Extensor Tendon Injury
An Occupational Therapy Perspective
Splinting and Kinematics
Howell, Merritt, & Robinson (2005).
It was determined from findings that the Relative Motion Splint is the best option for protecting the extensor digitorum tendon after injury. This type of splint allows for immediate active controlled motion without straining the injured extensor tendon (Merritt, 2014).
The splint holds the wrist in 25° extension and the affected finger in 15° more extension than the other digits as pictured in Fig. 1. (Sharma et al., 2006). Due to the single muscle belly the adjacent tendons take on most of the load (Merritt, 2014).
Merritt (2014)
Sharma et al (2006)
Sharma et al (2006)
Sharma et al (2006)
Outcomes using the splint show low incidence of extensor tendon lag and loss of flexion range of motion (Howell, Merritt, & Robinson, 2005). Extensor tendon lag and tendon adhesions are common issues that develop with static splinting (Sharma et al., 2006).
There are relatively few studies examining biomechanics and kinematics of the extensor tendons. For example, Fowler, Nicol, Condon, and Hadley (2001) were unable to examine the extensor tendon path and force vectors in their geometric model from MRI images at the proximal interphalangeal joint among other limitations. In most cases, research is done on cadaver models which raise some concerns regarding statistical significance versus clinical significance of findings in these studies. However we believe there is sufficient data here to demonstrate the efficacy of use of a relative motion splint design to reduce strain on the extensor tendon.
There is some promise in future research involving Hand and Wrist Motion Analysis using a Vicon motion capture system. Future use of this technology could include activity analysis while wearing the splint to improve recommendations of what activities may be appropriate at which point in rehabilitation. A YouTube video is included below to further explain the technology and its uses.
Biomechanical analysis in cadaver models show that there is less strain on the tendon throughout full range of motion. In Figure 2. (Sharma et al., 2006) it is demonstrated that splinting for an intact tendon still significantly reduces the strain on the long finger (the injured finger) in extension, flexion and at rest when compared to flexion and extension without the splint. The difference is even more dramatic when the tendon has been surgically repaired (Figure 3, Sharma et al. 2006).
Howell, Merritt, & Robinson (2005).
References
Fowler, N. K., Nicol, A. C., Condon, B., & Hadley, D. (2001). Method of determination of three dimensional index finger moment arms and tendon lines of action using high resolution MRI scans. Journal of biomechanics,34(6), 791-797.
Howell, J. W., Merritt, W. H., & Robinson, S. J. (2005). Immediate controlled active motion following zone 4–7 extensor tendon repair. Journal of Hand Therapy, 18(2), 182-190.
Merritt, W. H. (2014). Relative motion splint: active motion after extensor tendon injury and repair. The Journal of hand surgery, 39(6), 1187-1194.
Sharma, J. V., Liang, N. J., Owen, J. R., Wayne, J. S., & Isaacs, J. E. (2006). Analysis of relative motion splint in the treatment of zone VI extensor tendon injuries. The Journal of hand surgery, 31(7), 1118-1122.