How Do Wrist Surgical Salvage Procedures Limit Hand Strength?

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Wrist osteoarthritis has been described as “one of the most common conditions encountered by the orthopaedic surgeon”. In men older than 60, severe osteoarthritis is more frequently present at the wrist than the hip. The wrist is a complicated joint that implant technology has failed to effectively replicate. As a result, surgical salvage procedures are commonly used to treat osteoarthritis at the wrist, unlike at the hip or knee where joint replacement is the gold standard. The two most common surgical salvage procedures are scaphoid-excision four-corner fusion (SE4CF) and proximal row carpectomy (PRC). In each procedure, the arthritic scaphoid bone is removed. In SE4CF, the midcarpal joint (the interface between the remaining bones in the proximal and distal rows) is fused to prevent carpal collapse in the absence of the scaphoid. In PRC, the lengths of the carpus and distal upper limb are shortened because the two additional bones (lunate, triquetrum) that articulate with the forearm are also removed. These drastic geometric and kinematic re-designs permanently decrease wrist range of motion and grip strength. Loss of grip strength is particularly detrimental; it limits patient's abilities to perform activities of daily living, such as picking up a saucepan, unscrewing a jar lid, and opening a door. Why grip strength is lost following surgical salvage procedures is not understood. Our long-term goal is to develop innovative orthopaedic surgical interventions for wrist osteoarthritis. The objective of this proposal, the next step toward attainment of that goal, is to determine why grip force is limited following PRC and SE4CF. Our central hypothesis is that the surgical re-design of the wrist in PRC and SE4CF impose mechanical differences in muscle function at the wrist joint, and it is these effects that ultimately limit hand strength post-operatively. Our hypothesis was developed based on our preliminary work, in which we first characterized biomechanical differences between muscle mechanical capabilities in nonimpaired and surgically salvaged wrist joints in cadaveric specimens, and then demonstrated the impact of these mechanical effects on lateral pinch strength using computer simulation. The rationale that underlies the proposed research is that improving surgical interventions for wrist osteoarthritis first requires understanding how changing the kinematic and geometric design of the wrist joint influences the hand's ability to generate force. Ultimately, the research studies proposed here will improve the scientific understanding of how the design of the wrist influences both wrist and hand function. This knowledge will aid therapists in designing rehabilitation protocols targeted at specific points of biomechanical weakness and surgeons in developing novel surgical techniques to reduce biomechanical changes. For example, if muscle adaptations cause wrist extensors to be weaker following PRC, a tendon transfer to strengthen these muscles could be performed. Alternatively, SE4CF could be modified to minimize the effects of motion coupling by optimizing the position in which the carpals are fused. Additionally, engineers will be able to use our findings to design wrist implants that more effectively replicate key components of the wrist's design. All of these outcomes will improve the treatment options for wrist osteoarthritis, and thereby lead to improved patient outcomes and quality of life. The overwhelming success of treatment options for hip and knee osteoarthritis, as well as the scientific advances that have been achieved in these areas over the past 25 years, emphasizes the potential impact that an increased investment in research relevant to wrist osteoarthritis could have. Because the veteran population is so much more susceptible to wrist injuries than the general population, veterans would ultimately reap the most benefits from such improvements in clinical treatment of wrist osteoarthritis.