiliattion(s): Shahid Beheshti University of Medical Sciences, Tehran, Iran
* Corresponding Author
Vol 2, Num 1, January 2015
Dislocation of the first CMC is a rare occurrence. Treatment of this dislocation varies from closed reduction and casting to ligament repair. Neglected dislocation or incomplete reduction of the 1st CMC cause chronic instability and painful arthritis ,muscle imbalance and decreased grip force.
Dislocation of the first carpometacarpal (CMC) joint is a rare occurrence.(1) In 1976 Harrey used the phrase ' Bennett's fracture without a fracture ' in cases where there is joint instability after reduction. Gedda in 1954 mentioned dislocation without skeletal trauma associated with loss of function of the thumb without Bennett's fracture.(2) Most cases are posterior dislocation (1), although some believe all cases are posterior dislocation (3,4,5) some anterior dislocations have been reported.(6,7) CMC dislocation rarely occurs in children & adolescents.(5)
The most common mechanism of 1st CMC dislocation is axial loading while the thumb is in a semiflexed position.(1) Recurrent dislocation/subluxation of the 1st CMC can be traumatic or idiopathic.(3) Although CMC dislocation without a fracture is rare, the important functions of the thumb especially in gripping and grasping, causes significant effects on hand's functions.
The CMC joint is a saddle type joint.(6) The shape of the joint contributes little to its stability, instead the ligaments and joint capsule are the main stabilizers of this joint.(5)
The 1st CMC joint moves in three dimensions: flexion/extension, abduction/adduction, pronation/supination (opposition & retropulsion).(5)
Stability at the 1st CMC joint is dependent on static and dynamic forces. Static forces include the anatomic shape of the joint and anterior / posterior interosseous ligaments. Dynamic force include the force of the muscle acting on this joint.(8,9,10)
Four ligaments that provide stability include anterior oblique, dorsoradial, posterior oblique and intermetacarpal. Recent studies consider the dorsoradial ligament as the most important one in preventing dislocation.(6,11,12,13,14)
Five trapeziometacarpal ligaments are recognized; 3 intracapsular and 2 extracapsular.(15) The anterior oblique ligament, which is intracapsular, originates from palmar tubercle of the trapezium and attaches to the palmer tubercle of the first metacarpal. It is a thick and broad structure which becomes tense in extension, abduction and pronation.
The ulnar collateral ligament is extracapsular and extends obliquely from the flexor ligament to the proximal palmar aspect of the first metacarpal connecting with the inter metacarpal ligament. This ligament becomes tense in extension, abduction and pronation. This ligament is frequently elongated in degenerative trapeziometacarpal arthritis.
The intermetacarpal ligament, which is extracapsular and between the bases of the first and second metacarpals, originates from the dorsal aspect of the second metacarpal base near the attachment of extensor carpi radialis longus and becomes taut in extension , opposition and supination. It is a thin ligament and not involved in degenerative arthritis.
The posterior oblique ligament is the first intermetacarpal ligament originating like a fan from the dorsal lip of the first metacarpal. It becomes taut at the end of supination and doesn't become elongated in CMC arthritis until the final stages of the disease, when it become lax.(15)
Some authors believe that the anterior oblique ligament is the main in the stabilizer of the trapeziometacarpal joint supported by the ulnar collateral ligament (15), however, others consider the dorsoradial ligament as the main stabilizer, so that injury to this ligament is solely responsible for dislocation even if the other ligaments are intact.(14)
1st CMC dislocation is often initially missed. The affected patients present with localized pain and swelling.(11,12,13) Todiagnose this dislocation, an oblique view is needed in addition to standard AP & Lat views.(8) Stress radiographs is an AP view in which the two thumbs are pressed together parallel to the film are also important. In case of dislocation, the base of the metacarpal is displaced laterally over the trapezium.(5)
Ligament rupture, which usually occurs distally from the metacarpal attachment (4), can be complete or partial. The complete tears result in posterior dislocation of the 1st CMC and partial tears result in subluxation.(5)
Abductor policis longus force is a causative factor in recurrent dorsoradial dislocation of the 1st CMC joint, therefore supportive treatment will not be effective and surgical ligament reconstruction is necessary to prevent recurrent dislocations and secondary OA.(17) Neglected dislocation or incomplete reduction of the 1st CMC joint causes chronic instability and painful arthritis, muscle imbalance and decreased grip force.(5)
Due to instability of 1st CMC joint (18,19,20), surgical treatment is strongly recommended. Some advocate anchor suturing and pin fixation, which are removed after 6 weeks and ROM is begun.(4)
However primary reduction and thumb spica casting for 4-6 weeks seems to be appropriate.(4) In 1973 Walt & Hooper used casting with or without pinning in the treatment of 1st CMC dislocation. In this study, 7 patients presented on the day of injury and 5 patients presented between 3 days and 3 weeks after injury. For all patients, a thumb spica cast was applied, three of whom needed pinning to increase stability. During the follow-up, which lasted between 4 months and 7 years, 7 patients had complete recovery without pain and instability or any radiologic changes while 2 patients had posterior subluxation and weakness and discomfort in gripping. These patients were treated by Eaton method.(2)
Simoman & Trumble believe that closed reduction cannot prevent instability and arthritis in the long term. They treated 8 patients with closed reduction and pinning for 6 weeks, three patients with surgical reconstruction for symptomatic instability and one case with salvage procedure for post-traumatic arthritis.(21) Eaton believed that the results of reduction were largely unpredictable even when the joint is fixed with cross-pinning. However in most cases surgical reconstruction is necessary.
Shah & Patel treated three patients with open reduction and pin fixation and one patient with closed reduction and pin fixation with acceptable results in all patients.(5)
Walt & Hooper reported the treatment results in 12 patients. They treated nine patients with closed reduction and casting and three patients with closed reduction and pinning. Three patients from the first group and one from the second group showed joint instability.(22)
In pure 1st CMC dislocation, Henry recommended ligament repair and pin fixation for 6 weeks to achieve painless movement and stability. Light pinch and power pinch is gradually started after 3 months.(1)
Between 2008-2009, 6 patients (4 men and 2 women) with acute 1st CMC dislocation in Akhtar & Arad Hospitals (Tehran, Iran) were treated. All patients were admitted during the first 24 hours from their injury. All underwent primary reduction and later ligament repair.
The first patients was a 30 Y/O man who'd sustained direct trauma to both hands with pain at the base of both thumbs. He had an osteochondral fracture at the volar aspect of the base of the 1st metacarpal on the right hand (UCL injury) along with 1st carpometacarpal dislocation. He underwent ORIF of the joint with a pin and dorsal and oblique collateral ligament repair. At the end of surgery, a short thumb spica cast was applied. The cast and pins were removed after 6 weeks. The joint was stable and function was regained. In a six-month follow-up, the patient had no complaints about the carpometacarpal function.
The second case was a 25 years old man who fell from motor bike and had pain in the base of the thumb. The patient did not consent to surgery and had immediate closed reduction and discharged with a short thumb spica cast. After six months the patients had no complaints.
The third patient was a 32 year old man with 1st CMC dislocation who was treated by repairing the torn ligament and was discharged with a short thumb spica cast. After six months the patients didn't show any complaints.
The forth patient was a 17 years old girl who had a fall while skiing. She was treated by open repair of the dorsoradial ligament and the joint capsule and pinning of the 1st CMC, supported by a short thumb spica cast. In the last follow-up, she had no complaints about the function of thumb.
The 5th case was a 35 years old man who also had a fall during skiing. He underwent closed reduction in emergency room and then an open repair if the ligaments augmented by six weeks thumb spica cast. After six months, the patient had no complaints about his hand's function.
The last case was a 16 years old woman who sustained a fall and come with tenderness and swelling at the base of thumb. The 1st CMC dislocation was reduced closed and supported by a thumb spica cast for 6 weeks.
The dislocation of the 1st CMC occurs rarely, but important function of the thumb specially in gripping and grasping makes it a significant problem. Since neglected dislocation or incomplete reduction causes chronic instability and painful arthritis, the injured ligaments are strongly recommended to be repaired for increased stability of the 1st CMC joint.
Farivar A Lahiji MD Associate Professor, Orthopaedic Hand Surgeon, Shahid Beheshti University of Medical Sciences, Tehran, Iran Corresponding Author firstname.lastname@example.org
Reza Zandi MD Orthopaedic Surgeon, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Arash Maleki MD Fellow of Paediatric Orthopaedics, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Keyghobad Ashoori MD Orthopaedic Surgeon, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Farivar Bagheri MD Orthopaedic surgeon, Tehran, Iran
Acknowledgements: None declared.
Financial disclosure: None declared.
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