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Hand Biomechanics Literature Review
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Chinchalkar S. Biomechanics of the Small Finger MCP Joint Following an Extension Loss at the PIP Joint. Hand Writings-Newsletter of the New Jersey Chapter of the American Society of Hand Therapists. Jan 2000; Volume 5.No 1
Little finger is subject to repeat injury because of its location and use of the hand in everyday tasks. Loss of extension at the second knuckle, proximal inter-phalangeal joint (PIP) results in greater extension force at the metacarpal phalangeal (MCP) joint, leading to hyperextension and rotational deformity of the small finger. Hyperextension of MCP joint results when extension of the PIP joint is constrained by a flexion contractureW or tensor lag. Further, the MCP joint is abducted, rotated and hyperextended by the action of the abductor digiti minimi. Treatment includes splinting, exercises and the application of a dorsal MCP blocking splint, used 24 hours a day until PIP extension is possible, then intermittently for 4-6 weeks.
The splint prevents the loss of function of the saggital bands. When the extensor digitorum communis meets the resistance of the splint an equivalent force is transmitted to the PIP joint. A moment is created at the MCP joint which increases the tension in the digitorum communis. The additional force created at the PIP joint by the dorsal MCP blocking splint gradually corrects the problem.
Static Progressive versus Three-point Elbow Extension Splinting: A Mathematical Analysis
Chinchalkar S, Pearce J, Athwal G. Static Progressive versus Three-point Elbow Extension Splinting: A Mathematical Analysis. J HAND THER. 2009;22:37-43
The mathematical analysis of two different splinting techniques for the elbow is completed. Rotational and decompressive forces felt by the elbow are calculated based on elbow angle and the force applied by the splint. Good examples of force diagrams, and angle relationships. Additional diagrams in lab notebook.
Clinical Mechanics of the Hand Brand PW, Hollister AM. Clinical Mechanics of the Hand. 3rd ed. St. Louis, Missouri: Moshby, Inc; 1999.
- MCP joints are two axis joints. One is responsible for flexion and extension, the other allows abduction when the fingers are flexed
- Soft tissues within fingers modify, limit and transfer the effect of forces (bones transfer forces). If soft tissue is limited (unable to move or stretch), stiff joints that are hard to move result. Splints can be used to increase the range of motion, this is accomplished by creating a torque at the joint
- Splints used when regular joint motion may be harmful (think in the case of the little finger, hyperextension at MCP joint inhibiting PIP joint extension)
Hand Splinting Principles and Methods Fess EE, Philips, CA. Hand Splinting – Principles and Methods. 2nd ed. St. Louis, Missouri: Mosby, Inc; 1987.
- PIP joint flexion contracture occurs from direct injury to joint, or immobilization in flexed position